Time-dependent gray matter damage in the contusion-induced SCI model. Contusion insult (150 kdyn) was applied to T9 of rat spinal cords. Longitudinal sections (30 μm) were obtained from 6 h to 14 d after the injury. (A) Sections were stained with cresyl violet. Sham-operated animals were employed as controls. In left panels, gray matter (G) was intensely stained with cresyl violet (compare to white matter, W). Right panels (Area 1 and Area 2) are higher magnifications of Areas 1 and 2 indicated in the left panels. Large (black arrows) and small (white arrows) Nissl+ cells are neurons and glial cells, respectively. At 7 d, many small Nissl+ cells (white arrowheads) appeared. Dotted white lines in the left panel show the positions of Area 1 and Area 2 relative to the contusion sites. Black arrowheads: contusion sites. (B) The most damaged cresyl violet-stained sections obtained at the indicated times were selected, and the extent of damage was evaluated by measuring the length of gray matter, as described in Materials and Methods. Black arrowheads: contusion sites. (C) Graphic presentation of the values measured in (B). Values in (C) are means ± SEMs of four to six animals. (D) Relative positions of contusion site (arrowhead at T9), primary damage site (epicenter), delayed damage-occurring site (penumbra 1), and delayed damage-absent site (penumbra 2). Spinal cords between T7 and T10 were removed and analyzed. Scale bars: 500 μm (left panel in A) and 25 μm (right panel in A). Data shown are representative of three independent experiments. In each experiment, four to six animals were used for each time point.