Reinnervation of the lateral gastrocnemius and soleus muscles in the rat by their common nerve.

Abstract

SUMMARY1. To determine whether there is any specificity of regenerating nerves for their original muscles, the common lateral gastrocnemius soleus nerve (l.g.s.) innervating the fast-twitch lateral gastrocnemius (l.g.) and slow-twitch soleus muscles was sectioned in the hind limb of twenty adult rats. The proximal nerve stump was sutured to the dorsal surface of the l.g. muscle and 4-14 months later, the contractile properties of the reinnervated l.g. and soleus muscles and their single motor units were studied by dissection and stimulation of the ventral root filaments. Contractile properties of normal contralateral muscles were examined for comparison and motor units were isolated in l.g. and soleus muscles for study in a group of untreated animals.2. Measurement of time and rate parameters of maximal twitch and tetanic contractions showed that the rate of development of force increased significantly in reinnervated soleus muscles and approached the speed of l.g. muscles but rate of relaxation did not change appreciably. In reinnervated l.g. muscles, contraction speed was similar to normal l.g. muscles but relaxation rate declined toward the rates of relaxation in control soleus muscles.3. After reinnervation by the common l.g.s. nerve, the proportion of slow motor units in l.g. increased from 10 to 31 % and decreased in soleus from 80 to 31 %. The relative proportions of fast and slow motor units in each muscle were the same as the proportions of fast and slow units in the normal l.g. and soleus muscles combined. 4. It was concluded that fast and slow muscles do not show any preference for their former nerves and that the change in the force profile of the reinnervated muscles is indicative of the relative proportions of fast and slow motor units: fast units dominate the contraction phase and slow units the relaxation phase of twitch and tetanic contractions of the muscle.

Accuracy of reinnervation of rat internal intercostal muscles by their own segmental nerves

“…Wigston and Sanes (1985) have demonstrated that sympathetic preganglionic nerves show, even in the adult, a slight preference for intercostal muscle fibers taken from a rostrocaudal segment matching their own. On the whole, though, motoneurons in adult mammals have been found to be poor discriminators between their own and foreign muscles (Bemstein and Guth, 1961;Gillespie et al, 1983). Neonatal mammalian motoneurons, however, do show some selectivity in their ability to form synapses in different muscles (Gerding et al, 1977).…”

Differences between contractions in vitro of slow and fast rat skeletal muscle persist after random reinnervation.

“…Furthermore, the physiological and histochemical changes were in agreement in that they fit a model based only on the properties of control muscles. Gillespie et al (1986Gillespie et al ( , 1987 studied reinnervation under conditions very similar to ours, except that they used lateral gastrocnemius as the fast muscle and cut the combined lateral gastrocnemius-soleus nerve to allow random reinnervation. They saw histochemical differences similar to ours, in that reinnervated soleus had more type I fibres than the fast muscle.…”

“…Twitch time to peak (our terminology) was measured in the same way as contraction time (Fig. 3, Gillespie et al 1986) and half-relaxation time was the same as half-fall time (Fig. 4, Gillespie et al 1986).…”

“…One difficulty in this and later parts of the discussion is that we have made no direct estimate of the number of fast or slow motor units and have to assume that their proportions are (1986,1987) Reinnervated 1-4 2-2 2-5 Controls 2-0 3-5 8-0 Each number (slow: fast ratio) is calculated as the value of the parameter for soleus divided by the value of the same parameter for the fast muscle. For the present data, the fast muscle was plantaris and the ratio was calculated for individual muscles to give a mean and S.E.M; for Gillespie et al (1986for Gillespie et al ( , 1987) the fast muscle was medial gastrocnemius and the ratio was calculated from muscle means. Twitch time to peak (our terminology) was measured in the same way as contraction time (Fig.…”

“…We found that there were major differences between the reinnervated plantaris and soleus both in twitch speed and in the fibre type populations, and these have been reported briefly (Chamberlain & Lewis, 1987). While our work was in progress, Gillespie, Gordon & Murphy (1986 published the results of a study with an almost identical design and purpose, but came to a different conclusion: that reinnervated soleus and plantaris differed only in distribution of histochemical fibre types but not in their contractile properties. Although the work of Gillespie et al (1986Gillespie et al ( , 1987 was more extensive than ours (it included a study of individual motor units), our data demonstrate that there are real differences between the contractile properties of reinnervated soleus and plantaris and that these correlate well with the histochemical profiles.…”