Cortical activity and sleep in the rat lateral hypothalamic syndrome

Continuous EEG recordings were performed in lateral hypothalamic (LH) damaged rats from day 1 post-lesion when totally aphagic and adipsic until complete recovery of their feeding and drinking. During the early post-operative stage (days 1–3 post-lesion), LH rats showed a complete disorganization of their basal EEG which was characterized by two superimposed activities, a constant rapid low voltage activity modulated by high voltage low frequency waves. Except in the case of intense illumination, several arousing stimuli did not affect this activity. By day 4 post-lesion, the two overlapping activities were replaced by less abnormal waves on top of which the first normal sleep spindles appeared. Sleep increased gradually and normal amounts of both slow-wave and paradoxical sleep were observed during ‘stage 4’ of recovery when rats again ate food and drank water. During this stage, and contrary to normal rats, meal size was correlated only with sleep events occurring within the intermeal interval following the next meal, when most of the ingested nutrients reached the systematic compartment. The effect on sleep of intragastric or intravenous caloric repletion was, at least in part, in agreement with the view of indirect effect of LH lesions on sleep through metabolic impairment. Whatever the mechanism underlying sleep deficits, these are one of the major symptoms of the lateral hypothalamic syndrome.