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Because the majority of cold exposure studies are constrained to short-term durations of several hours, the long-term metabolic demands of cold exposure, such as during survival situations, remain largely unknown. The present study provides the first estimates of thermogenic rate, oxidative fuel selection, and muscle recruitment during a 24-h cold-survival simulation. Using combined indirect calorimetry and electrophysiological and isotopic methods, changes in muscle glycogen, total carbohydrate, lipid, protein oxidation, muscle recruitment, and whole body thermogenic rate were determined in underfed and noncold-acclimatized men during a simulated accidental exposure to 7.5°C for 12 to 24 h. In noncold-acclimatized healthy men, cold exposure induced a decrease of ∼0.8°C in core temperature and a decrease of ∼6.1°C in mean skin temperature (range, 5.4-6.9°C). Results showed that total heat production increased by approximately 1.3- to 1.5-fold in the cold and remained constant throughout cold exposure. Interestingly, this constant rise in Ḣprod and shivering intensity was accompanied by a large modification in fuel selection that occurred between 6 and 12 h; total carbohydrate oxidation decreased by 2.4-fold, and lipid oxidation doubled progressively from baseline to 24 h. Clearly, such changes in fuel selection dramatically reduces the utilization of limited muscle glycogen reserves, thus extending the predicted time to muscle glycogen depletion to as much as 15 days rather than the previous estimates of approximately 30–40 h. Further research is needed to determine whether this would also be the case under different nutritional and/or colder conditions.

Adapting to the cold extrauterine environment after birth is a great challenge for the newborn. Due to their high surface area-to-volume ratio, infants tend to lose more heat to the environment as compared to adults. In addition, human newborns lack sufficiently developed skeletal muscle mass to maintain body temperature through shivering thermogenesis, an important source of heat in cold-exposed adults. Evolution has provided humans and other placental mammals with brown adipose tissue (BAT), a tissue that converts chemically stored energy, in the form of fatty acids and glucose, into heat through non-shivering thermogenesis. The thermogenic activity of this tissue is significant for the human infant’s ability to maintain a sufficiently high core body temperature. Although BAT has been studied in human infants for more than a century, the literature covering different aspects of the tissue is rather limited. The aim of this review is to summarize the literature and describe what is actually known about the tissue and its importance for early human life.

As endotherms, humans exposed to a compensable cold environment rely on an increase in thermogenic rate to counteract heat lost to the environment, thereby maintaining a stable core temperature. This review focuses primarily on the most important contributor of heat production in cold-exposed adult humans, shivering skeletal muscles. Specifically, it presents current understanding on (1) the origins of shivering, (2) the contribution of shivering to total heat production and (3) the metabolic requirements of shivering. Although shivering had commonly been measured as a metabolic outcome measure, considerable research is still needed to clearly identify the neuroanatomical structures and circuits that initiate and modulate shivering and drives the shivering patterns (continuous and burst shivering). One thing is clear, the thermogenic rate in humans can be maintained despite significant inter-individual differences in the thermogenic contribution of shivering, the muscles recruited in shivering, the burst shivering rate and the metabolic substrates used to support shivering. It has also become evident that the variability in burst shivering rate between individuals, despite not influencing heat production, does play a key role in orchestrating metabolic fuel selection in the cold. In addition, advances in our understanding of the thermogenic role of brown adipose tissue have been able to explain, at least in part, the large inter-individual differences in the contribution of shivering to total heat production. Whether these differences in the thermogenic role of shivering have any bearing on cold endurance and survival remains to be established. Despite the available research describing the relative thermogenic importance of shivering skeletal muscles in humans, the advancement in our understanding of how shivering is initiated and modulated is needed. Such research is critical to consider strategies to either reduce its role to improve occupational performance or exploit its metabolic potential for clinical purposes.

During cold exposure, increase in heat production is produced via the activation of shivering thermogenesis and nonshivering thermogenesis, the former being the main contributor to compensatory heat production in non-acclimatized humans. In rats, it has been demonstrated that shivering thermogenesis is modulated solely by skin thermoreceptors but this modulation has yet to be investigated in humans. The aim of this study was to determine if cold-induced shivering in humans can be modulated by cutaneous thermoreceptors in conditions where increases in heat loss can be adequately compensated by increases in thermogenic rate. Using a liquid-conditioned suit, six non-acclimatized men were exposed to cold (6 °C) for four 30 min periods, each of them separated by 15 min of heat exposure (33 °C). Core temperature remained stable throughout exposures whereas skin temperatures significantly decreased by 12% in average during the sequential cold/heat exposures compared to baseline ( p 2 /min, respectively) and were significantly reduced during 33 °C exposure (0.5±0.1% MVC, 0.25±0.0 L O 2 /min; p

This study evaluated the thermogenic capacity of three species of fruit-eating phyllostomid bats (Carollia perspicillata, Sturnira lilium and Artibeus lituratus) during the dry-cool and wet-warm seasons, by measuring changes in body mass, basal metabolic rate (BMR), maximal metabolic rate (MMR), nonshivering thermogenesis and shivering thermogenesis. Body mass was lower, on average, during the dry-cool season and all species of fruit-eating bats showed an increase in oxygen consumption after noradrenaline injection and after exposure to a He–O2 atmosphere. However, the magnitude of this increase was similar in both seasons. BMR also did not vary between seasons. Although, our results showed for the first time that all three species studied were able to increase thermogenesis by both nonshivering and shivering thermogenesis, we did not find significant differences in any thermoregulatory variable measured when comparing data from the two different seasons. Probably the difference in the mean and variance of the temperature profile between seasons were not strong enough to alter the thermogenic capacity of these species. Furthermore, the use of alternative physiological (torpor) or behavioral (huddling) strategies might have alleviated the need to trigger energetic-costly thermogenic responses.

