The role of dopamine in regulation of thyrotropin-releasing hormone in the striatum and nucleus accumbens of the rat.

The effect of alpha-methyl-p-tyrosine (alpha-MT), FLA-63, amphetamine, apomorphine and quinpirole on the concentration of thyrotropin-releasing hormone (TRH) in the striatum and nucleus accumbens was studied in rats. It has been found that the TRH content was increased in both those structures after alpha-MT, an inhibitor of tyrosine hydroxylase which reduced the concentration of both dopamine (DA) and noradrenaline (NA), but not after FLA-63, an inhibitor of DA-beta-hydroxylase which decreased the NA level without affecting DA. On the other hand, the indirectly acting dopaminomimetic amphetamine, the non-selective DA receptor agonist apomorphine, and the selective D2 receptor agonist quinpirole reduced the TRH level in the striatum, but not in the nucleus accumbens. Moreover, the decrease in the striatal peptide content induced by DA-mimetics was antagonized by the selective D2-receptor antagonist sulpiride, but not by the selective D1 receptor antagonist SCH 23390. The effect of amphetamine was not modified by the selective alpha 1-adrenoceptor antagonist prazosin. These results indicate that DA and D2 receptors play a significant role in the regulation of the striatal TRH.