Cortical microinfarcts (CMIs) observed in brains of patients with Alzheimer’s disease tend to be located close to vessels afflicted with cerebral amyloid angiopathy (CAA). CMIs in Alzheimer’s disease are preferentially distributed in the arterial borderzone, an area most vulnerable to hypoperfusion. However, the causal association between CAA and CMIs remains to be elucidated. This study consists of two parts: (1) an observational study using postmortem human brains (n = 31) to determine the association between CAA and CMIs, and (2) an experimental study to determine whether hypoperfusion worsens CAA and induces CMIs in a CAA mouse model. In postmortem human brains, the density of CMIs was 0.113/cm2 in mild, 0.584/cm2 in moderate, and 4.370/cm2 in severe CAA groups with a positive linear correlation (r = 0.6736, p < 0.0001). Multivariate analysis revealed that, among seven variables (age, disease, senile plaques, neurofibrillary tangles, CAA, atherosclerosis and white matter damage), only the severity of CAA was a significant multivariate predictor of CMIs (p = 0.0022). Consistent with the data from human brains, CAA model mice following chronic cerebral hypoperfusion due to bilateral common carotid artery stenosis induced with 0.18-mm diameter microcoils showed accelerated deposition of leptomeningeal amyloid β (Aβ) with a subset of them developing microinfarcts. In contrast, the CAA mice without hypoperfusion exhibited very few leptomeningeal Aβ depositions and no microinfarcts by 32 weeks of age. Following 12 weeks of hypoperfusion, cerebral blood flow decreased by 26% in CAA mice and by 15% in wild-type mice, suggesting impaired microvascular function due to perivascular Aβ accumulation after hypoperfusion. Our results suggest that cerebral hypoperfusion accelerates CAA, and thus promotes CMIs.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-011-0925-9) contains supplementary material, which is available to authorized users.

White matter hyperintensities are associated with post-stroke cognitive dysfunction, but the underlying mechanisms are unclear. Chen et al. provide evidence from human and experimental studies that clasmatodendrosis – a marker of irreversible astrocyte damage – and gliovascular abnormalities are increased in the frontal white matter of subjects who succumb to vascular dementia.

Background and Purpose-The effect of telmisartan, an angiotensin II Type 1 receptor blocker with peroxisome proliferator-activated receptor-␥-modulating activity, was investigated against spatial working memory disturbances in mice subjected to chronic cerebral hypoperfusion. Methods-Adult C57BL/6J male mice were subjected to bilateral common carotid artery stenosis using external microcoils. Mice received a daily oral administration of low-dose telmisartan (1 mg/kg per day), high-dose telmisartan (10 mg/kg per day), or vehicle with or without peroxisome proliferator-activated receptor-␥ antagonist GW9662(1 mg/kg per day) for all treatments for 30 days after bilateral common carotid artery stenosis. Cerebral mRNA expression of monocyte chemoattractant protein-1 and tumor necrosis factor-␣ was measured 30 days after bilateral common carotid artery stenosis, and postmortem brains were analyzed for demyelinating change with Klüver-Barrera staining and immunostained for glial, oxidative stress, and vascular endothelial cell markers. Spatial working memory was assessed by the Y-maze test. Results-Mean systolic blood pressure and cerebral blood flow did not decrease with low-dose telmisartan but significantly decreased with high-dose telmisartan. Low-dose telmisartan significantly attenuated, but high-dose telmisartan provoked, spatial working memory impairment with glial activation, oligodendrocyte loss, and demyelinating change in the white matter. Such positive effects of low-dose telmisartan were partially offset by cotreatment with GW9662. Consistent with this, low-dose telmisartan reduced the degree of oxidative stress of vascular endothelial cells and the mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-␣ compared with vehicle. Conclusions-Anti-inflammatory and antioxidative effects of telmisartan that were exerted in part by peroxisome proliferator-activated receptor-␥ activation, but not its blood pressure-lowering effect, have protective roles against cognitive impairment and white matter damage after chronic cerebral hypoperfusion. (Stroke. 2010;41:1798-1806.)

Vascular cognitive impairment (VCI) or vascular dementia occurs as a result of brain ischemia and represents the second most common type of dementia after Alzheimer’s disease. To explore the underlying mechanisms of VCI, several animal models of chronic cerebral hypoperfusion have been developed in rats, mice, and primates. We established a mouse model of chronic cerebral hypoperfusion by narrowing the bilateral common carotid arteries with microcoils, eventually resulting in hippocampal atrophy. In addition, a mouse model of white matter infarct-related damage with cognitive and motor dysfunction has also been established by asymmetric common carotid artery surgery. Although most experiments studying chronic cerebral hypoperfusion have been performed in rodents because of the ease of handling and greater ethical acceptability, non-human primates appear to represent the best model for the study of VCI, due to their similarities in much larger white matter volume and amyloid β depositions like humans. Therefore, we also recently developed a baboon model of VCI through three-vessel occlusion (both the internal carotid arteries and the left vertebral artery). In this review, several animal models of chronic cerebral hypoperfusion, from mouse to primate, are extensively discussed to aid in better understanding of pathophysiology of VCI.