Neuropathologic changes in the gerbil brain after chronic hypoperfusion

Progressive lesion necrosis is related to increasing aphasia severity in chronic stroke

BACKGROUND

Volumetric investigations of cortical damage resulting from stroke indicate that lesion size and shape continue to change even in the chronic stage of recovery. However, the potential clinical relevance of continued lesion growth has yet to be examined. In the present study, we investigated the prevalence of lesion expansion and the relationship between expansion and changes in aphasia severity in a large sample of individuals in the chronic stage of aphasia recovery.

METHODS

Retrospective structural MRI scans from 104 S survivors with at least 2 observations (k = 301 observations; mean time between scans = 31 months) were included. Lesion demarcation was performed using an automated lesion segmentation software and lesion volumes at each timepoint were subsequently calculated. A linear mixed effects model was conducted to investigate the effect of days between scan on lesion expansion. Finally, we investigated the association between lesion expansion and changes on the Western Aphasia Battery (WAB) in a group of participants assessed and scanned at 2 timepoints (N = 54) using a GLM.

RESULTS

Most participants (81 %) showed evidence of lesion expansion. The mixed effects model revealed lesion volumes significantly increase, on average, by 0.02 cc each day (7.3 cc per year) following a scan (p < 0.0001). Change on language performance was significantly associated with change in lesion volume (p = 0.025) and age at stroke (p = 0.031). The results suggest that with every 10 cc increase in lesion size, language performance decreases by 0.9 points, and for every 10-year increase in age at stroke, language performance decreases by 1.9 points.

CONCLUSIONS

The present study confirms and extends prior reports that lesion expansion occurs well into the chronic stage of stroke. For the first time, we present evidence that expansion is predictive of longitudinal changes in language performance in individuals with aphasia. Future research should focus on the potential mechanisms that may lead to necrosis in areas surrounding the chronic stroke lesion.

Neuregulin1 attenuates cognitive deficits and hippocampal CA1 neuronal apoptosis partly via ErbB4 receptor in a rat model of chronic cerebral hypoperfusion

Neuregulin1 (NRG1) is an effective neuroprotectant. Previously we demonstrated that the expression of hippocampal NRG1/ErbB4 gradually decreased and correlates with neuronal apoptosis during chronic cerebral hypoperfusion (CCH). Here we aimed to further investigate the protective role of NRG1 in CCH. AG1478, an ErbB4 inhibitor, was used to explore the involvement of ErbB4 receptors in NRG1's action. Permanent bilateral common carotid artery occlusion (2VO) or sham operation was performed in Sprague-Dawley rats. NRG1 (100 μM) and AG1478 (50 mM) was administered intraventricularly. Eight weeks post-surgery, cognitive impairment was analyzed using Morris water maze (MWM) and radial arm water maze (RAWM) tests, followed by histological assessment of the survival and apoptosis of hippocampal CA1 neurons using NeuN and TUNEL immunostaining respectively. Expression of apoptosis-related proteins and ErbB4 activation (pErbB4/ErbB4) was evaluated by Western blotting. The results showed that NRG1 significantly improved the performances in MWM (spatial learning and memory) and RAWM (spatial working and reference memory), attenuated hippocampal CA1 neuronal loss and apoptosis, upregulated the expression of pErbB4/ErbB4 and the anti-apoptotic protein Bcl-2, and downregulated the expression of pro-apoptotic proteins of Cleaved (Cl)-caspase3 and Bax. In addition, the protective effects of NRG1 could be partly abolished by AG1478. Taken together, our study suggested that NRG1 ameliorates cognitive impairment and neuronal apoptosis partly via ErbB4 receptors in rats with CCH.

Assessing Mongolian gerbil emotional behavior: effects of two shock intensities and response-independent shocks during an extended inhibitory-avoidance task