Radio-telemetric monitoring of 70 free-ranging carpet pythons (Morelia spilota imbricata) at two sites in southwestern Australia provided extensive data on the body temperatures exhibited by these animals. The snake’s thermal regimes were affectedby season, time of d ay, location, microhabitat, size andsex, behaviour, andreprod uctive state. Over most of the year pythons exhibited relatively smooth unimodal diel curves of heating and cooling, attaining maximal temperatures around30 1C. The (small) male snakes heated and cooled more rapidly than did the (larger) females. Climatic differences between our two study sites generated substantial shifts in mean body temperatures and thus, in the diel timing of ambush foraging behaviour. Females wrapped tightly around their eggs after oviposition and brooded them throughout the ensuing 8-week incubation period. Throughout this time, females were facultatively endothermic, maintaining high constant temperatures through shivering thermogenesis. Females nesting in sites with relatively poor thermal buffering (under rootballs of fallen trees rather than rock crevices) supplemented endogenous heat prod uction with occasional basking, andhence overall maintainedlower andmore variable incubation temperatures than did females with ‘‘better’’ nest sites. r 2002 Elsevier Science Ltd. All rights reserved.

A brief overview on thermogenic mechanisms in young precocial birds is given. While shivering thermogenesis is well documented in these birds, evidence for a facultative non-shivering component of heat production, comparable to that found in the brown adipose tissue of mammals, is ambiguous. One reason for this is the confusion between thermoregulatory and obligatory thermogenesis. In particular, the existence of a thermogenic reaction, even a futile one, does not by itself constitute proof of true thermoregulatory non-shivering thermogenesis. More probably, such a reaction is another obligatory component of heat production. Heat increment of feeding and motor activity are classical examples of such mechanisms. Thermogenesis arising from such mechanisms can often be adaptively used by the thermoregulatory systems in young birds, as well as in adults.

International audience; Endotherms have evolved two major types of thermogenesis that allow them to actively produce heat in response to cold exposure, either through muscular activity (i.e. shivering thermogenesis) or through futile electro- chemical cycles (i.e. non-shivering thermogenesis). Amongst the latter, mitochondrial uncoupling is of key importance because it is suggested to drive heat production at a low cost in terms of oxidative stress. While this has been experimentally shown in mammals, the oxidative stress consequences of cold exposure and mitochondrial uncoupling are clearly less understood in the other class of endotherms, the birds. We compared metabolic and oxidative stress responses of zebra finches chronically treated with or without a chemical mitochondrial uncoupler (2,4-dinitrophenol: DNP), undergoing an acute (24 h) and a chronic (4 weeks) cold exposure (12 °C). We predicted that control birds should present at least a transient elevation of oxidative stress levels in response to cold exposure. This oxidative stress cost should be more pronounced in control birds than in DNP-treated birds, due to their lower basal uncoupling state. Despite similar increase in metabolism, control birds presented elevated levels of DNA oxidative damage in response to acute (but not chronic) cold exposure, while DNP-treated birds did not. Plasma antioxidant capacity decreased overall in response to chronic cold exposure. These results show that acute cold exposure increases oxidative stress in birds. However, uncoupling mitochondrial functioning appears as a putative compensatory mechanism preventing cold-induced oxidative stress. This result confirms previous observations in mice and underlines non-shivering thermogenesis as a putative key mechanism for endotherms in mounting a response to cold at a low oxidative cost.

To understand the mechanisms of improvement of cold-induced heat production in aged mice following exercise training, the relative contributions of shivering and nonshivering thermogenesis to cold-induced metabolic responses were assessed in adult and aged C57BL/6J male mice, which inhabited sedentarily at room temperature, or were subjected either to a regimen of moderate intensity exercise training at 6°C, or to sedentary repeated exposures to the same temperature. The main findings were that (1) aged mice had greater cold-induced nonshivering thermogenesis, but lower shivering than adult mice; (2) exercise training in a cold environment enhanced cold-induced nonshivering thermogenesis in adult mice, but suppressed it in aged animals; (3) exercise training in a cold environment increased shivering thermogenesis in both age groups, but this increase was much greater in aged mice; (4) the increase of cold-induced shivering thermogenesis was mainly responsible for increased cold tolerance in aged mice after exercise training in a cold environment.

