Centre for Neuroscience - Theses
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ItemNon-motor and extra-nigral aspects of Parkinson’s disease( 2009)Non-motor symptoms and extra-nigral features of Parkinson’s disease, the focus of this thesis, are very common and may result in significant disability. The increased focus on these important clinical features represents a major advance in the care of Parkinson’s disease patients. Chapter 1 provides a state-of-the-art overview of current understanding of the extra-nigral features of Parkinson’s disease, with an emphasis on the underlying patho-anatomical and patho-biochemical substrates. Although most of the discussion pertains to the non-motor symptoms of Parkinson’s disease, the importance of extra-nigral pathology in the pathogenesis of motor problems such as tremor and dopa-unresponsive axial motor features is also highlighted. Chapter 2 focuses on the relative contributions of disease versus medications in producing the non-motor symptom complex of Parkinson’s disease. Chapter 3 provides an original synthesis of the literature on pain, as it relates to Parkinson’s disease, with an emphasis on the putative pathophysiological mechanisms and management of this common and important clinical problem. Chapter 4 contains the major empirical part of the work presented in this thesis. The study provides evidence in support of the hypothesis that pain and dyskinesia (the latter being an almost universal phenomenon in Parkinson’s disease patients treated with levodopa) share common pathophysiological mechanisms in Parkinson’s disease (background discussed in Chapters 1-3). Chapter 5 provides an extensive review of Impulse control disorders and related disorders in Parkinson’s disease (including the Dopamine dysregulation syndrome and punding), problems that are increasingly recognised and frequently complicate (and limit) treatment of the motor symptoms of Parkinson’s disease. Chapter 6 contains an update on Parkinson’s disease therapy (aimed at general neurologists, geriatricians and family physicians), with a critical discussion of the pros and cons of various treatment strategies early in the disease phase, and an emphasis on the management of non-motor symptoms (Table 2 provides a comprehensive and up-to-date summary of the increasing variety of symptomatic treatments currently available for non-motor symptoms). Chapter 7 contains a critical review of the growing literature on the effects of deep brain stimulation surgery (a therapeutic modality that is increasingly being used), on the non-motor symptoms of Parkinson’s disease. It covers not only the neuropsychological and neuropsychiatric outcomes after surgery, but also the impact of surgery on Parkinson’s disease-related sleep, autonomic and sensory disorders. Chapter 8 contains the second part of the empirical work presented in this thesis. This is a case series of 21 operated (mostly bilateral subthalamic nucleus deep brain stimulation) Parkinson’s disease patients, exhibiting Dopamine dysregulation syndrome, Impulse control disorders or punding at some stage during the course of their disease. It provides further insights into the impact of deep brain stimulation on these disorders, currently a very contentious subject (background discussed in Chapters 5-7).
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ItemThe therapeutic effect of LIF in EAE-associated axonal injury( 2009)Axonal degeneration is a major pathological feature of the central nervous system (CNS) inflammatory demyelinating disease multiple sclerosis (MS). This axonal degeneration has major consequences, as functional axonal regeneration in the CNS is largely absent. Cumulative axonal degeneration is the likely cause of the majority of progressive MS-related disability, and therefore, the need for novel neuroprotective therapies for MS exists. Experimental autoimmune encephalomyelitis (EAE), an animal model of MS pathology, also produces axonal injury. In particular, the optic nerve and spinal cord are key sites of neuroinflammation in mouse EAE. By utilizing this model, the short term and long term effects of the putative neuroprotective cytokine, leukaemia inhibitory factor (LIF), were investigated in the optic nerve and spinal cord utilising a number of outcome measures of axonal dysfunction. These included MRI measures of water diffusivity along (ADC ||) and across (ADC┴) the optic nerves, serum levels of phosphorylated neurofilament heavy chain subunit (pNF-H) and histological morphometric measures. LIF treatment reduced EAE grade and pNF-H plasma levels, decreased ADC┴, but had no effect on ADC ||, axon counts or inflammatory infiltration. In contrast, genetic deletion of LIF and its sister cytokine ciliary neurotrophic factor (CNTF), not only increased EAE grade and pNF-H levels, but also decreased optic nerve ADC|| and optic nerve and spinal cord axon densities. After reviewing current literature, we hypothesize that the target cell for endogenously upregulated LIF in EAE may be the neuron or axon, whereas the target cell for exogenously administered therapeutic LIF may be another cell type, possibly infiltrating macrophages and activated microglial cells. LIF antagonist treatment did not have any affect on EAE grade, pNF-H levels or MRI parameters. This lack of effect may be due to the inability of the LIF antagonist to enter the CNS, supporting the hypothesis that endogenous LIF has a centrally acting mechanism.
