Rewarming rates and thermogenesis in hibernating echidnas.

We measured body temperatures (T(b)) in 14 free-ranging echidnas (Tachyglossus aculeatus) using implanted data-loggers. An average of 1020+/-744 days of T(b) data was recorded from each animal. The average maximum T(b) was 35.3+/-0.7 degrees C (n=14), and the lowest T(b) was 4.7 degrees C. Detailed analysis of rewarming events from four echidnas showed rewarming time to be dependent on initial T(b) (rewarming time in hours=15.6-0.41T(initial), n=31) with an average rewarming rate of 1.9+/-0.4 degrees C h(-1). Based on an hourly sampling rate, the peak rewarming rate was found to be 7.2+/-0.8 degrees C h(-1) (n=12), which was measured at a mean T(b) of 26.2+/-2.4 degrees C. This rate of heating was calculated to be equivalent to a peak oxygen consumption rate of 1.4+/-0.2 ml O2 g h(-1), approximately 9 times the basal metabolic rate. We found that a plot of rate of change of T(b) against T(b) for the entire data set from an individual echidna provided a useful summary and analytical tool.     

Influence of skeletal muscle glycogen on passive rewarming after hypothermia

To examine the influence of muscle glycogen on the thermal responses to passive rewarming subsequent to mild hypothermia, eight subjects completed two cold-water immersions (18 degrees C), followed by 75 min of passive rewarming (24 degrees C air, resting in blanket). The experiments followed several days of different exercise-diet regimens eliciting either low (LMG; 141.0 +/- 10.5 mmol.kg.dry wt-1) or normal (NMG; 526.2 +/- 44.2 mmol.kg.dry wt-1) prewarming muscle glycogen levels. Cold-water immersion was performed for 180 min or to a rectal temperature (Tre) of 35.5 degrees C. In four subjects (group A, body fat = 20 +/- 1%), postimmersion Tre was similar to preimmersion Tre for both trials (36.73 +/- 0.18 vs. 37.26 +/- 0.18 degrees C, respectively). Passive rewarming in group A resulted in an increase in Tre of only 0.13 +/- 0.08 degrees C. Conversely, initial rewarming Tre for the other four subjects (group B, body fat = 12 +/- 1%) averaged 35.50 +/- 0.05 degrees C for both trials. Rewarming increased Tre similarly in group B during both LMG (0.76 +/- 0.25 degrees C) and NMG (0.89 +/- 0.13 degrees C). Afterdrop responses, evident only in those individuals whose body core cooled during immersion (group B), were not different between LMG and NMG. These data support the contention that Tre responses during passive rewarming are related to body insulation. Furthermore these results indicate that low muscle glycogen levels do not impair rewarming time nor alter after-drop responses during passive rewarming after mild-to-moderate hypothermia.     

Radio frequency (13.56 MHz) energy enhances recovery from mild hypothermia

The rate of warming after hypothermia depends on the method of rewarming. This study compared the effectiveness of radio frequency (RF) energy against hot (41 degrees C) water immersion (HW) and an insulated cocoon (IC) for rewarming hypothermic men. Six men fasted overnight and were rewarmed for 1 h after attaining a 0.5 degree C reduction in rectal temperature (Tre). Tre and esophageal (Tes) temperature were recorded every 5 min with nonmetallic thermal probes. The base-line value for Tre and Tes just before rewarming was subtracted from each 5 min Tre and Tes during rewarming to give delta Tre and delta Tes. The 12 delta Tes values were averaged for each individual and were compared using analysis of variance. The average delta Tes for RF (1.15 +/- 0.22 degrees C/h) was faster (P less than 0.001) than either IC (0.37 +/- 0.16 degrees C/h) or HW (0.18 +/- 0.09 degree C/h). The present study shows the superiority of RF energy for rewarming mildly hypothermic men.     

