Previous Cold Exposure Research Articles

Fat accumulation in striped hamsters (Cricetulus barabensis) reflects the temperature of prior cold acclimation

BackgroundProper adjustments of metabolic thermogenesis play an important role in thermoregulation in endotherm to cope with cold and/or warm ambient temperatures, however its roles in energy balance and fat accumulation remain uncertain. Our study aimed to investigate the effect of previous cold exposure (10 and 0 °C) on the energy budgets and fat accumulation in the striped hamsters (Cricetulus barabensis) in response to warm acclimation. The body mass, energy intake, resting metabolic rate (RMR) and nonshivering thermogenesis (NST), serum thyroid hormone levels (THs: T3 and T4), and the activity of brown adipose tissue (BAT), indicated by cytochrome c oxidase (COX) activity and uncoupling protein 1 (ucp1) expression, were measured following exposure to the cold (10 °C and 0 °C) and transition to the warm temperature (30 °C).ResultsThe hamsters at 10 °C and 0 °C showed significant increases in energy intake, RMR and NST, and a considerable reduction in body fat than their counterparts kept at 21 °C. After being transferred from cold to warm temperature, the hamsters consumed less food, and decreased RMR and NST, but they significantly increased body fat content. Interestingly, the hamsters that were previously exposed to the colder temperature showed significantly more fat accumulation after transition to the warm. Serum T3 levels, BAT COX activity and ucp1 mRNA expression were significantly increased following cold exposure, and were considerably decreased after transition to the warm. Furthermore, body fat content was negatively correlated with serum T3 levels, BAT COX activity and UCP1 expression.ConclusionThe data suggest that the positive energy balance resulting from the decreased RMR and NST in BAT under the transition from the cold to the warm plays important roles in inducing fat accumulation. The extent of fat accumulation in the warm appears to reflect the temperature of the previous cold acclimation.

Metabolomes of bumble bees reared in common garden conditions suggest constitutive differences in energy and toxin metabolism across populations

Cold tolerance of ectotherms can vary strikingly among species and populations. Variation in cold tolerance can reflect differences in genomes and transcriptomes that confer cellular-level protection from cold; additionally, shifts in protein function and abundance can be altered by other cellular constituents as cold-exposed insects often have shifts in their metabolomes. Even without a cold challenge, insects from different populations may vary in cellular composition that could alter cold tolerance, but investigations of constitutive differences in metabolomes across wild populations remain rare. To address this gap, we reared Bombus vosnesenskii queens collected from Oregon and California (USA) that differ in cold tolerance (CTmin = -6 °C and 0 °C, respectively) in common garden conditions, and measured offspring metabolomes using untargeted LC-MS/MS. Oregon bees had higher levels of metabolites associated with carbohydrate (sorbitol, lactitol, maltitol, and sorbitol-6-phosphate) and amino acid (hydroxyproline, ornithine, and histamine) metabolism. Exogenous metabolites, likely derived from the diet, also varied between Oregon and California bees, suggesting population-level differences in toxin metabolism. Overall, our results reveal constitutive differences in metabolomes for bumble bees reared in common garden conditions from queens collected in different locations despite no previous cold exposure.

Plasma biomarkers of endothelial function, inflammation and oxidative stress in individuals with non-freezing cold injury.

