Morphogenesis of myoneural junctions induced postnatally in the tibialis anterior muscle of the rat.

Abstract

AbstractThe structure of myoneural junctions induced during nerve regeneration outside the zone of previously existing, degenerating myoneural junctions was studied with the light microscope after histochemical demonstration of acetylcholinesterase (AChE) activity in the tibialis anterior muscle of the postnatal rat. The escape of regenerating nerves from their original glial sheaths was produced by severe crushing of the sciatic nerve at different stages of development of the rat, from newborn animals to adults. New myoneural junctions were induced in the previously undifferentiated part of the muscle plasma membrane in animals of all age groups, although not in every individual animal, if the old myoneural junctions did not regenerate. New myoneural junctions were observed in about 70 % of the rats operated on before the age of 10 days and in less than 20 % in the older groups. The older the animal, the fewer new myoneural junctions were seen among the re‐innervated old ones, and in the adult animals a new myoneural junction was only sporadically foundMyoneural junctions were first seen outside the zone of previously existing junctions 14–16 days after the operation. Irrespective of the age of the animal at operation, the postnatally induced myoneural junction was plate‐like in structure during the early stages of morphogenesis. Postsynaptic infoldings appeared between the 16th and 25th days after the operation, the infoldings had become deeper between the 25th and 35th days, and the ramification of the AChE distribution typical of the mature myoneural junctions was observed between the 35th and 45th postoperative days.