Scanning electron microscopic study of nerve-muscle junctions in embryonic rat cell cultures

The morphology of neuromuscular junctions between embryonic rat spinal cord and muscle cells grown in vitro has been studied by scanning electron microscopy (SEM). Histochemical detection of acetylcholinesterase (AChE) spots and autoradiographic detection of acetylcholine receptor protein (AChR) were performed in parallel. At the scanning EM level the contacts exhibit a marked polymorphism; the nervous endings may present as a bulbous swelling, or often as a plexiform network on the surface of the myotubes. Many neuromuscular contacts seem to occur 'passing by'; in other places, neurites processes slide along myotubes without any differentiated contacts. The muscle cell surface does not look substantially modified in the contact area. The distribution of the contacts between nerve and muscle cells is at the same time convergent and divergent.