Anesthesia in Experimental Stroke Research

A minimally invasive thrombotic model to study stroke in awake mice

Experimental stroke models in rodents are essential for mechanistic studies and therapeutic development. However, these models have several limitations negatively impacting their translational relevance. Here we aimed to develop a minimally invasive thrombotic stroke model through magnetic particle delivery that does not require craniotomy, is amenable to reperfusion therapy, can be combined with in vivo imaging modalities, and can be performed in awake mice. We found that the model results in reproducible cortical infarcts within the middle cerebral artery (MCA) territory with cytologic and immune changes similar to that observed with more invasive distal MCA occlusion models. Importantly, the injury produced by the model was ameliorated by tissue plasminogen activator (tPA) administration. We also show that MCA occlusion in awake animals results in bigger ischemic lesions independent of day/night cycle. Magnetic particle delivery had no overt effects on physiologic parameters and systemic immune biomarkers. In conclusion, we developed a novel stroke model in mice that fulfills many requirements for modeling human stroke.

Acute Ischemic Stroke in the Clinic and the Laboratory: Targets for Translational Research

Ischemic stroke research has enabled significant advancements in diagnosis, treatment, and management of this debilitating disease, yet challenges remain standing in the way of better patient prognoses. In this narrative review, a fictional case illustrates challenges and uncertainties that medical professionals still face - penumbra identification, lack of neuroprotective agents, side-effects of tissue plasminogen activator, dearth of molecular biomarkers, incomplete microvascular reperfusion or no-reflow, post-recanalization hyperperfusion, blood pressure management and procedural anesthetic effects. The current state of the field is broadly reviewed per topic, with the aim to introduce a broad audience (scientist and clinician alike) to recent successes in translational stroke research and pending scientific queries that are tractable for preclinical assessment. Opportunities for co-operation between clinical and experimental stroke experts are highlighted to increase the size and frequency of strides the field makes to improve our understanding of this disease and ways of treating it.

Stroke and Translational Research - Review of Experimental Models with a Focus on Awake Ischaemic Induction and Anaesthesia

Animal models are an indispensable tool in the study of ischaemic stroke with hundreds of drugs emerging from the preclinical pipeline. However, all of these drugs have failed to translate into successful treatments in the clinic. This has brought into focus the need to enhance preclinical studies to improve translation. The confounding effects of anaesthesia on preclinical stroke modelling has been raised as an important consideration. Various volatile and injectable anaesthetics are used in preclinical models during stroke induction and for outcome measurements such as imaging or electrophysiology. However, anaesthetics modulate several pathways essential in the pathophysiology of stroke in a dose and drug dependent manner. Most notably, anaesthesia has significant modulatory effects on cerebral blood flow, metabolism, spreading depolarizations, and neurovascular coupling. To minimise anaesthetic complications and improve translational relevance, awake stroke induction has been attempted in limited models. This review outlines anaesthetic strategies employed in preclinical ischaemic rodent models and their reported cerebral effects. Stroke related complications are also addressed with a focus on infarct volume, neurological deficits, and thrombolysis efficacy. We also summarise routinely used focal ischaemic stroke rodent models and discuss the attempts to induce some of these models in awake rodents.

Propofol anesthesia improves stroke outcomes over isoflurane anesthesia-a longitudinal multiparametric MRI study in a rodent model of transient middle cerebral artery occlusion

General anesthesia is routinely used in endovascular thrombectomy procedures, for which volatile gas and/or intravenous propofol are recommended. Emerging evidence suggests propofol may have superior effects on disability and/or mortality rates, but a mode-of-action underlying these class-specific effects remains unknown. Here, a moderate isoflurane or propofol dosage on experimental stroke outcomes was retrospectively compared using serial multiparametric MRI and behavioral testing. Adult male rats (N = 26) were subjected to 90-min filament-induced transient middle cerebral artery occlusion. Diffusion-, T2- and perfusion-weighted MRI was performed during occlusion, 0.5 h after recanalization, and four days into the subacute phase. Sequels of ischemic damage-blood-brain barrier integrity, cerebrovascular reactivity and sensorimotor functioning-were assessed after four days. While size and severity of ischemia was comparable between groups during occlusion, isoflurane anesthesia was associated with larger lesion sizes and worsened sensorimotor functioning at follow-up. MRI markers indicated that cytotoxic edema persisted locally in the isoflurane group early after recanalization, coinciding with burgeoning vasogenic edema. At follow-up, sequels of ischemia were further aggravated in the post-ischemic lesion, manifesting as increased blood-brain barrier leakage, cerebrovascular paralysis and cerebral hyperperfusion. These findings shed new light on how isoflurane, and possibly similar volatile agents, associate with persisting injurious processes after recanalization that contribute to suboptimal treatment outcome.

Implications of Post-recanalization Perfusion Deficit After Acute Ischemic Stroke: a Scoping Review of Clinical and Preclinical Imaging Studies

The goal of reperfusion therapy for acute ischemic stroke (AIS) is to restore cerebral blood flow through recanalization of the occluded vessel. Unfortunately, successful recanalization does not always result in favorable clinical outcome. Post-recanalization perfusion deficits (PRPDs), constituted by cerebral hypo- or hyperperfusion, may contribute to lagging patient recovery rates, but its clinical significance remains unclear. This scoping review provides an overview of clinical and preclinical findings on post-ischemic reperfusion, aiming to elucidate the pattern and consequences of PRPD from a translational perspective. The MEDLINE database was searched for quantitative clinical and preclinical studies of AIS reporting PRPD based on cerebral circulation parameters acquired by translational tomographic imaging methods. PRPD and stroke outcome were mapped on a charting table, creating an overview of PRPD after AIS. Twenty-two clinical and twenty-two preclinical studies were included. Post-recanalization hypoperfusion is rarely reported in clinical studies (4/22) but unequivocally associated with detrimental outcome. Post-recanalization hyperperfusion is more commonly reported (18/22 clinical studies) and may be associated with positive or negative outcome. PRPD has been replicated in animal studies, offering mechanistic insights into causes and consequences of PRPD and allowing delineation of possible courses of PRPD. Complex relationships exist between PRPD and stroke outcome. Diversity in methods and lack of standardized definitions in reperfusion studies complicate the characterization of reperfusion patterns. Recommendations are made to advance the understanding of PRPD mechanisms and to further disentangle the relation between PRPD and disease outcome.

