A modified rehabilitation paradigm bilaterally increased rat extensor digitorum communis muscle size but did not improve forelimb function after stroke

Malnutrition after stroke may lessen the beneficial effects of rehabilitation on motor recovery through influences on both brain and skeletal muscle. Enriched rehabilitation (ER), a combination of environmental enrichment and forelimb reaching practice, is used preclinically to study recovery of skilled reaching after stroke. However, the chronic food restriction typically used to motivate engagement in reaching practice is a barrier to using ER to investigate interactions between nutritional status and rehabilitation. Thus, our objectives were to determine if a modified ER program comprised of environmental enrichment and skilled reaching practice motivated by a short fast would enhance post-stroke forelimb motor recovery and preserve forelimb muscle size and metabolic fiber type, relative to a group exposed to stroke without ER. At one week after photothrombotic cortical stroke, male, Sprague-Dawley rats were assigned to modified ER or standard care for 2 weeks. Forelimb recovery was assessed in the Montoya staircase and cylinder task before stroke and on days 5-6, 22-23, and 33-34 after stroke. ER failed to improve forelimb function in either task (p > 0.05). Atrophy of extensor digitorum communis (EDC) and triceps brachii long head (TBL) muscles was not evident in the stroke-targeted forelimb on day 35, but the area occupied by hybrid fibers was increased in the EDC muscle (p = 0.038). ER bilaterally increased EDC (p = 0.046), but not TBL, muscle size; EDC muscle fiber type was unchanged by ER. While the modified ER did not promote forelimb motor recovery, it does appear to have utility for studying the role of skeletal muscle plasticity in post-stroke recovery.

An Assessment of Physical and N6-Cyclohexyladenosine-Induced Hypothermia in Rodent Distal Focal Ischemic Stroke

Therapeutic hypothermia (TH) mitigates damage in ischemic stroke models. However, safer and easier TH methods (e.g., pharmacological) are needed to circumvent physical cooling complications. This study evaluated systemic and pharmacologically induced TH using the adenosine A1 receptor agonist, N6-cyclohexyladenosine (CHA), with control groups in male Sprague-Dawley rats. CHA was administered intraperitoneally 10 minutes following a 2-hour intraluminal middle cerebral artery occlusion. We used a 1.5 mg/kg induction dose, followed by three 1.0 mg/kg doses every 6 hours for a total of 4 doses, causing 20-24 hours of hypothermia. Animals assigned to physical hypothermia and CHA-hypothermia had similar induction rates and nadir temperatures, but forced cooling lasted ∼6 hours longer compared with CHA-treated animals. The divergence is likely attributable to individual differences in CHA metabolism, which led to varied durations at nadir, whereas physical hypothermia was better regulated. Physical hypothermia significantly reduced infarction (primary endpoint) on day 7 (mean reduction of 36.8 mm3 or 39% reduction; p = 0.021 vs. normothermic animals; Cohen's d = 0.75), whereas CHA-induced hypothermia did not (p = 0.33). Similarly, physical cooling improved neurological function (physical hypothermia median = 0, physical normothermia median = 2; p = 0.008) and CHA-induced cooling did not (p > 0.99). Our findings demonstrate that forced cooling was neuroprotective compared with controls, but prolonged CHA-induced cooling was not neuroprotective.

Tissue Compliance and Intracranial Pressure Responses to Large Intracerebral Hemorrhage in Young and Aged Spontaneously Hypertensive Rats

BACKGROUND

After a large intracerebral hemorrhage (ICH), the hematoma and swelling cause intracranial pressure (ICP) to increase, sometimes causing brain herniation and death. This is partly countered by widespread tissue compliance, an acute decrease in tissue volume distal to the stroke, at least in young healthy animals. Intracranial compensation dynamics seem to vary with age, but there is no data on old animals or those with hypertension, major factors influencing ICH risk and outcome.

METHODS

We assessed hematoma volume, edema, ICP, and functional deficits in young and aged spontaneously hypertensive rats (SHRs) and young normotensive control strains after collagenase-induced ICH. Macroscopic and microscopic brain volume fractions, such as contralateral hemisphere volume, cortical thickness, and neuronal morphology, were assessed via histological and stereological techniques.

RESULTS

Hematoma volume was 52% larger in young versus aged SHRs; surprisingly, aged SHRs still experienced proportionally worse outcomes following ICH, with 2× greater elevations in edema and ICP relative to bleed volume and 3× the degree of tissue compliance. Aged SHRs also experienced equivalent neurological deficits following ICH compared with their younger counterparts, despite the lack of significant age-related behavioral effects. Importantly, tissue compliance occurred across strains and age groups and was not impaired by hypertension or old age.

CONCLUSIONS

Aged SHRs show considerable capacity for tissue compliance following ICH and seem to rely on such mechanisms more heavily in settings of elevated ICP. Therefore, the ICP compensation response to ICH mass effect varies across the lifespan according to risk factors such as chronic hypertension.

Intracranial Pressure Dysfunction Following Severe Intracerebral Hemorrhage in Middle-Aged Rats

Rising intracranial pressure (ICP) aggravates secondary injury and heightens risk of death following intracerebral hemorrhage (ICH). Long-recognized compensatory mechanisms that lower ICP include reduced cerebrospinal fluid and venous blood volumes. Recently, we identified another compensatory mechanism in severe stroke, a decrease in cerebral parenchymal volume via widespread reductions in cell volume and extracellular space (tissue compliance). Here, we examined how age affects tissue compliance and ICP dynamics after severe ICH in rats (collagenase model). A planned comparison to historical young animal data revealed that aged SHAMs (no stroke) had significant cerebral atrophy (9% reduction, p ≤ 0.05), ventricular enlargement (9% increase, p ≤ 0.05), and smaller CA1 neuron volumes (21%, p ≤ 0.05). After ICH in aged animals, contralateral striatal neuron density and CA1 astrocyte density significantly increased (12% for neurons, 7% for astrocytes, p ≤ 0.05 vs. aged SHAMs). Unlike young animals, other regions in aged animals did not display significantly reduced cell soma volume despite a few trends. Nonetheless, overall contralateral hemisphere volume was 10% smaller in aged ICH animals compared to aged SHAMs (p ≤ 0.05). This age-dependent pattern of tissue compliance is not due to absent ICH-associated mass effect (83.2 mm3 avg. bleed volume) as aged ICH animals had significantly elevated mean and peak ICP (p ≤ 0.01), occurrence of ICP spiking events, as well as bilateral evidence of edema (e.g., 3% in injured brain, p ≤ 0.05 vs. aged SHAMs). Therefore, intracranial compliance reserve changes with age; after ICH, these and other age-related changes may cause greater fluctuation from baseline, increasing the chance of adverse outcomes like mortality.

Motor Rehabilitation Provides Modest Functional Benefits After Intracerebral Hemorrhage: a Systematic Review and Meta-Analysis of Translational Rehabilitation Studies

Few certainties exist regarding the optimal type, timing, or dosage of rehabilitation after stroke. Despite differing injury mechanisms and recovery patterns following ischemic and hemorrhagic stroke, most translational stroke research is conducted after ischemia. As we enter the era of personalized medicine, exploring subtype-specific treatment efficacy is essential to optimizing recovery. Our objective was to characterize common rehabilitation interventions used after in vivo preclinical intracerebral hemorrhage (ICH) and assess the impact of post-ICH rehabilitation (vs. no-rehabilitation) on recovery of motor function. Following PRISMA guidelines, a systematic review (Academic Search Complete, CINAHL, EMBASE, Medline, PubMed Central) identified eligible articles published up to December 2022. Risk of bias (SYRCLE) and study quality (CAMARADES) were evaluated, and random-effects meta-analysis was used to assess treatment efficacy in recovery of forelimb and locomotor functions. Thirty articles met inclusion criteria, and 48 rehabilitation intervention groups were identified. Most used collagenase to model striatal ICH in young, male rodents. Aerobic exercise, enriched rehabilitation, and constraint-induced movement therapy represented ~ 70% of interventions. Study quality was low (median 4/10, range 2-8), and risk of bias was unclear. Rehabilitation provided modest benefits in skilled reaching, spontaneous impaired forelimb use, and locomotor function; however, effects varied substantially by endpoint, treatment type, and study quality. Rehabilitation statistically improves motor function after preclinical ICH, but whether these effects are functionally meaningful is unclear. Incomplete reporting and variable research quality hinder our capacity to analyze and interpret how treatment factors influence rehabilitation efficacy and recovery after ICH.

