Role of nitric oxide synthases in early blood-brain barrier disruption following transient focal cerebral ischemia.

The role of nitric oxide synthases (NOSs) in early blood-brain barrier (BBB) disruption was determined using a new mouse model of transient focal cerebral ischemia. Ischemia was induced by ligating the middle cerebral artery (MCA) at its M2 segment and reperfusion was induced by releasing the ligation. The diameter alteration of the MCA, arterial anastomoses and collateral arteries were imaged and measured in real time. BBB disruption was assessed by Evans Blue (EB) and sodium fluorescein (Na-F) extravasation at 3 hours of reperfusion. The reperfusion produced an extensive vasodilation and a sustained hyperemia. Although expression of NOSs was not altered at 3 hours of reperfusion, L-NAME (a non-specific NOS inhibitor) abolished reperfusion-induced vasodilation/hyperemia and significantly reduced EB and Na-F extravasation. L-NIO (an endothelial NOS (eNOS) inhibitor) significantly attenuated cerebral vasodilation but not BBB disruption, whereas L-NPA and 7-NI (neuronal NOS (nNOS) inhibitors) significantly reduced BBB disruption but not cerebral vasodilation. In contrast, aminoguanidine (AG) (an inducible NOS (iNOS) inhibitor) had less effect on either cerebral vasodilation or BBB disruption. On the other hand, papaverine (PV) not only increased the vasodilation/hyperemia but also significantly reduced BBB disruption. Combined treatment with L-NAME and PV preserved the vasodilation/hyperemia and significantly reduced BBB disruption. Our findings suggest that nNOS may play a major role in early BBB disruption following transient focal cerebral ischemia via a hyperemia-independent mechanism

Protein expression of nNOS and eNOS in striatum (A) and parietal cortex (B) punched at the peri-infarct area and the contralateral corresponding areas at 3 hours of reperfusion.

<p>Protein expression of nNOS and eNOS in striatum (A) and parietal cortex (B) punched at the peri-infarct area and the contralateral corresponding areas at 3 hours of reperfusion.</p

Effects of topical treatment with L-NAME, L-NIO, L-NPA, 7-NI and AG on EB (A) and Na-F (B) extravasation at 3 hours of reperfusion.

<p>Values are means ± SE for 8 mice in each group. *P<0.05 vs. Control.</p

Effects of topical treatment with PV and L-NAME on EB (A) and Na-F (B) extravasation at 3 hours of reperfusion.

<p>Values are means ± SE for 8 mice in each group. *P<0.05 vs. Control.</p

Effects of topical treatment with L-NAME, L-NIO and AG on vasodilation of the MCA (A–B), arterial anastomoses (C) and terminal branches of the ACA/PCA (D) during reperfusion.

<p>Values are means ± SE for 8 mice in each group. *P<0.05 vs. Control.</p

Representative cranial windows showing MCAL/reperfusion induced by ligating (A) and releasing (B) the MCA at its M2 segment and the surface vasculature of frontal, parietal and temporal cortex before (C) and after (D) injection of EB and Na-F.

<p>Representative cranial windows showing MCAL/reperfusion induced by ligating (A) and releasing (B) the MCA at its M2 segment and the surface vasculature of frontal, parietal and temporal cortex before (C) and after (D) injection of EB and Na-F.</p

Effects of topical treatment with L-NPA and 7-NI on vasodilation of the MCA (A–B), arterial anastomoses (C) and terminal branches of the ACA/PCA (D) during reperfusion.

<p>Values are means ± SE for 8 mice in each group. *P<0.05 vs. Control.</p