Background
Recurrence of depressive symptoms after tryptophan depletion (TD) in selective serotonin
reuptake inhibitor (SSRI)-treated depression is an important, unexplained phenomenon.
With [18F] MPPF positron emission tomography (PET), serotonin (5-hydroxytryptamine, 5-HT)
1A receptor binding potential (5-HT1ABP) was measured after TD in various brain regions in citalopram-treated depression.
This 5-HT1ABP measurement is sensitive to changes in extracellular 5-HT in animal models.
Methods
Eight remitted patients with major depressive disorder received [18F] MPPF PET scans twice: once after TD and once after sham depletion. Behavioral measures
were evaluated with the Hamilton Depression Rating Scale and visual analog scales.
Results
No effect on regional 5-HT1ABP was observed after TD, despite an 86% decrease in total plasma tryptophan and transient
depressive relapse in six of eight patients.
Conclusions
Large-magnitude changes in extracellular 5-HT are not crucial for the mood effects
observed in SSRI-treated subjects after TD. Therefore, greater consideration must
be given to other mechanisms that involve vulnerability to small perturbations in
extracellular 5-HT, such as impairment of signal transduction.
Key words
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Article info
Publication history
Published online: September 20, 2004
Accepted:
July 19,
2004
Received in revised form:
July 9,
2004
Received:
April 14,
2004
Identification
Copyright
© 2004 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.
