Passage into the rat brain of dopa and dopamine injected into the lateral ventricle

1. The green fluorescence of catechols of the brain was studied in rats after intraventricular injection of L-dopa or dopamine in untreated rats as well as in rats in which dopa decarboxylase (DC) was inhibited by Ro 4602, or the monoamine oxidase by nialamide.2. From the patterns of fluorescence obtained in these conditions, it is concluded that in the areas close to the liquor space dopa is rapidly taken up by the endothelium of the brain capillaries and then converted into dopamine; when the DC is inhibited the dopa passes freely from the endothelium into the brain tissue.3. On the other hand, dopamine passes from the liquor space via the ependyma directly into the brain tissue and from there into the capillary endothelium which is thus permeable to the amine in the direction from the brain tissue, in contrast to the impermeability in the direction from the capillary lumen.