Naltrexone-reversible effects of flunitrazepam on locomotor activity and passive avoidance behaviour in mice

Some behavioural effects of flunitrazepam were investigated in two sets of experiments in C57BL/6 mice. In the first set, flunitrazepam administration (0.025 or 0.05 mg/kg) enhanced the locomotor activity of mice. In the second set, memory impairments were observed following posttraining (immediately or 30 min, but not 60 min) treatment with the drug (0.05 mg/kg). All effects were antagonized by a per se ineffective dose of naltrexone (0.5 mg/kg for the activity, 0.1 mg/kg for the memory experiments), suggesting the involvement of opioid receptors. The results are discussed on the basis of recent evidence suggesting a link between benzodiazepine and opiate mechanisms of action.