A rat model of reproducible cerebral infarction using thrombotic blood clot emboli

Modeling Distal Middle Cerebral Artery Occlusion in Neonatal Rodents with Magnetic Nanoparticles or Magnetized Red Blood Cells

It is challenging to establish animal models to mimic perinatal arterial ischemic stroke. Here, we provided two approaches that precisely occlude rodent pups' distal middle cerebral artery of rodent pups at any postnatal age. One uses magnetic nanoparticles to generate platelet-rich thrombus, and the other utilizes magnetized red blood cells (mRBCs) to generate an erythrocyte-rich embolus. Both approaches result in focal cerebral ischemia followed by controllable reperfusion while requiring no arterial surgery.

Hypoxia modeling techniques: A review

Hypoxia is the main cause and effect of a large number of diseases, including the most recent one facing the world, the coronavirus disease (COVID-19). Hypoxia is divided into short-term, long-term, and periodic, it can be the result of diseases, climate change, or living and traveling in the high mountain regions of the world. Since each type of hypoxia can be a cause and a consequence of various physiological changes, the methods for modeling these hypoxias are also different. There are many techniques for modeling hypoxia under experimental conditions. The most common animal for modeling hypoxia is a rat. Hypoxia models (hypoxia simulations) in rats are a tool to study the effect of various conditions on the oxygen supply of the body. These models can provide a necessary information to understand hypoxia and also provide effective treatment, highlighting the importance of various reactions of the body to hypoxia. The main parameters when choosing a model should be reproducibility and the goal that the scientist wants to achieve. Hypoxia in rats can be reproduced both ways exogenously and endogenously. The reason for writing this review was the aim to systematize the models of rats available in the literature in order to facilitate their selection by scientists. The relative strengths and limitations of each model need to be identified and understood in order to evaluate the information obtained from these models and extrapolate these results to humans to develop the necessary generalizations. Despite these problems, animal models have been and remain vital to understanding the mechanisms involved in the development and progression of hypoxia. The eligibility criteria for the selected studies was a comprehensive review of the methods and results obtained from the studies. This made it possible to make generalizations and give recommendations on the application of these methods. The review will assist scientists in choosing an appropriate hypoxia simulation method, as well as assist in interpreting the results obtained with these methods.

Optimized mouse model of embolic MCAO: From cerebral blood flow to neurological outcomes

The embolic middle cerebral artery occlusion (eMCAO) model mimics ischemic stroke due to large vessel occlusion in humans and is amenable to thrombolytic therapy with rtPA. However, two major obstacles, the difficulty of the eMCAO surgery and unpredictable occurrence of clot autolysis, had impeded its application in mice. In this study, we modified catheters to produce suitable fibrin-rich embolus and optimized the eMCAO model using cerebral blood flow (CBF) monitored by both laser Doppler flowmetry (LDF) and 2D laser speckle contrast imaging (LSCI) to confirm occlusion of MCA. The results showed that longer embolus resulted in higher mortality. There was a compensatory increase in MCA territory perfusion after eMCAO associated with decreased infarct volume; however, this was only partly dependent on recanalization as clot autolysis was only observed in ∼30% of mice. Cortical CBF monitoring with LSCI showed that the size of peri-core area at 3 h displayed the best correlation with infarct volume that is attributed to compensatory collateral blood flow. The peri-core area best predicted functional outcome after eMCAO. In summary, we developed a reliable eMCAO mouse model that better mimics embolic ischemic stroke in humans, which will increase the potential for successful translation of stroke neuroprotective therapies.

Precise control of embolic stroke with magnetized red blood cells in mice

Precise embolism control in immature brains can facilitate mechanistic studies of brain damage and repair after perinatal arterial ischemic stroke (PAIS), but it remains a technical challenge. Microhemorrhagic transformation is observed in one-third of infant patients who have suffered PAIS, but the underlying mechanism remains elusive. Building on an established approach that uses magnetic nanoparticles to induce PAIS, we develop a more advanced approach that utilizes magnetized erythrocytes to precisely manipulate de novo and in situ embolus formation and reperfusion in perinatal rodent brains. This approach grants spatiotemporal control of embolic stroke without any transarterial delivery of pre-formed emboli. Transmission electron microscopy revealed that erythrocytes rather than nanoparticles are the main material obstructing the vessels. Both approaches can induce microbleeds as an age-dependent complication; this complication can be prevented by microglia and macrophage depletion. Thus, this study provides an animal model mimicking perinatal embolic stroke and implies a potential therapeutic strategy for the treatment of perinatal stroke.

Blood-Brain Barrier Transporters: Opportunities for Therapeutic Development in Ischemic Stroke

Globally, stroke is a leading cause of death and long-term disability. Over the past decades, several efforts have attempted to discover new drugs or repurpose existing therapeutics to promote post-stroke neurological recovery. Preclinical stroke studies have reported successes in identifying novel neuroprotective agents; however, none of these compounds have advanced beyond a phase III clinical trial. One reason for these failures is the lack of consideration of blood-brain barrier (BBB) transport mechanisms that can enable these drugs to achieve efficacious concentrations in ischemic brain tissue. Despite the knowledge that drugs with neuroprotective properties (i.e., statins, memantine, metformin) are substrates for endogenous BBB transporters, preclinical stroke research has not extensively studied the role of transporters in central nervous system (CNS) drug delivery. Here, we review current knowledge on specific BBB uptake transporters (i.e., organic anion transporting polypeptides (OATPs in humans; Oatps in rodents); organic cation transporters (OCTs in humans; Octs in rodents) that can be targeted for improved neuroprotective drug delivery. Additionally, we provide state-of-the-art perspectives on how transporter pharmacology can be integrated into preclinical stroke research. Specifically, we discuss the utility of in vivo stroke models to transporter studies and considerations (i.e., species selection, co-morbid conditions) that will optimize the translational success of stroke pharmacotherapeutic experiments.

An In Vivo Mouse Model to Study Blood-Brain Barrier Destabilization in the Chronic Phase of Stroke

Cerebral ischemic injury evokes a complex cascade of pathophysiological events at the blood-vascular-parenchymal interface. These evolve over time and space and result in progressive neurological damage. Emerging evidence suggests that blood-brain barrier (BBB) recovery and reestablishment of BBB impermeability are incomplete and that these could influence stroke injury recovery, increase the risk of new stroke occurrence, and be a solid substrate for developing vascular dementia. Recent work from the author's laboratory has established the existence of incomplete BBB recovery in chronic stroke conditions that was induced by structural alterations to brain endothelial junctional complexes and persistent BBB leakage. The experimental methodology presented here is focused on modelling chronic stroke injury using an in vivo thromboembolic mouse stroke model and how to evaluate the kinetics and magnitude of BBB hyperpermeability in chronic stroke conditions using a combination of magnetic resonance imaging, tracer studies, and immunohistochemistry.

Thrombus Imaging Using 3D Printed Middle Cerebral Artery Model and Preclinical Imaging Techniques: Application to Thrombus Targeting and Thrombolytic Studies

Diseases with the highest burden for society such as stroke, myocardial infarction, pulmonary embolism, and others are due to blood clots. Preclinical and clinical techniques to study blood clots are important tools for translational research of new diagnostic and therapeutic modalities that target blood clots. In this study, we employed a three-dimensional (3D) printed middle cerebral artery model to image clots under flow conditions using preclinical imaging techniques including fluorescent whole-body imaging, magnetic resonance imaging (MRI), and computed X-ray microtomography (microCT). Both liposome-based, fibrin-targeted, and non-targeted contrast agents were proven to provide a sufficient signal for clot imaging within the model under flow conditions. The application of the model for clot targeting studies and thrombolytic studies using preclinical imaging techniques is shown here. For the first time, a novel method of thrombus labeling utilizing barium sulphate (Micropaque^®) is presented here as an example of successfully employed contrast agents for in vitro experiments evaluating the time-course of thrombolysis and thus the efficacy of a thrombolytic drug, recombinant tissue plasminogen activator (rtPA). Finally, the proof-of-concept of in vivo clot imaging in a middle cerebral artery occlusion (MCAO) rat model using barium sulphate-labelled clots is presented, confirming the great potential of such an approach to make experiments comparable between in vitro and in vivo models, finally leading to a reduction in animals needed.