The sections in this article are: 1 Cold Acclimation/Acclimatization in Birds 1.1 Metabolic Adjustments 1.2 Shivering Thermogenesis 1.3 Nonshivering Thermogenesis 1.4 Utilization of Energy Sources 2 Cold Acclimation/Acclimatization in Mammals: Monotremes and Marsupials 2.1 Metabolic Rate and Body Temperature 2.2 Cold Acclimation and Seasonal Acclimatization in Marsupials 2.3 Nonshivering Thermogenesis 3 Cold Acclimation/Acclimatization in Placental Mammals 3.1 Metabolic Adjustments 3.2 Shivering Thermogenesis 3.3 Nonshivering Thermogenesis 4 Summary

We measured daily energy expenditure (DEE) during the development periods of precocial chicks of five species of Arctic shorebirds spanning a broad range in size, in order to investigate the relationships between DEE, body size, and growth rate. We also quantified the effect of weather conditions on the energy expenditure of chicks to establish the impact of cold arctic weather on their time and energy budgets. We used the doubly labeled water method to measure DEE at ambient temperatures in an outside enclosure on the subarctic tundra at Churchill, Manitoba, Canada. Growth rate was highest in the smallest species, and in general decreased with adult size, as shown by the decrease in growth rate constant and later inflection point with increasing adult body mass. DEE ranged from 14 kJ day−1 in young chicks of the smaller species to 365 kJ day−1 in older chicks of the larger species. From hatching onward, DEE of shorebirds was high compared to DEE of chicks of altricial species, reflecting the high costs of locomotion and thermoregulation, and mass-specific DEE increased rapidly to adult levels. Chicks of smaller species metabolized more energy per unit mass and functioned at higher multiples of resting metabolic rate than chicks of larger species. As chicks of smaller species also had higher growth rates, and thus simultaneously invested in growth and mature function, it seems that shorebird chicks can adjust total metabolizable energy as well as its relative allocation between investment in growth and mature function. DEE was similar to cold-induced peak metabolic rates achieved by shivering thermogenesis. Because chicks were motionless during laboratory metabolism measurements, the relatively high level of DEE compared to these metabolic rates suggests that locomotion produces similar amounts of heat as shivering. Ambient temperature did not affect DEE in outdoor pens, although higher wind speed resulted in slightly increased energy expenditure. Heat produced by locomotion is possibly sufficient to sustain thermoregulation under local environments. Furthermore, when ambient temperatures are low, chicks spend more time brooding and less time foraging, which presumably counters the tendency to increase thermogenesis in response to cold.

Summary Finke C., Misovic, A. & Prinzinger, R. 1995. Growth, the development of endothermy, and torpidity in Blue-naped Mousebirds Urocolius macrourus. Ostrich 66:1-9. Blue-naped Mousebirds are altricial birds that are naked and blind at hatching. The nestling period is extremely short (12.5 ± 0.8 d). During the first 7 days the nestlings are unable to thermoregulate actively but from 3 day old the nestlings already show approximately the same body temperature (Tb) as adults under “natural conditions” in the nest with siblings. At an ambient temperature (Ta) of + 35°C the nestlings are nearly endothermic by the age of 9 days (Tb 39.1 ± 0.8°C) and within 12 days individual birds are essentially endothermic at Ta + 20°C (Tb 39.4 ± 0.4°C = 97% of adult-Tb). At this age the birds leave the nest. They are sufficiently feathered but still unable to fly and have only reached 55% of adult mass. Coordinated shivering thermogenesis was observed for the first time on day 6 (Ta ± 20°C), and panting and gular flutteri...

The ontogeny of shivering thermogenesis was investigated in the altricial red-winged blackbird (Agelaius phoeniceus). Two indices of heat production – the rate of oxygen consumption of the bird and the electromyographic (EMG) activity of the pectoralis (PECT) and gastrocnemius (GAST) muscles – were measured simultaneously in adult and nestling red-winged blackbirds as they were subjected first to thermoneutral temperatures and subsequently to progressively colder ambient temperatures (Ta). The ontogenetic changes in both indices indicated that the capability for thermogenesis in nestling red-winged blackbirds improved markedly with age. The metabolic rates of 3-day-old nestlings decreased during exposure to gradually falling ambient temperatures; at best, these nestlings were only able to maintain mass-specific at levels similar to or slightly above the resting metabolic rate at thermoneutral temperatures (RMR) for a short time before metabolic rates decreased with further cooling. Shivering was detected only in the PECT muscles and was of a relatively low intensity (maximum of sevenfold increase in intensity over basal levels). The 5-day-old nestlings increased mass-specific modestly (approximately 1.4-fold) above RMR and attained slightly higher maximal factorial increases in the EMG activity of the PECT (maximum of 18-fold basal levels) when exposed to the same experimental conditions. Shivering was also detected in the GAST muscles of these birds. The most striking improvements in both measures observed during the nestling period occurred between day 5 and day 8. Eight-day-old nestlings increased metabolic rates by approximately 2-to 2.5-fold over basal levels and sustained these elevated rates for longer before becoming hypothermic. Both the PECT and GAST muscles contributed significantly to shivering thermogenesis, and these older nestlings attained much higher factorial increases in the intensity of shivering (up to 72-fold) during exposure to cold temperatures. In addition, both the range and magnitude of the dominant frequencies of muscle activity in the PECT increased during postnatal development. The PECT muscles were a principal site of shivering thermogenesis in all nestling and adult red-winged blackbirds studied here. Shivering in these muscles was a ‘first line defense’ against cold; the threshold temperature for shivering in the PECT muscles coincided with the lower critical temperature for oxygen consumption (TLC), and the subsequent increases in EMG activity in this muscle with further cooling correlated well with the corresponding increases in mass-specific .

