Parabiotic reinnervation in normal and dystrophic mice. Part 2. Morphological studies

Further observations on myelinated axon numbers in normal and dystrophic mice

Counts of the number of myelinated axons in the nerves to slow-twitch soleus and fast-twitch plantaris muscles of 129 ReJ dy/dy dystrophic mice at 4, 15 and 24 weeks of age have shown statistically significant reductions when compared to normal values. In addition muscle fibre losses had occurred in both muscles at the earliest age point studied. There was no suggestion of a progressive loss of myelinated axons. There was a greater percentage reduction in the soleus than in the plantaris nerves. The number of myelinated axons in the nerves to the plantaris and soleus muscles of the 129 ReJ +/+ normal animals was approximately the same, in contrast to the C57BL/6J strain where the soleus nerve always contained a greater number. Statistically significant reductions in the number of myelinated axons in the nerves to the medial gastrocnemius muscles of C57BL/6J dy2J/dy2J dystrophic mice have been observed at both 15 and 72 weeks of age. Muscle fibre losses have also been recorded in 72 weeks dystrophic medial gastrocnemius muscles.

Parabiotic reinnervation in normal and myopathic (BIO 14.6) hamsters

Parabiotic reinnervation is a technique whereby the muscles of one animal can be reinnervated by peripheral nerves of another animal. This technique has been used to test the hypothesis that the myopathy in the BIO 14.6 strain of hamster may result from a derangement of the trophic function that a nerve exerts upon the muscle which it innervates. The percentage of internal nuclei in muscle fibres has been used as a criterion to define the myopathic state. The percentage of internal nuclei was high in myopathic hamster muscles but very low in normal or "self-reinnervated" normal muscles. There was no indication that the percentage of internal nuclei in myopathic muscles fell after parabiotic reinnervation with normal nerves. Similarly, there was no evidence that the percentage increased in normal muscles that had been parabiotically reinnervated with dystrophic nerves. On the basis of these results, it was concluded that there was no positive evidence in favour of a neural aetiology for the myopathy in the BIO 14.6 strain of hamsters.

Parabiotic reinnervation in normal and dystrophic mice. Part 1. Muscle weight and physiological studies

A technique called parabiotic reinnervation has been developed. This technique consisted of suturing the sectioned peripheral end of the common peroneal nerve of a normal mouse, strain 129 ReJ +/+ to that of the distal stump remaining after sectioning that same nerve in a dystrophic mouse, strain 129 ReJ dy/dy. The animals were then parabiosed and allowed to recover and thus it was possible to innervate a dystrophic muscle with a normal nerve and vice-versa. This made it possible to test the hypothesis that a derangement of the trophic function normally exerted by a nerve on a muscle might be an element in the pathogenesis of muscular dystrophy in the adult mouse. Studies on the weights and isometric twitch characteristics of such parabiotically reinnervated muscles led to the conclusion that a derangement of the trophic function exerted by a nerve on a muscle is not an element in the pathogenesis of muscular dystrophy in the adult 129 ReJ dy/dy strain of mouse.