The effect of dizocilpine (MK-801) on spatial and visual discrimination tasks in the rat

The present experiments investigated the effect of the non-competitive N-methyl-d-aspartate (NMDA)-receptor antagonist, dizocilpine (MK-801) (0.075mg/kg) on acquisition and reversal of either a spatial or a visual, appetitively rewarded, simultaneous discrimination task in a Y-maze. The experimental design for the spatial and the visual discriminations was identical, the only difference between the tasks being the nature of the stimulus. Dizocilpine had not effect on acquisition of the spatial task although, when this task was reversed, dizocilpine-treated rats took significantly more trials to reach criterion. On the visual task, dizocilpine impaired both acquisition and reversal. Thus, systemic administration of dizocilpine did not produce a specific spatial learning impairment. The fact that dizocilpine impaired reversal but not acquisition in the spatial task argues against a global performance deficit. Although both the acquisition and reversal phases of the experiment make equal sensory and motor demands on the animal, reversal involves specific learning processes that may be disrupted by dizocilpine.