During the fetal to neonatal transition, the newborn calf encounters severe thermolysis due to an abrupt change in thermal environment that is compounded by evaporation of fetal fluids and severe weather conditions. Maintenance of homeothermy during the neonatal period necessitates an acute and sustained thermogenic response by the newborn calf. It is now widely accepted that this thermogenic response is derived from both shivering thermogenesis in muscle tissue and nonshivering thermogenesis in brown adipose tissue (BAT). It is critical that newborn calves possess functional BAT during the neonatal period. This article focuses on the pre- and postnatal factors that influence nonshivering thermogenesis of BAT in the neonatal calf.

Six tufted ducks were trained to dive for food at summer temperatures (air, 26°C, water, 23°C) and at winter temperatures (air, 5.8°C, water 7.4°C). The mean resting oxygen consumption at winter temperatures (Twin) was 90% higher than that at summer temperatures (Tsum), but deep body temperatures (Tb) were not significantly different. Diving behaviour and mean oxygen consumption for dives of mean duration were similar at Twin and at Tsum, although the mean oxygen consumption for surface intervals of mean duration was 50% greater at Twin and Tb was significantly lower (1°C) at the end of a series of dives in winter than it was in summer. There appears to be an energy saving of 67 J per dive during winter conditions and this may, at least partially, be the result of the metabolic heat produced by the active muscles being used to maintain body temperature. While at rest under winter conditions, this would be achieved by shivering thermogenesis. Thus, the energetic costs of foraging in tufted ducks in winter are not as great as might be expected from the almost doubling of metabolic rate in resting birds.

In humans, the relative importance of oxidative fuels for sustaining shivering during passive hypothermic recovery or rewarming is still unclear. The main goals of this study were 1) to quantify the respective contributions of lipids and carbohydrates (CHO) during passive rewarming and 2) to determine the effects of precooling exercise on the pattern of fuel utilization. With indirect calorimetry methodologies, changes in fuel metabolism were quantified in nonacclimatized adult men shivering to rewarm from moderate hypothermia (core temperature ∼34.5°C) not following (Con) or following a precooling exercise at 75% V̇o2max for 15 min (Pre-CE). As hypothermic individuals shiver to normothermia, results showed that CHO dominate at all shivering intensities above 50% Shivpeak, while lipids were preferred at lower intensities. This change in the relative importance of CHO and lipids to total heat production was dictated entirely by modulating CHO oxidation rate, which decreased by as much as 10-fold from the beginning to the end of rewarming (from 1,611 ± 396 to 141 ± 361 mg/min for Con and 1,555 ± 230 to 207 ± 261 mg/min for Pre-CE). In contrast, lipid oxidation rate remained constant and low (relatively to maximal rates at exercise) throughout rewarming, averaging 183 ± 141 for Con and 207 ± 118 mg lipids/min for Pre-CE. In addition, this pattern of fuel selection remained the same between treatments. We concluded that fuel selection is regulated entirely by changes in CHO oxidation rate. Further research should focus on establishing the exact regulatory processes involved in achieving this large upregulation of CHO utilization rate following hypothermia.

Newly hatched precocial chicks of arctic shorebirds are able to walk and regulate their body temperatures to a limited extent. Yet, they must also grow rapidly to achieve independence before the end of the short arctic growing season. A rapid growth rate may conflict with development of mature function, and because of the allometric scaling of thermal relationships, this trade-off might be resolved differently in large and small species. We assessed growth (mass) and functional maturity (catabolic enzyme activity) in leg and pectoral muscles of chicks aged 1-16 d and adults of two scolopacid shorebirds, the smaller dunlin (Calidris alpina: neonate mass 8 g, adult mass 50 g) and larger whimbrel (Numenius phaeopus; neonate mass 34 g, adult mass 380 g). Enzyme activity indicates maximum catabolic capacity, which is one aspect of the development of functional maturity of muscle. The growth rate-maturity hypothesis predicts that the development of catabolic capacity should be delayed in faster-growing muscle masses. Leg muscles of both species were a larger proportion of adult size at hatching and grew faster than pectoral muscles. Pectoral muscles grew more rapidly in the dunlin than in the whimbrel, whereas leg muscles grew more rapidly in the whimbrel. In both species and in both leg and pectoral muscles, enzyme activities generally increased with age, suggesting increasing functional maturity. Levels of citrate synthase activity were similar to those reported for other species, but L-3-hydroxyacyl-CoA-dehydrogenase and pyruvate kinase (PK) activities were comparatively high. Catabolic capacities of leg muscles were initially high compared to those of pectoral muscles, but with the exception of glycolytic (PK) capacities, these subsequently increased only modestly or even decreased as chicks grew. The earlier functional maturity of the more rapidly growing leg muscles, as well as the generally higher functional maturity in muscles of the more rapidly growing dunlin chicks, contradicts the growth rate-maturity function trade-off and suggests that birds have considerable latitude to modify this relationship. Whimbrel chicks, apparently, can rely on allometric scaling of power requirements for locomotion and the thermal inertia of their larger mass to reduce demands on their muscles, whereas dunlin chicks require muscles with higher metabolic capacity from an earlier age. Thus, larger and smaller species may adopt different strategies of growth and tissue maturation.

