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A quantitative synthesis of and predictive framework for studying winter warming effects in reptiles. Oecologia 2022; 200:259-271. [PMID: 36100724 PMCID: PMC9547783 DOI: 10.1007/s00442-022-05251-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Accepted: 08/19/2022] [Indexed: 12/03/2022]
Abstract
Increases in temperature related to global warming have important implications for organismal fitness. For ectotherms inhabiting temperate regions, ‘winter warming’ is likely to be a key source of the thermal variation experienced in future years. Studies focusing on the active season predict largely positive responses to warming in the reptiles; however, overlooking potentially deleterious consequences of warming during the inactive season could lead to biased assessments of climate change vulnerability. Here, we review the overwinter ecology of reptiles, and test specific predictions about the effects of warming winters, by performing a meta-analysis of all studies testing winter warming effects on reptile traits to date. We collated information from observational studies measuring responses to natural variation in temperature in more than one winter season, and experimental studies which manipulated ambient temperature during the winter season. Available evidence supports that most reptiles will advance phenologies with rising winter temperatures, which could positively affect fitness by prolonging the active season although effects of these shifts are poorly understood. Conversely, evidence for shifts in survivorship and body condition in response to warming winters was equivocal, with disruptions to biological rhythms potentially leading to unforeseen fitness ramifications. Our results suggest that the effects of warming winters on reptile species are likely to be important but highlight the need for more data and greater integration of experimental and observational approaches. To improve future understanding, we recap major knowledge gaps in the published literature of winter warming effects in reptiles and outline a framework for future research.
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Hussan MT, Sakai A, Matsui H. Glutamatergic pathways in the brains of turtles: A comparative perspective among reptiles, birds, and mammals. Front Neuroanat 2022; 16:937504. [PMID: 36059432 PMCID: PMC9428285 DOI: 10.3389/fnana.2022.937504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 07/22/2022] [Indexed: 11/13/2022] Open
Abstract
Glutamate acts as the main excitatory neurotransmitter in the brain and plays a vital role in physiological and pathological neuronal functions. In mammals, glutamate can cause detrimental excitotoxic effects under anoxic conditions. In contrast, Trachemys scripta, a freshwater turtle, is one of the most anoxia-tolerant animals, being able to survive up to months without oxygen. Therefore, turtles have been investigated to assess the molecular mechanisms of neuroprotective strategies used by them in anoxic conditions, such as maintaining low levels of glutamate, increasing adenosine and GABA, upregulating heat shock proteins, and downregulating KATP channels. These mechanisms of anoxia tolerance of the turtle brain may be applied to finding therapeutics for human glutamatergic neurological disorders such as brain injury or cerebral stroke due to ischemia. Despite the importance of glutamate as a neurotransmitter and of the turtle as an ideal research model, the glutamatergic circuits in the turtle brain remain less described whereas they have been well studied in mammalian and avian brains. In reptiles, particularly in the turtle brain, glutamatergic neurons have been identified by examining the expression of vesicular glutamate transporters (VGLUTs). In certain areas of the brain, some ionotropic glutamate receptors (GluRs) have been immunohistochemically studied, implying that there are glutamatergic target areas. Based on the expression patterns of these glutamate-related molecules and fiber connection data of the turtle brain that is available in the literature, many candidate glutamatergic circuits could be clarified, such as the olfactory circuit, hippocampal–septal pathway, corticostriatal pathway, visual pathway, auditory pathway, and granule cell–Purkinje cell pathway. This review summarizes the probable glutamatergic pathways and the distribution of glutamatergic neurons in the pallium of the turtle brain and compares them with those of avian and mammalian brains. The integrated knowledge of glutamatergic pathways serves as the fundamental basis for further functional studies in the turtle brain, which would provide insights on physiological and pathological mechanisms of glutamate regulation as well as neural circuits in different species.
