Enhanced regeneration of corticospinal tract (CST) axons in MRL/MpJ mice after SCI.

<p><b>a</b>, <b>b</b>, Sagittal sections of BDA-labeled CST axons in C57BL/6 (<b>a</b>) and MRL/MpJ (<b>b</b>) mice. Two weeks after tracing, dorsal hemisections were performed. The CST was analyzed at 4 dpi ( = 18 days after tracing). In both mouse strains, axons are visible rostral and caudal from the injury site. No BDA-labeled fibers were found at the injury site, confirming that the CST was completely transected. <b>c</b>, <b>d</b>, Sagittal sections of BDA-labeled CST axons in injured C57BL/6 (<b>c</b>) and MRL/MpJ (<b>d</b>) mice at 54 dpi. Here, BDA tracing was performed right after SCI. C57BL/6 CST axons retracted from the lesion (arrowhead in <b>c</b>). In contrast, some MRL/MpJ CST fibers crossed through the lesion site (arrowhead in (<b>d</b>)). <b>e</b>, <b>f</b>, Montage of sagittal sections of BDA-labeled CST axons in C57BL/6 (<b>e</b>) and MRL/MpJ (<b>f</b>) mice at 109 dpi. Higher magnifications are shown in <b>g</b> (from boxed area in <b>e</b>) and <b>h</b> (from boxed area in <b>f</b>). We found no BDA-positive fibers below the injury site in C57BL/6 spinal cord (<b>e</b>, <b>g</b>), in contrast to MRL/MpJ mice (<b>f</b>, <b>h</b>). <b>i</b>, <b>j</b>, Data represent percentage of fibers and are reported as a function of the distance from the lesion at 54 dpi (i) and 109 dpi (j). MRL/MpJ mice exhibited significantly more regenerating axons at 0.5 mm caudal from the lesion site. Rostral end of the spinal cord is to the left. The arrows point at the injury site. Asterisks denote significant differences between MRL/MpJ and C57BL/6, P<0.02 (two-way ANOVA, Bonferroni Post-hoc). Scale bar, 250 µm (<b>a</b>–<b>d</b>); 300 µm (<b>e</b>, <b>f</b>); 100 µm (<b>g</b>, <b>h</b>).