Longer Periods of Hypothermia Provide Greater Protection Against Focal Ischemia: A Systematic Review of Animal Studies Manipulating Treatment Duration

Decades of animal research show therapeutic hypothermia (TH) to be potently neuroprotective after cerebral ischemic injuries. While there have been some translational successes, clinical efficacy after ischemic stroke is unclear. One potential reason for translational failures could be insufficient optimization of dosing parameters. In this study, we conducted a systematic review of the PubMed database to identify all preclinical controlled studies that compared multiple TH durations following focal ischemia, with treatment beginning at least 1 hour after ischemic onset. Six studies met our inclusion criteria. In these six studies, six of seven experiments demonstrated an increase in cerebroprotection at the longest duration tested. The average effect size (mean Cohen's d ± 95% confidence interval) at the shortest and longest durations was 0.4 ± 0.3 and 1.9 ± 1.1, respectively. At the longest durations, this corresponded to percent infarct volume reductions between 31.2% and 83.9%. Our analysis counters previous meta-analytic findings that there is no relationship, or an inverse relationship between TH duration and effect size. However, underreporting often led to high or unclear risks of bias for each study as gauged by the SYRCLE Risk of Bias tool. We also found a lack of investigations of the interactions between duration and other treatment considerations (e.g., method, delay, and ischemic severity). With consideration of methodological limitations, an understanding of the relationships between treatment parameters is necessary to determine proper "dosage" of TH, and should be further studied, considering clinical failures that contrast with strong cerebroprotective results in most animal studies.

A systematic review and meta-analysis on the efficacy of glibenclamide in animal models of intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating stroke with many mechanisms of injury. Edema worsens outcome and can lead to mortality after ICH. Glibenclamide (GLC), a sulfonylurea 1- transient receptor potential melastatin 4 (Sur1-Trpm4) channel blocker, has been shown to attenuate edema in ischemic stroke models, raising the possibility of benefit in ICH. This meta-analysis synthesizes current pre-clinical (rodent) literature regarding the efficacy of post-ICH GLC administration (vs. vehicle controls) on behaviour (i.e., neurological deficit, motor, and memory outcomes), edema, hematoma volume, and injury volume. Six studies (5 in rats and 1 in mice) were included in our meta-analysis (PROSPERO registration = CRD42021283614). GLC significantly improved behaviour (standardized mean difference (SMD) = -0.63, [-1.16, -0.09], n = 70-74) and reduced edema (SMD = -0.91, [-1.64, -0.18], n = 70), but did not affect hematoma volume (SMD = 0.0788, [-0.5631, 0.7207], n = 18-20), or injury volume (SMD = 0.2892, [-0.4950, 1.0734], n = 24). However, these results should be interpreted cautiously. Findings were conflicted with 2 negative and 4 positive reports, and Egger regressions indicated missing negative edema data (p = 0.0001), and possible missing negative behavioural data (p = 0.0766). Experimental quality assessed via the SYRCLE and CAMARADES checklists was concerning, as most studies demonstrated high risks of bias. Studies were generally low-powered (e.g., average n = 14.4 for behaviour), and future studies should employ sample sizes of 41 to detect our observed effect size in behaviour and 33 to detect our observed effect in edema. Overall, missing negative studies, low study quality, high risk of bias, and incomplete attention to key recommendations (e.g., investigating female, aged, and co-morbid animals) suggest that further high-powered confirmatory studies are needed before conclusive statements about GLC's efficacy in ICH can be made, and before further clinical trials are performed.

An Ambiguous Role for Fever in Worsening Outcome After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) accounts for 10-15% of all strokes and leaves most survivors with impairments. Fever, a rise in the thermoregulatory set point, complicates ICH. This review summarizes ICH fever studies and employs meta-analytic techniques to explore the relationship between fever and ICH. We discuss methodological considerations for future studies and provide an overview of mechanisms by which fever, and its treatment, may impact ICH. We searched the PubMed database using the following terms: ((fever OR hyperthermia) AND (intracerebral hemorrhage OR intraparenchymal hemorrhage OR intracerebral haemorrhage OR intraparenchymal haemorrhage)). Our search returned 727 studies, of which 21 were included in our final analysis, consisting of 19 clinical, and two preclinical, studies. We conducted a meta-analysis on the clinical data to quantify how fever is related to mortality, functional outcomes, and intraventricular hemorrhage. Analysis of clinical studies suggested that fever causes an increased risk of mortality but does not appear to be associated with poor outcomes among survivors, making it difficult to ascertain the extent of harm caused by post-ICH fever or the benefits of its treatment. Perhaps these inconsistencies stem from variable fever definitions, and temperature measurement and fever treatment protocols. Additionally, the lack of mechanistic data in clinical studies coupled with preclinical studies showing no harmful effects of moderate bouts of hyperthermia raise concerns about the direct contribution of hyperthermia and fever in post ICH outcome. Overall, the significance of temperature increases after ICH is unclear, making this an important area for future research.

Early, Intense Rehabilitation Fails to Improve Outcome After Intra-Striatal Hemorrhage in Rats

BACKGROUND

The formation and degradation of an intracerebral hemorrhage causes protracted cell death, and an extended window for intervention. Experimental studies find that rehabilitation mitigates late cell death, with accelerated hematoma clearance as a potential mechanism.

OBJECTIVE

We assessed whether early, intense, enriched rehabilitation (ER, environmental enrichment and massed skills training) enhances functional benefit, reduces brain injury, and augments hematoma clearance.

METHODS

In experiment 1, rats (n = 56) were randomized to intervention in the light (-L) or dark phase (-D) of their housing cycle, then to 10 days of ER or control (CON) treatment after collagenase-induced striatal intracerebral hemorrhage (ICH). ER rats were treated from 5 to 14 days after ICH. Behavior and residual hematoma volume was assessed on day 14. In experiment 2, rats (n = 72) were randomized to ER-D10, ER-D20, or CON-D. ER rats completed 10 or 20 days of training in the dark. Rats were euthanized on day 60 for histology. In both experiments, behavioral assessment was completed pre-ICH, pre-ER (day 4 post-ICH), and post-ER (experiment 1: days 13-14; experiment 2: days 16-17 and 30-31).

RESULTS

Reaching intensity was high but similar between ER-D10 and ER-L10. Unlike previous work, rehabilitation did not alter skilled reaching or hematoma resolution. Varying ER duration also did not affect reaching success or lesion volume.

CONCLUSIONS

In contrast to others, and under these conditions, our findings show that striatal ICH was generally unresponsive to rehabilitation. This highlights the difficulty of replicating and extending published work, perhaps owing to small inter-study differences.

Colchicine pre-treatment and post-treatment does not worsen bleeding or functional outcome after collagenase-induced intracerebral hemorrhage

Patients with intracerebral hemorrhage (ICH) are at increased risk for major ischemic cardiovascular and cerebrovascular events. However, the use of preventative antithrombotic therapy can increase the risk of ICH recurrence and worsen ICH-related outcomes. Colchicine, an anti-inflammatory agent, has the potential to mitigate inflammation-related atherothrombosis and reduce the risk of ischemic vascular events. Here we investigated the safety and efficacy of colchicine when used both before and acutely after ICH. We predicted that daily colchicine administration would not impact our safety measures but would reduce brain injury and improve functional outcomes associated with inflammation reduction. To test this, 0.05 mg/kg colchicine was given orally once daily to rats either before or after they were given a collagenase-induced striatal ICH. We assessed neurological impairments, intra-parenchymal bleeding, Perls positive cells, and brain injury to gauge the therapeutic impact of colchicine on brain injury. Colchicine did not significantly affect bleeding (average = 40.7 μL) at 48 hrs, lesion volume (average = 24.5 mm³) at 14 days, or functional outcome (median neurological deficit scale score at 2 days post-ICH = 4, i.e., modest deficits) from 1–14 days after ICH. Colchicine reduced the volume of Perls positive cells in the perihematomal zone, indicating a reduction in inflammation. Safety measures (body weight, food consumption, water consumption, hydration, body temperature, activity, and pain) were not affected by colchicine. Although colchicine did not confer neuroprotection or functional benefit, it was able to reduce perihematomal inflammation after ICH without increasing bleeding. Thus, our findings suggest that colchicine treatment is safe, unlikely to worsen bleeding, and is unlikely but may reduce secondary injury after an ICH if initiated early post ICH to reduce the risk of ischemic vascular events. These results are informative for the ongoing CoVasc-ICH phase II randomized trial (NCT05159219).

Consensus recommendations on therapeutic hypothermia after minimally invasive intracerebral hemorrhage evacuation from the hypothermia for intracerebral hemorrhage (HICH) working group

Background and purpose

Therapeutic hypothermia (TH), or targeted temperature management (TTM), is a classic treatment option for reducing inflammation and potentially other destructive processes across a wide range of pathologies, and has been successfully used in numerous disease states. The ability for TH to improve neurological outcomes seems promising for inflammatory injuries but has yet to demonstrate clinical benefit in the intracerebral hemorrhage (ICH) patient population. Minimally invasive ICH evacuation also presents a promising option for ICH treatment with strong preclinical data but has yet to demonstrate functional improvement in large randomized trials. The biochemical mechanisms of action of ICH evacuation and TH appear to be synergistic, and thus combining hematoma evacuation with cooling therapy could provide synergistic benefits. The purpose of this working group was to develop consensus recommendations on optimal clinical trial design and outcomes for the use of therapeutic hypothermia in ICH in conjunction with minimally invasive ICH evacuation.

Methods

An international panel of experts on the intersection of critical-care TH and ICH was convened to analyze available evidence and form a consensus on critical elements of a focal cooling protocol and clinical trial design. Three focused sessions and three full-group meetings were held virtually from December 2020 to February 2021. Each meeting focused on a specific subtopic, allowing for guided, open discussion.

