Divergent reserpine effects on amfonelic acid and amphetamine stimulation of synaptosomal dopamine formation from phenylalanine

Abstract

Some effects of a non-amphetamine central stimulant, amtbnelic acid, on the synaptosomal (P 2) formation and release of dopamine being produced continuously from [ 14C]phenylalanine substrate have been determined. How reserpine action may modify the effects of amfonelic acid and those of amphetamine (the latter was included for comparative purposes) was also examined. For these studies, P 2 preparation from rat caudate nuclei was incubated with [ 14C]phenylalanine with and without various drug additions, and the particulates were separated from the medium after incubation. The separated fractions were analyzed for labeled dopamine and for the synaptosomal content of the labeled substrate. Of the total labeled dopamine formed, the fraction that was present in the medium was determined and taken as a measure of the spontaneous release (no drug addition) or its enhancement by any addition. Amfonelic acid and amphetamine (0.91–18.2 μM) comparably stimulated the synthesis and release of [ 14C]dopamine. The addition of reserpine (1.8 μM) alone had an inhibitory effect on total synthesis and a stimulatory one on release. In the presence of reserpine, the synthesis stimulation by amphetamine was maintained or accentuated, but amfonelic acid induced an inhibitory effect additive to that due to reserpine alone. The release stimulations by amphetamine and amfonelic acid were comparable in the absence as well as in the presence of reserpine. Following reserpine pretreatments at 24 and 2 hr, amphetamine (9.1 μM) markedly stimulated, but AA (9.1 μM) affected nonsignificantly, the dopamine synthesis. The pretreatments did not abolish the release-enhancing effect of either stimulant. None of the drug additions resulted in a significant alteration of the paniculate [ 14C]phenylalanine substrate level. In summary, the results show that amfonelic acid, like amphetamine, may release continuously forming synaptosomal dopamine and stimulate dopamine synthesis. However, the synthesis stimulation by amfonelic acid, but not that by amphetamine, may he abolished by reserpine action, either in vitro or in vivo. The results suggest that. although amphetamine may stimulate by releasing the newly forming dopamine pool, a significant amfonelic acid action may he on the catecholamine storage system, and synaptosomal dopamine synthesis may be under the controlling influence of both the newly forming amine and the vesicular stores.