Turkey (Meleagris gallopavo) and guinea fowl (Numida meleagris) chicks (0-27 days posthatch) were exposed to decreasing or increasing ambient temperatures. Root mean square electromyographic activity of musculus pectoralis (m. pect.) and musculus iliotibialis (m. iliot.) was recorded simultaneously with O2 consumption and CO2 production. From both muscles, relative mass, water fraction and fibre type were determined. M. iliot. participated in shivering from hatching onwards. The relationship between its root mean square electromyographic activity and ambient temperature resembled that of metabolic rate and ambient temperature, and the shivering threshold temperature was indistinguishable from the lower critical temperature. This suggests that the leg muscles are major contributors to shivering thermogenesis. M. pect. participated in shivering only at days 6-20 in turkeys and at days 6-10 in guinea fowl. Both water fraction and histological analysis indicated that m. pect. was less developed than m. iliot. at hatching. We hypothesize that a minimal level of maturity is required before a muscle can participate in shivering, which is probably represented by a water fraction of about 0.85. Both species recruited the aerobic leg muscles first; the anaerobic breast muscle was recruited only when the rate of mass-specific heat loss was high.

Thermoregulatory responses of eight healthy subjects (six men and two women) were compared when they were head-out immersed in 15 degrees C water at both 1 and 6 ATA. Both trials were conducted in a hyperbaric chamber. During the immersions, esophageal temperature (T(es)) and skin temperature at two sites (chest and calf) were recorded at minute intervals. Oxygen uptake was determined at 5-min intervals with the Douglas bag method. The order of the two trials was alternated. The rate of T(es) cooling was greater during the 6-ATA trial [2.1 +/- 0.5 degrees C/h (SE)] than during the 1-ATA trial (1.3 +/- 0.5 degrees C/h; P < 0.01). Despite the greater rate of core cooling, and presumably a greater thermal drive for shivering, the oxygen uptake response for a similar decrement in T(es) was lower during exposure to 6 than to 1 ATA (P < 0.05). Also, for similar displacement in T(es), the subjects perceived the immersions at 6 ATA to be less cold than those at 1 ATA (P < 0.05). It is concluded that the development of hypothermia in compressed-air divers may be due, in large part, to the attenuation of heat production and cold perception. Most likely, the observed effects on the autonomic responses and thermal perception are due to an inhibitory action of hyperbaric nitrogen on central neural structures involved in temperature regulation.

(I) Shivering intensity and metabolic rate were determined in Large White pigs aged 2, 24, 48 h and 5 d, at temperatures ranging from thermoneutrality (36°C) to cold (20°C). (2) Shivering is the main heat producing mechanism, the absence of nonshivering thermogenesis being implied by both the absence of delay between the onset of shivering (Stt) and the increase in metabolic rate (Lct) and by the linearity of the relationship between metabolic rate and shivering intensity in the cold. (3) For a comparable thermal demand, shivering intensity decreased with age whereas cold induced heat production remained constant, which suggests that the thermogenic efficiency of shivering is improved during the first 5 days of life.

We report an observation of shivering thermogenesis and insulation by a brooding Python molurus bivittatus (Burmese Python) just outside the northern boundary of Everglades National Park, FL. Temperature data loggers were placed in and around the brooding female's nest, and video was taken of the female performing shivering thermogenesis. Nest temperatures were maintained both warmer and cooler than ambient temperatures. This observation of thermoregulation through shivering thermogenesis and clutch insulation is the first documented instance of a Burmese Python exhibiting this behavior in the wild.

A major financial and welfare problem is the loss of 1 to 4 million lambs annually in the United Kingdom (Slee, 1979) with many of these deaths being caused by failure of the lamb to maintain normal thermoregulatory responses in the cold. This may be associated with a change in the response to cold exposure from non-shivering thermogenesis (NST) to shivering thermogenesis (ST) as brown adipose tissue (BAT) is replaced by white adipose tissue over the first 2 weeks of life in the lamb (Symonds, Andrews and Johnson, 1989).It has been shown that environmental temperature can affect BAT development in the lamb (Gemmel, Bell and Alexander, 1972) and calf (Casteilla, Champigny, Bouilland, Robelin and Riquier, 1989) but it is not known what effect this has on the thermogenic capacity of BAT or how it may alter the ability of the lamb to thermoregulate.This study investigated the effect of artificially rearing lambs at warm or cold ambient temperatures on the thermogenic capacity of BAT and the extent to which metabolic rate and the ability to respond to warm and cold challenges was altered by these treatments over the first 9 days of life.

Djungarian hamsters,Phodopus sungorus, improved their cold limit during seasonal acclimatization from −24°C in summer to −68°CTa in winter. This was primarily due to an increase in their capacity for nonshivering thermogenesis from 23.4 mW/g in summer to 59.4 mW/g in winter, assisted by an improved utilization of heat in smaller winter acclimatized hamsters. BMR and shivering thermogenesis had only minor effects on seasonal improvements of cold tolerance.

