Browsing by Subject "cell death"
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Item Cerebellar Purkinje cell death in the P/Q -type voltage-gated calcium ion channel mutant mouse, leaner(Texas A&M University, 2006-04-12) Frank-Cannon, Tamy CatherineMutations of the ??1A subunit of P/Q-type voltage-gated calcium channels are responsible for several inherited disorders affecting humans, including familial hemiplegic migraine, episodic ataxia type 2 and spinocerebellar ataxia type 6. These disorders include phenotypes such as a progressive cerebellar atrophy and ataxia. The leaner mouse also carries a mutation in the alpha(1A) subunit of P/Q-type voltage-gated calcium channels, which results in a severe cerebellar atrophy and ataxia. The leaner mutation causes reduced calcium ion influx upon activation of P/Q-type voltage-gated calcium channels. This disrupts calcium homeostasis and leads to a loss of cerebellar neurons, including cerebellar Purkinje cells. Because of its similarities with human P/Qtype voltage-gated calcium channel mutations, leaner mouse has served as a model for these disorders to aid our understanding of calcium channel function and neurodegeneration associated with calcium channel dysfunction. The aims of this dissertation were: (1) to precisely define the timing and spatial pattern of leaner Purkinje cell death and (2) to assess the role of caspases and specifically of caspase 3 in directing leaner Purkinje cell death. We used the mechanism independent marker for cell death Fluoro-Jade and demonstrated the leaner Purkinje cell death begins around postnatal day 25 and peaks at postnatal day 40 to 50. Based on this temporal pattern of Purkinje cell death we then investigated the role of caspases in leaner Purkinje cell death. These studies showed that caspase 3 is specifically activated in dying leaner cerebellar Purkinje cells. In addition, in vitro inhibition of caspase 3 activity partially rescued leaner Purkinje cells. Further investigation revealed that caspase 3 activation may be working together with or in response to macroautophagy. This study also indicated a potential role for mitochondrial signaling, demonstrated by the loss of mitochondrial membrane potential in leaner cerebellar Purkinje cells. However, our study revealed that if the loss of mitochondrial membrane potential is associated with leaner Purkinje cell death, this process is not mediated by the mitochondrial protein cytochrome C.Item Comparative Neurotoxicity of Methylmercury and Mercuric Chloride In Vivo and In Vitro(2010-10-12) Thuett, Kerry A.It is impossible to remove methylmercury (MeHg) from biological systems because MeHg is found throughout our environment in many fresh and salt water fish. The consumption of fish is important to human nutrition and health. The mechanism of MeHg neurotoxicity must be understood to minimize adverse exposure consequences. The dissertation objective was to: 1) compare mechanisms of MeHg neurotoxicity between animals exposed as adults and those exposed during gestation, and 2) develop an in vitro test model of in vivo MeHg exposure. Total mercury (Hg) levels in tissue / cells were determined by combustion / trapping / atomic absorption. Cell death was determined by Fluoro-Jade histochemical staining and activated caspase 3 immunohistochemistry for in vivo studies, and Trypan blue exclusion, lactate dehydrogenase activity, and cytotoxicity assays for in vitro studies. Mitochondrial membrane potential (MMP), intracellular calcium ion concentration ([Ca2+]i), and production of reactive oxygen species (ROS) were determined using fluorescence microscopy or microplate reader assays. Young adult C57Bl/6 mice were exposed to a total dose of 0, 1.0, or 5.0 mg/kg body weight MeHg divided over postnatal days (P)35 to 39. Pregnant female mice were exposed to a total does of 0, 0.1, or 1.0 mg/kg body weight MeHg divided over gestational days (G)8 to 18. SY5Y cells were exposed to 0, 0.01, 0.1, or 1.0 ?M MeHg or HgCl2 for 24, 48, or 72 hours. Total Hg in brains of young adult mice, mouse pups, and SY5Y cells accumulated in a dose-dependent manner. Cell death increased in SY5Y cells exposed to the highest concentrations of MeHg and HgCl2 used in this study. Cell death increased in the molecular and granule cerebellar cell layers of young adult mice exposed to the highest doses of MeHg used in this study. P0 mouse pups showed no increase in cell death within the cerebellum following MeHg exposure. Cerebella of mice at P10 exhibited decreased dying cells only in the external germinal layer. Low concentrations of MeHg affected MMP in both in vivo and in vitro studies, but did not result in decreased MMP typically associated with higher MeHg concentrations. [Ca2+]i was increased throughout the in vivo experiments in an age- , sexand brain region-dependent manner. Generation of ROS was decreased in both in vivo and in vitro studies with both the MeHg and HgCl2 (in vitro) treatments. In summary, low and moderate MeHg exposure, both in vivo and in vitro, altered mitochondrial function, Ca2+ homeostasis, and ROS differently than what is reported in the literature for higher MeHg exposure concentrations. SY5Y cells were sensitive to low-levels of MeHg and HgCl2 and responded similarly to cells in the whole animal studies, thus making SY5Y cells realistic candidates for mechanistic MeHg studies. Cell culture and whole animal neuronal functional studies at chronic low-level MeHg exposure are limited. These data suggest that low-levels of MeHg may affect neuronal function. Therefore, further chronic low-level MeHg neuronal functional studies are warranted.