Malignant infarction in cats after prolonged middle cerebral artery occlusion: glutamate elevation related to decrease of cerebral perfusion pressure

Glutamate Neurotoxicity and Destruction of the Blood–Brain Barrier: Key Pathways for the Development of Neuropsychiatric Consequences of TBI and Their Potential Treatment Strategies

Traumatic brain injury (TBI) is associated with significant cognitive and psychiatric conditions. Neuropsychiatric symptoms can persist for years following brain injury, causing major disruptions in patients’ lives. In this review, we examine the role of glutamate as an aftereffect of TBI that contributes to the development of neuropsychiatric conditions. We hypothesize that TBI causes long-term blood–brain barrier (BBB) dysfunction lasting many years and even decades. We propose that dysfunction in the BBB is the central factor that modulates increased glutamate after TBI and ultimately leads to neurodegenerative processes and subsequent manifestation of neuropsychiatric conditions. Here, we have identified factors that determine the upper and lower levels of glutamate concentration in the brain after TBI. Furthermore, we consider treatments of disruptions to BBB integrity, including repairing the BBB and controlling excess glutamate, as potential therapeutic modalities for the treatment of acute and chronic neuropsychiatric conditions and symptoms. By specifically focusing on the BBB, we hypothesize that restoring BBB integrity will alleviate neurotoxicity and related neurological sequelae.

Central nervous system development of cats (Felis catus L. 1758)

The morphological similarities of vertebrates' embryonic development are used as a criterion for choosing animal models that can be used in biomedical research. This study describes the embryonic and fetal development of the domestic cat's central nervous system from 15 days after conception until birth. In total, fifty-seven samples of embryos and fetuses were carefully dissected and analyzed microscopically. The closure of the neural tube was observed between 14-15th days of gestation. The differentiation of the primordial cerebral vesicles was observed from the 17th day of gestation. On the 19th day of gestation, the formation of the choroid plexus began, and on the 20th day of gestation, the brain and brainstem were well-identified macroscopically. On the 24th day of gestation, four layers of cells from the cerebral cortex were described, and on the 60th day, six layers of cells were present. The cerebellar cortex had the three classic cortical layers at this stage. The morphological aspects of embryonic and fetal development in cats were very similar to the stages of development of the human nervous system. As such, this study provided relevant information that highlights the domestic cat as an animal model option for preclinical research on infectious and non-infectious neurological diseases in humans.

Elevated Intracranial Pressure and Cerebral Edema following Permanent MCA Occlusion in an Ovine Model

INTRODUCTION

Malignant middle cerebral artery (MCA) stroke has a disproportionately high mortality due to the rapid development of refractory space-occupying cerebral edema. Animal models are essential in developing successful anti-edema therapies; however to date poor clinical translation has been associated with the predominately used rodent models. As such, large animal gyrencephalic models of stroke are urgently needed. The aim of the study was to characterize the intracranial pressure (ICP) response to MCA occlusion in our recently developed ovine stroke model.

MATERIALS AND METHODS

30 adult female Merino sheep (n = 8-12/gp) were randomized to sham surgery, temporary or permanent proximal MCA occlusion. ICP and brain tissue oxygen were monitored for 24 hours under general anesthesia. MRI, infarct volume with triphenyltetrazolium chloride (TTC) staining and histology were performed.

RESULTS

No increase in ICP, radiological evidence of ischemia within the MCA territory but without space-occupying edema, and TTC infarct volumes of 7.9+/-5.1% were seen with temporary MCAO. Permanent MCAO resulted in significantly elevated ICP, accompanied by 30% mortality, radiological evidence of space-occupying cerebral edema and TTC infarct volumes of 27.4+/-6.4%.

CONCLUSIONS

Permanent proximal MCAO in the sheep results in space-occupying cerebral edema, raised ICP and mortality similar to human malignant MCA stroke. This animal model may prove useful for pre-clinical testing of anti-edema therapies that have shown promise in rodent studies.

