Cross-Talk Between Neurons and Astrocytes in Response to Bilirubin: Early Beneficial Effects
详细信息 查看全文
- 作者：Ana Sofia Falc?o (1) (2)
Rui F. M. Silva (1) (2)
Ana Rita Vaz (1)
Sandra Leit?o Silva (1)
Adelaide Fernandes (1) (2)
Dora Brites (1) (2) - 关键词：Co ; cultures ; Neurite extension and ramification ; Neuronal cell death ; Neuron ; astrocyte signaling ; Neuroprotection ; Unconjugated bilirubin
- 刊名：Neurochemical Research
- 出版年：2013
- 出版时间：March 2013
- 年：2013
- 卷：38
- 期：3
- 页码：644-659
- 全文大小：736KB
- 参考文献：1. Nair A, Frederick TJ, Miller SD (2008) Astrocytes in multiple sclerosis: a product of their environment. Cell Mol Life Sci 65:2702-720 CrossRef
2. Orellana JA, Saez PJ, Shoji KF, Schalper KA, Palacios-Prado N, Velarde V, Giaume C, Bennett MV, Saez JC (2009) Modulation of brain hemichannels and gap junction channels by pro-inflammatory agents and their possible role in neurodegeneration. Antioxid Redox Signal 11:369-99 CrossRef
3. Hertz L, Zielke HR (2004) Astrocytic control of glutamatergic activity: astrocytes as stars of the show. Trends Neurosci 27:735-43 CrossRef
4. Parpura V, Zorec R (2010) Gliotransmission: exocytotic release from astrocytes. Brain Res Rev 63:83-2 CrossRef
5. Renault-Mihara F, Okada S, Shibata S, Nakamura M, Toyama Y, Okano H (2008) Spinal cord injury: emerging beneficial role of reactive astrocytes-migration. Int J Biochem Cell Biol 40:1649-653 CrossRef
6. Faissner A, Pyka M, Geissler M, Sobik T, Frischknecht R, Gundelfinger ED, Seidenbecher C (2010) Contributions of astrocytes to synapse formation and maturation - Potential functions of the perisynaptic extracellular matrix. Brain Res Rev 63:26-8 CrossRef
7. Laird MD, Vender JR, Dhandapani KM (2008) Opposing roles for reactive astrocytes following traumatic brain injury. Neurosignals 16:154-64 CrossRef
8. Allaman I, Belanger M, Magistretti PJ (2011) Astrocyte-neuron metabolic relationships: for better and for worse. Trends Neurosci 34:76-7 CrossRef
9. Yang CZ, Zhao R, Dong Y, Chen XQ, Yu AC (2008) Astrocyte and neuron intone through glutamate. Neurochem Res 33:2480-486 CrossRef
10. Silva SL, Vaz AR, Diógenes MJ, van Rooijen N, Sebasti?o AM, Fernandes A, Silva RFM, Brites D (2012) Neuritic growth impairment and cell death by unconjugated bilirubin is mediated by NO and glutamate, modulated by microglia, and prevented by glycoursodeoxycholic acid and interleukin-10. Neuropharmacology 62:2398-408 CrossRef
11. Brites D (2011) Bilirubin injury to neurons and glial cells: new players, novel targets, and newer insights. Semin Perinatol 35:114-20 CrossRef
12. Shapiro SM (2010) Chronic bilirubin encephalopathy: diagnosis and outcome. Semin Fetal Neonatal Med 15:157-63 CrossRef
13. Falc?o AS, Silva RFM, Pancadas S, Fernandes A, Brito MA, Brites D (2007) Apoptosis and impairment of neurite network by short exposure of immature rat cortical neurons to unconjugated bilirubin increase with cell differentiation and are additionally enhanced by an inflammatory stimulus. J Neurosci Res 85:1229-239 CrossRef
14. Fernandes A, Falc?o AS, Abranches E, Bekman E, Henrique D, Lanier LM, Brites D (2009) Bilirubin as a determinant for altered neurogenesis, neuritogenesis, and synaptogenesis. Dev Neurobiol 69:568-82 CrossRef
15. Rodrigues CMP, Solá S, Brites D (2002) Bilirubin induces apoptosis via the mitochondrial pathway in developing rat brain neurons. Hepatology 35:1186-195 CrossRef
16. Falc?o AS, Fernandes A, Brito MA, Silva RFM, Brites D (2005) Bilirubin-induced inflammatory response, glutamate release, and cell death in rat cortical astrocytes are enhanced in younger cells. Neurobiol Dis 20:199-06 CrossRef
