No description available.

No description available.

No description available.

Blast-induced traumatic brain injury (bTBI) remains a significant problem among military populations. When an explosion occurs, a high magnitude positive pressure rapidly propagates away from the detonation source. Upon contact, biological tissues throughout the body undergo deformation at high strain rates and then return to equilibrium following a brief negative pressure phase. This mechanical disruption of the tissue is known to cause oxidative stress and neuroinflammation in the brain, which can lead to neurodegeneration and consequently poor cognitive and behavioral outcomes. Further, these clinical outcomes, which can include chronic headaches, problems with balance, light and noise sensitivity, anxiety, and depression, may be sustained years following blast exposure and there are currently no effective treatments. Thus, there is a need to investigate the acute molecular responses following bTBI in order to motivate the development of effective therapeutic strategies and ultimately improve or prevent long-term patient outcomes. It is important to not only understand the acute molecular response, but how the brain tissue mechanics drive these metabolic changes. The objective of this work was to identify the interplay between the tissue-level biomechanics and the acute bTBI pathophysiology. In a rodent bTBI model, using adult rats, intracranial pressure was mapped throughout the brain during blast exposure where frequency contributions from skull flexure and wave dynamics were significantly altered between brain regions and were largely dependent on blast magnitude. These findings informed the subsequent spatial and temporal changes in neurometabolism. Amino acid molecular precursor concentrations decreased at four hours post-blast in the cortex and hippocampus regions. This motivates further investigation of amino acids as therapeutic targets aimed to reduce oxidative stress and prevent prolonged injury cascades. However, neurochemical changes were not consistent across blast magnitudes, which may be explained by the disparities in biomechanics at lower blast pressures. Lastly, we investigated the acute changes in metabolic regulators influencing excitotoxicity where it was found that astrocytes maintained normal clearance of excitatory and inhibitory neurotransmitters prior to astrocyte reactivity. Outcomes of this work provide improved understanding of blast mechanics and associated acute pathophysiology and inform future therapeutic and diagnostic approaches following bTBI. / Doctor of Philosophy / Blast-induced traumatic brain injury (bTBI) remains a significant problem among military populations. When an explosion occurs, a high magnitude positive pressure wave rapidly propagates away from the detonation source. Upon contact, biological tissues throughout the body undergo deformation that can cause injury. This mechanical disruption of the tissue is known to trigger negative biological processes that lead to persistent cognitive and behavioral deficits. Further, these clinical outcomes, which can include chronic headaches, problems with balance, light and noise sensitivity, anxiety, and depression, may be sustained years following blast exposure. There are currently no effective treatments that can help those afflicted, and biomarkers for injury diagnostics are limited. Thus, there is a great need to investigate the early biological responses following bTBI in order to motivate the development of effective therapeutic strategies and ultimately improve or prevent long-term patient outcomes. It is important to not only understand the immediate responses, but also how the brain tissue mechanics drive these metabolic changes. The objective of this work was to identify the interplay between the brain biomechanics and the acute bTBI pathophysiology. Using a translational animal model, pressure inside the brain was measured with pressure sensors during blast exposure. Subsequent spatial and temporal changes in neurochemical concentrations were quantified. The results showed (1) significant disparities in the pressure dynamics inside the brain and it varied across brain regions, (2) neurochemical precursors may have therapeutic potential post-injury, and (3) biomechanical and neurochemical responses were dependent on blast severity. Outcomes of this work provide improved understanding of blast mechanics and associated pathophysiology and inform future therapeutic and diagnostic approaches to prevent prolonged injury cascades.