Rodent models for intravascular ischemic cerebral infarction: a review of influencing factors and method optimization

Rodent models for cerebral infarction are useful for studying human focal ischemic cerebral infarction, by simulating etiological and pathophysiological mechanisms. However, differences in the selection of anesthetic drugs, surgical methods and other factors may affect the extent to which preclinical models reflect the human condition. This review summarizes these factors. We searched pertinent literature from the MEDLINE and Web of Science databases, and reviewed differences in rodent strain, anesthesia method, sex, surgical method, timing of surgery, and factors influencing postoperative evaluation. In particular, circadian rhythm was found to have a significant impact on the outcome of cerebral infarction in rodent models. This information will enable researchers to quickly and clearly select appropriate modeling methods, acquire reliable quantitative experimental results, and obtain basic data for fundamental mechanism research.

Pathophysiology and Treatment of Stroke: Present Status and Future Perspectives

Stroke is the second leading cause of death and a major contributor to disability worldwide. The prevalence of stroke is highest in developing countries, with ischemic stroke being the most common type. Considerable progress has been made in our understanding of the pathophysiology of stroke and the underlying mechanisms leading to ischemic insult. Stroke therapy primarily focuses on restoring blood flow to the brain and treating stroke-induced neurological damage. Lack of success in recent clinical trials has led to significant refinement of animal models, focus-driven study design and use of new technologies in stroke research. Simultaneously, despite progress in stroke management, post-stroke care exerts a substantial impact on families, the healthcare system and the economy. Improvements in pre-clinical and clinical care are likely to underpin successful stroke treatment, recovery, rehabilitation and prevention. In this review, we focus on the pathophysiology of stroke, major advances in the identification of therapeutic targets and recent trends in stroke research.

Combined Treatment With 2-(2-Benzofu-Ranyl)-2-Imidazoline and Recombinant Tissue Plasminogen Activator Protects Blood-Brain Barrier Integrity in a Rat Model of Embolic Middle Cerebral Artery Occlusion

Recombinant tissue plasminogen activator (rt-PA) is used to treat acute ischemic stroke but is only effective if administered within 4.5 h after stroke onset. Delayed rt-PA treatment causes blood-brain barrier (BBB) disruption and hemorrhagic transformation. The compound 2-(-2-benzofuranyl)-2-imidazoline (2-BFI), a newly discovered antagonist of high-affinity postsynaptic N-methyl-D-aspartate (NMDA) receptors, has been shown to have neuroprotective effects in ischemia. Here, we investigated whether combining 2-BFI and rt-PA can ameliorate BBB disruption and prolong the therapeutic window in a rat model of embolic middle cerebral artery occlusion (eMCAO). Ischemia was induced in male Sprague Dawley rats by eMCAO, after which they were treated with 2-BFI (3 mg/kg) at 0.5 h in combination with rt-PA (10 mg/kg) at 6 or 8 h. Control rats were treated with saline or 2-BFI or rt-PA. Combined therapy with 2-BFI and rt-PA (6 h) reduced the infarct volume, denatured cell index, BBB permeability, and brain edema. This was associated with increased expression of aquaporin 4 (AQP4) and tight junction proteins (occludin and ZO-1) and downregulation of intercellular adhesion molecule 1 (ICAM-1) and matrix metalloproteinases 2 and 9 (MMP2 and MMP9). We conclude that 2-BFI protects the BBB from damage caused by delayed rt-PA treatment in ischemia. 2-BFI may therefore extend the therapeutic window up to 6 h after stroke onset in rats and may be a promising therapeutic strategy for humans. However, mechanisms to explain the effects oberved in the present study are not yet elucidated.

A novel approach to treatment of thromboembolic stroke in mice: Redirecting neutrophils toward a peripherally implanted CXCL1-soaked sponge

Neutrophils are considered key participants in post-ischemic stroke inflammation. They are the first white blood cells to arrive in ischemic brain and their presence in the brain tissue positively correlates with post-ischemic injury severity. CXCL1 is a neutrophil attractant chemokine and the present study evaluates whether redirecting neutrophil migration using a peripherally implanted CXCL1-soaked sponge can reduce brain inflammation and improve outcomes in a novel mouse model of thromboembolic (TE) stroke. TE stroke was induced by injection of a platelet-rich microemboli suspension into the internal carotid artery of adult C57BL/6 male mice. The model induced neuroinflammation that was associated with increases in multiple brain and serum cytokines/chemokines at the mRNA and protein levels, including very marked increases in CXCL1. In other groups of animals, an absorbable sterile hemostatic sponge, previously immersed in either saline (0.9%NaCl) or CXCL1, was implanted into subcutaneous pockets formed in the inguinal region on the left and right side following stroke surgery. Mice implanted with the sponge soaked with CXCL1 had significantly reduced neuroinflammation and infarct size after TE stroke compared to mice implanted with the sponge soaked with 0.9%NaCl. There was also reduced mortality and improved neurological deficits in the TE stroke + CXCL1 sponge group compared to the TE stroke +0.9%NaCl sponge group. In conclusion: redirecting bloodstream leukocytes toward a peripherally-implanted neutrophil chemokine CXCL1-soaked sponge improves outcomes in a novel mouse model of thromboembolic stroke. The present findings suggest a novel therapeutic strategy for patients with acute stroke.

The combination of Astragalus membranaceus extract and ligustrazine to improve the inflammation in rats with thrombolytic cerebral ischemia

The purpose of the study was to evaluate the effect of Astragalus membranaceus extract and ligustrazine combination on ameliorating inflammation in cerebral ischemic rats that have undergone thrombolysis. Astragalus membranaceus and ligustrazine per se, or a combination of A. membranaceus and ligustrazine was administered by intraperitoneal injection immediately after surgery and sham surgery. After the induction of thrombolysis, the neurological function was measured and cerebral lesion volume was determined. The regulatory T cells in the spleen were measured by flow cytometry. To explore the protective effects of the combination drug on the neurological function and inflammation, the expression of transcription factor Foxp3 and cytokines, including transforming growth factor beta 1, interleukin 10, interleukin 4, interleukin 1 beta, interferon gamma, interleukin 17, in damaged brain was examined using reverse transcription polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay. The cerebral lesion volume was markedly reduced in the combination drug-treated rats compared to the rats treated with either A. membranaceus or ligustrazine alone (P < 0.05). The neurological function, regulatory T cells, transcription factor Foxp3, transforming growth factor beta 1, interleukin 10, and interleukin 4 were markedly elevated in the rats treated with combination drugs (P < 0.05). The expression of interleukin 1 beta, interferon gamma, and interleukin 17 was reduced in the rats treated with combination drug therapy (P < 0.05). Treatment with a combination of A. membranaceus and ligustrazine can ameliorate inflammation after thrombolysis and regulate the related cytokines by elevating the expression of endogenous regulatory T cells.

