Browsing by Author "Dunn, Jeff F."
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- ItemOpen AccessCharacterizing Susceptibility Weighted MRI in the Experimental Autoimmune Encephalomyelitis Mouse Model of Multiple Sclerosis(2014-10-07) Nathoo, Nabeela; Dunn, Jeff F.; Yong, V. WeeSusceptibility-based magnetic resonance imaging (MRI) methods have been used in multiple sclerosis (MS) patients for lesion detection, visualization of the venous vasculature and to show abnormal iron accumulation in the deep grey matter structures of the brain. The overarching goal of this thesis was to characterize one of the susceptibility-based MRI methods, susceptibility weighted imaging (SWI), in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. First, we investigated if SWI could detect lesions (or hypointensities) in the lumbar spinal cords and cerebella of EAE mice. We found that SWI hypointensities were present in a region-specific manner in the CNS of EAE mice, where most of these lesions were attributed to deoxyhemoglobin and a smaller number were due to parenchymal iron deposition. Next, we validated a method to identify deoxyhemoglobin-based SWI hypointensities in vivo which entailed combining SWI with hyperoxygenation. Following this, we sought to investigate when SWI hypointensities appear during the EAE disease course and how they change over the course of the disease. This was studied by carrying out serial SWI in vivo in naïve mice and mice immunized for EAE. Here, we found that SWI hypointensities are prominent before signs of motor dysfunction in EAE mice. SWI hypointensities were also observed to evolve over the disease course. Of note, the number of SWI hypointensities was always at a maximum before or at the same time as maximum motor dysfunction. Unlike EAE mice, the number of SWI hypointensities remained stable through all imaging time points in naïve mice, suggesting that SWI hypointensities are linked to EAE pathophysiology. Lastly we used SWI to assess treatment response to an anti-inflammatory treatment (dexamethasone) in EAE mice. This was carried out under the premise that SWI hypointensities may be linked to inflammation, so reducing inflammation could reduce the number of SWI hypointensities present. Our preliminary data suggest that SWI may be able to act as a surrogate marker of inflammation. Overall, findings from this thesis support the use of SWI in future studies in the EAE model to investigate the venous vasculature and parenchymal iron deposition.
- ItemOpen AccessCortical excitability after pediatric mild traumatic brain injury(Elsevier, 2016-11-19) Seeger, Trevor A.; Kirton, Adam; Esser, Michael J.; Gallagher, Clare; Dunn, Jeff F.; Zewdie, Ephrem Takele; Damji, Omar; Ciechanski, Patrick; Barlow, Karen M.Introduction: Mild traumatic brain injury (mTBI) outcomes are variable, and 10e15% may suffer from prolonged symptoms beyond 3 months that impair the child's return to normal activities. Neurophysiological mechanisms of mTBI are incompletely understood, particularly in children, but alterations in cortical excitability have been proposed to underlie post-concussion syndrome. Improved understanding is required to advance interventions and improve outcomes. Objective/Hypothesis: To determine if cortical excitability is altered in children with mTBI, and its association with clinical symptoms. Methods: This was a cross-sectional controlled cohort study. School-aged children (8e18 years) with mTBI were compared to healthy controls. Cortical excitability was measured using multiple TMS paradigms in children with (symptomatic) and without (recovered) persistent symptoms one-month post-injury. Primary outcome was the cortical silent period (cSP), a potential neurophysiological biomarker of GABAergic inhibition. Secondary outcomes included additional TMS neurophysiology, safety and tolerability. Associations between neurophysiology parameters and clinical symptoms were evaluated. Results: Fifty-three children with mTBI (55% male; mean age 14.1 SD: 2.4 years; 35 symptomatic and 27 asymptomatic participants) and 28 controls (46% male; mean age 14.3 SD: 3.1 years) were enrolled. cSP duration was similar between groups (F (2, 73) ¼ 0.55, p ¼ 0.582). Log10 long interval intracortical inhibition (LICI) was reduced in symptomatic participants compared to healthy controls (F (2, 59) ¼ 3.83, p ¼ 0.027). Procedures were well tolerated with no serious adverse events. Conclusions: TMS measures of cortical excitability are altered at one month in children with mTBI. Long interval cortical inhibition is decreased in children who remain symptomatic at one month post-injury.
