Glial activation and white matter changes in the rat brain induced by chronic cerebral hypoperfusion: an immunohistochemical study

Association of matrix metalloproteinases with MRI indices of brain ischemia and aging

Magnetic resonance imaging (MRI) findings of large white matter hyperintensities (LWMH), decreased brain volume and silent cerebral infarcts (SCI) are subclinical indices of brain ischemia and aging. Although the pathophysiology of these findings remains uncertain, extracellular matrix (ECM) remodeling, a process regulated by matrix metalloproteinases (MMPs) and their inhibitors (TIMPs), may be implicated. We evaluated the cross-sectional relations of circulating MMP-9 and TIMP-1 to these MRI indices in 583 stroke and dementia-free, Framingham Offspring participants (mean age 57 years, 58% women). Using multivariable regression MMP-9 (detectable versus non-detectable) and TIMP-1 (modeled as sex-specific quartiles) were related to LWMH (>1S.D. above age-specific mean; yes/no), SCI (yes/no) and total brain volume (ratio of parenchymal to intracranial volume, TCBVr). Mean TCBVr was 0.78 (S.D. 0.03), 13% of subjects had LWMH and 12% had SCI. Detectable MMP-9 was associated with higher prevalence of LWMH (OR 2.09, 95%confidence interval (CI) 1.00-4.37), but not with TCBVr. TIMP-1 was associated with a high prevalence of LWMH (OR for Q4 versus Q1-3: 1.83, 95%CI 1.06-3.18) and with lower mean TCBVr (Q4 associated with 0.17 S.D. units lower value relative to Q1-3; p=0.04). Neither biomarker was associated with SCI. Our findings are preliminary but if confirmed in further studies, suggest a pathophysiological role for the MMP/TIMP pathway in processes of brain ischemia and aging.

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

Cerebral small vessel disease (SVD) is a major cause of stroke and dementia. Pathologically, three lesions are seen: small vessel arteriopathy, lacunar infarction, and diffuse white matter injury (leukoaraiosis). Appropriate experimental models would aid in understanding these pathologic states and also in preclinical testing of therapies. The objective was to perform a systematic review of animal models of SVD and determine whether these resemble four key clinicopathologic features: (1) small, discrete infarcts; (2) small vessel arteriopathy; (3) diffuse white matter damage; (4) cognitive impairment. Fifteen different models were included, under four categories: (1) embolic injuries (injected blood clot, photochemical, detergent-evoked); (2) hypoperfusion/ischaemic injury (bilateral common carotid occlusion/stenosis, striatal endothelin-1 injection, striatal mitotoxin 3-NPA); (3) hypertension-based injuries (surgical narrowing of the aorta, or genetic mutations, usually in the renin-angiotensin system); (4) blood vessel damage (injected proteases, endothelium-targeting viral infection, or genetic mutations affecting vessel walls). Chronic hypertensive models resembled most key features of SVD, and shared the major risk factors of hypertension and age with human SVD. The most-used model was the stroke-prone spontaneously hypertensive rat (SHR-SP). No model described all features of the human disease. The optimal choice of model depends on the aspect of pathophysiology being studied.

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.

Chronic hypoperfusion increases claudin-3 immunoreactivity in rat brain

Chronic hypoperfusion-induced changes in blood-brain barrier (BBB) tight junction components have not been well studied. In the present study, we investigated the temporal profiles of claudin-3 (a BBB tight junction element) and myleoperoxidase (MPO, a marker of neutrophil infiltration) in the cortical and thalamic regions of rat brain subjected to chronic cerebral hypoperfusion. Chronic cerebral hypoperfusion was induced by an occlusion of two common carotid arteries and the immunoreactivity of claudin-3 or MPO was determined at 1, 2, 3, or 6 weeks after the occlusion. A typical pattern of BBB breakdown was observed from 2 weeks of the occlusion in cortical and thalamic regions based on Evans Blue leakage. Claudin-3 immunoreactivity was increased only in cortical regions after 2 weeks of occlusion. However, after 3 weeks of occlusion, marked increases in claudin-3 immunoreactivity were observed in both cortical and thalamic regions (P<0.05), which persisted for at least 6 weeks after the occlusion despite a slight reduction. In contrast, MPO immunoreactivity was increased only in the thalamic regions after 2 weeks of occlusion. But the pattern of MPO immunoreactivity at 3 and 6 weeks after the occlusion was same as claudin-3. At these time points, MPO immunoreactivity was significantly increased in both cortical and thalamic regions (P<0.05). These results show that chronic cerebral hypoperfusion increases the immunoreactivity of claudin-3 and neutrophil infiltration in cortical and thalamic regions of the brain, and demonstrate changes in BBB tight junction status during chronic cerebral hypoperfusion.

Protective effects of cilostazol against transient focal cerebral ischemia and chronic cerebral hypoperfusion injury

Cilostazol increases intracellular cyclic adenosine monophosphate (cyclic AMP) levels by inhibiting type III phosphodiesterase. It was approved by the Food and Drug Administration for the treatment of intermittent claudication. Its principal actions include inhibition of platelet aggregation, antithrombotic action in cerebral ischemia, and vasodilation, mediated by increased cyclic AMP levels. In a multicenter, randomized, placebo-controlled, double-blind clinical trial, cilostazol has been shown to protect patients from recurrent cerebral infarction. It has been recently suggested that cilastozol could be useful in the treatment of transient focal cerebral ischemic injury. Beneficial effects of cilostazol in cerebral ischemic infarction and edema formation has been confirmed in rats by the magnetic resonance imaging (MRI). The preventive effect was ascribed to cAMP-dependent protein kinase (PKA)-coupled maxi-K channel activation with additional antioxidant and poly(adenosine diphosphate [ADP]-ribose) polymerase inhibitory actions. Most recently, cilostazol has been shown to prevent vacuolation and rarefaction in the white matter of the rats subjected to chronic cerebral hypoperfusion in association with suppression of astrocyte and microglial activation. Taken together, recent experimental studies with cilostazol showed promising results in cerebral ischemia and chronic cerebral hypoperfusion.

The leukoaraiosis is more prevalent in the large artery atherosclerosis stroke subtype among Korean patients with ischemic stroke

Background

Several studies have suggested that the specific stroke subtype may influence the presence of leukoaraiosis in patients with ischemic stroke. We investigated the association between stroke subtype and leukoaraiosis in Korean patients with ischemic stroke by MRI.

Methods

There were 594 patients included in this study that were classified as large artery disease, lacune and cardioembolic stroke. For large-artery disease, the analysis focused on the intracranial or extracranial location of the stenosis, and the multiplicity of the stenotic lesions. Leukoaraiosis grading was performed according to the Atherosclerosis Risk in Communities Study.

Results

There was a significant association between leukoaraiosis and the stroke subtypes; the large-artery-disease group had a higher prevalence of leukoaraiosis than did the other groups (55.4% in the large-artery-disease group, 30.3% in the lacunar group and 14.3% in the cardioembolic group, P = 0.016 by chi-square test). On the multivariate linear regression analysis, age, the presence of hypertension, previous stroke and stroke subtype were independently associated with the presence of leukoaraiosis. In the sub analysis of the large-artery-disease group, the leukoaraiosis had a tendency to be more prevalent in the mixed and intracranial stenosis group than did the extracranial stenosis group (45.5% in the mixed group, 40.3% in the intracranial group and 26.9% in the extracranial group, P = 0.08 by chi-square test).

Conclusion

The association of leukoaraiosis with large-artery disease in this study might be due to the relatively high prevalence of intracranial occlusive lesions in Korean stroke patients compared to other ethnic groups.

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.

Citicoline protects against cognitive impairment in a rat model of chronic cerebral hypoperfusion

Background and purpose

Cerebral white matter (WM) lesions are frequently observed in human cerebrovascular diseases, and are believed to be responsible for cognitive impairment. Various neuroprotective agents can suppress this type of WM or neuronal damage. In this study, we investigated whether citicoline, a drug used to treat acute ischemic stroke, can attenuate WM lesions and cognitive decline caused by chronic hypoperfusion in the rat.