Observations on thermoregulatory ontogeny of mink (Mustela vison)

(1) We measured cooling rate for neonatal mink during a 10min coldroom (3.9 degrees C) exposure and subsequent warming rate during a 20min incubator (37.2 degrees C) exposure, the behaviour of the kits and the changes in their pelage between 1 and 46d of age, in an attempt to monitor the ontogeny of their thermoregulatory capacity. (2) Body weight of the 1d old kits averaged only 12.8+/-2.3g (n=4), but they gained weight rapidly reaching 226.1+/-28.3g (males, n=4) and 207.6+/-16.1g (females, n=4) at 30-31d of age, and 562.3+/-43.2g (males, n=3) and 435.7+/-35.5g (females, n=4) at 45-46d of age. (3) Body cooling rate (C(rate) ( degrees C/min); n=80) was affected by the age (between 1 and 31d), BW, initial rectal temperature (T(r0)), and sex of the kits, in addition to their body posture (P(cold), 1=extended, 2=curled-up) during coldroom exposure. C(rate) ( degrees C/min)=-0.34-0.02age-0.002BW+0.05T(r0)-0.06sex-0.20P(cold) (R(2)=0.75). (4) Body warming rate (W(rate) ( degrees C/min); n=80) was influenced by the age(2) and rectal temperature of the kit after the coldroom exposure (T(r10)). W(rate)( degrees C/min)=1.24+0.0002age(2)-0.04T(r10) (R(2)=0.76). (5) Kit fur fibre length increased from 5.45+/-0.63mm (males, n=2) and 6.20+/-0.20mm (females, n=3) at 22-23d of age to 9.43+/-1.44mm (males, n=4) and 8.70+/-1.89mm (females, n=4) at 30-31d of age, and to 12.93+/-0.47mm (males, n=3) and 11.38+/-0.41mm (females, n=4) at 45-46d of age, the growth averaging about 0.26mm per day. (6) Under normal circumstances newborn mink kits are hypothermic.Their thermoregulation develops only gradually and is dependent on increase in body mass, insulation and behavioural thermoregulation. Their strategy of survival is based on the ability to withstand hypothermia and on the nutrition and warmth provided by the dam.     

Rewarming rates of two large hibernators: Comparison of a monotreme and a eutherian

We measured body temperatures in two large hibernating mammals, the eutherian alpine marmot (Marmota marmota) and the egg-laying echidna (Tachyglossus aculeatus) from unrestrained animals in their natural environment. In both species hibernation is broken every 13 days on average by rewarming to euthermic temperatures. We found that the time course of a rewarming could be closely fitted with a sigmoid curve, allowing calculation of peak rewarming rate and corresponding body temperature. Maximum rewarming rates were twice as high in marmots as in echidnas (12.1±1.3 °C h⁻¹, n=10 cf. 6.2±1.2 °C h⁻¹, n=10). Peak rewarming rates were positively correlated with body temperature in echidnas, but negatively correlated in marmots.     

Control of breathing in the echidna (Tachyglossus aculeatus) during hibernation

Resting non-hibernating echidnas are characterised by low metabolic rates, but also have a very low respiratory frequency and a variable respiratory minute volume, often resulting in low levels of arterial O(2) and high CO(2). As the echidna lies at one physiological extreme among the hibernators, in terms of its large size and low metabolism and ventilatory requirement when not hibernating, a study of control of breathing during hibernation in echidnas should provide a useful test of the generality of various models. We used non-invasive techniques to study breathing patterns and the control of ventilation in 6 echidnas. Hibernating echidnas (T(b) range 7-10 degrees C) showed episodic breathing with bursts of breaths (average 36+/-16 breaths in 24+/-5 min) followed by a period of apnea (76+/-17 min) then a series (8+/-4) of slow breaths at 14+/-1 min intervals leading up to the next burst. Increasing CO(2) levels in the inspired air increased the number of breaths in a burst, eventually leading to continuous breathing. Inter burst breaths were controlled by O(2): hypoxia increased inter burst breaths, and decreased burst length, while hyperoxia abolished inter burst breaths and increased the apneic period. Overall, while CO(2) was a strong respiratory stimulus in hibernating echidnas, O(2) had little effect on total ventilation, but did have a strong effect on the breathing pattern.     