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Affiliation(s)
- Mohammad Tufazzal Hussan
- Department of Neuroscience of Disease, Brain Research Institute, Niigata University, Niigata, Japan
- Department of Anatomy and Histology, Patuakhali Science and Technology University, Barishal, Bangladesh
- *Correspondence: Mohammad Tufazzal Hussan,
| | - Akiko Sakai
- Department of Neuroscience of Disease, Brain Research Institute, Niigata University, Niigata, Japan
| | - Hideaki Matsui
- Department of Neuroscience of Disease, Brain Research Institute, Niigata University, Niigata, Japan
- Hideaki Matsui,
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Sparks K, Couturier CS, Buskirk J, Flores A, Hoeferle A, Hoffman J, Stecyk JAW. Gene expression of hypoxia-inducible factor (HIF), HIF regulators, and putative HIF targets in ventricle and telencephalon of Trachemys scripta acclimated to 21 °C or 5 °C and exposed to normoxia, anoxia or reoxygenation. Comp Biochem Physiol A Mol Integr Physiol 2022; 267:111167. [PMID: 35182763 PMCID: PMC8977064 DOI: 10.1016/j.cbpa.2022.111167] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2022] [Revised: 02/10/2022] [Accepted: 02/10/2022] [Indexed: 12/20/2022]
Abstract
In anoxia-sensitive mammals, hypoxia inducible factor (HIF) promotes cellular survival in hypoxia, but also tumorigenesis. By comparison, anoxia-tolerant vertebrates likely need to circumvent a prolonged upregulation of HIF to survive long-term anoxia, making them attractive biomedical models for investigating HIF regulation. To lend insight into the role of HIF in anoxic Trachemys scripta ventricle and telencephalon, 21 °C- and 5 °C-acclimated turtles were exposed to normoxia, anoxia (24 h at 21 °C; 24 h or 14 d at 5 °C) or anoxia + reoxygenation and the gene expression of HIF-1α (hif1a) and HIF-2α (hif2a), two regulators of HIF, and eleven putative downstream targets of HIF quantified by qPCR. Changes in gene expression with anoxia at 21 °C differentially aligned with a circumvention of HIF activity. Whereas hif1a and hif2a expression was unaffected in ventricle and telencephalon, and BCL2 interacting protein 3 gene expression reduced by 30% in telencephalon, gene expression of vascular endothelial growth factor-A increased in ventricle (4.5-fold) and telencephalon (1.5-fold), and hexokinase 1 (2-fold) and hexokinase 2 (3-fold) gene expression increased in ventricle. At 5 °C, the pattern of gene expression in ventricle or telencephalon was unaltered with oxygenation state. However, cold acclimation in normoxia induced downregulation of HIF-1α, HIF-2α, and HIF target gene expression in telencephalon. Overall, the findings lend support to the postulation that prolonged activation of HIF is counterproductive for long-term anoxia survival. Nevertheless, quantification of the effect of anoxia and acclimation temperature on HIF binding activity and regulation at the protein level are needed to provide a strong scientific framework whereby new strategies for oxygen related pathologies can be developed.
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Affiliation(s)
- Kenneth Sparks
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Christine S Couturier
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Jacob Buskirk
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Alicia Flores
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Aurora Hoeferle
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Jessica Hoffman
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States
| | - Jonathan A W Stecyk
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States.
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Lari E, Buck LT. Exposure to low temperature prepares the turtle brain to withstand anoxic environments during overwintering. J Exp Biol 2021; 224:272110. [PMID: 34498078 DOI: 10.1242/jeb.242793] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 08/27/2021] [Indexed: 11/20/2022]
Abstract
In most vertebrates, anoxia drastically reduces the production of the essential adenosine triphosphate (ATP) to power its many necessary functions, and, consequently, cell death occurs within minutes. However, some vertebrates, such as the painted turtle (Chrysemys picta bellii), have evolved the ability to survive months without oxygen by simultaneously decreasing ATP supply and demand, surviving the anoxic period without any apparent cellular damage. The impact of anoxia on the metabolic function of painted turtles has received a lot of attention. However, the impact of low temperature has received less attention and the interactive effect of anoxia and temperature even less. In the present study, we investigated the interactive impacts of reduced temperature and severe hypoxia on the electrophysiological properties of pyramidal neurons in painted turtle cerebral cortex. Our results show that an acute reduction in temperature from 20 to 5°C decreases membrane potential, action potential width and amplitude, and whole-cell conductance. Importantly, acute exposure to 5°C considerably slows membrane repolarization by voltage-gated K+ channels. Exposing pyramidal cells to severe hypoxia in addition to an acute temperature change slightly depolarized membrane potential but did not alter action potential amplitude or width and whole-cell conductance. These results suggest that acclimation to low temperatures, preceding severe environmental hypoxia, induces cellular responses in pyramidal neurons that facilitate survival under low oxygen concentrations. In particular, our results show that temperature acclimation invokes a change in voltage-gated K+ channel kinetics that overcomes the acute inhibition of the channel.
