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Peña-Ortega F. Clinical and experimental aspects of breathing modulation by inflammation. Auton Neurosci 2018; 216:72-86. [PMID: 30503161 DOI: 10.1016/j.autneu.2018.11.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 11/06/2018] [Accepted: 11/07/2018] [Indexed: 12/19/2022]
Abstract
Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.
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Affiliation(s)
- Fernando Peña-Ortega
- Departamento de Neurobiología del Desarrollo y Neurofisiología, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Querétaro, QRO 76230, México.
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Millar LJ, Shi L, Hoerder-Suabedissen A, Molnár Z. Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges. Front Cell Neurosci 2017; 11:78. [PMID: 28533743 PMCID: PMC5420571 DOI: 10.3389/fncel.2017.00078] [Citation(s) in RCA: 206] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 03/07/2017] [Indexed: 12/11/2022] Open
Abstract
Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.
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Affiliation(s)
- Lancelot J. Millar
- Molnár Group, Department of Physiology, Anatomy and Genetics, University of OxfordOxford, UK
| | - Lei Shi
- Molnár Group, Department of Physiology, Anatomy and Genetics, University of OxfordOxford, UK
- JNU-HKUST Joint Laboratory for Neuroscience and Innovative Drug Research, College of Pharmacy, Jinan UniversityGuangzhou, China
| | | | - Zoltán Molnár
- Molnár Group, Department of Physiology, Anatomy and Genetics, University of OxfordOxford, UK
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Prenatal Systemic Hypoxia-Ischemia and Oligodendroglia Loss in Cerebellum. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 949:333-345. [PMID: 27714697 DOI: 10.1007/978-3-319-40764-7_16] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Hypoxic-ischemic (HI) injury is an important cause of death and disabilities. Despite all improvements in neonatal care, the number of children who suffer some kind of injury during birth has remained stable in the last decade. A great number of studies have shown alterations in neural cells and many animal models have been proposed in the last 5 decades. Robinson et al. (2005) proposed an HI model in which the uterine arteries are temporarily clamped on the 18th gestation day. The findings were quite similar to the ones observed in postmortem studies. The white matter is clearly damaged, and a great amount of astrogliosis takes place both in the gray and white matters. Motor changes were also found but no data regarding the cerebellum, an important structure related to motor performance, was presented. Using this model, we have shown an increased level of iNOS at P0 and microgliosis and astrogliosis at P9, and astrogliosis at P23 (up to 4 weeks from the insult). NO is important in migration, maturation, and synaptic plasticity, but in exacerbated levels it may also contribute to cellular and tissue damage. We have also evaluated oligodendroglia development in the cerebellum. At P9 in HI animals, we found a decrease in the number of PDGFRα+ cells and an apparent delay in myelination, suggesting a failure in oligodendroglial progenitors migration/maturation and/or in the myelination process. These results point to an injury in cerebellar development that might help to explain the motor problems in HI.
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Abstract
Resveratrol is a natural polyphenol enriched in Polygonum cuspidatum and has been found to afford neuroprotective effects against neuroinflammation in the brain. Activated microglia can secrete various pro-inflammatory cytokines and neurotoxic mediators, which may contribute to hypoxic brain injuries. The aim of this study is to investigate the potential role of resveratrol in attenuating hypoxia-induced neurotoxicity via its anti-inflammatory actions through in vitro models of the BV-2 microglial cell line and primary microglia. We found that resveratrol significantly inhibited hypoxia-induced microglial activation and reduced subsequent release of pro-inflammatory factors. In addition, resveratrol inhibited the hypoxia-induced degradation of IκB-alpha and phosphorylation of p65 NF-κB protein. Hypoxia-induced ERK1/2 and JNK phosphorylation was also strongly inhibited by resveratrol, whereas resveratrol had no effect on hypoxia-stimulated p38 MAPK phosphorylation. Importantly, treating primary cortical neurons with conditioned medium (CM) from hypoxia-stimulated microglia induced neuronal apoptosis, which was reversed by CM co-treated with resveratrol. Taken together, resveratrol exerts neuroprotection against hypoxia-induced neurotoxicity through its anti-inflammatory effects in microglia. These effects were mediated, at least in part, by suppressing the activation of NF-ĸB, ERK and JNK MAPK signaling pathways.
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5
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Xiang HF, Cao DH, Yang YQ, Wang HQ, Zhu LJ, Ruan BH, Du J, Wang MC. Isoflurane protects against injury caused by deprivation of oxygen and glucose in microglia through regulation of the Toll-like receptor 4 pathway. J Mol Neurosci 2014; 54:664-70. [PMID: 25012594 DOI: 10.1007/s12031-014-0373-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 07/01/2014] [Indexed: 12/19/2022]
Abstract
Oxygen and glucose deprivation (OGD) are the most important factors related to tissue damage resulting from stroke. Microglial cells have been found to be very vulnerable to ischemia and OGD. It has been reported that isoflurane exposure can protect the mammalian brain from insults such as ischemic stroke; however, the effects of isoflurane on OGD-induced injury in microglia are as yet unknown. In this study, we investigated the effects of isoflurane on OGD-induced injury in microglia. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and lactate dehydrogenase (LDH) revealed that OGD did indeed induce cell death in microglia. However, isoflurane preconditioning attenuated OGD-induced cell death. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay demonstrated that isoflurane treatment alleviated OGD-induced apoptosis. Toll-like receptor 4 (TLR4) plays a considerable role in the induction of innate immune and inflammatory responses. Our results indicate that isoflurane preconditioning inhibits the upregulation of TLR4 as well as the activation of its downstream molecules, such as c-Jun N-terminal kinase (JNK) and nuclear factor kappa B (NF-κB), in BV-2 microglia exposed to OGD. Importantly, we also found that isoflurane pretreatment significantly reduces the production of proinflammatory factors such as tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), IL-β, and nitric oxide (NO). The results indicate that TLR4 and its downstream NF-κB-dependent signaling pathway contribute to the neuroprotection of microglia exposed to OGD/reoxygenation by administration of isoflurane.
