Projections from the amygdaloid complex and adjacent olfactory structures to the entorhinal cortex and to the subiculum in the rat and cat

Abstract

Axonal projections are described from the lateral and hasolateral nuclei of the amygdaloid complex, and from the overlying periamygdaloid and pre‐piriform cortices and the endopiriform nucleus, to the lateral entorhinal area, the ventral part of the subiculum, and the parasubiculum in the cat and rat. All of these projections have well‐defined laminar patterns of termination, which are complementary to those of other projections to the same structure. Based on these results, and on cytoarchitectonic distinctions, the lateral entorhinal area has been divided into dorsal, ventral, and ventromedial subdivisions. The olfactory bulb and prepiriform cortex project to layers IA and IB, respectively, of all three subdivisions, but the lateral amygdaloid nucleus has a restricted projection to layer 111 of the ventral subdivision only. The periamygdaloid cortex projects to layer II of the ventromedial and adjoining parts of the ventral subdivisions. The ventral part of the subiculum receives fibers from the posterior division of the hasolateral nucleus, which terminate in the cellular layer and the deep half to one‐third of the plexiform layer. The periamygdaloid cortex and the endopiriform nucleus also project to the same part of the subiculum, but these fibers terminate in the outer part of the plexiform layer. None of these projections extend into the dorsal part of the subiculum. The posterior division of the basolateral nucleus also projects to the posterodorsal part of the parasubiculum (“parasubiculum a” of Blackstad, 1956). These fibers end in the deeper part of the plexiform layer and the superficial part of the cellular layer.