The anti-anxiety activity of the ethanolic extract of leaves of Alstonia scholaris (Family: Apocynaceae) has been well established. The aim of the present study is to evaluate the anti-anxiety activity of the dichloromethane fraction (known as DCM) fractionated from ethanolic extract of leaves of A. scholaris (known as EEAS).

DCM fraction (10 and 30mg/kg) was tested against various anti-anxiety models viz. elevated plus maze, open field, hole board, light dark test, mirror chamber and foot shock induced aggression models. The false positive results were overruled by actophotometer and rotarod tests. The change in brain monoamines was estimated. The possible dopaminergic effect was tested by haloperidol-induced catalepsy and 6-hydroxy dopamine induced Parkinsonism.

The DCM fraction of EEAS was found to be significantly active in all the tested models of anxiety, which confirmed their anti-anxiety activity. Lack of significant change in locomotion test indicated that DCM did not have stimulant or sedative effects. There was also no significant change in the time spent in the rotarod, which indicated its lack of motor or muscle in coordination. Increase in brain dopamine levels and reversal of dopamine-induced catalepsy confirmed that the mechanism of anti-anxiety activity is mediated through dopamine. The effect of DCM in 6-hydroxy dopamine-induced anxiety was conclusive of its dopaminergic activity.

The present study suggests that DCM possess anti-anxiety and the apparent mechanism of action is through dopaminergic mediation.