| dc.description.abstract | Introduction: Major Depressive Disorder is a significant cause of disability worldwide. In a 2017 report, the World Health Organisation estimated that 320 million people suffered from depression globally. Although several antidepressant drugs have been delivered to the market over recent years, many patients do not respond adequately, or at all, to treatment. This has created an urgent need for safer and more effective treatments, which requires a better understanding of the underlying pathophysiology of depression. Disruption in neuronal plasticity; the ability of neurons to physically and functionally change over time, has been implicated in the pathophysiology of depression in both preclinical and clinical investigations. Microtubule dynamics, the rapid assembly and disassembly of microtubules and its constituents is a cellular mechanism allowing for neuronal plasticity. Microtubules contribute to this process primarily through axonal and dendritic remodelling that is required for the maintenance of synaptic connections. Microtubule stability and dynamic states affecting neuronal plasticity can be measured by assessing one of the microtubule heterodimers, Introduction: Major Depressive Disorder is a significant cause of disability worldwide. In a 2017 report, the World Health Organisation estimated that 320 million people suffered from depression globally. Although several antidepressant drugs have been delivered to the market over recent years, many patients do not respond adequately, or at all, to treatment. This has created an urgent need for safer and more effective treatments, which requires a better understanding of the underlying pathophysiology of depression. Disruption in neuronal plasticity; the ability of neurons to physically and functionally change over time, has been implicated in the pathophysiology of depression in both preclinical and clinical investigations. Microtubule dynamics, the rapid assembly and disassembly of microtubules and its constituents is a cellular mechanism allowing for neuronal plasticity. Microtubules contribute to this process primarily through axonal and dendritic remodelling that is required for the maintenance of synaptic connections. Microtubule stability and dynamic states affecting neuronal plasticity can be measured by assessing one of the microtubule heterodimers, α-tubulin and its post-translational modifications. While α-tubulins have been studied in the brain, they can also be detected in blood plasma, providing the possibility of peripheral detection of neuronal states. In order to evaluate if α-tubulins indicate a depressed state and subsequently a treatment response, analysis of tissue from a preclinical model of depression and blood plasma from depressed individuals was conducted. Hypothesis: That α-tubulins are biomarkers for depression severity and treatment efficacy. Methods: The Forced Swim Test was used to measure ?depressive-like? behaviour of Wistar Kyoto and Sprague Dawley rats following chronic or acute antidepressant treatment. Due to the reported spontaneous immobility of the Wistar Kyoto rat, a pre-test session was omitted. The total time animals spent immobile during the test session was assessed in addition to individual behaviours of swimming, climbing, diving, and immobility. Following the Forced Swim Test, animals were immediately sacrificed for tissue collection. The hippocampi and prefrontal cortex were dissected out and blood plasma was isolated from trunk blood. For the human samples, blood plasma and corresponding medical histories from depressed individuals and healthy controls were obtained through academic collaborators at Trinity College Dublin and the University of Regensburg. Individuals with depression were selected that reported high Hamilton Depression Rating Scale Scores at time point one and returned to a ?normal? score at a second time point following a course of treatment. Blood plasma samples from healthy control participants were available for one of the two cohorts. Western blotting with the Li-Cor Odyssey imaging system was used to assess the levels of α-tubulin in all tissues. Acetylated-α-tubulin (Acet-Tub), Tyrosinated-α-tubulin (Tyr-Tub), Detyrosinated-α-tubulin (Glu-Tub), Deglutamylated-α-tubulin (Δ2-Tub), and Total¬-α-tubulin (Total-α;-Tub) were measured with commercially available antibodies. Two additional analyses were carried out to assess brain-derived neurotrophic factor (BDNF) and corticosterone levels in rodent hippocampus and blood plasma, respectively. These analyses were conducted using commercially available enzyme-linked immunosorbent assay (ELISA) kits. Statistical analyses were carried out using both Microsoft Excel and InVivoStat software. Results: Wistar Kyoto rats displayed higher spontaneous immobility in the FST compared to Sprague Dawley controls. Consistent with previous reports, Wistar Kyoto rats did not show reduced immobility following acute or chronic selective serotonin reuptake inhibitor (escitalopram) treatment but did show reduced immobility to acute and chronic desipramine and acute ketamine and pregnenolone-methyl-ether treatment. Sprague Dawley rats showed a significant decrease in immobility following chronic desipramine treatment, highlighting the adrenergic effects of desipramine. No significant changes in BDNF or corticosterone were found. No robust changes in α-tubulin