(-)-STEPHOLIDINE ANTAGONIZES THE INHIBITION BY D-2 RECEPTOR AGONISTS ON SYNAPTOSOMAL TYROSINE HYDROYLASE IN RAT CORPUS STRIATUM

AIM: To evaluate the action of (-)-stepholidine (SPD), a novel dopamin e (DA) receptor antagonist, on inhibition by presynaptic D-2 receptor agonists on the activity of synaptosomal tyrosine hydroxylase (TH) in the striatum. METHOD: The TH activity was measured by HPLC-ECD. RESULT S: The mixed DA receptor agonist apomorphine (Apo 10.4 nmol L(-1)) and selective D-2 receptor agonists N-0437 (0.4 pmol L(-1)) and quinpirol e (0.8 mu mol L(-1)) inhibited the activity of TH, while selective D-1 receptor agonist SKF 38393 (0.001-10 mu mol L(-1)) and SPD (1-100 mu mol L(-1)) failed to inhibit the TH activety. The inhibition of N-0437 and quinpirole were antagonized by D-2 receptor antagonist spiperone and SPD. CONCLUSION: The negative feedback regulation of presynaptic D A receptors is mediated via D-2 receptors and SPD is an antagonist on presynaptic D-2 DA receptors.