Abstract 3076: Microthrombosis and Microcirculatory Constriction after Experimental Subarachnoid Hemorrhage
Subarachnoid hemorrhage (SAH) accounts for about 6% of cases of stroke and afflicts more than 50,000 individuals annually in North America. Cerebral angiographic vasospasm has been recognized as being commonly associated with aneurysmal SAH for many years. However, recent studies showed that angiographic vasospasm does not always predict the location of infarction, and alleviation of vasospasm did not result in better outcome in SAH patients. One hypothesis gaining more attention is that separate or interacting pathways may cause delayed cerebral ischemia (DCI) after SAH, and that these, in combination with angiographic vasospasm, lead to poor outcome. Postulated mechanisms include acute brain injury, microcirculatory dysfunction, microthromboembolism, and cortical spreading ischemia. The focus of this study is to determine first, if experimental SAH is associated with microcirculatory constriction and thrombosis, second, to determine if any microthromboemboli are thrombi or emboli and third, to determine if these changes correlate with brain injury.
We used a prechiasmatic cistern injection model of SAH. 15 mice (n = 5 for each group) underwent sham surgery or injection of 100 μl 0.9% NaCl or autologous blood into the prechiasmatic cistern. Mice were sacrificed 2 days later and brains were examined by scanning (SEM) and transmission electron microscopy (TEM) and by immunohistochemistry for fibrinogen and P-selectin. Neuronal apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling. Nitric oxide (NO) was measured with 4,5-diaminofluorescein-2-diacetate. TEM and SEM demonstrated that mice with SAH had significantly more arterioles filled with lesions consistent with microthrombi. Quantification of microvessel constriction showed significantly decreased microvessel lumen area but increased micrvessel wall thickness in animals with SAH compared to sham or saline-injected controls (P < 0.01, ANOVA). This was accompanied by decreased concentration of NO in mice with SAH compared to saline and sham mice. There are a significantly increased number of TUNEL positive cells in both cerebral cortex and hippocampus (p < 0.01). Marked increase of fibrinogen positive microvessels are found in both cerebral cortex and hippocampus (p < 0.05 in cortex, p < 0.001 in hippocampus). The number of microthrombi correlates with the number of apoptotic neurons in cerebral cortex (R2=0.98). Cell membrane P-selectin is increased in the endothelium of arterioles in mice with SAH. This correlates with decreased NO in the brain.
In conclusion, SAH causes microthrombosis and constriction of arterioles, which correlates with neuronal death. Increased P-selectin and decreased NO suggest a mechanism for microthrombosis and arteriolar constriction.
- © 2012 by American Heart Association, Inc.