What is the central question of this study? Are biomarkers of endothelial function, oxidative stress and inflammation altered by non-freezing cold injury (NFCI)? What is the main finding and its importance? Baseline plasma [interleukin-10] and [syndecan-1] were elevated in individuals with NFCI and cold-exposed control participants. Increased [endothelin-1] following thermal challenges might explain, in part, the increased pain/discomfort experienced with NFCI. Mild to moderate chronic NFCI does not appear to be associated with either oxidative stress or a pro-inflammatory state. Baseline [interleukin-10] and [syndecan-1] and post-heating [endothelin-1] are the most promising candidates for diagnosis of NFCI. Plasma biomarkers of inflammation, oxidative stress, endothelial function and damage were examined in 16 individuals with chronic NFCI (NFCI) and matched control participants with (COLD, n=17) or without (CON, n=14) previous cold exposure. Venous blood samples were collected at baseline to assess plasma biomarkers of endothelial function (nitrate, nitrite and endothelin-1), inflammation [interleukin-6 (IL-6), interleukin-10 (IL-10), tumour necrosis factor alpha and E-selectin], oxidative stress [protein carbonyl, 4-hydroxy-2-nonenal (4-HNE), superoxide dismutase and nitrotyrosine) and endothelial damage [von Willebrand factor, syndecan-1 and tissue type plasminogen activator (TTPA)]. Immediately after whole-body heating and separately, foot cooling, blood samples were taken for measurement of plasma [nitrate], [nitrite], [endothelin-1], [IL-6], [4-HNE] and [TTPA]. At baseline, [IL-10] and [syndecan-1] were increased in NFCI (P<0.001 and P=0.015, respectively) and COLD (P=0.033 and P=0.030, respectively) compared with CON participants. The [4-HNE] was elevated in CON compared with both NFCI (P=0.002) and COLD (P<0.001). [Endothelin-1] was elevated in NFCI compared with COLD (P<0.001) post-heating. The [4-HNE] was lower in NFCI compared with CON post-heating (P=0.032) and lower than both COLD (P=0.02) and CON (P=0.015) post-cooling. No between-group differences were seen for the other biomarkers. Mild to moderate chronic NFCI does not appear to be associated with a pro-inflammatory state or oxidative stress. Baseline [IL-10] and [syndecan-1] and post-heating [endothelin-1] are the most promising candidates for diagnosing NFCI, but it is likely that a combination of tests will be required.

Peripheral sensory function in non-freezing cold injury patients and matched controls.

What is the central question of this study? Is peripheral sensory function impaired in the chronic phase of non-freezing cold injury (NFCI)? What is the main finding and its importance? Warm and mechanical detection thresholds are elevated and intraepidermal nerve fibre density is reduced in individuals with NFCI in their feet when compared to matched controls. This indicates impaired sensory function in individuals with NFCI. Interindividual variation was observed in all groups, and therefore a diagnostic cut-off for NFCI has yet to be established. Longitudinal studies are required to follow NFCI progression from formation to resolution ABSTRACT: The aim of this study was to compare peripheral sensory neural function of individuals with non-freezing cold injury (NFCI) with matched controls (without NFCI) with either similar (COLD) or minimal previous cold exposure (CON). Thirteen individuals with chronic NFCI in their feet were matched with the control groups for sex, age, race, fitness, body mass index and foot volume. All undertook quantitative sensory testing (QST) on the foot. Intraepidermal nerve fibre density (IENFD) was assessed 10cm above the lateral malleolus in nine NFCI and 12 COLD participants. Warm detection threshold was higher at the great toe in NFCI than COLD (NFCI 45.93 (4.71)°C vs. COLD 43.44 (2.72)°C, P=0.046), but was non-significantly different from CON (CON 43.92 (5.01)°C, P=0.295). Mechanical detection threshold on the dorsum of the foot was higher in NFCI (23.61 (33.59) mN) than in CON (3.83 (3.69) mN, P=0.003), but was non-significantly different from COLD (10.49 (5.76) mN, P>0.999). Remaining QST measures did not differ significantly between groups. IENFD was lower in NFCI than COLD (NFCI 8.47 (2.36) fibre/mm2 vs. COLD 11.93 (4.04) fibre/mm2 , P=0.020). Elevated warm and mechanical detection thresholds may indicate hyposensitivity to sensory stimuli in the injured foot for individuals with NFCI and may be due to reduced innervation given the reduction in IENFD. Longitudinal studies are required to identify the progression of sensory neuropathy from the formation of injury to its resolution, with appropriate control groups employed.

The peripheral vascular responses in non-freezing cold injury and matched controls.

