Graduation Year

2017

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Medicine

Major Professor

Edwin J. Weeber, Ph.D.

Committee Member

David Morgan, Ph.D.

Committee Member

Javier Cuevas, Ph.D.

Committee Member

Doug Shytle, Ph.D.

Abstract

The “two-hit” schizophrenia hypothesis suggests genetic and environmental abnormalities interrupt early CNS function. This increases vulnerability of a “second hit” and schizophrenia onset. Chronic stress and decreased Reelin signaling are reportedly associated with schizophrenia. Heterozygous Reeler Mice (HRM) show a 50% reduction in Reelin and display major schizophrenia phenotypes. Receptor-Associated Protein (RAP) blocks ligand-association to Reelin receptor Apolipoprotein E receptor 2 (ApoER2). In this study, we sought to replicate major heterozygous reeler mouse (HRM) phenotypes using in vivo RAP studies to establish an experimental in vitro model. Using an in vitro model, we investigated the effects of chronic stress and decreased Reelin signaling on AMPAR subunit expression.

Implantable Alzet osmotic pumps allowed bilateral ventricular 7nM RAP perfusion in 12-14 week-old mice. An assay revealed significant Dab-1 phosphorylation reduction in RAP-perfused animals. These results correspond with learning and memory and associative-fear conditioning abnormalities. Overall activity, sensory perception, and nociception remained unaltered. RAP-perfused mice displayed deficits in pre-pulse inhibition to acoustic startle, and therefore sensory-gating deficits. A significant decrease in Glur1 and Glur2/3 expression was observed in primary hippocampal/cortical neurons following chronic RAP and CORT exposure.

Collectively, our results show postnatal Reelin signaling disruption produces physiological, biochemical, and behavioral phenotypes similar to the HRM model. The exact mechanism of Reelin-dependent AMPAR insertion remains unclear. Glur1 and Glur2/3 appear to be inserted by differing mechanisms. Glur1 is reported to be inserted with Reelin activation of phosphoinositol-3-kinase (PI3K) signaling. Glur2/3, whose mechanism of insertion is unknown, has not been shown to be inserted via PI3K. Our findings also demonstrate the usefulness of in vitro RAP use, in which apolipoprotein E receptor 2 (ApoER2) expression is predominant compared to other lipoprotein receptors that may be affected with RAP application.

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Neurosciences Commons

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