Ambient temperature that induces maximum sleep in rats

Abstract

Changes in sleep and body temperature in rats at ambient temperatures below and above the self-selected temperature zone, are lacking in literature. In this report, the temperature preferred by the rats was first assessed before studying the changes in their sleep and body temperature, when they were exposed to ambient temperatures ranging from 18 °C to 36 °C. The rats preferred to stay at 27 °C when they were allowed to select their own ambient temperature, but maximum sleep was recorded when the rats were maintained at 30 °C. The ambient temperature-related changes in rapid eye movement sleep and deep slow wave sleep followed a bell-shaped curve, with a maximum at 30 °C. Of all the sleep parameters, rapid eye movement sleep showed a more marked ambient temperature-related change. Ambient temperatures above 33 °C and below 24 °C produced a significant reduction in sleep. Increase in sleep at 30 °C was associated with a slight elevation in body temperature, but a steep increase in body temperature at very high ambient temperature was associated with a decrease in sleep. Decrease in sleep at ambient temperatures below 24 °C was not related to any significant decrease in body temperature. Though maximum sleep was recorded at 30 °C, the sleep regulatory and thermoregulatory systems were at a functional equilibrium at 27 °C.