[Effects of combined administration of morphine and ethanol on drug selecting behaviors and the development of drug dependence].

The purpose of the present paper is to investigate the effect of combined treatment of morphine and ethanol on preference for morphine or ethanol and morphine dependence formation. Rats were treated with morphine by DAF (drug-admixed food; 0.5 and 1 mg/g food) method or subcutaneous injection (20-100 mg/kg body weight), and/or treated with ethanol solution (5 and 10 w/w %) or oral administration (2.5 g/kg body weight). There were no effects of chronic treatment of ethanol and morphine on preference for morphine and ethanol, respectively. While, preference for morphine did not increase and preference for ethanol enhanced markedly in rats chronically treated with morphine and ethanol. Effect of chronic ethanol treatment on morphine physical dependence formation in rats was evaluated by body weight loss after morphine withdrawal, and the weight loss significantly attenuated and diarrhea was suppressed in comparison with morphine alone group. These results indicated that preference for morphine and morphine physical dependence formation were reduced when rats were chronically treated with ethanol during chronic morphine treatment, and that preference for ethanol was enhanced.