Functional ultrasound imaging of stroke in awake rats

Anesthesia is a major confounding factor in preclinical stroke research as stroke rarely occurs in sedated patients. Moreover, anesthesia affects both brain functions and the stroke outcome acting as neurotoxic or protective agents. So far, no approaches were well suited to induce stroke while imaging hemodynamics along with simultaneous large-scale recording of brain functions in awake animals. For this reason, the first critical hours following the stroke insult and associated functional alteration remain poorly understood. Here, we present a strategy to investigate both stroke hemodynamics and stroke-induced functional alterations without the confounding effect of anesthesia, i.e., under awake condition. Functional ultrasound (fUS) imaging was used to continuously monitor variations in cerebral blood volume (CBV) in +65 brain regions/hemispheres for up to 3 hr after stroke onset. The focal cortical ischemia was induced using a chemo-thrombotic agent suited for permanent middle cerebral artery occlusion in awake rats and followed by ipsi- and contralesional whiskers stimulation to investigate on the dynamic of the thalamocortical functions. Early (0-3 hr) and delayed (day 5) fUS recording enabled to characterize the features of the ischemia (location, CBV loss), spreading depolarizations (occurrence, amplitude) and functional alteration of the somatosensory thalamocortical circuits. Post-stroke thalamocortical functions were affected at both early and later time points (0-3 hr and 5 days) after stroke. Overall, our procedure facilitates early, continuous, and chronic assessments of hemodynamics and cerebral functions. When integrated with stroke studies or other pathological analyses, this approach seeks to enhance our comprehension of physiopathologies towards the development of pertinent therapeutic interventions.

CCA repair or ECA ligation-Which middle cerebral artery occlusion is better in the reperfusion mouse model?

A reliable animal model is essential for ischemic stroke research. The implications of the external carotid artery (ECA) transection or common carotid artery (CCA) ligation have been described. Thus, a modified animal model, the CCA-repair model, has been established, and studies have shown that the CCA-repair model has potential advantages over the CCA-ligation model. However, whether the CCA-repair model is superior to the ECA-ligation model remains unclear. Sixty male C57BL/6 mice were randomly assigned to establish the CCA-repair (n = 34) or ECA-ligation (n = 26) models. Cerebral blood flow before middle cerebral artery occlusion (MCAO), immediately after MCAO and reperfusion were monitored and the operation duration, postoperative body weight, and food intake within 7 days, and the number of intraoperative and postoperative deaths within 7 days were recorded in the two models. Modified neurological severity scores and Bederson (0-5) scores were used to evaluate postoperative neurological function deficits on Days 1/3/5/7. 2,3,5-Triphenyltetrazolium chloride staining was used to quantify lesion volume on Day 7 after the operation. We found the establishment of the CCA-repair model required a longer total operation duration (p = 0.0175), especially the operation duration of reperfusion (p < 0.0001). However, there was no significant difference in body weight and food intake development, lesion volume and intragroup variability, neurological function deficits, mortality, and survival probability between the two groups. The CCA-repair model has no significant advantage over the ECA-ligation model. The ECA-ligation model is still a better choice for focal cerebral ischemia.

TRPM4 Blocking Antibody Protects Cerebral Vasculature in Delayed Stroke Reperfusion

Reperfusion therapy for acute ischemic stroke aims to restore the blood flow of occluded blood vessels. However, successful recanalization is often associated with disruption of the blood-brain barrier, leading to reperfusion injury. Delayed recanalization increases the risk of severe reperfusion injury, including severe cerebral edema and hemorrhagic transformation. The TRPM4-blocking antibody M4P has been shown to alleviate reperfusion injury and improve functional outcomes in animal models of early stroke reperfusion. In this study, we examined the role of M4P in a clinically relevant rat model of delayed stroke reperfusion in which the left middle cerebral artery was occluded for 7 h. To mimic the clinical scenario, M4P or control IgG was administered 1 h before recanalization. Immunostaining showed that M4P treatment improved vascular morphology after stroke. Evans blue extravasation demonstrated attenuated vascular leakage following M4P treatment. With better vascular integrity, cerebral perfusion was improved, leading to a reduction of infarct volume and animal mortality rate. Functional outcome was evaluated by the Rotarod test. As more animals with severe injuries died during the test in the control IgG group, we observed no difference in functional outcomes in the surviving animals. In conclusion, we identified the potential of TRPM4 blocking antibody M4P to ameliorate vascular injury during delayed stroke reperfusion. If combined with reperfusion therapy, M4P has the potential to improve current stroke management.

A retrospect and outlook on the neuroprotective effects of anesthetics in the era of endovascular therapy

Studies on the neuroprotective effects of anesthetics were carried out more than half a century ago. Subsequently, many cell and animal experiments attempted to verify the findings. However, in clinical trials, the neuroprotective effects of anesthetics were not observed. These contradictory results suggest a mismatch between basic research and clinical trials. The Stroke Therapy Academic Industry Roundtable X (STAIR) proposed that the emergence of endovascular thrombectomy (EVT) would provide a proper platform to verify the neuroprotective effects of anesthetics because the haemodynamics of patients undergoing EVT is very close to the ischaemia–reperfusion model in basic research. With the widespread use of EVT, it is necessary for us to re-examine the neuroprotective effects of anesthetics to guide the use of anesthetics during EVT because the choice of anesthesia is still based on team experience without definite guidelines. In this paper, we describe the research status of anesthesia in EVT and summarize the neuroprotective mechanisms of some anesthetics. Then, we focus on the contradictory results between clinical trials and basic research and discuss the causes. Finally, we provide an outlook on the neuroprotective effects of anesthetics in the era of endovascular therapy.

