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Positron Emission Tomography Quantification of Serotonin Transporter in Suicide Attempters with Major Depressive Disorder

      Background

      Several lines of evidence implicate abnormal serotonergic function in suicidal behavior and completed suicide, including low serotonin transporter binding in postmortem studies of completed suicide. We have also reported low in vivo serotonin transporter binding in major depressive disorder (MDD) during a major depressive episode using positron emission tomography (PET) with [11C]McN5652. We quantified regional brain serotonin transporter binding in vivo in depressed suicide attempters, depressed nonattempters, and healthy controls using PET and a superior radiotracer, [11C]DASB.

      Methods

      Fifty-one subjects with DSM-IV current MDD, 15 of whom were past suicide attempters, and 32 healthy control subjects underwent PET scanning with [11C]DASB to quantify in vivo regional brain serotonin transporter binding. Metabolite-corrected arterial input functions and plasma free-fraction were acquired to improve quantification.

      Results

      Depressed suicide attempters had lower serotonin transporter binding in midbrain compared with depressed nonattempters (p = .031) and control subjects (p = .0093). There was no difference in serotonin transporter binding comparing all depressed subjects with healthy control subjects considering six a priori regions of interest simultaneously (p = .41).

      Conclusions

      Low midbrain serotonin transporter binding appears to be related to the pathophysiology of suicidal behavior rather than of major depressive disorder. This is consistent with postmortem work showing low midbrain serotonin transporter binding capacity in depressed suicides and may partially explain discrepant in vivo findings quantifying serotonin transporter in depression. Future studies should investigate midbrain serotonin transporter binding as a predictor of suicidal behavior in MDD and determine the cause of low binding.

      Key Words

      Abnormal serotonergic function has been associated with suicidal behavior and completed suicide. Possible explanations for this association include serotonergic effects on aggression and on decision making (
      • Courtet P.
      • Gottesman I.I.
      • Jollant F.
      • Gould T.D.
      The neuroscience of suicidal behaviors: What can we expect from endophenotype strategies?.
      ,
      • Gonda X.
      • Fountoulakis K.N.
      • Harro J.
      • Pompili M.
      • Akiskal H.S.
      • Bagdy G.
      • Rihmer Z.
      The possible contributory role of the S allele of 5-HTTLPR in the emergence of suicidality.
      ) Postmortem studies quantifying serotonin transporter (5-HTT) protein in the brain of completed suicides have reported low Bmax (number of 5-HTT binding sites in vitro) in regions including prefrontal cortex, anterior cingulate, hippocampus, putamen, and hypothalamus, although others have reported no group differences, and one reported higher 5-HTT in frontal cortex (
      • Arango V.
      • Underwood M.D.
      • Mann J.J.
      Serotonin brain circuits involved in major depression and suicide.
      ,
      • Purselle D.C.
      • Nemeroff C.B.
      Serotonin transporter: A potential substrate in the biology of suicide.
      ). One study reported low 5-HTT binding capacity (a product of receptor binding×region volume that is more analogous to positron emission tomography [PET] outcome measures) in the dorsal raphe nuclei in depressed suicides (
      • Arango V.
      • Underwood M.D.
      • Boldrini M.
      • Tamir H.
      • Kassir S.A.
      • Hsiung S.
      • et al.
      Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims.
      ). Assessing the relationship between 5-HTT binding in vivo and suicidal behavior may clarify the pathophysiology of suicidal behavior and could potentially identify a biomarker for predicting suicide risk in patients.
      The serotonin (5-HT) neurotransmitter system has also been implicated in the pathophysiology of major depressive disorder (MDD). Acute tryptophan depletion provokes depressive symptoms in remitted depressed subjects and their relatives compared with healthy control subjects (
      • Ruhe H.G.
      • Mason N.S.
      • Schene A.H.
      Mood is indirectly related to serotonin, norepinephrine and dopamine levels in humans: A meta-analysis of monoamine depletion studies.
      ). Acute serotonergic challenges reveal blunted neuroendocrine responses in acutely depressed and remitted depressed subjects (
      • Bhagwagar Z.
      • Whale R.
      • Cowen P.J.
      State and trait abnormalities in serotonin function in major depression.
      ). The antidepressant efficacy of serotonergic medications in MDD is consistent with a role of 5-HT in the pathophysiology of depression (
      • Serrano-Blanco A.
      • Gabarron E.
      • Garcia-Bayo I.
      • Soler-Vila M.
      • Carames E.
      • Penarrubia-Maria M.T.
      • et al.
      Effectiveness and cost-effectiveness of antidepressant treatment in primary health care: A six-month randomised study comparing fluoxetine to imipramine.
      ,
      • Trivedi M.H.
      • Rush A.J.
      • Wisniewski S.R.
      • Nierenberg A.A.
      • Warden D.
      • Ritz L.
      • et al.
      Evaluation of outcomes with citalopram for depression using measurement-based care in STAR*D: Implications for clinical practice.
      ).
      Many studies have examined the role of the 5-HTT specifically in the pathophysiology of MDD (
      • Meyer J.H.
      Imaging the serotonin transporter during major depressive disorder and antidepressant treatment.
      ). Several, but not all, postmortem studies have found lower 5-HTT Bmax (binding density of 5-HTT in vitro) in prefrontal cortex regions in MDD compared with control subjects (
      • Stockmeier C.A.
      Involvement of serotonin in depression: Evidence from postmortem and imaging studies of serotonin receptors and the serotonin transporter.
      ). In vivo comparisons of 5-HTT binding between MDD and healthy control groups using PET and single photon emission computed tomography are inconsistent (
      • Meyer J.H.
      Imaging the serotonin transporter during major depressive disorder and antidepressant treatment.
      ). We previously described lower 5-HTT binding in 25 antidepressant-free MDD subjects during a current major depressive episode compared with 43 healthy control subjects across six regions of interest (ROIs) implicated in the pathophysiology of MDD using the radiotracer [11C]McN5652 (
      • Parsey R.V.
      • Hastings R.S.
      • Oquendo M.A.
      • Huang Y.Y.
      • Simpson N.
      • Arcement J.
      • et al.
      Lower serotonin transporter binding potential in the human brain during major depressive episodes.
      ). Post hoc testing showed lower binding in midbrain and amygdala. The [11C]McN5652 radiotracer has known limitations, including poor specific-to-nonspecific binding ratio and poor quantification of cortical binding (
      • Frankle W.G.
      • Huang Y.
      • Hwang D.-R.
      • Talbot P.S.
      • Slifstein M.
      • Van Heertum R.
      • et al.
      Comparative evaluation of serotonin transporter radioligands 11C-DASB and 11C-McN 5652 in healthy humans.
      ,
      • Szabo Z.
      • McCann U.D.
      • Wilson A.A.
      • Scheffel U.
      • Owonikoko T.
      • Mathews W.B.
      • et al.
      Comparison of (+)-(11)C-McN5652 and (11)C-DASB as serotonin transporter radioligands under various experimental conditions.
      ).
      [11C]DASB is a radiotracer that provides superior 5-HTT quantification compared with [11C]McN5652 (
      • Frankle W.G.
      • Huang Y.
      • Hwang D.-R.
      • Talbot P.S.
      • Slifstein M.
      • Van Heertum R.
      • et al.
      Comparative evaluation of serotonin transporter radioligands 11C-DASB and 11C-McN 5652 in healthy humans.
      ). Other groups have used [11C]DASB to examine 5-HTT in MDD, with divergent findings. Three reports from one research group with partially overlapping subject samples found no differences in [11C]DASB binding between MDD subjects and healthy control subjects (
      • Meyer J.H.
      • Wilson A.A.
      • Ginovart N.
      • Goulding V.
      • Hussey D.
      • Hood K.
      • Houle S.
      Occupancy of serotonin transporters by paroxetine and citalopram during treatment of depression: A [(11)C]DASB PET imaging study.
      ,
      • Meyer J.H.
      • Wilson A.A.
      • Sagrati S.
      • Hussey D.
      • Carella A.
      • Potter W.Z.
      • et al.
      Serotonin transporter occupancy of five selective serotonin reuptake inhibitors at different doses: An [(11)C]DASB positron emission tomography study.
      ,
      • Meyer J.H.
      • Houle S.
      • Sagrati S.
      • Carella A.
      • Hussey D.F.
      • Ginovart N.
      • et al.
      Brain serotonin transporter binding potential measured with carbon 11-labeled DASB positron emission tomography: Effects of major depressive episodes and severity of dysfunctional attitudes.
      ). One study found higher [11C]DASB binding in MDD subjects than healthy control subjects across a broad anatomic distribution (
      • Cannon D.M.
      • Ichise M.
      • Rollis D.
      • Klaver J.M.
      • Gandhi S.K.
      • Charney D.S.
      • et al.
      Elevated serotonin transporter binding in major depressive disorder assessed using positron emission tomography and [11C]DASB; comparison with bipolar disorder.
      ), while two others reported lower [11C]DASB binding, one in the thalamus specifically (
      • Reimold M.
      • Batra A.
      • Knobel A.
      • Smolka M.N.
      • Zimmer A.
      • Mann K.
      • et al.
      Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: A [11C]DASB PET study.
      ) and another across a broad range of cortical and subcortical regions (
      • Selvaraj S.
      • Venkatesha Murthy N.
      • Bhagwagar Z.
      • Bose S.K.
      • Hinz R.
      • Grasby P.M.
      • Cowen P.J.
      Diminished brain 5-HT transporter binding in major depression: A positron emission tomography study with [(11)C]DASB.
      ). These divergent findings may be partially explained by demographic and clinical differences in study populations, including rates of suicidal behavior, and by different PET outcome measures employed.
      In addition to examining effects of diagnosis on binding, we previously examined the effect of a functional promoter polymorphism in the 5-HTT gene (SLC6A4, polymorphism: serotonin-transporter-linked polymorphic region [5-HTTLPR]) that regulates in vitro expression of 5-HTT (
      • Hu X.
      • Oroszi G.
      • Chun J.
      • Smith T.L.
      • Goldman D.
      • Schuckit M.A.
      An expanded evaluation of the relationship of four alleles to the level of response to alcohol and the alcoholism risk.
      ,
      • Lesch K.P.
      • Bengel D.
      • Heils A.
      • Sabol S.Z.
      • Greenberg B.D.
      • Petri S.
      • et al.
      Association of anxiety-related traits with a polymorphism in the serotonin transporter gene regulatory region.
      ). A gene-environment interaction between the 5-HTTLPR polymorphism and the severity of stressful life events may predict the presence and severity of subsequent depression, as well as the later occurrence of suicidal behavior (
      • Caspi A.
      • Sugden K.
      • Moffitt T.E.
      • Taylor A.
      • Craig I.W.
      • Harrington H.
      • et al.
      Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene.
      ,
      • Hung C.F.
      • Lung F.W.
      • Chen C.H.
      • O'Nions E.
      • Hung T.H.
      • Chong M.Y.
      • et al.
      Association between suicide attempt and a tri-allelic functional polymorphism in serotonin transporter gene promoter in Chinese patients with schizophrenia.
      ,
      • Karg K.
      • Burmeister M.
      • Shedden K.
      • Sen S.
      The serotonin transporter promoter variant (5-HTTLPR), stress, and depression meta-analysis revisited: Evidence of genetic moderation.
      ). We found no effect of 5-HTTLPR on 5-HTT binding using [11C]McN5652 (
      • Parsey R.V.
      • Hastings R.S.
      • Oquendo M.A.
      • Hu X.
      • Goldman D.
      • Huang Y.Y.
      • et al.
      Effect of a triallelic functional polymorphism of the serotonin-transporter-linked promoter region on expression of serotonin transporter in the human brain.
      ). In vivo findings from other studies are discordant [reviewed in (
      • Willeit M.
      • Praschak-Rieder N.
      Imaging the effects of genetic polymorphisms on radioligand binding in the living human brain: A review on genetic neuroreceptor imaging of monoaminergic systems in psychiatry.
      )]. We also reported an effect of early life stress on 5-HTT binding using [11C]McN5652, with low 5-HTT binding in MDD subjects reporting childhood abuse (
      • Miller J.M.
      • Kinnally E.L.
      • Ogden R.T.
      • Oquendo M.A.
      • Mann J.J.
      • Parsey R.V.
      Reported childhood abuse is associated with low serotonin transporter binding in vivo in major depressive disorder.
      ), but the sample size was too small to examine gene-environment interactions.
      In the current study, we used [11C]DASB in the largest MDD cohort examined to date to examine the relationship between depression and suicide attempt history on serotonin transporter binding in vivo. Our primary hypotheses were that MDD subjects with a history of prior suicide attempt would have low [11C]DASB binding compared with control subjects and MDD nonattempters in the regions identified from postmortem studies of suicide: ventral prefrontal cortex (vPFC), anterior cingulate (ACN), and midbrain (containing dorsal raphe nuclei, which cannot be reliably delineated on magnetic resonance imaging [MRI]); and [11C]DASB binding would be low in unmedicated current MDD subjects as compared with healthy control subjects across the six brain regions identified in our study using [11C]McN5652. We anticipated that 5-HTTLPR genotype would not be associated with [11C]DASB binding. In exploratory analyses, we examined the effects of reported childhood abuse and of a gene-environment interaction between 5-HTTLPR and reported childhood abuse on [11C]DASB binding.

