Effects of opiate antagonists on social and aggressive behavior of isolated mice

Opiate antagonists naloxone (1 and 1.5 mg/kg IP) and naltrexone (2.5 and 5 mg/kg IP) inhibit aggressive responses of DBA/2 isolated mice, while increasing the duration of some social activities such as sniff-body, sniff-nose and following. At the doses employed naloxone and naltrexone did not affect motor activity and self-grooming of paired mice. These findings are discussed in terms of the endogenous opioids system involvement in arousability, in the response of the organism to stressful events, in the motivational mechanisms which control social behavior and in the functioning of some neurotransmitter systems which are known to play an important role in the control of isolation-induced aggressive behavior.