29 research outputs found

    Characterization of mouse preoptic area cellular populations involved in thermoregulation

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    Thermoregulation is a dynamic homeostatic process, tightly regulated by the autonomic nervous system. How the brain coordinates maintenance of the body temperature within a narrow range of 37˚C, a condition that is needed for the survival of most of the species, remains unclear. Among the brain regions implicated in thermoregulation is the anterior portion of the hypothalamus, the preoptic area (POA). In this region neurons that respond to direct temperature stimuli and to the skin and spinal cord warming were found, suggesting that these warm-sensitive neurons (WSNs), are the cells that detect deep brain temperature and integrate it with temperature information from the periphery. The limiting factor in studying the WSNs of the POA and their role in thermoregulation is the lack of specific molecular markers that identify them. Therefore, the goal of this thesis work was to characterize WSNs of the POA at the molecular level and to find their genetic marker(s). To achieve this goal I used a primary POA cell culture and performed calcium imaging while applying a temperature stimulus of 45˚C in the presence and the absence of the TRPM2 antagonist, 2-Aminoethoxydiphenyl borate (2-APB). I identified and hand-picked temperature responding cells and temperature non-responding cells for the single-cell RNA-sequencing (scRNA-seq). Analysis of the scRNA-seq data pointed to the limitations of the P9 cell culture used. The majority of the temperature non-responding cells expressed glial marker genes together with neuronal markers, a combination not found in vivo. I concluded that the genetic heterogeneity of the sequenced cells was too large and putative WSNs’ molecular markers identified from cultured neurons would be ambiguous. In addition, to find markers of WNSs one has to take another approach, such as Patch-seq to analyze these neurons in more natural conditions. One of the POA neuronal populations activated by a change in ambient temperature is expressing leptin receptor (POALepR). These neurons also exhibit an increase in action potential firing frequency (AP FF) during the process of chronic heat exposure to 36˚C that also leads to an increased heat endurance (at 39˚C). in mice. This intrinsic property of neurons (not affected by synaptic blockers), seems to be needed for a mouse to endure heat, as the animals in which the firing of POALepR is abolished fail to do so. To learn more about the role of the POALepR neurons in the heat acclimation process I used FACS (Fluorescence Activated Cell Sorting) to isolate the POALepR neurons from POA of non-acclimated and acclimated ( 5 and 30 days at 36 ˚C) LeprCreHTB mice and performed RNA sequencing. I identified three genes Kcnq2, Kcnn2, and Kcnh2, all three coding for potassium ion channels, whose expression level changed with the course of heat acclimation. I have tested the functionality of these ion channels in AP viii firing of the POALepR neurons, by employing electrophysiology and pharmacology in acute POA slices. Ion channels Kv7.2 and Kv11.1, coded by Kcnq2, and Kcnh2, respectively, exhibited a role in shaping the AP firing of POALepR neurons. Applying the antagonist of Kv7.2 disrupted harmonious AP firing of POALepR neurons coming from acclimated mice, rendering their membrane potential unsteady and their firing bursty. In addition, the application of the Kv11.1 antagonist increased the AP FF of POALepR neurons even further in the long-term acclimated condition. Heat acclimation is a naturally occurring process happening across mammalian species, including humans. It is important for enduring physical burdens in hotter climates as it leads to the improved function of the thermoregulatory system. It is forthright to hypothesize that the POA, the central regulator of temperature homeostasis, plays a role in heat acclimation. However, knowledge about it is scarce. Knowing which molecules change in POALepR neurons transcriptome to increase firing, and to which other thermoregulatory relays these neurons project will help us understand their role and the role of POA in heat acclimation

    Independent and combined impact of hypoxia and acute inorganic nitrate ingestion on thermoregulatory responses to the cold

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    Purpose: This study assessed the impact of normobaric hypoxia and acute nitrate ingestion on shivering thermogenesis, cutaneous vascular control, and thermometrics in response to cold stress. Method: Eleven male volunteers underwent passive cooling at 10 °C air temperature across four conditions: (1) normoxia with placebo ingestion, (2) hypoxia (0.130 FiO2) with placebo ingestion, (3) normoxia with 13 mmol nitrate ingestion, and (4) hypoxia with nitrate ingestion. Physiological metrics were assessed as a rate of change over 45 min to determine heat loss, and at the point of shivering onset to determine the thermogenic thermoeffector threshold. Result: Independently, hypoxia expedited shivering onset time (p = 0.05) due to a faster cooling rate as opposed to a change in central thermoeffector thresholds. Specifically, compared to normoxia, hypoxia increased skin blood flow (p = 0.02), leading to an increased core-cooling rate (p = 0.04) and delta change in rectal temperature (p = 0.03) over 45 min, yet the same rectal temperature at shivering onset (p = 0.9). Independently, nitrate ingestion delayed shivering onset time (p = 0.01), mediated by a change in central thermoeffector thresholds, independent of changes in peripheral heat exchange. Specifically, compared to placebo ingestion, no difference was observed in skin blood flow (p = 0.5), core-cooling rate (p = 0.5), or delta change in rectal temperature (p = 0.7) over 45 min, while nitrate reduced rectal temperature at shivering onset (p = 0.04). No interaction was observed between hypoxia and nitrate ingestion. Conclusion: These data improve our understanding of how hypoxia and nitric oxide modulate cold thermoregulation

