Morphine withdrawal-facilitated aggression is attenuated by morphine-conditioned stimuli

There is a considerable body of evidence indicating that stimuli associated with drug administration may become conditioned and evoke drug-like effect s. The purpose of this study was to evaluate the ability of morphine-paired stimuli to affect an expression of morphine withdrawal-facilitated aggress ion. Individually housed aggressive adult mice were subjected to the repeat ed subcutaneous administration of morphine (twice a day, 8 days, increasing doses 10-80 mg/kg. Morphine treatment cessation facilitated an aggressive behaviour of animals during the second day of withdrawal. Subcutaneous but not intraperitoneal injection of saline attenuated the aggressive behaviour in morphine-withdrawn mice. These results suggest that the site of drug in jection may serve as a conditioned stimulus. (C) 2001 Elsevier Science Inc. All rights reserved.