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Affiliation(s)
- Hai-Fei Xiang
- Department of Anesthesiology, Taizhou Hospital of Zhejiang Province, No. 150 Ximen Street, Linhai, Zhejiang Province, 317000, China
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Zhang Q, Yuan L, Liu D, Wang J, Wang S, Zhang Q, Gong Y, Liu H, Hao A, Wang Z. Hydrogen sulfide attenuates hypoxia-induced neurotoxicity through inhibiting microglial activation. Pharmacol Res 2014; 84:32-44. [DOI: 10.1016/j.phrs.2014.04.009] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Revised: 03/28/2014] [Accepted: 04/17/2014] [Indexed: 10/25/2022]
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Wang J, Hou J, Zhang P, Li D, Zhang C, Liu J. Geniposide Reduces Inflammatory Responses of Oxygen-Glucose Deprived Rat Microglial Cells via Inhibition of the TLR4 Signaling Pathway. Neurochem Res 2012; 37:2235-48. [DOI: 10.1007/s11064-012-0852-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 07/02/2012] [Accepted: 07/20/2012] [Indexed: 12/11/2022]
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Kaur C, Rathnasamy G, Ling EA. Roles of activated microglia in hypoxia induced neuroinflammation in the developing brain and the retina. J Neuroimmune Pharmacol 2012; 8:66-78. [PMID: 22367679 DOI: 10.1007/s11481-012-9347-2] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Accepted: 02/09/2012] [Indexed: 12/14/2022]
Abstract
Amoeboid microglial cells (AMCs) in the developing brain display surface receptors and antigens shared by the monocyte-derived tissue macrophages. Activation of AMCs in the perinatal brain has been associated with periventricular white matter damage in hypoxic-ischemic conditions. The periventricular white matter, where the AMCs preponderate, is selectively vulnerable to hypoxia as manifested by death of premyelinating oligodendrocytes and degeneration of axons leading to neonatal mortality and long-term neurodevelopmental deficits. AMCs respond vigorously to hypoxia by producing excess amounts of inflammatory cytokines e.g. the tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) along with glutamate, nitric oxide (NO) and reactive oxygen species which collectively cause oligodendrocyte death, axonal degeneration as well as disruption of the immature blood brain barrier. A similar phenomenon is observed in the hypoxic developing cerebellum in which activated AMCs induced Purkinje neuronal death through production of TNF-α and IL-1β via their respective receptors. Hypoxia is also implicated in retinopathy of prematurity in which activation of AMCs has been shown to cause retinal ganglion cell death through production of TNF-α and IL-1β and NO. Because AMCs play a pivotal role in hypoxic injuries in the developing brain affecting both neurons and oligodendrocytes, a fuller understanding of the underlying molecular mechanisms of microglial activation under such conditions would be desirable for designing of a novel therapeutic strategy for management of hypoxic damage.
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Affiliation(s)
- Charanjit Kaur
- Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, 4 Medical Drive, MD10, Singapore 117597, Singapore.
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9
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Changes in nitric oxide content following injury to the neonatal rat brain. Brain Res 2011; 1367:319-29. [DOI: 10.1016/j.brainres.2010.10.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2010] [Revised: 09/30/2010] [Accepted: 10/01/2010] [Indexed: 01/05/2023]
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10
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Haynes RL, Folkerth RD, Trachtenberg FL, Volpe JJ, Kinney HC. Nitrosative stress and inducible nitric oxide synthase expression in periventricular leukomalacia. Acta Neuropathol 2009; 118:391-9. [PMID: 19415311 DOI: 10.1007/s00401-009-0540-1] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2009] [Revised: 04/14/2009] [Accepted: 04/14/2009] [Indexed: 12/13/2022]
Abstract
Periventricular leukomalacia (PVL) is a lesion of the immature cerebral white matter in the perinatal period and associated predominantly with prematurity and cerebral ischemia/reperfusion as well as inflammation due to maternofetal infection. It consists of focal necrosis in the periventricular region and diffuse gliosis with microglial activation and premyelinating oligodendrocyte (pre-OL) injury in the surrounding white matter. We previously showed nitrotyrosine in pre-OLs in PVL, suggesting involvement of nitrosative stress in this disorder. Here we hypothesize that inducible nitric oxide synthase (iNOS) expression is increased in PVL relative to controls. Using immunocytochemistry in human archival tissue, the density of iNOS-expressing cells was determined in the cerebral white matter of 15 PVL cases [29-51 postconceptional (PC) weeks] and 16 control cases (20-144 PC weeks). Using a standardization score of 0-3, the density of iNOS-positive cells was significantly increased in the diffuse component of PVL (score of 1.8 +/- 0.3) cases compared to controls (score of 0.7 +/- 0.3) (P = 0.01). Intense iNOS expression occurred in reactive astrocytes in acute through chronic stages and in activated microglia primarily in the acute stage, suggesting an early role for microglial iNOS in PVL's pathogenesis. This study supports an important role for iNOS-induced nitrosative stress in the reactive/inflammatory component of PVL.
