Effects of l-stepholidine on tyrosine hydroxylase activity in rat corpus striatum

l-Stepholidine (SPD) 2.5 and haloperidol (Hal) 1.0 mg.kg-1 ip increased rat striatal L-3,4-dihydroxyphenylalanine (DOPA) and 3,4-dihydroxyphenylacetic acid (DOPAC) accumulation induced by NSD 1015 (50 mg.kg-1, ip), a decarboxylase inhibitor. SPD (2.5 mg.kg-1, ip) did not alter but apomorphine (2.0 mg.kg-1, ip) decreased the dopamine (DA) content elevated by gamma-butyrolactone (GBL, 750 mg.kg-1, ip) in the rat striatum. Ip injection of either SPD 5.0 or Hal 2.5 mg.kg-1 after NSD 1015 50 mg.kg-1 or NSD 1015 plus GBL 750 mg.kg-1 also augmented tyrosine hydroxylase (TH) activity in the rat striatum. These results suggest that SPD produces an antagonistic effect on presynaptic DA receptors.