Despite step-down inhibitory avoidance procedures that have been widely implemented in rats and mice to study learning and emotion phenomena, performance of other species in these tasks has received less attention. The case of the Mongolian gerbil is of relevance considering the discrepancies in the parameters of the step-down protocols implemented, especially the wide range of foot-shock intensities (i.e., 0.4–4.0 mA), and the lack of information on long-term performance, extinction effects, and behavioral patterning during these tasks. Experiment 1 aimed to (a) characterize gerbils’ acquisition, extinction, and steady-state performance during a multisession (i.e., extended) step-down protocol adapted for implementation in a commercially-available behavioral package (Video Fear Conditioning System—MED Associates Fairfax, VT, USA), and (b) compare gerbils’ performance in this task with two shock intensities – 0.5 vs. 1.0 mA—considered in the low-to-mid range. Results indicated that the 1.0 mA protocol produced more reliable and clear evidence of avoidance learning, extinction, and reacquisition in terms of increments in freezing and on-platform time as well as suppression of platform descent. Experiment 2 aimed to (a) assess whether an alternate protocol consisting of a random delivery of foot shocks could replicate the effects of Experiment 1 and (b) characterize gerbils’ exploratory behavior during the step-down task (jumping, digging, rearing, and probing). Random shocks did not reproduce the effects observed with the first protocol. The data also indicated that a change from random to response-dependent shocks affects (a) the length of each visit to the platform, but not the frequency of platform descends or freezing time, and (b) the patterns of exploratory behavior, namely, suppression of digging and rearing, as well as increments in probing and jumping. Overall, the study demonstrated the feasibility of the extended step-down protocol for studying steady performance, extinction, and reacquisition of avoidance behavior in gerbils, which could be easily implemented in a commercially available system. The observation that 1.0 mA shocks produced a clear and consistent avoidance behavior suggests that implementation of higher intensities is unnecessary for reproducing aversive-conditioning effects in this species. The observed patterning of freezing, platform descents, and exploratory responses produced by the change from random to periodic shocks may relate to the active defensive system of the gerbil. Of special interest is the probing behavior, which could be interpreted as risk assessment and has not been reported in other rodent species exposed to step-down and similar tasks.

An Experimental Infarct Targeting the Internal Capsule: Histopathological and Ultrastructural Changes

BACKGROUND

Stroke involving the cerebral white matter (WM) has increased in prevalence, but most experimental studies have focused on ischemic injury of the gray matter. This study was performed to investigate the WM in a unique rat model of photothrombotic infarct targeting the posterior limb of internal capsule (PLIC), focusing on the identification of the most vulnerable structure in WM by ischemic injury, subsequent glial reaction to the injury, and the fundamental histopathologic feature causing different neurologic outcomes.

METHODS

Light microscopy with immunohistochemical stains and electron microscopic examinations of the lesion were performed between 3 hours and 21 days post-ischemic injury.

RESULTS

Initial pathological change develops in myelinated axon, concomitantly with reactive change of astrocytes. The first pathology to present is nodular loosening to separate the myelin sheath with axonal wrinkling. Subsequent pathologies include rupture of the myelin sheath with extrusion of axonal organelles, progressive necrosis, oligodendrocyte degeneration and death, and reactive gliosis. Increase of glial fibrillary acidic protein (GFAP) immunoreactivity is an early event in the ischemic lesion. WM pathologies result in motor dysfunction. Motor function recovery after the infarct was correlated to the extent of PLIC injury proper rather than the infarct volume.

CONCLUSIONS

Pathologic changes indicate that the cerebral WM, independent of cortical neurons, is highly vulnerable to the effects of focal ischemia, among which myelin sheath is first damaged. Early increase of GFAP immunoreactivity indicates that astrocyte response initially begins with myelinated axonal injury, and supports the biologic role related to WM injury or plasticity. The reaction of astrocytes in the experimental model might be important for the study of pathogenesis and treatment of the WM stroke.

Considerations for the Optimization of Induced White Matter Injury Preclinical Models

White matter (WM) injury in relation to acute neurologic conditions, especially stroke, has remained obscure until recently. Current advances in imaging technologies in the field of stroke have confirmed that WM injury plays an important role in the prognosis of stroke and suggest that WM protection is essential for functional recovery and post-stroke rehabilitation. However, due to the lack of a reproducible animal model of WM injury, the pathophysiology and mechanisms of this injury are not well studied. Moreover, producing selective WM injury in animals, especially in rodents, has proven to be challenging. Problems associated with inducing selective WM ischemic injury in the rodent derive from differences in the architecture of the brain, most particularly, the ratio of WM to gray matter in rodents compared to humans, the agents used to induce the injury, and the location of the injury. Aging, gender differences, and comorbidities further add to this complexity. This review provides a brief account of the techniques commonly used to induce general WM injury in animal models (stroke and non-stroke related) and highlights relevance, optimization issues, and translational potentials associated with this particular form of injury.

Models that matter: white matter stroke models

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

Experimental models of vascular dementia and vascular cognitive impairment: a systematic review

Vascular cognitive impairment (VCI) encompasses vascular dementia and is the second most common cause of dementing illness after Alzheimer's disease. The main causes of VCI are: cerebral small vessel disease; multi-infarct dementia; strategic infarct (i.e. located in a functionally-critical brain area); haemorrhage/microbleed; angiopathy (including cerebral amyloid angiopathy); severe hypoperfusion (e.g. cardiac arrhythmia); and hereditary vasculopathy (e.g. cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, CADASIL). In this systematic analysis, we aimed to relate cognitive and neuropathological features of experimental models to clinical VCI. We extracted data from 107 studies covering 16 models. These included: brief global ischaemic insults (in rats, mice or gerbils); chronic global hypoperfusion (rats, mice, gerbils); chronic hypertension (in primates or stroke-prone, spontaneously-hypertensive rats); multiple ischaemic lesions because of intra-vascular emboli (in rodents, rabbits or primates); strategic ischaemic lesions (in rats or mini-pigs); generalised vasculopathies, because of mutant Notch3, hyperhomocysteinaemia, experimental diabetes mellitus or lack of cerebral vasodilator M(5) receptors (rats or mice). Most cognitive testing showed deficits in working and reference memory. The lesions observed were microinfarcts, diffuse white matter lesions, hippocampal neuronal death, focal ischaemic lesions and micro-haemorrhages. The most-used model was bilateral carotid artery occlusion in rats, leading to chronic hypoperfusion and white matter injury.