The central role of aquaporins in the pathophysiology of ischemic stroke

Stroke is a complex and devastating neurological condition with limited treatment options. Brain edema is a serious complication of stroke. Early edema formation can significantly contribute to infarct formation and thus represents a promising target. Aquaporin (AQP) water channels contribute to water homeostasis by regulating water transport and are implicated in several disease pathways. At least 7 AQP subtypes have been identified in the rodent brain and the use of transgenic mice has greatly aided our understanding of their functions. AQP4, the most abundant channel in the brain, is up-regulated around the peri-infarct border in transient cerebral ischemia and AQP4 knockout mice demonstrate significantly reduced cerebral edema and improved neurological outcome. In models of vasogenic edema, brain swelling is more pronounced in AQP4-null mice than wild-type providing strong evidence of the dual role of AQP4 in the formation and resolution of both vasogenic and cytotoxic edema. AQP4 is co-localized with inwardly rectifying K(+)-channels (Kir4.1) and glial K(+) uptake is attenuated in AQP4 knockout mice compared to wild-type, indicating some form of functional interaction. AQP4-null mice also exhibit a reduction in calcium signaling, suggesting that this channel may also be involved in triggering pathological downstream signaling events. Associations with the gap junction protein Cx43 possibly recapitulate its role in edema dissipation within the astroglial syncytium. Other roles ascribed to AQP4 include facilitation of astrocyte migration, glial scar formation, modulation of inflammation and signaling functions. Treatment of ischemic cerebral edema is based on the various mechanisms in which fluid content in different brain compartments can be modified. The identification of modulators and inhibitors of AQP4 offer new therapeutic avenues in the hope of reducing the extent of morbidity and mortality in stroke.

Glibenclamide in cerebral ischemia and stroke

The sulfonylurea receptor 1 (Sur1)-transient receptor potential 4 (Trpm4) channel is an important molecular element in focal cerebral ischemia. The channel is upregulated in all cells of the neurovascular unit following ischemia, and is linked to microvascular dysfunction that manifests as edema formation and secondary hemorrhage, which cause brain swelling. Activation of the channel is a major molecular mechanism of cytotoxic edema and "accidental necrotic cell death." Blockade of Sur1 using glibenclamide has been studied in different types of rat models of stroke: (i) in conventional non-lethal models (thromboembolic, 1-2 h temporary, or permanent middle cerebral artery occlusion), glibenclamide reduces brain swelling and infarct volume and improves neurological function; (ii) in lethal models of malignant cerebral edema, glibenclamide reduces edema, brain swelling, and mortality; (iii) in models with rtPA, glibenclamide reduces swelling, hemorrhagic transformation, and death. Retrospective studies of diabetic patients who present with stroke have shown that those whose diabetes is managed with a sulfonylurea drug and who are maintained on the sulfonylurea drug during hospitalization for stroke have better outcomes at discharge and are less likely to suffer hemorrhagic transformation. Here, we provide a comprehensive review of the basic science, preclinical experiments, and retrospective clinical studies on glibenclamide in focal cerebral ischemia and stroke. We also compare the preclinical work in stroke models to the updated recommendations of the Stroke Therapy Academic Industry Roundtable (STAIR). The findings reviewed here provide a strong foundation for a translational research program to study glibenclamide in patients with ischemic stroke.

High resolution MRI anatomy of the cat brain at 3 Tesla

BACKGROUND

Feline models of neurologic diseases, such as lysosomal storage diseases, leukodystrophies, Parkinson's disease, stroke and NeuroAIDS, accurately recreate many aspects of human disease allowing for comparative study of neuropathology and the testing of novel therapeutics. Here we describe in vivo visualization of fine structures within the feline brain that were previously only visible post mortem.

NEW METHOD

3Tesla MR images were acquired using T1-weighted (T1w) 3D magnetization-prepared rapid gradient echo (MPRAGE) sequence (0.4mm isotropic resolution) and T2-weighted (T2w) turbo spin echo (TSE) images (0.3mm×0.3mm×1mm resolution). Anatomic structures were identified based on feline and canine histology.

RESULTS

T2w high resolution MR images with detailed structural identification are provided in transverse, sagittal and dorsal planes. T1w MR images are provided electronically in three dimensions for unrestricted spatial evaluation.

COMPARISON WITH EXISTING METHODS

Many areas of the feline brain previously unresolvable on MRI are clearly visible in three orientations, including the dentate, interpositus and fastigial cerebellar nuclei, cranial nerves, lateral geniculate nucleus, optic radiation, cochlea, caudal colliculus, temporal lobe, precuneus, spinocerebellar tract, vestibular nuclei, reticular formation, pyramids and rostral and middle cerebral arteries. Additionally, the feline brain is represented in three dimensions for the first time.

CONCLUSIONS

These data establish normal appearance of detailed anatomical structures of the feline brain, which provide reference when evaluating neurologic disease or testing efficacy of novel therapeutics in animal models.

AC electrocorticographic correlates of peri-infarct depolarizations during transient focal ischemia and reperfusion

