Experimental model of small deep infarcts involving the hypothalamus in rats: changes in body temperature and postural reflex

Polygalasaponin F ameliorates middle cerebral artery occlusion-induced focal ischemia / reperfusion injury in rats through inhibiting TXNIP/NLRP3 signaling pathway

BACKGROUND

Polygalasaponin F (PGSF), an oleanane triterpenoid saponin extracted from Polygala japonica, has been demonstrated with neuroprotective effect. However, the therapeutic effects and mechanisms of PGSF on focal ischemia remain unknown; METHODS: In this study, male Sprague Dawley (SD) rats aged 6-8 weeks were initially selected to establish a rat model of middle cerebral artery occlusion (MCAO) to evaluate the therapeutic effect of PGSF intervention and to investigate the impact of PGSF on the thioredoxin-interacting protein/NOD-, LRR-, and pyrin domain-containing protein 3 (TXNIP/NLRP3) inflammatory pathway. Secondly, brain neuron cells were isolated, and the cells received oxygen-glucose deprivation/reoxygenation (OGD/R) culture to establish the cell injury model in vitro. The mechanism of PGSF on the TXNIP/NLRP3 pathway was further validated; RESULTS: Our results showed that PGSF treatment reduced neurological scores, brain tissue water content and infarct volume and ameliorated the pathological changes in cerebral cortex in MCAO-induced focal ischemia rats. The TNF-α, IL-1β and IL-6 levels decreased in MCAO-induced focal ischemia rats after PGSF treatment. Moreover, PGSF down-regulated the protein expressions of TXNIP, NLRP3, ASC, cleaved caspase-1, IL-1β, and IL-18 in MCAO-induced focal ischemia rats. Meanwhile, PGSF treatment inhibited apoptosis, and reduced the levels of ROS, inflammatory cytokine and TXNIP/NLRP3 pathway-related proteins (TXNIP, NLRP3, ASC, cleaved caspase-1, IL-1β, and IL-18) in OGD/R-induced neuronal injury cells. Finally, PGSF treatment also disrupted the interaction between NLRP3 and TXNIP in vitro; CONCLUSIONS: Our study demonstrated the therapeutic effects of PGSF on MCAO-induced focal ischemia rats. Moreover, the neuroprotective mechanism of PGSF on focal ischemia was associated with the inhibition of TXNIP/NLRP3 signaling pathway.

Deep cortical microinfarction induced by femtosecond laser in mice: Long-term secondary pathological changes in corresponding superficial cortex

BACKGROUND AND PURPOSE

Previous studies have explored the clinical consequences of cortical microinfarction, mainly age-related cognitive decline. However, functional impairment of deep cortical microinfarction remains poorly understood. Based on anatomical knowledge and previous research, we infer that damage to the deep cortex may lead to cognitive deficits and communication impairment between the superficial cortex and thalamus. This study aimed to develop a new model of deep cortical microinfarction based on femtosecond laser ablation of a perforating artery.

METHODS

Twenty-eight mice were anesthetized with isoflurane, and a cranial window was thinned using a microdrill. Intensively focused femtosecond laser pulses were used to produce perforating arteriolar occlusions and ischemic brain damage was examined using histological analysis.

RESULTS

Occlusion of different perforating arteries induced different types of cortical microinfarctions. Blocking the perforating artery, which enters the cerebral cortex vertically and has no branches within 300 μm below, can result in deep cortical microinfarction. Moreover, this model showed neuronal loss and microglial activation in the lesions as well as dysplasia of nerve fibers and β-amyloid deposition in the corresponding superficial cortex.

CONCLUSIONS

We present here a new model of deep cortical microinfarction in mice, in which specific perforating arteries are selectively occluded by a femtosecond laser, and we preliminarily observe several long-term effects related to cognition. This animal model is helpful in investigating the pathophysiology of deep cerebral microinfarction. However, further clinical and experimental studies are required to explore deep cortical microinfarctions in greater molecular and physiological detail.

Association between hyperpyrexia and poststroke outcomes in patients with recanalization after mechanical thrombectomy: a retrospective cohort study

BACKGROUND

Limited data are available for evaluating the relationship between the prognosis and body temperature (BT) in patients treated with mechanical thrombectomy (MT), especially in those with successful recanalization. We aimed to explore the prognostic value of BT in predicting outcomes of stroke recovery at 3 months poststroke.

METHODS

We retrospectively analyzed the relationship among BT levels as a continuous variable, with fever (BT ≥ 37.5℃) as a binary variable, and obtained several outcomes of interest. Subjects were stratified according to successful recanalization (thrombolysis in cerebral infarction scores of 2b-3) following MT. Functional independence was defined as a modified Rankin scale (mRS) score of 0-2.

RESULTS

In total, 258 patients were included. The proportion of patients with functional independence was significantly lower among patients with BT ≥ 37.5℃ than among those with BT < 37.5 °C (45.3 % versus 23.0 %; P < 0.001). In the multivariate analysis, hyperpyrexia (especially BT ≥ 38 °C) was significantly associated with poor 3-month outcomes in patients treated with MT. Subgroup analysis was conducted by comparing the successful recanalization group with the non-recanalization group, showing that BT ≥ 37.5 °C was associated with a significantly lower proportion of functional independence in the recanalized patients. Besides, the Kaplan-Meier model showed that the fever group had significantly lower survival rates than the non-fever group during the 3-month follow-up.

CONCLUSIONS

In patients treated with MT, hyperpyrexia is an independent predictor of poststroke outcomes at 3 months, particularly in those with successful recanalization.

Integrated analysis of gait parameters and gene expression profiles in a murine model of subarachnoid hemorrhage

Gait analysis has been widely used to examine the behavioral presentation of numerous neurological disorders. Thorough murine model evaluation of the subarachnoid hemorrhage (SAH)-associated gait deficits is missing. This study measures gait deficits using a clinically relevant murine model of SAH to examine associations between gait variability and SAH-associated gene expressions. A total of 159 dynamic and static gait parameters from the endovascular perforation murine model for simulating clinical human SAH were determined using the CatWalk system. Eighty gait parameters and the mRNA expression levels of 35 of the 88 SAH-associated genes were differentially regulated in the diseased models. Totals of 42 and 38 gait parameters correlated with the 35 SAH-associated genes positively and negatively with Pearson's correlation coefficients of >0.7 and <-0.7, respectively. p-SP1⁴⁵³ expression in the motor cortex in SAH animal models displays a significant correlation with a subset of gait parameters associated with muscular strength and coordination of limb movements. Our data highlights a strong correlation between gait variability and SAH-associated gene expression. p-SP1⁴⁵³ expression could act as a biomarker to monitor SAH pathological development and a therapeutic target for SAH.

Study of the association between gait variability and gene expressions in a mouse model of transient focal ischemic stroke

Purpose: Gait variability analysis has been clinically adopted to characterize the presentation of various neurological diseases. However, literature and practice lack a comprehensive murine model assessment of the gait deficits that result from transient focal ischemic stroke. Further, correlations between gait parameters and the gene expression profiles associated with brain ischemia have yet to be identified. This study quantitatively assesses gait deficits through a murine model of transient focal cerebral ischemia on day 7 to determine associations between gait deficits and ischemia-related gene expressions.Methods: A total of 182 dynamic and static gait parameters from the transient middle cerebral artery occlusion (MCAO) murine model for simulating human transient focal ischemic stroke on day 7 were measured using the CatWalk system. Pearson's correlation analysis and genes associated with ischemia were identified from the existing literature to aid the investigation of the relationship between gait variability and gene expression profiles.Results: Thirty-nine gait parameters and the mRNA expression levels of four of the eight ischemia-associated genes exhibited more significant change in the MCAO models (p < 0.005) on day 7. Twenty-six gait parameters exhibited strong correlations with four ischemia-associated genes.Conclusion: This examination of gait variability and the strong correlation to the gene expression profiles associated with transient focal brain ischemia on day 7 provides a quantitative and reliable assessment of the MCAO model's motor performance. This research provides valuable insights into the study of disease progression and offers novel therapeutic interventions in the murine modeling of ischemic stroke.

