Modern theoretical and practical problems of homoiothermia and thermoregulation

The adjuncts to the existing determinations of homoiothermia are made on the basis of new data, the principles of temperature adaptation of humans and homoiothermal animals are presented. The main purposes of the thermoregulation system of homoiothermal animals and humans in various temperature excesses are formulated. The arguments are advanced in favor of the fact that in the thermoneutral zone the thermoregulation system goes from the principles of regulating the temperature homeostasis by one or several temperature points of a body to the regulation by the fluctuations of the total heat content of an organism, which increases the sensitivity and the accuracy of the thermoregulation system operation. The physiological mechanisms are described of determining (measuring) the total heat content of a body.     

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

For subterranean rodents, searching for food by extension of the tunnel system and maintenance of body temperature are two of the most important factors affecting their life underground. In this study we assess the effect of ambient temperature on energetics and thermoregulation during digging in Ctenomys talarum. We measured VO2 during digging and resting at ambient temperature (Ta) below, within, and above thermoneutrality. Digging metabolic rate was lowest at Ta within the thermoneutral zone and increased at both lower and higher temperatures, but body temperature (Tb) remained constant at all Tas. Below thermoneutrality, the cost of digging and thermoregulation are additive. Heat production for thermoregulation would be compensated by heat produced as a by-product of muscular activity during digging. Above thermoneutrality, conduction would be an important mechanism to maintain a constant Tb during digging.     

Deposition of pathogenic Mycoplasma gallisepticum onto bird feeders: host pathology is more important than temperature-driven increases in food intake

Although ambient temperature has diverse effects on disease dynamics, few studies have examined how temperature alters pathogen transmission by changing host physiology or behaviour. Here, we test whether reducing ambient temperature alters host foraging, pathology and the potential for fomite transmission of the bacterial pathogen Mycoplasma gallisepticum (MG), which causes seasonal outbreaks of severe conjunctivitis in house finches (Haemorhous mexicanus). We housed finches at temperatures within or below the thermoneutral zone to manipulate food intake by altering energetic requirements of thermoregulation. We predicted that pathogen deposition on bird feeders would increase with temperature-driven increases in food intake and with conjunctival pathology. As expected, housing birds below the thermoneutral zone increased food consumption. Despite this difference, pathogen deposition on feeders did not vary across temperature treatments. However, pathogen deposition increased with conjunctival pathology, independently of temperature and pathogen load, suggesting that MG could enhance its transmission by increasing virulence. Our results suggest that in this system, host physiological responses are more important for transmission potential than temperature-dependent alterations in feeding. Understanding such behavioural and physiological contributions to disease transmission is critical to linking individual responses to climate with population-level disease dynamics.     

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

For subterranean rodents, searching for food by extension of the tunnel system and maintenance of body temperature are two of the most important factors affecting their life underground. In this study we assess the effect of ambient temperature on energetics and thermoregulation during digging in Ctenomys talarum. We measured V˙o₂ during digging and resting at ambient temperature (T_a) below, within, and above thermoneutrality. Digging metabolic rate was lowest at T_a within the thermoneutral zone and increased at both lower and higher temperatures, but body temperature (T_b) remained constant at all T_as. Below thermoneutrality, the cost of digging and thermoregulation are additive. Heat production for thermoregulation would be compensated by heat produced as a by-product of muscular activity during digging. Above thermoneutrality, conduction would be an important mechanism to maintain a constant T_b during digging.     

