Intermittent Hypoxia Training to Foster Brain Recovery after Ischemic Stroke in rats

Purpose: Ischemic stroke is the leading cause of disability and #5 cause of death in the US. Annually, nearly 800,000 Americans suffer an ischemic stroke, and 130,000 die. The only FDA approved treatment for stroke is recombinant tissue plasminogen activator, but this thrombolytic agent neither protects the affected tissue, nor mitigates the motor or cognitive impairments resulting from stroke. Intermittent hypoxia training (IHT) has been shown to increase cerebral blood flow, reduce oxidative stress, mobilize cerebroprotective signaling cascades and minimize behavioral deficits in a rat model of Alzheimer's Disease. Moreover, a 20 d IHT program attenuated behavioral deficits and protected neurons in ethanol-withdrawn (EW) rats, even when EW began 35 d after IHT. Therefore, we hypothesize that IHT, initiated in rats after stroke, preserves motor and cognitive function, relative to non-IHT rats. Methods: Ischemic stroke will be produced in rats by 90 min occlusion and abrupt reperfusion of the middle cerebral artery (MCA). Motor function and coordination will be evaluated by the rotarod test before and at 1 week intervals after MCA occlusion (MCAO). Rats must balance on a rotating cylinder that accelerates at a constant speed. High fall latency represents intact motor function. The Morris Water Maze (MWM) assesses spatial learning and memory. Rats are placed in an open, circular pool and must find a sunken platform within 90 s. 24 h after stroke, rats undergoing IHT will breathe moderately hypoxic gas (10% O2) for 5-8 cycles, each lasting 5-10 min, with intervening 4 min room air breathing, for 20 consecutive days. These rats will be compared to an MCAO group continuously exposed to 21% O2. At 21 d post-stroke, the brain will be harvested for analyses of infarct and neuroprotective proteins. Results: In pre-stroke testing, the time taken to solve the MWM fell progressively over 10 days, indicating spatial learning and memory, and fall latency on the rotarod lengthened over 5 days, reflecting improved coordination and possibly a training effect. These studies have established the pre-stroke baselines for assessment of IHT's impact on post-stroke recovery. Conclusions: We expect that IHT given after stroke will minimize motor and cognitive impairment by activating neuroprotective signaling cascades culminating in expression of anti-oxidant and anti-inflammatory proteins.