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.

Neuroprotective Effects of Nasopharyngeal Perfluorochemical Cooling in a Rat Model of Subarachnoid Hemorrhage

OBJECTIVE

Subarachnoid hemorrhage (SAH) frequently results in severe morbidity, even mortality. Hypothermia is known to have a neuroprotective effect in ischemic injuries. The aim of this study was to determine whether nasopharyngeal (NP) perfluorochemical (PFC) cooling could be used in a rat model of SAH model for neuroprotection.

METHODS

SAH was induced in 16 male Sprague-Dawley rats by cisterna magna injection of 0.3 mL autologous blood. Vital signs, temperatures, cerebral blood flow (CBF), and brain histology were assessed. Brain cooling was performed on the treatment group using the NP-PFC method starting from 20 minutes after SAH.

RESULTS

No SAH-related deaths were observed in either group. SAH caused an immediate decrease in mean arterial pressure (17.0% ± 4.90% below baseline values). SAH induction caused a significant and rapid decrease in CBF from baseline (approximately -65%, ranging from -32% to -85%) in both hemispheres. In the left hemisphere, cooling facilitated the return of CBF to baseline values within 20 minutes of treatment with further increase in CBF that stabilized by the 2 hours after injury time point. Quantitative immunohistochemistry showed that there were significantly more NeuN-positive cells in the cortex and significantly fewer IBA-1-positive microglia and glial fibrillary acidic protein-positive astrocytes cells in both cortex and hippocampus in the animals that received NP-PFC cooling compared with no treatment, reflecting preserved neuronal integrity and reduced inflammation.

CONCLUSIONS

The data from this study indicate that local hypothermia by NP-PFC cooling supports return of CBF and neuronal integrity and suppresses the inflammatory response in SAH, suggestive of a promising neuroprotective approach in management of SAH.

MRI Guiding of the Middle Cerebral Artery Occlusion in Rats Aimed to Improve Stroke Modeling

The middle cerebral artery occlusion (MCAO) model in rats closely imitates ischemic stroke and is widely used. Existing instrumental methods provide a certain level of MCAO guidance, but monitoring of the MCA-occluding intraluminal filament position and possible complications can be improved. The goal of this study was to develop a MRI-based method of simultaneous control of the filament position, blood flow in the intracranial vessels, and hemorrhagic complications. Rats were subjected to either MRI-guided MCAO (group 1, n = 51) or MCAO without MRI control (group 2, n = 38). After operation, group 1 rats were transferred into a MRI scanner for the control of the filament position and possible complications. Ninety minutes after the onset of MCAO, the filament was removed in rats of both groups and MRI control of the infarct volume and hemorrhagic complications performed. High-resolution T1- and T2-weighted imaging performed immediately after filament insertion provided visualization of the filament position, blood flow in brain arteries, and complications related to inappropriate filament insertion. It permitted replacement of wrongly positioned filaments and exclusion of animals with complications from the experiment. MRI-based MCAO guiding provided real-time intra-operational monitoring of crucial parameters determining MCAO suitability for stroke modeling, including better assessment of the operation outcomes in individual animals and significant enhancement of the model success rate. The possibility of simultaneous visualization of the filament, blood flow in the arteries, brain tissue, and hemorrhagic complications is the principal advantage of the proposed method over other instrumental methods of MCAO quality control. Graphical Abstract MRI-guided middle cerebral artery occlusion technique permits intra-operational monitoring via direct non-invasive simultaneous visualization of the filament, blood flow in the arteries, brain tissue, and hemorrhagic complications. It provides better assessment of MCAO outcomes in individual animals and significant enhancement of MCAO success rate.

Superfine Magnetic Resonance Imaging of the Cerebrovasculature Using Self-Assembled Branched Polyethylene Glycol-Gd Contrast Agent

Magnetic resonance angiography is an attractive method for the visualization of the cerebrovasculature, but small-sized vessels are hard to visualize with the current clinically approved agents. In this study, a polymeric contrast agent for the superfine imaging of the cerebrovasculature is presented. Eight-arm polyethylene glycol with a molecular weight of ≈17 000 Da conjugated with a Gd chelate and fluorescein (F-8-arm PEG-Gd) is used. The relaxivity rate is 9.3 × 10^-3 m^-1 s^-1 , which is threefold higher than that of free Gd chelate. Light scattering analysis reveals that F-8-arm PEG-Gd is formed by self-assembly. When the F-8-arm PEG-Gd is intravenously injected, cerebrovasculature as small as 100 µm in diameter is clearly visualized. However, signals are not enhanced when Gd chelate and Gd chelate-conjugated 8-arm PEG are injected. Furthermore, small vasculature around infarct region in rat stroke model can be visualized. These results suggest that F-8-arm PEG-Gd enhances the MR imaging of cerebrovasculature.

Middle Cerebral Artery Occlusion by an Intraluminal Suture Method

Stroke represents the most common fatal neurological disease especially in highly developed countries. Even today, treatment options are very limited. The development of new therapeutic approaches replies, to a great extent, on experimental rodent models of focal cerebral ischemia. Since ~80% of ischemic strokes occur in the area of middle cerebral artery (MCA), a number of these stroke models are based on this artery. The intraluminal monofilament model of MCA occlusion involves the insertion of a surgical filament inside the external carotid artery and its extension into the internal carotid artery until the tip occludes the source of the MCA-thus arresting blood flow with resultant infarction in the MCA area. This technique can be utilized to model both permanent and transient occlusions. A major advantage of this technique is that it does not require craniectomy, which may affect intracranial pressure and temperature. Although the restored blood flow is unlike the pathophysiology of spontaneous human stroke, it more closely mimics the therapeutic state of mechanical thrombectomy which is increasingly being applied to patients with stroke.

Combination of Emricasan with Ponatinib Synergistically Reduces Ischemia/Reperfusion Injury in Rat Brain Through Simultaneous Prevention of Apoptosis and Necroptosis

Apoptosis and receptor-interacting protein kinase 1/3(RIPK1/3)-mediated necroptosis contribute to the cerebral ischemia/reperfusion (I/R) injury. Emricasan is an inhibitor of caspases in clinical trials for liver diseases while ponatinib could be a potential inhibitor for RIPK1/3. This study aims to investigate the effect of emricasan and/or ponatinib on cerebral I/R injury and the underlying mechanisms. Firstly, we evaluated the status of apoptosis and necroposis in a rat model of cerebral I/R under different conditions, which showed noticeable apoptosis and necroptosis under condition of 2-h ischemia and 24-h reperfusion; next, the preventive or therapeutic effect of emricasan or ponatinib on cerebral I/R injury was tested. Administration of emricasan or ponatinib either before or after ischemia could decrease the neurological deficit score and infarct volume; finally, the combined therapeutic effect of emricasan with ponatinib on I/R injury was examined. Combined application of emricasan and ponatinib could further decrease the I/R injury compared to single application. Emricasan decreased the activities of capase-8/-3 in the I/R-treated brain but not the protein levels of necroptosis-relevant proteins: RIPK1, RIPK3, and mixed lineage kinase domain-like (MLKL), whereas ponatinib suppressed the expressions of these proteins but not the activities of capase-8/-3. Combination of emricasan with ponatinib could suppress both capase-8/-3 and necroptosis-relevant proteins. Based on these observations, we conclude that combination of emricasan with ponatinib could synergistically reduce I/R injury in rat brain through simultaneous prevention of apoptosis and necroptosis. Our findings might lay a basis on extension of the clinical indications for emricasan and ponatinib in treating ischemic stroke.

