Plate 1: Representative Micrographs of Thymus. (A,B) Control rat tissue showing that thymus is partially subdivided into lobules separated by thin bands of connective tissue (curved arrow). Cortex (C) contains numerous densely packed cells of thymocytes (T), epithelial cells (arrowhead), and deeply stained bodies (white arrows) and tingible body macrophages (arrow) enclosing paler staining medulla (M) with Hassell’s corpuscle (double arrows). (C, D) MSG-treated rat tissue evidencing thymic lobules separated by relatively thick bands (curved arrow) contain congested vessel (v). Dark-staining cortex shows increased numbers of lymphoytes with darkly stained nuclei (white arrows) and tingible body macrophages (arrow). The medulla shows many empty spaces (crossed arrow), Hassell’s corpuscles (double arrows) and vacuolated epithelial cells (arrowhead). H&E stain. (Images scale bar, A,C,; 100 μm & B, D; 25 μm) (E, F): Dramatically-affected lobules show expanded connective tissue septa (curved arrow) by edematous fluid with a few interspersed inflammatory cells. Marked decrease in cortical thymocytes with different sizes and darkly-stained nuclei and dilated blood sinusoids (s) are seen. Medullary region is enlarged and re-populated with small lymphocytes (arrow) and dilated blood sinusoids (s). Cortical-medullary differentiation is difficult to determine. (G, H) Recovery group rat tissues with re-population of cortical thymocytes enclosing paler staining medulla are seen. Relatively thick connective tissue septa (curved arrow) and T-lymphocytes with darkly stained nuclei are also seen (white arrow). H&E stain. (Images scale bar, E,G; 100 μm & F,H; 25 μm)