Expression and regulation of miR-449a and AREG in cerebral ischemic injury

Rodent focal ischemia models are widely used to mimic and examine human strokes. To the best of our knowledge, no investigation has systematically examined the expression changes of microRNA (miR)-449a and Amphiregulin (AREG) as well as their biological relationship during middle cerebral artery occlusion (MCAO) and oxygen and glucose deprivation/reperfusion (OGD/R). The present study examined the histological and behavioral outcomes of MCAO and the function of miR-449a and AREG in cerebral ischemic injury. Rats were subjected to 2 h MCAO, which was followed by reperfusion. miR-449a and AREG were examined in the injury tissues of MCAO rats and the OGD/R cell line by reverse transcription-quantitative polymerase chain reaction. Protein expressions of AREG in the injury tissues of MCAO rats was measured using an immunohistochemistry and the protein expression levels of AREG, epidermal growth factor receptor (EGFR), phosphatidylinositol 3-kinase (PI3K)/ protein kinase B (Akt) and the phosphorylation level of Akt (p-Akt) were analyzed by western blotting. Cell apoptosis was examined following the knock down and subsequent overexpression of AREG in a human OGD/R neuronal cell line by small interfering RNAs (siRNAs) and plasmid transfection. Luciferase reporter assays were used to validate the target of miR-449a. The expression changes and regulatory mechanisms of miR-449a and AREG in an ischemia/reperfusion (I/R) injury model were examined in vivo and in vitro. The neurological deficit score, brain edema volume, cerebral infarct area, and the number of apoptosis cells in ischemic rats were all markedly elevated, than that in the control rats. The expression of miR-449a was decreased and AREG was increased in the MCAO rats and human OGD/R neuronal cell line. miR-449a inhibition or AREG overexpression in OGD/R cells resulted in a significant decrease in apoptotic cells, and AREG was revealed to be one of the direct targets of miR-449a. Molecular recovery was observed following transfection with miR-449a mimics and AREG knockdown in an OGD/R model in vitro. The present study demonstrated that miR-449a was downregulated while AREG was upregulated in cerebral ischemic injury, and the recovery of neurological function can be obtained following the overexpression of miR-449a and the knockdown of AREG in an I/R injury model. miR-449a functions in ischemic stroke via directly targeting AREG. These findings suggest a novel mechanism involving in cerebral I/R injury model and may aid investigators in gaining a deeper understanding of strokes in a clinical setting.

Impact of C57BL/6 substrain on sex-dependent differences in mouse stroke models

We have recently found significant variation in stroke vulnerability among substrains of C57BL/6 mice, observing that commonly used N-lineage substrains exhibit larger infarcts than C57BL/6J and related substrains. Parallel variation was also seen with respect to sex differences in stroke vulnerability, in that C57BL/6 mice of the N-lineage exhibited comparable infarct sizes in males and females, whereas infarcts tended to be smaller in females than in males of J-lineage substrains. This adds to the growing list of recognized phenotypic and genetic differences among C57BL/6 substrains. Although no previous studies have explicitly compared substrains with respect to sex differences in stroke vulnerability, unrecognized background mismatch has occurred in some studies involving control and genetically modified mice. The aims of this review are to: present the evidence for associated substrain- and sex-dependent differences in a mouse permanent occlusion stroke model; examine the extent to which the published literature in other models compares with these recent results; and consider the potential impact of unrecognized heterogeneity in substrain background on the interpretation of studies investigating the impact of genetic modifications on sex differences in stroke outcome. Substrain emerges as a critical variable to be documented in any experimental stroke study in mice.

Early administration of pyrrolidine dithiocarbamate extends the therapeutic time window of tissue plasminogen activator in a male rat model of embolic stroke

Tissue plasminogen activator (tPA) is used in fewer than 4% of patients after ischemic stroke because of its narrow therapeutic time window. We tested whether pyrrolidine dithiocarbamate (PDTC), a drug with multiple mechanisms to provide neuroprotection, can be used to extend the therapeutic time window of tPA. Three-month-old male Sprague-Dawley rats were subjected to embolic stroke in the area supplied by the right middle cerebral artery. tPA at 10 mg/kg was given intravenously 4 h after the onset of stroke. PDTC at 50 mg/kg was given via gastric gavage at 30 min or 4 h after the onset of stroke. Two days after the stroke, neurological outcome was evaluated and the right frontal cortex area 1 (Fr1), an ischemic penumbral region, was harvested for analysis. PDTC given at 30 min after the stroke reduced infarct volumes and improved neurological functions no matter whether the rats received tPA. PDTC also reduced tPA-increased hemorrhagic volumes. Consistent with these results, PDTC in the presence or absence of tPA treatment attenuated the increase of proinflammatory cytokines, oxidative stress and matrix metalloprotease 2 activity in the right Fr1. However, PDTC given at 4 h after the onset of stroke did not improve the neurological outcome of rats treated with or without tPA. Our results suggest that PDTC given at an early time point but not in a delayed phase provides neuroprotection against embolic stroke and may be used to extend the therapeutic time window of tPA.

Collateral blood flow in different cerebrovascular hierarchy provides endogenous protection in cerebral ischemia

Collateral blood flow as vascular adaptions to focal cerebral ischemia is well recognized. However, few studies directly investigate the dynamics of collateral vessel recruitment in vivo and little is known about the effect of collateral blood flow in different cerebrovascular hierarchy on the neuropathology after focal ischemic stroke. Here, we report that collateral blood flow is critically involved in blood vessel compensations following regional ischemia. We occluded a pial arteriole using femtosecond laser ablating under the intact thinned skull and documented the changes of collateral flow around the surface communication network and between the surface communication network and subsurface microcirculation network using in vivo two photon microscopy imaging. Occlusion of the pial arteriole apparently increased the diameter and collateral blood flow of its leptomeningeal anastomoses, which significantly reduced the cortical infarction size. This result suggests that the collateral flow via surface communicating network connected with leptomeningeal anastomoses could greatly impact on the extent of infarction. We then further occluded the target pial arteriole and all of its leptomeningeal anastomoses. Notably, this type of occlusion led to reversals of blood flow in the penetrating arterioles mainly proximal to the occluded pial arteriole in a direction from the subsurface microcirculation network to surface arterioles. Interesting, the cell death in the area of ischemic penumbra was accelerated when we performed occlusion to cease the reversed blood flow in those penetrating arterioles, suggesting that the collateral blood flow from subsurface microcirculation network exerts protective roles in delaying cell death in the ischemic penumbra. In conclusion, we provide the first experimental evidence that collateral blood vessels at different cerebrovascular hierarchy are endogenously compensatory mechanisms in brain ischemia.

Control of cerebral ischemia with magnetic nanoparticles

The precise manipulation of microcirculation in mice can facilitate mechanistic studies of brain injury and repair after ischemia, but this manipulation remains a technical challenge, particularly in conscious mice. We developed a technology that uses micromagnets to induce aggregation of magnetic nanoparticles to reversibly occlude blood flow in microvessels. This allowed induction of ischemia in a specific cortical region of conscious mice of any postnatal age, including perinatal and neonatal stages, with precise spatiotemporal control but without surgical intervention of the skull or artery. When combined with longitudinal live-imaging approaches, this technology facilitated the discovery of a feature of the ischemic cascade: selective loss of smooth muscle cells in juveniles but not adults shortly after onset of ischemia and during blood reperfusion.

A novel mouse model of thromboembolic stroke

BACKGROUND

We previously demonstrated that tissue plasminogen activator (tPA) reduces infarct size after mechanical middle cerebral artery occlusion (MCAO) in wild-type (WT) mice and transgenic mice expressing human leukocyte antigen DR2 (DR2-Tg). Clinically, tPA limits ischemic damage by dissolving the clot blocking blood flow through a cerebral artery. To mimic the clinical situation, we developed a new mouse model of thromboembolic stroke, and tested the efficacy of tPA in WT and DR2-Tg mice. New Method Autologous blood is withdrawn into a PE-8 catheter filled with 2 IU α-thrombin. After exposing the catheter briefly to air, the catheter is reintroduced into the external (ECA) and advanced into the internal carotid artery (ICA) to allow for intravascular injection of thrombin at the MCA bifurcation. To validate the model, we tested the effect of tPA on laser-Doppler perfusion (LDP) over the MCA territory and infarct size in WT and DR2-Tg mice.

RESULTS

The procedure results in a consistent drop in LDP, and leads to a highly reproducible ischemic lesion. When administered at 15min after thrombosis, tPA restored LDP and resulted in a significant reduction in infarct size at 24h after thrombosis in both WT and DR2-Tg.

COMPARISON WITH EXISTING METHODS

Our model significantly reduces surgery time, requires a single anesthesia exposure, and produces a consistent and predictable infarction, with low variability and mortality.

CONCLUSION

We validated the efficacy of tPA in restoring blood flow and reducing infarct in a new model of endovascular thromboembolic stroke in the mouse.

