Fig. 6. Time course of muscle regeneration induced by focal freeze injury.
Transverse cryosections from TA muscles of 3-month-old C57 mice subjected to
focal damage in vivo were analyzed by HE staining. Uninjured muscle (U) shows
a typical pattern of evenly sized myofibers with peripheral nuclei. 30 minutes
after injury no histological changes are evident, whereas hyper-contracted
fibers (arrowhead) and infiltrating mononuclear cells (arrow) appear by 2 and
6 hours, respectively. Mononucleated cells (inflammatory cells and myoblasts)
increase in number in the lesion over the next 3 days. By 7 days post injury,
myoblast fusion results in centrally nucleated regenerating fibers (arrowhead)
of a smaller caliber than the adjacent uninjured fibers. The cross-sectional
area of regenerating fibers matures to that of undamaged fibers over the next
week (14d).
