The changes in thermal preference, sleep–wakefulness, body temperature and locomotor activity in the rats with medial septal lesion

Abstract

The effects of the destruction of the medial septal neurons (MS) with N-methyl- d-aspartic acid on sleep–wakefulness (S–W), body temperature ( T b), locomotor activity (LMA) and thermal preference were studied in male Wistar rats. When these rats were given a choice of three ambient temperatures ( T amb) of 24, 27 and 30 °C, they preferred 27 °C before the lesion. But they chose 30 °C during the initial days and 24 °C by the third week after the MS lesion. The MS lesion produced an increase in paradoxical sleep (PS) though this change was not very evident when the rats were not allowed to choose their T amb. Though there was a decrease in slow wave sleep (SWS), it recovered considerably, when the lesioned rats chose their preferred T amb. However, the frequency of SWS episodes did not show any recovery. There was a decrease in both T b and LMA by the third week after the MS lesion. It can, therefore, be concluded that the MS lesion affected the initiation of SWS, as there was a decrease in the frequency of SWS episodes. Study of S–W in the rats that were given freedom to select T amb helped to demonstrate the role of the MS in the inhibition of PS. It also showed that the thermostat of the rats was reset at a lower level by the third week after the MS lesion. Decrease in heat production resulting from a decrease in LMA, could have contributed towards the animals’ efforts to maintain a lower T b.