Anoxic Survival Research Articles

Effect of anoxia on the electroretinogram of three anoxia-tolerant vertebrates

To survive anoxia, neural ATP levels have to be defended. Reducing electrical activity, which accounts for 50% or more of neural energy consumption, should be beneficial for anoxic survival. The retina is a hypoxia sensitive part of the central nervous system. Here, we quantify the in vivo retinal light response (electroretinogram; ERG) in three vertebrates that exhibit varying degrees of anoxia tolerance: freshwater turtle ( Trachemys scripta), epaulette shark ( Hemiscyllium ocellatum) and leopard frog ( Rana pipiens). A virtually total suppression of ERG in anoxia, probably resulting in functional blindness, has previously been seen in the extremely anoxia-tolerant crucian carp ( Carassius carassius). Surprisingly, the equally anoxia-tolerant turtle, which strongly depresses brain and whole-body metabolism during anoxia, exhibited a relatively modest anoxic reduction in ERG: the combined amplitude of turtle ERG waves was reduced by ~ 50% after 2 h. In contrast, the shark b-wave amplitude practically disappeared after 30 min of severe hypoxia, and the frog b-wave was decreased by ~ 75% after 40 min in anoxia. The specific A 1 adenosine receptor antagonist CPT significantly delayed the suppression of turtle ERG, while the hypoxic shark ERG was unaffected by the non-specific adenosine receptor antagonist aminophylline, suggesting adenosinergic involvement in turtle but not in shark.

Mitochondrial ATP‐sensitive K+ channels regulate NMDAR activity in the cortex of the anoxic western painted turtle

Hypoxic mammalian neurons undergo excitotoxic cell death, whereas painted turtle neurons survive prolonged anoxia without apparent injury. Anoxic survival is possibly mediated by a decrease in N-methyl-d-aspartate receptor (NMDAR) activity and maintenance of cellular calcium concentrations ([Ca(2+)](c)) within a narrow range during anoxia. In mammalian ischaemic models, activation of mitochondrial ATP-sensitive K(+) (mK(ATP)) channels partially uncouples mitochondria resulting in a moderate increase in [Ca(2+)](c) and neuroprotection. The aim of this study was to determine the role of mK(ATP) channels in anoxic turtle NMDAR regulation and if mitochondrial uncoupling and [Ca(2+)](c) changes underlie this regulation. In isolated mitochondria, the K(ATP) channel activators diazoxide and levcromakalim increased mitochondrial respiration and decreased ATP production rates, indicating mitochondria were 'mildly' uncoupled by 10-20%. These changes were blocked by the mK(ATP) antagonist 5-hydroxydecanoic acid (5HD). During anoxia, [Ca(2+)](c) increased 9.3 +/- 0.3% and NMDAR currents decreased 48.9 +/- 4.1%. These changes were abolished by K(ATP) channel blockade with 5HD or glibenclamide, Ca(2+)(c) chelation with 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) or by activation of the mitochondrial Ca(2+) uniporter with spermine. Similar to anoxia, diazoxide or levcromakalim increased [Ca(2+)](c) 8.9 +/- 0.7% and 3.8 +/- 0.3%, while decreasing normoxic whole-cell NMDAR currents by 41.1 +/- 6.7% and 55.4 +/- 10.2%, respectively. These changes were also blocked by 5HD or glibenclamide, BAPTA, or spermine. Blockade of mitochondrial Ca(2+)-uptake decreased normoxic NMDAR currents 47.0 +/- 3.1% and this change was blocked by BAPTA but not by 5HD. Taken together, these data suggest mK(ATP) channel activation in the anoxic turtle cortex uncouples mitochondria and reduces mitochondrial Ca(2+) uptake via the uniporter, subsequently increasing [Ca(2+)](c) and decreasing NMDAR activity.