Methods

Animals were divided into immediate- and delayed-treatment groups. Those in the immediate-treatment group received a sham operation, citicoline (500 mg/kg/day), or phosphate buffered saline (PBS) treatment. Citicoline or PBS was administered intraperitoneally for 21 days after occluding the bilateral common carotid arteries. Rats in the delayed-treatment group were intraperitoneally administered with either 500 mg/kg/day citicoline or PBS for 21 days beginning on the 8th day after the operation. From the 17th day of administration, the rats were placed in an eight-arm radial maze to examine their cognitive abilities. After completing the administration, tissues were isolated for Klüver-Barrera and the terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL) staining.

Results

In the immediate-treatment group, cognitive functions were preserved in the citicoline-treated group, and WM damage and TUNEL-positive cells differed significantly between the citicoline- and PBS-treated animals. In the delayed-treatment group, there was no decrease in WM damage and TUNEL-positive cells, but cognitive improvement was evident for citicoline treatment relative to PBS treatment.

Conclusions

These results show that citicoline can prevent WM damage and aid cognitive improvement, even after a certain extent of disease progression. Citicoline might be useful in patients with acute ischemic stroke as well as in chronic stroke accompanied with cognitive impairment.

Mucosal tolerization to E-selectin protects against memory dysfunction and white matter damage in a vascular cognitive impairment model

Vascular cognitive impairment (VCI) is the second most prevalent type of dementia in the world. The white matter damage that characterizes the common subcortical ischemic form of VCI can be modeled by ligating both common carotid arteries in the Wistar rat to induce protracted cerebral hypoperfusion. In this model, we find that repetitive intranasal administration of recombinant E-selectin to induce mucosal tolerance and to target immunomodulation to activating blood vessels potently suppresses both white matter (and possibly gray matter) damage and markers of vessel activation (tumor necrosis factor and E-selectin); it also preserves behavioral function in T-maze spontaneous alternation, T-maze spatial discrimination memory retention, and object recognition tests. Immunomodulation may be an effective novel strategy to prevent progression of VCI.

An inhibition of ceruloplasmin expression induced by cerebral ischemia in the cortex and hippocampus of rats

OBJECTIVE

To explore effects of cerebral ischemia on the ceruloplasmin (Cp) expression in the cortex and hippocampus of rats.

METHODS

Male Wistar rats were randomly divided into cerebral ischemia group and control group. Cerebral ischemia was induced by ligating bilateral common carotid arteries and the ischemic rats were further subgrouped according to ischemia time. The control rats received a sham operation. The expression of Cp mRNA in the cortex and hippocampus was measured by reverse transcription polymerase chain reaction (RT-PCR). The Cp expression was shown by immunohistochemistrical (streptavidin peroxidase, SP) method.

RESULTS

In ischemia group, the expression of Cp mRNA in the cortex and hippocampus decreased compared with that in control group (P< 0.01); and the longer rats experienced cerebral ischemia, the lower Cp mRNA expressed. By immunohistochemistry, Cp was shown expressed in the neural cells including epithelial cells of choroid plexus, ependymal cells, astrocytes of cortex and hippocampus, and vascular endothelial cells, but not in pyramidal cells and granulosa cells of cortex and hippocampus. Cp levels in the cortex and hippocampus decreased in rats suffering from cerebral ischemia for 3 d, 7 d and 28 d but not in rats exposed to ischemia for 1 d compared with that in control group (P< 0.05). Iron concentration correlated negatively with Cp expression in the cortex and hippocampus of rats exposure to ischemia (the cortex, r = -0.831, P< 0.01; the hippocampus, r = -0.809, P< 0.01).

CONCLUSION

Cerebral ischemia inhibited Cp expression in the cortex and hippocampus of rats. The decrease of Cp might be involved in iron deposition in neurons.

Chronic cerebral hypoperfusion induced by right unilateral common carotid artery occlusion causes delayed white matter lesions and cognitive impairment in adult mice

Some lines of evidence have suggested that subcortical ischemic vascular dementia (SIVD) is a common form of vascular dementia (VaD), and that its pathological changes are the development of ischemic white matter (WM) lesions under chronic hypoperfusion and lacunes. Here, we have developed a novel mouse model of VaD with WM lesions, which was induced by right unilateral common carotid artery occlusion (rUCCAO). The mice subjected to rUCCAO exhibited chronic cerebral hypoperfusion in the cerebral hemisphere ipsilateral to rUCCAO monitored using a laser-Doppler flow meter (p<0.01), and significant WM damage in the corpus callosum (p<0.05) and deficits in object recognition test correlated with the damage of frontal-subcortical circuits (p<0.01). However, no differences in spontaneous alternation or spontaneous motor activity were observed. Furthermore, the levels of pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta) and interleukin-6 (IL-6), significantly increased (p<0.01), and those of anti-inflammatory cytokines, such as interleukin-4 (IL-4) and interleukin-10 (IL-10), significantly decreased in the ischemic brain (p<0.05). These results suggest that this model is a useful tool for investigating the associations among inflammatory reactions, cognitive impairment, and WM damage, which may help elucidating the pathomechanism of VaD, particularly SIVD.

Ramipril protects from free radical induced white matter damage in chronic hypoperfusion in the rat

We investigated whether the angiotensin converting enzyme inhibitor, ramipril, could attenuate white matter lesions caused by chronic hypoperfusion in the rat, and whether suppression of oxidative stress is involved in the resulting neuroprotection. The ramipril treatment group showed significant protection from development of white matter lesions in the optic tract, the anterior commissure, the corpus callosum, the internal capsule and the caudoputamen. The level of malondialdehyde (MDA) and the oxidized glutathione (GSSG)/total glutathione (GSH t) ratio was also significantly decreased in the ramipril group compared to the vehicle-treated group. These results suggest that ramipril can protect against white matter lesions that result from chronic ischemia due to its effects on free radical scavenging. Further efficacy should be studied in the treatment of cerebrovascular insufficiency states and vascular dementia.

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.

Selective Impairment of Working Memory in a Mouse Model of Chronic Cerebral Hypoperfusion

BACKGROUND AND PURPOSE

We recently designed a mouse model of chronic cerebral hypoperfusion, in which the cerebral white matter is damaged without significant gray matter lesions. The behavioral characteristics of these mice were studied using a test battery for neurological and cognitive functions.

METHODS

Adult C57Bl/6 male mice were subjected to either sham-operation or bilateral common carotid artery stenosis (BCAS) using microcoils with an internal diameter of 0.18 mm. At 30 days after BCAS, 70 animals were divided into 3 groups and subjected to behavioral test batteries. The first group underwent comprehensive behavioral test, including the neurological screen, prepulse inhibition, hot plate, open field, light/dark transition, Porsolt forced swim and contextual and cued fear conditioning (BCAS n=13; sham-operated n=11). The second group was for the working memory task of the 8-arm radial maze test (BCAS n=12; sham-operated n=10), and the third for the reference memory task of the 8-arm radial maze test (BCAS n=13; sham-operated n=11). Another batch of animals were examined for histological changes (BCAS n=11; sham-operated n=12).

RESULTS

The white matter including the corpus callosum was consistently found to be rarefied without clear ischemic lesions in the hippocampus. No apparent differences were observed in the comprehensive test batteries between the control and BCAS mice. However, in the working memory tasks tested with the 8-arm radial maze, the BCAS mice made significantly more errors than the control mice (P<0.0001). Again, there were no detectable differences in the reference memory tasks between the groups.

CONCLUSIONS

At 30 days after BCAS, working memory deficits as well as white matter changes were apparent in the mice. Working memory deficit was attributable to damage of the frontal-subcortical circuits, suggesting the BCAS model is useful to evaluate the substrates of subcortical vascular dementia.

