Time course of c-Fos expression in the cords incubated in 25°C normal aCSF. Photomicrographs show transverse sections of T3 from three preparations with different incubation time in hours: 1.5 (A), 3 (B), and 6 (C). After 1.5 h incubation, limited cells with intense c-Fos immunoreactivity (IR) were found in the IML (Ai). As the incubation time was prolonged to 3 h, c-Fos-positive cells in the IML increased (Bi), and were comparably abundant in the cord after the 6 h incubation (Ci). Note the presence of c-Fos-positive cells in the ventral horn and around the cc in (A) and the absence of these cells in (B, C). Also note the time-dependent spread of cell distribution to medial ventrolateral regions of the cord. Histological abbreviations in this and following figures: cc, central canal; dcs, dorsal corticospinal tract; IML, intermediolateral cell column; lfu, lateral funiculus. Scale bars = 150 μm in (A-C) and 30 μm in (Ai-Ci). Detailed distributions of c-Fos-positive cells in the cord are shown in following figures.