A Working Module for the Neurovascular Unit in the Sexually Dimorphic Nucleus of the Preoptic Area

The neurovascular unit (NVU) can be conceptualized as a functional entity consisting of neurons, astrocytes, pericytes, and endothelial and smooth muscle cells that operate in concert to affect blood flow to a very circumscribed area. Although we are currently in a "golden era" of bioengineering, there are, as yet, no living NVUs-on-a-chip modules available and the development of a neural chip that would mimic NVUs is a seemingly lofty goal. The sexually dimorphic nucleus of the preoptic area (SDN-POA) is a tiny brain structure (between 0.001~0.007 mm³ in rats) with an assessable biological function (i.e., male sexual behavior). The present effort was undertaken to determine whether there are identifiable NVUs in the SDN-POA by assessing its vasculature relative to its known neural components. First, a thorough and systematic review of thousands of histologic and immunofluorescent images from 201 weanling and adult rats was undertaken to define the characteristics of the vessels supplying the SDN-POA: its primary supply artery/arteriole and capillaries are physically inseparable from their neural elements. A subsequent immunofluorescent study targeting α-smooth muscle actin confirmed the identity of an artery/arteriole supplying the SDN-POA. In reality, the predominant components of the SDN-POA are calbindin D28k-positive neurons that are comingled with tyrosine hydroxylase-positive projections. Finally, a schematic of an SDN-POA NVU is proposed as a working model of the basic building block of the CNS. Such modules could serve the study of neurovascular mechanisms and potentially inform the development of next generation bioengineered neural transplants, i.e., the construct of an NVU neural chip.

A general protocol of ultra-high resolution MR angiography to image the cerebro-vasculature in 6 different rats strains at high field

BACKGROUND

Differences in the cerebro-vasculature among strains as well as individual animals might explain variability in animal models and thus, a non-invasive method tailored to image cerebral vessel of interest with high signal to noise ratio is required.

NEW METHOD

Experimentally, we describe a new general protocol of three-dimensional time-of-flight magnetic resonance angiography to visualize non-invasively the cerebral vasculature in 6 different rat strains. Flow compensated angiograms of Sprague Dawley, Wistar Kyoto, Lister Hooded, Long Evans, Fisher 344 and Spontaneous Hypertensive Rat strains were obtained without the use of contrast agents. At 11.7T using a repetition time of 60ms, an isotropic resolution of up to 62μm was achieved; total imaging time was 98min for a 3D data set.

RESULTS

The visualization of the cerebral arteries was improved by removing extra-cranial vessels prior to the calculation of maximum intensity projection to obtain the angiograms. Ultimately, we demonstrate that the newly implemented method is also suitable to obtain angiograms following middle cerebral artery occlusion, despite the presence of intense vasogenic edema 24h after reperfusion.

COMPARISON WITH EXISTING METHODS

The careful selection of the excitation profile and repetition time at a higher static magnetic field allowed an increase in spatial resolution to reliably detect of the hypothalamic artery, the anterior choroidal artery as well as arterial branches of the peri-amygdoidal complex and the optical nerve in six different rat strains.

CONCLUSIONS

MR angiography without contrast agent can be utilized to study cerebro-vascular abnormalities in various animal models.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A Comparative Study of Variables Influencing Ischemic Injury in the Longa and Koizumi Methods of Intraluminal Filament Middle Cerebral Artery Occlusion in Mice

The intraluminal filament model of middle cerebral artery occlusion (MCAO) in mice and rats has been plagued by inconsistency, owing in part to the multitude of variables requiring control. In this study we investigated the impact of several major variables on survival rate, lesion volume, neurological scores, cerebral blood flow (CBF) and body weight including filament width, time after reperfusion, occlusion time and the choice of surgical method. Using the Koizumi method, we found ischemic injury can be detected as early as 30 min after reperfusion, to a degree that is not statistically different from 24 h post-perfusion, using 2,3,5-Triphenyltetrazolium chloride (TTC) staining. We also found a distinct increase in total lesion volume with increasing occlusion time, with 30–45 min a critical time for the development of large, reproducible lesions. Furthermore, although we found no significant difference in total lesion volume generated by the Koizumi and Longa methods of MCAO, nor were survival rates appreciably different between the two at 4 h after reperfusion, the Longa method produces significantly greater reperfusion. Finally, we found no statistical evidence to support the exclusion of data from animals experiencing a CBF reduction of <70% in the MCA territory following MCAO, using laser-Doppler flowmetry. Instead we suggest the main usefulness of laser-Doppler flowmetry is for guiding filament placement and the identification of subarachnoid haemorrhages and premature reperfusion. In summary, this study provides detailed evaluation of the Koizumi method of intraluminal filament MCAO in mice and a direct comparison to the Longa method.

Considerations for the Optimization of Induced White Matter Injury Preclinical Models

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

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.

Lasting pure-motor deficits after focal posterior internal capsule white-matter infarcts in rats

Small white-matter infarcts of the internal capsule are clinically prevalent but underrepresented among currently available animal models of ischemic stroke. In particular, the assessment of long-term outcome, a primary end point in clinical practice, has been challenging due to mild deficits and the rapid and often complete recovery in most experimental models. We, therefore, sought to develop a focal white-matter infarction model that can mimic the lasting neurologic deficits commonly observed in stroke patients. The potent vasoconstrictor endothelin-1 (n=24) or vehicle (n=9) was stereotactically injected into the internal capsule at one of three antero-posterior levels (1, 2, or 3 mm posterior to bregma) in male Sprague-Dawley rats. Endothelin-injected animals showed highly focal (~1 mm(3)) and reproducible ischemic infarcts, with severe axonal and myelin loss accompanied by cellular infiltration when examined 2 and 4 weeks after injection. Only those rats injected with endothelin-1 at the most posterior location developed robust and pure-motor deficits in adhesive removal, cylinder and foot-fault tests that persisted at 1 month, without detectable sensory impairments. In summary, we present an internal capsule stroke model optimized to produce lasting pure-motor deficits in rats that may be suitable to study neurologic recovery and rehabilitation after white-matter injury.

