A blinded randomized assessment of laser Doppler flowmetry efficacy in standardizing outcome from intraluminal filament MCAO in the rat

High-density cortical µECoG arrays concurrently track spreading depolarizations and long-term evolution of stroke in awake rats

Spreading depolarizations (SDs) are widely recognized as a major contributor to the progression of tissue damage from ischemic stroke even if blood flow can be restored. They are characterized by negative intracortical waveforms of up to -20 mV, propagation velocities of 3 - 6 mm/min, and massive disturbance of membrane ion homeostasis. High-density, micro-electrocorticographic (μECoG) epidural electrodes and custom, DC-coupled, multiplexed amplifiers, were used to continuously characterize and monitor SD and µECoG cortical signal evolution in awake, moving rats over days. This highly innovative approach can define these events over a large brain surface area (~ 3.4 × 3.4 mm), extending across the boundaries of the stroke, and offers sufficient electrode density (60 contacts total per array for a density of 5.7 electrodes / mm2) to measure and determine the origin of SDs in relation to the infarct boundaries. In addition, spontaneous ECoG activity can simultaneously be detected to further define cortical infarct regions. This technology allows us to understand dynamic stroke evolution and provides immediate cortical functional activity over days. Further translational development of this approach may facilitate improved treatment options for acute stroke patients.

Head Down Tilt 15° in Acute Ischemic Stroke with Poor Collaterals: A Randomized Preclinical Trial

Cerebral collaterals are recruited after arterial occlusion with a protective effect on tissue outcome in acute ischemic stroke. Head down tilt 15° (HDT15) is a simple, low cost and accessible procedure that could be applied as an emergency treatment, before recanalization therapies, with the aim to increase cerebral collateral flow. Spontaneously hypertensive rats have been shown to display anatomical differences in morphology and function of cerebral collaterals, compared to other rat strains, resulting in an overall poor collateral circulation. We investigate the efficacy and safety of HDT15 in spontaneously hypertensive (SHR) rats, which were considered as an animal stroke model with poor collaterals. Cerebral ischemia was induced by 90 minute endovascular occlusion of the middle cerebral artery (MCA). SHR rats were randomized to HDT15 or flat position (n = 19). HDT15 was applied 30 minutes after occlusion and lasted 60 minutes, until reperfusion. HDT15 application increased cerebral perfusion (+16.6% versus +6.1%; p = 0.0040) and resulted in a small reduction of infarct size (83.6 versus 107.1 mm3; - 21.89%; p = 0.0272), but it was not associated with early neurological improvement, compared to flat position. Our study suggests that the response to HDT15 during MCA occlusion is dependent on baseline collaterals. Nonetheless, HDT15 promoted a mild improvement of cerebral hemodynamics even in subjects with poor collaterals, without safety concerns.

Post-reperfusion acute MR diffusion in stroke is a potential predictor for clinical outcome in rats

Middle cerebral artery occlusion (MCAO) models show substantial variability in outcome, introducing uncertainties in the evaluation of treatment effects. Early outcome predictors would be essential for prognostic purposes and variability control. We aimed to compare apparent diffusion coefficient (ADC) MRI data obtained during MCAO and shortly after reperfusion for their potentials in acute-phase outcome prediction. Fifty-nine male rats underwent a 45-min MCAO. Outcome was defined in three ways: 21-day survival; 24 h midline-shift and neurological scores. Animals were divided into two groups: rats surviving 21 days after MCAO (survival group, n = 46) and rats dying prematurely (non-survival/NS group, n = 13). At reperfusion, NS group showed considerably larger lesion volume and lower mean ADC of the initial lesion site (p < 0.0001), while during occlusion there were no significant group differences. At reperfusion, each survival animal showed decreased lesion volume and increased mean ADC of the initial lesion site compared to those during occlusion (p < 10^-6), while NS group showed a mixed pattern. At reperfusion, lesion volume and mean ADC of the initial lesion site were significantly associated with 24 h midline-shift and neurological scores. Diffusion MRI performed soon after reperfusion has a great impact in early-phase outcome prediction, and it works better than the measurement during occlusion.

