The Journal of Neuroscience, January 1, 2002, 22(1):357-364
The Suprachiasmatic Nucleus Is Essential for Circadian Body
Temperature Rhythms in Hibernating Ground Squirrels
Norman F.
Ruby1,
John
Dark2,
D. Erik
Burns1,
H. Craig
Heller1, and
Irving
Zucker2, 3
1 Department of Biological Sciences, Stanford
University, Stanford, California 94305, and Departments of
2 Psychology and 3 Integrative Biology,
University of California, Berkeley, California 94720
Body temperature (Tb) was
recorded at 10 min intervals over 2.5 years in female golden-mantled
ground squirrels that sustained complete ablation of the
suprachiasmatic nucleus (SCNx). Animals housed at an ambient
temperature (Ta) of 6.5°C were
housed in a 12 hr light/dark cycle for 19 months followed by 11 months
in constant light. The circadian rhythm of
Tb was permanently eliminated in euthermic
and torpid SCNx squirrels, but not in those with partial destruction of
the SCN or in neurologically intact control animals. Among control
animals, some low-amplitude Tb rhythms during torpor were driven by small (<0.1°C) diurnal changes in Ta. During torpor bouts in which
Tb rhythms were unaffected by Ta, Tb
rhythm period ranged from 23.7 to 28.5 hr. Both SCNx and control
squirrels were more likely to enter torpor at night and to arouse
during the day in the presence of the light/dark cycle, whereas entry
into and arousal from torpor occurred at random clock times in both
SCNx and control animals housed in constant light. Absence of circadian
rhythms 2.5 years after SCN ablation indicates that extra-SCN
pacemakers are unable to mediate circadian organization in euthermic or
torpid ground squirrels. The presence of diurnal rhythms of entry into
and arousal from torpor in SCNx animals held under a light/dark cycle,
and their absence in constant light, suggest that light can reach the
retina of hibernating ground squirrels maintained in the laboratory and
affect hibernation via an SCN-independent mechanism.
Key words:
suprachiasmatic nucleus; hibernation; circadian; torpor; body temperature; golden-mantled ground squirrel
Copyright © 2002 Society for Neuroscience 0270-6474/02/221357-08$05.00/0