Animal models of ischemic stroke. Part two: modeling cerebral ischemia

Animal models of stroke provide an essential tool for the understanding of the complex cellular and molecular pathophysiology of stroke and for testing novel recanalyzing, neuroprotective, neuroregenerative or anti- inflammatory drugs in pre- clinical setting. Since the first description of the distal occlusion of the middle cerebral artery (MCA) in rats, different techniques and methods to induce focal and global ischemia of the brains have been developed and optimized. The different models, ranging from proximal to distal MCA occlusion to embolic and photothrombotic stroke vary widely in their ability to model human disease and in their application to the study of cell death, inflammation and neural repair. In the first part of the review animal models developed for studying stroke related risk factors are described while this section discusses specific models that have been created for mimicking different types of stroke, focal and global ischemia in an experimental setup. Advantages and limits and the potential of the diverse models for the study of novel therapies as well as for the study of basic pathophysiological mechanisms are explored.

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.

Rit signaling contributes to interferon-gamma-induced dendritic retraction via p38 mitogen-activated protein kinase activation

The proinflammatory cytokine interferon-gamma (IFNgamma) alters neuronal connectivity via selective regressive effects on dendrites but the signaling pathways that mediate this effect are poorly understood. We recently demonstrated that signaling by Rit, a member of the Ras family of GTPases, modulates dendritic growth in primary cultures of sympathetic and hippocampal neurons. In this study, we investigated a role for Rit signaling in IFNgamma-induced dendritic retraction. Expression of a dominant negative Rit mutant inhibited IFNgamma-induced dendritic retraction in cultured embryonic rat sympathetic and hippocampal neurons. In pheochromacytoma cells and hippocampal neurons, IFNgamma caused rapid Rit activation as indicated by increased GTP binding to Rit. Silencing of Rit by RNA interference suppressed IFNgamma-elicited activation of p38 MAPK in pheochromacytoma cells, and pharmacological inhibition of p38 MAPK significantly attenuated the dendrite-inhibiting effects of IFNgamma in cultured sympathetic and hippocampal neurons without altering signal transducer and activator of transcription 1 activation. These observations identify Rit as a downstream target of IFNgamma and suggest that a novel IFNgamma-Rit-p38 signaling pathway contributes to dendritic retraction and may, therefore, represent a potential therapeutic target in diseases with a significant neuroinflammatory component.

White matter changes in dementia: does radiology matter?

White matter changes are frequently seen on MRI in elderly patients. The significance of these changes is still debated. The origin of white matter changes is heterogeneous but the majority are due to arteriosclerosis in brain vessels. The clinical consequence of the presence of white matter changes in relation to dementia is still unclear. Lately, however, many studies have found a relation between the presence and the degree of white matter changes and cognitive dysfunction. This is most obvious in vascular dementia, but has also been suggested to be of importance in Alzheimer's disease. In this review we discuss the background of these changes and the clinical consequences of them in relation to cognitive disorders.

Total cerebral blood flow, white matter lesions and brain atrophy: the SMART-MR study

We investigated whether total cerebral blood flow (CBF) was associated with brain atrophy, and whether this relation was modified by white matter lesions (WML). Within the Second Manifestations of ARTerial disease-magnetic resonance (SMART-MR) study, a prospective cohort study among patients with arterial disease, cross-sectional analyses were performed in 828 patients (mean age 58+/-10 years, 81% male) with quantitative flow, atrophy, and WML measurements on magnetic resonance imaging (MRI). Total CBF was measured with MR angiography and was expressed per 100 mL brain volume. Total brain volume and ventricular volume were divided by intracranial volume to obtain brain parenchymal fraction (BPF) and ventricular fraction (VF). Lower BPF indicates more global brain atrophy, whereas higher VF indicates more subcortical brain atrophy. Mean CBF was 52.0+/-10.2 mL/min per 100 mL, mean BPF was 79.2+/-2.9%, and mean VF was 2.03+/-0.96%. Linear regression analyses showed that lower CBF was associated with more subcortical brain atrophy, after adjusting for age, sex, vascular risk factors, intima-media thickness, and lacunar infarcts, but only in patients with moderate to severe WML (upper quartile of WML): Change in VF per s.d. decrease in CBF 0.18%, 95% CI: 0.02 to 0.34%. Our findings suggest that cerebral hypoperfusion in the presence of WML may be associated with subcortical brain atrophy.

