Y-maze behavior in the mouse after morphine or an enkephalin analog

The effects of morphine and an enkephalin analog on murine Y-maze behavior were examined. Vehicle-treated groups primarily showed an alternation response, entering the least recently visited alley of the maze. Treatment with morphine or the analog caused significantly reduced alternation, i.e., arms were entered with equal probability. Naloxone alone had no significant behavioral effects, but eliminated the behavioral effects of morphine and enkephalin.