Muscle satellite cells: A validated technique for light microscopic identification and a quantitative study of changes in their population following denervation

Abstract A staining technique, in which basic fuchsin, methylene blue, and Azure II is applied to 0.5 μ sections of striated rat muscle embedded in epoxy resin, has given sufficient differentiation of five nuclear types found in the muscle fascicle to warrant its use as a valid method for identifying satellite cells with the light microscope. The validity of this technique was assessed by studying serial thin and thick sections of denervated rat hind limb muscles. Nuclei “typed” light microscopically were examined under the electron microscope to determine the type of cell in which they were located. This stain technique was then applied to determine the effect of denervation on the satellite cell population of the tibialis anterior and extensor digitorum longus. In control muscle of 200 gm rats, satellite cells represented 2% of the total nuclear population. Two and three weeks after denervation they accounted for 6% and 12%, respectively. In 800 gm rats, satellite cells accounted for 0.7% of the total nuclei found in the normal muscle. Denervation increased the percentage to 3% (at 2 weeks) and 5% (at 3 weeks). Paired satellite cells were infrequently observed; however, in 0.5 μ sections a significant number of satellite cells were found to be less than 0.7 μ from a myonucleus of the same fiber. A model is proposed to explain the increase in satellite cells following denervation.