1. To test whether the preoptic area controls only non-shivering and the spinal cord only shivering thermogenesis, ten rats were chronically implanted with a preoptic and a spinal cord thermode each. The following were then studied: (a) the effect of propranolol (8 mg/kg.hr) on the metabolic response to cooling the preoptic area, and the spinal cord, (b) the effect of exogenous noradrenaline (0.5 mg/kg) on the metabolic response to cooling the preoptic area, and the spinal cord, and (c) the effect of warming the preoptic area on the metabolic response to cooling the spinal cord, and vice versa. 2. Administration of propranolol inhibited the metabolic response to cooling each of the thermosensitive areas, but the response to cooling the preoptic area was more strongly inhibited than that to cooling the spinal cord. 3. Administration of exogenous noradrenaline did not prevent the metabolic response to cooling either the preoptic area or the spinal cord. 4. Warming the spinal cord completely inhibited the metabolic response to cooling the preoptic area, and warming the preoptic area fully inhibited the metabolic response to cooling the spinal cord. 5. It is concluded that exogenous noradrenaline underestimates the capacity for non-shivering thermogenesis, and that both thermosensitive areas can control both forms of thermogenesis, but that the preoptic area threshold of non-shivering thermogenesis is probably lower than that of shivering, while the spinal cord threshold of shivering is probably lower than that of non-shivering thermogenesis.

Physiological thermogenesis in intemal organs as well as main muscle groups is one of the most important subjects in the study of human adaptability to cold environment. The experiments of the prediction of obligatory non-shivering thermogenesis were performed under optimal thermal condition in summer and in winter by using a prediction method of local muscle energy metabolic rate and quasi-basal metabolic rate B1 (Yokayama, 1980). B1 means the sum of metabolic rates other than those of main muscle groups. The subjects were eleven Japanese males in sumrner and ten Japanese males in winter. Subject YS was longitudinally examined to confirm seasonal change of obligatory non-shivering thermogenesis. Subject YS was performed to examine regulatory non-shivering thermogenesis and shivering thermogene-sis by using nine resting and static exercising items of back cold and front cold under three cold environments (T=-l0°C, -5°C and 0°C. In the summer experiments Bls were 32.43 (mean) ±12.59 (S.D.) kcal/h and B1/A= 19.81 ±9.26 kcal/m2 h. On the other hand, the results of the winter experiments were 67.32±7.83 kcal/h and B1/A=38.90±5.27 kcal/m3h. This tendency of the seasonal variation that the quasi-basal metabolic rate B1 in winter was greater than in summer was coincident with the results in winter and in summer obtained from the same subject YS. In subject YS the predicted B1S were 29.87 in summer, 57.84 in December and 55.55 and 57.92 kcal/h in March. In order to evaluate regulatory non-shivering thermogenesis, the predictions of B1 were performed from item-e of back cold and front cold under cold environments. B1 under T=-5°C and T=0°C were 78.19 and 83.13 kcal/h respectively. Therefore the value of regulatory non-shivering thermogenesis was about 22 kcal/h under the present experimental conditions. The shivering thermogenesis was predicted for six to nine muscle groups in nine resting and exercising items of back cold and front cold under three cold environments

1. 1. Loss of body temperature and metabolism were measured in nestling European Starlings (Sturnus vulgaris L.) for brood sizes of 1, 3, 5 and 7 at four air temperature ranges. Data were collected for age classes 1–6, 9, 12, 15 and 18 days. 2. 2. A distinction is made between effective homeothermy and effective endothermy as determined for broods under semi-natural conditions vs homeothermy and endothermy determined for isolated chicks. 3. 3. Endothermy developed slowly. Shivering thermogenesis began at about 6 days; peak metabolism was not reached until about 10–12 days. Analysis of variance indicated that brood size, air temperature, age, and all two-way interactions were significant. 4. 4. Homeothermy was achieved earlier than endothermy in chicks for all brood sizes under all test conditions. For a given air temperature effective homeothermy was achieved earlier by individuals within larger broods. This was primarily due to inertial effects retarding heat loss. 5. 5. The homeothermic status of broods of various sizes can be predicted from metabolic abilities of individuals within nests.

The purpose of the present study was to clarify the importance of skeletal muscle glycogen as a fuel for shivering thermogenesis in humans during cold-water immersion. Fourteen seminude subjects were immersed to the shoulders in 18 degrees C water for 90 min or until rectal temperature (Tre) decreased to 35.5 degrees C. Biopsies from the vastus lateralis muscle and venous blood samples were obtained before and immediately after the immersion. Metabolic rate increased during the immersion to 3.5 +/- 0.3 (SE) times resting values, whereas Tre decreased by 0.9 degrees C to approximately 35.8 degrees C at the end of the immersion. Intramuscular glycogen concentration in the vastus lateralis decreased from 410 +/- 15 to 332 +/- 18 mmol glucose/kg dry muscle, with each subject showing a decrease (P less than 0.001). Plasma volume decreased (P less than 0.001) markedly during the immersion (-24 +/- 1%). After correcting for this decrease, blood lactate and plasma glycerol levels increased by 60 (P less than 0.05) and 38% (P less than 0.01), respectively, whereas plasma glucose levels were reduced by 20% after the immersion (P less than 0.001). The mean expiratory exchange ratio showed a biphasic pattern, increasing initially during the first 30 min of the immersion from 0.80 +/- 0.06 to 0.85 +/- 0.05 (P less than 0.01) and decreasing thereafter toward basal values. The results demonstrate clearly that intramuscular glycogen reserves are used as a metabolic substrate to fuel intensive thermogenic shivering activity of human skeletal muscle.

