MECHANISMS OF SYNAPTIC TRANSMISSION

Abstract

Generally, the mechanisms of synaptic transmission can be divided into three types of transmission. At most junctions, the synaptic transmitter has been found to increase the permeability of the postsynaptic membrane to certain ions. At a few junctions, however, particularly in invertebrates and in lower vertebrates, transmission is not chemically mediated but is clearly electrical. Recently, a third type of transmission mechanism has been recognized, namely, chemical transmission that activates metabolic systems in the postsynaptic neuron without increasing the ion permeability of the postsynaptic membrane. The chapter discusses the various mechanisms of synaptic transmission. It illustrates the basic mechanisms of synaptic transmission by discussing those junctions where the mechanism of transmission has been most clearly elucidated. Communication between nerve cells—synaptic transmission—may be accomplished in several different ways. There may be direct electrical coupling between neural elements that transmit information in either direction or in one direction only. Alternatively, a chemical transmitter may be released presynaptically that may increase the postsynaptic ion permeability or may activate metabolic systems requiring cellular energy. The recent reports show that late, slow synaptic potentials increase the duration of synaptic action manifold but the durations of these synaptic potentials are still only in the range of seconds and, thus, do not bridge the gap to the long-term changes of memory. Nevertheless, the possibility that a synaptic transmitter may be able to activate metabolic systems of a nerve cell may provide a fruitful field for the future investigation of possible long-term changes resulting from synaptic activity.