Effects of bremazocine on locomotor activity in DBA/2 and C57BL/6 mice

The effects of the benzomorphan analogue bremazocine on locomotor activity were studied in DBA/2 (DBA) and C57BL/6 (C57) mice. Three sets of experiments were carried out. In a first set, bremazocine depressed activity in both strains, but DBA mice were more sensitive to the effects of the drug. In a second set of experiments the effects of bremazocine were antagonized by a per se ineffective dose (0.5 mg/kg) of the selective kappa-opioid receptor antagonist MR 1452, showing that they were mediated through an interaction with this sub-population of opioid receptors. In a third set of experiments the effects of bremazocine were enhanced by the administration of a per se ineffective dose (0.025 mg/kg) of haloperidol, showing the involvement of dopaminergic mechanisms.