INTRODUÇÃO: A autorregulação cerebral representa um dos mecanismos fisiopatológicos incertos na hemorragia intracerebral espontânea, cujo comprometimento pode influenciar no resultado prognóstico e terapêutico. O objetivo deste trabalho é avaliar a autorregulação cerebral dinâmica em modelo suíno de hemorragia intracerebral espontânea através do índice de reatividade pressórica cerebrovascular e determinar a eficácia das intervenções clínicas e cirúrgicas. MÉTODOS: Foram estudados 21 suínos híbridos machos com idade de 3 meses. O modelo experimental simulou o efeito expansivo de uma hemorragia intracerebral espontânea de grande volume quando comparado ao cérebro humano. Foram avaliados volumes de expansão diferentes, distribuídos em três grupos com sete suínos cada. O protocolo anestésico incluiu uma monitoração hemodinâmica invasiva associada a preservação da autorregulação cerebral. Os experimentos foram submetidos a monitoração neurológica multimodal e divididos em 5 fases. O índice de reatividade pressórica cerebrovascular estimou a autorregulacão cerebral durante todas as fases, sendo as três primeiras sem intervenções terapêuticas e as duas últimas para avaliar a eficácia das intervenções salina hipertônica e cirurgia. RESULTADOS: Os grupos avaliados foram homogêneos e sem diferença estatística quanto ao comprometimento da autorregulação cerebral comparando os diferentes volumes e tempos de compressão durante as duas primeiras horas da expansão do volume intracraniano. O comprometimento do índice de reatividade pressórica cerebrovascular ocorreu em alguns experimentos influenciando nas fases de tratamento subsequentes, salina hipertônica e cirurgia. CONCLUSÕES: Volumes expansivos elevados podem comprometer a autorregulação cerebral dinâmica e apresentar desfecho terapêutico desfavorável. A intervenção clínica e cirúrgica tem benefício nos experimentos com preservação do índice de reatividade pressórica cerebrovascular / INTRODUCTION: Cerebral autoregulation represents one of the uncertain pathophysiological mechanisms in spontaneous intracerebral hemorrhage, whose impairment may influence prognostic and therapeutic outcome. The aim of this study was to evaluate the dynamic cerebral autoregulation in the swine model of spontaneous intracerebral hemorrhage through the cerebrovascular reactivity index and to determine the efficacy of clinical and surgical interventions. METHODS: Twenty-one male hybrid pigs aged 3 months were studied. The experimental model simulated the expansive effect of a large intracerebral hemorrhage when compared to the human brain. Different volumes were evaluated, distributed in three groups with seven pigs each. Each experiment was divided in five phases. The anesthetic protocol included invasive hemodynamic monitoring associated with the preservation of cerebral autoregulation. Multimodallity monitoring was realised in all experiments. The cerebrovascular reactivity index estimated the cerebral autoregulation during all phases. The first three phases were without therapeutic interventions, and the last two phases were with therapeutic intervention of hypertonic saline solution and neurosurgery respectively. RESULTS: The evaluated groups were homogeneous and without statistical difference regarding the impairment of the cerebral autoregulation comparing different volumes and compression times during the first two hours of the intracranial volume expansion. CONCLUSIONS: Elevated expansive volumes may compromise dynamic cerebral autoregulation and have unfavorable therapeutic outcome. Clinical and surgical intervention had benefit in the experiments with preservation of cerebrovascular reactivity index

INTRODUÇÃO: A autorregulação cerebral representa um dos mecanismos fisiopatológicos incertos na hemorragia intracerebral espontânea, cujo comprometimento pode influenciar no resultado prognóstico e terapêutico. O objetivo deste trabalho é avaliar a autorregulação cerebral dinâmica em modelo suíno de hemorragia intracerebral espontânea através do índice de reatividade pressórica cerebrovascular e determinar a eficácia das intervenções clínicas e cirúrgicas. MÉTODOS: Foram estudados 21 suínos híbridos machos com idade de 3 meses. O modelo experimental simulou o efeito expansivo de uma hemorragia intracerebral espontânea de grande volume quando comparado ao cérebro humano. Foram avaliados volumes de expansão diferentes, distribuídos em três grupos com sete suínos cada. O protocolo anestésico incluiu uma monitoração hemodinâmica invasiva associada a preservação da autorregulação cerebral. Os experimentos foram submetidos a monitoração neurológica multimodal e divididos em 5 fases. O índice de reatividade pressórica cerebrovascular estimou a autorregulacão cerebral durante todas as fases, sendo as três primeiras sem intervenções terapêuticas e as duas últimas para avaliar a eficácia das intervenções salina hipertônica e cirurgia. RESULTADOS: Os grupos avaliados foram homogêneos e sem diferença estatística quanto ao comprometimento da autorregulação cerebral comparando os diferentes volumes e tempos de compressão durante as duas primeiras horas da expansão do volume intracraniano. O comprometimento do índice de reatividade pressórica cerebrovascular ocorreu em alguns experimentos influenciando nas fases de tratamento subsequentes, salina hipertônica e cirurgia. CONCLUSÕES: Volumes expansivos elevados podem comprometer a autorregulação cerebral dinâmica e apresentar desfecho terapêutico desfavorável. A intervenção clínica e cirúrgica tem benefício nos experimentos com preservação do índice de reatividade pressórica cerebrovascular / INTRODUCTION: Cerebral autoregulation represents one of the uncertain pathophysiological mechanisms in spontaneous intracerebral hemorrhage, whose impairment may influence prognostic and therapeutic outcome. The aim of this study was to evaluate the dynamic cerebral autoregulation in the swine model of spontaneous intracerebral hemorrhage through the cerebrovascular reactivity index and to determine the efficacy of clinical and surgical interventions. METHODS: Twenty-one male hybrid pigs aged 3 months were studied. The experimental model simulated the expansive effect of a large intracerebral hemorrhage when compared to the human brain. Different volumes were evaluated, distributed in three groups with seven pigs each. Each experiment was divided in five phases. The anesthetic protocol included invasive hemodynamic monitoring associated with the preservation of cerebral autoregulation. Multimodallity monitoring was realised in all experiments. The cerebrovascular reactivity index estimated the cerebral autoregulation during all phases. The first three phases were without therapeutic interventions, and the last two phases were with therapeutic intervention of hypertonic saline solution and neurosurgery respectively. RESULTS: The evaluated groups were homogeneous and without statistical difference regarding the impairment of the cerebral autoregulation comparing different volumes and compression times during the first two hours of the intracranial volume expansion. CONCLUSIONS: Elevated expansive volumes may compromise dynamic cerebral autoregulation and have unfavorable therapeutic outcome. Clinical and surgical intervention had benefit in the experiments with preservation of cerebrovascular reactivity index

