Effect of Structural Changes of Pro6 in Dermorphin Molecule on Its Antinociceptive Activity

We studied effect of dermorphin (H-Tyr-DAla-Phe-Gly-Tyr-Pro-Ser-NH₂) and its analogs with modified amino acid residue proline in position 6, H-Tyr-DAla-Phe-Gly-Tyr-[DPro]-Ser-NH₂, H-Tyr-DAla-Phe-Gly-Tyr-[dehydro-Pro]-Ser-NH₂, and H-Tyr-DAla-Phe-Gly-Tyr-[D-dehydro-Pro]-Ser-NH₂, on nociception in the tail-flick and hot plate tests after intraperitoneal injection. Replacement of LPro with the stereoisomer DPro as well as Pro dehydration (LdHPro) was shown to increase antinociceptive activity. Replacement of LdHPro with DdHPro cancelled the activity in the tail-flick test. All three dermorphin analogs retained antinociceptive activity in the hot plate test; however, the effect of dermorphin was more pronounced.     

Effect of [DAla4]-Dermorphin and Its Analogs on the Functional Status of the Thermoregulation System in Rats at Different Environmental Temperature

We studied the influence of [DAla⁴]-dermorphin ([DAla⁴]-DM), its fragments ([DAla⁴]-DM_2–7, [DAla⁴]-DM_3–7, and [DAla⁴]-DM_4–7) and analogs ([Trp¹, DAla⁴]-DM, [DArg², DAla⁴]-DM, and [DOrn², DAla⁴]-DM) on the functional status of the thermoregulation system in rats at different thermal environments: cold (4–6°C), thermoneutral (27–28°C) and hot (31–32°C). [DAla⁴]-DM administration proved to induce temperature- and dose-dependent hypothermia and vasomotor responses. No activity of the peptide was observed in the hot environment. N-terminal shortening of the peptide inhibits its thermoregulatory activity. Tyr¹ to Trp¹ substitution nearly completely suppressed the thermoregulatory effects. DAla² to DArg² substitution decreased the hypothermic effect and only the vasodilatory response was observed in the comfortable environment. DAla² to DOrn² substitution completely suppressed the hypothermic effect in the cold environment and considerably attenuated the vasodilatory response in the thermoneutral environment.     

Thermoregulatory Activity of Dermorphin Fragments

We studied the effect of C-terminal truncation of the dermorphin (DM) molecule and analogs of its N-terminal tetrapeptide, [DOrn²]-DM_1–4, [DArg²]-DM_1–4, [DAla⁴]-DM_1–4, [DArg², DAla⁴]-DM_1–4, Arg-DM_1–4, Arg-[DArg²]-DM_1–4, Arg-[DAla⁴]-DM_1–4, and Arg-[DArg², DAla⁴]-DM_1–4, on the functional status of the thermoregulation system in rats at different ambient temperatures. For the first time, we demonstrate that the N-terminal tetrapeptide is the minimal fragment with the hypothermic effect. Only the N-terminal octapeptide exerted the vasomotor effect. Amino acid substitutions in the tetrapeptide affected its hypothermic effect. [DArg²]-DM_1–4 and [DArg², DAla⁴]-DM_1–4 had the greatest effect. Addition of Arg to the N-terminus of DM_1–4 analogs changed their thermoregulatory activity. The greatest thermoregulatory effect was observed for Arg-[DArg²]-DM_1–4 and Arg-[DArg², DAla⁴]-DM_1–4.     

Effect of Neurotensin Peptidomimetics on Thermoregulation in Rats

The effects of the tripeptide analogues of neurotensin, GZR123 and GZR125, on thermoregulation was studied in rats that were kept at different ambient temperatures ( _c): in the cold ( _c = 4–6°C), thermoneutral ( _c = 27–28°C), and hot ( _c = 31–32°C) environment, as well as at room temperature ( _c = 20–21°C). In the cold environment, the injection of GZR123 disturbed the vegetative mechanisms of heat emission, leading to peripheral vasoconstriction and possibly changing heat production. Similar to neurotensin, GZR125 disturbed the development of compensatory vasoconstriction in the cold environment and at room temperature, which resulted in a decrease in body temperature. At high temperature, this peptide induced vasodilation.     

