Effects of DL-tetrahydropalmatine on motor activity and the brain monoamine concentration in rats

Behavioral and biochemical methods were used in this study to investigate the effect of DL-THP on motor activity and the concentration of monoamines in rats. Experimental results indicated that DL-THP significantly decreased the motor activity of rats and showed a dose-response pattern; in addition, it produced rigidity at a higher dosage. DL-THP also enhanced the hypomotility induced by haloperidol, but reduced the hypermotility produced by apomorphine. Furthermore, DL-THP significantly decreased the concentration of norepinephrine (NE), dopamine (DA) in the cortex and brain stem at lower and higher dosages, and the concentration of serotonin (5-HT) in the cortex at higher dosages. DL-THP also increased the concentration of homovanillic acid (HVA) in the cortex and brain stem at lower and higher dosages, and the concentration of 5-hydroxyindole acetic acid (5-HIAA) in the cortex at higher dosages. These results suggest that the hypomotility produced by DL-THP may be due to the increase in the turnover rate of dopamine in the cortex and brain stem at lower and higher dosages, and of serotonin in the cortex at higher dosages.