- ItemOpen AccessDetecting Deoxyhemoglobin in Spinal Cord Vasculature of the Experimental Autoimmune Encephalomyelitis Mouse Model of Multiple Sclerosis Using Susceptibility MRI and Hyperoxygenation(PLOS ONE, 2015-05-18) Nathoo, Nabeela; Rogers, James A.; Yong, V. Wee; Dunn, Jeff F.Susceptibility-weighted imaging (SWI) detects hypointensities due to iron deposition and deoxyhemoglobin. Previously it was shown that SWI detects hypointensities in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS), most of which are due to intravascular deoxyhemoglobin, with a small proportion being due to iron deposition in the central nervous system parenchyma and demyelination. However, animals had to be sacrificed to differentiate these two types of lesions which is impractical for time course studies or for human application. Here, we proposed altering the inspired oxygen concentration during imaging to identify deoxyhemoglobin-based hypointensities in vivo. SWI was performed on lumbar spinal cords of naive control and EAE mice using 30% O2 then 100% O2. Some mice were imaged using 30% O2, 100% O2 and after perfusion. Most SWI-visible hypointensities seen with 30% O2 changed in appearance upon administration of 100% O2, and were not visible after perfusion. That hypointensities changed with hyperoxygenation indicates that they were caused by deoxyhemoglobin. We show that increasing the inspired oxygen concentration identifies deoxyhemoglobin-based hypointensities in vivo. This could be applied in future studies to investigate the contribution of vascular-based hypointensities with SWI in EAE and MS over time.
- ItemOpen AccessThe development of a platform for hyperthermia induction in small animal cancer models using MRI guided Focused Ultrasound to test drug delivery of thermosensitive liposomes(2020-12) Siddiqui, Maryam; Pichardo, Samuel; Pichardo, Samuel; Curiel, Laura; Robbins, Stephen M.; Dunn, Jeff F.; Yanushkevich, Svetlana N.; Pike, G. BruceFocused ultrasound concentrates acoustic energy on a small volume. In tissues, this can have several bioeffects, including hyperthermia. Hyperthermia occurs when the body temperature is raised above its core value to about 43⁰C and is sustained for several tens of minutes. The increased temperature can cause damage to the tumour cells directly by denaturing proteins and DNA. It also leads to an increase in oxygenation, which leads to cell toxicity and can have synergistic effects for radio-sensitization. Localized hyperthermia can also be used to improve drug delivery to tumours using thermosensitive formulations. In particular, a liposome-based encapsulation of the chemotherapeutic drug, doxorubicin, has been used in studies for targeted drug delivery to tumours. Doxorubicin is commonly used to treat soft tissue sarcomas, which make up 4-8% of childhood cancers. The liposome dissolves when reaching hyperthermic temperatures and releases its load in tissues where localized hyperthermia takes place. A challenge when studying tumour response in preclinical models is performing precise localized hyperthermia delivery as tight temporal-spatial control of the temperature distribution is required. For this research project, Magnetic Resonance Imaging-guided Focused Ultrasound (MRIgFUS) is proposed as a method to deliver localized hyperthermia in small animal models. Focused ultrasound can precisely concentrate mechanical energy that is transformed into heat, and MRI can be used to target treatment location and monitor temperature spatially and temporally. This monitoring can be used to control hyperthermic levels in a tumour model. In this study, we present details on a platform to deliver MRIgFUS in small animal models. For a demonstration of MRIgFUS as an effective platform for localized hyperthermia in small animals, we performed two studies. The first study was conducted in healthy mice (n=30, C57BL/6) for technical development to establish the basic guidelines for MRIgFUS-based hyperthermia in small animals. The second study used a murine model of alveolar soft part sarcoma (ASPS) to demonstrate that MRIgFUS can increase thermosensitive liposomal doxorubicin delivery. ASPS is a rare type of soft tissue sarcoma commonly found in children and adolescents, with tumour location usually in the body’s extremities. A current challenge in the treatment of ASPS is that tumour resection is unfeasible in 45% of patients. We first used a small cohort of mice (n=6, CB17 SCID) to perform an MRI assessment of alveolar soft part sarcoma tumour growth in a lower limb. A comparison study was then conducted to test the delivery of a temperature-sensitive, liposome-encapsulated form of doxorubicin (ThermoDXR) to the tumour site using MRIgFUS-based hyperthermia. Drug concentrations were compared between four treatment groups. This study was done in ASPS-bearing mice (n=5 in each of four groups, CB17 SCID) with tumours growing subcutaneously, just below the skin. Mice in the first and second group received free doxorubicin with no hyperthermia and free doxorubicin with hyperthermia using MRIgFUS, respectively. Mice in the third and fourth groups received ThermoDXR with no hyperthermia, and ThermoDXR with hyperthermia, respectively. This study hypothesized that the treatment group with ThermoDXR and hyperthermia would have the greatest drug concentration at the tumour site, thereby indicating an improvement in targeted drug delivery. As ASPS tumours were implanted subcutaneously, special arrangements were implemented to target them correctly using MRIgFUS-based hyperthermia; the tumour’s position and the focal target for heating must be carefully planned. In this project, we demonstrated the delivery of the drug to ASPS tumours in mice was enhanced in the group using MRIgFUS based hyperthermia in combination with ThermoDXR. However, future experiments must be conducted with larger sample sizes to evaluate significant differences between groups. Additional studies for tumour growth and survival must also be conducted to test this treatment’s therapeutic effects.
