Anxiolytic properties of the antipsychotic alkaloid alstonine.

Anxiolytic properties may be a crucial feature of newer antipsychotics associated with the improvement of negative symptoms in schizophrenic patients. The indole alkaloid alstonine acts as an atypical antipsychotic in behavioral models, but differs in its dopamine and serotonin binding profile. The purpose of this study was to verify if alstonine possesses anxiolytic properties in mice. The hole-board and light/dark models were used; moreover, the participation of D(1), 5-HT(2), NMDA and gamma-aminobutyric acid (GABA) receptors was likewise investigated. Alstonine clearly behaves as anxiolytic in both hole-board and light/dark situations. Pretreatment with the 5-HT(2A/2C) serotonin receptor antagonist ritanserin reverted the effects of alstonine in both the hole-board and light/dark models, suggesting the involvement of these receptors in the alstonine mechanism of action. The involvement of glutamate NMDA receptors should also be considered, given that alstonine partially reversed the increase in locomotion induced by MK-801 in the hole board, as well as MK-801-induced hyperlocomotion in motor activity apparatus.