Abstract
The stereotyped morphology of dentate granule cells in rodents consists of apical dendrites arborizing in the molecular layer and an axon arising from the opposite pole of the soma. Recently, we showed that epilepsy induces the formation of basal dendrites on granule cells and that these dendrites extend into the hilus of the dentate gyrus. The present Golgi study of granule cells from adult rats shows two atypical features for granule cells in control rats. One is the occurrence of recurrent basal dendrites (RBDs) that are defined as basal dendrites arising at or near the hilar pole of the soma and then curving back to the molecular layer. The frequency of granule cells with RBDs was 3.8% in control rats. The second is apical axons of granule cells that were observed to originate from either the apical pole of the soma or an apical dendrite. The incidence of these "apical" axons was about 1%. These morphological findings in the present study suggest that rat granule cells are more heterogeneous than previously indicated. Furthermore, their frequency was not increased in epileptic rats.
Highlights
The classical studies in rats and mice indicated that hippocampal dentate granule cells are bipolar cells with apical dendrites arising from one pole and an axon from the other
Most of the oval somata located in the lower part of the granule cell layer are oriented with their long axis perpendicular to the plane formed by the hilus and this layer
The somata of many granule cells taper at their base and their axons arise from this location where it is directed toward the hilus (Fig. 1A)
Summary
The classical studies in rats and mice indicated that hippocampal dentate granule cells are bipolar cells with apical dendrites arising from one pole and an axon from the other I. Spigelman Division of Oral Biology and Medicine, UCLA School of Dentistry, Los Angeles, CA 90095, USA
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