Experimental cerebral hypoperfusion induces white matter injury and microglial activation in the rat brain

Though cerebral white matter injury is a frequently described phenomenon in aging and dementia, the cause of white matter lesions has not been conclusively determined. Since the lesions are often associated with cerebrovascular risk factors, ischemia emerges as a potential condition for the development of white matter injury. In the present study, we induced experimental cerebral hypoperfusion by permanent, bilateral occlusion of the common carotid arteries of rats (n=6). A sham-operated group served as control (n=6). Thirteen weeks after the onset of occlusion, markers for astrocytes, microglia, and myelin were found to be labeled by means of immunocytochemistry in the corpus callosum, the internal capsule, and the optic tract. The ultrastructural integrity and oligodendrocyte density in the optic tract were investigated by electron microscopy. Quantitative analysis revealed that chronic cerebral hypoperfusion caused mild astrogliosis in the corpus callosum and the internal capsule, while astrocytic disintegration in the optic tract increased by 50%. Further, a ten-fold increase in microglial activation and a nearly doubled oligodendrocyte density were measured in the optic tract of the hypoperfused rats as compared with the controls. Finally, vacuolization and irregular myelin sheaths were observed at the ultrastructural level in the optic tract. In summary, the rat optic tract appears to be particularly vulnerable to ischemia, probably because of the rat brains angioarchitecture. Since the detected glial changes correspond with those reported in vascular and Alzheimer dementia, this model of cerebral hypoperfusion may serve to characterize the causal relationship between ischemia and white matter damage.     

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.     

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.     

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

Activation of glial cells and white matter changes (rarefaction of the white matter) induced in the rat brain by permanent bilateral occlusion of the commom carotid arteries were immunohistochemically investigated up to 90 days. One day after ligation of the arteries, expression of the major histocompatibility complex (MHC) class I antigen in microglia increased in the white matter including the optic nerve, optic tract, corpus callosum, internal capsule, anterior commissure and traversing fiber bundles of the caudoputamen. After 3 days of occlusion, MHC class I antigen was still elevated and in addition MHC class II antigen and leukocyte common antigen were up-regulated in the microglia in these same regions. Astroglia, labeled with glial fibrillary acidic protein, increased in number in these regions after 7 days of occlusion. A few lymphocytes, labeled with CD4 or CD8 antibodies, were scattered in the neural parenchyma 1 h after occlusion. Activation of glial cells and infiltration of lymphocytes persisted after 90 days of occlusion in the white matter and the retinofugal pathway. However, cellular activation and infiltration in microinfarcts of the gray matter was less extensive and was substantially diminished 30 days after occlusion. The white matter changes were most intense in the optic nerve and optic tract, moderate in the medial part of the corpus callosum, internal capsule and anterior commissure, and slight in the fiber bundles of the caudoputamen. These results indicated that chronic cerebral hypoperfusion induced glial activation preferentially in the white matter. This activation seemed to be an early indicator of the subsequent changes in the white matter.     

Chronic cerebral hypoperfusion induces white matter lesions and loss of oligodendroglia with DNA fragmentation in the rat

Cerebrovascular white matter lesions represent an age-related neurodegenerative condition that appears as a hyperintense signal on magnetic resonance images. These lesions are frequently observed in aging, hypertension and cerebrovascular disease, and are responsible for cognitive decline and gait disorders in the elderly population. In humans, cerebrovascular white matter lesions are accompanied by apoptosis of oligodendroglia, and have been thought to be caused by chronic cerebral ischemia. In the present study, we tested whether chronic cerebral hypoperfusion induces white matter lesions and apoptosis of oligodendroglia in the rat. Doppler flow meter analysis revealed an immediate reduction of cerebral blood flow ranging from 30% to 40% of that before operation; this remained at 52–64% between 7 and 30 days after operation. Transferrin-immunoreactive oligodendroglia decreased in number and the myelin became degenerated in the medial corpus callosum at 7 days and thereafter. Using the TUNEL method, the number of cells showing DNA fragmentation increased three- to eightfold between 3 and 30 days post-surgery compared to sham-operated animals. Double labeling with TUNEL and immunohistochemistry for markers of either astroglia or oligodendroglia showed that DNA fragmentation occurred in both of these glia. Messenger RNA for caspase-3 increased approximately twofold versus the sham-operated rats between 1 and 30 days post-surgery. Immunohistochemistry revealed up-regulation of caspase-3 in the oligodendroglia of the white matter, and also in the astroglia and neurons of the gray matter. Molecules involved in apoptotic signaling such as TNF- and Bax were also up-regulated in glial cells. These results indicate that chronic cerebral hypoperfusion induces white matter degeneration in association with DNA fragmentation in oligodendroglia.     

