Introduction

Injury to motor and sensory neurones of the peripheral nervous system alters their electrical properties. In addition, chronically axotomized group la muscle afferents no longer generate excitatory postsynaptic potentials in spinal motoneurones. However, peripheral neurones readily regenerate and reinnervate their native tissue, following which they recover largely or completely their normal properties and capabilities. In recent years we have been interested in the ability of neurones of the peripheral nervous system to innervate foreign tissue (i.e. motoneurones and muscle afferents into skin; cutaneous afferents into muscle) and in the consequences of such innervation on their properties and capabilities.

The description below reviews the results of these series of experiments. The methods used were generally similar, starting with a sterile surgical procedure in which the distal connections of nerves of adult cats' hindlimbs were altered. The muscle nerve to the medial gastrocnemius (MG) may have been axotomized and capped, or partly or fully cross-united distally to the caudal cutaneous sural (CCS) nerve (Fig. 38.1). The cutaneous sensory CCS nerve may have been axotomized and capped, or cross-united distally to part of the MG nerve. Properties of the cross-united afferents and motoneurones were studied in acute electrophysiological experiments (e.g. Zengel et al., 1985) 3–36 months later.

Response by motoneurones

Motoneurones of the cat's normal MG muscle have predictable values for conduction velocity (CV), input resistance (RN), rheobase (Irh) and after-hyperpolarization (AHP; Zengel et al., 1985).