Expression and co‐localization of RFRP‐3 and kisspeptin during breeding and non‐breeding season in the hypothalamus of male rhesus monkey (Macaca mulatta)

The mechanism that underpins how RFRP-3 and kisspeptin interacts are not fully understood in higher primates. This study therefore set out to assess RFRP-3 and kisspeptin expression and their morphological interactions in the breeding, and in the non-breeding period in monkey hypothalamus.Eight mature male macaques (Macaca mulatta) in the breeding season (February; n = 4) and non-breeding season (June; n = 4) were used. To reveal the expression and co-localization of RFRP-3 and kisspeptin, double-labeled immunohistochemistry was performed. Testicular volume, sperm count, and plasma testosterone level were also measured to validate the breeding and non-breeding paradigms.Testicular volume, plasma testosterone level, and sperm count showed a significant reduction during non-breeding season. The number of kisspeptin-positive cells was significantly increased during the breeding season (p < 0.05), whereas more RFRP-3-positive cell bodies were seen in the non-breeding season (p < 0.01). Close contacts of RFRP-3 fibers with kisspeptin cells showed no significant difference (p > 0.05) across seasons. However, co-localization of RFRP-3-ir cell bodies onto kisspeptin IR cell bodies showed a statistical increase (p < 0.01) in non-breeding season.In higher primates, RFRP-3 decreases kisspeptin drives from the same cells to GnRH neurons in an autocrine manner causing suppression of the reproductive axis during the non-breeding period.