Growth rate and thermoregulation in reared king quails (Coturnix chinensis)

Growth rate was investigated in king quails between 1st and 60th day of life. Gompertz growth constants were 0.075 in males and 0.056 in females. Colonic temperature (Tb) was measured in quails divided into four age groups (1-3, 7-10, 16-19, and 44-59 days old) in ambient temperatures set separately for each group. Metabolic rate was measured only in 44-59-day-old birds. The mean value of the thermoneutral body temperature (Tb at TNZ) in the active phase in the youngest quails was 39.0 degrees C. In 44-59-day-old quails, the resting metabolic rate in the thermoneutral zone (RMR at TNZ) was on average 9.44 mW g(-1) (1.66 cm3 O2 g(-1)h(-1)), without sex-specific differences. No such differences were found in this age group neither in Tb at TNZ, nor in minimal thermal conductance (Cmin). However, differences were found in the rate of metabolic heat production below the thermoneutral zone, even when mass-independent units were used. The maximum metabolic rate (Mmax) in 2-month-old males was 34.08 mW g(-1) (5.98 cm3 O2 g(-1)h(-1)), while in females 29.73 mW g(-1) (5.21 cm3 O2 g(-1)h(-1)). Heat-stressed 44-59-day-old quails elevated their Tb to as much as an average 44.1 degrees C in Ta of about 45 degrees C. The obtained growth model and a gradual development of the body temperature regulation mechanism in king quails followed the known strategy of development, typical for precocial birds. The sexual size dimorphism in the studied quails did not result in differences in thermoregulation parameters between the sexes, except for the rate of metabolic rate below thermoneutral zone.     

Forecast of the Health Status, Working Capacity, and Professional Successes under Arid Zone Conditions

Forecasting data on the human heat resistance, professional successes, and health level under hot arid conditions of Turkmenistan are described. A relationship has been established between the characteristics of the thermoregulation system performance under thermoneutral environments, which is shown by the skin surface temperature, and the organism's capacity to maintain a high level of working capacity on heat exposure. The skin temperature patterns are shown to be informative when analyzing the organism's heat state and forecasting the extent to which the total working capacity decreases in response to the intensive heat effect. On the basis of the findings, we developed the criteria for psychophysiological professional selection of linemen for the work under hot arid zone conditions of Turkmenistan. A comparative analysis of the health status of women employed in industry and of housewives living in the arid zone has been carried out using the automated system for the quantitative estimation of risk of the major pathological syndromes (ASQEPS). Groups with tense adaptation have been detected. Analysis and comparison of the syndrome rating in the test groups make it possible to estimate the effect of natural climatic and industrial conditions on the risk of development of major noninfectious diseases and to formulate recommendations for health maintenance.     

Resting metabolic rate and erythrocyte morphology in early development of thermoregulation in the precocial grey partridge (Perdix perdix)

In the early stages of development of thermoregulation in grey partridge, a typical precocial species, I measured the resting metabolic rate (RMR) and body temperature (Tb) in the thermoneutral zone (TNZ) and the parallel changes in the size of erythrocytes and their cell nuclei. The strong positive correlation between the mass-independent (residuals versus body mass) values of Tb and RMR indicates a close relationship, between these physiological parameters in the first week of life of partridges. In the ontogeny of this species, the dimensions of erythrocytes correlated inversely with the mass-specific metabolic rate (expressed in mW g(-1)), claiming its status as an important and metabolically useful measure of development. The correlation coefficient of these two variables, at the level of individual development within a species, has been further enhanced in the inter-specific analysis at the level of the order Galliformes. The characteristics of changes in the erythrocyte size, in parallel with the dynamics of the resting level of heat production development, in the important period when the thermoregulation is assuming its form in precocial birds, supply new data pertaining to this strategy of avian development.     

The roles of energetics,water economy,foraging behavior,and geothermal refugia in the distribution of the bat,Macrotus californicus