The superiority and feasibility of 2,3,5-triphenyltetrazolium chloride-stained brain tissues for molecular biology experiments based on microglial properties

BACKGROUND

TTC (2,3,5-triphenyltetrazolium chloride) staining is the most commonly used method in identifying and assessing cerebral infarct volumes in the transient middle cerebral artery occlusion model. Given that microglia exhibit different morphologies in different regions after ischemic stroke, we demonstrate the superiority and necessity of using TTC-stained brain tissue to analyze the expression of various proteins or genes in different regions based on microglia character.

METHODS

We compared brain tissue (left for 10 min on ice) from the improved TTC staining method with penumbra from the traditional sampling method. We identified the feasibility and necessity of the improved staining method using real time (RT)-PCR, Western blot, and immunofluorescence analysis.

RESULTS

There was no protein and RNA degradation in the TTC-stained brain tissue group. However, the TREM2 specifically expressed on the microglia showed a significant difference between two groups in the penumbra region.

CONCLUSIONS

TTC-stained brain tissue can be used for molecular biology experiments without any restrictions. In addition, TTC-stained brain tissue shows greater superiority due to its precise positioning.

Optimizing intraluminal monofilament model of ischemic stroke in middle-aged Sprague-Dawley rats

Intraluminal monofilament model of middle cerebral artery occlusion (MCAO) is widely adopted for ischemic stroke; and Sprague-Dawley (SD) rats are commonly used rodents for preclinical research. Due to the paucity of information on the appropriate monofilament size for inducing MCAO in SD rats and the importance of including middle-aged models in ischemic stroke studies, we aimed to: (i). determine an appropriate Doccol^® monofilament size for middle-aged male SD rats which weighed > 500 g following 24-h transient MCAO survival as well as (ii). demonstrate the optimal Doccol^® filament size for middle-aged males (≤ 500 g) and females (273-300 g) while using young adult male SD rats (372-472 g) as control for severity of infarct volume following 7-days post-MCAO. All rats were subjected to 90-min transient MCAO. We show that 0.43 mm Doccol^® monofilament size is more appropriate to induce large infarct lesion and optimal functional deficit when compared to 0.45 mm and 0.47 mm at 24 h post-MCAO. Our data on infarct volumes at 7 days post-MCAO as well as the observed weight loss and functional deficits at post-MCAO days 1, 3 and 7 demonstrate that 0.41 mm, 0.37 mm and 0.39 mm are optimal Doccol^® filament sizes for middle-aged male (477.3 ± 39.61 g) and female (302.6 ± 26.28 g) as well as young-adult male (362.2 ± 28.38 g) SD rats, respectively.

Time-varying caloric vestibular stimulation for the treatment of neurodegenerative disease

Time-varying caloric vestibular stimulation (tvCVS) is a new form of non-invasive neuromodulation similar to, but different from, diagnostic caloric vestibular stimulation (CVS). Using a non-invasive, solid-state delivery device, tvCVS has been successfully used in a human clinical trial with Parkinson’s disease (PD) subjects. Additionally, the effects of tvCVS on brain activation have been studied in healthy human subjects using transcranial Doppler sonography (TCD) and functional magnetic resonance imaging (BOLD fMRI). A novel finding in the TCD and fMRI studies was the induction of cerebral blood flow velocity (CBFv) oscillations. How such oscillations might lead to the observed clinical effects seen in PD subjects will be discussed. Enabling studies of tvCVS with rodents is an attractive goal in support of explorations of the mechanism of action. Male Wistar rats were used in a proof-of-concept study described herein. Rats were anesthetized (isoflurane) and ventilated for the duration of the tvCVS runs. Time-varying thermal stimuli were administered using a digital temperature controller to modulate Peltier-type heater/cooler devices. Blunt ear bars conveyed the thermal stimulus to the external ear canals of the rats. Different thermal waveform combinations were evaluated for evidence of successful induction of the CVS effect. It was found that bilateral triangular thermal waveforms could induce oscillations in CBFv both during and after the application of tvCVS. These oscillations were similar to, but different from those observed in awake human subjects. The establishment of a viable animal model for the study of tvCVS will augment ongoing clinical investigations of this new form of neuromodulation in patients with neurodegenerative disease.

