Do in vivo experimental models reflect human cerebral small vessel disease? A systematic review

Differential gene expression in multiple neurological, inflammatory and connective tissue pathways in a spontaneous model of human small vessel stroke

AIMS

Cerebral small vessel disease (SVD) causes a fifth of all strokes plus diffuse brain damage leading to cognitive decline, physical disabilities and dementia. The aetiology and pathogenesis of SVD are unknown, but largely attributed to hypertension or microatheroma.

METHODS

We used the spontaneously hypertensive stroke-prone rat (SHRSP), the closest spontaneous experimental model of human SVD, and age-matched control rats kept under identical, non-salt-loaded conditions, to perform a blinded analysis of mRNA microarray, qRT-PCR and pathway analysis in two brain regions (frontal and mid-coronal) commonly affected by SVD in the SHRSP at age five, 16 and 21 weeks.

RESULTS

We found gene expression abnormalities, with fold changes ranging from 2.5 to 59 for the 10 most differentially expressed genes, related to endothelial tight junctions (reduced), nitric oxide bioavailability (reduced), myelination (impaired), glial and microglial activity (increased), matrix proteins (impaired), vascular reactivity (impaired) and albumin (reduced), consistent with protein expression defects in the same rats. All were present at age 5 weeks thus predating blood pressure elevation. 'Neurological' and 'inflammatory' pathways were more affected than 'vascular' functional pathways.

CONCLUSIONS

This set of defects, although individually modest, when acting in combination could explain the SHRSP's susceptibility to microvascular and brain injury, compared with control rats. Similar combined, individually modest, but multiple neurovascular unit defects, could explain susceptibility to spontaneous human SVD.

Pathophysiological Links Among Hypertension and Alzheimer's Disease

Genetic Alzheimer's disease (AD) accounts for only few AD cases and is almost exclusively associated to increased amyloid production in the brain. Instead, the majority of patients is affected with the AD sporadic form with typical alterations of clearance mechanisms of the brain. Most studies use engineered animal models that mimic genetic AD. Since it is emerging the existence of a pathophysiological link between cardiovascular risk factors and AD etiology, the strategy to develop animal models of vascular related AD pathology could be the key toward developing novel successful therapies. On this issue, we have demonstrated that mice that have been chronically subjected to high blood pressure show deposition of amyloid aggregates, the main histological feature of AD, and loss of memory in specific tasks. More importantly, we have identified that the hypertensive challenge increases the expression of the receptor for advanced glycated end products (RAGE), leading to beta-amyloid (Aβ) deposition and learning impairment. Here, we review different murine models of hypertension, induced either pharmacologically or mechanically, leading in the long time to plaque formation in the brain parenchyma and around blood vessels. The major findings obtained till now in this particular experimental setting allow us to suggest that this appears to be a unique possibility to study the pathogenetic mechanisms of sporadic AD triggered by vascular risk factors.

Endothelin-1-induced mini-stroke in the dorsal hippocampus or lateral amygdala results in deficits in learning and memory

Functional and structural alterations in brain connectivity associated with brain ischemia have been extensively studied. However, the mechanism whereby local ischemia in deep brain region affect brain functions is still unknown. Here, we first established a mini-stroke model by infusion of endothelin-1 (ET-1) into the dorsal hippocampus or the lateral amygdala, and then investigated how these mini-infarcts affected brain functions associated with these regions. We found that rats with ET-1 infusion showed deficit in recall of contextual fear memory, but not in learning process and recall of tone fear memory. In novel object task, ET-1 in the hippocampus also eliminated object identity memory. ET-1 in the lateral amygdale affected acquisition of fear conditioning and disrupted retention of tone-conditioned fear, but did not impair retention of contextual fear. These findings suggest that ET-1-induced mini-infarct in deep brain area leads to functional deficits in learning and memory associated with these regions.

Gliovascular disruption and cognitive deficits in a mouse model with features of small vessel disease

Cerebral small vessel disease (SVD) is a major cause of age-related cognitive impairment and dementia. The pathophysiology of SVD is not well understood and is hampered by a limited range of relevant animal models. Here, we describe gliovascular alterations and cognitive deficits in a mouse model of sustained cerebral hypoperfusion with features of SVD (microinfarcts, hemorrhage, white matter disruption) induced by bilateral common carotid stenosis. Multiple features of SVD were determined on T2-weighted and diffusion-tensor magnetic resonance imaging scans and confirmed by pathologic assessment. These features, which were absent in sham controls, included multiple T2-hyperintense infarcts and T2-hypointense hemosiderin-like regions in subcortical nuclei plus increased cerebral atrophy compared with controls. Fractional anisotropy was also significantly reduced in several white matter structures including the corpus callosum. Investigation of gliovascular changes revealed a marked increase in microvessel diameter, vascular wall disruption, fibrinoid necrosis, hemorrhage, and blood-brain barrier alterations. Widespread reactive gliosis, including displacement of the astrocytic water channel, aquaporin 4, was observed. Hypoperfused mice also demonstrated deficits in spatial working and reference memory tasks. Overall, gliovascular disruption is a prominent feature of this mouse, which could provide a useful model for early-phase testing of potential SVD treatment strategies.

DPP-4 inhibition with linagliptin ameliorates cognitive impairment and brain atrophy induced by transient cerebral ischemia in type 2 diabetic mice

Background

It is unclear whether dipeptidylpeptidase-4 (DPP-4) inhibition can counteract the impairment of cognitive function and brain injury caused by transient cerebral ischemia in type 2 diabetes. The present study was undertaken to test our hypothesis that linagliptin, a DPP-4 inhibitor, administration following transient cerebral ischemia can ameliorate cognitive impairment and brain injury in diabetic mice.

Methods

db/db mice, a model of obese type 2 diabetes, were subjected to transient cerebral ischemia by 17 min of bilateral common carotid artery occlusion (BCCAO), and were administered (1) vehicle or (2) linagliptin for 8 weeks or 1 week. For the long-term experiment on 8 weeks of linagliptin treatment, cognitive function, and volume and neuronal cell number of hippocampus and cortex were estimated in each group of mice. For the short-term experiment on 1 week of linagliptin treatment, cerebral IgG extravasation, Iba-1 positive cell number (reactive microglia), oxidative stress, and claudin-5 and gp91phox protein levels were measured in each group of mice.

Results

Linagliptin administration almost completely suppressed the circulating DPP-4 activity in db/db mice, but did not significantly reduce blood glucose or ameliorate glucose intolerance in db/db mice. Linagliptin administration following transient cerebral ischemia significantly counteracted cognitive impairment in diabetic mice, as estimated by water maze test and passive avoidance test. Linagliptin administration ameliorated the decrease in cerebral volume and neuronal cell number in hippocampus and cortex of diabetic mice. Linagliptin administration significantly reduced the increase in cerebral IgG extravasation and the increase in reactive microglia caused by transient cerebral ischemia in diabetic mice. Furthermore, linagliptin significantly suppressed the increase in cerebral oxidative stress in transient cerebral ischemia-subjected diabetic mice. Furthermore, linagliptin significantly increased cerebral claudin-5 and significantly decreased gp91phox in diabetic mice subjected to transient cerebral ischemia.

Conclusions

DPP-4 inhibition with linagliptin counteracted cognitive impairment and brain atrophy induced by transient cerebral ischemia in diabetic mice, independently of blood glucose lowering effect. This cerebroprotective effect of linagliptin was associated with the suppression of blood-brain barrier disruption and the attenuation of cerebral oxidative stress. Thus, our present work highlights DPP-4 inhibition as a promising therapeutic strategy for cognitive impairment and cerebral vascular complications in type 2 diabetes.