Influence of aging in the thermoregulatory efficiency of man

Studies were carried out to evaluate the effect of aging on the thermoregulatory efficiency in man. The efficiency of thermoregulatory system was assessed on the basis of tolerance to acute cold stress, Tromp test and cold induced vasodilatation (CIVD) response. The experiments were done in 9 groups (15 each) of human volunteers in the age ranges of 20–25, 26–30, 31–35, 36–40, 41–45, 46–50, 51–55, 56–60 and 61–70 years. They were made to relax in a thermoneutral laboratory (27 ± 1C) for one hour; thereafter their resting heart rate, blood pressure, oxygen consumption, oral, mean skin, mean body and peripheral temperatures were measured. Then they were exposed to cold (10C) in a cold chamber wearing shorts and vests for two hours. The above parameters and shivering responses were recorded at 30 min intervals during cold exposures. On other occasions, their thermoregulatory efficiency test (Tromp Test) and cold induced vasodilatation response were also studied in the same thermoneutral laboratory. The results showed comparatively poor cold tolerance and thermoregulatory efficiency in elderly people. The middle aged category (above 40 years) showed a gradual reduction in the thermoregulatory efficiency, but highly significant reduction was noticed in those who exceeded sixty years of age.     

Temperature regulation in a burrow-nesting tropical seabird,the Wedge-tailed Shearwater (Puffinus pacificus)

Summary At low air temperatures (2.3–13.9°C), Wedge-tailed Shearwaters (Puffinus pacificus) shivered and their oxygen consumption increased to as much as 283% of the mean value (0.77 ml O₂/g·h) within the thermoneutral zone of air temperature (23–34°C). The minimal thermal conductance of the tissues and plumage was similar to the value predicted from the body mass (320.5 g). The oxygen consumption of the birds within their thermoneutral zone was lower than predictions based on body mass. At elevated air temperatures, the shearwaters panted at respiratory frequencies as high as 260 respirations/min; maximal respiratory frequencies were not invoked until the birds had become hyperthermic. During exposure to a hot environment, the oxygen consumption of the birds increased and in most instances the shearwaters were not able to lose heat equivalent to their concurrent metabolic heat production.Symbols and abbreviations BMR basal metabolic rate - C _total total thermal conductance - f respiratory frequency - TEWL total evaporative water loss - T _st stomach temperature - T _re rectal temperature     

Hormonal growth-promotant effects on grain-fed cattle maintained under different environments

Six steers (3/4 Charolais×1/4 Brahman) (mean body weight 314±27 kg) and six spayed heifers (3/5 Shorthorn×2/5 Red Angus) (mean body weight 478±30 kg) were used to determine the effects of climatic conditions and hormone growth promotants (HGP) on respiration rate (RR; breaths/min), pulse rate (beats/min), rectal temperature (RT; °C), and heat production (HP; kJ). Cattle were exposed to the following climatic conditions prior to implantation with a HGP and then again 12 days after implantation: 2 days of thermoneutral conditions (TNL) [21.9±0.9°C ambient temperature (T_A) and 61.7±22.1% relative humidity (RH)] then 2 days of hot conditions [HOT; 29.2±4°C (T_A) and 78.3±13.2% (RH)], then TNL for 3 days and then 2 days of cold conditions [COLD; 17.6±0.9°C (T_A) and 63.4±1.8% (RH); cattle were wet during this treatment]. The HGP implants used were: estrogenic implant (E), trenbolone acetate implant (TBA), or both (ET). Both prior to and following administration of HGP, RRs were lower (P<0.05) on cold days and greater (P<0.05) on hot days compared to TNL. On hot days, RTs, were 0.62°C higher after compared to before implanting. Across all conditions, RTs were >0.5°C greater (P<0.05) for E cattle than for TBA or ET cattle. On cold days, RTs of steers were >0.8°C higher than for the heifers, while under TNL and HOT, RTs of steers were 0.2–0.35°C higher than those of heifers. Prior to implantation, HP per hour and per unit of metabolic body weight was higher (P<0.05) for cattle exposed to hot conditions, when compared to HP on cold days. After implantation, HP was greater (P<0.05) on hot days than on cold days. Under TNL, ET cattle had the lowest HP and greatest feed intake. On hot days, E cattle had the lowest HP, and the highest RT; therefore, if the potential exists for cattle death from heat episodes, the use of either TBA or ET may be preferred. Under cold conditions HP was similar among implant groups.     