Long-term measurement of cerebral blood flow and metabolism in a rat chronic hypoperfusion model

1. Rat bilateral common carotid artery occlusion (BCAO) was used as a chronic cerebral hypoperfusion model. We observed autoradiographically the long-term changes in regional cerebral blood flow (rCBF) and regional cerebral glucose utilization (rCGU) after 2 days and 1, 4 and 8 weeks of BCAO and in controls. Regions evaluated included the cerebral cortex, white matter and basal ganglia. Pathological changes were also observed with Klüver-Barrera and haematoxylin-eosin staining. 2. After 2 days, rCBF was significantly reduced to 33-58% in the cortex, white matter and amygdala and similar reductions were observed after 1 week. 3. After 4 weeks, rCBF recovered; however, rCBF remained significantly reduced in the occipital cortex, white matter, globus pallidus and substantia nigra. 4. After 2 days, rCGU was mostly maintained but, after 1 week, rCGU was reduced significantly to 40-70% in the cortex, white matter, basal ganglia and thalamus. Four weeks later, these reductions were no longer seen. 5. Rarefaction of the white matter was observed from 1 week. 6. These results showed that the BCAO in rats is an appropriate model for chronic cerebral hypoperfusion and that uncoupling of rCBF and rCGU was observed from 2 days until 4 weeks in the white matter.

HVJ-envelope vector for gene transfer into central nervous system

To overcome some problems of virus vectors, we developed a novel non-viral vector system, the HVJ-envelope vector (HVJ-E). In this study, we investigated the feasibility of gene transfer into the CNS using the HVJ-E both in vitro and in vivo. Using the Venus reporter gene, fluorescence could be detected in cultured rat cerebral cortex neurons and glial cells. In vivo, the reporter gene (Venus) was successfully transfected into the rat brain by direct injection into the thalamus, intraventricular injection, or intrathecal injection, without inducing immunological change. When the vector was injected after transient occlusion of the middle cerebral artery, fluorescence due to EGFP gene or luciferase activity could be detected only in the injured hemisphere. Finally, luciferase activity was markedly enhanced by the addition of 50 U/ml heparin (P<0.01). Development of efficient HVJ-E for gene transfer into the CNS will be useful for research and clinical gene therapy.

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.

Subcortical ischaemic vascular dementia

Vascular dementia is the second most common type of dementia. The subcortical ischaemic form (SIVD) frequently causes cognitive impairment and dementia in elderly people. SIVD results from small-vessel disease, which produces either arteriolar occlusion and lacunes or widespread incomplete infarction of white matter due to critical stenosis of medullary arterioles and hypoperfusion (Binswanger's disease). Symptoms include motor and cognitive dysexecutive slowing, forgetfulness, dysarthria, mood changes, urinary symptoms, and short-stepped gait. These manifestations probably result from ischaemic interruption of parallel circuits from the prefrontal cortex to the basal ganglia and corresponding thalamocortical connections. Brain imaging (computed tomography and magnetic resonance imaging) is essential for correct diagnosis. The main risk factors are advanced age, hypertension, diabetes, smoking, hyperhomocysteinaemia, hyperfibrinogenaemia, and other conditions that can cause brain hypoperfusion such as obstructive sleep apnoea, congestive heart failure, cardiac arrhythmias, and orthostatic hypotension. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL)and some forms of cerebral amyloid angiopathy have a genetic basis. Treatment is symptomatic and prevention requires control of treatable risk factors.

Interferon gamma induces retrograde dendritic retraction and inhibits synapse formation

The expression of interferon gamma (IFNgamma) increases after neural injury, and it is sustained in chronic inflammatory conditions such as multiple sclerosis and infection with human immunodeficiency virus. To understand how exposure to this proinflammatory cytokine might affect neural function, we examined its effects on cultures of neurons derived from the central and peripheral nervous systems. IFNgamma inhibits initial dendritic outgrowth in cultures of embryonic rat sympathetic and hippocampal neurons, and this inhibitory effect on process growth is associated with a decrease in the rate of synapse formation. In addition, in older cultures of sympathetic neurons, IFNgamma also selectively induces retraction of existing dendrites, ultimately leading to an 88% decrease in the size of the arbor. Dendritic retraction induced by IFNgamma represents a specific cellular response because it occurs without affecting axonal outgrowth or cell survival, and it is not observed with tumor necrosis factor alpha or other inflammatory cytokines. IFNgamma-induced dendritic retraction is associated with the phosphorylation and nuclear translocation of signal transducer and activator of transcription 1 (STAT1), and expression of a dominant-negative STAT1 construct attenuates the inhibitory effect of IFNgamma. Moreover, retrograde dendritic retraction is observed when distal axons are selectively exposed to IFNgamma. These data imply that IFNgamma-mediated STAT1 activation induces both dendritic atrophy and synaptic loss and that this occurs both at the sites of IFNgamma release and at remote loci. Regressive actions of IFNgamma on dendrites may contribute to the neuropathology of inflammatory diseases.

