Olfactory bulbectomy lengthens circadian period of locomotor activity in golden hamsters

Abstract

Removal of the olfactory bulbs (BX) of rats or mice lengthens the circadian period of locomotor activity. In golden hamsters, BX elevates serum gonadotropin levels of hamsters maintained in long or short photoperiod and prevents the testicular regression associated with short days without altering the secretion or action of pineal melatonin. The present study examined the influence of BX on circadian wheel-running activity in hamsters and tested whether this effect was related to changes in serum testosterone levels. BX lengthened the free-running period of locomotor activity in gonadally intact hamsters by a mean of 21.0 min, and BX had a similar effect in orchidectomized animals with or without testosterone replacement. These results suggest that the olfactory bulbs normally tend to increase the frequency of the hamster's circadian oscillator and that this effect is unrelated to altering gonadal steroid levels.