Interaction of drugs with apomorphine, tryptamine and norepinephrine. A new 'in vivo' approach: the ATN-test in rats.

A new experimental test procedure is described for the 'in vivo' study of drug interactions with dopamine (DA), 5 hydroxy-tryptamine (5-HT) and norepinephrine (NE). The ultimate aim of this study is to provide an empirical evaluation of the relative specificity with which drugs may affect particular neurotransmitter systems, and to allow a classification of new drugs in this respect. The data indicate that, within certain dosage limits, compounds may modulate specifically a single component of the test procedure and may thus be considered as interacting specifically to modify one neurotransmitter system: i.e. DA in the apomorphine-test (e.g. pimozide), 5-HT in the tryptamine-test (e.g. pizotifen) and NE in the norepinephrine-test (e.g. phenoxy-benzamine). Higher doses of the same compounds may, however, excert effects on other neurotransmitter systems as well, and these actions may be classified as nonspecific. Thus the concept of drug specificity as applied in the present study, is not exclusive, but refers to the dissociation, in terms of doses, which exists between a drug's effect on one neurotransmitter system and its possible effects on other systems. The ATN-test separates and delineates, in terms of doses, the specific and nonspecific effects of drugs.