Summary Energy metabolism, thermoregulation, and water flux ofMacrotus californicus, the most northerly representative of the Phyllostomidae, were studied in the laboratory using standard methods, and energy metabolism and water fluxes were studied in the field using the doubly labelled water method together with a time budget. Daily energy expenditures of free-living bats averaged 22.8 kJ during the winter study period. Approximately 60% of this was allocated to resting metabolism costs while in the primary roosts (22 h/day).Macrotus californicus is unable to use torpor. The thermoneutral zone (TNZ) in this species is narrow (33 to 40 °C) and metabolic rate increased rapidly as ambient temperature decreased below the TNZ. Basal metabolic rate was 1.25 ml O₂/g·h, or 24 J/g·h. Total thermal conductance below the TNZ. was 1.8 mW/g·°C, similar to values measured for other bats. Evaporative water loss showed a hyperbolic increase with increasing ambient temperature, and was approximately 1% of total body mass/h in the TNZ. The success of these bats as year-round residents in deserts in the southwestern United States is probably not due to special physiological adaptations, but to roosting and foraging behavior. They use geothermally-heated winter roost sites (stable year-round temperatures of approximately 29 °C) which minimize energy expenditures, and they have an energetically frugal pattern of foraging that relies on visual prey location. These seem to be the two major factors which have allowedM. californicus to invade the temperate zone.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - T _a ambient temperature - T _b body temperature - T _lc,T _uc lower and upper critical temperature, respectively - TBW total body water - TNZ thermoneutral zone     

Metabolism and thermoregulation in the Cabrera vole (Rodentia: Microtus cabrerae)

Metabolism and thermoregulation were studied for the first time in the Cabrera vole (Microtus cabrerae), an endemic and threatened rodent of the Iberian Peninsula. Low values of resting metabolic rate (RMR) were registered (1.13 mlO(2) g(-1) h(-1)) at the lower limit of the thermoneutral zone (TNZ) (around 33.5 degrees C). Body temperature increased near the TNZ up to 37.3 degrees C but remained stable, around 36 degrees C, at ambient temperatures below 25 degrees C. Values of thermal conductance remained quite stable at ambient temperatures of 10-25 degrees C (0.144-0.160 mlO(2) g(-1) h(-1) degrees C) and increased to 0.301 mlO(2) g(-1) h(-1) degrees C at 33.5 degrees C. Data revealed that M. cabrerae developed a highly adaptive ability of conserving energy and lowering the metabolic cost of thermoregulation at high ambient temperatures, allowing the body temperature to approximate that of the environment and exhibiting low resting metabolic rate and high conductance.     

Heterothermy in two mole-rat species subjected to interacting thermoregulatory challenges

Maintaining a high and constant body temperature (T(b) ) is often viewed as a fundamental benefit of endothermy, but variation in T(b) is likely the norm rather than an exception among endotherms. Thus, attempts to elucidate which factors cause T(b) of endotherms to deviate away from the T(b) that maximizes performance are becoming more common. One approach relies on an adaptive framework of thermoregulation, used for a long time to predict variation in T(b) of ectotherms, as a starting point to make predictions about the factors that should lead to thermoregulatory variation in endotherms. Here we test the predictions that when confronted with thermoregulatory challenges endotherms should (1) become more heterothermic, (2) lower their T(b) setpoint, and/or (3) increase behavioral thermoregulation (e.g., activity levels or social thermoregulation). We exposed two species of relatively homeothermic mole-rats to two such challenges: (a) ambient temperatures (T(a)) well below the thermoneutral zone and (b) increased heat loss caused by the removal of dorsal fur. In general, our results support the adaptive framework of endothermic thermoregulation with each species conforming to some of the predictions. For example, Mashona mole-rats (Fukomys darlingi) increased heterothermy as T(a) decreased, highveld mole-rats (Cryptomys hottentotus pretoriae) displayed lower T(b) 's after shaving, and both species increased behavioral thermoregulation as T(a) decreased. This suggests that there is some merit in extending the adaptive framework to endotherms. However, none of the three predictions we tested was supported under all experimental conditions, reiterating that attempts to determine universal factors causing variation in T(b) of endotherms may prove challenging.     