Results

These recommendations detail key elements of a clinical cooling protocol and an outline for the roll-out of clinical trials to test and validate the use of TH in conjunction with hematoma evacuation as well as late-stage protocols to improve the cooling approach. The combined use of systemic normothermia and localized moderate (33.5°C) hypothermia was identified as the most promising treatment strategy.

Conclusions

These recommendations provide a general outline for the use of TH after minimally invasive ICH evacuation. More research is needed to further refine the use and combination of these promising treatment paradigms for this patient population.

Therapeutic hypothermia for intracerebral hemorrhage: Systematic review and meta-analysis of the experimental and clinical literature

BACKGROUND

Intracerebral hemorrhage remains the deadliest form of stroke worldwide, inducing neuronal death through a wide variety of pathways. Therapeutic hypothermia is a robust and well-studied neuroprotectant widely used across a variety of specialties.

AIMS

This review summarizes results from preclinical and clinical studies to highlight the overall effectiveness of therapeutic hypothermia to improve long-term intracerebral hemorrhage outcomes while also elucidating optimal protocol regimens to maximize therapeutic effect.

SUMMARY OF REVIEW

A systematic review was conducted across three databases to identify trials investigating the use of therapeutic hypothermia to treat intracerebral hemorrhage. A random-effects meta-analysis was conducted on preclinical studies, looking at neurobehavioral outcomes, blood brain barrier breakdown, cerebral edema, hematoma volume, and tissue loss. Several mixed-methods meta-regression models were also performed to adjust for variance and variations in hypothermia induction procedures. Twwenty-one preclinical studies and five human studies were identified. The meta-analysis of preclinical studies demonstrated a significant benefit in behavioral scores (ES = -0.43, p = 0.02), cerebral edema (ES = 1.32, p = 0.0001), and blood brain barrier (ES = 2.73, p ≤ 0.00001). Therapeutic hypothermia was not found to significantly affect hematoma expansion (ES = -0.24, p = 0.12) or tissue loss (ES = 0.06, p = 0.68). Clinical study outcome reporting was heterogeneous; however, there was recurring evidence of therapeutic hypothermia-induced edema reduction.

CONCLUSIONS

The combined preclinical evidence demonstrates that therapeutic hypothermia reduced multiple cell death mechanisms initiated by intracerebral hemorrhage; yet, there is no definitive evidence in clinical studies. The cooling strategies employed in both preclinical and clinical studies were highly diverse, and focused refinement of cooling protocols should be developed in future preclinical studies. The current data for therapeutic hypothermia in intracerebral hemorrhage remains questionable despite the highly promising indications in preclinical studies. Definitive randomized controlled studies are still required to answer this therapeutic question.

Targeting focal ischemic and hemorrhagic stroke neuroprotection: Current prospects for local hypothermia

Therapeutic hypothermia (TH) has applications dating back millennia. In modern history, however, TH saw its importation into medical practice where investigations have demonstrated that TH is efficacious in ischemic insults, notably cardiac arrest and hypoxic-ischemic encephalopathy. As well, studies have been undertaken to investigate whether TH can provide benefit in focal stroke (i.e., focal ischemia and intracerebral hemorrhage). However, clinical studies have encountered various challenges with induction and maintenance of post-stroke TH. Most clinical studies have attempted to use body-wide cooling protocols, commonly hindered by side effects that can worsen post-stroke outcomes. Some of the complications and difficulties with systemic TH can be circumvented by using local hypothermia (LH) methods. Additional advantages include the potential for lower target temperatures to be achieved and faster TH induction rates with LH. This systematic review summarizes the body of clinical and preclinical LH focal stroke studies and raises key points to consider for future LH research. We conclude with an overview of LH neuroprotective mechanisms and a comparison of LH mechanisms with those observed with systemic TH. Overall, whereas many LH studies have been conducted preclinically in the context of focal ischemia, insufficient work has been done in intracerebral hemorrhage. Furthermore, key translational studies have yet to be done in either stroke subtype (e.g., varied models and time-to-treat, studies considering aged animals or animals with co-morbidities). Few clinical LH investigations have been performed and the optimal LH parameters to achieve neuroprotection are unknown.

Glibenclamide does not improve outcome following severe collagenase-induced intracerebral hemorrhage in rats

Intracerebral hemorrhage (ICH) is a devastating insult with few effective treatments. Edema and raised intracranial pressure contribute to poor outcome after ICH. Glibenclamide blocks the sulfonylurea 1 transient receptor potential melastatin 4 (Sur1-Trpm4) channel implicated in edema formation. While glibenclamide has been found to improve outcome and reduce mortality in animal models of severe ischemic stroke, in ICH the effects are less clear. In our previous study, we found no benefit after a moderate-sized bleed, while others have reported benefit. Here we tested the hypothesis that glibenclamide may only be effective in severe ICH, where edema is an important contributor to outcome. Glibenclamide (10 μg/kg loading dose, 200 ng/h continuous infusion) was administered 2 hours post-ICH induced by collagenase injection into the striatum of adult rats. A survival period of 24 hours was maintained for experiments 1–3, and 72 hours for experiment 4. Glibenclamide did not affect hematoma volume (~81 μL) or other safety endpoints (e.g., glucose levels), suggesting the drug is safe. However, glibenclamide did not lessen striatal edema (~83% brain water content), ionic dyshomeostasis (Na⁺, K⁺), or functional impairment (e.g., neurological deficits (median = 10 out of 14), etc.) at 24 hours. It also did not affect edema at 72 h (~86% brain water content), or overall mortality rates (25% and 29.4% overall in vehicle vs. glibenclamide-treated severe strokes). Furthermore, glibenclamide appears to worsen cytotoxic edema in the peri-hematoma region (cell bodies were 46% larger at 24 h, p = 0.0017), but no effect on cell volume or density was noted elsewhere. Overall, these findings refute our hypothesis, as glibenclamide produced no favorable effects following severe ICH.

A Systematic Review and Meta-Analysis of Animal Studies Testing Intra-Arterial Chilled Infusates After Ischemic Stroke

Background: As not all ischemic stroke patients benefit from currently available treatments, there is considerable need for neuroprotective co-therapies. Therapeutic hypothermia is one such co-therapy, but numerous issues have hampered its clinical use (e.g., pneumonia risk with whole-body cooling). Some problems may be avoided with brain-specific methods, such as intra-arterial selective cooling infusion (IA-SCI) into the arteries supplying the ischemic tissue. Objective: Our research question was about the efficacy of IA-SCI in animal middle cerebral artery occlusion models. We hypothesized that IA-SCI would be beneficial, but translationally-relevant study elements may be missing (e.g., aged animals). Methods: We completed a systematic review of the PubMed database following the PRISMA guidelines on May 21, 2020 for animal studies that administered IA-SCI in the peri-reperfusion period and assessed infarct volume, behavior (primary meta-analytic endpoints), edema, or blood-brain barrier injury (secondary endpoints). Our search terms included: "focal ischemia" and related terms, "IA-SCI" and related terms, and "animal" and related terms. Nineteen studies met inclusion criteria. We adapted a methodological quality scale from 0 to 12 for experimental design assessment (e.g., use of blinding/randomization, a priori sample size calculations). Results: Studies were relatively homogenous (e.g., all studies used young, healthy animals). Some experimental design elements, such as blinding, were common whereas others, such as sample size calculations, were infrequent (median methodological quality score: 5; range: 2-7). Our analyses revealed that IA-SCI provides benefit on all endpoints (mean normalized infarct volume reduction = 23.67%; 95% CI: 19.21-28.12; mean normalized behavioral improvement = 35.56%; 95% CI: 25.91-45.20; mean standardized edema reduction = 0.95; 95% CI: 0.56-1.34). Unfortunately, blood-brain barrier assessments were uncommon and could not be analyzed. However, there was substantial statistical heterogeneity and relatively few studies. Therefore, exploration of heterogeneity via meta-regression using saline infusion parameters, study quality, and ischemic duration was inconclusive. Conclusion: Despite convincing evidence of benefit in ischemic stroke models, additional studies are required to determine the scope of benefit, especially when considering additional elements (e.g., dosing characteristics). As there is interest in using this treatment alongside current ischemic stroke therapies, more relevant animal studies will be critical to inform patient studies.

An update to the Monro-Kellie doctrine to reflect tissue compliance after severe ischemic and hemorrhagic stroke

High intracranial pressure (ICP) can impede cerebral blood flow resulting in secondary injury or death following severe stroke. Compensatory mechanisms include reduced cerebral blood and cerebrospinal fluid volumes, but these often fail to prevent raised ICP. Serendipitous observations in intracerebral hemorrhage (ICH) suggest that neurons far removed from a hematoma may shrink as an ICP compliance mechanism. Here, we sought to critically test this observation. We tracked the timing of distal tissue shrinkage (e.g. CA1) after collagenase-induced striatal ICH in rat; cell volume and density alterations (42% volume reduction, 34% density increase; p < 0.0001) were highest day one post-stroke, and rebounded over a week across brain regions. Similar effects were seen in the filament model of middle cerebral artery occlusion (22% volume reduction, 22% density increase; p ≤ 0.007), but not with the Vannucci-Rice model of hypoxic-ischemic encephalopathy (2.5% volume increase, 14% density increase; p ≥ 0.05). Concerningly, this 'tissue compliance' appears to cause sub-lethal damage, as revealed by electron microscopy after ICH. Our data challenge the long-held assumption that 'healthy' brain tissue outside the injured area maintains its volume. Given the magnitude of these effects, we posit that 'tissue compliance' is an important mechanism invoked after severe strokes.

