The role of dopamine receptors in the release of thyrotropin-releasing hormone from the rat striatum and nucleus accumbens: an in vitro study.

In the present study we examined the influence of dopamine (DA) stimulants: amphetamine (an agent releasing DA), apomorphine (a non-selective agonist of DA receptors), quinpirole (a selective agonist of D2 receptors) and SKF-38393 (a selective agonist of D1 receptors) on the in vitro release of thyrotropin-releasing hormone (TRH) from the rat striatal slices and nucleus accumbens fragments. It was shown that amphetamine, apomorphine and quinpirole (all those drugs added in concentrations of 10(-8)-10(-5) M), concentration-dependently increased the release of TRH, a more potent effect being observed in striatal slices. On the other hand, SKF-38393 (10(-6)-10(-5) M) was ineffective. Furthermore, the increases in the TRH release from the striatal slices, induced by 10(-5) M of amphetamine, apomorphine or quinpirole, were completely blocked by the selective D2 receptor antagonist sulpiride (10(-5) M), but not by the selective D1 receptors antagonist SCH-23390 (10(-5) M). These results indicate that stimulation of D2 receptors is responsible for the TRH release from the striatum and nucleus accumbens in vitro, and that this effect may be involved in the decrease in the peptide content in the striatum following DA stimulants, observed earlier in in vivo studies.