The effects of warming by active and passive means on the subsequent responses to cold water immersion

Two experiments were undertaken to investigate the effects of warming the body upon the responses during a subsequent cold water immersion (CWI). In both experiments the subjects, wearing swimming costumes, undertook two 45-min CWIs in water at 15° C. In experiment 1, 12 subjects exercised on a cycle ergometer until their rectal temperatures (T _re) rose by an average of 0.73°C. They were then immediately immersed in the cold water. Before their other CWI they rested seated on a cycle ergometer (control condition). In experiment 2, 16 different subjects were immersed in a hot bath (40° C) until their T _re rose by an average of 0.9° C; they were then immediately immersed in the cold water. Before their other CWI they were immersed in thermoneutral water (35° C; control condition). Heart rate in both experiments and respiratory frequency in experiment 1 were significantly (P < 0.05) higher during the first 30 s of CWI following active warming. In experiment 1, the rate of fall of T _re during the final 15 min of CWI was significantly (P < 0.01) faster when CWI followed active warming (2.46° C · h^–1) compared with the control condition (1.68°C · h^–1). However, this rate was observed when absolute T _re was still above that seen in the control CWIs. It is possible, therefore, that if longer CWIs had been undertaken, the two temperature curves may have converged and thereafter fallen at similar rates; this was the case with the aural temperature (T _au) seen in experiment 1 and the T _au and T _re in experiment 2. It is concluded that pre-warming is neither beneficial nor detrimental to survival prospects during a subsequent CWI.     

The role of different anions in ionic liquids on Pseudomonas cepacia lipase catalyzed transesterification and hydrolysis

Lipase Pseudomonas cepacia (PS) catalyzed transesterification of ethyl 3-phenylpropanoate with eleven alcohols was investigated in three ionic liquids [ILs], [Bmim]BF₄, [Bmim]PF₆, and [Bmim]Tf₂N, consisting of an identical cation and different anions. The yields were higher in hydrophobic ILs [Bmim]Tf₂N (55–96%) and [Bmim]PF₆ (22–95%), than in hydrophilic [Bmim]BF₄ (0–19%). The incubation of lipase PS in hydrophobic ILs for a period of 20–300 days at room temperature resulted in an increased yield of 62–98% in [Bmim]Tf₂N and 45–98% in [Bmim]PF₆, respectively. The lipase PS-hydrophobic IL mixture was recycled five times without any decrease in the yield of the products. In another set of experiments, the hydrolytic activity of the enzyme was determined after incubation in each of the three ILs and in hexane for 20 days at room temperature. It was found to be 1.8- and 1.6-fold higher in [Bmim]Tf₂N and [Bmim]PF₆, respectively, remained unchanged in [Bmim]BF₄ and was 1.6 times lower in hexane as compared to the non-incubated enzyme.     

