Histological and histochemical studies of experimentally-induced degeneration and regeneration in normal and dystrophic mouse muscle

Abstract

A superficial crush lesion was induced in one triceps muscle in a series of 6 normal mice and in 8 dystrophic mice of the Bar Harbor strain aged between 2 and 4 months. The histological and histochemical changes occurring in the injured area were studied following removal of the affected muscle and of the comparable control muscle from the opposite limb at different stages after the injury. It was noted that the injury was induced in the so-called superficial "Type II fibre area" of the muscle, the deeper "Type I fibre area" being relatively uninvolved. Within 60 min it was found that in both normal and dystrophic muscle glycogen had disappeared almost totally from the injured area. It was also noted that Type II fibres disintegrated early and that Type I fibres were more resistant. There was a slight increase in the concentration of fat and free fatty acids in the injured fibres within the first hour after the lesion. Between 72 h and 11 days the histological characteristics of regenerative activity were clearly apparent in the area of injury and took the form of basophilia of sarcoplasm (in sections stained with haematoxylin and eosin), central migration of sarcolemmal nuclei and marked activity of these nuclei which were large and vesicular with prominent nucleoli. These regenerating fibres showed a high concentration of RNA in their sarcoplasm as demonstrated by the Azur B stain. It was noted that in the regenerating fibres the perinuclear area seemed initially to be devoid of lipid and glycogen in both normal and dystrophic muscle at 72 h and 8 days. By 11 days lipid was still absent from this area, but the area around the central nuclei in dystrophic muscle contained a high concentration of glycogen. The tempo of the regenerative process appeared to be more rapid in the dystrophic than in the normal muscle. Staining with succinic dehydrogenase confirmed that Type II fibres disintegrated early after physical injury and that Type I fibres were more resistant. At 72 h the regenerating fibres seemed to show intense mitochondrial activity except around the central unreacting vesicular nucleus. Eleven days after the lesion in normal muscle, differentiation into Type I and Type II fibres was clearly possible, but in dystrophic muscle the regenerating and newly-constituted fibres mostly showed a high concentration of succinic dehydrogenase in an area of muscle which is normally made up predominantly of Type II fibres. It was apparent that in the injured dystrophic muscle an area which was previously relatively non-dystrophic morphologically and which remained so in control muscle obtained from triceps on the opposite side had been converted into an area which now showed the histological characteristics of advanced muscular dystrophy.