Hemodynamics and Tissue Optical Properties in Bimodal Infarctions Induced by Middle Cerebral Artery Occlusion

Various infarct sizes induced by middle cerebral artery occlusion (MCAO) generate inconsistent outcomes for stroke preclinical study. Monitoring cerebral hemodynamics may help to verify the outcome of MCAO. The aim of this study was to investigate the changes in brain tissue optical properties by frequency-domain near-infrared spectroscopy (FD-NIRS), and establish the relationship between cerebral hemodynamics and infarct variation in MCAO model. The rats were undergone transient MCAO using intraluminal filament. The optical properties and hemodynamics were measured by placing the FD-NIRS probes on the scalp of the head before, during, and at various time-courses after MCAO. Bimodal infarction severities were observed after the same 90-min MCAO condition. Significant decreases in concentrations of oxygenated hemoglobin ([HbO]) and total hemoglobin ([HbT]), tissue oxygenation saturation (StO₂), absorption coefficient (μa) at 830 nm, and reduced scattering coefficient (μs’) at both 690 and 830 nm were detected during the occlusion in the severe infarction but not the mild one. Of note, the significant increases in [HbO], [HbT], StO₂, and μa at both 690 and 830 nm were found on day 3; and increases in μs’ at both 690 and 830 nm were found on day 2 and day 3 after MCAO, respectively. The interhemispheric correlation coefficient (IHCC) was computed from low-frequency hemodynamic oscillation of both hemispheres. Lower IHCCs standing for interhemispheric desynchronizations were found in both mild and severe infarction during occlusion, and only in severe infarction after reperfusion. Our finding supports that sequential FD-NIRS parameters may associated with the severity of the infarction in MCAO model, and the consequent pathologies such as vascular dysfunction and brain edema. Further study is required to validate the potential use of FD-NIRS as a monitor for MCAO verification.

Stem Cells as Drug-like Biologics for Mitochondrial Repair in Stroke

Stroke is a devastating condition characterized by widespread cell death after disruption of blood flow to the brain. The poor regenerative capacity of neural cells limits substantial recovery and prolongs disruptive sequelae. Current therapeutic options are limited and do not adequately address the underlying mitochondrial dysfunction caused by the stroke. These same mitochondrial impairments that result from acute cerebral ischemia are also present in retinal ischemia. In both cases, sufficient mitochondrial activity is necessary for cell survival, and while astrocytes are able to transfer mitochondria to damaged tissues to rescue them, they do not have the capacity to completely repair damaged tissues. Therefore, it is essential to investigate this mitochondrial transfer pathway as a target of future therapeutic strategies. In this review, we examine the current literature pertinent to mitochondrial repair in stroke, with an emphasis on stem cells as a source of healthy mitochondria. Stem cells are a compelling cell type to study in this context, as their ability to mitigate stroke-induced damage through non-mitochondrial mechanisms is well established. Thus, we will focus on the latest preclinical research relevant to mitochondria-based mechanisms in the treatment of cerebral and retinal ischemia and consider which stem cells are ideally suited for this purpose.

Transcranial contrast-enhanced ultrasound in the rat brain reveals substantial hyperperfusion acutely post-stroke

Direct and real-time assessment of cerebral hemodynamics is key to improving our understanding of cerebral blood flow regulation in health and disease states such as stroke. While a number of sophisticated imaging platforms enable assessment of cerebral perfusion, most are limited either spatially or temporally. Here, we applied transcranial contrast-enhanced ultrasound (CEU) to measure cerebral perfusion in real-time through the intact rat skull before, during and after ischemic stroke, induced by intraluminal filament middle cerebral artery occlusion (MCAO). We demonstrate expected decreases in cortical and striatal blood volume, flow velocity and perfusion during MCAO. After filament retraction, blood volume and perfusion increased two-fold above baseline, indicative of acute hyperperfusion. Adjacent brain regions to the ischemic area and the contralateral hemisphere had increased blood volume during MCAO. We assessed our data using wavelet analysis to demonstrate striking vasomotion changes in the ischemic and contralateral cortices during MCAO and reperfusion. In conclusion, we demonstrate the application of CEU for real-time assessment of cerebral hemodynamics and show that the ischemic regions exhibit striking hyperemia post-MCAO. Whether this post-stoke hyperperfusion is sustained long-term and contributes to stroke severity is not known.

Argon Inhalation for 24 Hours After Onset of Permanent Focal Cerebral Ischemia in Rats Provides Neuroprotection and Improves Neurologic Outcome

OBJECTIVES

We tested the hypothesis that prolonged inhalation of 70% argon for 24 hours after in vivo permanent or temporary stroke provides neuroprotection and improves neurologic outcome and overall recovery after 7 days.