What is the central question of this study? Does non-freezing cold injury (NFCI) alter normal peripheral vascular function? What is the main finding and its importance? Individuals with NFCI were more cold sensitive (rewarmed more slowly and felt more discomfort) than controls. Vascular tests indicated that extremity endothelial function was preserved with NFCI and that sympathetic vasoconstrictor response might be reduced. The pathophysiology underpinning the cold sensitivity associated with NFCI thus remains to be identified. The impact of non-freezing cold injury (NFCI) on peripheral vascular function was investigated. Individuals with NFCI (NFCI group) and closely matched controls with either similar (COLD group) or limited (CON group) previous cold exposure were compared (n=16). Peripheral cutaneous vascular responses to deep inspiration (DI), occlusion (PORH), local cutaneous heating (LH) and iontophoresis of acetylcholine and sodium nitroprusside were investigated. The responses to a cold sensitivity test (CST) involving immersion of a foot in 15°C water for 2min followed by spontaneous rewarming, and a foot cooling protocol (footplate cooled from 34°C to 15°C), were also examined. The vasoconstrictor response to DI was lower in NFCI compared to CON (toe: 73 (28)% vs. 91 (17)%; P=0.003). The responses to PORH, LH and iontophoresis were not reduced compared to either COLD or CON. During the CST, toe skin temperature rewarmed more slowly in NFCI than COLD or CON (10min: 27.4 (2.3)°C vs. 30.7 (3.7)°C and 31.7 (3.9)°C, P<0.05, respectively); however, no differences were observed during the footplate cooling. NFCI were more cold-intolerant (P<0.0001) and reported colder and more uncomfortable feet during the CST and footplate cooling than COLD and CON (P<0.05). NFCI showed a decreased sensitivity to sympathetic vasoconstrictor activation than CON and greater cold sensitivity (CST) compared to COLD and CON. None of the other vascular function tests indicated endothelial dysfunction. However, NFCI perceived their extremities to be colder and more uncomfortable/painful than the controls.

Beyond thermal melanism: association of wing melanization with fitness and flight behaviour in a butterfly

Cold developmental conditions can greatly affect adult life history of ectotherms in seasonal habitats. Such effects are mostly negative, but sometimes adaptive. Here, we tested how cold conditions experienced during pupal development affect adult wing melanization of an insect ectotherm, the Glanville fritillary butterfly, Melitaea cinxia. We also assessed how in turn previous cold exposure and increased melanization can shape adult behaviour and fitness, by monitoring individuals in a seminatural set-up. We found that, despite pupal cold exposure inducing more melanization, wing melanization was not linked to adult thermoregulation preceding flight, under the conditions tested. Conversely, wing-vibrating behaviour had a major role in producing heat preceding flight. Moreover, more melanized individuals were more mobile across the experimental set-up. This may be caused by a direct impact of melanization on flight ability or a more indirect impact of coloration on behaviours such as mate search strategies and/or eagerness to disperse to more suitable mating habitats. We also found that more melanized individuals of both sexes had reduced mating success and produced fewer offspring, which suggests a clear fitness cost of melanization. Whether the reduced mating success is dictated by impaired mate search behaviour, reduced physical condition leading to a lower dominance status or weakened visual signalling remains unknown. In conclusion, while there was no clear role of melanization in providing a thermal advantage under our seminatural conditions, we found a fitness cost of being more melanized, which potentially impacted adult space use behaviour.

Previous recreational cold exposure does not alter endothelial function or sensory thermal thresholds in the hands or feet.

What is the central question of this study? Does recreational cold exposure result in cold sensitivity and is this associated with endothelial dysfunction and impaired sensory thermal thresholds? What is the main finding and its importance? Previous cold exposure was correlated with cold sensitivity of the foot, which might indicate the development of a subclinical non-freezing cold injury. Endothelial function and thermal detection were not impaired in cold-sensitive individuals; therefore, further research is required to understand the pathophysiology of subclinical and clinical forms of non-freezing cold injury. In this study, we investigated whether cold-sensitive (CS) individuals, who rewarm more slowly after a mild cold challenge, have impaired endothelial function and sensory thermal thresholds (STTs) and whether this is related to reported cold exposure. Twenty-seven participants with varying previous cold exposure undertook three tests: an STT test, i.e. determination of warm and cold STTs of the fingers and dorsal foot; an endothelial function test, i.e. measurement of cutaneous vascular conductance (CVC) during iontophoresis of ACh on the forearm, finger and foot; and a CS test, involving immersion of a foot for 2min in water at 15°C followed by 10min of rewarming in air at 30°C. Toe skin temperature (Tsk ) measured during the CS test was used to form a CS group (<32°C before and 5min after immersion) and an otherwise closely matched control group [Tsk >32°C; n=9 (four women) for both groups]. A moderate relationship was found between cold exposure ranking and Tsk rewarming (r=0.408, P=0.035, n=27) but not STT or endothelial function. The Tsk and blood flow were lower in CS compared with control subjects before and after foot immersion [Tsk , mean (SD): 30.3(0.9) versus 34.8(0.8) and 27.9(0.8) versus 34.3(0.8)°C, P<0.001; and CVC: 1.08(0.79) versus 3.82(1.21) and 0.79(0.52) versus 3.45(1.07)fluxmmHg-1 , n=9, P<0.001, respectively]. However, no physiologically significant differences were observed between groups for endothelial function or STT. A moderate correlation between previous cold exposure and toe Tsk rewarming after foot immersion was observed; however, CS was not associated with impaired endothelial function or reduced thermal detection.

