Loss of long-term potentiation in the hippocampus after experimental subarachnoid hemorrhage in rats

Neurobehavioral Impairments Predict Specific Cerebral Damage in Rat Model of Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a severe form of stroke that can cause unpredictable and diffuse cerebral damage, which is difficult to detect until it becomes irreversible. Therefore, there is a need for a reliable method to identify dysfunctional regions and initiate treatment before permanent damage occurs. Neurobehavioral assessments have been suggested as a possible tool to detect and approximately localize dysfunctional cerebral regions. In this study, we hypothesized that a neurobehavioral assessment battery could be a sensitive and specific method for detecting damage in discrete cerebral regions following SAH. To test this hypothesis, a behavioral battery was employed at multiple time points after SAH induced via an endovascular perforation, and brain damage was confirmed via postmortem histopathological analysis. Our results demonstrate that impairment of sensorimotor function accurately predict damage in the cerebral cortex (AUC 0.905; sensitivity 81.8%; specificity 90.9%) and striatum (AUC 0.913; sensitivity 90.1%; specificity 100%), while impaired novel object recognition is a more accurate indicator of damage to the hippocampus (AUC 0.902; sensitivity 74.1%; specificity 83.3%) than impaired reference memory (AUC 0.746; sensitivity 72.2%; specificity 58.0%). Tests for anxiety-like and depression-like behaviors predict damage to the amygdala (AUC 0.900; sensitivity 77.0%; specificity 81.7%) and thalamus (AUC 0.963; sensitivity 86.3%; specificity 87.8%), respectively. This study suggests that recurring behavioral testing can accurately predict damage in specific brain regions, which could be developed into a clinical battery for early detection of SAH damage in humans, potentially improving early treatment and outcomes.

Functional effects of haemoglobin can be rescued by haptoglobin in an in vitro model of subarachnoid haemorrhage

During subarachnoid haemorrhage, a blood clot forms in the subarachnoid space releasing extracellular haemoglobin (Hb), which causes oxidative damage and cell death in surrounding tissues. High rates of disability and cognitive decline in SAH survivors are attributed to loss of neurons and functional connections during secondary brain injury. Haptoglobin sequesters Hb for clearance, but this scavenging system is overwhelmed after a haemorrhage. Whilst exogenous haptoglobin application can attenuate cytotoxicity of Hb in vitro and in vivo, the functional effects of sub-lethal Hb concentrations on surviving neurons and whether cellular function can be protected with haptoglobin treatment remain unclear. Here we use cultured neurons to investigate neuronal health and function across a range of Hb concentrations to establish the thresholds for cellular damage and investigate synaptic function. Hb impairs ATP concentrations and cytoskeletal structure. At clinically relevant but sub-lethal Hb concentrations, we find that synaptic AMPAR-driven currents are reduced, accompanied by a reduction in GluA1 subunit expression. Haptoglobin co-application can prevent these deficits by scavenging free Hb to reduce it to sub-threshold concentrations and does not need to be present at stoichiometric amounts to achieve efficacy. Haptoglobin itself does not impair measures of neuronal health and function at any concentration tested. Our data highlight a role for Hb in modifying synaptic function in surviving neurons, which may link to impaired cognition or plasticity after SAH and support the development of haptoglobin as a therapy for subarachnoid haemorrhage.

Neurobehavioral impairments predict specific cerebral damage in rat model of subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a severe form of stroke that can cause unpredictable and diffuse cerebral damage, which is difficult to detect until it becomes irreversible. Therefore, there is a need for a reliable method to identify dysfunctional regions and initiate treatment before permanent damage occurs. Neurobehavioral assessments have been suggested as a possible tool to detect and approximately localize dysfunctional cerebral regions. In this study, we hypothesized that a neurobehavioral assessment battery could be a sensitive and specific early warning for damage in discrete cerebral regions following SAH. To test this hypothesis, a behavioral battery was employed at multiple time points after SAH induced via an endovascular perforation, and brain damage was confirmed via postmortem histopathological analysis. Our results demonstrate that impairment of sensorimotor function accurately predict damage in the cerebral cortex (AUC: 0.905; sensitivity: 81.8%; specificity: 90.9%) and striatum (AUC: 0.913; sensitivity: 90.1%; specificity: 100%), while impaired novel object recognition is a more accurate indicator of damage to the hippocampus (AUC: 0.902; sensitivity: 74.1%; specificity: 83.3%) than impaired reference memory (AUC: 0.746; sensitivity: 72.2%; specificity: 58.0%). Tests for anxiety-like and depression-like behaviors predict damage to the amygdala (AUC: 0.900; sensitivity: 77.0%; specificity: 81.7%) and thalamus (AUC: 0.963; sensitivity: 86.3%; specificity: 87.8%), respectively. This study suggests that recurring behavioral testing can accurately predict damage in specific brain regions, which could be developed into a clinical battery for early detection of SAH damage in humans, potentially improving early treatment and outcomes.

