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Body-to-body contact is often recommended for rewarming mildly hypothermic victims in the field. This procedure involves a euthermic individual donating heat to the recipient by direct contact in an insulated bag. However, this technique has not been critically evaluated and may not be beneficial because there is limited direct contact between recipient and donor, peripheral vasoconstriction may impair heat transfer to the core, skin warming may blunt the recipient's shivering response, and cold stress to the donor may be excessive. The present study was designed to evaluate whether donation of heat by a donor would be sufficient to enhance rewarming of a hypothermic subject (recipient). Six pairs of recipients (5 men, 1 woman) and donors (2 men, 4 women) participated in the study. Esophageal and skin temperatures, cutaneous heat flux, and oxygen consumption were measured. Recipients were immersed in 8 degrees C water until esophageal temperature decreased to a mean of 34.6 +/- 0.7 degrees C (SD). They then were rewarmed by one of three methods: rewarming by the endogenous heat generated by shivering only (SH), body-to-body rewarming (BB), or rewarming with a constant-heat source manikin (MAN). Mean afterdrop for the three conditions was 0.54 +/- 0.2, 0.54 +/- 0.2, and 0.57 +/- 0.2 degrees C for SH, BB, and MAN, respectively (NS), and the rate of rewarming was 2.40 +/- 0.8, 2.46 +/- 1.1 and 2.55 +/- 0.9 degrees C/h for SH, BB, and MAN, respectively (NS).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of acute hypercapnia on human thermoregulation during cold exposure were investigated by immersion of eight male subjects to the neck in a 15 °C water bath until their core temperatures dropped to 35 °C or until 1 h of immersion had elapsed. Air was inspired throughout each experiment, with the exception of a 15-min period commencing with the attainment of an esophageal temperature (Tes) of 36.5 °C, during which subjects inspired a gas mixture containing 4% CO2, 20% O2, and 76% N2. Oxygen uptake ([Formula: see text], L∙min−1), inspired minute ventilation ([Formula: see text], L∙min−1), esophageal temperature (Tes, °C), rectal temperature (Tre, °C), mean unweighted skin temperature (Tsk, °C), mean heat flux (Q, W∙m−2), and electromyographic activity (EMG, mV) of the trapezius and masseter muscles were recorded continuously. [Formula: see text] and integrated EMG activity (IEMG) were used as the primary indicators of shivering thermogenesis. Shivering EMG was attenuated immediately following the switch of the inhaled gas mixture from air to 4% CO2. For both the massetter and trapezius muscles the IEMG was significantly suppressed (p < 0.05) during the hypercapnic period. The IEMG values preceding the switch to the hypercapnic mixture were 15% greater than those during the CO2 period. Similarly, IEMG values in the post-CO2 period were 55% greater than during the CO2 period. It is concluded that acute periods of hypercapnia during cold exposure may result in transient suppression of shivering tremor, but this does not appear to affect thermal balance, as reflected in the absence of any significant effect on Tes.Key words: temperature regulation, carbon dioxide, hypothermia, diving, cooling, cold water immersion, carbon dioxide retention.

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.

The present study investigated the effect of non-uniform skin temperature distribution on thermoregulatory responses and subjective thermal sensation during water immersion. Ten healthy male subjects carried out 60 min water immersion twice, once with uniform (UST) and once with non-uniform (NUST) skin temperature. In UST condition, subjects immersed at 29 degrees C in naked condition, while in NUST condition, subjects immersed at 26 degrees C with partial coverage wetsuit (PCWS). The PCWS covers trunk region, upper arms, and thighs. The non-uniform skin temperature distribution, higher at trunk and lower at distal extremities, was observed in NUST condition. Shivering thermogenesis was not influenced by the skin temperature distribution at the experimental condition of this study. On the other hand, the tissue insulation (I (tissue)) was significantly higher in NUST condition compared to the UST condition. The increment of I (tissue) might have been caused by the peripheral vasoconstriction induced by the cold input from the distal extremities in NUST condition. The higher I (tissue) in NUST condition might lead to the significantly higher esophageal temperature compared to UST condition. No difference was observed in thermal sensation between the two conditions. Subjects felt slightly more comfortable in NUST condition than in UST condition. In conclusion, the non-uniform skin temperature distribution, higher at trunk and lower at distal extremities, might affect the peripheral vasoconstriction to increase the I (tissue). On the other hand, shivering thermogenesis and subjective thermal sensation were not affected by the non-uniform skin temperature distribution at the present experimental condition.

