Differential Efferent Projections of the Lateral and Medial Septal Nuclei to the Hippocampus in the Cat

Abstract

The efferent connections of the septum in the cat were studied using the Fink-Heimer procedure for staining degenerating axons and their terminals.The results indicate a differential distribution of fibers from the lateral and medial septal nuclei to the ventral and dorsal hippocampus, respectively. Projections from the lateral septal nucleus to the subiculum and pyriform cortex adjacent to the ventral hippocampus were noted. Degenerating fibers could also be followed from the medial septal nucleus to the subiculum, posterior pyriform and entorhinal cortices. Other fibers, probably originating in the medial septal nucleus, join the cingulum bundle and reach the retrosplenial area and presubiculum.These findings taken together with the previous results indicate two distinct reciprocal pathways, the first connecting the lateral septal nucleus and ventral hippocampus, and the second relating the medial septal nucleus und dorsal hippocampus.A marked similarity in the projection pathways from the lateral and medial septal nuclei to other forebrain regions was noted.