Characterization of the in vitro uptake of monoamines into brain microvessels

Abstract

The ability of brain microvessels to take up and metabolize transmitter monoamines (DA, NA, A and 5‐HT) was studied in tissues from several species (rat, rabbit, guinea‐pig, cat, dog, baboon, man) in vitro. Following incubation, slices were analyzed by fluorescence histochemistry and isolated microvessels by measurement of radioactivity from tritiated amine. Provided the MAO activity was inhibited a strong accumulation, similar for all animals tested, occurred in the wall (endothelial cells and pericytes) of capillaries and venules—but not in larger vessels—of all species. The degree of amine uptake and accumulation and the conditions under which it was inhibited suggested that it reflected a saturable, energy‐dependent process, with characteristics of both the extraneuronal and neuronal type of uptake processes. The mechanism may serve as an inactivation of transmitter monoamines at the blood—brain interphase, thereby assisting in the control of transmitter levels in the cerebral extracellular compartment.