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Affiliation(s)
- Robin L Haynes
- Departments of Pathology, Children's Hospital Boston, Boston, MA 02115, USA.
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11
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Kaur C, Ling E. Periventricular white matter damage in the hypoxic neonatal brain: Role of microglial cells. Prog Neurobiol 2009; 87:264-80. [DOI: 10.1016/j.pneurobio.2009.01.003] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2008] [Revised: 11/12/2008] [Accepted: 01/08/2009] [Indexed: 01/22/2023]
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12
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Ji KA, Yang MS, Jeong HK, Min KJ, Kang SH, Jou I, Joe EH. Resident microglia die and infiltrated neutrophils and monocytes become major inflammatory cells in lipopolysaccharide-injected brain. Glia 2007; 55:1577-88. [PMID: 17823975 DOI: 10.1002/glia.20571] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Generally, it has been accepted that microglia play important roles in brain inflammation. However, recently several studies suggested possible infiltration of blood neutrophils and monocytes into the brain. To understand contribution of microglia and blood inflammatory cells to brain inflammation, the behavior of microglia, neutrophils, and monocytes was investigated in LPS (lipopolysaccharide)-injected substantia nigra pars compacta, cortex, and hippocampus of normal and/or leukopenic rats using specific markers of neutrophils (myeloperoxidase, MPO), and microglia and monocytes (ionized calcium binding adaptor molecule-1, Iba-1), as well as a general marker for these inflammatory cells (CD11b). CD11b-immunopositive (CD11b(+)) cells and Iba-1(+) cells displayed similar behavior in intact and LPS-injected brain at 6 h after the injection. Interestingly, however, CD11b(+) cells and Iba-1(+) cells displayed significantly different behavior at 12 h: Iba-1(+) cells disappeared while CD11b(+) cells became round in shape. We found that CD11b/Iba-1-double positive (CD11b(+)/Iba-1(+)) ramified microglia died within 6 h after LPS injection. The round CD11b(+) cells detected at 12 h were MPO(+). These CD11b(+)/MPO(+) cells were not found in leukopenic rats, suggestive of neutrophil infiltration. MPO(+) neutrophils expressed inducible nitric oxide synthase, interleukin-1beta, cyclooxygenase-2, and monocyte chemoattractant protein-1, but died within 18 h. CD11b(+) cells detected at 24 h appeared to be infiltrated monocytes, since these cells were once labeled with Iba-1 and were not found in leukopenic rats. Furthermore, transplanted monocytes were detectable in LPS-injected brain. These results suggest that at least a part of neutrophils and monocytes could have been misinterpreted as activated microglia in inflamed brain.
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Affiliation(s)
- Kyung-Ae Ji
- Neuroscience Graduate Program, Ajou University School of Medicine, Suwon, Korea
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Kaur C, Dheen ST, Ling EA. From blood to brain: amoeboid microglial cell, a nascent macrophage and its functions in developing brain. Acta Pharmacol Sin 2007; 28:1087-96. [PMID: 17640468 DOI: 10.1111/j.1745-7254.2007.00625.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Amoeboid microglial cells (AMC) in the developing brain are active macrophages. The macrophagic nature of these cells has been demonstrated by many methods, such as the localization of various hydrolytic enzymes and the presence of complement type 3 surface receptors in them. More importantly is the direct visualization of these cells engaged in the phagocytosis of degenerating cells at the ultrastructural level. Further evidence of them being active macrophages is the avid internalization of tracers administered by the intravenous or intraperitoneal routes in developing rats. The potential involvement of AMC in immune functions is supported by the induced expression of major histocompatibility complex class I and II antigens on them when challenged by lipopolysaccharide or interferon-gamma. Immunosuppressive drugs, such as glucocorticoids and immune function-enhancing drugs like melatonin, affect the expression of surface receptors and antigens and the release of cytokines by AMC. Recent studies in our laboratory have shown the expression of insulin-like growth factors, endothelins, 2',3'-cyclic nucleotide 3'-phosphodiesterase, and N-methyl-D-asparate receptors. This along with the release of chemokines, such as stromal derived factor-1a and monocyte chemoattractant protein-1, suggests multiple functional roles of AMC in early brain development.
