Changes in histochemical properties of muscle fibres in developing canine skeletal muscles
2005
Strbenc, M., Ljubljana Univ. (Slovenia). Veterinary Fac.
In the study changes in muscle fibres of canine skeletal muscles were observed during development from perinatal period to 6 months of age. Emphasis was put on the histochemical fibre type classification and general morphological properties. In neonates muscle fascicles contained one centrally located primary fibre which in some cases still retained a central space as seen in developing myotubes. These fibres started to stain differently from surrounding secondary fibres on foetal day 55. The classification of muscle fibres according to the myosin ATPase (mATPase) method was possible after third week post partum; prior to this the majority of fibres seemed to be undifferentiated. Between the third and the sixth week 7 different fibre phenotypes were found and in two-month-old dog the usual adult composition of muscles with 4 fibre types was first noted. The glycolytic and oxidative capacities were weak in neonates but increased gradually with age. The metabolic differentiation between fibres was first noted at the third week. The diameter of fibres was increasing constantly. The number of muscle fibres assessed by ratio between primary and secondary fibres increased in perinatal period. When compared to data in the literature, we ascertained that dog skeletal muscles are relatively immature at birth. There were parts of muscles which developed even more slowly and still had a myotubal morphology in neonates. Some muscle- dependent differences were noted: the diaphragm developed faster and an early distinction between slow (m. rhomboideus) and fast muscles (m. extensor carpi radialis and m. tibialis cranialis) was observed. Mature morphology with a random distribution of fibre types inside muscle fascicles and a defined metabolic profile was observed in all muscles in two-month-old dogs. The standard mATPase method became applicable to determine fibre types by this time.
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