Sustained Hypoxia On The Central Nervous System Immune Regulation

Stress disturbs the maintenance of homestasis proceeding, which intiates many physiological and pathological events in both human beings and animals. Stress inhibits immune system and affects metabolism and function of nervous system . Hypoxia,one of the environmental factors in plateau, is due to a lowered oxygen pressure,which leads to oxygen deficiency of the whole organism,and even in tissues and cells, consequently disturbs physiological activities and does harm to health. It has been reported ischemic and anoxic stress significantly inhibited immune system , and affected the function of the hypothalamus-pituitary-somatotropic(HPS)-axis, hypothalamus-pituitary-thyroid(HPT)-axis and hypothalamus-pituitary-gonad(BPG)-axis. Hypoxia and focal cerebral ischemia affected on neuroendocrinology and neuroimmunology, such as brain inflammation , brain edema formation, apoptotic cell death and brain function handicap. Little is knew regarding to the effect of continual hypoxia on central neuroimmunlogy. In this study ,we focus on the effects of continual hypoxia on response of central neuroimmunlogy ,which focus on expression relativity of corticotropin-releasing factor (CRF),interleukin-6 (IL-6) and endothelin-1(ET-1).It is believed that neuropeptides, hormones and cytokines in network of neuro-immuno-endocrine system regulated central neuroimmunlogy under stress. CRF in PVN not only is the primary physiologic regulator of the hypothalamo-pituitary adrenal (HPA) axis, but also is a proinflammatory factor which rugulated central neuroimmuniogy process. Cytokines are key players for central neuroimmunlogy process during stress. Among cytokines,IL-6 is a pleiotrophic cytokine. IL-6 production in CNS may contribute to the neuropathology and neurophysiology . IL-6 appears to be invovled in the central nervous systeminflammatory response, neurodegeneration, blood-brain barrier breakdown cerebral edema under CNS ischemia . Furthermore, inflammatory cytokines in brain influence expression of vascular active substances, such as increase expression of endothelin-1 (ET-1). ET-1 is a potent vasoconstrictor that increases brain ischemic and injury. The increase of ET-1 in brain induced neuron cell damage and brain edema etc.In conclusion, hypothalamus and hipppocampus in brain synthesize and release neuropeptide , cytokines and neurotransmitter correlate with central neuroimmunlogy. HPA axis, IL-6 and ET-1 coadjust entral neuroimmunlogy process under stress.The CRF protein . CRF mRNA, IL-6 protein and IL-6mRNA in hypothalamus andhippocampus were assayed by immunohistochemistry(IHC), radioimmunoassay (RIA), PT-PCR. in situ hybridization and Western blot. We observed morphologic change of neuron cells by HE staining and electrormicroscope. Using stimulated hypobaric chambers, we observed CRF, IL-6 and ET-1 production in brain and brain injury when male adult rats exposed to different altitudes of hypoxia for different time courses. Furthermore, the role of CRF-Rl in hypoxia-induced release of CRF, IL-6 and ET-1 were examined by pretreatment of CP-154526.The results are as followed:1. Effects of continual hypoxia on CRF in PVN and the involvement of CRF-Rl in CRF releaseCRF peptide level significantly decreased during continual hypoxia of 2km(CH2km) for 2d (P<0.05 ), and returned to control level for 5d. Plasma corticosterone levels significantly increased after CH2km for Id. CRF peptide level in PVN decreased during CH5km for Id and 2d(P<0.05 ) , and significantly increased for 5d and 10d(P<0.05 ). Plasma corticosterone levels increased for Id to 15d(P<0.05 ), then returned to control level for 25d.Preinjection ot CP-154,526 (s.c 30mg/kg/day, 5d ) following the hypoxia exposure showed a decrease in CRF peptide, CRF mRNA expression in PVN .and plasma corticosterone levels compared with 5km hypoxia+vehicle group(P<0.05 ).2. Continual hypoxia induced IL-6 production and CRF-Rl modulated the IL-6 level in the hypothalamusThe iminunostaining IL-6 in PVN and SON significantly increased after CH5km for 2d. 5d and lOd (PO.05) , then returned to control level after 15d and 25d. The IL-6 mRNA in the hypothalamus remarkably increased for 5d under CH5km(P<0.05).Under CH5km for 5d, with the injection of CRF-Rl antagonist(CP-154,526), the immunostaining IL-6 and IL-6 mRNA expression in PVN markedly decreased compared to hypoxia group (PO.05) .3. Continual hypoxia induced IL-6 production and CRF-Rl modulated the IL-6 level in the hippocampusFrom Id to 5d , the immunostaining IL-6 in the hippocampus