Aggression during morphine withdrawal: effects of method of withdrawal, fighting experience, and social role.

Offensive and defensive components of aggressive behavior were determined in resident and intruder mice. Withdrawal aggression was measured after the removal of a subcutaneous morphine pellet or after precipitation by naloxone in naive mice and after removal of a morphine pellet in mice with prior fighting experience. In naive mice, removal of a morphine pellet led to increases in attack bites and threats but naloxone-precipitated withdrawal led to decreases in these behaviors and to increases in defensive posturing, escape attempts and vocalizations. Prior fighting experience abolished the enhanced attack behaviors of resident mice following morphine pellet removal, but led to heightened defensive behavior in intruder mice. The behavior of intruder mice appeared more sensitive to naloxone administration than the behavior of resident mice; naloxone influenced not only intruder defensive behavior, but also other non-aggressive behaviors. The social role of the drug recipient and his prior history of aggressive behavior are important determinants of morphine and naloxone effects on aggression.