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Mdx mice are a model of Duchenne muscular dystrophy caused by deficiency of dystrophin. Striated muscle fibers (SMFs) of mdx mice are characterized by high level of death. As a result most SMFs of mdx mice have centrally located nuclei. Furthermore, neuromuscular junctions (NMJs) in mdx mouse are altered. Usually acetylcholine receptors (AChRs) of mdx mice are distributed as small islands in contrast to original AChRs branches of C57BL/6 mice NMJs. Our previous results showed that single intramuscular injection of C57BL/6 Lin(-) bone marrow (BM) stem cells ameliorate structure of NMJs of mdx mice SMF. 4 months after BM local transplantation total NMJs area was increased in 1.5 times due to increase of area of AChRs clusters simultaneously with increase of their number. The part of dystrophin-positive SMFs was increased from 0.5±0.1 % up to 1.8±0.4 %. We also changed mutant BM for BM of wild type. Male, 2 month old mdx mice (gift of Prof. T.A. Partridge, UK) were irradiated by X-ray in dose 3 Gy. BM cells were harvested from C57BL/6 mice (Rappolovo animal farm, St. Petersburg) killed by ether narcosis. 24 h after irradiation, mdx mice were anaesthetized with nembutal (40 mg kg-1, i.m.) and injected intravenously by BM cells. The study of m. quadriceps femoris and diaphragm was made at 2, 4, 6 month after transplantation. To localize NMJs we used tetramethylrhodamine-α-bungarotoxin (Biotium, USA) with help of Leica TCS SL confocal microscope. Values are means ± S.E.M. Experiments were performed at the animal care facility of Institute of Cytology of the RAS. We observed the increasing part of dystrophin-positive SMFs in m. quadriceps femoris mdx mice up to 27.6±6.7 % at 6 month after transplantation which was accompanied by decreasing of SMFs death from 2.2±0.6 % to 0.7±0.1 % and by accumulation of SMFs without central nuclei from 10.5±1.0 % up to 22.6±1.9 %. Similar to m. quadriceps femoris the increasing of part of dystrophin-positive SMFs was observed in diaphragm of mdx mice up to 12.0±3.2 % in 4 month after transplantation. The part of muscle SMFs without central nuclei increased from 8.4±0.6 % up to 30.4±1.5 % in diaphragm of mdx mice. The part of diaphragm NMJs with clusters of AChRs distributed as continuous branches was increased from 14±3 % up to 42.6±6 % and part of NMJs with AChRs clusters as islands was decreased from 75.8±3 % up to 53.7±6 %. Recovery of structure of NMJs was accompanied by recovery of the resting potential of the diaphragm end-plate membrane. Replacement of mutant BM stem cells for stem cells of wild type in condition of non-lethal X-ray irradiation is reason of recovery of dystrophin synthesis and of NMJs structure and function. This study was supported by Research Project #1.37.118.2011 of St. Petersburg State University, the Russian Foundation for Basic Research (#13-04-00973a). [ABSTRACT FROM AUTHOR]