Biomedical Sciences ETDs

Author

Robert Dietz

Publication Date

5-1-2010

Abstract

Spreading depression (SD) is a wave of severe depolarization that spreads across brain tissue. For several decades, it has been suggested that (SD) may play a role in the expansion of brain injury following ischemic insults, and may also be involved in non-injurious pathologies such as migraine aura. The major goals of this study were to examine cellular mechanisms that contribute to the initiation of different forms of SD, and in particular the potential roles of the cations Ca2+ and Zn2+. Work in this thesis examined SD in hippocampal slices acutely prepared from adult mice. Initial studies used the Na+/K+ ATPase inhibitor ouabain to generate SD, and showed that L-type Ca2+ channels are required for initiation of SD, but that Ca2+ influx through these channels was not involved. In fact, from NAD(P)H autofluorescence studies, it was suggested that Ca2+ influx may promote mitochondrial function prior to SD, rather than contribute to ionic deregulation. A combination of imaging approaches was then used to demonstrate that Zn2+ could enter neurons through L-type Ca2+ channels and depolarize the inner mitochondrial membrane prior to SD. Furthermore, chelation of Zn2+ completely prevented SD, showing for the first time that Zn2+ entry could be critically required for SD. It was then shown that very similar ionic mechanisms appeared to be involved in SD generated by oxygen/glucose deprivation (OGD), an in vitro model of ischemia. Zn2+, rather than Ca2+ influx appeared to be critically required for the onset of OGD/SD. SD generated by localized high K+ applications appeared to involve quite distinct ionic mechanisms. Zn2+-dependent mechanisms were not involved, but Ca2+ chelation effectively prevented the propagation of these events. Single-neuron Ca2+ imaging studies showed that high K+/SD resulted in recoverable Ca2+ loads throughout neurons, whereas OGD/SD and ouabain/SD lead to irrecoverably high Ca2+ levels and rapid neuronal injury. These results provide the first evidence that Zn2+ can selectively contribute to SD in pathological models, and suggest novel approaches to mitigating brain injury following stroke.

Keywords

Zinc, Calcium, Spreading Depression, Hippocampus

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Advisor

Shuttleworth, C. William

First Committee Member (Chair)

Valenzuela, C. Fernando

Second Committee Member

Resta, Tom

Third Committee Member

Mueller, Wolfgang

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