Abstract
Results of a previous experiment indicated that naive rats given a choice between morphine-admixed food (0.5 ?? 1 mg/g of food) and quinine-admixed food (0.5 ?? 1 mg/g of food) for 3 weeks gradually and spontaneously preferred the morphine-admixed food, and this choice behavior revealed one of the psychological aspects of morphine dependent rats. In the present work, the ability of preference formation was detected for morphine, phenobarbital and diazepam by a different choice test using drug dependent rats. Rats were pretreated with morphine, phenobarbital, and/or diazepam by drugadmixed food ingestion method for 12 ?? 15 weeks, and the choice test was practiced for one week at 3 weeks intervals (4 ?? 5 trials). Control groups of rats were given the same choice test as the naive rats. Results indicated that (a) of all the drugs employed, morphine showed the most rapid and intensive preference formation. (b) Phenobarbital and diazepam had almost the same degree of preference formation. (c) Phenobarbital showed no dose-dependent intensity of preference formation in the 50 ?? 90 mg/kg/day dose range, however, a more rapid development of preference was observed dose-dependently among the 80 ?? 120 mg/kg/day dose range of diazepam. Thus these studies utilizing a choice test provide a clear demonstration of drug-seeking behavior in rats. In addition, the present method is useful for drug screening tests involving weak psychological dependence liability, and moreover, the data could be analyzed statistically.