Dual Antioxidant DH-217 Mitigated Cerebral Ischemia-Reperfusion Injury by Targeting IKKβ/Nrf2/HO-1 Signal Axis

Antioxidants represent a potential therapy for cerebral ischemia-reperfusion injury (CIRI). Compounds which exhibit both direct and indirect antioxidative activity may potentially exert improved effects. Hence, we aimed to assess whether the dual antioxidant DH-217, a derivative of DHAP clinically used to treat coronary heart disease, can reduce oxidative stress damage and elucidate the underlying mechanism. Hydrogen peroxide (H₂O₂)-induced and Middle Cerebral Artery Occlusion (MCAO)-induced damages were used to imitate oxidative stress. The antioxidation of DH-217 was determined by MTT, ROS, colony and DPPH assay. Besides, immunofluorescence, Real-Time PCR Analyses, western blotting and si-RNA/Plasmid-induced protein expression were used for mechanism validation. DPPH scavenging assay evidenced DH-217 was a well free radical scavenger. Cell survival assay also showed that DH-217 had a significant cytoprotection through direct and indirect clearance mechanisms. Further, it clearly inhibited oxidative stress-induced IkappaB kinase beta (IKKβ) phosphorylation and increased heme oxygenase-1 (HO-1) expression. Significantly, these antioxidant beneficial effects were reversed by HO-1 inhibitor, si-nuclear erythroid 2-related factor 2 (Nrf2) and IKKβ plasmid. Meanwhile, DH-217 had a good neuroprotective effect on CIRI rats. The dual antioxidant DH-217 has potential reference value for drug development of CIRI. Furthermore, inhibition of IKKβ phosphorylation and activation of Nrf2/HO-1 could be a promising antioxidant pathway. Dual antioxidant DH-217 not only has the ability of directly scavenging ROS, but also can clear it by targeting IKKβ/Nrf2/HO-1 signal axis. Inhibition of IKKβ phosphorylation and activation of Nrf2/HO-1 may be a promising antioxidant pathway for CIRI.

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.

Effect of early Sanguinate (PEGylated carboxyhemoglobin bovine) infusion on cerebral blood flow to the ischemic core in experimental middle cerebral artery occlusion

BACKGROUND

Sanguinate, a bovine PEGylated carboxyhemoglobin-based oxygen carrier with vasodilatory, oncotic and anti-inflammatory properties designed to release oxygen in hypoxic tissue, was tested to determine if it improves infarct volume, collateral recruitment and blood flow to the ischemic core in hyperacute middle cerebral artery occlusion (MCAO).

METHODS

Under an IACUC approved protocol, 14 mongrel dogs underwent endovascular permanent MCAO. Seven received Sanguinate (8 mL/kg) intravenously over 10 min starting 30 min following MCAO and seven received a similar volume of normal saline. Relative cerebral blood flow (rCBF) was assessed using neutron-activated microspheres prior to MCAO, 30 min following MCAO and 30 min following intervention. Pial collateral recruitment was scored and measured by arterial arrival time (AAT) immediately prior to post-MCAO microsphere injection. Diffusion-weighted 3T MRI was used to assess infarct volume approximately 2 hours after MCAO.

RESULTS

Mean infarct volumes for control and Sanguinate-treated subjects were 4739 mm3 and 2585 mm3 (p=0.0443; r2=0.687), respectively. Following intervention, rCBF values were 0.340 for controls and 0.715 in the Sanguinate group (r2=0.536; p=0.0064). Pial collateral scores improved only in Sanguinate-treated subjects and AAT decreased by a mean of 0.314 s in treated subjects and increased by a mean of 0.438 s in controls (p<0.0276).

CONCLUSION

Preliminary results indicate that topload bolus administration of Sanguinate in hyperacute ischemic stroke significantly improves infarct volume, pial collateral recruitment and CBF in experimental MCAO immediately following its administration.

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.

Preclinical Stroke Research and Translational Failure: A Bird's Eye View on Preventable Variables

Despite achieving remarkable success in understanding the cellular, molecular and pathophysiological aspects of stroke, translation from preclinical research has always remained an area of debate. Although thousands of experimental compounds have been reported to be neuro-protective, their failures in clinical setting have left the researchers and stakeholders in doldrums. Though the failures described have been excruciating, they also give us a chance to refocus on the shortcomings. For better translational value, evidences from preclinical studies should be robust and reliable. Preclinical study design has a plethora of variables affecting the study outcome. Hence, this review focusses on the factors to be considered for a well-planned preclinical study while adhering to guidelines with emphasis on the study design, commonly used animal models, their limitations with special attention on various preventable attritions including comorbidities, aged animals, time of dosing, outcome measures and physiological variables along with the concept of multicentric preclinical randomized controlled trials. Here, we provide an overview of a panorama of practical aspects, which could be implemented, so that a well-defined preclinical study would result in a neuro-protectant with better translational value.

