A temporal MRI assessment of neuropathology after transient middle cerebral artery occlusion in the rat: correlations with behavior

Changes in Brain Electrical Activity after Transient Middle Cerebral Artery Occlusion in Rats

Objectives. Ischemic stroke is a leading cause of death and disability worldwide. To search for new therapeutic and pharmacotherapeutic strategies, numerous models of this disease have been proposed, the most popular being transient middle cerebral artery occlusion. Behavioral and sensorimotor testing, biochemical, and histological methods are traditionally used in conjunction with this model to assess the effectiveness of potential treatment options. Despite its wide overall popularity, electroencephalography/electrocorticography is quite rarely used in such studies. Materials and methods. In the present work, we explored the changes in brain electrical activity at days 3 and 7 after 30- and 45-min of transient middle cerebral artery occlusion in rats. Results. Cerebral ischemia altered the amplitude and spectral electrocorticogram characteristics, and led to a reorganization of inter- and intrahemispheric functional connections. Ischemia duration affected the severity as well as the nature of the observed changes. Conclusions. The dynamics of changes in brain electrical activity may indicate a spontaneous partial recovery of impaired cerebral functions at post-surgery day 7. Our results suggest that electrocorticography can be used successfully to assess the functional status of the brain following ischemic stroke in rats as well as to investigate the dynamics of functional recovery.

Emerging neuroprotective strategies for the treatment of ischemic stroke: An overview of clinical and preclinical studies

Stroke is the leading cause of disability and thesecond leading cause of death worldwide. With the global population aged 65 and over growing faster than all other age groups, the incidence of stroke is also increasing. In addition, there is a shift in the overall stroke burden towards younger age groups, particularly in low and middle-income countries. Stroke in most cases is caused due to an abrupt blockage of an artery (ischemic stroke), but in some instances stroke may be caused due to bleeding into brain tissue when a blood vessel ruptures (hemorrhagic stroke). Although treatment options for stroke are still limited, with the advancement in recanalization therapy using both pharmacological and mechanical thrombolysis some progress has been made in helping patients recover from ischemic stroke. However, there is still a substantial need for the development of therapeutic agents for neuroprotection in acute ischemic stroke to protect the brain from damage prior to and during recanalization, extend the therapeutic time window for intervention and further improve functional outcome. The current review has assessed the past challenges in developing neuroprotective strategies, evaluated the recent advances in clinical trials, discussed the recent initiative by the National Institute of Neurological Disorders and Stroke in USA for the search of novel neuroprotectants (Stroke Preclinical Assessment Network, SPAN) and identified emerging neuroprotectants being currently evaluated in preclinical studies. The underlying molecular mechanism of each of the neuroprotective strategies have also been summarized, which could assist in the development of future strategies for combinational therapy in stroke treatment.

A peptide mimetic of tyrosine phosphatase STEP as a potential therapeutic agent for treatment of cerebral ischemic stroke

Extensive research over the last two decades has advanced our understanding of the pathophysiology of ischemic stroke. However, current pharmacologic therapies are still limited to rapid reperfusion using thrombolytic agents, and neuroprotective approaches that can reduce the consequences of ischemic and reperfusion injury, are still not available. To bridge this gap, we have evaluated the long-term efficacy and therapeutic time window of a novel peptide-based neuroprotectant TAT-STEP, derived from the brain-enriched and neuron-specific tyrosine phosphatase STEP. Using a rat model of transient middle cerebral artery occlusion (90 min), we show that a single intravenous administration of the peptide at the onset of reperfusion (early) or 6 h after the onset of the insult (delayed) reduces mortality rate. In the surviving rats, MRI scans of the brain at days 1, 14 and 28 after the insult show significant reduction in infarct size and improvement of structural integrity within the infarcted area following peptide treatment, regardless of the time of administration. Behavioral assessments show significant improvement in normal gait, motor coordination, sensory motor function and spatial memory following early or delayed peptide treatment. The study establishes for the first time the therapeutic potential of a tyrosine phosphatase in ischemic brain injury.

Hyperhomocysteinemia leads to exacerbation of ischemic brain damage: Role of GluN2A NMDA receptors

Hyperhomocysteinemia has been implicated in several neurodegenerative disorders including ischemic stroke. However, the pathological consequences of ischemic insult in individuals predisposed to hyperhomocysteinemia and the associated etiology are unknown. In this study, we evaluated the outcome of transient ischemic stroke in a rodent model of hyperhomocysteinemia, developed by subcutaneous implantation of osmotic pumps containing L-homocysteine into male Wistar rats. Our findings show a 42.3% mortality rate in hyperhomocysteinemic rats as compared to 7.7% in control rats. Magnetic resonance imaging of the brain in the surviving rats shows that mild hyperhomocysteinemia leads to exacerbation of ischemic injury within 24 h, which remains elevated over time. Behavioral studies further demonstrate significant deficit in sensorimotor functions in hyperhomocysteinemic rats compared to control rats. Using pharmacological inhibitors targeting the NMDAR subtypes, the study further demonstrates that inhibition of GluN2A-containing NMDARs significantly reduces ischemic brain damage in hyperhomocysteinemic rats but not in control rats, indicating that hyperhomocysteinemia-mediated exacerbation of ischemic brain injury involves GluN2A-NMDAR signaling. Complementary studies in GluN2A-knockout mice show that in the absence of GluN2A-NMDARs, hyperhomocysteinemia-associated exacerbation of ischemic brain injury is blocked, confirming that GluN2A-NMDAR activation is a critical determinant of the severity of ischemic damage under hyperhomocysteinemic conditions. Furthermore, at the molecular level we observe GluN2A-NMDAR dependent sustained increase in ERK MAPK phosphorylation under hyperhomocysteinemic condition that has been shown to be involved in homocysteine-induced neurotoxicity. Taken together, the findings show that hyperhomocysteinemia triggers a unique signaling pathway that in conjunction with ischemia-induced pathways enhance the pathology of stroke under hyperhomocysteinemic conditions.

Neuroanatomy- and Pathology-Based Functional Examinations of Experimental Stroke in Rats: Development and Validation of a New Behavioral Scoring System

In experimental stroke studies, a neuroanatomy-based functional examination of behaviors is critical to predict the pathological extent of infarcts because brain-imaging studies are not always available. However, there is a lack of systematic studies to examine the efficiency of a behavioral test for this purpose. Our work aimed to design a new score for this goal in stroke rats, by simplifying the Garcia score (with subscore 1–6) and adding circling as subscore 7. MRI and 2,3,5-triphenyltetrazolium chloride staining were used to determine the pathological extent after transient middle cerebral artery occlusion. The modified summations of subscores were designed according to the predictability of each subscore for locations and sizes of infarcts in one group of stroke rats, and were validated in another group. The original Garcia score was able to predict the pathological extent of edema-adjusted infarct size ≥30%, and the summation of subscore 4, 6, and 7 (4: climbing, 6: vibrissae sensation, 7: circling) also could predict it well. The original Garcia score failed to predict infarct at the primary motor cortex, while the summation of subscore 4, 6, and 7 potentially could predict not only the primary motor cortex, but also the forelimb, hindlimb, and barrel field regions of the primary sensory cortex. Accordingly, this neuroanatomy-correlated functional assessment system composed of subscore 4, 6, and 7 was proposed, with less examination time and better inter-rater reliability than the original Garcia score. In summary, this new scoring system, summation (4,6,7) score, examined motor and sensory functions based on neuroanatomical involvement, having the potential to predict the pathological extent and specific relevant brain areas of infarcts, respectively.

Long-Term Changes of Diffusion Tensor Imaging and Behavioural Status after Acupuncture Treatment in Rats with Transient Focal Cerebral Ischaemia

Background

The effect of acupuncture treatment in cerebral ischaemia is controversial. A study was undertaken to assess its effects in rats with transient middle cerebral artery occlusion (tMCAO) and discuss its mechanisms.

