Establishment of neuromuscular contacts in cultures of rat embryonic cells: effect of tetrodotoxin on maturation of muscle fibers and on formation and maintenance of acetylcholinesterase and acetylcholine receptor clusters.

The part played by muscle activity was mainly studied in relation to the formation and persistence of cytochemically detectable spots of acetylcholinesterase (AChE) during synaptogenesis. A correlation was found between AChE spot evolution and that of two other morphological synapse markers, silver salt-impregnated nerve endings and clusters of acetylcholine receptors (AChR) exposed to 125I-alpha-bungarotoxin and revealed by radioautography. The formation and persistence of AChE spots were activity-dependent but in the case of neuronally induced synaptic nerve endings and AChR clusters, both morphological markers were independent of such activity. The final evolution and maturation of neuromuscular contacts were linked to the differentiation stage reached by the muscle fibers at the time when they established contact with nerve endings. The fibers acquired this differentiated state independently of tetrodotoxin-blocked muscle activity.