Frequent extreme cold exposure and brown fat and cold-induced thermogenesis: a study in a monozygotic twin.

IntroductionMild cold acclimation is known to increase brown adipose tissue (BAT) activity and cold-induced thermogenesis (CIT) in humans. We here tested the effect of a lifestyle with frequent exposure to extreme cold on BAT and CIT in a Dutch man known as ‘the Iceman’, who has multiple world records in withstanding extreme cold challenges. Furthermore, his monozygotic twin brother who has a ‘normal’ sedentary lifestyle without extreme cold exposures was measured.MethodsThe Iceman (subject A) and his brother (subject B) were studied during mild cold (13°C) and thermoneutral conditions (31°C). Measurements included BAT activity and respiratory muscle activity by [18F]FDG-PET/CT imaging and energy expenditure through indirect calorimetry. In addition, body temperatures, cardiovascular parameters, skin perfusion, and thermal sensation and comfort were measured. Finally, we determined polymorphisms for uncoupling protein-1 and β3-adrenergic receptor.ResultsSubjects had comparable BAT activity (A: 1144 SUVtotal and B: 1325 SUVtotal), within the range previously observed in young adult men. They were genotyped with the polymorphism for uncoupling protein-1 (G/G). CIT was relatively high (A: 40.1% and B: 41.9%), but unlike during our previous cold exposure tests in young adult men, here both subjects practiced a g-Tummo like breathing technique, which involves vigorous respiratory muscle activity. This was confirmed by high [18F]FDG-uptake in respiratory muscle.ConclusionNo significant differences were found between the two subjects, indicating that a lifestyle with frequent exposures to extreme cold does not seem to affect BAT activity and CIT. In both subjects, BAT was not higher compared to earlier observations, whereas CIT was very high, suggesting that g-Tummo like breathing during cold exposure may cause additional heat production by vigorous isometric respiratory muscle contraction. The results must be interpreted with caution given the low subject number and the fact that both participants practised the g-Tummo like breathing technique.

Long-term after-effects of cold exposure in adult Alphitobius diaperinus (Tenebrionidae): the need to link survival ability with subsequent reproductive success

1. The effects of cold acclimation and cold exposure on the survival and reproductive capabilities of Alphitobius diaperinus (Tenebrionidae) adult beetles are examined. 2. First, the impact of temperature on survival duration was assessed by placing beetles in a range of cool temperature treatments. Second, the importance of acclimation duration was assessed. Third, the impact of thermal stress on subsequent reproductive ability was examined for beetles that had no previous cold exposure, and for beetles that had been subjected to previous cold exposure (i.e. acclimated) at various conditions, including fluctuating temperatures. 3. In all groups, the number of recorded survivors was strongly impacted by recovery period duration (i.e. 2 vs. 10 days). Survival of non-acclimated and 3-day acclimated beetles, expressed as lethal time for 50% of the samples, was reduced significantly when the insects were re-assessed for survival at 10 days after being returned to optimal growth conditions (7.9 ± 0.4 vs. 5.1 ± 0.6 days and 8.8 ± 0.5 vs. 6.8 ± 0.6 days, respectively). 4. Insects that had been subject to cold acclimation expressed better subsequent reproduction success than non-acclimated beetles. This beneficial impact increased when the acclimation period was prolonged, but some longer acclimation periods had no significant impact on survival. 5. Our results indicate that cold exposure has the capacity to irreversibly damage the reproductive system and that insect survival depends on the duration of the recovery period. Both the survival ability and subsequent reproductive output have to be examined to objectively determine insect cold resistance.

