Askanas V, Kwan H, Alvarez R B, Engel W K, Kobayashi T, Martinuzzi A, Hawkins E F
Neuromuscular Center, University of Southern California School of Medicine, Hospital of the Good Samaritan, Los Angeles 90017.
J Neurocytol. 1987 Aug;16(4):523-37. doi: 10.1007/BF01668506.
Ultrastructural features of neuromuscular junction formation and transverse tubule development were studied utilizing a newly developed model in which human muscle fibres cultured in monolayer are innervated by foetal rat spinal cord with dorsal root ganglia attached. At early innervation (7-10 days), when distinct 'boutons' are contacting muscle fibres, the contacts of nerve terminals with the muscle fibres are, ultrastructurally, superficial and unorganized, and there is no basal lamina-like material between nerve terminals and muscle fibres. A bouton consists, ultrastructurally, of a cluster of small nerve terminals contacting the muscle fibre. At 2-3 weeks of innervation, shallow 'beds' are formed on the muscle fibre just beneath nerve terminals, and occasionally there are irregular and miniscule fragments of basal lamina-like material in the cleft. There is no Schwann cell apposing the nerve terminal at this stage of innervation. After 4-5 weeks of innervation there is more definite basal lamina material in the cleft and suggestive postsynaptic plasmalemmal densities and invaginations. However, there is no Schwann cell apposing the nerve terminal at this stage. At 6-8 weeks of innervation, deep postsynaptic folds are present, a Schwann cell apposes the nerve terminal, and basal lamina surrounds the entire muscle fibre. At all four stages of innervation examined, ultrastructural cytochemistry of alpha-bungarotoxin binding reveals that nicotinic ACh receptors are located exclusively at the neuromuscular junctions. After 1-2 weeks of innervation, very few lanthanum-positive transverse tubules are observed and only in close proximity to the surface membrane. After 3 weeks of innervation, more lanthanum-positive tubules are present, and they are located deeper within the muscle fibre. Five weeks after innervation, somewhat more elaborated tubules (but no lateral sacs) appear, and honeycomb structures are often present. After 6-7 weeks of innervation the tubular system is very elaborate and lateral sacs are present. Hence, this study describes consecutive stages of the formation of neuromuscular junctions and transverse tubules in innervated cultured human muscle, and provides an important basis to which similar studies related to the diseased human muscle can be compared.
利用一种新开发的模型研究神经肌肉接头形成和横小管发育的超微结构特征，在该模型中，单层培养的人肌纤维由附着有背根神经节的胎鼠脊髓支配。在早期神经支配阶段（7 - 10天），当明显的“终扣”与肌纤维接触时，神经末梢与肌纤维的接触在超微结构上是表面的且无组织的，神经末梢与肌纤维之间不存在类基膜物质。从超微结构来看，一个终扣由一簇与肌纤维接触的小神经末梢组成。在神经支配2 - 3周时，在神经末梢下方的肌纤维上形成浅的“床”，裂隙中偶尔有不规则的微小类基膜物质碎片。在这个神经支配阶段，没有施万细胞贴附在神经末梢上。神经支配4 - 5周后，裂隙中有更明确的基膜物质以及提示性的突触后质膜致密区和内陷。然而，在这个阶段也没有施万细胞贴附在神经末梢上。在神经支配6 - 8周时，出现深的突触后褶皱，一个施万细胞贴附在神经末梢上，并且基膜围绕整个肌纤维。在所检查的神经支配的所有四个阶段，α - 银环蛇毒素结合的超微结构细胞化学显示烟碱型乙酰胆碱受体仅位于神经肌肉接头处。神经支配后1 - 2周，仅在靠近表面膜处观察到极少数镧阳性横小管。神经支配3周后，出现更多镧阳性小管，并且它们位于肌纤维更深的部位。神经支配5周后，出现更精细的小管（但没有侧囊），并且经常存在蜂窝状结构。神经支配6 - 7周后，管状系统非常精细并且存在侧囊。因此，本研究描述了受支配的培养人肌肉中神经肌肉接头和横小管形成的连续阶段，并为与患病人类肌肉相关的类似研究提供了一个重要的比较基础。
