Identification of Gastrointestinal Neurotransmitters

There have been a number of attempts to define criteria which, if satisfied, would indicate that a substance is a neurotransmitter (e.g. Paton 1958; Curtis 1961; McLennan 1963; Eccles 1964; Werman 1966,1972; Phillis 1970; Orrego 1979). However, the underlying criteria that need to be met are that release is detectable and that there is identity of action. In experimental terms this means the following: That a transient increase in the concentration of the substance can be detected at the neuroeffector junction when the nerve is activated and that when the substance is applied at the junction, in the same concentration and with the same time course, the postjunctional events associated with activation of the nerve are reproduced.