[Changes in thermoregulation, sleep and the thyroid hormone concentration of the blood in the "critical" period of the entry into hibernation of the suslik Citellus parryi].

During the first entering into hibernation in the ground squirrels there are periodic cessations of the process, especially during the transition to moderate and deep torpidity ("critical" periods) which significantly increase energy expenditure in animals during the phase of entering. During this period, high amplitude near-the-hour fluctuations are observed in total duration of wakefulness and sleep, contractile muscle activity, oxygen consumption, heart rate, brain temperature, and thyroid hormone concentration in the blood; at the end of this period, as well as during the exiting from it the duration of deep slow wave sleep significantly increases, paradoxical sleep is not identified. The data obtained confirm a hypothesis of "kindling" homeostasis as neuro-hormonal mechanism of the increase in thermal range of the activity of functional systems of the organism during the entering into torpidity in homoiothermic animals.