A novel mouse model of subcortical infarcts with dementia

Subcortical white matter (WM) is a frequent target of ischemic injury and extensive WM lesions are important substrates of vascular cognitive impairment (VCI) in humans. However, ischemic stroke rodent models have been shown to mainly induce cerebral infarcts in the gray matter, while cerebral hypoperfusion models show only WM rarefaction without infarcts. The lack of animal models consistently replicating WM infarct damage may partially explain why many neuroprotective drugs for ischemic stroke or VCI have failed clinically, despite earlier success in preclinical experiments. Here, we report a novel animal model of WM infarct damage with cognitive impairment can be generated by surgical implantation of different devices to the right and left common carotid artery (CCA) in C57BL/6J mice. Implantation of an ameroid constrictor to the right CCA resulted in gradual occlusion of the vessel over 28 d, whereas placement of a microcoil to the left CCA induced ∼50% arterial stenosis. Arterial spin labeling showed a gradual reduction of cerebral blood flow over 28 d post operation. Such reductions were more marked in the right, compared with the left, hemisphere and in subcortical, rather than the cortical, areas. Histopathological analysis showed multiple infarct damage in right subcortical regions, including the corpus callosum, internal capsule, hippocampal fimbria, and caudoputamen, in 81% of mice. Mice displaying such damage performed significantly poorer in locomotor and cognitive tests. The current mouse model replicates the phenotypes of human subcortical VCI, including multiple WM infarcts with motor and cognitive impairment.

Oligodendrogenesis in the normal and pathological central nervous system

Oligodendrocytes (OLGs) are generated late in development and myelination is thus a tardive event in the brain developmental process. It is however maintained whole life long at lower rate, and myelin sheath is crucial for proper signal transmission and neuronal survival. Unfortunately, OLGs present a high susceptibility to oxidative stress, thus demyelination often takes place secondary to diverse brain lesions or pathologies. OLGs can also be the target of immune attacks, leading to primary demyelination lesions. Following oligodendrocytic death, spontaneous remyelination may occur to a certain extent. In this review, we will mainly focus on the adult brain and on the two main sources of progenitor cells that contribute to oligodendrogenesis: parenchymal oligodendrocyte precursor cells (OPCs) and subventricular zone (SVZ)-derived progenitors. We will shortly come back on the main steps of oligodendrogenesis in the postnatal and adult brain, and summarize the key factors involved in the determination of oligodendrocytic fate. We will then shed light on the main causes of demyelination in the adult brain and present the animal models that have been developed to get insight on the demyelination/remyelination process. Finally, we will synthetize the results of studies searching for factors able to modulate spontaneous myelin repair.

A microsurgical procedure for middle cerebral artery occlusion by intraluminal monofilament insertion technique in the rat: a special emphasis on the methodology

Introduction

Although there are many experimental studies describing the methodology of the middle cerebral artery occlusion (MCAO) in the literature, only limited data on these distinct anatomical structures and the details of the surgical procedure in a step by step manner. The aim of the present study simply is to examine the surgical anatomy of MCAO model and its modifications in the rat.

Materials and methods

Forty Sprague-Dawley rats were used; 20 during the training phase and 20 for the main study. The monofilament sutures were prepared as described in the literature. All surgical steps of the study were performed under the operating microscope, including insertion of monofilament into middle cerebral artery through the internal carotid artery.

Results

After an extensive training period, we lost two rats in four weeks. The effects of MCAO were confirmed by the evidence of severe motor deficit during the recovery period, and histopathological findings of infarction were proved in all 18 surviving rats.

Conclusion

In this study, a microsurgical guideline of the MCAO model in the rat is provided with the detailed description of all steps of the intraluminal monofilament insertion method with related figures.

Post-hypothermia fever is associated with increased mortality after out-of-hospital cardiac arrest

OBJECTIVE

Post-cardiac arrest fever has been associated with adverse outcome before implementation of therapeutic hypothermia (TH), however the prognostic implications of post-hypothermia fever (PHF) in the era of modern post-resuscitation care including TH has not been thoroughly investigated. The aim of the study was to assess the prognostic implication of PHF in a large consecutive cohort of comatose survivors after out-of-hospital cardiac arrest (OHCA) treated with TH.

METHODS

In the period 2004-2010, a total of 270 patients resuscitated after OHCA and surviving a 24-h protocol of TH with a target temperature of 32-34°C were included. The population was stratified in two groups by median peak temperature (≥38.5°C) within 36h after rewarming: PHF and no-PHF. Primary endpoint was 30-days mortality and secondary endpoint was neurological outcome assessed by Cerebral Performance Category (CPC) at hospital discharge.

RESULTS

PHF (≥38.5°C) was associated with a 36% 30-days mortality rate compared to 22% in patients without PHF, plog-rank=0.02, corresponding to an adjusted hazard rate (HR) of 1.8 (95% CI: 1.1-2.7), p=0.02). The maximum temperature (HR=2.0 per °C above 36.5°C (95% CI: 1.4-3.0), p=0.0005) and the duration of PHF (HR=1.6 per 8h (95% CI: 1.3-2.0), p<0.0001) were also independent predictors of 30-days mortality in multivariable models. Good neurological outcome (CPC1-2) versus unfavourable outcome (CPC3-5) at hospital discharge was found in 61% vs. 39% in the PHF group compared to 75% vs. 25% in the No PHF group, p=0.02.

CONCLUSIONS

Post-hypothermia fever ≥38.5°C is associated with increased 30-days mortality, even after controlling for potential confounding factors. Avoidance of PHF as a therapeutic target should be evaluated in prospective randomized trials.

Hyperbaric oxygen and hyperbaric air treatment result in comparable neuronal death reduction and improved behavioral outcome after transient forebrain ischemia in the gerbil

Anoxic brain injury resulting from cardiac arrest is responsible for approximately two-thirds of deaths. Recent evidence suggests that increased oxygen delivered to the brain after cardiac arrest may be an important factor in preventing neuronal damage, resulting in an interest in hyperbaric oxygen (HBO) therapy. Interestingly, increased oxygen supply may be also reached by application of normobaric oxygen (NBO) or hyperbaric air (HBA). However, previous research also showed that the beneficial effect of hyperbaric treatment may not directly result from increased oxygen supply, leading to the conclusion that the mechanism of hyperbaric prevention of brain damage is not well understood. The aim of our study was to compare the effects of HBO, HBA and NBO treatment on gerbil brain condition after transient forebrain ischemia, serving as a model of cardiac arrest. Thereby, we investigated the effects of repetitive HBO, HBA and NBO treatment on hippocampal CA1 neuronal survival, brain temperature and gerbils behavior (the nest building), depending on the time of initiation of the therapy (1, 3 and 6 h after ischemia). HBO and HBA applied 1, 3 and 6 h after ischemia significantly increased neuronal survival and behavioral performance and abolished the ischemia-evoked brain temperature increase. NBO treatment was most effective when applied 1 h after ischemia; later application had a weak or no protective effect. The results show that HBO and HBA applied between 1 and 6 h after ischemia prevent ischemia-evoked neuronal damage, which may be due to the inhibition of brain temperature increase, as a result of the applied rise in ambient pressure, and just not due to the oxygen per se. This perspective is supported by the finding that NBO treatment was less effective than HBO or HBA therapy. The results presented in this paper may pave the way for future experimental studies dealing with pressure and temperature regulation.