Persistent activation of microglia is associated with neuronal dysfunction of callosal projecting pathways and multiple sclerosis-like lesions in relapsing--remitting experimental autoimmune encephalomyelitis

Cortical pathology, callosal atrophy and axonal loss are substrates of progression in multiple sclerosis (MS). Here we describe cortical, periventricular subcortical lesions and callosal demyelination in relapsing-remitting experimental autoimmune encephalomyelitis in SJL mice that are similar to lesions found in MS. Unlike the T-cell infiltrates that peak during acute disease, we found that microglia activation persists through the chronic disease phase. Microglia activation correlated with abnormal phosphorylation of neurofilaments in the cortex and stripping of synaptic proteins in cortical callosal projecting neurons. There was significant impairment of retrograde labeling of NeuN-positive callosal projecting neurons and reduction in the labelling of their transcallosal axons. These data demonstrate a novel paradigm of cortical and callosal neuropathology in a mouse model of MS, perpetuated by innate immunity. These features closely mimic the periventricular and cortical pathology described in MS patients and establish a model that could be useful to study mechanisms of progression in MS.

l-3-n-Butylphthalide Improves Cognitive Impairment Induced by Chronic Cerebral Hypoperfusion in Rats

3-n-Butylphthalide (NBP) may be beneficial for the treatment of ischemic stroke with multiple actions on different pathophysiological processes. In the present study, we investigated the effect of NBP isomers on learning and memory impairment induced by chronic cerebral hypoperfusion in rats. Male Wistar rats were orally administered 10 and 30 mg/kg l-, d-, or dl-NBP daily for 23 days after bilateral permanent occlusion of the common carotid arteries. Rats receiving 10 mg/kg l-NBP performed significantly better in tests for spatial learning and memory, and they had attenuated cerebral pathology, including neuronal damage, white matter rarefaction, and glial activation compared with controls. Furthermore, 10 mg/kg l-NBP-treated rats had significantly higher choline acetyltransferase activity, decreased cortical lipid peroxide, and reduced hippocampal superoxide dismutase activity, compared with vehicle controls. However, d- and dl-NBP did not show significant beneficial effects. The present findings demonstrate that the beneficial effects of l-NBP on hypoperfusion-induced cognitive deficits may be due to preventing neuropathological alterations, inhibiting oxidative damage and increasing acetylcholine synthesis. Our results strongly suggest that l-NBP has therapeutic potential for the treatment of dementia caused by decreased cerebral blood flow.

Expression of S100 protein and protective effect of arundic acid on the rat brain in chronic cerebral hypoperfusion

S100 protein is expressed primarily by astroglia in the brain, and accumulates in and around the ischemic lesions. Arundic acid, a novel astroglia-modulating agent, is neuroprotective in acute cerebral infarction, whereas the protective effects remain unknown during chronic cerebral hypoperfusion. Rats undergoing chronic cerebral hypoperfusion were subjected to a bilateral ligation of the common carotid arteries, and were allowed to survive for 3, 7 and 14 days. The animals received a daily intraperitoneal injection of 5.0, 10.0 or 20.0 mg/kg of arundic acid, or vehicle, for 14 days. Alternatively, other groups of rats received a delayed intraperitoneal injection of 20.0 mg/kg of arundic acid or vehicle, which started from 1, 3 or 7 days after ligation and continued to 14 days. The degree of white matter (WM) lesions and the numerical density of S100 protein-immunoreactive astroglia were estimated. In the WM of rats with vehicle injections, the number of S100 protein-immunoreactive astroglia increased significantly after chronic cerebral hypoperfusion as compared to the sham-operation. A dosage of 10.0 and 20.0 mg/kg of arundic acid suppressed the numerical increase in S100 protein-immunoreactive astroglia and the WM lesions. These pathological changes were suppressed with delayed treatment up to 7 days in terms of astroglial activation, and up to 3 days in terms of the WM lesions. The protective effects of arundic acid against WM lesions were demonstrated in a dose-dependent manner, and even after postischemic treatments. These results suggest the potential usefulness of arundic acid in the treatment of cerebrovascular WM lesions.

Matrix Metalloproteinase-2 Plays a Critical Role in the Pathogenesis of White Matter Lesions After Chronic Cerebral Hypoperfusion in Rodents

BACKGROUND AND PURPOSE

Cerebrovascular white matter (WM) lesions contribute to cognitive impairment and motor dysfunction in the elderly. A disruption of the blood-brain barrier (BBB) is believed to be a critical early event leading to these WM lesions. Previous studies have suggested the involvement of matrix metalloproteinase-2 (MMP-2) in BBB disruptions and the upregulation of MMP-2 after chronic cerebral hypoperfusion in a rat model. In the present study, we asked whether MMP-2 is involved in the BBB disruption and the subsequent WM lesions after chronic cerebral hypoperfusion.

METHODS

We compared the severity of white matter lesions in rats after chronic cerebral hypoperfusion with or without an MMP inhibitor. Then, we also induced the chronic cerebral hypoperfusion in wild-type and MMP-2-null mice.

RESULTS

In the rats treated with a relatively selective MMP-2 inhibitor, AG3340, the WM lesions after chronic cerebral hypoperfusion were significantly less severe, and the number of activated astroglia and microglia were also significantly lower as compared with the vehicle-treated rats. Gene knockout of MMP-2 also reduced the severity of the WM lesions and the number of activated astroglia and microglia in a mice system. In both rodents, the disruption of BBB function, as assessed by IgM staining and the Evans blue extravasation test, was less severe when MMP-2 activity was attenuated.

CONCLUSIONS

These findings indicate that MMP-2 plays a critical role in the BBB disruption, glial cell activation, and WM lesions after chronic cerebral hypoperfusion and suggest the potential value of MMP-2 inhibitors as a therapeutic tool in cerebrovascular WM lesions.

Neuroprotection by cilostazol, a phosphodiesterase type 3 inhibitor, against apoptotic white matter changes in rat after chronic cerebral hypoperfusion

In the present study, we elucidated effect of cilostazol to prevent the occurrence of vacuolation and rarefaction of the white matter in association with apoptosis induced by bilateral occlusion of common carotid arteries in the male Wistar rats. Rats orally received vehicle (DMSO) or 60 mg kg(-1) day(-1) (orally) cilostazol for 3, 7, 14 or 30 days. In the vehicle group, increased vacuolation and rarefactions in the white matter were accompanied by extensive activation of both microglial and astroglial cells with suppression of oligodendrocytes in association with increased TNF-alpha production, caspase-3 immunoreactivity and TUNEL-positive cells in the white matter including optic tract. Post-treatment with cilostazol (60 mg kg(-1) day(-1)) strongly suppressed not only elevated activation of astroglia and microglia but also diminished oligodendrocytes following chronic cerebral hypoperfusion. In conclusion, cilostazol (60 mg kg(-1) day(-1), orally) significantly reduced the apoptotic cell death in association with decreased TNF-alpha production and caspase-3-positive cells in the white matter of rat brains subjected to bilateral occlusion of common carotid arteries, consequently ameliorating vacuoles and rarefaction changes in the white matter.

Age-related microvascular degeneration in the human cerebral periventricular white matter

Clinical studies have identified white matter (WM) lesions as hyperintensive regions in the MRI images of elderly patients. Since a cerebrovascular origin was attributed to such lesions, the present analysis set out to define the microvascular histopathologic changes in the periventricular WM in the aged. Post-mortem samples of the frontal, parietal, and occipital periventricular WM of 40-90-year-old subjects were prepared for quantitative light and electron microscopy. Light microscopic examination revealed microvascular fibrohyalinosis as the most common type of microvascular damage in the elderly. Ultrastructural analysis identified the microvascular thickening as collagen deposits affecting the basement membrane. The vascular density did not correlate with the age. The basement membrane pathology significantly increased, while the number of intact microvessels gradually decreased, with advancing age in the frontal and occipital WM. Finally, peripheral atherosclerosis coincided with massive microvascular fibrosis, particularly in the frontal WM. Our results demonstrate an age-related microvascular degeneration in the periventricular WM, which may contribute to the development of WM lesions by hindering a sufficient supply of nutrients to the affected WM sites. Furthermore, the data accord with previous observations identifying the frontal lobe as the site at which WM vulnerability is most pronounced. Finally, atherosclerosis in large, peripheral vessels is considered to be a predictive marker of microvascular pathology in the WM.

