Long-term cold adaptation in the rat

1. To determine whether long-term cold exposure induces insulative adaptation in the rat, two groups of eight adult animals each were exposed to 4 and 25 degrees C, respectively, for 18 months. 2. At any ambient temperature between -5 and 30 degrees C, the cold adapted animals had a higher rate of oxygen uptake, and higher unfurred skin temperatures than the controls. 3. At ambient temperatures below thermoneutrality, whole body thermal resistance increased continuously in both groups of animals. 4. It is concluded that long-term exposure does not induce insulative adaptation, and that thermal resistance is not maximal at the lower critical temperature.     

Participation of the prostacyclin-thromboxane system in the mechanisms of prevention of arrhythmia caused by occlusion of the coronary artery in adapted rats]

It was found, that adaptation of rats to cold and physical exercise prevented ventricular fibrillation, caused by the occlusion of the left anterior coronary artery. An adaptation to cold only or to physical exercise do not prevent ventricular arrhythmias. An significant increase of prostacyclin/thromboxane index in plasma and heats was estimated in rats adapted to cold and physical exercise in relation to control non-adapted group in condition of functional rest or acute myocardial ischemia. It was assumed that an increase of prostacyclin/thromboxane ratio has a significant role in antiarrhythmic action of adaptation.     

Impaired adaptation to repeated restraint and decreased response to cold in urocortin 1 knockout mice

Urocortin 1 (UCN1) is a corticotropin-releasing factor (CRF)-like peptide whose role in stress is not well characterized. To study the physiological role of UCN1 in the response of the hypothalamic-pituitary-adrenal (HPA) axis to stress, we generated UCN1-knockout (KO) mice and examined their adaptation to repeated restraint and to cold environment. Wild-type (WT) and UCN1-KO animals were restrained hourly for 15 min from 9 AM to 2 PM, and blood samples were obtained for corticosterone measurement. WT animals adapted to repeated restraint with a decreased corticosterone response; the restraint-stimulated corticosterone levels fell from 215 +/- 31 ng/ml in na?ve animals to 142 +/- 50 ng/ml in mice subjected to repeated restraint (P < 0.01) and from 552 +/- 98 to 314 +/- 58 ng/ml (P < 0.001) in males and females, respectively. Male UCN1-KO mice did not show any adaptation to repeated restraint; instead, restraint-stimulated corticosterone levels were increased from 274 +/- 80 ng/ml in na?ve animals to 480 +/- 75 ng/ml in mice subjected to repeated restraint (P < 0.001). Female UCN1-KO mice showed only a partial adaptation to repeated restraint, with a decrease in the restraint-stimulated corticosterone response from 631 +/- 102 ng/ml in na?ve animals to 467 +/- 78 ng/ml in mice subjected to repeated restraint (P < 0.01). In addition, UCN1-KO mice showed no corticosterone response to 2-h cold environment. These data demonstrate an important role for UCN1 in the HPA axis adaptation to repeated restraint and in the corticosterone response to a cold environment.     

Adaptive changes in temperature sensitivity in humans under the conditions of cold, heat, and prolonged exercise

In humans adapted for a long time to various conditions—cold, heat, and physical exercise—differently directed changes in temperature sensitivity are observed. During long-term adaptation of humans to cold, a decrease in cold sensitivity is observed. Vice versa, in humans adapted to a hot climate, sensitivity to heat is decreased. Prolonged physical exercise does not change the sensitivity to heat but considerably increases the sensitivity to cold. Some mechanisms and the role of noradrenaline, the postganglionic neurotransmitter of the sympathetic nervous system, in the adaptive processes of a change in temperature sensitivity are considered.     

Changes in physiological and neuroendocrine properties during thermal adaptation of golden hamsters (Mesocricetus auratus)