      Methods and Materials

      Sample

      Currently depressed participants (n = 51) with MDD and healthy control subjects (n = 32) were recruited prospectively through print and online advertisements. Eligibility was assessed by psychiatric and medical history, chart review, physical examination, routine blood tests, pregnancy test, and urine toxicology. Axis I diagnoses were based on the Structured Clinical Interview for DSM-IV (
      • First M.
      • Spitzer R.
      • Gibbon M.
      • Williams J.
      Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I/P, Version 2.0).
      ), conducted by doctoral or masters’ level psychologists and reviewed in a consensus conference of research psychologists and psychiatrists. Inclusion criteria for MDD subjects included 1) current major depressive episode; 2) 17-item Hamilton Depression Rating Scale (HDRS)≥16 at screening; 3) age 18 to 65 years; and 4) off all psychotropic and other types of drugs likely to interact with 5-HTT for a minimum of 14 days (off antipsychotics for≥3 weeks). While this was the minimum duration according to inclusion criteria, 11 MDD subjects were antidepressant-naïve, and among the 40 MDD subjects with prior psychotropic medication exposure, the mean duration off psychotropic medication at time of scan was 122 weeks (median = 11.5 weeks, range=14 days to 35.9 years). Short-acting benzodiazepines were allowed for distressing anxiety or insomnia up to 72 hours prior to PET scanning but were only used by six subjects. Exclusion criteria included 1) current or past psychotic illness or bipolar disorder, anorexia nervosa or bulimia nervosa in the past year, and drug or alcohol abuse within the past 2 months or dependence within 6 months; 2) first-degree family history of schizophrenia in subjects<33 years old to exclude individuals possibly presenting with the prodrome of schizophrenia [mean onset of schizophrenia = 21.4 in male subjects and 26.8 in female subjects (
      • Loranger A.W.
      Sex difference in age at onset of schizophrenia.
      )]; 3) significant active physical illness; 4) lack of capacity to consent to study participation; 5) pregnancy or lactation among women; 6) previous head injury with loss of consciousness; and 7) exposure to 3,4-methylenedioxymethamphetamine on more than two occasions.
      For healthy control subjects, inclusion criteria included: 1) absence of current or past DSM-IV Axis I diagnosis, with the exception of specific phobia; 2) absence of cluster B personality diagnosis as assessed using the Structured Clinical Interview for DSM-IV Axis II Personality Disorders (
      • First M.B.
      • Gibbon M.
      • Spitzer R.L.
      • Williams J.B.
      • Benjamin L.S.
      SCID-II Personality Questionnaire.
      ); and 3) age 18 to 65 years. Exclusion criteria included MDD exclusion criteria 3 through 7 above, as well as: 1) past or present alcohol/substance abuse or dependence; 2) first-degree relative with history of major depression, schizophrenia, schizoaffective disorder, or suicide attempt; and 3) two or more first-degree relatives with a history of substance dependence.
      The Beck Depression Inventory (
      • Beck A.T.
      • Ward C.H.
      • Mendelson M.
      • Mock J.
      • Erbauh J.
      An inventory for measuring depression.
      ) and HDRS (
      • Hamilton M.
      A rating scale for depression.
      ) were used to assess depression severity and functional impairment. Lifetime history of aggression was measured by the Brown Goodwin Aggression History Scale (
      • Brown G.L.
      • Goodwin F.K.
      • Ballenger J.C.
      • Goyer P.F.
      • Major L.F.
      Aggression in human correlates with cerebrospinal fluid amine metabolites.
      ). The Columbia Suicide History Form was used to assess suicide attempt history (
      • Oquendo M.A.
      • Halberstam B.
      • Mann J.J.
      Risk factors for suicidal behavior: The utility and limitations of research instruments.
      ), and the Beck Medical Lethality Scale was used to rate the degree of medical damage caused by their most lethal attempt (
      • Beck A.T.
      • Beck R.
      • Kovacs M.
      Classification of suicidal behaviors: I. Quantifying intent and medical lethality.
      ). The scale scores medical damage from 0 (no injury) to 8 (fatal), with anchor points dependent on the method of attempt. In a semistructured interview, participants were asked whether they experienced physical and/or sexual abuse over the course of their lifetime. If subjects endorsed a history of abuse, they were asked whether the abuse took place before age 15.

      Genotyping

      Genotyping of the triallelic 5-HTTLPR polymorphism (LA, LG, and S) was performed as previously described (
      • Hu X.
      • Oroszi G.
      • Chun J.
      • Smith T.L.
      • Goldman D.
      • Schuckit M.A.
      An expanded evaluation of the relationship of four alleles to the level of response to alcohol and the alcoholism risk.
      ). The triallelic genotypes were classified by their reported level of in vitro expression as follows: LA was reclassified as higher expressing L’; LG and S were classified as lower expressing S’.

      Radiochemistry and Input Function Measurement

      Preparation of [11C]DASB and measurement of arterial input function, metabolites, and plasma free fraction (fP) were performed as previously described (
      • Belanger M.J.
      • Simpson N.R.
      • Wang T.
      • Van Heertum R.
      • Mann J.J.
      • Parsey R.V.
      Biodistribution and radiation dosimetry of [11C]DASB in baboons.
      ,
      • Ogden R.T.
      • Ojha A.
      • Erlandsson K.
      • Oquendo M.A.
      • Mann J.J.
      • Parsey R.V.
      In vivo quantification of serotonin transporters using [(11)C]DASB and positron emission tomography in humans: Modeling considerations.
      ). The chemical purity of [11C]DASB was≥95%. Injected mass, injected dose, and fP did not differ between MDD and control subjects or between MDD suicide attempters and nonattempters (Table 1).
      Table 1[11C]DASB PET Scan Parameters of the Sample
      Control Subjects (n = 31)MDD (n = 51)t, p ValueMDD Suicide Attempters (n = 15)MDD Nonattempters (n = 36)t, p Value
      Injected Dose (mCi)16.14±2.3616.28±2.14−.27, .7916.34±1.8016.25±2.29.13, .90
      Corrected Mass (μg)4.36±2.314.49±2.18−.27, .915.07±2.304.25±2.111.24, .22
      Free Fraction (fP).12±.03.11±.021.59, .12.11±.03.11±.02−.13, .90
      MDD, major depressive disorder; PET, positron emission tomography.

      PET Protocol

      Details of the PET protocol are described elsewhere (
      • Ogden R.T.
      • Ojha A.
      • Erlandsson K.
      • Oquendo M.A.
      • Mann J.J.
      • Parsey R.V.
      In vivo quantification of serotonin transporters using [(11)C]DASB and positron emission tomography in humans: Modeling considerations.
      ). Briefly, a venous catheter was used for radiotracer injection and an arterial catheter was used to obtain arterial samples for the input function. A polyurethane head holder system (Soule Medical, Tampa, Florida) was molded around the subject’s head for immobilization purposes. Positron emission tomography imaging was performed with the ECAT HR+ (Siemens/CTI, Knoxville, Tennessee). A 10-minute transmission scan was obtained before radiotracer injection. At the end of the transmission scan, [11C]DASB was administered intravenously as a bolus over 30 seconds (Table 1). Emission data were collected in three-dimensional mode for 100 minutes with 19 frames of increasing duration (
      • Ogden R.T.
      • Ojha A.
      • Erlandsson K.
      • Oquendo M.A.
      • Mann J.J.
      • Parsey R.V.
      In vivo quantification of serotonin transporters using [(11)C]DASB and positron emission tomography in humans: Modeling considerations.
      ).

      Magnetic Resonance Imaging

      Acquisition of T1-weighted MRI images for co-registration of PET images and identification of ROIs was performed as previously described using a 1.5 T Signa Advantage or a 3 T Signa HDx system (General Electric Medical Systems, Milwaukee, Wisconsin) (
      • Parsey R.V.
      • Slifstein M.
      • Hwang D.R.
      • Abi-Dargham A.
      • Simpson N.
      • Mawlawi O.
      • et al.
      Validation and reproducibility of measurement of 5-HT1A receptor parameters with [carbonyl-11C]WAY-100635 in humans: Comparison of arterial and reference tisssue input functions.
      ).

      Image Analysis

      To correct for subject motion, PET frames were registered to the eighth frame using the FMRIB linear image registration tool, FLIRT, version 5.0 (FMRIB Image Analysis Group, Oxford, United Kingdom). An automated algorithm identified ROIs (midbrain, vPFC, putamen, amygdala, thalamus, hippocampus, and ACN), as well as cerebellar gray matter, on individuals’ T1-weighted MRIs (
      • Milak M.S.
      • DeLorenzo C.
      • Zanderigo F.
      • Prabhakaran J.
      • Kumar J.S.D.
      • Majo V.J.
      • et al.
      In vivo quantification of human serotonin 1A receptor using 11C-CUMI-101, an agonist PET radiotracer.
      ). Each subject’s mean PET image was co-registered to their MRI using FLIRT, optimized as previously described (
      • DeLorenzo C.
      • Klein A.
      • Mikhno A.
      • Gray N.
      • Zanderigo F.
      • Mann J.J.
      • Mann J.J.
      A new method for assessing PET-MRI coregistration. In: SPIE Medical Imaging.
      ). Time activity curves were generated by plotting measured activity within ROIs over the time course of the PET acquisition.

