Naloxone potentiates shock-induced aggressive behavior in mice

Naloxone (0.025 to 0.05 mg/kg IP) potentiates shock-induced aggressive behavior in C57BL/6 mice but not in DBA/2 mice which do not fight in absence of drug. This effect is not related to pain sensitivity since the doses used in this experiment do not lower tail-flick threshold in C57BL/6 mice. These findings are discussed in terms of the role of the endorphin system and of catecholamine related sensory attention in a number of social interactions in the mouse