Low oral doses of bisphenol A increase volume of the sexually dimorphic nucleus of the preoptic area in male, but not female, rats at postnatal day 21

Perinatal treatment with relatively high doses of bisphenol A (BPA) appears to have little effect on volume of the rodent sexually dimorphic nucleus of the preoptic area (SDN-POA). However, doses more relevant to human exposures have not been examined. Here, effects of pre- and post-natal treatment with low BPA doses on SDN-POA volume of postnatal day (PND) 21 Sprague-Dawley rats were evaluated. Pregnant rats were orally gavaged with vehicle, 2.5 or 25.0 μg/kg BPA, or 5.0 or 10.0 μg/kg ethinyl estradiol (EE₂) on gestational days 6-21. Beginning on the day after birth, offspring were orally treated with the same dose their dam had received. On PND 21, offspring (n=10-15/sex/group; 1/sex/litter) were perfused and volume evaluation was conducted blind to treatment. SDN-POA outline was delineated using calbindin D28K immunoreactivity. Pairwise comparisons of the significant treatment by sex interaction indicated that neither BPA dose affected female volume. However, females treated with 5.0 or 10.0 μg/kg EE₂ exhibited volumes that were larger than same-sex controls, respectively (p<0.001). Males treated with either BPA dose or 10.0 μg/kg/day EE₂ had larger volumes than same-sex controls (p<0.006). These data indicate that BPA can have sex-specific effects on SDN-POA volume and that these effects manifest as larger volumes in males. Sensitivity of the methodology as well as the treatment paradigm was confirmed by the expected EE₂-induced increase in female volume. These treatment effects might lead to organizational changes within sexually dimorphic neuroendocrine pathways which, if persistent, could theoretically alter adult reproductive physiology and socio-sexual behavior in rats.

Models that matter: white matter stroke models

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

Mild-to-moderate neurogenic pyrexia in acute cerebral infarction

BACKGROUND

Pyrexia is often associated with unfavorable stroke outcomes. However, limited information is available on the relationship between the causes of poststroke hyperthermia and stroke prognosis, especially for mild-to-moderate neurogenic pyrexia in acute cerebral infarction.

AIMS

To compare the differences in the clinical features and characteristics of pyrexia as well as its prognosis among acute cerebral infarction patients with mild-to-moderate neurogenic pyrexia, with infectious pyrexia, and without pyrexia. The focus was on mild-to-moderate neurogenic pyrexia.

METHODS

A total of 709 patients with acute cerebral infarction were prospectively recruited and their clinical data were analyzed.

RESULTS

No significant difference was detected in age, gender, history of smoking, hypertension, or diabetes among the 3 groups (p > 0.05). Patients with mild-to-moderate neurogenic pyrexia and those with infectious pyrexia had higher baseline National Institutes of Health Stroke Scale (NIHSS) scores (15.1 ± 6.7, p = 0.003; 14.3 ± 8.1, p = 0.002, respectively), lower 3-month Barthel index (BI) values (64.2 ± 40.7, p < 0.001; 61.9 ± 49.3, p < 0.001, respectively) and higher 3-month mortality rates (13%, p = 0.026; 16%, p < 0.001, respectively) than patients without pyrexia (NIHSS score 11.4 ± 7.9; BI 82.6 ± 39.8, and mortality rate 6%, respectively). No difference existed in these parameters between the 2 pyrexia groups (p > 0.05), but mild-to-moderate neurogenic pyrexia had an earlier onset and a shorter duration than infectious pyrexia (p < 0.001).

CONCLUSIONS

Acute cerebral infarction patients with mild-to-moderate neurogenic pyrexia had a similar prognosis compared to those with infectious pyrexia. Mild-to-moderate neurogenic pyrexia is possibly associated with stroke severity.

Too cold may not be so cool: spontaneous hypothermia as a marker of poor outcome after cardiac arrest

In a recent issue of Critical Care, den Hartog and colleagues show an association between spontaneous hypothermia, defined by an admission body temperature <35°C, and poor outcome in patients with coma after cardiac arrest (CA) treated with therapeutic hypothermia (TH). Given that TH alters neurological prognostication, studies aiming to identify early markers of injury severity and outcome are welcome, since they may contribute overall to optimize the management of comatose CA patients. This study provides an important message to clinicians involved in post-resuscitation care and raises important questions that need to be taken into account in future studies.

An experimental model of focal ischemia using an internal carotid artery approach

Animal models of cerebral ischemia represent an important contribution to both our understanding of stroke mechanism and the development of new therapies. The technique of MCAO (middle cerebral artery occlusion) via ECA (external carotid artery) occlusion is widely utilized. Disruption of the ECA and its branches leads to impaired mastication and oral intake, post-surgical body weight loss, and poor neurological recovery which can possibly confound one's interpretation of rats' neurological outcome. Here, we developed a novel modified technique for MCAO without ligation or coagulation of the ECA and its branches using an approach via the internal carotid artery (ICA). In our modified technique, we perform an additional fixation of the filament in the ICA which improves the stability of the model and increases the homogeneity in stroke size. Compared with the original MCAO technique via the ECA, our modified technique via the ICA demonstrated decreased variability in the percent infarcted volume and brain edema, as well as a decreased mortality. Additionally, we observed that with our modified technique, rats gained more weight after surgery and there was less initial weight loss after the surgical preparation. Our new approach may serve as an effective model for stroke, and may lead to a better understanding of stoke pathophysiology and to the future development of new drugs and other neuroprotective agents.

Different strokes for different folks: the rich diversity of animal models of focal cerebral ischemia

No single animal model is able to encompass all of the variables known to affect human ischemic stroke. This review highlights the major strengths and weaknesses of the most commonly used animal models of acute ischemic stroke in the context of matching model and experimental aim. Particular emphasis is placed on the relationships between outcome and underlying vascular variability, physiologic control, and use of models of comorbidity. The aim is to provide, for novice and expert alike, an overview of the key controllable determinants of experimental stroke outcome to help ensure the most effective application of animal models to translational research.

Neuronal precursor cell proliferation in the hippocampus after transient cerebral ischemia: a comparative study of two rat strains using stereological tools

Background

We are currently investigating microglial activation and neuronal precursor cell (NPC) proliferation after transient middle cerebral artery occlusion (tMCAo) in rats. This study aimed: (1) to investigate differences in hippocampal NPC proliferation in outbred male spontaneously hypertensive rats (SHRs) and Sprague-Dawley rats (SDs) one week after tMCAo; (2) to present the practical use of the optical fractionator and 2D nucleator in stereological brain tissue analyses; and (3) to report our experiences with an intraluminal tMCAo model where the occluding filament is advanced 22 mm beyond the carotid bifurcation and the common carotid artery is clamped during tMCAo.

Methods

Twenty-three SDs and twenty SHRs were randomized into four groups subjected to 90 minutes tMCAo or sham. BrdU (50 mg/kg) was administered intraperitoneally twice daily on Day 4 to 7 after surgery. On Day 8 all animals were euthanized. NeuN-stained tissue sections were used for brain and infarct volume estimation with the 2D nucleator and Cavalieri principle. Brains were studied for the presence of activated microglia (ED-1) and hippocampal BrdU incorporation using the optical fractionator.

Results

We found no significant difference or increase in post-ischemic NPC proliferation between the two strains. However, the response to remote ischemia may differ between SDs and SHRs. In three animals increased post-stroke NPC proliferation was associated with hippocampal ischemic injury. The mean infarct volume was 89.2 ± 76.1 mm³ in SHRs and 16.9 ± 22.7 mm³ in SDs (p < 0.005). Eight out of eleven SHRs had ischemic neocortical damage in contrast to only one out of 12 SDs. We observed involvement of the anterior choroidal and hypothalamic arteries in several animals from both strains and the anterior cerebral artery in two SHRs.

Conclusions

We found no evidence of an early hippocampal NPC proliferation one week after tMCAo in both strains. Infarction within the anterior choroidal artery could induce hippocampal ischemia and increase NPC proliferation profoundly. NPC proliferation was not aggravated by the presence of activated microglia. Intraluminal tMCAo in SHRs gave a more reliable infarct with neocortical involvement, but affected territories supplied by the anterior cerebral, anterior choroidal and hypothalamic arteries.

