Blast-induced traumatic brain injury (bTBI) has been a health concern in both military and civilian populations due to recent military and geopolitical conflicts. Military service members are frequently exposed to single and repeated blasts throughout their training and deployment. As a result of blast exposures, military personnel report symptoms of various neurological and neurosensory deficits. Our group has previously reported decreased long term potentiation (LTP) following either single or repeated bTBI in a rat organotypic hippocampal slice culture (OHSC) model. LTP is a neuronal correlate for learning and memory and is a neurological metric that can be used to evaluate blast injury severity and the efficacy of therapeutic interventions. In the first aim of this thesis, we characterized LTP deficits following repeated bTBI to develop tolerance criteria for blast exposures. We did so by varying the blast injury severity, the inter-blast interval between blasts, and the recovery period following blast exposure. We determined that LTP deficits were compounded as a result of repeated mild bTBI. LTP deficits were attenuated with increasing inter-blast intervals and with increasing recovery periods after injury. Even after three repeated mild bTBIs, LTP spontaneously recovered after 6 days. In the second aim, we investigated the pathological changes in OHSCs following repeated blast exposures. Following injury, we observed robust microglial activation, evidenced by increased expression of the pro-inflammatory marker, CD-68, and decreased expression of the anti-inflammatory marker, CD-206. We also observed increased expression of MIP-1α, IL-1β, MCP-1, IP-10, and RANTES and decreased expression of IL-10 in the acute period after both single and repeated bTBI. Following partial depletion of microglia prior to injury, injury induced LTP deficits were significantly reduced. Lastly, treatment with a novel drug, MW-189, immediately after a repeated bTBI prevented LTP deficits. In the third aim, we investigated changes in inflammatory markers like cyclooxygenase (COX) and tested the efficacy of COX or prostaglandin receptor (EP3R) inhibitors in attenuating LTP deficits. We observed that expression of COX-2 increased 48 hours following repeated blast injury; however, COX-1 expression was unchanged. Following repeated bTBI, EP3R expression was upregulated and cyclic adenosine monophosphate (cAMP) concentration was decreased. Treatment of blast injured OHSCs with a COX-1 specific inhibitor, SC-560, a COX-2 specific inhibitor, rofecoxib, a pan-COX inhibitor, ibuprofen, or an EP3R inhibitor, L-798,106 improved LTP deficits. Delayed treatment with L-798,106 and ibuprofen also improved LTP deficits. Our data suggests that bTBI induced neuroinflammation may be partially responsible for the functional deficits that we have observed in blast-injured OHSCs. Additionally, we also conclude that COX and EP3R inhibition may be viable therapeutic strategies to reduce bTBI induced neurophysiological deficits. In the final aim, we investigated bTBI induced changes to the electrophysiological network of OHSCs. Following blast exposure, sham and injured OHSCs were administered increasing concentrations of bicuculline, a GABAA receptor antagonist. Doing so revealed an increase in connectivity and clustering coefficients in sham slices compared to injured slices. This suggested that the underlying neuronal network of injured slices was dysfunctional. Biologically, this dysfunction could be explained by the decreased expression of GABAA receptor α1 and α5 subunits. A loss of GABAA receptor expression or function may explain the electrophysiological network disruptions that we observed. More work will be required to determine how blast exposure decreases the expression of GABAA receptors and how these receptors may contribute to network deficits. This thesis has expanded upon the tolerance criteria for repeated blast exposures. These studies have also further characterized the pathological changes in microglial activation and explored promising therapeutic pathways that could be used to attenuate functional deficits. Lastly, this thesis has also provided novel ways to interrogate neuronal networks following blast injury, revealing subtle deficits that will need to be explored in more detail.