      Outcome Measure Estimation

      As we previously demonstrated that no brain region is devoid of specific binding with [11C]DASB (
      • Parsey R.V.
      • Kent J.M.
      • Oquendo M.A.
      • Richards M.C.
      • Pratap M.
      • Cooper T.B.
      • et al.
      Acute occupancy of brain serotonin transporter by sertraline as measured by [11C]DASB and positron emission tomography.
      ), we used an outcome measure that does not rely on a reference region (REF): VT/fP (where VT = volume of distribution in the region of interest). This outcome measure has been used in several studies by different groups in cases where a reference region is not available (

      Ichise M (2009): Neuroreceptor imaging and kinetic modeling. In: Van Heertum RL, Tikofsky RS, Ichise M, editors. Functional Cerebral SPECT and PET Imaging, 4th ed. Philadelphia: Lippincott Williams & Wilkins, 44.

      ,
      • Chin C.L.
      • Carr R.A.
      • Llano D.A.
      • Barret O.
      • Xu H.
      • Batis J.
      • et al.
      Pharmacokinetic modeling and [(1)(2)(3)]5-IA-85380 single photon emission computed tomography imaging in baboons: Optimization of dosing regimen for ABT-089.
      ,
      • Mukhin A.G.
      • Kimes A.S.
      • Chefer S.I.
      • Matochik J.A.
      • Contoreggi C.S.
      • Horti A.G.
      • et al.
      Greater nicotinic acetylcholine receptor density in smokers than in nonsmokers: A PET study with 2-18F-FA-85380.
      ,
      • Fujita M.
      • Hines C.S.
      • Zoghbi S.S.
      • Mallinger A.G.
      • Dickstein L.P.
      • Liow J.S.
      • et al.
      Downregulation of brain phosphodiesterase type IV measured with (11)C-(R)-rolipram positron emission tomography in major depressive disorder.
      ,
      • Esterlis I.
      • Cosgrove K.P.
      • Batis J.C.
      • Bois F.
      • Stiklus S.M.
      • Perkins E.
      • et al.
      Quantification of smoking-induced occupancy of beta2-nicotinic acetylcholine receptors: Estimation of nondisplaceable binding.
      ). [11C]DASB regional VT values were derived using likelihood estimation in the graphical approach, which reduces the noise-dependent bias inherent in the graphical approach (
      • Ogden R.T.
      On estimation of kinetic parameters in graphical analysis of PET imaging data.
      ,
      • Parsey R.V.
      • Ogden R.T.
      • Mann J.J.
      Determination of volume of distribution using likelihood estimation in graphical analysis: Elimination of estimation bias.
      ). Brain activity was corrected for the contribution of plasma activity, assuming a 5% blood volume in the regions of interest (
      • Mintun M.A.
      • Raichle M.E.
      • Kilbourn M.R.
      • Wooten G.F.
      • Welch M.J.
      A quantitative model for the in vivo assessment of drug binding sites with positron emission tomography.
      ). For purposes of comparison with other [11C]DASB studies using different outcome measures, the following types of binding potential (BP) were also estimated [see (51) for more details]: BPF [(VT(ROI)−VT(REF))/fP]; BPP (VT(ROI)−VT(REF)); and BPND [(VT(ROI)−VT(REF))/VT(REF)], using cerebellar gray matter as reference region. As there is approximately 30% specific/displaceable [11C]DASB binding in the reference region (
      • Parsey R.V.
      • Kent J.M.
      • Oquendo M.A.
      • Richards M.C.
      • Pratap M.
      • Cooper T.B.
      • et al.
      Acute occupancy of brain serotonin transporter by sertraline as measured by [11C]DASB and positron emission tomography.
      ), VT(REF) overestimates the distribution volume of the nondisplaceable compartment (VND) (
      • Innis R.B.
      • Cunningham V.J.
      • Delforge J.
      • Fujita M.
      • Gjedde A.
      • Gunn R.N.
      • et al.
      Consensus nomenclature for in vivo imaging of reversibly binding radioligands.
      ), leading to biases in estimates of these binding potential measures (
      • Turkheimer F.E.
      • Selvaraj S.
      • Hinz R.
      • Murthy V.
      • Bhagwagar Z.
      • Grasby P.
      • et al.
      Quantification of ligand PET studies using a reference region with a displaceable fraction: Application to occupancy studies with [lsqb]11C[rsqb]-DASB as an example.
      ). Results with these alternate outcome measures are described concisely in the Results section and are presented in greater detail in Supplement 1.

      Statistics

      To borrow strength across all ROIs and properly account for correlation among ROIs measured on the same subject, we fit linear mixed-effects models to the ROI-level VT/fP estimates with region and diagnostic group as fixed effects and subject as the random effect, and this approach was taken for all analyses involving more than one ROI. Other fixed effects considered in linear mixed-effects modeling include sex, age, antidepressant exposure, depression severity, and genetic and environmental factors. Data entered in linear mixed-effects models were first log transformed to remedy slight skewness of VT/fP estimates (
      • Meltzer C.C.
      • Price J.C.
      • Mathis C.A.
      • Butters M.A.
      • Ziolko S.K.
      • Moses-Kolko E.
      • et al.
      Serotonin 1A receptor binding and treatment response in late-life depression.
      ,
      • Rabiner E.A.
      • Wilkins M.R.
      • Turkheimer F.
      • Gunn R.N.
      • Udo de J.
      • de Vries M.
      • Grasby P.M.
      5-Hydroxytryptamine1A receptor occupancy by novel full antagonist 2-[4-[4-(7-chloro-2,3-dihydro-1,4-benzdioxyn-5-yl)-1-piperazinyl]butyl]-1,2-benzisothiazol-3-(2H)-one-1,1-dioxide: a[11C][O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY-100635) positron emission tomography study in humans.
      ,
      • Hirvonen J.
      • Karlsson H.
      • Kajander J.
      • Lepola A.
      • Markkula J.
      • Rasi-Hakala H.
      • et al.
      Decreased brain serotonin 5-HT1A receptor availability in medication-naive patients with major depressive disorder: An in-vivo imaging study using PET and [carbonyl-11C]WAY-100635.
      ), to stabilize the variance, and because our principal hypothesis of a difference between groups specifies that differences in each ROI are proportional to each ROI’s binding level. Log transformation has been used in numerous PET studies by our group and others to address these issues (
      • Parsey R.V.
      • Hastings R.S.
      • Oquendo M.A.
      • Huang Y.Y.
      • Simpson N.
      • Arcement J.
      • et al.
      Lower serotonin transporter binding potential in the human brain during major depressive episodes.
      ,
      • Parsey R.V.
      • Hastings R.S.
      • Oquendo M.A.
      • Hu X.
      • Goldman D.
      • Huang Y.Y.
      • et al.
      Effect of a triallelic functional polymorphism of the serotonin-transporter-linked promoter region on expression of serotonin transporter in the human brain.
      ,
      • Miller J.M.
      • Kinnally E.L.
      • Ogden R.T.
      • Oquendo M.A.
      • Mann J.J.
      • Parsey R.V.
      Reported childhood abuse is associated with low serotonin transporter binding in vivo in major depressive disorder.
      ,
      • Hirvonen J.
      • Karlsson H.
      • Kajander J.
      • Lepola A.
      • Markkula J.
      • Rasi-Hakala H.
      • et al.
      Decreased brain serotonin 5-HT1A receptor availability in medication-naive patients with major depressive disorder: An in-vivo imaging study using PET and [carbonyl-11C]WAY-100635.
      ,
      • Parsey R.V.
      • Oquendo M.A.
      • Ogden R.T.
      • Olvet D.M.
      • Simpson N.
      • Huang Y.Y.
      • et al.
      Altered serotonin 1A binding in major depression: A [carbonyl-C-11]WAY100635 positron emission tomography study.
      ,
      • Parsey R.V.
      • Ojha A.
      • Ogden R.T.
      • Erlandsson K.
      • Kumar D.
      • Landgrebe M.
      • et al.
      Metabolite considerations in the in vivo quantification of serotonin transporters using 11C-DASB and PET in humans.
      ,
      • Parsey R.V.
      • Ogden R.T.
      • Miller J.M.
      • Tin A.
      • Hesselgrave N.
      • Goldstein E.
      • et al.
      Higher serotonin 1A binding in a second major depression cohort: Modeling and reference region considerations.
      ,
      • Oquendo M.A.
      • Hastings R.S.
      • Huang Y.Y.
      • Simpson N.
      • Ogden R.T.
      • Hu X.Z.
      • et al.
      Brain serotonin transporter binding in depressed patients with bipolar disorder using positron emission tomography.
      ,
      • Parsey R.V.
      • Olvet D.M.
      • Oquendo M.A.
      • Huang Y.Y.
      • Ogden R.T.
      • Mann J.J.
      Higher 5-HT1A receptor binding potential during a major depressive episode predicts poor treatment response: Preliminary data from a naturalistic study.
      ,
      • Sullivan G.M.
      • Oquendo M.A.
      • Simpson N.
      • Van Heertum R.L.
      • Mann J.J.
      • Parsey R.V.
      Brain serotonin1A receptor binding in major depression is related to psychic and somatic anxiety.
      ,
      • Miller J.M.
      • Brennan K.G.
      • Ogden T.R.
      • Oquendo M.A.
      • Sullivan G.M.
      • Mann J.J.
      • Parsey R.V.
      Elevated serotonin 1A binding in remitted major depressive disorder: Evidence for a trait biological abnormality.
      ,
      • Milak M.S.
      • Severance A.J.
      • Prabhakaran J.
      • Kumar J.S.
      • Majo V.J.
      • Ogden R.T.
      • et al.
      In vivo serotonin-sensitive binding of [11C]CUMI-101: A serotonin 1A receptor agonist positron emission tomography radiotracer.
      ,
      • Ogden R.T.
      • Zanderigo F.
      • Choy S.
      • Mann J.J.
      • Parsey R.V.
      Simultaneous estimation of input functions: An empirical study.
      ,
      • Sullivan G.M.
      • Ogden R.T.
      • Oquendo M.A.
      • Kumar J.S.
      • Simpson N.
      • Huang Y.Y.
      • et al.
      Positron emission tomography quantification of serotonin-1A receptor binding in medication-free bipolar depression.
      ,
      • Miller J.M.
      • Oquendo M.A.
      • Ogden R.T.
      • Mann J.J.
      • Parsey R.V.
      Serotonin transporter binding as a possible predictor of one-year remission in major depressive disorder.
      ,
      • Milak M.S.
      • Ogden R.T.
      • Vinocur D.N.
      • Van Heertum R.
      • Cooper T.B.
      • Mann J.J.
      • Parsey R.V.
      Effects of tryptophan depletion on the binding of [11C] DASB to the serotonin transporter in baboons: Response to acute serotonin defic.
      ). As the natural log is a monotone transformation, demonstrating a difference in log(VT/fP) is equivalent to demonstrating a difference (in the same direction) in VT/fP. Estimated VT/fP values were weighted in the model according to standard errors computed using a bootstrap algorithm taking into account errors in metabolite, plasma, and brain data (
      • Ogden R.T.
      • Tarpey T.
      Estimation in regression models with externally estimated parameters.
      ). Analyses on single regions were performed using linear models. SPSS Statistics 19 (IBM Corporation, New York, New York; http://www.spss.com/software/statistics/) was used to perform t tests. All other analyses were performed in R 2.10.0 (

      R Core Team (2012): R: A Language and Environment for Statistical Computing. Vienna: R Foundation for Statistical Computing. Available at: http://www.R-project.org

      ).