17. Fernandes A, Brites D (2009) Contribution of inflammatory processes to nerve cell toxicity by bilirubin and efficacy of potential therapeutic agents. Curr Pharm Des 15:2915-926 CrossRef
18. Falc?o AS, Fernandes A, Brito MA, Silva RFM, Brites D (2006) Bilirubin-induced immunostimulant effects and toxicity vary with neural cell type and maturation state. Acta Neuropathol 112:95-05 CrossRef
19. Fernandes A, Falc?o AS, Silva RFM, Gordo AC, Gama MJ, Brito MA, Brites D (2006) Inflammatory signalling pathways involved in astroglial activation by unconjugated bilirubin. J Neurochem 96:1667-679 CrossRef
20. Rigato I, Pascolo L, Fernetti C, Ostrow JD, Tiribelli C (2004) The human multidrug-resistance-associated protein MRP1 mediates ATP-dependent transport of unconjugated bilirubin. Biochem J 383:335-41 CrossRef
21. Calligaris S, Cekic D, Roca-Burgos L, Gerin F, Mazzone G, Ostrow JD, Tiribelli C (2006) Multidrug resistance associated protein 1 protects against bilirubin-induced cytotoxicity. FEBS Lett 580:1355-359 CrossRef
22. Falc?o AS, Bellarosa C, Fernandes A, Brito MA, Silva RFM, Tiribelli C, Brites D (2007) Role of multidrug resistance-associated protein 1 expression in the in vitro susceptibility of rat nerve cell to unconjugated bilirubin. Neuroscience 144:878-88 CrossRef
23. McDonagh AF (1979) Bile pigments: bilatrienes and 5,15 biladienes. In: Dolphin D (ed) The Porphyrins. Academic Press, New York, pp 294-91
24. Ahlfors CE, Herbsman O (2003) Unbound bilirubin in a term newborn with kernicterus. Pediatrics 111:1110-112 CrossRef
25. Silva RFM, Rodrigues CMP, Brites D (2002) Rat cultured neuronal and glial cells respond differently to toxicity of unconjugated bilirubin. Pediatr Res 51:535-41 CrossRef
26. Blondeau JP, Beslin A, Chantoux F, Francon J (1993) Triiodothyronine is a high-affinity inhibitor of amino acid transport system L1 in cultured astrocytes. J Neurochem 60:1407-413 CrossRef
27. Silva R, Mata LR, Gulbenkian S, Brito MA, Tiribelli C, Brites D (1999) Inhibition of glutamate uptake by unconjugated bilirubin in cultured cortical rat astrocytes: role of concentration and pH. Biochem Biophys Res Commun 265:67-2 CrossRef
28. Hansen TWR (2000) Pioneers in the scientific study of neonatal jaundice and kernicterus. Pediatrics 106:E15 CrossRef
29. Hansen TWR (1995) Acute entry of bilirubin into rat brain regions. Biol Neonate 67:203-07 CrossRef
30. Azevedo FA, Carvalho LR, Grinberg LT, Farfel JM, Ferretti RE, Leite RE, Jacob FW, Lent R, Herculano-Houzel S (2009) Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. J Comp Neurol 513:532-41 CrossRef
31. Brito MA, Rosa AI, Falc?o AS, Fernandes A, Silva RFM, Butterfield DA, Brites D (2008) Unconjugated bilirubin differentially affects the redox status of neuronal and astroglial cells. Neurobiol Dis 29:30-0 CrossRef
32. Vaz AR, Delgado-Esteban M, Brito MA, Bola?os JP, Brites D, Almeida A (2010) Bilirubin selectively inhibits cytochrome / c oxidase activity and induces apoptosis in immature cortical neurons: assessment of the protective effects of glycoursodeoxycholic acid. J Neurochem 112:56-5 CrossRef
33. Weisiger RA, Ostrow JD, Koehler RK, Webster CC, Mukerjee P, Pascolo L, Tiribelli C (2001) Affinity of human serum albumin for bilirubin varies with albumin concentration and buffer composition: results of a novel ultrafiltration method. J Biol Chem 276:29953-9960 CrossRef
34. Palmela I, Sasaki H, Cardoso FL, Moutinho M, Kim KS, Brites D, Brito MA (2012) Time-dependent dual effects of high levels of unconjugated bilirubin on the human blood-brain barrier lining. Front Cell Neurosci 6:22 CrossRef
