GFAP activation correlates with tumor location and tumor size. (A) GFAP-luc mice were injected with RFP-labeled human glioma cells, incubated for 4 weeks and six 1 mm coronal brain sections (numbered 1-6, anterior to posterior) were made for each animal. Tumor (red, left panel) and tumor-induced GFAP activation (luciferase, right panel) were localized in the same sections. A representative image of brain sections is shown. (B) Tumor burden (measured by its fluorescent intensity) and GFAP activation (measured by luciferase activity) from four tumor-bearing animals (at least five sections from each animal) were quantified. GFAP activity correlates with tumor size. Kendall's rank correlation test, two-sided, coefficient index τ = 0.54, P < 0.01.