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 fo und to prevent completely the decrease of dopamine D-1 receptor functi on. 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 behavio r 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 a lso prevented imipramine-induced down-regulation of beta-adrenoceptor function.