FIGURE 1.

Formaldehyde excites and sensitizes rat cutaneous nociceptors by lateral diffusion in vivo. (a) Schematic drawing of the rat hindpaw, showing location and extent of the mechanoreceptive field of a C‐MH fiber (0.85 m/s, threshold 22.6 mN) and the adjacent site of the injection. (b) Formaldehyde was injected to reach the receptive field by diffusion, note the delayed onset of formaldehyde‐induced activity. (c) Activity evoked by a radiant heat ramp to 52°C. Compared to before, the heat response 5 min after injection of formaldehyde was sensitized, although the mechanosensitivity was lost in half of the receptive field (specimen, representative for 3 C‐MH fibers)