The effect of l,3-diphenyl-5-(2-dimethylaminopropionamide)-pyrazole[difenamizole], an analgesic synthesized by the present authors, on the performance of a conditioned avoidance was compared with that of analgesic doses of morphine, aminopyrine, chlorpromazine and chlordiazepoxide in rats. Experiments were conducted in a two-compartment rat shuttle-box system using 20-trial sessions and a 5-sec conditioned stimulus-unconditioned stimulus interval. Difenamizole (100-400 mg/kg, p.o.) increased significantly the number of avoidance failures, decreased the number of fecal boluses excreted, and prolonged response latency times. Aminopyrine (100-400 mg/kg, p.o.) produced a dose-related prolongation in response latency time, but the effect of this drug on the percentage avoidance was less than that produced by difenamizole at low doses. The avoidance behaviour was hardly influenced by analgesic doses of morphine (10-40 mg/kg, p.o.) and chlordiazepoxide (10-40 mg/kg, P.O.). Chlorpromazine (5-20 mg/kg, p.o.) produced a dose-related depression in percentage avoidance and a doserelated prolongation in response latency time. The effect of difenamizole on conditioned avoidance performance was similar to that produced by chlorpromazine.
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