A second postcooling afterdrop: more evidence for a convective mechanism.

An attempt was made to demonstrate the importance of increased perfusion of cold tissue in core temperature afterdrop. Five male subjects were cooled twice in water (8 degrees C) for 53-80 min. They were then rewarmed by one of two methods (shivering thermogenesis or treadmill exercise) for another 40-65 min, after which they entered a warm bath (40 degrees C). Esophageal temperature (Tes) as well as thigh and calf muscle temperatures at three depths (1.5, 3.0, and 4.5 cm) were measured. Cold water immersion was terminated at Tes varying between 33.0 and 34.5 degrees C. For each subject this temperature was similar in both trials. The initial core temperature afterdrop was 58% greater during exercise (mean +/- SE, 0.65 +/- 0.10 degrees C) than shivering (0.41 +/- 0.06 degrees C) (P < 0.005). Within the first 5 min after subjects entered the warm bath the initial rate of rewarming (previously established during shivering or exercise, approximately 0.07 degrees C/min) decreased. The attenuation was 0.088 +/- 0.03 degrees C/min (P < 0.025) after shivering and 0.062 +/- 0.022 degrees C/min (P < 0.025) after exercise. In 4 of 10 trials (2 after shivering and 2 after exercise) a second afterdrop occurred during this period. We suggest that increased perfusion of cold tissue is one probable mechanism responsible for attenuation or reversal of the initial rewarming rate. These results have important implications for treatment of hypothermia victims, even when treatment commences long after removal from cold water.     

The effects of temperature change on lung liquid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs of 58-65 days of gestation were supported in vitro for 3 h, and lung liquid production rates were measured by a dye dilution technique. In 36 control preparations, incubated continuously at 37 degrees C, the average production rate in the first hour was 1.46 +/- 0.23 ml/h per kg body weight; there was no significant change over the following two h. In 36 further preparations the temperature was changed during the middle hour (ABA), with the following % reductions in production rates: at -1 degrees C (relative to 37 degrees C), 68.2 +/- 17.1%; -2 degrees C, 125.5 +/- 30.1% (reabsorption); -3 degrees C, 103.8 +/- 32.8% (reabsorption); -5 degrees C, 82.7 +/- 16.6%, -8 degrees C, 94.7 +/- 1.8 %; +2 degrees C, 100.7 +/- 12.6% (all significant, P less than 0.025-0.005). Slow recoveries followed a return to starting conditions, except after the increase in temperature, 10(-6) M amiloride abolished reabsorption, but not depression, during the maximal effects of temperature reduction (at -2 degrees C, n = 6); amiloride had no effect on control preparations (n = 6). These results suggest that: (a) reductions of 2-3 degrees C, as seen in the delivery room, abolish secretion, but not reabsorption of lung fluid; larger reductions stop both processes; (b) the reabsorptions seen after a fall in temperature depend on Na(+)-transport mechanisms; (c) lung liquid production was sensitive to a rise in temperature, so that fevers might adversely affect lung development, and (d) the fall in temperature at birth may be an important factor in the early reabsorption of lung liquid.     

Possible biphasic sweating response during short-term heat acclimation protocol for tropical natives