Summary Golden hamsters raised at 22°C were adapted in the early summer for 3 weeks to either 28°C or 5°C. To achieve profound changes the photoperiod was also shortened from 14 h to 11 h during adaptation to cold. During the investigation body weight, food consumption, water intake, urine production, and osmolality, as well as secreted amounts of noradrenaline (NA) and dopamine (DA), were recorded in each animal before, during, and after the adaptation period. In another group of golden hamsters the brains were processed for immunocytochemical detection of arginine-vasopressin (AVP) and corticotropin releasing factor (CRF) in the third week of adaptation to a cold or warm environment. In warm-adapted animals food and water consumption and urine production remained unchanged or were only slightly reduced. NA and DA secretion were reduced by 50%. The AVP-immunoreactivity reflected an antidiuretic state in these animals. In fibers influencing the adrenal axis, AVP-immunoreactivity was weak compared to CRF fibers. Food and water consumption, urine production, and DA secretion increased two-fold during cold adaptation. Daily secreted amounts of NA increased nine-fold. AVP-immunoreactivity was weak in projections to the neurohypophysis. Fibers influencing the adrenal axis, however, displayed strong AVP-immunoreactivity in comparison to that of CRF. The immunocytochemically determined patterns of AVP and CRF distribution indicated an activation of the osmoregulative axis in the warm-adapted animals and of the adrenal axis in the cold-adapted golden hamsters.Abbreviations NA noradrenaline - DA dopamine - AVP argininevasopressin - CRF corticotropin releasing factor - SON supraoptic nucleus     

Temperature adaptation influences the aggregation state of hemocyanin from Astacus leptodactylus

When Astacus leptodactylus were kept at various temperatures for several weeks, different ratios between di-hexameric and hexameric hemocyanins were observed in their hemolymph. The higher the temperature the more hexamers were present. This long-term adaptation to different temperatures or/and to temperature-induced pH-shifts as observed in the hemolymph has different effects on the expression of subunit types building up hexamers and those which covalently link two hexamers within the di-hexamers. The oxygen binding behaviour of di-hexameric hemocyanins from cold and warm adapted animals do not show differences with respect to affinity, Bohr effect and cooperativity.     

Influence of increased catecholamine levels in blood plasma during cold-adaptation and intramuscular infusion on thresholds of thermoregulatory reactions in guinea-pigs

Summary Catecholamines and some of their metabolites were determined in urine and blood plasma of guinea-pigs before, during and after acclimation to a cold or warm environment. During adaptation to 5°C the amounts of noradrenaline in plasma and 24-h urine samples continuously increased up to 600% compared with values obtained at an ambient temperature of 22°C. Higher levels of dihydroxyphenylglycol and 3-methoxy-4-hydroxyphenylglycol further indicated an increased turnover of noradrenaline during cold adaptation. Acclimation to an ambient temperature of 28°C reduced the peripheral release of noradrenaline in comparison to the release observed at 22°C. Cold-induced increases in metabolic rate and electrical muscle activity both occur at a considerably lower mean body temperature in cold-than in warm-adapted guinea-pigs. The shift of thermoregulatory cold defence reactions to a lower mean body temperature could also be observed in warm-adapted animals after intramuscular infusion of noradrenaline in amounts comparable to those released during cold adaptation.It is concluded that high peripheral sympathetic activity directly or indirectly inhibits noradrenergic neurons in the lower brain stem that modulate the thermoregulatory control system by means of their afferents to the hypothalamus. As a consequence of this peripheral influence the thermoregulatory set point is shifted to a lower mean body temperature.Abbreviations A adrenaline - CA cold adapted - CNS central nervous system - DHPG dihydroxyphenylglycol - EMA electrical muscle activity - HPLC high performance liquid chromatography - 5-HT 5-hydroxytryptamine (serotonine) - MHPG 3-methoxy-4-hydroxypheyylglycol - MR metabolic rate - NA noradrenaline - T _b mean body temperature - WA warm adapted     

Indices of hormonal regulation of water-electrolyte metabolism and reception of cyclic AMP in the kidney papilla of rats during cold adaptation

Antidiuretic hormone plasma concentration and urine aldosterone excretion decrease during adaptation to cold in rats. At the same time diuresis and natriuresis considerably increase. Specific 3H-cAMP kidney papilla cytosol binding enhances significantly in cold adapted rats. Alterations in hormonal regulation of fluid-electrolyte metabolism may be regarded as homeostatic response aimed at stabilization of hydration level in conditions of cold hypermetabolism.     

Effect of adaptation to altitude hypoxia in early ontogeny on the indices of higher nervous activity]

Newborn male and female Wistar rats were adapted to hypoxia in a pressure chamber. Adaptation was started from the "altitude" of 1000 m, 1 hour daily, and then the time and the intensity of hypoxic actions were gradually increased: beginning from the 17th day the animals were subjected to adaptation to the "altitude" of 5000 m, for 5 hours, 5 days a week. The defence conditioned reflex of active avoidance was provoked in the animals after 2-month adaptation. A tendency to a more rapid elaboration of the reflex and a markedly enhanced degree of its retention in comparison with control was revealed in the adapted males. No significant changes in the elaboration and rentention of the reflex were found in the female animals adapted to hypoxia under analogous conditions.     