were found in brain tissue between Sprague Dawley and Wistar Kyoto rats nor was there a robust response to treatment, although a number of markers showed nominally significant differences. Wistar Kyoto rats overexpressed all α-tubulins in blood plasma compared to Sprague Dawley rats but no treatment effects were found. In the first human cohort, no significant changes in α-tubulins were found between the healthy controls and depressed individuals at either time point, nor were any significant changes found in α-tubulin for depressed individuals between the two time points where their symptoms improved following electroconvulsive therapy. Likewise, no significant changes in α-tubulin were found in the second cohort where their symptoms subsided following six weeks of pharmacological antidepressant treatment. Conclusions: From the studies carried out here it is reasonably clear that α-tubulins are not effective markers for either a depressed state or treatment efficacy and provide no intuitive translational value. Acknowledging that neuronal plasticity plays a meaningful role in the pathophysiology of depression, further investigation into related markers is warranted α-tubulin and its post-translational modifications. While α-tubulins have been studied in the brain, they can also be detected in blood plasma, providing the possibility of peripheral detection of neuronal states. In order to evaluate if α-tubulins indicate a depressed state and subsequently a treatment response, analysis of tissue from a preclinical model of depression and blood plasma from depressed individuals was conducted. Hypothesis: That α-tubulins are biomarkers for depression severity and treatment efficacy. Methods: The Forced Swim Test was used to measure ?depressive-like? behaviour of Wistar Kyoto and Sprague Dawley rats following chronic or acute antidepressant treatment. Due to the reported spontaneous immobility of the Wistar Kyoto rat, a pre-test session was omitted. The total time animals spent immobile during the test session was assessed in addition to individual behaviours of swimming, climbing, diving, and immobility. Following the Forced Swim Test, animals were immediately sacrificed for tissue collection. The hippocampi and prefrontal cortex were dissected out and blood plasma was isolated from trunk blood. For the human samples, blood plasma and corresponding medical histories from depressed individuals and healthy controls were obtained through academic collaborators at Trinity College Dublin and the University of Regensburg. Individuals with depression were selected that reported high Hamilton Depression Rating Scale Scores at time point one and returned to a ?normal? score at a second time point following a course of treatment. Blood plasma samples from healthy control participants were available for one of the two cohorts. Western blotting with the Li-Cor Odyssey imaging system was used to assess the levels of α-tubulin in all tissues. Acetylated-α-tubulin (Acet-Tub), Tyrosinated-α-tubulin (Tyr-Tub), Detyrosinated-α-tubulin (Glu-Tub), Deglutamylated-α-tubulin (Δ2-Tub), and Total¬-α-tubulin (Total-α-Tub) were measured with commercially available antibodies. Two additional analyses were carried out to assess brain-derived neurotrophic factor (BDNF) and corticosterone levels in rodent hippocampus and blood plasma, respectively. These analyses were conducted using commercially available enzyme-linked immunosorbent assay (ELISA) kits. Statistical analyses were carried out using both Microsoft Excel and InVivoStat software. Results: Wistar Kyoto rats displayed higher spontaneous immobility in the FST compared to Sprague Dawley controls. Consistent with previous reports, Wistar Kyoto rats did not show reduced immobility following acute or chronic selective serotonin reuptake inhibitor (escitalopram) treatment but did show reduced immobility to acute and chronic desipramine and acute ketamine and pregnenolone-methyl-ether treatment. Sprague Dawley rats showed a significant decrease in immobility following chronic desipramine treatment, highlighting the adrenergic effects of desipramine. No significant changes in BDNF or corticosterone were found. No robust changes in α-tubulin were found in brain tissue between Sprague Dawley and Wistar Kyoto rats nor was there a robust response to treatment, although a number of markers showed nominally significant differences. Wistar Kyoto rats overexpressed all α-tubulins in blood plasma compared to Sprague Dawley rats but no treatment effects were found. In the first human cohort, no significant changes in α-tubulins were found between the healthy controls and depressed individuals at either time point, nor were any significant changes found in α-tubulin for depressed individuals between the two time points where their symptoms improved following electroconvulsive therapy. Likewise, no significant changes in α-tubulin were found in the second cohort where their symptoms subsided following six weeks of pharmacological antidepressant treatment. Conclusions: From the studies carried out here it is reasonably clear that α-tubulins are not effective markers for either a depressed state or treatment efficacy and provide no intuitive translational value. Acknowledging that neuronal plasticity plays a meaningful role in the pathophysiology of depression, further investigation into related markers is warranted. | en |
