TRPV1 expression. Transient receptor potential vanilloid 1 (TRPV1) expression was evaluated in the L3, L4 and L5 ipsilateral dorsal root ganglia (DRG) of control and 500 U collagenase injected rats. (A, B) TRPV1 expressed in small-sized L4 DRG neurons of control rats (A) and 500 U collagenase-injected rats (B), six weeks after injection. C: Six weeks after the injection of 500 U of collagenase there is an increase in the expression of TRPV1. Mean ± SEM. **P <0.01, significantly different from control rats at the same time-point. ¥P <0.05, significantly different from control rats at a different time-point.