Increased enzymatic activity of antioxidant protection of the heart in the adaptation of rats to short-term stress exposure

It has been shown that adaptation to short-term emotional-painful stresses leads to an increase in antioxidant enzyme activities but does not change vitamin E content in the myocardium. The most labile enzyme was catalase (35% increase). During stress in nonadapted animals the enzyme activity decreased, as compared to the control, while in the group of adapted animals with subsequent stress the activity was even higher than in the control. During initiation of lipid peroxidation in the heart homogenates in vitro there was a 3-fold increase and a 1%-fold decrease in the oxidation intensity in rats exposed to stress and in adapted animals, respectively. The role of adaptation activation of cardiac antioxidant system in the prevention of stress-induced heart damage is discussed.     

Changes in blood glucose, blood and muscle lactate,and plasma lactic dehydrogenase levels in the pigeon on acute exposure to cold.

Adult pigeons were subjected to acute cold exposure (-25 degrees C; 30 min) after which the levels of blood glucose, blood and muscle lactate and plasma lactic dehydrogenase were measured. Partially defeathered (dorsum and pectoral regions) birds, following exposure to cold, showed marked reduction in blood glucose and blood and muscle (pectoralis) lactate. Fully plumed birds, in contrast, showed no significant reduction in body temperature or blood glucose and only moderately reduced lactate levels indicating the effectiveness of the insulative feather coat in maintaining thermal and metabolic homeostasis. The partially-defeathered pigeons exposed to cold showed a two-to-three-fold increase in plasma lactic dehydrogenase activity, which may reflect a molecular adaptation in their calorigenic response to cold.     

The immune system response to antigen in cold- and warm-adapted rats

In rat experiments, it was shown that long-term adaptation to cold modified the response pattern of the immune system to antigen stimulus by variously changing the different components of the response. There was a considerable decrease in the number of antigen-binding cells in spleen and peritoneal exudate and also a marked decrease in general antibodies in blood. Conversely, the number of antibody-forming cells in spleen increased twofold. The shift in the thermal conditions after immunization caused changes in the immune response. After the placement of cold-adapted animals to the warm environments the number of antigen binds and antibody-forming cells in spleen, as well as hemagglutinin titers in serum normalized, became indistinguishable from those in the warm-adapted control group. The placement from warm to cold after immunization of warm-adapted rats also produced considerable shifts in parameters of the immune response. However, these shifts were not entirely consistent with those observed for long-term adapted to cold. The obtained data evidence that the thermal factor of the environment is of major importance to the function of immunocompetent cells.     

Thermosensitivity changes in cold-adapted rats

Cold-adapted rats (unlike non-adapted animals) respond to an acute exposure to external cold by an overshoot increase in metabolic rate and a paradoxical increase in body core temperature. In contrast to external cooling, internal cooling with the aid of a chronically implanted intravenous heat exchanger elicited comparable increase in metabolic rate, coupled with a large fall in core temperature. It is concluded that cold adaptation alters peripheral thermosensitivity (enhances cold sensitivity), while the thermosensitivity of the core is not affected by the adaptation process.     

Absence of rapid sensory adaptation in neocortex during information processing states

One prominent feature of sensory responses in neocortex is that they rapidly adapt to increases in frequency, a process called "sensory adaptation." Here we show that sensory adaptation mainly occurs during quiescent states such as anesthesia, slow-wave sleep, and awake immobility. In contrast, during behavior-ally activated states, sensory responses are already adapted. For instance, during learning of a behavioral task, when an animal is very alert and expectant, sensory adaptation is mostly absent. After learning occurs, and the task becomes routine, the level of alertness lessens and sensory adaptation becomes robust. The primary sensory thalamocortical pathway of alert and expectant animals is in the adapted state, which may be required for adequate sensory information processing.     

