published_or_final_version / abstract / Medicine / Master / Master of Philosophy

Stroke is a serious cerebral vascular event and a leading cause of death and disability worldwide, and ischemic stroke is the most common type. Evidence from animal research in acute cerebral ischemia shows that a combination of neuroprotectants might be more efficacious than the single agent given individually. Both melatonin and electro-acupuncture (EA) have been suggested to be effective treatments against cerebral ischemia. However, it is unknown whether a combination of these two therapies could be beneficial against focal cerebral ischemia. In the first study, the effect of post-treatment with a combination of melatonin and EA on regional cerebral blood flow (rCBF), neurological deficit score and infarct volume was investigated in both permanent and transient middle cerebral artery occlusion (MCAO) models in rats. When compared with the single treatment of melatonin or EA, the combination therapy resulted in a significant improvement of neurological function and a dramatic reduction of infarct volume at 72 hr after transient MCAO. A significant upregulatory effect on rCBF has been exerted by the combined treatment. The effect of a combination of melatonin and EA on inflammatory reaction was investigated in the second study. Post-treatment of the combination therapy effectively inhibited neutrophil infiltration as well as the expression of some pro-inflammatory mediators, and increased the anti-inflammatory protein expression at 72 hr after transient MCAO. This beneficial effect may be due to the respective anti-inflammatory effects of melatonin and EA. In the third study, the effect of a combination of melatonin and EA on apoptosis was examined. When compared with the EA treatment alone, post-treatment of the combination therapy exerted a greater inhibitory effect on tissue apoptosis and expression of the pro-apoptotic proteins as well as an upregulatory effect on the anti-apoptotic protein expression. In the fourth study, the effect of continuous post-treatment of a combination of melatonin and EA on transient MCAO was investigated. The combination treatment significantly improved neurological function and decreased infarct volume at 7 days after transient MCAO. Cell proliferation and expression of the neurotrophic factor were increased by the combined treatment. The effect of pretreatment with a combination of melatonin and EA was examined in the fifth study. Neurological function was improved and infarct volume was reduced by the combination pretreatment at 24 hr after transient MCAO. The inflammatory and apoptotic reaction were inhibited by the combined pretreatment through the modulatory effect of the related proteins. In summary, our results show that, when compared with the single treatment of either melatonin or EA, post-treatment with a combination of melatonin and EA induced a complementary neuroprotective effect on improvement of neurological function and a dramatic reduction of infarct volume after transient MCAO. The complementary protection may be partially mediated via anti-inflammation and anti-apoptosis after transient cerebral ischemia. Pretreatment with a combination of melatonin and EA may be more effective in preventing ischemic brain injury after transient focal cerebral ischemia. / published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Diagnostic Radiology / Master / Master of Philosophy

published_or_final_version / Medicine / Master / Master of Philosophy

published_or_final_version / Paediatrics and Adolescent Medicine / Doctoral / Doctor of Philosophy

Cerebral ischaemia is a leading cause of disability and death world-wide. The only effective treatments are thrombolytic therapy (plasminogen activator; tPA) and hypothermia (33?C). However, tPA has limited clinical application due to its short therapeutic time window and its specific application in thrombo-embolic stroke. Moderate hypothermia (33?C) is only being used following cardiac arrest in comatose survivors. Hence more treatments are urgently required. The first step in developing new treatments is the identification and characterisation of a potential therapeutic target. Since brain damage following cerebral ischaemia is associated with disturbances in intracellular calcium homeostasis, the sodium-calcium exchanger (NCX) is a potential therapeutic target due to its ability to regulate intracellular calcium. Currently, however there is uncertainty as to whether the plasma membrane NCX has a neuroprotective or neurodamaging role following cerebral ischemia. To address this issue I compared hippocampal neuronal injury in NCX3 knockout mice (Ncx3-/-) and wild-type mice (Ncx3+/+) following global cerebral ischaemia. In order to perform this study I first established a bilateral common carotid occlusion (BCCAO) model of global ischaemia in wild-type C57/BlHsnD mice using controlled ventilation. After trials of several ischaemic time points, 17 minutes was established as the optimum duration of ischaemia to produce selective hippocampal CA1 neuronal loss in the wild-type mice. I then subjected NCX3 knockout and wild-type mice to 17 minutes of ischaemia. Following the 17 minute period of ischaemia, wild-type mice exhibited 80% CA1 neuronal loss and 40% CA2 neuronal loss. In contrast, NCX3 knockout mice displayed > 95% CA1 neuronal loss and 95% CA2 neuronal loss. Following experiments using a 17 minute duration of global ischaemia, a 15 minute duration of ischaemia was also evaluated. Wild-type mice exposed to a 15 minute period of ischaemia, did not exhibit any significant hippocampal neuronal loss. In contrast, NCX3 knockout mice displayed 45% CA1 neuronal loss and 25% CA2 neuronal loss. The results clearly demonstrate that mice deficient for the NCX3 protein are more susceptible to global cerebral ischaemia than wild-type mice. My findings showing a neuroprotective role for NCX3 following ischaemia, suggest that the exchanger has a positive role in maintaining neuronal intracellular calcium homeostasis. When this function is disrupted, neurons are more susceptible to calcium deregulation, with resultant cell death via calcium mediated pathways. Therefore, improving NCX activity following cerebral ischaemia may provide a therapeutic strategy to reduce neuronal death.