<p>During brain activity neurons release the major excitatory transmitter glutamate, which is taken up by astrocytes and converted to glutamine. Glutamine returns to neurons for re-conversion to glutamate. This glutamate-glutamine cycle is energy demanding. Glutamate turnover in injured brain was studied using an animal iron-induced posttraumatic epilepsy model and using neurointensive care data from 33 patients with spontaneous subarachnoid hemorrhage (SAH). Immunoblotting revealed that the functional form of the major astrocytic glutamate uptake protein GLT-1 was decreased 1-5 days following a cortical epileptogenic iron-injection, presumably due to oxidation-induced aggregation. Using microdialysis it was shown that the GLT-1 decrease was associated with increased interstitial glutamate levels and decreased interstitial glutamine levels. The results indicate a possible posttraumatic and post-stroke epileptogenic mechanism. Analysing 3600 microdialysis hours from patients it was found that the interstitial lactate/pyruvate (L/P) ratio correlate with the glutamine/glutamate ratio (r =-0.66). This correlation was as strong as the correlation between L/P and glutamate (r=0.68) and between lactate and glutamate (r=0.65). Pyruvate and glutamine correlated linearly (r=0.52). Energy failure periods, defined as L/P>40, were associated with high interstitial glutamate levels. Glutamine increased or decreased during energy failure periods depending on pyruvate. Energy failure periods were clinically associated with delayed ischemic neurological deficits (DIND) or development of radiologically verified infarcts, confirming that L/P>40 is a pathological microdialysis pattern that can predict ischemic deterioration after SAH. DIND-associated microdialysis patterns were L/P elevations and surges in interstitial glutamine. Glutamine and pyruvate correlated with the cerebral perfusion pressure (r=0.25, r=0.24). Glutamine and the glutamine/glutamate ratio correlated with the intracranial pressure (r=-0.29, r=0.40). Glutamine surges appeared upon substantial lowering of the intracranial pressure by increased cerebrospinal fluid drainage. Increased interstitial glutamine and pyruvate levels may reflect augmented astrocytic glycolysis in recovering brain tissue with increased energy demand due to a high glutamate-glutamine turnover.</p>

No description available.