Magnetic resonance imaging in dementia. A study of brain white matter changes

Non-specific white matter changes (WMC) in the brain are common findings in the elderly population. Although they are frequently seen in non-demented persons, WMC seem to be more common in demented patients. The significance of these changes, as well as their pathophysiological background, is incompletely understood. The aim of this thesis was to study different aspects of WMC using MR imaging (MRI) and to investigate the clinical significance of such changes in subjects with mild cognitive impairment or dementia. In study I post-mortem MRI of the brain was compared to corresponding neuropathology slices. WMC were quantified and found to be more extensive on neuropathology. The areas that appeared normal on MRI but not on histopathology represented only minor changes with increased distance between the myelinated fibres but with preserved axonal network and glial cell density. Study II evaluated the blood-brain barrier (BBB) integrity to investigate if an increased permeability could be shown in WMC. A contrast-enhanced MRI technique was used to detect small degrees of enhancement. No general increase in BBB could be detected in the WMC areas. In study III the relation between WMC and apolipoprotein E (APOE) genotype was explored in patients with Alzheimer's disease (AD). Results showed that AD patients, who were homozygous for the APOE epsilon 4 allele had more WMC than patients with other genotypes. This was most significant for changes in the deep white matter. Results also indicated that in AD patients carrying the epsilon 4 allele, WMC are not age-related phenomena, but might be related to the aetiology of the disease. Study IV aimed to investigate if WMC in a specific brain region affect cognitive functions related to that area. Periventricular WMC in the left frontal lobe predicted a decrease in initial word fluency, a test though to reflect left frontal lobe functioning. This indicates that WMC might have specific effects in different brain regions. In study V we evaluated the prognostic significance of WMC in patients with memory impairment, regarding the rate of further global cognitive decline. There was no difference in outcome between patients having extensive WMC and a matched control group, during 2-4 years of follow up, and assessed by the "Mini-Mental State Examination". In conclusion, this work has shown and characterised pathological changes in the white matter not visible on conventional MRI. We have also shown that there is no major general increase in BBB permeability in areas of WMC. In addition, homozygosity with regard to the APOE epsilon 4 gene allele implies an increased extent of WMC in AD patients. In AD patients carrying this gene allele, WMC are not merely age-related phenomena, but might be related to the aetiology of the disease. We also claim that WMC in a specific location might impair cognitive functions that rely on those specific pathways. In contrast, WMC do not seem to have any prognostic value in predicting the rate of global cognitive decline in patients at a memory clinic.

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.

Vascular dementia, a new beginning: shifting focus from clinical phenotype to ischemic brain injury

Dementia may result from complete or incomplete infarction of brain regions subserving memory and cognition. Several effective treatments reduce the risk of initial and recurrent stroke. Presumably, these interventions reduce the risk of vascular cognitive impairment. Incomplete infarction caused by recurrent, chronic, or subclinical ischemia appears to represent another important cause of ischemic brain injury, but has been relatively neglected. A shift in focus from the serendipitous clinical phenotype of vascular dementia to preventing and ameliorating the broad spectrum of ischemic brain injury is recommended.

Cerebral hypoperfusion yields capillary damage in the hippocampal CA1 area that correlates with spatial memory impairment

The impact of chronic cerebral hypoperfusion on cognitive function and cerebral capillary morphology in the hippocampus was examined. Young adult Wistar rats were subjected to permanent ligation of both common carotid arteries (two-vessel occlusion). One month after vascular occlusion, a small but non-significant impairment in the acquisition of spatial information was registered compared with sham-operated controls. Two months after surgery, the occluded animals displayed an impaired performance throughout the training period. One year after surgery, the acquisition curves demonstrated a significant attenuation of the learning rate in the occluded rats group, whereas no significant differences in long-term retention were observed. Thus, chronic hypoperfusion induced by two-vessel occlusion gave rise to impairment of spatial memory. Following behavioural testing, the rats were killed at the age of 17 months, and capillaries in the CA1 and dentate gyrus were examined using transmission electron microscopy. Typical age-related capillary abnormalities such as degenerative pericytes and thickened basement membranes (with or without fibrosis) were detected in the hippocampus of sham animals. In occluded rats, the occurrence of capillaries displaying such abnormalities almost doubled in the CA1 region, but was similar in the dentate gyrus, compared with sham controls. A highly significant correlation was found between the last Morris maze performance and the percentage of capillaries with deposits in the basement membrane in the hippocampal CA1 area of occluded rats, which was not present in the sham animals. We conclude that a long-term hypoperfusion accelerated the development of age-related ultrastructural aberrations of capillaries in the hippocampal CA1 area, but not in the dentate gyrus. Thus, not only neurons, but also capillaries in the hippocampal CA1 area are sensitive to an impaired microcirculation. Moreover, the cognitive performance of hypoperfused rats correlated closely with the condition of the capillaries in the CA1 area, suggesting that capillary integrity is one of the important determinants of brain function in conditions that compromise cerebral microcirculation.

