Acetylcholine receptors and neuronal nitric oxide synthase distribution atthe neuromuscular junction of regenerated muscle fibers

We investigated whether the changes in acetylcholine receptor (AChR) distri bution and neuronal nitric oxide synthase (nNOS) expression reported for th e skeletal muscle of mdx mice were a consequence of muscle fiber regenerati on rather than of the absence of dystrophin. Degenerative-regenerative chan ges in muscle fibers of the sternomastoid muscle of normal mice were induce d by injecting lidocaine hydrochloride. Twenty-one days later, AChRs were l abeled with alpha-bungarotoxin and nNOS with anti-nNOS antibody, and observ ed under a confocal microscope. AChRs were distributed in continuous branch es in normal fibers. Regenerated fibers showed disruption of AChRs distribu tion similar to that seen in muscle of mdx mice. This suggests that changes in AChRs distribution seen in mdx mice were probably a consequence of musc le fiber degeneration and regeneration, rather than a symptom of dystrophin deficiency. Conversely, there were no changes in nNOS distribution and exp ression in normal regenerated fibers, suggesting that the decrease in nNOS expression reported for mdx mice might be attributed to the absence of dyst rophin. (C) 2001 John Wiley & Sons, Inc.