Effect of adaptation to cold on the alpha1- and beta-adrenergic reactions of arterial vessels of the small intestine in rabbits

Changes in major paraments of alpha 1- and beta-adrenergic responses (EC50 and Pm) were studied in the intestine arterial blood vessels of rabbits adapted to cold for 1-30 days (daily cold exposures for 6 hours at -10 degrees C). It was shown that responses to phenylephrine, noradrenaline, adrenaline (alpha 1-agonists), isopropylnoradrenaline (beta-agonist) corresponded to the equation p = (Pm.An)/(EC50n + An) with n = 1 and n = 2, respectively. Adaptation to cold induced radically different changes in the major parameters of alpha- and beta-adrenergic responses. In the alpha-adrenergic responses, the parameters EC50 and Pm changed reciprocally. In the beta-adrenergic response, only Pm value changed while EC50 did not differ from the control over the entire period of adaptation to cold. The pronounced differences from the control gradually decreased within 1-30 days of adaptation.     

Thermal, cardiac and adrenergic responses to repeated local cooling

The aim of this study was to ascertain whether repeated local cooling induces the same or different adaptational responses as repeated whole body cooling. Repeated cooling of the legs (immersion into 12 degrees C water up to the knees for 30 min, 20 times during 4 weeks = local cold adaptation - LCA) attenuated the initial increase in heart rate and blood pressure currently observed in control subjects immersed in cold water up to the knees. After LCA the initial skin temperature decrease tended to be lower, indicating reduced vasoconstriction. Heart rate and systolic blood pressure appeared to be generally lower during rest and during the time course of cooling in LCA humans, when compared to controls. All these changes seem to indicate attenuation of the sympathetic tone. In contrast, the sustained skin temperature in different areas of the body (finger, palm, forearm, thigh, chest) appeared to be generally lower in LCA subjects than in controls (except for temperatures on the forehead). Plasma levels of catecholamines (measured 20 and 40 min after the onset of cooling) were also not influenced by local cold adaptation. Locally cold adapted subjects, when exposed to whole body cold water immersion test, showed no change in the threshold temperature for induction of cold thermogenesis. This indicates that the hypothermic type of cold adaptation, typically occurring after systemic cold adaptation, does not appear after local cold adaptation of the intensity used. It is concluded that in humans the cold adaptation due to repeated local cooling of legs induces different physiological changes than systemic cold adaptation.     

Glycerokinase activity in brown and white adipose tissues of cold-adapted obese Zucker rats

Glycerokinase activity was measured in the brown and white adipose tissues compared with that in the liver obese Zucker rats adapted or not adapted to cold. In white adipose tissue total activity was low but higher in the fa/fa rats than in the Fa/ones; cold adaptation did not modify this activity. In brown adipose tissue specific activity was higher than in white; specific activity was twice as high in the fa/fa rats than in the Fa/-. Cold-adaptation induced an increase in the activity in the Fa rats and a decrease in the fa/fa rats. The results are discussed with regard to the cold-induced increase in the energetic efficiency of the tissue.     

水生动物和大鼠线粒体的呼吸链比较

用陆生哺乳动物线粒体呼吸链与水生动物线粒体呼吸链相比较的研究方法,探讨了呼吸链的功能与环境相适应的关系。研究了淡水中生活的草鱼肝丝线粒体,观察到琥珀酸脱氢酶的活性非常低,而ＮＡＤＨ脱氢酶和泛醌细胞色素Ｃ还原酶的活性较高。但海洋生物海绵的线粒体ＮＡＤＨ脱氢酶和琥垢酸脱氢酶的活性都非常低。     

Indirect selection of thermal tolerance during experimental evolution of Drosophila melanogaster

Natural selection alters the distribution of a trait in a population and indirectly alters the distribution of genetically correlated traits. Long‐standing models of thermal adaptation assume that trade‐offs exist between fitness at different temperatures; however, experimental evolution often fails to reveal such trade‐offs. Here, we show that adaptation to benign temperatures in experimental populations of Drosophila melanogaster resulted in correlated responses at the boundaries of the thermal niche. Specifically, adaptation to fluctuating temperatures (16–25°C) decreased tolerance of extreme heat. Surprisingly, flies adapted to a constant temperature of 25°C had greater cold tolerance than did flies adapted to other thermal conditions, including a constant temperature of 16°C. As our populations were never exposed to extreme temperatures during selection, divergence of thermal tolerance likely reflects indirect selection of standing genetic variation via linkage or pleiotropy. We found no relationship between heat and cold tolerances in these populations. Our results show that the thermal niche evolves by direct and indirect selection, in ways that are more complicated than assumed by theoretical models.