Effects of bremazocine on passive avoidance behaviour in mice.

The effects of bremazocine on memory processes were studied in DBA/2 mice tested in a passive avoidance apparatus. In a first set of experiments, memory impairments following immediately posttraining bremazocine administration (0.025 and 0.05 but not 0.01 mg/kg), and memory improvements following immediately posttraining administration of the kappa-opioid-receptor antagonist MR-1452 (1.0 and 2.0 but not 0.5 mg/kg), were observed. No effect was evident when the drugs were injected starting 120 min after training. In a second set of experiments, the effects of bremazocine (0.05 mg/kg) were antagonized by a per se ineffective dose of MR-1452 (0.5 mg/kg), suggesting involvement of kappa-opioid-receptors. In a third set of experiments, the effects of bremazocine were enhanced by a per se ineffective (15 min) immobilization stress, and were decreased by familiarization with the passive avoidance apparatus. The results are discussed in terms of attenuation of emotionality following bremazocine administration.