Chronic intermittent hypoxia alters hypothalamic transcription of genes involved in metabolic regulation

Time- and behavioral state-dependent changes in posterior hypothalamic GABAA receptors contribute to the regulation of sleep

Sleep-wake behavior is regulated by a circadian rhythm, homeostatically and by additional mechanisms that determine the timing of slow-wave sleep and rapid eye movement sleep (REMS) episodes. The posterior hypothalamus coordinates the neural and humoral signals with the rest-activity cycle. It contains wake-active neurons, and is a site where stimulation of inhibitory GABA_A receptors promotes sleep, whereas their antagonism enhances wakefulness. We explored whether GABAergic mechanisms present in the posterior hypothalamus contribute to the homeostatic and other aspects of sleep-wake regulation. Using micropunches of tissue extracted from either the perifornical (PF) or dorsomedial (DM) regions of the posterior hypothalamus of rats, we determined that mRNA levels for selected subunits of GABA_A receptors (β1, β3 and ε) were higher at the end of the active period or following sleep deprivation, when the need for sleep is high, than after several hours of sleep, when sleep need is partially fulfilled. Such a pattern was present in the PF region only, and was consistent with changes in β1 subunit and GABA synthesizing enzyme (GAD) protein levels. In contrast, in the DM region, the levels of GABA_A receptor subunit mRNAs and proteins (α1, α2, β1) and GAD varied with circadian time, but were not responsive to sleep deprivation. Separate experiments with sleep-wake monitoring and local perfusion of the PF region with the GABA_A receptor antagonist bicuculline revealed that the antagonist had a weaker sleep-reducing effect when sleep need was enhanced by sleep deprivation and that the increased amount of REMS characteristic of the late sleep period was dependent on endogenous GABAergic inhibition. These results support the concept that a varying magnitude of GABAergic inhibition exerted within the PF region contributes to the homeostatic regulation of sleep and shapes its temporal pattern, whereas GABAergic mechanisms in the DM region contribute to circadian regulation.

Obstructive sleep apnoea and cardiovascular complications: perception versus knowledge

Epidemiological evidence has confirmed that obstructive sleep apnoea (OSA) significantly promotes cardiovascular risk, independent of age, sex, race and other common risk factors for cardiovascular diseases, such as smoking, drinking, obesity, diabetes mellitus, dyslipidaemia and hypertension. Patients with severe OSA exhibit a higher prevalence of coronary artery disease, heart failure and stroke. Despite the tight correlation between sleep apnoea and these comorbidities, the mechanisms behind increased cardiovascular risk in OSA remain elusive. Several theories have been postulated, including sympathetic activation, endothelial dysfunction, oxidative stress and inflammation. The association between OSA and cardiovascular diseases may be rather complicated and compounded by the presence of components of metabolic syndrome, such as obesity, hypertension, diabetes mellitus and dyslipidaemia. The present minireview updates current knowledge with regard to the cardiovascular sequelae of OSA and the mechanisms involved.

Effect of maternal chronic intermittent hypoxia during gestation on offspring growth in the rat

OBJECTIVE

Obstructive sleep apnea, a breathing disorder caused by the repetitive collapse of the upper airway during sleep, results in a state of chronic intermittent hypoxia (CIH). Although the etiology and consequences of CIH are extensively investigated in the adult, the developmental ramifications of this disease process are unknown.

DESIGN

This study was done to investigate the effect of CIH during gestation on offspring development. Pregnant female Spraque-Dawley rats were exposed to daily CIH throughout the gestational period.

RESULTS

Postnatal day-1 offspring from CIH mothers were asymmetrically growth restricted, with decreased body weights and elevated brain-weight:liver-weight ratios. Furthermore, CIH newborns had elevated heart- and brain-weight:body weight ratios, and decreased liver-weight:body weight ratios. By adulthood, body weights of growth restricted offspring were significantly greater, as were the liver-weight:body weight ratios. CIH offspring also had greater body fat deposition, were hyperglycemic and had elevated plasma levels of insulin during development into adults.

