ACTA ENDOCRINOLOGICA (BUC)

Hypothalamic kisspeptin signaling has been recently observed to correlate with seasonal breeding in free ranging male rhesus monkeys. Recent evidence also suggests that excitatory and inhibitory amino acid neurotransmitters contribute in regulation of kisspeptin neurons. Objective. The present study was focused on analyzing the interplay of Kiss1 neurons with afferent excitatory and inhibitory signals in the brain of male rhesus monkeys during the breeding and non breeding seasons. We hypothesized that: kisspeptin stimulation may occur due to the increase in N-methyl-D,L-aspartate (NMDA) dependant excitatory inputs and decrease in inhibitory γ-aminobutyric acid (GABA) based cues during the breeding season Materials and Methods. Messenger ribonucleic acid (mRNA) was extracted from the medio basal hypothalamus (MBH) of five free ranging adult male rhesus monkeys (Macaca mulatta) during the breeding season (n=3; October; plasma testosterone levels: 26.15±2.64 nmol/L; testicular volume: 69.00 ± 0.57 ml); and the non-breeding season (n=2; July; plasma testosterone levels: 4.09±1.64 nmol/L; testicular volume: 12.88±0.31 ml). Real time polymerase chain reaction (RT-PCR) was used to quantify the levels of Kiss1, Kiss1r, NR1 and glutamic acid decarboxylase (GAD67) mRNA, relative to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Results. Significantly high (p<0.05) expression of Kiss1, Kiss1r and NR1 mRNA and low (p<0.05) expression of GAD67 mRNA in the hypothalamus were found to be in synchrony with the breeding season. Conclusion. Based on correlative gene expression changes in the adult male monkey hypothalamus we suggest that in higher primates increased kisspeptin signaling during breeding season may be entrained by an increase in NMDA excitatory inputs; while decreased kisspeptin signaling during the non-breeding season may be driven by an increase in GABA based inhibitory cues.