DESIGN

Controlled, randomized, double-blinded laboratory study.

SETTING

Animal research laboratories.

SUBJECTS

Adult Wistar male rats (n = 110).

INTERVENTIONS

Rats were subjected to permanent or temporary focal cerebral ischemia via middle cerebral artery occlusion, followed by inhalation of 70% argon or nitrogen in 30% oxygen for 24 hours. On postoperative day 7, a 48-point neuroscore and histologic lesion size were assessed.

MEASUREMENTS AND MAIN RESULTS

After argon inhalation for 24 hours immediately following "severe permanent ischemia" induction, neurologic outcome (neuroscore, p = 0.034), overall recovery (body weight, p = 0.02), and infarct volume (total infarct volume, p = 0.0001; cortical infarct volume, p = 0.0003; subcortical infarct volume, p = 0.0001) were significantly improved. When 24-hour argon treatment was delayed for 2 hours after permanent stroke induction or until after postischemic reperfusion treatment, neurologic outcomes remained significantly improved (neuroscore, p = 0.043 and p = 0.014, respectively), as was overall recovery (body weight, p = 0.015), compared with nitrogen treatment. However, infarct volume and 7-day mortality were not significantly reduced when argon treatment was delayed.

CONCLUSIONS

Neurologic outcome (neuroscore), overall recovery (body weight), and infarct volumes were significantly improved after 24-hour inhalation of 70% argon administered immediately after severe permanent stroke induction. Neurologic outcome and overall recovery were also significantly improved even when argon treatment was delayed for 2 hours or until after reperfusion.

Stroke gets in your eyes: stroke-induced retinal ischemia and the potential of stem cell therapy

Stroke persists as a global health and economic crisis, yet only two interventions to reduce stroke-induced brain injury exist. In the clinic, many patients who experience an ischemic stroke often further suffer from retinal ischemia, which can inhibit their ability to make a functional recovery and may diminish their overall quality of life. Despite this, no treatments for retinal ischemia have been developed. In both cases, ischemia-induced mitochondrial dysfunction initiates a cell loss cascade and inhibits endogenous brain repair. Stem cells have the ability to transfer healthy and functional mitochondria not only ischemic neurons, but also to similarly endangered retinal cells, replacing their defective mitochondria and thereby reducing cell death. In this review, we encapsulate and assess the relationship between cerebral and retinal ischemia, recent preclinical advancements made using in vitro and in vivo retinal ischemia models, the role of mitochondrial dysfunction in retinal ischemia pathology, and the therapeutic potential of stem cell-mediated mitochondrial transfer. Furthermore, we discuss the pitfalls in classic rodent functional assessments and the potential advantages of laser Doppler as a metric of stroke progression. The studies evaluated in this review highlight stem cell-derived mitochondrial transfer as a novel therapeutic approach to both retinal ischemia and stroke. Furthermore, we posit the immense correlation between cerebral and retinal ischemia as an underserved area of study, warranting exploration with the aim of these treating injuries together.

Does the Apparent Diffusion Coefficient Value Predict Permanent Cerebral Ischemia/Reperfusion Injury in Rats?

RATIONALE AND OBJECTIVES

Variation in tissue damage after cerebral ischemia/reperfusion (I/R) can cause uncertainty in stroke-related studies, which can be reduced if the damage can be predicted early after ischemia by measuring the apparent diffusion coefficient (ADC). We investigated whether ADC measurement in the acute phase can predict permanent cerebral I/R injury.

MATERIALS AND METHODS

The middle cerebral artery occlusion model was established using the intraluminal suture method to induce 60 minutes of ischemia followed by reperfusion in rats. T2-weighted images and diffusion-weighted images were obtained at 30 minutes and 24 hours after ischemia. Neuronal cell survival was assessed by neuronal nuclei (NeuN) immunofluorescence staining. The correlation between relative ADC (rADC) values at 30 minutes and I/R injury at 24 hours after ischemia was analyzed. Magnetic resonance imaging results were confirmed by histologic analysis.