A novel mouse model of subcortical infarcts with dementia

Subcortical white matter (WM) is a frequent target of ischemic injury and extensive WM lesions are important substrates of vascular cognitive impairment (VCI) in humans. However, ischemic stroke rodent models have been shown to mainly induce cerebral infarcts in the gray matter, while cerebral hypoperfusion models show only WM rarefaction without infarcts. The lack of animal models consistently replicating WM infarct damage may partially explain why many neuroprotective drugs for ischemic stroke or VCI have failed clinically, despite earlier success in preclinical experiments. Here, we report a novel animal model of WM infarct damage with cognitive impairment can be generated by surgical implantation of different devices to the right and left common carotid artery (CCA) in C57BL/6J mice. Implantation of an ameroid constrictor to the right CCA resulted in gradual occlusion of the vessel over 28 d, whereas placement of a microcoil to the left CCA induced ∼50% arterial stenosis. Arterial spin labeling showed a gradual reduction of cerebral blood flow over 28 d post operation. Such reductions were more marked in the right, compared with the left, hemisphere and in subcortical, rather than the cortical, areas. Histopathological analysis showed multiple infarct damage in right subcortical regions, including the corpus callosum, internal capsule, hippocampal fimbria, and caudoputamen, in 81% of mice. Mice displaying such damage performed significantly poorer in locomotor and cognitive tests. The current mouse model replicates the phenotypes of human subcortical VCI, including multiple WM infarcts with motor and cognitive impairment.

Improving the translation of animal ischemic stroke studies to humans

Despite testing more than 1,026 therapeutic strategies in models of ischemic stroke and 114 therapies in human ischemic stroke, only one agent tissue plasminogen activator has successfully been translated to clinical practice as a treatment for acute stroke. Though disappointing, this immense body of work has led to a rethinking of animal stroke models and how to better translate therapies to patients with ischemic stroke. Several recommendations have been made, including the STAIR recommendations and statements of RIGOR from the NIH/NINDS. In this commentary we discuss additional aspects that may be important to improve the translational success of ischemic stroke therapies. These include use of tissue plasminogen activator in animal studies; modeling ischemic stroke heterogeneity in terms of infarct size and cause of human stroke; addressing the confounding effect of anesthesia; use of comparable therapeutic dosage between humans and animals based on biological effect; modeling the human immune system; and developing outcome measures in animals comparable to those used in human stroke trials. With additional study and improved animal modeling of factors involved in human ischemic stroke, we are optimistic that new stroke therapies will be developed.

Pharmacological treatment and prevention of cerebral small vessel disease: a review of potential interventions

Small vessel disease encompasses lacunar stroke, white matter hyperintensities, lacunes and microbleeds. It causes a quarter of all ischemic strokes, is the commonest cause of vascular dementia, and the cause is incompletely understood. Vascular prophylaxis, as appropriate for large artery disease and cardioembolism, includes antithrombotics, and blood pressure and lipid lowering; however, these strategies may not be effective for small vessel disease, or are already used routinely so precluding further detailed study. Further, intensive antiplatelet therapy is known to be hazardous in small vessel disease through enhanced bleeding. Whether acetylcholinesterase inhibitors, which delay the progression of Alzheimer's dementia, are relevant in small vessel disease remains unclear. Potential prophylactic and treatment strategies might be those that target brain microvascular endothelium and the blood brain barrier, microvascular function and neuroinflammation. Potential interventions include endothelin antagonists, neurotrophins, nitric oxide donors and phosphodiesterase 5 inhibitors, peroxisome proliferator‐activated receptor‐gamma agonists, and prostacyclin mimics and phosphodiesterase 3 inhibitors. Several drugs that have relevant properties are licensed for other disorders, offering the possibility of drug repurposing. Others are in development. Since influencing multiple targets may be most effective, using multiple agents and/or those that have multiple effects may be preferable. We focus on potential small vessel disease mechanistic targets, summarize drugs that have relevant actions, and review data available from randomized trials on their actions and on the available evidence for their use in lacunar stroke.

Next generation sequencing for systematic assessment of genetics of small-vessel disease and lacunar stroke

BACKGROUND

The pathogenesis of cerebral small-vessel disease (SVD) is still incompletely understood, although evidence from family and twin studies supports the hypothesis that genetic factors may contribute to SVD pathogenesis. Identification of genetic susceptibility factors for SVD may improve our knowledge on SVD pathogenesis. SVE-LA (Small Vessel and Lacunar) project is a multicenter prospective Lombardia region study aimed at applying innovative genetic technologies and accurate patient phenotyping to discover the genetic basis of SVD.

METHODS

A continuous series of subjects (aged 15-80 years) with a clinically and radiologically defined lacunar stroke referring to the participating Lombardia region stroke centers and an adequate number of age- and sex-matched controls are being included into the study. For each patient, clinical, demographic, instrumental, and familial data are collected applying standardized forms. After informed consent, a DNA sample for genetic analysis from patients and controls has been collected. The next generation sequencing (NGS) technology was applied to systematically screen patients for the most important genetic factors both monogenic and polygenic associated with SVD. The study includes also a centralized quantitative and qualitative analysis of neuroimaging studies.

RESULTS

Between March 2011 and October 2013, 212 lacunar stroke patients and 78 controls have been collected. Mean age of cases was 65.8 ± 11.1 years and 67% were men.

CONCLUSIONS

This is the first study applying systematically NGS technology on a wide series of lacunar stroke patients. A translational approach combining a systematic genetic screening with a detailed phenotyping may facilitate the discovery of genetic basis and improve our knowledge in the pathogenesis of SVD.

Antihypertensive drugs, prevention of cognitive decline and dementia: a systematic review of observational studies, randomized controlled trials and meta-analyses, with discussion of potential mechanisms

BACKGROUND

Chronic hypertension, particularly midlife high blood pressure, has been associated with an increased risk for cognitive decline and dementia. In this context, antihypertensive drugs might have a preventive effect, but the association remains poorly understood.

OBJECTIVES

The aim of this systematic review was to examine all published findings that investigated this relationship and discuss the mechanisms underlying the potential benefits of antihypertensive medication use.

METHODS

A literature search was conducted using MEDLINE, Embase, and the Cochrane Library for publications from 1990 onwards mentioning hypertension, antihypertensive drugs, cognitive decline, and dementia.

RESULTS

A total of 38 relevant publications, corresponding to 18 longitudinal studies, 11 randomized controlled trials, and nine meta-analyses were identified from the 10,251 articles retrieved in the literature search. In total, 1,346,176 subjects were included in these studies; the average age was 74 years. In the seven longitudinal studies assessing the effect of antihypertensive medication on cognitive impairment or cognitive decline, antihypertensive drugs appeared to be beneficial. Of the 11 longitudinal studies that assessed the effect of antihypertensive medication on incidence of dementia, only three did not find a significant protective effect. Antihypertensive medication could decrease the risk of not only vascular dementia but also Alzheimer's disease. Four randomized controlled trials showed a potentially preventive effect of antihypertensive drugs on the incidence of dementia or cognitive decline: SYST-EUR (Systolic Hypertension in Europe Study) I and II, with a 55% reduction in dementia risk (3.3 vs. 7.4 cases per 1,000 patient years; p<0.001); HOPE (Heart Outcomes Prevention Evaluation), with a 41% reduction in cognitive decline associated with stroke (95% confidence interval [CI] 6-63); and PROGRESS (Perindopril Protection against Recurrent Stroke Study), with a 19% reduction in cognitive decline (95% CI 4-32; p=0.01). Meta-analyses have sometimes produced conflicting results, but this may be due to methodological considerations. The lack of homogeneity across study designs, patient populations, exposition, outcomes, and duration of follow-up are the most important methodological limitations that might explain the discrepancies between some of these studies.