Cold exposure and adipose nitric oxide and mast cells: influence on aorta contractility

Both nitric oxide (NO) and mast cells play important roles in adipose and vascular tissue biology. Chronic cold stress decreases the sensitivity of vascular smooth muscle to various contractile agents including norepinephrine (NE). In our previous cold exposure study we found that the contractile response of isolated rat aortas to NE was significantly reduced, and the number of rat aortic adventitial mast cells decreased. Histologically and functionally, white and brown adipose tissue (WAT and BAT) can be distinguished. Beyond its significance in energy store/release and heat production, adipose tissue secretes multiple signaling molecules that have endocrine and paracrine role in the regulation of vascular functions. The aims of the present study were to examine chronic cold exposure-induced alterations in (i) the concentration of NO released from selected regions of WAT and BAT in female and male rats, (ii) the histochemistry of white and brown adipose mast cells, and (iii) whether adipose-derived NO affects the contraction of isolated rat aorta to NE. Twelve females and 12 males Spraque-Dawley rats (150-200 g body weight) were used. The rats were exposed to a cold/freely moving stress for 2 hours each day for 5 consecutive days. At the end of cold exposure, the rats were sacrificed, and samples of thoracic aorta with associated periadventitial adipose tissue (tunica adiposa) were obtained. WAT and BAT were isolated from subcutaneous abdominal and interscapular areas, respectively. The concentration of NO was measured by capillary electrophoresis and mast cells were evaluated histochemically. The response of aorta smooth muscles to NE was recorded in the isolated organ bath. To determine whether adipose-derived NO affects aorta contraction to NE, cumulative dose response curves to NE (10 -8 -10 -3 M) were obtained with or without isolated WAT/BAT suspended in the organ bath medium. In control animals, a gender-related significant difference in NO production in both WAT and BAT was found, NO levels being significantly higher in female than male rats. Data from the contractile response of isolated aorta to NE suggest that receptor affinity to NE is significantly different between female and male controls. Presence of BAT and WAT (isolated from cold-exposure animals) in the bath changed the response of aorta smooth muscle to NE. Displaying a gender dimorphism, BAT/WAT-derived NO, or other vasorelaxing factors, seem to reduce receptor density and/or affinity to NE. Adipose mast cell histochemistry also showed diversity in respect to subtype, gender, and cold exposure. Altogether, we found (i) a gender difference in adipose-released NO and in adipose mast cell histochemistry to cold exposure, and (ii) peripheral adipose tissues affect aortic contractile responses to NE likely by a NO-mediated pathway during cold exposure, suggesting that adipose tissue may limit cold-induced excessive vasoconstriction. Our ongoing study aims at the evaluation of whether aortic tunica adiposa itself could also contribute to this phenomenon. Adipobiology 2009; 1: 67-75.

Effect of Cold Exposure and Photoperiod on Diapause Termination of the Predatory MiteEuseius finlandicus(Acari: Phytoseiidae)

The effect of cold storage and photoperiod on diapause termination of the predatory mite Euseius finlandicus was studied under laboratory conditions. Females in diapause that developed under a short-day photoperiod of L:D 8:16 h and 20°C were exposed for 1–13 wk to 5°C and subsequently maintained under L:D 8:16 h and 20°C, after which the percentage of females terminating diapause was recorded. After 1–4 wk at 5°C, the number of days required for diapause termination in 50% of females (TA50) was similar to that of the control mites maintained continuously at L:D 8:16 h and 20°C. This indicates that cold is not a prerequisite for the completion of diapause development. Furthermore, when mites were maintained for longer periods (7, 10, or 13 wk) at 5°C, TA50 was significantly longer than in the control mites. This may indicate an adverse effect of cold storage on the completion of diapause development or on postdiapause development. However, the longer exposures to cold resulted in synchronous diapause termination. When diapause females were maintained under a series of different photoperiods and 20°C without previous cold exposure, diapause was terminated rapidly under the photoperiods of L:D 16:8, 14:10, and 13:11 h. In contrast, under the shorter-day photoperiods of LD 8:16, 10:14, and 12:12 h, diapause was maintained and eventually ended spontaneously after a long period of time. These results may be useful for the long-term storage of this predatory mite, which could be required for use in biological control programs.