RESULTS

The correlation between rADC values at 30 minutes and 24 hours was strong in the ischemic core and peri-infarct region but moderate in the anterior choroidal and hypothalamic region. Histologic analysis revealed that the correlation between rADC values at 30 minutes and the number of NeuN-positive cells at 24 hours was strong in the ischemic core and peri-infarct region but moderate in the anterior choroidal and hypothalamic region. Furthermore, there was a strong positive correlation between the sum of rADC values of three regions at 30 minutes and the infarct volume at 24 hours.

CONCLUSION

ADC measurement in the acute phase can predict permanent cerebral I/R injury and provide important information for the evaluation of ischemic stroke.

The brain and eye: Treating cerebral and retinal ischemia through mitochondrial transfer

Stroke remains a devastating disease with limited treatment options, despite our growing understanding of its pathology. While ischemic stroke is traditionally characterized by a blockage of blood flow to the brain, this may coincide with reduced blood circulation to the eye, resulting in retinal ischemia, which may in turn lead to visual impairment. Although effective treatment options for retinal ischemia are similarly scarce, new evidence suggests that deleterious changes to mitochondrial structure and function play a major role in both cerebral and retinal ischemia pathologies. Prior studies establish that astrocytes transfer healthy mitochondria to ischemic neurons following stroke; however, this alone is not enough to significantly mitigate the damage caused by primary and secondary cell death. Thus, stem cell-based regenerative medicine targeting amelioration of ischemia-induced mitochondrial dysfunction via the transfer of functional mitochondria to injured neural cells represents a promising approach to improve stroke outcomes for both cerebral and retinal ischemia. In this review, we evaluate recent laboratory evidence supporting the remedial capabilities of mitochondrial transfer as an innovative stroke treatment. In particular, we examine exogenous stem cell transplants in their potential role as suppliers of healthy mitochondria to neurons, brain endothelial cells, and retinal cells.

Impact statement

Stroke constitutes a global health crisis, yet potent, applicable therapeutic options remain effectively inaccessible for many patients. To this end, stem cell transplants stand as a promising stroke treatment and as an emerging subject of research for cell-based regenerative medicine. This is the first review to synthesize the implications of stem cell-derived mitochondrial transfer in both the brain and the eye. As such, this report carries fresh insight into the commonalities between the two stroke-affected organs. We present the findings of this developing area of research inquiry with the hope that our evaluation may advance the use of stem cell transplants as viable therapeutic alternatives for ischemic stroke and related disorders characterized by mitochondrial dysfunction. Such lab-to-clinic translational advancement has the potential to save and improve the ever increasing millions of lives affected by stroke.

Reducing myeloperoxidase activity decreases inflammation and increases cellular protection in ischemic stroke

Myeloperoxidase (MPO) is a pro-inflammatory enzyme abundantly secreted by activated myeloid cells after stroke. We show that when MPO activity is either blocked by the specific inhibitor 4-aminobenzoic acid hydrazide (ABAH) in wildtype (WT) mice or congenitally absent (MPO-/-), there was decreased cell loss, including degenerating neurons and oligodendrocytes, in the ischemic brains compared to vehicle-treated WT mice after stroke. MPO inhibition also reduced the number of activated myeloid cells after ischemia. MPO inhibition increased cytoprotective heat shock protein 70 (Hsp70) by 70% and p-Akt by 60%, while decreased the apoptotic marker p53 level by 62%, compared to vehicle-treated mice after ischemia. Similarly, MPO inhibition increased the number of Hsp70+/NeuN+ cells after stroke by 60%. Notably, MPO inhibition significantly improved neurological outcome compared with the vehicle-treated group after stroke. We further found longer treatment periods resulted in larger reduction of infarct size and greater neurobehavioral improvement from MPO inhibition, even when given days after stroke. Therefore, MPO inhibition with ABAH or MPO deficiency creates a protective environment that decreased inflammatory cell recruitment and increased expression of survival factors to improve functional outcome. MPO inhibition may represent a promising therapeutic target for stroke therapy, possibly even days after stroke has occurred.

Eye Opener in Stroke

Supplemental Digital Content is available in the text.

Retinal ischemia is a major cause of visual impairment in stroke patients, but our incomplete understanding of its pathology may contribute to a lack of effective treatment. Here, we investigated the role of mitochondrial dysfunction in retinal ischemia and probed the potential of mesenchymal stem cells (MSCs) in mitochondrial repair under such pathological condition.

