Abstract
Electron microscopy of the dwarf-cell cap of the olfactory tubercle revealed the characteristic spatial distribution of the four types of nerve terminals. Type A with a rather light appearance contains round vesicles of the equivalent diameter 416±62Å and is found through the whole extent of layer I. This type of terminals makes asymmetrical synapses with the dendritic spines of the dwarf cells. Terminals having granulated vesicles together with a few round ones (type B) are restricted to the superficial portion of layer I. Type C containing flattened vesicles is distributed over the whole layers but occurs particularly often on the perikarya and the proximal parts of the dendrites of the polymorphic cells in the deeper portion of layer III. Type D terminals are densely packed with round vesicles which are smaller (equivalent diameter 350±33Å) than those in the type A. Terminals of this type are found mostly in layer II and the superficial part of layer III and make seemingly complicated synaptic junction with a cluster of tiny projections on the proximal portions of both apical and basal dendrites of the dwarf cells. The three dimensional models made from the serial electron micrographs revealed, however, that the synaptic contact is simply formed by the type D terminals and dwarf cells.
Considering these findings together with results of the silver method and the autoradiography, it was supposed that the type A and type D terminals might represent the olfactory bulbar input and the association input from other olfactory cortices, respectively.