CONCLUSION

Antihypertensive drugs, particularly calcium channel blockers and renin-angiotensin system blockers, may be beneficial in preventing cognitive decline and dementia. However, further randomized controlled trials with longer periods of follow-up and cognition as the primary outcome are needed to confirm these findings.

Hypertension fails to disrupt white matter integrity in young or aged Fisher (F44) Cyp1a1Ren2 transgenic rats

Hypertension is linked with an increased risk of white matter hyperintensities; however, recent findings have questioned this association. We examined whether hypertension and additional cerebrovascular risk factors impacted on white matter integrity in an inducible hypertensive rat. No white matter hyperintensities were observed on magnetic resonance imaging either alone or in conjunction with ageing and high-fat diet. Aged hypertensive rats that were fed a high-fat diet had moderately reduced fractional anisotropy in the corpus callosum with no overt pathological features. Herein we show that moderate hypertension alone or with additional risk factors has minimal impact on white matter integrity in this model.

Cortical Ischemic Lesion Burden Measured by DIR Is Related to Carotid Artery Disease Severity

Background: Over time, exposure to cerebrovascular risk factors and carotid artery disease may cause multiple asymptomatic brain cortical and subcortical microinfarcts, which are commonly found at brain autopsy. So far, lack of convenient neuroimaging tools limited the investigation of grey matter ischemic damage in vivo. We applied the Double Inversion Recovery (DIR) sequence to explore the impact of carotid artery disease on intracortical ischemic lesion load in vivo, taking into account the impact of demographic characteristics and vascular risk factors. Methods: DIR was acquired in 62 patients with common cerebrovascular risk factors stratified in three groups according to carotid artery disease severity. Intracortical lesions scored on DIR (DIRlns) were classified by vascular territory, lobe and hemisphere. White matter hyperintensities (WMHs) volume was also quantified on Fluid Attenuated Inversion Recovery sequence (FLAIR). Results: Among demographic characteristics and cerebrovascular risk variables explored, General Linear Model indicated that age and carotid artery disease were significantly associated to DIRlns. After correcting for age, DIRlns load was found to be significantly dependent on carotid artery stenosis severity (F(2, 58) = 5.56, p = 0.006). A linear positive correlation between DIRlns and WMHs was found after correcting for age (p = 0.003). Conclusions: Carotid disease severity is associated with DIRlns accrual. Microembolism and impaired cerebral hemodynamics may act as physiopathological mechanisms underlying cortical ischemic damage. The role of other factors, such as small vessel disease and the possible interaction with carotid disease, remains to be further explored.

Spontaneous white matter damage, cognitive decline and neuroinflammation in middle-aged hypertensive rats: an animal model of early-stage cerebral small vessel disease

Introduction

Cerebral small vessel disease (cSVD) is one of the most prevalent neurological disorders. The progressive remodeling of brain microvessels due to arterial hypertension or other vascular risk factors causes subtle, but constant cognitive decline through to manifest dementia and substantially increases the risk for stroke. Preliminary evidence suggests the contribution of the immune system to disease initiation and progression, but a more detailed understanding is impaired by the unavailability of appropriate animal models. Here, we introduce the spontaneously hypertensive rat (SHR) as a model for early onset cSVD and unveiled substantial immune changes in conjunction with brain abnormalities that resemble clinical findings.

Results

In contrast to age-matched normotensive Wistar Kyoto (WKY) rats, male SHR exhibited non-spatial memory deficits. Magnetic resonance imaging showed brain atrophy and a reduction of white matter volumes in SHR. Histological analyses confirmed white matter demyelination and unveiled a circumscribed blood brain barrier dysfunction in conjunction with micro- and macrogliosis in deep cortical regions. Flow cytometry and histological analyses further revealed substantial disparities in cerebral CD45high leukocyte counts and distribution patterns between SHR and WKY. SHR showed lower counts of T cells in the choroid plexus and meningeal spaces as well as decreased interleukin-10 levels in the cerebrospinal fluid. On the other hand, both T and NK cells were significantly augmented in the SHR brain microvasculature.

Conclusions

Our results indicate that SHR share behavioral and neuropathological characteristics with human cSVD patients and further undergird the relevance of immune responses for the initiation and progression of cSVD.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-014-0169-8) contains supplementary material, which is available to authorized users.

Altered expression of neurofilament 200 and amyloid-β peptide (1-40) in a rat model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH) is damaging to white matter in the brain. So far few studies have investigated long-term axonal damage following CCH. The aim of this study was to investigate the involvement of neurofilament 200 (NF200) and amyloid-β (1-40) [Aβ (1-40)] in the pathological mechanism for neuronal damage, and to quantify changes in their expression over time in a rat model of CCH. A rat model of CCH was established using partial bilateral ligation of the common carotid arteries. The extent of stenosis was verified by measuring the changes in cerebral blood flow after surgery. Histology was used to assess hippocampal neuronal pathology, and immunohistochemistry was used to quantify the expression of NF200 and Aβ (1-40) at 2, 4, and 12 weeks after surgery. The cerebral blood flow reduced to 33.89 ± 5.48 % at 2 weeks, 36.83 ± 4.63 % at 4 weeks and 51.44 ± 4.90 % at 12 weeks. Immunofluorescence staining of neuronal perikarya sections revealed a marked decrease in the population of surviving pyramidal cells in the hippocampal CA1 region, a significant up-regulation in the expression of Aβ (1-40), and a significant reduction in the expression of NF200 following CCH surgery. Moreover, this trend was increasingly obvious over time. Our data demonstrate that CCH leads to axonal damage over time. We also confirmed that the expression of Aβ (1-40) and NF200 may be useful biomarkers of axonal damage following CCH.

Hemorrhagic Transformation after Tissue Plasminogen Activator Reperfusion Therapy for Ischemic Stroke: Mechanisms, Models, and Biomarkers

Intracerebral hemorrhagic transformation (HT) is well recognized as a common cause of hemorrhage in patients with ischemic stroke. HT after acute ischemic stroke contributes to early mortality and adversely affects functional recovery. The risk of HT is especially high when patients receive thrombolytic reperfusion therapy with tissue plasminogen activator, the only available treatment for ischemic stroke. Although many important publications address preclinical models of ischemic stroke, there are no current recommendations regarding the conduct of research aimed at understanding the mechanisms and prediction of HT. In this review, we discuss the underlying mechanisms for HT after ischemic stroke, provide an overview of the models commonly used for the study of HT, and discuss biomarkers that might be used for the early detection of this challenging clinical problem.