The aim of the present study was to evaluate the sweat loss response during short-term heat acclimation in tropical natives. Six healthy young male subjects, inhabitants of a tropical region, were heat acclimated by means of nine days of one-hour heat-exercise treatments (40+/-0 degrees C and 32+/-1% relative humidity; 50% (.)VO(2peak) on a cycle ergometer). On days 1 to 9 of heat acclimation whole-body sweat loss was calculated by body weight variation corrected for body surface area. On days 1 and 9 rectal temperature (T(re)) and heart rate (HR) were measured continuously, and rating of perceived exertion (RPE) every 4 minutes. Heat acclimation was confirmed by reduced HR (day 1 rest: 77+/-5 b.min(-1); day 9 rest: 68+/-3 b.min(-1); day 1 final exercise: 161+/-15 b.min(-1); day 9 final exercise: 145+/-11 b.min(-1), p<0.05), RPE (13 vs. 11, p<0.05) and T(re) (day 1 rest: 37.2+/-0.2 degrees C; day 9 rest: 37.0+/-0.2 degrees C; day 1 final exercise: 38.2+/-0.2 degrees C; day 9 final exercise: 37.9+/-0.1 degrees C, p<0.05). The main finding was that whole-body sweat loss increased in days 5 and 7 (9.49+/-1.84 and 9.56+/-1.86 g.m(-2).min(-1), respectively) compared to day 1 (8.31+/-1.31 g.m(-2).min(-1), p<0.05) and was not different in day 9 (8.48+/-1.02 g.m(-2).min(-1)) compared to day 1 (p>0.05) of the protocol. These findings are consistent with the heat acclimation induced adaptations and suggest a biphasic sweat response (an increase in the sweat rate in the middle of the protocol followed by return to initial values by the end of it) during short-term heat acclimation in tropical natives.     

Body temperature in captive long-beaked echidnas (Zaglossus bartoni)

The routine occurrence of both short-term (daily) and long-term torpor (hibernation) in short-beaked echidnas, but not platypus, raises questions about the third monotreme genus, New Guinea's Zaglossus. We measured body temperatures (T(b)) with implanted data loggers over three and a half years in two captive Zaglossus bartoni at Taronga Zoo, Sydney. The modal T(b) of both long-beaks was 31 degrees C, similar to non-hibernating short-beaked echidnas, Tachyglossus aculeatus, in the wild (30-32 degrees C) and to platypus (32 degrees C), suggesting that this is characteristic of normothermic monotremes. T(b) cycled daily, usually over 2-4 degrees C. There were some departures from this pattern to suggest periods of inactivity but nothing to indicate the occurrence of long-term torpor. In contrast, two short-beaked echidnas monitored concurrently in the same pen showed extended periods of low T(b) in the cooler months (hibernation) and short periods of torpor at any time of the year, as they do in the wild. Whether torpor or hibernation occurs in Zaglossus in the wild or in juveniles remains unknown. However, given that the environment in this study was conducive to hibernation in short-beaks, which do not easily enter torpor in captivity, and their large size, we think that torpor in wild adult Zaglossus is unlikely.     

Assessment of reproductive status in male echidnas

This study reports the development and application of techniques to assess the reproductive status of male echidnas. The pattern of testosterone secretion over a 24-h period in five echidnas was documented. Testosterone secretion after injection i.m. of either 1000 IU hCG (n=4) or 4 microg GnRH agonist (n=6) was determined to establish whether this could be used as a practical index of the prevailing steroidogenic capacity of the testes. hCG (1000 IU) was also used to assess seasonal changes in testosterone secretion in six echidnas over a 13-month period. Seasonal changes in testicular volume were examined by transabdominal ultrasonography. Electroejaculation was attempted to monitor seasonal changes in sperm production, which was also determined by spermatorrhea. There was no apparent diurnal pattern of testosterone secretion in echidnas and circulating concentrations of testosterone remained relatively low (maximum 1.2 ng/mL) and stable over 24h. Injection of hCG resulted in an increase (P<0.01; n=4) in testosterone concentration with a peak (2.9+/-0.3 ng/mL) approximately 4h after injection. GnRH also induced an increase (P<0.01; n=6) in circulating testosterone that was apparent after 1h (2.6+/-0.3 ng/mL) and concentrations remained elevated (3.4+/-0.3 ng/mL) for up to 8h after injection. Seasonal changes in testosterone secretion determined after injection of hCG, increased (P=0.03; n=6) from late-autumn, peaked in late-winter, and decreased by early-spring. Testicular volume followed a similar seasonal pattern (P<0.01; n=6) with an increase from late-autumn, peak in winter and a decline in mid-spring. There was no seasonal change in live weight. Electroejaculation was attempted throughout two breeding seasons but no semen was obtained. Spermatorrhoea in the echidna was described for the first time and was subsequently used to assess seasonal sperm production. Spermatozoa were found in the urine from June to September. This study has demonstrated that exogenous hormones can be used to obtain an index of the prevailing steroidogenic capacity of the testes in echidnas, which is not apparent with repetitive non-stimulated samples over 24 h. The assessment of testosterone secretion after injection of trophic hormones provides a valuable and practical procedure for the assessment of reproductive status. Testicular ultrasonography and spermatorrhea are useful in assessing reproductive status and in this study were successfully used to determine seasonal reproduction in captive echidnas.     

