Permanent, bilateral common carotid artery occlusion in the rat: a model for chronic cerebral hypoperfusion-related neurodegenerative diseases

Luteolin promotes long-term potentiation and improves cognitive functions in chronic cerebral hypoperfused rats

Processes of synaptic plasticity, such as long-term potentiation (LTP), has been considered a cellular correlate of learning and memory and many neurological disorders accompanied by cognitive deficits exhibit abnormal synaptic function. This emerging concept is exemplified by Alzheimer's disease. Mounting evidence suggests that Alzheimer's disease begins with subtle alterations of hippocampal synaptic efficacy prior to frank neuronal degeneration, which make it critical to identify LTP enhancers to slow down or stop the progression of Alzheimer's disease. In this study, we found flavonoid luteolin could enhance basal synaptic transmission and facilitate the induction of LTP by high frequency stimulation in the dental gyrus of rat hippocampus. Furthermore, we investigated the effects of luteolin on chronic cerebral hypoperfusion-induced spatial learning dysfunction and LTP impairment in rat. The results showed chronic cerebral hypoperfusion produced by 2-vessel occlusion significantly impaired spatial learning and memory, and luteolin reversed the learning and memory deficit. 2-vessel occlusion resulted in dramatic inhibition of LTP formation in the hippocampus and luteolin significantly rescued the LTP impairment. These results demonstrate that luteolin not only directly modulates LTP formation, but also protects synapses from the detrimental effects of chronic cerebral hypoperfusion on LTP formation, which may contribute to the protective effects of luteolin on learning and memory. By immunoblotting, we found the effects of luteolin on LTP and memory may due to the activation of cAMP response element-binding protein (CREB). Therefore, flavonoid luteolin shows great potential as a novel treatment agent for protecting synaptic function and enhancing memory in neurodegenerative disorders.

Experimental models for analysis of oligodendrocyte pathophysiology in stroke

White matter damage is a clinically important part of stroke. However, compared to the mechanisms of neuronal injury in gray matter, white matter pathophysiology remains relatively understudied and poorly understood. This mini-review aims at summarizing current knowledge on experimental systems for analyzing the role of white matter injury relevant to stroke. In vitro platforms comprise primary cultures of both mature oligodendrocytes (OLGs) as well as oligodendrocyte precursor cells (OPCs). Tissue platforms involve preparations of optic nerve systems. Whole-animal platforms comprise in vivo models of cerebral ischemia that attempt to target white matter brain areas. While there is no single perfect model system, the collection of these experimental approaches have recently allowed a better understanding of the molecular and cellular pathways underlying OLG/OPC damage and demyelination. A systematic utilization of these cell, tissue and whole-animal platforms may eventually lead us to discover new targets for treating white matter injury in stroke and other CNS disorders.

Evaluation of the protective effects of PACAP with cell-specific markers in ischemia-induced retinal degeneration

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurotrophic and neuroprotective peptide that has been shown to exert protective effects in different neuronal injuries, such as traumatic brain injury, models of neurodegenerative diseases and cerebral ischemia. We have provided evidence that PACAP is neuroprotective in several models of retinal degeneration in vivo. In our previous studies we showed that PACAP treatment significantly ameliorated the damaging effects of permanent bilateral common carotid artery occlusion (BCCAO). In the present study cell-type-specific markers were used in the same models in order to further specify the protective effects of PACAP. In rats BCCAO led to severe degeneration of all retinal layers that was attenuated by PACAP (100 pmol) administered unilaterally immediately following BCCAO into the vitreous body of one eye. Retinas were processed for immunohistochemistry after 3 weeks. Immunolabeling was executed for vesicular glutamate transporter 1 (VGLUT 1), vesicular gamma-aminobutyric acid transporter (VGAT), protein kinase Calpha (PKCalpha), glial fibrillary acidic protein (GFAP) and calcium-binding proteins, such as calbindin, calretinin, parvalbumin. In BCCAO retinas, intensity of immunopositivity for all antisera was dramatically decreased, except in the case of GFAP. In PACAP-treated retinas, immunostaining was similar to that of the control animals. In summary, our study presented immunohistochemical identification of cell types sensitive to chronic retinal hypoperfusion and the protective effects of PACAP. This analysis revealed that the retinoprotective effects of PACAP are not phenotype-specific, but it rather influences general cytoprotective pathways irrespective of the neuronal subtypes in the retina subjected to chronic hypoperfusion.

