A hippocampal interneuron observed in the inferior region

In the process of an extensive Golgi analysis of the inferior region of the rat hippocampus, a hitherto undescribed cell type was discovered. The cell has a round, elliptical, or fusiform cell body and an apical dendritic plume reminiscent of dentate granule cells. The axon is thick, with many collateral and ramifies within, above and below the pyramidal layer. The proximal dendrites have stubby spines whereas the distal dendrites have long thin spines. All impregnated cells of this type were found in the inferior region (CA₃ and CA₄ of Lorente de Nó) of the hippocampus and most were found in a circumscribed suprapyramidal region at the mouth of the hilus. The majority of impregnated cells of this type were found in the middle to temporal portion of the hippocampus. Nissl-stained sections confirmed the predominant occurence of this cell type in the inferior region of the middle to temporal hippocampus. In these preparations, the cells have a large nucleus, several nucleoli and very scanty cytoplasm with Nissl substance essentially confined to the initial dendritic segments. The unique morphology of this cell type allows relatively easy identification using Nissl staining.