| Objective:In recent years, with the incidence of obesity and metabolic syndrome rising, incidence of obstructive sleep apnea hypopnea syndrome (OSAHS) increased year by year. The disease’s characteristic is recurrent upper airway obstruction during sleep. Long-term hypoxia, hypercapnia and low sleep quality can induce hypertension, myocardial infarction, stroke and other diseases. At present the reason and mechanisms of OSAHS development are not fully clear. Orexin from the neurons in the hypothalamus has established as important neuropeptide for feeding, energy metabolism, endocrine, cardiovascular activity, sleep-arousal cycle and other physiological function. Recently, Orexin has been found to regulate respiratory activity in respiratory center. Further more, plasma Orexin A levels was lower in OSAHS patients. Orexin-knockout mice performed sleep apnea. In the present study, we used a rat model of chronic hypobaric hypoxia (CHH) to investigate Orexin A (OXA) expression in the hypothalamus and its effect on respiration. Test the hypothesis that chronic hypobaric hypoxia treatment changes ventilation, hypoglossal nerve discharge and Orexin system in rat. It will determine Orexin contribution in the regulation respiration of OSAHS.Methods:1. Animal preparation and (CHH) model:(1) The Sprague-Dawley rats were exposed to hypobaric hypoxia in a complete airtight chamber (the altitude at 5000m, PO2 53.9KPa, concentration of O2 10%-11.2%) 6h/day for 28 days. The rats were observed their behavior in and out of chamber.2. At the end of 28 days, (1) Rats were measured of blood gas, lung pathology and pulmonary function; (2) Expression and distribution of Orexin A-like-immunoreactivity in hypothalamus were observed by immunohistochemistry. The staining density of Orexin A expression neurons in hypothalamus was evaluated as relative optical density. (3) Hypoglossal nerve discharge was recorded by bipolar platinum-iridium electrode. (4) The upper airway (throat+main bronchus) of rat was scanned by CT and three-dimensional image was reconstructed. 3. The Orexin containing neurons of LH were lesioned by microinjection of Orexin-SAP bilaterally. Two weeks after the treatment, the lung function, Orexin A expression in LH, hypoglossal nerve discharge were detected by the methods mentioned above.Results:1. The CHH model was evaluated on the basis of blood gas, lung pathology and pulmonary function. Blood gas analysis showed:pH and PO2 decreased, PCO2 increased. Lung pathological change showed pulmonary edema, congestive and hemorrhage. Compared with control rats, pulmonary function in CHH rats had deteriorated with evidence of decreased dynamic compliance (P<0.05, n=6) and increased airway resistance (P<0.05, n=6).2. In the hypothalamus, OXA expression was located mainly in the lateral hypothalamus and perifornical nucleus with significantly higher OXA expression detected in CHH compared with control rats. The relative optical density (ROD) of OXA positive cells in hypothalamus was greater in the CHH rats than in control rats (**P<0.01,n=5).3. The intensity and frequency of hypoglossal nerve discharge were both significantly decreased in CHH compared with control groups (**P<0.01, *P<0.05, respectively, n=6).4. The upper airway volume was no significant difference between CHH and control rats using three-dimensional image reconstruction.5. There was significant loss of Nissl bodies and Orexin neurons in the LH of Orexin-SAP-treated rats relative to the normal saline (NS) treated rats. Few residual Orexin neurons remained in Orexin-SAP treated rats, two weeks after treatment. There was significantly decreased in pulmonary dynamic compliance and increased in airway resistance in LH lesion group (both ***P<0.001, n=6 v.s. NS treated group). And the intensity and frequency of hypoglossal nerve discharge were significantly decreased in LH lesion group compared with the NS treated group (**P<0.01, *P<0.05 respectively, n=6). Conclusions:1. A rat model of chronic hypobaric hypoxia was produced in hypobaric hypoxia chamber successfully.2. At the end of 28 days, there were decreased pH, PO2 and increased PCO2 in CHH rats. The Lung pathological changed and pulmonary function had deteriorated in CHH rats. Hypoglossal nerve discharge was significantly reduced. There was no significant difference in upper airway between CHH and control rat by CT.3. OXA maybe the important role in central regulation on respiration in CHH rats with the experimental evidences of OXA’s synthesis are significantly increased in hypothalamus.4. In Orexin-SAP treated rats, expression of Orexin A neurons, lung ventilation and hypoglossal nerve discharge were decreased significantly than in NS treated rats. It shows that Orexin neurons administrate hypoglossal nerves on the upper airway control activities.5. The findings of the present study demonstrate the weakened hypoglossal nerve discharge is due to endogenous Orexin less, as in number or amount. Following it genioglossus activity decreased, which caused the upper airway collapse and hypoventilation in OSAHS. Expression of Orexin A increased may be attributed to enhancing respiratory activity in CHH rats. |
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