Upregulation of MAP1B and MAP2 in the rat brain after middle cerebral artery occlusion: effect of age

Although stroke in humans usually afflicts the elderly, most experimental studies on the nature of cerebral ischemia have used young animals. This is especially important when studying restorative processes that are age dependent. To explore the potential of older animals to initiate regenerative processes after cerebral ischemia, the authors studied the expression of the juvenile-specific cytoskeletal protein, microtubule-associated protein (MAP) 1B, and the adult-specific protein, MAP2, in male Sprague-Dawley rats at 3 months and 20 months of age. The levels of MAP1B and MAP2 transcripts and the corresponding proteins declined with increasing age in the hippocampus. In the cortex, the levels of the transcripts did not change significantly with age, but the morphologic features of immunostained fibers were clearly affected by age; that is, cortical MAP1B fibers became thicker, and MAP2 fibers, more diffuse, in aged rats. Focal cerebral ischemia, produced by reversible occlusion of the right middle cerebral artery, resulted in a large decrease in the expression of both MAP1B and MAP2 in the infarct core at the messenger ribonucleic acid and protein levels. However, at 1 week after the stroke, there was vigorous expression of MAP1B and its messenger ribonucleic acid, as well as MAP2 protein, in the border zone adjacent to the infarct of 3-month-old and 20 month-old male Sprague-Dawley rats. The upregulation of these key cytologic elements generally was diminished in aged rats compared with young animals, although the morphologic features of fibers in the infarct border zone were similar in both age groups. These results suggest that the regenerative potential of the aged rat brain appears to be competent, although attenuated, at least with respect to MAP1B and MAP2 expression up to 20 months of age.

Posthemorrhagic hydrocephalus and brain injury in the preterm infant: dilemmas in diagnosis and management

Advances in neonatal critical care have reduced the incidence of intraventricular hemorrhage (IVH) in the newborn. Paradoxically, however, the prevalence of the complications of IVH including posthemorrhagic hydrocephalus (PHHC) has increased. By virtue of its association with long-term neurodevelopmental disability, posthemorrhagic hydrocephalus is an ominous diagnosis in the premature infant. Animal models have demonstrated that ventricular distention may cause direct cerebral parenchymal injury. Evidence for secondary parenchymal injury in the premature infant with PHHC is by necessity indirect. The precise impact of secondary parenchymal injury on the overall neurological outcome of premature infants with PHHC remains unclear in large part because of the vulnerability of the immature brain to other forms of injury (e.g., periventricular leukomalacia) that may be difficult to distinguish from injury due to distention. Furthermore, parenchymal injury due to PVL may cause ventricular enlargement that does not benefit from CSF diversion. Because these primary and secondary mechanisms of injury may operate concurrently, the precise or dominant cause of ventricular enlargement is often difficult to establish with certainty in the neonatal period. These diagnostic dilemmas have in turn impeded the development and evaluation of therapies specifically aimed at reversing ventricular distention and preventing secondary parenchymal injury. This article focuses on the current dilemmas in diagnosis and management of this potentially reversible form of injury as well as on potential future strategies for its prevention.

Spreading depression induces depletion of MAP2 in area CA3 of the hippocampus in a rat unilateral carotid artery occlusion model

Traumatic brain injury (TBI) induces neuronal cell loss in area CA3 of the hippocampus. However, it has not yet been established why traumatic injury of the cortex induces neuronal damage in more remote areas. Spreading depression (SD) may be one potential mechanism for this pathophysiology. The present study evaluated whether SD on the cortex evokes a pathological change in the hippocampus. Forty-two Fisher rats were assigned to four groups: Group I: sham operation (n = 7), Group II: right carotid occlusion (UO) for 7 days (n = 7), Group III: repeated induction of SD by KCl application on dura for 7 days (n = 7), Group III' for 3 h (n = 7), Group IV: SD induction and UO for 7 days (n = 14) Group IV' for 3 h (n = 7). In 5 out of 7 animals in Groups III' and IV', cerebral blood flow (CBF) was monitored using laser Doppler flowmetry for 3 h during the passage of SD. The brains were processed for immunohistochemical analysis of microtubule-associated protein 2 (MAP2). Reactive hyperemia induced by SD was not significantly suppressed by right carotid occlusion (194 +/- 25% and 181 +/- 42% UO in Groups III and IV, respectively). In 6 out of 7 animals in a 7-day model of Group IV, and 3 animals in a 7-day model of Group III, MAP2 depletion in the CA3 area of the hippocampus (partly including CA2) was observed, although no change in the hippocampus was observed in other groups. In conclusion, SD in combination with UO yielded reproducible lesions in CA3. Neuronal injury in the hippocampus after brain trauma may be attributable to SD in combination with the blood flow restriction.