The effect of short-term fasting on shivering thermogenesis in Japanese quail chicks (Coturnix coturnix japonica): indications for a significant role of diet-induced/growth related thermogenesis

(1) The effect of short-term fasting on metabolism and shivering thermogenesis was studied in 9-day-old Japanese quail. (2) After 31 h of fasting, heat production decreased 39% and body temperature over 2°C in the thermoneutral zone. The difference in heat production between control and fasting groups decreased with decreasing ambient temperature. (3) Despite the lower metabolic rate, the amplitudes of shivering EMGs were higher in fasted chicks, especially in pectoralis. This indicates that fasted quails used shivering to compensate the decrease in diet-induced/growth related thermogenesis. (4) In cold, conductance of control birds decreased simultaneously with increasing heat production while in fasted chicks, conductance decreased to its minimum before heat production was activated. (5) Japanese quail chicks adapt quickly to short-term fasting by decreasing metabolism but they maintain their ability to thermoregulate in cold. Diet-induced/growth related thermogenesis has a significant role in thermoregulation since it reduces the need of shivering thermogenesis.     

Energy budget of the chicken foot

1. 1.|A mathematical model predicts the energy loss from a chicken foot provided the following variables are known: body temperature, air temperature, wind velocity, blood flow to the foot, and the relative partitioning of blood flow via two distinct venous returns.

2. 2.|Chickens are capable of keeping their feet from freezing at temperatures as low as −30°C ambient, but at a high energy cost.

3. 3.|Chickens can modulate blood flow to their feet at thermoneutral temperatures enough to vary heat loss to environment by about one-fourth metabolic heat production.

Regional blood flow changes in response to thermal stimulation of the brain and spinal cord in the Pekin duck

Summary In conscious Pekin ducks, carotid and sciatic blood flows, respiratory rate, core and skin temperatures were measured during selective thermal stimulations of the spinal cord and rostral brain stem in thermoneutral (20 °C) and warm (32 °C) ambient conditions.At thermoneutral ambient temperature selective heating of the spinal cord by 2–3 °C (to 43–44 °C) increased the carotid blood flow by 138% and the sciatic blood flow by 46%. Increase in blood flows was correlated with increased breathing rate and beak and web skin temperatures.Selective cooling of the spinal cord at warm ambient temperatures and panting reduced the blood flow in both arteries and decreased the breathing rate.Heating or cooling of the brain stem showed generally very weak but otherwise similar responses as thermal stimulation of the spinal cord. In one duck out of six there was a marked effect on regional blood flow during brain stimulation.The results show that thermal stimulation of the spinal cord exerts a marked influence on regional blood flow important in thermoregulation, whereas the lower brain stem shows only a weak thermosensitivity, and stimulation caused only small cardiovascular changes of no major consequence in thermoregulation.     

Simple roost nests confer large energetic savings for sparrow-weavers

White-browed sparrow-weavers (Plocepasser mahali, body mass 40 g) are group-living passerines adapted to the semi-arid environment of north-eastern and south-western Africa. During winter, the nocturnal ambient temperature of these regions often falls below 0 degrees C. imposing conditions demanding an increase in thermoregulatory heat production. Individuals roost throughout the year in inverted U-shaped roost nests. We investigated the energetic advantages of roosting by measuring nest and ambient temperatures in the field, as well as the resting metabolic rate (RMR) of the birds. The sparrow-weavers exhibited a wide thermoneutral zone (13 degrees C - 32 degrees C). Although RMR at thermoneutrality (40.2 J g.h(-1)) conforms with those of other passerines. the value at 0 degrees C (74.8 J g.h(-1)) is significantly lower than expected. The slope of the line below the lower critical temperature is unexpectedly steep, however, and appears to cause the physiological requirement for nest roosting due to a high cost of thermoregulation at low temperatures, perhaps due to shivering or non-shivering thermogenesis. The nest temperature at 0 degrees C ambient is 5 degrees C. resulting in a saving of some 7% in the energy spent during winter nights when food resources are in short supply compared with the rest of the year.     