Hyperthermia Exacerbates Ischaemic Brain Injury

Hyperthermia frequently occurs in stroke patients. Hyperthermia negatively correlates with clinical outcome and adversely effects treatment regiments otherwise successful under normothermic conditions. Preclinical studies also demonstrate that hyperthermia converts salvageable penumbra to ischaemic infarct. The present article reviews the knowledge accumulated from both clinical and preclinical studies about hyperthermia and ischaemic brain injury, examines current treatment strategies and discusses future research directions.

Novel microcatheters for selective intra-arterial injection of fluid in the rat brain

BACKGROUND AND PURPOSE

The internal carotid artery (ICA) in the rat has a single extracranial branch, which supplies the muscles of mastication. The rat ICA also has multiple intracranial branches including (from proximal to distal): multiple small perforating arteries which supply the hypothalamus and the anterior choroidal artery which supplies the choroid plexus and part of the basal ganglia. At the ICA terminus, the vessel bifurcates into the anterior and middle cerebral arteries. The purpose of this study was to demonstrate selective injection of ICA branches in the rat.

MATERIALS AND METHODS

Microcatheters (mucath1 and mucath2) were fabricated by plugging the tip of 169-mum outer diameter polyimide tubing and perforating the sidewalls. A 450-mum polydimethyl-siloxane cylinder was affixed to the distal tip of mucath2 but not mucath1. We evaluated the territory of mucath1 injection ex vivo using magnetization-prepared rapid acquisition of gradient echo MR imaging of brain specimens injected at necropsy. Territories of mucath1 and mucath2 injection were evaluated in vivo with dynamic susceptibility-weighted contrast-enhanced MR imaging. The territory of mucath2 also was evaluated in vivo with fused static microPET/T1 MR images performed after [(18)F] fluorodeoxyglucose ((18)FDG) injection. We evaluated additional catheterized and injected animals at 48 hours using physical examination, T2 MR images, and postmortem brain histologic specimens.

RESULTS

Gadolinium-diethylene-triamine pentaacetic acid (Gd-DTPA) and (18)FDG injected through mucath1 selectively opacified the ipsilateral cerebral hemisphere, with no contralateral opacification. Gd-DTPA injected through mucath2 selectively opacified the territories of the hypothalamic perforating arteries, and anterior choroidal artery. There was no iatrogenic complication 48 hours after 20- to 25-minute injections performed with mucath1 or mucath2.

CONCLUSIONS

We have developed 2 microcatheters which can be placed in the ICA for selective injection of its branches. One microcatheter selectively injects the ipsilateral cerebral hemisphere. The other selectively injects only the hypothalamus and lateral thalamus.

Identification of ischemic regions in a rat model of stroke

BACKGROUND

Investigations following stroke first of all require information about the spatio-temporal dimension of the ischemic core as well as of perilesional and remote affected tissue. Here we systematically evaluated regions differently impaired by focal ischemia.

METHODOLOGY/PRINCIPAL FINDINGS

Wistar rats underwent a transient 30 or 120 min suture-occlusion of the middle cerebral artery (MCAO) followed by various reperfusion times (2 h, 1 d, 7 d, 30 d) or a permanent MCAO (1 d survival). Brains were characterized by TTC, thionine, and immunohistochemistry using MAP2, HSP72, and HSP27. TTC staining reliably identifies the infarct core at 1 d of reperfusion after 30 min MCAO and at all investigated times following 120 min and permanent MCAO. Nissl histology denotes the infarct core from 2 h up to 30 d after transient as well as permanent MCAO. Absent and attenuated MAP2 staining clearly identifies the infarct core and perilesional affected regions at all investigated times, respectively. HSP72 denotes perilesional areas in a limited post-ischemic time (1 d). HSP27 detects perilesional and remote impaired tissue from post-ischemic day 1 on. Furthermore a simultaneous expression of HSP72 and HSP27 in perilesional neurons was revealed.

CONCLUSIONS/SIGNIFICANCE

TTC and Nissl staining can be applied to designate the infarct core. MAP2, HSP72, and HSP27 are excellent markers not only to identify perilesional and remote areas but also to discriminate affected neuronal and glial populations. Moreover markers vary in their confinement to different reperfusion times. The extent and consistency of infarcts increase with prolonged occlusion of the MCA. Therefore interindividual infarct dimension should be precisely assessed by the combined use of different markers as described in this study.

Ischemic stroke in mice and rats

Ischemic stroke occurs most often in the territory of the middle cerebral artery (MCA) in humans. Since its description in rats more than two decades ago, the minimally invasive intraluminal suture occlusion of MCA is an increasingly used model of stroke in both rats and mice due to its ease of inducing ischemia and achieving reperfusion under well-controlled conditions. This method can be used under the guidance of laser-Doppler flowmetry to ascertain the magnitude of occlusion or reperfusion and to decrease the rate of subarachnoid hemorrhage. Ninety minutes of transient ischemia in the territory of MCA results in substantial and reproducible ischemic lesions in both the striatum and the cortex, with characteristics of lesion core and penumbra. Thus, this model is applicable to neuroprotective drug studies, including ischemic brain lesion evaluation (either in vivo with magnetic resonance imaging or post-mortem with brain tissue staining) and neurological status (motor deficits simply assessed by a six-point neurological score scale) as outcome parameters.

Severe hyperthermia caused by four-vessel occlusion of main cerebral arteries

We present the case of a comatose patient with acute large infarction of posterior cerebral and cerebellar areas and severe hyperthermia (max. 40.4 degrees C). Angiography demonstrated four-vessel occlusion of the main cerebral arteries, suggesting the possibility that both internal carotid and left vertebral arteries were already occluded and he became unconscious following additional occlusion of the right vertebral artery. Autopsy findings revealed bilateral ischemic damage of the hypothalamus in addition to the above infarct areas. Sudden ischemic involvement of both hypothalamic regions may have caused the extremely high fever in this case.

Therapeutic hypothermia in experimental models of focal and global cerebral ischemia and intracerebral hemorrhage

Experimental evidence shows that therapeutic hypothermia (TH) protects the brain from cerebral injury in multiple ways. In different models of focal and global cerebral ischemia, mild-to-moderate hypothermia reduces mortality and neuronal injury and improves neurological outcome. In models of experimental intracerebral hemorrhage (ICH), TH reduces edema formation but does not show consistent benefi cial effects on functional outcome parameters. However, the number of studies of hypothermia on ICH is still limited. TH is most effective when applied before or during the ischemic event, and its neuroprotective properties vary according to species, strains and the model of ischemia used. Intrinsic changes in body and brain temperature frequently occur in experimental models of focal and global cerebral ischemia, and may have infl uenced studies on other neuroprotectants. This might be one explanation for the failure of a large amount of translational clinical neuroprotective trials. Hypothermia is the only neuroprotective therapeutic agent for cerebral ischemia that has successfully managed the transfer from bench to bedside, and it is an approved therapy for patients after cardiac arrest and children with hypoxic-ischemic encephalopathy. However, the implementation of hypothermia in the treatment of stroke patients is still far from routine clinical practice. In this article, the authors describe the development of TH in different models of focal and global cerebral ischemia, point out why hypothermia is so efficient in experimental cerebral ischemia, explain why temperature regulation is essential for further neuroprotective studies and discuss why TH for acute ischemic stroke still remains a promising but controversial therapeutic option.

