Studies on anterograde trophic interactions based on general muscle properties

General properties of rat skeletal muscle (extrajunctional membrane and contractile properties) are subjected to tight physiological neural regulation, as indicated by their striking alterations (up- or down-regulation) following denervation. The main contributions of the literature concerning the nature of the neural signals which mediate this regulation, are reviewed. The physiological regulation of these general properties appears to be operated by the action potential activity evoked by motoneurons in the muscle fibres. No need to postulate the participation of nerve-borne chemical substances, acetylcholine or unidentified "trophic factors", arises from the main experimental evidence. The stronger response to denervation of extrajunctional membrane properties with respect to pure paralysis is best explained by actions of factors released during wallerian degeneration of the transected nerves.