Several studies have highlighted a delayed secondary pathology developing after reperfusion in animals subjected to prolonged cerebral ischemia, and recently we have shown that peri-infarct depolarizations (PIDs) occur not only during ischemia, but also in this delayed period of infarct maturation. Here we study the electrocorticographic (ECoG) manifestations of PIDs as signatures of developing secondary pathology. DC- and traditional AC-ECoG signals were recorded continuously from epidural, nonpolarizable electrodes during 2 h of middle cerebral artery occlusion (MCAo) and 22 h of reperfusion in freely behaving rats. During MCAo, seizures and PIDs recurred frequently and their incidence was significantly correlated. After reperfusion, seizures and PIDs ceased, and for the next several hours delta wave abnormalities dominated the ECoG with progressively increasing amplitude. After a variable period (5 to 15 h), the ECoG amplitude decremented with the onset of a prolonged repetitive series of PIDs. Initial PIDs in this delayed phase produced transient depressions of the high amplitude ECoG signal, but thereafter the ECoG was persistently attenuated, with no transient depressions during subsequent PIDs. The time of onset of postreperfusion PIDs, and hence measures of ECoG attenuation, correlated with 24 h infarct volumes. PIDs could always be detected in baseline shifts of the AC-ECoG signal with a low high-pass cutoff setting. These results suggest that delayed PIDs after reperfusion contribute to a complex secondary pathology involving delayed edema, intracranial hypertension, and hypoperfusion. The manifestation of PIDs in ECoG/electroencephalography recordings may enable continuous real-time monitoring of infarct progression.

Rodent models of focal stroke: size, mechanism, and purpose

Rodent stroke models provide the experimental backbone for the in vivo determination of the mechanisms of cell death and neural repair, and for the initial testing of neuroprotective compounds. Less than 10 rodent models of focal stroke are routinely used in experimental study. These vary widely in their ability to model the human disease, and in their application to the study of cell death or neural repair. Many rodent focal stroke models produce large infarcts that more closely resemble malignant and fatal human infarction than the average sized human stroke. This review focuses on the mechanisms of ischemic damage in rat and mouse stroke models, the relative size of stroke generated in each model, and the purpose with which focal stroke models are applied to the study of ischemic cell death and to neural repair after stroke.

Peri-infarct depolarizations reveal penumbra-like conditions in striatum

Spreading depression-like peri-infarct depolarizations not only characterize but also worsen penumbra conditions in cortical border zones of experimental focal ischemia. We intended to investigate the relevance of ischemic depolarization in subcortical regions of ischemic territories. Calomel electrodes measured DC potentials simultaneously in the lateral and medial portions of the caudate nucleus (CN) of 11 anesthetized cats after permanent occlusion of the middle cerebral artery. Additionally, platinum electrodes measured cerebral blood flow (CBF) in the CN, and laser Doppler probes CBF in the cortex. Depolarizations (negative DC shifts >10 mV) were obtained in 10 of 11 cats. Further differentiation revealed that short-lasting spreading depression-like depolarizations (SDs; 5 of 10 cats: 5.24 +/- 1.22 min total duration; 23.3 +/- 4.2 mV amplitude) were predominantly found in medial and longer depolarizations (LDs; 4 of 10 cats: 64.7 +/- 47.5 min; 25.0 +/- 11.3 mV) in the lateral CN. Terminal depolarizations (TDs; 6 of 10 cats; without repolarization) occurred immediately after occlusion or at later stages, being then accompanied by elevations of intracranial pressure presumably inducing secondary CBF reduction. CBF tended to be lower in regions with TDs (33.3 +/- 29.9% of control) and LDs (37.3 +/- 22.8%) than in regions with SDs (51.5 +/- 48.0%). We conclude that in focal ischemia, transient peri-infarct depolarizations emerge not only in cortical but also in striatal gray matter, thereby demonstrating the existence of subcortical zones of ischemic penumbra. The generation of these ischemic depolarizations is a multifocal process possibly linked to brain swelling and intracranial pressure rise in the later course of focal ischemia, and therefore a relevant correlate of progressively worsening conditions.

Prediction of malignant infarction: perifocal neurochemical monitoring following prolonged MCA occlusion in cats

Neurochemical monitoring in the ischemic core predicts malignancy in focal ischemia in cats. Since perifocal regions are more suitable for clinical microdialysis (MD) applications, we tested whether monitoring at such site predicts also malignancy.--Laser Doppler (LD) probes, pressure microsensors, and MD/HPLC measured cerebral blood flow (CBF), intracranial pressure (ICP), and extracellular glutamate (Glu), respectively. The middle cerebral artery was occluded (MCAO) for 3 hours followed by 6 hours reperfusion. Additionally, LD measured CBF in ischemic core.--MCAO reduced CBF in the core in all below 25% of control. In animals exhibiting malignancy (eye dilatation during reperfusion), MCAO decreased CBF in the perifocal site to around 35%. CBF primarily recovered following recirculation but decreased thereafter as ICP rose due to progressive edema formation. Glu increased concomitantly. In cats exhibiting a benign course, MCAO decreased CBF in the perifocal site to around 55%. Recirculation normalized CBF, and Glu did not increase. During MCAO, Glu differences between both groups were not significant.--Glu determinations in perifocal sites taken during MCAO do not predict fatal outcome. This contrasts with determinations in the core. After reperfusion, Glu elevation in perifocal sites may serve as a rather late predictor of malignancy.