Methods

21 Sprague–Dawley rats were divided into three groups. Group 1 underwent tMCAO and subsequently received acupuncture treatment, Group 2 underwent tMCAO without treatment and Group 3 only underwent sham operation. The evolution of diffusion tensor imaging (DTI) features in ischaemic lesions from acute to chronic periods was assessed and the correlations with behavioural tests and histopathological changes were examined.

Results

tMCAO rats displayed side-specific sensorimotor deficits after occlusion. Behavioural scores of rats in group 1 reduced gradually with acupuncture treatment. No significant difference in lesion size on T2-weighted imaging was found between the two tMCAO groups. Relative apparent diffusion coefficient (rADC) and relative fractional anisotropy (rFA) values in the centre and at the edge of the ischaemic lesions reduced at first and then increased to varying degrees. Only changes in the rFA value at the edge of the ischaemic lesions were significantly different between the two tMCAO groups. A more significant increase in growth-associated protein B-50 and synaptophysin protein expression was found in group 1 than in the other groups. No significant correlations were found between behavioural scores, DTI appearances and immunohistochemical results.

Conclusions

The acupuncture points applied were effective, and improving neuronal regeneration may have a role in the mechanism of acupuncture treatment of post-stroke paralysis of the limbs in rats. MRI, particularly the fractional anisotropy value of DTI, is an appropriate parameter to evaluate the recovery status.

Making Stem Cell Lines Suitable for Transplantation

Human stem cells, progenitor cells, and cell lines have been derived from embryonic, fetal, and adult sources in the search for graft tissue suitable for the treatment of CNS disorders. An increasing number of experimental studies have shown that grafts from several sources survive, differentiate into distinct cell types, and exert positive functional effects in experimental animal models, but little attention has been given to developing cells under conditions of good manufacturing practice (GMP) that can be scaled up for mass treatment. The capacity for continued division of stem cells in culture offers the opportunity to expand their production to meet the widespread clinical demands posed by neurodegenerative diseases. However, maintaining stem cell division in culture long term, while ensuring differentiation after transplantation, requires genetic and/or oncogenetic manipulations, which may affect the genetic stability and in vivo survival of cells. This review outlines the stages, selection criteria, problems, and ultimately the successes arising in the development of conditionally immortal clinical grade stem cell lines, which divide in vitro, differentiate in vivo, and exert positive functional effects. These processes are specifically exemplified by the murine MHP36 cell line, conditionally immortalized by a temperature-sensitive mutant of the SV40 large T antigen, and cell lines transfected with the c-myc protein fused with a mutated estrogen receptor (c-mycERTAM), regulated by a tamoxifen metabolite, but the issues raised are common to all routes for the development of effective clinical grade cells.

Evolution of ischemic damage and behavioural deficit over 6 months after MCAo in the rat: Selecting the optimal outcomes and statistical power for multi-centre preclinical trials

Key disparities between the timing and methods of assessment in animal stroke studies and clinical trial may be part of the reason for the failure to translate promising findings. This study investigates the development of ischemic damage after thread occlusion MCAo in the rat, using histological and behavioural outcomes. Using the adhesive removal test we investigate the longevity of behavioural deficit after ischemic stroke in rats, and examine the practicality of using such measures as the primary outcome for future studies. Ischemic stroke was induced in 132 Spontaneously Hypertensive Rats which were assessed for behavioural and histological deficits at 1, 3, 7, 14, 21, 28 days, 12 and 24 weeks (n>11 per timepoint). The basic behavioural score confirmed induction of stroke, with deficits specific to stroke animals. Within 7 days, these deficits resolved in 50% of animals. The adhesive removal test revealed contralateral neglect for up to 6 months following stroke. Sample size calculations to facilitate the use of this test as the primary experimental outcome resulted in cohort sizes much larger than are the norm for experimental studies. Histological damage progressed from a necrotic infarct to a hypercellular area that cleared to leave a fluid filled cavity. Whilst absolute volume of damage changed over time, when corrected for changes in hemispheric volume, an equivalent area of damage was lost at all timepoints. Using behavioural measures at chronic timepoints presents significant challenges to the basic science community in terms of the large number of animals required and the practicalities associated with this. Multicentre preclinical randomised controlled trials as advocated by the MultiPART consortium may be the only practical way to deal with this issue.

GSK249320, A Monoclonal Antibody Against the Axon Outgrowth Inhibition Molecule Myelin-Associated Glycoprotein, Improves Outcome of Rodents with Experimental Stroke

Myelin-associated glycoprotein (MAG) is an inhibitor of axon growth. MAG levels increase after stroke. GSK249320 is a monoclonal antibody that neutralizes MAG-mediated inhibition and so may promote axon outgrowth and improve post-stroke outcomes. The current study tested the hypothesis that GSK249320 initiated 24 hours or 7 days after experimental stroke improves behavioural outcomes. Rats with right middle cerebral artery occlusion for 90 minutes were randomized to receive 6 weeks of intravenous (a) GSK249320 starting 24 hours post-stroke, (b) GSK249320 starting 7 days post-stroke, or (c) vehicle. Behavioral testing was performed over 7 weeks. Serial MRI demonstrated no differences in infarct volume across groups. Animals treated with GSK249320 24 hours post-stroke showed larger increases in Neuroscore (time X group, p = 0.0008) and staircase test (main effect of group, p = 0.0214) as compared to controls, but animals treated 7 days post-stroke showed no significant behavioral benefit. No significant results were found for the sticky tape or cylinder tests. A separate set of animals with experimental stroke received a single intravenous dose of GSK249320 or vehicle at 1 hour, 24 hours, 48 hours or 1 week post-stroke, and immunohistochemistry methods were used to measure GSK249320 distribution; GSK249320 was found in the ipsilesional hemisphere only, the extent of which increased with later times of injection. These data suggest that intravenous GSK249320 penetrates the lesion site and is associated with a small effect on functional outcomes when initiated 24 hours post-stroke and so support the translational potential of this monoclonal antibody as a restorative therapy for patients with stroke.

Bystander Effect Fuels Human Induced Pluripotent Stem Cell-Derived Neural Stem Cells to Quickly Attenuate Early Stage Neurological Deficits After Stroke

: Present therapies for stroke rest with tissue plasminogen activator (tPA), the sole licensed antithrombotic on the market; however, tPA's effectiveness is limited in that the drug not only must be administered less than 3-5 hours after stroke but often exacerbates blood-brain barrier (BBB) leakage and increases hemorrhagic incidence. A potentially promising therapy for stroke is transplantation of human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSCs). To date, the effects of iPSCs on injuries that take place during early stage ischemic stroke have not been well studied. Consequently, we engrafted iPSC-NSCs into the ipsilesional hippocampus, a natural niche of NSCs, at 24 hours after stroke (prior to secondary BBB opening and when inflammatory signature is abundant). At 48 hours after stroke (24 hours after transplant), hiPSC-NSCs had migrated to the stroke lesion and quickly improved neurological function. Transplanted mice showed reduced expression of proinflammatory factors (tumor necrosis factor-α, interleukin 6 [IL-6], IL-1β, monocyte chemotactic protein 1, macrophage inflammatory protein 1α), microglial activation, and adhesion molecules (intercellular adhesion molecule 1, vascular cell adhesion molecule 1) and attenuated BBB damage. We are the first to report that engrafted hiPSC-NSCs rapidly improved neurological function (less than 24 hours after transplant). Rapid hiPSC-NSC therapeutic activity is mainly due to a bystander effect that elicits reduced inflammation and BBB damage.