The macrosphere model-an embolic stroke model for studying the pathophysiology of focal cerebral ischemia in a translational approach

The main challenge of stroke research is to translate promising experimental findings from the bench to the bedside. Many suggestions have been made how to achieve this goal, identifying the need for appropriate experimental animal models as one key issue. We here discuss the macrosphere model of focal cerebral ischemia in the rat, which closely resembles the pathophysiology of human stroke both in its acute and chronic phase. Key pathophysiological processes such as brain edema, cortical spreading depolarizations (CSD), neuroinflammation, and stem cell-mediated regeneration are observed in this stroke model, following characteristic temporo-spatial patterns. Non-invasive in vivo imaging allows studying the macrosphere model from the very onset of ischemia up to late remodeling processes in an intraindividual and longitudinal fashion. Such a design of pre-clinical stroke studies provides the basis for a successful translation into the clinic.

Animal models of ischemic stroke and their application in clinical research

This review outlines the most frequently used rodent stroke models and discusses their strengths and shortcomings. Mimicking all aspects of human stroke in one animal model is not feasible because ischemic stroke in humans is a heterogeneous disorder with a complex pathophysiology. The transient or permanent middle cerebral artery occlusion (MCAo) model is one of the models that most closely simulate human ischemic stroke. Furthermore, this model is characterized by reliable and well-reproducible infarcts. Therefore, the MCAo model has been involved in the majority of studies that address pathophysiological processes or neuroprotective agents. Another model uses thromboembolic clots and thus is more convenient for investigating thrombolytic agents and pathophysiological processes after thrombolysis. However, for many reasons, preclinical stroke research has a low translational success rate. One factor might be the choice of stroke model. Whereas the therapeutic responsiveness of permanent focal stroke in humans declines significantly within 3 hours after stroke onset, the therapeutic window in animal models with prompt reperfusion is up to 12 hours, resulting in a much longer action time of the investigated agent. Another major problem of animal stroke models is that studies are mostly conducted in young animals without any comorbidity. These models differ from human stroke, which particularly affects elderly people who have various cerebrovascular risk factors. Choosing the most appropriate stroke model and optimizing the study design of preclinical trials might increase the translational potential of animal stroke models.

Focal embolic cerebral ischemia in the rat

Animal models of focal cerebral ischemia are well accepted for investigating the pathogenesis and potential treatment strategies for human stroke. Occlusion of the middle cerebral artery (MCA) with an endovascular filament is a widely used model to induce focal cerebral ischemia. However, this model is not amenable to thrombolytic therapies. As thrombolysis with recombinant tissue plasminogen activator (rtPA) is a standard of care within 4.5 h of human stroke onset, suitable animal models that mimic cellular and molecular mechanisms of thrombosis and thrombolysis of stroke are required. By occluding the MCA with a fibrin-rich allogeneic clot, we previously developed an embolic model of MCA occlusion in the rat, which recapitulates the key components of thrombotic development and of thrombolytic therapy of rtPA observed from human ischemic stroke. Here we describe in detail the surgical procedures of our model, including preparing emboli from rat donors. These procedures can be typically completed within ∼30 min, and they are highly adaptable to other strains of rats, as well as mice, in both sexes. Thus, this model provides a powerful tool for translational stroke research.

The combination of astragalus membranaceus and ligustrazine ameliorates micro-haemorrhage by maintaining blood-brain barrier integrity in cerebrally ischaemic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Haemorrhagic transformation is an asymptomatic event that frequently occurs after following ischaemic stroke, particularly when pharmaceutical thrombolysis is used. However, the mechanism responsible for haemorrhagic transformation remains unknown, and therapeutics have not been identified. In this study, we administered a combination of astragalus membranaceus and ligustrazine to rats with cerebral ischaemia that had undergone thrombolysis. We analysed the effect of this combination on the attenuation of haemorrhagic transformation and the maintenance of blood-brain barrier integrity.

METHODS

A rat model of focal cerebral ischaemia was induced with autologous blood clot injections. Thrombolysis was performed via the intravenous injection of rt-PA. Astragalus membranaceus, ligustrazine or a combination of Astragalus membranaceus and ligustrazine was administered immediately after the clot injection. The cerebral infarct area, neurological deficits, blood-brain barrier integrity, and cerebral haemorrhage status were determined after 3, 6 and 24h of ischaemia. The ultrastructure of the blood-brain barrier was examined with a transmission electron microscope. The expression of tight junction proteins, including claudin-1, claudin-5, occludin, and zonula occludens-1, and matrix metallopeptidase-9 activation was further evaluated in terms of their roles in the protective effects of the combination drug on the integrity of the blood-brain barrier.

RESULTS

Ischaemia-induced Evans blue leakage and cerebral haemorrhage were markedly reduced in the combination drug-treated rats compared to the rats treated with either astragalus membranaceus or ligustrazine alone (p<0.05). The disruption of the ultrastructure of the blood-brain barrier and the neurological deficits were ameliorated by the combination treatment (p<0.05). The reductions in the expression of laudin-1, claudin-5, occludin, and ZO-1 were smaller in the rats that received the combination treatment. In addition, MMP-9 activity was suppressed in the combination-treated rats compared to the controls (p<0.05).

CONCLUSIONS

Treatment with a combination of astragalus membranaceus and ligustrazine alleviated ischaemia-induced micro-haemorrhage transformation by maintaining the integrity of the blood-brain barrier.

Embolic middle cerebral artery occlusion (MCAO) for ischemic stroke with homologous blood clots in rats

Clinically, thrombolytic therapy with use of recombinant tissue plasminogen activator (tPA) remains the most effective treatment for acute ischemic stroke. However, the use of tPA is limited by its narrow therapeutic window and by increased risk of hemorrhagic transformation. There is an urgent need to develop suitable stroke models to study new thrombolytic agents and strategies for treatment of ischemic stroke. At present, two major types of ischemic stroke models have been developed in rats and mice: intraluminal suture MCAO and embolic MCAO. Although MCAO models via the intraluminal suture technique have been widely used in mechanism-driven stroke research, these suture models do not mimic the clinical situation and are not suitable for thrombolytic studies. Among these models, the embolic MCAO model closely mimics human ischemic stroke and is suitable for preclinical investigation of thrombolytic therapy. This embolic model was first developed in rats by Overgaard et al.(1) in 1992 and further characterized by Zhang et al. in 1997(2). Although embolic MCAO has gained increasing attention, there are technical problems faced by many laboratories. To meet increasing needs for thrombolytic research, we present a highly reproducible model of embolic MCAO in the rat, which can develop a predictable infarct volume within the MCA territory. In brief, a modified PE-50 tube is gently advanced from the external carotid artery (ECA) into the lumen of the internal carotid artery (ICA) until the tip of the catheter reaches the origin of the MCA. Through the catheter, a single homologous blood clot is placed at the origin of the MCA. To identify the success of MCA occlusion, regional cerebral blood flow was monitored, neurological deficits and infarct volumes were measured. The techniques presented in this paper should help investigators to overcome technical problems for establishing this model for stroke research.

Biochemical and inflammatory biomarkers in ischemic stroke: translational study between humans and two experimental rat models

Background

our objective was to examine the plasma levels of three biological markers involved in cerebral ischemia (IL-6, glutamate and TNF-alpha) in stroke patients and compare them with two different rat models of focal ischemia (embolic stroke model- ES and permanent middle cerebral artery occlusion ligation model-pMCAO) to evaluate which model is most similar to humans. Secondary objectives: 1) to analyze the relationship of these biological markers with the severity, volume and outcome of the brain infarction in humans and the two stroke models; and 2) to study whether the three biomarkers are also increased in response to damage in organs other than the central nervous system, both in humans and in rats.

Methods

Multi-center, prospective, case-control study including acute stroke patients (n = 58) and controls (n = 19) with acute non-neurological diseases Main variables: plasma biomarker levels on admission and at 72 h; stroke severity (NIHSS scale) and clinical severity (APACHE II scale); stroke volume; functional status at 3 months (modified Rankin Scale [mRS] and Barthel index [BI]). Experimental groups: ES (n = 10), pMCAO (n = 6) and controls (tissue stress by leg compression) (n = 6). Main variables: plasma biomarker levels at 3 and 72 h; volume of ischemic lesion (H&E) and cell death (TUNEL).

