Suprachiasmatic nuclei influence hibernation rhythms of golden-mantled ground squirrels.

Hibernation and body mass rhythms were studied in 13 golden-mantled ground squirrels maintained in an LD 12:12 photoperiod at 5 degrees C. Complete or partial ablation of the suprachiasmatic nuclei (SCN) disrupted normal hibernation rhythms. Over the course of 2 years, several animals progressed through 4 hibernation cycles, one squirrel manifested two abnormally long hibernation seasons, and another failed to hibernate. Squirrels with intact SCN exhibited normal circannual hibernation rhythms at intervals of 11.5 +/- 0.3 months. Hibernation coincided with the weight loss phase of the body mass cycle in control squirrels, but these two rhythms were dissociated in animals with lesions of the SCN. The annual plasma testosterone rhythm was normal or slightly phase-delayed in squirrels with SCN lesions maintained at 23 degrees C. The SCN may be part of a neural circuit that mediates circannual organization of hibernation rhythms.