Effects of phencyclidine, amphetamine and related compounds on dopamine release from and uptake into striatal...

The ability of phencyclidine (PCP), amphetamine and other substances to stimulate dopamine release from and inhibit dopamine uptake into rat striatal synaptosomes was examined in a continuous superfusion system. Inhibition of uptake was measured by determining inhibition of [3H]dopamine displacement by unlabeled dopamine ([1H]dopamine). The displacement of [3H]dopamine by 10(-7) M [1H]dopamine was temperature- and sodium-sensitive and calcium-independent. [1H]Dopamine was an order of magnitude more potent than serotonin or norepinephrine in displacing [3H]dopamine. The concentrations of reserpine required to inhibit [3H]dopamine uptake and [3H]dopamine displacement by [1H]dopamine were similar. Nomifensine, benztropine, PCP and amphetamine also inhibited the displacement of [3H]dopamine by [1H]dopamine at concentrations which have been shown previously to inhibit the uptake of [3H]dopamine, suggesting that the mechanism behind displacement and uptake are very similar. PCP, at 10(-7) to 10(-5) M, significantly inhibited [3H]dopamine displacement by 10(-7) M [1H]dopamine, PCP was less potent than nomifensine or benztropine in inhibiting [3H]-dopamine displacement by 10(-7) M [1H]dopamine, but was equipotent to amphetamine. Superfusion of the synaptosomes for 6 min with PCP, 10(-6)M, induced increases in the spontaneous release of dopamine. In this regard, PCP was less potent than amphetamine, reserpine, flupenthixol, or benztropine. Upon initial exposure of the synaptosomes to amphetamine at 10(-7) to 10(-5) M, a substantial calcium-dependent release of dopamine was induced. In contrast, PCP did not stimulate the early calcium-dependent release of dopamine. These results indicate that PCP is less potent than amphetamine at releasing dopamine and may affect dopamine metabolism in the striatum primarily by inhibiting the reuptake of this catecholamine.