Innervation and function of hind‐limb muscles in the cat after cross‐union of the tibial and peroneal nerves.

Abstract

SUMMARY1. Peripheral nerves to flexor (common peroneal) and extensor (tibial) nerves in a hind limb of seven 2-6 month old cats were cut and cross-united to study the plasticity in the spinal cord. The extent to which motoneurones from extensor and flexor motor pools were misdirected to their antagonistic muscles was determined by measuring the potentials generated at the spinal roots from the crossed nerves. The axons contributing to the extensor nerves normally leave the cord in the L7 and S1 ventral and dorsal roots while the axons contributing to the flexor nerves normally leave the cord in the L6 and L7 ventral and dorsal roots. Following cross-union, medial gastrocnemius (m.g.) and lateral gastrocnemius-soleus (l.g.s.) nerves were primarily supplied by L6 and L7 ventral and dorsal roots, and common peroneal (c.p.) nerves were primarily supplied by L7 and S1 ventral and dorsal roots. A method for quantifying the completeness of cross-reinnervation was developed.2. The pattern of e.m.g. activity in cross-reinnervated muscles during locomotion was primarily determined by the innervating nerve with the reinnervated flexor muscles being activated during the extensor phase. However, the cross-reinnervated extensor muscles showed evidence of extensor activity in addition to the double-burst pattern typical of flexor nerves. This extensor activity was more prominent when the nerve cross was less complete.3. We conclude that during locomotion the activity of spinal motoneurones was not substantially modified by inappropriate peripheral connexions, even when the nerve cross was carried out in young animals. This conclusion is discussed in relation to previous studies which suggested some degree of functional modification.

Increased Neuromuscular Activity Reduces Sprouting in Partially Denervated Muscles

“…The study showed that the mean difference between the two sides in the innervation contributions of L4 and L5 spinal roots caused by experimental and physiological variability was well within the acceptable limits. Similar findings have also been shown in studies using cats (Buller and Pope, 1977;Gordon et al, 1986). Therefore, we determined the contributions of L4 and L5 spinal roots to the muscles on the contralateral side to obtain a reasonable estimate of extent of partial denervation of the muscles on the experimental side.…”

Neural control of locomotion; Part 1: The central pattern generator from cats to humans

“…For example, experiments in newts have shown that transplantations of flexors and exten sors, or the implantation of inverted supernumary limbs do not alter the pattern, even if this pattern is entirely contra productive [7]. Similar experiments with trans plantation of antagonist muscles in cats [8,9] and rats [10,114,115], have confirmed this lack of adaptability of the locomotor pattern. Why is it that the system here seems so rigidly captured in a certain pattern and how is this pattern generated?…”

Organization of motor units following cross‐reinnervation of antagonistic muscles in the cat hind limb.

“…Thus, although they may be activated in order of increasing size, they may be activated for quite inappropriate movements. In our study an indication of inappropriate muscle function was demonstrated by abnormal movement patterns during locomotion (Gordon et al 1986). In human subjects fine motor control of hand muscles is usually poor following severance and surgical repair of ulnar and median nerves.…”

“…activity during locomotion was recorded from the cross-reinnervated and normally innervated hind-limb muscles. The methods and results of these experiments have been reported in the preceding paper (Gordon et al 1986).…”