Variable Interhemispheric Asymmetry in Layer V of the Supplementary Motor Area following Cervical Hemisection in Adult Macaque Monkeys

CS projection of SMA. A, upper panel, Schematic representation of a macaque brain showing the location of pre-SMA (area F6), SMA-proper (area F3), and M1. Lower panel, Schematic representation of the CS projections of F6 (bilateral). B, lower panel, Upper cervical spinal cord section showing the localization of CS axons labeled by a unilateral BDA injection in the SMA. Upper panel, Pie chart reporting the percentage of BDA-positive CS axons present in the ipsilateral ventromedial, ipsilateral dorsolateral, and contralateral dorsomedial part of the spinal cord. The majority of BDA positive CS axons are located in the contralateral dorsolateral part of the spinal cord. C, Photomicrographs of sagittal histologic sections of the spinal cord of a lesioned animal (Mk-CS) showing the induced permanent lesion at the C7/C8 level. The histologic sections derived from two different series processed to visualize SMI-32 staining (left) or Nissl staining (right). Scale bar: 500 μm. D, Graphical representation of behavioral performance in the modified Brinkman board task of the macaque monkeys included in this study (SCI in green and SCI + anti-Nogo-A treatment in dark gray). The manual performance of the ipsilesional hand is given by the score (number of pellets retrieved in the first 30 s of the task from the randomly distributed wells) as a function of time (days) before and after a SCI. Day 0 corresponds to the day of the lesion (vertical red line). Prelesional and postlesional average of the scores are indicated with horizontal gray lines. The total duration of functional recovery of manual dexterity after lesion is given by the time interval between the lesion (red vertical line) and the onset of the postlesion plateau (brown area). Figure Contributions: E. M. Rouiller and E. Schmidlin performed and supervised the experiments on the monkeys and analyzed the data.

Neuronal density in the Layer V of SMA in intact and SCI monkeys. A, Photomicrograph of coronal brain histologic section of an intact macaque monkey (Mk-IR) stained with SMI-32 and magnified in F3 (scale bar: 40 μm). Layers III and V are visible and SMI-32-positive pyramidal neurons are indicated with arrows. B–D, Localization of SMI-32-positive Layer V neurons in bilateral F3 and F6 areas of three representative macaque monkeys (intact: Mk-IR, SCI: Mk-CG and SCI + anti-Nogo-A treatment: Mk-AM). Four sections per macaque monkeys are shown and the relative rostro-caudal position of the sections from the F3-F6 border is reported in millimeters. Negative distance values belong to F6 and positive distance values belong to F3. E, Graphs representing the rostro-caudal gradient (from F6 to F3) of SMI-32-positive cell density in Layer V of all monkeys (intact: Mk-IC, Mk-IE, Mk-IR, and Mk-IZ; SCI: Mk-CG, Mk-CGa, Mk-CH, Mk-CP, and Mk-CS; SCI + anti-Nogo-A treatment: Mk-AG, Mk-AM, and Mk-AP). The cell density for each hemisphere is plotted as a function of the distance from the F3-F6 border, which has been set to 3 mm rostrally to the genu of the arcuate sulcus. Negative distance values belong to F6 and positive distance values belong to F3. The symbol # was used to indicate that the analyzed cortex region was not complete (sections lacking for the analysis). Figure Contributions: E. M. Rouiller and E. Schmidlin performed the experiments on the monkeys and generated the histologic sections. A. Contestabile and R. Colangiulo performed the microscopic analysis of the histologic sections. A. Contestabile analyzed the data.

IDCD after SCI in F3 and F6. A, Histograms reporting the cell density of Layer V SMI-32-positive neurons in F3 for intact (white background), SCI (light gray background), and SCI-treated monkeys (dark gray background). For each couple of histograms are reported the side (L = left and R = right) and the location in function of the SCI (Ipsi = ipsilesional and Contra = contralesional). As statistical test, a paired t test or Wilcoxon test was performed (p values are reported) comparing the cell density in the two hemispheres in each consecutive histologic section. B, Histograms showing the IDCD of Layer V SMI-32-positive neurons of F3 for intact (white background), SCI (light gray background), and SCI-treated monkeys (dark gray background). A positive IDCD corresponds to an ipsilesional bias in pyramidal cell density, while a negative IDCD corresponds to a contralesional bias in pyramidal cell density. B’, upper left inset, Comparison of calculated IDCD in F3 between groups. No statistical difference is observed (unpaired t test: t₍₁₀₎ = 0.8276, p = 0.4272). C, Histograms reporting the cell density of Layer V SMI-32-positive neurons in F6 for intact (white background), SCI (light gray background), and SCI-treated monkeys (dark gray background). For each couple of histograms, are reported the side (L = left and R = right) and the location in function of the SCI (Ipsi = ipsilesional and Contra = contralesional). As statistical test, a paired t test or Wilcoxon test was performed (p values are reported) comparing the cell density in the two hemispheres in each consecutive histologic section. D, Histograms showing the IDCD of Layer V SMI-32-positive neurons of F6 for intact (white background), SCI (light gray background), and SCI-treated monkeys (dark gray background). D’, upper left inset, Comparison of calculated IDCD in F6 between groups. No statistical difference is observed (unpaired t test: t₍₇₎ = 1.084, p = 0.3142). For A, C, the median and the interquartile range are indicated. For B, D, the mean ± SD are reported. L = left hemisphere, R = right hemisphere, *p ≤ 0.05, **p ≤ 0.01). Figure Contributions: E. M. Rouiller and E. Schmidlin performed the experiments on the monkeys and generated the histologic sections. A. Contestabile and R. Colangiulo performed the microscopic analysis of the histologic sections. A. Contestabile analyzed the data.

Arborization of Layer V SMI-32-positive neurons in F3 after a SCI. A, Neuronal reconstruction example of basal dendrites of a Layer V SMI-32-positive neuron. B–F, Sholl profiles of basal dendrites of Layer V SMI-32-positive neurons in each hemisphere in two intact monkeys (A, B) and in three SCI monkeys (D–F). For each monkey, the IDCD are reported in the upper right angle. G, Neuronal reconstruction example of apical dendrite of a Layer V SMI-32-positive neuron. H–L, Sholl profiles of apical dendrites of Layer V SMI-32-positive neurons in each hemisphere in two intact monkeys (H, I) and in three SCI monkeys (J–L). The curves represent the mean intersection values ± SD. As statistical test, a two-way ANOVA wit Bonferroni’s multiple comparison post hoc test was performed (*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001). The p values for the distance to soma main effect (up) and hemisphere main effect (right) are report for each monkey. # in the upper right angle means a significative p value for the interaction between the distance to soma and the hemisphere main effect. Figure Contributions: A. Contestabile and M. Lucchini performed the microscopic analysis of the histologic sections. A. Contestabile analyzed the data.