Cuppini R, Sartini S, Ambrogini P, Gallo G
Istituto di Anatomia e Fisiologia, Università di Urbino, Italy.
J Peripher Nerv Syst. 1996;1(3):223-9.
Reinnervation of extensor digitorum longus muscle following crush of sciatic nerve was studied in rats made hypothyroid after weaning. In vitro intracellular recordings of muscle cell postsynaptic potentials were carried out; moreover twitch and tetanus following direct muscle stimulation and nerve stimulation were recorded. Frequency of miniature end-plate potentials (mepps) may be regarded as an index of presynaptic mechanism in regenerated nerve endings: when regenerating axons reach the muscle, the frequency of spontaneous acetylcholine quantal release is very low and increases in subsequent weeks. No significant differences were noted in miniature end-plate potential frequency between muscles of normal and hypothyroid rats at the same time from denervation; mepp amplitude was higher in hypothyroids, in accordance with the smaller muscle fibre diameters. Regenerating nerve fibres entering the muscle extensively sprout, giving rise to a number of nerve endings which exceeding the number of muscle cells, are subsequently withdrawn; correspondingly, muscle cells are transiently polyinnervated and the number of polyinnervated muscle cells peaks decreases subsequently approximating zero. The percentage of polyinnervated cells peaked sooner in hypothyroid rats than in controls and afterwards decreased; a tail of polyinnervation was found at long term. Tension recording experiments showed a shorter time of reinnervation of muscles in hypothyroid rats, but no difference in regeneration rate could be argued. These findings suggest an influence of thyroid hormones in the stabilization of motor innervation of reinnervated muscle, but not in nerve regeneration process.
对断奶后甲状腺功能减退的大鼠坐骨神经挤压伤后趾长伸肌的再支配情况进行了研究。对肌肉细胞的突触后电位进行了细胞内体外记录；此外，还记录了直接肌肉刺激和神经刺激后的抽搐和强直收缩。微小终板电位（mepps）的频率可被视为再生神经末梢突触前机制的一个指标：当再生轴突到达肌肉时，乙酰胆碱量子自发释放的频率非常低，并在随后几周内增加。在去神经支配后的同一时间，正常大鼠和甲状腺功能减退大鼠的肌肉之间，微小终板电位频率没有显著差异；甲状腺功能减退大鼠的微小终板电位幅度更高，这与较小的肌纤维直径一致。进入肌肉的再生神经纤维广泛发芽，产生大量超过肌肉细胞数量的神经末梢，随后这些神经末梢会退缩；相应地，肌肉细胞会暂时接受多神经支配，多神经支配的肌肉细胞数量峰值随后会下降并接近零。甲状腺功能减退大鼠多神经支配细胞的百分比峰值出现得比对照组早，随后下降；长期观察发现有多神经支配的残余现象。张力记录实验表明，甲状腺功能减退大鼠肌肉的再支配时间较短，但再生速率没有差异。这些发现表明甲状腺激素对再支配肌肉运动神经支配的稳定有影响，但对神经再生过程没有影响。