Subarachnoid hemorrhage triggers neuroinflammation of the entire cerebral cortex, leading to neuronal cell death

BACKGROUND

Subarachnoid hemorrhage (SAH) is a fatal disease, with early brain injury (EBI) occurring within 72 h of SAH injury contributes to its poor prognosis. EBI is a complicated phenomenon involving multiple mechanisms. Although neuroinflammation has been shown to be important prognosis factor of EBI, whether neuroinflammation spreads throughout the cerebrum and the extent of its depth in the cerebral cortex remain unknown. Knowing how inflammation spreads throughout the cerebrum is also important to determine if anti-inflammatory agents are a future therapeutic strategy for EBI.

METHODS

In this study, we induced SAH in mice by injecting hematoma into prechiasmatic cistern and created models of mild to severe SAH. In sections of the mouse cerebrum, we investigated neuroinflammation and neuronal cell death in the cortex distal to the hematoma injection site, from anterior to posterior region 24 h after SAH injury.

RESULTS

Neuroinflammation caused by SAH spread to all layers of the cerebral cortex from the anterior to the posterior part of the cerebrum via the invasion of activated microglia, and neuronal cell death increased in correlation with neuroinflammation. This trend increased with the severity of the disease.

CONCLUSIONS

Neuroinflammation caused by SAH had spread throughout the cerebrum, causing neuronal cell death. Considering that the cerebral cortex is responsible for long-term memory and movement, suppressing neuroinflammation in all layers of the cerebral cortex may improve the prognosis of patients with SAH.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Delayed Cerebral Ischemia After Subarachnoid Hemorrhage: Is There a Relevant Experimental Model? A Systematic Review of Preclinical Literature

Delayed cerebral ischemia (DCI) is one of the main prognosis factors for disability after aneurysmal subarachnoid hemorrhage (SAH). The lack of a consensual definition for DCI had limited investigation and care in human until 2010, when a multidisciplinary research expert group proposed to define DCI as the occurrence of cerebral infarction (identified on imaging or histology) associated with clinical deterioration. We performed a systematic review to assess whether preclinical models of SAH meet this definition, focusing on the combination of noninvasive imaging and neurological deficits. To this aim, we searched in PUBMED database and included all rodent SAH models that considered cerebral ischemia and/or neurological outcome and/or vasospasm. Seventy-eight publications were included. Eight different methods were performed to induce SAH, with blood injection in the cisterna magna being the most widely used (n = 39, 50%). Vasospasm was the most investigated SAH-related complication (n = 52, 67%) compared to cerebral ischemia (n = 30, 38%), which was never investigated with imaging. Neurological deficits were also explored (n = 19, 24%). This systematic review shows that no preclinical SAH model meets the 2010 clinical definition of DCI, highlighting the inconsistencies between preclinical and clinical standards. In order to enhance research and favor translation to humans, pertinent SAH animal models reproducing DCI are urgently needed.

