Effect of ambient temperature on sleep-wakefulness in normal and medial preoptic area lesioned rats

The changes in sleep-wakefulness were studied in rats during their exposure to different ambient temperatures of 18 degrees C, 24 degrees C and 30 degrees C, before and after the destruction of the medial preoptic area neurons by N-Methyl D-aspartic acid. In normal rats, there was an increase in paradoxical sleep and slow wave sleep and a decrease in wakefulness at higher ambient temperatures. The increase in sleep was primarily due to an increase in the duration of sleep episodes. Destruction of the medial preoptic area neurons produced a decrease in sleep at all three different ambient temperatures. But, there was a linear increase in sleep with higher temperatures in the lesioned rats that was qualitatively different from that in the normal animals, as the increase in sleep was associated with an increase in the number of short duration slow wave sleep episodes. The findings indicate that the medial preoptic area is essential for sleep maintenance and improving the quality of sleep with higher ambient temperatures. It is possible that the medial preoptic area serves as a fine-tuning mechanism to regulate sleep for energy homeostasis, including thermoregulation.