A, Schematic diagram of experimental design. WT, hSOD1G93A, and hSOD1WT mice were retrogradely labeled by FG injections to be analyzed at P30 (pre-symptomatic); P60 (symptomatic); and P120 (end-stage). In a subset of experiments, CSMN were retrogradely labeled at P50 and analyzed at P120 (#). B, Retrogradely labeled CSMN reside in layer V of the motor cortex, and display distinct CSMN morphology (inset). C–D, Confocal analysis reveals co-localization of the CSMN/SCPN-specific (within neocortex) transcription factor CTIP2 (C) and exclusion of the CSMN-excluded transcription factor LMO4 (D) in retrogradely labeled CSMN. E–F, Comparable and representative coronal sections of the motor cortex from WT, hSOD1WT, and hSOD1G93A mice at P30 (E) and at P120 (F). The boxed areas are enlarged in the adjacent panels to show retrogradely labeled CSMN. G, Bar graph representation of average CSMN soma diameter in WT, hSOD1WT, and hSOD1G93A mice at P30, P60, and P120. H, Bar graph representation of the average number of CSMN per 20× field in WT, hSOD1WT, and hSOD1G93A mice at P30, P60, and P120. CSMN that were retrogradely labeled at P50 and analyzed at P120 are labeled with “#”. WT, wild-type; FG, FluoroGold; CSMN, corticospinal motor neurons; SCPN, subcerebral projection neurons. Scale bars: C, 40µm; D, 50µm; Data presented as mean ± SEM. *p<0.05; ** p<0.0001; G,H, Bonferroni Test preceded by two-way ANOVA.