Kucera J, Walro J M
Department of Neurology, School of Medicine, Boston University, MA 02118.
Anat Embryol (Berl). 1987;176(4):449-61. doi: 10.1007/BF00310086.
Whether the motor innervation can direct the morphological and histochemical differentiation of developing muscle spindles in the absence of sensory innervation was investigated by deafferentation of the soleus muscle in immature rats. Dorsal root ganglia containing the cell bodies of afferents from the soleus muscle were removed surgically at a stage of postnatal development when spindles already contain the full complement of intrafusal fibers innervated by both afferents and efferents, but when the fibers are histochemically and structurally immature. Experimental soleus muscles were excised one year after deafferentation and sectioned frozen at a thickness of 8 micron. Sections were stained for enzymes indicative of types of muscle fibers and sites of neuromuscular junctions, and were examined by light microscopy. Spindles of muscles that matured in the absence of sensory innervation were abnormal. They lacked the periaxial fluid space and contained fewer intrafusal fibers than did normal spindles. The morphological and histochemical profiles of the encapsulated fibers present in the deafferented spindles more closely resembled extrafusal rather than intrafusal muscle fibers. These observations suggest that deafferentation of the immature spindles induces disintegration of some intrafusal fibers and alters maturation of others. Moreover, motor axons terminated less frequently along muscle fibers in deafferented spindles than on intrafusal fibers of normal spindles. Thus, maintenance of a full complement of intrafusal fibers in the developing spindle, emergence of histochemical profiles typical of normal intrafusal fibers, and development of adult pattern of fusimotor innervation require intact sensory innervation.
通过对未成熟大鼠比目鱼肌进行去传入神经支配实验，研究了在没有感觉神经支配的情况下，运动神经支配是否能引导发育中的肌梭进行形态学和组织化学分化。在出生后发育的某个阶段，当肌梭已经包含由传入和传出神经纤维支配的完整梭内纤维，但这些纤维在组织化学和结构上尚未成熟时，手术切除含有比目鱼肌传入神经细胞体的背根神经节。去传入神经支配一年后，切除实验性比目鱼肌，并将其冷冻切片，厚度为8微米。切片用指示肌纤维类型和神经肌肉接头部位的酶进行染色，并通过光学显微镜检查。在没有感觉神经支配的情况下成熟的肌肉的肌梭是异常的。它们缺乏轴周液间隙，并且比正常肌梭含有更少的梭内纤维。去传入神经支配的肌梭中存在的被囊纤维的形态学和组织化学特征更类似于梭外肌纤维而不是梭内肌纤维。这些观察结果表明，未成熟肌梭的去传入神经支配会导致一些梭内纤维解体，并改变其他纤维的成熟过程。此外，与正常肌梭的梭内纤维相比，去传入神经支配的肌梭中运动轴突在肌纤维上的终止频率更低。因此，发育中的肌梭中完整的梭内纤维的维持、正常梭内纤维典型的组织化学特征的出现以及成年模式的梭内肌运动神经支配的发育都需要完整的感觉神经支配。
