Morphologic characterization of SOD1-G93A clusters in sensory and motor axons of asymptomatic rats. (A1) SOD1-G93A detected with immunofluorescence in lumbar sensory axons from 65-day-old SOD1-G93A rats. Note that no clusters were observed. (A2) SOD1-G93A detected in the ventral root at the same root level and from the same animal. Note the striking density of clusters. (B) Distribution of wild-type rat SOD1 in non-transgenic control littermates, as detected by using a panspecific anti-SOD1. (B1) Dorsal sensory axons; (B2) ventral motor axons. Note the homogeneous distribution of rat SOD1. (C1–C6) Six consecutive confocal images of 35-day-old SOD1-G93A motor axons showing SOD1 distribution through the axonal volume. (D1) Differential interference contrast (DIC) image; and (D2) SOD1-G93A staining of axons displaying clusters. Note that the affected axons were not morphologically altered. (E1) DIC image, and (E2) anti-human SOD1 staining of non-transgenic motor axons. Note the lack of immunoreactivity of rat SOD1. Scale bars: A, D, and E, 20 μm; B and C, 10 μm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).