Introduction: This Thesis will discuss the importance of stroke disease, and review the existing literature regarding acute stroke blood pressure (BP) changes and management. It will also review methods of measuring cerebral autoregulation, and the effects of stroke, hypertension, and antihypertensive therapy on cerebral autoregulation. Using an established method of measuring cerebral autoregulation this Thesis will examine the reproducibility of this method in a study of healthy volunteers. The same measurement technique will then be used to examine the effects of ageing on cerebral autoregulation in a cohort of healthy volunteers. The effects of acute stroke and early recovery on cerebral autoregulation will then be studied and compared to healthy controls. In addition it will consider the potential effects of stroke type, clinical features, and history of hypertension on cerebral autoregulation post-stroke.

Neural cell death plays a crucial role in the pathogenesis of various ischaemic disorders of the central nervous system (CNS), most prominently stroke, causing very significant mortality and morbidity. Severe ischaemia rapidly kills both neurons and astrocytes, two CNS cell types whose interactions are essential to normal brain functioning, so ideally a target needs to be found which will protect both. Glutamate mediated excitotoxicity, the process whereby excessive extracellular glutamate causes cell death via the over-activation of ionotropic glutamate receptors, is known to operate during ischaemia. However, there is increasing evidence that ATP mediated excitotoxicity may also occur. Using an in vitro model of ischaemia (oxygen-glucose deprivation: OGD) and various murine primary cortical cell cultures, I investigated the hypothesis that parallel pathways of ATP and glutamate mediated excitotoxicity contribute to the death of both astrocytes and neurons during ischaemia. OGD produced rapid and significant ATP and glutamate release from co-cultures of astrocytes and neurons, as measured using microelectrode biosensors. Glutamate release was mainly from astrocytes, whereas the cellular origin of ATP was less clear. Ca2+ imaging of Fura-2 loaded cells confirmed functional P2 receptor expression in all astrocytes and 60% of neurons along with glutamate receptor expression in all neurons but only a small proportion of astrocytes. During OGD, blocking NMDA and AMPA/kainate receptors significantly reduced neuronal death, while non-selective P2 receptor antagonists as well as selective P2Y1 (but not P2X7) receptor antagonists prevented the death of both neurons and astrocytes. Furthermore, a synergistic protective effect was produced by combining low concentrations of P2 and glutamate receptor antagonists, reducing cell death to control levels. These results suggest that ATP and glutamate, acting at P2 and ionotropic glutamate receptors, are the main mediators of early cell death during severe CNS ischaemia, and thus represent a potential target for powerful neuroprotective strategies.

Huntington’s disease (HD) is a hereditary progressive neurodegenerative disorder characterised by chorea, general motor impairment, psychiatric disturbances and dementia, leading to death within 10 to 20 years of onset. It is caused by a (CAG)n trinucleotide repeat expansion in the gene IT15 that is translated into a prolonged polyglutamine tract in the protein huntingtin. This mutation leads to the self-association of huntingtin to form aggregates in the brains of affected people. Work in Professor Nicotera’s group at the MRC Toxicology Unit identified expression changes in Rab11, a protein involved in endosomal recycling, in a cell culture model of HD. The aim of this thesis was to investigate whether endosomal recycling is affected in this model. Monitoring the trafficking of labelled transferrin by Western blotting and live-cell imaging showed rapid uptake of transferrin into all cells, but a significantly reduced rate of clearance in cells containing huntingtin aggregates, which was associated with the accumulation of transferrin in the endosomal recycling compartment (ERC). This finding demonstrates an aggregate-specific lesion in the exit of cargo from the ERC in the absence of cell death. As endosomal recycling is essential for correct neuronal function, this process provides a mechanism whereby protein inclusions may contribute to the cognitive and motor deficits seen in HD. A second project focused on purification of aggregates to determine if they could sequester material important for cellular function. Many attempts to purify the aggregates in their intact globular form revealed their highly unspecific affinity towards other proteins, which renders purification methods very susceptible to artefacts. The large globular aggregates could, however, be dispersed by SDS-treatment into fibrils of approximately 10 nm diameter, which were subsequently purified and visualised by electron microscopy.