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ItemPain perception and processing in ageing and Alzheimer's disease( 2008)The prevalence of chronic pain is known to increase with advancing age, with over 50% of community dwelling older adults (aged 65 years and over) and up to 80% of those residing in nursing homes estimated to be suffering some form of persistent or recurring pain complaint. In addition to a greater likelihood of pain, advancing age is associated with increased reports of pain interference. It is possible to ascribe age-related changes in pain report and impact to increased disease prevalence and severity in older people. However, there is also evidence that ageing has effects on pain perception, central pain processing, and plasticity of pain responses that are not explained by co-morbid disease. The increased prevalence of chronic pain in older adults represents a major public health concern. As a result of increased life expectancy and the post-World War II baby boom, there will be a dramatic change in the demographic structure of our population over the coming decades, with older adults representing the fastest-growing segment of our communities. The proportion of the total population over the age of 65 in Australia has risen from 9% in 1976, to 12% in 2001, and is predicted to reach 16% by the year 2016. Pain that is undetected or under-treated can adversely affect quality of life for older adults, leading to diminished mood, impaired cognition, behavioural problems, as well as increased functional dependence. This in turn contributes to greater demands for daily personal care and a resultant increase in health-care costs. Pain management is a particularly salient issue in the case of older adults with dementia, who are at increased risk of undetected pain on account of impaired cognition and communication skills. Indeed, clinical reports show that patients with Alzheimer’s disease (AD) are routinely administered fewer pain-relief medications compared with their cognitively-intact peers. Understandably, reports of reduced analgesia in AD have sparked considerable research interest, and over recent years there has been a marked increase in the number of studies aimed at better characterising the experience of pain in patients with AD. However, despite these efforts, the effects of neurodegeneration on pain processing, and the specific ways in which the disease process impacts on brain responses to noxious stimulation and the ensuing experience of pain have not been previously determined. Improved management of pain is fundamental to the clinical care of older adults, particularly those with dementia. However, the potential to adequately counteract pro-nociceptive processes and facilitate endogenous inhibitory mechanisms in the treatment of ongoing pain in older adults will only become possible once the effects of ageing and age-related neurodegeneration on central pain processing are identified and described. The overarching goal of this thesis was therefore to improve current understanding of the ways in which normal ageing and Alzheimer’s disease impact on the perception and central nervous system processing of pain. The findings of this thesis provide valuable new insights into the impact of ageing and AD on the central mechanisms contributing to pain perception, and may therefore contribute toward better management and treatment of pain in this vulnerable and rapidly growing sector of our community. Thesis outline: Chapter 2 provides a review of the background literature and rationale for the thesis. The chapter begins with a discussion of current understanding of pain as a multidimensional phenomenon shaped by sensory, emotional and cognitive components, and leads into a description of neural mechanisms of nociception, as well as the supraspinal processes involved in the elaboration of nociceptive signals into these aspects of pain. The impact of ageing on the structure and function of central nervous system regions underlying these processes are discussed, along with the findings from previous clinical and empirical data which suggest age-related changes in pain perception. Current understanding of the neuropathological and clinical aspects of AD is reviewed, with particular emphasis on potential ways in which the disease may impact on central nociceptive processing and the behavioural response to pain. This is followed by a review of the previous clinical and empirical literature examining pain perception in AD. Finally, the aims of the current thesis are outlined. Chapter 3 describes the general methods which were employed in the subsequent empirical chapters in order to address the aims of the thesis. The equipment and psychophysical procedures used to assess pain perception in healthy young and older adults and patients with AD are described. The basic principals of magnetic resonance imaging (MRI) are then outlined, and the utility of structural and functional MRI for assessing age-related and disease-related changes to brain regions involved in pain perception and processing are discussed. The empirical studies which were undertaken to identify the impact of ageing and AD on central pain processing are presented in the next three chapters. Chapter 4 begins with psychophysical studies comparing sensory and emotional responses to pain in healthy young and older adults, and follows with MRI investigations of age-related differences in brain volumetry and pain-related brain activity. Studies of pain sensitivity and pain-evoked brain activity in patients with AD compared with age-matched controls are presented in Chapter 5. Following on from these findings of AD-related differences in pain-evoked brain activation, the study described in Chapter 6 used functional connectivity analysis in order to assess the impact of AD on the functional integration of brain regions underlying the sensory, emotional, and cognitive aspects of pain. The key findings presented in the preceding three chapters are summarized in a general discussion in Chapter 7. The implications of the findings, in terms of the clinical management of pain in older adults with and without Alzheimer’s disease are discussed. The opportunity is also taken to discuss some of the limitations of the present research, and finally, recommendations are made for future research directions.
