SOMATOTOPIC REDISTRIBUTION OF C-FOS EXPRESSING NEURONS IN THE SUPERFICIAL DORSAL HORN AFTER PERIPHERAL-NERVE INJURY

The functional somatotopic reorganization of the lumbar spinal cord do rsal horn after nerve injury was studied in the rat by mapping the sti mulus-evoked distribution of neurons expressing proto-oncogene c-fos. In three different nerve injury paradigms, the saphenous nerve was ele ctrically stimulated at C-fibre strength at survival times ranging fro m 40 h to more than six months: 1) Saphenous nerve stimulation from th ree weeks onwards after ipsilateral sciatic nerve transection resulted in an increase in the number of Fos-immunoreactive neurons within the dorsal horn saphenous territory in laminae I-II, and an expansion of the saphenous territory into the denervated sciatic territory until 24 weeks postinjury. 2) Saphenous nerve stimulation from five days onwar ds after ipsilateral sciatic nerve section combined with saphenous ner ve crush resulted in an increase in the number of Fos-immunoreactive n eurons within the dorsal horn saphenous nerve territory, and an expans ion of the saphenous nerve territory into the denervated sciatic nerve territory. 3) Stimulation of the crushed nerve (without previous adja cent nerve section) at five days, but not al eight months resulted in a temporary increase in the number of Fos-immunoreactive neurons withi n the territory of the injured nerve, and no change in area at either survival time. The results indicate that nerve injury results in an in creased capacity of afferents in an adjacent uninjured, or regeneratin g nerve, to excite neurons both in its own and in the territory of the permanently injured nerve in the dorsal horn. The onset and duration of the increased postsynaptic excitability and expansion depends on th e types of nerve injuries involved. These findings indicate the comple xity of the central changes that follows in nerve injuries that contai n a mixture of uninjured, regenerating and permanently destroyed affer ents. (C) 1998 IBRO. Published by Elsevier Science Ltd.