Spinal cord lesion and number of pyramidal neurons in layer V of the motor cortex. A: Reconstruction from paralongitudinal sections of the lesion performed in eight monkeys at cervical level C7/C8. The lesion area is indicated in red for the anti-Nogo-A antibody treated monkeys and in blue for the control antibody treated monkeys. The gray zone in the center corresponds to the gray matter. In one monkey (Mk-AT), the tissue was damaged in the zone of the cervical cord lesion and it was not possible to precisely assess the position and extent of the lesion. The lesions have already been shown in recent reports [10,22]. Although some lesions were on the left side and others on the right side, for simplification they were all represented here as a left side lesion. B: Photomicrograph showing the part of M1 corresponding to the hindlimb representation on both hemispheres and stained with SMI-32. On both sides, SMI-32 typically labeled the pyramidal cells in the layers III and V. However, typically at such low magnification, the layer V appears more densely stained on the ipsilesional hemisphere than on the contralesional one (see text). The hindlimb area in M1 was thus visible on the same section for the two hemispheres and the observer could thus delineate roughly equally long portions of the layer V in each hemisphere on which the counts were performed (dashed line), as explained in detail earlier . The length of the portion of layer V in which counts were made (in mm) was determined for data normalization. CIN = cingulate sulcus. C: Bar graph indicating the mean number of SMI-32 positive neurons per unit length (and SD) counted in layer V of the hindlimb area in M1 of each hemisphere, on the sample of sections examined in the three groups of monkeys (green is for intact monkeys). * is for p <= 0.05; n.s. is for p > 0.05 (t-test for small samples as explained in the methods section). D: A portion of the hindlimb area in M1, on which morphometric measurements were conducted, is shown at higher magnification, for a typical contralesional hemisphere (left photomicrograph). At low magnification (panel B), due to lighter SMI-32 staining than in the ipsilesional hemisphere, very few SMI-32 positive neurons were visible in layer V. At this magnification (left photomicrograph), some SMI-32 positive neurons appear. The observer then identified at high magnification all SMI-32 positive neurons with a visible nucleus in layer V (neurons highlighted on top of a yellow background), as shown on the right photomicrograph. In general, it turned out that, in spite of a lighter SMI-32 staining, the positive neurons with a visible nucleus were on average as numerous as in the ipsilesional hemisphere. In each photomicrograph, the cortical surface is on top and the white matter on bottom. The SMI-32 positive neurons are typically found in layers III and V.