Vol. 274, Issue 3, R754-R759, March 1998
Estradiol phase shifts circannual body mass rhythms of male
ground squirrels
Sara M.
Hiebert1,
Theresa M.
Lee2,
Paul
Licht3, and
Irving
Zucker1,3
Departments of 1 Psychology and
3 Integrative Biology, University
of California, Berkeley, California 94720; and
2 Department of Psychology,
University of Michigan, Ann Arbor, Michigan 48109
Gonadectomized
male golden-mantled ground squirrels (Spermophilus
lateralis) were implanted with estradiol benzoate
(EB)-filled or empty capsules. Body mass was monitored before, during,
and for at least 1 yr after hormone treatment. EB treatment during the
mass-gain phase of the annual cycle significantly decelerated increases
in body mass; the period of the circannual rhythm (CAR) of body mass
was 54 days longer in EB- than blank-treated squirrels. Hormone
treatment during the mass-loss phase accelerated mass loss; although
this effect only approached statistical significance, some phase
markers of the CAR were significantly advanced in subsequent cycles. We
conclude that, as in females, estradiol affects the waveform of the CAR
of males differently at different phases of the circannual cycle.
Sexual differentiation does not eliminate responsiveness of CARs of
squirrels to estradiol; sex differences, if any, are subtle rather than
absolute and, in this respect, differ from circadian rhythms.
body mass; circadian; sex differences
