ABSTRACT
An attempt has been made to discriminate synaptic diversity in the neostriatum of the cat with emphasis on the characteristic structures of axon terminals and postsynaptic profiles. The differentiation of the axon terminals was based on the size and shape of synaptic vesicles in the axoplasm. Three types of axon terminals could be differentiated: Type I, the terminals contained small round (45 nm in diameter) vesicles; type II, the terminals with large pleomorphic (50 nm) vesicles; and type III, the terminals contained flattened (45 x 25 nm) vesicles. The type I terminals were making asymmetrical or symmetrical synapses in contact with the somata, dendrites and dendritic spines of neurons in the neostriatum, and a few type I terminals making asymmetrical or symmetrical contact with axons were also observed. The type II and III terminals were making symmetrical contact with the somata and dendrites of neostriatal neurons. A few type II terminals formed at the node of Ranvier of myelinated nerve fibers were making symmetrical contact with large dendrites. Additionally, dendro-dendritic and serial syanpses were rarely found in the neostriatum. In the serial synapses composed of axo-dendritic and dendro-dendritic synapses, the type I terminals making asymmetrical contact and the type II making symmetrical contact were identified.