SIGNIFICANCE

Clinically, cerebral vessel occlusion is rarely permanent because of spontaneous or thrombolytic therapy-mediated reperfusion. These results have clinical implications indicating a much extended therapeutic window for transplantation of human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSCs; 24 hours after stroke as opposed to the 5-hour window with tissue plasminogen activator [tPA]). In addition, there is potential for a synergistic effect by combining hiPSC-NSC transplantation with tPA to attenuate stroke's adverse effects.

Human neural stem cells rapidly ameliorate symptomatic inflammation in early-stage ischemic-reperfusion cerebral injury

Introduction

Clinically, a good deal of injury from stroke results from ischemic-reperfusion. There is a loss of cerebral parenchyma and its associated cells, disruption of neuronal connections, compromise of the blood-brain barrier, and inflammation. We tested whether exogenously engrafted human neural stem cells could migrate rapidly and extensively to damaged regions, following transplantation into a neurogenic site where migration cues are already underway during stroke onset, then counteract a number of these pathological processes.

Methods

One day post-injury, we injected human neural stem cells (hNSCs) into the ipsilesional hippocampus of a mouse model of stroke with middle cerebral artery occlusion to induce focal ischemia followed by reperfusion (MCAO/R). The time frame for hNSC transplantation corresponded to upregulation of endogenous proinflammatory cytokines. We examined the effect of hNSC transplantation on pathological processes and behavioral dysfunction 48 hours post-injury.

Results

Twenty-four hours after transplantation, engrafted hNSCs had migrated extensively to the lesion, and infarct volume was reduced relative to MCAO/R controls. The behavioral deficits seen in MCAO/R controls were also significantly improved. Given this rapid response, we hypothesized that the mechanisms underlying therapeutic activity were anti-inflammatory rather than due to cell replacement. In support of this idea, in hNSC-transplanted mice we observed reduced microglial activation, decreased expression of proinflammatory factors (tumor necrosis factor-α, interleukin (IL)-6, IL-1β, monocyte chemotactic protein-1, macrophage inflammatory protein-1α) and adhesion molecules (intercellular adhesion molecule-1, vascular cell adhesion molecule-1), and amelioration of blood-brain barrier damage.

Conclusions

While long-term effects of engrafted hNSCs on the amelioration of ischemic stroke-induced behavioral dysfunction in a rodent model have been reported, our study is the first to show rapid, beneficial impacts on behavioral function (within 24 hours) upon early delivery of hNSCs into the hippocampus.

Electronic supplementary material

The online version of this article (doi:10.1186/scrt519) contains supplementary material, which is available to authorized users.

Resveratrol attenuates oxidative stress and improves behaviour in 1 -methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) challenged mice

Background

Parkinson's disease (PD) is the most common neurodegenerative disorder, characterized by loss of dopaminergic neurons in substantia nigra and depletion of dopamine in striatum due to mitochondrial dysfunction, oxidative stress, excitotoxicity, apoptosis, inflammation and proteasome failure.

Purpose

The present study deals with the neuroprotective effect of resveratrol, a wine polyphenol (50 mg/kg body weight) against MPTP (30mg/kg body weight as i.p. administration) induced mice model of idiopathic Parkinson's disease.

Methods

A combination of behaviour tasks and biochemical parameters were tested using standard molecular tools.

Results

Pretreatment of resveratrol significantly reversed toxic effects of MPTP by increasing the levels of dopamine, its metabolites, GSH and activities of GPx and reducing levels of TBARS, catalase and SOD activities along with enhanced behavior performance.

Conclusion

The multifactorial etiology of these diseases suggests that drugs with multiple targets such as resveratrol could have therapeutic potential for these pathologies.

Acute neuromuscular adaptation at the spinal level following middle cerebral artery occlusion-reperfusion in the rat

The purpose of the study was to highlight the acute motor reflex adaptation and to deepen functional deficits following a middle cerebral artery occlusion-reperfusion (MCAO-r). Thirty-six Sprague-Dawley rats were included in this study. The middle cerebral artery occlusion (MCAO; 120 min) was performed on 16 rats studied at 1 and 7 days, respectively (MCAO-D1 and MCAO-D7, n = 8 for each group). The other animals were divided into 3 groups: SHAM-D1 (n = 6), SHAM-D7 (n = 6) and Control (n = 8). Rats performed 4 behavioral tests (the elevated body swing test, the beam balance test, the ladder-climbing test and the forelimb grip force) before the surgery and daily after MCAO-r. H-reflex on triceps brachii was measured before and after isometric exercise. Infarction size and cerebral edema were respectively assessed by histological (Cresyl violet) and MRI measurements at the same time points than H-reflex recordings. Animals with cerebral ischemia showed persistent functional deficits during the first week post-MCAO-r. H-reflex was not decreased in response to isometric exercise one day after the cerebral ischemia contrary to the other groups. The motor reflex regulation was recovered 7 days post-MCAO-r. This result reflects an acute sensorimotor adaptation at the spinal level after MCAO-r.

Stroke-induced brain parenchymal injury drives blood-brain barrier early leakage kinetics: a combined in vivo/in vitro study

The disappointing clinical outcomes of neuroprotectants challenge the relevance of preclinical stroke models and data in defining early cerebrovascular events as potential therapeutic targets. The kinetics of blood-brain barrier (BBB) leakage after reperfusion and the link with parenchymal lesion remain debated. By using in vivo and in vitro approaches, we conducted a kinetic analysis of BBB dysfunction during early reperfusion. After 60 minutes of middle cerebral artery occlusion followed by reperfusion times up to 24 hours in mice, a non-invasive magnetic resonance imaging method, through an original sequence of diffusion-weighted imaging, determined brain water mobility in microvascular compartments (D*) apart from parenchymal compartments (apparent diffusion coefficient). An increase in D* found at 4 hours post reperfusion concurred with the onset of both Evans blue/Dextran extravasations and in vitro BBB opening under oxygen-glucose deprivation and reoxygenation (R). The BBB leakage coincided with an emerging cell death in brain tissue as well as in activated glial cells in vitro. The co-culture of BBB endothelial and glial cells evidenced a recovery of endothelium tightness when glial cells were absent or non-injured during R. Preserving the ischemic brain parenchymal cells within 4 hours of reperfusion may improve therapeutic strategies for cerebrovascular protection against stroke.

Functional assessment of sensory functions after photothrombotic stroke in the barrel field of mice

Motor, sensory and cognitive deficits are common impairments observed in human stroke as well as in animal stroke models. Using a battery of behavioural tests we assessed sensorimotor deficits after photothrombotic stroke localized within or beyond cortical representation of mouse sensory vibrissae. We found restricted, modality specific behavioural consequences in the acute post-stroke period. Among incorporated tests, adhesive removal test, novelty exploration test and sensory labyrinth task were sensitive to the somatosensory cortical deficits. Injured animals explored new objects significantly longer, they also needed distinctly more time to contact and to remove the adhesive tape placed on whiskers contralateral to the infarct. Moreover, we observed that after stroke animals were unable to solve the sensory labyrinth depending only upon tactile sensation from whiskers with injured cortical representation. Spontaneous recovery could be observed within the first post-stroke week for adhesive tape removal and within 14 days for labyrinth performance. However, for the novel object exploration we did not observed the recovery for the period of 18 days after stroke. Moreover, new object exploration test performance differed between the somatosensory and visual cortical impairments. We suggest that those three tests might be valuable in assessing the usefulness of therapies designed to support brain repair after experimental stroke.

