Abstract

The accumulations of H³-serotonin (H³-5-HT) and H³-norepinephrine (H³-NE) into rat brain slices have been compared. Regional differences in accumulation of both amines occurred with highest uptakes for both amines in the corpus striatum. Other areas, however, showed significant differences with respect to amine accumulation after reserpine pretreatment and with respect to inhibition of uptake of the two amines by a variety of antidepressant drugs. Kinetic analyses indicated two components of 5-HT accumulation, one representing a high (uptake 1) and the other a low (uptake 2) affinity transport system. The K₁ values for the competitive inhibition of dl-H³NE uptake by 5-HT were approximately equal to the Km values for uptake 2 of 5-HT, suggesting that the low affinity transport for 5-HT might involve uptake by the catecholatnine transport system. Further evidence supporting the notion that 5-HT can be transported by cerebral catecholaminergic transport systems as follows. 1) The relative potency of d-and l-NE and of dopamine in inhibiting 5-HT uptake in the hypothalamus and striatum paralleled their affinity for the catecholamine uptake process in these two areas. 2) Catecholamines were better inhibitors of H³-5-HT uptake in the striatum when 5-HT concentration was increased to levels at which uptake 2 should predominate. Our findings suggest that doses of 5-HT administered into the brain in a variety of studies may enter catecholaminergic neurons in significant quantities.