Figure 22 Glia cells do not exhibit cytoplasmic abnormalities.

(A and B) At P30, both astrocytes (A) and oligodendrocytes (O) appear to have normal mitochondria (arrowheads) and cytoplasm, although swollen mitochondria can be seen in surrounding neuropil. (C and … Initial NMJ denervation is associated with motor deficits Previous gait analysis of SOD1G93A mice have indicated supranormal gait prior to neurodegeneration and the onset of gait disturbances at ~13 weeks of age, when the animals were tested walking horizontally at speeds of 24 and 36 cm/sec (Amende et al. 2005). We did Inhibitors,research,lifescience,medical not detect any overt deficits in gait when SOD1 mice voluntarily traversed the walking compartment floor. Initial clinical symptom onset of ALS in patients often occurs as small and subtle changes in muscle Inhibitors,research,lifescience,medical strength (e.g., occasional foot drop, difficulty turning a key, slurring of speech). It is difficult to assess these kinds of changes by simple observation of mouse behavior. We therefore challenged the animals with a more rigorous treadmill walking protocol. The treadmill, walking compartment, and camera system were pitched at an angle so that the animals walked up an incline Inhibitors,research,lifescience,medical of 15 degrees and the motor speed was set to 40 cm/sec. Under these conditions there

was a significant increase in the variability of hindlimb Inhibitors,research,lifescience,medical paw placement angle in SOD1 mice at P28 and P30 (Fig. ​(Fig.23).23). We believe that the variability of hind paw placement angle corresponds to muscle weakness due to initial denervation that occurs in the TA as reported in this study and medial gastrocnemius muscle in a previous study (Gould et al. 2006). These behavior changes may Inhibitors,research,lifescience,medical also reflect denervation in other hindlimb muscles that were not studied (e.g.,

extensor digitorum longus). The difference in paw placement angle tends to disappear by P40. At the same time the differences in hindlimb stance width become more prominent and increases with age. There was also an apparent decrease in hindlimb stance width at P32, secondly although the difference between SOD1 and WT was not statistically significant until P40; a decrease in beta-catenin tumor forelimb stance width was also detected at day 40 (Fig. ​(Fig.23).23). These more profound changes correspond with increased muscle denervation that occurs with disease progression. Figure 23 SOD1G93A mice exhibit deficits in motor function that correlate with early muscle denervation. (A) Schematic of forelimb and hindlimb stance width in WT and SOD1G93A mice walking 40 cm/sec up an incline (~15 degrees). Forelimb stance width is … Using the loaded grid test as an assay of forelimb muscle strength, SOD1 mutant mice at P29 (but not at P27 or P28) exhibited the first signs of muscle weakness as indicated by a significantly decreased duration of time before dropping a 15 g weight.