Minocycline attenuates white matter damage in a rat model of chronic cerebral hypoperfusion

White matter lesions are thought to result from chronic cerebral ischemia and constitute a core pathology of subcortical vascular dementia. This rarefaction has been known to be associated with microglial activation. We investigated whether minocycline, a microglial inhibitor, attenuates the white matter damage induced by chronic cerebral hypoperfusion that is used as a model of vascular dementia. Male Wistar rats were subjected to bilateral, permanent occlusion of the common carotid arteries (BCCAO) to induce chronic cerebral hypoperfusion. Minocycline or saline was injected daily for 2 weeks after BCCAO. In the corpus callosum and the optic tract, white matter damage observed with Klüver-Barrera staining was significantly attenuated in the minocycline-treated group compared to saline-treated controls. In control rats, immunoreactivities of major basic protein (MBP), Ox-42 as a microglial marker, and matrix metalloproteinase (MMP)-2 were increased in the corpus callosum. Minocycline significantly reduced these changes. Co-expression of Ox-42 and MMP-2 was confirmed by double immunofluorescence histochemistry. Our results suggest that chronic treatment with minocycline could be protective against at least some ischemic white matter damage, and its mechanism may be related to suppressing microglial activation.

Enhanced brain angiogenesis in chronic cerebral hypoperfusion after administration of plasmid human vascular endothelial growth factor in combination with indirect vasoreconstructive surgery

OBJECT

Vascular endothelial growth factor (VEGF) is a secreted mitogen associated with angiogenesis. The conceptual basis for therapeutic angiogenesis after plasmid human VEGF gene (phVEGF) transfer has been established in patients presenting with limb ischemia and myocardial infarction. The authors hypothesized that overexpression of VEGF using a gene transfer method combined with indirect vasoreconstruction might induce effective brain angiogenesis in chronic cerebral hypoperfusion, leading to prevention of ischemic attacks.

METHODS

A chronic cerebral hypoperfusion model induced by permanent ligation of both common carotid arteries in rats was used in this investigation. Seven days after induction of cerebral hypoperfusion, encephalomyosynangiosis (EMS) and phVEGF administration in the temporal muscle were performed. Fourteen days after treatment, the VEGF gene therapy group displayed numbers and areas of capillary vessels in temporal muscles that were 2.2 and 2.5 times greater, respectively, in comparison with the control group. In the brain, the number and area of capillary vessels in the group treated with the VEGF gene were 1.5 and 1.8 times greater, respectively, relative to the control group.

CONCLUSIONS

In rat models of chronic cerebral hypoperfusion, administration of phVEGF combined with indirect vasoreconstructive surgery significantly increased capillary density in the brain. The authors' results indicate that administration of phVEGF may be an effective therapy in patients with chronic cerebral hypoperfusion, such as those with moyamoya disease.

Astrocytes react to oligemia in the forebrain induced by chronic bilateral common carotid artery occlusion in rats

The effects of oligemia (moderate ischemia) on the brain need to be explored because of the potential role of subtle microvascular changes in vascular cognitive impairment and dementia. Chronic bilateral common carotid artery occlusion (BCCAO) in adult rats has been used to study effects of oligemia (hypoperfusion) using neuropathological and neurochemical analysis as well as behavioral tests. In this study, BCCAO was induced for 1 week, or 2, 4, and 6 months. Sensitive immunohistochemistry with marker proteins was used to study reactions of astrocytes (GFAP, nestin), and lectin binding to study microglial cells during BCCAO. Overt neuronal loss was visualized with NeuN antibodies. Astrocytes reacted to changes in the optic tract at all time points, and strong glial reactions also occurred in the target areas of retinal fibers, indicating damage to the retina and optic nerve. Astrocytes indicated a change in the corpus callosum from early to late time points. Diffuse increases in GFAP labeling occurred in parts of the neocortex after 1 week of BCCAO, in the absence of focal changes of neuronal marker proteins. No significant differences emerged in the cortex at longer time points. Nestin labeling was elevated in the optic tract. Reactions of microglia cells were seen in the cortex after 1 week. Measurements of the basilar artery indicated a considerable hypertrophy, indicative of macrovascular compensation in the chronic occlusion model. These results indicate that chronic BCCAO and, by inference, oligemia have a transient effect on the neocortex and a long-lasting effect on white matter structures.

Upregulation of ceramide and its regulating mechanism in a rat model of chronic cerebral ischemia

Ceramide is a key mediator of apoptosis, and is involved in the cellular stress response. We examined the alterations in the ceramide levels and their synthetic/degradative pathway in a rat model of chronic cerebral ischemia, in which ischemic white matter (WM) lesions occur in association with oligodendroglial cell apoptosis. Chronic cerebral ischemia was induced by clipping both common carotid arteries in male Wistar rats. After predetermined periods of 1, 3, 7 and 14 days, the animals were subjected to immunohistochemical and biochemical investigations for ceramide in the region containing the frontal cortex and corpus callosum (region 1), and the region containing the internal capsule and globus pallidus (region 2). After 14 days, the myelin was degraded in the corpus callosum, internal capsule and the optic tract in Klüver-Barrera staining. There was a significant increase in the ceramide level and the activity of its synthetic enzyme, acidic sphingomyelinase (SMase), whereas its degrading enzyme, glucosylceramide synthase (GCS), was downregulated in both regions 1 and 2 as compared to the sham-operated rats. Simultaneously, ceramide immunoreactive glia increased in number in the corpus callosum and the internal capsule after 3, 7 and 14 days. Double labeling for ceramide with glial fibrillary acidic protein but not with leukocyte common antigen indicated the astroglial nature of these glia. These findings indicate that chronic cerebral ischemia induces an increased ceramide level in astroglia as a result of downregulation of GCS and an upregulation of ASMase activity.

Phosphate-related energy compounds are not exhausted in chronically hypoperfused rat brain cortex after cortical spreading depression

Long-term bilateral common carotid occlusion (BCCAO) in rats induces brain hypoperfusion and structural injury, and could have relevance as a model of vascular dementia in which cortical metabolism is reduced. The present study was designed to assess whether phosphate-related energy compounds and blood supplies are markedly affected by KCI-induced cortical spreading depression (CSD), which leads to metabolic and cerebral blood flow changes in rats with chronic BCCAO, by means of near-infrared spectroscopy and phosphorus magnetic resonance spectroscopy. Male Wistar rats were divided into 4 groups: BCCAO for 1 week (n = 6) and 4 weeks (n = 15), and sham operation for 1 week (n = 7) and 4 weeks (n = 7). The phosphocreatine (Pcr) index (PCr/PCr+Pi) and intracellular pH (pHi) were measured pre-CSD, just after KCl application, and at 20 and 40 minutes after CSD. Brains were evaluated by histology with hematoxylin and eosin and immunohistochemical reaction for glial fibrillary acidic protein (GFAP). Rapid signal changes of oxy-, deoxy-, and total hemoglobin were observed in all KCl-applied brains. The PCr index and pHi values in BCCAO were not different than those in control rats. The percentage of vacuolated area in the optic tract and percentage values of GFAP-positive area in the frontoparietal cortex were significantly increased in BCCAO. The generation of CSD was seen in regions of cortical gliosis induced by BCCAO, and severe energy exhaustion did not occur during or after CSD. Our results may suggest that the functional interaction of neurons and glia is sustained even in brain tissue where the metabolic state of neurons is impaired and astrocytes are proliferated.

White Matter Lesions and Glial Activation in a Novel Mouse Model of Chronic Cerebral Hypoperfusion

Background and Purpose— Cerebrovascular white matter (WM) lesions are closely associated with cognitive impairment and gait disorders in the elderly. We have successfully established a mouse model of chronic cerebral hypoperfusion that may provide new strategies for the molecular analysis of cerebrovascular WM lesions.