35. Ahlfors CE, Wennberg RP, Ostrow JD, Tiribelli C (2009) Unbound (free) bilirubin: improving the paradigm for evaluating neonatal jaundice. Clin Chem 55:1288-299 CrossRef
36. Silva SL, Vaz AR, Barateiro A, Falc?o AS, Fernandes A, Brito MA, Silva RFM, Brites D (2010) Features of bilirubin-induced reactive microglia: from phagocytosis to inflammation. Neurobiol Dis 40:663-75 CrossRef
37. Silva MF, Ruiter JP, Illst L, Jakobs C, Duran M, de Almeida IT, Wanders RJ (1997) Valproate inhibits the mitochondrial pyruvate-driven oxidative phosphorylation in vitro. J Inherit Metab Dis 20:397-00 CrossRef
38. Leite MC, Galland F, Brolese G, Guerra MC, Bortolotto JW, Freitas R, Almeida LM, Gottfried C, Goncalves CA (2008) A simple, sensitive and widely applicable ELISA for S100B: methodological features of the measurement of this glial protein. J Neurosci Methods 169:93-9 CrossRef
39. Cekic D, Bellarosa C, Garcia-Mediavilla MV, Rigato I, Pascolo L, Ostrow JD, Tiribelli C (2003) Upregulation in the expression of multidrug resistance protein Mrp1 mRNA and protein by increased bilirubin production in rat. Biochem Biophys Res Commun 311:891-96 CrossRef
40. Zou J, Wang YX, Dou FF, Lu HZ, Ma ZW, Lu PH, Xu XM (2010) Glutamine synthetase down-regulation reduces astrocyte protection against glutamate excitotoxicity to neurons. Neurochem Int 56:577-84 CrossRef
41. Struzynska L (2009) A glutamatergic component of lead toxicity in adult brain: the role of astrocytic glutamate transporters. Neurochem Int 55:151-56 CrossRef
42. Lovatt D, Xu Q, Liu W, Takano T, Smith NA, Schnermann J, Tieu K, Nedergaard M (2012) Neuronal adenosine release, and not astrocytic ATP release, mediates feedback inhibition of excitatory activity. Proc Natl Acad Sci USA 109:6265-270 CrossRef
43. Hu J, Castets F, Guevara JL, Van Eldik LJ (1996) S100 beta stimulates inducible nitric oxide synthase activity and mRNA levels in rat cortical astrocytes. J Biol Chem 271:2543-547 CrossRef
44. Lam AG, Koppal T, Akama KT, Guo L, Craft JM, Samy B, Schavocky JP, Watterson DM, Van Eldik LJ (2001) Mechanism of glial activation by S100B: involvement of the transcription factor NFkappaB. Neurobiol Aging 22:765-72 CrossRef
45. Donato R, Sorci G, Riuzzi F, Arcuri C, Bianchi R, Brozzi F, Tubaro C, Giambanco I (2009) S100B’s double life: intracellular regulator and extracellular signal. Biochim Biophys Acta 1793:1008-022 CrossRef
46. Donato R (2007) RAGE: a single receptor for several ligands and different cellular responses: the case of certain S100 proteins. Curr Mol Med 7:711-24 CrossRef
47. Edwards MM, Robinson SR (2006) TNF alpha affects the expression of GFAP and S100B: implications for Alzheimer’s disease. J Neural Transm 113:1709-715 CrossRef
48. Brites D, Brito MA (2012) Bilirubin toxicity. In: Stevenson DK, Maisels MJ, Watchko JF (eds) Neonatal jaundice. Mc-Graw-Hill Companies, Inc., New York, pp 115-43
49. Brites D (2012) The evolving landscape of neurotoxicity by unconjugated bilirubin: role of glial cells and inflammation. Front Pharmacol 3:88 CrossRef
50. Radio NM, Mundy WR (2008) Developmental neurotoxicity testing in vitro: models for assessing chemical effects on neurite outgrowth. Neurotoxicology 29:361-76 CrossRef
51. Wade JJ, McDaid LJ, Harkin J, Crunelli V, Kelso JA (2011) Bidirectional coupling between astrocytes and neurons mediates learning and dynamic coordination in the brain: a multiple modeling approach. PLoS One 6:e29445 CrossRef