1. 1. The body temperatures of five echidnas in Australia's Southern Alps were monitored by radio telemetry from February to December 1987. 2. 2. All five hibernated throughout the winter, showing very low body temperatures (4–9°C, close to ambient) when torpid, compared with 28–33°C in a typical day during the active season. 3. 3. Spontaneous arousals from hibernation occurred every 2–3 weeks, during which body temperatures rose rapidly to over 30°C for several hours before dropping to be close to ambient again. 4. 4. The identification of “classical” hibernation in a monotreme, with a similar pattern to that seen in Eutheria and in an animal as large as the largest eutherian hibernator, has important implications for current ideas about the evolution of endothermy.

1. 1.|Chicks were subjected to three stresses—handling alone or handling plus heat or cold. An immediate hyperlipacidaemia occurred only in the cold-stressed birds thus indicating the importance of lipid in the thermoregulatory response to cold. 2. 2.|Lipolysis in chicks treated with prostaglandin E1 (PGE1) was reduced by one quarter but the birds did not show impaired thermoregulatory ability. 3. 3.|Plasma lactate concentrations were significantly increased in PGE1-treated chicks exposed to cold, indicating an enhanced shivering thermogenesis. 4. 4.|Impairment of muscular activity with propranolol reduced the thermoregulatory ability of PGE1-treated chicks. 5. 5.|The nature of an avian non-shivering thermoregulatory mechanism is discussed.

Existing stimulus-response expressions predicting shivering thermogenesis are based on static peripheral, core, and central temperatures. These expressions predict a linear increase in metabolic heat production in response to displacements of either central or core and peripheral temperatures from set-point temperature values. A model of shivering thermogenesis has been developed incorporating the nonlinear static and dynamic characteristics of thermosensitive neural structures in the body. The parameters defining receptor activities, dynamics of response, regional summation, and thermoneutral set points are based on data published in the literature. Predictions of metabolic heat generation (in units of ml O2 ·kg-1 ·min-1) are derived by integrating excitatory and inhibitory thermogenic drives, resulting from thermoreceptor stimulation in various regions of the body. The relative gains of the thermogenic drives were determined by least-squares regression using empirical data from a series of cold water immersions. The present model demonstrated improved simulations of shivering thermogenesis during cooling and rewarming, when compared to existing stimulus-response predictive expressions.

Miniature temperature-sensitive radiotransmitters were surgically implanted into free-ranging adult diamond pythons (Morelia s. spilota), which are medium-sized boid snakes of south-eastern Australia. Four female pythons oviposited during the study, and constructed incubation mounds. These apparently provided excellent insulation, and the snakes maintained high (approx. 31 C) and relatively constant body temperatures throughout the two-month incubation period. They apparently maintained these temperatures primarily by endogenous heat production (shivering thermogenesis), but also basked briefly on most mornings. Brooding females maintained a body temperature differential above ambient of about 9C, occasionally up to 13C; their temperatures were significantly higher amd less variable than those of non-brooding females or males. The energetic cost of brooding must be high, but these costs may be outweighed by the benefits of rapid embryonic development and high embryonic survivorship.

1. Brown adipose tissue has been earlier shown in this laboratory to represent a highly vascularized thermogenic effector system which in response to cold supplies heat to cervical and thoracic neural and visceral elements. 2. In respect to rats, evidence is adduced to show that during cold exposure the hyperplastic development and rising QO2 of the brown adipose tissue coincides in point of time with the gradual disappearance of the shivering thermogenesis normally occurring during the first two or three weeks of exposure. 3. Factors which may limit the amount and hyperplastic rate of growth of the tissue are suggested.

An evaluation was made of the effects of an acute exercise bout on nonshivering thermogenesis (NST) in cold-acclimated rats (4 degrees C for 6 weeks) and shivering thermogenesis in 24 degrees C-acclimated rats (24 degrees C for 6 weeks). Assessment techniques included indirect calorimetry during treadmill running and brown adipose tissue (BAT) mitochondrial guanosine diphosphate (GDP) binding immediately following a treadmill run. Calorimetric results for 24 degrees C-acclimated rats running at 4 degrees C indicated total substitution of shivering thermogenesis by exercise-derived heat. No difference in GDP-binding, an index of BAT nonshivering thermogenic activity, was observed between exercised and nonexercised 24 degrees C-acclimated rats. Calorimetric results for cold-acclimated rats running at 4 degrees C indicated a total suppression in the energy cost associated with NST, exercise-derived heat replacing or substituting for NST. Examining BAT properties in the exercised cold-acclimated rats revealed a significant 40% decrease in BAT mitochondrial GDP-binding. These results suggest that during running, metabolic heat due to the exercise totally replaces shivering in 24 degrees C-acclimated rats and totally replaces BAT nonshivering thermogenesis in cold-acclimated rats.

Publisher Summary This chapter describes the importance of the pilomotor response in temperature regulation. The capability of a perfect regulation of body temperature is only found in mammalian and avian species. The members of the two classes of vertebrates are equipped with the ability to regulate autonomically their heat dissipation and their internal heat production. Some autonomic features of heat loss and heat conservation are already established in the ectothermic reptiles. These animals are unable to increase their internal heat production by shivering thermogenesis. The capability of shivering in homeotherms appears to be enclosed with the development of the insulation of the body surface. This assumption is supported by observations of the thermogenesis during the ontogeny of endothermic animals. In newborn mammals and birds, shivering follows when the growth of hairs or feathers results in a good peripheral insulation. In contrast to mammals, the thickness of plumage of the birds does not vary so much between summer and winter and between inhabitants of warm and cold regions with the exception of antarctic birds.

