Mutations of the á1A 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.

Due to two different mutations in the gene that encodes the a1A subunit of voltage-activated CaV 2.1 calcium ion channels, the compound heterozygous tottering/leaner (tg/tgla) mouse exhibits numerous neurological deficits. Human disorders that arise from mutations in this voltage dependent calcium channel are familial hemiplegic migraine, episodic ataxia-2, and spinocerebellar ataxia 6. The tg/tgla mouse exhibits ataxia, movement disorders and memory impairment, suggesting that both the cerebellum and hippocampus are affected. To gain greater understanding of the many neurological abnormalities that are exhibited by the 90-120 day old tg/tgla mouse the following aspects were investigated: 1) the morphology of the cerebellum and hippocampus, 2) proliferation and death in cells of the hippocampal dentate gyrus and 3) changes in basic biochemical parameters in granule cells of the cerebellum and hippocampus. This study revealed no volume abnormalities within the hippocampus of the mutant mice, but a decrease in cell density with the pyramidal layer of CA3 and the hilus of the dentate gyrus. Cell size in the CA3 region was unaffected, but cell size in the hilus of the dentate gyrus did not exhibit the gender difference seen in the wild type mouse. The cerebellum showed a decrease in volume without any decrease in cerebellar cellular density. Cell proliferation and differentiation in the subgranular zone of the hippocampal dentate gyrus remained normal. This region also revealed a decrease in cell death in the tg/tgla mice. Basal intracellular calcium levels in granule cells show no difference within the hippocampus, but an increase in the tg/tgla male cerebellum compared to the wild type male cerebellum. There was no significant difference in granule cell mitochondrial membrane potential within the wild type and mutant animals in either the hippocampus or cerebellum. The rate of reactive oxygen species (ROS) production in granule cells revealed no variation within the hippocampus or cerebellum. The amount of ROS was decreased in cerebellar granule cells, but not granule cells of the hippocampus. Inducing ROS showed no alteration in production or amount of ROS produced in the hippocampus, but did show a ceiling in the amount of ROS produced, but not rate of production, in the cerebellum.