Results

in stroke patients, IL-6 correlated significantly with clinical severity (APACHE II scale), stroke severity (NIHSS scale), infarct volume (cm³) and clinical outcome (mRS) (r = 0.326, 0.497, 0.290 and 0.444 respectively; P < 0.05). Glutamate correlated with stroke severity, but not with outcome, and TNF-alpha levels with infarct volume. In animals, The ES model showed larger infarct volumes (median 58.6% vs. 29%, P < 0.001) and higher inflammatory biomarkers levels than pMCAO, except for serum glutamate levels which were higher in pMCAO. The ES showed correlations between the biomarkers and cell death (r = 0.928 for IL-6; P < 0.001; r = 0.765 for TNF-alpha, P < 0.1; r = 0.783 for Glutamate, P < 0.1) and infarct volume (r = 0.943 for IL-6, P < 0.0001) more similar to humans than pMCAO. IL-6, glutamate and TNF-α levels were not higher in cerebral ischemia than in controls.

Conclusions

Both models, ES and pMCAO, show differences that should be considered when conducting translational studies. IL-6, Glutamate and TNF-α are not specific for cerebral ischemia either in humans or in rats.

A model of rat embolic cerebral infarction with a quantifiable, autologous arterial blood clot

We developed a novel model of a rat embolic cerebral infarction with a quantifiable autologous arterial blood clot. The left femoral artery had 0.15 ml of blood withdrawn and mixed with 10 units of thrombin in 50 μl saline. After 30 min, the clot was suctioned into a 4-French polyvinyl chloride tube. A 24-gage catheter was inserted up through the internal carotid artery via the external carotid artery stump. The 1-cm clot, at a volume of 7.2 mm3, was pushed and inserted into the internal carotid artery via the catheter. After withdrawing the catheter, the ICA blood flow recovered. We checked neurological status after 24 h (neurological free was 15, and worst was 1) and measured the infarction volume by the TTC method. Twelve rats were examined, and five sham-operated rats were included. Two rats were not able to achieve an 80% reduction in CBF. One rat died due to cerebral infarction. The success rate in producing infarction was 83%. The total infarction volume was 368.5 mm3±61.2 se. Median neurological score was 6. Hemorrhagic transformation was not detected. Sham-operated rats revealed no infarction and no neurological deficit. The volume of infarction correlated significantly with the neurological score. We conclude that this embolic stroke model is useful in producing a human, severe cardioembolic cerebral infarction.

Embolic middle cerebral artery occlusion model using thrombin and fibrinogen composed clots in rat

Ischemic stroke accounts for over 80% in total human stroke which mostly affect middle cerebral artery (MCA) territory. Embolic stroke models induced by injection of homologous clots into the internal carotid artery and MCA closely mimic human stroke and have been commonly used in stroke research. Studies indicate that the size and composition of clots are critical for the reproducibility of the stroke model. In the present study, we modified the homologous clots formation by addition of thrombin and fibrinogen which produced even distribution of fibrin with tight cross linkage of red blood cells. We optimized the embolic MCA occlusion model in rats using different size of the mixed clots. A precise lodgment of the clots at the MCA bifurcation and highly reproducible ischemic lesion in the MCA territory were demonstrated in the embolic MCA occlusion model induced by injection of 10 pieces of 1-mm long mixed clots made in PE-60 catheter. We further tested the effect of recombinant tissue plasminogen activator (rtPA) in this embolic MCA occlusion model. rtPA induced thrombolysis, improved neurological outcome, and significantly reduced ischemic lesion volume when administered at 1h after embolism as compared with control. In summary, we have established a reproducible embolic MCA occlusion model using clots made of homologous blood, thrombin and fibrinogen. The mixed clots enable precise lodgment at the MCA bifurcation which is responsive to thrombolytic therapy of rtPA.

Comparison of quantitative estimation of intracerebral hemorrhage and infarct volumes after thromboembolism in an embolic stroke model

BACKGROUND

Strokes have both ischemic and hemorrhagic components, but most studies of experimental stroke only address the ischemic component. This is likely because investigations of hemorrhagic transformation are hindered by the lack of methods based on unbiased principles for volume estimation.

AIMS

We evaluated different methods for estimating the volume of infarcts, hemorrhages, after embolic middle cerebral artery occlusion with or without thrombolysis.

METHODS

An experimental thromboembolytic rat model was used in this study. The rats underwent surgery and were placed in two groups. Group 1 was treated with saline, and group 2 was treated with 20 mg/kg recombinant tissue plasminogen activator to promote intracerebral hemorrhages. Stereology, semiautomated computer estimation, and manual erythrocyte counting were used to test the precision and efficiency of determining the size of the infarct and intracerebral hemorrhage.

RESULTS

No differences were observed in the infarct volume or amount of bleeding when comparing the three methods of volume estimation. Although semiautomated computer estimation and manual erythrocyte counting provided similar results as the stereological measurements, the stereological method was the most efficient and advantageous.

CONCLUSIONS

We found that stereology was the superior method for quantification of hemorrhagic volume, especially for rodent petechial bleeding, which is otherwise difficult to measure. Our results suggest the possibility of measuring both the ischemic and the hemorrhagic components of stroke, two parameters that may be differentially regulated when therapeutic regimens are tested.

Direct Thrombus Imaging as a Means to Control the Variability of Mouse Embolic Infarct Models

Background and Purpose—

High experimental variability in mouse embolic stroke models could mask the effects of experimental treatments. We hypothesized that imaging thrombus directly would allow this variability to be controlled.

Methods—

We optically labeled thrombi with a near-infrared fluorescent (NIRF) probe C15 that is covalently linked to fibrin by factor-XIIIa. Labeled thrombus was injected into the left distal internal carotid artery (ICA) of C57/BL6 mice (n=47), near its bifurcation, and laser-Doppler cerebral-blood-flow (CBF) was assessed for 30 minutes. NIRF thrombus imaging was done ex vivo at 24 hours.

Results—

CBF variably decreased to 43.9±17.3% at 5 minutes (rCBF; 11.2∼80.4%). NIRF thrombus imaging at 24 hours showed variability in distribution (ICA bifurcation, adjacent and/or remote areas) and burden (2279±1270 pixels; 0∼5940 pixels). Final infarct size was also variable (21.0±10.3%; 4.7∼60.3% of the bihemispheric volume). Despite this heterogeneity, a strong thrombus-infarct correlation was maintained. The left hemispheric target infarct size (% of the hemisphere) correlated with thrombus burden, as a stronger predictor of infarct volume ( P <0.001, r=0.50) than rCBF ( P =0.02, r=−0.34). The infarct size was best predicted by a combination of thrombus imaging and CBF: left-hemispheric big-thrombi (>1865 pixels)/low-rCBF (≤42%) had an infarct volume of 56.9±10.4% (n=12), big-thrombi/high-rCBF had 45.9±23.5% (n=11), small-thrombi/low-rCBF 35.7±17.3% (n=11) and small-thrombi/ high-rCBF 27.3±16.4% (n=12).

Conclusions—

This is the first study to demonstrate that the highly heterogeneous nature of the mouse embolic stroke model can be characterized and managed by using near-infrared fluorescent thrombus imaging combined with CBF monitoring to stratify animals into useful subgroups.

Acute but not delayed amphetamine treatment improves behavioral outcome in a rat embolic stroke model

OBJECTIVES

The objective of this study was to examine the effects of d-amphetamine (amph) upon recovery after embolic stroke in rats.

METHODS

Ninety-three rats were embolized in the right middle cerebral artery and assigned to: (1) controls; (2) combination (acute amph and later amph-facilitated retraining); (3) late amph (later amph-facilitated retraining alone); and (4) acute amph (acute amph alone). Animals in the combination and in the acute amph groups received a high dose of amph immediately after embolization, while later amph-facilitated retraining in the combination and late amph groups was done by administering a low dose of amph on post-stroke days 2, 5, 8, and 11 followed by retraining in Montoya's Staircase Test.

