Effect of neonatal DEX treatment on HI-induced brain injury. (A) Schematic representation of the experimental design for examining the effect of neonatal DEX treatment on subsequent HI-induced brain injury. Rat pups were treated with a 3-day tapering course (0.5, 0.3 and 0.1 mg/kg) of DEX or equal volume of SAL from P1 to P3 and were subjected to cerebral HI by unilateral ligation of the right common carotid artery followed by exposure to hypoxia (92% N2 + 8% O2) for 2 hours on P7. Brain injury was analyzed on P8. (B) TTC (left column) and Nissl staining (right column) of serial coronal sections 24 hours after HI. DEX-treated group exhibited more marked infarctions (white areas), particularly in the ipsilateral cerebral cortex and the hippocampus, than SAL-treated group. Scale bar is 0.5 cm. (C) Brain injury was quantified at 24 hours after HI by TTC staining. Sham denotes animals received right carotid artery exposure without ligation and were exposed to normoxic condition. (D) Fluorescent TUNEL staining (TUNEL-positive cells are green) with DAPI counterstain (blue) was utilized to visualize TUNEL labeling of apoptotic cells in the frontal cortex of neonatal SAL- or DEX-treated rat pups 24 hours after HI. Similar results were observed in another four rat pups in each group. Scale bar is 100 μm. The numbers in parentheses indicate the number of animals examined. Data are presented as means ± S.E. M.