Translational Intracerebral Hemorrhage Research: Has Current Neuroprotection Research ARRIVEd at a Standard for Experimental Design and Reporting?

One major aim of preclinical intracerebral hemorrhage (ICH) research is to develop and test potential neuroprotectants. Published guidelines for experimental design and reporting stress the importance of clearly and completely reporting results and methodological details to ensure reproducibility and maximize information availability. The current review has two objectives: first, to characterize current ICH neuroprotection research and, second, to analyze aspects of translational design in preclinical ICH studies. Translational design is the adoption and reporting of experimental design characteristics that are thought to be clinically relevant and critical to reproducibility in animal studies (e.g., conducting and reporting experiments according to the STAIR and ARRIVE guidelines, respectively). Given that ICH has no current neuroprotective treatments and an ongoing reproducibility crisis in preclinical research, translational design should be considered by investigators. We conducted a systematic review of ICH research from 2015 to 2019 using the PubMed database. Our search returned 281 published manuscripts studying putative neuroprotectants in animal models. Contemporary ICH research predominantly uses young, healthy male rodents. The collagenase model is the most commonly used. Reporting of group sizes, blinding, and randomization are almost unanimous, but group size calculations, mortality and exclusion criteria, and animal model characteristics are infrequently reported. Overall, current ICH neuroprotection research somewhat aligns with experimental design and reporting guidelines. However, there are areas for improvement. Because failure to consider translational design is associated with inflation of effect sizes (and possibly hindered reproducibility), we suggest that researchers, editors, and publishers collaboratively consider enhanced adherence to published guidelines.

Infusion of Cold Saline into the Carotid Artery Does Not Affect Outcome After Intrastriatal Hemorrhage

Localized brain hypothermia (HYPO) can be achieved by infusing cold saline into the carotid artery of animals and patients. Studies suggest that HYPO improves behavioral and histological outcomes in focal ischemia models. Given that ischemic stroke and intracerebral hemorrhage (ICH) share pathophysiological overlap, we tested whether cold saline infusion is safe and neuroprotective when given during collagenase-induced ICH. Eighty-five adult male Sprague-Dawley rats were used. Experiment 1 investigated brain and body temperature changes associated with a cold saline infusion paradigm that was scaled from patients according to brain weight and blood volume (3 mL/20-minute infusion). Experiment 2 determined whether HYPO aggravated bleeding volume. Experiment 3 investigated if cerebral edema or elemental concentrations were altered by HYPO. We also collected core body temperature and activity data through telemetry. Experiment 4 investigated whether behavioral outcomes (e.g., skilled reaching) and tissue loss were influenced by HYPO. Our HYPO protocol decreased the ipsilateral striatal temperature by ∼0.20°C (p < 0.001), with no other effects. HYPO did not affect hematoma volume (p = 0.64), cerebral edema (p = 0.34), or elemental concentrations (p = 0.49) at 24 hours post-ICH. Although ICH caused persistent behavioral impairments, HYPO did not improve behavioral outcomes (measured by a neurological deficit scale, cylinder, and the staircase test; p > 0.05 for all). Brain tissue loss was not different between groups on day 28 post-ICH (p = 0.90). Although cold saline infusion appears to be safe in the acute post-ICH period, there was no evidence that this therapy improved outcome. However, our treatment protocol was relatively mild and additional interventions might help improve efficacy. Finally, our findings may also speak to the safety of this cooling approach in focal ischemia where hemorrhagic transformation is a risk; future studies on this issue are needed.

Therapeutic Hypothermia in Acute Ischemic Stroke-a Systematic Review and Meta-Analysis

PURPOSE OF REVIEW

Therapeutic hypothermia (TH) in stroke demonstrates robust neuroprotection in animals but clinical applications remain controversial. We assessed current literature on the efficacy of TH in ischemic stroke.

RECENT FINDINGS

We conducted a meta-analysis comparing TH versus controls in studies published until June 2019. Controlled studies reporting on ≥ 10 adults with acute ischemic stroke were included. Primary outcome was functional independence (modified Rankin Scale [mRS] ≤ 2). Twelve studies (n = 351 TH, n = 427 controls) were included. Functional independence did not differ between groups (RR 1.17, 95% CI 0.93-1.46, random-effects p = 0.2). Five studies reported individual mRS outcomes and demonstrated a shift toward better outcome with TH (unadjusted cOR 1.57, 95% CI 1.01-2.44, p = 0.05). Overall complications were higher with TH (RR 1.18, 95% CI 1.06-1.32, p < 0.01). We did not observe an overall beneficial effect of TH in this analysis although some studies showed a shift toward better outcome. TH was associated with increased complications.

A Review of ex vivo Elemental Mapping Methods to Directly Image Changes in the Homeostasis of Diffusible Ions (Na+, K+, Mg2 +, Ca2 +, Cl-) Within Brain Tissue

Diffusible ions (Na+, K+, Mg2+, Ca2+, Cl-) are vital for healthy function of all cells, especially brain cells. Unfortunately, the diffusible nature of these ions renders them difficult to study with traditional microscopy in situ within ex vivo brain tissue sections. This mini-review examines the recent progress in the field, using direct elemental mapping techniques to study ion homeostasis during normal brain physiology and pathophysiology, through measurement of ion distribution and concentration in ex vivo brain tissue sections. The mini-review examines the advantages and limitations of specific techniques: proton induced X-ray emission (PIXE), X-ray fluorescence microscopy (XFM), secondary ion mass spectrometry (SIMS), laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and the sample preparation requirements to study diffusible ions with these methods.

The collagenase model of intracerebral hemorrhage in awake, freely moving animals: The effects of isoflurane

Intracerebral hemorrhage (ICH) is a devastating stroke often modelled in rats. Isoflurane anesthetic, commonly used in preclinical research, affects general physiology (e.g., blood pressure) and electrophysiology (e.g., burst suppression) in many ways. These physiological changes may detract from the clinical relevance of the model. Here, we revised the standard collagenase model to produce an ICH in rats without anesthetic. Guide cannulas were implanted stereotaxically under anesthetic. After 3 days of recovery, collagenase was infused through an internal cannula into the striatum of animals randomly assigned to the non-anesthetized or isoflurane group. We assessed whether isoflurane affected hematoma volume, core temperature, movement activity, pain, blood pressure, and seizure activity. With a small ICH, there was a hematoma volume increased from 8.6 (±3.3, 95% confidence interval) µL in anesthetized rats to 13.2 (±3.1) µL in non-anesthetized rats (P = 0.008), but with a larger ICH, hematoma volumes were similar. Isoflurane decreased temperature by 1.3 °C (±0.16 °C, P < 0.001) for 2 h and caused a 35.1 (±1.7) mmHg group difference in blood pressure (P < 0.007) for 12 m. Blood glucose increased twofold after isoflurane procedures (P < 0.001). Pain, as assessed with the rat grimace scale, did not differ between groups. Seizure incidence rate (62.5%) in non-anesthetized ICH rats was similar to historic amounts (61.3%). In conclusion, isoflurane appears to have some significant and injury size-dependent effects on the collagenase model. Thus, when anesthetic effects are a known concern, the use of the standardized cannula infusion approach is scientifically and ethically acceptable.

Poly-arginine-18 peptides do not exacerbate bleeding, or improve functional outcomes following collagenase-induced intracerebral hemorrhage in the rat

Background

Cationic arginine-rich peptides (CARPs) have demonstrated neuroprotective and/or behavioural efficacy in ischemic and hemorrhagic stroke and traumatic brain injury models. Therefore, in this study we investigated the safety and neuroprotective efficacy of the CARPs poly-arginine-18 (R18; 18-mer of arginine) and its D-enantiomer R18D given in the acute bleeding phase in an intracerebral hemorrhage (ICH) model.

Methods

One hundred and fifty-eight male Sprague-Dawley rats received collagenase-induced ICH. Study 1 examined various doses of R18D (30, 100, 300, or 1000 nmol/kg) or R18 (100, 300, 1000 nmol/kg) administered intravenously 30 minutes post-collagenase injection on hemorrhage volume 24 hours after ICH. Study 2 examined R18D (single intravenous dose) or R18 (single intravenous dose, plus 6 daily intraperitoneal doses) at 300 or 1000 nmol/kg commencing 30 minutes post-collagenase injection on behavioural outcomes (Montoya staircase test, and horizontal ladder test) in the chronic post-ICH period. A histological assessment of tissue loss was assessed using a Nissl stain at 28 days after ICH.

Results

When administered during ongoing bleeding, neither R18 or R18D exacerbated hematoma volume or worsened functional deficits. Lesion volume assessment at 28 days post-ICH was not reduced by the peptides; however, animals treated with the lower R18D 300 nmol/kg dose, but not with the higher 1000 nmol/kg dose, demonstrated a statistically increased lesion size compared to saline treated animals.