Rodent neonatal bilateral carotid artery occlusion with hypoxia mimics human hypoxic-ischemic injury

We report a new clinically relevant model of neonatal hypoxic-ischemic injury in a 10-day-old rat pup. Bilateral carotid artery occlusion and 8% hypoxia (1 to 15 mins, BCAO-H) was induced with varying degrees of injury (mild, moderate, severe), which was quantified using magnetic resonance imaging including diffusion-weighted and T2-weighted imaging at 24 h and 21/28 days. We developed a magnetic resonance imaging-based rat pup severity score and compared 3D ischemic injury volumes/rat pup severity score with histology and behavioral testing. At 24 h, hypoxic-ischemic injury was observed in 17/27 animals; long-term survival was 81%. Magnetic resonance imaging lesion volumes did not correlate with hypoxia duration but correlated with rat pup severity score, which was used to classify animals into mild (n=21), moderate (n=6), and severe (n=10) groups with average brain lesion volumes of 0.9%, 33.2%, and 56.3%, respectively. Histology confirmed lesion location and histologic scoring correlated with the rat pup severity score. We also found excellent correlation between injury severity and multiple behavioral tasks. Bilateral carotid artery occlusion and hypoxia in the P10 rat pup is an excellent model of neonatal hypoxic-ischemic injury because it induces diffuse global injury similar to the term infant. This model can produce graded injury severity, similar to that seen in human neonates, but manipulation with hypoxia duration is unpredictable.

Protection against chronic hypoperfusion-induced retinal neurodegeneration by PARP inhibition via activation of PI-3-kinase Akt pathway and suppression of JNK and p38 MAP kinases

Poly(ADP-ribose) polymerase (PARP) activation is considered as a major regulator of cell death in various pathophysiological conditions, however, no direct information is available about its role in chronic hypoperfusion-induced neuronal death. Here, we provide evidence for the protective effect of PARP inhibition on degenerative retinal damage induced by bilateral common carotid artery occlusion (BCCAO), an adequate chronic hypoperfusion murine model. We found that BCCAO in adult male Wistar rats led to severe degeneration of all retinal layers that was attenuated by a carboxaminobenzimidazol-derivative PARP inhibitor (HO3089) administered unilaterally into the vitreous body immediately following carotid occlusion and then 4 times in a 2-week-period. Normal morphological structure of the retina was preserved and the thickness of the retinal layers was increased in HO3089-treated eyes compared to the BCCAO eyes. For Western blot studies, HO3089 was administered immediately after BCCAO and retinas were removed 4 h later. According to Western blot analysis utilizing phosphorylation-specific primary antibodies, besides activating poly-ADP-ribose (PAR) synthesis, BCCAO induced phosphorylation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK). HO3089 inhibited PAR synthesis, and decreased the phosphorylation of these proapoptotic MAPKs. In addition, HO3089 treatment induced phosphorylation, that is activation, of the protective Akt/glycogen synthase kinase (GSK)-3beta and extracellular signal-regulated kinase (ERK1/2) signaling pathways. These data indicate that PARP activation has a major role in mediating chronic hypoperfusion-induced neuronal death, and inhibition of the enzyme prevents the pathological changes both in the morphology and the kinase signaling cascades involved. These results identify PARP inhibition as a possible molecular target in the clinical management of chronic hypoperfusion-induced neurodegenerative diseases including ocular ischemic syndrome.

