SUPRAMAMMILLARY NEURAL DISCHARGE PATTERNS AND HIPPOCAMPAL EEG

Rhythmic multiunit activity, leading the negative peak of concurrently recorded dentate rhythmical slow-wave activity (RSA, theta) by a cons tant degree over a range of RSA frequencies, was observed in the supra mammillary nucleus (SUM) after carbachol infusion (5%, 0.25-0.5 mu l) into the nucleus pontis oralis (RPO). As the rhythmic SUM activity sur vived bilateral transection anterior to SuM, its occurrence is not dep endent on descending influences from the septum or hippocampus. Infusi on of additional carbachol into the RPO resulted in epileptiform ''sha rp-waves'' in the hippocampal EEG, and correlated nonrhythmic cell dis charge in the SUM. Bilateral transection rostral to SuM abolished the sharp-wave related SUM activity (and restored SuM rhythmical activity) . Thus, in contrast to RSA related rhythmical SUM discharge, sharp-wav e related SuM discharge seems dependent on descending projections from the hippocampus. Copyright (C) 1997 Elsevier Science Inc.