Effects of hypothermosol, an experimental acellular solution for tissue preservation and cardiopulmonary bypass, on isolated newborn lamb coronary vessels subjected to ultra profound hypothermia and anoxia.

Ultra profound hypothermia (4 to 10 degrees C) is an experimental method aiming at safely prolonging organ and total body preservation. For this purpose, Hypothermosol (HTS), an investigational acellular solution for blood substitution, was demonstrated to be beneficial in animal models undergoing cardiopulmonary bypass. We investigated the beneficial versus deleterious effects of cold preservation and the role of HTS on isolated coronary arteries (CA) during cold exposure, rewarming, and post-rewarming exposure to anoxia. Newborn lamb CA rings were studied using a tissue bath technique. CA were subjected to cold (7 degrees C for 3 h) and treated with either Krebs' buffer (Krebs/hypothermia) or HTS (HTS/hypothermia) (n = 15 each). A third group maintained at 37 degrees C (Krebs/normothermia) (n = 18) served as a time control. After rewarming (37 degrees C), precontracted CA were exposed to anoxia. In Krebs/hypothermia a substantial hypercontraction (g) occurred during rewarming (1.21+/-0.07) (mean +/- SEM) but not in HTS/hypothermia (0.79+/-0.03); P<0.05. Precontraction force generated by indomethacin/U46619 was identical in all three groups. However, Krebs/hypothermia vessels demonstrated a significantly higher relative vasoconstriction (percentage) in the early (approximately 10 min) and late (30 min) anoxia exposure than the HTS/hypothermia and time control (119.5%+/- 3.7 vs. 109.5%+/-4.4 and 101.5%+/-3, and 71%+/-7.6 vs. 38.9%+/-7 and 51.5%+/-5.9, respectively; P<0.05). In conclusion, Ultra profound hypothermia promotes coronary vasoconstriction upon rewarming, which is detrimental to relaxant response to hypoxia. Both phenomena are alleviated by performing ultra profound hypothermia under HTS protection.     

Plasma catecholamines in rats during rewarming from induced hypothermia

The present study sought to quantitate the levels of plasma catecholamines [norepinephrine (NE), epinephrine (E), and dopamine (DA)] during induction and rewarming from hypothermia. Male rats (317 +/- 8 g) were made hypothermic by exposure to 0.9% halothane at -10 to -15 degrees C while blood pressure (carotid artery), heart rate, and colonic temperature (Tc) were monitored. Anesthesia was discontinued when Tc reached 28 degrees C. Tc continued to fall but was held at 20-20.5 degrees C for 30 min. Rewarming was then initiated by raising ambient temperature to 22 degrees C. Arterial blood samples were taken 1) before cooling, 2) just before rewarming, 3) when Tc reached 22 degrees C during rewarming, and 4) when Tc reached 27 degrees C during rewarming. Plasma was assayed radioenzymatically for catecholamines using both phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase procedures, and hypothermic induction resulted in significant increases in NE, E, and DA above control levels (P less than 0.01). With rewarming to Tc = 22 degrees C, all catecholamines increased above the level observed during hypothermia (P less than 0.01), and NE and DA increased still further (P less than 0.01) when Tc reached 27 degrees C. The levels of plasma catecholamines observed during hypothermia and during the rewarming phase indicate a role of the sympathoadrenal medullary system in the metabolic adjustments associated with hypothermia and recovery. During rewarming, the levels of E and NE attained exceed those at which both substances may be expected to act as circulating hormones.     

