Aim and Background. It has been suggested that histamine has modulatory influence on anxiety-related behaviors both in animals and humans.

Material and methods. In the present study, we investigated the effects of intraperitoneal of histaminergic agents on anxiety-related behaviors in rats, using elevated plus-maze test of anxiety.

Results. Intraperitoneal histamine administration (5, 10 and 20mg/kg) decreased %OAT (Open Arm Times) and but not locomotor activity, thus showing an anxiogenic response.Subcutaneous administration of ranitidine, a H2 histamine receptor antagonist at doses of 12.5, 25 and 50 mg/kg before histamine (20 mg/ kg) increased %OAT (Open Arm Times) and %OAE (Open Arm Entries) but not locomotor activity, thus showing an anxiolytic responses.

Conclusions. This effect showed that ranitidine antagonizes histamine anxiolytic effects.Our results indicated that the anxiogenic-like effects induced by histamine in the intraperitoneal reverse in presence of ranitidine.