SEPTOHIPPOCAMPAL NEURONS IN THE RAT - AN INVIVO INTRACELLULAR STUDY

In vivo intracellular recordings were obtained from septohippocampal neurons indentified by their antidromic response to electrical stimulation of the fimbria in rats anesthetized with pentobarbital or urethane. Beside the antidromic response, fimbria stimulation evoked a short-latency depolarizing potential (EPSP [excitatory postsynaptic potential]) following by an hyperpolarizing potential which reversed polarity when recorded with KC-1 filled electrodes. This IPSP [inhibitory post-synaptic potential] may be chloride-dependent. It was followed by a long-lasting (80-250 ms) depolarizing potential often associated with a burst of spikes. Septohippocampal neurons therefore receive an inhibitory, chloride-mediated, input which itself triggers a long-lasting excitatory event. Consistent with extracellular observations, their significance in the septohippocampal circuitry is discussed.