ROUND AND FLAT SYNAPTIC VESICLES IN THE FISH CENTRAL NERVOUS SYSTEM

Abstract

This chapter discusses round and flat synaptic vesicles in the fish central nervous system based on the study conducted with the electron microscope on various regions of the aldehyde-fixed central nervous system of the teleost fish. The initial fixation of fish central nervous system with aldehyde reveals two categories of synaptic knobs. One contains round vesicles and the other contains flat ones. Axodendritic and axosomatic synapses in the cord without tight junctions show the two categories in approximately equal numbers. Such synapses with tight junctions always have round vesicles. Flat-vesicled synapses on axon initial segments occur much more frequently than those with round vesicles. Mauthner axon collaterals have endings with round vesicles. In the cerebellar cortex, Purkinje spine synapses and mossy endings have round vesicles and basket endings and Golgi endings have flat vesicles. Neurosecretory endings have only one category: They contain predominantly round vesicles. The evidence shows that these two categories are correlated with morphologically different types of synapse and, as far as it goes, support the theory that round vesicles occur at excitatory synapses and flat ones at inhibitory synapses.