Extreme anoxia tolerance in embryos of the annual killifishAustrofundulus limnaeus: insights from a metabolomics analysis

The annual killifish Austrofundulus limnaeus survives in ephemeral pond habitats by producing drought-tolerant diapausing embryos. These embryos probably experience oxygen deprivation as part of their normal developmental environment. We assessed the anoxia tolerance of A. limnaeus embryos across the duration of embryonic development. Embryos develop a substantial tolerance to anoxia during early development, which peaks during diapause II. This extreme tolerance of anoxia is retained during the first 4 days of post-diapause II development and is then lost. Metabolism during anoxia appears to be supported mainly by production of lactate, with alanine and succinate production contributing to a lesser degree. Anoxic embryos also accumulate large quantities of gamma-aminobutyrate (GABA), a potential protector of neural function. It appears that the suite of characters associated with normal development and entry into diapause II in this species prepares the embryos for long-term survival in anoxia even while the embryos are exposed to aerobic conditions. This is the first report of such extreme anoxia tolerance in a vertebrate embryo, and introduces a new model for the study of anoxia tolerance in vertebrates.

KILLIFISH: CHAMPION ANOXIA SURVIVORS

The annual killifish Austrofundulus limnaeus lives life on the edge. The Venezuelan ponds where it lives rapidly evaporate in the dry season,killing off the adults and exposing their mud-buried embryos to extended periods of drought. Not that drought is the first of the embryo's problems:microbes living in the soil use up all the oxygen. `Not only are they coping with life without water, but also with life without oxygen,' says Jason Podrabsky from Portland State University, who has investigated with his colleagues the root of the embryos' extreme anoxia tolerance(p. 2253).The key to the embryos' survival is that they go into periods of dormancy,or diapause, twice during their development, even if conditions are ideal.`Their environment is very harsh and unpredictable, so diapause occurs as a part of their natural developmental program,' says Podrabsky. Unlike most annual killifish, A. limnaeus embryos skip diapause I at four days of development, but enter diapause II at around 24 days old and diapause III near the end of development. During diapause the metabolism slows down greatly, so could this be the key to surviving anoxia?To assess anoxia tolerance during development, the team collected fertilised embryos from 4 to 32 days old and put them in embryo medium at 25°C before sealing the jars and bubbling nitrogen through them to remove all the oxygen. They then kept a close eye on the developing embryos, opening the jars when they started dying and counting how many of them were still alive. They found that the later embryos were exposed to anoxia, the longer they survived: 4-day-old embryos suffered 50% mortality after 20 days of anoxia, while 32-day-old embryos, in diapause II, suffered 50% mortality after more than 60 days anoxia. This is the longest anoxia survival of any vertebrate at 25°C.The team knew from the brine shrimp, another anoxia tolerant animal that enters diapause, that there is a window of opportunity after diapause where the animal can shut down again even if it has restarted its development. To find out if this window existed in the killifish embryos, they collected embryos just out of diapause II and tested their anoxia tolerance. They found that embryos exposed to anoxia 4 days after the end of diapause were still very tolerant, but lost this tolerance when they were tested 8 days after,showing that post-diapause safety cushion in the killifish is about 4 days.But what about changes in metabolism? The team took embryos of different developmental stages and flash froze them to preserve their metabolites. After mashing them up and extracting their metabolites, which they analysed using chromatrography and mass spectrometry, they found that anoxic embryos produced lactate, succinate and the amino acid alanine, which are end-products of anaerobic metabolism. This suggests that the embryos survive by relying on glycogen stores and reducing their metabolic rate, but that they haven't developed an alternative strategy for dealing with anoxia. Embryos that accumulated lactate at the slowest rate also survived the longest.They also found that anoxic embryos produced lots of the neurotransmitter GABA, which is known to protect neurons in other anoxia tolerant species, such as turtles and the crucian carp. Podrabsky explains that it's possible that GABA is protecting the traditionally anoxia-sensitive brain and heart tissue in diapause II embryos. For now, the killifish embryo can elbow its way onto the roll-call of champion vertebrate anoxia survivors.

