Contribution of peripheral N-methyl-D-aspartate receptors to c-fos expression in the trigeminal spinal nucleus following acute masseteric inflammation.
In this study, we examined the contribution of N-methyl-D-aspartate (NMDA) receptors on c-fos expression in the trigeminal brainstem nuclei following acute muscle inflammation. Mustard oil (MO; 20%, 30 microL) injected into the masseter muscle induced extensive peripheral edema and Fos-like immunoreactivity (Fos-LI) in several trigeminal brainstem areas including the subnucleus caudalis of the trigeminal spinal nucleus (Vc), the ventral and dorsal regions of the Vc/subnucleus interpolaris transition zone, and the paratrigeminal nucleus. In order to assess the effect of antagonizing NMDA receptors on MO-induced Fos-LI, rats were pre-treated with two different doses of i.v. MK-801 (0.3 mg/kg, 3 mg/kg), a non-competitive NMDA receptor antagonist, 30 min prior to MO injection. Additional groups of rats received MK-801 (0.3 mg/kg) directly in the masseter muscle or in the biceps muscle 5 min prior to MO injection. A higher dose of i.v. MK-801 (3 mg/kg) and MK-801 given locally into the masseter muscle (0.3 mg/kg) produced a significant reduction in total number of MO-induced Fos-LI. Further analyses revealed that pre-treatment with MK-801 (3 mg/kg i.v.) significantly reduced the Fos-LI all throughout the Vc. Only at the caudal Vc, there was a dose-dependent reduction of MO induced Fos-LI. Pre-treatment with masseteric MK-801 also significantly reduced the Fos-LI in the caudal Vc, with the effect greater than that produced by the same dose of MK-801 given intravenously. These results suggest that peripheral NMDA receptors contribute to nociceptive processing from craniofacial muscles.
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Department of Oral and Craniofacial Biological Sciences, University of Maryland Baltimore, School of Dentistry, 666 West Baltimore Street, Baltimore, MD 21201, USA. jyr001@dental.umaryland.edu
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D000818:Animals; D016291:Dizocilpine Maleate / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D016762:Genes, fos / Q000187:drug effects / Q000502:physiology*; D007249:Inflammation / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008406:Masseter Muscle / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014279:Trigeminal Nucleus, Spinal / Q000378:metabolism*
D016194:Receptors, N-Methyl-D-Aspartate; D016291:Dizocilpine Maleate