POSTLESION ADMINISTRATION OF THE NMDA RECEPTOR ANTAGONIST MK-801 DOES NOT IMPAIR MOTOR RECOVERY AFTER UNILATERAL SENSORIMOTOR CORTEX INJURY IN THE RAT

Although treatment with N-methyl-D-aspartate (NMDA) receptor antagonists reduce neuronal loss after cerebral infarction and brain trauma in laboratory animals, there is little data concerning the effects of these drugs on behavioral recovery. Because NMDA receptor antagonists impede certain kinds of learning, and because motor recovery after sensorimotor cortex injury in the rat is dependent on post-lesion experience, we hypothesized that treatment with MK-801 after focal brain injury would be detrimental. Groups of rats were first trained to traverse a narrow elevated beam and then subjected a right sensorimotor cortex suction-ablation lesion. In the first experiment, 24 h later, each rat received a single dose of either saline or the NMDA receptor antagonist MK-801 (0.5, 1.0, or 2.0 mg/kg). Beam-walking recovery was measured over the next 12 days. In a second experiment, rats were given 3 doses of MK-801 (0.5 mg/kg) at 24 h intervals beginning 24 h after cortex injury. In a third experiment, lesioned and sham-operated rats were allowed to recover for 12 days and then given MK-801 (0.5 mg/kg). Despite obvious behavioral effects of the drug, there was no overall difference in beam-walking performances among the treatment groups in any of the experiments. If 're-learning' is involved in motor recovery after cortex injury, the present results suggest that the process is not susceptible to permanent disruption by the early or late administration of an NMDA receptor antagonist.