Effects of the selective kappa-opioid receptor agonist U-50,488 on locomotor activity and passive avoidance behaviour in DBA/2 and C57BL/6 mice.

Some behavioural effects of the kappa-opioid receptor agonist U-50,488 were investigated in DBA/2 (DBA) and C57BL/6 (C57) mice. In a first set of experiments, which was carried out with the toggle-floor box, U-50,488 depressed locomotor activity in both strains. Moreover, this activity depression was enhanced in both strains by the administration of haloperidol and muscimol, showing the involvement of dopaminergic and gabaergic mechanisms. In a second set of experiments, which were carried out with a passive avoidance apparatus, memory impairments, in DBA mice, and improvements, in C57 mice, were observed following immediately posttraining U-50,488 administrations. The results are compared with those of previous researches carried out, in the same strains of mice, with mu-opioid receptor agonists.