A study of the reinnervation of stretch receptors in cat muscle following nerve injury

Abstract

An histological investigation into the reinnervation of stretch receptors necessarily requires a reliable staining technique. To achieve this, silver staining has been investigated and standardised. The use of a diffusion-limiting barrier during the impregnation stage has greatly improved the quality and extent of staining. The process of reinnervation has been examined in the peroneal muscles of the cat following different types of nerve injury, including crush, section and freeze. After nerve crush, most motor and sensory axons form endings of a recognisable form in the usual positions on muscle spindles and tendon organs. The late arrival of some sensory axons, and aberrant motor formations on the poles of spindles, are attributed to the fact that large axons are damaged more than small axons during the nerve crush. It is suggested that some of these motor axons may have previously supplied only extrafusal muscle fibres. Although abnormalities in the restoration of the primary ending are common, none is sufficiently consistent to explain the abnormalities in the responses of reinnervated spindles. This implies that these may be caused by a maturing transduction mechanism. The fact that after nerve section the restoration of spindle innervation is poor, whereas after nerve freeze ( during which damage to supporting tissue is minimised), it is close to normal, indicates that physical guidance plays an important role in the reinnervation process. It is argued that, after short periods of denervation, muscle spindles show a marked " site-type " specificity of sensory reinnervation. This is seen to diminish after longer periods of denervation, possibly being influenced by the fusimotor innervation.