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Comparative Immunology
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
Reptiles, being ectotherms, are unable to change their body temperature by physiologic mechanisms. As a result, they will not develop a fever if maintained in a constant temperature environment. If maintained in an environment with cool and warm areas, they will cycle between these areas and maintain their body temperature within well-defined limits. It has been observed that normal iguanas (Dipsosaurus dorsalis) maintain their temperature between 37° and 41 °C. However iguanas infected with Aeromonas hydrophila modify their behavior, so that they spend more time in the warm environment. As a result, their temperatures cycle between 40° and 43°C. Once the bacterial infection is cured, the iguanas resume their normal behavior. Thus the iguanas effectively induce a fever by their behavior.
Wasted days and wasted nights
Published in James Kennaway, Rina Knoeff, Lifestyle and Medicine in the Enlightenment, 2020
Yet, such simple metaphors have enduring appeal. Matthew Walker, in describing the neuroscience of sleep deprivation, compares the rising level of adenosine in the brain to “rising water in a plugged sink when a faucet has been on” (2017, p. 34). When we at last fall asleep, the drain opens. Dean Buonomano, a professor of neurobiology and psychology at UCLA, compares the “circadian clock” that controls our sleep patterns to a water tank on a toilet with a tiny leak: the float slowly descends until it triggers the valve to fill again. “The circadian clock,” Buonomano writes, “is, of course, way more complicated than your toilet, but the idea is the same” (2017, p. 46). The same idea, I suppose, if one thinks at a level of generality so high as to be nearly meaningless. Buonomano concludes:Like the clockmakers of the eighteenth century who struggled with the effects of temperature on pendulum and mechanical clocks, evolution had to overcome the problem that the speed of biomechanical reactions changes with temperature. We still do not fully understand how ectothermic organisms … maintain a period of approximately 24 hours over daily and seasonal temperature fluctuations. But we know that there are a lot of additional proteins and genes that interact with the basic molecular machinery … and some of these bells and whistles likely contribute to temperature compensation.(Buonomano, 2017, p. 47)
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
Both endotherms and ectotherms use a variety of mechanisms to affect body temperature. (1) Altered heat exchange with the environment: increasing BLOOD flow (VASODILATION) of vessels near the body surface (in the SKIN) produces heat loss; VASOCONSTRICTION helps retain heat. A mechanism known as counter-current heat exchange is used by many endotherms—warmer blood in arteries travelling from the body core heats cooler blood in veins returning. In addition many animals have fur or feathers which insulate them: PILOERECTION (adjustment of the position of individual hairs) aids heat loss. (2) Evaporation: water is lost during BREATHING (either normal breathing or panting; dogs for example lose heat in this way) and by perspiration— SWEAT GLANDS in the skin allow evaporation of water which produces heat loss. (3) Behavioural responses: moving to warmer or cooler environments helps regulate temperature. SOCIAL BEHAVIOUR (for example huddling together to share and conserve heat) is also important. The construction of clothing or specialized dwellings (burrows, nests and so on) is also a behavioural adaptation to aid thermoregulation. MIGRATION, HIBERNATION and AESTIVATION are all behavioural adaptations to enable animals to deal with changed environmental temperatures. All of these processes can be used by endotherms and ectotherms. (4) In addition, endotherms have another mechanism: endogenous heat production. Muscle activity is important in this, as is SHIVERING (which is caused by neural impulses causing muscles to contract desynchronously) a response triggered by the brain's detection of lowered body temperature. NON-SHIVERING THERMOGENESIS is the production of heat by other endogenous means, principally through the action of BROWN ADIPOSE TISSUE (popularly known as BROWN FAT) and in the LIVER—some 20% of the body's heat is generated here.
Temperature signaling underlying thermotaxis and cold tolerance in Caenorhabditis elegans
Published in Journal of Neurogenetics, 2020
Asuka Takeishi, Natsune Takagaki, Atsushi Kuhara
Among various environmental cues, temperature is an unavoidable stimulus which animals are constantly exposed to. Each animal has an acceptable environmental temperature range that matches their living conditions. For instance, parasitic worms prefer hosts’ body temperature, such as the human parasite A. ceylanicum which prefers around 38 °C (Bryant et al., 2018), and some species have a tolerance for extreme temperature, such as Diamesa kohshimai that lives at the North Pole and survives even at 16°C (Kohshima, 1984). The environmental temperature is particularly important for ectotherms as it largely regulates their body temperature as well as affects all internal biochemical reactions. Animals thus have evolved behavioral strategies to seek an appropriate environmental temperature. Thermotaxis is the initial behavior choice for most animals to relocate themselves to the appropriate temperature circumstances when they encounter an unpreferable temperature environment. Species-specific thermotaxis mechanisms have been described (Garrity, Goodman, Samuel, & Sengupta, 2010; Glauser & Goodman, 2016; Hoffstaetter, Bagriantsev, & Gracheva, 2018); however, the mechanism of thermosensation and signal transduction in the neural network is not fully understood.
In vitro metabolism of imidacloprid and acetamiprid in rainbow trout and rat
Published in Xenobiotica, 2020
Richard C. Kolanczyk, Mark A. Tapper, Barbara R. Sheedy, Jose A. Serrano
Kinetic data was determined for the microsomal conversion of IMI to IMI-1 in both the RBT and rat. Comparison of IMI-1 kinetics showed a lower Km for the fish (79.2 µM) versus rat (158.7 µM) and hence a greater enzymatic affinity for IMI substrate for this reaction. A much higher rate of formation (Vmax) for this reaction was observed in the rat (38.4 pmole/min/mg) versus the fish (0.75 pmole/min/mg). A calculation ignoring species differences for Q10 resulted in a value of 4.5 which is outside of the typical range of Q10 =2 to 3. There is an inherent problem with comparing rates across species with vastly different physiological temperatures at different levels of evolution as well as comparison of an ectotherm with an endotherm.
Regulatory systems that mediate the effects of temperature on the lifespan of Caenorhabditis elegans
Published in Journal of Neurogenetics, 2020
Byounghun Kim, Jongsun Lee, Younghun Kim, Seung-Jae V. Lee
Temperature is an important environmental factor, which affects lifespan and aging. The ‘rate-of-living’ theory asserts that the faster the metabolism, the shorter the lifespan (Pearl, 1928). Therefore, it was widely accepted that chemical reactions are facilitated as temperature rises, leading to increased metabolic rates and consequently short lifespan. This scenario is particularly plausible for ectotherms, whose body temperatures are subject to changes in environmental temperatures. Interestingly, however, many studies using ectotherms, including C. elegans, indicate that genetic factors modulate lifespan changes in response to external temperatures (Jeong, Artan, Seo, & Lee, 2012; Xiao, Liu, & Xu, 2015).