Alpha-methyl-para-tyrosine antagonizes the effect of chronic imipramine on learned helplessness in rats.

alpha-Methyl-para-tyrosine, co-administered with imipramine to rats at a dose that only partially inhibits tyrosine hydroxylase, has been found to prevent completely the decrease of dopamine D1 receptor function. The present report shows that, in the same experimental conditions, alpha-methyl-para-tyrosine significantly antagonized the capacity of imipramine to prevent the development of learned helplessness behavior in rats. This suggests that a catecholaminergic mechanism is crucial in determining the effect of imipramine on the development of learned helplessness behavior. alpha-Methyl-para-tyrosine co-administration also prevented imipramine-induced down-regulation of beta-adrenoceptor function.