Chronic treatment with (-)-stepholidine alters density and turnover of D1 and D2 receptors in striatum.

ABSTRACT

AIM: To study the effects of chronic administration of SPD on the density and turnover of striatal D1 and D2 dopamine (DA) receptors. METHODS: Receptor density was monitored by radio-receptor binding assay. The receptor recovery and turnover were studied after irreversible inactivation by N-ethoxycarbonyl-2-ethoxy-1, 2-dihydro-quinoline (EEDQ). RESULTS: Chronic SPD treatment (sc, 20 mg.kg-1.d-1 x 21 d) upregulated both striatal D1 and D2 receptor density. As compared to vehicle-treated rats, SPD increased D1 and D2 receptors by 41.5% and 43.7%, respectively SPD also altered the turnover of both D1 and D2 receptors. The degradation rate constant (k = 0.0082.h-1) and the synthesis rate (r = 2.65 pmol.h-1/g protein) of D2 receptors in SPD-treated rats were significantly increased vs vehicle-treated rats (k = 0.0049.h-1; r = 1.10 pmol.h-1/g protein). The degradation rate constant (k = 0.0059.h-1) and the synthesis rate (r = 3.1 pmol.h-1/g protein) of D1 receptors was also increased in SPD-treated rats vs vehicle-treated rats (k = 0.0048.h-1; r = 1.8 pmol.h-1/g protein), but the alteration of degradation rate constant missed significance (P > 0.05). As a result, receptor recovery following EEDQ was accelerated. The half time for D1 and D2 receptors recovery in SPD group were 117.5 h and 84.5 h, respectively, shorter than 144.4 h and 141.4 h in vehicle-treated rats. CONCLUSION: Chronic SPD treatment upregulated D1 and D2 receptors, and accelerated DA receptor turnover and recovery mainly by increasing receptor synthesis.