Investigating the Mechanisms of Pharmacological Preconditioning In Vitro and In Vivo

Abstract

Preconditioning involves the induction of endogenous protective mechanisms to prevent damage due to subsequent insult. The acute window of protection could provide a neuroprotective strategy for patients with a known risk of ischemia, such as those undergoing heart surgery, for which there are currently no such prophylactic options available. The aim of this thesis was to identify contributing factors to the mechanism of preconditioning protection. By understanding the mechanisms behind the protective effect, it may be possible to develop safe and effective pharmaceuticals to induce acute protection for clinical use.

Previous experiments in our lab had demonstrated in vitro preconditioning protection induced by high potassium (Butler, 2008), kainic acid (Hesp et al., 2004) and GYKI-52466 (Hesp et al., 2004). Using the hippocampal slice preparation and electrophysiological recordings it was found that exposure to kainic acid (500 nM) was the most effective preconditioning stimulus against the suppression of evoked field responses during strong excitotoxic insult (p < 0.05). Using this model, the potential contribution of Na+K+-ATPase as an effector of preconditioning was investigated. Na+K+-ATPase is important for maintaining ionic homeostasis by actively extruding Na+, so an up-regulation in its pumping capacity could potentially cause a resistance to depolarising insult. Following kainic acid preconditioning, Na+K+-ATPase activity was elevated in hippocampal slices at the time point when an excitotoxic challenge would normally be administered (p < 0.01). A subset of slices was tested using electrophysiology and a corresponding resistance to excitotoxic insult was found. Interestingly, this preconditioning induced increase was not observed in cortical slices (p = 0.640). Overall, these experiments did support a contribution of Na+K+-ATPase regulation to preconditioning protection in the hippocampus, an area of the brain known to be particularly sensitive to excitotoxic insult.