Effect of Cold Exposure and Photoperiod on Diapause Termination of the Predatory Mite &lt;I&gt;Euseius finlandicus&lt;/I&gt; (Acari: Phytoseiidae)

The effect of cold storage and photoperiod on diapause termination of the predatory mite Euseius finlandicus was studied under laboratory conditions. Females in diapause that developed under a short-day photoperiod of L:D 8:16 h and 20°C were exposed for 1–13 wk to 5°C and subsequently maintained under L:D 8:16 h and 20°C, after which the percentage of females terminating diapause was recorded. After 1–4 wk at 5°C, the number of days required for diapause termination in 50% of females (TA50) was similar to that of the control mites maintained continuously at L:D 8:16 h and 20°C. This indicates that cold is not a prerequisite for the completion of diapause development. Furthermore, when mites were maintained for longer periods (7, 10, or 13 wk) at 5°C, TA50 was significantly longer than in the control mites. This may indicate an adverse effect of cold storage on the completion of diapause development or on postdiapause development. However, the longer exposures to cold resulted in synchronous diapause termination. When diapause females were maintained under a series of different photoperiods and 20°C without previous cold exposure, diapause was terminated rapidly under the photoperiods of L:D 16:8, 14:10, and 13:11 h. In contrast, under the shorter-day photoperiods of LD 8:16, 10:14, and 12:12 h, diapause was maintained and eventually ended spontaneously after a long period of time. These results may be useful for the long-term storage of this predatory mite, which could be required for use in biological control programs.

Short-term cold-exposure does not improve insulin sensitivity in rats.

Effects of noradrenergic activation induced by short-term cold-exposure (7 days at 4 degrees C) on whole-body glucose utilization and tissue glucose uptake were investigated in rats. Measurements were realized on anesthetized normothermic animals at four different levels of insulinemia, within physiological range, allowing calculation of insulin sensitivity and responsiveness. Whole-body glucose utilization increased as a logarithmic function of insulinemias, and was always higher in cold-exposed than in control rats. However, neither insulin sensitivity nor responsiveness, literally, appeared different between the two groups. In the diaphragm, the only studied working muscle, glucose uptake was largely higher than in restin muscles. At basal insulin concentration, glucose uptake was higher in cold-exposed than in control rats and increased in the two groups with insulinemia. Among resting muscles, glucose uptake was increased by previous cold exposure in gastrocnemius, soleus, and tibialis. However, insulin sensitivity and responsiveness were found augmented only in the two former. In interscapular brown adipose tissue, glucose uptake was largely higher in cold-exposed than in control rats, but no difference could be evidenced in insulin sensitivity or responsiveness. In white adipose tissues, glucose uptake increased with insulinemia. Insulin responsiveness and sensitivity were higher only in the retroperitoneal depot.

Alteration of nyctohemeral changes in body core temperature by repeated cold exposure given at a fixed time daily in rats [corrected

The effects of cold exposure for several hours at a fixed time once a day on nyctohemeral variations of hypothalamic temperature (Thy), heat balance, and feeding and locomotor activities were examined in rats. The cold-exposed group was subjected to an ambient temperature of 3 degrees C for about 5 h in the last half of the dark phase daily for 10 or more than 21 consecutive days, while the control rats were kept constant at 24 degrees C. The 10-d cold exposure had little effect on nyctohemeral changes in Thy and locomotor activity. However, after completing a 3- to 4-week cold exposure schedule, the levels of Thy, heat loss, heat production, and feeding and locomotor activities of the cold-exposed rats significantly decreased for 1-2 h during the period of the previous cold exposure time. These decreases lasted for at least 2 d after the end of the cold exposure schedule. These results suggest that the patterns of nyctohemeral changes in body core temperature and feeding and locomotor activities were altered after repeated cold exposure at a fixed time once a day in rats.

