Electrical stimulation of rewarding hypothalamic sites in the 13-lined ground squirrel, Citellus tridecemlineatus, during hibernation: Sensitivity and thermogenic effects

1. 1. Ground squirrels were chronically prepared for the determination of hypothalamic stimulus thresholds during hibernation at brain temperatures (T_br) of 9-15°C by observations of heart rate (HR), neck muscle activity (EMG) and T_br changes. 2. 2. Preliminary tests on euthermic squirrels showed that the hypothalamic sites were rewarding since animals self-stimulated the sites at a rate proportional to the stimulus intensity. 3. 3. During bouts of hibernation, the threshold for increased HR varied from 2- to 5-fold but did not vary significantly with T_br or the percentage of the hibernation bout elapsed. 4. 4. Stimulation of the hypothalamus resulted in rises of T_br during hibernation only if the stimulus produced cardioacceleration.