Repeated administration of MK-801 produces sensitization to its own locomotor stimulant effects but blocks sensitization to amphetamine.

Repeated amphetamine administration produced behavioral sensitization to subsequent amphetamine challenge. The development of sensitization was blocked by coadministration of the N-methyl-D-aspartate (NMDA) antagonist MK-801. Conditioned locomotion, as revealed by saline challenge, was also blocked by MK-801, suggesting that behavioral sensitization and conditioned locomotion may share a requirement for NMDA receptor stimulation. Repeated MK-801 administration produced behavioral sensitization to MK-801 but not amphetamine challenge, suggesting that MK-801 itself produces sensitization through a different mechanism than amphetamine.