Strain differences in intraluminal thread model of middle cerebral artery occlusion in rats

Stroke is despite of progressive improvements in treatment and reperfusion strategies one of the most devastating human pathology. However, as quality of acute health care improves and more people survive ischemic attack, healthcare specialists have to solve new challenges to preserve reasonable quality of life to these patients. Thus, novel approaches which prevents comorbidities of stroke and improve quality of life of stroke survivors in general has to be developed and experimentally tested. The aim of the present paper was to establish reliable rat model of middle cerebral occlusion and set of methods allowing selection of animals suitable for long-term experiments. We have compared mortality rates, cerebral blood flow and extension of ischemic lesion induced by intraluminal filament in three widely used outbred rat strains. We have additionally used an animal 18F-DG PET scans to verify its reliability in noninvasive detection of ischemic infarct in acute period (24 h after MCAO) for selecting animals eligible for long survival experiments. Our data clearly indicates that high variability between rat strains might negatively influence stroke induction by intraluminal thread occlusion of middle cerebral artery. Most reliable outbred rat strain in our hands was Sprague-Dawley where maximal reduction of cerebral blood flow and extensive ischemic lesion was observed. Contrary, Wistar rats exhibited higher mortality and Long-Evans rats significantly smaller or no ischemic region in comparison to Sprague-Dawley. Additionally, we have confirmed a positron emission tomography with 18F-fluorodeoxyglucose as suitable method to assess extension of ischemic region in acute period after the experimental arterial occlusion in rats.

Effect of laser Doppler flowmetry and occlusion time on outcome variability and mortality in rat middle cerebral artery occlusion: inconclusive results

Background

Stroke is among the leading causes of death and disability. Although intense research efforts have provided promising treatment options in animals, most clinical trials in humans have failed and the therapeutic options are few. Several factors have been suggested to explain this translational difficulty, particularly concerning methodology and study design. Consistent infarcts and low mortality might be desirable in some, but not all, studies. Here, we aimed to investigate whether the use of laser Doppler flowmetry (LDF) and the occlusion time (60 vs. 45 min) affected outcome variability and mortality in a rat stroke model. Eighty ovariectomized female Wistar rats were subjected to ischemic stroke using intraluminal filament middle cerebral artery occlusion with or without LDF and with occlusion times of 45 or 60 min. Outcome was evaluated by triphenyl tetrazolium chloride staining of brain slices to measure infarct size and a modified sticky tape test.

Results

Neither LDF nor occlusion times of 45 versus 60 min significantly affected mortality, outcome variability or outcome severity.

Conclusions

Due to the unexpectedly high mortality and variability the statistical power was very low and thus the results were inconclusive.

Electronic supplementary material

The online version of this article (10.1186/s12868-018-0425-0) contains supplementary material, which is available to authorized users.

The macroscopic and microscopic effect of low-frequency whole-body vibration after cerebral ischemia in rats

Whole body vibration (WBV) has been applied in stroke patients with uncertain effects on motor and sensory dysfunction, and its effects on neurogenesis have not been studied yet. Here, we intended to explore the effects of daily WBV on neurological behavior, brain structure, and neurogenesis after cerebral ischemia in rats for 4 weeks. Results showed that improvements in weight or comprehensive neurological deficits were not significantly different under WBV or control treatment, and the degrees of brain damage and the numbers of necrotic neurons in the ischemic cortex were similar in two groups. However, WBV markedly improved animals' coordination from 14d to 28d (P < 0.05) and muscle strength of the upper limbs at 21d and 28d (P < 0.05 & P < 0.001) compared with the control group. WBV promoted the increase in the number of bromodeoxyuridine-positive (BrdU⁺) cells at 3d (P < 0.05) and 14d (P < 0.001) and the number of BrdU⁺/nestin⁺ cells at 14d (P < 0.01) after ischemia when compared to the control group. The numbers of BrdU⁺/NeuN⁺ cells at 21d and 28d (P < 0.001) were enhanced by WBV treatment. In addition, WBV significantly promoted the proliferation of astrocytes and their neural processes thickening after 14d. The expression levels of neural markers, such as doublecortin, microtubule-associated protein 2, and glial fibrillary acidic protein, were upregulated in the ipsilateral cortex at different time points. Low-frequency WBV showed inconspicuous improvements in behavioral performance and brain damage after cerebral ischemia, but showed the potential in improving coordination and muscle strength and promoted neurogenesis after long-term exposure.

