CATECHOLAMINE UPTAKE BY SYNAPTOSOMES IN HOMOGENATES OF RAT BRAIN: STEREOSPECIFICITY IN DIFFERENT AREAS

Abstract

We have examined the uptake of dl -H3-norepinephrine and H3-dopamine into homogenates from different regions of the rat brain. When the homogenates were centrifuged on continuous sucrose gradients, the H3-amine uptake was localized to fractions that were enriched with synaptosomes. We studied the inhibition of H3-amine uptake into homogenates by d -and l -norepinephrine and d -and l -amphetamine. In the rat cerebral cortex, hypothalamus, medulla oblongata-pons and cerebellum, the Km for dl -H3-norepinephrine was about 4 x 10-7 M. In all of these areas, the uptake of norepinephrine was stereospecific with a marked preference for l -norepinephrine; K1 values for l -norepineplirine were about one-fourth those for d -norepinephrine. The rat corpus striatum, on the other hand, showed no differential preference for d - or l -norepinephrine. Both d - and l -norepinephrine had considerably less affinity than dopamine for the catecholamine transport system in the corpus striatum. Norepinephrine uptake in the cerebral cortex of the monkey and the guinea pig also was stereospecific with K1 values for l -norepinephrine about one-fourth those for d - norepinephrine. In the rat cerebral cortex, d -amphetamine was 10-fold more potent an inhibitor of dl -H3-norepinephrine uptake than l -amphetamine; however, in the rat corpus striatum, d - and l -amphetamine were equipotent as inhibitors of H3-dopamine uptake.