[The temporal characteristics of "winter" paradoxical sleep in the hibernating suslik Citellus major]. / Vremennye kharakteristiki "zimnego" paradoksal'nogo sna u giberniruiushchego suslika Citellus major.

It has been shown that paradoxical sleep (PS) total time (TT) in euthermia phase of hibernation cycle (winter sleep) can be compared with its mean values in euthermia season. Ultradian fluctuations of PS episodes duration, TT and phase number as well as bradycardia microintervals are revealed in euthermia phase dynamics. Amplitude of these fluctuations increases before hibernation entry; in transitional "start" period PSTT increases up to maximum critical values. In hibernation cycle PSTT rapidly decreases at the first stage owing to reduction of PS phase number and their duration. These data support and supplement earlier suggested hypothesis about endogenous "swinging up" of ultradian rhythms of sleep and thermoregulation promoting stage-to-stage expansion of homeostasis temperature limits in various critical periods of preparation and entry of homeotherms into natural hypometabolic states (torpor, hibernation and others).

[The recovery of the sleep-wakefulness cycle during arousal from hibernation in the long-tailed Arctic suslik Citellus parryi]. / Vosstanovlenie tsikla son--bodrstvovanie v protsesse vykhoda iz zimnei spiachki arkticheskogo dlinnokhvostogo suslika Citellus parryi.

New data and analysis are presented concerning the recovery of the sleep cycle during onset of deep winter hibernation (T brain = 3 degrees C) and arousal from hibernation in the Arctic ground squirrel at temperatures of the brain 3-35 degrees C. It was shown that natural arousal from hibernation is associated with gradual development of the sleep phases on a basis of the resting forms which are typical of the lower level of development of the central nervous system in vertebrates.

[Changes in the wakefulness-sleep cycle in mice induced by endogenous substances from the tissues of the susliks Citellus parryi and C. undulatus during hibernation]. / Izmenenie tsikla bodrstvovanie-son u myshei éndogennymi veshchestvami iz tkanei suslikov Citellus parryi i C. undulatus v sostoianii spiachki.

Intraabdominal injections of albino mice of extracts from the brain (2mg/g) and epithelial tissue of the small intestine (1.3 mg/g) of hibernating ground squirrels result within 6 hours in the decrease of the duration of the awake state (by 2.1-2.4 times), inhibition of paradoxical sleep, the increase in the duration of the slow wave sleep, and the decrease in the brain temperature (by 4.5-6 degrees). These indices are affected to a significantly lower extent by injections of intestinal extracts from non-hibernating animals. It is suggested that in homoiothermic animals, changes of temperature homeostasis and sleep cycle are controlled by endogeneous substances which are present in the brain and tissues of the internal organs.

[Changes in thermoregulation in the white mouse treated with endogenous substances from the intestinal tissue of hibernating animals]. / Izmeneniia termoreguliatsii u belykh myshei pri deistvii éndogennykh veshchestv iz tkani kishechnika zimospiashchikh.

Intraperitoneal administration of extracts of the small intestine epithelium of hibernating ground squirrels (C. Parryi Rich., C. undulatus) to white mice caused a decrease in oxygen consumption by 50-80%, the 5.5-14.0 degrees C drop in body temperature, inhibition of the muscle shivering thermogenesis, a decrease in heart rate, reduction of locomotor activity, development of hypnogenic effect and a closer dependence of body temperature on environmental fluctuations. The effects lasted for 30-40 hrs. Extracts from the small intestine tissue of non-hibernating ground squirrels caused insignificant changes of these parameters.