Methods— Adult C57Bl/6 male mice were subjected to bilateral common carotid artery stenosis (BCAS) using external microcoils with varying inner diameters from 0.16 to 0.22 mm. Cerebral blood flow (CBF) in the frontal cortices was measured by laser-Doppler flowmetry at 2 hours and at 1, 3, 7, 14, and 30 days after BCAS. The brains were then removed and examined at 30 days with histological stains and immunohistochemistry for markers of microglia and astroglia.

Results— At 2 hours, the CBF values (ratio to the preoperative value) did not change in the 0.22 mm group but decreased significantly to 77.3±13.4% in the 0.20 mm group, 67.3±18.5% in the 0.18 mm group, and 51.4±11.5% in the 0.16 mm group. At day 1, the CBF began to recover in all groups but remained significantly lower until 14 days in comparison to the control group. In the 0.20 mm and 0.18 mm groups, WM lesions occurred after 14 days without any gray matter involvement. These lesions were the most intense in the corpus callosum adjacent to the lateral ventricle but were mild in the anterior commissure and optic tract. In contrast, 4 of 5 mice developed some gray matter changes in the 0.16 mm group. The proliferation of activated microglia and astroglia was observed in the WM beyond 3 days after BCAS.

Conclusions— WM lesions were successfully induced after chronic cerebral hypoperfusion with relative preservation of the visual pathway. These features in this mouse model are appropriate for cognitive assessment and genetic analysis, and it may provide a powerful tool to understand the pathophysiology of WM lesions.

Diazoxide and dimethyl sulphoxide alleviate experimental cerebral hypoperfusion-induced white matter injury in the rat brain

Aging and dementia are accompanied by cerebral white matter (WM) injury, which is considered to be of ischemic origin. A causal link between cerebral ischemia and WM damage has been demonstrated in rats; however, few attempts appear to have been made to test potential drugs for the alleviation of ischemia-related WM injury. We induced cerebral hypoperfusion via permanent, bilateral occlusion of the common carotid arteries of rats. A mitochondrial ATP-sensitive potassium channel opener diazoxide (5 mg/kg) or its solvent dimethyl sulphoxide (DMSO) was administered i.p. (0.25 ml) on 5 consecutive days after surgery. Sham-operated animals served as control for surgery, and non-treated rats as controls for treatments. Thirteen weeks after surgery, the animals were sacrificed and astrocytes and microglia were labeled immunocytochemically in the internal capsule, the corpus callosum and the optic tract. The astrocytic proliferation was enhanced by cerebral hypoperfusion in the optic tract, and reduced by diazoxide in DMSO, but not by DMSO alone in the corpus callosum. After carotid artery occlusion, microglial activation was enhanced two-fold in the corpus callosum and four-fold in the optic tract. DMSO decreased microglial activation in the optic tract, while diazoxide in DMSO, but not DMSO alone, restored microglial activation to the control level in the corpus callosum. In summary, the rat optic tract appeared to be particularly vulnerable to ischemia, while the effect of diazoxide was restricted to the corpus callosum. We conclude that diazoxide dissolved in DMSO can moderate ischemia-related neuroinflammation by suppressing glial reaction in selective cerebral WM areas.

Ketamine attenuates hypocapnia-induced neuronal damage in the caudoputamen in a rat model of chronic cerebral hypoperfusion

We previously demonstrated that the caudoputamen was exclusively further damaged by hypocapnia in a rat with chronic cerebral hypoperfusion which is characterized by white matter lesions (WML) and a well-established model for patients with cerebrovascular diseases and/or dementia, and suggest that this process may be the cause of long lasting postoperative delirium or brain dysfunction in such patients. In the present study, we investigated whether ketamine, a non-competitive N-methyl-D-aspartate receptor antagonist, could attenuate the neuronal damage in the caudoputamen. Ketamine, at doses of 10 and 20 mg/kg, which was given intraperitoneally before hypocapnia induction, attenuated the aggravation of WML score, neuronal damage, and astroglial proliferation in the rat caudoputamen. These results suggest that ketamine may be beneficial for preventing postoperative brain dysfunction, especially in patients with cerebrovascular diseases and/or dementia induced by hypocapnia, which is likely to occur in the mechanical ventilation used during surgery.

Ibudilast, a phosphodiesterase inhibitor, protects against white matter damage under chronic cerebral hypoperfusion in the rat

Cerebrovascular white matter (WM) lesions, which are frequently observed in vascular cognitive impairment and vascular dementia, can be produced in rats by clipping the common carotid arteries bilaterally. Since TNF-alpha is known to cause the degeneration of myelin, we examined whether these lesions can be ameliorated by ibudilast, a cyclic AMP phosphodiesterase (PDE) inhibitor that suppresses tumor necrosis factor (TNF)-alpha production. After the ligation of both common carotid arteries in 29 rats, 21 rats received a daily oral administration of 10, 30 or 60 mg/kg ibudilast and 8 rats received vehicle for 14 days. The pathological changes in the white matter were quantified in terms of white matter lesions and the emergence of activated microglia immunoreactive for major histocompatibility complex (MHC) antigen. In the vehicle-treated animals, white matter lesions and microglial activation occurred in the optic tract, internal capsule and corpus callosum. A low dose (10 mg/kg) of ibudilast failed to suppress the white matter lesions and microglial activation, whereas a dose of either 30 or 60 mg/kg ibudilast ameliorated these lesions (p<0.001). Without an alterations in laboratory blood data, 60 mg/kg ibudilast exhibited percent reduction of the white matter lesions ranging between 50% and 70%, which was more effective than 30 mg/kg ibudilast (p<0.05). The TNF-alpha immunoreactive glia decreased in number in the 60 mg/kg ibudilast-treated group as compared to the vehicle-treated group (p<0.001). These results indicate a dose-dependent protective effect of ibudilast against cerebrovascular white matter lesions and suggest a potential use for ibudilast in the treatment of vascular dementia.

Quercetin, a natural flavonoid, attenuates vacuolar formation in the optic tract in rat chronic cerebral hypoperfusion model

Epidemiological studies suggest that the intake of flavonoids is inversely associated with risk of cardiovascular diseases and stroke, but there is no evidence showing the effect of flavonoids on vascular dementia. Because quercetin, a natural flavonoid, is known to scavenge free radicals, we investigated whether quercetin attenuates white matter damage in rats with chronic cerebral hypoperfusion, as a model of vascular dementia. Chronic hypoperfusion was induced by ligation of the bilateral carotid arteries in male Wistar rats, which received vehicle alone, 100 mg/kg quercetin, or 200 mg/kg quercetin intraperitoneally at 4-day intervals for 8 weeks after operation. Sham-operated rats were also studied. The area of vacuoles in the optic tract observed after hematoxylin and eosin staining was significantly reduced in the 200 mg/kg quercetin-treated hypoperfusion group versus the vehicle-treated hypoperfusion group (1.7+/-0.2% versus 3.9+/-0.3%; P<0.05). The present results are consistent with the idea that chronic treatment with quercetin could be protective against at least a part of ischemic white matter damage.

Cognitive impairment and chronic cerebral hypoperfusion: what can be learned from experimental models

The relation between chronic cerebral hypoperfusion and cognitive functions has not been completely clarified. The resolution of cerebral hypoperfusion states, such as those induced by arteriovenous malformations or carotid stenosis/occlusion, has been reported to improve mental decline in humans. Subcortical vascular dementia is another human condition supposed to be linked with chronic cerebral hypoxia/ischemia. The extent of this cause/effect relation is, however, difficult to be assessed in humans, where different factors, such as ageing or subtle degenerative processes, can coexist and interact influencing cognitive performances. Experimental studies can help to elucidate this relation because they can use models of pure chronic/moderate cerebral hypoperfusion. An experimental model of chronic ischemia is the bilateral common carotid artery occlusion in the rat. In this paper, we present a review of experimental studies that evaluated cognitive functions in the rat with bilateral common carotid artery occlusion. We then present an experimental model of bilateral common carotid artery occlusion in the rat modified with respect to previous papers regarding both the surgical procedure and the neurocognitive evaluation that is focused on cognitive domains depending on subcortical-frontal circuits. We propose this model to investigate subcortical vascular dementia.