Increased apparent diffusion coefficients on MRI linked with matrix metalloproteinases and edema in white matter after bilateral carotid artery occlusion in rats

White matter (WM) injury after bilateral common carotid artery occlusion (BCAO) in rat is associated with disruption of the blood-brain barrier (BBB) by matrix metalloproteinases (MMPs). We hypothesized that WM injury as seen on magnetic resonance imaging (MRI) would correlate with regions of increased MMP activity. MRI was performed 3 days after BCAO surgery in rats. Apparent diffusion coefficients (ADC) were calculated and vascular permeability was quantified by the multiple-time graphical analysis (MTGA) method, using gadolinium-diethylenetriamine pentaacid (Gd-DTPA). After MRI, one group of animals had BBB permeability measured in the WM with (14)C-sucrose, and another had Evans blue (EB) injected for fluorescent microscopy for MMP-2, MMP-9, tight junction proteins (TJPs), and in situ zymography. We found that ADC values were increased in WM in BCAO rats compared with controls (P<0.05). WM with increased ADC had leakage of EB. MMP-2 and MMP-9 activity on in situ zymograms corresponded with leakage of EB. Although increased permeability to EB could be visualized, permeability quantification with (14)C-sucrose and Gd-DTPA failed to show increases and TJPs were intact. We propose that increased ADC, which is a marker of vasogenic edema, is related to activity of MMP-2 and MMP-9. MRI provides unique information that can be used to guide tissue studies of WM injury.

Oxaloacetate restores the long-term potentiation impaired in rat hippocampus CA1 region by 2-vessel occlusion

Various acute brain pathological conditions are characterized by the presence of elevated glutamate concentrations in the brain interstitial fluids. It has been established that a decrease in the blood glutamate level enhances the brain-to-blood efflux of glutamate, removal of which from the brain may prevent glutamate excitotoxicity and its contribution to the long-lasting neurological deficits seen in stroke. A decrease in blood glutamate level can be achieved by exploiting the glutamate-scavenging properties of the blood-resident enzyme glutamate-oxaloacetate transaminase, which transforms glutamate into 2-ketoglutarate in the presence of the glutamate co-substrate oxaloacetate. The present study had the aim of an evaluation of the effects of the blood glutamate scavenger oxaloacetate on the impaired long-term potentiation (LTP) induced in the 2-vessel occlusion ischaemic model in rat. Transient (30-min) incomplete forebrain ischaemia was produced 72 h before LTP induction. Although the short transient brain hypoperfusion did not induce histologically identifiable injuries in the CA1 region (Fluoro-Jade B, S-100 and cresyl violet), it resulted in an impaired LTP function in the hippocampal CA1 region without damaging the basal synaptic transmission between the Schaffer collaterals and the pyramidal neurons. This impairment could be fended off in a dose-dependent manner by the intravenous administration of oxaloacetate in saline (at doses between 1.5 mmol and 0.1 mumol) immediately after the transient hypoperfusion. Our results suggest that oxaloacetate-mediated blood and brain glutamate scavenging contributes to the restoration of the LTP after its impairment by brain ischaemia.

The plasticity of posterior communicating artery influences on the outcome of white matter injury induced by chronic cerebral hypoperfusion in rats

OBJECTIVE

This study was performed to identify which factors are involved in the development of white matter lesions induced by chronic cerebral hypoperfusion in rats.

METHODS

Male Wistar and Sprague-Dawley (SD) rats (250-270 g) were subjected to the permanent occlusion of bilateral common carotid arteries (BCCAO). The regional cerebral blood flow (rCBF) was measured by laser Doppler flowmetry and the plasticity of the posterior communicating artery (PcomA) was visualized by transcardiac perfusion of latex solution. For the histological examination, Klüver-Barrera staining was used to evaluate white matter damage.

RESULTS

When compared with SD rats, Wistar rats showed lower rCBF after BCCAO, as well as thinner PcomAs. Moreover, 21 days after BCCAO, Wistar rats showed marked vacuolation of white matter in the optic tract, whereas SD rats had an almost intact optic tract.

DISCUSSION

These results suggest that the plasticity of the PcomA and the reduction of rCBF in Wistar rats are important factors in the development of BCCAO-induced white matter lesions.