NKCC1 Inhibition Attenuates Chronic Cerebral Hypoperfusion-Induced White Matter Lesions by Enhancing Progenitor Cells of Oligodendrocyte Proliferation

Cerebral white matter is vulnerable to ischemic condition. However, no effective treatment to alleviate or restore the myelin damage caused by chronic cerebral hypoperfusion has been found. Na⁺-K⁺-Cl^? cotransporter 1 (NKCC1), a Na⁺-K⁺-Cl^? cotransporter widely expressed in the central nervous system (CNS), involves in regulation of cell swelling, EAA release, cell apoptosis, and proliferation. Nevertheless, the role of NKCC1 in chronic hypoperfusion-induced white matter lesions (WMLs) has not been explored. Here, mice subjected to bilateral common carotid artery stenosis (BCAS) were used as model of chronic cerebral hypoperfusion; density of progenitor cells of oligodendrocyte (OPCs), oligodendrocytes (OLs), astrocytes, and microglia was assessed by immunofluorescent staining and Western blot analysis; working memory was examined by eight-arm radial maze test; expression of MAPK signaling pathway was determined by Western blot analysis. After BCAS, white matter integrity disruption and working memory impairment were observed. NKCC1 inhibition by bumetanide administration enhanced OPC proliferation, attenuated chronic hypoperfusion-induced white matter damage, and promoted recovery of neurological function. However, NKCC1 inhibition caused no significant change in the densities of GFAP- and Iba-1-positive cells in the corpus callosum. Bumetanide administration significantly increased the expression of p-ERK and decreased the expression of p-JNK and p-p38 in comparison to vehicle-BCAS groups. In conclusion, NKCC1 inhibition might significantly ameliorate chronic cerebral hypoperfusion-induced WMLs and cognitive impairment by enhancing progenitor cells of oligodendrocyte proliferation, and this protective function of bumetanide might be mediated by modulation of the MAPK signaling pathway.     

Dose-dependent, protective effect of FK506 against white matter changes in the rat brain after chronic cerebral ischemia

Neuroprotective effects of immunosuppressive agents have been shown in cerebral ischemia. To investigate the role of immunosuppressive agents in chronic cerebral ischemia and to design a drug protocol with safe therapeutic windows, we examined the effects of FK506, a potent immunosuppressive agent, on chronic cerebral ischemia. Both common carotid arteries were ligated in 73 male Wistar rats. Fifty-eight of these rats received a chronic injection of FK506 (0.2, 0.5, 1.0 mg/kg) and the remaining 15 received a vehicle solution injection. Microglia/macrophage was investigated with immunohistochemistry for leukocyte common antigen and major histocompatibility complex, and astroglia was examined with glial fibrillary acidic protein as markers. White matter rarefaction and the number of immunopositive glial cells were assessed from 7 to 30 days after the ligation. In the vehicle-treated animals, there was persistent and extensive activation of the microglia/macrophages and astroglia in the white matter, including the optic nerve, optic tract, corpus callosum, internal capsule, anterior commissure and traversing fiber bundles of the caudoputamen. In the FK506-treated rats, the number of activated microglia/macrophages was significantly reduced in a dose-dependent manner (p<0.01) as compared to the vehicle-treated rats. Rarefaction of the white matter was also inhibited by FK506 in a dose-dependent manner (p<0.01). Thus, a clinically-relevant dosage of FK506 attenuated both glial activation and white matter changes in chronic cerebral ischemia in the rat. These results indicate a potential use for FK506 in cerebrovascular diseases.     

