Conditioned morphine withdrawal in the hamster

Conditioned withdrawal among golden Syrian hamsters was studied in two experiments. In experiment 1, morphine-pelleted (75 mg) hamsters were observed for signs of withdrawal (wet-dog shakes, etc.) before and after a naloxone (1 mg/kg) injection that was administered in a distinctive environment. Withdrawal signs that occurred in the distinctive environment before the naloxone injection were defined as anticipatory conditioned withdrawal responses. Two, 9, and 30 days following pellet removal, retention of conditioned withdrawal responding was assessed in the distinctive environment before and after a saline injection. Results indicated that: a) withdrawal intensity was a direct function of the number of implanted pellets; b) conditioned withdrawal occurred among animals withdrawn in the distinctive environment, but not among those withdrawn in the home cage; c) conditioned withdrawal was a nonmonotonic function of precipitated withdrawal intensity; d) conditioned withdrawal was evident up to 30 days after pellet removal. In experiment 2, conditioned withdrawal was extinguished by repeated exposure to the distinctive environment in the absence of precipitated withdrawal. It was concluded that environmental stimuli associated with the absence of morphine (i.e., precipitated withdrawal) elicit conditioned withdrawal. The results are compared to similar findings in rats and humans.