AMP does not induce torpor

Torpor, a state characterized by a well-orchestrated reduction of metabolic rate and body temperature (T(b)), is employed for energetic savings by organisms throughout the animal kingdom. The nucleotide AMP has recently been purported to be a primary regulator of torpor in mice, as circulating AMP is elevated in the fasted state, and administration of AMP causes severe hypothermia. However, we have found that the characteristics and parameters of the hypothermia induced by AMP were dissimilar to those of fasting-induced torpor bouts in mice. Although administration of AMP induced hypothermia (minimum T(b) = 25.2 +/- 0.6 degrees C) similar to the depth of fasting-induced torpor (24.9 +/- 1.5 degrees C), ADP and ATP were equally effective in lowering T(b) (minimum T(b): 24.8 +/- 0.9 degrees C and 24.0 +/- 0.5 degrees C, respectively). The maximum rate of T(b) fall into hypothermia was significantly faster with injection of adenine nucleotides (AMP: -0.24 +/- 0.03; ADP: -0.24 +/- 0.02; ATP: -0.25 +/- 0.03 degrees C/min) than during fasting-induced torpor (-0.13 +/- 0.02 degrees C/min). Heart rate decreased from 755 +/- 15 to 268 +/- 17 beats per minute (bpm) within 1 min of AMP administration, unlike that observed during torpor (from 646 +/- 21 to 294 +/- 19 bpm over 35 min). Finally, the hypothermic effect of AMP was blunted with preadministration of an adenosine receptor blocker, suggesting that AMP action on T(b) is mediated via the adenosine receptor. These data suggest that injection of adenine nucleotides into mice induces a reversible hypothermic state that is unrelated to fasting-induced torpor.     

Water and heat balance during flight in the rose-colored starling (Sturnus roseus)

Water imbalance during flight is considered to be a potentially limiting factor for flight ranges in migrating birds, but empirical data are scarce. We studied flights under controlled ambient conditions with rose-colored starlings in a wind tunnel. In one experiment, we measured water fluxes with stable isotopes at a range of flight speeds (9-14 m s(-1)) at constant temperature (15 degrees C). In a second experiment, we measured evaporation rates at variable ambient temperatures (Ta = 5 deg -27 deg C) but constant speed (12 m s(-1)). During all flights, the birds experienced a net water loss. On average, water influx was 0.98 g h(-1) (SD = 0.16; n = 8), and water efflux was 1.29 g h(-1) (SD = 0.14; n = 8), irrespective of flight speed. Evaporation was related to temperature in a biphasic pattern. At temperatures below 18.2 degrees C, net evaporation was constant at 0.36 g h(-1) (SD = 0.18; n = 10), rising at higher temperatures with a slope of 0.11 per degree to about 1.5 g h(-1) at 27 degrees C. We calculated the relative proportion of dry and evaporative heat loss during flight. Evaporative heat loss at Ta < 18.2 deg C was 14% of total heat production during flight, and dry heat loss accounted for 84%. At higher temperatures, evaporative heat loss increased linearly with T(a) to about 25% at 27 degrees C. Our data suggest that for prolonged flights, rose-colored starlings should adopt behavioral water-saving strategies and that they cannot complete their annual migration without stopovers to replenish their water reserves.     

Central CO-heme oxygenase pathway raises body temperature by a prostaglandin-independent way.