Leukoencephalopathy in diffuse hemorrhagic cerebral amyloid angiopathy

We have studied 12 patients with diffuse hemorrhagic cerebral amyloid angiopathy clinically and at postmortem examination. The brains in 8 patients had diffuse bilateral loss of myelin in the hemispheric white matter sparing the U fibers, corpus callosum, and internal capsules. The periventricular areas were predominantly affected. Microscopic examination of the white matter showed an association with subacute or chronic edematous lesions: spongiosis, swollen oligodendroglia, widening of the perivascular spaces with edema fluid or siderophages, hyalinization of the blood vessel walls, incomplete myelin loss, and astrocytic gliosis. Three of 8 autopsied patients had undergone computed tomographic examination, which showed bilateral hypodensity of the hemispheric white matter. The brains of 4 patients with illnesses of shorter duration showed only discrete but similar lesions in the centrum semiovale. These white matter changes are similar to those observed in Binswanger's subcortical encephalopathy. We suggest that a common mechanism of hypoperfusion of the distal white matter causes the leukoencephalopathy.     

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.     

Minocycline reduces microgliosis and improves subcortical white matter function in a model of cerebral vascular disease

Chronic cerebral hypoperfusion is a key mechanism associated with white matter disruption in cerebral vascular disease and dementia. In a mouse model relevant to studying cerebral vascular disease, we have previously shown that cerebral hypoperfusion disrupts axon‐glial integrity and the distribution of key paranodal and internodal proteins in subcortical myelinated axons. This disruption of myelinated axons is accompanied by increased microglia and cognitive decline. The aim of the present study was to investigate whether hypoperfusion impairs the functional integrity of white matter, its relation with axon‐glial integrity and microglial number, and whether by targeting microglia these effects can be improved. We show that in response to increasing durations of hypoperfusion, the conduction velocity of myelinated fibres in the corpus callosum is progressively reduced and that paranodal and internodal axon‐glial integrity is disrupted. The number of microglial cells increases in response to hypoperfusion and correlates with disrupted paranodal and internodal integrity and reduced conduction velocities. Further minocycline, a proposed anti‐inflammatory and microglia inhibitor, restores white matter function related to a reduction in the number of microglia. The study suggests that microglial activation contributes to the structural and functional alterations of myelinated axons induced by cerebral hypoperfusion and that dampening microglia numbers/proliferation should be further investigated as potential therapeutic benefit in cerebral vascular disease.     

MCP-1-mediated activation of microglia promotes white matter lesions and cognitive deficits by chronic cerebral hypoperfusion in mice

Microglia activation played a vital role in the pathogenesis of white matter lesions (WMLs) by chronic cerebral hypoperfusion. In addition, hypoxia induced up-regulated expression of MCP-1, promotes the activation of microglia. However, the role of MCP-1-mediated microglia activation in chronic cerebral ischemia is still unknown. To explore that, chronic cerebral hypoperfusion model was established by permanent stenosis of bilateral common carotid artery in mice. The activation of microglia and the related signal pathway p38MAPK/PKC in white matter, and working memory of mice were observed. We found that stenosis of common carotid arteries could induce MCP-1-mediated activation of microglia through p38MAPK/PKC pathway and white matter lesions. Taken together, our findings represent a novel mechanism of MCP-1 involved in activation of microglia and provide a novel therapeutical strategy for chronic cerebral hypoperfusion.     

