Novotová M, Soukup T
Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava.
Acta Neuropathol. 1995;89(1):85-95. doi: 10.1007/BF00294263.
The ultrastructure of muscle spindles de-efferented by the extirpation of the lumbosacral spinal cord at the age of 2 days and subsequently deprived of their sensory innervation by the section of the sciatic nerve at 3-4 weeks of age was studied in serial sections of 2-month-old rat hindlimb muscles. De-efferentation leaves the primary sensory neurons and their peripheral axons intact and capable of inducing the muscle spindle morphogenesis during the critical period of their development. In de-efferented and subsequently denervated muscle spindles, new supernumerary intrafusal muscle profiles (SIPs) appeared in the muscle spindle A region. They were formed in intimate spatial relation with the original intrafusal muscle fibres (IMFs) predominantly from activated satellite cells derived from both nuclear bag (larger diameter) and nuclear chain fibres. SIPs, however, lacked the typical nuclear accumulations, as well as other ultrastructural distinctions present in control IMFs. The majority of differentiated SIPs separated from original IMFs, whereas the less differentiated SIPs were usually closely apposed to the surface of the parent IMFs and both were covered by the common basal lamina. In some spindles, the original IMFs and/or new SIPs at different stages of their differentiation were found together and they formed clusters of variable shape and composition. In the majority of clusters, all profiles seemed to be isolated along their entire length, although in few clusters, occasional cytoplasmic connections of variable length between intrafusal profiles were found. This result is important for the interpretation of the forthcoming study of expression of muscle spindle-specific myosin heavy chain isoforms in denervated SIPs in rat muscle spindles gradually deprived of their motor and sensory innervation.
在2月龄大鼠后肢肌肉的连续切片中，研究了在2日龄时通过切除腰骶脊髓去传出神经支配，并随后在3 - 4周龄时通过切断坐骨神经剥夺其感觉神经支配的肌梭超微结构。去传出神经支配使初级感觉神经元及其外周轴突保持完整，并能够在其发育的关键时期诱导肌梭形态发生。在去传出神经支配并随后失神经支配的肌梭中，肌梭A区域出现了新的多余的梭内肌轮廓（SIPs）。它们与原始梭内肌纤维（IMFs）形成紧密的空间关系，主要由来自核袋（较大直径）和核链纤维的活化卫星细胞形成。然而，SIPs缺乏典型的核聚集以及对照IMFs中存在的其他超微结构特征。大多数分化的SIPs与原始IMFs分离，而分化程度较低的SIPs通常紧密贴附于亲代IMFs的表面，两者都被共同的基膜覆盖。在一些肌梭中，发现处于不同分化阶段的原始IMFs和/或新的SIPs在一起，它们形成了形状和组成各异的簇。在大多数簇中，所有轮廓在其整个长度上似乎都是分离的，尽管在少数簇中，发现梭内轮廓之间偶尔存在可变长度的细胞质连接。这一结果对于解释即将进行的关于在逐渐失去运动和感觉神经支配的大鼠肌梭中失神经支配的SIPs中肌梭特异性肌球蛋白重链异构体表达的研究很重要。
