Degenerating nerve products affect innervated muscle fibres

Abstract

THE main factor controlling mammalian muscle fibre membrane characteristics is the fibre's activity^1,2. Other influences may be a trophic factor^3–5, and a loosely termed ‘inflammatory effect’^1,6. The latter effect is unspecific, appearing when a thread or degenerating nerve is placed over the muscle⁶, after operative procedures near the muscle (ref. 2 and our unpublished observations) and after axonal degeneration within the muscle's own nerve^1,7,8. This inflammatory effect may underlie the observations of Cangiano and Lutzemberger⁷ that the innervated fibres in a partially denervated muscle show certain membrane changes similar to those seen on inactive muscle fibres. Such surface changes in inactive muscles have been implicated as the cause of α motoneuronal terminal sprouting⁹, and that they may also occur on innervated fibres in partially denervated muscles provides an explanation for the occurrence of terminal sprouting here too without invoking additional mechanisms. However Cangiano and Lutzemberger's results have been disputed¹⁰. We now report an experiment which demonstrates that degenerating nerve fibres can affect innervated muscle fibres, and that this interaction may well stimulate motoneuronal terminal sprouting.