MORPHOLOGICAL AND FUNCTIONAL-STUDY OF EXTENSOR DIGITORUM LONGUS MUSCLE REGENERATION AFTER ITERATIVE CRUSH LESIONS IN MDX MOUSE

The regenerative capacity of mdx Extensor Digitorum Longus (EDL) muscl e after iterative muscle crush injuries was examined and compared with that of age-matched control C57BL/10 mice. Muscle crush injuries were performed at 8 weeks and repeated at 12 and 16 weeks. Contralateral n on-crushed EDLs from mdx and C57BL/10 mice were used as internal contr ols for histopathology, histoenzymology, morphometry and for the study of the contractile properties. Morphological examinations were perfor med at 12, 16 and 20 weeks, respectively one month after a single, a s econd or a third crush. Contractile properties were studied at 12 and 20 weeks. By 20 weeks, no difference in the number of fibres with inte rnal nuclei could be observed between crushed EDL from both strains, a nd non-crushed mdr EDL; the area and the diameter of crushed EDL from mdx mice were, respectively, 1.5- and 1.2-fold higher than the ones fr om crushed EDL from C57BL/10 strain. By 20 weeks, diameter distributio n of crushed EDL muscles from C57BL/10 mice were shifted towards small er fibre diameter, whereas in mdx mice, diameter distribution of crush ed EDL muscles paralleled that of non-crushed EDL muscles. By 20 weeks , crushed mdx and C57BL/10 EDL muscles produced 77 and 47% of normaliz ed tetanus tension respectively of non-crushed mdx and C57BL/10 EDL mu scles, Following crush injury, both 12- and 20-week mdx and C57BL/10 E DL exhibited a slowed time to peak (TTP) and half-relaxation time (H1/ 2R) of twitch. There was no difference in posttetanic potentiation bet ween the different groups. Crushed EDL of both strains showed an incre ased resistance to fatigue, compared to the non-crushed controls. The present study provides morphological and functional evidence for the g reater recovery of mdx muscle compared to C57BL/10 muscle following it erative crush injury; however, the recovery does not completely preven t the appearance of necrosis/regeneration features.