Unusual pattern of cerebral electrical activity in the mongolian hamster (Allocricetulus curtatus) during heterothermia

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Abstract

Electroencephalogram (EEG), brain and abdominal temperature, and motor activity were recorded for the first time in 18 adult males of facultative hibernator, the Mongolian hamster, during hibernation under controlled laboratory conditions in winter. At room temperature, clear synchronous circadian rhythms of motor activity and body temperature were observed. In most animals, a gradual decrease in external temperature (from 24°C to 4°C) led to a significant increase in motor activity, combined with an increase in the amplitude of circadian oscillations of body temperature. Six hamsters demonstrated torpor bouts and hibernation with radical changes in the EEG up to reaching the isoelectric line, as well as the disappearance of oscillations of brain temperature. It has been found that Mongolian hamsters can easily enter and exit both a state of torpor and a fairly deep hibernation with a decrease in body temperature down to 10ºC during normal sleep periods.

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About the authors

V. M. Kovalzon

Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences

Author for correspondence.
Email: kovalzon@sevin.ru
Russian Federation, Moscow

A. D. Komarova

Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences

Email: kovalzon@sevin.ru
Russian Federation, Moscow

M. Yu. Smagina

Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences

Email: kovalzon@sevin.ru
Russian Federation, Moscow

N. Yu. Feoktistova

Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences

Email: kovalzon@sevin.ru
Russian Federation, Moscow

A. V. Surov

Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences

Email: kovalzon@sevin.ru

Corresponding Member of the RAS

Moscow

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2. Fig. 1. Averaged 10-day fragment of a two-month record of body temperature (upper curve, left ordinate, °C) and motor activity (lower curve, right ordinate, δG) in two hamsters that did not enter a hypothermic state when the chamber temperature was reduced from 24°C (in this fragment – ​​from 13°C) to 4°C. Accordingly, the light period was reduced from 12 h (in this fragment – ​​from 5 h) to 2 h per day. The abscissa axis shows the time of day in h. The dotted line indicates the trend line; r=0.62 is the correlation coefficient between the two curves (p < 0.05).

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3. Fig. 2. Typical cold hibernation in a male Mongolian hamster in the laboratory for two months in winter. At the top is body temperature (°C, left ordinate), at the bottom is motor activity (δG, right ordinate). The temperature in the experimental chamber was lowered from 24°C (13.01, beginning of the experiment) to 4°C (4.02) and maintained at this level until the end of the experiment. The photoperiod was also reduced from 12 h (13.01) to 2 h (4.02). The frame with a darkening highlights the fragment shown in detail in Fig. 5.

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4. Fig. 3. Radical changes in EEG during hibernation at a chamber temperature of 4⁰C. 20-sec epochs of native recording are shown. On a white background, EEG (Channel 2) is at the top, motor activity (Accelerometer) is at the bottom. On a black background are the spectral characteristics of the EEG. The column on the right is the result of processing (staging) the EEG by 20-sec epochs. A, 1 hour 15 minutes after the start of the bout. Body temperature is 30.6⁰C. B, 12 hours 30 minutes after the start of the bout. The lowest point of the bout, body temperature is 11.2⁰C.

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5. Fig. 4. Dynamics of EEG, brain temperature, and motor activity at a chamber temperature of 22⁰C and a brain temperature of 36.2⁰C. Native recording. A, 1-min episode of slow sleep (SW). On a white background, top to bottom: brain temperature (Channel 1, a downward deviation means an increase in temperature, and vice versa), EEG (Channel 2), motor activity (Accelerometer). Temperature calibration is 0.01⁰C. The upper graph on a black background is the spectral characteristic of the EEG. The column on the right is the result of processing (staging) the EEG into 20-sec epochs. B, 5-min episode of slow sleep (S), turning into fast sleep (R) and ending with a short awakening (W). The upper curve is brain temperature (Channel 1, a downward deviation means an increase in temperature, and vice versa). Temperature calibration is 0.25⁰C. The middle curve is EEG (Channel 2), the lower one is motor activity (Accelerometer). The column on the right is the result of processing (staging) EEG by 20-second epochs.

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6. Fig. 5. Representative hibernation bout. A, Body temperature (upper curve, °C, left ordinate) and motor activity (lower curve, δG, right ordinate). Abscissa – time of day. B, Compressed result of EEG processing: Q – immobile state, different from sleep and wakefulness; W – wakefulness; S – slow-wave sleep; R – rapid (paradoxical, REM) sleep. C, Hourly representation of wakefulness (Wake), slow-wave sleep (SWS), and rapid-wave sleep (REM) during two interbout periods. D – Total percentage of three states for the entire interbout period. Shaded part – dark period in the chamber.

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