Kucera J, Walro J M
Department of Neurology, School of Medicine, Boston University, MA 02118.
Anat Embryol (Berl). 1992 Sep;186(4):301-9. doi: 10.1007/BF00185978.
Muscle spindles form de novo in reinnervated muscles of neonatal rats treated with nerve growth factor. Whether the spindles can also form in muscle reinnervated only by afferents was investigated by removing the lumbosacral segment of the spinal cord immediately after crushing the nerve to the medial gastrocnemius muscle at birth, and administering nerve growth factor for 10 days afterwards. As predicted, the medial gastrocnemius muscles were reinnervated by afferents, but not efferents. No motor endplates were visible on any muscle fibers, and extrafusal fibers were atrophied. The reinnervated muscles contained spindle-like encapsulations of one to four fibers at 5, 7, 9 and 30 days after the nerve crush. The number of spindles as well as encapsulated fibers exceeded that of normal medial gastrocnemius muscles. The encapsulated fibers resembled typical intrafusal fibers. They had normal sensory-muscle contacts, but no motor endings. The fibers displayed equatorial clusters of myonuclei and expressed the spindle-specific slow-tonic myosin heavy chain isoform at postnatal day 30. Thus, efferents are not essential for the formation and differentiation of muscle spindles in reinnervated muscles of neonatal rats.
在接受神经生长因子治疗的新生大鼠的再支配肌肉中，肌梭会重新形成。为了研究仅由传入神经再支配的肌肉中肌梭是否也能形成，研究人员在新生大鼠出生时将其腓肠肌内侧神经切断后立即切除脊髓腰段，并在之后的10天内给予神经生长因子。正如所预测的，腓肠肌内侧由传入神经而非传出神经重新支配。在任何肌纤维上都看不到运动终板，肌外纤维萎缩。在神经切断后的5天、7天、9天和30天，再支配的肌肉中含有一到四根纤维的纺锤状包裹结构。纺锤体以及被包裹纤维的数量超过了正常腓肠肌内侧的数量。被包裹的纤维类似于典型的梭内纤维。它们有正常的感觉 - 肌肉接触，但没有运动终末。这些纤维在出生后第30天显示出肌核的赤道簇，并表达纺锤体特异性的慢张力肌球蛋白重链同工型。因此，传出神经对于新生大鼠再支配肌肉中肌梭的形成和分化并非必不可少。
