A Novel Rat Model of Focal Ischemia using N5-(1-iminoethyl)-L-ornithine: Development and Therapeutic Application

Abstract

The overall objectives of this thesis were to establish an in vivo model of focal ischemia within our laboratory and to investigate the therapeutic potential of this model. We hypothesised that we would be able to establish a model with a reproducible infarct that was relevant for preclinical studies of ischemic stroke therapies. It was further hypothesised that acute delivery of a connexin43 (Cx43) mimetic peptide would improve tissue outcomes following focal ischemia. Focal ischemia was induced in adult male Sprague Dawley rats by transient middle cerebral artery occlusion (MCAo) and by intrastriatal injection of N5-(1- iminoethyl)-L-ornithine (L-NIO) in combination with jugular vein occlusion. Infarct volume was quantified by cresyl violet staining or NeuN immunoreactivity. Blood-brain barrier leakage, hypoxia, neurodegeneration and inflammation were investigated using immunohistochemistry. Functional deficits were quantified using rotarod and cylinder tests. MK801 was administered systemically to determine the potential for neuroprotection and the therapeutic potential of the Cx43 mimetic peptide was investigated via intrastriatal and systemic delivery routes. The major original contribution of this thesis to the preclinical stroke field is the successful development of a novel rat model of focal striatal ischemia: the L-NIO model. This model is associated with high success rates, zero mortality, reduced surgical complexity and a consistent, reproducible infarct, thus providing advantages over intraluminal MCAo. The LNIO model also exhibits characteristics of established models of ischemic stroke including blood-brain barrier dysfunction, neuroinflammation and chronic functional impairment. Importantly, evidence of neuroprotection demonstrates the potential use of the L-NIO model for testing neuroprotective interventions. When examining the therapeutic potential of Cx43 mimetic peptide delivery, no beneficial changes to tissue outcomes were found following intrastriatal peptide administration immediately or 3 days post-ischemia. Systemic peptide administration appeared to increase the inflammatory response. However, potential protection by intrastriatal peptide injection against a vehicle-mediated increase in L-NIO infarct volume justifies further investigations into Cx43 mimetic peptide as an acute intervention following ischemic stroke. In conclusion, we propose that the L-NIO model of focal ischemia in the rat striatum is a useful tool for preclinical investigations into therapeutic strategies for ischemic stroke.