Contribution of peripheral NMDA receptors in craniofacial muscle nociception and edema formation.

Contribution of peripheral NMDA receptors in craniofacial muscle nociception and inflammation was examined. Nocifensive paw-shaking behavior following masseteric injection of mustard oil (MO) was quantified in lightly anesthetized rats. MK-801 (0.3 mg/kg) preadministered in the masseter muscle significantly reduced the peak and overall magnitude of the MO-induced noficensive behavior. The reduction was greater than that produced by the same dose of MK-801 given intravenously or in the biceps muscle. Rats were sacrificed 2 h later and masseter muscles dissected and weighed. The injected muscle was 27.29+/-6.7% heavier than the contralateral muscle. The weight difference was significantly less only in rats pretreated with masseteric MK-801. These data provide evidence that peripheral NMDA receptors play an important role in craniofacial muscle nociception and inflammation.