[Dependence on and preference for morphine (II). Comparison among morphine, phenobarbital and diazepam]

Results of a previous experiment indicated that naive rats given a choice between morphine-admixed food (0.5 similar to 1mg/g of food) and quinine-admixed food (0.5 similar to 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 defferent chioce test using drug dependent rats. Rats were pretreated with morpnine, phenobarbital, and/or diazepam by drug admixed food ingestion method for 12 similar to 15 weeks, and the choice test was practiced for one week at 3 intervals (4 similar to 5 trials). Control groups of rats were given the same choice testas 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.