Biochemical and behavioural studies on the interference between catecholaminergic and serotonergic central systems

L-DOPA, apomorphine and amphetamine increase emotional reactivity and aggressiveness, and/or evoke spontaneous attack behaviour in male rats. At the same time these compounds accelerate the turnover of endogenous serotonin (5-HT), increasing the brain concentration of 5-HIAA. L-DOPA, amphetamine and apomorphine antagonize the depressive effects of 6-tryptophan on behaviour. After the injection of L-tryptophan these dopaminomimetics facilitate the turnover of 5-HT in the brain. On the other hand, the tranquillizing effect of L-tryptophan correlates not only to the increased level of 5-HT but also to an accelerated catabolism of dopamine. After the simultaneous injection of L-DOPA and L-tryptophan, cross-influence on the turnover of 5-HT and dopamine is noted, while in behaviour the effects of L-DOPA prevail over those of L-tryptophan. PCPA blocks the behavioural effects of dopaminomimetics.