Conclusion

Overall, both R18 and R18D appeared to be safe when administered during a period of ongoing bleeding following ICH. Neither peptide appears to have any statistically significant effect in reducing lesion volume or improving functional recovery after ICH. Additional studies are required to further assess dose efficacy and safety in pre-clinical ICH studies.

Hypothermia: Impact on plasticity following brain injury

Therapeutic hypothermia (TH) is a potent neuroprotectant against multiple forms of brain injury, but in some cases, prolonged cooling is needed. Such cooling protocols raise the risk that TH will directly or indirectly impact neuroplasticity, such as after global and focal cerebral ischemia or traumatic brain injury. TH, depending on the depth and duration, has the potential to broadly affect brain plasticity, especially given the spatial, temporal, and mechanistic overlap with the injury processes that cooling is used to treat. Here, we review the current experimental and clinical evidence to evaluate whether application of TH has any adverse or positive effects on postinjury plasticity. The limited available data suggest that mild TH does not appear to have any deleterious effect on neuroplasticity; however, we emphasize the need for additional high-quality preclinical and clinical work in this area.

Failure of bumetanide to improve outcome after intracerebral hemorrhage in rat

After intracerebral hemorrhage (ICH), brain edema commonly occurs and can cause death. Along with edema, there are significant alterations in the concentrations of key ions such as sodium, potassium, and chloride, which are essential to brain function. NKCC1, a cation-chloride cotransporter, is upregulated after brain damage, such as traumatic injury and ischemic stroke. NKCC1 brings sodium and chloride into the cell, possibly worsening ion dyshomeostasis. Bumetanide, a specific NKCC1 antagonist, blocks the transport of chloride into cells, and thus should attenuate the increases in chloride, which should lessen brain edema and improve neuronal functioning post-ICH, as with other injuries. We used the collagenase model of ICH to test whether bumetanide treatment for three days (vs. vehicle) would improve outcome. We gave bumetanide beginning at two hours or seven days post-ICH and measured behavioural outcome, edema, and brain ion content after treatment. There was some evidence for a minor reduction in edema after early dosing, but this did not improve behaviour or lessen injury. Contrary to our hypothesis, bumetanide did not normalize ion concentrations after late dosing. Bumetanide did not improve behavioural outcome or affect lesion volume. After ICH, bumetanide is safe to use in rats but does not improve functional outcome in the majority of animals.

N-acetylcysteine targets 5 lipoxygenase-derived, toxic lipids and can synergize with prostaglandin E2 to inhibit ferroptosis and improve outcomes following hemorrhagic stroke in mice

Objectives

N‐acetylcysteine (NAC) is a clinically approved thiol‐containing redox modulatory compound currently in trials for many neurological and psychiatric disorders. Although generically labeled as an “antioxidant,” poor understanding of its site(s) of action is a barrier to its use in neurological practice. Here, we examined the efficacy and mechanism of action of NAC in rodent models of hemorrhagic stroke.

Methods

Hemin was used to model ferroptosis and hemorrhagic stroke in cultured neurons. Striatal infusion of collagenase was used to model intracerebral hemorrhage (ICH) in mice and rats. Chemical biology, targeted lipidomics, arachidonate 5‐lipoxygenase (ALOX5) knockout mice, and viral‐gene transfer were used to gain insight into the pharmacological targets and mechanism of action of NAC.

Results

NAC prevented hemin‐induced ferroptosis by neutralizing toxic lipids generated by arachidonate‐dependent ALOX5 activity. NAC efficacy required increases in glutathione and is correlated with suppression of reactive lipids by glutathione‐dependent enzymes such as glutathione S‐transferase. Accordingly, its protective effects were mimicked by chemical or molecular lipid peroxidation inhibitors. NAC delivered postinjury reduced neuronal death and improved functional recovery at least 7 days following ICH in mice and can synergize with clinically approved prostaglandin E₂ (PGE₂).

Interpretation

NAC is a promising, protective therapy for ICH, which acted to inhibit toxic arachidonic acid products of nuclear ALOX5 that synergized with exogenously delivered protective PGE₂ in vitro and in vivo. The findings provide novel insight into a target for NAC, beyond the generic characterization as an antioxidant, resulting in neuroprotection and offer a feasible combinatorial strategy to optimize efficacy and safety in dosing of NAC for treatment of neurological disorders involving ferroptosis such as ICH. Ann Neurol 2018;84:854–872

Hyperoxia enhances slow-wave forebrain states in urethane-anesthetized and naturally sleeping rats

Oxygen (O₂) is a crucial element for physiological functioning in mammals. In particular, brain function is critically dependent on a minimum amount of circulating blood levels of O₂ and both immediate and lasting neural dysfunction can result following anoxic or hypoxic episodes. Although the effects of deficiencies in O₂ levels on the brain have been reasonably well studied, less is known about the influence of elevated levels of O₂ (hyperoxia) in inspired gas under atmospheric pressure. This is of importance due to its typical use in surgical anesthesia, in the treatment of stroke and traumatic brain injury, and even in its recreational or alternative therapeutic use. Using local field potential (EEG) recordings in spontaneously breathing urethane-anesthetized and naturally sleeping rats, we characterized the influence of different levels of O₂ in inspired gases on brain states. While rats were under urethane anesthesia, administration of 100% O₂ elicited a significant and reversible increase in time spent in the deactivated (i.e., slow-wave) state, with concomitant decreases in both heartbeat and respiration rates. Increasing the concentration of carbon dioxide (to 5%) in inspired gas produced the opposite result on EEG states, mainly a decrease in the time spent in the deactivated state. Consistent with this, decreasing concentrations of O₂ (to 15%) in inspired gases decreased time spent in the deactivated state. Further confirmation of the hyperoxic effect was found in naturally sleeping animals where it similarly increased time spent in slow-wave (nonrapid eye movement) states. Thus alterations of O₂ in inspired air appear to directly affect forebrain EEG states, which has implications for brain function, as well as for the regulation of brain states and levels of forebrain arousal during sleep in both normal and pathological conditions. NEW & NOTEWORTHY We show that alterations of oxygen concentration in inspired air biases forebrain EEG state. Hyperoxia increases the prevalence of slow-wave states. Hypoxia and hypercapnia appear to do the opposite. This suggests that oxidative metabolism is an important stimulant for brain state.

Acetazolamide Mitigates Intracranial Pressure Spikes Without Affecting Functional Outcome After Experimental Hemorrhagic Stroke

Increased intracranial pressure (ICP) after stroke can lead to poor outcome and death. Novel treatments to combat ICP rises are needed. The carbonic anhydrase inhibitor acetazolamide diminishes cerebrospinal fluid (CSF) production, reduces ICP in healthy animals, and is beneficial for idiopathic intracranial hypertension patients. We tested whether acetazolamide mitigates ICP elevations by presumably decreasing CSF volume after collagenase-induced striatal hemorrhage in rats. We confirmed that acetazolamide did not adversely affect hematoma formation in this model or physiological variables, such as temperature. Then, we assessed the effects of acetazolamide on ICP. Lastly, we tested the effects of acetazolamide on behavioral and histological outcome. Acetazolamide reduced the magnitude and occurrence of short-timescale ICP spikes, assessed as disproportionate increases in ICP (sudden ICP increases > 10 mmHg), 1-min peak ICP, and the magnitude of spikes > 20 mmHg. However, mean ICP was unaffected. In addition, acetazolamide reduced ICP variability, reflecting improved intracranial compliance. Compliance measures were strongly correlated with high peak and mean ICP, whereas ipsilateral hemisphere water content was not correlated with ICP. Despite effects on ICP, acetazolamide did not improve behavioral function or affect lesion size. In summary, we show that intracerebral hemorrhage creates an impaired compliance state within the cranial space that can result in large, transient ICP spikes. Acetazolamide ameliorates intracranial compliance and mitigates ICP spikes, but does not improve functional outcome, at least for moderate-severity ICH in rats.

Prolonged Blood-Brain Barrier Injury Occurs After Experimental Intracerebral Hemorrhage and Is Not Acutely Associated with Additional Bleeding

Intracerebral hemorrhage (ICH) causes blood-brain barrier (BBB) damage along with altered element levels in the brain. BBB permeability was quantified at 3, 7, and 14 days with Evans Blue dye after collagenase-induced ICH in rat. At peak permeability (day 3), a gadolinium (Gd)-based contrast agent was injected to further characterize BBB disruption, and X-ray fluorescence imaging (XFI) was used to map Gd, Fe, Cl, and other elements. XFI revealed that Ca, Cl, Gd, and Fe concentrations were significantly elevated, whereas K was significantly decreased. Therefore, using Gd-XFI, we co-determined BBB dysfunction with alterations in the metallome, including those that contribute to cell death and functional outcome. Warfarin was administered 3 days post-ICH to investigate whether additional or new bleeding occurs during peak BBB dysfunction, and hematoma volume was assessed on day 4. Warfarin administration prolonged bleeding time after a peripheral cut-induced bleed, but warfarin did not worsen hematoma volume. Accordingly, extensive BBB leakage occurred after ICH, but did not appear to affect total hematoma size.