A Long-Term Clearing Cranial Window for Longitudinal Imaging of Cortical and Calvarial Ischemic Injury through the Intact Skull

Skull is a reservoir for supplying immune cells that mediate brain immune surveillance. However, during intravital optical imaging of brain, conventional cranial windows requiring skull thinning or removal disrupt brain immunity integrity. Here, a novel long-term clearing cranial window (LCCW) based on the intact skull, dedicated to chronic skull transparency maintenance, is proposed. It significantly improves optical imaging resolution and depth, by which the cortical and calvarial vascular injury and regeneration processes after ischemic injury are longitudinally monitored in awake mice. Results show that calvarial blood vessels recover earlier than the cortex. And the transcriptome analysis reveals that gene expression patterns and immune cells abundances exist substantial differences between brain and skull after ischemic injury, which may be one of the causes for the time lag between their vascular recovery. These findings bring great enlightenment to vascular regeneration and reconstruction. Moreover, LCCW provides a minimally invasive approach for imaging the brain and skull bone marrow.

Triple bypass for multisystem smooth muscle dysfunction syndrome due to Arg179His ACTA2 mutation

Missense mutations in the smooth muscle-specific isoform of the alpha-actin (ACTA2) gene, which encodes smooth muscle actin, congenitally cause systemic smooth muscle dysfunction, leading to multiple systemic smooth muscle dysfunction syndrome. This disease is often diagnosed through the development of congenital mydriasis, patent ductus arteriosus, or thoracic aortic aneurysm at a young age. Some patients develop cerebrovascular lesions, also known as ACTA2 cerebral arteriopathy, which cause ischemic stroke and require surgical revascularization. However, an effective and safe treatment has not yet been established owing to the rarity of the disease. Furthermore, most reports of this disease involve children, with only a few reports on adults and few detailed reports on treatment outcomes published to date. We report a 46-year-old woman with ACTA2 cerebral arteriopathy caused by Arg179His, the most common mutation in this disease; she is the oldest patient reported with this disease to the best of our knowledge. The patient was diagnosed with multiple systemic smooth muscle dysfunction syndrome and ACTA2 cerebral arteriopathy after experiencing a stroke in the right cingulate gyrus. She underwent direct triple bypass with three anastomoses of the right superficial temporal artery to the middle and anterior cerebral arteries. She developed an ischemic stroke as a postoperative complication.The efficacy and safety of this procedure have not been clearly confirmed owing to the frailty of the donor superficial temporal artery and the poor development of collateral circulation; however, direct bypass should be considered a treatment option for patients experiencing progressive multiple strokes.

Anesthesia modality does not affect clinical outcomes of intra-arterial vasodilator treatment in patients with symptomatic cerebral vasospasms

Background: Delayed cerebral ischemia and cerebral vasospasm remain the leading causes of poor outcome in survivors of aneurysmal subarachnoid hemorrhage. Refractory cerebral vasospasms can be treated with endovascular vasodilator therapy, which can either be performed in conscious sedation or general anesthesia. The aim of this study is to compare the effect of the anesthesia modality on long-term clinical outcomes in patients undergoing endovascular vasodilator therapy due to cerebral vasospasm and hypoperfusion.

Methods: Modified Rankin Scale (mRS) scores were retrospectively analyzed at time of discharge from the hospital and six months after aneurysmal subarachnoid hemorrhage. Additionally, National Institutes of Health Stroke Scale (NIHSS) was assessed 24 hours before, immediately before, immediately after, and 24 hours after endovascular vasodilator therapy, and at discharge and six months. Interventional parameters such as duration of intervention, choice and dosage of vasodilator and number of arteries treated were also recorded.

Results: A total of 98 patients were included in this analysis and separated into patients who had interventions in conscious sedation, general anesthesia and a mix of both. Neither mRS at discharge nor at six months showed a significant difference for functionally independent outcomes (mRS 0-2) between groups. NIHSS before endovascular vasodilator therapy was significantly higher in patients receiving interventions in general anesthesia but did not differ anymore between groups six months after the initial bleed.

Conclusion: This study did not observe a difference in outcome whether patients underwent endovascular vasodilator therapy in general anesthesia or conscious sedation for refractory cerebral vasospasms. Hence, the choice should be made for each patient individually.

Translational challenges of remote ischemic conditioning in ischemic stroke - a systematic review

Remote ischemic conditioning (RIC) has well‐established cardioprotective effects in preclinical studies and promising results in preclinical stroke research. Effective translation from preclinical studies to clinical trials has yet to be accomplished, perhaps because of the use of multiple applications of RIC (e.g., pre‐, per‐, or post‐conditioning) in preclinical studies by both invasive and non‐invasive protocols, some of which not clinically applicable. Our systematic review conformed to PRISMA guidelines and addressed differences in clinically relevant RIC applications and outcomes between preclinical and clinical studies. We retrieved a total of 30 studies (8 human; 22 animal) that met the inclusion criteria of testing clinically relevant procedures; namely, non‐invasive and per‐ or post‐conditioning protocols. Per‐conditioning was applied in 6 animal and 3 human studies, post‐conditioning was applied in 16 animal and 5 human studies, and both conditioning methods were applied in 2 animal studies. Application of RIC varied between human and animal studies regarding initiation, duration, repetition, and number of limbs included. Study designs did not systematically apply blinding, randomization, or placebo controls. On only a few occasions did preclinical studies include animals with clinically relevant comorbidities. Clinical trials were challenged by not completing the intended number of RIC cycles or addressing this deficit in the data analysis. Consistency and transferability of methods used for positive animal studies and subsequent human studies are essential for the optimal translation of results. Consensus on preclinical and clinical RIC procedures should be reached for a full understanding of the possible beneficial effects of RIC treatment in stroke.

