Dim light at night alters photoperiodic perception in male Syrian hamsters (Mesocricetus auratus)

Photoperiod determines the timing of reproduction in seasonal breeders. Long-day breeders breed when the photoperiod is above the critical photoperiod and plenty of food is available for the offspring, while short photoperiod prevents breeding during unfavorable conditions. The urban night-light environment is rapidly expanding and may alter perceptions of day length, creating a conflicting situation for animals. The present study examined the effects of exposure to dim light (0.0064 W/m²) coupled with a short photoperiod (8L:16D/day) on the hypothalamic-pituitary-gonadal axis and metabolism in long-day breeder Syrian hamsters (Mesocricetus auratus). Group one (SD; n = 5) was exposed to short photoperiod (8L:16D) while group two (dSD; n = 5) was exposed to short photoperiod coupled with an illuminated night with dim light of 0.0064 W/m2. After four weeks, animals were sampled. There was an increase in testicular volume and upregulation of testicular steroidogenic markers. Further, upregulation of transcripts involved in reproduction (Tshβ, Dio2, and GnRh), epigenetic regulation (Tet1 and Hat1), and downregulation of Dnmt3A and Hdac3 were observed in hypothalamic tissue. We also observed upregulation of liver metabolic transcripts in dSD animals. These findings suggest that dim light at night during a short photoperiod can mislead photoperiodic information and subsequent downstream processes linked to reproduction.