The influence of ambient temperature and lighting on the duration of tonic immobility (TI) in birds was studied in conjunction with simultaneous shivering measurements. Contrary to what has been found in mammals, low ambient temperature did not disrupt TI in pigeons and house sparrows: the TI durations were equal at +2°C and +25°C. Electromyographic recordings in pigeons showed that after an initial suppression, shivering soon reappeared and reached normal levels during TI at +2°C. When the duration of TI was prolonged (indicating slower recovery of postural activity) by experimental manipulation (darkness), shivering likewise reappeared more slowly. The ability of birds to maintain shivering during TI, and the congruent changes in the duration of TI and the intensity of shivering suggest that shivering has neuromuscular and evolutionary connections to the postural activity of skeletal muscles also in birds. The difference between birds and mammals in reference to the effects of low ambient temperature on TI may be related to a differential recruitment of muscles for shivering thermogenesis.

A slowly increasing ptiloerection was seen after the intrahypothalamic injections of NA; 5-HT was followed by preening and subsequent rapid feather fluffing, and carbachol produced an immediate sleeking of feathers. The naturally occurring complementary relationship between shivering thermogenesis and ptilomotion diminished or disappeared after the drugs, but feather position seemed to remain well related to the arousal state of the pigeon.

No change could be detected in the adenyl cylase system (basal activity, noradrenaline-stimulated activity, adrenaline-stimulated activity, fluoride-stimulated activity) of skeletal muscle of cold-acclimated rats. It is concluded that the enhancement of metabolic response to noradrenaline during cold-acclimation, which occurs principally in skeletal muscle, can not be attributed to an alteration in this component of the receptor system for noradrenaline.An increase in the activity of the catecholamine-stimulated and fluoride-stimulated adenyl cyclase of skeletal muscle occurs during the 1st week of exposure to cold and has disappeared by the time the rats are fully acclimated. This increase coincides with the period of shivering thermogenesis rather than with the development of nonshivering thermogenesis; it may be related to the intense and repeated stimulation of plasma membrane associated with shivering.

Adult birds maintain high body temperatures in cold environments by thick insulation (West 1972, Dawson and Carey 1976, Dawson et al. 1983), huddling and communal roosting (Knorr 1957, Mackenzie 1959), use of protected microsites (Kendeigh 1961, Mayer et al. 1982), and high capacity for thermogenesis. Several studies have shown that basal metabolic rate (BMR) increases with latitude (Weathers 1979, Ellis 1984), that temperature tolerances vary seasonally (Barnett 1970) and geographically (Blem 1973) owing to increased insulation as well as thermogenic capacity (Hart 1962, Dawson and Carey 1976, Dawson et al. 1983), particularly shivering thermogenesis of the flight muscles (Hart 1962, West 1965).

1. 1. Electromyographic, thermal and metabolic measurements were made on pigeons subjected to stepwise ambient cooling. Subsequent signal analysis of the EMG-recordings from the pectoral muscle showed that the mean rectified value (Umrv) is the most reliable EMG-based indicator of metabolic heat production (M). 2. 2. The muscle-abdomen temperature difference was linearly related to M and correlated strongly with Umrv. 3. 3. The long-term and short-term fluctuations of shivering intensity (Umrv) highly synchronous in the two main muscles, m. pectoralis and m. supracoracoideus. 4. 4. The EMG-signal approached a Gaussian process at high shivering intensities. Evaluation of the changes in EMG median frequency suggested a size-dependent recruitment of motor units for shivering. 5. 5. It is pointed out that Umrv and the integrated value of EMG are interconvertible and that Umrv should be preferred, because it has more physiological relevance.

SummaryChickens cold exposed to 2-3° had significantly elevated levels of plasma CPK compared with controls. After an initial increase during the first week, no significant difference was seen in plasma CPK activity of chickens cold acclimated at either 8-11 or 4-7° for 2-4 weeks when compared with controls. It is concluded that muscle activity (shivering thermogenesis) in cold-exposed chickens resulted in elevated plasma CPK, while the absence of muscle involvement (nonshivering thermogenesis) in cold-acclimated chickens resulted in no alterations in plasma CPK activity.

AND R. A. DANIELS. 1982. Distribution and ecology of stream fishes of the Sacramento-SanJoaquin drainage system, California. I. Fishes of the Pit River system, McCloud River system, and Surprise Valley region. Univ. Calif. Publ. Zool. 115. PIMENTEL, R. A. 1979. Morphometrics. The multivariate analysis of biological data. Kendall/Hunt Publishing Co., Dubuque. , AND D. S. FREY. 1978. Multivariate analysis of variance and discriminant analysis, p. 247-274. In: Quantitative ethology. P. W. Colgan (ed.). John Wiley, New York. ROBINS, C. R., AND R. R. MILLER. 1957. Classification, variation, and distribution of the sculpins, genus Cottus, inhabiting Pacific slope waters in California and southern Oregon, with a key to the species. Calif. Fish Game 43:213-233. RUTTER, C. 1908. The fishes of the Sacramento-San Joaquin basin, with a study of their distribution and variation. US Bur. Fish. Bull. 27:103-152. SNYDER, J. 0. 1917. The fishes of the Lahontan system of Nevada and northeastern California. Ibid. 35:31-86.