Dynamic causal modeling of the working memory system of aneurysmal subarachnoid hemorrhage patients: Searching for targets for cortical intervention

INTRODUCTION

Aneurysmal subarachnoid hemorrhage (aSAH), caused by rupture of an intracranial aneurysm and bleeding into the subarachnoid space, is a life-threatening cerebrovascular disease. Because of improvements in clinical interventions, the mortality rate of aSAH is gradually decreasing. Thus, many survivors recover from aSAH but still have sequelae. Working memory (WM) deficit is one of the most common and severe sequelae after aSAH. Interestingly, the severity of WM deficit is not identical to the extent or localization of brain damage, which implies an underlying mechanism of WM deficit other than direct hemorrhagic brain damage. Previous studies have revealed altered neural activity of several brain regions during stimulus tasks. However, the behaviors and functional organization of these corresponding areas in the resting state remain unclear. Insights into the organization of the WM network could reveal novel information about the mechanism of WM deficits, which will be of great value in developing new therapeutic strategies.

METHODS

In this study, we recruited 50 aSAH patients consisting of survivors with either impaired or intact WM (two groups). Independent component analysis was performed on resting state data to extract the WM network. Dynamic causal modeling was then performed to assess the intrinsic coupling between key regions of the WM network. A model describing the neural activity and functional organization of the WM network was established, although some connections were not consistent in the resting state.

RESULTS

We found that effective connectivity of the precuneus (PCUN)-middle temporal gyrus (MTG), MTG-PCUN, and middle frontal gyrus-inferior parietal lobule was significantly decreased in the impaired WM group, which suggests a vital and central role of affected regions or connections and provides new targets for brain stimulation.

CONCLUSIONS

The results of this study may contribute to new therapeutic or rehabilitation strategies for aSAH patients with WM deficits.

Hydrogen Sulfide Reduces Cognitive Impairment in Rats After Subarachnoid Hemorrhage by Ameliorating Neuroinflammation Mediated by the TLR4/NF-κB Pathway in Microglia

Background and Aims: Cognitive impairment is one of the major complications of subarachnoid hemorrhage (SAH) and is closely associated with neuroinflammation. Hydrogen sulfide (H₂S) has been shown to have an anti-inflammatory effect and reduce cognitive impairment in neurodegenerative diseases, but its effects in SAH have been little studied. This study aimed to investigate the effects of H₂S on cognitive impairment after SAH and the possible underlying mechanisms.

Methods: Forty-eight male Sprague–Dawley (SD) rats were randomly divided into three groups: a sham group, a SAH group, and a SAH + NaHS (an H₂S donor) group. The endovascular perforation technique was used to establish the experimental SAH model. NaHS was administered intraperitoneally. An active avoidance test (AAT) was performed to investigate cognitive function. The expression of TNF-α, toll-like receptor 4 (TLR4), and NF-κB p65 in the hippocampus was measured by Western blot and immunohistochemistry. The types of cells expressing TNF-α were detected by double immunofluorescence staining.

Results: Compared to that in the sham group, the learning and memory ability of rats in the SAH group was damaged. Furthermore, the expression of TNF-α, TLR4, and NF-κB p65 in the hippocampus was elevated in the SAH group (p < 0.05). TNF-α was mainly expressed in activated microglia, which was consistent with the expression of TLR4. Treatment with NaHS significantly decreased the cognitive impairment of rats after SAH and simultaneously reduced the expression of TNF-α, TLR4, and NF-κB p65 and alleviated the nuclear translocation of NF-κB p65 (p < 0.05).

Conclusions: The neuroinflammation reaction in microglia contributes to cognitive impairment after SAH. H₂S reduced the cognitive impairment of rats after SAH by ameliorating neuroinflammation in microglia, potentially via the TLR4/NF-κB pathway.

Altered Neural Networks in the Papez Circuit: Implications for Cognitive Dysfunction after Cerebral Ischemia

Cerebral ischemia remains a leading cause of mortality worldwide. Although the incidence of death has decreased over the years, surviving patients may suffer from long-term cognitive impairments and have an increased risk for dementia. Unfortunately, research aimed toward developing therapies that can improve cognitive outcomes following cerebral ischemia has proved difficult given the fact that little is known about the underlying processes involved. Nevertheless, mechanisms that disrupt neural network activity may provide valuable insight, since disturbances in both local and global networks in the brain have been associated with deficits in cognition. In this review, we suggest that abnormal neural dynamics within different brain networks may arise from disruptions in synaptic plasticity processes and circuitry after ischemia. This discussion primarily concerns disruptions in local network activity within the hippocampus and other extra-hippocampal components of the Papez circuit, given their role in memory processing. However, impaired synaptic plasticity processes and disruptions in structural and functional connections within the Papez circuit have important implications for alterations within the global network, as well. Although much work is required to establish this relationship, evidence thus far suggests there is a link. If pursued further, findings may lead toward a better understanding of how deficits in cognition arise, not only in cerebral ischemia, but in other neurological diseases as well.