- ItemOpen AccessThe Effect of High-Intensity Exertion on Sport Concussion Assessment Tool 5 Subcomponents(2020-09-12) Burma, Joel Stephen; Schneider, Kathryn J.; Dunn, Jeff F.; Debert, Chantel Teresa; Phillips, AaronIntroduction: The Sport Concussion Assessment Tool 5 (SCAT5) is a commonly used assessment tool following a suspected sport-related concussion. However, little is known how SCAT5 subcomponent scores change following high-intensity exertion. Methods: Participants were recruited from the varsity womens rugby and mens and womens wrestling teams at the University of Calgary. The SCAT5 was administered prior to and following the 30-15 Intermittent Fitness test, where the primary outcome measures included: total symptom scores and severity, standardized assessment of concussion, neurological screening, and balance error during the modified balance error scoring system, as measured with the SCAT5. Wilcoxon signed-rank tests were utilized to evaluate differences in ordinal data between pre- and post-exertion. Bonferroni corrections were performed to account for multiple comparisons (0.05/9, p<0.006). Results: Thirty-seven varsity athletes (median age: 19 years, range: 17-23, 28 female) consented to participate in this investigation. The SCAT5 was administered by trained health care professionals a median of 20 minutes (range: 1–47 minutes) following exertion. No differences were found before and after the exertion test for Post-Concussion Symptom Score total number of symptoms (z=1.05, p=0.29), standardized assessment of concussion (z=-1.98, p=0.048), neurological screen (z=0.58, p=0.56), and modified Balance Error System Score (z=0.37, p=0.71). Conclusions: SCAT5 subcomponent scores were not significantly altered following high-intensity exertion in collision and combative varsity athletes. In agreement with previous literature, a 20 minute recovery period appears to be an acceptable timeframe for SCAT5 subcomponent scores to return to resting/baseline levels.
- ItemOpen AccessFunctional Near-Infrared Spectroscopy (fNIRS) imaging of Functional Connectivity and Task-Activity in the Cerebral Cortex of patients with mTBI(2020-09-04) Duszynski, Christopher; Dunn, Jeff F.; Bray, Signe L.; Debert, Chantel TeresaFunctional near-infrared spectroscopy (fNIRS) is a novel neuroimaging technology which has shown potential as a biomarker of mTBI. In this thesis, we developed novel easy-to-use software for analyzing measures of functional coherence and task-activity in the brain using fNIRS. We then applied this software to characterize fNIRS measures in healthy individuals, and to investigate whether fNIRS is sensitive to altered brain activity following mTBI. The software provides a full pipeline for preprocessing and utilizes wavelet analysis methods to estimate coherence, variability, phase, and power of fNIRS hemodynamic data. Using the software, we investigated the within-subject and between-subject variability of fNIRS coherence in healthy adults, finding poor-moderate between-subject reproducibility and high within-subject reliability, as well as task-effects of reduced interhemispheric coherence (IHC) and reduced power of low-frequency oscillations (LFOs) that were focused in the prefrontal brain regions during execution of a working memory task. In youth 30 days following mTBI, reduced IHC and IHC variability in the prefrontal cortex was observed during working memory, as well as a group effect of mTBI on power of LFO, compared to controls. In adults, fNIRS was used to study brain activity in pre, post, and two weeks following therapeutic repetitive transcranial magnetic stimulation (rTMS) as a treatment for persistent mTBI-related headache. In this case series, abnormal activation in the prefrontal cortex during working memory was observed on fNIRS in one subject prior to treatment which persisted at the post-treatment time point, but appeared to normalize by two weeks post-treatment, in comparison to controls, suggesting fNIRS as a potential method to study treatment effect in therapeutic rTMS trials in patients with mTBI. In this thesis, software was developed and published in the online repository GitHub, and utilized to characterize the variability and task effect in healthy individuals, informing future studies wanting to apply wavelet methodologies to investigate clinical populations. In subsequent observational studies, we observed alterations in fNIRS brain activity in pediatric patients with mTBI 1 month post-injury, as well as in an adult mTBI patient undergoing rTMS treatment, suggesting a potential role for fNIRS as an accessible technology to study mTBI-associated pathophysiology.