52. Amiri M, Bahrami F, Janahmadi M (2012) Functional contributions of astrocytes in synchronization of a neuronal network model. J Theor Biol 292:60-0 CrossRef
53. Barreto GE, Gonzalez J, Torres Y, Morales L (2011) Astrocytic-neuronal crosstalk: implications for neuroprotection from brain injury. Neurosci Res 71:107-13 CrossRef
54. Fellin T, Carmignoto G (2004) Neurone-to-astrocyte signalling in the brain represents a distinct multifunctional unit. J Physiol 559:3-5 CrossRef
55. Sauvageot CM, Stiles CD (2002) Molecular mechanisms controlling cortical gliogenesis. Curr Opin Neurobiol 12:244-49 CrossRef
56. Ullian EM, Sapperstein SK, Christopherson KS, Barres BA (2001) Control of synapse number by glia. Science 291:657-61 CrossRef
57. Barres BA (2008) The mystery and magic of glia: a perspective on their roles in health and disease. Neuron 60:430-40 CrossRef
58. Pfrieger FW (2010) Role of glial cells in the formation and maintenance of synapses. Brain Res Rev 63:39-6 CrossRef
59. Dowell JA, Johnson JA, Li L (2009) Identification of astrocyte secreted proteins with a combination of shotgun proteomics and bioinformatics. J Proteome Res 8:4135-143 CrossRef
60. Au E, Richter MW, Vincent AJ, Tetzlaff W, Aebersold R, Sage EH, Roskams AJ (2007) SPARC from olfactory ensheathing cells stimulates Schwann cells to promote neurite outgrowth and enhances spinal cord repair. J Neurosci 27:7208-221 CrossRef
61. Lamarche F, Signorini-Allibe N, Gonthier B, Barret L (2004) Influence of vitamin E, sodium selenite, and astrocyte-conditioned medium on neuronal survival after chronic exposure to ethanol. Alcohol 33:127-38
62. Watts LT, Rathinam ML, Schenker S, Henderson GI (2005) Astrocytes protect neurons from ethanol-induced oxidative stress and apoptotic death. J Neurosci Res 80:655-66 CrossRef
63. Yanni PA, Rising LJ, Ingraham CA, Lindsley TA (2002) Astrocyte-derived factors modulate the inhibitory effect of ethanol on dendritic development. Glia 38:292-02 CrossRef
64. Rao KV, Panickar KS, Jayakumar AR, Norenberg MD (2005) Astrocytes protect neurons from ammonia toxicity. Neurochem Res 30:1311-318 CrossRef
65. Giordano G, Kavanagh TJ, Costa LG (2009) Mouse cerebellar astrocytes protect cerebellar granule neurons against toxicity of the polybrominated diphenyl ether (PBDE) mixture DE-71. Neurotoxicology 30:326-29 CrossRef
66. Paradisi S, Sacchetti B, Balduzzi M, Gaudi S, Malchiodi-Albedi F (2004) Astrocyte modulation of in vitro b-amyloid neurotoxicity. Glia 46:252-60 CrossRef
67. Slezak M, Pfrieger FW, Soltys Z (2006) Synaptic plasticity, astrocytes and morphological homeostasis. J Physiol Paris 99:84-1 CrossRef
68. Scheiber IF, Dringen R (2011) Copper-treatment increases the cellular GSH content and accelerates GSH export from cultured rat astrocytes. Neurosci Lett 498:42-6 CrossRef
69. Hirrlinger J, Schulz JB, Dringen R (2002) Glutathione release from cultured brain cells: multidrug resistance protein 1 mediates the release of GSH from rat astroglial cells. J Neurosci Res 69:318-26 CrossRef
70. Brito MA, Zurolo E, Pereira P, Barroso C, Aronica E, Brites D (2012) Cerebellar axon/myelin loss, angiogenic sprouting, and neuronal increase of vascular endothelial growth factor in a preterm infant with kernicterus. J Child Neurol 27:615-24 CrossRef
71. Ostrow JD, Pascolo L, Brites D, Tiribelli C (2004) Molecular basis of bilirubin-induced neurotoxicity. Trends Mol Med 10:65-0 CrossRef
72. Gazzin S, Berengeno AL, Strazielle N, Fazzari F, Raseni A, Ostrow JD, Wennberg R, Ghersi-Egea JF, Tiribelli C (2011) Modulation of Mrp1 (ABCc1) and Pgp (ABCb1) by bilirubin at the blood-CSF and blood-brain barriers in the Gunn rat. PLoS One 6:e16165 CrossRef