Protective effects of astaxanthin on subarachnoid hemorrhage-induced early brain injury: Reduction of cerebral vasospasm and improvement of neuron survival and mitochondrial function

The purpose of this study was to evaluate the neuroprotective effects of astaxanthin on early brain injury (EBI) caused by subarachnoid hemorrhage (SAH) in rats and to explore possible molecular mechanisms. Experimental SAH model was introduced in adult male SD rats by injecting autologous arterial blood into the prechiasmatic cistern. Astaxanthin (75 mg/kg bodyweight) or olive oil was administered by oral gavage at 3 h after SAH. Our results showed that astaxanthin attenuated SAH-induced cerebral vasospasm and reduced neuronal apoptosis. Astaxanthin inhibited mitochondria-associated neuron apoptosis in the prefrontal cortex after SAH: increased mitochondrial membrane potential, decreased Bax/Bcl-2 ratio, inhibited cytochrome C release in cytoplasm, and suppressed caspase-3 enzyme activity. Furthermore, the cerebral expression levels of synaptic proteins (Synapsin-1, postsynaptic density-95 and growth-associated protein-43) and nerve growth and neuronal differentiation factors (brain-derived neurotropic factor and purine-rich binding protein-alpha) were reduced following SAH. Astaxanthin partly restored their expression. In conclusion, our current work demonstrates that astaxanthin attenuates SAH-induced EBI, possibly by improving neuronal survival and mitochondrial function.

Cognitive Sequelae of Unruptured and Ruptured Intracranial Aneurysms and their Treatment: Modalities for Neuropsychological Assessment

BACKGROUND

Cognitive sequelae frequently follow subarachnoid hemorrhage (SAH) and include deficits across multiple domains of executive function. This factor affects overall functional outcomes negatively, especially in younger patients. Several clinical correlates predict development and severity of cognitive dysfunction after SAH. Hypothetical mechanisms of cognitive dysfunction in the absence of radiographic lesion include cerebral hypoperfusion and blood breakdown products, resulting in perturbed interneuronal communication and network synchrony, excitotoxicity, and altered microRNA expression.

METHODS

The PubMed database was searched for articles discussing cognitive outcomes in patients with unruptured and ruptured intracranial aneurysmal disease, sequelae of treatment, and modalities for neuropsychologic testing.

RESULTS

Treatment of unruptured intracranial aneurysms, although capable of preventing SAH, comes with its own set of complications and may also affect cognitive function. Neuropsychological tests such as the Montreal Cognitive Assessment, Mini-Mental Status Examination, and others have proved useful in evaluating cognitive decline. Studies using functional neurologic imaging modalities have identified regions with altered activation patterns during various cognitive tasks. The sum of research efforts in this field has provided useful insights and an initial understanding of cognitive dysfunction after aneurysm treatment and SAH that should prove useful in guiding and rendering future investigations more fruitful.

CONCLUSIONS

Development of finer and more sensitive neuropsychological tests in evaluating the different domains of cognitive function after aneurysm treatment and SAH in general will be useful in accurately determining outcomes after ictus and comparing efficacy of different therapeutic strategies.

Visual Working Memory Encoding and Recognition in Good Outcome Aneurysmal Subarachnoid Patients

Objectives: Aneurysmal subarachnoid hemorrhage (aSAH) accounts for less than 5% of strokes but is associated with significant morbidity and mortality. Amongst survivors, neurocognitive complaints are common, often despite normal imaging. We used magnetoencephalography (MEG) to investigate neurophysiological function during a visual working memory task in aSAH survivors with good recovery and normal structural imaging.

Methods: Patients with aSAH treated with coiling and exhibiting good outcome measured by Glasgow Outcome Scale (GOS) and without related parenchymal structural lesions in post-treatment MRI, were recruited and compared to age- and sex-matched controls. All participants underwent intelligence and cognitive screening, structural MRI, and MEG testing in conjunction with a 1-back visual working memory task. Sensor-level global field power and virtual electrode source analysis of neuronal activity and connectivity in aSAH were assessed.

