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PubMed1987

Hibernation in garter snakes (Thamnophis sirtalis parietalis): seasonal cycles of cold tolerance.

1. The red-sided garter snake hibernates for about six months each year in Manitoba, Canada, where winter temperatures are often as low as -40 degrees C. Mammalian hibernators typically undergo profound changes in preparation for hibernation, but little is known about corresponding changes in reptiles. 2. We tested the importance of seasonal changes in the ability of red-sided garter snakes to hibernate successfully by exposing them to winter conditions at different times of year. 3. Animals that began hibernation in the fall were more likely to survive hibernation than animals that began hibernation in either early or late summer, despite the fact that the animals were kept on seasonally constant conditions prior to hibernation. 4. We suggest that these changes are derived from endogenous components of the yearly hibernation cycle of red-sided garter snakes but that only part of the cycle proceeds endogenously, i.e. it is not a completely endogenous circannual cycle.

Acclimatization↗
PubMed1985

Diurnal changes in sensitivity to melatonin in intact and pinealectomized Djungarian hamsters: effects on thermogenesis, cold tolerance, and gonads.

Djungarian hamsters kept in long photoperiod (16:8 L:D) were injected daily at 0800, 1200, or 1600 with 25 micrograms of melatonin. During 90 days of treatment, body weight and fur coloration were checked at weekly intervals, and at the end of the treatment the reproductive status of the hamsters and their thermoregulatory properties (could limit, maximum thermoregulatory heat production, nonshivering thermogenesis, cytochrome oxidase activity in brown adipose tissue) were measured. Hamsters injected at 1600 changed from summer to winter status with regard to all functions investigated responding simultaneously; i.e., their body weights decreased, their fur became white, their gonads regressed, and their thermoregulatory properties improved. All these changes were identical to the effects of short photoperiod (8:16 L:D) exposure. Injections of melatonin at 0800 and 1200 were ineffective for reproductive functions, but the injection of melatonin at 0800 caused slight improvements of thermogenesis. The response to melatonin injected at 1600 could be suppressed by an additional injection of melatonin at 0800 (75 micrograms). Pinealectomized or ganglionectomized hamsters kept in long photoperiod did not respond to daily injections of melatonin at 1600 for the first 60 days of treatment, but during a prolonged treatment their sensitivity to melatonin was restored. Similarly, pinealectomized or ganglionectomized hamsters failed to respond to short photoperiod for about 40 days, but during prolonged exposure their sensitivity to short photoperiod was restored.

Animals↗
PubMed2006

The role of abscisic acid and low temperature in chickpea (Cicer arietinum) cold tolerance. II. Effects on plasma membrane structure and function.

The frost hardiness of many plants such as chickpea can be increased by exposure to low non-freezing temperatures and/or the application of abscisic acid (ABA), a process known as frost acclimation. Experiments were conducted to study the response over a 14 d period of enriched plasma membrane fractions isolated from chickpea plants exposed to low temperature and sprayed with exogenous ABA. Measurement of the temperatures inducing 50% foliar cell death (LT50), and subsequent statistical analysis suggest that, like many plants, exposure to low temperatures (5/-2 degrees C; day/night) induces a significant level (P <0.05) of frost acclimation in chickpea when compared with control plants (20/7 degrees C; day/night). Spraying plants with exogenous ABA also increased frost tolerance (P <0.05), but was not as effective as low temperature-induced frost acclimation. Both pre-exposure to low temperatures and pre-treatment with ABA increased the levels of fatty acid desaturation in the plasma membrane (measured as the double bond index, DBI). Exposure of chickpea plants to low temperatures increased the DBI by 15% at day 4 and 19% at day 14 when compared with untreated control plants. Application of ABA alone did not increase the DBI by more than 6% at any time; the effects of both treatments applied together was more than additive, inducing a DBI increase of 27% at day 14 when compared with controls. There was a good correlation (P <0.05) between the DBI and LT50, suggesting that the presence of more unsaturated lipid in the plasma membrane may prevent cell lysis at low temperatures. Both pre-exposure to low, non-freezing temperatures and pre-treatment with ABA induced measurable changes in membrane fluidity, but these changes did not correlate with changes in LT50, suggesting that physical properties of the plasma membrane other than fluidity are involved in frost acclimation in chickpea.

