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The effects of annomontine, a pyrimidine- β-carboline alkaloid isolated from the root of ANNONA PURPUREA, on anxiety was studied in mice using the elevated plus-maze. The behavioral effects of this alkaloid on the pentobarbital-induced hypnosis, the locomotor activity in an open field, and the motor coordination in the rotarod test were also evaluated. The intraperitoneal injection of annomontine (1-30 mg/kg) increased in a dose-dependent way the number of visits to and the time spent in the open arms of the elevated plus-maze in comparison to the control animals. Such effects were blocked by the prior application of flumazenil (3 mg/kg; i. p.), a specific antagonist for the binding of benzodiazepines on the GABA (A) receptor. Under the same experimental conditions annomontine failed to affect the behavior of the animals in the pentobarbital-induced hypnosis test and had no effects on locomotion and motor coordination. These results suggest that annomontine possesses anxiolytic-like effects which may be mediated at the level of the benzodiazepine binding site on the GABA (A) receptor.