Effects of hippocampal and hypothalamic afferents on neuronal activities in the rat septum

Michael J. Gutnick*, Shaul Feldman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Field potentials and extracellular unit activities were recorded in the septal nuclei of urethane-anesthetized rats during stimulation of the ipsilateral fimbria and the medial forebrain bundle. Fimbrial stimulation caused monosynaptic excitation in dorsal regions of the lateral septal nucleus, monosynaptic and polysynaptic excitation in ventral regions of the lateral septal nucleus, and antidromic activation followed by prolonged inhibition in the medial septal nucleus. Polysynaptic excitatory responses differed from monosynaptic responses in that they had lower stimulus thresholds and underwent frequency potentiation at low stimulus frequencies. Polysynaptic responses were abolished by acute ipsilateral hippocampectomy, indicating that the pathways responsible for their generation relay through the hippocampus. Fimbrial stimulation also produced inhibition throughout the septum. Inhibition was particularly pronounced following stimulation of the fimbrial stump in animals that had undergone chronic hippocampectomy. Since the stimulus was antidromic in these preparations, it is evident that the fimbria-induced inhibition is mediated, in part, by recurrently activated intraseptal interneurons. Medial forebrain bundle stimulation produced a variety of excitatory and inhibitory responses which were not topographically distributed within the septum. In chronically hippocampectomized animals, stimulation of the bundle consistently evoked prominent positive field potentials and widespread, prolonged inhibition of septal neuronal activities.

Original languageEnglish
Pages (from-to)212-230
Number of pages19
JournalExperimental Neurology
Volume57
Issue number1
DOIs
StatePublished - Oct 1977

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