Results: Thirteen patients and 13 matched controls were enrolled (age: 56 ± 11 years, 19 female). The 1-back task was completed with similar accuracy despite a trend for a longer reaction time in aSAH patients (p = 0.054). During encoding and recognition phases, aSAH patients showed significantly increased neuronal activation and hyperconnectivity in periventricular areas, specifically the anterior and posterior cingulate gyri.

Conclusions: Increased posterior and anterior cingulate gyri neuronal activity is demonstrated in aSAH patients during visual working memory tasks, in the absence of structural lesions. These areas work mainly as a hub to “organize” memory storage and retrieval. Increased activity in these areas might be compensatory due to injury and consequently loss of neuronal response in connected areas in the working memory networks.

In Vogue: Ketamine for Neuroprotection in Acute Neurologic Injury

Neurologic deterioration following acute injury to the central nervous system may be amenable to pharmacologic intervention, although, to date, no such therapy exists. Ketamine is an anesthetic and analgesic emerging as a novel therapy for a number of clinical entities in recent years, including refractory pain, depression, and drug-induced hyperalgesia due to newly discovered mechanisms of action and new application of its known pharmacodynamics. In this focused review, the evidence for ketamine as a neuroprotective agent in stroke, neurotrauma, subarachnoid hemorrhage, and status epilepticus is highlighted, with a focus on its applications for excitotoxicity, neuroinflammation, and neuronal hyperexcitability. Preclinical modeling and clinical applications are discussed.

Increased Frontal Lobe Activation After Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

Neurocognitive deficits are common among survivors of aneurysmal subarachnoid hemorrhage, even among those with good outcomes and no structural lesions. This study aims to probe the neurophysiological underpinnings of cognitive dysfunction among patients with ruptured intracranial aneurysms using magnetoencephalography (MEG).

METHODS

Thirteen patients who had undergone uncomplicated coiling for aneurysmal subarachnoid hemorrhage and 13 matched controls were enrolled. Neuropsychological tests were done before magnetoencephalography scans. Magnetoencephalography data were acquired in a 151-channel, whole-head magnetoencephalography system for resting state and 2 cognitive tasks (go-no-go and set-shifting). Mean time from treatment to test was 18.8 months.

RESULTS

Cognitive tasks of inhibition (go-no-go) indicated greater activation in the right anterior cingulate and inferior frontal gyrus, and cognitive set-shifting tasks (mental flexibility) indicated greater activity in the bilateral anterior cingulate cortex and right medial frontal gyrus among aneurysmal subarachnoid hemorrhage patients, with significantly different timing of activation between groups. Resting-state, beta-band connectivity of the anterior cingulate correlated negatively with Montreal Cognitive Assessment scores (left: r=-0.56; P<0.01 and right: r=-0.55; P<0.01): higher connectivity of this region was linked to poorer cognitive test performance.

CONCLUSIONS

We have shown increased activation in areas of the anterior cingulate gyrus and frontobasal regions during the execution of more demanding tasks in good grade. The degree of activation in the anterior cingulate gyrus has a negative correlation with cognitive (Montreal Cognitive Assessment) scores. These subtle differences may be related to the common neurocognitive and behavioral complaints seen in this patient population.

Increased ICP promotes CaMKII-mediated phosphorylation of neuronal NOS at Ser⁸⁴⁷ in the hippocampus immediately after subarachnoid hemorrhage