RESULTS

Rats receiving acute amph immediately after embolization achieved an 11% increase in median blood pressure (P<0.05). An investigation of performances with the ipsilateral paws during days 14-21 showed that the acute amph group performed better than the control group (P<0.02). Infarct volumes were lower among animals in the acute amph group than in both the combination and the late amph groups (P<0.05), while the controls did not differ from any group.

DISCUSSION

In conclusion, results showed that the acute amph group performed the best, while the late amph and the combination groups performed the worst. Amphetamine treatment in acute stroke may be warranted due to reduced detrimental effects of hypotension and improved brain plasticity.

The site of embolization related to infarct size, oedema and clinical outcome in a rat stroke model - further translational stroke research

Background and purpose

Reliable models are essential for translational stroke research to study the pathophysiology of ischaemic stroke in an effort to find therapies that may ultimately reduce oedema, infarction and mortality in the clinic. The purpose of this study was to investigate the relation between the site of arterial embolization and the subsequent oedema, infarction and clinical outcome in a rat embolic stroke model.

Methods

Thirty-six male Sprague-Dawley rats were thromboembolized into the internal carotid artery. The site of occlusion was demonstrated by arteriography. Following histological preparation and evaluation, the size of the hemispheres and the infarcts were measured by quantitative histology and planimetry. Another parallel stroke model study was subsequently examined to investigate if the conclusions from the first study could be applied to the second study.

Results

The median size of the infarct was 40% of the ipsilateral hemisphere in both the 19 animals with occlusion localised to the intracranial part of the internal carotid artery and in the 11 animals where the main trunk of the middle cerebral artery was occluded. In 5 animals, occlusion of the extracranial part of the internal carotid artery resulted in significantly smaller infarcts compared to other groups (p < 0.01). Another independent study re-confirmed these results. Furthermore, significant correlations (R > 0.76, p < 0.0001) were found between 1) cortical, subcortical, and total infarct volumes, 2) oedema in percent of the left hemisphere, 3) clinical score before termination and 4) postoperative weight loss.

Conclusions

Distal occlusions of the intracranial part of the internal carotid or middle cerebral arteries resulted in comparable large sized infarctions and oedema. This indicates that investigators do not need a similar number of such occlusions in each experimental group. Contrary to observations in the clinic, distal internal carotid artery occlusions did not result in worse outcome than middle cerebral stem occlusions, but this finding may be explained by the controlled emboli size in this experimental stroke model.

A novel embolic model of cerebral infarction and evaluation of Stachybotrys microspora triprenyl phenol-7 (SMTP-7), a novel fungal triprenyl phenol metabolite

The aim of the present study was to establish a novel embolic model of cerebral infarction and to evaluate the effect of Stachybotrys microspora triprenyl phenol-7 (SMTP-7), a novel fungal triprenyl phenol metabolite. Thrombotic occlusion was induced by transfer of acetic acid-induced embolus into the brain. The regional cerebral blood flow was measured by a laser Doppler flowmeter to check the ischemic condition. Infarction area was assessed by 2% 2,3,5-triphenyltetrazolium chloride (TTC) staining. Neurological scores were determined by a modified version of the method described by Longa et al. Emboli were accumulated at the temporal or parietal region of the middle cerebral artery. Additionally, we found that this model showed decreased cerebral blood flow and increased infarction area and neurological scores. Treatment with tissue plasminogen activator (t-PA) reduced infarction area and the neurological scores in a dose-dependent manner; moreover, the decreased cerebral blood flow recovered. SMTP-7 also reduced these values. The therapeutic time window of SMTP-7 was longer than that of t-PA. These results indicate that this model may be useful for understanding the pathophysiological mechanisms of cerebral infarction and evaluating the effects of therapeutic agents. Additionally, SMTP-7 is a promising approach to extend the therapeutic time window. Therefore, this novel compound may represent a novel approach for the treatment of cerebral infarction.

Thrombolysis with reteplase, an unglycosylated plasminogen activator variant, in experimental embolic stroke

We incorporated diffusion-weighted magnetic resonance imaging (MRI) (DWI) and perfusion-weighted MRI (PWI) to evaluate the efficacy of thrombolysis in experimental embolic stroke using a plasminogen activator, reteplase. Reteplase (rPA) is an unglycosylated plasminogen activator with enhanced fibrinolytic potency. Right internal carotid arteries of 34 rabbits were embolized using aged heterologous thrombi. Baseline DWI and PWI scans 0.5 hours after embolization confirmed successful embolization among 32. Intravenous treatment with rPA (n=11; 1 mg/kg bolus), recombinant tissue plasminogen activator (rt-PA) (n=11; 6 mg/kg bolus over 1 hour), or placebo (n=10) commenced 1 hour after stroke induction. MRIs were performed at 1.75, 3, and 5 hours after embolization. Six hours after embolization, brains were harvested and examined for hemorrhage. Posttreatment areas of diffusion abnormality and perfusion delay were graded using both a semiquantitative scale and percent areas expressed as a ratio of the baseline values. Improved perfusion was seen among the rt-PA, and rPA-treated groups compared with placebo, using a semiquantitative scale (P<.01 rt-PA v controls, P<.05, rPA v controls). DWI scans, however, were not improved with thrombolysis. Cerebral hemorrhage was not increased with thrombolytic treatment, although the incidence of wound site hemorrhage was higher with either rPA or rt-PA. One fatal systemic hemorrhage was observed in each of the thrombolytic-treated groups. Cerebral perfusion was equally improved with either rt-PA or rPA without causing excess cerebral hemorrhage. An advantage of rPA is single-bolus dosing rather than continuous infusion. Use of rPA for stroke treatment should be further explored.

Rodent models of focal cerebral ischemia: procedural pitfalls and translational problems

Rodent models of focal cerebral ischemia are essential tools in experimental stroke research. They have added tremendously to our understanding of injury mechanisms in stroke and have helped to identify potential therapeutic targets. A plethora of substances, however, in particular an overwhelming number of putative neuroprotective agents, have been shown to be effective in preclinical stroke research, but have failed in clinical trials. A lot of factors may have contributed to this failure of translation from bench to bedside. Often, deficits in the quality of experimental stroke research seem to be involved. In this article, we review the commonest rodent models of focal cerebral ischemia - middle cerebral artery occlusion, photothrombosis, and embolic stroke models - with their respective advantages and problems, and we address the issue of quality in preclinical stroke modeling as well as potential reasons for translational failure.

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.

Effects of microplasmin on recovery in a rat embolic stroke model

OBJECTIVES

The purpose of the present study was to examine the effects of microplasmin on behavioral performance and infarct volume after middle cerebral artery occlusion (MCAO) in rats. Some experiments support that microplasmin may have neuroprotective and thrombolytic properties.

METHODS

Eighty rats underwent surgery and were embolized in the right carotid territory with a fibrin-rich embolus and randomly assigned into three groups: 5 mg/kg microplasmin, 10 mg/kg microplasmin or saline (control). Groups treated with microplasmin received 50% bolus injection 10 minutes after embolization and 50% continuous infusion during the following hour. Animals from all groups were trained to obtain high baseline scores in Montoya's staircase test before embolization and were retested during 7-14 days after surgery.

RESULTS

When pre-maturely dead animals were excluded, no differences were observed among groups regarding infarct volumes. Furthermore, mortality was significantly lower in Group 1 than in Group 2 (p<0.05) and when performances were evaluated 7-14 days after surgery, Group 1 was significantly better than Group 2 concerning fine motor performance (p<0.05) and also achieved more normal bodyweight (p<0.05).

DISCUSSION

Among surviving animals, 5 mg/kg microplasmin treatment had no effect compared to saline-treated control animals; 5 mg/kg microplasmin reduced mortality and improved both behavioral rehabilitation and bodyweight compared to 10 mg/kg microplasmin treatment, while saline-treated animals did not differ from animals treated with 10 mg/kg microplasmin. Overall, these results indicate a potential beneficial effect of 5 mg/kg microplasmin treatment, while 10 mg/kg may worsen outcomes.