Abscisic Acid↗
PubMed2002

Identification of quantitative trait loci for cold-tolerance of photosynthesis in maize (Zea mays L.).

The effects of low growth temperature (15 degrees C) on the photosynthetic apparatus of maize were investigated in a set of 233 recombinant inbred lines by means of chlorophyll fluorescence, gas exchange measurements and analysis of photosynthetic pigments. A quantitative trait loci (QTL) analysis of five traits related to the functioning of the photosynthetic apparatus revealed a total of eight genomic regions that were significantly involved in the expression of the target traits. Four of these QTLs, located on chromosomes 1 (around 146 cM), 2 (around 138 cM), 3 (around 70 cM), and 9 (around 62 cM), were identified across several traits and the phenotypic correlation observed among those traits confirmed at the genetic level. The two QTLs on chromosomes 1 and 9 were also expressed in leaves developed at near-optimal temperature (25 degrees C) whilst the two QTLs on chromosomes 2 and 3 were specific to leaves developed at sub-optimal temperature. A QTL analysis conducted on traits related to the pigment composition of the leaves developed at 15 degrees C detected the QTL on chromosome 3 around 70 cM in 7 of the 11 traits analysed. This QTL accounted for up to 28% of the phenotypic variance of the quantum yield of electron transport at PSII in the fourth leaf after about 3 weeks at a sub-optimal temperature. The results presented here suggest that key gene(s) involved in the development of functional chloroplasts of maize at low temperature should be located on chromosome 3, close to the centromere.

Adaptation, Physiological↗
PubMed2005

Vitrification assays with embryos from a cold tolerant sub-arctic fish species.

Pseudopleuronectes americanus is a Northern teleost species that produces antifreeze proteins (AFPs) to protect them from freezing during the winter. These AFPs bind to ice crystals to inhibit their growth, and they also protect cell membranes at low temperatures. In this study, vitrification trials were done with fish embryos at three different developmental stages, using two different protocols for incorporating the vitrifying solutions. Toxicity of the cryoprotectants and permeability to dimethyl sulfoxide were analyzed. Embryos were vitrified in 0.5 ml straws by direct immersion in liquid nitrogen, and their morphology and development analyzed following thaw. The embryos responded well to vitrification as evidenced by the high percentage that exhibited good morphology following thaw. Although none of the embryos hatched, a small percentage (0.92%) of them showed active movements within the chorion and continued to develop for a number of days following thaw. This is the first record of post-thaw development of vitrified fish embryos.

Animals↗
PubMed2001

Effects of summer frost exposures on the cold tolerance strategy of a sub-Antarctic beetle.