Potential rules of anesthetic gases on glioma

Glioma is one of the most frequent primary brain tumors. Currently, the most common therapeutic strategy for patients with glioma is surgical resection combined with radiotherapy or/and adjuvant chemotherapy. However, due to the metastatic and invasive nature of glioma cells, the recurrence rate is high, resulting in poor prognosis. In recent years, gas therapy has become an emerging treatment. Studies have shown that the proliferation, metastasis and invasiveness of glioma cells exposed to anesthetic gases are obviously inhibited. Therefore, anesthetic gas may play a special therapeutic role in gliomas. In this review, we aim to collect existing research and summarize the rules of using anesthetic gases on glioma, providing potential strategies for further clinical treatment.

Melatonin Improves Reduced Activities of Membrane ATPases and Preserves Ultrastructure of Gray and White Matter in the Rat Brain Ischemia/Reperfusion Model

Ischemia/reperfusion (I/R) is among the most frequent neurological problems and early intervention to limit the damage is crucial in decreasing mortality and morbidity. Based on reports regarding beneficial effects of melatonin, we investigated its impact on Na+-K+/Mg2+ ATPase and Ca2+/Mg2+ ATPase activities and ultrastructure of gray and white matter in the rat forebrain I/R model. Adult Wistar-albino rats (n = 78), were randomized into control, ischemia (I), ischemia/reperfusion (I/R), low (I/R + melatonin 400 µg/kg), moderate (I/R + melatonin 1200 µg/kg), and high (I/R + melatonin 2400 µg/kg) dose melatonin. Two-vessel occlusion combined with hypotension (15 min) induced ischemia and reperfusion (75 min) achieved by blood reinfusion were performed. Activities of the membrane-bound enzyme, brain malondialdehyde levels, and brain matter ultrastructure were examined in frontoparietal cortices. Melatonin lowered production of malondialdehyde in a dose-dependently. The enzyme activities attenuated under I and I/R, improved with melatonin treatment. I and I/R severely disturbed gray and white matter morphology. Melatonin, in all applied doses, decreased ultrastructural damages in both gray and white matter. Favorable effects of melatonin can be attributed to its antioxidant properties suggesting that it could be a promising neuroprotective agent against I/R injury being effective both for gray and white matter due to favorable biological properties.

Novel Mechanistic Insights and Potential Therapeutic Impact of TRPC6 in Neurovascular Coupling and Ischemic Stroke

Ischemic stroke is one of the most disabling diseases and a leading cause of death globally. Despite advances in medical care, the global burden of stroke continues to grow, as no effective treatments to limit or reverse ischemic injury to the brain are available. However, recent preclinical findings have revealed the potential role of transient receptor potential cation 6 (TRPC6) channels as endogenous protectors of neuronal tissue. Activating TRPC6 in various cerebral ischemia models has been found to prevent neuronal death, whereas blocking TRPC6 enhances sensitivity to ischemia. Evidence has shown that Ca2+ influx through TRPC6 activates the cAMP (adenosine 3',5'-cyclic monophosphate) response element-binding protein (CREB), an important transcription factor linked to neuronal survival. Additionally, TRPC6 activation may counter excitotoxic damage resulting from glutamate release by attenuating the activity of N-methyl-d-aspartate (NMDA) receptors of neurons by posttranslational means. Unresolved though, are the roles of TRPC6 channels in non-neuronal cells, such as astrocytes and endothelial cells. Moreover, TRPC6 channels may have detrimental effects on the blood-brain barrier, although their exact role in neurovascular coupling requires further investigation. This review discusses evidence-based cell-specific aspects of TRPC6 in the brain to assess the potential targets for ischemic stroke management.

The role of spreading depolarizations and electrographic seizures in early injury progression of the rat photothrombosis stroke model

Spreading depolarization (SD) and seizures are pathophysiological events associated with cerebral ischemia. Here, we investigated their role for injury progression in the cerebral cortex. Cerebral ischemia was induced in anesthetized male Wistar rats using the photothrombosis (PT) stroke model. SD and spontaneous neuronal activity were recorded in the presence of either urethane or ketamine/xylazine anesthesia. Blood-brain barrier (BBB) permeability, cerebral perfusion, and cellular damage were assessed through a cranial window and repeated intravenous injection of fluorescein sodium salt and propidium iodide until 4 h after PT. Neuronal injury and early lesion volume were quantified by stereological cell counting and manual and automated assessment of ex vivo T2-weighted magnetic resonance imaging. Onset SDs originated at the thrombotic core and invaded neighboring cortex, whereas delayed SDs often showed opposite propagation patterns. Seizure induction by 4-aminopyridine caused no increase in lesion volume or neuronal injury in urethane-anesthetized animals. Ketamine/xylazine anesthesia was associated with a lower number of onset SDs, reduced lesion volume, and neuronal injury despite a longer duration of seizures. BBB permeability increase inversely correlated with the number of SDs at 3 and 4 h after PT. Our results provide further evidence that ketamine may counteract the early progression of ischemic injury.

Animal models for neonatal brain injury induced by hypoxic ischemic conditions in rodents

Neonatal hypoxia-ischemia and resulting encephalopathies are of significant concern. Intrapartum asphyxia is a leading cause of neonatal death globally. Among surviving infants, there remains a high incidence of hypoxic-ischemic encephalopathy due to neonatal hypoxic-ischemic brain injury, manifesting as mild conditions including attention deficit hyperactivity disorder, and debilitating disorders such as cerebral palsy. Various animal models of neonatal hypoxic brain injury have been implemented to explore cellular and molecular mechanisms, assess the potential of novel therapeutic strategies, and characterize the functional and behavioural correlates of injury. Each of the animal models has individual advantages and limitations. The present review looks at several widely-used and alternative rodent models of neonatal hypoxia and hypoxia-ischemia; it highlights their strengths and limitations, and their potential for continued and improved use.

