als, the neuromodulators, also affect nervous system function. These substances are produced by secretory neurons, or glia, and alter the responsiveness of transmission. Rather than being directly responsible for the transfer of an impulse from an axon to a dendrite, neuromodulators either amplify or dampen the effectiveness of different neurotransmitters (Barchas et al., 1978, p. 965).
Of the different neurochemical substances associated with mental disorders, the biogenic amines, norepinephrine, dopamine, and serotonin, as well as the endorphins have received considerable attention (Brown & Mann, 1985, p. 143). The first of these, norepinephrine, is a catecholamine neurotransmitter which occurs in the c
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