Mild Contralesional Hypothermia Reduces Use of the Unimpaired Forelimb in a Skilled Reaching Task After Motor Cortex Injury in Rats

Therapeutic hypothermia (TH) mitigates neuronal injury in models of ischemic stroke. Although this therapy is meant for injured tissue, most protocols cool the whole body, including the contralesional hemisphere. Neuroplasticity responses within this hemisphere can affect functional outcome. Thus, cooling the contralesional hemisphere serves no clear neuroprotective function and may instead be detrimental. In this study, we cooled the contralesional hemisphere to determine whether this harms behavioral recovery after cortical injury in rats. All rats were trained on skilled reaching and walking tasks. Rats then received a motor cortex insult contralateral to their dominant paw after which they were randomly assigned to focal contralesional TH (∼33°C) for 1-48, 1-97, or 48-96 hours postinjury, or to a normothermic control group. Contralesional cooling did not impact lesion volume (p = 0.371) and had minimal impact on neurological outcome of the impaired limb. However, rats cooled early were significantly less likely to shift paw preference to the unimpaired paw (p ≤ 0.043), suggesting that cooling reduced learned nonuse. In a second experiment, we tested whether cooling impaired learning of the skilled reaching task in naive rats. Localized TH applied to the hemisphere contralateral or ipsilateral to the preferred paw did not impair learning (p ≥ 0.677) or dendritic branching/length in the motor cortex (p ≥ 0.105). In conclusion, localized TH did not impair learning or plasticity in the absence of neural injury, but contralesional TH may reduce unwanted shifts in limb preference after stroke.

Measurement of Intracranial Pressure in Freely Moving Rats

Brain injury, such as from stroke and trauma, can be complicated by elevated intracranial pressure (ICP). Although raised ICP can be a significant determinant of morbidity and mortality, clinical studies often report widely varying ICP measurements depending on location of measurement and technique used. For the same reasons, reported ICP measurements also vary widely in animal models. The need for anesthesia or tethered connections with some methods of ICP measurement in animals may introduce additional confounds. Moreover, these methods are not well suited for prolonged, continuous measurement. Here, we describe an approach to continually measure ICP in awake, freely moving rats for several days. This technique uses a commercially available, wireless pressure sensor mounted on the head to measure ICP from the epidural space via a fluid-filled catheter. We have demonstrated that this approach reliably detects elevations in ICP that last for several days after ischemic and hemorrhagic strokes in rat.

Evidence for Decreased Brain Parenchymal Volume After Large Intracerebral Hemorrhages: a Potential Mechanism Limiting Intracranial Pressure Rises

Potentially fatal intracranial pressure (ICP) rises commonly occur after large intracerebral hemorrhages (ICH). We monitored ICP after infusing 100-160 μL of autologous blood (vs. 0 μL control) into the striatum of rats in order to test the validity of this common model with regard to ICP elevations. Other endpoints included body temperature, behavioral impairment, lesion volume, and edema. Also, we evaluated hippocampal CA1 sector and somatosensory cortical neuron morphology to assess whether global ischemic injury occurred. Despite massive blood infusions, ICP only modestly increased (160 μL 10.8 ± 2.1 mmHg for <36 h vs. control 3.4 ± 0.5 mmHg), with little peri-hematoma edema at 3 days. Body temperature was not affected. Behavioral deficits and tissue loss were infusion volume-dependent. There was no histological evidence of hippocampal or cortical injury, indicating that cell death was confined to the hematoma and closely surrounding tissue. Surprisingly, the most severe hemorrhages significantly increased cell density (~15-20%) and reduced cell body size (~30%) in regions outside the injury site. Additionally, decreased cell size and increased density were observed after collagenase-induced ICH. Parenchymal volume is seemingly reduced after large ICH. Thus, in addition to well-known compliance mechanisms (e.g., displacement of cerebrospinal fluid and cerebral blood), reduced brain parenchymal volume appears to limit ICP rises in rodents with very large mass lesions.

Examining potential side effects of therapeutic hypothermia in experimental intracerebral hemorrhage

Studies treating intracerebral hemorrhage (ICH) with therapeutic hypothermia (TH) have shown inconsistent benefits. We hypothesized that TH's anti-inflammatory effects may be responsible as inflammatory cells are essential for removing degrading erythrocytes. Here, we subjected rats to a collagenase-induced striatal ICH followed by whole-body TH (∼33℃ for 11-72 h) or normothermia. We used X-ray fluorescence imaging to spatially quantify total and peri-hematoma iron three days post-injury. At three and seven days, we measured non-heme iron levels. Finally, hematoma volume was quantified on one, three, and seven days. In the injured hemisphere, total iron levels were elevated ( p < 0.001) with iron increasing in the peri-hematoma region ( p = 0.007). Non-heme iron increased from three to seven days (p < 0.001). TH had no effect on any measure of iron ( p ≥ 0.479). At one and three days, TH did not affect hematoma volume ( p ≥ 0.264); however, at seven days there was a four-fold increase in hematoma volume in 40% of treated animals ( p = 0.032). Thus, even when TH does not interfere with initial increases in total and non-heme iron or its containment, TH can cause re-bleeding post-treatment. This serious complication could partly account for the intermittent protection previously observed. This also raises serious concerns for clinical usage of TH for ICH.

Therapeutic targeting of oxygen-sensing prolyl hydroxylases abrogates ATF4-dependent neuronal death and improves outcomes after brain hemorrhage in several rodent models

Disability or death due to intracerebral hemorrhage (ICH) is attributed to blood lysis, liberation of iron, and consequent oxidative stress. Iron chelators bind to free iron and prevent neuronal death induced by oxidative stress and disability due to ICH, but the mechanisms for this effect remain unclear. We show that the hypoxia-inducible factor prolyl hydroxylase domain (HIF-PHD) family of iron-dependent, oxygen-sensing enzymes are effectors of iron chelation. Molecular reduction of the three HIF-PHD enzyme isoforms in the mouse striatum improved functional recovery after ICH. A low-molecular-weight hydroxyquinoline inhibitor of the HIF-PHD enzymes, adaptaquin, reduced neuronal death and behavioral deficits after ICH in several rodent models without affecting total iron or zinc distribution in the brain. Unexpectedly, protection from oxidative death in vitro or from ICH in vivo by adaptaquin was associated with suppression of activity of the prodeath factor ATF4 rather than activation of an HIF-dependent prosurvival pathway. Together, these findings demonstrate that brain-specific inactivation of the HIF-PHD metalloenzymes with the blood-brain barrier-permeable inhibitor adaptaquin can improve functional outcomes after ICH in several rodent models.

Rehabilitation Augments Hematoma Clearance and Attenuates Oxidative Injury and Ion Dyshomeostasis After Brain Hemorrhage

BACKGROUND AND PURPOSE

We assessed the elemental and biochemical effects of rehabilitation after intracerebral hemorrhage, with emphasis on iron-mediated oxidative stress, using a novel multimodal biospectroscopic imaging approach.

METHODS

Collagenase-induced striatal hemorrhage was produced in rats that were randomized to enriched rehabilitation or control intervention starting on day 7. Animals were euthanized on day 14 or 21, a period of ongoing cell death. We used biospectroscopic imaging techniques to precisely determine elemental and molecular changes on day 14. Hemoglobin content was assessed with resonance Raman spectroscopy. X-ray fluorescence imaging mapped iron, chlorine, potassium, calcium, and zinc. Protein aggregation, a marker of oxidative stress, and the distribution of other macromolecules were assessed with Fourier transform infrared imaging. A second study estimated hematoma volume with a spectrophotometric assay at 21 days.

RESULTS

In the first experiment, rehabilitation reduced hematoma hemoglobin content (P=0.004) and the amount of peri-hematoma iron (P<0.001). Oxidative damage was highly localized at the hematoma/peri-hematoma border and was decreased by rehabilitation (P=0.004). Lipid content in the peri-hematoma zone was increased by rehabilitation (P=0.016). Rehabilitation reduced the size of calcium deposits (P=0.040) and attenuated persistent dyshomeostasis of Cl^- (P<0.001) but not K⁺ (P=0.060). The second study confirmed that rehabilitation decreased hematoma volume (P=0.024).

CONCLUSIONS

Rehabilitation accelerated clearance of toxic blood components and decreased chronic oxidative stress. As well, rehabilitation attenuated persistent ion dyshomeostasis. These novel effects may underlie rehabilitation-induced neuroprotection and improved recovery of function. Pharmacotherapies targeting these mechanisms may further improve outcome.

