Persistence of functional neuromuscular junctions formed in a denervated skeletal muscle of the adult rat by axons that have regrown from the injured spinal cord through a peripheral nerve autograft
Affiliations: Département de Neurobiologie des Signaux Intercellulaires, Institut des Neurosciences, URA CNRS 1488, Université Pierre et Marie Curie, 7 quai Saint-Bernard, F-75252 Paris cedex. 05, France | Laboratoire de Neurobiologie, URA CNRS 1448, Université René Descartes, 45 rue des Saints-Pères, F-75270 Paris cedex 06, France
Note: [] Correspondence: J.C. Horvat, Laboratoire de Neurobiologie, URA CNRS 1448, Université René Descartes, Centre Universitaire des Saints-Pères, 45 rue des Saints-Pères, F-75270 Paris cedex 06, France. Fax: (33)(1) 42 86 87 48.
Abstract: In previous ‘short-term’ (2 to 7 months) experiments, we had demonstrated, in the adult rat, that motoneurons of the injured cervical spinal cord could extend lengthy axons into an autologous peripheral nerve segment which was connected to a nearby denervated skeletal muscle. In addition, we had shown that new functional motor endplates were formed by these axons both at the original sites of innervation and at ectopic locations of the denervated muscle. This substitution motor system, although quite functional, was anatomically very different from the original model of innervation in the intact animal, relating to its motoneuronal pool, the course of its motor axons and the sites of terminal innervation. The present ‘long-term’ (11 to 21 months) experiments demonstrate the anatomical and functional permanency of the new motor circuitry, despite a lack of strict specificity in the new neuromuscular connections. However, some minor modifications or adjustments were observed with time: (i) the maintenance of functional ectopic endplates could be consistently demonstrated, while functional reinnervated endplates at the initial sites of innervation were rare or even lacking; (ii) there was a definitive withdrawal of all non target-specific regenerated axons from the vicinity of the muscle. It is now necessary to address the question to what extent this substitution motor system is actually controlled by central and/or peripheral inputs.
Keywords: Adult rat, Spinal cord reconstruction, Motoneuron, Axonal regeneration, Peripheral nerve autograft, Motor endplate, Retrograde axonal tracing, Electrophysiological recording
