Neuroprotection in hippocampal slices from the hibernating species Arctic ground squirrel, Spermophilus parryii

Thesis (Ph.D.) University of Alaska Fairbanks, 2005Stroke is the third leading cause of death in the U.S. and the leading cause of adult onset disability worldwide. Despite tremendous efforts to find therapeutics, only one currently approved treatment for stroke exists which is indicated for use in less than 5% of stroke victims. During a stroke, the brain experiences oxygen and nutrient deprivation due to lack of blood flow (i.e., ischemia) and tissue destruction ensues. Hibernating Arctic ground squirrels (AGS), Spermophilus parryii, are able to survive profound decreases in blood flow and cerebral perfusion during torpor, and return of blood flow (i.e., reperfusion) during intermittent euthermic periods without neurological damage. Hibernating species are a natural model of tolerance to insults, such as ischemia, that would be injurious to non-hibernating species, and are a novel model for investigating much needed therapeutics for pathologies such as stroke. Tolerance to traumatic brain injury demonstrated in hibernating AGS in vivo could be due to tissue properties, circulating factors or hypothermia. To investigate mechanisms of tolerance in brain of hibernating animals, the current project established a chronic culture system for hippocampal slices from AGS at 37°C. By using this in vitro approach, tissue properties of AGS brain could be assessed without effects of circulating factors or the protective nature of hypothermia. This project determined whether an intrinsic tissue tolerance to oxygen and nutrient deprivation, an in vitro model of ischemia-reperfusion, persists in chronic AGS slice culture and addressed associated mechanisms. Here, for the first time, slices from hibernating AGS were shown to possess a persistent tolerance to oxygen and nutrient deprivation. Thus, intrinsic tissue properties in hippocampus of hibernating AGS confer tolerance to oxygen and nutrient deprivation in addition to hypothermia. Evidence in the literature supports that neuroprotective factors are present in serum and tissue of hibernating animals, and here a preliminary investigation suggests that factors in AGS serum may play a role in protection in brain of hibernating AGS. Finally, a model is proposed that incorporates these findings, which suggests that mimicking properties of tissue and serum from hibernating animals in non-hibernating species may yield success in developing efficacious stroke therapeutics.Introduction -- Hibernating species are a natural model of tolerance in which to investigate neuroprotective mechanisms -- Investigation of protective mechanisms relevant to stroke is well warrented -- Etiology of ischemia -- Pathogenesis of ischemia -- The hippocampus is selectively vulnerable to ischemia -- Hibernation as a model of neuroprotection -- Hibernation as a model of neuroprotection -- Hibernation physiology -- Evidence of neuroprotection in hibernating animals -- Evidence of protective factors in tissue and serum of hibernating species -- Hypothermia occurs during hibernation and is a therapeutic strategy for stroke -- Hippocampal slice culture is an approach to investigate neuroprotection -- Establishing a chronic culture system for Arctic ground squirrel hippocampus -- Selection of euthermic controls -- Arctic ground squirrel hippocampus is selectively vulnerable -- Scope and aims of the project -- References -- Rationale and methods for hippocampal slice culture -- Tolerance to oxygen and nutrient deprivation and N-methyl-D-aspartate persists in cultured hippocampal slices from hibernating Arctic ground squirrel -- Potential for discovery of neuroprotective factors in serum and tissue isolated from hibernating species -- Conclusion -- Summary of findings -- Alternative explanation of tolerance to oxygen and nutrient deprivation and N-methyl-D-aspartate in Arctic ground squirrel slices -- Maintenance of energy balance can yield tolerance -- Evidence of maintenance of energy balance in hibernating animals -- Proposed model of tolerance in brain of hibernating animals -- What hibernating animals and ischemi preconditioning have in common -- What can be learned from hibernating animals regarding selective vulnerability -- What can be learned from hibernating animals regarding stroke therapeutics -- References -- Appendices