Inclusion criteria update for the rat intraluminal ischaemic model for preclinical studies

Proper occlusion of the medial cerebral artery, as determined by laser Doppler monitoring, during cerebral ischaemia in rat models is an important inclusion criterion in experimental studies. However, successful occlusion of the artery does not always guarantee a reproducible infarct volume, which is crucial for validating the efficacy of new protective drugs. In a rat intraluminal ischaemic model, laser Doppler monitoring alone was compared with laser Doppler monitoring in combination with magnetic resonance angiography (MRA) and diffusion-weighted imaging (DWI). Twenty-eight animals showed successful occlusion and reperfusion determined with Doppler monitoring, with an infarct size at 24 h of 16.7±11.5% (determined as ischaemic damage with respect to the ipsilateral hemisphere volume). However, when arterial occlusion and infarct damage were analysed in these animals using MRA and DWI, respectively, 15 animals were excluded and only 13 animals were included, with an infarct size at 24 h of 21.6±6.1%, showing a variability in the infarct size significantly lower (P<0.05, F-test) than that obtained with Doppler monitoring alone. We also observed that blocking of the pterygopalatine artery (a maxillary artery that is usually occluded in the intraluminal ischaemic model) was not relevant for this model, at least in terms of infarct variability. These results show that laser Doppler monitoring is a necessary procedure, but not sufficient to guarantee a reproducible infarct volume, in a rat ischaemic model. Therefore, laser Doppler monitoring in combination with DWI and MRA represents a reliable inclusion protocol during ischaemic surgery for the analysis of new protective drugs.

Summary: Laser Doppler monitoring in combination with diffusion-weighted imaging and magnetic resonance angiography represents a reliable inclusion protocol during ischaemic surgery for the analysis of protective drugs in the acute phase of stroke.

Non-invasive remote ischemic postconditioning stimulates neurogenesis during the recovery phase after cerebral ischemia

Ischemic postconditioning (IPostC) has been reported to have neuroprotection against ischemic diseases, and one cycle of IPostC induces neurogenesis when treated nearby. To expanding these effects, we explored the effects of repetitively remote IPostC (NRIPostC) on neurogenesis in the subgranular zone (SGZ) and subentricular zone (SVZ) during stroke recovery. Animals underwent transient cerebral ischemia were treated with vehicle or NRIPostC immediately after reperfusion. Neurological severity scores, infarct size, neurogenesis, and protein expression levels of nestin and GFAP were quantified at 3d, 7d, 14d, 21d and 28d post-ischemia. Results showed that NRIPostC significantly reduced acute infarction and improved neurological outcomes during the recovery phase. Meanwhile, NRIPostC significantly increased the number of BrdU⁺/nestin⁺ cells in SGZ on day 14 and in the SVZ on days 3, 7 and 14 respectively, and the number of DCX⁺ cells from days 3 to 14. There were significant increments in the number of BrdU⁺/NeuN⁺ and BrdU⁺/GFAP⁺ cells in the SGZ and SVZ during the stroke recovery. The changing tendency of the protein expression of nestin and GFAP in DG was consistent with the result mentioned above. In conclusion, NRIPostC reduced acute infarction and improved functional outcomes up to 28d, and it induced neurogenesis both in the SGZ and SVZ.

Cerebral collateral therapeutics in acute ischemic stroke: A randomized preclinical trial of four modulation strategies

Cerebral collaterals are dynamically recruited after arterial occlusion and highly affect tissue outcome in acute ischemic stroke. We investigated the efficacy and safety of four pathophysiologically distinct strategies for acute modulation of collateral flow (collateral therapeutics) in the rat stroke model of transient middle cerebral artery (MCA) occlusion. A composed randomization design was used to assign rats (n = 118) to receive phenylephrine (induced hypertension), polygeline (intravascular volume load), acetazolamide (cerebral arteriolar vasodilation), head down tilt (HDT) 15° (cerebral blood flow diversion), or no treatment, starting 30 min after MCA occlusion. Compared to untreated animals, treatment with collateral therapeutics was associated with lower infarct volumes (62% relative mean difference; 51.57 mm³ absolute mean difference; p < 0.001) and higher chance of good functional outcome (OR 4.58, p < 0.001). Collateral therapeutics acutely increased cerebral perfusion in the medial (+40.8%; p < 0.001) and lateral (+19.2%; p = 0.016) MCA territory compared to pretreatment during MCA occlusion. Safety indicators were treatment-related mortality and cardiorespiratory effects. The highest efficacy and safety profile was observed for HDT. Our findings suggest that acute modulation of cerebral collaterals is feasible and provides a tissue-saving effect in the hyperacute phase of ischemic stroke prior to recanalization therapy.