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The role of adverse life events and trauma on the onset and development of psychotic experiences and psychosis has been widely researched. Findings from such studies have revealed that prior to the onset of psychosis or psychotic experiences individuals tend to have encountered a number of stressful or personally significant events (Shevlin et al., 2008: Beards et al., 2013). Previous research in the area of female sexual victimisation has found that sexual victimization significantly increased the likelihood of an anxiety disorder diagnosis, furthermore, an earlier study of the same sample demonstrated a 10 fold increase in the likelihood of a psychosis diagnosis following sexual victimisation (Elkit & Shevlin, 2011; Elkit & Shevlin, 2013). The aim of this thesis was to develop and test a model that demonstrates how experiencing psychological and physical intimate partner violence with and without sexual victimisation in childhood can negatively impact on psychological functioning and increase the risk of psychotic experiences. Retrospective data were collected from 107 female intimate partner violence survivors and 79 control participants. Results demonstrated that the associations with all abuse related outcomes were significant for the traumatised group with the exception of alcohol use. Moreover, subsequent analysis revealed that females who experience IPV with and without childhood trauma have very different sequelae of psychopathology. Both groups experience significantly more depression, stress, anxiety and loneliness than non-traumatised females, however the experience of intimate partner violence (alone) predicts increased shame, which then mediates the relationship from IPV to paranoia. Experience of childhood abuse compounded by revictimisation in adulthood directly and indirectly increases the risk of psychotic experiences significantly. The result~ further demonstrate that victims of childhood sexual abuse may be more vulnerable to revictimisation, highlighting the need for appropriate early intervention. Mental health issues uncovered in the course of IPV counselling and treatment, for many, may be better understood within the wider context of lifetime abuse rather than as a direct consequence of the individuals' current circumstances.

To date, no candidate markers of upper motor neuron (UMN) function have performed sufficiently well to enter widespread clinical use, and the lack of such markers impedes both the diagnostic process and clinical trials in motor neuron disease (MND). We studied 15-30Hz intermuscular coherence (IMC), a novel marker of UMN function, and central motor conduction time (CMCT), an established marker of UMN function based on transcranial magnetic stimulation (TMS), in healthy volunteers and patients newly diagnosed with MND. To clarify the relative contributions of different parts of the motor system to IMC generation, we examined IMC in patients with longstanding diagnoses of hereditary spastic paraparesis (HSP), multifocal motor neuropathy (MMN) and inclusion body myositis (IBM). Previous studies reported conflicting results for the relationship between CMCT and predictors such as age and height. We only found a significant correlation between lower limb CMCT and height. IMC did not vary significantly with age, allowing data from healthy subjects across all ages to be pooled into a single normative dataset. The variability of IMC between subjects was considerable, and within a given subject variability was greater between than within recording sessions; potential contributors are discussed. Anodal transcranial direct current stimulation (tDCS) caused a significant increase in IMC, but interindividual variability was substantial, which might hinder its future use as an adjunct to IMC. To compare individual disease groups to the normal cohort, we evaluated the area under the receiver-operating characteristic curve (AUC). IMC generally matched or exceeded the performance of CMCT in discriminating patients with MND from normal, achieving AUCs of 0.83 in the upper and 0.79 in the lower limb. Previous evidence suggests that IMC abnormalities are primarily attributable to corticospinal tract (CST) dysfunction. In line with this, most patients with HSP exhibited diminished IMC. However, patients with MMN also showed decreased IMC, suggesting either that subclinical CST involvement was present or that dysfunction of lower motor neurons (LMNs) may affect IMC; clarification through computational modelling is suggested. In iii IBM, IMC was generally increased, which might reflect that the altered motor unit discharge pattern makes synchronisation more readily detectable. IMC appears to be a promising marker of CST function. It remains to be clarified how strongly it is influenced by LMN lesions, and optimisation of methods should help to minimise the variability of results. Since IMC is non-invasive and can be measured using commonly available EMG equipment, wider dissemination should prove straightforward.