Therapeutic Hypothermia for Resuscitated Cardiac Arrest Patients with Anoxic Encephalopathy-Neurologic and Survival Results after the Implementation of an Inter-Disciplinary Protocol

Therapeutic Hypothermia for Resuscitated Cardiac Arrest Patients with Anoxic Encephalopathy-Neurologic and Survival Results after the Implementation of an Inter-Disciplinary Protocol

Polycyclic Aromatic Hydrocarbons and Ecotoxicological Characterization of Seawater, Sediment, and Mussel Mytilus galloprovincialis from the Gulf of Rijeka, the Adriatic Sea, Croatia

The pattern of spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in seawater, sediment, and mussels, potential toxicity of different matrices, and mussel anoxic survival from six sampling sites of the Gulf of Rijeka, the Adriatic Sea, Croatia was examined. The total concentrations of 10 PAHs vary from below detection limit to 305 ng/L in seawater, from 213 to 695 microg/kg dry weight in sediment and from 49.2 to 134 ng/g wet weight in mussel tissue. Combustion is the principal source of PAH contamination in seawater and sediment samples. Sediment samples are distinguished from the majority of seawater and mussel samples by the presence of high molecular weight PAHs, whereas mussels from majority of sampling sites tend to accumulate PAHs of lower molecular weight. The PAH dynamic between different matrices is complex and site specific. Toxicity of seawater and sediment organic extract is correlated with PAH content, indicating that PAHs are the predominant toxic compounds. There is no correlation between toxicity of mussel biological fluids and toxicity of seawater and sediment, or between toxicity of mussel biological fluid and PAH content in mussel, seawater, or sediment. There is a positive correlation between potential toxicity of mussel biological fluids and reduction of anoxic survival time. Mussel anoxic survival is influenced by the presence of complex mixture of toxic contaminants, not only PAHs. The relationship between PAH contents in different marine matrices and their ability to affect mussels revealed specific interactions between an organism and complex mixture of toxic contaminants present in the marine environment.

Hypoxia Tolerance in Reptiles, Amphibians, and Fishes: Life with Variable Oxygen Availability

The ability of fishes, amphibians, and reptiles to survive extremes of oxygen availability derives from a core triad of adaptations: profound metabolic suppression, tolerance of ionic and pH disturbances, and mechanisms for avoiding free-radical injury during reoxygenation. For long-term anoxic survival, enhanced storage of glycogen in critical tissues is also necessary. The diversity of body morphologies and habitats and the utilization of dormancy have resulted in a broad array of adaptations to hypoxia in lower vertebrates. For example, the most anoxia-tolerant vertebrates, painted turtles and crucian carp, meet the challenge of variable oxygen in fundamentally different ways: Turtles undergo near-suspended animation, whereas carp remain active and responsive in the absence of oxygen. Although the mechanisms of survival in both of these cases include large stores of glycogen and drastically decreased metabolism, other mechanisms, such as regulation of ion channels in excitable membranes, are apparently divergent. Common themes in the regulatory adjustments to hypoxia involve control of metabolism and ion channel conductance by protein phosphorylation. Tolerance of decreased energy charge and accumulating anaerobic end products as well as enhanced antioxidant defenses and regenerative capacities are also key to hypoxia survival in lower vertebrates.

The heart as a working model to explore themes and strategies for anoxic survival in ectothermic vertebrates

