Physical dependence on morphine, phenobarbital and diazepam in rats by drug-admixed food ingestion.

To produce physical dependence on morphine, phenobarbital and diazepam in rats, these drugs were mixed with powder form of rat food in concentrations of 0.5 mg/g, 1 mg/g and 2 mg/g of food. One group of rats (the lower dose group) was continuously exposed for 1 week to two morphine-admixed foods with morphine to food ratios of 0.5 mg/g and 1 mg/g in a cage. The other group (the higher dose group) could choose between two morphine-admixed foods with morphine to food ratios of 1 mg/g and 2 mg/g. After 1 week, morphine-admixed foods were replaced with morphine free food for 2 days. Both groups of rats showed greatly reduced body weight and food intake after the first 24-48 hr withdrawal. The body weight decrease was greater for rats in the higher dose group. Control groups of morphine dependent rats were kept on the morphine added food diets and showed the same body weight increase as well as normal control rats during the course of these experiments. Physical dependence on phenobarbital and diazepam was produced using the same dosage schedules as with morphine. Both the lower and higher dose groups showed significant decrease in body weight due to withdrawal after 1 week of drug-food exposure. Levallorphan (0.5, 1, 3 and 5 mg/kg, s.c.) administered to morphine dependent rats had dose-dependent effects on the intensity of abstinence symptoms (e.g., diarrhea, piloerection and wet shakes phenomena), maximal decrease in body weight and duration of decreased body weight. Cross-physical dependence between phenobarbital and diazepam was demonstrated by this method.