Rhythmical slow wave electroencephalographic activity elicited by hippocampal injection of muscarinic agents in the rat.

In freely moving male Wistar rats the hippocampal EEG was recorded by using chemitrodes (combinations of guide cannulas with bipolar recording electrodes) chronically implanted into the dorsal hippocampus (CAI). The muscarinic agents oxotremorine and arecoline applied intrahippocampally caused a long-lasting increase in the amount of rhythmical slow wave activity (RSA) of the hippocampal EEG accompanied by a decrease of the dominating frequency. At the same time, the well-known relationship between defined behavioral states and EEG patterns was abolished. The effect of oxotremorine could be blocked by subsequent application of the muscarinic antagonist scopolamine. The results support the hypothesis that a non-rhythmic activation of hippocampal muscarinic receptors may result in the generation of RSA within the hippocampal formation.