Most vertebrates die within minutes when deprived of molecular oxygen (anoxia), in part because of cardiac failure, which can be traced to an inadequate matching of cardiac ATP supply to ATP demand. Cardiac power output (PO; estimated from the product of cardiac output and central arterial pressure and an indirect measure of cardiac ATP demand) is directly related to cardiac ATP supply up to some maximal level during both normoxia (ATP supply estimated from myocardial O(2) consumption) and anoxia (ATP supply estimated from lactate production rates). Thus, steady state PO provides an excellent means to examine anoxia tolerance strategies among ectothermic vertebrates by indicating a matching of cardiac glycolytic ATP supply and demand. Here, we summarize in vitro measurements of PO data from rainbow trout, freshwater turtles and hagfishes to provide a reasonable benchmark PO of 0.7 mW g(-1) for maximum glycolytic potential of ectothermic hearts at 15 degrees C, which corresponds to a glycolytic ATP turnover rate of about 70 nmol ATP g(-1) s(-1). Using this benchmark to evaluate in vivo PO data for hagfishes, carps and turtles, we identify two cardiac survival strategies, which in conjunction with creative waste management techniques to reduce waste accumulation, allow for long-term cardiac survival during anoxia in these anoxia-tolerant species. Hagfish and crucian carp exemplify a strategy of evolving such a low routine PO that routine cardiac ATP demand lies within the range of the maximum cardiac glycolytic potential. Common carp and freshwater turtles exemplify an active strategy of temporarily and substantially decreasing cardiac and whole body metabolism so that PO is below maximum cardiac glycolytic potential during chronic anoxia despite being quite close to this potential under normoxia.

Hsp72 is neuroprotective in the the anoxia tolerant turtle, Trachemys scripta elegans

Cardiac ischemia, stroke and some neurodegenerative disorders are all characterized by cell damage and death due to low oxygen levels. Heat shock proteins, Hsp72 in particular, are neuroprotective in species from the fruit fly to humans. While increases in Hsp72 and Hsc73 have been reported in anoxia in the highly anoxia-tolerant turtle Trachemys scripta, the protective role of these stress proteins in cell death has yet to be determined. We examined the levels of Hsp72 in neuronally enriched primary cell cultures established from the turtle, and utilized siRNA to knockdown Hsp72 in vitro. Hsp72 protein and RNA levels increased during late anoxia (4 hours) and prolonged anoxia (16hour) with respect to normoxic controls. As in the whole brain, significant levels of Hsp72 protein were observed even in normoxia, which increased 2 to 3-fold after 16 hours of anoxia (P<0.05) indicating a probable role in long-term anoxic cell survival. SiRNA mediated knockdown of Hsp72 resulted in increased cell death compared to controls in both anoxic cells and following reoxygenation after 4 hours anoxia, as evidenced by Propidium Iodide (PI) staining. Hsp72 knockdown has also resulted in increased ROS release upon reoxygenation (P<0.05) in a dose dependent manner, implicating Hsp72 as a key element of anoxic and reoxygenation cell survival that does play a role in the suppression of ROS production. The mechanisms by which Hsp72 promotes neuronal survival in anoxia and reoxygenation are currently under investigation.

Comparative shell buffering properties correlate with anoxia tolerance in freshwater turtles

Freshwater turtles as a group are more resistant to anoxia than other vertebrates, but some species, such as painted turtles, for reasons not fully understood, can remain anoxic at winter temperatures far longer than others. Because buffering of lactic acid by the shell of the painted turtle is crucial to its long-term anoxic survival, we have tested the hypothesis that previously described differences in anoxia tolerance of five species of North American freshwater turtles may be explained at least in part by differences in their shell composition and buffering capacity. All species tested have large mineralized shells. Shell comparisons included 1) total shell CO2 concentration, 2) volume of titrated acid required to hold incubating shell powder at pH 7.0 for 3 h (an indication of buffer release from shell), and 3) lactate concentration of shell samples incubated to equilibrium in a standard lactate solution. For each measurement, the more anoxia-tolerant species (painted turtle, Chrysemys picta; snapping turtle, Chelydra serpentina) had higher values than the less anoxia-tolerant species (musk turtle, Sternotherus odoratus; map turtle, Graptemys geographica; red-eared slider, Trachemys scripta). We suggest that greater concentrations of accessible CO2 (as carbonate or bicarbonate) in the more tolerant species enable these species, when acidotic, to release more buffer into the extracellular fluid and to take up more lactic acid into their shells. We conclude that the interspecific differences in shell composition and buffering can contribute to, but cannot explain fully, the variations observed in anoxia tolerance among freshwater turtles.

