Potassium-induced release of [3H]catecholamine from brain: effects of pre-exposure to catecholamine uptake inhibitors.

Cocaine, nomifensine, mazindol, dita and desmethylimipramine markedly decreased the potassium-stimulated release of [3H]-dopamine from rat striatum, an area of brain enriched with dopamine. In contrast, only desmethylimipramine had a similar effect on the release of (3H]norepinephrine from the occipital cortex, a brain area comprised mainly of norepinephrine nerve terminals. These results were obtained under the following experimental conditions: the brain tissue was labeled with the appropriate [3H]catecholamine, incubated with a drug, rinsed twice with drug-free medium and subsequently stimulated with 20 mM potassium ions to induce release of the [3H]catecholamine. The radioactivity present in the medium before, during and after stimulation was primarily the unmetabolized [3H]catecholamine. The diminished response to potassium-stimulation in the striatum after exposure to drug was not related to the ability or potency of the drug to act as an inhibitor of neuronal uptake of catecholamines. The data indicate a relatively selective interaction of the drugs with dopamine nerve terminals rather than norepinephrine nerve terminals.