Entorhinal cortical innervation of parvalbumin-containing neurons (basket and chandelier cells) in the rat ammon's horn

Physiological data suggest that in the CA1–CA3 hippocampal areas of rats, entorhinal cortical efferents directly influence the activity of interneurons, in addition to pyramidal cells. To verify this hypothesis, the following experiments were performed: 1) light microscopic double‐immunostaining for parvalbumin and the anterograde tracer Phaseolus vulgaris‐leucoagglutinin injected into the entorhinal cortex; 2) light and electron microscopic analysis of cleaved spectrin‐immunostained (i.e., degenerating axons and boutons) hippocampal sections following entorhinal cortex lesion; and 3) an electron microscopic study of parvalbumin‐immunostained hippocampal sections after entorhinal cortex lesion. The results demonstrate that in the stratum lacunosum‐moleculare of the CA1 and CA3 regions, entorhinal cortical axons form asymmetric synaptic contacts on parvalbumin‐containing dendritic shafts. In the stratum lacunosum‐moleculare, parvalbumin‐immunoreactive dendrites represent processes of GABAergic, inhibitory basket and chandelier cells; these interneurons innervate the perisomatic area and axon initial segments of pyramidal cells, respectively. A feed‐forward activation of these neurons by the entorhinal input may explain the strong, short‐latency inhibition of pyramidal cells. © 1996 Wiley‐Liss, Inc.