Anoxia tolerance in turtles: Metabolic regulation and gene expression

Freshwater turtles of the Trachemys and Chrysemys genera are champion facultative anaerobes able to survive for several months without oxygen during winter hibernation in cold water. They have been widely used as models to identify and understand the molecular mechanisms of natural anoxia tolerance and the molecular basis of the hypoxic/ischemic injuries that occur in oxygen-sensitive systems and underlie medical problems such as heart attack and stroke. Peter L. Lutz spent much of his career investigating turtle anaerobiosis with a particular focus on the mechanisms of brain ion homeostasis and neurotransmitter responses to anoxia exposure and the mechanisms that suppress brain ion channel function and neuronal excitability during anaerobiosis. Our interests intersected over the mechanisms of metabolic rate depression which is key to long term anoxia survival. Studies in my lab have shown that a key mechanism of metabolic arrest is reversible protein phosphorylation which provides coordinated suppression of the rates of multiple ATP-producing, ATP-utilizing and related cellular processes to allow organisms to enter a stable hypometabolic state. Anoxia tolerance is also supported by selective gene expression as revealed by recent studies using cDNA library and DNA array screening. New studies with both adult T. scripta elegans and hatchling C. picta marginata have identified prominent groups of genes that are up-regulated under anoxia in turtle organs, in several cases suggesting aspects of cell function and metabolic regulation that have not previously been associated with anaerobiosis. These groups of anoxia-responsive genes include mitochondrially-encoded subunits of electron transport chain proteins, iron storage proteins, antioxidant enzymes, serine protease inhibitors, transmembrane solute carriers, neurotransmitter receptors and transporters, and shock proteins.

Gene transcription of neuroglobin is upregulated by hypoxia and anoxia in the brain of the anoxia-tolerant turtle Trachemys scripta

Neuroglobin is a heme protein expressed in the vertebrate brain in mammals, fishes, and birds. The physiological role of neuroglobin is not completely understood but possibilities include serving as an intracellular oxygen-carrier or oxygen-sensor, as a terminal oxidase to regenerate NAD(+) under anaerobic conditions, or involvement in NO or ROS metabolism. As the vertebrate nervous system is particularly sensitive to hypoxia, an intracellular protein that helps sustain cellular respiration would aid hypoxic survival. However, the regulation of Neuroglobin (Ngb) under conditions of varying oxygen is controversial. This study examines the regulation of Ngb in an anoxia-tolerant vertebrate under conditions of hypoxia and anoxia. The freshwater turtle Trachemys scripta can withstand complete anoxia for days, and adaptations that permit neuronal survival have been extensively examined. Turtle neuroglobin specific primers were employed in RT-PCR for determining the regulation of neuroglobin mRNA expression in turtles placed in normoxia, hypoxia (4 h), anoxia (1 and 4 h), and anoxia-reoxygenation. Whole brain expression of neuroglobin is strongly upregulated by hypoxia and post-anoxic-reoxygenation in T. scripta, with a lesser degree of upregulation at 1 and 4 h anoxia. Our data implicate neuroglobin in mediating brain anoxic survival.

Fermentation metabolism in roots of wheat seedlings after hypoxic pre-treatment in different anoxic incubation systems

A hypoxic pre-treatment (HPT) can improve the anoxic survival of flooding sensitive plants. Here, we tested whether a 4-d HPT of wheat plants (Triticum aestivum L.) would improve their anoxic resistance, and if so, why. We found that the metabolic adjustment during prolonged HPT involved an increased lactate excretion rate, the up-regulation of glycolytic and fermentative enzymes as well as the accumulation of various sugars. Therefore, HPT wheat roots could sustain a 3 times higher ethanolic fermentation rate during an anoxic period compared to non-pre-treated (NHPT) roots. Nevertheless, the enhanced fermentation rate provided temporary relief to the energy crisis only, and both NHPT and HPT plants died after 5d of anoxia in illumination. Comparison of different low oxygen incubation systems using excised roots or roots of intact plants revealed striking differences. The benefits of intact shoots, oxygen transport as well as additional sugar supply enabled a more stable energy supply of anoxia-treated NHPT and HPT roots. However, the height of the fermentation rate was correlated with a high ATP content during dark anoxic incubation, but not in illumination.