Hot water extract of wheat bran attenuates white matter injury in a rat model of vascular dementia

Vascular dementia is characterized by white matter lesions involving the demyelination and activation of astrocytes and microglia. In a previous study, we showed that the supernatant of a laboratory-scale, hot water extract of ground whole wheat (TALE) attenuated white matter injury and astrocytic activation in a rat model of bilateral common carotid artery occlusion (BCCAO). In the present study, we made several modifications to the hot water extraction process to remove starch and enable large-scale production. We used wheat bran (WB), which contains less starch, instead of ground whole wheat. In addition, we removed starch granules with a decanter before hot water extraction. The final product, wheat bran extract (WBE), contained 2.42% arabinose, a surrogate marker of arabinoxylan, which is an active constituent of WBE. Supplementation of the rat model of BCCAO with WBE (400 mg/kg/day) for 33 days attenuated white matter injury, which was assessed by Luxol Fast Blue staining, in the corpus callosum (cc) and optic tract (opt) regions. Attenuation of white matter injury in the opt region was accompanied by improvement of the pupillary light reflex. Immunochemical staining revealed that supplementation with WBE reduced astrocytic activation in the cc and opt regions and reduced microglial activation in the opt region. These findings indicate that supplementation with WBE is effective at attenuating white matter injury accompanied by the inhibition of astrocytic and microglial activation. Therefore, extracts from WB, a cheap by-product of wheat milling, can be developed as a nutraceutical to prevent vascular dementia, a disease for which there is no approved pharmaceutical treatment.

DWI and complex brain network analysis predicts vascular cognitive impairment in spontaneous hypertensive rats undergoing executive function tests

The identification of biomarkers of vascular cognitive impairment is urgent for its early diagnosis. The aim of this study was to detect and monitor changes in brain structure and connectivity, and to correlate them with the decline in executive function. We examined the feasibility of early diagnostic magnetic resonance imaging (MRI) to predict cognitive impairment before onset in an animal model of chronic hypertension: Spontaneously Hypertensive Rats. Cognitive performance was tested in an operant conditioning paradigm that evaluated learning, memory, and behavioral flexibility skills. Behavioral tests were coupled with longitudinal diffusion weighted imaging acquired with 126 diffusion gradient directions and 0.3 mm³ isometric resolution at 10, 14, 18, 22, 26, and 40 weeks after birth. Diffusion weighted imaging was analyzed in two different ways, by regional characterization of diffusion tensor imaging (DTI) indices, and by assessing changes in structural brain network organization based on Q-Ball tractography. Already at the first evaluated times, DTI scalar maps revealed significant differences in many regions, suggesting loss of integrity in white and gray matter of spontaneously hypertensive rats when compared to normotensive control rats. In addition, graph theory analysis of the structural brain network demonstrated a significant decrease of hierarchical modularity, global and local efficacy, with predictive value as shown by regional three-fold cross validation study. Moreover, these decreases were significantly correlated with the behavioral performance deficits observed at subsequent time points, suggesting that the diffusion weighted imaging and connectivity studies can unravel neuroimaging alterations even overt signs of cognitive impairment become apparent.

Harnessing the power of neuroplasticity for intervention

A fundamental property of the brain is its capacity to change with a wide variety of experiences, including injury. Although there are spontaneous reparative changes following injury, these changes are rarely sufficient to support significant functional recovery. Research on the basic principles of brain plasticity is leading to new approaches to treating the injured brain. We review factors that affect synaptic organization in the normal brain, evidence of spontaneous neuroplasticity after injury, and the evidence that factors including postinjury experience, pharmacotherapy, and cell-based therapies, can form the basis of rehabilitation strategies after brain injuries early in life and in adulthood.

Real-time high resolution laser speckle imaging of cerebral vascular changes in a rodent photothrombosis model

The study of hemodynamic and vascular changes following ischemic stroke is of great importance in the understanding of physiological and pathological processes during the thrombus formation. The photothrombosis model is preferred by researchers in stroke study for its minimal invasiveness, controllable infarct volume and lesion location. Nevertheless, there is a lack in high spatiotemporal resolution techniques for real time monitoring of cerebral blood flow (CBF) changes in 2D-profile. In this study, we implemented a microscopic laser speckle imaging (LSI) system to detect CBF and other vascular changes in the rodent model of photothrombotic stroke. Using a high resolution and high speed CCD (640 × 480 pixels, 60 fps), online image registration technique, and automatic parabolic curve fitting, we obtained real time CBF and blood velocity profile (BVP) changes in cortical vessels. Real time CBF and BVP monitoring has been shown to reveal details of vascular disturbances and the stages of blood coagulation in photothrombotic stroke. Moreover, LSI also provides information on additional parameters including vessel morphologic size, blood flow centerline velocity and CBF spatiotemporal fluctuations, which are very important for understanding the physiology and neurovascular pathology in the photothrombosis model.

Tissue oxygen is reduced in white matter of spontaneously hypertensive-stroke prone rats: a longitudinal study with electron paramagnetic resonance

Small vessel disease is associated with white-matter (WM) magnetic resonance imaging (MRI) hyperintensities (WMHs) in patients with vascular cognitive impairment (VCI) and subsequent damage to the WM. Although WM is vulnerable to hypoxic-ischemic injury and O₂ is critical in brain physiology, tissue O₂ level in the WM has not been measured and explored in vivo. We hypothesized that spontaneously hypertensive stroke-prone rat (SHR/SP) fed a Japanese permissive diet (JPD) and subjected to unilateral carotid artery occlusion (UCAO), a model to study VCI, would lead to reduced tissue oxygen (pO₂) in the deep WM. We tested this hypothesis by monitoring WM tissue pO₂ using in vivo electron paramagnetic resonance (EPR) oximetry in SHR/SP rats over weeks before and after JPD/UCAO. The SHR/SP rats experienced an increase in WM pO₂ from 9 to 12 weeks with a maximal 32% increase at week 12, followed by a dramatic decrease in WM pO₂ to near hypoxic conditions during weeks 13 to 16 after JPD/UCAO. The decreased WM pO₂ was accompanied with WM damage and hemorrhages surrounding microvessels. Our findings suggest that changes in WM pO₂ may contribute to WM damage in SHR/SP rat model, and that EPR oximetry can monitor brain pO₂ in the WM of small animals.

Recognition memory impairments after subcortical white matter stroke in mice

BACKGROUND AND PURPOSE

Small subcortical white matter infarcts are a common stroke subtype often associated with cognitive deficits. The lack of relevant models confined to white matter has limited the investigation of its pathophysiology. Here, we examine tissue and functional outcome after an ischemic lesion within corpus callosum in wild-type (WT) mice and in mice null for a gene, NOTCH3, linked to white matter ischemic injury in patients.

METHODS

WT and NOTCH3 knockout mice were subjected to stereotactic microinjections of the potent vasoconstrictor endothelin-1 at the level of periventricular white matter to induce a focal ischemic lesion. Infarct location was confirmed by MRI, and brains were examined for lesion size and histology; behavioral deficits were assessed ≤1 month in WT mice.

RESULTS

Ischemic damage featured an early cerebral blood flow deficit, blood-brain barrier opening, and a lesion largely confined to white matter. At later stages, myelin and axonal degeneration and microglial/macrophage infiltration were found. WT mice displayed prolonged cognitive deficit when tested using a novel object recognition task. NOTCH3 mutants showed larger infarcts and greater cognitive deficit at 7 days post stroke.

CONCLUSIONS

Taken together, these data show the usefulness of microinjections of endothelin-1 into periventricular white matter to study focal infarcts and cognitive deficit in WT mice. In short-term studies, stroke outcome was worse in NOTCH3 null mice, consistent with the notion that the lack of the NOTCH3 receptor affects white matter stroke susceptibility.

