Daily Rhythmic Changes in Kisspeptin Gene Expression and Testosterone Hormone in Male Syrian Hamsters (Mesocricetus auratus).

Abstract

This study examines how testosterone levels and kisspeptin gene expression are affected in male Syrian hamsters following pinealectomy and photoperiod modification. By examining the rhythmic changes in these parameters under long (16L: 8D) and short (8L: 16D) photoperiods, we aim to elucidate the role of melatonin and photoperiod in regulating seasonal reproductive physiology. One hundred and ninety-two male Syrian hamsters were equally divided into four groups (n = 48/group). Two groups were pinealectomized (pinx) and the other two groups were sham-operated (control). Treatment and control groups were then exposed to either a long photoperiod (LP) of 16 hours light/8 hours dark or a short photoperiod (SP) of 8 hours light/16 hours dark for 30 days and then sampled at specific temporal intervals (ZT0, ZT4, ZT8, ZT12, ZT16, and ZT20) at which hypothalamic tissues and serum samples were collected. Kiss1 mRNA expression and protein levels were measured using qPCR and Western blotting, while testosterone and melatonin levels were determined via ELISA. Under a long photoperiod, Kiss1 mRNA expression and protein levels exhibited significant diurnal variation, peaking during the light phase (P < 0.05). Pinealectomy disrupted these rhythms, leading to altered testosterone levels. Under a short photoperiod, a marked change in Kiss1 expression and testosterone was also observed, emphasizing photoperiod and melatonin's role in synchronizing reproductive rhythms. These findings highlight the central role of melatonin not just in modulating levels, but also in synchronizing the daily reproductive rhythms necessary for seasonal adaptation.