Enhancement in cognitive function recovery by granulocyte-colony stimulating factor in a rodent model of traumatic brain injury

Traumatic brain injury (TBI) is characterized by neuronal damage and commonly, secondary cell death, leading to functional and neurological dysfunction. Despite the recent focus of TBI research on developing therapies, affective therapeutic strategies targeting neuronal death associated with TBI remain underexplored. This study explored the efficacy of granulocyte-colony stimulating factor (G-CSF) as an intervention for improving cognitive deficits commonly associated with TBI. Although G-CSF has been studied with histological techniques, to date, its effects on functional outcome remain unknown. To this end, we used a closed head injury (CHI) model in Wistar rats that were randomly assigned to one of four groups (untreated TBI, G-CSF treated TBI, G-CSF treated Control, Control). The treatment groups were administered subcutaneous injections of G-CSF 30 min (120 μg/kg) and 12 h (60 μg/kg) post-trauma. The Morris Water Maze test was used to measure any treatment-associated changes in cognitive deficits observed in TBI animals at days 2-6 post-injury. Our findings demonstrate a significant improvement in cognitive performance in the G-CSF treated TBI animals within a week of injury, compared to untreated TBI, indicative of immediate and beneficial effect of G-CSF on cognitive performance post CHI. Our model suggests that early G-CSF exposure may be a promising therapeutic approach in recovery of cognitive deficits due to TBI.

Multi-modal approach for investigating brain and behavior changes in an animal model of traumatic brain injury

Use of novel approaches in imaging modalities is needed for enhancing diagnostic and therapeutic outcomes of persons with a traumatic brain injury (TBI). This study explored the feasibility of using functional magnetic resonance imaging (fMRI) in conjunction with behavioral measures to target dynamic changes in specific neural circuitries in an animal model of TBI. Wistar rats were randomly assigned to one of two groups (traumatic brain injury/sham operation). TBI rats were subjected to the closed head injury (CHI) model. Any observable motor deficits and cognitive deficits associated with the injury were measured using beam walk and Morris water maze tests, respectively. fMRI was performed to assess the underlying post-traumatic cerebral anatomy and function in acute (24 hours after the injury) and chronic (7 and 21 days after the injury) phases. Beam walk test results detected no significant differences in motor deficits between groups. The Morris water maze test indicated that cognitive deficits persisted for the first week after injury and, to a large extent, resolved thereafter. Resting state functional connectivity (rsFC) analysis detected initially diminished connectivity between cortical areas involved in cognition for the TBI group; however, the connectivity patterns normalized at 1 week and remained so at the 3 weeks post-injury time point. Taken together, we have demonstrated an objective in vivo marker for mapping functional brain changes correlated with injury-associated cognitive behavior deficits and offer an animal model for testing potential therapeutic interventions options.

EEG patterns from acute to chronic stroke phases in focal cerebral ischemic rats: correlations with functional recovery

Monitoring the neural activities from the ischemic penumbra provides critical information on neurological recovery after stroke. The purpose of this study is to evaluate the temporal alterations of neural activities using electroencephalography (EEG) from the acute phase to the chronic phase, and to compare EEG with the degree of post-stroke motor function recovery in a rat model of focal ischemic stroke. Male Sprague-Dawley rats were subjected to 90 min transient middle cerebral artery occlusion surgery followed by reperfusion for seven days (n = 58). The EEG signals were recorded at the pre-stroke phase (0 h), acute phase (3, 6 h), subacute phase (12, 24, 48, 72 h) and chronic phase (96, 120, 144, 168 h) (n = 8). This study analyzed post-stroke seizures and polymorphic delta activities (PDAs) and calculated quantitative EEG parameters such as the alpha-to-delta ratio (ADR). The ADR represented the ratio between alpha power and delta power, which indicated how fast the EEG activities were. Forelimb and hindlimb motor functions were measured by De Ryck's test and the beam walking test, respectively. In the acute phase, delta power increased fourfold with the occurrence of PDAs, and the histological staining showed that the infarct was limited to the striatum and secondary sensory cortex. In the subacute phase, the alpha power reduced to 50% of the baseline, and the infarct progressed to the forelimb cortical region. ADRs reduced from 0.23 ± 0.09 to 0.04 ± 0.01 at 3 h in the acute phase and gradually recovered to 0.22 ± 0.08 at 168 h in the chronic phase. In the comparison of correlations between the EEG parameters and the limb motor function from the acute phase to the chronic phase, ADRs were found to have the highest correlation coefficients with the beam walking test (r = 0.9524, p < 0.05) and De Ryck's test (r = 0.8077, p < 0.05). This study measured EEG activities after focal cerebral ischemia and showed that functional recovery was closely correlated with the neural activities in the penumbra. Longitudinal EEG monitoring at different phases after a stroke can provide information on the neural activities, which are well correlated with the motor function recovery.

Proteomic analysis of rat plasma following transient focal cerebral ischemia

AIM

This study aimed to identify plasma protein changes in a rat model of ischemic stroke using a proteomic approach.

MATERIALS & METHODS

Four male Sprague-Dawley rats (3-6 months old) were subjected to 90 min of left middle cerebral artery occlusion under anesthesia with 1.5% isoflurane in O(2)/air followed by 24-h reperfusion. Blood samples (~100 µl) were collected at baseline, at the end of 90-min middle cerebral artery occlusion and at 24-h postreperfusion. Brain injuries were assessed by MRI at 24-h postreperfusion. Quantitative comparison of global plasma protein expression was performed using 2D differential in-gel electrophoresis. Differentially expressed protein spots were identified using peptide sequencing tandem mass spectrometry.

RESULTS

These rats had clear brain infarction in the left hemisphere detected by MRI. Thirty-three protein spots of plasma samples were differentially expressed following focal cerebral ischemia/reperfusion. These protein spots belonged to eight proteins. Six of them (α2-macroglobulin, complement C3, inter-α- trypsin inhibitor heavy chain H3, serum albumin, haptoglobin and transthyretin), which are a class of acute-phase proteins, changed significantly.

CONCLUSION

This study describes the responses of young rats to focal cerebral ischemia and suggests that future studies should use aged animals to better mimic the clinical ischemic stroke setting.

Visualizing cell death in experimental focal cerebral ischemia: promises, problems, and perspectives

One of the hallmarks of stroke pathophysiology is the widespread death of many different types of brain cells. As our understanding of the complex disease that is stroke has grown, it is now generally accepted that various different mechanisms can result in cell damage and eventual death. A plethora of techniques is available to identify various pathological features of cell death in stroke; each has its own drawbacks and pitfalls, and most are unable to distinguish between different types of cell death, which partially explains the widespread misuse of many terms. The purpose of this review is to summarize the standard histopathological and immunohistochemical techniques used to identify various pathological features of stroke. We then discuss how these methods should be properly interpreted on the basis of what they are showing, as well as advantages and disadvantages that require consideration. As there is much interest in the visualization of stroke using noninvasive imaging strategies, we also specifically discuss how these techniques can be interpreted within the context of cell death.

On the importance of long-term functional assessment after stroke to improve translation from bench to bedside

Despite extensive research efforts in the field of cerebral ischemia, numerous disappointments came from the translational step. Even if experimental studies showed a large number of promising drugs, most of them failed to be efficient in clinical trials. Based on these reports, factors that play a significant role in causing outcome differences between animal experiments and clinical trials have been identified; and latest works in the field have tried to discard them in order to improve the scope of the results. Nevertheless, efforts must be maintained, especially for long-term functional evaluations. As observed in clinical practice, animals display a large degree of spontaneous recovery after stroke. The neurological impairment, assessed by basic items, typically disappears during the firsts week following stroke in rodents. On the contrary, more demanding sensorimotor and cognitive tasks underline other deficits, which are usually long-lasting. Unfortunately, studies addressing such behavioral impairments are less abundant. Because the characterization of long-term functional recovery is critical for evaluating the efficacy of potential therapeutic agents in experimental strokes, behavioral tests that proved sensitive enough to detect long-term deficits are reported here. And since the ultimate goal of any stroke therapy is the restoration of normal function, an objective appraisal of the behavioral deficits should be done.