- ItemOpen AccessGray matter hypoxia in the brain of the experimental autoimmune encephalomyelitis model of multiple sclerosis(2016-01-14) Johnson, Thomas W.; Dunn, Jeff F.; Wu, Ying; Nathoo, Nabeela; Rogers, James A.; Yong, V. WeeBackground: Multiple sclerosis has a significant inflammatory component. As inflammation can induce and be modulated by hypoxia, the presence of hypoxia could provide clues about immune response regulation in MS. Objective: quantify oxygenation in gray matter (GM) of mice with the experimental autoimmune encephalomyelitis (EAE) model to determine if hypoxia exists in a demyelination model associated with chronic inflammation. Methods: C57BL/6 mice were implanted with a fiber-optic sensor in the cerebellum (n=13) and cortex (n=21). We measured PO2 in awake, unrestrained animals from baseline up to 36 days post-induction for EAE. Results: There were more days with hypoxia compared with hyperoxia (cerebellum: 13/67 vs. 7/67 days; cortex: 15/112 vs. 2/112). Cerebellum showed the largest differences between days 13-17, corresponding to high behavioral deficits. This occurred later for cortex (day 23). Hypoxia in the cortex correlated with increased behavioral deficits and increased variation (based on z-score comparisons with baseline and age-matched controls) in the cerebellum correlated with clinical deficits. Conclusions: The presence of hypoxia and increased variation in GM oxygenation indicates that oxygen may change enough to modulate the immune response. The cause may relate to increased metabolic dysfunction, disruption of neurovascular coupling or increased oxidative metabolism in activated microglia.
- ItemOpen AccessIn Vivo MR Imaging of Tumor-Associated Macrophages: The Next Frontier in Cancer Imaging(SAGE Publications, 2018-03-22) Yang, Runze; Sarkar, Susobhan; Yong, Voon Wee E.; Dunn, Jeff F.There is a complex interaction between cancer and the immune system. Tumor-associated macrophages (TAMs) can be subverted by the cancer to adopt a pro-tumor phenotype to aid tumor growth. These anti-inflammatory, pro-tumor TAMs have been shown to contribute to a worsened outcome in several different types of cancer. Various strategies aimed at combating the pro-tumor TAMs have been developed. Several therapies, such as oncolytic viral therapy and high-intensity focused ultrasound, have been shown to stimulate TAMs and suppress tumor growth. Targeting TAMs is a promising way to combat cancer, but sensitive imaging methods that are capable of detecting these therapeutic responses are needed. A promising idea is to use imaging contrast agents to label TAMs to determine their relative number and location within, and around the tumor. This can provide information about the efficacy of TAM depletion therapies, as well as macrophage-stimulating therapies. In this review, we describe various in vivo MRI methods capable of tracking TAMs, and conclude with a short section on tracking TAMs in patients.
- ItemOpen AccessIn Vivo Open-Bore MRI Reveals Region- and Sub-Arc-Specific Lengthening of the Unloaded Human Posterior Cruciate Ligament(PLoS, 2012-11-07) King, Alison J.; Deng, Qunli; Tyson, Randy; Sharp, Jonathan C.; Matwiy, Jarod; Tomanek, Boguslaw; Dunn, Jeff F.
- ItemOpen AccessInstrumentation for Functional Brain Monitoring with Intrinsic Optical Signals(2019-12-05) Yu, Linhui; Murari, Kartikeya; Dunn, Jeff F.; Fear, Elise C.; Kiss, Zelma H. T.; Curiel, Laura; Côté, Daniel C.Intrinsic optical signals are widely used in functional brain imaging techniques for measuring hemodynamic parameters, such as oxygen saturation and blood volume. These parameters indicate brain metabolism and serve as an indirect measurement of neural activity. In this thesis, I describe two techniques for hemodynamic monitoring from freely-moving animals. The first technique is single fiber spectroscopy, which enables measurements from a highly-localized volume in deep brain structures. I describe the optical system design for measuring reflectance spectra, Monte Carlo simulations for estimating the sampling volume, phantom experiments for rating the accuracy of hemodynamic parameter quantification, and finally, animal experiments for evaluating system performance in in-vivo experiments. I demonstrate that the single fiber spectroscopic system is capable of measuring spontaneous and stimulus-evoked hemodynamic response through a small diameter multimode fiber from non-line-of-sight brain regions in anesthetized and freely-moving animals. The second system is a miniaturized intrinsic optical sensing system (MiniIOS), a cost-effective, integrated system for measurement from the brain surface. The thesis covers the design and characterization of two versions of MiniIOS, the development of an empirical model for extracting hemodynamic parameters from the measured reflectance, as well as system validation in optical phantoms and animal experiments. The final system has a dimension of 5.5 mm×4.7 mm×1.8 mm and weight of 0.12 g. The system can be powered with a battery and operated as a stand-alone device integrating light source, detector, power supply, data acquisition and storage. Phantom experiments showed that the system was sensitive to both changes in oxygen saturation and blood volume fraction. A pilot animal experiment showed the system can be mounted on the head of a mouse without affecting its movement.