An experimental model of lacunar infarction: embolization of microthrombi

OBJECTIVES

Microthrombi are undoubtedly the most common embolic material in the cerebral circulation, originating from even minor irregularities of the arterial wall, fibrillating atria, cardiac valves, and patent foramen ovale. Thrombus fragments are globular and likely to completely obstruct terminal vessels. In contrast, previous work with "atheroemboli" of needle-like cholesterol crystals rarely cause occlusions or infarctions instead creating small foci of inflammation. In this work, we asked if microthrombi would occlude terminal vessels and create lacunar type infarctions in the subcortical tissues of the rat brain where, as in human brain, collateral flow is limited relative to the cortex.

METHODS

Three treatment groups of adult male Sprague-Dawley rats were studied. All groups underwent general anesthesia with monitoring of temperature and blood pressure during cannulation of the right internal carotid artery. In the group embolized with thrombus fragments (n = 12), animals had injections of 300 fragments of thrombus size 60 to 100 microns, the cholesterol group (n = 6) had injections of 300 cholesterol crystals of similar size, and the control group (n = 4) had injections of saline. Brains were harvested at 4 days with perfusion fixation and were examined by immunohistochemical staining for breaks in the blood brain barrier (BBB) (albumin), microglial activation (CD11b), astrocyte activation (GFAP), and infarction (loss of NeuN staining). Size and location of the areas of injury and infarction were recorded.

RESULTS

Clot fragments caused discreet infarcts in 10/12 animals that were 0.1-1.7 mm in diameter and coincided with activation of microglia and astrocytes. In some areas, necrosis was already underway at this early time point. Consistent with our previous work, the infarcts caused by cholesterol crystals were smaller (P = .014). Foci of BBB disruption and microglial activation were distributed throughout the brain whereas areas of infarction were found almost exclusively in subcortical tissues (P = .029).

CONCLUSIONS

Injecting microthrombi reproducibly caused areas of necrosis resembling lacunar type infarctions. These were primarily located in the striatum and thalamus presumably because these areas lack the branching, collateral network seen in the cortex. In addition, these data give further evidence that the extent of brain injury from emboli depends upon composition and shape as well as size.

Tumor necrosis factor and stroke: role of the blood-brain barrier

The progression and outcome of stroke is affected by the intricate relationship between the blood-brain barrier (BBB) and tumor necrosis factor alpha (TNFalpha). TNFalpha crosses the intact BBB by a receptor-mediated transport system that is upregulated by CNS trauma and inflammation. In this review, we discuss intracellular trafficking and transcytosis of TNFalpha, regulation of TNFalpha transport after stroke, and the effects of TNFalpha on stroke preconditioning. TNFalpha can activate cytoprotective pathways by pretreatment or persistent exposure to low doses. This explains the paradoxical observation that transport of this proinflammatory cytokine improves the survival and function of hypoxic cells and of mice with stroke. The dual effects of TNFalpha may be related to differential regulation of TNFalpha trafficking downstream to TNFR1 and TNFR2 receptors. As we better understand how peripheral TNFalpha affects its own transport and modulates neuroregeneration, we may be in a better position to pharmacologically manipulate its regulatory transport system to treat stroke.

Efficacy of recombinant annexin 2 for fibrinolytic therapy in a rat embolic stroke model: a magnetic resonance imaging study

Efficacy of recombinant annexin 2 (rAN II) in a rat model of embolic stroke was examined using a magnetic resonance imaging (MRI) and histology. The right middle cerebral artery of male Wistar rats was occluded by autologous clots under anesthesia. Four doses of rAN II (0.125, 0.25, 0.5 and 1.0 mg/kg, n=10 for each group) or saline (1 ml/kg, n=10) were administrated intravenously within 5 min before clot infusion. Serial changes in apparent diffusion coefficient (ADC) and relative blood flow (CBF) were measured with the use of MRI in half of the animals in each group. The remaining half of the animals in each group was evaluated for hemorrhage and final infarct size by histology at 48 h after embolization. At 3 h after embolization, lesion volumes with ADC were abnormality and CBF in the peripheral lesion was improved in groups treated with 0.25, 0.5 and 1.0 mg/kg, but not 0.125 mg/kg, of rAN II in comparison with the saline-treated group (P<0.05). Histological analyses were consistent with MRI findings. More importantly, no hemorrhagic transformation was documented in rats treated with 0.125 and 0.25 mg/kg of rAN II, whereas it was observed at higher doses. We concluded that rAN II at 0.25 mg/kg significantly reduced infarct size and improved CBF without hemorrhagic complications. rAN II is a novel compound that has the potential to be a promising fibrinolytic agent to treat embolic stroke.

Acute ischemic stroke: overview of major experimental rodent models, pathophysiology, and therapy of focal cerebral ischemia

Ischemic stroke is a devastating disease with a complex pathophysiology. Animal modeling of ischemic stroke serves as an indispensable tool first to investigate mechanisms of ischemic cerebral injury, secondly to develop novel antiischemic regimens. Most of the stroke models are carried on rodents. Each model has its particular strengths and weaknesses. Mimicking all aspects of human stroke in one animal model is not possible since ischemic stroke is itself a very heterogeneous disorder. Experimental ischemic stroke models contribute to our understanding of the events occurring in ischemic and reperfused brain. Major approaches developed to treat acute ischemic stroke fall into two categories, thrombolysis and neuroprotection. Trials aimed to evaluate effectiveness of recombinant tissue-type plasminogen activator in longer time windows with finer selection of patients based on magnetic resonance imaging tools and trials of novel recanalization methods are ongoing. Despite the failure of most neuroprotective drugs during the last two decades, there are good chances to soon have effective neuroprotectives with the help of improved preclinical testing and clinical trial design. In this article, we focus on various rodent animal models, pathogenic mechanisms, and promising therapeutic approaches of ischemic stroke.

Selective, reversible occlusion of the middle cerebral artery in rats by an intraluminal approach

These studies optimized design and application of an intraluminal filament method to achieve selective middle cerebral artery (MCA) occlusion in rats. Silicone plugs of 300 microm diameter and 700-800 microm length were molded onto 6-0 suture. These were introduced into Wistar rats previously fitted with telemetric probes, using established placement procedures, with and without heparinization. Temperature and activity were monitored for 3 days, after which lesion volumes were assessed by triphenyltetrazolium chloride staining. Optimized filaments entered the MCA in 85% of Wistar rats, failures being attributable to anatomical variation at its origin from the internal carotid artery. Infarcts restricted to the MCA territory were apparent after 90 min occlusion, and maximal after 3 h occlusion. Intraischemic hyperthermia was noted in a third of occlusions performed without heparin, but never with anticoagulant treatment. Permanent occlusions were also evaluated in Fisher, Lewis, Long-Evans, Spontaneously Hypertensive and Sprague-Dawley rats, and Wistar rats from a second supplier, and compared with data for surgical MCA occlusions. Success rates varied among strains, but infarct volumes correlated with those obtained after surgical occlusions in respective populations. These studies demonstrate the feasibility and limitations of reversible and selective intraluminal filament occlusion of the MCA in rats.

A new model of thromboembolic stroke in the posterior circulation of the rat

The prognosis of vertebrobasilar occlusion is grave and therapeutic options are limited. The aim of the present study was to develop a new model of embolic hindbrain ischemia in the rat that closely resembles the clinical situation and that can be used to study pathophysiology and treatment options. After thoracotomy in 20 male Wistar rats, 15 animals received an injection of in vitro prepared autologous blood clots into the left vertebral artery. Five animals without clot injection served as controls. Neurological deficits were assessed in all animals 2 h after embolism. After 2 h, five animals were sacrificed to measure cerebral blood flow (CBF) by iodo-antipyridine autoradiography, and to calculate early cerebellar swelling by comparison of both hemispheres in brain slices. In these animals, autoradiography revealed ipsilesional brain swelling and significantly reduced blood flow values relative to the contralateral (unaffected) structures. Immunohistology showed the typical pattern of focal cerebral ischemia in the brain stem and/or cerebellum in 7 of 10 animals allowed to recover to 24 h. Hence, successful thromboembolism was achieved in 12 of 15 animals (80%). With this novel model, the pathophysiology and potential treatments of posterior circulation stroke can be investigated.

