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 sti mulation of the sciatic nerve central to the injury, at C-fiber streng th, 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 uninju red side served as control. The results with electrical stimulation sh owed, with some exceptions, that the distribution of c-fos expressing cells in the spinal cord on the normal and on the previously injured s ide were similar after both crush and transection with repair. The mai n finding was an up-regulation of the number of Fos protein immunoreac tive neurons in the inner portion of Rexed's lamina II. The results fo llowing 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-depende nt alterations in the distribution of stimulus evoked c-fos expression in spinal cord neurons during regeneration after nerve injury. Furthe rmore, the results from heat stimulation may indicate a slower and per haps more incomplete restoration process after transection with repair than after crush.