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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Experimental alterations of spinal cord and hypothalamic temperature affecting behavioral and autonomic cold defense were investigated in pigeons under external cold load with access to instrumental heat reinforcement. Warming and cooling spinal cord resulted in negative-feedback effects on both instrumental and autonomic cold defense. Hypothalamic warming produced similar negative-feedback effects, whereas hypothalamic cooling produced either no effect or positive-feedback effects on both kinds of cold defense. As determined in previous studies, hypothalamic temperature displacements under heat-load conditions produced only negative-feedback effects on instrumental heat defense. However, only positive-feedback effects were observed on autonomic heat defense by panting. The diverse response patterns of autonomic and behavioral thermoregulatory effectors to changing hypothalamic temperature under heat- and cold-load conditions could be quantitatively described by a mathematical model that takes into account 1) a greater Q10 for intrahypothalamic transmission of the cold signal input than of the warm signal input, and 2) different weights of extra- and intrahypothalamic temperature signal inputs for the control of different effectors.
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PMID:Negative and positive feedback of central nervous system temperature in thermoregulation of pigeons. 711 92

Rather high Q10 (Q10 greater than 2) of brain and skeletal muscle tissue respiration (incubation at 13 degrees and 23 degrees C) was observed in cold (7 degrees C) and warm (23 degrees C) acclimated frogs. The transfer of animals from cold to warm environment caused a significant decrease in Q10 within 1.4-24 hrs whereas no change in Q10 followed the reverse transfer: 24-hr cooling of warm-acclimated frogs. This trace reaction: the Q10 reduction of brain tissue respiration, is absent in 1 hour after the transfer to warm environment, and gradually appears within 24 hrs. In an hour after rewarming, Q10 of skeletal muscle tissues sharply increases (1.87 to 2.27), then a 6 to 18-hr plateau follows and by the 24th hour the Q10 is reduced to 1.78. These events are supposed to be based on a discordance in the time of membrane permeability and enzyme activity changes which result in cellular alterations in enzyme/substrate ratio.
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PMID:[Trace reactions in tissue metabolism to changes in the ambient temperature of Rana ridibunda Pall. frogs]. 711 99

The efflux of 45Ca from mammalian slow twitch muscle fibres has been studied to provide a measure of the concentration of free Ca2+ in the sarcoplasm. The kinetically complex early phases of washout of the isotope are succeeded by a prolonged slower phase which exhibits first-order kinetics. This later phase is accelerated by caffeine, by preventing oxidative phosphorylation and also during an isometric contraction, whether this contraction is produced by lowering the temperature or by electrical stimulation. The local anaesthetic tetracaine abolishes the contraction caused by cold and in this case the rate constant for efflux is progressively lowered as the temperature is reduced (Q10 value of 2.3). The removal of external Na+ and Ca2+ reduces the efflux rate constant. Caffeine, sodium removal and the inhibition of oxidative phosphorylation, all potentiate the cold contraction and the associated extra 45Ca efflux. Ca removal causes the cold contraction to become phasic. It appears that caffeine, sodium removal, the inhibition of oxidative phosphorylation and a decrease in temperature to below 10 degrees C are all treatments which, like electrical stimulation, increase the sarcoplasmic free calcium concentration to varying degrees.
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PMID:Calcium efflux during the cold-induced contraction of mammalian striated muscle fibres. 717 81

Hepatocytes prepared by collagenase perfusion from Antarctic nototheniid fish of genus Trematomus are active in uptake of [14C]leucine at 0, 5, and 10 degrees C. The system is saturable with apparent Km about 1.0 mM. Isoleucine and phenylalanine were major competitors, valine was about one-half as effective, while alanine, glycine and histidine had no effect. Temperature dependency of rates in the 0-10 degrees C range yielded Ea = 65 kJ/mol (Q10 = 2.7). The average first-order rate constant at 0 degrees C was 0.1 min-1, one-third the value of 0.3 min-1 estimated for clearance of [14C]leucine by liver of these species in vivo. Affinity and specificity agreed well with in vivo data on liver clearance of leucine, both in Antarctic fish at 0 degrees C and in temperate fish acclimated to 10 degrees C and 20 degrees C. The results indicate similar modifications of leucine transport associated with evolutionary cold adaptation and seasonal acclimation in fish.
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PMID:Characteristics of leucine transport by isolated hepatocytes of Antarctic fish at low temperatures. 717 5

Neurophysiological studies on avian hypothalamic thermosensitivity have presented evidence for a higher Q10 of cold than of warm signal transmission in the CNS of birds. An identical temperature dependence of central cold and warm signal transmission in mammals is suggested by considerations on the phylogeny of temperature regulation. By taking into account the experimental evidence for the existence of thermosensory afferents in the CNS of mammals and birds, being differently developed in the various sections of the neural axis and exerting quantitatively different influences on the various thermoregulatory effectors, a common concept of homeothermic thermoregulation is proposed resting on the same basic assumptions for mammals and birds. The great diversity of negative as well as positive feedback effects of CNS temperature displacements on homeothermic thermoregulation, which is particularly expressed in avian autonomic and behavioral thermoregulation and, further, certain pathophysiological conditions of disturbed thermoregulation could be accounted for by assuming quantitatively different contributions of the central thermosensory inputs of thermoregulatory effector control, but maintaining the Q10 values of hypothalamic warn and cold signal transmission constant. The proposed model, while basically additive in its mathematical design, meets a number of properties described by multiplicative models of thermoregulation. In additionally generalizes these models of predicting that changes of hypothalamic temperature modify the sensitivities with which any thermoregulatory effector responds to any thermosensory input.
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PMID:Effects of CNS temperature on generation and transmission of temperature signals in homeotherms. A common concept for mammalian and avian thermoregulation. 732 37

