Abstract
Effects of repeated administration of morphine on ambulatory activity were studied in mice treated with morphine-admixed food. The ambulatory activity was determined by the tilting cage method. Morphine injection (10 mg/kg s.c.) was repeated at 3-4 day intervals. The ambulatory activity was enhanced progressively when morphine was repeatedly given to mice. However, the enhancing effect was not observed in mice treated with morphine-admixed food (1 mg/g food). These results suggested that the reverse tolerance to morphine did not develop under the condition of exposure to morphine by DAF (drug-admixed food) method. In case of treatment with morphine-admixed food of increasing concentration (1, 2 and 3 mg/g food), the ambulatory activity of morphine was decreased. According to the studies done so far, tolerance development to the stimulant effects was not observed. This study demonstrates that the tolerance develops to the stimulant effects of morphine on the schedule of treatment with morphine of increasing doses by the DAF method.