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.

Experiments were carried out to determine the role of nitric oxide in mediating autonomic and behavioral thermoregulatory control in rat pups on postnatal days 1-2, 5-6, and 10-11. For an experiment, each pup received a subcutaneous injection of vehicle, NG-nitro-d-arginine methyl ester (d-NAME; 100 mg/kg), or NG-nitro-l-arginine methyl ester (l-NAME; 100 mg/kg) before being placed in a metabolic chamber or in a thermocline with a linear temperature gradient of 23 to 43°C. In the metabolic chamber, oxygen consumption and core temperature were measured as ambient temperature was decreased from 40 to 15°C over a 60-min period. Decreasing ambient temperature elicited an increase in oxygen consumption in all age groups that received vehicle or d-NAME. The lower critical temperature and peak oxygen consumption upon exposure to cold after vehicle were 41 ± 10 ml · kg-1 · min-1 at 30°C, 43 ± 12 ml · kg-1 · min-1 at 28°C, and 55 ± 11 ml · kg-1 · min-1 at 25°C in the 1- to 2-, 5- to 6-, and 10- to 11-day-old pups, respectively. Administration of l-NAME abolished the oxygen consumption response to cold in the 1- to 2- and 5- to 6-day-old pups and significantly attenuated the oxygen consumption response to cold in the 10- to 11-day-old pups. Selected ambient temperature in the thermocline was not significantly affected by prior administration of d-NAME or l-NAME compared with vehicle. Thus our data provide evidence that the nitric oxide system plays a role in mediating autonomic but not behavioral thermoregulatory control in rat pups during early postnatal maturation.

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.

Thermal physiology - brief history and perspectives, A.S. Milton body temperature, C.M. Blatteis biophysics of heat exchange between the body and the environment, J. Werner heat production mechanisms - shivering thermogenesis, L. Jansky heat production mechanisms - nonshivering thermogenesis, B. Cannon heat loss mechanisms, T. Morimoto neural thermoreception and regulation of body temperature, J.A. Boulant behavioural temperature regulation, M. Cabanac temperature regulation in exercise - thermal factors, B.N. Johannsen temperature regulation in exercise - nonthermal factors, H. Kaciuba-Uscilko body temperature and age - neonates H.P. Laburn body temperature and age - elderly, K.E. Cooper fever, C.M. Blatteis thermoregulatory consequences of prolonged exposure to thermal extremes - heat, M. Horowitz thermoregulatory consequences of prolonged exposure to thermal extremes - cold, E. Zeisberger pathophysiological consequences of exposure to thermal extremes - heat illnesses and hyperthermia, M. Horowitz pathophysiological consequences of exposure to thermal extremes - cold injuries and hypothermia, J.B. Mercer temperature regulation in different environments or in special cases, C.M. Blatteis.

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.

The present study investigated whether nitrous oxide (N2O) attenuates shivering thermogenesis during cold water immersion in a dose-dependent manner. Seven male subjects were immersed to the neck for 60 min in 20 degrees C water on five separate occasions while breathing either air (AIR) or a normoxic mixture of 10, 15, 20, or 25% N2O balanced with N2. All N2O concentrations investigated caused a significant (P < 0.02) reduction in shivering thermogenesis compared with AIR. Despite similar heat flux from the skin, the relative changes in esophageal temperature from resting preimmersion levels were significantly greater (P < 0.05) during the N2O trials compared with AIR, with no significant difference among the N2O conditions. A dose-dependent trend in the perception of thermal comfort was observed for the N2O conditions. It is concluded that shivering thermogenesis, and thus thermal balance, is affected to the same degree for the range of inspired N2O concentrations investigated, with no discernable dose-dependent effect.

