How the Neuropeptide PACAP Affects Male Fertility Through Brain Hormone Signaling

In PACAP knockout male mice, GnRH neuron numbers and immunoreactivity were reduced in the medial preoptic area. Paradoxically, kisspeptin neuron numbers were elevated in both the RP3V and arcuate nucleus, along with increased estrogen receptor alpha (ERα) expression. The medial preoptic area showed fewer androgen receptor-positive cells but more ERα-positive cells, suggesting a disrupted balance between estrogenic and androgenic signaling. These neuroendocrine changes likely underlie the reproductive dysfunction observed in PACAP-deficient males.

Researchers used PACAP knockout (KO) mice and wild-type controls. They performed immunofluorescent staining, immunohistochemistry, and RNAscope in situ hybridization to detect protein and mRNA expression of GnRH, kisspeptin, estrogen receptor alpha (ERα), and androgen receptor (AR) in the hypothalamus across key reproductive brain regions (MPOA, RP3V, arcuate nucleus).

Male infertility affects millions worldwide, and the brain's hormone control center is often overlooked as a contributing factor. This study reveals that a single neuropeptide — PACAP — plays a significant role in maintaining the delicate balance of reproductive signaling in the male brain, opening new avenues for understanding and potentially treating neuroendocrine causes of male infertility.

PACAP is increasingly recognized as a multifunctional neuropeptide with roles far beyond its original discovery in pituitary regulation. This study adds male reproductive function to its portfolio, connecting neuropeptide signaling to the HPG axis — the hormonal cascade that controls fertility. Understanding these connections could eventually inform treatments for unexplained male infertility.

This is a knockout mouse study, which shows what happens when PACAP is completely absent — a more extreme scenario than reduced PACAP levels in humans. The study is observational (describing changes in KO mice) without interventional rescue experiments to confirm causality. Sample sizes were not specified in the abstract. Human relevance of these specific hypothalamic changes needs confirmation.