HIF-1α involvement in low temperature and anoxia survival by a freeze tolerant insect

Winter survival for many insect species relies on the ability to endure the freezing of extracellular body fluids. Because freezing impedes oxygen delivery to tissues, one component of natural freeze tolerance is a well-developed anoxia/ischemia resistance. The present study explores the responses of the hypoxia-inducible factor-1alpha (HIF-1alpha) to cold, freezing and anoxia exposures in the freeze tolerant goldenrod gall fly larva, Eurosta solidaginis. Reverse transcription-PCR was used to quantify hif-1alpha transcript levels; transcripts were significantly elevated by approximately 70% in chilled (3 ( composite function)C), frozen (-16 ( composite function)C) and thawed (returned to 3 ( composite function)C) insects, compared with 15 ( composite function)C controls. Transcripts also rose by approximately 3-fold in insects given anoxia exposure under a nitrogen gas atmosphere. Cold and freezing exposure also elevated HIF-1alpha protein content in the larvae and HIF-1alpha levels increased over the winter months in insects sampled from an outdoor population; levels peaked in February at 2.1-fold higher than in September. A partial sequence of HIF-1alpha that covers the bHLH and PAS domains of the protein was obtained from E. solidaginis and sequence analysis revealed that this segment shared 62% identity overall with Drosophila melanogaster HIF-1alpha and higher percent identities within specific domains: 76% within the bHLH domain and 70% within the PAS domain. The data provide the first documentation of a potential role for HIF-1 in regulating the expression of genes that can aid freezing survival in a cold-hardy animal.

Respiratory adaptations to oxygen lack in three species of Glossiphoniidae (Hirudinea) in Lake Esrom, Denmark

The weight-specific respiration rate (μl O 2 mg −1 AFDW h −1) of three species of leech from Lake Esrom, Denmark, Glossiphonia concolor, G. complanata and Helobdella stagnalis was measured in a closed stirred chamber with a micro electrode. At declining oxygen concentration (mg O 2 l −1) all three species expressed moderate ability to regulate respiration, in G. concolor and G. complanata down to 2 mg O 2 l −1, in H. stagnalis down to 0.75 mg O 2 l −1. Survival in anoxia was measured in closed bottles. The time to 50% survival (LD 50) was 30 days in G. concolor at 20 °C and 30 and 4 days in H. stagnalis at 10 and 20 °C, respectively. The results were discussed in relation to habitat and spatial distribution of the three species in the lake.

