Different Kinds of Synapses

Abstract

Various biochemical assays demonstrate a variety of neurons and of synapses suggesting different roles in their functional interplay. These different roles may well coincide with the two fundamental interactions postulated by neural net models, excitation and inhibition, and with the other distinction which such models sometimes make between fixed and modifiable synapses. The functional interpretation of the biochemical variety remains hypothetical for the most part, although the identification of a certain transmitter (glutamate) with excitatory interactions and of another (GABA) with inhibition seems to be generally accepted. We have not done any cytochemistry ourselves but follow the standard usage of the distinction between two types of synapses according to their appearance in the electron micrographs. They are widely thought to correspond to excitatory and inhibitory interactions respectively. The distinction of two types of synapses was introduced by Gray (1959) and later refined by Colonnier (1968). Uchizono (1965) was mainly responsible for their interpretation in terms of excitation and inhibition on the basis of the well worked-out anatomy and physiology of the cerebellum.