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.

Restraint hypothermia has often been described, but its cause has never been clarified. We hypothesized that it might be due to a suppression of shivering thermogenesis. Thus, we restrained conscious rats in an ambient temperature of 2 degrees C while measuring rectal (Tre) and tail skin temperatures, metabolic rate (MR), and shivering activity. When rats were cold exposed but not restrained, Tre fell 1.4 +/- 0.2 degrees C (SE) during the 1st h. When these same rats were restrained, Tre fell at a rate of 6.5 +/- 0.2 degrees C/h. MR averaged 15.7 +/- 1.4 W/kg for the unrestrained rats, but it averaged only 9.0 +/- 1.1 W/kg for the restrained rats. The restrained rats showed no signs of shivering. The animals were then subjected to a restraint adaptation regimen and then reexposed to cold. Restraint now produced a fall in Tre of only 2.6 +/- 0.7 degrees C/h. The animals shivered and generated an MR of 15.8 +/- 0.9 W/kg. Naive rats became hypothermic because restraint suppressed shivering activity. However, adapted rats continued to shiver and remained normothermic. We suggest that a stressful or threatening situation, such as restraint for a naive rat, inhibits shivering and leads to hypothermia in a cold environment. This would not occur in adapted rats because restraint is no longer stressful.

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.

Cardiorespiratory responses of the conscious pigeon to (1) spinal cord heating to 43.7 C in a cold environment ($T_{a} = 5 C$) and (2) spinal cord cooling to 37.5 C in a hot environment ($T_{a} = 39-40 C$) were measured. Ambient cooling caused increases in respiration and cardiac output that were proportional to the increased heat production caused by shivering thermogenesis. Under this condition, selective heating of the spinal cord suppressed shivering, whereupon heat production and cardiorespiratory responses returned rapidly to control levels. Selective cooling of the spinal cord suppressed panting caused by ambient heating. Cardiovascular and blood gas changes accompanying panting were small; any responses that did occur returned rapidly to control levels during spinal cord cooling. The results on the conscious pigeon show that selective thermal stimulation of the spinal cord, when applied in the opposite direction to an external temperature stress, can inhibit not only shivering or panting but also ...

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.

Infant rats aged 1 to 5 days lose heat rapidly when first exposed to room temperature; they also are initially very active and cannot be immobilized when turned over onto their sides and restrained for a few seconds. However, once core temperature drops closer to ambient levels, the stimulus for movement (rapid loss of heat from skin to environment) is diminished and immobility occurs. If the rapid heat loss, a source of apparent spontaneity, is prevented by precooling or continuous warmth, activity is blocked and prolonged restraint-related immobility can be readily produced. The warmed pups frequently made small twitches typical of those associated with paradoxical sleep. By 10 days, the pups can no longer be immobilized on their sides when pre-cooled, possibly because motor subsystems related to shivering thermogenesis (i.e., behaviors, including righting, that actively maintained a crouched upright position) begin to develop. At this age the pups can still be immobilized when warmed, but by 25 days of age slight warming is no longer effective because of the emergence of other sources of spontaneous locomotion that cannot be blocked by warmth, and/or because warmth can no longer induce paradoxical sleep. To test for the influence of the developing neocortex on immobility, pups were decorticated at 6 days of age. The activity and restraint immobility durations of the decorticate pups were not different from controls under any thermal condition at any postoperative age. Warmth-induced immboility was present following decortication in adult rats, but only in the early postoperative days, perhaps relating to subcortical diaschisis. It is suggested that the neocortex is not a major inhibitory influence on immobility induced by restraint.

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.