Thermal sensitivity of heart rate and insensitivity of blood pressure in the Antarctic nototheniid fish <Emphasis Type="Italic">Pagothenia borchgrevinki</Emphasis>

The Antarctic notothenioids are among the most stenothermal of fishes, well adapted to their stable, cold and icy environment. The current study set out to investigate the thermal sensitivity/insensitivity of heart rate and ventral aortic blood pressure of the Antarctic nototheniid fish Pagothenia borchgrevinki over a range of temperatures. The heart rate increased rapidly from –1 to 6°C (Q₁₀=2.0–3.3), but was relatively insensitive to temperature above the ~6°C lethal limit of the species (Q₁₀=1.2). The increase in heart rate from –1 to 6°C was the result of a 45% increase in excitatory adrenergic tone, masking a 37% increase in inhibitory cholinergic tone. Ventral aortic pressure was regulated well above the lethal limit, up to at least 10°C. With the return of the fish to environmental temperatures, the heart rate rapidly decreased back to control levels, while ventral aortic pressure increased and remained elevated for over an hour following a 6°C exposure.     

Cold thermoregulatory changes induced by sleep deprivation in men

The aim of this study was to evaluate the thermoregulatory changes induced by 27-h of sleep deprivation (SD) in men at rest both in a comfortable ambient temperature and in cold air. A group of 12 male subjects were placed in a comfortable ambient temperature (dry bulb temperature,T _db = 25° C, relative humidity, rh = 40%–50% , clothing insulation = 1 clo) for 1 h and then they were submitted to a standard cold air test in a climatic chamber for 2h (T _db=1° C, rh = 40%–50%, wind speed = 0.8 m·s^–1, nude), before and after 27 h of sleep deprivation. Thermoregulatory changes (rectal temperature,T _re; mean skin temperature, _sk; metabolic heat production ) were monitored continuously. At comfortable ambient temperature, no significant change was observed after SD forT _re, _sk and . During the cold test,T _re did not change but _sk and were higher after SD (P<0.05). Increased (+ 6%,P < 0.05) was related to earlier and higher shivering, with a possible increase in the sensitivity of the thermoregulatory system as shown by the shorter time to onset of continous shivering (d): 8.66 (SEM 1.33) min versus 28.20 (SEM 1.33) min (P < 0.001) and by a higher _sk observed at d: 27.60 (SEM 1.40)° C versus 21.40 (SEM 0.60)° C (P < 0.001). These results were associated with higher cold sensations and shivering following SD. They also suggested that SD modified thermoregulatory responses at a central level especially in a cold environment.     

Seasonal effects on thermoregulatory abilities of the Wahlberg's epauletted fruit bat (Epomophorus wahlbergi) in KwaZulu-Natal,South Africa

Seasonal variations in ambient temperature (T_a) require changes in thermoregulatory responses of endotherms. These responses vary according to several factors including taxon and energy constraints. Despite a plethora of studies on chiropteran variations in thermoregulation, few have examined African species. In this study, we used the Wahlberg's epauletted fruit bat (Epomophorus wahlbergi, body mass≈115 g) to determine how the thermoregulatory abilities of an Afrotropical chiropteran respond to seasonal changes in T_a. Mass specific Resting Metabolic Rates (RMR_Ta) and basal metabolic rate (BMR) were significantly higher in winter than in summer. Furthermore, winter body mass was significantly higher than summer body mass. A broad thermoneutral zone (TNZ) was observed in winter (15–35 °C) compared with summer (25–30 °C). This species exhibited heterothermy (rectal and core body temperature) during the photophase (bats' rest-phase) particularly at lower T_as and had a low tolerance of high T_as. Overall, there was a significant seasonal variation in the thermoregulatory abilities of E. wahlbergi. The relative paucity of data relating to the seasonal thermoregulatory abilities of Afrotropical bats suggest further work is needed for comparison and possible effects of climate change, particularly extreme hot days.     