Approximately 1.7 million traumatic brain injuries (TBI) occur annually in the United States, with an annual estimated societal cost of at least $76.5 billion. Addressing the growing TBI epidemic will require a multi pronged approach: developing novel treatment strategies and enhancing existing preventative measures. The specific aims of this thesis are: (1) to modulate astrocyte activation as a potential therapeutic strategy post TBI, (2) to determine the relationship between tissue deformation and alterations in electrophysiological function in the living brain, and (3) to investigate underlying mechanisms of functional changes post TBI by utilizing stretchable microelectrode arrays (SMEAs). In response to disease or injury, astrocytes become activated in a process called reactive astrogliosis. Activated astrocytes generate harmful radicals that exacerbate brain damage and can hinder regeneration of damaged neural circuits by secreting neuro developmental inhibitors and glycosaminoglycans (GAGs). Since mechanically-activated astrocytes upregulate GAG production, delivery of GFP-TAT, a mock therapeutic protein conjugated to the cell-penetrating peptide TAT, increased significantly after activation. A TAT-conjugated peptide JNK inhibitor was delivered to activated astrocytes and significantly reduced activation. These results suggest a potentially new, targeted therapeutic utilizing TAT for preventing astrocyte activation with the possibility of limiting off-target, negative side effects. While modulating astrocyte activation is a promising treatment strategy for TBI, effective therapeutic treatments are still lacking. Preventing TBI, by developing more effective safety systems, remains crucial. We determined functional tolerance criteria for the hippocampus and cortex based on alterations in electrophysiological function in response to controlled mechanical stimuli. Organotypic hippocampal and cortical slice cultures were mechanically injured at tissue strains and strain rates relevant to TBI, and changes in electrophysiological function were quantified. Most changes in electrophysiological function were dependent on strain and strain rate in a complex, nonlinear manner. Our results provide functional data that can be incorporated into finite element (FE) models to improve their biofidelity of accident and collision reconstructions. TBI causes alterations in macroscopic function and behavior, which can be characterized by alterations in electrophysiological function in vitro. We utilized a novel in vitro platform for TBI research, the SMEA, to investigate the effects of TBI on pharmacologically induced, long lasting network synchronization in the hippocampus. Mechanical stimulation of organotypic hippocampal slice cultures significantly disrupted this network synchronization 24 hours after injury. Our results suggest that the ability of the hippocampal neuronal network to develop and sustain network synchronization was disrupted after mechanical injury, while also demonstrating the utility of the SMEA for TBI research. Herein, we identified a novel therapeutic strategy for treating the deleterious effects of astrocyte activation post-TBI. We also developed tolerance criteria relating mechanical injury parameters to electrophysiological function, an important step in developing more accurate computational simulations of TBI. Equipping FE models with new information on the functional response of the living brain will enhance their biofidelity, potentially leading to improved safety systems while reducing development costs. Finally, we utilized a novel in vitro TBI research platform, the SMEA, to investigate the effects of TBI on long-lasting network synchronization in the hippocampus. Compared to more labor intensive in vivo approaches, the ability of the SMEA to efficiently test TBI hypotheses within a single organotypic slice culture over extended durations could increase the speed of drug discovery through high-content screening. This multi-pronged approach is necessary to address the growing public health concern of TBI.

Traumatic brain injury (TBI) is the signature injury of modern military conflicts due to widespread use of improvised explosive devices (IEDs) and modern body armor. However, the exact biophysical mechanisms of blast-induced traumatic brain injury (bTBI) and its pathological effects on the blood-brain barrier (BBB) – a structure essential for maintaining brain homeostasis – remain poorly understood. The specific aims of this thesis are to: 1) determine a threshold for primary blast-induced BBB dysfunction in vitro; 2) determine the effect of repeated blast on BBB integrity in vitro; 3) improve BBB recovery in vitro as a potential therapeutic strategy for mitigating effects of blast; and 4) quantify the time course and pore-size of BBB opening in vivo. In this work we utilized a shock tube driven by compressed gas to generate operationally relevant, ideal pressure profiles consistent with IEDs. By multiple measures, the barrier function of an in vitro BBB model was disrupted after exposure to a range of blast-loading conditions. Trans-endothelial electrical resistance (TEER) decreased acutely in a dose-dependent manner that was most strongly correlated with impulse, as opposed to peak overpressure or duration. Significantly increased hydraulic conductivity and solute permeability post-injury further confirmed acute alterations in barrier function. Compromised ZO-1 immunostaining identified a structural basis for BBB breakdown. These results are the first to demonstrate acute disruption of an in vitro BBB model after primary blast exposure; defined tolerance criteria may be important for development of novel helmet designs to help mitigate effects of blast on the BBB. After determining that exposure to a single primary blast caused BBB disruption, we hypothesized that exposure to two consecutive blast injuries would result in exacerbated damage to the BBB in vitro. However, contrary to our hypothesis, repeated mild or moderate primary blast delivered within 24 or 72 hours did not significantly exacerbate reductions in TEER across a brain endothelial monolayer compared to sister cultures receiving a single exposure. Single blast exposure significantly reduced immunostaining of ZO-1 and claudin-5 tight junction proteins, but subsequent exposure did not cause additional damage to tight junctions. The second injury delayed recovery of TEER and hydraulic conductivity in BBB cultures. Extending the inter-injury interval to 72 hours, the effects of repeated injury on the BBB were independent given sufficient recovery time between consecutive exposures. Investigation of repeated blast on the BBB will help identify a temporal window of vulnerability to repeated exposure. Restoration of the BBB after blast injury has emerged as a promising therapeutic target. We hypothesized that treatment with dexamethasone (DEX) after primary blast would potentiate recovery of an in vitro BBB model. DEX treatment resulted in complete recovery of TEER and hydraulic conductivity 1 day after injury, compared with 3 days for vehicle-treated injured cultures. Administration of RU486 (mifepristone) inhibited effects of DEX, confirming that barrier restoration was mediated by glucocorticoid receptor signaling. Potentiated recovery with DEX treatment was accompanied by stronger ZO-1 tight junction immunostaining and expression, suggesting that increased ZO-1 expression was a structural correlate to BBB recovery. This is the first study to provide a mechanistic basis for potentiated functional recovery of an in vitro BBB model due to glucocorticoid treatment after blast injury. Using an in vivo bTBI model, systemic administration of sodium fluorescein (NaFl; 376 Da), Evans blue (EB; 69 kDa when bound to serum albumin) and dextrans (3 – 500 kDa) was used to estimate the pore-size of BBB opening and time required for recovery. Exposure to blast resulted in significant acute extravasation of NaFl, 3 kDa dextran, and EB. However, there was no significant acute extravasation of 70 kDa or 500 kDa dextrans, and minimal to no extravasation of NaFl, dextrans, or EB 1 day after exposure. This work is the first to quantify the time course and size of BBB opening after bTBI, suggesting that the BBB recovered 1 day post-injury. This study supports our hypothesis that transient opening of the BBB may permit serum-components to infiltrate the brain parenchyma and contribute to pathological secondary cascades. This research has shown that BBB damage, demonstrated in vitro and in vivo, is a major mechanism contributing to vascular and neuronal pathology of bTBI at exposure levels above a critical threshold. Compared with published studies on blast-induced damage to the BBB, we have developed primary blast injury tolerance criteria by precisely controlling the biomechanical initiators of injury and measuring resulting alterations to the structure and function of an in vitro BBB model by methods not possible in vivo. We have also developed a potential glucocorticoid treatment to rapidly restore the BBB after injury, which may lead to more promising therapeutic strategies to treat TBI-related pathologies. This work will also guide the development of novel armor designs to protect service members and civilians in order to more effectively address the burden to society of bTBI.