      Results

      Demographics

      Demographic and clinical variables are presented in Table 2. Among MDD participants, 36 (70.6%) had at least one comorbid Axis I diagnosis, including 8 (15.7%) with remitted alcohol or substance use disorder, 32 (62.8%) with current or past anxiety disorder, 4 (7.8%) with lifetime dysthymia, 3 (5.9%) with current attention-deficit/hyperactivity disorder, and one (2%) with remitted bulimia. Rates of these comorbidities did not differ between MDD attempters and nonattempters (remitted alcohol or substance use disorder: Fisher’s exact p = .41; comorbid anxiety: p = .13; Table 2). MDD attempters had an earlier age of onset than MDD nonattempters. While age differed between MDD subjects and control subjects, it did not differ between MDD attempters and MDD nonattempters (Table 2). 5-HTTLPR genotype did not differ between MDD subjects and control subjects or between MDD attempters and MDD nonattempters (Table 3).
      Table 2Clinical and Demographic Characteristics of the Sample
      Control Subjects n = 31MDD n = 51Control vs. MDD (χ2, p Value)MDD Suicide Attempters n = 15MDD Nonattempters n = 36Attempter vs. Nonattempter (χ2, p Value)
      Female Subjects16 (51.6%)28 (54.9%).08, .778 (53.3%)20 (55.6%).021, .88
      Inpatient14 (27.5%)6 (40.0%)8 (22.2%)2.13, .15
      Number with Family History of MDD in First-Degree Relatives25 (49.0%)5 (33.3%)20 (55.6%)2.09, .15
      Current or Past Comorbid Anxiety Disorder327 (46.7%)25 (69.4%)2.35, .13
      Axis II Comorbidity21 (37.2)6 (40.0%)13 (36.1%).069, .69
      Race/Ethnicity.105
      Fisher’s exact p value as cells contain values too small to fulfill assumptions of χ2 test.
      .09
      Fisher’s exact p value as cells contain values too small to fulfill assumptions of χ2 test.
      Asian6 (19.4%)3 (5.9%)0 (0%)3 (8.3%)
      African American6 (19.4%)5 (9.8%)3 (20%)2 (5.6%)
      Caucasian15 (48.4%)33 (64.7%)8 (53.3%)26 (72%)
      Hispanic2 (3.2%)8 (15.7%)2 (13.3%)5 (13.9%)
      >1 race1 (3.2%)2 (3.9%)2 (13.3%)0 (0%)
      Unknown1 (3.2%)0 (0%)0 (0%)0 (0%)
      Any Current Tobacco Use2 (6.5%)7 (13.7%).47
      Fisher’s exact p value as cells contain values too small to fulfill assumptions of χ2 test.
      1 (6.7%)6 (16.7%).66
      Fisher’s exact p value as cells contain values too small to fulfill assumptions of χ2 test.
      (t, p Value)(t, p Value)
      Age32.6±11.340.3±10.7−3.02, .00438.5±11.541.0±10.5−.76, .45
      Hamilton Depression Rating Scale (24-Item)1.7±2.424.6±6.4−19.01, <.00126.5±6.223.8±6.4 1.40, .17
      Beck Depression Inventory1.3±1.725.7±8.8−15.19, <.00127.5±9.224.9±8.7  .94, .35
      Median Number of Depressive Episodes452.5 −1.70, .088
      Mann-Whitney test presented as (Z, p value), as data are not normally distributed.
      Median Length of Current Depressive Episode (Weeks)
      Best estimate from patient self-report.
      525252−1.15, .25
      Mann-Whitney test presented as (Z, p value), as data are not normally distributed.
      Age at First Depressive Episode19.3±10.814.7±5.821.2±11.9−2.03, .05
      Number of Suicide Attempters15 (29.4%)15 (100%)
      Mean Number of Attempts2.1±1.6
      Maximum Lethality of Attempts
      From the Beck Medical Lethality Scale (details in Methods and Materials).
      2.3±2.0
      Lethality of Most Recent Attempt1.5±1.6
      MDD, major depressive disorder.
      a Fisher’s exact p value as cells contain values too small to fulfill assumptions of χ2 test.
      b Mann-Whitney test presented as (Z, p value), as data are not normally distributed.
      c Best estimate from patient self-report.
      d From the Beck Medical Lethality Scale (details in Methods and Materials).
      Table 35-HTTLPR Triallelic Genotype Distribution
      Goldman Functional GenotypeS'S'L'S'L'L'Fisher’s Exact p ValueS’ Allelic FrequencyL’ Allelic Frequencyχ2 p Value
      Control Subjects (n = 31)11133.323519.21
      MDD (n = 51)1622135448
      MDD Attempters (n = 15)663.741812.48
      MDD Nonattempters (n = 36)1016103636
      MDD, major depressive disorder.

      Possible Covariates

      Across the six ROIs, there was no effect of sex (F = 1.55, df = 1,79, p = .22) or prior antidepressant exposure (F = .68, df = 1,79, p = .41) on 5-HTT binding. Because the MDD and control groups differed in age, we explored the relationship between age and binding. There was no effect of age on binding in the combined sample (F = .02, df = 1,79, p = .89) and no interactions were detected between age and diagnosis (F = 2.13, df = 1,78, p = .15) or age and region (F = 1.60, df = 5,400, p = .16) on binding. Nonetheless, as some studies have previously described a regional age-related decline in 5-HTT binding (
      • Meyer J.H.
      • Wilson A.A.
      • Ginovart N.
      • Goulding V.
      • Hussey D.
      • Hood K.
      • Houle S.
      Occupancy of serotonin transporters by paroxetine and citalopram during treatment of depression: A [(11)C]DASB PET imaging study.
      ,
      • Reimold M.
      • Batra A.
      • Knobel A.
      • Smolka M.N.
      • Zimmer A.
      • Mann K.
      • et al.
      Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: A [11C]DASB PET study.
      ,

      R Core Team (2012): R: A Language and Environment for Statistical Computing. Vienna: R Foundation for Statistical Computing. Available at: http://www.R-project.org

      ,
      • Ichimiya T.
      • Suhara T.
      • Sudo Y.
      • Okubo Y.
      • Nakayama K.
      • Nankai M.
      • et al.
      Serotonin transporter binding in patients with mood disorders: A PET study with [11C](+)McN5652.
      ,
      • Yamamoto M.
      • Suhara T.
      • Okubo Y.
      • Ichimiya T.
      • Sudo Y.
      • Inoue M.
      • et al.
      Age-related decline of serotonin transporters in living human brain of healthy males.
      ,
      • Newberg A.B.
      • Amsterdam J.D.
      • Wintering N.
      • Ploessl K.
      • Swanson R.L.
      • Shults J.
      • Alavi A.
      123I-ADAM binding to serotonin transporters in patients with major depression and healthy controls: A preliminary study.
      ,
      • van Dyck C.H.
      • Malison R.T.
      • Seibyl J.P.
      • Laruelle M.
      • Klumpp H.
      • Zoghbi S.S.
      • et al.
      Age-related decline in central serotonin transporter availability with [(123)I]beta-CIT SPECT.
      ,
      • Hesse S.
      • Barthel H.
      • Murai T.
      • Muller U.
      • Muller D.
      • Seese A.
      • et al.
      Is correction for age necessary in neuroimaging studies of the central serotonin transporter?.
      ,
      • Jacobsen L.K.
      • Staley J.K.
      • Malison R.T.
      • Zoghbi S.S.
      • Seibyl J.P.
      • Kosten T.R.
      • Innis R.B.
      Elevated central serotonin transporter binding availability in acutely abstinent cocaine-dependent patients.
      ,
      • Kuikka J.T.
      • Tammela L.
      • Bergstrom K.A.
      • Karhunen L.
      • Uusitupa M.
      • Tiihonen J.
      Effects of ageing on serotonin transporters in healthy females.
      ,
      • Cannon D.M.
      • Ichise M.
      • Fromm S.J.
      • Nugent A.C.
      • Rollis D.
      • Gandhi S.K.
      • et al.
      Serotonin transporter binding in bipolar disorder assessed using [11C]DASB and positron emission tomography.
      ,
      • Pirker W.
      • Asenbaum S.
      • Hauk M.
      • Kandlhofer S.
      • Tauscher J.
      • Willeit M.
      • et al.
      Imaging serotonin and dopamine transporters with 123I-beta-CIT SPECT: Binding kinetics and effects of normal aging.
      ), we included age and age-by-region interaction as covariates in statistical models.

      Suicide Attempt History

      Serotonin transporter binding differed between control subjects, MDD attempters, and MDD nonattempters in midbrain (F = 3.77, df = 2,78, p = .027; Figure 1), with MDD attempters having lower midbrain binding than both MDD nonattempters (F = 5.88, df = 1,78, p = .031) and control subjects (F = 7.12, df = 1,78, p = .0093); midbrain binding did not differ significantly between MDD nonattempters and control subjects (F = .40, df = 1,78, p = .53). Low midbrain 5-HTT binding in MDD suicide attempters compared with MDD nonattempters was significant in all analyses with alternative PET outcome measures examined (BPF: F = 7.27, df = 1,78, p = .0086; BPP: F = 6.15, df = 1,78, p = .015; BPND: F = 7.51, df = 1,78, p = .0076; Table S1 in Supplement 1). Serotonin transporter binding did not differ as a function of suicide attempt history in the two other regions examined, vPFC and ACN (vPFC: F = .87, df = 1,78, p = .35; ACN: F = .13, df = 1,78, p = .72).
      Figure thumbnail gr1
      Figure 1Comparison of serotonin transporter binding (raw VT [volume of distribution in the region of interest]/fP [plasma free fraction]) as a function of suicide attempt history in midbrain. Scatter plot displays each subject’s midbrain VT/fP value with its associated standard error, computed using a bootstrap algorithm that takes into account errors in metabolite, plasma, and brain data. Horizontal lines indicate weighted means for each group; thick error bars indicate the corresponding equivalent of the standard deviation of the weighted means. Depressed suicide attempters have lower serotonin transporter binding than depressed nonattempters (p = .031) and control subjects (p = .0093). MDD, major depressive disorder.

      Diagnosis Effect

      Considering six a priori ROIs simultaneously (dorsal putamen, amygdala, thalamus, hippocampus, midbrain, and anterior cingulate), 5-HTT binding did not differ between MDD and control subjects (F = .69, df = 1,79, p = .41; Table S2 in Supplement 1). This finding was consistent for all alternative outcome measures examined (BPF: F = 1.53, df = 1,79, p = .22; BPP: F = 3.49, df = 1,79, p = .066; BPND: F = 1.79, df = 1,79, p = .19; Table S2 in Supplement 1). Within the MDD group, we did not observe a relationship between depression severity assessed by the HDRS and binding across the six ROIs (F = .009, df = 1,48, p = .93).