73. Schousboe A, Sickmann HM, Bak LK, Schousboe I, Jajo FS, Faek SA, Waagepetersen HS (2011) Neuron-glia interactions in glutamatergic neurotransmission: roles of oxidative and glycolytic adenosine triphosphate as energy source. J Neurosci Res 89:1926-934 CrossRef
74. Hamilton NB, Attwell D (2010) Do astrocytes really exocytose neurotransmitters? Nat Rev Neurosci 11:227-38 CrossRef
75. Bal-Price A, Moneer Z, Brown GC (2002) Nitric oxide induces rapid, calcium-dependent release of vesicular glutamate and ATP from cultured rat astrocytes. Glia 40:312-23 CrossRef
76. Brown GC, Bal-Price A (2003) Inflammatory neurodegeneration mediated by nitric oxide, glutamate, and mitochondria. Mol Neurobiol 27:325-55 CrossRef
77. Vaz AR, Silva SL, Barateiro A, Fernandes A, Falc?o AS, Brito MA, Brites D (2011) Pro-inflammatory cytokines intensify the activation of NO/NOS, JNK1/2 and caspase cascades in immature neurons exposed to elevated levels of unconjugated bilirubin. Exp Neurol 229:381-90 CrossRef
78. Chen Y, Vartiainen NE, Ying W, Chan PH, Koistinaho J, Swanson RA (2001) Astrocytes protect neurons from nitric oxide toxicity by a glutathione-dependent mechanism. J Neurochem 77:1601-610 CrossRef
79. Desagher S, Glowinski J, Premont J (1996) Astrocytes protect neurons from hydrogen peroxide toxicity. J Neurosci 16:2553-562
80. Haskew-Layton RE, Payappilly JB, Smirnova NA, Ma TC, Chan KK, Murphy TH, Guo H, Langley B, Sultana R, Butterfield DA, Santagata S, Alldred MJ, Gazaryan IG, Bell GW, Ginsberg SD, Ratan RR (2010) Controlled enzymatic production of astrocytic hydrogen peroxide protects neurons from oxidative stress via an Nrf2-independent pathway. Proc Natl Acad Sci USA 107:17385-7390 CrossRef
81. Lucius R, Sievers J (1996) Postnatal retinal ganglion cells in vitro: protection against reactive oxygen species (ROS)-induced axonal degeneration by cocultured astrocytes. Brain Res 743:56-2 CrossRef
82. Makar TK, Nedergaard M, Preuss A, Gelbard AS, Perumal AS, Cooper AJ (1994) Vitamin E, ascorbate, glutathione, glutathione disulfide, and enzymes of glutathione metabolism in cultures of chick astrocytes and neurons: evidence that astrocytes play an important role in antioxidative processes in the brain. J Neurochem 62:45-3 CrossRef
83. Tobinick E (2009) Tumour necrosis factor modulation for treatment of Alzheimer’s disease: rationale and current evidence. CNS Drugs 23:713-25 CrossRef
84. Okumus N, Turkyilmaz C, Onal EE, Atalay Y, Serdaroglu A, Elbeg S, Koc E, Deda G, Cansu A, Gunduz B (2008) Tau and S100B proteins as biochemical markers of bilirubin-induced neurotoxicity in term neonates. Pediatr Neurol 39:245-52 CrossRef
85. Michetti F, Corvino V, Geloso MC, Lattanzi W, Bernardini C, Serpero L, Gazzolo D (2012) The S100B protein in biological fluids: more than a lifelong biomarker of brain distress. J Neurochem 120:644-59 CrossRef
86. Villarreal A, Aviles Reyes RX, Angelo MF, Reines AG, Ramos AJ (2011) S100B alters neuronal survival and dendrite extension via RAGE-mediated NF-kappaB signaling. J Neurochem 117:321-32 CrossRef
87. Adami C, Bianchi R, Pula G, Donato R (2004) S100B-stimulated NO production by BV-2 microglia is independent of RAGE transducing activity but dependent on RAGE extracellular domain. Biochim Biophys Acta 1742:169-77 CrossRef
88. Li Y, Barger SW, Liu L, Mrak RE, Griffin WS (2000) S100β induction of the proinflammatory cytokine interleukin-6 in neurons. J Neurochem 74:143-50
