An Increased Hypothalamic Kisspeptin Signaling Is Associated with the Non Breeding to Breeding Season Switch in Free Ranging Adult Male Rhesus Monkeys

Kisspeptin is one of the fundamental regulators of the neuroendocrine reproductive axis. We hypothesized that the expression of hypothalamic kisspeptin, kisspeptin receptor (KISS1R) and GnRH underlies the seasonal changes of reproduction in Rhesus monkey. We examined the expression of kisspeptin, KISS1R and GnRH (mRNA and protein levels) in the medio-basal hypothalamus (MBH) of adult male rhesus monkeys maintained under free ranging conditions during breeding (BS; January; N = 3) and non-breeding season (NBS, July; n=3). Cerebrospinal fluid (CSF) was collected (four samples collected at 30 min interval/animal from the lumbar vertebrae) for the determination of kisspeptin during BS (November) and NBS (July) along with the determination of peripheral testosterone levels by using specific RIA. A significant increase in the relative mRNA expression of kisspeptin (P < 0.01), KISS1R (P < 0.0005) and GnRH (P < 0.0001) in the MBH was observed during the breeding season. The number of kisspeptin cell bodies significantly increased in the arcuate nucleus (ARC) during the BS (P < 0.0001). The number of GnRH, KISS1R positive, KISS1R positive GnRH cell bodies and contacts between the GnRH and kisspeptin cell bodies were significantly increased (P < 0.01; P < 0.01, P < 0.001 and P < 0.01, respectively) in the BS. The CSF kisspeptin levels (P < 0.0001), peripheral testosterone concentrations (P < 0.0001) and paired testis weight (P < 0.0001) were also increased during the BS monkeys. In conclusion, present study suggested that seasonal changes in the reproductive activity in higher nonhuman-primates are associated with alteration in the hypothalamic kisspeptin system.