Rationale: Sleep fragmentation (SF) is one of the major characteristics of sleep apnea, and has been implicated in its morbid consequences, which encompass excessive daytime sleepiness and neurocognitive impairments. We hypothesized that absence of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity is neuroprotective in SF-induced cognitive impairments. Objectives: To examine whether increased NADPH oxidase activity may play a role in SF-induced central nervous system dysfunction. Methods: The effect of chronic SF during the sleep-predominant period on sleep architecture, sleep latency, spatial memory, and oxidative stress parameters was assessed in mice lacking NADPH oxidase activity (gp91phox-/Y ) and wild-type littermates. Measurements and Main Results: SF for 15 days was not associated with differences in sleep duration, sleep state distribution, or sleep latency in both gp91phox-/Y and control mice. However, on a standard place training task, gp91phox-/Y mice displayed normal learning and were protected from the spatial learning deficits observed in wildtype littermates exposed to SF. Moreover, anxiety levels were increased in wild-type mice exposed to SF, whereas no changes emerged in gp91phox-/Y mice. Additionally, wild-type mice, but not gp91phox-/Y mice, had significantly elevated NADPH oxidase gene expression and activity, and in malondialdehyde and 8-oxo-29-deoxyguanosine levels in cortical and hippocampal lysates after SF exposures. Conclusions: This work substantiates an important role for NADPH oxidase in hippocampal memory impairments induced by SF, modeling sleep apnea. Targeting NADPH oxidase, therefore, is expected to minimize hippocampal impairments from both intermittent hypoxia and SF associated with the disease. Keywords: NADPH oxidase; sleep fragmentation; neurocognitive impairmentsThe manifestations of obstructive sleep apnea (OSA) reflect the interactions of intermittent hypoxia (IH), intermittent hypercapnia, increased intrathoracic pressure swings, and sleep fragmentation (SF) as elicited by the episodic changes in upper airway resistance during sleep. SF is a common phenomenon among several clinical disorders, and can lead to impaired cognitive function via mechanisms that remain poorly understood (1). Indeed, uninterrupted sleep for a minimum length of time is required for optimal daytime vigilance and neurocognitive function (1-3). Preliminary studies in rodents using short-term SF paradigms have also confirmed the adverse effects of SF on learning and seem to be independent of adenosine-mediated synaptic inhibition (4-7).In clinical populations with severe SF (e.g., in OSA) total sleep time typically diminishes only slightly (8). The effects of experimentally induced SF on sleep patterns have not been critically characterized in rodents. It is likely that OSA-induced sleep perturbations are accompanied by obvious cognitive deficits because of increased levels of systemic markers of oxidative stress and inflammation, the latter leading to gray matter loss in neural...

BackgroundSleepiness and cognitive dysfunction are recognized as prominent consequences of sleep deprivation. Experimentally induced short-term sleep fragmentation, even in the absence of any reductions in total sleep duration, will lead to the emergence of excessive daytime sleepiness and cognitive impairments in humans. Tumor necrosis factor (TNF)-α has important regulatory effects on sleep, and seems to play a role in the occurrence of excessive daytime sleepiness in children who have disrupted sleep as a result of obstructive sleep apnea, a condition associated with prominent sleep fragmentation. The aim of this study was to examine role of the TNF-α pathway after long-term sleep fragmentation in mice.MethodsThe effect of chronic sleep fragmentation during the sleep-predominant period on sleep architecture, sleep latency, cognitive function, behavior, and inflammatory markers was assessed in C57BL/6 J and in mice lacking the TNF-α receptor (double knockout mice). In addition, we also assessed the above parameters in C57BL/6 J mice after injection of a TNF-α neutralizing antibody.ResultsMice subjected to chronic sleep fragmentation had preserved sleep duration, sleep state distribution, and cumulative delta frequency power, but also exhibited excessive sleepiness, altered cognitive abilities and mood correlates, reduced cyclic AMP response element-binding protein phosphorylation and transcriptional activity, and increased phosphodiesterase-4 expression, in the absence of AMP kinase-α phosphorylation and ATP changes. Selective increases in cortical expression of TNF-α primarily circumscribed to neurons emerged. Consequently, sleepiness and cognitive dysfunction were absent in TNF-α double receptor knockout mice subjected to sleep fragmentation, and similarly, treatment with a TNF-α neutralizing antibody abrogated sleep fragmentation-induced learning deficits and increases in sleep propensity.ConclusionsTaken together, our findings show that recurrent arousals during sleep, as happens during sleep apnea, induce excessive sleepiness via activation of inflammatory mechanisms, and more specifically TNF-α-dependent pathways, despite preserved sleep duration.

TNF-α plays critical roles in host-defense, sleep-wake regulation, and the pathogenesis of various disorders. Increases in the concentration of circulating TNF-α after either sleep deprivation or sleep fragmentation (SF) appear to underlie excessive daytime sleepiness in patients with sleep apnea (OSA). Following baseline recordings, mice were subjected to 15 days of SF (daily for 12 h/day from 07.00 h to 19.00 h), and sleep parameters were recorded on days1, 7 and 15. Sleep architecture and sleep propensity were assessed in both C57BL/6J and in TNF-α double receptor KO mice (TNFR KO). To further confirm the role of TNF-α, we also assessed the effect of treatment with a TNF- α neutralizing antibody in C57BL/6J mice. SF was not associated with major changes in global sleep architecture in C57BL/6J and TNFR KO mice. TNFR KO mice showed higher baseline SWS delta power. Further, following 15 days of SF, mice injected with TNF-α neutralizing antibody and TNFR KO mice showed increased EEG SWS activity. However, SWS latency, indicative of increased propensity to sleep, was only decreased in C57BL/6J, and was unaffected in TNFR KO mice as well as in C57BL/6J mice exposed to SF but treated with TNF-α neutralizing antibody. Taken together, our findings show that the excessive sleepiness incurred by recurrent arousals during sleep may be due to activation of TNF-alpha-dependent inflammatory pathways, despite the presence of preserved sleep duration and global sleep architecture.

Kaushal N, Ramesh V, Gozal D. Human apolipoprotein E4 targeted replacement in mice reveals increased susceptibility to sleep disruption and intermittent hypoxia.

Sleep is an important physiological process underlying maintenance of physical, mental and emotional health. Consequently, sleep deprivation (SD) is associated with adverse consequences and increases the risk for anxiety, immune, and cognitive disorders. SD is characterized by increased energy expenditure responses and sleep rebound upon recovery that are regulated by homeostatic processes, which in turn are influenced by stress. Since all previous studies on SD were conducted in a setting of social isolation, the impact of the social contextual setting is unknown. Therefore, we used a relatively stress-free SD paradigm in mice to assess the impact of social isolation on sleep, wakefulness and delta electroencephalogram (EEG) power during non-rapid eye movement (NREM) sleep. Paired or isolated C57BL/6J adult chronically-implanted male mice were exposed to SD for 6 hours and telemetric polygraphic recordings were conducted, including 18 hours recovery. Recovery from SD in the paired group showed a significant decrease in wake and significant increase in NREM sleep and rapid eye movement (REM), and a similar, albeit less robust response occurred in the isolated mice. Delta power during NREM sleep was increased in both groups immediately following SD, but paired mice exhibited significantly higher delta power throughout the dark period. The increase in body temperature and gross motor activity observed during the SD procedure was decreased during the dark period. In both open field and elevated plus maze tests, socially isolated mice showed significantly higher anxiety than paired mice. The homeostatic processes altered by SD are differentially affected in paired and isolated mice, suggesting that the social context of isolation stress may adversely affect the quantity and quality of sleep in mice.