Astroglial and cognitive effects of chronic cerebral hypoperfusion in the rat

The permanent occlusion of common carotid arteries (2VO) causes a significant reduction of cerebral blood flow (hypoperfusion) in rats and constitutes a well established experimental model to investigate neuronal damage and cognitive impairment that occurs in human ageing and Alzheimer's disease. In the present study, we evaluated two astroglial proteins--S100B and glial fibrillary acidic protein (GFAP)--in cerebral cortex and hippocampus tissue, glutamate uptake and glutamine synthetase activity in hippocampus tissue, as well as S100B in cerebrospinal fluid. Cognition, as assessed by reference and working spatial memory protocols, was also investigated. Adult male Wistar rats were submitted to 10 weeks of chronic cerebral hypoperfusion by the 2VO method. A significant increase of S100B and GFAP in hippocampus tissue was observed, as well a significant decrease in glutamate uptake. Interestingly, we observed a decrease in S100B in cerebrospinal fluid. As for the cognitive outcome, there was an impairment of both reference and working spatial memory in the water maze; positive correlation between cognitive impairment and glutamate uptake decrease was evidenced in hypoperfused rats. These data support the hypothesis that astrocytes play a crucial role in the mechanisms of experimental neurodegeneration and that hippocampal pathology arising after chronic hypoperfusion gives rise to memory deficits.

The cognitive and histopathological effects of chronic 4-vessel occlusion in rats depend on the set of vessels occluded and the age of the animals

Continuing previous efforts to develop the 4-vessel occlusion (4-VO) model of chronic cerebral hypoperfusion (CCH), here we evaluated whether permanent, stepwise 4-VO causes both learning deficits, hippocampal neurodegeneration and retinal lesion in young, middle-aged or aged rats. Chronic 4-VO was induced by ligation of different sets of vessels, i.e., the vertebral arteries (VA) plus common carotid arteries (CCA) (4-VO/CCA model) or the VA plus internal carotid arteries (ICA) (4-VO/ICA model) with a 1-week interstage interval. Forty days after the 4-VO, the rats were tested for spatial learning impairment, and then examined for hypoxic/ischemic damage. Young, 4-VO/CCA rats exhibited cognitive impairment, hippocampal neurodegeneration and retinal lesion (p<0.0001-0.05). After 4-VO/ICA, neither young nor middle-aged rats exhibited any learning deficits, hippocampal or retinal damage. In aged rats, chronic 4-VO/ICA caused a mild learning deficit (p<0.05). A significant effect of training was observed for the old, sham-operated rats (p<0.0001-0.001), but not for the aged 4-VO/ICA rats (p>0.05). On average, hippocampal cell density did not change after 4-VO/ICA in aged rats, but 3 of 10 subjects exhibited reduced pyramidal cell counts in all hippocampal subfields. Retinal morphology appeared to be unaffected in the 4-VO/ICA aged rats. These data suggest that the 4-VO/ICA model, but not the 4-VO/CCA model, is a suitable paradigm to study the behavioral outcome of CCH given the preservation of the retina after 4-VO/ICA. Moreover, the age at which 4-VO/ICA occurs seems to be an important factor for determining the behavioral and neuropathological changes.

Baicalein protects rat brain mitochondria against chronic cerebral hypoperfusion-induced oxidative damage

This study investigated the effects of baicalein, a natural compound isolated from the root of scutellaria, on cognitive and motor ability impaired by chronic cerebral hypoperfusion in rats, as well as its effects on brain mitochondria. Rats subjected to permanent bilateral common carotid artery occlusion experienced cognitive deficits, oxidative stress and mitochondria dysfunction, which was associated with the elevation of reactive oxygen species level, the decrease of oxidative phosphorylation parameters, the loss of mitochondrial membrane potential, the reduce in Bcl-2/Bax ratio, and the release of cytochrome c. Baicalein alleviated cognitive and motor impairments and decreased mitochondria reactive oxygen species production, in accordance with its improvements on membrane potential level, oxidative phosphorylation process, mitochondrial swelling degree, Bcl-2/Bax ratio and cytochrome c release. These data indicated that baicalein might have therapeutic potential for the treatment of dementia caused by chronic cerebral hypoperfusion, contributed to its protections on brain mitochondrial homeostasis and function.

