Seasonal reproductive periodicity and thyroid fluctuations in female Indian palm squirrel, Funambulus pennanti.

Seasonal reproductive rhythmicity and concomitant thyroid fluctuations have been studied in the female Indian palm squirrel, Funambulus pennanti. The majority of the squirrels enter estrus during March and April when ovarian follicles attain maximum diameter. Ovulation starts in April and continues till June. A large number of degenerating follicles, indicating decline in ovarian functions, is a characteristic feature of the ovary in August. Minimum percent thyroid 131I uptake is recorded during May and June, i.e. at the onset of mating season. In July, which also marked the gestation period in the majority of the squirrels dissected, thyroid activity significantly increases. Gonadal regression begins in August and this is accompanied by corresponding fall in the thyroid 131I uptake. Alterations in thyroid cytoarchitecture during different months of the year are in accordance with the results obtained from radioiodine uptake studies. Fluctuations in thyroid functions during gonadal regression, recrudescence and peak gonadal activity are discussed in the present communication.