Inflammatory Response and Chemokine Expression in the White Matter Corpus Callosum and Gray Matter Cortex Region During Cuprizone-Induced Demyelination

Brain inflammation plays a central role in multiple sclerosis (MS). Besides lymphocytes, the astroglia and microglia mainly contribute to the cellular composition of the inflammatory infiltrate in MS lesions. Several studies were able to demonstrate that cortical lesions are characterized by lower levels of inflammatory cells among activated microglia/macrophages. The underlying mechanisms for this difference, however, remain to be clarified. In the current study, we compared the kinetics and extent of microglia and astrocyte activation during early and late cuprizone-induced demyelination in the white matter tract corpus callosum and the telencephalic gray matter. Cellular parameters were related to the expression profiles of the chemokines Ccl2 and Ccl3. We are clearly able to demonstrate that both regions are characterized by early oligodendrocyte stress/apoptosis with concomitant microglia activation and delayed astrocytosis. The extent of microgliosis/astrocytosis appeared to be greater in the subcortical white matter tract corpus callosum compared to the gray matter cortex region. The same holds true for the expression of the key chemokines Ccl2 and Ccl3. The current study defines a model to study early microglia activation and to investigate differences in the neuroinflammatory response of white vs. gray matter.     

Protective effects of carnosine on white matter damage induced by chronic cerebral hypoperfusion

Carnosine is a dipeptide that scavenges free radicals,inhibits inflammation in the central nervous system,and protects against ischemic and hypoxic brain damage through its anti-oxidative and anti-apoptotic actions.Therefore,we hypothesized that carnosine would also protect against white matter damage caused by subcortical ischemic injury.White matter damage was induced by right unilateral common carotid artery occlusion in mice.The animals were treated with 200,500 or 750 mg/kg carnosine by intraperitoneal injection 30 minutes before injury and every other day after injury.Then,37 days later,Klüver-Barrera staining,toluidine blue staining and immunofluorescence staining were performed.Carnosine(200,500 mg/kg) substantially reduced damage to the white matter in the corpus callosum,internal capsule and optic tract,and it rescued expression of myelin basic protein,and alleviated the loss of oligodendrocytes.However,carnosine at the higher dose of 750 mg/kg did not have the same effects as the 200 and 500 mg/kg doses.These findings show that carnosine,at a particular dose range,protects against white matter damage caused by chronic cerebral ischemia in mice,likely by reducing oligodendroglial cell loss.     

A clinico-pathological study of so-called "acute multiple sclerosis" mimicking a brain tumor on the MRI findings]

We are reporting an autopsy case of so-called "acute multiple sclerosis" that was difficult to differentiate from a brain tumor on MRI findings. This case was a 69-year-old man, whose initial symptoms consisted of headache and unsteadiness in walking. Neurological findings included mild ataxia of the left upper extremity and positive Romberg sign. T 2-weighted MRI showed high intensity areas in the posterior limb of the right internal capsule and white matter near the posterior horn of the right lateral ventricle. Although the headache improved, the unsteadiness was exacerbated and the patient became unable to keep standing. Psychiatric symptoms and left hemiparesis were added to the clinical picture. The following MRI proved expansion of the previous lesions and the diffusely enhanced lesion spreading into the contralateral side through the corpus callosum. Stereotaxic biopsy showed the perivascular accumulation of small lymphocytes and a large number of bizarre astrocytes. Primary brain malignant lymphoma was diagnosed and radiation therapy was carried out. However, he developed perforation of the intestinal tract and died. Autopsy findings revealed scattered and disseminated small lesions in the cerebral white matter and the corpus callosum. There were a large number of lipid-laden macrophages, no stainable myelin and preserved axis cylinders in those lesions. Thus, those were interpreted as demyelinting lesions. They were scattered and multiple. This case was radiologically characterised by the diffusely enhanced, expanding butterfly-shaped lesion in bilateral cerebral hemisphere through the corpus callosum, and pathologically proven to be acute demyelination associated with severe perivascular infiltration of inflammatory cells. Multiple sclerosis may mimic neoplastic processes as trans-callosal hyperplastic neuroimage on neuroimaging like the present case.     

A cyclooxygenase-2 inhibitor attenuates white matter damage in chronic cerebral ischemia.

