DISTRIBUTION OF C-FOS EXPRESSING DORSAL HORN NEURONS AFTER ELECTRICAL-STIMULATION OF LOW-THRESHOLD SENSORY FIBERS IN THE CHRONICALLY INJURED SCIATIC-NERVE

The distribution of proto-oncogene c-Fos protein-immunoreactive cells in the spinal cord dorsal horn was studied after electrical stimulatio n at A alpha/A beta-fiber intensity of normal and previously injured s ciatic nerves in urethane anesthetized rats. No or only occasional Fos protein-like immunoreactive cells were seen after stimulation of the normal uninjured nerve or after nerve transection without stimulation. Electrical nerve stimulation at 3, 12, and 21 days after sciatic nerv e transection resulted in substantial increases in the numbers of Fos protein-like immunoreactive cell nuclei in each of Rexed's laminae I-V . Combined demonstration of Fos protein-like immunoreactivity and of g lial fibrillary acidic protein-like immunoreactivity (astroglia) or OX -42 immunoreactivity (microglia), indicated that the observed Fos prot ein-like response was confined to neurons and not to astroglia or micr oglia. Combined demonstration in the spinal cord of Fos protein-like i mmunoreactive neurons and neurons labeled retrogradely with Fluoro-Gol d from the gracile nucleus showed that some of the Fos protein-like im munoreactive neurons in Rexed's laminae III and IV contributed to the postsynaptic dorsal column pathway. The results indicate that stimulat ion at A alpha/A beta-fiber intensity of a previously injured nerve gi ves rise to an abnormally increased activation pattern of postsynaptic neurons in the dorsal horn, some of which contribute to the postsynap tic dorsal column pathway.