The effect of anaesthetic exposure in presurgical period on delayed cerebral ischaemia and neurological outcome in patients with aneurysmal subarachnoid haemorrhage undergoing clipping of aneurysm: A retrospective analysis

Background and Aims:

Delayed cerebral ischaemia is one of the major contributors to morbidity in aneurysmal subarachnoid haemorrhage (aSAH). General anaesthesia (GA) in the presurgical period may have a preconditioning effect. The primary aim was to assess the effect of preoperative exposure to GA during digital subtraction angiography (DSA) on neurological outcome in patients presenting with aSAH.

Methods:

After Ethical Committee approval, we conducted a retrospective analysis of the data of patients with aSAH treated surgically. Patients, admitted to neurosurgical ICU (June 2014 and December 2017) with a computed tomography (CT) diagnosis of aSAH and underwent DSA, were included. DSA, done with or without exposure to a general anaesthetic, was classified to GA group and LA group, respectively. Propensity score matching was done on the baseline variables. Appropriate statistical methods were applied.

Results:

Of the 278 patients, 116 (41.7%) patients had received GA during DSA. Propensity matching yielded 114 (57 in each group) matched patients. In a logistic regression model, the odds ratio (OR) for poor outcome at discharge in GA group as compared to LA group was 4.4 (CI: 2.7–7.4), P = 0.001, whereas, in the matched data, the OR for poor outcome at discharge in GA group as compared to LA group was 1.2 (CI: 0.6–2.6), P = 0.57.

Conclusion:

The presurgical exposure to GA did not offer any neuroprotection and the odds of poor outcome were higher compare to non-exposure to GA group.

Pathophysiological and clinical considerations in the perioperative care of patients with a previous ischaemic stroke: a multidisciplinary narrative review

With an ageing population and increasing incidence of cerebrovascular disease, an increasing number of patients presenting for routine and emergency surgery have a prior history of stroke. This presents a challenge for pre-, intra-, and postoperative management as the neurological risk is considerably higher. Evidence is lacking around anaesthetic practice for patients with vascular neurological vulnerability. Through understanding the pathophysiological changes that occur after stroke, insight into the susceptibilities of the cerebral vasculature to intrinsic and extrinsic factors can be developed. Increasing understanding of post-stroke systemic and cerebral haemodynamics has provided improved outcomes from stroke and more robust secondary prevention, although this knowledge has yet to be applied to our delivery of anaesthesia in those with prior stroke. This review describes the key pathophysiological and clinical considerations that inform clinicians providing perioperative care for patients with a prior diagnosis of stroke.

Defining and Managing Pain in Stroke and Traumatic Brain Injury Research

Neurologic conditions such as stroke and traumatic brain injury are challenging conditions to study in humans. Animal models are necessary to uncover disease processes and develop novel therapies. When attempting to model these or other neurologic diseases, the accompanying anesthesia and analgesia create variables that are not part of the onset of the clinical disease in the human population but are critical components of the postinjury care both in humans and animals. To maximize model validity, researchers must consider whether the disease process or a novel therapy is being studied. Damage to the neurons of the brain or the spinal cord is not painful at the neural tissue itself, but alterations to nociceptive signaling along the pain pathway can induce chronic pain. In addition, trauma or surgery leading to the event is associated with damage to peripheral tissue. Inflammation is inextricably associated with tissue injury. Inflammation is known to evoke nociception in the periphery and drive long-term changes to neurons in the CNS. Analgesics and anesthetics alter these responses yet are required as part of humane animal care. Careful planning for effective drug administration consistent with the standard of care for humans and equivalent animal care is required.

Recombinant Slit2 attenuates neuronal apoptosis via the Robo1-srGAP1 pathway in a rat model of neonatal HIE

Apoptosis following hypoxic-ischemic injury to the brain plays a major role in neuronal cell death. The neonatal brain is more susceptible to injury as the cortical neurons are immature and there are lower levels of antioxidants. Slit2, an extracellular matrix protein, has been shown to be neuroprotective in various models of neurological diseases. However, there is no information about the role of Slit2 in neonatal hypoxia-ischemia. In this study, we evaluated the effect of Slit2 and its receptor Robo1 in a rat model with neonatal HIE. 10-day old rat pups were used to create the neonatal HIE model. The right common carotid artery was ligated followed by 2.5 h of hypoxia. Recombinant Slit2 was administered intranasally 1 h post HI, recombinant Robo1 was used as a decoy receptor and administered intranasally 1h before HI and srGAP1-siRNA was administered intracerebroventricularly 24 h before HI. Brain infarct area measurement, short-term and long-term neurological function tests, Western blot, immunofluorescence staining, Fluoro-Jade C staining, Nissl staining and TUNEL staining were the assessments done following drug administration. Recombinant Slit2 administration reduced neuronal apoptosis and neurological deficits after neonatal HIE which were reversed by co-administration of recombinant Robo1 and srGAP1-siRNA administration. Recombinant Slit2 showed improved outcomes possibly via the robo1-srGAP1 pathway which mediated the inhibition of RhoA. In this study, the results suggest that Slit2 may help in attenuation of apoptosis and could be a therapeutic agent for treatment of neonatal hypoxic ischemic encephalopathy.

Association of Anesthetic Exposure Time With Clinical Outcomes After Endovascular Therapy for Acute Ischemic Stroke

Background: The optimal sedative regimen with general anesthesia (GA) or conscious sedation for patients undergoing endovascular therapy (EVT) remains controversial. Apart from sedative regimen, the duration of anesthetic exposure may affect clinical outcomes. We aimed to determine whether there is an association between anesthetic exposure time and clinical outcomes in mechanically ventilated stroke patients undergoing EVT for large vessel occlusion.

Methods: This was an observational study of consecutive ischemic stroke patients who underwent EVT for anterior circulation large vessel occlusion under GA from January 2016 to March 2018. To minimize confounding by indication, we restricted our analysis to patients whose anesthetic exposure lasted <72 h. Multivariable logistic regression modeling adjusted for covariates was employed to evaluate whether 90-days independent functional outcome (defined as modified Rankin Scale scores 0–2) and 90-days survival could be predicted by anesthetic exposure time.

