Haltia M, Berlin O, Schucht H, Sourander P
J Neurol Sci. 1978 Mar;36(1):25-39. doi: 10.1016/0022-510x(78)90159-4.
The postnatal differentiation and growth patterns of the different histochemical muscle fibre types were studied at frequent age intervals in the extensor digitorum longus (EDL) muscle of normal rats and animals subjected to pre- and postnatal protein-calorie undernutrition. Three stepwise changes were seen in the fibre type composition of the EDL muscle during maturation. In newborn normal rats 2 histochemically and morphometrically distinct fibre populations occurred: small foetal type (type F) fibres or myotubes (about 90%), with the staining characteristics of the so-called type 2C fibres, and larger type 1 fibres (10%). At 5 days of age the percentage of type F fibres had dropped to 50 simultaneously with the emergence of a new population (40%) of type 2B fibres, intermediate in cross-sectional area between the remaining type F fibres and type 1 fibres. Between 15 and 20 days the small type F fibres practically disappeared with the emergence of a corresponding percentage (40%) of type 2A fibres, smaller than both type 1 and type 2B fibres; Between 20 and 60 days the percentage of type 1 rose from 10 to almost 30, type 2B fibres correspondingly diminishing in number but growing at a faster rate than either type 1 or type 2A fibres. In the undernourished rats the histochemical differentiation was retarded at birth, all fibres or myotubes being of the foetal type; However, large type 1 and type 2B fibres were seen at the age of 5 days and the histochemical maturation proceeded almost normally at later stages. On the other hand, at all ages there was a proportional reduction in the cross-sectional area of all fibre types, amounting to about 50% at 180 dyas, and not fully restituted by nutritional rehabilitation. These observations suggest that type F (type 2C) fibres are the undifferentiated precursors of all mature muscle fibres, their stepwise histochemical transformation raising the question of maturational differences in the different types of motoneurones.
在正常大鼠以及出生前后经历蛋白质 - 热量营养不良的动物的趾长伸肌（EDL）中，以频繁的年龄间隔研究了不同组织化学类型肌纤维的出生后分化和生长模式。在成熟过程中，EDL肌的纤维类型组成出现了三个逐步变化。在新生正常大鼠中，出现了两种在组织化学和形态测量上不同的纤维群体：小的胎儿型（F型）纤维或肌管（约90%），具有所谓2C型纤维的染色特征，以及较大的1型纤维（10%）。在5日龄时，F型纤维的百分比降至50%，同时出现了新的群体（40%）的2B型纤维，其横截面积介于其余F型纤维和1型纤维之间。在15至20日龄之间，小的F型纤维几乎消失，同时出现了相应百分比（40%）的2A型纤维，其比1型和2B型纤维都小；在20至60日龄之间，1型纤维的百分比从10%上升到近30%，2B型纤维数量相应减少，但生长速度比1型或2A型纤维都快。在营养不良的大鼠中，出生时组织化学分化延迟，所有纤维或肌管均为胎儿型；然而，在5日龄时可见大型1型和2B型纤维，后期组织化学成熟几乎正常进行。另一方面，在所有年龄段，所有纤维类型的横截面积都成比例减小，在180日龄时约减小50%，营养恢复后也未完全恢复。这些观察结果表明，F型（2C型）纤维是所有成熟肌纤维未分化的前体，它们逐步的组织化学转变引发了不同类型运动神经元成熟差异的问题。
