The role of nitric oxide in orofacial pain.

Nitric oxide (NO) is a free radical gas that has been shown to be produced by nitric oxide synthase (NOS) in different cell types and recognized to act as a neurotransmitter or neuromodulator in the nervous system. NOS isoforms are expressed and/or can be induced in the related structures of trigeminal nerve system, in which the regulation of NOS biosynthesis at different levels of gene expression may allow for a fine control of NO production. Several lines of evidence suggest that NO may play a role through multiple mechanisms in orofacial pain processing. This report will review the latest evidence for the role of NO involved in orofacial pain and the potential cellular mechanisms are also discussed.