One in three people over a life time will develop a stroke, dementia or both but little is known about stroke - related cognitive impairment despite current epidemiologic transition in sub - Saharan Africa. The CogFAST Study was established in Newcastle to unmask risk factors, pathological substrates and cellular mechanisms underlying cerebral injury and cognitive impairment following stroke. The overall aim of this thesis was to establish a comparative cohort in Nigerian African stroke survivors and explore mechanisms in post - mortem brains accrued from the Newcastle cohort. Two hundred and twenty Nigerian African stroke survivors were screened three months after index stroke out of whom 143 eligible participants underwent cognitive assessment in comparison with 74 stroke - free healthy controls. We found a high frequency (49.3%) of early vascular cognitive impairment and significant association with older age and low education. Pre-stroke daily fish intake and moderate – to - heavy physical activity were inversely associated. The frequency of vascular cognitive impairment no dementia (vCIND) in the cohort (39.9%) was relatively higher than earlier report from Newcastle (32%) but neuroimaging studies revealed significant findings of MTLA and correlative white matter changes in tandem with previous reports from the Newcastle cohort. Given these, we investigated neurodegenerative hippocampal Alzheimer pathology and synaptic changes, as well as frontal and temporal white matter abnormalities in post - mortem brain tissue from the Newcastle cohort. We found increased Alzheimer pathology in the post - stroke groups but largely this did not differ between the demented (PSD) and non - demented (PSND) sub - groups. However, we found significantly higher hippocampal expression of synaptic markers (vesicular glutamate transporter – 1 and Drebrin) but lower expression of microglial, astrocytic and axonal injury markers in PSND compared to PSD subjects. The protective effect of educational attainment, pre-stroke physical activity and fish intake have public brain health implications.

The single greatest risk factor for the development of idiopathic Parkinson’s Disease is advancing age. The differences at the cellular level that cause some individuals to develop this highly debilitating disease over healthy ageing are not fully understood. Mitochondrial dysfunction has been implicated in the pathogenesis of Parkinson’s disease (PD) since the drug MPTP, known to cause Parkinson’s like symptoms, was shown to invoke its deleterious effect through inhibition of Complex I (CI) of the mitochondrial electron transport chain. Since this discovery in the 1980s, several causative genes in the much rarer familial forms of PD have been shown to encode proteins which function within, or in association with mitochondria. Through inherited cases of the disorder the process through which mitochondria are removed, mitophagy, a specialized form of autophagy has also been associated with the pathogenesis that leads to en masse cell death in this disorder. This work explores the interplay between mitochondrial deficiencies, through complex I dysfunction, and changes to autophagic processes. The methodologies to enable these observations are also described in detail with the development of novel and specialized techniques necessary to answer many of the specific research questions. The mechanisms behind complex I deficiency’s impact upon cellular processes is also explored as part of this thesis. Mitochondria and autophagy are irrevocably linked through mitochondrial dynamics, to this end an exploration of the greater impact complex I dysfunction has upon mitochondrial motility, fission and fusion was investigated. As the most prevalent neurodegenerative movement disorder of old age, understanding the molecular changes that result in Parkinson's Disease is vital to increase knowledge and offer novel therapeutic targets. Parallel studies in human upper midbrain tissue and cybrid cell lines within this work have revealed significant changes to both autophagy and mitochondrial dynamics in response to complex I deficiency. Given that mitochondrial ‘health’ and autophagic regulation directly impact upon one another identifying how exactly these may contribute to neuronal loss will hopefully allow therapeutic modulation at a point of PD pathogenesis where cells can still be retained.