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Affiliation(s)
- Charanjit Kaur
- Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
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Ock J, Jeong J, Choi WS, Lee WH, Kim SH, Kim IK, Suk K. Regulation of Toll-like receptor 4 expression and its signaling by hypoxia in cultured microglia. J Neurosci Res 2007; 85:1989-95. [PMID: 17461416 DOI: 10.1002/jnr.21322] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Hypoxia is an important biological signal that regulates a wide variety of physiological responses. At the same time, hypoxia is involved in multiple pathological situations. In particular, hypoxia is closely associated with neural injury in the brain. Hypoxia has been recently proposed as a neuroinflammatogen, as it can induce the inflammatory activation of microglia, a major cellular source of inflammatory mediators in the brain. In this article, we present evidence that hypoxia enhances Toll-like receptor 4 (TLR4) expression in cultured microglia and differentially regulates the downstream signaling pathways of TLR4. Hypoxia up-regulated TLR4 expression at the mRNA and protein levels in a microglia cell line, as well as in primary microglia cultures. Hypoxia, however, differentially regulated MyD88-dependent and -independent pathways of TLR4 signaling: Hypoxia enhanced lipopolysaccharide (LPS)-induced interferon regulatory factor-3 (IRF-3) activation and the subsequent expression of IFNbeta (MyD88-independent pathway), whereas it suppressed LPS-induced NF-kappaB activation (MyD88-dependent pathway). Hypoxia did not affect IFNgamma signaling, which was represented by signal transducer and activator of transcription-1 (STAT1) activation and interferon-regulatory factor-1 (IRF-1) induction. Taken together, although hypoxia up-regulates TLR4 expression, its downstream signaling pathways appear to be differentially modulated by hypoxia.
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Affiliation(s)
- Jiyeon Ock
- Department of Pharmacology, Kyungpook National University School of Medicine, Daegu, Korea
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Askalan R, Deveber G, Ho M, Ma J, Hawkins C. Astrocytic-inducible nitric oxide synthase in the ischemic developing human brain. Pediatr Res 2006; 60:687-92. [PMID: 17065568 DOI: 10.1203/01.pdr.0000246226.89215.a6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Variability in the expression of apoptotic and inflammatory mediators with time after an ischemic insult and their role in the expansion of cerebral infarcts are still controversial. This study examines DNA degradation and the expression of activated caspase-3 and iNOS, inducible nitric oxide (iNOS) in the human developing brain. Autopsy specimens from children with a neuropathologic diagnosis of focal ischemic infarct were included in the study. The specimens were classified based on the clinical history as acute (< 24 h, n = 5), subacute (24-72 h, n = 8), or old (> 72 h, n = 6) infarcts. Immunohistochemical staining for caspase-3, iNOS and TUNEL were then performed on all infarcts alongside age-matched controls. TUNEL staining was detected in regions of all infarcts. Expression of iNOS was significantly higher than that of caspase-3 in the penumbra of subacute infarcts (p = 0.02). Glial fibrillary acidic protein and iNOS staining co-localized in the penumbra of acute and subacute infarcts. These results suggest that cell death continues to occur for more than 3 d post ischemic insult. Cell death in the penumbra of subacute infarcts is partially caspase-3 independent and may be attributed to nitric oxide. Astrocytes are a source of iNOS and may play a role in the evolution of pediatric brain injury days after the initial insult.
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Affiliation(s)
- Rand Askalan
- Division of Neurology, Hospital for Sick Children, M5G 1X8 Toronto, Ontario, Canada.
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Lu DY, Liou HC, Tang CH, Fu WM. Hypoxia-induced iNOS expression in microglia is regulated by the PI3-kinase/Akt/mTOR signaling pathway and activation of hypoxia inducible factor-1α. Biochem Pharmacol 2006; 72:992-1000. [PMID: 16919605 DOI: 10.1016/j.bcp.2006.06.038] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2006] [Revised: 06/25/2006] [Accepted: 06/28/2006] [Indexed: 11/19/2022]
Abstract
Exposure to hypoxia induced microglia activation and animal studies have shown that neuronal cell death is correlated with microglial activation following cerebral ischemia. Thus, it is likely that toxic inflammatory mediators produced by activated microglia under hypoxic conditions may exacerbate neuronal injury following cerebral ischemia. The hypoxia-inducible factor-1 (HIF-1) is primarily involved in the sensing and adapting of cells to changes in the O(2) level, which is regulated by many physiological functions. However, the role of HIF-1 in microglia activation under hypoxia has not yet been defined. In the current work, we investigate the signaling pathways of HIF-1alpha involved in the regulation of hypoxia-induced overexpression of inducible NO synthase (iNOS) in microglia. Exposure of primary rat microglial cultures as well as established microglial cell line BV-2 to hypoxia induced the expression of iNOS, indicating that hypoxia could lead to the inflammatory activation of microglia. iNOS induction was accompanied with NO production. Moreover, the molecular analysis of these events indicated that iNOS expression was regulated by the phosphatidylinositol 3-kinase (PI3-kinase)/AKT/ mammalian target of rapamycin (mTOR) signaling pathway and activation of hypoxia inducible factor-1alpha (HIF-1alpha). Thus, during cerebral ischemia, hypoxia may not only directly damage neurons, but also promote neuronal injury indirectly via microglia activation. In this study, we demonstrated that hypoxia induced iNOS expression by regulation of HIF-1alpha in microglia.
