[Muscle-nerve ephapse in chronic denervation? Axonal localization]

Muscle-to-nerve ephaptic responses, taking place between a reinnervated motor unit and a motor axon, have been reported in the case of chronic denervation (Roth and Magistris, 1985). One of these responses is described here. Its main features are that it manifests itself as a motor unit potential, which, when present, is evoked either as a direct tardive response (RE), or as an indirect F response, the two potentials never being observed together on any recording. The characteristics of these potentials show that two distinct competitive pathways lead to the same muscular fiber group which suggests the existence of an ephaptic connection. Furthermore, a slight difference in the shape of the RE and F potentials suggests an axon terminal branch localisation of this ephapse.