Animal models of vascular dementia: translational potential at the present time and in 2050

ABSTRACT: Vascular dementia is a heterogeneous syndrome, and includes subcortical ischemic vascular dementia. For translational research, subcortical ischemic vascular dementia is an appropriate target since this is the most prevalent subtype and exhibits relatively uniform clinical and neuropathological changes. These changes consist of hypertensive arteriolar changes, lacunar infarctions, hypertensive hemorrhage and white matter lesions. Among various species, rodents are most frequently used, but their small volume of white matter may impede analysis of white matter lesions. Primate models have a larger volume, but the degree of white matter lesions is inconsistent. Animal models should accommodate the effect of aging and comorbidities, and in the case of primate models, low accessibility should be overcome by repeated and quantitative examinations using modern neuroimaging techniques and functional measures, especially for memory and motor function. There is no model that replicates all features of subcortical ischemic vascular dementia and, therefore, rodent and primate models should be selected appropriately for translational research.

Vascular and parenchymal lesions along with enhanced neurogenesis characterize the brain of asymptomatic stroke-prone spontaneous hypertensive rats

BACKGROUND AND OBJECTIVES

Spontaneously hypertensive stroke-prone rats (SHRSPs) develop hypertension, cerebrovascular abnormalities and a stroke phenotype in association with higher levels of proteinuria. Here, we focus on cerebral abnormalities preceding lesions detectable by MRI.

METHODS

Longitudinal assessment of brain histology was performed in salt-loaded male SHRSPs (n = 26) and Wistar-Kyoto (WKY) normotensive control animals (n = 27). Groups of rats were sacrificed at different time points: Time 0, before the salt diet administration; Time 1, when proteinuria achieved 40 mg/day; Time 2, when proteinuria exceeded 100 mg/day.

RESULTS

At Time 0, no brain lesions were observed. At Time 1, changes of the cortical penetrating arteries, vasogenic oedema, lacunae and focal cell loss appeared in SHRSPs and worsened at Time 2, although no lesions were yet detected by MRI. Staining for proliferation markers revealed a significant boost of cellular mitosis in the subventricular zone (SVZ) of SHRSPs. Moreover, we observed higher immunopositivity for nestin, glial fibrillary acidic protein and doublecortin (markers for neural stem cells, astrocytes and immature neurons, respectively). At Time 2, apoptotic caspase-3 as well as 4-hydroxynonenal-positive neurons were associated to decreased nestin and doublecortin staining. High expression levels of glial fibrillary acidic protein were maintained in the SVZ. No comparative alterations and SVZ activation were recorded in WKYs.

CONCLUSION

Appearance of vascular changes in SHRSPs, before any MRI-detectable brain lesion, is coupled to active neural proliferation in the SVZ. With disease progression, only newborn astrocytes can survive, likely because of the neurotoxicity triggered by brain oedema and oxidative stress.

Improving Bioscience Research Reporting: The ARRIVE Guidelines for Reporting Animal Research

In the last decade the number of bioscience journals has increased enormously, with many filling specialised niches reflecting new disciplines and technologies. The emergence of open-access journals has revolutionised the publication process, maximising the availability of research data. Nevertheless, a wealth of evidence shows that across many areas, the reporting of biomedical research is often inadequate, leading to the view that even if the science is sound, in many cases the publications themselves are not “fit for purpose”, meaning that incomplete reporting of relevant information effectively renders many publications of limited value as instruments to inform policy or clinical and scientific practice [1–21]. A recent review of clinical research showed that there is considerable cumulative waste of financial resources at all stages of the research process, including as a result of publications that are unusable due to poor reporting [22]. It is unlikely that this issue is confined to clinical research [2–14,16–20].

Apoptosis signal-regulating kinase 1 is a novel target molecule for cognitive impairment induced by chronic cerebral hypoperfusion

OBJECTIVE

There are currently no specific strategies for the treatment or prevention of vascular dementia. White matter lesions, a common pathology in cerebral small vessel disease, are a major cause of vascular dementia. We investigated whether apoptosis signal-regulating kinase 1 (ASK1) might be a key molecule in cerebral hypoperfusion, associated with blood-brain barrier breakdown and white matter lesions.

APPROACH AND RESULTS

A mouse model of cognitive impairment was developed by inducing chronic cerebral hypoperfusion in white matter including the corpus callosum via bilateral common carotid artery stenosis (BCAS) surgery. BCAS-induced white matter lesions caused cognitive decline in C57BL/6J (wild-type) mice but not in ASK1-deficient (ASK1(-/-)) mice. Phosphorylated ASK1 increased in wild-type mouse brains, and phosphorylated p38 and tumor necrosis factor-α expression increased in corpus callosum cerebral endothelial cells after BCAS in wild-type mice but not in ASK1(-/-) mice. BCAS decreased claudin-5 expression and disrupted blood-brain barrier in the corpus callosum of wild-type but not ASK1(-/-) mice. Cerebral nitrotyrosine was increased in wild-type and ASK1(-/-) BCAS mice. Cerebral phosphorylated ASK1 did not increase in wild-type mice treated with NADPH-oxidase inhibitor. A p38 inhibitor and NADPH-oxidase inhibitor mimicked the protective effect of ASK1 deficiency against cognitive impairment. Specific ASK1 inhibitor prevented cognitive decline in BCAS mice. In vitro oxygen-glucose deprivation and tumor necrosis factor-α stimulation caused the disruption of endothelial tight junctions from wild-type mice but not ASK1(-/-) mice.

CONCLUSIONS

Oxidative stress-ASK1-p38 cascade plays a role in the pathogenesis of cognitive impairment, through blood-brain barrier breakdown via the disruption of endothelial tight junctions. ASK1 might be a promising therapeutic target for chronic cerebral hypoperfusion-induced cognitive impairment.

The ins and outs of the BCCAo model for chronic hypoperfusion: a multimodal and longitudinal MRI approach

Cerebral hypoperfusion induced by bilateral common carotid artery occlusion (BCCAo) in rodents has been proposed as an experimental model of white matter damage and vascular dementia. However, the histopathological and behavioral alterations reported in this model are variable and a full characterization of the dynamic alterations is not available. Here we implemented a longitudinal multimodal magnetic resonance imaging (MRI) design, including time-of-flight angiography, high resolution T1-weighted images, T2 relaxometry mapping, diffusion tensor imaging, and cerebral blood flow measurements up to 12 weeks after BCCAo or sham-operation in Wistar rats. Changes in MRI were related to behavioral performance in executive function tasks and histopathological alterations in the same animals. MRI frequently (70%) showed various degrees of acute ischemic lesions, ranging from very small to large subcortical infarctions. Independently, delayed MRI changes were also apparent. The patterns of MRI alterations were related to either ischemic necrosis or gliosis. Progressive microstructural changes revealed by diffusion tensor imaging in white matter were confirmed by observation of myelinated fiber degeneration, including severe optic tract degeneration. The latter interfered with the visually cued learning paradigms used to test executive functions. Independently of brain damage, BCCAo induced progressive arteriogenesis in the vertebrobasilar tree, a process that was associated with blood flow recovery after 12 weeks. The structural alterations found in the basilar artery were compatible with compensatory adaptive changes driven by shear stress. In summary, BCCAo in rats induces specific signatures in multimodal MRI that are compatible with various types of histological lesion and with marked adaptive arteriogenesis.

