Projection from the nucleus reuniens thalami to the hippocampal region: Light and electron microscopic tracing study in the rat with the anterograde tracer Phaseolus vulgaris ‐leucoagglutinin

Abstract

In order to study the morphological substrate of possible thalamic influence on the cells of origin and area of termination of the projection from the entorhinal cortex to the hippocampal formation, we examined the pathways, terminal distribution, and ultrastructure of the innervation of the hippocampal formation and parahippocampal region by the nucleus reuniens of the thalamus (NRT). We employed anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Injections of PHA-L in the NRT produce fiber and terminal labeling in the stratum lacunosum-moleculare of field CA1 of the hippocampus, the molecular layer of the subiculum, layers I and III/IV of the dorsal subdivision of the lateral entorhinal area (DLEA), and layers I and III-VI of the ventral lateral (VLEA) and medial (MEA) divisions of the entorhinal cortex. Terminal labeling is most dense in the stratum lacunosum-moleculare of field CA1, the molecular layer of the ventral part of the subiculum, MEA, and layer I of the perirhinal cortex. In layer I of the caudal part of DLEA and in MEA, terminal labeling is present in clusters. Injections in the rostral half of the NRT produce the same distribution in the hippocampal region as those in the caudal half of the NRT, although the projections from the rostral half of the NRT are much stronger. A topographical organization is present in the projections from the head of the NRT, so that the dorsal part projects predominantly to dorsal parts of field CA1 and the subic…