[Ultrastructural localization of the acetylcholinesterase (AChE) activity in the diaphragm of the rat embryo (author's transl)].

Electron histochemistry revealed intense AChE activity in the diaphragm of 15 days old rat embryos. The reaction product was localized to the perinuclear cisterna and the cisternae of the sarcoplasmic reticulum of myoblasts. The development of myoneural contacts at day 17 of gestation was preceded by the appearance of AChE activity of muscle cells. Sarcoplasmic cisternae and vesicles in the subjunctional sarcoplasm may play an important role in the development of the AChE activity of the postjunctional sarcolemm.