Recognition of specific individuals is fundamental to mammalian social behavior and is mediated in most mammals by the main and accessory olfactory systems. Both these systems innervate the medial amygdala (MeA), where activity of the neuropeptide oxytocin is thought to mediate social recognition memory (SRM). The specific contribution of the MeA to SRM formation and the specific actions of oxytocin in the MeA are unknown.
We used the social discrimination test to evaluate short-term and long-term SRM in adult Sprague-Dawley male rats (n = 38). The role of protein synthesis in the MeA was investigated by local application of the protein synthesis blocker anisomycin (n = 11). Synaptic plasticity was assessed in vivo by recording the MeA evoked field potential responses to stimulation of the main (n = 21) and accessory (n = 56) olfactory bulbs before and after theta burst stimulation. Intracerebroventricular administration of saline, oxytocin, or oxytocin receptor antagonist was used to measure the effect of oxytocin on synaptic plasticity.
Anisomycin application to the MeA prevented the formation of long-term SRM. In addition, the responses of MeA neurons underwent long-term depression (LTD) after theta burst stimulation of the accessory olfactory bulb, but not the main accessory bulb, in an oxytocin-dependent manner. No LTD was found in socially isolated rats, which are known to lack long-term SRM. Finally, accessory olfactory bulb stimulation before SRM acquisition blocked long-term SRM, supporting the involvement of LTD in the MeA in formation of long-term SRM.
Our results indicate that long-term SRM in rats involves protein synthesis and oxytocin-dependent LTD in the MeA.
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Published online: March 28, 2014
Accepted: March 19, 2014
Received in revised form: March 19, 2014
Received: November 6, 2013
© 2014 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.
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- Amygdala, Oxytocin, and Social Cognition in Autism Spectrum DisordersBiological PsychiatryVol. 76Issue 5
- PreviewIn the past decade, the elaboration of animal models has brought significant advances in understanding the development of the limbic neural circuitry and the modulatory role of hormones and neuropeptides in complex behaviors, such as social cognition. The study of Gur et al. (1) in this issue of Biological Psychiatry yields important and exciting results elucidating the molecular mechanism by which oxytocin (OT) enhances social recognition memory (SRM) in adult Sprague-Dawley male rats. In rodents, the acquisition of information about conspecifics is mediated by olfactory and pheromonal signals, conveyed via the main olfactory bulb and the accessory olfactory bulb (AOB), both projecting to the medial amygdala (MeA).