In vivo observations of pre- and postsynaptic changes during the transition from multiple to single innervation at developing neuromuscular junctions

摘要: Synaptic rearrangements in developing muscle were studied by visualizing individual neuromuscular junctions the sternomastoid of living neonatal mice as they underwent transition from multiple to single innervation. Vital staining ACh receptors (AChRs) with rhodamine-conjugated alpha-bungarotoxin showed that while still multiply innervated (usually two motor axons), regions postsynaptic membrane within each junction became depleted receptors. Usually, several small areas lost AChRs succession. In these areas, already rapidly disappeared compared a low level receptor turnover elsewhere junction. Moreover, there was no evidence new being inserted into areas. Within area undergoing AChR depletion, intensity decreased gradually over 1-2 d. some junctions, it appeared migrating away The depletion sites combination spreading apart entire receptor-rich due fiber growth accounts for transformation plaque-like branched distributions at junctions. presynaptic nerve terminals whose also stained same postsynaptically. Postsynaptic began be before any obvious loss or intracellular overlying terminal. Only when innervating axon remained did and underlying largely cease. That former synaptic could later times identified uninnervated indicates synapse elimination during development leaves an indelible mark on structure. These observations suggest withdrawal occurs consequence stepwise all its synapses fiber. results important aspect competition leading is precocious beneath will eliminated. A similar early one axon's has been shown occur reinnervated adult (Rich Lichtman, 1989a).(ABSTRACT TRUNCATED AT 400 WORDS)