Innervation of the synovium.

This review will describe the normal innervation of the joints, in particular the synovium, and then show how this changes in the rheumatoid arthritis (RA) joint in the human. Substance P will be described in detail, as an example of a particular neuropeptide. The concepts surrounding neuropeptide release and the role of neuropeptides in inflammatory joint disease (neurogenic inflammation) will then be explored. The in vitro and in vivo effects of substance P will be described. The receptors for substance P and the effects of antagonists, peptide and synthetic, for the receptor on inflammatory models will also be discussed. The synovial distribution of the enzyme systems that break down neuropeptides and how this may lead to functional compartmentalisation will be described. Finally, some mechanisms by which pain may arise will be presented.