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Affiliation(s)
- Dah-Yuu Lu
- Pharmacological Institute, College of Medicine, National Taiwan University, Taipei, Taiwan
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17
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Kaur C, Sivakumar V, Ang LS, Sundaresan A. Hypoxic damage to the periventricular white matter in neonatal brain: role of vascular endothelial growth factor, nitric oxide and excitotoxicity. J Neurochem 2006; 98:1200-16. [PMID: 16787408 DOI: 10.1111/j.1471-4159.2006.03964.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The present study examined factors that may be involved in the development of hypoxic periventricular white matter damage in the neonatal brain. Wistar rats (1-day old) were subjected to hypoxia and the periventricular white matter (corpus callosum) was examined for the mRNA and protein expression of hypoxia-inducible factor-1alpha (HIF-1alpha), endothelial, neuronal and inducible nitric oxide synthase (eNOS, nNOS and iNOS), vascular endothelial growth factor (VEGF) and N-methyl-D-aspartate receptor subunit 1 (NMDAR1) between 3 h and 14 days after hypoxic exposure by real-time RT-PCR, western blotting and immunohistochemistry. Up-regulated mRNA and protein expression of HIF-1alpha, VEGF, NMDAR1, eNOS, nNOS and iNOS in corpus callosum was observed in response to hypoxia. NMDAR1 and iNOS expression was found in the activated microglial cells, whereas VEGF was localized to astrocytes. An enzyme immunoassay showed that the VEGF concentration in corpus callosum was significantly higher up to 7 days after hypoxic exposure. NO levels, measured by colorimetric assay, were also significantly higher in hypoxic rats up to 14 days after hypoxic exposure as compared with the controls. A large number of axons undergoing degeneration were observed between 3 h and 7 days after the hypoxic exposure at electron-microscopic level. Our findings point towards the involvement of excitotoxicity, VEGF and NO in periventricular white matter damage in response to hypoxia.
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MESH Headings
- Animals
- Animals, Newborn/physiology
- Blotting, Western
- Brain/pathology
- Colorimetry
- Corpus Callosum/metabolism
- Fluorescent Antibody Technique, Indirect
- Glial Fibrillary Acidic Protein/metabolism
- Hypoxia-Inducible Factor 1, alpha Subunit/metabolism
- Hypoxia-Ischemia, Brain/pathology
- Immunoenzyme Techniques
- Immunohistochemistry
- Lateral Ventricles/metabolism
- Microscopy, Electron
- Myelin Basic Protein/metabolism
- Myelin Sheath/pathology
- Nitric Oxide/metabolism
- Nitric Oxide/physiology
- Nitric Oxide Synthase Type II/metabolism
- Nitric Oxide Synthase Type III/metabolism
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- Rats
- Rats, Wistar
- Receptors, N-Methyl-D-Aspartate/biosynthesis
- Reverse Transcriptase Polymerase Chain Reaction
- Vascular Endothelial Growth Factor A/physiology
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Affiliation(s)
- Charanjit Kaur
- Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
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Lai AY, Todd KG. Hypoxia-activated microglial mediators of neuronal survival are differentially regulated by tetracyclines. Glia 2006; 53:809-16. [PMID: 16541436 DOI: 10.1002/glia.20335] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The tetracycline derivatives minocycline (MINO) and doxycycline (DOXY) have been shown to be neuroprotective in in vivo and in vitro models of stroke. This neuroprotection is thought to be due to the suppression of microglial activation. However, the specific molecular parameters in microglia of the tetracyclines' effect are not understood. We subjected cultured rat microglial and neuronal cells to in vitro hypoxia and examined the effects of MINO and DOXY pre-treatments. Our data showed that MINO and DOXY protect against hypoxia-induced neuronal death by a mechanism dependent on regulation of microglial factors, but likely unrelated to regulation of microglial proliferation/viability. Both MINO and DOXY suppressed the hypoxic activation of ED-1, a marker for microglial activation. Morphological analyses of hypoxic microglia using the microglial marker Iba1 revealed that treatment with MINO and DOXY caused a higher percentage of microglia to remain in a non-activated state. MINO suppressed the hypoxic upregulation of pro-inflammatory agents nitric oxide (NO), interleukin-1 beta (IL-1beta), and tumor necrosis factor alpha (TNF-alpha), while DOXY down-regulated only NO and IL-1beta. In contrast, the hypoxic activation of pro-survival/neuroprotective microglial proteins, such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), were unaffected by tetracycline treatments. Taken together, these results suggest that MINO and DOXY may provide neuroprotection against stroke by selectively down-regulating microglial toxic factors while maintaining functional pro-survival factors.
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Affiliation(s)
- Aaron Y Lai
- Neurochemical Research Unit, Department of Psychiatry and Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada
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19
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Li RC, Row BW, Kheirandish L, Brittian KR, Gozal E, Guo SZ, Sachleben LR, Gozal D. Nitric oxide synthase and intermittent hypoxia-induced spatial learning deficits in the rat. Neurobiol Dis 2004; 17:44-53. [PMID: 15350964 DOI: 10.1016/j.nbd.2004.05.006] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2003] [Revised: 03/18/2004] [Accepted: 05/18/2004] [Indexed: 01/01/2023] Open
Abstract
Intermittent hypoxia (IH) during sleep induces significant neurobehavioral deficits in the rat. Since nitric oxide (NO) has been implicated in ischemia-reperfusion-related pathophysiological consequences, the temporal effects of IH (alternating 21% and 10% O(2) every 90 s) and sustained hypoxia (SH; 10% O(2)) during sleep for up to 14 days on the induction of nitric oxide synthase (NOS) isoforms in the brain were examined in the cortex of Sprague-Dawley rats. No significant changes of endothelial NOS (eNOS) and neuronal NOS (nNOS) occurred over time with either IH or SH. Similarly, inducible NOS (iNOS) was not affected by SH. However, increased expression and activity of iNOS were observed on days 1 and 3 of IH (P < 0.01 vs. control; n = 12/group) and were followed by a return to basal levels on days 7 and 14. Furthermore, IH-mediated neurobehavioral deficits in the water maze were significantly attenuated in iNOS knockout mice. We conclude that IH is associated with a time-dependent induction of iNOS and that the increased expression of iNOS may play a critical role in the early pathophysiological events leading to IH-mediated neurobehavioral deficits.
