OLFACTORY BULBECTOMY IMPEDES SOCIAL BUT NOT PHOTIC REENTRAINMENT OF CIRCADIAN-RHYTHMS IN FEMALE OCTODON-DEGUS

Recent studies demonstrated that nonphotic (social) cues markedly acce lerate reentrainment to large phase shifts of the light-dark (LD) cycl e in female Octodon degus and that such changes are likely effected by chemosensory stimuli. This experiment investigated the effects of olf actory bulbectomies on (1) socially facilitated reentrainment rates of circadian rhythms following a 6-h phase advance of the LD cycle, (2) photic reentrainment rates of circadian rhythms following a 6-h advanc e of the LD cycle, (3) photic entrainment, and (4) the circadian perio d (tau) of activity rhythms in constant darkness (DD). Olfactory bulbe ctomies (BX) blocked socially facilitated reentrainment rates but did not alter reentrainment rates of circadian rhythms to photic cues alon e, In addition, BX lowered mean daily locomotor activity levels and de creased the amplitude of the activity rhythm in degus housed in entrai ned (LD 12:12) conditions but did not alter Ae phase of activity onset or offset duration (alpha) of activity, or mean daily core body tempe rature. Bulbectomies also failed to modify tau of free-running activit y rhythms. This experiment confirms that the olfactory bulbs and chemo sensory cues are necessary for socially facilitated reentrainment. In contrast to their effects in nocturnal rodents, BX do not produce sign ificant circadian photic changes in diurnal degus. This is the first e xperiment to determine that chemosensory stimuli modulate the circadia n system in a diurnal rodent.