A study was conducted on the self-reported symptoms of Mild Traumatic Brain Injury sustained in Rugby Union at the pre- and post-season stages. A full sample of 30 rugby players at Rhodes University was compared to 27 non-contact sport controls. A reduced sample of 20 rugby players and 9 control participants provided improved control for education and IQ and was compared. Measures included the WAIS-III Vocabulary and Picture Completion Sub-tests to estimate IQ level, the symptom checklist on a widely used computer-based program (ImPACT), and a paper and pencil self-report 31-Item Post-Concussion Symptom Questionnaire. Independent and Dependent T-Test comparisons were conducted on the full and reduced samples. The symptoms reported by the rugby group appeared to be more pronounced on both the ImPACT Symptom Scale and the 31-Item Post-Concussion Symptom Questionnaire when compared to the control group at both the pre-and post-season stages. It was concluded that the rugby players demonstrated evidence to support the hypothesis of having sustained more previous concussions and reporting more symptoms at the pre-season stage when compared to comtrol participants. No prevalent changes for either the rugby or control groups were seen in dependent comparisons from pre-to post-season.

No description available.

One of the consequences of traumatic brain injury is the postconcussion syndrome. The symptoms in this syndrome include headache, dizziness, poor memory, poor concentration, easy fatigue, drowsiness, irritability, sensitivity to light, sensitivity to noise, low alcohol tolerance, visual problems, auditory problems, nausea, vomiting, anxiety, and depression. Several factor analytic studies have shown that these symptoms load onto cognitive and noncognitive factors (Bohnen, Twijnstra, & Jolles, 1992). The aim of this study was to determine whether patients who report different symptoms also evidence differences in cognitive deficits, as indexed by reaction time. For this purpose 106 subjects (mean age 25.92 years; SD=6.05) of both sexes were tested on 8 reaction time tasks adapted from Shum, McFarland, Bain, and Humphreys (1990). There were 54 traumatic brain injury patients (mean age 26.40 years; SD=6.23) drawn from three Pretoria hospitals. They were heterogeneous with respect to diagnosis and severity of injury. For the controls (N=52), the mean age was 25.43 years (SD=5.88). The eight reaction time tasks constituted 4 task variables, each with 21evels. From these tasks, 36 reaction time indexes were derived. The indexes were classified into 4 groups, viz., reaction time (RT), movement time (MT), total reaction time (TT), and subtraction scores (SB, the difference between the 2 levels for each task variable). RT reflects the decision component and MT reflects the response execution component of reaction time. Partial correlation coefficients for all symptoms (p0,01) showed that some symptoms were most frequently associated with RT whilst others were most frequently associated with MT. On factor analysis with varimax rotation, symptoms loaded predominantly with SB scores. Symptoms also loaded with different task variablseuiggesting that they correlated with deficits on different stages of information processing. Taking into account possible methodological constraints that were discussed, these results confirm that different symptoms within the postconcussion syndrome correlate with different cognitive deficits. The correlations between symptoms and indices of reaction time are moderated by the characteristics of the symptoms (frequency & intensity), and the duration since injury. These findings have significance for understanding the aetiology of the postconcussion symptoms and for planning treatment. / Psychology / Ph. D. (Psychology)

No description available.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Medicine / Master / Doctor of Medicine

published_or_final_version / Diagnostic Radiology / Doctoral / Doctor of Philosophy