The sub-Antarctic beetle Hydromedion sparsutum (Coleoptera, Perimylopidae) is common locally on the island of South Georgia where sub-zero temperatures can be experienced in any month of the year. Larvae were known to be weakly freeze tolerant in summer with a mean supercooling point (SCP) around -4 degrees C and a lower lethal temperature of -10 degrees C (15min exposure). This study investigated the effects of successive freezing exposures on the SCP and subsequent survival of summer acclimatised larvae. The mean SCP of field fresh larvae was -4.2+/-0.2 degrees C with a range from -1.0 to -6.1 degrees C. When larvae were cooled to -6.5 degrees C on 10 occasions at intervals of 30min and one and four days, survival was 44, 70 and 68%, respectively. The 'end of experiment' SCP of larvae surviving 10 exposures at -6.5 degrees C showed distinct changes and patterns from the original field population depending on the interval between exposure. In the 30min interval group, most larvae froze between -6 and -8 degrees C, a depression of up to 6 degrees C from the original sample; all larvae were dead when cooling was continued below the SCP to -12 degrees C. In the one and four day interval groups, most larvae froze above -6 degrees C, showing no change as a result of the 10 exposures at -6.5 degrees C. As with the 30min interval group, some larvae froze below -6 degrees C, but with a wider range, and again, all were dead when cooled to -12 degrees C. However, in the one and four day interval groups, some larvae remained unfrozen when cooled to -12 degrees C, a depression of their individual SCP of at least 6 degrees C, and were alive 24h after cooling. In a further experiment, larvae were cooled to their individual SCP temperature at daily intervals on 10 occasions to ensure that every larva froze every day. Most larvae which showed a depression of their SCP of 2-4 degrees C from their day one value became moribund or died after six or seven freezing events. Survival was highest in larvae with SCPs of -2 to -3 degrees C on day one and which froze at this level on all 10 occasions. The results indicate that in larvae in which the SCP is lowered following sub-zero exposure, the depression of the SCP is greatest in individuals that do not actually freeze. Further, the data suggest that after successive frost exposures in early winter the larval population may become segregated into two sub-populations with different overwintering strategies. One group consists of larvae that freeze consistently in the temperature range from -1 to -3 degrees C and can survive multiple freeze-thaw cycles. A second group with lower initial SCPs (around -6 degrees C), or which fall to this level or lower (down to -12 degrees C) after freezing on one or more occasions, are less likely to freeze through extended supercooling, but more likely to die if freezing occurs.

Journal Article↗
PubMed1977

C(4) Pathway Photosynthesis at Low Temperature in Cold-tolerant Atriplex Species.

Two species of Atriplex were grown under low temperature (8 C day/6 C night) and high temperature (28 C day/20 C night) regimes. The photosynthetic capacity of these plants was studied as a function of temperature in a leaf gas exchange cuvette. Both species showed substantial photosynthetic capacity between 4 and 10 C and this was not enhanced by growth at low temperatures but rather, was somewhat greater in plants grown at higher temperature. Photosynthetic capacity of low temperature-grown plants at high temperature was greater in Atriplex confertifolia (Torr. and Frem.) S. Watts., a native of cool deserts, than in Atriplex vesicaria (Hew. ex. Benth.) from warmer desert areas. Leaves of both species were also subjected to (14)CO(2) pulse-chase and steady-state feeding experiments under controlled temperature conditions. These experiments revealed that the kinetics of carbon assimilation through the intermediates of the C(4) pathway is not substantially disrupted at low temperature in either species. There was, however, a substantial interchange of label between aspartate and malate at low temperature which was not evident at high temperature. There was also an increase in the pool sizes of the C(4) acids involved in photosynthesis of A. confertifolia. Speculation as to the explanation of these changes and their possible significance in promoting low temperature C(4) photosynthesis in these plants is presented.

Journal Article↗
PubMed2003

Freezing survival and cryoprotective dehydration as cold tolerance mechanisms in the Antarctic nematode Panagrolaimus davidi.

The relative importance of freezing tolerance and cryoprotective dehydration in the Antarctic nematode Panagrolaimus davidi has been investigated. If nucleation of the medium is initiated at a high subzero temperature (-1 degree C), the nematodes do not freeze but dehydrate. This effect occurs in deionised water, indicating that the loss of water is driven by the difference in vapour pressure of ice and supercooled water at the same temperature. If the nematodes are held above their nucleation temperature for a sufficient time, or are cooled slowly, enough water is lost to prevent freezing (cryoprotective dehydration). However, if the medium is nucleated at lower temperatures or if the sample is cooled at a faster cooling rate, the nematodes freeze and can survive intracellular ice formation. P. davidi thus has a variety of mechanisms that ensure its survival in its harsh terrestrial Antarctic habitat.

Acclimatization↗
PubMedDate not supplied

Interactions between environmental pollution and cold tolerance of soil invertebrates: a neglected field of research.

The adaptations to climatic stress of invertebrates have been extensively studied and the underlying physiology is relatively well understood. It is therefore possible to predict critical lower temperature and moisture limits at which a species will suffer increased mortality. Environmental pollution can reduce the tolerance to climatic stress considerably but it is not known how significant these synergistic effects are in polluted areas. Results are presented showing examples of synergism between toxic and climatic stress. The physiological mechanisms involved in the synergistic effects are discussed.

