[Determination of mental dependence liability of drugs using small animals. 3. Selective drinking behavior of mice caused by dependence-liable drugs].

Using mice, drug solution-directed drinking behavior was investigated in the choice test between drug solution and tap water following various regimes of pretreatment. In the preliminary experiments, the concentration of the drug solution for the pretreatment and choice test and also the dose of injection was determined for each drug, depending on the amount of the drug to produce its CNS action without any undesirable toxic effect. The duration of pretreatment and the succeeding choice test was also settled as 6 days. Animals forcedly given morphine or cocaine as the drinking solution during pretreatment showed elevated preference for drug solution in the choice test. High grade preference was demonstrated for cocaine and amphetamine solution after pretreatment with injections of the drugs. Combined pretreatment potentiated the effect of these drugs. With barbital or ethanol, no appreciable reinforcing effect was found under the present experimental conditions. Thus, in addition to the experience with the drug solution, the injection of the drug facilitated the development of preference for the drug and demonstrates the positive reinforcing properties of the drugs which possess high grade psychic dependence liability. The validity of mice for the purpose of screening psychic dependence liable drugs and the restrictions on its application are discussed.