Early brain injury has recently been identified as an indicator of poor prognosis after subarachnoid hemorrhage (SAH). Calmodulin-dependent protein kinase IIα (CaMKIIα) has been shown to phosphorylate neuronal NOS (nNOS) at Ser(847), resulting in a reduction in nNOS activity. In this study, we revealed chronological changes in the phosphorylation of nNOS at Ser(847) in the hippocampus and cortex immediately after SAH. In a rat single-hemorrhage model of SAH, the hippocampus and adjacent cortex were collected up to 24h after SAH. Samples from rats that were not injected with blood were used as controls. NOS was partially purified from the crude samples using ADP-agarose affinity chromatography. Western blot analysis revealed that nNOS phosphorylated (p-nNOS) at Ser(847) was significantly increased in the hippocampus, but not in the cortex, at 1h after SAH compared with that resulting from the control treatment. Immunoreactivity of p-nNOS at Ser(847) was observed in interneurons of the hippocampus at 1h after SAH. Injection of saline instead of blood also significantly induced p-nNOS at Ser(847) levels in the hippocampus at 1h after injection. The colocalization of CaMKIIα and nNOS was transiently increased in the hippocampus at 0.5h after SAH. Our data suggest that immediately after SAH, an increase in intracranial pressure might induce transient cerebral ischemia, potentially promoting the phosphorylation of nNOS at Ser(847) by CaMKIIα in the hippocampus. The activation of p-nNOS at Ser(847) in the hippocampus may alleviate ischemic insults immediately after SAH to exert a neuroprotective effect against early brain injury.

Platelet-mediated changes to neuronal glutamate receptor expression at sites of microthrombosis following experimental subarachnoid hemorrhage

Object

Glutamate is important in the pathogenesis of brain damage after cerebral ischemia and traumatic brain injury. Notably, brain extracellular and cerebrospinal fluid as well as blood glutamate concentrations increase after experimental and clinical trauma. While neurons are one potential source of glutamate, platelets also release glutamate as part of their recruitment and might mediate neuronal damage. This study investigates the hypothesis that platelet microthrombi release glutamate that mediates excitotoxic brain injury and neuron dysfunction after subarachnoid hemorrhage (SAH).

Methods

The authors used two models, primary neuronal cultures exposed to activated platelets, as well as a whole-animal SAH preparation. Propidium iodide was used to evaluate neuronal viability, and surface glutamate receptor staining was used to evaluate the phenotype of platelet-exposed neurons.

Results

The authors demonstrate that thrombin-activated platelet-rich plasma releases glutamate, at concentrations that can exceed 300 μM. When applied to neuronal cultures, this activated plasma is neurotoxic, and the toxicity is attenuated in part by glutamate receptor antagonists. The authors also demonstrate that exposure to thrombin-activated platelets induces marked downregulation of the surface glutamate receptor glutamate receptor 2, a marker of excitotoxicity exposure and a possible mechanism of neuronal dysfunction. Linear regression demonstrated that 7 days after SAH in rats there was a strong correlation between proximity to microthrombi and reduction of surface glutamate receptors.

Conclusions

The authors conclude that platelet-mediated microthrombosis contributes to neuronal glutamate receptor dysfunction and might mediate brain injury after SAH.

Endovascular perforation subarachnoid hemorrhage fails to cause Morris water maze deficits in the mouse

Cognitive dysfunction is the primary driver of poor long-term outcome in aneurysmal subarachnoid hemorrhage (SAH) survivors; modeling such deficits preclinically is thus key for mechanistic and translational investigation. Although rat SAH causes long-term deficits in learning and memory, it remains unknown whether similar deficits are seen in the mouse, a species particularly amenable to powerful, targeted genetic manipulation. We thus subjected mice to endovascular perforation SAH and assessed long-term cognitive outcome via the Morris water maze (MWM), the most commonly used metric for rodent neurocognition. No significant differences in MWM performance (by either of two protocols) were seen in SAH versus sham mice. Moreover, SAH caused negligible hippocampal CA1 injury. These results undercut the potential of commonly used methods (of SAH induction and assessment of long-term neurocognitive outcome) for use in targeted molecular studies of SAH-induced cognitive deficits in the mouse.

