Anatomical evidence for a projection from the entorhinal cortex to the contralateral dentate gyrus of the rat

Abstract

A relatively sparse direct projection from the entorhinal cortex to the rostral part of the contralateral dentate gyrus of the hippocampus has been demonstrated by the Fink-Heimer and autoradiographic techniques in normal rats. The fibers terminate in the outer two-thirds of the molecular layer, similar to the projection to the ipsilateral dentate gyrus. Thus extrinsic cortical input is bilaterally directed, further illustrating the principle of the bilaterality of hippocampal projections. A contralateral entorhinal projection has been reported previously only as a consequence of apparent axon sprouting following a unilateral entorhinal lesion. The demonstration of this projection in normal rats indicates the changes following recovery from unilateral entorhinal lesions need not involve extensive new fiber growth as had been previously hypothesized.