Glial control of neurogenesis in rodent models of epilepsy

Abstract

The aim of this thesis is to investigate the control of dentate neurogenesis, especially after seizure, and to identify the principle cells involved in these processes.  I have used a combination of in vivo and in vitro techniques to investigate the mechanisms and control of seizure induced denatate neurogenesis, chemoconvulsant kainate was used to induce seizures in all seizure models, maximizing the potential for comparison between experiments.

Initial in vitro work established conditions in which cell death and proliferation could be accurately and reproducibly quantified in organotypic hippocampal slice cultures.  Subsequent experiments established that in immature tissue kainate induced cell death, followed by increased neurogenesis.

In vivo experiments in adult rats using a ‘clonal; BrdU labelling technique, where a cohort of cells labelled prior to seizure induction were followed in recovery, found that the prelabelled cohort contributed less to seizure induced cell proliferation than the cohort of cells that were not dividing prior to seizures implying the recruitment of an additional dividing cell population by seizures.

Astrocytes with radial glial like morphology are putative stem cells for dentate neurogenesis.  To test our recruitment hypothesis, I used transgenic mice expressing enhanced green fluorescent protein under the hGFAP promoter to readily identify a subset of the radial glial like cells, and found their proliferation was selectively increased (10 fold vs. 2.5 fold overall increase in proliferation) in response to seizures.

The data obtained suggest that seizures result in either death or inactivation of a progenitor cell population with a consequent recruitment of either quiescent or slowly dividing stem cells, which divide to replenish the progenitor cell population and restore neurogenesis.  This work also identifies GFAP expressing cells with a radial glial morphology as a quiescent stem cell population selectively recruited to divide by brain injury due to seizures, and is the first report of recruitment of an identified stem cell population in the dentate after brain injury.

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