Nonaneurysmal perimesencephalic subarachnoid hemorrhage: diagnosis, pathophysiology, clinical characteristics, and long-term outcome

Patients with nonaneurysmal perimesencephalic subarachnoid hemorrhage (NAPSAH) have no discernible source for the bleeding and generally are considered to have a benign condition. Correctly diagnosing these patients is essential because a missed aneurysm can have catastrophic consequences. Those presenting with NAPSAH have a low risk of complications and better outcome than patients presenting with aneurysmal subarachnoid hemorrhage; however, a limited body of literature suggests that not all of these patients are able to return to their premorbid functional status. Clinical screens of cognitive status, such as the mini-mental status examination, suggest good recovery of these patients, although these tests may lack sensitivity for identifying deficits in this patient population. More comprehensive neuropsychologic testing in some studies has identified deficits in a wide range of cognitive domains at long-term follow-up in patients with NAPSAH. Because these patients often do not lose consciousness (and thus do not have substantial transient global ischemia) and they do not undergo a procedure for aneurysm repair, the cognitive sequelae can be explained by the presence of blood in the subarachnoid space. NAPSAH presents an opportunity to understand the effects of subarachnoid blood in a clinical setting.

Inflammation, vasospasm, and brain injury after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) can lead to devastating neurological outcomes, and there are few pharmacologic treatments available for treating this condition. Both animal and human studies provide evidence of inflammation being a driving force behind the pathology of SAH, leading to both direct brain injury and vasospasm, which in turn leads to ischemic brain injury. Several inflammatory mediators that are elevated after SAH have been studied in detail. While there is promising data indicating that blocking these factors might benefit patients after SAH, there has been little success in clinical trials. One of the key factors that complicates clinical trials of SAH is the variability of the initial injury and subsequent inflammatory response. It is likely that both genetic and environmental factors contribute to the variability of patients' post-SAH inflammatory response and that this confounds trials of anti-inflammatory therapies. Additionally, systemic inflammation from other conditions that affect patients with SAH could contribute to brain injury and vasospasm after SAH. Continuing work on biomarkers of inflammation after SAH may lead to development of patient-specific anti-inflammatory therapies to improve outcome after SAH.

Molecular alterations in the hippocampus after experimental subarachnoid hemorrhage

Patients with aneurysmal subarachnoid hemorrhage (SAH) frequently have deficits in learning and memory that may or may not be associated with detectable brain lesions. We examined mediators of long-term potentiation after SAH in rats to determine what processes might be involved. There was a reduction in synapses in the dendritic layer of the CA1 region on transmission electron microscopy as well as reduced colocalization of microtubule-associated protein 2 (MAP2) and synaptophysin. Immunohistochemistry showed reduced staining for GluR1 and calmodulin kinase 2 and increased staining for GluR2. Myelin basic protein staining was decreased as well. There was no detectable neuronal injury by Fluoro-Jade B, TUNEL, or activated caspase-3 staining. Vasospasm of the large arteries of the circle of Willis was mild to moderate in severity. Nitric oxide was increased and superoxide anion radical was decreased in hippocampal tissue. Cerebral blood flow, measured by magnetic resonance imaging, and cerebral glucose metabolism, measured by positron emission tomography, were no different in SAH compared with control groups. The results suggest that the etiology of loss of LTP after SAH is not cerebral ischemia but may be mediated by effects of subarachnoid blood such as oxidative stress and inflammation.

Evidence for direct impairment of neuronal function by subarachnoid metabolites following SAH

Dysfunction of neuronal signal processing and transmission occurs after subarachnoid hemorrhage (SAH) and contributes to the high morbidity and mortality of this pathology. The underlying mechanisms include early brain injury due to elevation of the intracranial pressure, disruption of the blood-brain barrier, brain edema, reduction of cerebral blood flow, and neuronal cell death. Direct influence of subarachnoid blood metabolites on neuronal signaling should be considered. After SAH, some metabolites were shown to directly induce disruption of neuronal integrity and neuronal signaling, whereas the effects of other metabolites on neurotoxicity and neuronal signaling have not yet been investigated. Therefore, this mini-review will discuss recent evidence for a direct influence of subarachnoid blood and its metabolites on neuronal function.