- ItemEmbargoInvestigating the Effect of Inflammation Induced by Bacterial Lipopolysaccharide on Cerebral Blood Flow and Brain Oxygenation(2023-06) Shafqat, Qandeel; Dunn, Jeff F.; Camara-Lemarroy, Carlos; Yong, V. WeeBrain hypoxia is a pathological feature of various neurodegenerative diseases. Over 40% of people with multiple sclerosis (MS), an inflammatory disease of the central nervous system, experience brain hypoxia. It is proposed that hypoxia and inflammation are linked, where inflammation can cause hypoxia and hypoxia can then further contribute to inflammation, leading to a vicious cycle of damage. Given that hypoxia is present in MS, and in other neurological conditions, further research on putative mechanisms for its cause are needed. To better understand the hypoxia-inflammation cycle, we sought to determine whether systemic inflammation induces brain hypoxia and/or alterations in cerebral hemodynamics using non-invasive magnetic resonance imaging (MRI) techniques. We found that inflammation in a mouse model causes significant reductions in cerebral blood blow and an increase in brain R2* (an MRI marker of increased deoxyhemoglobin) in the cortex and hippocampus. We also discovered that LPS challenge causes significant changes in hippocampal oxygenation, with hypoxia occurring in all animals assessed, and hyperoxia occurring in 57% of the animals. Our findings suggest that inflammation may impair cerebrovascular regulation in the brain and contribute to brain hypoxia.
- ItemOpen AccessIron Oxide as an MRI Contrast Agent for Cell Tracking(Libertas Academica, 2015-08-19) Korchinski, Daniel; Taha, Mai; Yang, Runze; Nathoo, Nabeela; Dunn, Jeff F.Iron oxide contrast agents have been combined with magnetic resonance imaging for cell tracking. In this review, we discuss coating properties and provide an overview of ex vivo and in vivo labeling of different cell types, including stem cells, red blood cells, and monocytes/macrophages. Furthermore, we provide examples of applications of cell tracking with iron contrast agents in stroke, multiple sclerosis, cancer, arteriovenous malformations, and aortic and cerebral aneurysms. Attempts at quantifying iron oxide concentrations and other vascular properties are examined. We advise on designing studies using iron contrast agents including methods for validation.
- ItemOpen AccessMagnetic Resonance Imaging of Demyelination and Remyelination in the Lysolecithin Model of Multiple Sclerosis(2017-02) Dhaliwal, Raveena; Dunn, Jeff F.; Yong, V. Wee; Pike, Bruce; Ousman, ShalinaWe require magnetic resonance imaging methods sensitive to remyelination for evaluation of remyelinating therapies for multiple sclerosis (MS). The goal of this thesis was to characterize the sensitivity of quantitative magnetization transfer (qMT) and diffusion tensor imaging (DTI) to myelin and axonal loss and remyelination in the lysolecithin model. This model is being used to develop remyelinating therapies for MS. We found that the qMT parameters of bound pool fraction (f), T1 and several DTI parameters were able to detect demyelination in the lysolecithin model. The qMT parameters did not change with remyelination but several DTI parameters did recover slightly. f had the strongest correlation to the histological measure of myelin and T1 had the strongest correlation to the histological measure of axon content. Overall, the findings from this thesis support the inclusion of DTI and qMT as an outcome measure in future studies of potential MS therapeutics in the lysolecithin model.
