Adult rat lumbrical muscle fibres are not polyneuronally innervated

The existence of polyneuronal innervation in adult rat skeletal muscle reported by Taxt (1983) has been reinvestigated. The extent of polyneuronal innervation was measured by intracellular recording in cut muscle fibre preparations. Only fibres in which spontaneously occurring miniature end-plate potentials were visible were tested for the presence of multiple inputs. Only one in sixty-nine fibres penetrated was found to have more than one axonal input. High-threshold, low-amplitude end-plate potentials were sought, but none was found. Thus we were unable to find any evidence for extensive polyneuronal innervation persisting in rats of 40 days of age.