Respiration of juvenile Arctic cod (Boreogadus saida): effects of acclimation,temperature, and food intake

Oxygen consumption (VO₂) of juvenile Arctic cod (Boreogadus saida) was investigated at low tempera tures (six temperatures; range -0.5 to 2.7°C). Small (mean wt. 6–8 g) and large (mean wt. 14 g) fish were acclimated, or adjusted to a constant temperature (0.4°C), for 5 months and then tested for metabolic cold adaptation (elevated metabolic rates in polar fishes). Short-term (2 weeks) acclimated fish showed elevated VO₂ similar to previously established values for polar fishes, but there was no such evidence after longterm acclimation. Long-term acclimation caused VO₂ values to drop significantly (from 86.0 to 46.5 mg O₂·kg^–1·h^–1, at 0.4°C), which showed that metabolic cold adaptation was a phenomenon caused by insufficien: acclimation time for fish in respiration experiments. We also measured the effects of temperature and feeding on VO₂. A temperature increase of 2.3°C resulted in relatively large increases in VO₂ for both longand short-term acclimated fish (Q₁₀ = 6.7 and 7.1, respectively), which suggests that metabolic processes are strongly influenced by temperature when it is close to zero. Feeding individuals to satiation caused significant increases in VO₂ above pre-fed values (34–60% within 1–2 days after feeding). Respiration budgets of starved and fed Arctic cod at ambient temperatures in Resolute Bay N.W.T., Canada, were used to model annual respiration costs and potential weight loss. Low respiration costs for Arctic cod at ambient temperatures result in high growth efficiency during periods of feeding and low weight loss during periods of starvation.     

Effects of simulated natural air movement on thermoregulatory response during head-down bed rest

Spaceflight and its bed rest analog impair thermoregulatory responses, including elevated core temperature observed at rest and during exercise. Natural air flow has been found to increase cold sensation significantly compared to artificial constant air flow (CAF). The present study tested the hypothesis that simulated natural air flow (SNAF) ventilation would ameliorate impaired thermoregulatory function to a greater extent than CAF under simulated microgravity conditions. Seven healthy males underwent 30 days of −6° head-down bed rest (HDBR). During pre-HDBR and the day 29 of HDBR (HDBR 29), the subjects were exposed to three air flow patterns at 23 °C while in a supine posture: a still air flow control (CON), CAF, and SNAF. The mean air velocity of the latter two patterns was 0.2 m/s. Subjective perception of the thermal environment was recorded by thermal sensation vote (TSV), and rectal temperature (T_re), skin temperature (T_sk), and cutaneous vascular conductance (CVC) were also measured during the sessions. T_re was significantly elevated after 29 days of HDBR and decreased to a greater extent in SNAF than in CAF on HDBR 29. However, there was no significant difference between T_re in SNAF on HDBR 29 and that in CON on pre-HDBR. Mean T_sk, CVC, and TSV in SNAF were also significantly lower than those in CAF on HDBR 29. Moreover, TSV was close to ‘neutral’ under SNAF on HDBR 29. These data indicate that simulated natural air movement might be more effective than constant air movement at preserving core temperature at a thermoneutral ambient temperature during HDBR.     

Thermoregulation in three species of Afrotropical subterranean mole-rats (Rodentia: Bathyergidae) from Zambia and Angola and scaling within the genus Cryptomys

The thermoregulatory characteristics of three species of Cryptomys from Zambia and Angola are examined and, together with published data on four other species of Cryptomys from southern Africa, used to determine whether scaling occurs in this genus of subterranean rodents. The thermoregulatory properties of acclimated giant Zambian mole-rats, Cryptomys mechowi ( =267 g), Angolan mole-rats, Cryptomys bocagei ( =94 g) and Zambian common mole-rats Cryptomys hottentotus amatus ( =77 g) are as follows. Mean resting metabolic rates (RMRs) within the respective thermoneutral zones were 0.60±0.08 cm³ O₂ g^-1 h^-1 (n=12) for C. mechowi; 0.74±0.06 cm³ O₂ g^-1 h^-1 (n=8) for C. bocagei and 0.63±0.06 cm³O₂ g^-1 h^-1 (n=21) for C. h. amatus. The thermoneutral zones (TNZs) of all three species are narrow: 29–30°C for C. mechowi; 31.5–32.5°C for C. bocagei and 28–32° C for C. h. amatus. The increase in mean RMR at the lowest temperatures tested (15° C for C. mechowi, 18° C for C. bocagei and C. h. amatus) was 2.35, 2.2 and 3.82 times their RMR in the TNZ respectively. Body temperatures are low, 34±0.53° C (n=24) for C. mechowi, 33.7±0.32° C (n=20) for C. bocagei and 33.8±0.43° C (n=40) for C. h amatus. At the lower limit of thermoneutrality, conductances are 0.09±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=30) in C. mechowi; 0.12±0.01 cm³ O₂ g^-1 h^-1 °C^-1 (n=20) in C. bocagei and 0.12±0.03 cm³ O₂ g^-1 h^-1 °C^-1 (n=32) in C. h. amatus. The range in mean body mass among the seven species of Cryptomys examined for scaling was 60 g (C. darlingi) to 267 g (C. mechowi). There is no clear relationship between RMR within the TNZ and body mass. The resultant relationship is represented by the power curve RMR=2.45 mass^-0.259.     