Menstrual blood cells display stem cell-like phenotypic markers and exert neuroprotection following transplantation in experimental stroke

Cell therapy remains an experimental treatment for neurological disorders. A major obstacle in pursuing the clinical application of this therapy is finding the optimal cell type that will allow benefit to a large patient population with minimal complications. A cell type that is a complete match of the transplant recipient appears as an optimal scenario. Here, we report that menstrual blood may be an important source of autologous stem cells. Immunocytochemical assays of cultured menstrual blood reveal that they express embryonic-like stem cell phenotypic markers (Oct4, SSEA, Nanog), and when grown in appropriate conditioned media, express neuronal phenotypic markers (Nestin, MAP2). In order to test the therapeutic potential of these cells, we used the in vitro stroke model of oxygen glucose deprivation (OGD) and found that OGD-exposed primary rat neurons that were co-cultured with menstrual blood-derived stem cells or exposed to the media collected from cultured menstrual blood exhibited significantly reduced cell death. Trophic factors, such as VEGF, BDNF, and NT-3, were up-regulated in the media of OGD-exposed cultured menstrual blood-derived stem cells. Transplantation of menstrual blood-derived stem cells, either intracerebrally or intravenously and without immunosuppression, after experimentally induced ischemic stroke in adult rats also significantly reduced behavioral and histological impairments compared to vehicle-infused rats. Menstrual blood-derived cells exemplify a source of "individually tailored" donor cells that completely match the transplant recipient, at least in women. The present neurostructural and behavioral benefits afforded by transplanted menstrual blood-derived cells support their use as a stem cell source for cell therapy in stroke.

Long-term survival and serial assessment of stroke damage and recovery - practical and methodological considerations

Impairments caused by stroke remain the main cause for adult disability. Despite a vigorous research effort, only 1 thrombolytic treatment has been approved in acute stroke (<3h). The limitations of preclinical studies and how these can be overcome have been the subject of various guidelines. However, often these guidelines focus on the acute stroke setting and omit long-term outcome measures, such as behaviour and neuroimaging. The considerations and practicalities of including the serial assessment of these approaches and their significance to establish therapeutic efficacy are discussed here.

Longitudinal in vivo MRI of alterations in perilesional tissue after transient ischemic stroke in rats

Spontaneous restoration of function after stroke is associated with remodelling of functional neuronal networks in and around the ischemic lesion. However, the spatiotemporal profile of structural alterations in (peri)lesional tissue in relation to post-stroke recovery of neuronal function remains largely to be elucidated. We performed neurological testing in combination with in vivo serial T(2)-weighted magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) to assess functional recovery in relation to longitudinal changes in tissue integrity from 3 h up to 9 weeks after experimental unilateral stroke in rats (n=7). Subsequently, to evaluate perilesional neuronal connectivity, we conducted manganese-enhanced MRI after MnCl(2) injection in cortical tissue at the boundary of the lesion at 10 weeks post-stroke (n=5). All animals showed significant improvement of neurological function over time. Normalization of tissue T(2) and fractional diffusion anisotropy (FA) after significant subacute change was observed in cortical and subcortical lesion borderzones between 3 and 9 weeks post-stroke. Progressive FA increase above baseline levels was detected in perilesional white matter areas (n=4). In these animals particularly, significant manganese enhancement appeared within the neuronal network around the chronic lesion, including areas that were part of the lesion at day 3 post-stroke. This longitudinal multi-parametric MRI study suggests that resolution of early ischemic damage and reorganization of white matter in perilesional tissue is chronically accompanied by preservation or restoration of neuronal connectivity, which may significantly contribute to post-stroke functional recovery.

Differential recovery of behavioral status and brain function assessed with functional magnetic resonance imaging after mild traumatic brain injury in the rat

OBJECTIVE

The relationship between cerebral integrity, recovery of brain function, and neurologic status after mild traumatic brain injury is incompletely characterized.

DESIGN

Prospective and randomized study in rodents.

SETTING

University laboratory.

SUBJECTS

Male Wistar rats (290-310 g).

INTERVENTIONS

In rats, quantitative diffusion weighted imaging (DWI), perfusion weighted imaging (PWI), T2-weighted imaging (T2WI), and functional magnetic resonance imaging (fMRI) were performed up to 21 days after weight-induced, closed-head, mild traumatic brain injury (MTBI, n = 6) or sham operation (n = 6). Pixel-by-pixel analysis and region of interest analysis were used to evaluate structural (apparent diffusion coefficient [ADC] and basal cerebral blood flow [bCBF]) and functional magnetic resonance signal changes within the brain, respectively. Quantitative fMRI signal changes were correlated with behavioral measures.

MEASUREMENTS AND MAIN RESULTS

Despite normal appearing DWI and T2WI findings following MTBI, persistent hypoperfusion developed that was not associated with cytotoxic edema. In contrast, the ADC was significantly increased by approximately 5% at 1 and 7 days post-MTBI. Post-MTBI fMRI responses to hypercapnia and forepaw stimulation were significantly impaired and showed a differential recovery rate between and within investigated region of interests. Significant dysfunction in forepaw placement test persisted up to day 1 and correlated significantly with fMRI signal changes in the primary somatosensory and motor cortices.

CONCLUSIONS

MTBI produced distinct changes on multimodal MRI and behavioral variables acutely and chronically. Following MTBI, fMRI and ADC-bCBF pixel-by-pixel analysis identified subtle structural and functional alterations in the brain that appeared completely normal on conventional DWI and T2WI after concussion injury. The former techniques may therefore provide great potential for understanding mild traumatic brain injury, identifying mechanisms underlying recovery, and investigating specific interventions to enhance functional outcome.

Therapeutic efficacy of basic fibroblast growth factor on experimental focal ischemia studied by magnetic resonance imaging

The purpose of this study was to evaluate the effect of intravenous infusion of basic fibroblast growth factor (bFGF) in a permanent ischemia model at the subacute phase (2 weeks) as well as at 24 hours and 1 week using T2-weighted magnetic resonance imaging (MRI). The middle cerebral artery (MCA) in Sprague-Dawley rats was occluded using an intraluminal suture method. The rats were randomly divided into 2 groups to receive either bFGF (45 mircrog/kg/hr) or saline solution. The infusion was started 30 minutes after MCA occlusion (MCAO) and continued for 3 hours. Regional cerebral blood flow (rCBF) was measured using laser Doppler flowmetry throughout the infusion. T2-weighted MRI was carried out before MCAO, 24 hours after MCAO, and days 7 and 14 after MCAO. Although an elevation in rCBF was seen after the infusion, no significant change between the groups was observed. A significant difference between the bFGF and saline groups in T2-derived lesion volume was observed at 24 hours (P < .05), on day 7 (P < .05), and on day 14 (P < .01). The percentage of lesion area calculated from the ipsilateral hemisphere using hematoxylin and eosin staining on day 14 showed a significant difference between the bFGF and saline groups (P < .05). No significant change in the number of bromodeoxyuridine (BrdU)-labeled cells between the groups was observed. This study demonstrates that bFGF, infused intravenously starting 30 minutes after the induction of permanent MCAO, significantly reduces region volume even at day 14, as well as at days 1 and 7, compared with the corresponding saline group.

Brain MRI and neurological deficit measurements in focal stroke: rapid throughput validated with isradipine

BACKGROUND/AIMS

Isradipine, a calcium channel blocker, provides consistent protection of the brain from injury and reduces neurological deficits produced by ischemic stroke in hypertensive rats. In these experiments, isradipine was utilized to cross-validate both the serial MRI measurement of brain infarctions with histology measurements and to validate a series of simple neurological deficit tests in order to establish a more rapid, higher throughput approach to screening compounds for utility in stroke.