Pathological lesions in vascular dementia

According to current diagnostic criteria, a definite diagnosis of vascular dementia (VaD) can be reached on pathological grounds by showing the presence of vascular lesions and the absence of degenerative changes exceeding those expected for age. However, while it is commonly accepted that VaD is a group of heterogeneous entities rather than a process with a unique pathological substrate, the spectrum of vessel and parenchyma changes etiologically associated with the clinical syndrome remains basically unidentified. The review of some recent clinical-pathological series shows that different studies have assessed the presence of dissimilar vascular lesions and that, in many cases, no pathological definition was given. This has hindered the clarification of clinical-pathological correlations in the field of VaD. In this scenario, the use of animal models of cerebrovascular diseases may help to elucidate the type of lesions possibly linked with cognitive impairment in humans and might provide insight into some of the pathophysiological mechanisms of vascular cognitive impairment. A consensus is today needed in order to harmonize the pathological examination of vascular lesions in cases of dementia. An ongoing survey aimed at collecting information about the procedures used in different pathological laboratories in the assessment of lesions possibly associated with dementia is finally presented.

Persistent impairment of gait performances and working memory after bilateral common carotid artery occlusion in the adult Wistar rat

BACKGROUND

The clinical and pathophysiological effects of a chronic reduction of cerebral blood flow in humans are not completely known. We investigated whether rats subjected to bilateral common carotid artery occlusion (bCCA-o) developed focal neurological deficits, gait dysfunction, and working memory alterations.

METHODS

Eighteen male Wistar rats were subjected to bCCA-o, 13 were sham-operated. We assessed sensorimotor functions, gait on a 60 cm-long elevated bridge, and working memory (object recognition and Y maze tests) before and 30, 60, and 90 days after surgery. Histological analysis was performed in a subgroup of 10 rats.

RESULTS

No rat showed sensorimotor alterations after surgery. Although gait performances of both bCCA-o and sham-operated rats declined over time, the differences reached statistical significance only for the bCCA-o group (mean+/-SE: 26.8+/-5.0; 22.4+/-4.9; 24.5+/-5.5 cm at 30, 60, and 90 days, respectively) in comparison with baseline (52.9+/-5.2 cm; P<0.05). At 60 and 90 days, bCCA-o rats in comparison with sham-operated rats showed decreased performances on object recognition (discrimination index: 0.15+/-0.03 vs. 0.29+/-0.05 at 60 days and 0.10+/-0.04 vs. 0.41+/-0.07 at 90 days; P<0.05) and on Y maze test (alternating rats: 9.9 vs. 85.7% at 60 days and 16.6 vs. 100% at 90 days; P<0.01). In none of the animals were cerebral infarcts detected. Selective neuronal necrosis was observed in the cortex and hippocampus of both bCCA-o and sham-operated rats without any obvious difference.

CONCLUSIONS

bCCA-o in the Wistar rat induces persistent and progressive gait and working memory impairment without producing sensorimotor deficit or cerebral infarcts. This model may help to elucidate some physiopathological aspects of neurological impairment associated with states of cerebral chronic ischemia.

Regional vulnerability to chronic hypoxia and chronic hypoperfusion in the rat brain

The purpose of this study was to compare the pathological findings of injury induced by chronic hypoperfusion and by chronic hypoxia in rat brain. Adult male Wistar rats were divided into three groups: chronic hypoperfusion (n=5), chronic hypoxia (n=5), and normal control groups (n=5). Hypoperfusion was induced by ligation of the bilateral carotid arteries under 2.5% halothane anesthesia. Chronic hypoxia was induced by keeping the animals in a chamber with an atmosphere of 10% O(2) in N(2) for 3 weeks. Twelve weeks later (chronic hypoperfusion group) and 3 weeks later (chronic hypoxia group), the animals were sacrificed and perfused through the femoral artery with a fixative containing 4% paraformaldehyde. Hematoxylin and eosin staining was done in all sections in the three groups, and the number of normal-appearing cells was counted. Normal-appearing cells in CA3 were significantly decreased in the chronic hypoperfusion group compared with those in the chronic hypoxia group, although neurons in CA1, CA2 and CA4 in both groups were equally damaged. We concluded that the CA3 hippocampus shows different vulnerabilities to chronic hypoperfusion and chronic hypoxia, possibly owing to a difference in the kinds of glutaminergic receptors.

Immunoglobulin G induces microglial superoxide production

Activating microglias observed in the white matter after chronic cerebral hypoperfusion may play an important role in white matter changes (WMC). Microglial activation has been considered as a result of neuronal damage, however, recently it came to be recognized as a possible cause of the damage in various neurodegenerative diseases. The protective effect of an immunosuppressant on the WMC suggests that an immunologic reaction participates in the pathogenesis. Using a MCLA-dependent chemiluminescence method, we investigated the effect of immunoglobulin G (IgG) on microglial superoxide production. IgG stimulated microglias to produce superoxide. Microglial superoxide production by the Fab fragment of rat IgG was significantly less than that by the Fc fragment of rat IgG. The protective effect of an immunosuppressant on WMC may use the inhibiting effect on IgG. Our results suggest that if microglias come in contact with IgG in lesions, oxidative stress mediated by superoxide from microglial deteriorates WMC.

Chronic cerebral hypoperfusion induces striatal alterations due to the transient increase of NO production and the depression of glutathione content

We examined the effects of chronic cerebral hypoperfusion on the endogenous oxidative stress-related indices, nitrite and nitrate (NOx) concentration, glutathione (GSH) content, superoxide dismutase and catalase activities, and thiobarbituric acid-reactive substances level in the rat striatum, to clarify the participation of oxidative stress in the chronic cerebral hypoperfusion-induced alterations. Our present results indicate that chronic cerebral hypoperfusion produces oxidative stress and disturbs intracellular redox regulation in two distinct phases: at 1 day, "acute" and at 6 weeks, "chronic" alterations after the operation. Therefore, striatal neural cell damage may be mainly attributed to the transient increase of NOx production at 1 day after, and the delayed reduction of muscarinic acetylcholine receptor binding in the striatum may be mostly attributed to the continuous depression of GSH content from the 1st to the 6th postoperative week. In particular, the continuous GSH depression may be considered to accompany the pathophysiology of chronic cerebral hypoperfusion.

Axonal damage and demyelination in the white matter after chronic cerebral hypoperfusion in the rat

Cerebral white matter (WM) lesions are observed frequently in human ischemic cerebrovascular disease and have been thought to contribute to cognitive impairment. This type of lesion can be experimentally induced in rat brains under chronic cerebral hypoperfusion by the permanent occlusion of both common carotid arteries. However, it remains uncertain whether chronic ischemia can damage both the gray and white matter, and whether it can induce demyelination with or without axonal damage. Therefore, we examined axonal damage using immunohistochemistry for the amyloid beta/A4 precursor protein (APP), chromogranin A (CgA) and demyelination using immunohistochemistry for the encephalitogenic peptide (EP) in this model. Severe WM lesions such as vacuolation and the loss of nerve fibers appeared in the optic nerve and optic tract after 3 days of ligation, and less intense changes were observed in the corpus callosum, internal capsule, and fiber bundles of the caudoputamen after 7 days with Klüver-Barrera and Bielschowsky staining. These WM lesions persisted even after 30 days. The APP, CgA, and EP-immunopositive fibers increased in number from 1 to 30 days after the ligation in the following WM regions: the optic nerve, optic tract, corpus callosum, internal capsule, and fiber bundles of the caudoputamen. In contrast, only a few APP, CgA, or EP-immunopositive fibers were detected in the gray matter regions, including the cerebral cortex and hippocampus. These results indicate that the WM is more susceptible to chronic cerebral hypoperfusion than the gray matter, with an involvement of both axonal and myelin components. Furthermore, immunohistochemistry for APP, CgA, and EP is far superior to routine histological staining in sensitivity and may become a useful tool to investigate WM lesions caused by various pathoetiologies.