White Matter Damage and Hippocampal Neurodegeneration Induced by Permanent Bilateral Occlusion of Common Carotid Artery in the Rat: Comparison between Wistar and Sprague-Dawley Strain

In order to reproduce chronic cerebral hypoperfusion as it occurs in human aging and Alzheimer's disease, we introduced permanent, bilateral occlusion of the common carotid arteries (BCCAO) in rats (Farkas et al, 2007). Here, we induced BCCAO in two different rat strains in order to determine whether there was a strain difference in the pathogenic response to BCCAO. Male Wistar and Sprague-Dawley (SD) rats (250-270 g) were subjected to BCCAO for three weeks. Klüver-Barrera and cresyl violet staining were used to evaluate white matter and gray matter damage, respectively. Wistar rats had a considerably higher mortality rate (four of 14 rats) as compared to SD rats (one of 15 rats) following BCCAO. Complete loss of pupillary light reflex occurred in all Wistar rats that survived, but loss of pupillary light reflex did not occur at all in SD rats. Moreover, BCCAO induced marked vacuolation in the optic tract of Wistar rats as compared to SD rats. In contrast, SD rats showed fewer CA1 hippocampal neurons than Wistar rats following BCCAO. These results suggest that the neuropathological process induced by BCCAO takes place in a region-specific pattern that varies according to the strain of rat involved.

DDPH: improving cognitive deficits beyond its alpha 1-adrenoceptor antagonism in chronic cerebral hypoperfused rats

DDPH (1-(2, 6-dimethylphenoxy)-2-(3, 4-dimethoxyphenylethylamino) propane hydrochloride), a candidate drug known to be an alpha(1)-adrenoceptor antagonist, can efficiently penetrate through blood brain barrier and inhibit the contraction of vascular smooth muscle in the brain. In rats with chronic cerebral hypoperfusion after permanent bilateral carotid artery ligation, we found that DDPH treatment at 6 or 12 mg/kg per day for 30 days significantly reversed pathological changes such as glial cell proliferation and nuclei shrinkage and reduced neuronal cell loss. In vivo electrophysiological studies revealed that DDPH increased long-term potentiation that was inhibited in these animals. In water maze tests, the percentage of time spent in the target quadrant (Q3) for ischemic rats (20.17+/-2.87%) was much shorter than that for the sham rats (45.39+/-3.68%), but DDPH at 12 mg/kg increased the time (39.58+/-3.77%) spent in Q3 in ischemic rats by 96.23%. These data suggested that DDPH improved the learning and memory performance significantly in rats with ischemia induced by bilateral carotid artery ligation. DDPH also lowered the levels of malondialdehyde (MDA), which was increased in the hypoperfused rats, and enhanced the activities of superoxide dismutase (SOD) and glutathione peroxidase, which were decreased in these rats. Further more, immunohistochemistry, RT-PCR assays and Western blot study demonstrated that DDPH attenuated the decreased expression of NMDAR2B (NR2B) in cortex and hippocampal CA1 region of the rats after bilateral carotid artery ligation. Our results suggest that DDPH may have favorable effects for the subjects in cerebrovascular insufficiency state following ischemic stroke.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Effects of cyclooxygenase (COX) inhibition on memory impairment and hippocampal damage in the early period of cerebral hypoperfusion in rats

Chronic cerebral hypoperfusion is related to neurological disorders and contributes to a cognitive decline. Its experimental model in rats is permanent, bilateral common carotid artery occlusion. The cyclooxygenase (COX) system plays a pivotal role in the evolution of ischemic brain damage. Several COX inhibitors have proved to be neuroprotective in stroke models. We set out to characterize the effects of COX inhibitors in rats with permanent cerebral hypoperfusion. Some of the animals were exposed to two-vessel occlusion (n=72), while the others served as sham-operated controls (n=54). This was followed by a 3-day post-treatment with the nonselective COX inhibitor indomethacin (3 mg/kg) or with the selective COX-2 inhibitor NS-398 (15 mg/kg) or with the solvent. Some groups of the animals were sacrificed after 3 days, while the remainder were tested in the Morris watermaze for 5 days, and were sacrificed after 2 weeks. Neurons in the hippocampus were subjected to immunocytochemical labeling with cresyl violet, the dendrites with microtubule-associated protein-2, astrocytes with glial fibrillary acidic protein and microglia activation with OX-42 antibody. Two-vessel occlusion induced a learning impairment, mild neuronal damage, marked dendritic injury and moderate astrocytic reaction in the hippocampus. NS-398, but not indomethacin improved the survival rate and abolished the learning disability. However, both drugs increased the proportion of animals displaying neuronal damage. Glial markers revealed a time-dependent elevation in both the sham and the two-vessel occluded group, and were unaffected by the treatments. In summary, NS-398 prevented the hypoperfusion-induced memory impairment, but not by protecting the hippocampal neurons.