Effects of chronic and intermittent cold exposure on metabolic capacity ofPeromyscus andMicrotus

The effect of 30 days of acclimation at 5°C and of a semiweekly series of short severe cold exposures (T_b 20–30°C) on metabolic capacity (M_max) was measured in Alaskan meadow voles(Microtus pennsylvanicus tananaensis) and Wisconsin deer mice(Peromyscus maniculatus bairdii). Meadow voles, with an M_max of 12–14 ml/(g.h) or 8–9 met (M_max/M_st), showed little response to either treatment. In deer mice, however, acclimation at 5°C increased M_max by about half (from 11.0 to 15.4 ml/(g.h) or from 6.0 to 9.1 met). In 25°C-acclimated deer mice 7 severe cold exposures produced a similar increase of which about half was seen with the first 2 exposures. In 5°C-acclimated deer mice, M_max averaged a 0.3 ml/(g.h) increase for each cold exposure to reach a level of 19 ml/(g.h) or 11 met after 6 weeks.     

Stimulation of potato tuber respiration by cold stress is associated with an increased capacity of both plant uncoupling mitochondrial protein (PUMP) and alternative oxidase

The CO₂ evolution of intact potato tubers (Solanum tuberosum, L., var. Bintje) was analyzed during a 10-day period of their warm (25 ± 2°C) or cold (5 ± 1°C) storage, to evaluate cold-stress effects on expression and activities of plant uncoupling mitochondrial protein (PUMP) and alternative oxidase (AOX). CO₂ evolution rates were analyzed at 20°C, to reflect their possible capacities. The 20°C CO₂ production declined from 13 to 8 mg kg^–1 h^–1 after 2 days of warm storage and then (after 3 to 7 days) decreased from 8 to 6.5 mg kg^–1 h^–1. In contrast, 20°C CO₂ evolution did not change after the first day of cold storage, increased up to 14.5 mg kg^–1 h^–1 after 2 days, and decreased to about 12 mg kg^–1 h^–1 after 3 to 7 days of cold storage. Cold storage increased PUMP expression as detected by Western blots and led to elevated capacities of both PUMP (44%) and CN-resistant AOX (10 times), but not the cytochrome pathway. Since we found that cold storage led to about the same mitochondrial respiration of 40 nmol O₂ min^–1 mg^–1 attributable to each of the respective proteins, we conclude that both AOX and PUMP equally contribute to adaptation of potato tubers to cold.     

[125I]calmodulin binding to synaptic plasma membrane from rat brain: Kinetic and arrhenius analysis