Local Heat Shock Priming Promotes Recanalization of Thromboembolized Microvasculature by Upregulation of Plasminogen Activators

OBJECTIVE

Thromboembolization and subsequent microvascular perfusion failure is implicated in the pathology of a variety of diseases, including transient ischemic attack (TIA), stroke, and myocardial infarction, and also for the complications after interventional and microsurgical procedures in coronary heart disease and peripheral arterial occlusive disease. In vitro heat shock priming has been suggested to induce plasminogen activators, which are the major upregulators of the fibrinolytic system. Herein, we determined whether local heat shock priming endogenously upregulates plasminogen activators also in vivo, and whether this promotes recanalization of thromboembolized microvasculature.

METHODS AND RESULTS

To induce thromboembolization, a suspension of preformed microthrombi (maximum diameter: 40 microm) was injected via the femoral artery into the left hindlimbs of anesthetized rats. Local heat shock priming (42.5 degrees C, 30 minutes) was performed 24 hours before embolization and resulted in a significant increase of endothelium-derived plasminogen activator expression. The study of the microcirculation by intravital microscopy revealed in all tissues analyzed (muscle, periosteum, subcutis, and skin) that heat shock priming significantly (P<0.05) accelerates recanalization of the thromboembolized microvasculature when compared with nonprimed and sham-primed controls. Importantly, the addition of plasminogen activator inhibitor-1 to the microthrombi suspension completely blunted the heat shock-induced acceleration of microvascular recanalization.

CONCLUSIONS

Heat shock induces endogenous hyperfibrinolysis by upregulation of plasminogen activators that promote recanalization of thromboembolized microvasculature.

Effect of combined therapy with thrombolysis and citicoline in a rat model of embolic stroke

An approach combining reperfusion mediated by thrombolytics with pharmacological neuroprotection aimed at inhibiting the physiopathological disorders responsible for ischemia-reperfusion damage, could provide an optimal treatment of ischemic stroke. We investigate, in a rat embolic stroke model, the combination of rtPA with citicoline as compared to either alone as monotherapy, and whether the neuroprotector should be provided before or after thrombolysis to achieve a greater reduction of ischemic brain damage. One hundred and nine rats have been studied: four were sham-operated and the rest embolized in the right internal carotid artery with an autologous clot and divided among 5 groups: 1) control; 2) iv rtPA 5 mg/kg 30 min post-embolization 3) citicoline 250 mg/kg ip x3 doses, 10 min, 24 h and 48 h post-embolization; 4) citicoline combined with rtPA following the same pattern; 5) rtPA combined with citicoline, with a first dose 10 min after thrombolysis. Mortality, neurological score, volume of ischemic lesion and neuronal death (TUNEL) after 72 h and plasma levels of IL-6 and TNF-alpha, were considered to assess ischemic brain damage. Compared with controls, the use of citicoline after thrombolysis produced the greatest reduction of mortality caused by the ischemic lesion (p<0.01), infarct volume (p=0.027), number of TUNEL positive cells in striatum (p=0.014) and plasma levels of TNF-alpha at 3 h (p=0.027) and 72 h (p=0.011). rtPA induced reperfusion provided a slight non-significant reduction of infarct volume and neuronal death, but it reduced mortality due to brain damage (p<0.01) although an increase in the risk of fatal bleeding was noted. CiT as monotherapy only produced a significant reduction of neuronal death in striatum (p=0.014). The combination of CiT before rtPA did not add any benefit to rtPA alone. The superiority of the combined treatment with rtPA followed by citicoline suggests that early reperfusion should be followed by effective neuroprotection to inhibit ischemia-reperfusion injury and better protect the tissue at risk.

Thrombolysis and neuroprotection in cerebral ischemia

Stroke is a major cause of death and disability worldwide. The resulting burden on society grows with the increase in the incidence of stroke. The term brain attack was introduced to describe the acute presentation of stroke and emphasize the need for urgent action to remedy the situation. Though a large number of therapeutic agents, like thrombolytics, NMDA receptor antagonists, calcium channel blockers and antioxidants, have been used or are being evaluated, there is still a large gap between the benefits of these agents and the properties of an ideal drug for stroke. So far, only thrombolysis with rtPA within a 3-hour time window has been shown to improve the outcome of patients with ischemic stroke. Understanding the mechanisms of injury and neuroprotection in these diseases is important to target news sites for treating ischemia. Better evaluation of the drugs and increased similarity between the results of animal experimentation and in the clinical setting requires critical assessment of the selection of animal models and the parameters to be evaluated. Our laboratory has employed a rat embolic stroke model to investigate the combination of rtPA with citicoline as compared to monotherapy alone and investigated whether neuroprotection should be provided before or after thrombolysis in order to achieve a greater reduction of ischemic brain damage.

D-amphetamine improves cognitive deficits and physical therapy promotes fine motor rehabilitation in a rat embolic stroke model

BACKGROUND AND PURPOSE

The purpose of this study was to examine the effects of D-amphetamine (D-amph) and physical therapy separately or combined on fine motor performance, gross motor performance and cognition after middle cerebral artery thromboembolization in rats.

METHODS

Seventy-four rats were trained in appropriate cognitive and motor behaviours. Thirteen animals were sham-operated and fifty-nine animals were embolized in the right carotid territory. Animals were randomly assigned to five groups: 1) SHAM (non-embolized, saline), 2) CONTROL (embolized, saline), 3) D-AMPH (embolized, D-amph), 4) THERAPY (embolized, saline + physical therapy) and 5) D-AMPH + THERAPY (embolized, D-amph + physical therapy). Rats of the groups 4-5 underwent d-amph or saline treatment on days 1, 3, 5 and 7 after surgery and were re-trained for 1 h starting 60 min after each treatment. During this time, rats were allowed to voluntarily engage in suitable cognitive or motor behaviours in order to obtain food. Animals from all groups were re-tested during days 21-28 after surgery.

RESULTS

No differences in infarct volumes were observed between the groups of embolized animals. When evaluating performances on days 21-28 after surgery, rats of the SHAM and THERAPY groups had better fine motor performance than those of the CONTROL (P < 0.05), whereas rats of SHAM and D-AMPH groups achieved better cognitive performance than CONTROL rats (P < 0.05). No significant differences were observed between any groups regarding gross motor performance.

CONCLUSIONS

After embolization, physical therapy improved fine motor performance and D-amph accelerated rehabilitation of cognitive performance as observed in the rats of the THERAPY and D-AMPH groups. As a result of the administration of a high dose of D-amph, the rats of the D-AMPH + THERAPY combination group failed to engage in physical therapy during D-amph intoxication, thereby limiting any promotion of rehabilitation by combining physical therapy and D-amph.

Selective MCA occlusion: a precise embolic stroke model

The present study describes a method for improving the precision and accuracy of clot placement within the middle cerebral artery (MCA) of rats, utilizing a micro-catheter and laser Doppler flowmetry. This technique reduces the size of clot needed to achieve stable occlusion with no failed embolizations and a low percentage of early recanalizations. Infarctions were consistent in both size and distribution within the MCA perfusion territory. Selective embolization in aged animals (n = 10) resulted in substantially larger infarctions than those seen in aged animals (n = 10) following non-selective embolization (P < 0.05), or young animals (n = 10) subjected to filamentous occlusion (P < 0.001). Clots were localized to the MCA by direct examination at 0, 60 and 120 min post-embolization (n = 14). All aged animals surviving 24h exhibited moderate to severe functional deficits, with selectively occluded animals having a higher mean score on the modified neurologic severity scale (P = 0.002). This model provides a highly reproducible method for embolization of the MCA and reliable reperfusion with rt-PA.