      Genetic and Environmental Effects

      Considering 5-HTTLPR, we did not observe a stepwise effect of the number of L’ alleles on 5-HTT binding across the six ROIs (F = .04, df = 1,74, p = .84). MDD subjects reporting childhood abuse had higher binding than nonabused MDD subjects across the six ROIs (F = 4.34, df = 1,48, p = .043). There was no gene-environment interaction detected between number of 5-HTTLPR LA alleles and childhood abuse status on binding in MDD (F = .65, df = 1,47, p = .42). Including childhood abuse as a covariate did not alter the significance of the contrast of midbrain 5-HTT binding between MDD suicide attempters and nonattempters (F = 6.31, df = 1,78, p = .014).

      Discussion

      Primary Findings and Comparison with Existing Literature

      This study examined the effects of prior suicide attempt and diagnosis in the largest cohort to date of MDD subjects undergoing 5-HTT quantification using PET or single photon emission computed tomography. We observed lower 5-HTT binding in MDD attempters compared with both MDD nonattempters and control subjects in midbrain and no differences as a function of suicide attempt history in vPFC or ACN. In addition, we found no difference in 5-HTT binding between MDD and control groups in six a priori regions. Taken together, these findings suggest that regionally specific, lower 5-HTT binding in midbrain in MDD attempters may be related to the pathophysiology of suicidal behavior, rather than of MDD. The lack of a depression effect on 5-HTT binding is consistent with a series of previous [11C]DASB studies using the outcome measure BPND (
      • Meyer J.H.
      • Wilson A.A.
      • Ginovart N.
      • Goulding V.
      • Hussey D.
      • Hood K.
      • Houle S.
      Occupancy of serotonin transporters by paroxetine and citalopram during treatment of depression: A [(11)C]DASB PET imaging study.
      ,
      • Meyer J.H.
      • Wilson A.A.
      • Sagrati S.
      • Hussey D.
      • Carella A.
      • Potter W.Z.
      • et al.
      Serotonin transporter occupancy of five selective serotonin reuptake inhibitors at different doses: An [(11)C]DASB positron emission tomography study.
      ,
      • Meyer J.H.
      • Houle S.
      • Sagrati S.
      • Carella A.
      • Hussey D.F.
      • Ginovart N.
      • et al.
      Brain serotonin transporter binding potential measured with carbon 11-labeled DASB positron emission tomography: Effects of major depressive episodes and severity of dysfunctional attitudes.
      ), although others have reported lower (
      • Reimold M.
      • Batra A.
      • Knobel A.
      • Smolka M.N.
      • Zimmer A.
      • Mann K.
      • et al.
      Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: A [11C]DASB PET study.
      ,
      • Selvaraj S.
      • Venkatesha Murthy N.
      • Bhagwagar Z.
      • Bose S.K.
      • Hinz R.
      • Grasby P.M.
      • Cowen P.J.
      Diminished brain 5-HT transporter binding in major depression: A positron emission tomography study with [(11)C]DASB.
      ) and higher (
      • Cannon D.M.
      • Ichise M.
      • Rollis D.
      • Klaver J.M.
      • Gandhi S.K.
      • Charney D.S.
      • et al.
      Elevated serotonin transporter binding in major depressive disorder assessed using positron emission tomography and [11C]DASB; comparison with bipolar disorder.
      ) [11C]DASB binding in MDD using BPP and BPND. It is notable that the current finding was replicated with all alternative PET outcome measures examined (BPF, BPP, and BPND).
      Our data suggest that discrepant [11C]DASB PET findings in MDD may be at least partly due to differences in the proportion of suicide attempters in previous samples. Four of six previous [11C]DASB MDD studies did not report rates of suicide attempt history in their samples (
      • Meyer J.H.
      • Wilson A.A.
      • Ginovart N.
      • Goulding V.
      • Hussey D.
      • Hood K.
      • Houle S.
      Occupancy of serotonin transporters by paroxetine and citalopram during treatment of depression: A [(11)C]DASB PET imaging study.
      ,
      • Meyer J.H.
      • Wilson A.A.
      • Sagrati S.
      • Hussey D.
      • Carella A.
      • Potter W.Z.
      • et al.
      Serotonin transporter occupancy of five selective serotonin reuptake inhibitors at different doses: An [(11)C]DASB positron emission tomography study.
      ,
      • Meyer J.H.
      • Houle S.
      • Sagrati S.
      • Carella A.
      • Hussey D.F.
      • Ginovart N.
      • et al.
      Brain serotonin transporter binding potential measured with carbon 11-labeled DASB positron emission tomography: Effects of major depressive episodes and severity of dysfunctional attitudes.
      ,
      • Reimold M.
      • Batra A.
      • Knobel A.
      • Smolka M.N.
      • Zimmer A.
      • Mann K.
      • et al.
      Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: A [11C]DASB PET study.
      ). Of the two [11C]DASB studies reporting suicide attempt status, one found lower 5-HTT binding in anteroventral striatum in MDD attempters compared with MDD nonattempters in the same direction as our finding (
      • Cannon D.M.
      • Ichise M.
      • Rollis D.
      • Klaver J.M.
      • Gandhi S.K.
      • Charney D.S.
      • et al.
      Elevated serotonin transporter binding in major depressive disorder assessed using positron emission tomography and [11C]DASB; comparison with bipolar disorder.
      ). The other study had only 2 attempters out of 12 MDD subjects, which did not allow direct examination of an effect of suicide attempt status on binding (
      • Selvaraj S.
      • Venkatesha Murthy N.
      • Bhagwagar Z.
      • Bose S.K.
      • Hinz R.
      • Grasby P.M.
      • Cowen P.J.
      Diminished brain 5-HT transporter binding in major depression: A positron emission tomography study with [(11)C]DASB.
      ).
      There are some clinical and demographic differences between the MDD attempters and nonattempters in our sample: while depression severity did not differ between attempters and nonattempters, attempters had an earlier onset of major depressive illness, consistent with previous studies (
      • Zisook S.
      • Lesser I.
      • Stewart J.W.
      • Wisniewski S.R.
      • Balasubramani G.K.
      • Fava M.
      • et al.
      Effect of age at onset on the course of major depressive disorder.
      ). This raises the possibility that low midbrain 5-HTT binding among attempters is driven by specific genetic loading associated with early-onset depression (
      • Neuman R.J.
      • Geller B.
      • Rice J.P.
      • Todd R.D.
      Increased prevalence and earlier onset of mood disorders among relatives of prepubertal versus adult probands.
      ). Moreover, attempters had a trend toward greater depression chronicity as measured by number of prior major depressive episodes. While this may be a potential confound in the interpretation of our results, we did not find a relationship between age of onset of major depressive illness and midbrain 5-HTT VT/fP (r = .03, p = .84).
      We found no effect of suicide attempt status in vPFC or ACN. The low signal-to-noise ratio in vPFC (binding is only 14% higher in vPFC than in cerebellar gray matter) may have limited our ability to detect group differences. We did not examine the relationship between regional 5-HTT binding and suicide attempt lethality or objective medical damage, given the limited range of lethality in the current sample.

      Interpretation of Findings

      Low regional 5-HTT binding among MDD attempters may be due to less gene expression. Consistent with our previous findings, 5-HTT binding was not associated with 5-HTTLPR genotype in this study, but other functional promoter 5-HTT loci need to be examined. Additionally, epigenetic differences may drive differential 5-HTT binding: studies in nonhuman primates find that DNA methylation, but not 5-HTT genotype, is significantly associated with peripheral blood mononuclear cell 5-HTT messenger RNA expression (
      • Kinnally E.L.
      • Capitanio J.P.
      • Leibel R.
      • Deng L.
      • LeDuc C.
      • Haghighi F.
      • Mann J.J.
      Epigenetic regulation of serotonin transporter expression and behavior in infant rhesus macaques.
      ). Discrepant findings reported regarding the potential association between 5-HTT binding and 5-HTTLPR genotype may also be due to biallelic versus triallelic genotyping and different brain imaging outcome measures, as well as racial stratification differences in study populations.
      An alternative explanation for low regional 5-HTT binding among suicide attempters is that it is a result of accelerated 5-HTT internalization in response to low 5-HT release. Evidence supporting a 5-HT deficiency related to suicidal behavior includes low cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) associated with suicidal behavior and risk of suicide (
      • Asberg M.
      • Traskman L.
      • Thoren P.
      5-HIAA in the cerebrospinal fluid. A biochemical suicide predictor?.
      ), postmortem studies reporting lower brainstem 5-HT or 5-HIAA in suicides (
      • Kamali M.
      • Oquendo M.A.
      • Mann J.J.
      Understanding the neurobiology of suicidal behavior.
      ), and lower CSF 5-HIAA in more lethal suicide attempters with MDD (
      • Mann J.J.
      • Malone K.M.
      Cerebrospinal fluid amines and higher-lethality suicide attempts in depressed inpatients.
      ).
      Serotonergic abnormalities may contribute to suicidal behavior through effects on aggressive traits, decision making, or problem solving. Measures of aggression have been correlated with several serotonergic measures, including low in vivo serotonin 1A receptor binding (
      • Parsey R.V.
      • Oquendo M.A.
      • Simpson N.R.
      • Ogden R.T.
      • Van Heertum R.
      • Arango V.
      • Mann J.J.
      Effects of sex, age, and aggressive traits in man on brain serotonin 5-HT(1A) receptor binding potential measured by PET using [C-11]WAY-100635.
      ), blunted prolactin responses to serotonergic challenge with fenfluramine (
      • Manuck S.B.
      • Flory J.D.
      • McCaffery J.M.
      • Matthews K.A.
      • Mann J.J.
      • Muldoon M.F.
      Aggression, impulsivity, and central nervous system serotonergic responsivity in a nonpatient sample.
      ,
      • New A.S.
      • Trestman R.F.
      • Mitropoulou V.
      • Goodman M.
      • Koenigsberg H.H.
      • Silverman J.
      • Siever L.J.
      Low prolactin response to fenfluramine in impulsive aggression.
      ), and low CSF 5-HIAA (
      • Stanley B.
      • Molcho A.
      • Stanley M.
      • Winchel R.
      • Gameroff M.J.
      • Parsons B.
      • Mann J.J.
      Association of aggressive behavior with altered serotonergic function in patients who are not suicidal.
      ). However, we do not find an effect of lifetime aggression assessed via the Brown Goodwin Lifetime History of Aggression scale on 5-HTT VT/fP in vPFC (F = .084, df = 1,77, p = .77).

      Reported Childhood Abuse

      In exploratory analyses, we did not replicate our previous finding of low 5-HTT in MDD with reported childhood abuse history compared with MDD without childhood abuse history (
      • Miller J.M.
      • Kinnally E.L.
      • Ogden R.T.
      • Oquendo M.A.
      • Mann J.J.
      • Parsey R.V.
      Reported childhood abuse is associated with low serotonin transporter binding in vivo in major depressive disorder.
      ). Given these discrepant findings and the report of lower 5-HTT binding in adult monkeys with a history of maternal deprivation (
      • Ichise M.
      • Vines D.
      • Gura T.
      • Anderson G.
      • Suomi S.
      • Higley J.
      • Innis R.B.
      Effects of early life stress on [11C]DASB positron emission tomography imaging of serotonin transporters in adolescent peer- and mother-reared rhesus monkeys.
      ), replication is required with a larger sample, using a validated measure of childhood abuse such as the Childhood Trauma Questionnaire (
      • Bernstein D.P.
      • Fink L.
      ). We did not observe a gene-environment interaction between reported childhood abuse and 5-HTTLPR genotype on 5-HTT binding within the MDD sample. A definitive examination of a gene-environment interaction affecting 5-HTT binding as a mediator of depression risk would necessitate a large sample stratified across a continuous range of depression severity.

