Hippocampal rhythmical slow activity following ibotenic acid lesions of the septal region. II. Changes in hippocampal activity during sleep.

Ibotenic acid injections in the septal nuclei of the forebrain produced severe cell loss in the dorsal lateral septal nucleus and the septohippocampal nucleus. Chronic recording of hippocampal and neocortical slow-wave activity and muscle activity showed that the ibotenic acid treatment had selectively abolished the atropine-sensitive (presumably cholinergic) form of hippocampal rhythmical slow activity (RSA) normally seen during the tonic component of active sleep. Large-amplitude irregular activity (LIA), that is normally associated with waking immobility and quiet sleep, and the atropine-resistant (probably serotonergic) RSA that normally accompanies phasic muscular activity during active sleep, were also somewhat depressed. However, clear RSA was seen during phasic muscular activity in active sleep and LIA was clearly seen during quiet sleep in all rats. Neocortical activity was not affected by the ibotenic acid treatment. The results are consistent with the hypothesis that, both in the sleeping and the waking state, RSA can be produced by either of two distinctive inputs to the hippocampus. No support was found for the hypothesis that RSA during active sleep has a different basis than RSA in the waking state.