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Affiliation(s)
- Richard C Li
- Department of Pediatrics, Kosair Children's Hospital Research Institute, University of Louisville, Louisville, KY 40202, USA
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20
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Guan J, Miller OT, Waugh KM, McCarthy DC, Gluckman PD, Gunn AJ. TGFβ-1 and neurological function after hypoxia-ischemia in adult rats. Neuroreport 2004; 15:961-4. [PMID: 15076715 DOI: 10.1097/00001756-200404290-00006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The present study compared the short-term and long-term neuroprotective and neurobehavioral effects of transforming growth factor beta-1 (TGF beta-1) after hypoxic-ischemic injury in adult rats. TGF beta-1 (10 ng) or vehicle were administered intracerebroventricularly (i.c.v.) 2 h after hypoxia-ischemia. Adhesive removal test was assessed after 10 or 40 days, and the neuronal outcome then determined. TGF beta-1 significantly increased the area of intact cortex compared with vehicle 10 days after the injury, with a significant improvement in neurological function. In contrast, after 40 days recovery TGFbeta-1 neither improved neuronal outcome nor neurological function, suggesting TGFbeta-1 can transiently improve functional and histological recovery from hypoxia-ischemia.
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Affiliation(s)
- Jian Guan
- Liggins Institute, Faculty of Medicine and Health Sciences The University of Auckland, Private Bag 92019, Auckland, New Zealand.
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21
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Kim NG, Lee H, Son E, Kwon OY, Park JY, Park JH, Cho GJ, Choi WS, Suk K. Hypoxic induction of caspase-11/caspase-1/interleukin-1beta in brain microglia. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2003; 114:107-14. [PMID: 12829320 DOI: 10.1016/s0169-328x(03)00135-9] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Caspase-11 is an inducible protease that plays an important role in both inflammation and apoptosis. Inflammatory stimuli induce and activate caspase-11, which is required for the activation of caspase-1 or interleukin-1beta (IL-1beta) converting enzyme (ICE). Caspase-1 in turn mediates the maturation of proinflammatory cytokines such as IL-1beta, which is one of the crucial mediators of neurodegeneration in the central nervous system. Here, we report that hypoxic exposure of cultured brain microglia (BV-2 mouse microglia cells and rat primary microglial cultures) induces expression and activation of caspase-11, which is accompanied by activation of caspase-1 and secretion of mature IL-1beta and IL-18. Hypoxic induction of caspase-11 was observed in both mRNA and protein levels, and was mediated through p38 mitogen-activated protein kinase pathway. Transient global ischemia in rats also induced caspase-11 expression and IL-1beta production in hippocampus supporting our in vitro findings. Caspase-11-expressing cells in hippocampus were morphologically identified as microglia. Taken together, our results indicate that hypoxia induces a sequential event-caspase-11 induction, caspase-1 activation, and IL-1beta release-in brain microglia, and point out the importance of initial caspase-11 induction in hypoxia-induced inflammatory activation of microglia.
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Affiliation(s)
- Nam-Gon Kim
- Department of Anatomy and Neurobiology, Institute of Health Sciences, and Research Institute of Natural Science, Gyeongsang National University College of Medicine, 92 Chilam-dong, Jinju, Kyungnam 660-751, South Korea
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22
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Park SY, Lee H, Hur J, Kim SY, Kim H, Park JH, Cha S, Kang SS, Cho GJ, Choi WS, Suk K. Hypoxia induces nitric oxide production in mouse microglia via p38 mitogen-activated protein kinase pathway. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2002; 107:9-16. [PMID: 12414118 DOI: 10.1016/s0169-328x(02)00421-7] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In vitro exposure of microglial cells to hypoxia induces cellular activation. Also, in vivo studies of glial activation following ischemic hypoxia have shown that neuronal cell death is followed by microglial activation. Thus, it is likely that toxic inflammatory mediators produced by activated microglial cells under hypoxic conditions may exacerbate neuronal injury following cerebral ischemia. Nitric oxide (NO), which is known to be produced by activated microglia, may participate in this process. In the current work, we sought to determine whether and how the production of NO and the expression of inducible NO synthase (iNOS) are triggered by hypoxia in microglial cells. Exposure of established microglial cell lines as well as primary mouse microglial cultures to mild hypoxia (8 h) followed by reoxygenation (24 h) induced the production of NO and TNFalpha, indicating that hypoxia could lead to the inflammatory activation of microglia. Hypoxic induction of NO was accompanied by iNOS induction. Moreover, hypoxia induced the activation of p38 MAPK, but not ERK or JNK/SAPK, in BV-2 mouse microglial cells. SB203580, a specific inhibitor of p38 MAPK, blocked the hypoxic induction of NO and iNOS. Taken together, our results indicated that hypoxia could induce inflammatory activation of microglia, and the hypoxic induction of NO production in microglia is mediated through p38 MAPK pathway. Thus, during cerebral ischemia, hypoxia may not only directly damage neurons, but may also promote neuronal injury indirectly via microglial activation.
