Olfactory bulb removal lengthens the period of circannual rhythms and disrupts hibernation in golden-mantled ground squirrels.

Removal of the olfactory bulbs lengthened the period of circannual rhythms (CARs) of body mass and plasma testosterone (T) concentrations in male golden-mantled ground squirrels, but did not otherwise alter their expression. The period of the CAR was approximately 2 months longer in bulbectomized than in sham-operated animals. Peak values of body mass and T were unaffected by bulbectomy. All neurologically intact, but only 50% of bulbectomized, squirrels displayed normal hibernation patterns. We conclude that the olfactory bulbs are not the site of essential circannual oscillators. Circannual reproductive and hibernation cycles of ground squirrels are less subject to modulation by the olfactory bulbs than are the corresponding rhythms of several non-circannual hamster species.