    Bearded dragons (Pogona vitticeps) with reduced scalation lose water faster but do not have substantially different thermal preferences.

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    Whether scales reduce cutaneous evaporative water loss in lepidosaur reptiles (Superorder Lepidosauria) such as lizards and snakes has been a contentious issue for nearly half a century. Furthermore, while many studies have looked at whether dehydration affects thermal preference in lepidosaurs, far fewer have examined whether normally hydrated lepidosaurs can assess their instantaneous rate of evaporative water loss and adjust their thermal preference to compensate in an adaptive manner. We tested both of these hypotheses using three captive-bred phenotypes of bearded dragon (Pogona vitticeps) sourced from the pet trade: ‘Wild Types’ with normal scalation, ‘Leatherbacks’ exhibiting scales of reduced prominence, and scaleless bearded dragons referred to as ‘Silkbacks’. Silkbacks on average lost water evaporatively at about twice the rate that Wild Types did. Leatherbacks on average were closer in their rates of evaporative water loss to Silkbacks than they were to Wild Types. Additionally, very small (at most ~1°C) differences in thermal preference existed between the three phenotypes that were not statistically significant. This suggests a lack of plasticity in thermal preference in response to an increase in rate of evaporative water loss, and may be reflective of a thermal ‘strategy’ as employed by thermoregulating bearded dragons that prioritises immediate thermal benefits over the threat of future dehydration. The results of this study bolster an often-discounted hypothesis regarding the present adaptive function of scales and have implications for the applied fields of animal welfare and conservation.Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada (Grant RGPIN-2014-05814)

    Naked mole-rat brown fat thermogenesis is diminished during hypoxia through a rapid decrease in UCP1

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    Naked mole-rats are among the most hypoxia-tolerant mammals. During hypoxia, their body temperature (Tb) decreases via unknown mechanisms to conserve energy. In small mammals, non-shivering thermogenesis in brown adipose tissue (BAT) is critical to Tb regulation; therefore, we hypothesize that hypoxia decreases naked mole-rat BAT thermogenesis. To test this, we measure changes in Tb during normoxia and hypoxia (7% O2; 1–3 h). We report that interscapular thermogenesis is high in normoxia but ceases during hypoxia, and Tb decreases. Furthermore, in BAT from animals treated in hypoxia, UCP1 and mitochondrial complexes I-V protein expression rapidly decrease, while mitochondria undergo fission, and apoptosis and mitophagy are inhibited. Finally, UCP1 expression decreases in hypoxia in three other social African mole-rat species, but not a solitary species. These findings suggest that the ability to rapidly down-regulate thermogenesis to conserve oxygen in hypoxia may have evolved preferentially in social species.An NSERC Discovery grants, a Canada Research Chair and an University of Ottawa Research Chair. Collection and housing of mole-rats in Africa were funded by a SARChI grant.http://www.nature.com/naturecommunicationsam2022Zoology and Entomolog

    Evaporative cooling and vasodilation mediate thermoregulation in naked mole-rats during normoxia but not hypoxia

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    Naked mole-rats are among the most hypoxia-tolerant mammals but have a poor thermoregulatory capacity due to their lack of insulating fur and fat, and small body size. In acute hypoxia, naked mole-rat body temperature (Tb) decreases to ambient temperature (Ta) but the mechanisms that underlie this thermoregulatory response are unknown. We hypothesized 1) that naked mole-rat blood vessels vasodilate during hypoxia to shunt heat toward the body surface and/or 2) that they augment heat loss through evaporative cooling. Using open-flow re- spirometry (indirect calorimetry) we explored metabolic and thermoregulatory strategies of naked mole-rats exposed to hypoxia (7% O2 for 1 h) at two relative humidities (RH; 50 or 100% water saturation), and in two Ta's (25 and 30 °C), alone, and following treatment with the vasoconstrictor angiotensin II (ANGII). We found that Tb and metabolic rate decreased in hypoxia across all treatment groups but that neither RH nor ANGII effected either variable in hypoxia. Conversely, both Tb and metabolic rate were reduced in 100% RH or by ANGII treatment in normoxia at 25 °C, and therefore the absolute change in both variables with the onset of hypoxia was reduced when vasodilation or evaporative cooling were prevented. We conclude that naked mole-rats employ evaporative cooling and vasodilation to thermoregulate in normoxia and in 25 °C but that neither mechanism is involved in thermoregulatory changes during acute hypoxia. These findings suggest that NMRs may employ passive strategies such as reducing thermogenesis to reduce Tb in hypoxia, which would support metabolic rate suppression