      Strengths and Limitations

      Strengths of this imaging study include the large sample size, favorable properties of [11C]DASB, quantitative estimation of VT/fP using a metabolite-corrected arterial input function, and careful diagnostic assessment. A limitation of this study is the lack of age matching between MDD subjects and control subjects. This is unlikely to have impacted the reported findings for the following reasons: 1) we did not observe an effect of age on 5-HTT binding in our sample; 2) we covaried for age in all analyses; 3) age did not differ between MDD attempters and MDD nonattempters, who nonetheless differed in midbrain 5-HTT binding; and 4) if age-related decline in 5-HTT binding were present, it would bias our results toward lower binding in MDD subjects than control subjects, which we did not observe.
      A longer minimum antidepressant-free interval than the 2-week minimum used in the present study may be preferable, but ethical requirements prevent this approach. An alternative strategy would be to recruit drug naïve participants. Nonetheless, in this sample, the median antidepressant-free interval in those MDD subjects with prior antidepressant exposure was 11.5 weeks. Moreover, we did not observe a difference in 5-HTT VT/fP as a function of prior antidepressant exposure status, nor did mean antidepressant-free interval differ between MDD attempters and MDD nonattempters, which makes the minimum antidepressant-free interval employed in this study an unlikely explanation for reported findings.
      Other clinical and demographic factors have previously been associated with 5-HTT binding, including cigarette smoking (
      • Ruhe H.G.
      • Booij J.
      • Reitsma J.B.
      • Schene A.H.
      Serotonin transporter binding with [123I]beta-CIT SPECT in major depressive disorder versus controls: Effect of season and gender.
      ,
      • Staley J.K.
      • Krishnan-Sarin S.
      • Zoghbi S.
      • Tamagnan G.
      • Fujita M.
      • Seibyl J.P.
      • et al.
      Sex differences in [123I]beta-CIT SPECT measures of dopamine and serotonin transporter availability in healthy smokers and nonsmokers.
      ) and anxiety (
      • Reimold M.
      • Batra A.
      • Knobel A.
      • Smolka M.N.
      • Zimmer A.
      • Mann K.
      • et al.
      Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: A [11C]DASB PET study.
      ). We did not include these as covariates in the current analysis, given the large number of covariates examined and as smoking history did not differ between groups and anxiety comorbidity did not differ between MDD attempters and nonattempters. It should be noted that while differences in midbrain VT/fP between MDD suicide attempters and nonattempters are statistically significant, there is overlap between groups in binding, and as such, this measure cannot be used alone to differentiate these groups. Future studies with improved 5-HTT quantification and the combination of imaging and clinical measures may improve group differentiation.
      A limitation common to most studies quantifying 5-HTT in vivo is the lack of a reference region in the brain that is devoid of 5-HTT. We chose one approach to address this issue, using the outcome measure VT/fP, thereby avoiding the error introduced when using other available outcome measures that subtract out, or subtract and then divide by, the volume of distribution measured in a reference region that actually contains specific binding. Use of VT/fP does not account for nonspecific binding in the brain, and it is thus possible that low midbrain binding in MDD attempters is due to differences in nonspecific binding. Other approaches to address this methodological challenge have been proposed (
      • Turkheimer F.E.
      • Selvaraj S.
      • Hinz R.
      • Murthy V.
      • Bhagwagar Z.
      • Grasby P.
      • et al.
      Quantification of ligand PET studies using a reference region with a displaceable fraction: Application to occupancy studies with [lsqb]11C[rsqb]-DASB as an example.
      ). However, our results were similar when using all other outcome measures that do attempt to correct for nonspecific binding in the brain using a reference region (BPF, BPP, and BPND), so this methodological issue is unlikely to be driving our reported findings.

      Conclusions

      Serotonin transporter binding is low in vivo in the midbrain of depressed suicide attempters. This abnormality is consistent with postmortem findings in suicides and with a serotonergic deficit model of suicidal behavior. We are currently studying the prognostic significance of low 5-HTT binding as a predictor of repeated suicide attempt.
      Research presented in this manuscript was supported by National Institute of Mental Health Grants 5P50 MH62185 (Dr. Mann, principal investigator) and 2 R01 MH040695 (Dr. Mann, principal investigator).
      Dr. Ogden and Ms. Hesselgrave report no biomedical financial interests or potential conflicts of interest. Dr. Miller has received financial compensation for psychiatric evaluations of subjects enrolled in medication studies sponsored by Pfizer and Orexigen Therapeutics unrelated to the current manuscript. His family owns stock in Johnson & Johnson. Dr. Sullivan serves as a member of the Scientific Advisory Board of TONIX Pharmaceuticals, Inc. and has received compensation in the form of stock shares; he has served as a consultant for Ono Pharma USA, Inc. and he has a US patent application for a use of tianeptine. None are related to the current manuscript. Dr. Mann received past unrelated grants from GlaxoSmithKline and Novartis and royalties for a rating scale, Columbia Suicide Severity Rating Scale. Dr. Oquendo receives royalties for the use of the Columbia Suicide Severity Rating Scale and received financial compensation from Pfizer for the safety evaluation of a clinical facility unrelated to the current manuscript. She was the recipient of a grant from Eli Lilly to support a year of the salary for the Lilly Suicide Scholar, Enrique Baca-Garcia, M.D., Ph.D. She has received unrestricted educational grants and/or lecture fees from Astra-Zeneca, Bristol Myers Squibb, Eli Lilly, Janssen, Otsuko, Pfizer, Sanofi-Aventis, and Shire. Her family owns stock in Bristol Myers Squibb. Dr. Parsey was the recipient of grants from Pfizer, Lundbeck, Sepracor, Novartis, and General Electric, all unrelated to this manuscript. He has a US patent on voxel-based methods for assessing subjects using positron emission tomography.

