[Interactions of dopamine receptor agonists and antagonists with regard to dopamine synthesis and metabolism]

Intraperitioneal injection of d-amphetamine sulfate, 0.3-3 mg/kg, led to a marked rise in dopa formation in the dopamine rich areas c. striatum and mesolibbic cortex of the rat brain inhibiton of the aromatic amino acid decarboxylase with 3-hydroxybenzylhydrazine HCL (NSD 1015). However, amphetamine given in a dose of 10 mg/kg decreased the tyrosine hydroxylation rate in the mesolimbic cortex as well as the norepinephrine containing neocortex. In combination with haloperidol the stimulating effect of the neuroleptic on dopa formation was markedly potentiated by amphetamine in rat forebrain. Also, amphetamine potentiated the haloperidol induced increase in dopamine release in vivo measured as 3-methoxytyramine formation. The functional antagonists haloperidol and d-amphetamine appear to have synergistic effects on dopaminergic neurons.