METHODS

Spontaneously hypertensive rats were treated with vehicle, or 2.5 or 5.0 mg/kg isradipine and middle cerebral artery occlusion. T(2)-weighted MRI image analysis was compared to standard triphenyltetrazolium chloride-stained histological image analysis of brain sections to quantify isradipine neuroprotection 1, 3, and 30 days after middle cerebral artery occlusion (MCAO; stroke). In addition, serial evaluation (i.e. 1, 2, 5, 12, 20 and 30 days after MCAO) of four simple neurobehavioral tests were completed for each animal. Tests included assessment of hindlimb and forelimb function, and balance beam and proprioception performance.

RESULTS

At 1, 3 and 30 days there was a significant positive correlation of the percent hemispheric infarct for T(2)-weighted MRI and histology (p < 0.05). Practically identical isradipine dose-response neuroprotection curves were observed for both measurement procedures. Isradipine produced a dose-related reduction in all neurological deficits scored by the four neurological deficit tests (p < 0.05). In addition, a significant time-related recovery from neurological deficits in vehicle-treated rats was observed (p < 0.05). The four different neurological deficit tests did provide unique time-related profiles of neurological recovery.

CONCLUSIONS

The present study validates the use of serial MRI in experimental stroke and establishes several simple neurological tests that can be used to measure neurological/behavioral deficits associated with brain injury and brain recovery of function over time. Under these conditions, T(2)-weighted MRI and neurological testing required only about 10 min each per animal, thus providing rapid data collection and analysis and requiring reduced scientific personnel.

A beam-walking apparatus to assess behavioural impairments in MPTP-treated mice: pharmacological validation with R-(-)-deprenyl

A beam-walking apparatus has been evaluated for its ability to detect motor impairments in mice acutely treated with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg, s.c., single or double administration). Mice subjected to MPTP lesioning showed deficits in motor performance on the beam-walking task, for up to 6 days post-MPTP administration, as compared to saline-treated controls. In addition, MPTP-treated mice were detected to have a marked depletion in striatal dopamine levels and a concomitant reduction in substantia nigra (SN) tyrosine hydroxylase (TH) immunoreactivity, at 7 days post-MPTP administration, indicative of dopaminergic neuronal loss. Pre-administration of the potent MAO-B inhibitor R-(-)-deprenyl at 3 or 10 mg/kg, 30 min, s.c, significantly inhibited the MPTP-induced reduction in SN TH-immunoreactivity, striatal dopamine depletions and impairments in mouse motor function. The data described in the present study provides further evidence that functional deficits following an acute MPTP dosing schedule in mice can be quantified and are related to nigro-striatal dopamine function.

Photochemically induced cerebral ischemia in a mouse model

BACKGROUND

MCAO has been widely used to produce ischemic brain lesions. The lesions induced by MCAO tend to be variable in size because of the variance in the collateral blood supply found in the mouse brain.

METHODS

We modified the rat photothrombosis model for use in mice. Male C57BL/6 mice were subjected to focal cerebral ischemia by photothrombosis of cortical microvessels. Cerebral infarction was produced by intraperitoneal injection of rose bengal, a photosensitive dye, and by focal illumination through the skull. Motor impairment was assessed by the accelerating rotarod and staircase tests. The brain was perfusion fixed for histologic determination of infarct volume 4 weeks after stroke.

RESULTS

The lesion was located in the frontal and parietal cortex and the underlying white matter was partly affected. A relatively constant infarct volume was achieved 1 month after photothrombosis. The presence of the photothrombotic lesion significantly impaired the motor performance as measured by the rotarod and staircase tests. Our findings show that photothrombotic infarction in mice is highly reproducible in size and location.

CONCLUSION

This procedure can provide a simple model of cerebral infarction for a unilateral motor cortex lesion. In addition, it can provide a suitable model for the study of potential neuroprotective and therapeutic agents in human stroke.

Multi-modal characterisation of the neocortical clip model of focal cerebral ischaemia by MRI, behaviour and immunohistochemistry

The neocortical clip model of focal cerebral ischaemia has previously been used with success in neuroprotection studies. To further improve its translational qualities, we have characterised this model using a combination of serial Magnetic Resonance Imaging (MRI), neurological assessment, the bilateral asymmetry test (BAT) and immunohistochemistry. The right MCA was occluded in spontaneously hypertensive rats for 0, 60 and 120 min. MRI was performed pre-surgery, 1, 3 and 7 days post-surgery. Behavioural assessment was performed 2 days before and 3 and 7 days post-surgery whilst neurological deficits were monitored daily. Neuroimaging results showed that 0 min of MCA occlusion did not produce a lesion, whereas occlusion for 60 min produced a lesion that remained stable over time. Occlusion for 120 min caused a more severe lesion 1 day post-surgery, but decreased by 7 days. Behaviour, neurological scores and histological lesion volumes correlated strongly with MRI lesion volume. Immunohistochemistry revealed neuronal loss, astrogliosis and macrophage infiltration in lesioned cortices. The neocortical clip model produced ischaemic lesions that are restricted to cortical territories of the MCA. The duration of occlusion dictates lesion severity which may prove useful for probing therapeutic interventions at different stages of stroke progression. The correlation of MRI with two different behavioural measures and post-mortem histology strengthens the basis for MRI providing an in vivo surrogate marker for structural and behavioural deficits caused by a cortical stroke.

Quantitative measurement of neurological deficit after mild (30 min) transient middle cerebral artery occlusion in rats

Although 30-min transient middle cerebral artery occlusion (30-min tMCAo) causes reproducible subcortical infarction in rats, it is difficult to evaluate the resulting neurological deficit using common behavioral tests such as the rota-rod test, adhesive-removal test, or narrow beam test. Establishment of a method of quantitative evaluation would help to develop a novel therapeutic approach to treat cerebral infarction. To solve this problem, we examined whether the neurological deficit could be detected by the Montoya staircase test or methamphetamine-induced rotation, which are commonly used in a Parkinson disease model induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA). From 10 to 14 days after tMCAo, the Montoya staircase test showed significant clumsiness in forelimb tasks contralateral to the lesion side, whereas sham-operated rats showed no significant clumsiness in both forelimbs. The number of ipsilateral rotations induced by methamphetamine was also increased in tMCAo-rats at 21 days after tMCAo. Although Pearson's correlations coefficient showed that the results of these tests were correlated with the infarction volume, there was no significant correlation between the results of these two tests. These findings imply that the neurological deficit detected by both tests might reflect the severity of ischemic injury, but each test might evaluate different aspects of neurological deficit. Thus, the Montoya staircase test and methamphetamine-induced rotation are useful to evaluate neurological deficit in the chronic stage of subcortical infarction induced by 30-min tMCAo.

Differential recovery of multimodal MRI and behavior after transient focal cerebral ischemia in rats

The association between recovery of brain function and behavior after transient cerebral ischemia in animals and humans is incompletely characterized. Quantitative diffusion- (DWI), perfusion- (PWI), T(2)-weighted (T(2)WI), and functional magnetic resonance imaging (fMRI) were performed before, during, and up to 1 day after 20-mins transient middle cerebral artery occlusion (tMCAO; n=6) or sham operation (n=6) in male Sprague-Dawley rats. Viability thresholds were employed to calculate diffusion, perfusion, and T(2) lesion volumes. Region of interest analysis was used to evaluate structural and functional MR signal changes within the sensorimotor network, which were then related to corresponding behavioral measures. Post-mortem 2,3,5-triphenyltetrazolium chloride (TTC) staining was performed 24 h after ischemia. Transient middle cerebral artery occlusion produced lesions on DWI and PWI, which fully recovered by 30 mins after reperfusion. Ipsilesional fMRI responses to hypercapnia and forepaw stimulation were significantly impaired after ischemia and did not fully normalize until 3 and 24 h after tMCAO, respectively. No abnormalities were observed on imaging or TTC at 24 h despite significant behavioral dysfunctions including contralesional forelimb impairment and ipsilesional neglect. No MRI, behavioral, or TTC anomalies were observed in sham-operated rats. There were no significant correlations between MRI parameters, behavior, and TTC in either group. Together, these results suggest that normal findings on diffusion, perfusion, and T(2) imaging shortly after transient ischemia may not indicate normal tissue status as indicated by fMRI and behavior, which may help explain the persistence of neurologic deficits in patients with normal conventional MRI after cerebral ischemia.

