Effect of pinealectomy on photoperiodic gonadal response of Indian palm squirrel, Funambulus pennanti

Abstract

The role of the pineal gland in mediating the effects of photoperiod on the reproductive axis is not well established in tropical mammals. Indian palm squirrels (Funambulus pennanti) were exposed to experimental long (16L:8D) and short (6L:18D) photoperiods. It was observed that the testes regressed in response to short photoperiod, while during the long photoperiod the gonads were active. When squirrels were maintained for a long experimental period (130 days) under the short photoperiodic schedule (6L:18D), gonadal regrowth eventually occurred even though the photoperiod was the same one that initially induced testicular regression. Pinealectomized animals maintained the gonadal activity even in short photoperiod, suggesting that the effect of photoperiod is mediated through the pineal gland.

Temporal synergism of neurotransmitter affecting drugs and seasonal reproductive responses of Indian Palm Squirrel,Funambulus pennanti

“…But again in late November, spontaneous recrudescence occurs and by December-January the reproductive system is fully developed. At this phase the development occurs even under the short days suggesting the squirrels are scotorefractory (Haldar and Srivastava, 1987). This seasonal photoperiod/humidity response is successfully manipulated by 12-hour-relation of 5-HTP and L-DOPA and eliminated annual testicular regression.…”

“…While white throated sparrow (Wolfson, 1959), Red headed bunting (Thapliyal and Lal, 1984) and Japanese quail (Robinson and Follett, 1982) use long photoperiod; Spotted munia, a non-photoperiodic sub-tropical finch does not correlate with any change in environmental factors (photoperiod or temperature- Thapliyal and Pandha, 1965;Chandola et al, 1982). Syrian hamster uses short photoperiod (Reiter, 1974) and Palm squirrel uses humidity for its seasonal testicular regression (Haldar and Srivastava, 1987;Haldar and Saxena, 1988). It is obvious that in all the above species 12-hour-relation affected the actual mechanism of seasonality inspite of the variables in seasonal environmental/ endogenous controlling factor.…”

“…Chaturvedi and R. Jaiwal bulus pennantO the reproductive system regresses in August/September when they are subjected to short day length, but is unaffected by similar treatment in October/November. In nature also after regression in August/September the reproductive system spontaneously recrudesces during November attaining maximum in beginning of January (Haldar and Srivastava, 1987). The onset of spontaneous gonadal recrudescence probably marks the beginning of the scotorefractory period when the reproductive system no longer responds to the inhibitory effect of the short days.…”

Elimination of testicular regression by 12-hr temporal relationship of serotonergic and dopaminergic activity in Indian Palm Squirrel,Funambulus pennanti

“…This subtropical species differs from temperate hamsters (syrian and Golden) in certain respects.While photoperiod has full control on the breeding cycle of hamsters (Reiter, 1975) in Indian Palm Squirrel, other environmental factor (humidity) determines the termination of seasonal breeding (Haldar and Saxena, 1988). On the other hand, phenomenon of scotorefractoriness (gonadal development under short days, which are normally inhibitory) observed in hamsters (Elliott, 1976;Stetson etal., 1977) is not yet proved experimentally in Indian Palm Squirrel, however, latter shows annual gonadal recrudescence in November/December when annual photoperiod is minimum (Haldar and Srivastava, 1987).…”

Circadian Locomotor Activity Rhythms of the Diurnal Indian Palm Squirrel in Constant Light

“…While palm squirrels do not hibernate, their reproductive activity is photoperiodic (1). There is increasing evidence that the effects of photoperiod on the reproductive state of male and female F. pennanti are mediated by the pineal gland (2)(3)(4).…”