D₁ dopamine receptor binding was assessed in membranes prepared from control and lesioned striata using the selective D₁dopamine receptor antagonist [³H]SCH23390 as ligand. For saturation binding, striatal membranes were incubated at 37°C for 30 min with increasing concentrations of [³H]SCH23390 (0.1–6.4 nM) and terminated by vacuum filtration through Whatman GF/B filters. Nonspecific binding was defined as binding in the presence of 10 μMcis-flupenthixol. To prevent nonspecific association of [³H]SCH23390 with serotonin receptors, 10 μM mesulergine was added to the assay mixture. Maximal binding (B_max) and binding affinity (K_d) were calculated by Scatchard analysis of specific [³H]SCH23390 binding. For competition experiment, [³H]SCH23390 (1 nM) binding was carried out in the presence of 10⁻¹⁰ to 10⁻⁴ M dopamine (eight concentrations in 10-fold increments). The dopamine-mediated competition curve was fitted and the percentage of high- (B_high) and low- (B_low) affinity binding sites were calculated according to a two-site binding model (Munson and Rodbard, 1980). Data are presented as mean ± S.E.M. derived from four individual experiments each performed in duplicate.

• ↵1-150  p < 0.05 compared with respective values of control group by two-tailed Student's t test.