SPINY NEURONS OF AREA CA3C IN RAT HIPPOCAMPAL SLICES HAVE SIMILAR ELECTROPHYSIOLOGICAL CHARACTERISTICS AND SYNAPTIC RESPONSES DESPITE MORPHOLOGICAL VARIATION

Area CA3c is an area of morphologically diverse neurons, In addition to the presence of interneurons and pyramidal cells that are similar to those found in other subfields of area CA3, many neurons of area CA3c are different. They do not resemble interneurons, since they bear numerous spines, yet they also differ substantially from pyramidal cells in their morphology. To determine if the variants of area CA3c spiny cells are distinct physiologically as well as morphologically, intracellular recordings were made to record the electrophysiological properties of area CA3c cells in rat hippocampal slices, and each cell was identified morphologically following intracellular dye injection. The results show that the spiny cells, regardless of their often extensive morphological variation, have relatively uniform, pyramidal-like electrophysiological properties. The aspiny cells are quite different from the spiny cells morphologically (i.e., in their paucity or complete lack of spines), and are also extremely different electrophysiologically, exhibiting features of ''fast-spiking'' cells. Thus, spiny cells in area CA3c correspond to cells with pyramidal-like electrophysiology, and the aspiny cells in area CA3c correspond to cells with interneuronal physiological properties. This correlation between structure and function appears to be a rule that pertains to each of the subfields of the hippocampus.