Metabolic performance and survival of medusae in estuarine hypoxia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 294:189-200 (2005) - doi:10.3354/meps294189 Metabolic performance and survival of medusae in estuarine hypoxia Ladd D. Rutherford Jr*, Erik V. Thuesen Laboratory One, The Evergreen State College, Olympia, Washington 98505, USA *Email: rutherfl@evergreen.edu ABSTRACT: Increasing eutrophication and hypoxia in marine environments appear to differentially promote the survival of some medusae species and the disappearance of others. To understand the physiological basis for this phenomenon, respiration rates and critical oxygen tensions (Pc) were measured for 12 species of medusae from Puget Sound (Washington State, USA). Mean mass-specific respiration rates ranged between 0.064 µmol O2 g–1 h–1 for Aequorea victoria to 0.78 µmol O2 g–1 h–1 for Cyanea capillata. Six of 12 species studied were oxyregulators; including the scyphomedusae Aurelia labiata, C. capillata, and Phacellophora camtschatica and the hydromedusae A. victoria, Polyorchis penicillatus, and Proboscidactyla flavicirrata. Mean Pcs ranged from 5.5 hPa in Muggiaea atlantica to 39.5 hPa in Euphysa flammea. The relationship between mass-specific metabolic rate and Pc was significant for oxyregulators but not oxyconformers. An apparent metabolic depression occurred variably within all oxyregulating species and 2 oxyconforming species, Clytia gregaria and Sarsia sp., whereby sub-Pc oxygen uptake decreased by 77 to 99% relative to standard aerobic metabolic rate (SMR). Anoxia survival varied from less than 2 h for E. flammea and Eutonina indicans to more than 10 h for A. victoria. The poor low oxygen tolerance of several Puget Sound species in our study was consistent with the historical disappearance of related species in the Adriatic Sea following increased frequency of dysaerobic events. Interspecies variation in aerobic metabolic characteristics and hypoxia and anoxia tolerance may explain why some medusae thrive in low-oxygen conditions, while others disappear. KEY WORDS: Medusae · Oxyregulation · Hypoxia tolerance · Critical PO2 · Hydromedusae · Scyphomedusae Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 294. Online publication date: June 09, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

110 Reduced Expression of Microsomal Prostaglandin Synthase 1 Attenuates Ventilatory Effects of Interleukin-1â in Neonatal DBA/1LACJ Mice

Background: Infection and apnea represent major medical concerns in the neonatal population, and the pro-inflammatory cytokine interleukin-1Â (IL-1Â ) may serve as a critical link between these events. We recently showed that IL-1Â depresses respiration and anoxic survival via a prostaglandin-dependent mechanism (Olsson et al, 2003). In brain, microsomal prostaglandin E synthase 1 (mPGES-1) has been demonstrated crucial for the development of endotoxin-induced fever and is widely expressed in endothelial cells of the blood-brain-barrier after IL-1Â provocation. These same cells also express the IL-1 receptor as well as cyclooxygenase-2, which catalyzes the formation of prostaglandin H2 (PGH2) from arachidonic acid. mPGES-1 subsequently synthesizes prostaglandin E2 (PGE2) from PGH2. This study tested the hypothesis that IL-1Â alters respiratory control in newborn mice via a PGE2-mediated pathway.Methods: Respiratory behavior was examined using flow plethysmography in 9 day-old DBA/1lacJ wildtype mice and heterozygote knockout mice for mPGES-1. At 70 min after an intraperitoneal injection of either IL-1Â or saline, mice were placed unrestrained in the plethysmograph chamber. Basal respiration and the ventilatory response to anoxia (100% N2) and hyperoxia (100% O2) were then examined. Genotyping was performed after experimentation in all animals.Results: During normoxia, wildtype mice given IL-1Â exhibited a reduced respiratory frequency and tidal volume compared to control animals. Heterozygote knockout mice for mPGES-1 experienced less depression of basal respiration by IL-1Â. In response to anoxia, the IL-1Â -treated wildtype mice displayed fewer gasps and were unable to sustain gasping efforts for as long as control animals. They also were less able to autoresuscitate and survive following severe hypoxic apnea compared to control animals. These deleterious effects of IL-1Â were prevented in mice with a reduced expression of mPGES-1. Skin temperature was similar between groups prior to and following experimentation, suggesting that the results observed here are not due to confounding systemic changes induced by IL-1Â.Conclusion: This study indicates that IL-1Â adversely affects respiration and autoresuscitation in newborn mice and that these changes are mediated by PGE2. These findings may have clinical implications for the screening and treatment of neonatal apnea associated with infection.

Negotiating brain anoxia survival in the turtle.

