Beyond Serotonin: A Multiaminergic Perspective on Abnormal Behavior

This chapter argues that diminished DA metabolism in the nigro-striatal system underlies decreased motor activity and lowered level of initiative, irrespective of nosological diagnosis. L-dopa, in combination with a peripheral decarboxylase inhibitor, was first studied in a group of biochemically undifferentiated, melancholically depressed patients and found to be lacking in overall therapeutic effects. The sequence leading to goal-directed behavior can be disturbed at any junction. The human data suggest that DA is involved in the mobilization, facilitation, and sustenance of goal-directed behavior. The large pool of animal data available is in accord with this conclusion. If 5-HTP’s therapeutic superiority to tryptophan is related to its combined effects on the 5-HT and CA systems, one would expect tryptophan’s antidepressant efficacy to be raised above the significance level by combining it with a compound capable of increasing CA availability. Anxiety is a psychopathological dimension occurring in depression, but by no means specific for that disorder, that also seems to be 5-HT related.