DRG neurons from TRPA1-deficient mice are unresponsive to formalin. (A) Pseudocolor ratiometric images of DRG neurons acutely isolated from TRPA1+/+ and TRPA1−/− mice loaded with the calcium indicator Fura-2. Formalin application elicited a calcium response in TRPA1+/+ neurons. No formalin sensitivity was detected in neurons from TRPA1-deficient mice, whereas capsaicin sensitivity was unperturbed. (B) Representative responses of DRG neurons to formalin, AITC, and capsaicin. Traces represent an average of 15 cells cultured from TRPA1+/+ (black) or TRPA1−/− (red) mice. (C) Quantification of responses to formalin in neurons isolated from TRPA1+/+ (black) or TRPA1−/− (red) mice (n ≥ 328 per genotype; *, < 0.05; **, P < 0.01; ***, P < 0.001; Student's t test).