The effects of nimesulide, a cyclooxygenase-2 inhibitor, were examined during chronic cerebral hypoperfusion. After bilateral ligation of the common carotid arteries in 30 rats, 21 received dosages of 2 or 5 mg/kg nimesulide daily and nine received vehicle daily for 14 days. The serum was then analyzed biochemically, and pathological changes were estimated in the white matter by the emergence of major histocompatibility complex (MHC) antigen-immunoreactive activated microglia and white matter lesions. In the vehicle-treated animals, activated microglia and white matter lesions were observed. Following treatment with either 2 or 5mg/kg nimesulide, the magnitude of these changes was reduced (p < 0.001) without significant side effects. These results indicate a potential use for cyclooxygenase-2 inhibitors in cerebrovascular disease.     

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.     

Amyloid beta peptide-induced corpus callosum damage and glial activation in vivo

The effects of stereotaxic injection of amyloid beta-peptide (Abeta1-42) into rat brain to induce white matter damage have been studied. Administration of 1 nmol Abeta1-42 into corpus callosum resulted in considerable damage to axons as evidenced by the loss of neurofilament-immunoreactive (NF-ir) fibers 6 h and 3 and 7 days post-injection. Significant damage was also evident to myelin (using Luxol fast blue myelin staining) and oligodendrocytes (using CC1 immunocytochemistry); in the latter case marked caspase-3 immunoreactivity was evident in oligodendrocytes. Additionally, the numbers of GFAP-ir astrocytes and OX-42/OX-6-ir microglia were markedly increased following Abeta1-42 injection. These results suggest that Abeta plays an important pathophysiological role in white matter damage and that inflammatory responses may contribute to Abeta-induced demyelination and oligodendrocyte injury in corpus callosum. Loss of function of cells in corpus callosum could provide a potential new model for the study of white matter damage in Alzheimer's disease.     

Intraventricular transplantation of oligodendrocyte progenitors into a fetal myelin mutant results in widespread formation of myelin.

Transplantation of myelin-forming cells is a promising strategy for the treatment of myelin disorders. In this study, transplantation of glial cell progenitors into the cerebral ventricles of the embryonic myelin-deficient rat, a model of Pelizaeus-Merzbacher disease, was performed to assess the ability of these cells to incorporate into the developing brain and produce myelin. The donor cells migrated into the white and gray matter and produced myelin at widespread sites ranging from the corpus callosum and optic nerve to the cerebellum. These data suggest that myelin repair might be achieved by intraventricular delivery and transependymal incorporation of myelin-producing cells. Because these cells were genetically transduced to express a reporter gene, similar ex vivo manipulation with genes known to promote survival, migration, or proliferation of the transplanted cells could be used to enhance repair. Such a therapeutic strategy may be feasible in patients with inherited myelin disorders or in multiple sclerosis, particularly where the lesions are periventricular.     

Morphometry of myelin fibers in corpus callosum and optic nerve of aging rats.

Results of morphometric studies are presented, conducted on myelin fibers of corpus callosum and optic nerve of old rats. The studies were performed on 2 and 2.5 years old rats of Wistar strain. The control group consisted of 4 months old animals. The measurements were conducted on electron micrographs taken at magnification of 35,000 X. Aging was associated with increased thickness of myelin sheaths resulting both from increased number of myelin lamellae and from increased interlamellae distances (i.e. decreased compactness of myelin). The increased transversal size of myelin fibers, analogous to that observed in human material, was particularly evident in 2 years old rats. In the oldest, 2.5 years old rats size of myelin fibers decreased compared to 2 years old rats, approaching values observed in the control group. Moreover, disturbances in axon-myelin sheath ratio took place in the course od aging of rat brain white matter; axon cross-section area ratio to number of myelin lamellae in corpus callosum fibers was decreased while it was increased in fibers of optic nerve in 2 years old animals. In the process of aging most pronounced alterations were noted in thin fibers but thick fibers became more numerous and showed greater number of myelin lamellae.     

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.