Amphetamine: evaluation of d- and l-isomers as releasing agents and uptake inhibitors for 3H-dopamine and 3H-norepinephrine in slices of rat neostriatum and cerebral cortex.

Release of 3H-doapamine or of 3H-norepinephrine and inhibition of accumulation of 3H-dopamine or 3H-norepinephrine by d- and l-amphetamine were studied in slices of rat neostriatum and in slices of rat cerebral cortex. The two stereoisomers of amphetamine were equally potent as inhibitors of accumulation in the cortex, whereas d-amphetamine was approximately 3-fold more potent than l-amphetamine in the neostriatum. A similar relationship was observed between the two stereoisomers in release experiments. Some spontaneous efflux of 3H-dopamine from tissue slices was evident in absence of added drug in release experiments. When cocaine (2 X 10(-5) M), a known inhibitor of biogenic amine uptake, was added to the medium, there was very little increment in spontaneous efflux of 3H-dopamine in neostriatal slices, but cocaine blocked the release caused by d-amphetamine. This showed that the apparent releasing action of d-amphetamine in the neostriatum was not due to blockade of reuptake of spontaneously released material and that d-amphetamine itself must be taken up to evoke a releasing action. Experiments were designed to compare directly the releasing and uptake inhibiting actions of d-amphetamine. In the cortex, uptake inhibition of 3H-norepinephrine was greater than release over a wide concentration range, while in the neostriatum the two actions were essentially identical in magnitude for 3H-dopamine. We conclude that in the cortex, d-amphetamine can act both to release and to block uptake of 3H-norepinephrine. In the neostriatum, on the other hand, there is releasing action of 3H-dopamine by d-amphetamine (which is stronger than that in the cortex), but the apparent blockade of "uptake" is of questionable significance and appears to result from the release of previously accumulated 3H-dopamine