had no siginficant difference compared to control level under CH2km(P>0.05). During CH5km for 2d. 5d. lOd and 15d, the immunostaining IL-6 in hippocampus CAl, CA2 and CA3 significantly increased(P<0.05). During CH5km for 25d, IL-6 in hippocampus CAl still increased (P<0.05), but IL-6 in hippocampus CA2 and CA3 returned to control level.Under CH5km for 3d . IL-6 mRNA in hippocampus markedly increased by 139.24% compared to control level(P<0.05). Under CH5km for 5d, with the injection of CRF-Rl antagonist(CP-154,526), the immunostaining IL-6 and IL-6 mRNA decreased in hippocampus CAl compared to hypoxia group(P<0.05).4. Effects of continual hypoxia on brain water content and ET-1 expression in hippocampusCompared to control. CH5km for 5d increased brain water (P<0.05 ). Using HE staining and electrormicroscope technique, we obverved that necrosis and apoptotic hippocampus cells increased and chondriosome swelling etc.CH5km for 5d. lOd. 15d and 25d, the immnuostaining of ET-1 in hippocampusCA1, CA2 and CA3 markedly increased(P<0.05).Under CH5km for 5d, HIF-la in hippocampus significantly increased(P<0.05).5. Acute and continual hypoxia increased plasama IL-6 levelCompared to control level, plasma IL-6 level had no significantly difference during CH2km for Id and 2d. Plasma IL-6 levels remarkably increased under hypoxia of 5km for 4h,8h , 24h, 2d and 5d (PO.05). then returned to control level for 25d.Under CH5km for 5d, with the injection of CRF-R1 antagonist(CP-154,526), plasma IL-6 level decreased compared to hypoxia group(P<0.05).6.Hypoxia-stimulatcd prolactin release and prolactin mRNA expression in rat pituitary and CRF-R1 regulated PRL levelAcute hypoxia of 5km for 8h and 24h increased the plasma PRL(pPRL) levels , but decreased for 2h (PO.05).CH2km for 2 and 5 d markedly reduced immunostaining PRL(iPRL) in the pituitary and increased pPRL levels(P<0.05). CH5km for 5d, lOd, 15d, and 25d markedly reduced the iPRL in the pituitary(P<0.05) and increased the pPRL level in all the hypoxic groups (for l-25d) (PO.05). Intermittent hypoxia of 2km(IH2km) for 2d and 5d(4h/d) decreased the iPRL in the pituitary(PO.OS) and significantly increased pPRL levels(PO.05). IH5km for Id. 5d and 10 d markedly decreased the iPRL in the pituitary (PO.05), but significantly increased the pPRL level for 2d and 5d(P<0.05). During IH2km or IH5km exposures for 15d both the iPRL and pPRL returned to control levels .Sole IH2km and cold caused no significant changes of pPRL levels. While pPRL levels were significantly increased following IH5km+cold, IH5km, IH5km+restraint, and restraint(P<0.05).Under CH5km for 5d. CRF-R1 antagonist(CP-154,526) markedly result in an increase of iPRL levels and PRL mRNA expression in the pituitary(P<0.05) compared to hypoxia group.The results above suggested that:1. Continual hypoxia affect on CRF expression in PVN , which depended on the severity and duration of hypoxia. Hypoxia-induced CRF via CRF-Rl increase of CRF expression in PVN(positively feedback).2. Continual hypoxia enhanced IL-6 production in hypothalamus. Hypoxia-induced CRF might modulate IL-6 expression in hypothalamus via CRF-Rl.3. Continual hypoxia enhanced expression of IL-6 and IL-6mRNA in hippocampus. Hypoxia-induced CRF via CRF-Rl parkly modulated IL-6 expression in hippocampus.4. Continual hypoxia elicited brain injury and edema, which may be associated with IL-6 and ET-1 expression in brain.5. Acute and chronic hypoxia increased plasma IL-6 level. Hypoxia-induced CRF via CRF-Rl might enhanced the increase of plasma IL-6.6. Hypoxia enhanced PRL release from pituitary, which depended on the severity and duration of hypoxia.Continual hypoxia had more obvious effects than that of intermittent hypoxia, and psychological stress had more notable effect than that of physiological stress.Hypoxia-induced CRF in the hypothalamus via CRF-Rl might enhanced PRL relaease from pituitary.In conclusion, continual hypoxia induced CRF expression and release in hypothalamus. Hypoxia-induced CRF not only activated HPA axis ,but also enhanced IL-6 production in hypothalamus ,hippocampus and plasma . An increase of IL-6 in CNS during continual hypoxia might associated brain inflammation , brain inury(brain edema.neuron apoptotisis et al.) and increased ET-1 production. Hypoxia-induced CRF in the hypothalamus via CRF-Rl might regulated CRF expression in PVN. IL-6 level in brain and plasma. CRF, IL-6 and ET-1 induced central neuroimmunlogy process, then arosed brain injury under hypoxia stress. y Continual hypoxia-acrivated PRL might affect and regulate IL-6 production and...