SYNAPTIC EVOKED-POTENTIALS FROM REGENERATING DORSAL-ROOT AXONS WITHINFETAL SPINAL-CORD TISSUE-TRANSPLANTS

Previously injured dorsal roots were electrically stimulated to determ ine if regenerating sensory axons can form physiologically active syna ptic contacts with neurons within fetal spinal cord tissue transplants . Dorsal rootlets, sectioned at their spinal cord entry zone, were app osed to intraspinal transplants of fetal spinal cord tissue grafted al ong each side of a nerve growth factor-treated nitrocellulose implant. Two to six months later the rootlets were transected between the spin al cord and their respective ganglia and electrically stimulated. Evok ed potentials were recorded from the dorsal surface of the transplant, but were absent from adjacent ipsilateral and contralateral spinal co rd regions. A glass micropipette was advanced through the transplant a nd used to record intramedullary field potentials evoked by dorsal roo t stimulation. Maximal negative potentials occurred 400-700 mu m below the dorsal surface of the transplant, shifting to positive potentials deeper into the transplant. Additionally, both spontaneous and electr ically evoked single neuronal action potentials were observed along th e microelectrode track. Evoked potentials were abolished following tra nsection of the rootlets between the stimulation site and the transpla nt. Immunocytochemical evidence of the production of fos protein follo wing electrical stimulation of the regenerated dorsal rootlets was dem onstrated within transplant neurons and some ventrally located host ne urons, providing an anatomical correlate to the electrophysiological r ecordings of synaptic activation. These results provide evidence of th e structural and functional integration of regenerated sensory areas w ith both transplant and host neurons. (C) 1996 Academic Press, Inc.