N-Methyl-d-aspartate receptor antagonist MK-801 suppresses glial pro-inflammatory cytokine expression in morphine-tolerant rats

► MK-801 preserves morphine's antinociceptive effect in the morphine-tolerant rats. ► MK-801 provides anti-inflammatory effect. ► NMDA receptor antagonist can be an adjuvant to treat morphine-tolerant patients.