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Lack of involvement of alpha 2 adrenoceptors in the regulation of striatal dopaminergic transmission

, : Lack of involvement of alpha 2 adrenoceptors in the regulation of striatal dopaminergic transmission. European Journal of Pharmacology 86(3-4): 427-434

The effect of the .alpha.2-adrenoceptor antagonists RX 781094 [2-(2-(1,4-benzodioxanyl))-2-imidazoline-hydrochloride], rauwolscine and piperoxan on the metabolism of striatal dopamine and acetylcholine and of cerebral noradrenaline [norepinephrine] was investigated in the rat. All compounds increased hypothalamic DOPEG-SO4 [3,4-dihydroxyphenylethyleneglycol sulfate] levels, cerebral MOPEG-SO4 [3-methoxy,4-hydroxyphenylethyleneglycol sulfate] concentrations and noradrenaline utilization. Rauwolscine and piperoxan also enhanced HVA [homovanillic acid] and DOPAC [3,4-dihydroxyphenylacetic acid] levels and dopamine utilization in the striatum, whereas RX 781094 did not. Rauwolscine and piperoxan, but not RX 781094, reduced striatal acetylcholine concentrations in vivo and antagonized the dopamine-induced inhibition of K-evoked release of [3H]acetylcholine from striatal slices. Rauwolscine and piperoxan competitively antagonized the apomorphine-induced decrease in striatal DOPAC levels. Rauwolscine and piperoxan, but not RX 781094, evidently possess dopamine receptor blocking properties. The divergent effects of these .alpha.-adrenoceptor antagonists on striatal dopamine turnover, together with the inability of clonidine to antagonize the rauwolscine and piperoxan-induced elevation of striatal DOPAC, strongly argue against an involvement of .alpha.2-adrenoceptors in the regulation of striatal dopaminiergic transmission.


PMID: 6299760

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