Photoperiodic regulation of ovarian steroidogenesis in a tropical rodent, Funambulus pennanti: role of melatonin and MT1

摘要

To elucidate the role of photoperiodically modulated endogenous melatonin and its receptor MT1 in the ovary of a diurnal rodent, adult Indian palm squirrel Funambulus pennanti were exposed to Short Day (SD; 16L:8D) and Long Day (LD; 16L:8D) and compared with natural day controls (NDL; 12L:12D). Plasma 17-beta estradiol level was significantly low in SD group while expression of StAR, P450SCC, 17-beta HSD, and aromatase showed significant down-regulation in the ovary of squirrels maintained under SD when compared to LD and NDL groups suggesting an overall decrease in steroidogenesis. Expression of ER alpha in the ovary was significantly lower in SD than both LD and NDL groups, having a positive correlation with plasma estradiol level. Circulatory melatonin level was significantly high in SD-exposed squirrels, while expression of MT1R decreased in the ovary when compared to LD and NDL groups, showing a negative correlation with plasma melatonin levels. Expression of cell proliferation marker Proliferating Cell Nuclear Antigen (PCNA) was positively correlated to MT1R expression in the ovary being significantly low in SD-exposed squirrels. Our results suggest that even in tropical rodents seasonal variation in photoperiod is responsible for initiating female reproductive activities where circulatory melatonin via MT1R plays an important role.