1. Shivering in response to changes in ambient or core temperature has been measured in control rats and rats injured by bilateral hind-limb ischaemia, both with and without fur. 2. Removal of the fur increased the threshold ambient temperature for the onset of shivering. 3. This threshold was lower than in uninjured controls during the latter half of a 4 hr period of bilateral hind-limb ischaemia in rats with or without fur. 4. The threshold was also lower than in uninjured controls after the period of bilateral hind-limb ischaemia but was not significantly different from that during the period of ischaemia. 5. The alterations in threshold were not accompanied by any significant changes in the slope of the regression line relating intensity of shivering and ambient temperature. 6. When the core temperature fell after limb ischaemia to levels which provoked shivering in uninjured controls, no shivering was seen in the injured rats. 7. These results are interpreted as further evidence for the lowering of the ‘set-point’ for thermogenesis after injury in the rat and are discussed in relation to the changes in body temperature after injury in that species.

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.

Eviscerated, nephrectomized rats were used as peripheral tissue preparations to study the rate of utilization of glucose after acute (24 h) exposure of intact animals to cold. The preparations taken from fed (but not fasted) rats 1) required more glucose infused IV to maintain normoglycemia and 2) disposed of single IV loads of glucose more rapidly than normal. Cold lowered both glucose concentration in blood and liver glycogen, although more food was eaten. Plasma insulin was normal or below. Conclusion: Acute cold-induced shivering thermogenesis in fed rats is associated with increased rates of utilization of glucose by skeletal muscle that are not dependent on insulin.

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.

Serum free fatty acid versus glycerol ratios were decreased in human newborn infants during pyrexia or cold injury, but remained practically unchanged in older infants and children. Decreased ratios in the newborn resulted exclusively from an increase in serum glycerol. In children a parallel increase in both serum glycerol and free fatty acids was observed in pyrexia. The results suggest that in pyrexia both newborn infants and older children behave as if they were cold, mobilizing the mechanisms of nonshivering and shivering thermogenesis respectively to adjust the temperature of their body at a relatively higher reference level.

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.

Rectal temperature cooling rate (Tre) is a consequence of an imbalance between heat production and heat loss mechanisms. However, Tre is often related to body insulation, as determined by the thickness of the subcutaneous fat layer, without consideration of the contribution of shivering thermogenesis. The present study investigated the combined effects of insulation and heat production on Tre during cold water (10°and 20°C immersion. It is concluded that relating core temperature cooling rate simply to the insulative adipose layer is inadequate. On the basis of the present results, it is suggested that the following variables be taken into account when attempting to model cooling rate of immersed individuals : 1) The rate of heat production. 2) The insulation provided by the adipose layer. In addition, other tissues may contribute to the overall body insulation. During prolonged immersion total body insulation may vary and will also be affected by the level of peripheral perfusion. 3) The rate of storage of body heat will depend on body composition. It may be insufficient to assume identical specific heat of the body for a range of body types, when determining total body insulation.

We inadvertently subjected a group of goats to 5 mo of cold exposure (mean minimum temperature less than −13°C) during an experiment designed to examine the effects of training by daily running on one member of each sibling pair. During the three coldest months, the sedentary but cold-exposed goats experienced a 34% increase in maximal oxygen uptake (V˙o 2 max, P < 0.01) and a 29% increase in running speed at maximal ( P < 0.05). When temperatures increased in the spring, both oxygen uptake and running speed decreased. We interpret these findings as evidence that cold is a sufficient stimulus to invoke the development of aerobic structures in muscle and that these structures subsequently can be utilized for the novel task of running. When the experiment was subsequently repeated without the cold exposure, running speed andV˙o 2 max of trained animals increased less than in either group of cold-exposed animals. However, the cost of transport of these warm runners was lower than either group of cold-exposed animals (from 13–19%, P < 0.0001). Thus, although aerobic capacity was increased with acclimation to severe winter weather, cold-acclimated goats operated with lower efficiency during locomotion.

Active heating of susliks on emerging from hibernation is closely linked with the intensification of shivering thermogenesis. Intraperitoneal injection of 5-hydroxytryptophan (a serotonin precursor) into susliks reduces shivering thermogenesis markedly in the awakening animals and delays their rewarming.

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.