Potential contribution of hypoxia-inducible factor-1α, aquaporin-4, and matrix metalloproteinase-9 to blood-brain barrier disruption and brain edema after experimental subarachnoid hemorrhage

The current research aimed to investigate the role of hypoxia-inducible factor-1α (HIF-1α), aquaporin-4 (AQP-4), and matrix metalloproteinase-9 (MMP-9) in blood-brain barrier (BBB) dysfunction and cerebral edema formation in a rat subarachnoid hemorrhage (SAH) model. The SAH model was induced by injection of 0.3 ml fresh arterial, non-heparinized blood into the prechiasmatic cistern in 20 s. Anti-AQP-4 antibody, minocycline (an inhibitor of MMP-9), or 2-methoxyestradiol (an inhibitor of HIF-1α), was administered intravenously at 2 and 24 h after SAH. Brain samples were extracted at 48 h after SAH and examined for protein expressions, BBB impairment, and brain edema. Following SAH, remarkable edema and BBB extravasations were observed. Compared with the control group, the SAH animals have significantly upregulated expressions of HIF-1α, AQP-4, and MMP-9, in addition to decreased amounts of laminin and tight junction proteins. Brain edema was repressed after inhibition of AQP-4, MMP-9, or HIF-1α. Although BBB permeability was also ameliorated after inhibition of either HIF-1α or MMP-9, it was not modulated after inhibition of AQP-4. Inhibition of MMP-9 reversed the loss of laminin. Finally, inhibition of HIF-1α significantly suppressed the level of AQP-4 and MMP-9, which could induce the expression of laminin and tight junction proteins. Our results suggest that HIF-1α plays a role in brain edema formation and BBB disruption via a molecular signaling pathway involving AQP-4 and MMP-9. Pharmacological intervention of this pathway in patients with SAH may provide a novel therapeutic strategy for early brain injury.

Free recall memory performance after aneurysmal subarachnoid hemorrhage

Memory deficits for survivors of aneurysmal subarachnoid hemorrhage (SAH) are common, however, the nature of these deficits is not well understood. In this study, 24 patients with SAH and matched control participants were asked to study six lists containing words from four different categories. For half the lists, the categories were presented together (organized lists). For the remaining lists, the related words were presented randomly to maximize the use of executive processes such as strategy and organization (unorganized lists). Across adjoining lists, there was overlap in the types of categories given, done to promote intrusions. Compared to control participants, SAH patients recalled a similar number of words for the organized lists, but significantly fewer words for the unorganized lists. SAH patients also reported more intrusions than their matched counterparts. Separating patients into anterior communicating artery ruptures (ACoA) and ruptures in other regions, there was a recall deficit only for the unorganized list for those with ACoA ruptures and deficits across both list types for other rupture locations. These results suggest that memory impairment following SAH is likely driven by impairment in the executive components of memory, particularly for those with ACoA ruptures. Such findings may help direct future cognitive-therapeutic programs.

The new pyridoindole antioxidant SMe1EC2 and its intervention in hypoxia/hypoglycemia-induced impairment of longterm potentiation in rat hippocampus

Previously, the pyridoindole SMe1EC2 was proved to inhibit lipoperoxidation and carbonylation of proteins in rat brain cortex in the system Fe²⁺/ascorbate and improvement of resistance of the rat hippocampus was reported against ischemic conditions in vitro (hypoxia/hypoglycemia) expressed by the enhanced neuronal response recovery in reoxygenation. The hippocampus fulfils many of the criteria for a neuronal correlate of learning and memory. Recently, an impairment of hippocampal long-term potentiation (LTP) was reported under oxidative stress. Different therapies, including antioxidants, have been studied intensively concerning the impairment of neuronal plasticity. In this study marked reduction of LTP, elicited by a single burst (100 Hz, 1s) in the CA3-CA1 area of rat hippocampal slices, was shown due to transient hypoxia/hypoglycemia compared to control slices. On the basis of previously reported antioxidant and neuroprotective effects of SMe1EC2, its effect on loss of LTP in the hippocampus due to ischemic conditions was studied in vitro. The pyridoindole tested improved hypoxia/hypoglycemia-induced reduction of LTP compared to untreated hypoxic slices. An opposite effect of SMe1EC2 on LTP induction was found in control slices. The mechanism of SMe1EC2 action on LTP in ischemic conditions has been suggested to differ from the mechanism of its effect in “normoxia” and may be due to different redox status in control and ischemic brain tissue. The manifested LTP-protective effect of SMe1EC2 observed in the rat hippocampus exposed to ischemia in vitro may find exploitation in therapy associated with injured neuronal plasticity in some conditions, including ischemia, trauma and aging in man.