Effect of pinealectomy and testosterone on gonadal regression and accessory sex organs in Indian palm squirrel, Funambulus pennanti.

ABSTRACT

Indian palm squirrel (Funambulus pennanti), is a tropical seasonal breeder presents a short gonadal regression period (October-November), concomitant with declining plasma testosterone level. If pinealectomized (Px), however, squirrels maintain full gonadal activity and plasma testosterone levels. The aim of the present study was, therefore, to determine if the Px and exogenous testosterone in intact and Px squirrels would prevent natural gonadal regression. Experiment was performed during testicular regression phase (i.e. August end to November) revealed that both the Px (60 days) and exogenous testosterone (100 micrograms/day/squirrel/30 days) prevented gonadal and accessory sex organ regression. This could be due to negative feedback by testosterone treatment which was more obvious in intact than the Px squirrels. A decline in day time plasma melatonin level after testosterone treatment was also indicative of inverse relationship between the gonadal and pineal hormones which in turn did not allow the collapse of accessory sex organs. Further, the pineal gland is under direct control of steroid hormones since receptors and aromatizing enzymes are noted in the same. Therefore, a pineal secreted melatonin stimulation of hypothalamic negative feedback centers for gonadal regression could be suggested in this tropical rodent as receptors for melatonin have been detected in above areas.