    Trematode Parasite Infection Affects Temperature Selection in Aquatic Host Snails

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    Animals infected by parasites or pathogens can exhibit altered behaviors that may reduce the costs of infection to the host or represent manipulations that benefit the parasite. Given that temperature affects many critical physiological processes, changes in thermoregulatory behaviors are an important consideration for infected hosts, especially ectotherms. Here we examined the temperature choices of freshwater snails (Helisoma trivolvis) that were or were not infected by a trematode (flatworm) parasite (Echinostoma trivolvis). Active snails that explored the experimental temperature gradient differed in their thermal preference based on their infection status, as parasitized snails chose to position themselves at a significantly higher temperature (mean: 25.4°C) compared to those that were uninfected (mean: 23.3°C). Given that snails rarely eliminate established trematode infections, we suggest that this altered thermal preference shown by infected hosts likely benefits the parasite by increasing the odds of successful transmission, either through enhanced production and emergence of infectious stages or by increasing spatial overlap with the next hosts of the complex life cycle. Further studies that employ experimental infections to examine temperature selection at different time points will be needed to understand the extent of altered host thermal preferences, as well as the possible benefits to both host and parasite

    Trematodes modulate aquatic food webs by altering host feeding behaviour

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    Parasiten können den Energietransfer in Lebensgemeinschaften ĂŒber trophische Kaskaden beeinflussen, indem sie Änderungen in den Konsumenten-Ressourcen-Interaktionen induzieren. In der vorliegenden Arbeit wurde die Rolle von Trematoden auf das Freßverhalten ihrer Wirte auf zwei trophischen Ebenen untersucht. Vier verschiedene SĂŒĂŸwasserschnecken-Trematoden-Systeme wurden verwendet, um zu testen, ob ein allgemeines Muster fĂŒr die Auswirkung von Infektionen auf die GrazingaktivitĂ€t von Schnecken auf das Periphyton nachgewiesen werden kann. Die Grazingraten auf Periphyton bei infizierten Schnecken entweder höher, niedriger oder Ă€hnlich denen derjenigen von nicht infizierten Artgenossen. Augenparasiten können die LeistungsfĂ€higkeit ihres Wirtes beeintrĂ€chtigen, was die Auswirkungen auf das Erkennen von Beutetieren, Raubtieren und Artgenossen hat. Mit Tylodelphys clavata experimentell infizierte Flussbarsche wurden mit zwei verschiedenen Beutetierarten eingesetzt, um das Fraßverhalten in Konkurrenz mit nicht infizierten Artgenossen zu untersuchen. Die Entfernung, aus der infizierte Fische die beiden Beutetierarten attackierten, war im Vergleich zu nicht infizierten Artgenossen signifikant kĂŒrzer. Die Tendenz war, dass nicht infizierte Fische mehr von den verfĂŒgbaren Beutetieren verzehrten. Um zu prĂŒfen, ob der Fisch als Kompensation seine BeuteprĂ€ferenz verĂ€ndert, wurde die Beutezusammensetzung von Flussbarschen aus dem MĂŒggelsees mittels Mageninhalts- und Stabilisotopenanalysen untersucht. Beide Methoden ergaben, dass sich die Fische mit zunehmender IntensitĂ€t der Infektion selektiver ernĂ€hrten, wĂ€hrend sich geringer infizierte Fische Generalisten herausstellten. Die Ergebnisse dieser Studie bestĂ€tigen, dass Trematoden eine wichtige Rolle in Nahrungsnetzen spielen können, indem sie das Freßverhalten ihres Wirtes verĂ€ndern. DarĂŒber hinaus können Trematoden so die StĂ€rke der Interaktion ihrer Wirte mit anderen Arten auf verschiedenen trophischen Ebenen beeinflussen.Parasites can influence energy transfer through communities via trophic cascades by inducing alterations on consumer-resource interactions. This study evaluated the role of trematodes on their host’s feeding behaviour at two trophic levels. Four different freshwater snail–trematode systems were used to test whether a general pattern can be detected for the impact of infections on snail periphyton grazing activity. Mass-specific periphyton grazing rates of infected snails were higher, lower, or similar to rates of non-infected conspecifics. The variation across systems may result from differences on how the parasites use the resources of the snail and thus affect its energy budget. Eye parasites can impair their host’s sensory performance with important consequences for the detection of prey, predators and conspecifics. European perch experimentally infected with Tylodelphys clavata were used to evaluate their feeding behaviour under competition with non-infected conspecifics, for two different prey species (Asellus aquaticus and Daphnia magna). The distance at which infected fish attacked both prey species was significantly shorter in comparison to non-infected conspecifics. Additionally, infected fish had more unsuccessful attacks and there was a general tendency that non-infected fish consumed more of the available prey. To evaluate whether fish alter their prey preference as a compensatory mechanism, perch from Lake MĂŒggelsee were sampled and their diet was evaluated using both stomach content and stable isotope analyses. Both methods indicated that with increasing infection intensity fish had a more selective diet, while less intensively infected fish appeared to be generalist feeders. The results from this study confirm that trematodes can play a relevant role within food webs by altering their hosts’ feeding behaviour. Furthermore, in this way trematodes can affect the interaction strengths of their hosts with other species at various trophic levels

