Abstract
Non-pyramidal neurons of the CA 1 area of the rat hippocampus were identified with a combined Golgi-electron microscopic method. They were observed to have distinctive light and electron microscopic characteristics that are different from those of pyramidal cells. These features included smooth dendrites, locally arborizing axons, infolded cell nuclei with intranuclear rods or sheets, and a well-developed perikaryal cytoplasm with many organelles. In addition, the axon terminals that contact the somata and dendrites of local circuit neurons may form asymmetric as well as symmetric synapses. The axons of these cells form symmetric synapses with dendrites and somata of pyramidal cells. Some of these features were utilized to identify non-pyramidal neurons of the CA 1 area for studies of connectivity. Degenerating commissural terminals were found to form synapses with the dendrites and somata of non-pyramidal neurons. These results indicate that these neurons are a significant population of hippocampal neurons that may provide feed-forward inhibition of pyramidal neurons.
Highlights
The morphological features of the non-pyramidal neurons of CA 1 have been described in separate light and electron microscopic preparations (Ram6n y Cajal, 1911; Lorente deN6, 1934; Gayoso et al, 1979; T6mb0i et aI., 1979)
Seven non-pyramidal and four pyramidal neurons of the CA 1 area were included in this description from which three non-pyramidal neurons are illustrated (Figs 1-14)
The non-pyramidal neurons included in this study were different from pyramidal neurons in regard to their light and electron microscopic characteristics
Summary
The morphological features of the non-pyramidal neurons of CA 1 have been described in separate light and electron microscopic preparations N6, 1934; Gayoso et al, 1979; T6mb0i et aI., 1979). These neurons have multipolar, fusiform or stellate shaped somata that are located in all layers. Smooth, beaded dendrites arise from these somata and spread out in all directions. Their axons arborize locally in the different layers of CA 1. At the electron microscopic level, the basic criterion used for the identification of a non-pyramidal neuron has been the location of a soma outside the stratum pyramidale.
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