A comparison of the effects of methylphenidate and amphetamine on the simultaneous release of radiolabelled dopamine and p- or m-tyramide from rat striatal slices

Abstract

The release of [ 14C]dopamine (DA) from slices of rat caudate nucleus was studied simultaneously with the release of either [ 3 H]para- tyramine (pTA) or [ 3 H]meta- tyramine (mTA). Amphetamine (10 −5 M) caused a large concurrent release of [ 14C]DA and [ 3H]pTA; similar results were obtained when [ 14C]DA and [ 3H]mTA release were studied. The release of all three amines by amphetamine was quantitatively similar. In contrast, methylphenidate caused a release of [ 3H]pTA similar to that seen with amphetamine, but only a very small simultaneous release of [ 14C]DA. [ 3H]mTA was also strongly released by methylphenidate concurrent with a minimal release of [ 14C]DA. The inclusion of reserpine in the incubation medium had no detectable effect on the release of any of the three amines by amphetamine. Methylphenidate-induced release of tritiated mTA and pTA was also unaffected by reserpine. However, the release of [ 14C]DA by methylphenidate was potentiated in the presence of reserpine. The uptake of radiolabelled pTA, mTA and DA was inhibited by both amphetamine and methylphenidate, although amphetamine was a stronger inhibitor of the uptake of all three amines. It is suggested that release of endogenous tyramines may be involved in mediating some actions of psychomotor stimulant drugs.