Sensorimotor and cognitive deficits after transient middle cerebral artery occlusion in the mouse

Whereas behavioral impairments after stroke are increasingly studied in the rat, little is known about the long-term functional consequences of focal ischemia in the mouse. To address this issue, Swiss mice underwent transient (60 min) intraluminal occlusion of the middle cerebral artery (MCAo) or sham surgery. Sensorimotor (chimney, accelerating rotarod, pole, corner, adhesive removal and staircase tests) and cognitive (passive avoidance and Morris water maze) performances were regularly assessed during 1 month, after which the final histological lesion was measured. Motor coordination and balance, assessed by the chimney and rotarod tests, were transiently altered by MCAo. Moreover, bradykinesia was evidenced by the pole test. The most striking and long-lasting (1 month) sensorimotor deficits were postural asymmetries on the corner test, bilateral skilled forepaw reaching deficits on the staircase test and a contralateral sensorimotor impairment on the adhesive removal test. MCAo animals showed normal spatial learning abilities on the Morris water maze test, but they displayed learning deficits measured by the passive avoidance test. This latter deficit was significantly correlated with both cortical and striatal damage. Our findings demonstrate the usefulness of three tests that had never been reported in the mouse after ischemia: the adhesive removal, staircase and pole tests, which showed deficits 1 month after ischemia and should therefore constitute meaningful tools in mice for assessing both neuroprotective and regenerative therapies in stroke preclinical studies.

AM-36 modulates the neutrophil inflammatory response and reduces breakdown of the blood brain barrier after endothelin-1 induced focal brain ischaemia

BACKGROUND AND PURPOSE

Following transient focal stroke, rapid accumulation and activation of neutrophils in the ischaemic region is deleterious due to release of reactive oxygen species and myeloperoxidase (MPO). The purpose of this study was to examine whether AM-36, both a Na+ channel blocker and an antioxidant, afforded neuroprotection by modulating neutrophil accumulation into brain, following endothelin-1 (ET-1) induced middle cerebral artery occlusion (MCAo) in conscious rats.

EXPERIMENTAL APPROACH

AM-36 was administered at 3 and 24 h after ET-1-induced MCAo. Functional recovery was determined using grid-walking and cylinder tests. Image analysis of brain sections was used to determine infarct volume. The effect of AM-36 on neutrophil infiltration and their interaction with macrophages was examined in rats at 48 h following MCAo by both an MPO assay and double-label immunofluorescence. Blood brain barrier (BBB) breakdown was measured by the area stained by intravenous Evans Blue.

KEY RESULTS

AM-36 reduced functional deficits in both tests such that no difference existed from pre-ischaemic values at 48 h. Neutrophil infiltration, assessed by MPO activity, and infarct volume were significantly reduced following AM-36 administration by 54 and 60% respectively. Similarly, immunofluorescence revealed that AM-36 reduced neutrophil infiltration by approximately 50% in selected brain regions, when compared to controls, and also modulated macrophage phagocytosis of neutrophils. Breakdown of the BBB was significantly reduced by 60% following AM-36 treatment.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that AM-36 can directly modulate the neutrophil inflammatory response and reduce BBB breakdown following MCAo.

Long-term changes of functional MRI-based brain function, behavioral status, and histopathology after transient focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

The relation between recovery of brain function and neurological status after clinical and experimental cerebral ischemia is incompletely characterized. We assessed the evolution of ischemic injury, behavioral status, and brain activity at acute to chronic periods after transient middle cerebral artery occlusion (tMCAO) in rats.

METHODS

Male Sprague-Dawley rats were subjected to 20-minute tMCAO (n=10) or sham operation (n=10). Sensorimotor behavioral testing and multimodal (diffusion, perfusion, T2, and functional) MRI, as well as postmortem hematoxylin-eosin staining, were performed before and up to 21 days after tMCAO. MRI and histological parameters were evaluated in 5 regions of interest within the sensorimotor network. Diffusion, perfusion, and T2 lesion volumes were calculated according to previously established viability thresholds.

RESULTS

Diffusion and perfusion lesions were present during occlusion but disappeared completely and permanently within 30 minutes after reperfusion, with no T2 lesions seen. Functional MRI and behavioral deficits did not normalize until 1 and 21 days after tMCAO, respectively. Histology demonstrated selective neuronal cell death at 7 and 21 days after reperfusion.

CONCLUSIONS

Twenty-minute tMCAO produced distinct changes on multimodal MRI, histology, and behavioral parameters acutely and chronically. Normal findings on MRI after transient ischemia may not indicate normal tissue status, as behavioral and histological anomalies remain. Behavioral dysfunction persisting long after the recovery of MRI parameters may relate to the subtle neuronal damage seen on histology. Together, these results may help explain unremitting neurological deficits in stroke or transient ischemic attack patients with normal MRI findings.

Rodent models of focal stroke: size, mechanism, and purpose

Rodent stroke models provide the experimental backbone for the in vivo determination of the mechanisms of cell death and neural repair, and for the initial testing of neuroprotective compounds. Less than 10 rodent models of focal stroke are routinely used in experimental study. These vary widely in their ability to model the human disease, and in their application to the study of cell death or neural repair. Many rodent focal stroke models produce large infarcts that more closely resemble malignant and fatal human infarction than the average sized human stroke. This review focuses on the mechanisms of ischemic damage in rat and mouse stroke models, the relative size of stroke generated in each model, and the purpose with which focal stroke models are applied to the study of ischemic cell death and to neural repair after stroke.

Temporal profile of T2-weighted MRI distinguishes between pannecrosis and selective neuronal death after transient focal cerebral ischemia in the rat

Transient middle cerebral artery occlusion (MCAO) by an intraluminal thread leads to primarily subcortical infarctions with little sensorimotor impairment in the Wistar rat strain. We investigated the course of infarct development in this lesion type for 10 weeks using magnetic resonance imaging (MRI) along with histological characterization. MCAO was induced in male Wistar rats (260 to 300 g) for 60 mins. Animals received follow-up T1- and T2-weighted MRI from day 1 until week 10. Separate groups of animals were analyzed histologically after 2, 6, and 10 weeks. Histology included immunohistochemistry for neuronal and astrocytic markers as well as hematoxylin eosin and luxol fast blue-cresyl violet staining. In contrast to lesions involving the cortex, exclusively subcortical infarctions were characterized by a complete resolution of initially increased T1 and T2 relaxation times by 10 weeks. Between 2 and 10 weeks, neuronal death and gliosis as well as a dense inflammatory infiltrate were evident in these lesions, without damage to fiber tracts or development of cystic cavities. Exclusively subcortical lesions in Wistar rats are characterized by normalization of T1 and T2 relaxation times, which might, however, not be mistaken for tissue recovery. Despite this MRI normalization, selective neuronal death and gliosis develop. Although MRI at individual time points might therefore be ambiguous, the temporal profile of relaxation time changes over the chronic time period allows discrimination of the lesion development into selective neuronal death or pannecrosis.

