5-FU induces transient inflammation and apoptosis of microvasculature endothelial cells in a subset of treated animals. Representative photographs showing the inflammatory response on day 1 after treatment with (a) vehicle or (b) 5-FU treatment as indicated by immunostaining for the activated microglia/macrophage marker F4/80. The basal level of F4/80 staining was very low in the controls but increased after treatment. These sections are from the CC (the region between the two dotted lines), with similar evidence of inflammation seen in the DG and cortex of this same mouse. The scale bar represents 50 μm. (c-e) TUNEL/PECAM (CD31) double immunostaining was performed in 5-FU-treated animals, with representative images taken from the DG showing double-labeling of the vascular endothelial cell marker PECAM (CD31) with TUNEL+ nuclei. In the subset of animals in which evidence of endothelial cell death was observed, similar TUNEL+ profiles were also found in the cortex and CC.