Temperature Control in Rodent Neuroprotection Studies: Methods and Challenges

Extensive animal research facilitated the clinical translation of therapeutic hypothermia for cardiac arrest in adults and hypoxic-ischemic injury in infants. Similarly, clinical interest in hypothermia for other brain injuries, such as stroke, has been greatly supported by positive findings in preclinical work. The reliability, validity, and utility of animal models, among many research practices (blinding, randomization, etc.), are key to successful clinical translation. Here, we review methods used to induce and maintain hypothermia in animal models. These include physical and pharmacological methods. We emphasize the advantages and limitations of each approach, and the importance of using clinically relevant cooling protocols and appropriate monitoring and reporting approaches. Moreover, we performed a literature survey of ischemic stroke studies published in 2015 to highlight the continuing risk of temperature confounds in neuroprotection studies. For example, many still do not accurately monitor and report temperature during surgery (23.5%), even though almost half of these studies (46.0%) use pharmaceutical agents that likely influence temperature. We hope this review stimulates awareness and discussion of the importance of temperature in neuroprotective studies.

Therapeutic Hypothermia Does Not Mitigate Iron-Induced Injury in Rat

Intracerebral hemorrhage (ICH) is often a devastating stroke, and there are no clinically proven neuroprotective treatments. Considerable research points to iron toxicity as a leading contributor to secondary damage after ICH. Iron, released from degraded erythrocytes, catalyzes free radical production, thereby causing cell death in the ensuing days and weeks. Therapeutic hypothermia (TH) is a potential neuroprotective strategy for ICH, but results from animal studies are inconsistent and generally weaker than that found in ischemia models. Thus, we examined whether TH (∼33°C for 24-72 hours) would specifically mitigate iron toxicity, which we modeled by infusing 3.8 μg of FeCl2 in 30 μL of sterile saline into the striatum of rats. Rats were subjected to whole-body cooling beginning 1 hour after FeCl2 infusion. Use of TH reduced (p = 0.025) the small bleed caused by FeCl2 infusion (∼6 μL). However, TH did not lessen FeCl2-induced edema at 24 and 72 hours postinfusion, nor were behavioral impairments (e.g., walking) or brain injury (at 7 and 28 days) attenuated by TH. These results suggest that TH does not directly protect against iron toxicity, which indicates that this is not a means by which TH improves the outlook after ICH.

Prolonged Localized Mild Hypothermia Does Not Affect Seizure Activity After Intracerebral Hemorrhage in Rats

Intracerebral hemorrhage (ICH) is a devastating stroke with high morbidity and mortality. Post-ICH seizures are a common complication, potentially increasing brain injury and the risk of delayed epilepsy. Mild therapeutic hypothermia (HYPO, ∼33°C) is neuroprotective against several brain insults, such as ischemia, while also mitigating seizure incidence and severity in some instances. Therefore, we tested whether brain-selective HYPO reduced electrographic seizure activity after a collagenase-induced striatal ICH in rats. Animals were injected unilaterally with 0.14 U of bacterial collagenase, implanted with a unilateral brain cooling device, and a probe to bilaterally record electroencephalographic (EEG) activity. Cooling began 6 hours after collagenase infusion and was maintained for 48 hours, followed by rewarming over 6 hours. Our protocol did not affect EEG activity in naïve rats, nor did it increase bleeding after ICH (∼50 μL). Epileptiform activity commonly occurred in untreated ICH rats (∼60% of animals), but HYPO did not affect the incidence, timing, total duration of seizures, or the peaks occurring during epileptiform activity. However, longer average duration was detected on the ipsilateral side to stroke in the HYPO group (p < 0.05). Cooling did not affect neurological deficits (e.g., circling), measured 7 and 14 days after ICH, or lesion volume (∼35 mm(3)). In addition, there was no relationship among endpoints (e.g., seizures and lesion size). In summary, HYPO failed to reduce seizure activity after ICH, which fits with our separate findings that cooling does not mitigate thrombin and iron-mediated secondary injury mechanisms thought to cause seizures after ICH. Additional research is needed to identify better HYPO protocols and the use of cotreatments to maximize the benefit of HYPO to ICH patients.

Delayed localized hypothermia reduces intracranial pressure following collagenase-induced intracerebral hemorrhage in rat

Brain injury, such as from intracerebral hemorrhage (ICH), causes edema and raises intracranial pressure (ICP)--a potentially life-threatening complication. Clinical studies suggest that therapeutic hypothermia (TH) reduces edema and ICP after ICH. Similarly, animal studies show that TH can sometimes reduce edema, but whether ICP would be attenuated is not known. Here we tested whether 24-h delayed TH reduces edema and ICP in rats with severe striatal ICH (collagenase model). First, we showed that ICH increased epidural ICP (mean of 18 vs. 6.5mm Hg in controls), measured via telemetry. Second, we confirmed that delayed TH did not affect hematoma size at 7d ay (~65 vs. ~61 µL in controls). A cranial cooling device lowered striatal temperature to ~33 °C from 24 to 72 h after ICH. Third, we compared normothermic rats to those with TH that were rewarmed immediately or over 6h. Both TH protocols significantly reduced average and peak ICP by the second treatment day, and benefits persisted after rewarming. However, TH with slow rewarming failed to mitigate edema at 96 h (83.2% vs. 83.6% in controls) whereas rapid rewarming worsened edema (85.7%). Finally, we compared normothermic and TH rats without rewarming and found no impact on edema at 72 h (~81%). In summary, it appears that 24-h delayed local TH lowers ICP by a mechanism other than edema. Rapid rewarming worsens edema after local cooling, but this did not markedly impact ICP. Thus, TH should reduce ICP in patients with severe ICH, but not necessarily through mitigating edema.

A new method to image heme-Fe, total Fe, and aggregated protein levels after intracerebral hemorrhage

An intracerebral hemorrhage (ICH) is a devastating stroke that results in high mortality and significant disability in survivors. Unfortunately, the underlying mechanisms of this injury are not yet fully understood. After the primary (mechanical) trauma, secondary degenerative events contribute to ongoing cell death in the peri-hematoma region. Oxidative stress is thought to be a key reason for this delayed injury, which is likely due to free-Fe-catalyzed free radical reactions. Unfortunately, this is difficult to prove with conventional biochemical assays that fail to differentiate between alterations that occur within the hematoma and peri-hematoma zone. This is a critical limitation, as the hematoma contains tissue severely damaged by the initial hemorrhage and is unsalvageable, whereas the peri-hematoma region is less damaged but at risk from secondary degenerative events. Such events include oxidative stress mediated by free Fe presumed to originate from hemoglobin breakdown. Therefore, minimizing the damage caused by oxidative stress following hemoglobin breakdown and Fe release is a major therapeutic target. However, the extent to which free Fe contributes to the pathogenesis of ICH remains unknown. This investigation used a novel imaging approach that employed resonance Raman spectroscopic mapping of hemoglobin, X-ray fluorescence microscopic mapping of total Fe, and Fourier transform infrared spectroscopic imaging of aggregated protein following ICH in rats. This multimodal spectroscopic approach was used to accurately define the hematoma/peri-hematoma boundary and quantify the Fe concentration and the relative aggregated protein content, as a marker of oxidative stress, within each region. The results revealed total Fe is substantially increased in the hematoma (0.90 μg cm(-2)), and a subtle but significant increase in Fe that is not in the chemical form of hemoglobin is present within the peri-hematoma zone (0.32 μg cm(-2)) within 1 day of ICH, relative to sham animals (0.22 μg cm(-2)). Levels of aggregated protein were significantly increased within both the hematoma (integrated band area 0.10 AU) and peri-hematoma zone (integrated band area 0.10 AU) relative to sham animals (integrated band area 0.056 AU), but no significant difference in aggregated protein content was observed between the hematoma and peri-hematoma zone. This result suggests that the chemical form of Fe and its ability to generate free radicals is likely to be a more critical predictor of tissue damage than the total Fe content of the tissue. Furthermore, this article describes a novel approach to colocalize nonheme Fe and aggregated protein in the peri-hematoma zone following ICH, a significant methodological advancement for the field.

Incomplete Assessment of Experimental Cytoprotectants in Rodent Ischemia Studies

Background:

Inadequate preclinical testing (e.g., rodent studies) has been partly blamed for the failure of many cytoprotectants to effectively treat stroke in humans. For example, some drugs went to clinical trial without rigorous functional and histological assessment over long survival times. In this study, we characterized recent experimental practices in rodent cytoprotection experiments to determine whether the limitations of early studies have been rectified.

Methods:

We identified 138 rodent cytoprotection studies published in several leading journals (Journal of Neuroscience, Stroke, Journal of Cerebral Blood Flow and Metabolism and Experimental Neurology) for 2000 - 2002 and compared these to those published in 1990. From each study we determined the ischemia model, age and sex of the animal, the histological and functional endpoints used, and the methodology used to assess intra- and postischemic temperature.

Results:

Ninety-eight percent of recent studies used young adult rodents and most used males. Most studies (60%) did not assess functional outcome and survival times were often ≤ 48 hr (66%) for focal ischemia and ≤ 7 days (80%) for global ischemia. Over 60% of the experiments relied solely upon rectal temperature during ischemia and only 32.6% of ischemia studies measured temperature after surgery. The 1990 data were similar.

Conclusion:

Many investigators ignore the need to assess long-term functional and histological outcome and do not accurately represent clinical conditions of ischemia (e.g., use of aged animals). In addition, intra- and postischemic temperature measurement and control is frequently neglected or inadequately performed. Further clinical failures are likely.