Results: During the study period, 138 patients with ischemic stroke who underwent EVT received GA and fulfilled our study criteria: median age was 77 years (interquartile range, 65–82); 46.4% were men; median NIHSS score was 18 (15–21), median ASPECT score was 7 (6–8). Median duration of GA was 5.4 (2.5–19.7) h. Logistic regression modeling revealed an independent association between duration of anesthetic exposure and both 90-days independent functional outcome (p = 0.034) and 90-days survival (p = 0.011). Each additional 15-min of anesthetic exposure decreased the likelihood of achieving an independent functional outcome at 90 days by 1.5% and of being alive at 90 days by 1.0%.

Conclusion: Our data promotes the notion that ischemic stroke patients who require peri-interventional GA for EVT should be extubated as soon as possible after the procedure.

Developing a standardized system of exposure and intervention endpoints for isoflurane in preclinical stroke models

Isoflurane is a regularly used anesthetic in translational research. Isoflurane facilitates invasive surgery and a rapid recovery. Specifically, in the pathology of stroke, controversy has surrounded isoflurane's intrinsic neuroprotective abilities, affecting apoptosis, excitotoxicity, and blood brain barrier disruption. Due to the intrinsic neuroprotective nature and lack of standardized guidelines for the use of isoflurane, research has shifted away from this gas in most animal models. Antagonistically, studies have also reported that no neuroprotective effects are observed when a surgery is accompanied with isoflurane exposure under 20 minutes. Isoflurane affects the pathophysiology in stroke patients by altering critical pathways in endothelial, neuronal, and microglial cells. Current studies have elucidated isoflurane neuroprotection to be time dependent and may be minimized in experimental designs if the exposure time is limited to a specific window. Therefore, with detailed and extensive literature on anesthetics, we can hypothesize that isoflurane exposure under the 20-minute benchmark, behavior and molecular pathways can be evaluated at any time-point following ischemic insult without confounding artifacts from isoflurane; however, If the exposure to isoflurane exceeds 20 minutes, the acute neuroprotective effects are evident for 2 weeks in the model, which should be accounted for in molecular and behavioral assessments, with either isoflurane inhibitors or a control group at 2 weeks post middle cerebral artery occlusion. The purpose of this review is to suggest a detailed and standardized outline for interventions and behavioral assessments after the use of isoflurane in experimental designs.

The insights into molecular pathways of hypoxia-inducible factor in the brain

The objectives of this present work were to review recent developments on the role of hypoxia-inducible factor (HIF) in the survival of cells under normoxic versus hypoxic and inflammatory brain conditions. The dual nature of HIF effects appears well established, based on the accumulated evidence of HIF playing both the role of adaptive factor and mediator of cell demise. Cellular HIF responses depend on pathophysiological conditions, developmental phase, comorbidities, and administered medications. In addition, HIF-1α and HIF-2α actions may vary in the same tissues. The multiple roles of HIF in stem cells are emerging. HIF not only regulates expression of target genes and thereby influences resultant protein levels but also contributes to epigenetic changes that may reciprocally provide feedback regulations loops. These HIF-dependent alterations in neurological diseases and its responses to treatments in vivo need to be examined alongside with a functional status of subjects involved in such studies. The knowledge of HIF pathways might be helpful in devising HIF-mimetics and modulating drugs, acting on the molecular level to improve clinical outcomes, as exemplified here by clinical and experimental data of selected brain diseases, occasionally corroborated by the data from disorders of other organs. Because of complex role of HIF in brain injuries, prospective therapeutic interventions need to differentially target HIF responses depending on their roles in the molecular mechanisms of neurologic diseases.

Cerebral venous collaterals: A new fort for fighting ischemic stroke?

Stroke therapy has entered a new era highlighted by the use of endovascular therapy in addition to intravenous thrombolysis. However, the efficacy of current therapeutic regimens might be reduced by their associated adverse events. For example, over-reperfusion and futile recanalization may lead to large infarct, brain swelling, hemorrhagic complication and neurological deterioration. The traditional pathophysiological understanding on ischemic stroke can hardly address these occurrences. Accumulating evidence suggests that a functional cerebral venous drainage, the major blood reservoir and drainage system in brain, may be as critical as arterial infusion for stroke evolution and clinical sequelae. Further exploration of the multi-faceted function of cerebral venous system may add new implications for stroke outcome prediction and future therapeutic decision-making. In this review, we emphasize the anatomical and functional characteristics of the cerebral venous system and illustrate its necessity in facilitating the arterial infusion and maintaining the cerebral perfusion in the pathological stroke content. We then summarize the recent critical clinical studies that underscore the associations between cerebral venous collateral and outcome of ischemic stroke with advanced imaging techniques. A novel three-level venous system classification is proposed to demonstrate the distinct characteristics of venous collaterals in the setting of ischemic stroke. Finally, we discuss the current directions for assessment of cerebral venous collaterals and provide future challenges and opportunities for therapeutic strategies in the light of these new concepts.