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Affiliation(s)
- Sun Young Park
- Department of Anatomy and Neurobiology, College of Medicine, Gyeongsang National University, 92 Chilam-dong, Jinju, Kyungnam 660-751, South Korea
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23
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Acarin L, Peluffo H, González B, Castellano B. Expression of inducible nitric oxide synthase and cyclooxygenase-2 after excitotoxic damage to the immature rat brain. J Neurosci Res 2002; 68:745-54. [PMID: 12111835 DOI: 10.1002/jnr.10261] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
It is well established that after adult brain damage the enzymes cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) play an important role in the inflammatory processes and oxidative stress, which are considered to be the leading factors contributing to delayed cell death. The contribution of these enzymes to postnatal brain damage, however, is poorly understood. In our study, excitotoxic lesions were induced by the injection of N-methyl-D-aspartate in the cortex of postnatal day 9 rats. After different survival times ranging from 4 hr to 7 days post-lesion, brain sections were processed for the immunocytochemical demonstration of COX-2 and iNOS and double labeling with neuronal, glial and neutrophil markers. First and maximal de novo induction of iNOS and COX-2 expression was found at 10 hr post-lesion. Expression of both enzymes started to diminish at 24 hr, reaching basal levels at day 3. iNOS-expressing cells were mainly identified as infiltrated neutrophils as well as highly ramified protoplasmic astrocytes closely associated with blood vessels. Moreover, scattered iNOS-positive neurons were found at the lesion borders. In contrast, COX-2 was mainly observed in reactive microglial cells and neuronal cells. COX-2-positive neurons were found within the degenerating area at 10 hr and at the borders of the lesion later on. This study shows that maximal iNOS and COX-2 expression precedes the period of massive neuronal death observed at 24 hr post-lesion, and may therefore contribute to the evolution of the inflammatory response and the neurodegenerative process after an excitotoxic lesion to the postnatal brain.
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Affiliation(s)
- Laia Acarin
- Unit of Histology, School of Medicine, Department of Cell Biology, Physiology and Immunology, Autonomous University of Barcelona, Spain.
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24
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Wang JY, Shum AYC, Wang JY. Hypoxia/reoxygenation induces cell injury via different mechanisms in cultured rat cortical neurons and glial cells. Neurosci Lett 2002; 322:187-91. [PMID: 11897169 DOI: 10.1016/s0304-3940(02)00102-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Hypoxia/reoxygenation (H/R) causes cell injury/death. We examined the protection by drugs intervening at various stages of the injury cascade in cultured neurons and glia. Primary cultures of rat cortical neurons and mixed glia were subjected to H/R. Measurements of cell death (by lactate dehydrogenase release into the medium) and viability (by MTT reduction) indicated that H/R led to time-dependent injury in both neuronal and mixed glial cultures. The extent of cell injury in neurons was significantly greater than in glia cells. Pretreatment with (+)-MK-801 hydrogen maleate (MK-801) (an N-methyl-D-aspartate antagonist), N(omega)-nitro-L-arginine methyl ester (L-NAME) (an inhibitor of nitric oxide synthase) or free radical scavengers reduced the extent of the H/R-elicited neuronal damage. MK-801, in contrast, was without effect on glial cells while L-NAME was effective. Our results suggest differential mechanism(s) and susceptibility to injury caused by H/R for neurons and mixed glia.
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Affiliation(s)
- Ju-Yu Wang
- Department of Basic Medical Science, Hung-Kuang Institute of Technology, Sha-Lu, Taichung, Taiwan.
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25
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Guan J, Miller OT, Waugh KM, McCarthy DC, Gluckman PD. Insulin-like growth factor-1 improves somatosensory function and reduces the extent of cortical infarction and ongoing neuronal loss after hypoxia-ischemia in rats. Neuroscience 2002; 105:299-306. [PMID: 11672597 DOI: 10.1016/s0306-4522(01)00145-2] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Treatment with insulin-like growth factor-1 has been demonstrated to reduce the extent of cortical infarction 5 days after hypoxic-ischemic brain injury. As neuronal death can be progressive and long lasting after initial injury, the present study examined the long-term effects of insulin-like growth factor-1 on late neuronal loss 20 days after hypoxic-ischemic injury, together with evaluating neurobehavioral outcome as assumed by somatosensory function. Unilateral brain injury was induced in adult rats by carotid artery ligation followed by 10 min of hypoxia (6% O2). A single dose of insulin-like growth factor-1 (50 microg) was administered intracerebroventricularly via a stereotaxically pre-fixed cannula 2 h after injury. A bilateral tactile stimulation test was used to examine the degree of somatosensory function at 3, 5, 10 and 20 days after the hypoxia in both insulin-like growth factor-1- (n=12) and its vehicle- (n=12) treated rats, along with sham-operated rats (n=9). Cortical infarction and percentage of selective neuronal loss in the cerebral cortex were examined 20 days after the hypoxic-ischemic injury in both treatment groups. Hypoxic-ischemic injury resulted in a significant delay in the time taken to contact the patch over the period examined (left/right ratio 5.1+/-0.79), particularly at 3 days (7.0+/-2.8) after the hypoxia, compared to sham-operated rats (1.1+/-0.9, P<0.05). The overall effect of insulin-like growth factor-1 in reducing the time taken to contact the patch was significant (P=0.03, 2.6+/-0.79) compared to the vehicle group. There was a trend towards a reduction of cortical infarction after insulin-like growth factor-1 treatment (P=0.058), however insulin-like growth factor-1 significantly reduced the percentage of selective neuronal loss (P=0.027) 20 days following the hypoxia. From these data we suggest that insulin-like growth factor-1 improves somatosensory function by reducing both the extent of cortical infarction and ongoing progressive neuronal death during brain recovery from hypoxic-ischemic injury.
