Naloxone potentiates the depressant effect of chlordiazepoxide on spontaneous activity in mice.

Recent reports suggest that at least some of the behavioural effects of benzodiazepines may involve interaction with endogenous opioid mechanisms. In the present study, chlordiazepoxide (CDP, 10-20 mg/kg, i.p.) induced dose-dependent reductions in spontaneous locomotor activity and rearing in mice. Although naloxone (1 mg/kg) was itself without effect, and did not alter behavioural changes induced by the lower dose of CDP, it enhanced the depressant effects of 20 mg/kg CDP on locomotor activity. Results are discussed in relation to previous studies in which opiate antagonists have been found to block or to have no effect upon behavioural actions of benzodiazepines.