The Functional organization of astrocytes in normal and epileptic brain

Thesis (Ph. D.)--University of Rochester. School of Medicine & Dentistry. Interdepartmental Graduate Program in Neuroscience, 2008.A key for understanding the physiology and pathology of the human nervous system is knowledge of its structural and functional organization. In this thesis work, I hypothesize that the human brain is characterized by increased diversity and complexity of its astrocytes compared to our common rodent models. I describe several unique characteristics of human astrocytic structure and identify a novel subclass of human astrocytes in cortex: the varicose projection astrocytes. Some features are conserved through evolution; human protoplasmic astrocytes, like rodent, are organized into spatially non-overlapping domains that encompass both neurons and vasculature. Functionally, human astrocytes behave like our common models in that they transiently increase cytosolic Ca2+ in response to glutamatergic and purinergic receptor agonists, and can support calcium waves, albeit at significantly greater velocities than in rodent. In the second part of my thesis, I demonstrate that reactive astrocytes associated with seizures have structural and functional changes that may contribute to the underlying pathology of epilepsy. Using the technique of diolistic labeling, I demonstrate that in three mouse models of epilepsy: post-traumatic injury, genetic susceptibility, and systemic kainate exposure, reactive astrocytes had a chronic loss in domain organization. The loss of the domain organization was not a universal property of gliosis in that reactive astrocytes associated with neurodegeneration maintained the domain organization. There was an increase in spine density of cortical excitatory neurons in concert with loss of the domain organization suggesting that changes in both neurons and astrocytes may form the structural basis for recurrent excitation in the epileptic brain. Functionally, reactive astrocytes near and within the seizure foci had chronic decreased expression of glutamate transporter 1 and glutamine synthetase as well as intracellular glutamate accumulation. Additionally, reactive astrocytes had increased spontaneous calcium oscillations that were independent of neuronal activity. These reactive changes of astrocytes may play a role in the pathogenesis of epilepsy. Overall, this thesis highlights the importance of interspecies differences in the structure, organization, and function of astrocytes and how reactive changes in astrocytes may contribute to epilepsy

The immunohistochemical, DNA methylation, and chromosomal copy number profile of cauda equina paraganglioma is distinct from extra-spinal paraganglioma.

Paragangliomas are neuroendocrine tumors of the autonomic nervous system that are variably clinically functional and have a potential for metastasis. Up to 40% occur in the setting of a hereditary syndrome, most commonly due to germline mutations in succinate dehydrogenase (SDHx) genes. Immunohistochemically, paragangliomas are characteristically GATA3-positive and cytokeratin-negative, with loss of SDHB expression in most hereditary cases. In contrast, the rare paragangliomas arising in the cauda equina (CEP) or filum terminale region have been shown to be hormonally silent, clinically indolent, and have variable keratin expression, suggesting these tumors may represent a separate pathologic entity. We retrospectively evaluated 17 CEPs from 11 male and 6 female patients with a median age of 38 years (range 21-82), none with a family history of neuroendocrine neoplasia. Six of the 17 tumors demonstrated prominent gangliocytic or ganglioneuromatous differentiation. By immunohistochemistry, none of the CEPs showed GATA3 positivity or loss of SDHB staining; all 17 CEPs were cytokeratin positive. Genome-wide DNA methylation profiling was performed on 12 of the tumors and compared with publicly available genome-wide DNA methylation data. Clustering analysis showed that CEPs form a distinct epigenetic group, separate from paragangliomas of extraspinal sites, pheochromocytomas, and other neuroendocrine neoplasms. Copy number analysis revealed diploid genomes in the vast majority of CEPs, whereas extraspinal paragangliomas were mostly aneuploid with recurrent trisomy 1q and monosomies of 1p, 3, and 11, none of which were present in the cohort of CEP. Together, these findings indicate that CEPs likely represent a distinct entity. Future genomic studies are needed to further elucidate the molecular pathogenesis of these tumors

Myxoid glioneuronal tumor, PDGFRA p.K385-mutant: clinical, radiologic, and histopathologic features.

"Myxoid glioneuronal tumor, PDGFRA p.K385-mutant" is a recently described tumor entity of the central nervous system with a predilection for origin in the septum pellucidum and a defining dinucleotide mutation at codon 385 of the PDGFRA oncogene replacing lysine with either leucine or isoleucine (p.K385L/I). Clinical outcomes and optimal treatment for this new tumor entity have yet to be defined. Here, we report a comprehensive clinical, radiologic, and histopathologic assessment of eight cases. In addition to its stereotypic location in the septum pellucidum, we identify that this tumor can also occur in the corpus callosum and periventricular white matter of the lateral ventricle. Tumors centered in the septum pellucidum uniformly were associated with obstructive hydrocephalus, whereas tumors centered in the corpus callosum and periventricular white matter did not demonstrate hydrocephalus. While multiple patients were found to have ventricular dissemination or local recurrence/progression, all patients in this series remain alive at last clinical follow-up despite only biopsy or subtotal resection without adjuvant therapy in most cases. Our study further supports "myxoid glioneuronal tumor, PDGFRA p.K385-mutant" as a distinct CNS tumor entity and expands the spectrum of clinicopathologic and radiologic features of this neoplasm