CONCLUSION

These data suggest that alteration of the maternal intrauterine environment by gestational CIH effects the long-term development of the offspring and increases the risk of the offspring to metabolic diseases in adulthood.

Circadian dependence of receptors that mediate wake-related excitatory drive to hypoglossal motoneurons

Serotonin (5-HT), norepinephrine and orexins (ORX) are the three best established mediators of wake-related activation of hypoglossal (XII) motoneurons that innervate the muscles of the tongue. Since the tongue's use is temporarily closely aligned with the rest-activity cycle, we tested whether expression of mRNA for relevant 5-HT, norepinephrine and ORX receptors varies in the XII nucleus with the rest-activity cycle. Adult rats (n=7-9/group) were decapitated at 8-9 am (near rest period onset) or at 6-7 pm (near active period onset). Tissue micropunches were extracted from medullary slices containing the XII motor and sensory external cuneate (ECN) nuclei. 5-HT2A, α1-adrenergic and ORX type 2 receptor mRNAs were quantified using RT-PCR. Only 5-HT2A receptor mRNA levels differed between the two time points and were higher at the active period onset; no differences were detected in the ECN. Consistent with the mRNA results, 5-HT2A protein levels were also higher in the XII nucleus at the active period onset than at rest onset. Thus, the endogenous serotonergic excitatory drive to XII motoneurons may be enhanced through circadian- or activity-dependent mechanisms that increase the availability of 5-HT2A receptors prior to the active period. Conversely, reduced levels of 5-HT2A receptors during the rest-sleep period may exacerbate the propensity for sleep-disordered breathing in subjects with anatomically compromised upper airway.

Proteomic analysis of mitochondrial proteins in cardiomyocytes from rats subjected to intermittent hypoxia

Intermittent hypoxia (IH) markedly enhances cardiac tolerance against ischemia/reperfusion injury, but its mechanism and molecular basis remain unclear. For exploring the expression of mitochondrial proteins induced by IH, two-dimensional electrophoresis and Thermo Finnigan LTQ mass spectrometer (MS) were applied. After comparing the protein profiles of myocardial mitochondria between IH and normoxic hearts, 14 protein spots were found to be altered more than threefold between the two groups, 11 of which were identified by Finnigan LTQ MS. Among these 11 proteins, 9 were involved in energy metabolism, including 7 that were increased after IH. The latter were identified as aldehyde dehydrogenase, methylmalonate-semialdehyde dehydrogenase, ATP synthase β chain, mitochondrial aconitase, malate dehydrogenase, electron transfer flavoprotein α subunit and sirtuin 5. Two other proteins, ubiquinol-cytochrome C reductase iron-sulfur subunit and aspartate aminotransferase, were decreased after IH. Biochemical tests for energy metabolism in mitochondria supported the proteomic results. IH exposure also increased the expression of a molecular chaperone-heat shock protein 60 and an antioxidant protein, peroxiredoxin 5. These findings will provide clues for understanding the mechanism of IH-induced cardiac protection and may lead to the development of interventional strategies designed to utilize the advantages of IH clinically.

Regionally selective effects of GABA on hypothalamic GABAA receptor mRNA in vitro

We tested whether GABAA receptor (R) subunit mRNA levels are homeostatically influenced by short-term exposure to GABA in two adjacent regions of the posterior hypothalamus. mRNA levels for seven GABAAR subunits and GABA-synthesizing enzyme (GAD) were quantified in the perifornical (PF) and dorsomedial (DM) hypothalamus following superfusion of slices for 90 min with a drug-free medium, GABA uptake blocker with or without GABAAR antagonist, gabazine, or GABAAR agonist with tetrodotoxin. Increasing endogenous GABA decreased mRNAs for all seven GABAAR subunits in the PF, and for three also in the DM, region; gabazine antagonized these effects in the PF region only and increased GAD-65 mRNA. Stimulation of GABAARs in the presence of tetrodotoxin decreased mRNA for one GABAAR subunit (beta1). We conclude that, in the PF region where GABA facilitates sleep, increased GABA release may limit GABAAR-mediated inhibition, whereas in the DM region, GABA-induced changes are mainly mediated by non-GABAA receptors.