Strain-dependent effects of naloxone on discrimination learning in mice.

The effects of post-trial naloxone administration were studied in two inbred strains of mice. C57BL/6 (C57) and DBA/2 (DBA), tested in two different experimental conditions. These were a Y-water maze (requiring escape from water) and the Yerkes--Thompson--Bovet-Nitti apparatus for pattern discrimination (requiring escape from electric shock). Two series of experiments were carried out. In the first series, naloxone improved acquisition in DBA and impaired acquisition in C57 mice either trained to swim towards tha dark or to discriminate between oblique bars. Light-oriented behavior, perhaps due to non-conditioned tendencies, was improved in the Y-water maze following naloxone administration on both strains.