Early microvascular dysfunction in cerebral small vessel disease is not detectable on 3.0 Tesla magnetic resonance imaging: a longitudinal study in spontaneously hypertensive stroke-prone rats

BACKGROUND

Human cerebral small vessel disease (CSVD) has distinct histopathologic and imaging findings in its advanced stages. In spontaneously hypertensive stroke-prone rats (SHRSP), a well-established animal model of CSVD, we recently demonstrated that cerebral microangiopathy is initiated by early microvascular dysfunction leading to the breakdown of the blood-brain barrier and an activated coagulatory state resulting in capillary and arteriolar erythrocyte accumulations (stases). In the present study, we investigated whether initial microvascular dysfunction and other stages of the pathologic CSVD cascade can be detected by serial magnetic resonance imaging (MRI).

FINDINGS

Fourteen SHRSP and three control (Wistar) rats (aged 26-44 weeks) were investigated biweekly by 3.0 Tesla (3 T) MRI. After perfusion, brains were stained with hematoxylin-eosin and histology was correlated with MRI data. Three SHRSP developed terminal CSVD stages including cortical, hippocampal, and striatal infarcts and macrohemorrhages, which could be detected consistently by MRI. Corresponding histology showed small vessel thromboses and increased numbers of small perivascular bleeds in the infarcted areas. However, 3 T MRI failed to visualize intravascular erythrocyte accumulations, even in those brain regions with the highest densities of affected vessels and the largest vessels affected by stases, as well as failing to detect small perivascular bleeds.

CONCLUSION

Serial MRI at a field strength of 3 T failed to detect the initial microvascular dysfunction and subsequent small perivascular bleeds in SHRSP; only terminal stages of cerebral microangiopathy were reliably detected. Further investigations at higher magnetic field strengths (7 T) using blood- and flow-sensitive sequences are currently underway.

Mechanisms of sporadic cerebral small vessel disease: insights from neuroimaging

The term cerebral small vessel disease (SVD) describes a range of neuroimaging, pathological, and associated clinical features. Clinical features range from none, to discrete focal neurological symptoms (eg, stroke), to insidious global neurological dysfunction and dementia. The burden on public health is substantial. The pathogenesis of SVD is largely unknown. Although the pathological processes leading to the arteriolar disease are associated with vascular risk factors and are believed to result from an intrinsic cerebral arteriolar occlusive disease, little is known about how these processes result in brain disease, how SVD lesions contribute to neurological or cognitive symptoms, and the association with risk factors. Pathology often shows end-stage disease, which makes identification of the earliest stages difficult. Neuroimaging provides considerable insights; although the small vessels are not easily seen themselves, the effects of their malfunction on the brain can be tracked with detailed brain imaging. We discuss potential mechanisms, detectable with neuroimaging, that might better fit the available evidence and provide testable hypotheses for future study.

Two genomic regions of chromosomes 1 and 18 explain most of the stroke susceptibility under salt loading in stroke-prone spontaneously hypertensive rat/Izm

To clarify the genetic mechanisms of stroke susceptibility in the stroke-prone spontaneously hypertensive rat (SHRSP), a quantitative trait locus (QTL) analysis was performed. Using 295 F2 rats of a cross between SHRSP/Izm and SHR/Izm, 2 major QTLs for stroke latency under salt loading were identified on chromosomes (chr) 1 and 18. Evaluation of 6 reciprocal single and double congenic rats for these QTLs showed that substitution of the SHRSP for the SHR fragment at the chr 1 and 18 QTLs increased the relative risk for stroke by 8.4 and 5.0, respectively. The combined effect of the 2 QTLs was 10× greater than that of the background genome (by Cox hazard model). Blood pressure monitoring by radio telemetry indicated that the combination of the 2 QTLs had a clear effect on the salt-dependent blood pressure increase, suggesting an important role for the salt-sensitive blood pressure increase in the susceptibility of SHRSP to stroke. A haplotype analysis of 11 substrains of SHRSP and SHR using 340 simple sequence repeat markers in the chr 1 QTL suggested that the 7-Mbp fragment between D1Rat260 and D1Rat178 was most likely to harbor the responsible gene(s), which was confirmed by a study of additional subcongenic strains. This study indicated a major role for 2 QTLs on chr 1 and 18 in stroke susceptibility in SHRSP under salt loading. The salt-sensitive blood pressure increase was implied to play a key role in the stroke susceptibility.

An MRI-histological study of white matter in stroke-free SHRSP

Hypertension is associated with cerebral small vessel disease (SVD) and with diffuse white matter hyperintensities (WMH) on T2-weighted magnetic resonance imaging (MRI). We tested whether stroke-prone spontaneously hypertensive rats (SHRSP), a model of chronic hypertension, exhibit WMH. Male SHRSP (age 10 months) without stroke symptoms were compared with age-matched male WKY rats. Stroke-prone spontaneously hypertensive rats exhibited no WMH on MRI scans (T2, T2*, diffusion tensor imaging) and no neuropathological lesions. While leptomeningeal arteries exhibited fibrohyaline wall thickening, with decreased smooth muscle actin relative to WKY, deep penetrating arterioles within the caudate nuclei had no vasculopathy. We conclude that WMH are not an obligate feature of stroke-free SHRSP aged up to 10 months.

Involvement of matrix metalloproteinases-2 and -9 in the formation of a lacuna-like cerebral cavity

We used a modified pial vessel disruption (PVD) protocol with adult male Wistar rats to mimic small-vessel stroke in the cerebral cortex. Within 3 weeks, this lesion develops into a single lacuna-like cavity, which is fluid-filled and encapsulated by reactive astrocytes. Minocycline treatment that commences 1 hr after lesion and continues for 6 days prevents the cavitation and causes a filling of the lesion with reactive astrocytes and no barrier. Here, we determined whether inhibition of matrix metalloproteinases-2 and -9 (MMPs) mediates this minocycline action. Confocal microscopy revealed increased punctate staining of MMPs inside the lesion sites after 2 days of PVD. Astrocytes lined the lesion border but showed sparse localization inside the lesion. In contrast, increased MMP levels inside the lesion coincided with increased ED1 or OX-42 immunostaining, suggesting that MMP elevation reflected increased secretions from microglia/macrophages. Imaging analyses also revealed that minocycline administered for 2 days before animal euthanasia, significantly decreased MMP levels within the lesion. Moreover, Western blot analysis of cortical tissue extracts showed a significant 30-40% upregulation of MMPs 2 days after lesion. Minocycline administered 2 hr before the lesion significantly inhibited both MMP-9 and MMP-2 levels by ∼40%. In contrast, minocycline administered 1 hr after the lesion only decreased MMP-9 levels by ∼30%. Because MMP inhibition with batimastat injection also prevented cavity formation at 21 days, we conclude that minocycline prevented the creation of a lacuna-like cyst in the cerebral cortex by inhibiting the MMP secretion from microglia in the affected tissue.

Effects of N-stearoyl-L-tyrosine on the hippocampal ubiquitin-proteasome system in rats with chronic cerebral hypoperfusion

OBJECTIVES

Chronic cerebral hypoperfusion (CCH) leads to neurodegeneration and cognitive impairment. Ubiquitinated protein aggregates are commonly present in neurodegenerative disorders and are believed to cause neuronal degeneration. Here, we investigated the effects of N-stearoyl-L-tyrosine (NSTyr) on the hippocampal ubiquitin-proteasome system (UPS) in rats with CCH.

