Effects of difenamizole on behavior maintained by schedule of positive reinforcement.

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Abstract
The anti-nociceptive dose of difenamizole, morphine, aminopyrine and aspirin was studied for effects on behavior maintained by schedule of positive reinforcement. Male albino rats were trained to press a lever for food pellets on a fixed-ratio (FR) 10 and 30 schedule of reinforcement or a differential reinforcement of low rates of responding (DRL) schedule. Difenamizole (200 and 400 mg/kg, p.o. [per os]) produced a dose-related decrease in the response under FR-10 schedule. The response rate decrease observed under the FR-10 schedule was similar to that resulting from the oral administration of 400 mg/kg of aminopyrine. Response in the FR-30 schedule was not affected by any dose of difenamizole (100-400 mg/kg, p.o.) and aminopyrine (200-400 mg/kg, p.o.). In the response maintained by the DRL schedule, the overall response rate and the mean interresponse time were not altered significantly by most doses of difenamizole, aminopyrine and aspirin given; however, food reinforcement was decreased significantly with ingestion of these drugs. Morphine (20 mg/kg, p.o.) shortened the mean interresponse time and increased the response in DRL schedule. The central action of difenamizole is similar to that produced by aminopyrine, but not that produced by morphine.