Journal Article↗
PubMed1985

Increased tolerance to cold induced by hyperoxia in hypothermic dogs.

In dogs acutely immersed in cold water (8-13 degrees C) oxygen uptake increased and rapidly reached a maximum value (CV02 Max). A few minutes after the start of immersion colonic temperature began to fall more or less rapidly depending on the dog but always in a linear fashion. Twenty min. after the start of immersion the inspired air was switched from air to a 60% O2/40% N2 gas mixture. The switch to the hyperoxia gas mixture slowed down or even stopped the fall in colonic temperature. Concomitantly a lowering of plasma lactate concentration was observed. It may be concluded that hyperoxia improves the cold tolerance of dogs exposed to a severe cold stress. This improvement may be due to a direct effect of hyperoxia on cellular metabolism. However other effects induced by hyperoxia cannot be ruled out.

Animals↗
PubMed1985

A longitudinal study of tolerance to cold stress among C57BL/6J mice.

C57BL/6J male mice of different ages were movement-restricted and exposed to 10 degrees C for 3-hr periods every other week while colonic temperature was measured. A longitudinal trend in cold tolerance related to age and to initial colonic temperature was demonstrated. Adaptative thermoregulatory changes during cold exposure occurred during the first two tests. These were similar for all age groups except 30-month-old mice. There was no adaptation of colonic temperature during cold exposure among aged mice with repeated testing; however, their baseline colonic temperatures prior to testing increased after the first two tests. This finding suggests that old animals adjust to repeated cold stress differently than do younger mice. Specifically, younger animals are capable of adjusting their thermoregulatory response during cold stress with no change in baseline (pre-stress) temperature. Old animals do not modify the responses emitted during the stress; however, they do adapt by raising their baseline temperatures. Repeated cold exposure started later in life increased mortality among old animals but did not affect maximum lifespan.

Adaptation, Physiological↗
PubMed2004

Cold and heat tolerance of drosophilid flies with reference to their latitudinal distributions.

The relation between thermal tolerance and latitudinal distribution was studied with 30 drosophilid species collected from the cool-temperate region (Sapporo), the warm-temperate region (Tokyo and Kyoto) and the subtropical region (Iriomote island) in Japan. In addition, intraspecific variation was examined for five species collected from two localities. The subtropical strains of Scaptodrosophila coracina, Drosophila bizonata and D. daruma were less tolerant to cold than their temperate strains. However, the difference of cold tolerance between these two geographic strains was much smaller than the difference between the species restricted to the subtropical region and those occurring in the temperate region. In D. auraria and D. suzukii, no difference was observed in thermal tolerance between their cool- and warm-temperate strains. Thus, geographic variation in thermal tolerance within species was low or negligible. Interspecific comparisons by phylogenetic independent contrasts revealed that species which had the northern boundaries of their distributions at higher latitudes were generally more tolerant to cold than those which had their boundaries at lower latitudes. However, the data for some species did not agree with this trend. The use of man-protected warm places for overwintering, competition or predation would also affect their distributions. It also appeared that species which had their southern boundaries at higher latitudes were generally more cold-tolerant. The acquisition of cold tolerance may lower a fly's capacity to compete, survive or reproduce in warmer climates. On the other hand, no relation was observed between heat tolerance and latitudinal distribution. Heat tolerance was higher in species inhabiting openlands or the forest canopy than in those inhabiting the forest understorey.

Adaptation, Physiological↗
PubMed1998

Heat- and cold-shock responses and temperature adaptations in subtropical and temperate species of Drosophila.