METHODS

After induction of CCH, NSTyr was intraperitoneally administered daily for 3 months. Protein aggregation was analyzed by ethanolic phosphotungstic acid (EPTA) electron microscopy (EM), immunogold EM, laser-scanning confocal microscopy, and Western blot. Proteasome peptidase activity was measured by peptidase activity assays.

RESULTS

By using EPTA EM, immunogold EM and high-resolution laser-scanning confocal microscopy, we found that CCH resulted in the accumulation of ubiquitinated protein aggregates in rat hippocampal CA1 neurons. Western blot revealed that the levels of free ubiquitin were significantly reduced and that the levels of ubiquitinated proteins were markedly increased in the hippocampus of CCH rats. Direct activity measurements demonstrated that proteasome peptidase activity in the hippocampal region of rats was decreased after CCH induction. In the hippocampal tissue of CCH rats treated with NSTyr, however, ubiquitinated protein aggregates decreased and proteasome peptidase activity increased.

DISCUSSION

These data indicate that NSTyr may exert protective effects on rat hippocampal UPS function via endogenous regulation.

Blood brain barrier breakdown as the starting point of cerebral small vessel disease? - New insights from a rat model

Cerebral small vessel disease (CSVD, cerebral microangiopathy) leads to dementia and stroke-like symptoms. Lacunes, white matter lesions (WML) and microbleeds are the main pathological correlates depicted in in-vivo imaging diagnostics. Early studies described segmental arterial wall disorganizations of small penetrating cerebral arteries as the most pronounced underlying histopathology of lacunes. Luminal narrowing caused by arteriolosclerosis was supposed to result in hypoperfusion with WML and infarcts.We have used the model of spontaneously hypertensive stroke-prone rats (SHRSP) for a longitudinal study to elucidate early histological changes in small cerebral vessels. We suggest that endothelial injuries lead to multiple sites with blood brain barrier (BBB) leakage which cause an ongoing damage of the vessel wall and finally resulting in vessel ruptures and microbleeds. These microbleeds together with reactive small vessel occlusions induce overt cystic infarcts of the surrounding parenchyma. Thus, multiple endothelial leakage sites seem to be the starting point of cerebral microangiopathy. The vascular system reacts with an activated coagulatory state to these early endothelial injuries and by this induces the formation of stases, accumulations of erythrocytes, which represent the earliest detectable histological peculiarity of small vessel disease in SHRSP.In this review we focus on the meaning of the BBB breakdown in CSVD and finally discuss possible consequences for clinicians.

High energy diets-induced metabolic and prediabetic painful polyneuropathy in rats

To establish the role of the metabolic state in the pathogenesis of polyneuropathy, an age- and sex-matched, longitudinal study in rats fed high-fat and high-sucrose diets (HFSD) or high-fat, high-sucrose and high-salt diets (HFSSD) relative to controls was performed. Time courses of body weight, systolic blood pressure, fasting plasma glucose (FPG), insulin, free fatty acids (FFA), homeostasis model assessment-insulin resistance index (HOMA-IR), thermal and mechanical sensitivity and motor coordination were measured in parallel. Finally, large and small myelinated fibers (LMF, SMF) as well as unmyelinated fibers (UMF) in the sciatic nerves and ascending fibers in the spinal dorsal column were quantitatively assessed under electron microscopy. The results showed that early metabolic syndrome (hyperinsulinemia, dyslipidemia, and hypertension) and prediabetic conditions (impaired fasting glucose) could be induced by high energy diet, and these animals later developed painful polyneuropathy characterized by myelin breakdown and LMF loss in both peripheral and central nervous system. In contrast SMF and UMF in the sciatic nerves were changed little, in the same animals. Therefore the phenomenon that high energy diets induce bilateral mechanical, but not thermal, pain hypersensitivity is reflected by severe damage to LMF, but mild damage to SMF and UMF. Moreover, dietary sodium (high-salt) deteriorates the neuropathic pathological process induced by high energy diets, but paradoxically high salt consumption, may reduce, at least temporarily, chronic pain perception in these animals.

Hypertension-induced peripheral neuropathy and the combined effects of hypertension and diabetes on nerve structure and function in rats

Diabetic neuropathy includes damage to neurons, Schwann cells and blood vessels. Rodent models of diabetes do not adequately replicate all pathological features of diabetic neuropathy, particularly Schwann cell damage. We, therefore, tested the hypothesis that combining hypertension, a risk factor for neuropathy in diabetic patients, with insulin-deficient diabetes produces a more pertinent model of peripheral neuropathy. Behavioral, physiological and structural indices of neuropathy were measured for up to 6 months in spontaneously hypertensive and age-matched normotensive rats with or without concurrent streptozotocin-induced diabetes. Hypertensive rats developed nerve ischemia, thermal hyperalgesia, nerve conduction slowing and axonal atrophy. Thinly myelinated fibers with supernumerary Schwann cells indicative of cycles of demyelination and remyelination were also identified along with reduced nerve levels of myelin basic protein. Similar disorders were noted in streptozotocin-diabetic rats, except that thinly myelinated fibers were not observed and expression of myelin basic protein was normal. Superimposing diabetes on hypertension compounded disorders of nerve blood flow, conduction slowing and axonal atrophy and increased the incidence of thinly myelinated fibers. Rats with combined insulinopenia, hyperglycemia and hypertension provide a model for diabetic neuropathy that offers an opportunity to study mechanisms of Schwann cell pathology and suggests that hypertension may contribute to the etiology of diabetic neuropathy.

Etiology of stroke and choice of models

Animal models of stroke contribute to the development of better stroke prevention and treatment through studies investigating the pathophysiology of different stroke subtypes and by testing promising treatments before trials in humans. There are two broad types of animal models: those in which stroke is induced through artificial means, modeling the consequences of a vascular insult but not the vascular pathology itself; and those in which strokes occur spontaneously. Most animal models of stroke are in rodents due to cost, ethical considerations, availability of standardized neurobehavioral assessments, and ease of physiological monitoring. While there are similarities in cerebrovascular anatomy and pathophysiology between rodents and humans, there are also important differences, including brain size, length and structure of perforating arteries, and gray to white matter ratio, which is substantially lower in humans. The wide range of rodent models of stroke includes models of global and focal ischemia, and of intracerebral and sub-arachnoid hemorrhage. The most widely studied model of spontaneous stroke is the spontaneously hypertensive stroke-prone rat, in which the predominant lesions are small subcortical infarcts resulting from a vascular pathology similar to human cerebral small vessel disease. Important limitations of animal models of stroke - they generally model only certain aspects of the disease and do not reflect the heterogeneity in severity, pathology and comorbidities of human stroke - and key methodological issues (especially the need for adequate sample size, randomization, and blinding in treatment trials) must be carefully considered for the successful translation of pathophysiological concepts and therapeutics from bench to bedside.

Do basophile structures as age dependent phenomenon indicate small vessel wall damage?

Here we demonstrate basophile structures located in the arteriolar wall and being associated with a plasma-protein-leakage. We assume, that the structures indicate blood-brain-barrier-disturbances and degenerative small vessel wall alterations.

