Reduction of morphine-withdrawal body shakes by a conditional stimulus in the rat

Narcotic dependence in rats was established, in five days, by administering intravenous injections of morphine sulfate in increasing doses. From day six onward, dependence was maintained by administering a morphine injection (15 mg/kg) every 6 h throughout the day, and each of these injections was paired with a tone. After 16 morphine-tone pairings, test trials, in which the tone was presented in the absence of morphine, were instituted. These tone presentations significantly reduced morphine-withdrawal "wet shakes" in rats which received morphine-tone pairings, but not in rats which received control treatments.