Mice lacking the neuropeptide PACAP show disrupted hormone signaling in the hypothalamus, including fewer GnRH neurons and imbalanced sex hormone receptors, which may explain male fertility problems.
Fewer GnRH neurons + more kisspeptin neuronsPACAP knockout mice showed opposing changes in two key reproductive neuron populations, revealing a disrupted hormonal control circuit
What the researchers found
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.
Why it matters
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.
How the study worked
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).
What this study cannot tell us
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.
How to read the evidence
This is a preclinical study using knockout mice with thorough molecular and histological analysis. While it provides strong mechanistic evidence for PACAP's role in male reproductive neuroendocrinology, the findings need validation in human contexts.
When this study was published
Published in 2025, this is very recent research contributing to the growing understanding of PACAP's role beyond its classical functions, making it highly current in the neuropeptide field.
The bigger picture
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.
Questions still open
- Could PACAP supplementation or receptor agonists restore normal reproductive signaling in PACAP-deficient males?
- Do men with unexplained infertility show altered PACAP levels or signaling in the hypothalamus?
- Why do kisspeptin neurons increase when GnRH neurons decrease — is this a compensatory mechanism?
Common questions
What is PACAP and what does it do in the body?
How could a brain neuropeptide affect male fertility?
Read the original research
The hypothalamic effects of PACAP on the hypothalamic-pituitary-gonadal axis in male mice.
Frontiers in endocrinology, 16, 1677085
Citation
Faludi, Péter; Barabás, Klaudia; Lengyel, Ferenc; Udvarácz, Ildikó; Pham, Dániel; Kisjós, Olivér; Nagy, Zsuzsanna; Reglődi, Dóra; Kovács, Gergely. (2025). The hypothalamic effects of PACAP on the hypothalamic-pituitary-gonadal axis in male mice.. Frontiers in endocrinology, 16, 1677085. https://doi.org/10.3389/fendo.2025.1677085