The development of endothermy during pouch life in the eastern barred bandicoot (Perameles gunnii), a marsupial

Marsupials are born ectothermic and gradually become endothermic during pouch occupancy. In order to study the timing of this transition, we measured the metabolic rates of eight pouch-young eastern barred bandicoots (Perameles gunnii) at 25 degrees C (the thermoneutral zone of adults), at 35 degrees C (pouch temperature), and after injection with norepinephrine. From 5 to 7 wk of age, oxygen consumption (VO(2)) was higher at 35 degrees C than at 25 degrees C. At 8 wk, VO(2) was significantly higher at 25 degrees C than at 35 degrees C. Norepinephrine administration at 5 and 6 wk had no effect on metabolic rate, but at 8 wk, near pouch vacation, it resulted in a significant increase in metabolic rate. Our results indicate that signs of thermoregulation for P. gunnii begin at 7 wk, and at 8 wk the species is endothermic, that is, able to increase heat production in response to both cold and norepinephrine. The appearance of fur, first seen at the age of 6 wk and fully developed at 8 wk, coincides with the onset of endothermy.     

布氏田鼠静止代谢率特征

本文以布氏田鼠的耗氧量为指标,探讨了布氏田鼠的能量代谢特征。布氏田鼠的热中性区为27.5至32.5℃,最低静止代谢率(RMR)为1.836mlO₂/g·h,是期望RMR的l32.6%。最低热传导率为0.189mlO₂/g·h,是期望热传导率的I14.5%。环境温度（Ta）在5-27.5℃范围内,RMR与Ta呈负相关,回归方程为RMR=6.968 5-0.185 2Ta,体温稍有降低。T_a35℃时,RMR升高,体温升高1.9℃。布氏田鼠较高的RMR和热传导率,较宽的热中性区,及良好的化学体温调节强度等生理生态特征,是对生存环境的适应性反应。     

Cost reduction in the cold: heat generated by terrestrial locomotion partly substitutes for thermoregulation costs in Knot Calidris canutus

To test whether heat generated during locomotion substitutes for the thermoregulation cost, oxygen consumption of four post-absorptive temperate-wintering Knot Calidris canutus was measured at air temperatures of 25̀C (thermoneutral) and 10̀C (c. 10̀ below the lower critical temperature) when the birds were at rest at night and during running on a treadmill. After allowing for body mass, the thermoregulation cost at 10̀C was significantly lower in active birds compared with birds at rest. At rest, the birds spent, on average, 0.50 watt (W; range, 0.47-0.57 W) on thermoregulation. During exercise, this cost factor averaged 0.33 W (range, 0.25-0.42 W). The average difference in thermoregulation cost was 35% (ranging from 26% to 49% between individuals) and provides an estimate of the amount of substituted heat. A review of nine studies, all restricted to small birds, showed that substitution is a widespread phenomenon. The consequences of such partial substitution for the annual energetics of Knot wintering in the temperate Wadden Sea v tropical west Africa are examined. Compared with a previous additive model, the model which includes substitution (i.e. the use of heat produced during activity) reduces the differences in maintenance metabolism between the two wintering strategies by 17%, from 1.19 W to 0.99 W.     

Statistical investigation of the effect of local temperature changes on posterior hypothalamic single unit activity

The distribution of interspike intervals (ISI) in discharges of posterior hypothalamic neurons at a temperature of 39.1-0.02°C (thermoneutral zone) and during a rise and fall of the temperature of this region of the brain by 0.6–1.5°C was investigated in chronic experiments on rabbits. Spontaneous posterior hypothalamic unit activity recorded in the thermoneutral zone was characterized by several types of ISI distributions. Thermosensitive posterior hypothalamic neurons responded to a rise and fall of the temperature of this brain region by changes in the type of ISI distribution; the discharge pattern returned to its original form after temperature stimulation ended.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 360–367, July–August, 1978.     

Influence of single administration of different diets on the energy metabolism at temperatures of 10,20 and 30 degrees C in the golden hamster.

