Pharmacological evaluation of a modified open-field test sensitive to anxiolytic drugs.

In a recent study it has been shown that benzodiazepine receptor agonists attenuate novelty-induced suppression of feeding and increase the percentage of animals feeding in the open field. Food-deprived rats were placed in one corner of the open field containing food in the center. The number of rats beginning to eat in the first 5 min was recorded. In the present study this test was validated pharmacologically using known "anxiolytic" or "nonanxiolytic" drugs. The following substances (effective doses, given IP) increased the number of rats feeding within 5 min in the center of the open field: meprobamate (30.0-300 mg/kg), 8-OH-DPAT (10 and 30 microg/kg), ipsapirone (1.0 and 2.0 mg/kg), ritanserin (0.125-0.5 mg/kg), tropisetron (0.1-10.0 microg/kg), ondansetron (0.3-3.0 microg/kg), lisuride (0.28-0.55 mg/kg), morphine (0.3 and 1.0 mg/kg), propranolol (0.3 and 1.0 mg/kg), clozapine (1.0 mg/kg). Drugs without "anxiolytic" effects in other animal models or in humans, including amphetamine, apomorphine, haloperidol, sulpiride, and mCPP did not increase the incidence of food intake in this test. Ethanol and hexobarbital, in nonsedative doses, had no effect in this paradigm. Drugs and doses effective in the modified open-field test caused no increase in food intake in an independent food consumption test using food-deprived rats staying in the familiar cages. The results suggest that the modified open-field test can detect "anxiolytic" drug properties and is valid for the assessment of "anxiolytic" effects from different classes of drugs.