Figure 2.
Motoneurons contain numerous cytoplasmic vacuoles that are an early sign of impending degeneration. (A) Photomicrograph of 1 μm section through P60 lateral motor column of SOD1G93A mice. MNs are easily identified by their large size, nucleus, and prominent nucleolus (arrows). Many MNs contain numerous cytoplasmic vacuoles that can be viewed by light microscopy (arrowheads). (B) MNs were counted using well-established criteria that have been previously described (Clarke and Oppenheim 1995). At P60 in the SOD1G93A mouse spinal cord, however, many MNs meet some or all of these criteria even though they contain numerous cytoplasmic vacuoles that are an early sign of impending degeneration viewed by light microscopy. However, if the presumptive degenerating MNs containing cytoplasmic vacuoles are included in cell counts, total numbers are comparable to WT. If vacuolated MNs are excluded from the counts, then there is a 20% decrease at P60 and a 30% decrease at P70 in mutant spinal cords. By P115–140, there are few remaining vacuolated MNs in mutant mice and the number of surviving MNs at this age is reduced by approximately 50%. The number of animals for each condition is indicated in the bars of the graph; *P ≤ 0.05; **P ≤ 0.01; statistical significance determined by t-test with Bonferroni correction.