Upregulation of CXCR2 ligands in the brain after exposure to bacterial toxins. a, Quantification of the mRNAs encoding each of the CXCR2 ligands by quantitative RT-PCR using RNA samples prepared from the brains of mice killed 6 h after intraperitoneal injection of PBS, PTX (20 μg/kg), or LPS (1 mg/kg). The means were compared with the Kruskal-Wallis test (P-values as indicated) followed by post hoc Wilcoxon tests. For the weakly expressed genes, the means are indicated in parentheses. *Significantly different from the PBS group. Δ = fold change relative to PBS. n = 5 per group. b, Dark-field micrographs showing in situ hybridization signals for CXCL1 or CXCL2 mRNA in the cerebral cortex of mice treated with PTX or LPS. No signal was detected in control mice (PBS). Arrows show clusters of emulsion grains indicating the presence of cells expressing the transcripts. Scale bar = 100 μm. c, Double labeling for CXCL1 mRNA (black grains, in situ hybridization) and different cell type-specific markers (red-brown, immunohistochemistry) in brain sections from PTX-treated mice. Arrows indicate double-labeled cells. Arrowheads show examples of immunostained cell bodies negative for CXCL1 mRNA. *Blood vessel lumen. Scale bar = 10 μm.