Objective To follow glial cell activation and delayed neuronal death in vivo using MEMRI.
Methods The RCA was ligated in 14 P7 Wistar pups followed by 8% O2 for 75 min. Eight HI pups were injected with MnCl2 (100 mM, 40 mg/kg) i.p. 8 hrs after HI, and 24 hrs prior to MRI at 6 wks. Six HI pups received NaCl. 3D T1-w MRI (7T) was performed 1 and 6 wks after HI. Pups were sacrificed at 6 wks. Coronal slices were stained with HE, MAP-2, ED-1, GFAP and Fluorojade B and compared with MRI.
Results ME areas at 1 week appeared cystic at 6 wks. At 6 wks, ED-1 positive cells (microglia), GFAP positive cells (astrocytes) and a few Fluorojade B cells (dying neurons) were seen on the brim of the remaining cortex, hippocampus and amygdale in most animals (Figure A,B,C), and correlated with ME on MRI in HI+Mn pups, but not in HI Controls. The clearest ME-area at 6 weeks was in thalamus and was related to calcification (Fig D).
Conclusion Inflammation can still be detected 6 wks after HI in the neonatal rat brain in vivo using MEMRI, but manganese also accumulates in calcifications.