Despite the introduction of microsurgical techniques into clinical practice, the results of surgical procedures involving the brachial plexus and peripheral nerves are still far from spectacular. We therefore studied the rat brachial plexus and its terminal branches in 203 rats. Detailed anatomic and morphologic analyses of the biceps brachii and musculocutaneous nerve, finger flexors, flexor carpi radialis, and the median nerve were performed. Various sources of conventional and vascularized nerve grafts were explored. After musculocutaneous nerve section or median nerve section, there were no articular contractures or automutilations, which constitutes an advantage for these experimental models over the sciatic nerve model. The brachial plexus and its terminal branches provide a good experimental model which can be used to assess the development and normal control of muscle function, examine the mechanisms underlying functional recovery, and test the effects of treatments to enhance recovery.
A light microscopical, histochemical and electron microscopical investigation of the frog neuromuscular junction has been performed on muscles from animals in different functional states of activity. The combined staining of axon terminals and cholinesterase (ChE) allows a precise description of the nerve terminal arborization and its synaptic contacts. Most terminal arborizations form long continuous contacts with the muscle cell. Distinquishable from these are nerve branches (usually of small diameter)d or distal endings of branches with one or several small and isolated contacts. It is assumed that these are sprouts with newly-formed synaptic sites. Other sprouts end without apparent synaptic contact. At the uttrastructural levet, nerve sprouts end without apparent synaptic contact. At the uttrastructural levet, nerve sprouts growing into empty, well-differentiated synaptic gutters or inducing the formation of new synaptic sites were observed. In other sites, ChE is apparently located at postsynaptic gutters with no nerve present. Similarly, in the electron microscope, well-differentiated synaptic gutters lacking any nerve or Schwann cell elements were observed. In addition, synaptic gutters only partially occupied by the nerve were frequently seen. These features have been interpreted as signs of regression of the nerve terminals. Nerve regression and sprouting were found in animals chronically paralysed with curare over several weeks as well as in untreated frogs (winter and summer frogs, laboratory frogs, fed and unfed). When quantitatively evaluating the occurence of presumed features of nerve sprouting and nerve regression, differences were found between different experimental groups. From this it is concluded that, in addition to developmental changes, the degree of nerve sprouting and regression is controlled by external factors such as muscle activity and seasonal variations. Signs of sprouting and nerve regression can be simultaneously present in a single synapse. It appears that the frog neuromuscular synapse is not a static structure, but is in a state of permenent remodelling.
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