Dim light at night alters pubertal timing and reproductive parameters in male and female Sprague-Dawley rats

This study investigated whether dim light at night (dLAN) can alter pubertal timing and reproductive parameters in male and female Sprague-Dawley(SD) rats.

Male and female SD rats were assigned to dLAN or control groups from PND21. Pubertal onset was assessed by vaginal opening (VO) in females and preputial separation (PS) in males. Body weight, estrous cycle, reproductive organ weights, plasma melatonin, serum leptin, and sex hormones were measured before and after puberty. Ovarian histology and hypothalamic expression of puberty- and circadian-related genes, as well as gonadal steroidogenesis and receptor genes, were analyzed.

dLAN advanced VO in females and PS in males. In females, this was accompanied by disrupted estrous cycles, increased atretic/cystic follicles, and decreased corpora lutea. However, in males, the advancement of PS occurred despite a paradoxical decrease in circulating testosterone and the downregulation of key Leydig cell steroidogenic genes (Star and Hsd17b3), revealing a marked discordance between central and peripheral reproductive markers. dLAN upregulated hypothalamic Kiss1, GnRH, and Gpr54, and elevated circulating leptin, GnRH, and LH, but suppressed testosterone.

dLAN exposure leads to sex-specific disruption of the reproductive axis. In females, dLAN induces accelerated pubertal onset accompanied by ovulatory dysfunction. In contrast, in males, dLAN precipitates a functional decoupling and desynchronization within the HPG axis, characterized by central neuroendocrine activation but peripheral steroidogenic impairment. These findings highlight that low-intensity nocturnal light disturbs the coordinated temporal organization of the reproductive system.