Sexual differences and seasonal variations in vasoactive intestinal peptide immunoreactivity in the suprachiasmatic nucleus of jerboa ( Jaculus orientalis)

Abstract

The sexual differences and the seasonal variation in the vasoactive intestinal peptide (VIP) content of the suprachiasmatic nucleus (SCN) of a desert rodent, the jerboa ( Jaculus orientalis) were studied using immunocytochemical techniques. During the period of sexual activity (spring-early summer), the VIP immunoreactivity in the SCN was higher in females than in males. In the period of sexual quiescence (autumn), both males and females exhibited an even more intense VIP immunoreaction in the SCN as compared to spring. However, during this period, the sex-related differences in the VIP content of the SCN observed in spring were no longer detectable. The direct possible influence of sex hormones on the VIP content in the SCN, and the physiological significance of the seasonal variation observed in the VIP immunoreactivity in the SCN in this species remains to be determined.