Cerebral Microvascular Damage Occurs Early after Hypoxia–Ischemia via nNOS Activation in the Neonatal Brain

Abstract

Microvascular injury early after hypoxic ischemia (HI) may contribute to neonatal brain damage. N-methyl-D-aspartate receptor overstimulation activates neuronal nitric oxide synthases (nNOS). We hypothesized that microvascular damage occurs early post-HI via nNOS activation and contributes to brain injury. Postpartum day-7 rat pups were treated with 7-nitroindazole (7-NI) or aminoguanidine (AG) before or after HI. Electron microscopy was performed to measure neuronal and endothelial cell damage. There were vascular lumen narrowing at 1 hour, pyknotic neurons at 3 hours, and extensive neuronal damage and loss of vessels at 24 hours post HI. Early after reoxygenation, there were neurons with heterochromatic chromatin and endothelial cells with enlarged nuclei occluding the lumen. There was also increased 3-nitrotyrosin in the microvessels and decreased cerebral blood perfusion. 7-NI and AG treatment before hypoxia provided complete and partial neuroprotection, respectively. Early post-reoxygenation, the AG group showed significantly increased microvascular nitrosative stress, microvascular interruptions, swollen nuclei that narrowed the vascular lumen, and decreased cerebral perfusion. The 7-NI group showed significantly decreased microvascular nitrosative stress, patent vascular lumen, and increased cerebral perfusion. Our results indicate that microvascular damage occurs early and progressively post HI. Neuronal nitric oxide synthases activation contributes to microvascular damage and decreased cerebral perfusion early after reoxygenation and worsens brain damage.

Early Recruitment of Cerebral Microcirculation by Neuronal Nitric Oxide Synthase Inhibition in a Juvenile Ischemic Rat Model

“…However, a similar vasoactive effect is also rapidly observed with 7-NI given after re-flow, suggesting that 7-NI, nevertheless, may have a direct and/or indirect role in collateral recruitment and patency in the P14 rat. Our data at P14 (with one dose of 7-NI) highlight those reported in the ischemic P7 rat pup (only demonstrated with US imaging [9] ), and in the hypoxic-ischemic P7 rat [10] . We cannot completely exclude that using others doses, this effect would be or not seen, because by using various doses of nNOS inhibitor(s), authors reported opposite effects (see the discussion in ref [25] ).…”

“…In the adult brain, 7-NI significantly reduces arteriole dilation and prevents the increase in erythrocyte velocity and flux through capillaries (thus reducing hyperemia) during early reperfusion [12,24] . Interestingly, 7-NI significantly decreased microvascular nitrosative stress, improved patent vascular lumen, reduced blood-brain barrier damage, and increased cerebral perfusion in the neonatal model of hypoxia-ischemia [10] . As we report here that 7-NI did not reduce BF in the BT, our data also suggest that collateral supply may be originated in the occipital pole toward the distal segment of the MCA (penumbra).…”

“…The use of a neuronal NO synthase (nNOS) inhibitor was also tested in this P14 stroke model, as it has been recently reported to increase BF in the ischemic P7 rat brain [9] and cerebral perfusion in the neonatal model of hypoxia-ischemia in P7 rat [10] .…”

The role of the nitric oxide pathway in brain injury and its treatment — From bench to bedside

“…Inhaled NO given during the reperfusion period appears to have neurotoxic effects (Charriaut-Marlangue et al, 2012). This may be due to the activation of nNOS as inhibition leads to improved CBF and perfusion early after reoxygenation (Hsu et al, 2014). As in the developed brain, iNOS activation may be responsible for damage in the late (N 24 h) phase (Higuchi et al, 1998).…”

Targeting the vasculature for cerebroprotection in the immature brain

“…For many other brain disorders, impaired vascular health seems at least partially to contribute to the damage. Hsu et al recently found that microvascular damage occurs early and progressively after neonatal HI, and interventions that reduced vascular injury also improved outcome (Hsu et al, 2014). Both animal and clinical studies have shown damage to the blood-brain barrier following neonatal HI, further indicating that these insults are associated with vascular damage (Kumar et al, 2008;Muramutsi et al, 1997).…”