Blood-brain barrier disruption in white matter lesions in a rat model of chronic cerebral hypoperfusion

Blood-brain barrier damage has been implicated in the pathogenesis of cerebrovascular white matter lesions. This type of lesion is responsible for cognitive impairment in the elderly and can be induced by permanent ligation of the bilateral common carotid arteries in the rat. Because it is unclear whether the blood-brain barrier is impaired, we examined whether vascular permeability to horseradish peroxidase is altered using this model. According to light microscopic results, the reaction product of horseradish peroxidase was most intensely localized to the paramedian part of the corpus callosum in the brain, occurring to a small degree at 3 hours, day 1, markedly on day 3, but reduced on days 7 and 14. By electron microscopic study of the same area, the reaction product of horseradish peroxidase was localized to the plasmalemmal vesicles in the endothelial cells 3 hours after ligation, but appeared in the cytoplasm on days 1 and 3, suggesting a diffuse leakage of horseradish peroxidase. In addition, the reaction product was dispersed into the cytoplasm of glial cells in the perivascular regions on day 3. The luminal surface of the endothelial cell cytoplasm appeared irregular on day 7, suggesting a conformational change of the endothelial cells. Collagen fibrils proliferated in the thickened basal lamina and mitochondria degenerated in the pericyte on days 7 and 14. Perivascular glial endfeet were swollen throughout the survival period. In sham-operated rats, the reaction product of horseradish peroxidase was not observed at any time interval, except in vesicular structures. These findings indicate that chronic cerebral hypoperfusion induces blood-brain barrier damage with subsequent morphologic changes of the vascular structures in the corpus callosum. An extravasation of macromolecules, such as proteases and immunoglobulins, may contribute to the pathogenesis of white matter lesions.

A small dose of the immunosuppressive agent FK506 (tacrolimus) protects peripheral nerve from ischemic fiber degeneration

The immunosuppressant agent FK506 (tacrolimus) has proven to be neuroprotective against brain ischemia, but there are no data on potential neuroprotective effects of FK506 in peripheral nerve ischemia. We examined the potential effects of two doses of FK506 in protecting peripheral nerve from ischemic fiber degeneration. Ischemia in the left sciatic nerve of the rat was produced by injecting 2 x 10(6) microspheres (14 microm) into the left femoral, hypogastric, and superior gluteal arteries in proportions of 47%, 37%, and 17%, respectively. After embolization, FK506 was injected into the left femoral, hypogastric, and superior gluteal arteries in doses of 9.4, 7.4, and 3.4 microg, respectively, for the high-dose group and 4.7, 3.7, and 1.7 microg, respectively, for the low-dose group. The control rats were injected with saline. FK506 treatment resulted in dramatic behavioral improvement in nerve function, in the number of functioning nerve fibers, and in the salvage of a majority of nerve fibers from ischemic fiber degeneration in a dose-dependent fashion. These results suggest that a small dose of FK506 protects peripheral nerve from ischemic fiber degeneration and that it may have potential in the treatment of ischemic neuropathy.

Caudoputamen is damaged by hypocapnia during mechanical ventilation in a rat model of chronic cerebral hypoperfusion

BACKGROUND AND PURPOSE

Postoperative brain dysfunction, such as delirium, is a common complication of anesthesia and is sometimes prolonged, especially in patients with cerebrovascular disease. In the present study we investigated the effect of hypocapnia during anesthesia on neuronal damage using a rat model of chronic cerebral hypoperfusion.

METHODS

Chronic cerebral hypoperfusion was induced by clipping the bilateral common carotid arteries in male Wistar rats. Fourteen days after the operation, these animals were mechanically ventilated for 2 hours and then kept in suitable conditions for an additional 14 days. Twenty-four rats were assigned to 4 groups: those with chronic cerebral hypoperfusion with either hypocapnia or normocapnia during anesthesia, and those given sham operation with either hypocapnia or normocapnia. White matter lesions in the brain sections were evaluated with Klüver-Barrera staining. Proliferation of glial cells was estimated with the use of immunohistochemistry of glial fibrillary acidic protein, a marker for astroglia, and CD11b, a marker for microglia. Computer-assisted morphometry was applied to the immunohistochemical results of microtubule-associated protein 2 to evaluate the loss of neurons.

RESULTS

The histological damage was localized almost exclusively in the white matter in the rats subjected to chronic cerebral hypoperfusion but without hypocapnia. Neuronal damage and astroglial proliferation occurred with aggravated white matter lesions in the caudoputamen in the rats with chronic cerebral hypoperfusion and hypocapnia. No lesions were observed in sham-operated rats with either hypocapnia or normocapnia.

CONCLUSIONS

These results indicate that hypocapnia during anesthesia causes tissue damage in the caudoputamen, which may be responsible for long-lasting postoperative delirium in patients with stroke and/or dementia.

In vivo gene transfer to cerebral white matter lesions with a recombinant adenovirus vector

Ischemic white matter lesions have been reported in rats after bilateral common carotid ligation (BCAL). Previously, comparing normotensive rats (WKY) with spontaneously hypertensive rats (SHR), we too found that sustained moderate ischemia with spontaneous hypertension accelerated the formation of ischemic white matter lesions. In this study, we explored the feasibility of gene therapy for lesioned white matter by means of an adenovirus vector expressing a reporter gene, LacZ. Using sham-operated and hypoperfused SHR as well as sham-operated and hypoperfused WKY, we demonstrated that (i) adenovirus vectors could deliver a foreign gene into oligodendrocytes and astrocytes in the cerebral white matter; (ii) the transduction efficiency was most effective in SHR after BCAL; and (iii) the level of alpha(V)-integrin was significantly correlated with adenoviral transduction efficiency.

FK506 ameliorates the discrimination learning impairment due to preventing the rarefaction of white matter induced by chronic cerebral hypoperfusion in rats

We examined the effects of the immunosuppressant tacrolimus (FK506) on the discrimination learning impairment induced by chronic cerebral hypoperfusion in rats. Chronic cerebral hypoperfusion was prepared by permanent ligation of bilateral common carotid arteries for male Wistar rats aged 9 weeks. FK506 (0.05 mg/kg, s.c.) recovered the learning impairment and also prevented the rarefaction of white matter and striatal neuronal cell damage. Our findings suggest that FK506 ameliorates the learning impairment mainly due to preventing neuropathological alterations.

White matter lesions and alteration of vascular cell composition in the brain of spontaneously hypertensive rats

There have been few studies on the white matter lesions of spontaneously hypertensive rats (SHR). From the point of view of hypertension and arteriosclerosis, white matter lesions were examined in SHR and stroke-prone SHR (SHRSP), and were then compared with Wistar-Kyoto (WKY) rats. The vasculopathy was analyzed by morphometric immunohistochemistry for collagen and smooth muscle actin. Both SHR and SHRSP had hypertension at > or = 12 weeks of age, and the latter developed severe white matter lesions at 20 weeks. Immuno- histochemistry revealed proliferation of microglia in the white matter and an increase in smooth muscle actin in the vessels of SHRSP compared with the WKY rats and SHR, but there were no changes in the collagen. These results indicate a role of hypertension in the pathogenesis of white matter lesions. However, genetic difference may also be responsible since SHR and SHRSP showed similar hypertension.

