AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 4 472-R480, Copyright © 1983 by American Physiological Society
Suprachiasmatic nuclei influence circannual and circadian rhythms of ground squirrels
I. Zucker, M. Boshes and J. Dark
Golden-mantled ground squirrels, maintained under constant conditions of
photoperiod and temperature sustained lesions of the suprachiasmatic nuclei
(SCN) or of the medial basal hypothalamus. Destruction of the SCN
eliminated or disrupted circadian activity rhythms and shortened the period
of the circannual reproductive cycle. Circannual body weight cycles were
eliminated or disrupted in several SCN-lesioned animals and one squirrel
had a 3- to 5-mo body weight rhythm; however, most SCN-lesioned squirrels
with disrupted circadian activity cycles manifested normal circannual body
weight rhythms. The SCN are important for circadian organization of
locomotor activity of this diurnal rodent, but the generation and
expression of circannual body weight and reproductive rhythms can proceed
in the absence of coherent circadian organization. The SCN are less
essential for the generation and expression of circannual than of circadian
cycles.
