The effect of dizocilpine (MK-801) on conditional discrimination learning in the rat.

The effect of the non-competitive N-methyl-D-aspartate (NMDA)-receptor antagonist, dizocilpine (MK-801) on the acquisition and reversal of conditional tasks was investigated using a Y-maze. Dizocilpine-treated rats were severely impaired on acquisition of a visuo-spatial task and were unable to learn the reversal of this task. 'Worse than chance' performance by dizocilpine-treated (and saline-treated) rats at the beginning of reversal testing, which was given 24 h after achieving criterion on acquisition, indicated that dizocilpine-treated animals simultaneously exhibited good memory but impaired learning for the type of information required for this task. Dizocilpine-treated rats were unable to acquire a visuo-visual conditional discrimination and therefore could not be assessed on reversal of this task. These very substantial impairments were larger than those found in comparable experiments using non-conditional tasks.