- ItemOpen AccessMeasuring Cerebral Oxygenation in Healthy and Concussed Brain Using Frequency Domain Near-Infrared Spectroscopy (fdNIRS)(2018-06-14) Dleikan, Diane; Dunn, Jeff F.; Yeates, Keith Owen; Debert, Chantel T.Concussion or mild traumatic brain injury (mTBI) is a major public health concern that affects millions of people annually. The current metrics used to assess and diagnose concussion are largely subjective. There is a need for an objective neuroimaging tool to directly measure brain physiology and provide insight into recovery. Such a tool would supplement current subjective metrics used to monitor and index severity of injury. There is also a need to better understand the pathophysiology of concussion. Near-infrared spectroscopy (NIRS) is a non-invasive optical imaging tool used to measure aspects of microvascular hemoglobin oxygenation. In this study, we apply NIRS to quantify cerebral oxygenation (StO2), which has been used as an indicator of oxygen delivery to assess injury severity and tissue damage. We measured StO2 in a large cohort population with varying ages, and compared this to two post-concussive groups. In the first, a small varsity cohort, cerebral oxygenation was reduced in athletes who reported increased symptom severity. In the second, a pediatric sports-related concussion (SRC) cohort, cerebral oxygenation was increased when compared to age and gender matched controls. We also found that exercise is a potential confounding variable to consider when assessing concussion on the sideline, as we reported increases in StO2 in most varsity football players after practice. We report intriguing but not conclusive evidence that concussion can cause acute reduction in oxygenation, which may indicate changes in brain physiology immediately after injury. Overall, this thesis demonstrated that prefrontal cortex StO2, measured by NIRS, has the potential for monitoring brain physiology during concussion recovery in a clinical and sport setting.
- ItemOpen AccessA multimodal Near-Infrared and MRI technique to assess cerebral metabolic changes in mouse models of neurological diseases(2022-03-23) Hashem, Mada; Dunn, Jeff F.; Stys, Peter; Murari, KartikeyaThe central nervous system is highly dependent on oxidative metabolism. Adequate delivery, and consumption of oxygen are achieved via regulation of blood flow and oxygen or energy demand. These mechanisms are vulnerable to failure, which might affect the optimal function of the brain and eventually cause cellular damage and/or death. Disruptions in oxidative metabolism have been found in many neurological disorders, such as Multiple Sclerosis, Alzheimer's Disease, Parkinson’s Disease. These involve changes in the blood flow, the metabolic rate and levels of oxygen in the brain, and/or abnormalities in the mitochondria. This thesis focuses on developing, validating, and applying a multimodal method which combines Near-Infrared Spectroscopy (NIRS) and Magnetic Resonance Imaging (MRI), to non-invasively study oxidative metabolism in rodent cerebral cortex. The MRI provides information regarding the brain structure and the cerebral blood flow (CBF). The NIRS detects hemoglobin (Hb), and the mitochondrial enzyme cytochrome c oxidase (CCO) which are both strongly linked to oxygenation and metabolism. A new algorithm for measuring the absolute redox state of CCO from NIRS data, was introduced and validated. Oxygen saturation in the cerebral tissue (StO2) was assessed from the absolute concentration of deoxygenated, and total Hb. Oxygen Extraction Fraction (OEF) and CMRO2 were calculated using the modified Fick Principle. Challenges such as hypothermia, hypercapnia, and varying levels of oxygenation were applied to mice, to validate the absolute quantification of CMRO2, CBF, OEF, StO2 and CCO redox state, and investigate the association between these parameters. We applied the method to investigate oxidative metabolism in neurological disorders by studying the time course of metabolic changes in a cuprizone mouse model of demyelination and spontaneous remyelination. NIRS-MRI showed evidence of altered CCO redox state during cuprizone exposure, increased oxygenation and reduced metabolic rate associated with reduced myelination in the gray and white matter. Multimodal NIRS-MRI was capable to noninvasively assess parameters associated with oxidative metabolism. The development of such a technology may allow researchers and clinicians to follow the pathological progression and treatment response, of neurological diseases associated with mitochondrial dysfunction and abnormal oxidative metabolism.
- ItemOpen AccessMultiple sclerosis disease progression: Contributions from a hypoxia–inflammation cycle.(SAGE Publications, 2018-07-08) Yang, Runze; Dunn, Jeff F.Hypoxia has been associated with multiple sclerosis (MS) and is an important area of research. Hypoxia can exacerbate inflammation via the prolylhydroxylase pathway. Inflammation can also trigger hypoxia by damaging mitochondria and endothelial cells to impair blood flow regulation. We hypothesize that there is a “hypoxia–inflammation cycle” in MS which plays an important role in MS disease progression. Therapies that break this cycle may be an interesting area of exploration for treatment of MS.