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 rat model of cerebral infarction based on the injury of vascular endothelial cell]

OBJECTIVE

A new rat model of cerebral infarction was developed to elucidate the contribution of vascular endothelial cell during focal cerebral infarction formation.

METHODS

Forty-eight Sprague-Dawley (SD) rats were randomly divided into the model group, sham operation group, and control group for indexes observation of triphenyltetrazolium chloride (TTC) dyeing, neurological deficit, plasma tissue-type plasminogen activator (tPA) activity, plasminogen activator inhibitor (PAI) activity, thromboxane B(2) (TXB(2)) content, and 6-keto-prostaglandin (6-keto-PGF(1alpha)) content.

RESULTS

(1) The highest neurological score appeared at 6 h after operation, descending significantly at sequential time. (2) Using TTC dyeing and optical microscope technique, pathological changes in brains were observed. (3) Compared with control group and sham operation groups, there was a decrease in tPA activity of model rats at the initial 12 h after injection of sodium laurate (P < 0.05), PAI activity decreased markedly in the model group at 24 h after injection of sodium laurate. (4) In plasma TXB(2) concentration reached the highest level compared at 6 h after injection of sodium laurate, but there were not obvious differences in plasma 6-keto-PGF(1alpha) concentration among all groups (P > 0.05).

CONCLUSION

Focal cerebral infarction in rats could be induced by some sodium laurate, showing ischemic cerebrum necrosis, function disorder of vascular endothelium-platelet, fibrinolysis abnormality. This model could play an important role in researching the contribution of vascular endothelial cell during cerebral infarction development, preventing and curing by traditional Chinese medicine.

Proximal occlusion of the middle cerebral artery in C57Black6 mice: relationship of patency of the posterior communicating artery, infarct evolution, and animal survival

Object. The intraluminal suture model for focal cerebral ischemia is increasingly used, but not without problems. It causes hypothalamic injury, subarachnoid hemorrhage, and inadvertent premature reperfusion. The patency of the posterior communicating artery (PCoA) potentially affects the size of the infarct. In addition, survival at 1 week is unstable. The authors operated on C57Black6 mice to produce proximal middle cerebral artery occlusion (MCAO) so that drawbacks with the suture model could be circumvented.

Methods. The MCA segment just proximal to the olfactory branch was occluded either permanently or temporarily. After 1 hour of MCAO the infarct volume was significantly smaller than that found after 2 hours or in instances of permanent MCAO. The differences were assessed at 24 hours and 7 days after surgery (p < 0.05 and p < 0.001, respectively). The patency of the PCoA, as visualized using carbon black solution, did not correlate with the infarct size. Neurologically, the 1- and 2-hour MCAO groups displayed significantly less severe deficits than the permanent MCAO group on Days 1, 4, and 7 (p < 0.005 and p < 0.01, respectively). Although the infarct size, neurological deficits, and body weight loss were more severe in the permanent MCAO group, the survival rate at Day 7 was 80%.

Conclusions. This model provides not only a robust infarct size (which is not affected by the patency of the PCoA), but also a better survival rate.

Hypothermic protection in rat focal ischemia models: strain differences and relevance to "reperfusion injury"

Hypothermic protection was compared in Long-Evans and spontaneously hypertensive rat (SHR) strains using transient focal ischemia, and in Wistar and SHR strains using permanent focal ischemia. Focal ischemia was produced by distal surgical occlusion of the middle cerebral artery and tandem occlusion of the ipsilateral common carotid artery (MCA/CCAO). Moderate hypothermia of 2 hours' duration was produced by systemic cooling to 32 degrees C, with further cooling of the brain achieved by reducing to 30 degrees C the temperature of the saline drip superfusing the exposed occlusion site. Infarct volume was determined from serial hematoxylin and eosin-stained frozen sections obtained routinely at 24 hours, or in some cases after 3 days' survival. In the SHR, moderate hypothermia was only effective when initiated before recirculation after a 90-minute occlusion period. In contrast, the same intervention was strikingly effective in the Long-Evans rat even when initiated after as long as 30-minute reperfusion after a 3-hour occlusion. This magnitude and duration of cooling was not protective in permanent MCA/CCAO in the SHR, but such transient hypothermia did effectively reduce infarct volume after permanent occlusions in Wistar rats. These results show striking differences in the temporal window for hypothermic protection among rat focal ischemia models. As expected, "reperfusion injury" in the Long-Evans strain is particularly responsive to delayed cooling. The finding that the SHR can be protected by hypothermia initiated immediately before recirculation suggests a rapidly evolving component of injury occurs subsequent to reperfusion in this model as well. Hypothermic protection after permanent occlusion in Wistar rats identifies a transient, temperature-sensitive phase of infarct evolution that is not evident in the unreperfused SHR. These observations confirm that distinct mechanisms can underlie the temporal progression of injury in rat stroke models, and emphasize the critical importance of considering model and strain differences in extrapolating results of hypothermic protection studies in animals to the design of interventions in clinical stroke.

The macrosphere model: evaluation of a new stroke model for permanent middle cerebral artery occlusion in rats

BACKGROUND AND PURPOSE

The suture middle cerebral artery occlusion (MCAO) model is widely used for the simulation of focal cerebral ischemia in rats. This technique causes hypothalamic injury resulting in hyperthermia, which can worsen outcome and obscure neuroprotective effects. Herein, we introduce a new MCAO model that avoids these disadvantages.

METHODS

Permanent MCAO was performed by intraarterial embolization using six TiO(2) macrospheres (0.3-0.4 mm in diameter) or by the suture occlusion technique. Body temperature was monitored, functional and histologic outcome was assessed after 24 h. Additional 16 rats were subjected to macrosphere or suture MCAO. Lesion progression was evaluated using magnetic resonance imaging (MRI).

RESULTS

The animals subjected to suture MCAO developed hyperthermia (>39 degrees C), while the temperature remained normal in the macrosphere MCAO group. Infarct size, functional outcome and model failure rate were not significantly different between the groups. Lesion size on MRI increased within the first 90 min and remained unchanged thereafter in both groups.

CONCLUSIONS

The macrosphere MCAO model provides reproducible focal cerebral ischemia, similar to the established suture technique, but avoids hypothalamic damage and hyperthermia. This model, therefore, may be more appropriate for the preclinical evaluation of neuroprotective therapies and can also be used for stroke studies under difficult conditions, e.g., in awake animals or inside the MRI scanner.

New method for the quantitative assessment of axonal damage in focal cerebral ischemia

Quantification of damage in both grey and white matter is required for comprehensive assessment of neuroprotective drug efficacy. Although methods for quantification of neuronal perikaryal damage after ischemia are well established, assessment of axonal damage has been limited. This article describes a new method for quantitation of axonal injury after middle cerebral artery (MCA) occlusion in rats and its application to the study of the antioxidant ebselen. The methodology is based on immunohistochemical detection of amyloid precursor protein (APP) accumulation in deformed, swollen axons in zones of ischemia. Sixty-five axon-rich sites throughout the MCA territory are assessed for the presence (scored 1) or absence (scored 0) of accumulated APP in axonal swellings. Scores for individual sites are summated in predefined neuroanatomic regions (e.g. corpus callosum), stereotaxic levels, or for a total hemisphere APP score. Both intra-rater and inter-rater reproducibility were high (r = 0.87 and 0.80, respectively). Ebselen (1 mg kg(-1) hr(-1), intravenously) significantly reduced the volume of neuronal perikaryal damage (24%, P < 0.01) and axonal damage (total APP score reduced from 27 [23.9 to 35.1, 95% CI] to 21.5 [18.2 to 23.3], P = 0.002 with ebselen treatment). In conclusion, a robust and generally applicable method is described for assessing pathologic features in myelinated fiber tracts that is sensitive for detection of drug effects on axonal damage.