Accumulation of Hsp70 mRNA was investigated with relation to heat and cold tolerance in adult males of three Drosophila species. The subtropical lowland species (D. watanabei) and the cool-temperate species (D. triauraria) were more tolerant to heat than the subtropical highland species (D. trapezifrons), and the cool-temperate species were much more tolerant to cold than the two subtropical species. Thus, heat and cold tolerance was related to temperature conditions in the habitats. The threshold temperatures for the induction of Hsp70 mRNA at heat and cold were higher in D. watanabei than in D. trapezifrons or D. triauraria, but were not different between the latter two species in spite of the difference in their heat and cold tolerance. In D. trapezifrons, exposures to 0 degrees C for 12h and 6 degrees C for 24h killed about 40% of individuals, but the former treatment induced Hsp70 mRNA while the latter one did not. Thus, the relation between the heat- and cold-shock responses and temperature tolerance was not rigid in the species studied. In D. triauraria, the threshold temperatures for the induction of Hsp70 mRNA at heat and cold were lower when reared at a lower temperature.

Journal Article↗
PubMed1994

Mechanisms of cold intolerance in patients with angina.

OBJECTIVES: Patients with angina often report that symptoms are worse in cold weather. This study was designed to determine differences between cold-tolerant and cold-intolerant patients in the hemodynamic and ischemic response to exercise at cold temperatures and to assess the role of catecholamines and baroreceptor function. BACKGROUND: Studies have suggested that the heart rate response may differ at cold temperatures, but the mechanism and role of this variation have not been examined. METHODS: Seven cold-intolerant and seven cold-tolerant patients with angina underwent exercise treadmill testing at 6 and 25 degrees C with measurement of catecholamines. Baroreceptor function was assessed by the decrease in systolic blood pressure after patients stood up from the supine position. RESULTS: Norepinephrine levels increased by 139% in the cold environment, but there were no differences between cold-intolerant and cold-tolerant patients. Consequently, blood pressure was higher in the cold environment in all patients, but the heart rate response was similar. However, cold-intolerant patients had a steeper heart rate response in the cold and developed ischemia (mean [+/- SEM] 201 +/- 58 vs. 242 +/- 50 s, p = 0.05) and angina (348 +/- 87 vs. 449 +/- 60 s, p = 0.04) earlier in the cold environment, a difference not seen in the cold-tolerant patients. Baroreceptor function was impaired in cold-intolerant patients (decrease in systolic blood pressure after patients stood up from the supine position 19 +/- 7 vs. 0 +/- 4 mm Hg, p = 0.04). CONCLUSIONS: Exposure to cold causes an increase in blood pressure with an associated increase in myocardial oxygen demand in all patients. In cold-tolerant patients, this increase may be offset by a reduction in heart rate if baroreceptor function is normal. If baroreceptor function is abnormal, heart rate may not decrease in response to a cold-induced increase in blood pressure. This mechanism may account for some of the variability in tolerance to cold exposure that affects patients with exertional angina.

Angina Pectoris↗
PubMed1982

Hypothalamic catecholamines and tolerance for severe cold in ethanol-treated guinea-pigs.

1 The effect of ethanol (2g/kg) on hypothalamic catecholamines in guinea-pigs kept at room temperature (20 degrees C) and in severe cold (-20 degrees C) for 1.5 h was determined. Serum glucose, triacyl-glycerols and free fatty acids (FFAs), glycogen in liver and skeletal muscle and total lipid and triacyglycerols in the interscapular adipose tissue were also determined. 2 Ethanol increase the noradrenaline and adrenaline content of the hypothalamus at 20 degrees C and reduced ther rectal temperature by about 2 degrees C. The hypothalamic noradrenaline content of the ethanol-treated guinea-pigs exposed to cold, in which the fall in rectal temperature was about 8 degrees C, was higher than in the controls, whose rectal temperature decreased only by about 2 degrees C. 3 Cold exposure increased FFA concentration in serum and reduced skeletal muscle glycogen and serum glucose concentrations in both groups, but no significant differences were found in the carbohydrate and lipid values between the groups at -20 degrees C. 4 It is possible that the diminished cold tolerance in the ethanol-treated guinea-pigs might be due, at least in part, to the effect of ethanol on the catecholamines in the hypothalamus.

Adaptation, Physiological↗