Respiratory responses in heat-exposed rabbits: inhibition of tachypnoea offset by increase in tidal volume.

Rabbits in which thermal panting has been inhibiting by previous cold exposure or by water deprivation respond to a raised ambient temperature with an increase in tidal volume. By so doing, they are able to maintain a minute volume appropriate to their thermoregulatory requirements.

Effects of cold on nest-building by wild and domestic mice, Mus musculus L.

Nest-building by male and virgin female wild and laboratory mice kept at a temperature of 2o C was compared with that of controls kept at 23o C. The amount of cotton wool pulled into the cage was recorded over 24 hours. Nest quality was also assessed. The tests of nest-building were conducted in both cold and warm environments. Cotton pulling was usually at a lower rate in the cold environment, but there was no corresponding decrement in final nest quality. Previous experience in the cold, compared with absence of such experience, resulted in higher scores by wild mice tested in either environment, and by laboratory mice tested in the cold environment. Wild mice that built high quality nests used less cotton wool in the cold than in the warm environment. The tendency for wild mice to pull more cotton wool and build better nests than laboratory mice was more pronounced among cold-treated animals. Differences in body weight did not account for the differences between wild and laboratory mice. In further experiments nest-building was observed over 16 days. In the cold environment there was an initial depression of nest-building by both wild and laboratory mice, followed by a steady improvement over 6 days. Both males and virgin females sometimes made well constructed nests even in the warm environment. In the cold environment the effect of previous cold-exposure on wild mice was the rapid construction of a good nest.

Inhibition of thermal tachypnoea in rabbits following exposure to cold and water deprivation.

1. Rabbits were clipped and exposed in turn to four environmental conditions: control (C), cold exposure (CE), water deprivation (WD) and water deprivation and cold exposure together (WD/CE). 2. Following each type of treatment, the rabbits were exposed for 1 hr to an ambient temperature (Ta) of 35 degrees C. During this time, respiratory frequency (RF), rectal temperature (Tre), activity and oxygen consumption (V02) were recorded. 3. It was found that under both cold exposure and water deprivation conditions, the mean respiratory frequency during the first 30 min of heat exposure was reduced when compared with controls. This was associated with a delay in the onset of thermal tachypnoea. Under conditions of water deprivation and cold exposure together, the mean respiratory frequency was further reduced and the length of the delay was increased. 4. Previous cold exposure led to an increase in the V02 measured at 35 degrees C, whereas the V02, after water deprivation and water deprivation and cold exposure together were not significantly different from the control. 5. Neither the initial Tre nor the change in the Tre during the course of the heat exposure were significantly different from the controls under any of the experimental conditions. 6. It is concluded that both water deprivation and previous cold exposure cause a block to panting in the heat and that the blocking mechanisms involved are closely interrelated. It is also concluded that neither the metabolic rate of the animal nor its initial or final Tre are important factors in determing the degree to which thermal tachypnoea is inhibited.

Effects of cold exposure on urinary and adrenal catecholamines in a hibernator, the golden hamster

1. 1. After 24 hr exposure of the golden hamster ( Mesocricetus auratus) to 3°C, the urinary excretion of norepinephrine (NE) increased significantly by fourfold and reached a peak in 48 hr. Epinephrine (E) excretion did not show a statistically significant increase after 24 hr. Adrenal catecholamime content did not change after 24 hr of cold exposure. 2. 2. During 21 days of cold exposure, urinary NE remained significantly higher than control levels. When hamsters previously exposed to 3°C for 3 weeks were removed to 22°C for 1 day and then re-exposed to 3°C, the urinary NE increased, but was lower than any of the levels found during previous cold exposure. 3. 3. Urinary E increased (not statistically significant) during the first week of cold exposure and returned to control levels thereafter. 4. 4. The results suggest that the thermogenic response of the hamster (a hibernator) to 3°C involves a greater sensitivity of thermogenic tissues to NE and a lower requirement for E secretion than in the rat (a non-hibernator).

Adaptive changes in rats exposed to cold; caloric exchange.

Adaptive changes in rats exposed to cold; caloric exchange.