EFFECT OF CAPSAICIN ON SUBSTANCE-P AND NERVE GROWTH-FACTOR IN ADJUVANT ARTHRITIC RATS

We have investigated the effect of capsaicin pretreatment (50 mg kg(-1 ) s.c.) on substance P, preprotachykinin (PPT) mRNA, and nerve growth factor (NGF), plus its high-affinity receptor, trkA, in adult rats wit h adjuvant arthritis. Twenty one days after induction of adjuvant arth ritis, sciatic nerve levels of substance P were significantly increase d whilst there was a small but non-significant increase in gamma-PPT m RNA and substance P in L-4/L-5 dorsal root ganglia (DRG). NGF levels i n sciatic nerve and foot skin as well as DRG trkA mRNA were unaltered after 21 days arthritis suggesting that NGF may not play a role in chr onic inflammation. Capsaicin treatment of naive rats significantly red uced substance P in all tissues and NGF levels in the sciatic nerve. I n contrast, gamma-PPT mRNA and trkA mRNA expression in DRG were signif icantly increased after capsaicin treatment. The nervous and skin tiss ues used in this study were harvested from the same rats in which we h ad previously shown that capsaicin pretreatment significantly attenuat ed the severity of arthritis (Cruwys, S.C., Garrett, N.E. and Kidd, B. L., Sensory denervation with capsaicin attenuates inflammation and noc iception in arthritic rats, Neurosci. Lett., 193 (1995) 205-207). Arth ritis in capsaicin-treated rats had no effect on substance P or NGF le vels in any tissue when compared with capsaicin-treated control rats, suggesting that pharmacological impairment of the sensory nervous syst em can reduce the severity of inflammatory joint disease. (C) 1997 Els evier Science Ireland Ltd.