Activation of microglial cells and the expression of proinflammatory mediators following LPS injection. Iba-1 IHC staining showed the processes of microglial cells are ramified in control (A). At six hours after LPS injection the processes of microglial cells became thicker and shorter, and cell bodies became larger (B). ISH results showed IL-1β mRNA expression appeared in choroid plexus and hippocampal fimbria at one hour after LPS injection (arrows in C), and occurred extensively in the whole brain at six hours after LPS injection, here is an example in cerebral cortex (D). iNOS mRNA expression appeared only in choroid plexus at twenty-four hours after LPS injection (arrows in E), and then developed in the cerebral cortex (F). Quantitative analysis of the number of IL-1β mRNA- (G) and iNOS mRNA- (H) expressing cells in the cerebral cortex at different time points after LPS injection. *P < 0.05, compared with six hours, twelve hours (G); forty-eight hours, seventy-two hours (H). Scale bar = 20 μm (A, B, F); 50 μM (C); 50 μM (D, E). n = 5 per condition. Cat C, cathepsin C; Iba-1, ionized calcium binding adaptor molecule-1; IHC, immunohistochemistry; iNOS, inducible nitric oxide synthase; ISH, in situ hybridization; LPS, lipopolysaccharide.