Recently, the carbon monoxide (CO)-heme oxygenase pathway has been shown to play an important role in fever generation by acting on the central nervous system, but the mechanisms involved have not been assessed. Thus the present study was designed to determine whether prostagandins participate in the rise in body temperature (T(b)) observed after induction of the CO-heme oxygenase pathway in the central nervous system. Intracerebroventricular (ICV) injection of heme-lysinate (152 nmol/4 microl), which is known to induce the CO-heme oxygenase pathway, caused an increase in T(b) [thermal index (TI) = 5.3 +/- 0.5 degrees C. h], which was attenuated by ICV administration of the heme oxygenase inhibitor ZnDPBG (200 nmol/4 microl; TI = 2.5 +/- 1.7 degrees C. h; P < 0.05). No change in T(b) was observed after intraperitoneal injection of the cyclooxygenase inhibitor indomethacin (5 mg/kg), whereas indomethacin at the same dose attenuated the fever induced by ICV administration of lipopolysaccharide (LPS) (10 ng/2 microl) (vehicle/LPS: TI = 4.5 +/- 0.5 degrees C. h; indomethacin/LPS: TI = 1.7 +/- 1.0 degrees C. h; P < 0.05). Interestingly, indomethacin did not affect the rise in T(b) induced by heme-lysinate (152 nmol/4 microl) ICV injection (vehicle/heme: TI = 4.5 +/- 1.4 degrees C. h; indomethacin/heme: TI = 4.2 +/- 1.0 degrees C. h). Finally, PGE(2) (200 ng/2 microl) injected ICV evoked a rise in T(b) that lasted 1.5 h. The heme oxygenase inhibitor ZnDPBG (200 nmol/4 microl) failed to alter PGE(2)-induced fever. Taken together, these results indicate that the central CO-heme oxygenase pathway increases T(b) independently of prostaglandins.     

Body temperature-related structural transitions of monotremal and human hemoglobin

In this study, temperature-related structural changes were investigated in human, duck-billed platypus (Ornithorhynchus anatinus, body temperature T(b) = 31-33 degrees C), and echidna (Tachyglossus aculeatus, body temperature T(b) = 32-33 degrees C) hemoglobin using circular dichroism spectroscopy and dynamic light scattering. The average hydrodynamic radius (R(h)) and fractional (normalized) change in the ellipticity (F(obs)) at 222 +/- 2 nm of hemoglobin were measured. The temperature was varied stepwise from 25 degrees C to 45 degrees C. The existence of a structural transition of human hemoglobin at the critical temperature T(c) between 36-37 degrees C was previously shown by micropipette aspiration experiments, viscosimetry, and circular dichroism spectroscopy. Based on light-scattering measurements, this study proves the onset of molecular aggregation at T(c). In two different monotremal hemoglobins (echidna and platypus), the critical transition temperatures were found between 32-33 degrees C, which are close to the species' body temperature T(b). The data suggest that the correlation of the structural transition's critical temperature T(c) and the species' body temperature T(b) is not mere coincidence but, instead, is a more widespread structural phenomenon possibly including many other proteins.     

Seasonal rhythms of body temperature in the free-ranging raccoon dog (Nyctereutes procyonoides) with special emphasis on winter sleep

The raccoon dog (Nyctereutes procyonoides) is the only canid with passive overwintering in areas with cold winters, but the depth and rhythmicity of wintertime hypothermia in the wild raccoon dog are unknown. To study the seasonal rhythms of body temperature (T(b)), seven free-ranging animals were captured and implanted with intra-abdominal T(b) loggers and radio-tracked during years 2004-2006. The average size of the home ranges was 306+/-26 ha, and the average 24 h T(b) was 38.0+/-<0.01 degrees C during the snow-free period (May-November). The highest and lowest T(b) were usually recorded around midnight (21:00-02:00 h) and between 05:00-11:00 h, respectively, and the range of the 24 h oscillations was 1.2+/-0.01 degrees C. The animals lost approximately 43+/-6% of body mass in winter (December-April), when the average size of the home ranges was 372+/-108 ha. During the 2-9-wk periods of passivity in January-March, the average 24 h T(b) decreased by 1.4-2.1 degrees C compared to the snow-free period. The raccoon dogs were hypothermic for 5 h in the morning (06:00-11:00 h), whereas the highest T(b) values were recorded between 16:00-23:00 h. The range of the 24 h oscillations increased by approximately 0.6 degrees C, and the rhythmicity was more pronounced than in the snow-free period. The ambient temperature and depth of snow cover were important determinants of the seasonal T(b) rhythms. The overwintering strategy of the raccoon dog resembled the patterns of winter sleep in bears and badgers, but the wintertime passivity of the species was more intermittent and the decrease in the T(b) less pronounced.     

Effect of temperature on spike-triggered average torque and electrophysiological properties of low-threshold motor units.

