Regulation of the Release of Coexisting Neurotransmitters

Abstract

The joy of neurobiologists at the discovery of the coexistence of several neuroactive substances within the same neuron terminals can be compared with the delight of a man who has bought a radio he thought would only receive AM broadcasts, but who then discovers that it also gets all the FM stations. The discovery that the given neuronal network has the possibility of transmitting several different signals at the same time, at many of its syn­ apses, lends new dimensions to the workings of this network. The pace of morphological discovery of ever new examples of the coexistencel colocalization of two or more neuroactive substances in the same neuron is very high, producing several hundred new examples of coexistence phe­ nomena in the periphery and eNS (cf. 1-6). The work on the functional implications of the possibility of multiple signalling through the same syn­ apse-using several coexisting neurotransmitters-has been much slower. In this review, we discuss some important questions concerning the release of coexisting neurotransmitters and through these get some insight into the functional implications of coexistence. These questions are as follows: (a) Will a neuron at every one of its processes (dendrites and axon