Innervation of muscle receptors in the cross-reinnervated soleus muscle of the cat.

It has recently been reported (Gregory et al., J. Physiol., 331:367-383, 1982) that cutting a muscle nerve and letting it grow back into the muscle or cross-uniting the muscle with a foreign nerve results in major disruption of the normal response patterns of muscle spindles and tendon organs. Here we report observations on the structure of muscle receptors in cross-reinnervated and self-reinnervated soleus muscles in an attempt to detect abnormalities that might account for their disturbed function. Eight soleus muscles were reinnervated with the extensor digitorum longus nerve for periods up to 449 days and two were self-reinnervated. Following the physiological investigation, the muscle was fixed and stained according to the method of Barker and Ip (J. Physiol., 69:73P-74P, 1963). Spindles and tendon organs were teased from the muscle and photographed. In one cross-reinnervated muscle an attempt was made to isolate all receptors. About two-thirds of the normal number of spindles and tendon organs were found. Three categories of receptor were identified: normal, abnormal, and those having no visible nerve endings. There appeared to be little difference in degree of abnormality of receptors in self- and cross-reinnervated muscles. Of the 180 spindles, 3% were normal, 43% had no visible endings, and 54% had abnormal endings. Of 80 tendon organs, 38% were normally innervated, 33% were without visible innervation, and 29% had abnormal endings. We conclude that following long-term cross-reinnervation and self-reinnervation of soleus there is extensive disruption of the normal innervation pattern of both spindles and tendon organs which could account for their functional abnormalities.

Reinnervation of the soleus muscle by its own or by an alien nerve.

The rates of reinnervation of the rat soleus muscle by its own or an alien nerve were compared using physiological and morphological criteria. The muscle's own nerve was more effective than the alien nerve in establishing functional connections with the original endplates. The relative ineffectiveness of the alien nerve during early stages of reinnervation was more apparent using physiological rather than morphological criteria. Five to six weeks after nerve injury there was no longer any difference between the muscles supplied by either nerve.

Structural differences of pale and strongly stained motor end-plates of the rat diaphragm.

According to the staining intensities for AChE, the motor end-plates of the rat diaphragm can be classified into strong (S) and pale (P) types. About 34% of the total end-plates of the rat diaphragm are of S type and 50% of P type. The P end-plates differ from S end-plates in two aspects. First, the secondary subneural clefts of the S end-plates are well developed. They are numerous, long, closely packed and often branched. On the other hand, the secondary subneural clefts of the P end-plates are short, sparse and usually unbranched. Secondly, there seems to be a variation in AChE activity in the P end-plates. Focal negative AChE areas are found in the subneural apparatus of some P end-plates. It is concluded that the less well developed secondary subneural clefts and focal areas of negative AChE activity contribute to the paler staining of the P end-plates.

A combined method for demonstrating the cholinesterase activity and the nervous structure of mammalian peripheral motor endings in teased preparations.

Both the neural and subneural components of mammalian peripheral motor endings in teased preparations have been shown by a new method which combines a silver method with a cholinesterase technique. The significant application of this method to the study of the motor terminals is suggested.