The aim of the study was to jointly analyze temperature-induced changes in low-threshold single motor unit twitch torque and action potential properties. Joint torque, multichannel surface, and intramuscular electromyographic signals were recorded from the tibialis anterior muscle of 12 subjects who were instructed to identify the activity of a target motor unit using intramuscular electromyographic signals as feedback. The target motor unit was activated at the minimum stable discharge rate in seven 3-min-long contractions. The first three contractions (C1-C3) were performed at 33 degrees C skin temperature. After 5 min, the subject performed three contractions at 33 degrees C (T1), 39 degrees C (T2), and 45 degrees C (T3), followed by a contraction at 33 degrees C (C4) skin temperature. Twitch torque and multichannel surface action potential of the target motor unit were obtained by spike-triggered averaging. Discharge rate (mean +/- SE, 7.1 +/- 0.5 pulses/s), interpulse interval variability (35.8 +/- 9.2%), and recruitment threshold (4.5 +/- 0.4% of the maximal voluntary torque) were not different among the seven contractions. None of the investigated variables were different among C1-C3, T1, and C4. Conduction velocity and peak twitch torque increased with temperature (P < 0.05; T1: 3.53 +/- 0.21 m/s and 0.82 +/- 0.23 mN x m, T2: 3.93 +/- 0.24 m/s and 1.17 +/- 0.36 mN x m, T3: 4.35 +/- 0.25 m/s and 1.46 +/- 0.40 mN x m, respectively). Twitch time to peak and surface action potential peak-to-peak amplitude were smaller in T3 (61.8 +/- 2.0 ms and 27.4 +/- 5.1 microV, respectively) than in T1 (71.9 +/- 4.1 ms and 35.0 +/- 6.5 microV, respectively) (P < 0.05). The relative increase in conduction velocity between T1 and T3 was positively correlated (P < 0.05) with the increase in twitch peak amplitude (r2 = 0.48), with the decrease in twitch time to peak (r2 = 0.43), and with the decrease in action potential amplitude (r2 = 0.50). In conclusion, temperature-induced modifications in fiber membrane conduction properties may have a direct effect on contractile motor unit properties.     

Circadian rhythms of body temperature and activity levels during 63 h of hypoxia in the rat

The hypothermic response of rats to only brief ( approximately 2 h) hypoxia has been described previously. The present study analyzes the hypothermic response in rats, as well as level of activity (L(a)), to prolonged (63 h) hypoxia at rat thermoneutral temperature (29 degrees C). Mini Mitter transmitters were implanted in the abdomens of 10 adult Sprague-Dawley rats to continuously record body temperature (T(b)) and L(a). After habituation for 7 days to 29 degrees C and 12:12-h dark-light cycles, 48 h of baseline data were acquired from six control and four experimental rats. The mean T(b) for the group oscillated from a nocturnal peak of 38.4 +/- 0.18 degrees C (SD) to a diurnal nadir of 36.7 +/- 0.15 degrees C. Then the experimental group was switched to 10% O(2) in N(2). The immediate T(b) response, phase I, was a disappearance of circadian rhythm and a fall in T(b) to 36.3 +/- 0.52 degrees C. In phase II, T(b) increased to a peak of 38.7 +/- 0.64 degrees C. In phase III, T(b) gradually decreased. At reoxygenation at the end of the hypoxic period, phase IV, T(b) increased 1.1 +/- 0.25 degrees C. Before hypoxia, L(a) decreased 70% from its nocturnal peak to its diurnal nadir and was entrained with T(b). With hypoxia L(a) decreased in phase I to essential quiescence by phase II. L(a) had returned, but only to a low level in phase III, and was devoid of any circadian rhythm. L(a) resumed its circadian rhythm on reoxygenation. We conclude that 63 h of sustained hypoxia 1) completely disrupts the circadian rhythms of both T(b) and L(a) throughout the hypoxic exposure, 2) the hypoxia-induced changes in T(b) and L(a) are independent of each other and of the circadian clock, and 3) the T(b) response to hypoxia at thermoneutrality has several phases and includes both hypothermic and hyperthermic components.