Alteration of second messengers during acute cerebral ischemia - adenylate cyclase, cyclic AMP-dependent protein kinase, and cyclic AMP response element binding protein

A variety of neurotransmitters and other chemical substances are released into the extracellular space in the brain in response to acute ischemic stress, and the biological actions of these substances are exclusively mediated by receptor-linked second messenger systems. One of the well-known second messenger systems is adenylate cyclase, which catalyzes the generation of cyclic AMP, triggering the activation of cyclic AMP-dependent protein kinase (PKA). PKA controls a number of cellular functions by phosphorylating many substrates, including an important DNA-binding transcription factor, cyclic AMP response element binding protein (CREB). CREB has recently been shown to play an important role in many physiological and pathological conditions, including synaptic plasticity and neuroprotection against various insults, and to constitute a convergence point for many signaling cascades. The autoradiographic method developed in our laboratory enables us to simultaneously quantify alterations of the second messenger system and local cerebral blood flow (lCBF). Adenylate cyclase is diffusely activated in the initial phase of acute ischemia (< or = 30 min), and its activity gradually decreases in the late phase of ischemia (2-6 h). The areas of reduced adenylate cyclase activity strictly coincide with infarct areas, which later become visible. The binding activity of PKA to cyclic AMP, which reflects the functional integrity of the enzyme, is rapidly suppressed during the initial phase of ischemia in the ischemic core, especially in vulnerable regions, such as the CA1 of the hippocampus, and it continues to decline. By contrast, PKA binding activity remains enhanced in the peri-ischemia area. These changes occur in a clearly lCBF-dependent manner. CREB phosphorylation at a serine residue, Ser(133), which suggests the activation of CREB-mediated transcription of genes containing a CRE motif in the nuclei, remains enhanced in the peri-ischemia area, which is spared of infarct damage. On the other hand, CREB phosphorylation at Ser133 rapidly diminishes in the ischemic core before the histological damage becomes manifest. The Ca2+ influx during membrane depolarization contributes to CREB phosphorylation in the initial phase of post-ischemic recirculation, while PKA activation and other signaling elements seem to be responsible in the later phase. These findings suggest that derangement of cyclic AMP-related intracellular signal transduction closely parallels ischemic neuronal damage and that persistent enhancement of this signaling pathway is important for neuronal survival in acute cerebral ischemia.

Neuroprotection in ischemia-reperfusion injury: an antiinflammatory approach using a novel broad-spectrum chemokine inhibitor

Cerebral ischemia-reperfusion injury is associated with a developing inflammatory response with pathologic contributions from vascular leukocytes and endogenous microglia. Signaling chemokines orchestrate the communication between the different inflammatory cell types and the damaged tissue leading to cellular chemotaxis and lesion occupation. Several therapies aimed at preventing this inflammatory response have demonstrated neuroprotective efficacy in experimental models of stroke, but to date, few investigators have used the chemokines as potential therapeutic targets. In the current study, the authors investigate the neuroprotective action of NR58-3.14.3, a novel broad-spectrum inhibitor of chemokine function (both CXC and CC types), in a rat model of cerebral ischemia-reperfusion injury. Rats were subjected to 90 minutes of focal ischemia by the filament method followed by 72 hours of reperfusion. Both the lesion volume, measured by serial magnetic resonance imaging, and the neurologic function were assessed daily. Intravenous NR58-3.14.3 was administered, 2 mg/kg bolus followed by 0.5 mg/kg hour constant infusion for the entire 72-hour period. At 72 hours, the cerebral leukocytic infiltrate, tumor necrosis factor-alpha (TNF-alpha), and interleukin-8 (IL-8)-like cytokines were analyzed by quantitative immunofluorescence. NR58-3.14.3 significantly reduced the lesion volume by up to 50% at 24, 48, and 72 hours post-middle cerebral artery occlusion, which was associated with a marked functional improvement to 48 hours. In NR58-3.14.3-treated rats, the number of infiltrating granulocytes and macrophages within perilesional regions were reduced, but there were no detectable differences in inflammatory cell numbers within core ischemic areas. The authors reported increased expression of the cytokines, TNF-alpha, and IL-8-like cytokines within the ischemic lesion, but no differences between the NR58-3.14.3-treated rats and controls were reported. Although chemokines can have pro- or antiinflammatory action, these data suggest the overall effect of chemokine up-regulation and expression in ischemia-reperfusion injury is detrimental to outcome.

Definition of the anterior choroidal artery territory in rats using intraluminal occluding technique

This manuscript delineates the territory of the anterior choroidal artery (AChA) in rats, as defined by the induction of an AChA infarction. By advancing a 0.24-mm surgical suture up the internal carotid artery (ICA) to a point 0.5-2 mm proximal to the middle cerebral artery (MCA) origin, the AChA could be occluded and a reliable AChA distribution infarction was produced in 62% (23/37) of animals. The infarct volume, as defined by TTC staining, was 55+/-7 mm(3). Maps of the infarction, generated by measuring the entire area of overlapping coronal slices, demonstrated that the internal capsule was always damaged. Other areas that might be affected included the hippocampus, thalamus, amygdaloid complex, piriform cortex, dorsal caudatoputamen, and lateral ventricular wall. Positioning the coated suture proximal to the AChA produced a much smaller infarct involving the medial and lateral hypothalamus, preoptic region, optic chiasm, and marginal region of the internal capsule near to the lateral hypothalamus exempt from AChA territory damage. A causative relationship between AChA occlusion and a deep cerebral infarct centered on the internal capsule was further established by: (1) identifying the AChA on the non-ischemic side with colored silicone perfusion, and subsequent similar delineation on the ischemic side, and (2) delineating infarction in the silicone perfused AChA region using hematoxylin and eosin staining and the TUNEL method. The AChA usually originated from the ICA (91% of cases), 1.75+/-0.12 mm proximal to the MCA bifurcation. Approximately 27% of the AChAs had periamygdaloid branch(es) on its initial segment.

Postischemic temperature as a modulator of the stress response in brain: dissociation of heat shock protein 72 induction from ischemic tolerance after bilateral carotid artery occlusion in the gerbil

Brief ischemia induces tolerance to subsequent more severe insults, and induction of the 70 kDa heat shock/stress protein, hsp72, has been suggested to play a role. This study tested the requirement for hsp72 expression in a gerbil tolerance model in which postischemic temperature was varied to modulate the level of hsp72 induction. Gerbils were subjected to 2 min bilateral common carotid artery occlusion and kept under halothane anesthesia for 90 min, during which rectal temperature was either maintained at 37 degrees C (normothermic, NT) or elevated to 39.5 degrees C (hyperthermic, HT) during 15-60 min recirculation. Hsp72 mRNA expression was determined by in situ hybridization with a (35)S-labeled oligonucleotide probe at 3, 24 and 48 h. Separate groups were subjected to a test challenge of 5 min ischemia 48 h after the priming insult, and CA1 neuron counts were obtained at 1 week. Significant protection was observed in both NT and HT groups. However, while 90% of hippocampi from NT animals showed detectable protection of CA1 neurons, less than half showed detectable hsp72 mRNA induction. These results indicate that, within the limits of experimental detection, hsp72 expression is not required for induction of ischemic tolerance.