Effects of flunitrazepam on passive avoidance behaviour in mice subjected to immobilization stress or familiarized with the testing apparatus.

The effects of flunitrazepam on passive avoidance behaviour were investigated in DBA/2 mice. In a first set of experiments retention performance impairment was observed in mice injected with the drug immediately but not 120 min after training. In a second set of experiments, immobilization stress enhanced, while familiarization with the apparatus decreased, the effects of flunitrazepam, suggesting involvement of emotional factors. All the effects observed were antagonized by naltrexone, showing involvement of opioid receptors.