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Affiliation(s)
- J Guan
- Liggins Institute, Faculty of Medicine and Health Sciences, The University of Auckland, New Zealand.
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26
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Affiliation(s)
- Bruce R Pitt
- Department of Environmental and Occupational Health, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
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27
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Abstract
Neonatal stroke occurs in approximately 1 in 4,000 to 1 in 10,000 newborns, and more than 80% involve the vascular territory supplied by the middle cerebral artery. Neonatal stroke is associated with many acquired and genetic prothrombotic factors, and follow-up studies indicate that as many as two thirds of neonates develop neurologic deficits. In the past two decades unilateral carotid occlusion with 8% hypoxia has been used to study focal and global ischemia in the newborn, and recently a filament model of middle cerebral artery occlusion has been developed. This review describes the results of studies in these two newborn models covering aspects of the injury cascade that occurs after focal ischemia. A likely requirement is that therapeutic efforts be directed less at using thrombolytic therapy and more toward treatment of events associated with reperfusion injury, the inflammatory cascade, and apoptosis. Additional areas of research that have received attention in the past year include inhibition of nitric oxide and free-radical formation, use of iron chelating agents, the potential role of hypoxia-inducible factors and mediators of caspase activity, use of growth factors, hypothermia, and administration of magnesium sulfate.
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Affiliation(s)
- S Ashwal
- Department of Pediatrics, Division of Child Neurology, Loma Linda University School of Medicine, Loma Linda, California 12350, USA.
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28
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Ling EA, Ng YK, Wu CH, Kaur C. Microglia: its development and role as a neuropathology sensor. PROGRESS IN BRAIN RESEARCH 2001; 132:61-79. [PMID: 11545023 DOI: 10.1016/s0079-6123(01)32066-6] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Affiliation(s)
- E A Ling
- Department of Anatomy, Faculty of Medicine, National University of Singapore, MD 10, 4 Medical Drive, Singapore 117597, Singapore.
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29
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Acarin L, González B, Castellano B. Glial activation in the immature rat brain: implication of inflammatory transcription factors and cytokine expression. PROGRESS IN BRAIN RESEARCH 2001; 132:375-89. [PMID: 11545004 DOI: 10.1016/s0079-6123(01)32089-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Affiliation(s)
- L Acarin
- Department of Cell Biology, Physiology and Immunology, Unit of Histology, School of Medicine, Universitat Autònoma de Barcelona, Campus de Bellaterra, 08193 Bellaterra, Spain.
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30
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Sharp FR, Bernaudin M, Bartels M, Wagner KR. Glial expression of heat shock proteins (HSPs) and oxygen-regulated proteins (ORPs). PROGRESS IN BRAIN RESEARCH 2001; 132:427-40. [PMID: 11545009 DOI: 10.1016/s0079-6123(01)32093-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Affiliation(s)
- F R Sharp
- Department of Neurology, University of Cincinnati, Vontz Center for Molecular Studies, Room 2327, 3125 Eden Avenue, Cincinnati, OH 45267-0536, USA.
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31
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Kaur C, You Y. Ultrastructure and function of the amoeboid microglial cells in the periventricular white matter in postnatal rat brain following a hypoxic exposure. Neurosci Lett 2000; 290:17-20. [PMID: 10925164 DOI: 10.1016/s0304-3940(00)01306-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The ameboid microglial cells (AMC), located in the periventricular white matter, were examined ultrastucturally in neonatal rats following a hypoxic exposure. For 10 min to 1 day, following the hypoxic exposure, a large number of glial cells with nuclear chromatin condensation, undergoing degeneration, were observed in the white matter. Such cells were often being phagocytosed by the AMC. At 3-7 days after the hypoxic exposure, the cytoplasm of many AMC contained a number of phagosomes whereas at 14-28 days a large amount of lipid accumulation was observed in them. AMC were labeled intensely with horseradish peroxidase (HRP) administered intraperitoneally following the hypoxic exposure. The phagocytosis of degenerating cells by the AMC and uptake of HRP by them indicates that these cells efficiently remove the degenerating cells/debris from the neonatal white matter following hypoxia in an attempt to protect it from any harmful substances that may be secreted by the degenerating cells or from serum derived substances that may enter the brain through blood circulation.
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Affiliation(s)
- C Kaur
- Department of Anatomy, Faculty of Medicine, MD10, 4 Medical Drive, National University of Singapore, 117597, Singapore, Singapore.
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