Pre-treatment and post-treatment with α-tocopherol attenuates hippocampal neuronal damage in experimental cerebral hypoperfusion

Alpha-tocopherol, a potent antioxidant, has been widely investigated as a dietary supplement with which to reduce the risk of atherosclerosis, and has recently been considered as a potential supplement to moderate oxidative neuronal damage in Alzheimer's disease patients. Since alpha-tocopherol appears beneficial in vascular and neurodegenerative disorders, we set out to identify its neuroprotective action in a rat model of chronic cerebral hypoperfusion-induced brain injury. The bilateral common carotid arteries of male Wistar rats were permanently occluded (2VO). Sham-operated animals served as controls. Half of the animals were pre- or post-treated repeatedly with alpha-tocopherol (5x100 mg/kg daily, i.p.), the other half receiving only soybean oil, the alpha-tocopherol vehicle. One week after the onset of 2VO, the spatial learning capacity of the animals was assessed in the Morris water maze. After testing, hippocampal slices were stained with cresyl violet in order to examine the pyramidal cell layer integrity. The density of microtubule-associated protein-2 (MAP-2)-positive dendrites and the OX-42-labeled microglial activation level were determined immunocytochemically. Finally, alpha-tocopherol was determined in the peripheral tissues, blood and brain. Alpha-tocopherol moderated the 2VO-induced learning impairment. The various forms of alpha-tocopherol treatment, and particularly the post-treatment, prevented the 2VO-induced pyramidal cell death and the activation of microglia in the hippocampus CA1 region, and the degeneration of MAP-2-positive dendrites in the CA3 region. The alpha-tocopherol concentration was elevated in the peripheral tissues and the blood, but not in the brain. The data indicate that alpha-tocopherol, particularly when administered as post-treatment, is neuroprotective in chronic cerebral hypoperfusion.

The enigma of vascular cognitive disorder and vascular dementia

The prevalence, morphology and pathogenesis of vascular dementia (VaD), recently termed vascular cognitive impairment, are a matter of discussion, and currently used clinical diagnostic criteria show moderate sensitivity (average 50%) and variable specificity (range 64-98%). In Western clinic-based series, VaD is suggested in 8-10% of cognitively impaired aged subjects. Its prevalence in autopsy series varies from 0.03 to 58%, with reasonable values of 8-15%, while in Japan it is seen in 22-35%. Neuropathologic changes associated with cognitive impairment include multifocal and/or diffuse disease and focal lesions: multi-infarct encephalopathy, white matter lesions or arteriosclerotic subcortical (leuko)encephalopathy, multilacunar state, mixed cortico-subcortical type, borderline/watershed lesions, rare granular cortical atrophy, post-ischemic encephalopathy and hippocampal sclerosis. They result from systemic, cardiac and local large or small vessel disease. Recent data indicate that cognitive decline is commonly associated with widespread small ischemic/vascular lesions (microinfarcts, lacunes) throughout the brain with predominant involvement of subcortical and functionally important brain areas. Their pathogenesis is multifactorial, and their pathophysiology affects neuronal networks involved in cognition, memory, behavior and executive functioning. Vascular lesions often coexist with Alzheimer disease (AD) and other pathologies. Minor cerebrovascular lesions, except for severe amyloid angiopathy, appear not essential for cognitive decline in full-blown AD, while both mild Alzheimer pathology and small vessel disease may interact synergistically. The lesion pattern of "pure" VaD, related to arteriosclerosis and microangiopathies, differs from that in mixed-type dementia (AD with vascular encephalopathy), more often showing large infarcts, which suggests different pathogenesis of both types of lesions. Due to the high variability of cerebrovascular pathology and its causative factors, no validated neuropathologic criteria for VaD are available, and a large variability across laboratories still exists in the procedures for morphologic examination and histology techniques.