[Thyrotropin-releasing hormone (TRH): action mechanism of an enhanced dopamine release from rat striatal slices (author's transl)].

The enhancing effect of TRH on dopamine(DA) release from rat striatal slices was investigated in relation to Ca2+ and cholinergic mechanisms. TRH(10(-5)--10(-3) M) facilitated concentration dependently the uptake of 14C-DA by rat striatal slices, while methamphetamine (10(-6)--10(-4)M) exhibited a considerable inhibitory effect. TRH (10(-7)--10(--3)M) alone did not increase the DA release into the incubation medium, but it clearly enhanced the DA release in the concomitant presence of desipramine (5 x 10(-5)M). In the superfusion study, TRH (10(-5)--10(-3)M), methamphetamine (10(-6)--10(-4)M) and KCl (2.5--5.0 x 10(-2)M) enhanced the DA release into the perfusion fluid. The DA releasing effect of TRH was completely blocked by cholinergic blockers (scopolamine, hexamethonium and hemicholinium), Ca2+ chelator(EGTA), Ca2+ antagonist(CoCl2) and Ca2+ influx blocker(D-600) or by the removal of Ca2+ from the medium. The methamphetamine-enhanced DA release, however, was not modified by the above treatments except for a partial decline produced by EGTA coupled with the removal of Ca2+. TRH(10(-4)M) also facilitated the uptake of norepinephrine (NE) by rat cerebral cortex slices, but methamphetamine (10-(6)--10(-4)M) exhibited a considerable inhibitory effect. In the superfusion study, TRH (10(-5)--10(-4)M) and methamphetamine (10(-7)--10(-4)M) enhanced the NE release into the perfusion fluid. Therefore, it can be concluded that TRH facilitated the DA release from rat striatal slices by mediating through a cholinergic mechanism and enhancing the influx of Ca2+.