Mild increase of temperature from the thermoneutral zone inhibits reproductive activation in Syrian hamsters through epigenetic inhibition

The rapid increase in urbanization is drastically altering the habitat composition of the wild population. Urbanization is predominantly changing the landscape, composition of flora and fauna, availability of night light, and the rise in temperature. In the natural habitat, photoperiod and temperature are inseparable. In the present study, we examined the effect of mild temperature change from the thermoneutral zone of Syrian hamsters on reproduction-linked activities. To investigate the neuroendocrine mechanisms underlying heat stress effects on reproduction in hamsters, two experiments were performed on adult male animals. In experiment one, animals were divided into two groups (n = 5/group) and exposed to a long photoperiod (15L:9D) with either low (LT; 20 ± 2°C) or high temperature (HT; 32 ± 2°C). After 21 days, all animals were sampled. In experiment two, hamsters (n = 20) were divided equally into two groups and were exposed to the first short photoperiod of 8L:16D, but with low temperature (LT; 20 ± 2°C) or high temperature (HT; 32 ± 2°C). After 30 days, all animals were exposed to a long day (15L:9D), but animals from each temperature treatment were divided equally into two groups (n = 5/group). Half of the animals (n = 5) of low temperature remained in low temperature (LL group) while the remaining animals were moved to high temperature (LH group). Similarly, half of the animals (n = 5) of high temperature remained in high temperature (HH group), and the rest of the animals were moved to low temperature (HL group). Body mass and testicular volume were measured at different intervals. After 30 days of long-day treatment, the animals were sampled. Findings suggest that exposure to 3 weeks of high temperature attenuates testicular growth, coupled with low testosterone levels and downregulation of Kiss1, Eya3, Tshβ, GnRh, Tet1, Tet2, and Hat1, while upregulation of Dio3, GnIh, Dnmt1, Dnmt3A, Hdac1, and Hdac5 occurs in HT groups. Results from experiment two suggest that low temperature promotes, while high temperature attenuates reproduction and the linked phenomenon. Together, these findings suggest that high temperature modulates the reproductive responses of Syrian hamsters.