Visible changes in lesion borders on CT scan after five years poststroke, and long-term recovery in aphasia

This study examined 12 aphasia patients at approximately 1 year poststroke (Time 1) and again at 5-12 years poststroke (Time 2) with language testing and CT scan. Significant increases in naming scores, and phrase length in nonfluent speech were observed after 5 years poststroke. Significant expansion in visible lesion borders (lesion size) was observed after 5 years poststroke; an increase in lesion size of > 1% was present in 9/12 cases (75%). Not one case had a second stroke. Thus, it appears that even though lesion expansion may occur after 5 years poststroke, as long as this expansion is unilateral and gradual, it has no adverse effect on language, and in fact, continued recovery in naming and nonfluent speech may also occur. Long-term recovery patterns in aphasia which may be associated with brain reorganization deserve further study, especially with functional brain imaging techniques.

Cognitive impairment and cellular/vascular changes in the cerebral white matter

A possible relation between cerebral white-matter injury and dementia was intuitively attributed by Alzheimer to changes affecting the small penetrating vessels that supply the cerebral white matter. Several observations support the view that white-matter changes detectable by neuroimaging may contribute to cognitive deficits in the elderly. But many questions concerning this matter remain partially answered. In this communication we review: (1) Selected anatomic features of the blood vessels supplying the white matter; (2) possible pathogenetic mechanisms responsible for the white-matter changes; (3) observations on humans and animals suggesting a causal relationship between ischemia/hypoxemia and white-matter injury; (4) epidemiologic studies linking white-matter abnormalities with cognitive disorders. We conclude that abnormalities in the small vessels caused by aging and arterial hypertension, or other processes (cerebral amyloid angiopathy, CADASIL) together with systemic circulatory disturbances, such as abrupt variations in blood pressure values or cardiac diseases, may be the substrate of selective white-matter injury. The damage is structurally characterized by incomplete infarction or selective cellular injury.

Reduced local cerebral blood flow in periventricular white matter in experimental neonatal hydrocephalus-restoration with CSF shunting

The extent to which the reduction in CBF occurring in hydrocephalus is a primary or secondary event in the pathogenesis of the brain injury that ensues has not been clearly established. This is particularly true in neonatal hydrocephalus, where the disorder is most common, and where timing of the treatment of the developing nervous system is so important. We investigated the changes in local CBF (lCBF) in an animal model of severe progressive neonatal hydrocephalus before and after CSF shunting. Hydrocephalus was induced in 27 1-week-old kittens by percutaneous injection of 0.05 ml of 25% kaolin into the cisterna magna. Fourteen littermates acted as controls. The lCBF was measured by 14C-iodoantipyrine quantitative autoradiography after 1 week in 15 animals (8 hydrocephalic, 7 controls) and after 3 weeks in 26 animals (19 hydrocephalic, 7 controls) following induction of hydrocephalus. Twelve of the 3-week hydrocephalic group received a ventriculoperitoneal shunt 10 days following kaolin injection. At 1 week following induction of hydrocephalus, lCBF was globally reduced in cortical gray matter and white matter as well as deep subcortical structures. The maximum reduction was in the parietal white matter, to 37% of control levels. At 3 weeks a significant reduction in lCBF persisted only in the white matter (parietal, occipital, and corpus callosum; average, 42% of control levels), whereas cortical gray and deep subcortical structures had returned to normal levels spontaneously.(ABSTRACT TRUNCATED AT 250 WORDS)

Variable response of the Mongolian gerbil to unilateral carotid occlusion: magnetic resonance imaging and neuropathological characterization

In the present investigation, we estimated both the evolution and the severity of ischemic damage following unilateral carotid occlusion (UCO) in Mongolian gerbils by using conventional magnetic resonance imaging (MRI, i.e. T2 weighted imaging) and histological techniques. Immediately after UCO, the animals showed different clinical effects. The mortality (46%) detected within the first 48h was considered an "stroke-sensitivity", the "stroke-resistant" animals showed wide variability in terms of both temporal evolution and the extent of ischemic damage. The signal hyperintensity and negative MRI observed during the first 30h after UCO did not always correlate with the cerebral damage presented after 14 days, although a close correlation was established between the T2 weighted images taken more than 30h after UCO and neuropathology: the gerbils negative to imaging showed no morphological changes, whereas an enhanced signal was always prognostic of ischemic injury. Moreover, late MRI documented ventricular dilatation. Histopathology showed that the ischemic damage differed among the stroke-resistant gerbils and was often bilateral. The present study confirms the differences in gerbil susceptibility to hemispheric infarction after permanent UCO and suggests that conventional MRI may be a useful non-invasive method for i) identifying the stroke-resistant animals prone to mature ischemic injury and ii) monitoring the evolution of therapeutic efficacy without sacrificing animals.