Chronic cerebral hypoperfusion induces MMP-2 but not MMP-9 expression in the microglia and vascular endothelium of white matter

White matter lesions are closely associated with cognitive impairment and motor dysfunction in the aged. To explore the pathophysiology of these lesions, the authors examined the expression of matrix metalloproteinase-2 (MMP-2) and MMP-9 in the white matter in a rat model of chronic cerebral hypoperfusion. After bilateral clipping of the common carotid arteries, myelin staining revealed demyelinating changes in the optic tract and the corpus callosum on day 7. Zymographic analyses indicated an increase in the level of MMP-2, but not MMP-9, after the hypoperfusion. Immunohistochemical analyses revealed the presence (most abundantly on day 3) of MMP-2-expressing activated microglia in the optic tract and corpus callosum. In contrast, the capillary endothelial cells expressed MMP-2 later. IgM-immunoreactive glial cells were absent in the sham-operated animals, but were present in the hypoperfused animals by day 3, reflecting the disrupted blood-brain barrier. These findings suggest that the main sources of the elevated MMP-2 were the microglia and the endothelium, and that these cells may contribute to the remodeling of the white matter myelin and microvascular beds in chronic cerebral hypoperfusion.

Chronic ischemia preferentially causes white matter injury in the neonatal rat brain

Chronic ischemic brain injuries were studied in 7- and 14-day-old rat pups, which were subjected to bilateral carotid artery occlusion (BCAO) on postnatal day 1. BCAO preferentially injured white matter in the corpus callosum, subcortex and internal capsule areas while largely spared cortical neurons. White matter rarefaction in the corpus callosum was observed in 12 out of the 17 BCAO rat brains and significantly enlarged lateral ventricles were found in five out of seven P14 BCAO rat brains. These white matter changes were similar to injuries found in newborn infants with periventricular leukomalacia (PVL). White matter injuries in the 7-day-old BCAO rat brain were accompanied with increased activation of microglia/macrophages, as indicated by ED1 and OX42 positive immunostaining. Immature oligodendrocytes in the 7-day-old BCAO rat brain, as indicated by O4+/O1+ staining, were much fewer than in the sham-operated rat brain. Immunostaining for myelin basic protein (MBP) at the fimbria hippocampus and the internal capsule areas in the 7-day-old BACO rat brain was also much less than in the control rat brain. Consistent with the immunostaining data, MBP mRNA expression in the 7-day-old, but not in the 14-day-old, BCAO rat brain was significantly less than in the control rat brain. The overall results suggest that pre-oligodendrocytes and immature oligodendrocytes might be major targets for chronic ischemic insults and activated microglia/macrophages are possibly involved in the process of white matter injury.

Oligodendroglial cell death with DNA fragmentation in the white matter under chronic cerebral hypoperfusion: comparison between normotensive and spontaneously hypertensive rats

We investigated the neuropathological and biochemical changes in the white matter of normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) after bilateral carotid artery ligation (BCAL). One week after BCAL, both WKY and SHR showed white matter rarefaction and vacuolation with reduced oligodendrocytes, but there was no difference between WKY and SHR. On the other hand, vacuoles formed by oligodendroglial cell death were increased significantly from 2 to 4 weeks in the optic tract and fimbria fornix of hypoperfused SHR. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP in situ nick end labeling (TUNEL)-positive cells and lectin-positive microglia increased in number and intensities of staining more markedly in SHR than in WKY. In situ cell death detection ELISA supported these results quantitatively. RT-PCR represented the expression of TNF-alpha, TNF receptor 1 (p55), caspase-2 (Ich-1) and -3 (CPP32) mRNAs in both WKY and SHR brains after BCAL. Immunohistochemical analyses revealed that TNF-alpha, TNF receptor 1 (p55), Ich-1 and CPP32 immunoreactive cells could also be detected in the white matter regions of hypoperfused SHR. These results suggested that local production of TNF-alpha by the activated microglia might selectively induce oligodendroglial cell death through the death domain-containing TNF receptor 1 (p55), caspase-2 or -3 activation, resulting in white matter changes as a primary pathological feature.

Increased amyloid precursor protein expression and serotonergic sprouting following excitotoxic lesion of the rat magnocellular nucleus basalis: neuroprotection by Ca(2+) antagonist nimodipine

In the present study plastic neural responses to N-methyl-D-aspartate-induced excitotoxic lesions and the neuroprotective effects of the L-type voltage-dependent Ca(2+) channel antagonist nimodipine were investigated in the rat magnocellular nucleus basalis. Assessment of spontaneous behaviour in the elevated plus maze and small open-field paradigms on day 5 and day 14 post-surgery indicated anxiety and persistent hypoactivity of N-methyl-D-aspartate-lesioned rats, as compared with sham-operated controls. Nimodipine administration significantly alleviated the behavioural deficits. Quantitative histochemical analysis of acetylcholinesterase-positive fibre innervation of the somatosensory cortex and determination of the numbers of choline-acetyltransferase-positive proximal fibre branches of cholinergic projection neurons in the magnocellular nucleus basalis demonstrated a severe cholinergic deficit as a consequence of the excitotoxic lesion 14 days post-surgery. Nimodipine pre-treatment significantly attenuated the loss of cortical cholinergic innervation and preserved the functional integrity of cholinergic projection neurons in the magnocellular nucleus basalis. Double-labelling immunocytochemistry demonstrated increased amyloid precursor protein expression in shrinking and presumably apoptotic choline-acetyltransferase-positive neurons, whereas surviving cholinergic nerve cells were devoid of excessive amyloid precursor protein immunoreactivity. Moreover, as a consequence of N-methyl-D-aspartate infusion, rim-like accumulation of amyloid precursor protein-positive astrocytes was visualized in a penumbra-like zone of the excitotoxic injury. Furthermore, abundant sprouting of serotonergic projection fibres invading the damaged magnocellular nucleus basalis subdivision was demonstrated. Pharmacological blockade by the Ca(2+) antagonist nimodipine significantly attenuated both neuronal and glial amyloid precursor protein immunoreactivity and serotonergic fibre sprouting following N-methyl-D-aspartate infusion. The present data characterize plastic endogenous glial and neuronal responses in the magnocellular nucleus basalis model of acute excitotoxic brain damage. The increased amyloid precursor protein expression may indicate effective means of intrinsic neuroprotection, as secreted amyloid precursor protein isoforms are suggested to play a role in neuronal rescue following excitotoxic injury. From a pharmacological point of view, extensive sprouting of serotonergic projections in the damaged magnocellular nucleus basalis may also counteract N-methyl-D-aspartate excitotoxicity via serotonin-induced inhibition of Ca(2+) currents and membrane hyperpolarization. Hence, lesion-induced changes in spontaneous animal behaviour, such as anxiety and novelty-induced hypoactivity, may well be attributed to the considerable re-distribution of serotonergic projections in the basal forebrain. In conclusion, our present data emphasize a role of neuron-glia and neurotransmitter-system interactions in functional recovery after acute excitotoxic brain injury, and the efficacy of L-type Ca(2+) channel blockade by the selective 1,4-dihydropyridine antagonist nimodipine.

Progressive cortical atrophy after forebrain ischemia in diabetic rats

The morphological changes in the brain of diabetic rats were examined up to 8 weeks after transient forebrain ischemia produced by transient occlusion of both carotid arteries. Using histochemistry, we also examined the extent and rate of development of atrophic changes in the brain, appearance of astrocytes, activated microglia, and glucose transporter 1 (GLUT1) in streptozotocin-treated rat brains after forebrain ischemia. Atrophic changes appeared in the hippocampus in both non-diabetic-- and diabetic--ischemic groups 4 weeks after ischemia. In diabetic--ischemic rats, the atrophic changes were more severe and progressed more rapidly in the hippocampus, and were also observed in the frontal, temporal and parietal cortices, but not in any cortical areas of the non-diabetic--ischemic rats and non-ischemic--diabetic rats. We observed reduced density of GLUT1 in all cortical regions and hippocampus in ischemic-diabetic rats at 4--8 weeks, when the number of activated microglias and astroglias increased in all cortical regions. Although severe atrophic changes were observed in the gray matter, no serious injury was noted in the white matter in the diabetic-ischemic group. Our results indicate that brain ischemia in the presence of diabetes causes more severe late-onset damage culminating in brain atrophy, compared with non-diabetics.