THE EFFECT OF MONOAMINE OXIDASE INHIBITORS ON SOME ARYLALKYLAMINES IN RAT STRIATUM

The trace amines phenylethylamine, tryptamine, p-tyramine and m-tyramine have been measured in the striatum of both control and MAO-treated rats. Dose-response and time-response studies have been carried out with clorgyline and deprenyl, inhibitors which preferentially inhibit the A and B forms of MAO, respectively, and with tranylcypromine and phenylethylhydrazine, which are used clinically in the treatment of depression. Phenylethylamine was increased by 1 mg/kg of deprenyl, but was unaffected by clorgyline at doses up to 50 mg/kg, while the tyramines and tryptamine were increased by low doses of clorgyline, but were increased only by much greater doses of deprenyl than those required to affect phenylethylamine. Phenylethylamine is oxidized by the B form of MAO, but tryptamine and the tyramines appear to be oxidized by both A and B MAO. The observed proportional increases in trace amine levels are much greater than those observed for the classical neurotransmitters, noradrenaline, dopamine and 5-hydroxytryptamine. As these increases are differential, selective manipulation of trace amine concentrations is possible.