Localized hypothermia aggravates bleeding in the collagenase model of intracerebral hemorrhage

Animal studies testing whether therapeutic hypothermia is neuroprotective after intracerebral hemorrhage (ICH) have been inconclusive. In rodents, ICH is often produced in the striatum by infusing collagenase, which causes prolonged hemorrhaging from multiple vessels. Our previous data shows that this bleeding (hematoma) is worsened by systemic hypothermia given soon after collagenase infusion. In this study we hypothesized that localized brain hypothermia would also aggravate bleeding in this model (0.2 U of collagenase in 1.2 μL of saline). We also evaluated cooling after intrastriatal thrombin infusion (1 U in 30 μL of saline)-a simplified model of ICH thought to cause bleeding. Focal hypothermia was achieved by flushing cold water through an implanted cooling device attached to the skull underneath the temporalis muscle of adult rats. Previous work and data at this time shows this method cools the striatum to ∼33°C, whereas the body remains normothermic. In comparison to normothermic groups, cooling significantly worsened bleeding when instituted at 6 hours (∼94 vs. 42 μL, p=0.018) and 12 hours (79 vs. 61 μL, p=0.042) post-ICH (24-hour survival), but not after a 24-hour delay (36-hour survival). Rats were cooled until euthanasia when hematoma size was determined by a hemoglobin-based spectrophotometry assay. Cooling did not influence cerebral blood volume after just saline or thrombin infusion. The latter is explained by the fact that thrombin did not cause bleeding beyond that caused by saline infusion. In summary, local hypothermia significantly aggravates bleeding many hours after collagenase infusion suggesting that bleeding may have confounded earlier studies with hypothermia. Furthermore, these findings serve as a cautionary note on using cooling even many hours after cerebral bleeding.

Intracranial pressure measured in freely moving rats for days after intracerebral hemorrhage

In some patients, intracerebral hemorrhage (ICH) causes life-threatening elevations in intracranial pressure (ICP) arising from mass effect of the hematoma and edema. Accordingly, edema is a common endpoint to gauge treatment efficacy in rodent ICH models. Despite widespread reliance on edema, its relationship with ICP and cerebral perfusion pressure (CPP) is unknown. Blood pressure (BP) and ICP were measured by telemetry devices in rats after collagenase ("severe" - 0.3U, and "moderate" - 0.15U doses) or blood infusion (100μL) into striatum (vs. saline infused shams). We compared epidural and intraparenchymal ICP readings (collagenase), evaluated CPP (collagenase), and compared models. Moderate (9.46mmHg±4.72 SD, 3day average) and severe collagenase ICHs (10.79±3.50) significantly increased ICP versus shams (4.02±2.09), whereas blood infusion did not (5.37±0.55). The two monitoring locations gave similar readings after severe collagenase ICH. Increased ICP reduced CPP by ~7.5mmHg for days after the larger collagenase infusion. CPP averaged from 103-112mmHg in shams. Edema occurred in all ICH models and predicted ICP. However, ICP and CPP were only modestly changed even after severe ICH and edema. Thus, small changes in edema typically reported in the literature, which often use smaller bleeds than presently used, likely minimally affects ICP and CPP. Further research into the face validity of these models, endpoints, and their ability to evaluate therapeutics is needed.

Rehabilitation Improves Behavioral Recovery and Lessens Cell Death Without Affecting Iron, Ferritin, Transferrin, or Inflammation After Intracerebral Hemorrhage in Rats

Background. Rehabilitation aids recovery from stroke in animal models, including in intracerebral hemorrhage (ICH). Sometimes, rehabilitation lessens brain damage. Objective. We tested whether rehabilitation improves recovery and reduces perihematoma neuronal death. We also evaluated whether rehabilitation influences iron toxicity and inflammation, mediators of secondary degeneration after ICH. Methods. Rats were trained to retrieve food pellets in a staircase apparatus and later subjected to striatal ICH (via collagenase infusion). After 1 week, they were given either enriched rehabilitation (ER), including reach training with group housing and environmental enrichment, or control treatment (group housing). Rats in the first experiment were treated for 2 weeks, functionally assessed, and killed humanely at 1 month to determine brain levels of nonheme iron. A second experiment used a similar approach, except that animals were euthanized at 14 days to evaluate perihematoma neuronal death (FluoroJade), iron distribution (Perls), and astrocyte (GFAP) and microglia (Iba-1) activity. A third experiment measured levels of iron-binding proteins (ferritin and transferrin) at 14 days. Results. Striatal ICH caused functional impairments, which were significantly improved with ER. The ICH caused delayed perihematoma neuronal death, which ER significantly reduced. Hemispheric iron levels, the amount of iron-binding proteins, and perihematoma astrocytes and microglia numbers were significantly elevated after ICH (vs normal side) but were not affected by ER. Conclusions. Rehabilitation is an effective behavioral and neuroprotective strategy for ICH. Neither effect appears to stem from influencing iron toxicity or inflammation. Thus, additional work must identify underlying mechanisms to help further therapeutic gains.

Abstract TP108: 2,2 Dipyridyl, An Iron Chelator, Does Not Reduce Intracerebral Iron Toxicity Or Improve Outcome After Intracerebral Hemorrhagic Stroke In Rats

Background — After an intracerebral hemorrhage (ICH) iron is released from degrading erythrocytes over days, which causes secondary damage by increasing free radicals. Many studies show that iron chelators, such as deferoxamine, lessen injury, but not all studies support this.

Hypothesis — The ferrous iron chelator, 2,2 Dipyridyl (DP), will decrease injury after ICH or intraparenchymal FeCl 2 infusion in rats.

Experiment 1— Rats were given a collagenase-induced striatal ICH. In experiments 1 and 3, we tested whether behavior was improved (e.g., walking) from administering DP (25mg/kg/day, 12 hours after surgery for 3 days). They were euthanized after 7 days to determine non-heme iron levels in the brain.

Experiment 2— Rats were injected with DP (20mg/kg) 6 hours after collagenase infusion and every 24 hours till euthanasia at 3 days for measuring edema.

Experiment 3— After injecting FeCl 2 in the striatum rats were given DP (25mg/kg every 12 hr starting 2 hours prior to surgery for 3 days). The volume of tissue loss and Fluoro-jade staining (degenerating neurons) was measured.

Results — DP did not improve behavioral or histological outcome or reduce edema in either the collagenase ICH or FeCl 2 model. DP also did not affect parenchymal non-heme iron level.

Conclusion — Our data suggests that DP on its own is not an effective strategy for ICH.

Intra-parenchymal ferrous iron infusion causes neuronal atrophy, cell death and progressive tissue loss: implications for intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating stroke causing considerable tissue destruction from mechanical trauma and secondary degeneration. Free iron, released over days from degrading erythrocytes, causes free radicals that likely contribute to delayed injury. Indeed, an intracerebral injection of iron rapidly kills cells and causes cerebral edema. We expanded upon these observations by: determining a dose-response relationship of iron infusion, examining the structural appearance of surviving striatal neurons, and evaluating injury over months. First, we measured 24-h edema in rats given 3.8, 19.0 or 38.0 μg infusions of FeCl₂ (i.e., 30 μL of a 1, 5 or 10 mmol/L solution). Second, rats were given these infusions (vs. saline controls) followed by behavioral assessment and histology at 7 days. Third, dendritic structure was measured in Golgi-Cox stained neurons at 7 days after a 0.95-μg dose (30 μL of a 0.25 mmol/L solution). Last, rats survived 7 or 60 days post-injection (19.0 μg) for histological assessment. Larger doses of iron caused greater injury, but this was generally not reflected in behavior that indicated similar deficits among the 3.8-38.0 μg groups. Similarly, edema occurred but was not linearly related to dose. Even after a low iron dose the surviving neurons in the peri-injury zone were considerably atrophied (vs. contralateral side and controls). Finally, continuing tissue loss occurred over weeks with prominent neuronal death and iron-positive cells (e.g., macrophages) at 60 days. Iron alone may account for the chronic degeneration found after ICH in rodent models.

Prolonged hypothermia in rat: a safety study using brain-selective and systemic treatments

Hypothermia is an effective neuroprotectant for cardiac arrest and perinatal ischemic injury. Hypothermia also improves outcome after traumatic brain injury and stroke. Although the ideal treatment parameters (duration, delay, and depth) are not fully delineated, prolonged cooling is usually more effective than shorter periods. There is the concern that extended cooling may be hazardous to brain plasticity and cause damage. In order to evaluate this possibility, we assessed the effects of 3 days of systemic hypothermia (32°C) in rats subjected to a sham stroke surgery. There were no detrimental behavioral effects or signs of brain damage. As even longer cooling may be needed in some patients, we cooled (∼32°C) the right hemisphere of rats for 3 or 21 days. Physiological variables, functional outcome, and measures of cell injury were examined. Focal brain cooling for 21 days modestly decreased heart rate, blood pressure, and core temperature. However, focal hypothermia did not affect subsequent behavior (e.g., spontaneous limb usage), cell morphology (e.g., dendritic arborization, ultrastructure), or cause cell death. In conclusion, prolonged mild hypothermia did not harm the brain of normal animals. Further research is now needed to evaluate whether such treatments affect plasticity after brain injury.