Physiological and morphological identification of a nonpyramidal hippocampal cell type.

In intracellular recordings from the CA1 region of the hippocampal slice preparation, an infrequent cell type different from the predominant pyramidal cell has been characterized. The cells have very brief spikes, hyperpolarizing after-potentials, and tend to fire at a high spontaneous rate; unitary synaptic potentials are visible in the baseline. Stimulation in stratum radiatum evokes an EPSP which often triggers a short burst of spikes; an IPSP invariably follows the initial excitation. Intracellular injection of HRP into these cells shows them to be a non-pyramidal cell type with extensive local axon ramification; however, they do not resemble the classical basket cell. These cells are, nevertheless, candidates for an interneuron in hippocampus.