The turtle brain's extraordinary ability to tolerate anoxia is based on constitutive and expressed factors. Constitutive factors that predispose for anoxia tolerance include enhanced levels of glycogen stores, increased densities of protective receptors, elevated antioxidant capacities and elevated heat shock protein. However, to survive an anoxic insult, three distinct phases must be negotiated successfully. (1) A coordinated downregulation of ATP demand processes to basal levels. This phase, which takes 1-2 h, includes a reduction in voltage-gated K(+) (Kv) channel transcription and a substantial increase in Hsp72 and Hsc73 levels. During this period, adenosine and K(ATP) channels mediate several key events including channel arrest initiation and a reduction in the release of excitatory amino acids (EAAs). (2) Long-term survival (days) at basal levels of ATP expenditure. Neuronal network integrity is preserved through the continued operation of core activities. These include periodic electrical activity, an increased release of GABA and a continued release of glutamate and dopamine. Adenosine and GABA modulate the glutamate release. There is a further increase in Hsc73, indicating a 'housekeeping' role for this protein during this period. (3) A rapid upregulation of neuronal processes when oxygen becomes available to restore full function, together with the activation of protection mechanisms against reperfusion-generated reactive oxygen species.

Vertebrate brains at the pilot light.

While the brains of most vertebrates are unable to tolerate more than a few minutes of anoxia, some freshwater turtles (Trachemys and Chrysemys), crucian carp (Carassius carassius) and frogs (Rana pipens and Rana temporaria) can survive anoxia for hours to months. Obviously, anoxia tolerance has evolved separately several times and this is also reflected in the divergent strategies these animals utilize to survive without oxygen. The turtles and crucian carp defend their brain ATP levels and avoid a loss of ion homeostasis by reducing ATP use. In the turtles, the early release of adenosine and the activation of K(ATP) channels, a progressive release of GABA and a drastic reduction in electric activity and ion fluxes send the brain into a comatose like state. The crucian carp displays a more modest depression of ATP use, probably achieved through a moderated release of GABA and adenosine, allowing the animal to maintain physical activity in anoxia. The anoxic frog, on the other hand, seems to rely on mechanisms that greatly retard the anoxia induced fall in ATP levels and loss of ion homeostasis, so that the brain can be saved as long as the anoxia is limited to a few hours. The sequence of events characterizing the anoxic frog brain is similar to that of failing anoxic mammalian brain, although over a greatly extended time frame, allowing the frog to die slowly in anoxia, rather than survive. By contrast the only factor that limits anoxic survival in turtles and crucian carp may be the final depletion of their glycogen reserves.

Adenosine as a signal for ion channel arrest in anoxia-tolerant organisms*1

Certain freshwater turtles and fish are extremely anoxia-tolerant, capable of surviving hours of anoxia at high temperatures and weeks to months at low temperatures. There is great interest in understanding the cellular mechanisms underlying anoxia-tolerance in these groups because they are anoxia-tolerant vertebrates and because of the far-reaching medical benefits that would be gained. It has become clear that a pre-condition of prolonged anoxic survival must involve the matching of ATP production with ATP utilization to maintain stable ATP levels during anoxia. In most vertebrates, anoxia leads to a severe decrease in ATP production without a concomitant reduction in utilization, which inevitably leads to the catastrophic events associated with cell death or necrosis. Anoxia-tolerant organisms do not increase ATP production when faced with anoxia, but rather decrease utilization to a level that can be met by anaerobic glycolysis alone. Protein synthesis and ion movement across the plasma membrane are the two main targets of regulatory processes that reduce ATP utilization and promote anoxic survival. However, the oxygen sensing and biochemical signaling mechanisms that achieve a coordinated reduction in ATP production and utilization remain unclear. One candidate-signaling compound whose extracellular concentration increases in concert with decreasing oxygen availability is adenosine. Adenosine is known to have profound effects on various aspects of tissue metabolism, including protein synthesis, ion pumping and permeability of ion channels. In this review, I will investigate the role of adenosine in the naturally anoxia-tolerant freshwater turtle and goldfish and give an overview of pathways by which adenosine concentrations are regulated.