Figure 5.

Spontaneous compensatory CST sprouting after injury. Contacts of BDA-labeled CST axons (brown-black) with ChAT-immunolabeled motoneurons (blue) were quantified in the medial motoneuron column (mmc) and lateral motoneuron columns (lmc) at C4. (A) Ventral horn and ventral white matter are shown, with ChAT-labeled motoneurons in the medial and lateral motor columns. Animal with dorsal CST lesion. (B) Higher magnification of the boxed area in A. A BDA-labeled axon (arrowheads) branches off the ventral CST (arrows) and projects to the medial motoneuron column, Rexed's lamina IX. (C) A BDA-labeled CST axon (arrowheads) projects from the ventral white matter into the medial motoneuron column and contacts a ChAT-labeled motoneuron, exhibiting a bouton-like swelling at the site of this contact (arrow). This point of putative contact is shown at higher magnification in the Inset. The total number of bouton-like contacts was quantified through the full thickness of ten coronal sections at C4 in every animal. (D and E) Total number of BDA-labeled CST axons contacting ChAT-labeled motoneurons in lamina IX at C4. (D) BDA-labeled CST axon contacts in the medial motoneuron column of lamina IX are significantly increased only in dCST-lesioned animals compared with intact animals (ANOVA, P < 0.01). (E) All lesions disrupting the dorsal CST (d/vCST, MED, dCST) yield a significant reduction of BDA-labeled CST terminations in the lateral motoneuron column of lamina IX (ANOVA, P < 0.001). (F) The total number of CST terminations on medial + lateral motor neurons correlates significantly with functional performance on the pellet retrieval task (r² = 0.89; P = 0.03; scale bars: A = 91 μm, B = 13.4 μm, C = 11.1).