Neuronal death during combined intermittent hypoxia / hypercapnia is due to mitochondrial 1 dysfunction 2

23 24 Breathing-disordered states, such as in obstructive sleep apnea (OSA), which are cyclical in 25 nature, have been postulated to induce neurocognitive morbidity in both pediatric and adult 26 populations. The oscillatory nature of intermittent hypoxia, especially when chronic, may mimic 27 the paradigm of ischemia/reperfusion in that tissues and cells are exposed to episodes of low and 28 high O2 and this may lead to oxidant stress. Therefore, we decided to explore the potential 29 contribution of oxidant stress in our intermittent hypoxia/hypercapnia animal model and the role 30 that mitochondria might play in this stress. Neonatal mice were exposed to intermittent 31 hypoxia/hypercapnia for 10d and 2 weeks. Combined intermittent hypoxia/hypercapnia led to a 32 marked increase in apoptotic cell death in the cerebral cortex. Oxygen consumption studies in 33 isolated mitochondria from intermittent hypoxia/hypercapnia-exposed brains demonstrated 34 significant reductions in both state 4 and state 3 respiratory activities by approximately 60% and 35 75%, respectively. Electron paramagnetic resonance (EPR) spectroscopy registered a significant 36 increase in superoxide production during non-phosphorylating state 4 by 37% although 37 superoxide leakage during state 3 didn’t increase upon treatment. Neuronal superoxide-specific 38 dihydroethidium-oxidation was also greater in exposed animals. These studies indicate that 39 intermittent hypoxia/hypercapnia leads to oxidative stress due to mitochondrial response within 40 the mouse CNS. 41 42