    No experimental evidence of stress-induced hyperthermia in zebrafish (Danio rerio)

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    NJ was supported by a studentship from The Fisheries Society of The British Isles.Stress-induced hyperthermia (SIH) is characterised by a rise in body temperature in response to a stressor. In endotherms SIH is mediated by the autonomic nervous system, whereas ectotherms must raise their body temperature via behavioural means by moving to warmer areas within their environment (behavioural thermoregulation). A recent study suggested that zebrafish (Danio rerio), an important model species, may move to warmer water in response to handling and confinement and thus exhibit SIH, which, if accepted, may have important practical and welfare implications. However an alternative hypothesis proposed that the observed movements may been produced by avoidance behaviour rather than behavioural thermoregulation. Investigating the claims for SIH in zebrafish further we conducted two experiments that extend the earlier study. The first experiment incorporated new conditions that considered fish behaviour in the absence of thermal variation, i.e. their null distribution, an important condition that was not performed in the original study. The second was a refined version of the experiment to reduce the numbers of fish and aid movement between areas for the fish. In contrast to the previous study, we saw no effect of handling or confinement on preference for warmer areas, and no evidence for SIH in either experiment. Instead we observed a short-lived reduction in preference for warmer areas immediately post stress. Our work suggests that zebrafish may not experience SIH and claims regarding fish consciousness based on SIH may need to be revised.PostprintPeer reviewe

    Some like it hot: factors impacting thermal preferences of two Ponto-Caspian amphipods Dikerogammarus villosus (Sovinsky, 1894) and Dikerogammarus haemobaphes (Eichwald, 1841)

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    Temperature is a crucial factor determining biology and ecology of poikilothermic animals. It often constitutes an important barrier for invasive species originating from different climate zones but, on the other hand, may facilitate the invasion process of animals with wide thermal preferences and high resistance to extreme temperatures. In our experimental study, we investigated the thermal behaviour of two Ponto-Caspian amphipod crustaceans—Dikerogammarus villosus and Dikerogammarus haemobaphes. Both species are known to live under a wide range of thermal conditions which may promote their invasion. Moreover, both these amphipods are hosts for microsporidian parasites which co-evolved with them within the Ponto-Caspian region and spread in European waters. As the presence of a parasite may influence the thermal preferences of its host, we expected to observe behavioural changes in infected individuals of the studied amphipods leading to (1) behavioural fever (selecting a warmer habitat) or (2) anapyrexia (selecting a colder habitat). The experiment (N = 20) was carried out for 30 min in a 100 cm. 20 cm from boths sides were not avaliable for amphipods long thermal gradient (0–40 °C), using 30 randomly selected adult amphipod individuals of one species. At the end of each trial, we checked the position of amphipods along the gradient and determined their sex and infection status (uninfected or infected by one of microsporidium species). D. villosus was infected with Cucumispora dikerogammari whereas D. haemobaphes was a host for C. dikerogammari, Dictyocoela muelleri or D. berillonum. Thermal preferences of amphipods depended on their species and sex. Females of D. villosus preferred warmer microhabitats (often much above 30 °C) than conspecific males and females of D. haemobaphes, whereas no significant differences were found among males of both species and both sexes of D. haemobaphes. Moreover, infected males of D. villosus stayed in warmer water more often than uninfected males of this species, selecting temperatures higher than 30 °C, which may be explained either as a behavioural fever constituting a defence mechanism of a host against the infection, or as a parasite manipulation of the host behaviour increasing the parasite fitness. On the other hand, none of the parasite species affected the thermal preferences of D. haemobaphes, including also C. dikerogammari, changing the behaviour of D. villosus. Our research presents the complexity of the thermal behaviour of studied amphipods and the evidence that microsporidia may trigger a change in temperature preferendum of their host species and those observations may be the result of different host-parasite coevolution time which may vary for the two host species (Poulin, 2010)
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