      Appendix A. Supplementary materials

      References

        • Courtet P.
        • Gottesman I.I.
        • Jollant F.
        • Gould T.D.
        The neuroscience of suicidal behaviors: What can we expect from endophenotype strategies?.
        Transl Psychiatry. 2011; 1: e7
        • Gonda X.
        • Fountoulakis K.N.
        • Harro J.
        • Pompili M.
        • Akiskal H.S.
        • Bagdy G.
        • Rihmer Z.
        The possible contributory role of the S allele of 5-HTTLPR in the emergence of suicidality.
        J Psychopharmacol. 2011; 25: 857-866
        • Arango V.
        • Underwood M.D.
        • Mann J.J.
        Serotonin brain circuits involved in major depression and suicide.
        Prog Brain Res. 2002; 136: 443-453
        • Purselle D.C.
        • Nemeroff C.B.
        Serotonin transporter: A potential substrate in the biology of suicide.
        Neuropsychopharmacology. 2003; 28: 613-619
        • Arango V.
        • Underwood M.D.
        • Boldrini M.
        • Tamir H.
        • Kassir S.A.
        • Hsiung S.
        • et al.
        Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims.
        Neuropsychopharmacology. 2001; 25: 892-903
        • Ruhe H.G.
        • Mason N.S.
        • Schene A.H.
        Mood is indirectly related to serotonin, norepinephrine and dopamine levels in humans: A meta-analysis of monoamine depletion studies.
        Mol Psychiatry. 2007; 12: 331-359
        • Bhagwagar Z.
        • Whale R.
        • Cowen P.J.
        State and trait abnormalities in serotonin function in major depression.
        Br J Psychiatry. 2002; 180: 24-28
        • Serrano-Blanco A.
        • Gabarron E.
        • Garcia-Bayo I.
        • Soler-Vila M.
        • Carames E.
        • Penarrubia-Maria M.T.
        • et al.
        Effectiveness and cost-effectiveness of antidepressant treatment in primary health care: A six-month randomised study comparing fluoxetine to imipramine.
        J Affect Disord. 2006; 91: 153-163
        • Trivedi M.H.
        • Rush A.J.
        • Wisniewski S.R.
        • Nierenberg A.A.
        • Warden D.
        • Ritz L.
        • et al.
        Evaluation of outcomes with citalopram for depression using measurement-based care in STAR*D: Implications for clinical practice.
        Am J Psychiatry. 2006; 163: 28-40
        • Meyer J.H.
        Imaging the serotonin transporter during major depressive disorder and antidepressant treatment.
        J Psychiatry Neurosci. 2007; 32: 86-102
        • Stockmeier C.A.
        Involvement of serotonin in depression: Evidence from postmortem and imaging studies of serotonin receptors and the serotonin transporter.
        J Psychiatr Res. 2003; 37: 357-373
        • Parsey R.V.
        • Hastings R.S.
        • Oquendo M.A.
        • Huang Y.Y.
        • Simpson N.
        • Arcement J.
        • et al.
        Lower serotonin transporter binding potential in the human brain during major depressive episodes.
        Am J Psychiatry. 2006; 163: 52-58
        • Frankle W.G.
        • Huang Y.
        • Hwang D.-R.
        • Talbot P.S.
        • Slifstein M.
        • Van Heertum R.
        • et al.
        Comparative evaluation of serotonin transporter radioligands 11C-DASB and 11C-McN 5652 in healthy humans.
        J Nucl Med. 2004; 45: 682-694
        • Szabo Z.
        • McCann U.D.
        • Wilson A.A.
        • Scheffel U.
        • Owonikoko T.
        • Mathews W.B.
        • et al.
        Comparison of (+)-(11)C-McN5652 and (11)C-DASB as serotonin transporter radioligands under various experimental conditions.
        J Nucl Med. 2002; 43: 678-692
        • Meyer J.H.
        • Wilson A.A.
        • Ginovart N.
        • Goulding V.
        • Hussey D.
        • Hood K.
        • Houle S.
        Occupancy of serotonin transporters by paroxetine and citalopram during treatment of depression: A [(11)C]DASB PET imaging study.
        Am J Psychiatry. 2001; 158: 1843-1849
        • Meyer J.H.
        • Wilson A.A.
        • Sagrati S.
        • Hussey D.
        • Carella A.
        • Potter W.Z.
        • et al.
        Serotonin transporter occupancy of five selective serotonin reuptake inhibitors at different doses: An [(11)C]DASB positron emission tomography study.
        Am J Psychiatry. 2004; 161: 826-835
        • Meyer J.H.
        • Houle S.
        • Sagrati S.
        • Carella A.
        • Hussey D.F.
        • Ginovart N.
        • et al.
        Brain serotonin transporter binding potential measured with carbon 11-labeled DASB positron emission tomography: Effects of major depressive episodes and severity of dysfunctional attitudes.
        Arch Gen Psychiatry. 2004; 61: 1271-1279
        • Cannon D.M.
        • Ichise M.
        • Rollis D.
        • Klaver J.M.
        • Gandhi S.K.
        • Charney D.S.
        • et al.
        Elevated serotonin transporter binding in major depressive disorder assessed using positron emission tomography and [11C]DASB; comparison with bipolar disorder.
        Biol Psychiatry. 2007; 62: 870-877
        • Reimold M.
        • Batra A.
        • Knobel A.
        • Smolka M.N.
        • Zimmer A.
        • Mann K.
        • et al.
        Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: A [11C]DASB PET study.
        Mol Psychiatry. 2008; 13: 557
        • Selvaraj S.
        • Venkatesha Murthy N.
        • Bhagwagar Z.
        • Bose S.K.
        • Hinz R.
        • Grasby P.M.
        • Cowen P.J.
        Diminished brain 5-HT transporter binding in major depression: A positron emission tomography study with [(11)C]DASB.
        Psychopharmacolog (Berl). 2009; 213: 555-562
        • Hu X.
        • Oroszi G.
        • Chun J.
        • Smith T.L.
        • Goldman D.
        • Schuckit M.A.
        An expanded evaluation of the relationship of four alleles to the level of response to alcohol and the alcoholism risk.
        Alcohol Clin Exp Res. 2005; 29: 8-16
        • Lesch K.P.
        • Bengel D.
        • Heils A.
        • Sabol S.Z.
        • Greenberg B.D.
        • Petri S.
        • et al.
        Association of anxiety-related traits with a polymorphism in the serotonin transporter gene regulatory region.
        Science. 1996; 274: 1527-1531
        • Caspi A.
        • Sugden K.
        • Moffitt T.E.
        • Taylor A.
        • Craig I.W.
        • Harrington H.
        • et al.
        Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene.
        Science. 2003; 301: 386-389
        • Hung C.F.
        • Lung F.W.
        • Chen C.H.
        • O'Nions E.
        • Hung T.H.
        • Chong M.Y.
        • et al.
        Association between suicide attempt and a tri-allelic functional polymorphism in serotonin transporter gene promoter in Chinese patients with schizophrenia.
        Neurosci Lett. 2011; 504: 242-246
        • Karg K.
        • Burmeister M.
        • Shedden K.
        • Sen S.
        The serotonin transporter promoter variant (5-HTTLPR), stress, and depression meta-analysis revisited: Evidence of genetic moderation.
        Arch Gen Psychiatry. 2011; 68: 444-454
        • Parsey R.V.
        • Hastings R.S.
        • Oquendo M.A.
        • Hu X.
        • Goldman D.
        • Huang Y.Y.
        • et al.
        Effect of a triallelic functional polymorphism of the serotonin-transporter-linked promoter region on expression of serotonin transporter in the human brain.
        Am J Psychiatry. 2006; 163: 48-51
        • Willeit M.
        • Praschak-Rieder N.
        Imaging the effects of genetic polymorphisms on radioligand binding in the living human brain: A review on genetic neuroreceptor imaging of monoaminergic systems in psychiatry.
        Neuroimage. 2010; 53: 878-892
        • Miller J.M.
        • Kinnally E.L.
        • Ogden R.T.
        • Oquendo M.A.
        • Mann J.J.
        • Parsey R.V.
        Reported childhood abuse is associated with low serotonin transporter binding in vivo in major depressive disorder.
        Synapse. 2009; 63: 565-573
        • First M.
        • Spitzer R.
        • Gibbon M.
        • Williams J.
        Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I/P, Version 2.0).
        Biometrics Research Department, New York State Psychiatric Institute, New York1995
        • Loranger A.W.
        Sex difference in age at onset of schizophrenia.
        Arch Gen Psychiatry. 1984; 41: 157-161
        • First M.B.
        • Gibbon M.
        • Spitzer R.L.
        • Williams J.B.
        • Benjamin L.S.
        SCID-II Personality Questionnaire.
        DC: American Psychiatric Press., Washington1997
        • Beck A.T.
        • Ward C.H.
        • Mendelson M.
        • Mock J.
        • Erbauh J.
        An inventory for measuring depression.
        Arch Gen Psychiatry. 1961; 4: 53-63
        • Hamilton M.
        A rating scale for depression.
        J Neurol Neurosurg Psychiatry. 1960; 23: 56-62
        • Brown G.L.
        • Goodwin F.K.
        • Ballenger J.C.
        • Goyer P.F.
        • Major L.F.
        Aggression in human correlates with cerebrospinal fluid amine metabolites.
        Psychiatry Res. 1979; 1: 131-139
        • Oquendo M.A.
        • Halberstam B.
        • Mann J.J.
        Risk factors for suicidal behavior: The utility and limitations of research instruments.
        in: First M.B. Standardized Evaluation in Clinical Practice. American Psychiatric Publishing, Arlington, VA2003: 103-130
        • Beck A.T.
        • Beck R.
        • Kovacs M.
        Classification of suicidal behaviors: I. Quantifying intent and medical lethality.
        Am J Psychiatry. 1975; 132: 285-287
        • Belanger M.J.
        • Simpson N.R.
        • Wang T.
        • Van Heertum R.
        • Mann J.J.
        • Parsey R.V.
        Biodistribution and radiation dosimetry of [11C]DASB in baboons.
        Nucl Med Biol. 2004; 31: 1097-1102
        • Ogden R.T.
        • Ojha A.
        • Erlandsson K.
        • Oquendo M.A.
        • Mann J.J.
        • Parsey R.V.
        In vivo quantification of serotonin transporters using [(11)C]DASB and positron emission tomography in humans: Modeling considerations.
        J Cereb Blood Flow Metab. 2007; 27: 205-217
        • Parsey R.V.
        • Slifstein M.
        • Hwang D.R.
        • Abi-Dargham A.
        • Simpson N.
        • Mawlawi O.
        • et al.
        Validation and reproducibility of measurement of 5-HT1A receptor parameters with [carbonyl-11C]WAY-100635 in humans: Comparison of arterial and reference tisssue input functions.
        J Cereb Blood Flow Metab. 2000; 20: 1111-1133
        • Milak M.S.
        • DeLorenzo C.
        • Zanderigo F.
        • Prabhakaran J.
        • Kumar J.S.D.
        • Majo V.J.
        • et al.
        In vivo quantification of human serotonin 1A receptor using 11C-CUMI-101, an agonist PET radiotracer.
        J Nucl Med. 2010; 51: 1892-1900
        • DeLorenzo C.
        • Klein A.
        • Mikhno A.
        • Gray N.
        • Zanderigo F.
        • Mann J.J.
        • Mann J.J.
        A new method for assessing PET-MRI coregistration. In: SPIE Medical Imaging.
        SPIE, Bellingham, WA2009 (72592W–72598)
        • Parsey R.V.
        • Kent J.M.
        • Oquendo M.A.
        • Richards M.C.
        • Pratap M.
        • Cooper T.B.
        • et al.
        Acute occupancy of brain serotonin transporter by sertraline as measured by [11C]DASB and positron emission tomography.
        Biol Psychiatry. 2006; 59: 821-828
      1. Ichise M (2009): Neuroreceptor imaging and kinetic modeling. In: Van Heertum RL, Tikofsky RS, Ichise M, editors. Functional Cerebral SPECT and PET Imaging, 4th ed. Philadelphia: Lippincott Williams & Wilkins, 44.