Talampanel improves the functional deficit after transient focal cerebral ischemia in rats. A 30-day follow up study

The neuroprotective effect of talampanel, a negative allosteric modulator of alpha-amino-3-hydroxy-methyl-4-isoxazolyl-propionic acid (AMPA) receptors has been described previously. However, in these studies the histological changes and not the functional consequences of the brain damage were evaluated. The aim of present investigation was to analyze the sensorimotor function after stroke and to test the influence of talampanel (GYKI-53773, LY-300164) by 30-day monitoring in rats. After 1h middle cerebral artery occlusion (MCAO) general 'well-being', neurological status, spontaneous motor activity, rotation, motor coordination, balancing, muscle strength and reaction time were followed for 1 month. Talampanel (6 x 10 mg/kg i.p. given on the day of stroke) improved the motor coordination in rotarod (p < 0.01) and beam walking (p < 0.01) tests, reduced the number of stroke-induced rotations (p < 0.05), shortened the reflex time on the forelimb contralateral to brain ischemia and improved the survival rate comparing with vehicle treated control. After stroke, serious sensorimotor deficits appeared in rats but they showed partial spontaneous recovery after 30 days. Talampanel treatment enhanced the rate of functional improvement without changing the morphology at the end of the experiment. Our results indicate that modulation of AMPA receptors by talampanel can be a promising therapeutic approach to the treatment of stroke.

New Goals in Ischemic Stroke Therapy: The Experimental Approach – Harmonizing Science with Practice

Undeniable advances have been made in clinical and experimental investigation into the pathophysiology, diagnosis, and treatment of cerebral ischemia. However, with the exception of intravenous thrombolysis and some neuroprotectors, such as citicoline, the majority of the drugs successfully tested in experimental studies have failed in clinical trials. Valuable lessons for the improvement of research methodology and appropriate coordination of experimental and clinical research can be learnt from the analysis of discrepancies between the laboratory and clinic, which will allow us to increase the power and cost-effectiveness of the studies. In addition, this progress has opened the way for the investigation of very promising new therapeutic strategies, such as combined pharmacological and mechanical thrombolysis, thrombolysis and neuroprotection, or the combination of various neuroprotectors, antiapoptotic therapies, and neurorestoration therapies, such as stem cell transplants.

Nogo receptor antagonism promotes stroke recovery by enhancing axonal plasticity

After ischemic stroke, partial recovery of function frequently occurs and may depend on the plasticity of axonal connections. Here, we examine whether blockade of the Nogo-NogoReceptor (NgR) pathway might enhance axonal sprouting and thereby recovery after focal brain infarction. Mutant mice lacking NgR or Nogo-AB recover complex motor function after stroke more completely than do control animals. After a stroke, greater numbers of axons emanating from the undamaged cortex cross the midline to innervate the contralateral red nucleus and the ipsilateral cervical spinal cord; this axonal plasticity is enhanced in ngr -/- or nogo-ab -/- mice. In rats with middle cerebral artery occlusion, both the recovery of motor skills and corticofugal axonal plasticity are promoted by intracerebroventricular administration of a function-blocking NgR fragment. Behavioral improvement occurs when therapy is initiated 1 week after arterial occlusion. Thus, delayed pharmacological blockade of the NgR promotes subacute stroke recovery by facilitating axonal plasticity.

Subcortical lesions after transient thread occlusion in the rat: T2-weighted magnetic resonance imaging findings without corresponding sensorimotor deficits

PURPOSE

To investigate infarct evolution and functional consequences of exclusive subcortical or cortico-subcortical strokes, transient middle cerebral artery occlusion (MCAO) was conducted in Wistar rats.

MATERIALS AND METHODS

MCAO was induced in male Wistar rats (260-300 g) for 60 minutes. Lesion volumes and absolute T2 times on magnetic resonance imaging (MRI) were assessed 1 and 14 days after MCAO using a 4.7-T MRI animal scanner in conjunction with functional testing (adhesive tape removal, cylinder test, and ledged beam walking).

RESULTS

Functional test scores were not distinguishable between sham-operated animals (N = 5) and those with exclusive caudoputaminal infarct (N = 8; group cp), but showed significant deficits in animals with cortico-subcortical infarction (N = 10; group cp+). The cp group had lower absolute T2 times and a more pronounced reduction in T2 lesion volume over time than the subcortical component in the cp+ group. There was no correlation of T2 lesion size or absolute T2 times and functional impairment in either group.

CONCLUSION

When judged from functional tests alone, subcortical ischemic lesions may not be diagnosed reliably. Furthermore, T2-weighted (T2-w) MRI does not well anticipate functional deficits in primarily striatal lesions.

Identification of neuroprotective properties of anti-MAG antibody: a novel approach for the treatment of stroke?

The inhibitory activity of myelin-associated glycoprotein (MAG) on neurons is thought to contribute to the lack of regenerative capacity of the CNS after injury. The interaction of MAG and its neuronal receptors mediates bidirectional signaling between neurons and oligodendrocytes. The novel finding that an anti-MAG monoclonal antibody not only possesses the ability to neutralise the inhibitory effect of MAG on neurons but also directly protects oligodendrocytes from glutamate-mediated oxidative stress-induced cell death is reported here. Furthermore, administration of anti-MAG antibody (centrally and systemically) starting 1 hour after middle cerebral artery occlusion in the rat significantly reduced lesion volume at 7 days. This neuroprotection was associated with a robust improvement in motor function compared with animals receiving control IgG1. Together, these data highlight the potential for the use of anti-MAG antibodies as therapeutic agents for the treatment of stroke.

Evidence for bilateral control of skilled movements: ipsilateral skilled forelimb reaching deficits and functional recovery in rats follow motor cortex and lateral frontal cortex lesions

Unilateral damage to cortical areas in the frontal cortex produces sensorimotor deficits on the side contralateral to the lesion. Although there are anecdotal reports of bilateral deficits after stroke in humans and in experimental animals, little is known of the effects of unilateral lesions on the same side of the body. The objective of the present study was to make a systematic examination of the motor skills of the ipsilateral forelimb after frontal cortex lesions to either the motor cortex by devascularization of the surface blood vessels (pial stroke), or to the lateral cortex by electrocoagulation of the distal branches of the middle cerebral artery (MCA stroke). Plastic processes in the intact hemisphere were documented using Golgi-Cox dendritic analysis and by intracortical microstimulation analysis. Although tests of reflexive responses in forelimb placing identified a contralateral motor impairment following both cortical lesions, quantitative and qualitative measures of skilled reaching identified a severe ipsilateral impairment from which recovery was substantial but incomplete. Golgi-impregnated pyramidal cells in the forelimb area showed an increase in dendritic length and branching. Electrophysiological mapping showed normal size forelimb representations in the lesioned rats relative to control animals. The finding of an enduring ipsilateral impairment in skilled movement is consistent with a large but more anecdotal literature in rats, nonhuman primates and humans, and suggests that plastic changes in the intact hemisphere are related to that hemisphere's contribution to skilled movement.

In vivo monitoring of cellular transplants by magnetic resonance imaging and positron emission tomography

Cellular loss is a common pathological observation in many disease conditions. Recent evidence that these cells can be replaced has generated huge excitement over possible clinical applications. The use of stem or progenitor cells, which can differentiate into site-appropriate phenotypes required to "repair" the damaged tissue, has already demonstrated potential in animal models, but many aspects of this novel treatment strategy require further elucidation. Most importantly, the monitoring of the safety of cellular transplants in patients remains a challenge. Traditional histological methods do not address the dynamic nature of transplant-induced recovery and highlight the necessity of in vivo imaging to probe the survival, migration and functional consequences of transplanted cells. This paper reviews how non-invasive imaging technology can be used to serially assess intact living organisms in order to visualise and monitor cellular transplants.