Development of the neuromuscular junction in the chick embryo: The number, distribution, and stability of acetylcholine receptors☆

[摘要] Thenumber,distribution,andstabilityofskeletalmuscleacetylcholinereceptorsduringdevelopmentoftheneuromuscularjunctioninthechickembryowerestudied.Thedistributionandturnoverofreceptorslabeledwith125I-labeledα-bungarotoxinweredeterminedbyquantitativeautoradiographyonindividualteasedmusclefibers.Eachposteriorlatissimusdorsimusclefiber,whichintheadultissinglyinnervated,hasahighdensityofacetylcholinereceptorsatasinglespotfromembryonicDay10throughhatching.Thespotsstainmoreintenselythanelsewhereforacetylcholinesteraseandareassumedtobeendplates.Thereceptorsatthesespotsarepresumedtobejunctionalreceptors.Thejunctionalreceptordensityremainsconstantat104/μm2fromembryonicDay14throughadultlife,althoughtheareaofthejunctionincreases40-fold.Incontrast,theextrajunctionalreceptordensitydropsprecipitouslyfrom250/μm2onDay14toonly10/μm2onDay19.Thisdecreaseinextrajunctionalreceptordensitycanbepreventedbychronicparalysiswithcurare.Therateofautoradiographicgrainlossfromjunctionalandextrajunctionalregionsafterapulseinjectionof125I-labeledα-bungarotoxinindicatesthatbothclassesofembryonicreceptorsturnoveratthesamerate(t12⋍30hr).

[学科分类] 生物科学（综合）