Variation in Gonadal Steroid and Melatonin during Gestation of a Diurnal Seasonal Breeder Indian Palm Squirrel Funambulus pennanti

Very little information is available to delineate the role of melatonin during the complex process of gestation in seasonally breeding mammals. The present study was aimed at understanding the physiology of gestation and fetal growth in relation to maternal hormonal levels, including melatonin, of a tropical seasonal breeder, Funambulus pennanti. Through assessment of the vaginal smear during breeding season (March) we selected the early pregnant females (∼5 days) from nature and provided them adequate facility in laboratory as in nature. The total length of gestation period i.e., ∼45 days, comparatively a long gestation period for a diurnal rodent, was recorded. The litter size was small (3-4), with the maximum number of pregnancies during March to May (in August to September, very less) depending upon the availability of food. The intrauterine growth of the fetus is divisible into three phases, i) implantation and cell division, ii) organ formation, and iii) growth and completion of intrauterine development. A method for the quantitative analysis of fetal growth was devised. A correlation with the levels of maternal hormones suggests that a direct relationship of progesterone and melatonin exists during pregnancy, which declined immediately after parturition. The high melatonin level during gestation, having an almost inverse relationship with estradiol level, suggests that melatonin might play a role in maintenance of pregnancy. Variations, if any, in the melatonin receptor expression in the uterus throughout the gestation period may throw some light on the role of melatonin in maintenance of pregnancy.