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Affiliation(s)
- Ebrahim Lari
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada, M5S 3G5.,Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2E9
| | - Leslie T Buck
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada, M5S 3G5.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada, M5S 3B2
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Stecyk JAW, Barber RG, Cussins J, Hall D. Indirect evidence that anoxia exposure and cold acclimation alter transarcolemmal Ca 2+ flux in the cardiac pacemaker, right atrium and ventricle of the red-eared slider turtle (Trachemys scripta). Comp Biochem Physiol A Mol Integr Physiol 2021; 261:111043. [PMID: 34332046 DOI: 10.1016/j.cbpa.2021.111043] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2021] [Revised: 07/22/2021] [Accepted: 07/23/2021] [Indexed: 12/15/2022]
Abstract
We indirectly assessed if altered transarcolemmal Ca2+ flux accompanies the decreased cardiac activity displayed by Trachemys scripta with anoxia exposure and cold acclimation. Turtles were first acclimated to 21 °C or 5 °C and held under normoxic (21N; 5N) or anoxic conditions (21A; 5A). We then compared the response of intrinsic heart rate (fH) and maximal developed force of spontaneously contracting right atria (Fmax,RA), and maximal developed force of isometrically-contracting ventricular strips (Fmax,V), to Ni2+ (0.1-10 mM), which respectively blocks T-type Ca2+ channels, L-type Ca2+ channels and the Na+-Ca2+-exchanger at the low, intermediate and high concentrations employed. Dose-response curves were established in simulated in vivo normoxic (Sim Norm) or simulated in vivo anoxic extracellular conditions (Sim Anx; 21A and 5A preparations). Ni2+ decreased intrinsic fH, Fmax,RA and Fmax,V of 21N tissues in a concentration-dependent manner, but the responses were blunted in 21A tissues in Sim Norm. Similarly, dose-response curves for Fmax,RA and Fmax,V of 5N tissues were right-shifted, whereas anoxia exposure at 5 °C did not further alter the responses. The influence of Sim Anx was acclimation temperature-, cardiac chamber- and contractile parameter-dependent. Combined, the findings suggest that: (1) reduced transarcolemmal Ca2+ flux in the cardiac pacemaker is a potential mechanism underlying the slowed intrinsic fH of anoxic turtles at 21 °C, but not 5 °C, (2) a downregulation of transarcolemmal Ca2+ flux may aid cardiac anoxia survival at 21 °C and prime the turtle myocardium for winter anoxia and (3) confirm that altered extracellular conditions with anoxia exposure can modify turtle cardiac transarcolemmal Ca2+ flux.
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Affiliation(s)
- Jonathan A W Stecyk
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States of America.
| | - Riley G Barber
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States of America
| | - Jace Cussins
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States of America
| | - Diarmid Hall
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States of America
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Stecyk JAW, Couturier CS, Abramochkin DV, Hall D, Arrant-Howell A, Kubly KL, Lockmann S, Logue K, Trueblood L, Swalling C, Pinard J, Vogt A. Cardiophysiological responses of the air-breathing Alaska blackfish to cold acclimation and chronic hypoxic submergence at 5°C. J Exp Biol 2020; 223:jeb225730. [PMID: 33020178 PMCID: PMC7687868 DOI: 10.1242/jeb.225730] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 09/28/2020] [Indexed: 01/29/2023]
Abstract
The Alaska blackfish (Dallia pectoralis) remains active at cold temperatures when experiencing aquatic hypoxia without air access. To discern the cardiophysiological adjustments that permit this behaviour, we quantified the effect of acclimation from 15°C to 5°C in normoxia (15N and 5N fish), as well as chronic hypoxic submergence (6-8 weeks; ∼6.3-8.4 kPa; no air access) at 5°C (5H fish), on in vivo and spontaneous heart rate (fH), electrocardiogram, ventricular action potential (AP) shape and duration (APD), the background inward rectifier (IK1) and rapid delayed rectifier (IKr) K+ currents and ventricular gene expression of proteins involved in excitation-contraction coupling. In vivo fH was ∼50% slower in 5N than in 15N fish, but 5H fish did not display hypoxic bradycardia. Atypically, cold acclimation in normoxia did not induce shortening of APD or alter resting membrane potential. Rather, QT interval and APD were ∼2.6-fold longer in 5N than in 15N fish because outward IK1 and IKr were not upregulated in 5N fish. By contrast, chronic hypoxic submergence elicited a shortening of QT interval and APD, driven by an upregulation of IKr The altered electrophysiology of 5H fish was accompanied by increased gene expression of kcnh6 (3.5-fold; Kv11.2 of IKr), kcnj12 (7.4-fold; Kir2.2 of IK1) and kcnj14 (2.9-fold; Kir2.4 of IK1). 5H fish also exhibited a unique gene expression pattern that suggests modification of ventricular Ca2+ cycling. Overall, the findings reveal that Alaska blackfish exposed to chronic hypoxic submergence prioritize the continuation of cardiac performance to support an active lifestyle over reducing cardiac ATP demand.
