Purpose
Cerebral white matter damages are often observed in human ischemic cerebrovascular disease and have been thought to contribute to cognitive impairment. This damage can be induced in rat brains under chronic cerebral hypo-perfusion by the permanent occulusion of both internal carotid arteries. However it remains uncertain how the oxidasive stress damages the white matter in chronic cerebral hypo-perfuion. Therefore, we investigated that the oxidative stress contributed to the white matter damages in chronic cerebral hypo-perfusion in rat model, using immunohistochemistory for 4-hydroxy-2-nonenal (HNE) of the oxidative stress marker. We observed the relationships of phosphorylated cyclic AMP responsive element binding protein (p-CREB) for the progression of white matter damage.
Method
Studies were conducted in 7∼8weeks old male Wister rat. (n=3/group) Rat underwent permanently ligation of the bilateral internal carotid arteries. Cerebral blood flow (CBF) was measured using echo doppler method. 7, 14, 21, 28 days after the ischemia, the brains were perfusion-fixed 4% paraformaldehyde in 0.1 M phosphate buffer. The fixed brains were 20-micrometers thick coronal sections were prepared in a cryostat. To clarify the distribution and function of glial cells, staining of H-E, Kluver-Barrela, and immunohistochemical staining of glial fibrillary acid protein (GFAP), ionized calcium binding adapter molecule 1 (Iba-1), GST-pi, HNE, and p-CREB were performed. For behavioral study, Morris's water maze test was performed at 7, 14, 21, 28 days after the ischemia.
Result
After the operation, CBF was decreased about 50% compared with pre-operation. However 14 days after the ischemia, CBF appeared to be slightly recovered. White matter damages were observed as the impairment of nerve fibers by H-E and Kluver-Barrela stain. Immunoreactivity for GFAP and Iba-1 were observed at 7days after ischemia and GFAP positive astrocyte and Iba-1 positive microglia were observed until 28 days after the ischemia. GST-pi and HNE were observed at 7days after the ischemia, marked increase in GST-pi positive oligodendroglia and HNE positive cells were observed at 14 days. These cells were gradually decreased in a time dependent manner. Immunoreactivity for p-CREB was observed at 7days after the ischemia, gradually decreased in time course. Morris's water maze test in chronic hypo-perfusion group showed impairment of spatial learning compared with sham group. (p<0.05)
Conclusion
These results demonstrated that the accumulation of HNE-modified proteins and the suppression of p-CREB might be an important role of white matter damage for the chronic cerebral hypo-perfusion.