Inhalants are a loosely defined diverse group of volatile substances which people abuse. Despite widespread misuse of inhalants, there are limited preclinical methods available to study the reinforcement-like properties of inhalants. One procedure which has demonstrated substantial promise as a tool to investigate inhalant pharmacology is the intracranial self-stimulation (ICSS) procedure. ICSS utilizes pulses of electrical stimulation to the mesolimbic reward pathway to serve as a temporally defined and controlled operant reinforcer with a highly adjustable efficacy. The first aim of the project was to characterize the effects of commonly abused inhalants: including toluene, trichloroethane, nitrous oxide, isoflurane and R134a in ICSS. The second aim was to attenuate inhalant-facilitated ICSS by utilization of compounds which would attenuate the pharmacological actions of toluene on GABAA receptors. The low efficacy benzodiazepine negative modulator Ro15-4513 significantly attenuated the ability of toluene to facilitate ICSS without itself significantly altering baseline ICSS responding. Pretreatment with Ro15-4513 also attenuated methamphetamine ICSS even though there is no evidence of methamphetamine interacting with GABAA receptors. Given these unexpected results, I employed a microdialysis procedure to examine the effect of Ro15-4513 on methamphetamine stimulated dopamine release in the nucleus accumbens. Pretreatment with Ro15-4513 significantly attenuated methamphetamine stimulated dopamine release while having a negligible effect on dopamine release when administered alone. These results suggest that a modest level of benzodiazepine-site negative modulation can reduce the reinforcement enhancing effects of abused drugs regardless of their primary mechanism of action through allosteric modulation of GABAergic neurons within the mesolimbic pathway. Further, these results may have implications for expanding the examination of GABAA negative modulator medications beyond those trials currently being conducted with alcohol. Finally, the effects of chronic intermittent toluene exposure on ICSS and nesting behaviors were examined. Subjects were systemically exposed to air, chronic intermittent toluene (CIT), or escalating chronic intermittent (ECIT) toluene for 15 min at 3300 PPM toluene vapor per exposure. The results show that ECIT resulted in decreased overall responding in ICSS relative to air control and showed a tolerance-like effect to facilitatory effects of 3300 ppm toluene during ICSS compared to CIT group. These results indicate that escalating use of toluene produces reductions in its reward-like effects and may contribute to escalation to other drugs of abuse.

An intracranial aneurysm (IA) is a balloon-like focal lesion on the cerebral arterial wall. IAs are poorly understood, but are commonly considered to be a disease caused by multiple factors. Current interventional treatments are accompanied with risks. Given the low incidence of rupture, it would be ideal to only treat aneurysms identified with rupture risk. Numerical models of aneurysm development may provide insight into the disease mechanisms, and contribute to the prediction of disease progression. Better understanding of the disease aetiology will also guide clinical decision making. Different hypotheses have been proposed on the influence of haemodynamic stimuli on IA inception. We investigate this influence by examining the haemodynamic stimuli of the 'pre-aneurysmal' vasculature in the locations of IA formation in 22 clinical cases. The 'pre aneurysmal' geometries are obtained by applying a novel numerical vessel reconstruction method on the aneurysmal geometries. This automated reconstruction method propagates a closed curve along the vessel skeleton using the local Frenet frames to smoothly morph the upstream boundary into the downstream boundary. We observe that locally elevated wall shear stress (WSS) and gradient oscillatory number (GON) are highly correlated with regions susceptible to sidewall IA formation, whilst haemodynamic indices associated with the oscillation of the WSS vectors have much lower correlations. A common assumption made in the literature on arterial growth and remodelling (G&R) is that the 'state of stretch' (denoted as the attachment stretch) at which collagen fibres are configured in the extracellular matrix (ECM) is assumed to be constant. This will lead to an unrealistically thickened arterial wall in modelling aneurysm evolution. We propose a novel 1D mathematical model of collagen microstructural adaption during IA evolution. We assume new collagen fibres are configured into the ECM in a state of attachment stretch distribution which can be temporally adaptive. We explicitly define the functional form of this distribution and model its temporal adaption during IA evolution. This model is then implemented into two 3D models of IA evolution: a solid structural model and Fluid-Solid-Growth (FSG) model. In the solid structural model, the artery is modelled as a two-layer, nonlinear elastic cylindrical membrane using a physiologically realistic constitutive model. The development of the aneurysm is considered as a consequence of the growth and remodelling of its material constituents: elastinous constituents are prescribed to degrade in a localised circular patch; collagen concentration and recruitment variables enable the growth and remodelling of collagen fabric to be simulated; adaption of the attachment stretch distribution is confined locally within the region of aneurysm evolution. The sophisticated solid model predicts stabilised saccular IAs with realistic sizes and wall thicknesses. The FSG model simulates the IA development on patient-specific vasculature: the updated 3D solid structural model is integrated into a patient-specific geometry of the vasculature and the growth and remodelling of the constituents is now linked to the local haemodynamic stimuli obtained from a rigid-wall computational fluid dynamics analysis. Adaption of the attachment stretch distribution is also confined locally in the region where the constituents degrade. An illustrative case of IA development on patient specific geometry is provided. Based on our study, we conclude that incorporating the adaption of attachment stretch distribution is necessary to simulate IA evolution with physiological evolving wall thicknesses. However, how vascular cells confine this adaption heterogeneously needs further investigation. Improved understanding and modelling of the biology of the arterial wall is needed for more sophisticated models of aneurysm evolution. It will in turn assist in understanding the aetiology of IA formation. Ultimately we hope to have a patient-specific growth model that could have the potential be used to assist diagnostic decisions.