Studies on drug dependence (Rept.100): A study on the quantitative evaluation of drug-seeking behavior for codeine in rats by the weight-pulling method

Abstract

The quantitative evaluation of the drug-seeking behavior for codeine was studied in rats, and the result was compared with one in the previous report on morphine. The preference rates for codeine-admixed food gradually increased and then became stable approx. at 80% irrespective of the length of treatment. After these treatments, the intensities of the desire for codeine were compared among C7, C8, C10 and C14 groups using the weight-pulling method. The number of animals who did pull the weight to take drug-admixed food depended on the treatment period like in the case of morphine, and the relationship between the length of treatment and the maximum pulling weight showed high correlation. Thus the intensity of the desire for codeine depended on the treatment period, although all groups indicated similar preference rate for codeine before loading the weight, and more animals pulled the weight in morphine C7 group than codeine C7 group. Furthermore, the intensity of the desire for codeine in Ce group was equal to or weaker than one for morphine in C7 group. We conclude that the drug-seeking behavior for codeine can be quantitatively evaluated using the weight-pulling method; and the intensity of the desire for codeine is weaker than one for morphine, and long period of treatment of codeine is required in order to produce the similar intensity of desire for morphine.