- ItemOpen AccessThe Natural History of Bone Marrow Lesions and Cysts in the Dunkin-Hartley Guinea Pig Knee Osteoarthritis Model(2020-10-14) Francis, Destiny; Manske, Sarah Lynn; Matyas, John Robert; Dunn, Jeff F.Idiopathic knee osteoarthritis (OA) is a disease with unknown etiology, where age is described as a major risk factor. There is a need to document OA's natural history to gain insight into its etiology. Therefore, an animal model like the Dunkin-Hartley (DH) guinea pig that spontaneously develops a knee OA phenotype similar to idiopathic OA observed in humans can be used to study the disease-related bony degeneration. This phenotype includes osteophyte formation, sclerosis, bone marrow lesions (BMLs), and cysts within a relatively short period. This thesis employs advanced magnetic resonance imaging (MRI), micro-computed tomography (μCT), and histological techniques to assess knee joint degeneration in DH guinea pigs at ages 2, 4, 6, 12, and 24 months. The results from this project show evidence of cartilage degradation and bone cyst formation in the 6-month age group, which becomes more apparent in the 12 and 24-month age groups. When present, cysts were primarily located in the central compartment of the bone and often accompanied by osteophytes and sclerosis. Joint degeneration was most severe in the 24-month age group with the largest cysts as well as the greatest osteophyte size and number. Bone microarchitecture was also significantly affected in this age group. Overall femoral and tibial trabecular number (Tb.N) was lowest in the 24-month age group, and it had the highest medial femoral subchondral bone plate thickness (Sbp.Th), femoral and tibial subchondral bone plate porosity (Sbp.Po), femoral trabecular separation (Tb.Sp), and medial tibial trabecular thickness (Tb.Th). The medial compartment also revealed greater joint degeneration, as demonstrated by greater femoral and tibial Sbp.Th and femoral Sbp.Po in the 12 and 24-month age groups compared with the lateral compartment. This project demonstrates that age-related joint degeneration occurs in the DH guinea pig spontaneous knee OA model with evidence of osteophytes, cysts, and bone microarchitecture alterations in older age groups. Although histology revealed abnormalities in the bone that have been associated with MRI-defined BMLs, I am unable to conclude whether or not BMLs occur in this model as a further investigation with MRI is still required.
- ItemOpen AccessNear-infrared measurements of brain oxygenation in stroke(Society of Photo-optical Instrumentation Engineers, 2016-02-11) Moreau, Francois; Yang, Runze; Nambiar, Vivek; Demchuk, Andrew M.; Dunn, Jeff F.We investigated the feasibility of using frequency-domain near-infrared spectroscopy (fdNIRS) to study brain oxygenation in the first few hours of stroke onset. The OxiplexTS® fdNIRS system was used in this study. Using a standard probing protocol based on surface landmarks, we measured brain tHb and StO2 in healthy volunteers, cadavers, and acute stroke patients within 9 h of stroke onset and 3 days later. We obtained measurements from 11 controls, 5 cadavers, and 5 acute stroke patients. StO2 values were significantly lower in cadavers compared to the controls and stroke patients. Each stroke patient had at least one area with reduced StO2 on the stroke side compared to the contralateral side. The evolution of tHb and StO2 at 3 days differed depending on whether a large infarct occurred. This study shows the proof of principle that quantified measurements of brain oxygenation using NIRS could be used in the hectic environment of acute stroke management. It also highlights the current technical limitations and future challenges in the development of this unique bedside monitoring tool for stroke.
- ItemOpen AccessOptimizing Multi-Well Micro-Electrode Array (MW-MEA) Design to Study the Electrophysiology of Neurons(2020-07-27) Pishgar, Roofia Sara; Dalton, Colin; Syed, Naweed I.; Teskey, G. Campbell; Dunn, Jeff F.; Murari, Kartikeya; Chu, Angus; Frayne, RichardMicroelectrode arrays (MEAs) have been widely utilized to measure and study neuronal activities, both in vitro and in vivo. The main focus of this study was to optimize the MEA design to improve the recording efficiency from a group of cells in an area to have a better understanding of what is happening over a larger network. This study included three phases: investigating the effectiveness of a preliminary version of multi-well MEA design with two electrode types featuring a different number of wells (5 and 6) and diameter of wells (15 and 20 μm); 2) optimization of the first design with the second version of multi-well MEA, featuring a wider range of diameters and number of wells on each electrode; 3) investigating the adaptability of rigid glass-based MW-MEAs to flexible substrates. The results of this study showed that electrodes with 6-wells had the ability to capture stronger signals occasionally, while electrodes with 5-wells could consistently record signals, albeit with less peak-to-peak amplitudes. It was found out that the effect of diameter and number of wells and their correlation (i.e., the open surface area of the electrode, A) on the signal to noise ratio (SNR) were significant and thus should all be regarded as important parameters when designing MEAs. Cell signal recording was performed on the second MEA design, using snail brain neurons. Snail brain neurons were used to limit the complexity of neuronal recordings and to be able to focus the analysis on the electrode characteristics. However, due to the COVID-19 related shutdown, the snail recording could not be pursued further in the lab. The study on the suitability of using flexible substrates instead of the traditional rigid glass substrate to make a flexible MEA (fMEA) showed oxidation, electrode degradation, and formation of residues in long-term mice cell plating. It indicated the incompatibility of the materials used with living cells. In parallel, a gold wire bonding process was attempted to create 3D microelectrodes on the fMEA. 3D-fMEA fabrication proved to be challenging due to several difficulties in the wire bonding process, used for converting the planar fMEA to 3D-fMEA. Thus, to further the study on the effectiveness of fMEA and 3D-fMEA, the choice of material and fabrication protocol of fMEA and 3D-fMEA needs further investigation.
