A new animal model of obstructive sleep apnea responding to continuous positive airway pressure.

STUDY OBJECTIVES: An improved animal model of obstructive sleep apnea (OSA) is needed for the development of effective pharmacotherapies. In humans, flexion of the neck and a supine position, two main pathogenic factors during human sleep, are associated with substantially greater OSA severity. We postulated that these two factors might generate OSA in animals. DESIGN: We developed a restraining device for conditioning to investigate the effect of the combination of 2 body positions-prone (P) or supine (S)-and 2 head positions-with the neck flexed at right angles to the body (90°) or in extension in line with the body (180°)-during sleep in 6 cats. Polysomnography was performed twice on each cat in each of the 4 sleeping positions-P180, S180, P90, or S90. The effect of continuous positive airway pressure (CPAP) treatment was then investigated in 2 cats under the most pathogenic condition. SETTING: NA. PATIENTS OR PARTICIPANTS: NA. INTERVENTIONS: NA. MEASUREMENTS AND RESULTS: Positions P180 and, S90 resulted, respectively, in the lowest and highest apnea-hypopnea index (AHI) (3 ± 1 vs 25 ± 2, P < 0.001), while P90 (18 ± 3, P<0.001) and S180 (13 ± 5, P<0.01) gave intermediate values. In position S90, an increase in slow wave sleep stage 1 (28% ± 3% vs 22% ± 3%, P<0.05) and a decrease in REM sleep (10% ± 2% vs 18% ± 2%, P<0.001) were also observed. CPAP resulted in a reduction in the AHI (8 ± 1 vs 27 ± 3, P<0.01), with the added benefit of sleep consolidation. CONCLUSION: By mimicking human pathogenic sleep conditions, we have developed a new reversible animal model of OSA.

Orexin/hypocretin and histamine: distinct roles in the control of wakefulness demonstrated using knock-out mouse models.

To determine the respective role played by orexin/hypocretin and histamine (HA) neurons in maintaining wakefulness (W), we characterized the behavioral and sleep-wake phenotypes of orexin (Ox) knock-out (-/-) mice and compared them with those of histidine-decarboxylase (HDC, HA-synthesizing enzyme)-/- mice. While both mouse strains displayed sleep fragmentation and increased paradoxical sleep (PS), they presented a number of marked differences: (1) the PS increase in HDC(-/-) mice was seen during lightness, whereas that in Ox(-/-) mice occurred during darkness; (2) contrary to HDC(-/-), Ox(-/-) mice had no W deficiency around lights-off, nor an abnormal EEG and responded to a new environment with increased W; (3) only Ox(-/-), but not HDC(-/-) mice, displayed narcolepsy and deficient W when faced with motor challenge. Thus, when placed on a wheel, wild-type (WT), but not littermate Ox(-/-) mice, voluntarily spent their time in turning it and as a result, remained highly awake; this was accompanied by dense c-fos expression in many areas of their brains, including Ox neurons in the dorsolateral hypothalamus. The W and motor deficiency of Ox(-/-) mice was due to the absence of Ox because intraventricular dosing of orexin-A restored their W amount and motor performance whereas SB-334867 (Ox1-receptor antagonist, i.p.) impaired W and locomotion of WT mice during the test. These data indicate that Ox, but not HA, promotes W through enhanced locomotion and suggest that HA and Ox neurons exert a distinct, but complementary and synergistic control of W: the neuropeptide being more involved in its behavioral aspects, whereas the amine is mainly responsible for its qualitative cognitive aspects and cortical EEG activation.

Application of histamine or serotonin to the hypoglossal nucleus increases genioglossus muscle activity across the wake-sleep cycle.

The decrease in genioglossus (GG) muscle activity during sleep, especially rapid eye movement (REM) or paradoxical sleep, can lead to airway occlusion and obstructive sleep apnoea (OSA). The hypoglossal nucleus innervating the GG muscle is under the control of serotonergic, noradrenergic and histaminergic neurons that cease firing during paradoxical sleep. The objectives of this study were to determine the effect on GG muscle activity during different wake-sleep states of the microdialysis application of serotonin, histamine (HA) or noradrenaline (NE) to the hypoglossal nucleus in freely moving cats. Six adult cats were implanted with electroencephalogram, electro-oculogram and neck electromyogram electrodes to record wake-sleep states and with GG muscle and diaphragm electrodes to record respiratory muscle activity. Microdialysis probes were inserted into the hypoglossal nucleus for monoamine application. Changes in GG muscle activity were assessed by power spectrum analysis. In the baseline conditions, tonic GG muscle activity decreased progressively and significantly from wakefulness to slow-wave sleep and even further during slow-wave sleep with ponto-geniculo-occipital waves and paradoxical sleep. Application of serotonin or HA significantly increased GG muscle activity during the wake-sleep states when compared with controls. By contrast, NE had no excitatory effect. Our results indicate that both serotonin and HA have a potent excitatory action on GG muscle activity, suggesting multiple aminergic control of upper airway muscle activity during the wake-sleep cycle. These data might help in the development of pharmacological approaches for the treatment of OSA.

Regional age-related changes in neuronal nitric oxide synthase (nNOS), messenger RNA levels and activity in SAMP8 brain.

BACKGROUND: Nitric oxide (NO) is a multifunctional molecule synthesized by three isozymes of the NO synthase (NOSs) acting as a messenger/modulator and/or a potential neurotoxin. In rodents, the role of NOSs in sleep processes and throughout aging is now well established. For example, sleep parameters are highly deteriorated in senescence accelerated-prone 8 (SAMP8) mice, a useful animal model to study aging or age-associated disorders, while the inducible form of NOS (iNOS) is down-regulated within the cortex and the sleep-structures of the brainstem. Evidence is now increasing for a role of iNOS and resulting oxidative stress but not for the constitutive expressed isozyme (nNOS). To better understand the role of nNOS in the behavioural impairments observed in SAMP8 versus SAMR1 (control) animals, we evaluated age-related variations occurring in the nNOS expression and activity and nitrites/nitrates (NOx-) levels, in three brain areas (n = 7 animals in each group). Calibrated reverse transcriptase (RT) and real-time polymerase chain reaction (PCR) and biochemical procedures were used. RESULTS: We found that the levels of nNOS mRNA decreased in the cortex and the hippocampus of 8- vs 2-month-old animals followed by an increase in 12-vs 8-month-old animals in both strains. In the brainstem, levels of nNOS mRNA decreased in an age-dependent manner in SAMP8, but not in SAMR1. Regional age-related changes were also observed in nNOS activity. Moreover, nNOS activity in hippocampus was found lower in 8-month-old SAMP8 than in SAMR1, while in the cortex and the brainstem, nNOS activities increased at 8 months and afterward decreased with age in SAMP8 and SAMR1. NOx- levels showed profiles similar to nNOS activities in the cortex and the brainstem but were undetectable in the hippocampus of SAMP8 and SAMR1. Finally, NOx- levels were higher in the cortex of 8 month-old SAMP8 than in age-matched SAMR1. CONCLUSION: Concomitant variations occurring in NO levels derived from nNOS and iNOS at an early age constitute a major factor of risk for sleep and/or memory impairments in SAMP8.