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Background: Research on regenerative medicine using basic fibroblast growth factor (bFGF) has recently advanced in the field of laryngology. We previously reported that local administration of bFGF 1 month after recurrent laryngeal nerve (RLN) paralysis compensated for atrophy of the thyroarytenoid muscle. The objective of this study was to elucidate the effects of early bFGF administration on the thyroarytenoid muscle after RLN transection and to investigate the underlying mechanisms. Methods: A rat model of RLN paralysis was established in this study. One day after RLN transection, low- (200 ng) or high-dose (2000 ng) bFGF or saline (control) was administered to the thyroarytenoid muscle. The larynges were excised for histological and immunohistochemical examinations at 1, 7, 14, 28, and 56 days after administration. Results: The cross-sectional thyroarytenoid muscle area was significantly larger in the high-dose group than in the saline and low-dose groups on days 28 and 56. Immunohistochemistry indicated that bFGF significantly increased the number of satellite cells in the thyroarytenoid muscle up to day 14 and that of neuromuscular junctions on days 28 and 56. Conclusions: A single, early local administration of high-dose bFGF prevented atrophic changes in the thyroarytenoid muscles by activating satellite cell proliferation and reforming neuromuscular junctions. As increased neuromuscular junctions are expected to maintain myofiber volume, bFGF administration may prevent thyroarytenoid muscle atrophy in the mid to long term. [ABSTRACT FROM AUTHOR]