Chandelier cells in the hippocampal formation of the rat: The entorhinal area and subicular complex

Abstract

In the present study we describe the characteristics of the chandelier cells in the rat entorhinal cortex and subicular complex by using the Golgi method and combined Golgi‐electron microscopic techniques. In the entorhinal cortex, chandelier cells were frequently stained in layers II/III. Two types of axonal complexes were noted. One had a preferential horizontal orientation and gave rise to terminals located in the upper portion of layers II/III. The second type of chandelier cell axon was observed in the medial entorhinal area, innervating the entire extent of layers II/III. In the subicular complex, chandelier cells were frequently stained in the parasubiculum, whereas only a few cells were found in the presubiculum. In both subfields, chandelier cell axons were restricted to layers II/III. In the subiculum, most chandelier cells were present in the stratum radiatum, giving rise to a descending axon that branched in the stratum pyramidale. Both the size and morphological features of the chandelier cell terminal portions were found to be region‐specific. Electron microscopically, the cell body and dendrites of gold‐toned chandelier cells displayed typical features of nonpyramidal cells, such as the presence of nuclear infoldings, symmetric and asymmetric synapses on the cell body, and moderate numbers of axon terminals covering the smooth dendritic surface. Five gold‐toned chandelier cell axonal complexes were analyzed at the fine structural level. In all parahippocampal regions, gold‐labeled axon terminals formed symmetric contacts with axon initial segments. Our results demonstrate the presence, morphological characteristics, and target selectivity of identified chandelier cells in the parahippocampal region of the rat. Together with previous data, these results suggest a wide distribution of this specialized type of cortical interneuron and indicate that it is a constant and essential component of inhibitory circuits in the cerebral cortex. The possible significance of chandelier cells for the circuits linking several subfields of the hippocampal formation is discussed. © 1993 Wiley‐Liss,Inc.