title: Spatial distribution and size of acetylcholine receptor clusters determined by motor nerves in developing chick muscles.
abstract: The size and distribution of acetylcholine receptor clusters (AChR-C) on normal and aneural developing muscle fibres of the chick wing were studied by labelling AChR with fluorescent conjugates of alpha-bungarotoxin (alpha-BGT). AChR-C of a size typical of initial synaptic contacts (5 micron long) were present at 7 days incubation, shortly after the appearance of nerves, and were grouped in bands corresponding to muscle nerve branches. A regular distribution of large (approximately equal to 5 micron) AChR-C separated by 100-200 micron had developed by 10-14 days in the slow-tonic anterior latissimus dorsi and ulnimetacarpalis dorsalis muscles. The role of motor innervation in the formation of AChR-C was assessed by removing the brachial neural tube at 2 days incubation in order to prevent nerves entering the wing. Neural-tube removal prevented the appearance of the large AChR-C normally associated with the early synaptic contacts. Small AChR-C (less than 2 micron long) appeared in aneural muscles, but these were not grouped into bands characteristic of the large AChR-C in normal muscles. The results suggest that the formation of junctional AChR-C is dependent on nerves.
mesh_terms: D000818:Animals; D002038:Bungarotoxins / Q000378:metabolism; D002642:Chick Embryo; D005456:Fluorescent Dyes; D009046:Motor Neurons / Q000648:ultrastructure*; D009132:Muscles / Q000196:embryology / Q000294:innervation*; D011950:Receptors, Cholinergic / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology; D013997:Time Factors; D014921:Wings, Animal / Q000196:embryology / Q000294:innervation
chemical_list: D002038:Bungarotoxins; D005456:Fluorescent Dyes; D011950:Receptors, Cholinergic