- Title
- Model perturbations of glial synaptomodulatory and immune functions
- Creator
- Mayhew, Jack
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The content presented in this thesis spans several disciplines and topic areas. This arose due to a change in supervision in the first half of my candidature, with a corresponding change in experimental laboratory and topic. Notwithstanding this, there is a common narrative through the work in that each chapter addresses remodelling within the CNS resulting from some type of perturbation. In Chapter 2, alterations in the expression of purinergic signalling receptors in the rat hippocampus were assessed following exposure to chronic restraint stress. These changes were determined via semi-quantitative immunohistochemistry, demonstrating that the expression of the vesicular transporter of adenosine triphosphate, and that of purinergic receptors involved in the modulation of glutamate transmission were considerably altered following exposure to chronic stress. Chapter 3 examines the effect of acute stress, but also overlays subsequent immune stimulation via peripheral injection of the bacterial endotoxin lipopolysaccharide. This investigation focussed on the ability of priming events (stress) to enhance subsequent neuroimmune responses, with the morphological characteristics of hippocampal and prefrontal microglia used as an outcome measure. Surprisingly, this study was unable to detect an effect of prior stress exposure on the morphological alterations that emerge following immune stimulation. While this area of scientific enquiry is of considerable interest and impact, further investigation was precluded by the aforementioned change in supervision, however, a number of future directions that could resolve this result are noted. A transition in research focus is demarcated in Chapter 4, where the effect of age on the CNS is addressed. Specifically, the topic of age-related changes in sensory processing at the level of the spinal cord dorsal horn was addressed, with a particular relevance to the well-described increase in incidence of chronic pain states in the elderly. In this study, ageing-related changes in the dorsal horn were assessed using qPCR to determine the expression changes in a wide-range of functional domains, including genes involved in inflammatory, glial and neurotransmitter systems. The experiments performed in this study revealed considerable upregulation in proinflammatory genes with age, including a number that have been shown to be essential for the development of neuropathic pain. Chapter 5 seeks to characterise the functional consequences of the altered gene expression identified in the preceding chapter. This research addressed the question of how ageing might perturb the baseline characteristics of dorsal horn neural signalling, examined using of patch-clamp electrophysiology. Our findings identified a number of subtle changes that may have in fact counteracted each other to produce at best only modest changes in neural signalling within the dorsal horn with advancing age. This produced a model where balanced reduction to excitatory drive, enhanced intrinsic excitability and shifted inhibitory balance to GABA dominant mechanisms may act to preserve relatively normal dorsal horn output with advanced age. Given the scope of these studies, the following introduction will canvas the literature and key concepts contained within the ensuing chapters. This will provide a broad introduction to the role of purines in the modulation of glutamate neurotransmission in the central nervous system. Particular emphasis will be placed on the utilization of purines by astrocytes and microglia, both in the modulation of glutamate signalling, and in their functions more broadly. Subsequently, the current literature on the effect of chronic stress on the brain will be presented, highlighting evidence 6 describing glutamatergic dysfunction precipitated by chronic stress. The ability of stress to disrupt glial functions and purinergic signalling, potentially upstream from glutamate signalling, will also be explored in this context. The literature on stress-induced priming of the central immune responses will then be presented with a focus on the response of microglia. Here the concept of priming will be elaborated, as will the ability of peripheral immune challenges to induce central inflammatory responses. The topic of neuroinflammation will then be explored through the effect of ageing on the CNS, which is known to be in a chronic neuroinflammatory state. In this section age-related changes in central inflammatory processes and glial structure and function will be outlined, as well as the necessary background on CNS immune cells and signalling mechanisms. A further goal of this section will be to highlight the evidence, or lack thereof, on the effect of age on the spinal cord. Finally, the subsequent passages will provide an overview of the spinal cord and the contribution of the dorsal horn to sensory processing, and how dysfunction in this region contributes to chronic pain. The involvement of central inflammatory processes and glia in these functional alterations will receive particular attention, primarily to provide context to the age-related gene expression and functional changes observed in dorsal horn. A common thread throughout most of this work is the relevance of glia to CNS functions and their alterations by, and contributions to various pathological states. As such, it is fitting for the following introduction to begin with a broad perspective on the contribution of glia to CNS functions.
- Subject
- purinergic signalling receptors; central nervous system; stress exposure; altered gene expression; neuroinflammation
- Identifier
- http://hdl.handle.net/1959.13/1412128
- Identifier
- uon:36432
- Rights
- Copyright 2020 Jack Mayhew
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 8 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 488 KB | Adobe Acrobat PDF | View Details Download |