Effects of naloxone administration on attack by castrated male mice on lactating intruders.

The effect of the narcotic antagonist naloxone (a mu blocker at low doses) on the attack displayed by castrated male mice towards lactating intruders was investigated. Naloxone at doses of 1 mg and 2 mg/kg decreased attacks an effect which was also evident to a lesser extent at 0.75 mg/kg. These findings suggest a role for endogenous opiates in the expression of this form of aggression although one must warn that naloxone at some of the higher doses used here can influence kappa and delta receptors as well as gabaergic activity. The interrelationships between endogenous opioids, gabaergic neurotransmission and gonadal hormones in the regulation of this attack response are discussed.