Projections from the subiculum to the deep layers of the ipsilateral presubicular and entorhinal cortices in the guinea pig.

Projections from the subiculum to retrohippocampal areas were studied by reduced silver impregnation of anterograde degeneration and by autoradiographic tracing of transported proteins following injections of radioactive amino acids. The subiculum was found to project to the presubiculum and to the medial and lateral parts of the entorhinal area. The projections are exclusively ipsilateral, and arranged in a dorso-ventral topographical order with the terminations confined to the deep cortical layers. The projections form part of multisynaptic chains within the hippocampal region and must also be implicated in output routes for hippocampal activity additional to the fimbria-fornix system.