Cytoskeletal derangements following central nervous system injury: modulation by neurotrophic gene transfection

This paper reviews important new evidence indicating that traumatic brain injury can produce more widespread derangements to the neuronal cytoskeleton than previously recognized. Although cytoskeletal derangements in axons have long been documented, recent data suggest that traumatic brain injury can produce structural derangements to dendrites and cell bodies as well. Many of these investigations have employed in vivo models to provide important insights into mechanisms possibly mediating the acute loss of cytoskeletal proteins, including disturbances in calcium homeostasis and activation of calcium-dependent proteolytic enzymes. However, we have little understanding of processes mediating the recovery of cytoskeletal proteins following injury. This paper provides recent evidence from in vitro models of central nervous system injury that neurotrophic proteins can enhance the recovery of the neuronal cytoskeleton. Neurotrophin-based therapy could employ either administration of exogenous neurotrophic proteins and/or transfection of cDNA for appropriate neurotrophins.

Correlates between nuclear magnetic resonance spectroscopy, diffusion weighted imaging, and CA1 morphometry following chronic brain ischemia

Chronic brain ischemia (CBI) was induced in aging (13 month) rats by ligating the left subclavian artery and placing temporary occluders in each common carotid artery [three-vessel occlusion (3-VO)]. Carotid artery occluders were removed after 1, 2, or 3 weeks following brain ischemia or maintained for 9 weeks. Two rats were kept with their occluders in place for 25 weeks. On weeks 3 and 9 after CBI, 31P-/1H-nuclear magnetic resonance (NMR) spectroscopy and high resolution diffusion weighted imaging were performed in vivo, non-invasively for detection of hippocampal high energy phosphates, lactate, intracellular pH, N-acetyl-aspartate, choline, glutamate, creatine, and structural alterations of the brain following CBI. Brains were histologically processed for morphometry of glial fibrillary acidic protein (GFAP) and CA1 damaged neurons 9 weeks after CBI. 31P-/1H-NMR spectroscopy showed that high energy substrates remained normal in ischemic animals when compared to non-ischemic controls except for an elevation of phosphomonesters in the hippocampal region. Rats deoccluded 1 and 2 weeks after initiation of CBI had no NMR spectroscopic or imaging changes. Rats kept ischemic for 9 weeks showed high signal intensities in the parietal cortex detected by diffusion weighted imaging as well as CA1 damage and increased GFAP density but no cortical atrophy or neuronal damage could be detected histologically. Rats kept ischemic for 25 weeks showed extensive cortical atrophy which corresponded to the high signal intensity observed with diffusion weighted imaging in the group kept ischemic for 9 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurofilament 68 and neurofilament 200 protein levels decrease after traumatic brain injury

We have examined the effect of lateral cortical impact injury on the levels of axonal cytoskeletal proteins in adult rats. Traumatic brain injury (TBI) causes a significant decrease in the protein levels of two prominent neurofilament (NF) proteins, NF68 and NF200. We employed quantitative immunoreactivity measurements on Western blots to examine NF68 and NF200 levels in homogenates of hippocampal and cortical tissue taken at several intervals postinjury. Sham injury had no effect on NF protein levels. However, injury was associated with a significant loss of NF68, restricted to the cortex ipsilateral to the injury site. NF68 loss was detectable as early as 3 h and lasted at least 2 weeks postinjury. Similarly, TBI induced a decrease in NF200 protein, although losses were observed both ipsilateral and contralateral to the injury site. No loss of NF68 or NF200 protein was detected in hippocampal samples obtained from the same injured animals. An increase in the presence of lower molecular weight (MW) NF68 immunopositive bands was associated with the decrease of NF68 in the ipsilateral cortex. This NF68 antigenicity pattern suggests the production of NF68 breakdown products caused by the pathologic activation of neuronal proteases, such as calpain. Putative NF68 breakdown products increase significantly until 1 day postinjury, suggesting that NF degradation may be ongoing until that time and indicating that a potential therapeutic window may exist within the first 24 h postinjury. In summary, these data identify specific biochemical alterations of the neuronal cytoskeleton following TBI and lay a foundation for further investigation of postinjury cytoskeletal changes in neuronal processes.