Photoperiod and crowding effects on testicular serotonin metabolism and lack of effects on melatonin synthesis in Uinta ground squirrels (Spermophilus armatus).

Abstract

AbstractThe photoperiod (i.e., constant light vs a 14/10 hour light/dark cycle) and “physical” crowding (group caging) on Uinta ground squirrels (Spermophilus armatus) was investigated to ascertain what effects these two environmental parameters would have on testicular metabolism of serotonin (MAO activity) and melatonin synthesis by pineal glands in organ culture. Testicular MAO activity was decreased by both constant light and crowding. Melatonin synthesis was not significantly affected by either treatment. These data are consistent with the normal reproductive activity of unconfined ground squirrels where the testes normally develop while the animals are in their burrows under constant darkness. Failure of the pineal gland to respond to constant darkness appears to be an adaptation of the animal to eliminate this source of antigonadal activity that would serve to retard gonadal development while the animal is in constant darkness. Failure of the testes to respond to a 14/10 hour Light/Dark cycle indicates that the hypothalamus is insensitive to lighting as a triggering mechanism for initiating testicular development.