Changes in tactile stimuli-induced behavior and c-Fos expression in the superficial dorsal horn and in parabrachial nuclei after sciatic nerve crush

Neurons in the superficial laminae of the dorsal horn are dominated by inpu t from peripheral nociceptors. Following peripheral nerve injury, low thres hold mechanoreceptive A beta- fibers sprout from their normal termination s ite in laminae III/IV into laminae I-II and this structural reorganization may contribute to neuropathic tactile pain hypersensitivity. We have now in vestigated whether a sciatic nerve crush injury alters the behavioral respo nse in rats to tactile stimuli and whether this is associated with a change in the pattern of c-Fos expression in the dorsal horn and the parabrachial area of the brainstem. Sciatic nerve crush resulted in a patchy but marked tactile allodynia manifesting first at 3 weeks and persisting for up to 52 weeks. C-Fos expression in the dorsal horn and parabrachial region was nev er observed on brushing the skin of the sciatic nerve territory in animals with intact nerves, but was found after sciatic nerve crush with peripheral regeneration. We conclude that after nerve injury, low threshold mechanore ceptor fibers may play a major role in producing pain-related behavior by a ctivating normally nociceptive-specific regions of the central nervous syst em such as the superficial laminae of the dorsal horn and the parabrachial area. (C) 2000 Wiley-Liss, Inc.