Fed animals have a higher resting metabolic rate in the thermoneutral zone than fasting ones. The metabolic increase is due to the specific dynamic action of food. With a decline of environmental temperature this increase in metabolism either declines or remains unchanged; decisive is whether the heat is used for thermoregulation or not (Mejsnar and Jansky 1971). The objective of our work was to find out to what extent a single intake of a diet with a different ratio of nutrients can influence resting metabolism in the golden hamster and whether this heat can be used for thermoregulation in the cold. Female golden hamsters aged 6-8 weeks kept at a constant temperature of 22 +/-1 degrees C with twelve-hour alternation of light (6 a.m. - 6 p.m.) and darkness ( 6 p.m. - 6 a.m.) were used for the experiments. The oxygen consumption was assessed after a single intake of a standard, high-carbohydrate (76 cal.% starch), high-fat (80 cal.% margarine) and high-protein (82 cal.% casein) diet-for detailed composition see Fábry (1959). The food was given at 6.m. after previous 20 hours of fasting. Animals were then transferred into the respiration chamber and kept there for three hours, including one hour when they were left to settle down; during this period the oxygen consumption was not measured. Oxygen consumption measurement started at 9 a.m. and lasted till 11 a.m. The metabolism of the animals at rest was assessed at temperatures of 10, 20 and 30 degrees C by measuring the oxygen consumption by the interferometric method (Wollschitt et al. 1935). The results are expressed in ml of oxygen per g of body weight per hour. The relationship between the metabolism at rest and environmental temperatures in hamsters given a single dose of standard, high-proetin, high-fat or high-carbohydrate diet is apparent from Table 1. The maximum increase of oxygen consumption after administration of the experimental diets was found at a temperature of 30 degrees C. At an environmental temperature of 20 degrees C the administration of the high-protein and high-fat diet causes roughly the same increase of metabolism. The high-carbohydrate diet increase is only one third of thevalues found, in the remaining two diets at the same temperature and is non-significant. At the environmental temperature of 10 degrees C all the diets used increased the oxygen consumption insignificantly. The changes in metabolism at different environmental temperatures after administration of various diets expressed as percentage of metabolism at 30 degrees C in animals fed the standard diet indicate that the specific dynamic action of the high-protein and high-fats diets is lower at lowered temperatures. We may thus assume that the heat produced as a result of specific dynamic action of the high-protein and high-fat diets is perhaps used for thermoregulation. The role of specific dynamic action of high-carbohydrate diet for thermoregulation is not clear from our experiments. The role of specific dynamic action of food was assessed by several authors...     

Effects of Ambient Temperature on Sleep and Cardiovascular Regulation in Mice: The Role of Hypocretin/Orexin Neurons

The central neural pathways underlying the physiological coordination between thermoregulation and the controls of the wake-sleep behavior and cardiovascular function remain insufficiently understood. Growing evidence supports the involvement of hypocretin (orexin) peptides in behavioral, cardiovascular, and thermoregulatory functions. We investigated whether the effects of ambient temperature on wake-sleep behavior and cardiovascular control depend on the hypothalamic neurons that release hypocretin peptides. Orexin-ataxin3 transgenic mice with genetic ablation of hypocretin neurons (n = 11) and wild-type controls (n = 12) were instrumented with electrodes for sleep scoring and a telemetric blood pressure transducer. Simultaneous sleep and blood pressure recordings were performed on freely-behaving mice at ambient temperatures ranging between mild cold (20°C) and the thermoneutral zone (30°C). In both mouse groups, the time spent awake and blood pressure were higher at 20°C than at 30°C. The cold-related increase in blood pressure was significantly smaller in rapid-eye-movement sleep (REMS) than either in non-rapid-eye-movement sleep (NREMS) or wakefulness. Blood pressure was higher in wakefulness than either in NREMS or REMS at both ambient temperatures. This effect was significantly blunted in orexin-ataxin3 mice irrespective of ambient temperature and particularly during REMS. These data demonstrate that hypocretin neurons are not a necessary part of the central pathways that coordinate thermoregulation with wake-sleep behavior and cardiovascular control. Data also support the hypothesis that hypocretin neurons modulate changes in blood pressure between wakefulness and the sleep states. These concepts may have clinical implications in patients with narcolepsy with cataplexy, who lack hypocretin neurons.