The effect of Morinda officinalis How, a Chinese traditional medicinal plant, on the DRL 72-s schedule in rats and the forced swimming test in mice.

The present study observed the antidepressant-like action of the medicinal plant Morinda officinalis in the differential reinforcement of low rate 72-s (DRL 72-s) schedule, a behavioral screen selective and sensitive to antidepressant drugs, and the forced swimming test, a well-known animal model of depression. In the DRL 72-s schedule in rats, the plant extract (25-50 mg/kg), similar to clinically effective antidepressant drug desipramine (5-10 mg/kg), significantly reduced response rate and efficiency ratio while at the same time increasing reinforcement rate. In the forced swimming test in mice, the plant extract (50 mg/kg), like the effect of desipramine (20 mg/kg), also elicited a significant reduction in the duration of immobility. A tendency to this phenomenon could be seen at the dose of 100 mg/kg. Meanwhile, the plant extract, in the effective doses for the forced swimming test, had no effects on spontaneous motor activity in mice. These findings provide further support for the conclusion that M. officinalis extract possesses the antidepressant effect.