Soukup T, Novotová M
Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic.
Acta Neuropathol. 2000 Oct;100(4):435-44. doi: 10.1007/s004010000194.
Extensor digitorum longus (EDL) muscles from 2- to 28-day-old rats were grafted into EDL muscles of adult inbred recipients (n = 8). At 1-6 months after the operation, experimental muscles were excised and the ultrastructure and innervation of regenerated muscle spindles was examined. Regenerated muscle spindles (n = 36) in isografted EDL muscles contained 4.3 +/- 0.2 (mean +/- SEM) encapsulated muscle fibres. These "intrafusal" muscle fibres lacked nuclear bag and nuclear chain accumulations, which are characteristic of normal muscle spindles; thus, they rather resembled thin encapsulated extrafusal muscle fibres. In the same sample, myelinated axons were found in 33 (92%) muscle spindles, but no sensory terminals were found. These findings demonstrate that regenerated spindles in isografted EDL muscles were not reinnervated by spindle-specific sensory axons, but exclusively by motor axons. Typical intracapsular motor endplates (MEPs) were found in one third of regenerated spindles examined. Their motor terminals contained accumulated mitochondria and synaptic vesicles. As is characteristic for MEPs, axolemma and sarcolemma were separated by a synaptic cleft about 60 nm wide that contained a basal lamina. The underlying sarcolemma formed either small infoldings or none at all, and the subsynaptic area contained only small subsarcolemmal accumulations of mitochondria. It is apparent that the structures described here as "regenerated muscle spindles" do not perform their normal physiological function as stretch receptors because they lack the sensory innervation. The present results show that regeneration and reinnervation in heterochronous isografts corresponds to that previously described in autotransplanted free muscle grafts. The results also show that, during muscle spindle regeneration, intrafusal satellite cells develop into extrafusal-like muscle fibres, apparently due to their motor innervation.
将2至28日龄大鼠的趾长伸肌（EDL）移植到成年近交系受体（n = 8）的EDL肌肉中。术后1至6个月，切除实验肌肉，检查再生肌梭的超微结构和神经支配情况。同基因移植的EDL肌肉中的再生肌梭（n = 36）包含4.3±0.2（平均值±标准误）条被囊化肌纤维。这些“梭内”肌纤维缺乏正常肌梭特有的核袋和核链聚集；因此，它们更类似于细的被囊化梭外肌纤维。在同一样本中，33个（92%）肌梭中发现有髓轴突，但未发现感觉终末。这些发现表明，同基因移植的EDL肌肉中的再生梭未被梭特异性感觉轴突重新支配，而是仅被运动轴突支配。在所检查的三分之一再生梭中发现了典型的囊内运动终板（MEP）。它们的运动终末含有聚集的线粒体和突触小泡。正如MEP的特征一样，轴膜和肌膜被约60nm宽的突触间隙隔开，突触间隙内含有基膜。其下方的肌膜要么形成小的褶皱，要么根本不形成褶皱，突触下区域仅含有少量肌膜下线粒体聚集。显然，这里描述为“再生肌梭”的结构不能作为牵张感受器发挥其正常生理功能，因为它们缺乏感觉神经支配。目前的结果表明，异时同基因移植中的再生和再支配与先前自体移植游离肌肉移植物中所描述的情况一致。结果还表明，在肌梭再生过程中，梭内卫星细胞显然由于其运动神经支配而发育成梭外样肌纤维。
