Seasonal regulation of social communication by photoperiod and testosterone: Effects of arginine–vasopressin, serotonin and galanin in the medial preoptic area–anterior hypothalamus

Arginine–vasopressin (AVP) activation of V1a AVP receptors in the medial preoptic area–anterior hypothalamus (MPOA–AH) plays a critical role in the control of a form of social communication called flank marking. The ability of AVP and V1a receptors in the MPOA–AH to regulate flank marking is modulated by a number of factors including galanin (GAL), serotonin (5-HT) and gonadal hormones. More recent studies suggest that there may be seasonal differences in the number or type of AVP receptors in the MPOA–AH controlling flank marking or in the modulation of these mechanisms by GAL or 5-HT. The purpose of the present study was to examine how exposure to “summer-like” and “winter-like” photoperiods alters the neural mechanisms regulating flank marking. These studies confirmed that V1a AVP receptors, but not V1b AVP receptors play a significant role in controlling flank marking in the MPOA–AH in both LP and SP-housed hamsters. These studies also found that there were no significant differences between hamsters housed in LP and SP in the ability of serotonin 5-HT1a/7 and 5-HT1b receptor agonists injected into the MPOA–AH to inhibit odor-induced flank marking. Finally, these studies found that GAL could significantly inhibit the ability of AVP to stimulate flank marking in SP-housed hamsters and that there were no differences between hamsters housed in LP and SP in the ability of a GAL antagonist to inhibit AVP-induced flank marking. The present study confirms that V1a receptors are critical for AVP regulation of flank marking and that photoperiodic mechanisms do not alter the modulation of flank marking by GAL or 5-HT in the MPOA–AH.