Dopa-induced locomotor stimulation after inhibition of extracerebral decarboxylase

Abstract

In rats, a combination of small doses of the dopa decarboxylase inhibitor Ro 4–4602 [N-(DL-seryl)-N’-(2,3,4-trihydroxybenzyl)hydrazine] with dopa causes a marked enhancement of the spontaneous locomotor activity which is not seen with dopa alone. If high instead of low doses of Ro 4–4602 are used, locomotor stimulation does not occur. Low doses of Ro 4–4602, owing to selective inhibition of extracerebral decarboxylase, enhance the dopa-induced rise of dopa and catecholamines in the brain, whereas high doses of Ro 4–4602, which also inhibit the cerebral dopa decarboxylase, increase only the level of dopa but not that of the catecholamines. It is concluded that the locomotor activation after small doses of Ro 4–4602 in combination with dopa is due to cerebral accumulation of catecholamines which consist mainly of dopamine.