Microglia activation. (A) Nitrite levels were measured in microglial media after 24 h incubation with fresh media (control), MCP-1 (10-200 ng/ml), LPS (0.1, 1 μg/ml) or MCP-1 50 ng/ml in combination with LPS. Data are expressed as μM of nitrites and are expressed as mean ± SE for n = 10 replicates per group. ***p < 0.0001 versus control, p < 0.005 versus LPS 1 μg/ml (a). (B) Microglia were incubated for 24 h with fresh media (control), LPS 1 μg/ml, MCP-1 50 ng/ml or the combination of LPS and MCP-1 at the indicated concentrations. RNA was isolated and NOS2 mRNA levels determined by RT-PCR. Data are expressed as percentage of control values (set to 100%); ***p < 0.0001 versus control. Data are expressed as mean ± SE for n = 6 replicates per group. (C) Representative images corresponding to microglia incubated for 24 h with fresh media (control), MCP-1 (50 ng/ml) or LPS 1 μg/ml. The images shown are representative of experiments done on three separate microglial preparations.