Criteria for Transmitter Status

To be accepted as a neurotransmitter, a candidate chemical must (1) be present in higher concentration in the synaptic area than in other areas (ie, must be localized in appropriate areas), (2) be released by electrical or chemical stimulation via a calcium-dependent mechanism, and (3) produce the same sort of postsynaptic response that is seen with physiologic activation of the synapse (ie, must exhibit synaptic mimicry).