Attenuation of experimental arthritis in TRPV1R knockout mice.

The Transient Receptor Potential Vanilloid 1 (TRPV1R) is a ligand-gated, non-selective cation channel expressed predominantly by sensory neurons. TRPV1Rs respond to a variety of noxious stimuli including capsaicin, intense heat and acid. These factors, combined with behavioral studies, show that TRPV1Rs are involved in nociception. The aim of our study was to determine whether TRPV1Rs play a role in the development and maintenance of inflammation and mechanical hyperalgesia by studying the development of unilateral joint inflammation in TRPV1R-/- mice. Knee joints of TRPV1R-/- or wild-type (WT) mice were injected with FCA (200 microg) under temporary anesthesia, and the resulting inflammation and hyperalgesia measured for 35 days. Histological analysis was performed on joints at the end of the study. TRPV1R-/- mice developed mild joint swelling which was significantly less than that obtained in WT mice (P < 0.05, Mann-Whitney). The ratio of the weight distribution between the hind limbs in TRPV1R-/- mice was also significantly less than in WT mice (P < 0.05, Mann-Whitney). Neither swelling nor hypersensitivity was completely absent in the knockout mice, indicating either that other mechanisms are involved or that a compensatory mechanism operates in TRPV1R-/- mice. These results suggest that TRPV1 receptors are important for the development of joint inflammation and the associated mechanical hypersensitivity observed in this model.