89. Ahlemeyer B, Beier H, Semkova I, Schaper C, Krieglstein J (2000) S-100beta protects cultured neurons against glutamate- and staurosporine-induced damage and is involved in the antiapoptotic action of the 5 HT(1A)-receptor agonist, Bay x 3702. Brain Res 858:121-28 CrossRef
90. Eriksen JL, Druse MJ (2001) Astrocyte-mediated trophic support of developing serotonin neurons: effects of ethanol, buspirone, and S100B. Brain Res Dev Brain Res 131:9-5 CrossRef
91. Mendes-de-Aguiar CB, Alchini R, Zucco JK, Costa-Silva B, Decker H, Alvarez-Silva M, Tasca CI, Trentin AG (2010) Impaired astrocytic extracellular matrix distribution under congenital hypothyroidism affects neuronal development in vitro. J Neurosci Res 88:3350-360 CrossRef
92. Domenici MR, Paradisi S, Sacchetti B, Gaudi S, Balduzzi M, Bernardo A, Ajmone-Cat MA, Minghetti L, Malchiodi-Albedi F (2002) The presence of astrocytes enhances beta amyloid-induced neurotoxicity in hippocampal cell cultures. J Physiol Paris 96:313-16 CrossRef
93. Malchiodi-Albedi F, Domenici MR, Paradisi S, Bernardo A, Ajmone-Cat MA, Minghetti L (2001) Astrocytes contribute to neuronal impairment in βA toxicity increasing apoptosis in rat hippocampal neurons. Glia 34:68-2 CrossRef - 作者单位：Ana Sofia Falc?o (1) (2)
Rui F. M. Silva (1) (2)
Ana Rita Vaz (1)
Sandra Leit?o Silva (1)
Adelaide Fernandes (1) (2)
Dora Brites (1) (2)
1. Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL/CPM), Faculty of Pharmacy, University of Lisbon, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal
2. Department of Biochemistry and Human Biology, Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal - ISSN：1573-6903
文摘
Hyperbilirubinemia remains one of the most frequent clinical diagnoses in the neonatal period. This condition may lead to the deposition of unconjugated bilirubin (UCB) in the central nervous system, causing nerve cell damage by molecular and cellular mechanisms that are still being clarified. To date, all the studies regarding bilirubin-induced neurological dysfunction were performed in monotypic nerve cell cultures. The use of co-cultures, where astrocyte-containing culture inserts are placed on the top of neuron cultures, provides the means to directly evaluate the cross-talk between these two different cell types. Therefore, this study was designed to evaluate whether protective or detrimental effects are produced by astrocytes over UCB-induced neurodegeneration. Our experimental model used an indirect co-culture system where neuron-to-astrocyte signaling was established concomitantly with the 24?h exposure to UCB. In this model astrocytes abrogated the well-known UCB-induced neurotoxic effects by preventing the loss of cell viability, dysfunction and death by apoptosis, as well as the impairment of neuritic outgrowth. To this protection it may have accounted the induced expression of the multidrug resistance-associated protein 1 and the 3.5-fold increase in the values of S100B, when communication between both cells was established independently of UCB presence. In addition, the presence of astrocytes in the neuronal environment preserved the UCB-induced increase in glutamate levels, but raised the basal concentrations of nitric oxide and TNF-α although no UCB effects were noticed. Our data suggest that bidirectional signalling during astrocyte-neuron recognition exerts pro-survival effects, stimulates neuritogenesis and sustains neuronal homeostasis, thus protecting cells from the immediate UCB injury. These findings may help explain why irreversible brain damage usually develops only after the first day of post-natal life.