- ItemOpen AccessPathophysiology and Proteogenomics of Post-infectious and Post-hemorrhagic Hydrocephalus in Infants(2020-07-21) Isaacs, Albert M.; Dunn, Jeff F.; Limbrick, David D.; McAllister, James Patterson; Smyser, Christopher D.; Shimony, Joshua S.; Hamilton, Mark G.; Ballabh, PraveenPost-infectious (PIH) and post-hemorrhagic (PHH) hydrocephalus occur as sequalae of neonatal sepsis or intraventricular hemorrhage (IVH) of prematurity, respectively. Together, PIH and PHH represent the most common form of infantile hydrocephalus, the most common indication for neurosurgery in children globally, and the leading cause of neurological morbidity and mortality worldwide. The lack of understanding of the pathophysiology of PIH and PHH, particularly with regards to the host central nervous system response to the antecedent infection and hemorrhage, perturbation of differentiating neural stems in the ventricular (VZ) and subventricular (SVZ) zones, and damage to periventricular white matter (PVWM) tracts carrying sensorimotor fibers, has hindered the identification of therapeutic targets to prevent these two debilitating conditions. To this end, we hypothesized that PIH and PHH share a common pathophysiological mechanism characterized by host immune response to infection or hemorrhage, activation of the metalloprotease ADAM10 and cleavage of the cell-junctional protein, N-cadherin, which results in impaired VZ/SVZ differentiation and PVWM damage. The studies presented in this dissertation collectively explore novel overarching lines of scientific inquiry - the concept that there are unique host immune responses to PIH and PHH, as well as ones that are common to both conditions that underlie their observed clinical similarities. To test the hypothesis, we leveraged the cerebrospinal fluid (CSF) of human PIH, PHH and matched non-infectious non-hemorrhagic hydrocephalic control infants. First, we defined the differentially expressed proteome and transcriptome of PIH using high throughput proteomics and RNA-seq, respectively. The integration of proteogenomic techniques defined critical gene networks and pathway level mechanisms of PIH pathophysiology. Second, our validated proteomics pipeline was used to identify the common and unique molecular pathways that underlie the pathophysiology of PIH and PHH. Third, our CSF findings were related to VZ/SVZ development and PVWM microstructural damage with diffusion MRI (dMRI) in PHH and control infants. Neurocytology of human postmortem brain tissues of PIH, PHH and controls was performed to correlate the dMRI findings. Fourth, we defined the mechanistic triggers underlying PIH and PHH pathogenesis utilizing a mouse in vitro cell culture model of periventricular VZ cells. Finally, we developed in vivo animal models of PIH (mice) and PHH (ferrets), to recapitulate our findings of VZ/SVZ disruption, neuroinflammation and PVWM injury in both PIH and PHH. Through our comprehensive experiments, we determined the following: 1) human CSF profiles of PIH and PHH reflect similar alterations in gene-activated pathways related to neuroinflammation and cell-cell junction structure; 2) neuroinflammation-associated cell junction (VZ/SVZ) disruption and PVWM injury is a pathophysiological mechanism that is common to both PIH and PHH; 3) dMRI can non-invasively assess the VZ/SVZ region as well as differentiate and quantify tract-specific patterns of PVWM injury. Therefore, it can distinguish direct effects on axons/myelin from changes in the extracellular milieu to reflect neuroinflammation, axonal fiber loss, and dysmyelination; 4) VZ/SVZ disruption in PIH and PHH is mediated by metalloprotease (e.g., ADAM10) cleavage of cell junctional proteins (e.g., N-cadherin); and 5) pharmacologic inhibition of ADAM10-mediated N-cadherin cleavage represents a viable therapeutic approach to prevent PIH and PHH. These novel insights into the pathophysiology of PIH and PHH may enable investigation of ADAM10 inhibitors and other therapeutic strategies to minimize the developmental disability in PIH and PHH patients. The biomarkers we identified can be further investigated as diagnostic measures for monitoring and providing therapy to infants who develop neonatal sepsis or IVH to prevent PHH/PIH. Finally, the in vitro and in vivo experimental models we generated are poised for future preclinical and translational studies into the pathogenesis of these previously inaccessible and debilitating conditions.