Stases are associated with blood-brain barrier damage and a restricted activation of coagulation in SHRSP

Cerebral small vessel disease (CSVD) is a chronically proceeding pathology of small brain vessels associated with white matter lesions, lacunar infarcts, brain atrophy and microbleeds. CSVD leads to slowly increasing cognitive and functional deficits but may also cause stroke-like symptoms, if vessels in critical brain areas are affected. Spontaneously hypertensive stroke-prone rats (SHRSP) exhibit several vascular risk factors, develop infarcts and hemorrhages and therefore represent a relevant model for the study of CSVD. Using this animal model, we recently demonstrated that intravasal accumulations of erythrocytes, we interpreted as stases, stand at the beginning of a pathological vascular cascade. After stases microbleeds occur, which are followed by reactive microthromboses. Bleeds and thromboses finally cause hemorrhagic infarcts. Immunohistochemical stainings show, that plasma proteins like IgG are deposited in the walls of vessels affected by stases. Further, we found small clots and thread-shaped aggregations of thrombocytes as well as thread-shaped structures of von Willebrand-Factor within stases. Thus, we conclude that blood-brain barrier damages occur in the neighborhood of stases and stases seem to be associated with a restricted activation of blood coagulation without formation of obstructive thromboses. Finally, we demonstrate that small vessel damage rarely appears in the cerebellum. Even animals with multiple cerebral infarcts may be free of any cerebellar vascular pathology.

Standards and pitfalls of focal ischemia models in spontaneously hypertensive rats: with a systematic review of recent articles

We reviewed the early development of various focal ischemia models in spontaneously hypertensive rats (SHR), and summarized recent reports on this topic. Among 6 focal ischemia models established in divergent substrains of SHR, distal middle cerebral artery occlusion is the most frequently used and relevant method of focal ischemia in the light of penumbra concept. We performed an online PubMed search (2001–2010), and identified 118 original articles with focal ischemia in SHR. Physiological parameters such as age, body weight, and even blood pressure were often neglected in the literature: the information regarding the physiological parameters of SHR is critical, and should be provided within the methodology section of all articles related to stroke models in SHR. Although the quality of recent studies on neuroprotective strategy is improving, the mechanisms underlying the protection should be more clearly recognized so as to facilitate the translation from animal studies to human stroke. To overcome the genetic heterogeneity in substrains of SHR, new approaches, such as a huge repository of genetic markers in rat strains and the congenic strategy, are currently in progress.

Two-photon microscopy as a tool to study blood flow and neurovascular coupling in the rodent brain

The cerebral vascular system services the constant demand for energy during neuronal activity in the brain. Attempts to delineate the logic of neurovascular coupling have been greatly aided by the advent of two-photon laser scanning microscopy to image both blood flow and the activity of individual cells below the surface of the brain. Here we provide a technical guide to imaging cerebral blood flow in rodents. We describe in detail the surgical procedures required to generate cranial windows for optical access to the cortex of both rats and mice and the use of two-photon microscopy to accurately measure blood flow in individual cortical vessels concurrent with local cellular activity. We further provide examples on how these techniques can be applied to the study of local blood flow regulation and vascular pathologies such as small-scale stroke.

Pre-clinical models of human cerebral small vessel disease: utility for clinical application

Small vessel disease (SVD) is a frequent cause of vascular cognitive impairment (VCI), encompassing vascular dementia. SVD is characterised by vasculopathy in deep penetrating arteries, diffuse white matter lesions (seen radiologically as leukoaraiosis) and focal, lacunar infarcts. Risk factors are age and hypertension but the pathogenic mechanism is unknown. Recent systematic reviews assessed experimental models of SVD or VCI. Chronically hypertensive animals (e.g. stroke-prone spontaneously hypertensive rats) display some features of SVD vasculopathy, such as vessel wall thickening. White matter lesions are seen in chronic hypoperfusion states (e.g. carotid occlusion/stenosis models). Small focal infarcts are induced by targeted ischemic challenge (surgical occlusion of a small artery, or stereotaxic endothelin-1 injection). Some degree of cognitive impairment is detectable in most cerebrovascular models, probably reflecting the broad neuroanatomical mapping of cognitive function. Important confounds to be considered in animal models of VCI are somatosensory impairment and hippocampal damage. Advances in clinical understanding will come from targeting specific questions on some aspect of SVD (e.g. vasculopathy, white matter damage) to the appropriate model in vivo. In vivo models of SVD are likely to benefit experimental studies of pathological processes, interactions with other brain disease states (such as Alzheimer disease), and therapeutic strategies.

Environmental enrichment prevents behavioral deficits and oxidative stress caused by chronic cerebral hypoperfusion in the rat

AIMS

The aim of the present study was to evaluate the neuroprotective effects of environmental enrichment (EE), assessed by cognitive activity in the Morris water maze, and on brain oxidative status, through measurement of macromolecules damage, lipid peroxidation levels, total cellular thiols and antioxidant enzymes in hippocampus, striatum and cerebral cortex.

MAIN METHODS

Adult male Wistar rats were submitted to the modified permanent bilateral occlusion of the common carotid arteries (2VO) method, with right common carotid artery being first occluded, and tested three months after the ischemic event. Cognitive and physical stimulation, named Environmental Enrichment, consisted of one-hour sessions run 3 times per week during 12weeks, following two different stimulation protocols: pre-ischemia and pre+post-ischemia. Rats were then tested for both reference and working spatial memory tasks in the water maze and later sacrificed for measurement of oxidative stress parameters.

KEY FINDINGS

A significant cognitive deficit was found in both spatial tasks after hypoperfusion; this effect was reversed in the 2VO enriched group. Moreover, hippocampal oxidative damage and antioxidant enzyme activity were decreased by environmental enrichment.

SIGNIFICANCE

These results suggest that both stimulation protocols exert a neuroprotective effect against the cognitive impairment and the reduction of biomarkers for oxidative damage caused by chronic cerebral hypoperfusion.

Mixed cerebrovascular disease and the future of stroke prevention

Stroke prevention efforts typically focus on either ischemic or hemorrhagic stroke. This approach is overly simplistic due to the frequent coexistence of ischemic and hemorrhagic cerebrovascular disease. This coexistence, termed “mixed cerebrovascular disease”, offers a conceptual framework that appears useful for stroke prevention strategies. Mixed cerebrovascular disease incorporates clinical and subclinical syndromes, including ischemic stroke, subclinical infarct, white matter disease of aging (leukoaraiosis), intracerebral hemorrhage, and cerebral microbleeds. Reliance on mixed cerebrovascular disease as a diagnostic entity may assist in stratifying risk of hemorrhagic stroke associated with platelet therapy and anticoagulants. Animal models of hemorrhagic cerebrovascular disease, particularly models of cerebral amyloid angiopathy and hypertension, offer novel means for identifying underlying mechanisms and developing focused therapy. Phosphodiesterase (PDE) inhibitors represent a class of agents that, by targeting both platelets and vessel wall, provide the kind of dual actions necessary for stroke prevention, given the spectrum of disorders that characterizes mixed cerebrovascular disease.

Models that matter: white matter stroke models

Stroke is a devastating neurological disease with limited functional recovery. Stroke affects all cellular elements of the brain and impacts areas traditionally classified as both gray matter and white matter. In fact, stroke in subcortical white matter regions of the brain accounts for approximately 30% of all stroke subtypes, and white matter injury is a component of most classes of stroke damage. However, most basic scientific information in stroke cell death and neural repair relates principally to neuronal cell death and repair. Despite an emerging biological understanding of white matter development, adult function, and reorganization in inflammatory diseases, such as multiple sclerosis, little is known of the specific molecular and cellular events in white matter ischemia. This limitation stems in part from the difficulty in generating animal models of white matter stroke. This review will discuss recent progress in studies of animal models of white matter stroke, and the emerging principles of cell death and repair in oligodendrocytes, axons, and astrocytes in white matter ischemic injury.