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ItemTargeted knockdown of CREB1 in brain nuclei critically involved in drug-seeking behaviour( 2009)The purpose of this thesis was to characterise the contribution that a specific molecule, CREB1, plays in the many facets of a developing addiction phenotype. Indeed, CREB1 is known to contribute to long term learning and memory, and present an altered activation profile upon exposure to reinforcing substances, in brain regions implicated in addiction. Together, these observations provide a prima facie driver to investigate the specific involvement of CREB1 in brain regions implicated in reinforcement and drug-seeking. Initially, I investigated Sprague Dawley rats whom had undergone behavioural sensitization to the repeated administration of the psychostimulant d-Amphetamine. Detailed in Chapter 3, the aims of this study were to determine the impact that environmental drug-context associations and psychostimulant sensitization makes upon expression of the activated or phosphorylated form of CREB1 (pCREB1). The data presented in the study reveals that many brain nuclei relevant to the behavioural effects of drug exposure show expression of pCREB1 subsequent to enduring amphetamine abuse, as well as upon return to an environment previously paired with amphetamine. The profile of pCREB1 expression within brains was unique to each pattern of drug dosing and context exposure, suggesting that unique sub-circuits underlie these different behavioural repertoires. Using the impetus from this study, I determined to further investigate the contribution of CREB1 from specific brain regions, and the impact of its deletion upon behaviours characteristic of addiction. Indeed, the aims of this section of the project were to firstly employ relevant detection systems and current genetic-engineering technologies in creating appropriate expression animal lines, emphasising reward and reinforcement pathways. In addition, I aimed to understand the signalling systems and pathways which are activated by neurotransmitters, culminating in the phosphorylation of CREB and subsequently altered gene expression and long-term cellular and neuronal adaptation, induced by ongoing exposure to drugs of abuse. Detailed in Chapter 4, I created a novel mutant mouse which was deficient in CREB1 within the dorsal telencephalon. Mice 'floxed' for the Creb1 gene expressed loxP DNA sequence around an exon critical to CREB1 function. These mice were interbred with mice expressing the enzyme Cre recombinase in dorsal telencephalic brain regions. Thus, mice expressing Cre recombinase and floxed for Creb1 demonstrated the deletion of CREB1 protein in these brain regions, which is demonstrated through experiments presented in Chapter 4. Further in vitro characterisation of this mutant mouse was carried out and presented in Chapter 5. As CREB1 is important in synaptic plasticity and growth, it was necessary to evaluate any impact upon ontogeny through stereological analysis of cell number and volume, for relevant brain nuclei. The experiments demonstrate that mutant CREB1 mice were no different to control mice, however, it was possible that this lack of phenotype was partly contributed though changes in the level of other CREB/ATF-1/CREM bZIP family members. To this end, I determined to assay for transcript changes in these and related genes, finding confirmation of the deletion of the Creb1 transcript in the cortex and hippocampus, whilst observing a concomitant increase in Crem transcript. These data suggested that compensatory changes in brain regions receiving a recombination of Creb1 were apparent, contributing to the lack of an obvious phenotype in these mice. Having confirmed the specific deletion of CREB1 in the appropriate brain nuclei, I then moved to examine the impact of the deletion behaviourally, both in terms of general ethology, and in regard to drug-induced phenotypes. Presented in Chapter 6, experiments assaying general ethology of the CREB1 mutant revealed a spontaneous hypoactivity when placed in a small open field environment. As CREB1 is involved in neural plasticity, I wished to assay for the impact on behavioural sensitization, a paradigm which reveals long-lived neural change. Experiments to this effect showed no perturbation of behavioural sensitization to the effects of cocaine in the mutant. In addition, mutant mice also showed a similar response to the rewarding effects cocaine as witnessed in the control mice, however, the CREB1 mutants demonstrated a perturbed drug-environment contextual memory, which was not retained in long-term place preference experiments. Operant conditioning studies for intravenous self administration of cocaine revealed that CREB1 mutants displayed a dose-specific diminished drive to self-administer cocaine, whereas in contrast, self administration of a natural reward was no different to control mice. These data suggest that there is a specific role for CREB1 in telencephalic glutamatergic neurons regulating the motivational and associative properties of cocaine. Together, these data provide evidence that CREB1 functions as a key molecular substrate in long lived drug-context environment associations and neural change underlying the developing addicted state, warranting future investigation for its properties in producing drug related functional and behavioural change.