Near-infrared diffuse reflectance signals for monitoring spreading depolarizations and progression of the lesion in a male rat focal cerebral ischemia model

In ischemic stroke research, a better understanding of the pathophysiology and development of neuroprotection methods are crucial, for which in vivo imaging to monitor spreading depolarizations (SDs) and evolution of tissue damage is desired. Since these events are accompanied by cellular morphological changes, light-scattering signals, which are sensitive to cellular and subcellular morphology, can be used for monitoring them. In this study, we performed transcranial imaging of near-infrared (NIR) diffuse reflectance at ∼800 nm, which sensitively reflects light-scattering change, and examined how NIR reflectance is correlated with simultaneously measured cerebral blood flow (CBF) for a rat middle cerebral artery occlusion (MCAO) model. After MCAO, wavelike NIR reflectance changes indicating occurrence of SDs were generated and propagated around the ischemic core for ∼90 min, during which time NIR reflectance increased not only within the ischemic core but also in the peripheral region. The area with increased reflectance expanded with increase in the number of SD occurrences, the correlation coefficient being 0.7686 (n = 5). The area with increased reflectance had become infarcted at 24 hr after MCAO. The infarct region was found to be associated with hypoperfusion or no-flow response to SD, but hyperemia or hypoperfusion followed by hyperemia response to SD was also observed, and the regional heterogeneity seemed to be connected with the rat cerebrovasculature and hence existence/absence of collateral flow. The results suggest that NIR reflectance signals depicted early evolution of tissue damage, which was not seen by CBF changes, and enabled lesion progression monitoring in the present stroke model.

General Anesthesia Versus Conscious Sedation for Endovascular Treatment of Acute Ischemic Stroke

Background and Purpose—

Retrospective studies have found that patients receiving general anesthesia for endovascular treatment in acute ischemic stroke have worse neurological outcome compared with patients receiving conscious sedation. In this prospective randomized single-center study, we investigated the impact of anesthesia technique on neurological outcome in acute ischemic stroke patients.

Methods—

Ninety patients receiving endovascular treatment for acute ischemic stroke in 2013 to 2016 were included and randomized to general anesthesia or conscious sedation. Difference in neurological outcome at 3 months, measured as modified Rankin Scale score, was analyzed (primary outcome) and early neurological improvement of National Institutes of Health Stroke Scale and cerebral infarction volume. Age, sex, comorbidities, admission National Institutes of Health Stroke Scale score, intraprocedural blood pressure, blood glucose, Paco 2 and Pco 2 modified Thrombolysis in Cerebral Ischemia score, and relevant time intervals were recorded.

Results—

In the general anesthesia group 19 of 45 patients (42.2%) and in the conscious sedation group 18 of 45 patients (40.0%) achieved a modified Rankin Scale score ≤2 ( P =1.00) at 3 months, with no differences in intraoperative blood pressure decline from baseline ( P =0.57); blood glucose ( P =0.94); PaCO2 ( P =0.68); time intervals ( P =0.78); degree of successful recanalization, 91.1% versus 88.9% ( P =1.00); National Institutes of Health Stroke Scale score at 24 hours 8 (3–5) versus 9 (2–15; P =0.60); infarction volume, 20 (10–100) versus 20(10–54) mL ( P =0.53); and hospital mortality (13.3% in both groups; P =1.00).

Conclusions—

In endovascular treatment for acute ischemic stroke, no difference was found between general anesthesia and conscious sedation in neurological outcome 3 months after stroke.

Clinical Trial Registration—

URL: https://www.clinicaltrials.gov . Unique identifier: NCT01872884.

Alpha-7 Nicotinic Receptor Signaling Pathway Participates in the Neurogenesis Induced by ChAT-Positive Neurons in the Subventricular Zone

Choline acetyltransferase-positive (ChAT+) neurons within the subventricular zone (SVZ) have been shown to promote neurogenesis after stroke in mice by secreting acetylcholine (ACh); however, the mechanisms remain unclear. Receptors known to bind ACh include the nicotinic ACh receptors (nAChRs), which are present in the SVZ and have been shown to be important for cell proliferation, differentiation, and survival. In this study, we investigated the neurogenic role of the alpha-7 nAChR (α7 nAChR) in a mouse model of middle cerebral artery occlusion (MCAO) by using α7 nAChR inhibitor methyllycaconitine. Mice subjected to MCAO exhibited elevated expression of cytomembrane and nuclear fibroblast growth factor receptor 1 (FGFR1), as well as increased expression of PI3K, pAkt, doublecortin (DCX), polysialylated - neuronal cell adhesion molecule (PSA-NCAM), and mammalian achaete-scute homolog 1 (Mash1). MCAO mice also had more glial fibrillary acidic protein (GFAP)/5-bromo-2'-deoxyuridine (BrdU)-positive cells and DCX-positive cells in the SVZ than did the sham-operated group. Methyllycaconitine treatment increased cytomembrane FGFR1 expression and GFAP/BrdU-positive cells, upregulated the levels of phosphoinositide 3-kinase (PI3K) and phospho-Akt (pAkt), decreased nuclear FGFR1 expression, decreased the number of DCX-positive cells, and reduced the levels of DCX, PSA-NCAM, and Mash1 in the SVZ of MCAO mice compared with levels in vehicle-treated MCAO mice. MCAO mice treated with α7 nAChR agonist PNU-282987 exhibited the opposite effects. Our data show that α7 nAChR may decrease the proliferation of neural stem cells and promote differentiation of existing neural stem cells after stroke. These results identify a new mechanism of SVZ ChAT+ neuron-induced neurogenesis.

Neuroprotection provided by isoflurane pre-conditioning and post-conditioning

Isoflurane, a volatile and inhalational anesthetic, has been extensively used in perioperative period for several decades. A large amount of experimental studies have indicated that isoflurane exhibits neuroprotective properties when it is administrated before or after (pre-conditioning and post-conditioning) neurodegenerative diseases (e.g., hypoxic ischemia, stroke and trauma). Multiple mechanisms are involved in isoflurane induced neuroprotection, including activation of glycine and γ-aminobutyric acid receptors, antagonism of ionic channels and alteration of the function and activity of other cellular proteins. Although neuroprotection provided by isoflurane is observed in many animal studies, convincing evidence is lacking in human trials. Therefore, there is still a long way to go before translating its neuroprotective properties into clinical practice.