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Affiliation(s)
- Jonathan A W Stecyk
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Christine S Couturier
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Denis V Abramochkin
- Department of Human and Animal Physiology, Lomonosov Moscow State University, 1-12 Leninskiye Gory, 119991 Moscow, Russia
- Ural Federal University, 19 Mira Street, 620002 Ekaterinburg, Russia
- Laboratory of Cardiac Physiology, Institute of Physiology of Kоmi Science Centre of the Ural Branch of the Russian Academy of Sciences, FRC Komi SC UB RAS, 50 Pervomayskaya Str., 167982 Syktyvkar, Komi Republic, Russia
| | - Diarmid Hall
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Asia Arrant-Howell
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Kerry L Kubly
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Shyanne Lockmann
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Kyle Logue
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Lenett Trueblood
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Connor Swalling
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Jessica Pinard
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
| | - Angela Vogt
- Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA
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Cox GK, Gillis TE. Surviving anoxia: the maintenance of energy production and tissue integrity during anoxia and reoxygenation. J Exp Biol 2020; 223:223/13/jeb207613. [DOI: 10.1242/jeb.207613] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
ABSTRACT
The development of anoxia within tissues represents a significant challenge to most animals because of the decreased capacity for aerobic ATP production, the associated loss of essential cellular functions and the potential for detrimental tissue oxidation upon reoxygenation. Despite these challenges, there are many animals from multiple phyla that routinely experience anoxia and can fully recover. In this Review, we integrate knowledge gained from studies of anoxia-tolerant species across many animal taxa. We primarily focus on strategies used to reduce energy requirements, minimize the consequences of anaerobic ATP production and reduce the adverse effects of reactive oxygen species, which are responsible for tissue damage with reoxygenation. We aim to identify common strategies, as well as novel solutions, to the challenges of anoxia exposure. This Review chronologically examines the challenges faced by animals as they enter anoxia, as they attempt to maintain physiological function during prolonged anoxic exposure and, finally, as they emerge from anoxia. The capacity of animals to survive anoxia is also considered in relation to the increasing prevalence of anoxic zones within marine and freshwater environments, and the need to understand what limits survival.
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Affiliation(s)
- Georgina K. Cox
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
| | - Todd E. Gillis
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
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Bundgaard A, Qvortrup K, Rasmussen LJ, Fago A. Turtles maintain mitochondrial integrity but reduce mitochondrial respiratory capacity in the heart after cold acclimation and anoxia. ACTA ACUST UNITED AC 2019; 222:jeb.200410. [PMID: 31097599 DOI: 10.1242/jeb.200410] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Accepted: 05/11/2019] [Indexed: 12/21/2022]
Abstract
Mitochondria are important to cellular homeostasis, but can become a dangerous liability when cells recover from hypoxia. Anoxia-tolerant freshwater turtles show reduced mitochondrial respiratory capacity and production of reactive oxygen species (ROS) after prolonged anoxia, but the mechanisms are unclear. Here, we investigated whether this mitochondrial suppression originates from downregulation of mitochondrial content or intrinsic activity by comparing heart mitochondria from (1) warm (25°C) normoxic, (2) cold-acclimated (4°C) normoxic and (3) cold-acclimated anoxic turtles. Transmission electron microscopy of heart ventricle revealed that these treatments did not affect mitochondrial volume density and morphology. Furthermore, neither enzyme activity, protein content nor supercomplex distribution of electron transport chain (ETC) enzymes changed significantly. Instead, our data imply that turtles inhibit mitochondrial respiration rate and ROS production by a cumulative effect of slight inhibition of ETC complexes. Together, these results show that maintaining mitochondrial integrity while inhibiting overall enzyme activities are important aspects of anoxia tolerance.
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Affiliation(s)
- Amanda Bundgaard
- Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark
| | - Klaus Qvortrup
- Department of Biomedical Sciences/CFIM, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Lene Juel Rasmussen
- Center for Healthy Aging, Department of Cellular and Molecular medicine, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Angela Fago
- Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark
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