AN ENZYMIC BARRIER MECHANISM FOR MONOAMINE PRECURSORS IN THE NEWLY‐FORMING BRAIN CAPILLARIES FOLLOWING ELECTROLYTIC OR MECHANICAL LESIONS

Abstract

Abstract— The intracerebral capillaries of the rat constitute an enzymic trapping mechanism for certain systemically administered monoamine precursors, which are taken up into the capillary walls, decarboxylated locally to the corresponding amine and this is then metabolized by monoamine oxidase. The amine can be directly demonstrated histochemically in the endothelial cells and pericytes of the capillaries, particularly after inhibition of monoamine oxidase. The question of whether or not these barrier properties appear also in the regenerating capillaries following electrolytic or mechanical lesions in the cerebellar parenchyma was studied after intraperitoneal injection of l ‐DOPA to rats pretreated with nialamide. A very pronounced formation of new capillaries, starting at the periphery of the lesions, could be established 3–4 weeks postoperatively. Also these new, regenerating capillaries were able to trap l ‐DOPA in a manner indistinguishable from that of the normal capillaries in the surrounding parenchyma. It is concluded that a complete barrier mechanism with regard to the enzymic trapping of certain monoamine precursors can reestablish after complete regeneration of the brain capillary bed in unspecific lesions.