Figure 7.

Aging causes complete degeneration of sensory axons innervating the extensor digitorum longus (EDL) muscle in middle age and old mice. Sensory axons innervating the portion of the EDL muscle that controls the 2nd digit were analyzed using transgenic mice expressing YFP in neurons (A–C). Axon number was determined by digitally slicing through the 3D image plane (A′–C′). Fewer sensory axons innervating the EDL muscle were found in 11- and 15-month-old mice (D). Aged sensory axons also often exhibited deleterious structural changes that include thinning and large swellings. At least three animals per age group were analyzed. Scale bar = 10 µm. Error bar = STE. ***p < .001.