        • Chin C.L.
        • Carr R.A.
        • Llano D.A.
        • Barret O.
        • Xu H.
        • Batis J.
        • et al.
        Pharmacokinetic modeling and [(1)(2)(3)]5-IA-85380 single photon emission computed tomography imaging in baboons: Optimization of dosing regimen for ABT-089.
        J Pharmacol Exp Therapeutics. 2011; 336: 716-723
        • Mukhin A.G.
        • Kimes A.S.
        • Chefer S.I.
        • Matochik J.A.
        • Contoreggi C.S.
        • Horti A.G.
        • et al.
        Greater nicotinic acetylcholine receptor density in smokers than in nonsmokers: A PET study with 2-18F-FA-85380.
        J Nucl Med. 2008; 49: 1628-1635
        • Fujita M.
        • Hines C.S.
        • Zoghbi S.S.
        • Mallinger A.G.
        • Dickstein L.P.
        • Liow J.S.
        • et al.
        Downregulation of brain phosphodiesterase type IV measured with (11)C-(R)-rolipram positron emission tomography in major depressive disorder.
        Biol Psychiatry. 2012; 72: 548-554
        • Esterlis I.
        • Cosgrove K.P.
        • Batis J.C.
        • Bois F.
        • Stiklus S.M.
        • Perkins E.
        • et al.
        Quantification of smoking-induced occupancy of beta2-nicotinic acetylcholine receptors: Estimation of nondisplaceable binding.
        J Nucl Med. 2010; 51: 1226-1233
        • Ogden R.T.
        On estimation of kinetic parameters in graphical analysis of PET imaging data.
        Stat Med. 2003; 22: 3557-3568
        • Parsey R.V.
        • Ogden R.T.
        • Mann J.J.
        Determination of volume of distribution using likelihood estimation in graphical analysis: Elimination of estimation bias.
        J Cereb Blood Flow Metab. 2003; 23: 1471-1478
        • Mintun M.A.
        • Raichle M.E.
        • Kilbourn M.R.
        • Wooten G.F.
        • Welch M.J.
        A quantitative model for the in vivo assessment of drug binding sites with positron emission tomography.
        Ann Neurol. 1984; 15: 217-227
        • Innis R.B.
        • Cunningham V.J.
        • Delforge J.
        • Fujita M.
        • Gjedde A.
        • Gunn R.N.
        • et al.
        Consensus nomenclature for in vivo imaging of reversibly binding radioligands.
        J Cereb Blood Flow Metab. 2007; 27: 1533-1539
        • Turkheimer F.E.
        • Selvaraj S.
        • Hinz R.
        • Murthy V.
        • Bhagwagar Z.
        • Grasby P.
        • et al.
        Quantification of ligand PET studies using a reference region with a displaceable fraction: Application to occupancy studies with [lsqb]11C[rsqb]-DASB as an example.
        J Cereb Blood Flow Metab. 2012; 32: 70-80
        • Meltzer C.C.
        • Price J.C.
        • Mathis C.A.
        • Butters M.A.
        • Ziolko S.K.
        • Moses-Kolko E.
        • et al.
        Serotonin 1A receptor binding and treatment response in late-life depression.
        Neuropsychopharmacology. 2004; 29: 2258-2265
        • Rabiner E.A.
        • Wilkins M.R.
        • Turkheimer F.
        • Gunn R.N.
        • Udo de J.
        • de Vries M.
        • Grasby P.M.
        5-Hydroxytryptamine1A receptor occupancy by novel full antagonist 2-[4-[4-(7-chloro-2,3-dihydro-1,4-benzdioxyn-5-yl)-1-piperazinyl]butyl]-1,2-benzisothiazol-3-(2H)-one-1,1-dioxide: a[11C][O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY-100635) positron emission tomography study in humans.
        J Pharmacol Exp Ther. 2002; 301: 1144-1150
        • Hirvonen J.
        • Karlsson H.
        • Kajander J.
        • Lepola A.
        • Markkula J.
        • Rasi-Hakala H.
        • et al.
        Decreased brain serotonin 5-HT1A receptor availability in medication-naive patients with major depressive disorder: An in-vivo imaging study using PET and [carbonyl-11C]WAY-100635.
        Int J Neuropsychopharmacol. 2008; 11: 465-476
        • Parsey R.V.
        • Oquendo M.A.
        • Ogden R.T.
        • Olvet D.M.
        • Simpson N.
        • Huang Y.Y.
        • et al.
        Altered serotonin 1A binding in major depression: A [carbonyl-C-11]WAY100635 positron emission tomography study.
        Biol Psychiatry. 2006; 59: 106-113
        • Parsey R.V.
        • Ojha A.
        • Ogden R.T.
        • Erlandsson K.
        • Kumar D.
        • Landgrebe M.
        • et al.
        Metabolite considerations in the in vivo quantification of serotonin transporters using 11C-DASB and PET in humans.
        J Nucl Med. 2006; 47: 1796-1802
        • Parsey R.V.
        • Ogden R.T.
        • Miller J.M.
        • Tin A.
        • Hesselgrave N.
        • Goldstein E.
        • et al.
        Higher serotonin 1A binding in a second major depression cohort: Modeling and reference region considerations.
        Biol Psychiatry. 2010; 68: 170-178
        • Oquendo M.A.
        • Hastings R.S.
        • Huang Y.Y.
        • Simpson N.
        • Ogden R.T.
        • Hu X.Z.
        • et al.
        Brain serotonin transporter binding in depressed patients with bipolar disorder using positron emission tomography.
        Arch Gen Psychiatry. 2007; 64: 201-208
        • Parsey R.V.
        • Olvet D.M.
        • Oquendo M.A.
        • Huang Y.Y.
        • Ogden R.T.
        • Mann J.J.
        Higher 5-HT1A receptor binding potential during a major depressive episode predicts poor treatment response: Preliminary data from a naturalistic study.
        Neuropsychopharmacology. 2006; 31: 1745-1749
        • Sullivan G.M.
        • Oquendo M.A.
        • Simpson N.
        • Van Heertum R.L.
        • Mann J.J.
        • Parsey R.V.
        Brain serotonin1A receptor binding in major depression is related to psychic and somatic anxiety.
        Biol Psychiatry. 2005; 58: 947-954
        • Miller J.M.
        • Brennan K.G.
        • Ogden T.R.
        • Oquendo M.A.
        • Sullivan G.M.
        • Mann J.J.
        • Parsey R.V.
        Elevated serotonin 1A binding in remitted major depressive disorder: Evidence for a trait biological abnormality.
        Neuropsychopharmacology. 2009; 34: 2275-2284
        • Milak M.S.
        • Severance A.J.
        • Prabhakaran J.
        • Kumar J.S.
        • Majo V.J.
        • Ogden R.T.
        • et al.
        In vivo serotonin-sensitive binding of [11C]CUMI-101: A serotonin 1A receptor agonist positron emission tomography radiotracer.
        J Cereb Blood Flow Metab. 2011; 31: 243-249
        • Ogden R.T.
        • Zanderigo F.
        • Choy S.
        • Mann J.J.
        • Parsey R.V.
        Simultaneous estimation of input functions: An empirical study.
        J Cereb Blood Flow Metab. 2010; 30: 816-826
        • Sullivan G.M.
        • Ogden R.T.
        • Oquendo M.A.
        • Kumar J.S.
        • Simpson N.
        • Huang Y.Y.
        • et al.
        Positron emission tomography quantification of serotonin-1A receptor binding in medication-free bipolar depression.
        Biol Psychiatry. 2009; 66: 223-230
        • Miller J.M.
        • Oquendo M.A.
        • Ogden R.T.
        • Mann J.J.
        • Parsey R.V.
        Serotonin transporter binding as a possible predictor of one-year remission in major depressive disorder.
        J Psychiatr Res. 2008; 42: 1137-1144
        • Milak M.S.
        • Ogden R.T.
        • Vinocur D.N.
        • Van Heertum R.
        • Cooper T.B.
        • Mann J.J.
        • Parsey R.V.
        Effects of tryptophan depletion on the binding of [11C] DASB to the serotonin transporter in baboons: Response to acute serotonin defic.
        Biol Psychiatry. 2005; 57: 102-106
        • Ogden R.T.
        • Tarpey T.
        Estimation in regression models with externally estimated parameters.
        Biostatistics. 2006; 7: 115-129
      2. R Core Team (2012): R: A Language and Environment for Statistical Computing. Vienna: R Foundation for Statistical Computing. Available at: http://www.R-project.org

        • Ichimiya T.
        • Suhara T.
        • Sudo Y.
        • Okubo Y.
        • Nakayama K.
        • Nankai M.
        • et al.
        Serotonin transporter binding in patients with mood disorders: A PET study with [11C](+)McN5652.
        Biol Psychiatry. 2002; 51: 715-722
        • Yamamoto M.
        • Suhara T.
        • Okubo Y.
        • Ichimiya T.
        • Sudo Y.
        • Inoue M.
        • et al.
        Age-related decline of serotonin transporters in living human brain of healthy males.
        Life Sci. 2002; 71: 751-757
        • Newberg A.B.
        • Amsterdam J.D.
        • Wintering N.
        • Ploessl K.
        • Swanson R.L.
        • Shults J.
        • Alavi A.
        123I-ADAM binding to serotonin transporters in patients with major depression and healthy controls: A preliminary study.
        J Nucl Med. 2005; 46: 973-977
        • van Dyck C.H.
        • Malison R.T.
        • Seibyl J.P.
        • Laruelle M.
        • Klumpp H.
        • Zoghbi S.S.
        • et al.
        Age-related decline in central serotonin transporter availability with [(123)I]beta-CIT SPECT.
        Neurobiol Aging. 2000; 21: 497-501
        • Hesse S.
        • Barthel H.
        • Murai T.
        • Muller U.
        • Muller D.
        • Seese A.
        • et al.
        Is correction for age necessary in neuroimaging studies of the central serotonin transporter?.
        Eur J Nucl Med Mol Imaging. 2003; 30: 427-430
        • Jacobsen L.K.
        • Staley J.K.
        • Malison R.T.
        • Zoghbi S.S.
        • Seibyl J.P.
        • Kosten T.R.
        • Innis R.B.
        Elevated central serotonin transporter binding availability in acutely abstinent cocaine-dependent patients.
        Am J Psychiatry. 2000; 157: 1134-1140
        • Kuikka J.T.
        • Tammela L.
        • Bergstrom K.A.
        • Karhunen L.
        • Uusitupa M.
        • Tiihonen J.
        Effects of ageing on serotonin transporters in healthy females.
        Eur J Nucl Med. 2001; 28: 911-913
        • Cannon D.M.
        • Ichise M.
        • Fromm S.J.
        • Nugent A.C.
        • Rollis D.
        • Gandhi S.K.
        • et al.
        Serotonin transporter binding in bipolar disorder assessed using [11C]DASB and positron emission tomography.
        Biol Psychiatry. 2006; 60: 207-217
        • Pirker W.
        • Asenbaum S.
        • Hauk M.
        • Kandlhofer S.
        • Tauscher J.
        • Willeit M.
        • et al.
        Imaging serotonin and dopamine transporters with 123I-beta-CIT SPECT: Binding kinetics and effects of normal aging.
        J Nucl Med. 2000; 41: 36-44
        • Zisook S.
        • Lesser I.
        • Stewart J.W.
        • Wisniewski S.R.
        • Balasubramani G.K.
        • Fava M.
        • et al.
        Effect of age at onset on the course of major depressive disorder.
        Am J Psychiatry. 2007; 164: 1539-1546
        • Neuman R.J.
        • Geller B.
        • Rice J.P.
        • Todd R.D.
        Increased prevalence and earlier onset of mood disorders among relatives of prepubertal versus adult probands.
        J Am Acad Child Adolesc Psychiatry. 1997; 36: 466-473
        • Kinnally E.L.
        • Capitanio J.P.
        • Leibel R.
        • Deng L.
        • LeDuc C.
        • Haghighi F.
        • Mann J.J.
        Epigenetic regulation of serotonin transporter expression and behavior in infant rhesus macaques.
        Genes Brain Behav. 2010; 9: 575-582
        • Asberg M.
        • Traskman L.
        • Thoren P.
        5-HIAA in the cerebrospinal fluid. A biochemical suicide predictor?.
        Arch Gen Psychiatry. 1976; 33: 1193-1197
        • Kamali M.
        • Oquendo M.A.
        • Mann J.J.
        Understanding the neurobiology of suicidal behavior.
        Depress Anxiety. 2001; 14: 164-176
        • Mann J.J.
        • Malone K.M.
        Cerebrospinal fluid amines and higher-lethality suicide attempts in depressed inpatients.
        Biol Psychiatry. 1997; 41: 162-171
        • Parsey R.V.
        • Oquendo M.A.
        • Simpson N.R.
        • Ogden R.T.
        • Van Heertum R.
        • Arango V.
        • Mann J.J.
        Effects of sex, age, and aggressive traits in man on brain serotonin 5-HT(1A) receptor binding potential measured by PET using [C-11]WAY-100635.
        Brain Res. 2002; 954: 173-182
        • Manuck S.B.
        • Flory J.D.
        • McCaffery J.M.
        • Matthews K.A.
        • Mann J.J.
        • Muldoon M.F.
        Aggression, impulsivity, and central nervous system serotonergic responsivity in a nonpatient sample.
        Neuropsychopharmacology. 1998; 19: 287-299
        • New A.S.
        • Trestman R.F.
        • Mitropoulou V.
        • Goodman M.
        • Koenigsberg H.H.
        • Silverman J.
        • Siever L.J.
        Low prolactin response to fenfluramine in impulsive aggression.
        J Psychiatr Res. 2004; 38: 223-230
        • Stanley B.
        • Molcho A.
        • Stanley M.
        • Winchel R.
        • Gameroff M.J.
        • Parsons B.
        • Mann J.J.
        Association of aggressive behavior with altered serotonergic function in patients who are not suicidal.
        Am J Psychiatry. 2000; 157: 609-614
        • Ichise M.
        • Vines D.
        • Gura T.
        • Anderson G.
        • Suomi S.
        • Higley J.
        • Innis R.B.
        Effects of early life stress on [11C]DASB positron emission tomography imaging of serotonin transporters in adolescent peer- and mother-reared rhesus monkeys.
        J Neurosci. 2006; 26: 4638-4643
        • Bernstein D.P.
        • Fink L.
        Childhood Trauma Questionnaire: A Retrospective Self-Report. The Psychological Corporation, San Antonio, TX1998
        • Ruhe H.G.
        • Booij J.
        • Reitsma J.B.
        • Schene A.H.
        Serotonin transporter binding with [123I]beta-CIT SPECT in major depressive disorder versus controls: Effect of season and gender.
        Eur J Nucl Med Mol Imaging. 2009; 36: 841-849
        • Staley J.K.
        • Krishnan-Sarin S.
        • Zoghbi S.
        • Tamagnan G.
        • Fujita M.
        • Seibyl J.P.
        • et al.
        Sex differences in [123I]beta-CIT SPECT measures of dopamine and serotonin transporter availability in healthy smokers and nonsmokers.
        Synapse. 2001; 41: 275-284