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in morphine-withdrawn mice.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.
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