The organization of the hippocampal connections with the perirhinal, postrhinal, and entorhinal cortices of the rat
Rebecca D. Burwell
Department of Psychology, Brown University , Providence , Rhode Island , USA
The perirhinal, postrhinal, and entorhinal cortices provide the predominant interface between the neocortex and the hippocampal formation. Many of the connections among these regions have been described, but most reports focus on a limited number of the existing connections. We have completed a comprehensive analysis of the hippocampal efferents and afferents of the perirhinal, postrhinal, and entorhinal cortices. Using anterograde and retrograde tract tracing methods in the rat, we quantified the hippocampal and subicular connections with the perirhinal cortex (areas 35 and 36), postrhinal cortex, and the lateral and medial subdivisions of the entorhinal cortex (LEA and MEA). For quantification of the hippocampal efferents, thirty-seven retrograde injections distributed in the five cortical regions were included in the analysis. Total numbers of retrogradely labeled cells were estimated in the septal and temporal halves of each hippocampal formation substructure, including the dentate gyrus, CA3, CA2, CA1, and subiculum, as well as in the presubiculum and parasubiculum. Percentages of input to the cortical regions and densities of labelled cells in the hippocampal regions will be reported. For analysis of the hippocampal afferents, twenty-five anterograde tracers distributed throughout the perirhinal, postrhinal, and entorhinal cortices were available for analysis. Densities of terminal fiber labelling in the septal and temporal hippocampal subregions will be reported. Topics will include comparisons of the strength and topography of the perirhinal, postrhinal, and entorhinal connections with the septal and temporal hippocampus and subicular regions. Implications for hippocampal function will be discussed.