GAMMA-IRRADIATION CAN REDUCE MUSCLE DAMAGE IN MDX DYSTROPHIC MICE

We report the effects of a single gamma irradiation delivered to the s oleus muscle of one limb of normal and mdx mice at the age of 16-20 da ys. At 45, 75 and 90 days of age transverse cryostat sections from the mid-belly of the muscles were used for microscopic examination. In no rmal mice the growth of fibres was appreciably reduced by irradiation without fibre loss. In the irradiated soleus of mdx mice the number of the regenerated centrally nucleated fibres was very small and the tot al number of fibres was remarkably reduced. The number of the peripher ally nucleated fibres, presumably surviving since the birth of the ani mal, was almost consistently larger than in the contralateral non-irra diated limb. The cross-sectional area of the irradiated fibres was sma ller It is well known that proliferation and fusion of satellite cells are required both for regeneration after fibre damage and for the nor mal postnatal growth of muscle fibres: irradiation appears to reduce r egeneration and growth. It is suggested that irradiation reduces damag e by reducing fusion associated with growth. Our hypothesis indirectly indicates a significant link between dystrophin deficiency and fibre necrosis and accounts well for many features of mouse dystrophy under natural and experimental conditions.