The distribution of C-Fos protein immunolabeled cells in the spinal cord of the rat after electrical and noxious thermal stimulation following sciatic nerve crush, or transection and repair

The distribution of stimulus evoked Fos protein-like immunoreactivity in spinal cord neurons was studied in adult rats at different survival times after sciatic nerve crush or transection and epineural repair. Fos protein-like immunoreactivity was induced either by electrical stimulation of the sciatic nerve central to the injury, at C-fiber strength, at 21, 39, and 92 days post-lesion, or by noxious heat applied to the skin of the hind paw 92 days post-lesion. The contralateral uninjured side served as control. The results with electrical stimulation showed, with some exceptions, that the distribution of c-fos expressing cells in the spinal cord on the normal and on the previously injured side were similar after both crush and transection with repair. The main finding was an up-regulation of the number of Fos protein immunoreactive neurons in the inner portion of Rexed's lamina II. The results following heat stimulation 92 days post-lesion showed a decrease in the number of labeled neurons in most laminae after both types of injury. This was more pronounced in cases with sciatic nerve transection with repair compared to cases with crush. The results indicate time-dependent alterations in the distribution of stimulus evoked c-fos expression in spinal cord neurons during regeneration after nerve injury. Furthermore, the results from heat stimulation may indicate a slower and perhaps more incomplete restoration process after transection with repair than after crush.