Ultrastructure of the pyramidal basket cells in the dentate gyrus of the rat.

Light and electron microscopic preparations were used to examine the somata and dendrites of the large pyramidal basket cells in the dentate gyrus. Results from previous Golgi studies have shown that the somata of these neurons are located beneath the granule cell layer and that their axons are distributed around the granule cell somata, where they form basket endings. The results of the present study indicate that the morphology of the pyramidal basket cell differs in many ways from that of the granule cell, aside from the obvious difference of their greater size. The pyramidal baseket cells display unfolded nuclei and intranuclear rods and sheets, and these characteristics are not found in granule cells. The pyramidal basket cells also show a greater abundance of cisternae of granular endoplasmic reticulum and other perikaryal organelles. Furthermore, the somata and the smooth dendrites of these neurons form both symmetric and asymmetric synaptic junctions. The results of this study indicate that the pyramidal basket cells have distinct ultrastructural characteristics that are shared by other GABAergic neurons in the cerebral cortex. It is suggested that some of these characteristics may underlie the role played by these cells in providing GABA-mediated, tonic inhibition of other neurons.