Cold exposure and sleep in the rat: effects on sleep architecture and the electroencephalogram.
OBJECTIVE
Acute exposure to low ambient temperature modifies the wake-sleep cycle due to stage-dependent changes in the capacity to regulate body temperature. This study was carried out to make a systematic analysis of sleep parameters during the exposure to different low ambient temperatures and during the following recoveries at ambient temperature 24 degrees C.


METHODS
Electroencephalographic activity, hypothalamic temperature, and motor activity were studied during a 24-hour exposure to ambient temperatures ranging from 10 degrees C to -10 degrees C and for 4 days during the recovery.


METHODS
Laboratory of Physiological Regulation during the Wake-Sleep Cycle, Department of Human and General Physiology, Alma Mater Studiorum-University of Bologna.


METHODS
Twenty-four male albino rats.


METHODS
Animals were implanted with electrodes for electroencephalographic recording and a thermistor for measuring hypothalamic temperature.


RESULTS
Wake-sleep stage duration and the electroencephalographic spectral analysis performed by fast Fourier transform were compared among baseline, exposure, and recovery conditions. The amount of non-rapid eye movement sleep was slightly depressed by cold exposure, but no rebound was observed during the recovery period. Delta power during non-rapid eye movement sleep was decreased in animals exposed to the lowest ambient temperatures and increased during the first day of the recovery. In contrast, rapid eye movement sleep was greatly depressed by cold exposure and showed an increase during the recovery. Both of these effects were dependent on the ambient temperature of the exposure. Moreover, theta power was increased during rapid eye movement sleep in both the exposure and the first day of the recovery.


CONCLUSIONS
These findings show that sleep-stage duration and electroencephalogram power are simultaneously affected by cold exposure. The effects on rapid eye movement sleep appear mainly as changes in the duration, whereas those on non-rapid eye movement sleep are shown by changes in delta power. These effects are temperature dependent, and the decrease of both parameters during the exposure is reciprocated by an increase in the subsequent recovery.
Cerri
Matteo
M
Department of Human and General Physiology, Alma Mater Studiorum-University of Bologna, Italy.
Ocampo-Garces
Adrian
A
Amici
Roberto
R
Baracchi
Francesca
F
Capitani
Paolo
P
Jones
Christine Ann
CA
Luppi
Marco
M
Perez
Emanuele
E
Parmeggiani
Pier Luigi
PL
Zamboni
Giovanni
G
D000818:Animals; D001921:Brain / Q000502:physiology; D003080:Cold Temperature; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004777:Environment; D007031:Hypothalamus / Q000502:physiology; D008124:Locomotion / Q000502:physiology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012890:Sleep / Q000502:physiology*; D020178:Sleep Disorders, Circadian Rhythm / Q000175:diagnosis; D012895:Sleep, REM / Q000502:physiology; D014851:Wakefulness / Q000502:physiology