Journal of Dental Research, Vol 75, 1835-1841, Copyright © 1996 by International & American Associations for Dental Research Online Journals
A morphometric investigation of myotube formation in rabbit embryo medial pterygoid muscle
R. Benoit and C. Baudoin
Laboratoire d'Histologie, Faculte de Chirurgie Dentaire, Universite Rene-Descartes, Paris V, Montrouge, France.
To determine the times of the appearance of myoblasts, early myotubes, late
myotubes, and myofibers, we studied a region between two aponeuroses of the
medial pterygoid masticatory muscle in embryos of two strains of rabbits,
without disturbing the normal innervation. The objectives of this study
were to define the quantitative relations among these cells and to
determine their kinetics statistically. We used Fauve de Bourgogne and New
Zealand rabbit embryos on day 17, day 17 plus 12 hours, day 18, day 18 plus
12 hours, and days 20, 22, and 28 of gestation. Cell proliferation was
studied with a light microscope, by means of counting methods. Similar
development was observed in the two strains of rabbits. The numbers of
myoblasts decreased as follows: (i) a marked decrease; (ii) a sudden
cessation of the decrease, marked by a rebound at 18 days, and lasting less
than 24 hours; and (iii) a plateau between embryonic days 22 and 28. The
onset of reduction in the number of early myotubes coincided with the
rebound of myoblasts. The number of late myotubes increased at the time of
maximal early myotube density and during rebound of the myoblasts. Myofiber
densities were similar to late myotube densities on day 22. We suggest that
early myotubes are formed very gradually by fusion of myoblasts, and that
the significant increase in the numbers of myoblasts corresponds to the
second generation of myoblasts necessary for differentiation of late
myotubes.