Early Functional Recovery and the Fate of the Diffusion/Perfusion Mismatch in Patients with Proximal Middle Cerebral Artery Occlusion

BACKGROUND

The relationship between early neurological recovery, time to recanalization and the salvage of hypoperfused, but not diffusion-restricted tissue was investigated.

METHODS

In 17 patients with acute middle cerebral artery occlusion, a multiparametric stroke MRI protocol was performed < 6 h after symptom onset, as well as at day 2 and 7. Recanalization was monitored with transcranial Doppler or with conventional angiography (during local thrombolysis). Functional improvement was defined as a change of > or = 4 points on the National Institutes of Health Stroke Scale score.

RESULTS

In patients with functional improvement, 78% (median, range 66-95%) of the acute mean transit time (MTT) lesion escaped infarction compared with 28% (median, range -13 to 78%) in patients without neurological improvement (p < 0.01). Similarly, the percentage of tissue with a time-to-peak (TTP) delay of > or = 2 s not progressing to infarction was 80 and 4% in the groups with and without improvement, respectively (p < 0.01). Neurological improvement was more frequent in patients with early (< or = 3 h after presentation) recanalization, due to the salvage of larger areas of initially hypoperfused tissue.

CONCLUSIONS

The salvage of hypoperfused tissue is a major factor influencing early neurological improvement.

Extracellular Concentrations of Non–Transmitter Amino Acids in Peri-Infarct Tissue of Patients Predict Malignant Middle Cerebral Artery Infarction

Background and Purpose— Space-occupying brain edema is a life-threatening complication in patients with large middle cerebral artery (MCA) infarction. To determine predictors of this detrimental process, we investigated alterations of extracellular non–transmitter amino acid concentrations in peri-infarct tissue.

Methods— Thirty-one patients with infarctions covering >50% of the MCA territory in early cranial CT scans were included in the study. Probes for microdialysis, intracranial pressure, and tissue oxygen pressure were placed into the noninfarcted ipsilateral frontal lobe. Positron emission tomography imaging was performed in 16 of these patients to measure cerebral blood flow in the tissue around the neuromonitoring probes.

Results— Fourteen of the 31 patients developed a malignant MCA infarction, and 17 did not. The patients in the malignant group had significantly lower extracellular concentrations of non–transmitter amino acids than those in the benign group in the first 12 hours of neuromonitoring. At this time, CBF values determined in regions of interest around the probes by positron emission tomography and tissue oxygen pressure showed that the monitored tissues were not yet infarcted, and no differences in transmitter amino acids concentrations were found between the 2 groups. Furthermore, extracellular concentrations of non–transmitter amino acids were negatively correlated with size of infarction.

Conclusions— We assume that reduction of non–transmitter amino acid concentrations reflects an expansion of the extracellular space by vasogenic edema formation in peri-infarct tissue of patients with malignant MCA infarction. Our findings facilitate early prediction of malignant edema formation and may help to increase knowledge of the pathophysiology of the peri-infarct zone of large MCA infarction.

Prediction of malignant course in MCA infarction by PET and microdialysis

BACKGROUND AND PURPOSE

To predict malignant course in patients with large middle cerebral artery (MCA) infarction, we combined PET imaging and neuromonitoring, including microdialysis.

METHODS

Thirty-four patients with stroke of >50% of the MCA territory in early cerebral CT scan were included. Probes for microdialysis and measurement of intracranial pressure and tissue oxygen pressure (Pto2) were placed into the ipsilateral frontal lobe. PET was performed with 11C-flumazenil to assess CBF and irreversible neuronal damage.

RESULTS

PET measurements within 24 hours after stroke showed larger volumes of ischemic core (mean, 144.5 versus 62.2 cm3) and larger volumes of irreversible neuronal damage (157.9 versus 47.0 cm3) in patients with malignant course (ie, edema formation with midline shift) than in patients with benign course. Mean cerebral blood flow values within the ischemic core were significantly lower and the volume of the ischemic penumbra was smaller in the malignant than in the benign group. In patients with malignant course, cerebral perfusion pressure dropped to <50 to 60 mm Hg 22 to 72 hours (mean, 52.0 hours) after onset of symptoms; subsequently, Pto2 dropped and glutamate increased, indicating secondary ischemia. Maximal changes in the monitored variables reached significant levels for glutamate, aspartate, GABA, glycerol, lactate-to-pyruvate ratio, hypoxanthine, intracranial pressure, cerebral perfusion pressure, and Pto2.

CONCLUSIONS

PET allowed prediction of malignant MCA infarction within the time window suggested for hemicraniectomy. Neuromonitoring helped to classify the clinical courses by characterizing pathophysiological sequelae of malignant edema formation. In contrast to PET, however, it did not predict fatal outcome early enough for successful implementation of invasive therapies.