Dopa accumulation is a measure of dopamine synthesis in the median eminence and posterior pituitary

Abstract

Summary A radioenzymatic assay was employed to measure the accumulation of DOPA in a variety of rat brain tissues 30 min after the administration of a decarboxylase inhibitor in order to estimate the activity of dopamine (DA) nerves which terminate in these regions. In the median eminence and posterior pituitary the accumulation of DOPA appears to occur primarily in DA nerves since: (1) the rate of synthesis of norepinephrine (NE), as estimated from theα-methyltyrosine-induced decline of catecholamines, accounts for less than 10% of total catecholamine synthesis in these two brain regions; and (2) the accumulation of DOPA is not significantly altered when the NE concentrations in these regions are reduced to 40–50% of control by prior intraventricular injections of 6-hydroxydopamine. These results suggest that the accumulation of DOPA in the median eminence and the posterior pituitary can be used to estimate the activity of tuberoinfundibular and tuberohypophyseal DA nerves, respectively.