[Effect of mu- and kappa-opioid receptor antagonists on aggressiveness of male mice with repeated experience of aggression].

Mu and kappa opioid receptors often show opposite actions in the regulation ofphysiological functions and behaviors including aggressive behavior. In the present study, effects ofmu antagonist CTAP (1 and 2 mg/kg, sc) and kappa antagonist nor-BNI (0.5 mg/kg, sc) on the manifestation of aggressive behavior of C57BL/6J male mice with a short (3 days) and a long (20 days) experience of victories in daily intermale confrontations were investigated. It was shown that the mice with a short experience of aggression are tolerant to blockade of both mu and kappa opioid receptors. In the mice with a long experience of aggression, CTAP increased latency of aggression in dose-dependent manner, but did not change the duration of attacks. Nor-BNI had no influence on the behavior of the male mice with a long experience of aggression in the intermale confrontation. The possible changes in opioid receptor sensitivity in C57BL/6J male mice under the influence ofa long experience of aggression are discussed.