Multi-site laser Doppler flowmetry for assessing collateral flow in experimental ischemic stroke: Validation of outcome prediction with acute MRI

High variability in infarct size is common in experimental stroke models and affects statistical power and validity of neuroprotection trials. The aim of this study was to explore cerebral collateral flow as a stratification factor for the prediction of ischemic outcome. Transient intraluminal occlusion of the middle cerebral artery was induced for 90 min in 18 Wistar rats. Cerebral collateral flow was assessed intra-procedurally using multi-site laser Doppler flowmetry monitoring in both the lateral middle cerebral artery territory and the borderzone territory between middle cerebral artery and anterior cerebral artery. Multi-modal magnetic resonance imaging was used to assess acute ischemic lesion (diffusion-weighted imaging, DWI), acute perfusion deficit (time-to-peak, TTP), and final ischemic lesion at 24 h. Infarct volumes and typology at 24 h (large hemispheric versus basal ganglia infarcts) were predicted by both intra-ischemic collateral perfusion and acute DWI lesion volume. Collateral flow assessed by multi-site laser Doppler flowmetry correlated with the corresponding acute perfusion deficit using TTP maps. Multi-site laser Doppler flowmetry monitoring was able to predict ischemic outcome and perfusion deficit in good agreement with acute MRI. Our results support the additional value of cerebral collateral flow monitoring for outcome prediction in experimental ischemic stroke, especially when acute MRI facilities are not available.

Video training and certification program improves reliability of postischemic neurologic deficit measurement in the rat

Scoring systems are used to measure behavioral deficits in stroke research. Video-assisted training is used to standardize stroke-related neurologic deficit scoring in humans. We hypothesized that a video-assisted training and certification program can improve inter-rater reliability in assessing neurologic function after middle cerebral artery occlusion in rats. Three expert raters scored neurologic deficits in post-middle cerebral artery occlusion rats using three published systems having different complexity levels (3, 18, or 48 points). The system having the highest point estimate for the correlation between neurologic score and infarct size was selected to create a video-assisted training and certification program. Eight trainee raters completed the video-assisted training and certification program. Inter-rater agreement ( Κ: score) and agreement with expert consensus scores were measured before and after video-assisted training and certification program completion. The 48-point system correlated best with infarct size. Video-assisted training and certification improved agreement with expert consensus scores (pretraining = 65 ± 10, posttraining = 87 ± 14, 112 possible scores, P < 0.0001), median number of trainee raters with scores within ±2 points of the expert consensus score (pretraining = 4, posttraining = 6.5, P < 0.01), categories with Κ:  > 0.4 (pretraining = 4, posttraining = 9), and number of categories with an improvement in the Κ: score from pretraining to posttraining (n = 6). Video-assisted training and certification improved trainee inter-rater reliability and agreement with expert consensus behavioral scores in rats after middle cerebral artery occlusion. Video-assisted training and certification may be useful in multilaboratory preclinical studies.

Ischemic postconditioning protects against ischemic brain injury by up-regulation of acid-sensing ion channel 2a

Ischemic postconditioning renders brain tissue tolerant to brain ischemia, thereby alleviating ischemic brain injury. However, the exact mechanism of action is still unclear. In this study, a rat model of global brain ischemia was subjected to ischemic postconditioning treatment using the vessel occlusion method. After 2 hours of ischemia, the bilateral common carotid arteries were blocked immediately for 10 seconds and then perfused for 10 seconds. This procedure was repeated six times. Ischemic postconditioning was found to mitigate hippocampal CA1 neuronal damage in rats with brain ischemia, and up-regulate acid-sensing ion channel 2a expression at the mRNA and protein level. These findings suggest that ischemic postconditioning up-regulates acid-sensing ion channel 2a expression in the rat hippocampus after global brain ischemia, which promotes neuronal tolerance to ischemic brain injury.

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.