Direct projections from the entorhinal area to the anteroventral and laterodorsal thalamic nuclei in the rat

The present study provides the evidence for the existence of direct projections from the entorhinal area to the anteroventral (AV) and laterodorsal thalamic nuclei (LD) in the rat. The retrograde tract-tracing method with cholera toxin B subunit and the anterograde tract-tracing method with Phaseolus vulgaris leucoagglutinin were used. The projection fibers originate from layers V and VI of the medial entorhinal area and terminate in the rostral and dorsolateral parts of the AV and the dorsal part of the LD. The projections are organized in a coarse topographic fashion. The rostral part of the medial entorhinal area projects preferentially to the AV whereas the caudal part projects preferentially to the LD. The results show that the medial entorhinal area is connected reciprocally with the AV and LD. Thus, the AV and LD are intimately connected with the limbic cortex implicated in memory and learning.