Reproductive activity in the free ranging rhesus monkeys is seasonal (November-February). Kisspeptin is known as one of the fundamental regulators of neuroendocrine reproductive axis. We hypothesized that the expression of hypothalamic kisspeptin, GPR54 and GnRH underlies the seasonal changes of reproduction in this higher primate. To prove our hypothesis, we examined the expression of kisspeptin, GPR54 and GnRH (mRNA and protein levels using RT-qPCR and IHC/ICC techniques) in the medio-basal hypothalamus (MBH) of adult male rhesus monkeys during breeding season (BS; December; n=3) and non-breeding season (NBS; June; n=3). The animals were maintained under free ranging conditions in the primate breeding colonies of Kunming Institute of Zoology (102.71ºlongitude, 25.03º latitude). Additionally, we measured CSF (four samples collected at 20 min interval/animal from the lumbar vertebrae; n=3) kisspeptin and peripheral testosterone levels in BS and NBS (n=4) by using specific RIA’s.

The relative mRNA expression showed significant increase in the breeding season for kisspeptin (p < 0.01), GPR54 (p < 0.0005) and GnRH (p < 0.0001) in the MBH. The number of kisspeptin cell bodies significantly increased in the arcuate nucleus (ARC) during the BS (p < 0.0001). The number of GnRH, GPR54 positive and GPR54 positive GnRH cell bodies was significantly increased (p < 0.01; p < 0.01 and p < 0.001, respectively) in the BS. The number of contacts between the GnRH and kisspeptin cell bodies was also enhanced in the BS (p < 0.01). The CSF kisspeptin levels were significantly increased during the breeding season (p < 0.0001). Peripheral testosterone concentrations (p < 0.0001) and paired testis weight (p < 0.0001) were also increased in the BS monkeys.

Present data suggest that in higher primates, season related reproductive activity is associated with increased hypothalamic kisspeptin signaling impinging on GnRH neurons.