Electrophysiological analysis of the hippocampal-septal projections: I. Response and topographical characteristics

Summary The hippocampal input to the septal region was studied, in rats, by electrophysiological methods. The major observations were: 1. the hippocampal fibers are excitatory with respect to their target cells in the lateral septal nucleus (LSN); 2. the distribution of the subcallosal fornix is restricted to the dorsomedial regions of the LSN; 3. the fimbria contains fibers terminating throughout the dorsal aspect of the ipsilateral and contralateral septum; 4. there is an extensive overlapping in the distribution of the ipsi-and contra-lateral fimbria components with convergence upon single septal cells frequently seen; 5. the posterior part of hippocampal region CA1 contributes fibers to the fimbria as well as to the fornix.Abbreviations ACB Bed nucleus of the anterior commissure - AP Ref 0 The anterior-posterior and midline reference zero - CA Anterior commissure - CC Corpus callosum - CCA 3–4 Contralateral hippocampal fields CA-3–4 - Cd Pt Caudate putamen complex - CFim Contralateral fimbria - CMA Corticomedial maygdaloid division - GP Globus pallidus - Hipp Hippocampus - ICA1 (a) Anterior part of the ipsilateral hippocampal field CA1 - ICA1 (p) Posterior part of the ipsilateral hippocampal field CA1 - ICA3–4 Ipsilateral hippocampal field CA3–4 - IFim Ipsilateral fimbria - IFx Ipsilateral fornix - LSN Lateral septal nucleus - ME Microelectrode - MSN Medial septal nucleus - POA Pre-optic area This study was supported by U.S. Public Health Service Grants RR 5384 and NB 00405.