Neuroendocrine Control of the Testis: Focus on Orexinergic Modulation of Spermatogenesis

Orexins are hypothalamic neuropeptides that play an essential role in managing the sleep-wake cycle, food intake, and energy balance. There are two forms of orexins, namely orexin A (OXA) and orexin B (OXB). Orexins exert their effects through two different G-protein-coupled receptors (OX1R and OX2R). Apart from the hypothalamus, expressions of orexins and their receptors are also reported in peripheral organs including the testis, prostate, epididymis, seminal vesicle, and penis. Several studies have explored the mechanisms of action of orexin in the male gonad. This review article summarizes recent knowledge on how the orexin system regulates testicular functions like steroidogenesis, germ cell dynamics, glucose metabolism, and oxidative stress responses. By elucidating these mechanisms, the present study may prove helpful in a better understanding of the spermatogenic process. Additionally, this review article may provide new insights into the interaction of the hypothalamus with the testis and the auto/paracrine role of various neuropeptides in the regulation of male reproduction.