Effect of naloxone on the locomotor stimulatory action of chlordiazepoxide in mice.

Locomotor activity was measured, during 60 min, in CD-1 mice receiving chlordiazepoxide (2.5 or 5 mg/kg) after a pretreatment with saline solution or naloxone (0.5, 1, 2.5 or 5 mg/kg). Both doses of chlordiazepoxide significantly increased locomotor activity in saline-pretreated mice. Naloxone prevented chlordiazepoxide-induced hyperactivity, at doses that did not themselves affect activity. This antagonistic action of naloxone indicates that opioid mechanisms are involved in the locomotor stimulatory effects exerted by chlordiazepoxide in mice.