Binding of [¹²⁵I]calmodulin was characterized in highly purified synaptic plasma membrane (SPM) prepared from rat brain. By Scatchard analysis, the Ca²⁺-dependent membrane binding of [¹²⁵I]calmodulin was found to have a B_max of 284 pmol/mg protein and an apparent affinity with a K_d of 131 nM. Kinetic analysis indicates that at 37°C, the dissociation of [¹²⁵I]calmodulinmembrane complexes follows first-order reaction and consists of two components: a dissociation constant (k) of 3.7×10^–1 min^–1 and a half-time (t_1/2) of 1.8 min for the fast component, and a k of 4.8×10^–2 min^–1 and a t_1/2 of 14.5 min for the slow component. At 0°C, substantial dissociation still occurred, with a k of 4.5×10^–2 min^–1 and a t_1/2 of 15.3 min for the fast component, and a k of 5.5×10^–3 min^–1 and a t_1/2 of 125.5 min for the slow component. These data on binding affinity and dissociation kinetics are consistent with the notion that SPM can readily and rapidly associated and dissociate calmodulin. In Arrhenius analysis of temperature effects, [¹²⁵I]calmodulin binding to SPM exhibits a biphasic function, with the transition temperature (T_d) estimated to be 23.8°C, suggesting that binding is influenced by lipid phase transition of the membrane. The binding of [¹²⁵I]calmodulin to the synaptic membrane was found to be increased by corticosterone (10^–7–10^–6 M), a steroid hormone, and decreased by ethanol (50–200 mM), a centrally acting drug. Our data on the characteristics of calmodulin binding to the SPM provide groundwork for future studies on physiological and pharmacological regulation of calmodulin translocation to and from the plasma membrane in synaptic terminals.Abbreviations used CaM calmodulin - SPM synaptic plasma membrane - ATPase adenosine triphosphatase - Tris tris(hydroxymethyl)aminomethane - EGTA ethylene-bis(oxyethylenenitrilo)tetraacetic acid - SDS sodium dodecyl sulfate - TFP trifluoperazine - K_d dissociation constant - B_max maximum binding - k first-order rate constant - t_1/2 half-time - T_d transition temperature     

Maximal aerobic performance of deer mice in combined cold and exercise challenges

In nature, animals frequently need to deal with several physiological challenges simultaneously. We examined thermoregulatory performance (body temperature stability) and maximal oxygen consumption of deer mice (Peromyscus maniculatus) during intense exercise at room temperature, acute cold exposure, and exercise during cold exposure. Results with exercise and cold exposure alone were consistent with previous studies: there was little difference between maximal metabolism elicited by exercise alone or cold exposure alone in warm-acclimated mice; after cold acclimation (9 weeks at 5 °C), maximal exercise metabolism did not change but maximum thermogenic capacity increased by >60%. Warm acclimated animals did not increase maximal oxygen consumption when exercise was combined with moderate cold (0 °C) and had decreased maximal oxygen consumption when exercise was combined with severe cold (–16 °C). Combined cold and exercise also decreased thermoregulatory performance and exercise endurance time. Cold acclimation improved thermoregulatory performance in combined cold and exercise, and there was also a slight increase in endurance. However, as for warm-acclimated animals, maximal exercise metabolism did not increase at low temperatures. We interpret these results as an indication of competition between thermoregulatory and locomotor effectors (brown adipose tissue and skeletal muscle) under the combined challenges of cold exposure and maximal exercise, with priority given to the locomotor function.Abbreviations BAT brown adipose tissue - T _b body temperature - O ₂ rate of oxygen consumption - O ₂ max maximal O₂ in exercise - O ₂ sum maximal O₂ during cold exposure Communicated by G. Heldmaier     

Thermoregulatory behavior of the triggerfish Balistes fuscus in an electronic shuttlebox

Ten blue triggerfish,Balistes fuscus, were tested individually for 3 days each in Ichthyotron electronic shuttleboxes to measure their thermoregulatory behavior. The modal thermal preferendum, a species-specific measure of temperature preference which is independent of prior thermal acclimation, was 25 °C. The triggerfish voluntarily occupied a 16–27 °C range of temperature, out of a potentially available range of 0–50 °C. There was no significant difference in preferred temperature between night and day, indicating lack of a thermoregulatory rhythm in this species. The preferred temperature range of this tropical marine reef species is similar to that of cool temperate freshwater and marine fishes; many warm temperate species prefer higher temperatures.