The thermosensitivity of 15 warm-sensitive neurons (WSNs) and 19 cold-sensitive neurons (CSNs) from the medial preoptic/anterior hypothalamus (POAH) was tested during wakefulness, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep by local POAH warming and cooling in freely moving cats. Thermosensitivity was quantified by three criteria, Q10, impulses per second per degree Celsius, and percent change per degree Celsius. Irrespective of the criterion used, WSNs did not exhibit a significant change in thermosensitivity during REM sleep compared with wakefulness and NREM sleep. In contrast, CSNs exhibited decreased mean thermosensitivity during REM sleep compared with wakefulness. CSNs as a group did not retain significant thermosensitivity in REM sleep. These findings are consistent with evidence that thermoeffector responses to cooling are lost in REM sleep, whereas some responses to warming are preserved.
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PMID:Preoptic/anterior hypothalamic neurons: thermosensitivity in rapid eye movement sleep. 750 17

The effect of thermal acclimation on the activity of carnitine palmitoyltransferase I (CPT I), the rate-limiting enzyme for beta-oxidation of long-chain fatty acids, was determined in oxidative red muscle of striped bass (Morone saxatilis) acclimated at 5 or 25 degrees C. As observed in mammalian tissues, malonyl-CoA potently inhibited CPT I activity of mitochondria. Inhibition by malonyl-CoA required inclusions of both bovine serum albumin (BSA) and palmitoyl-CoA in the reaction media. Because BSA binds long-chain fatty acyl-CoAs, this observation suggests that free fatty acyl-CoAs may disrupt mitochondrial membranes and affect the CPT I protein. Cold acclimation increased citrate synthase activity 1.6-fold and total CPT activity 2-fold in homogenates of red muscle; free carnitine increased 62%, and specific activity of CPT I in mitochondria increased 2-fold. No differences were observed between cold- and warm-acclimated fish in substrate-binding properties of CPT I at an assay temperature of 15 degrees C, as judged by the Michaelis constant (Km) for carnitine (0.11 +/- 0.02 vs. 0.13 +/- 0.02 mM) or inhibition of CPT I, as determined by the half-maximal inhibition concentration (IC50) for malonyl-CoA (0.14 +/- 0.05 vs. 0.09 +/- 0.03 microM). Thermal sensitivity of CPT I (Q10 = 2.91 +/- 0.12 vs. 3.02 +/- 0.20) and preference of CPT I for different long-chain fatty acyl-CoA substrates (16:1-CoA = 16:0-CoA > 18:1-CoA) were not altered by thermal acclimation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cold acclimation increases carnitine palmitoyltransferase I activity in oxidative muscle of striped bass. 814 97

Since there are complex regulations of paradoxical sleep at the supra-pontine level, the chronic pontine preparation appears to be the best model for studying the mechanisms of the ultradian rhythm of PS (tau'). In these preparations, which are ectothermic, tau' is considerably dependent upon temperature conditions. a) PS never occurs above a central temperature (Tc) of 36 degrees C which constitutes the absolute threshold for PS. b) If Tc is regulated at a plateau between 34.5 degrees C and 35.5 degrees C, the duration of tau' corresponds to about 60 min (circhoral) whereas the duration of PS is 5 min, thus the cyclic ratio: tau'/duration of PS is 12. During deep hypothermia (from 35 degrees C to 25 degrees C), tau' of PS is temperature-compensated. It remains close to 60 min, so that its Q10 is about 1. c) However, in the same conditions, the duration of PS episodes increases from 5 min to 55 min, so that the Q10 of PS is 0.1 (8% at 35 degrees C - 80% at 25 degrees C). These data are discussed in the light of the present theories explaining tau' (i.e., the reciprocal inhibition between monoaminergic permissive systems and cholinergic executive systems). An increase in PS during hypothermia might be possible provided that it should be proved that permissive mechanisms are excited by heat while executive mechanisms would be cold-sensitive. But there are no data on this point. However, even this "differential thermosensitivity hypothesis" would not explain the striking fixity of tau' between 35 degrees C and 25 degrees C. For this reason, one should hypothetize that there is a temperature-compensated oscillator or pacemaker which would act upon both executive and permissive mechanisms. This oscillator would also be controlled by metabolic factors as shown by the effect of O2 and prolactin.
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PMID:[Is there a bulbar pacemaker responsible for the ultradian rhythm of paradoxical sleep?]. 891 91

Na+ and K+ currents were measured by the patch-clamp method in the paranodal region of single sciatic nerve fibres of rats and of warm-adapted and cold-adapted golden hamsters. Kinetic parameters and temperature dependence of the Na+ currents were determined. The time constant for activation (about 0.2 ms for rats and hamsters) as well as the time constant for inactivation (about 1.6 ms for rats and hamsters) at 15 degrees C and at -35 mV compared well with single fibre voltage-clamp data from the rat. Differences amongst the three groups of animals were not significant. The temperature coefficient, Q10, for the activation and the inactivation time constant as well as for the time-to-peak of the Na+ current ranged between 2.3 and 3.1. No data have previously been published on the temperature dependence of the delayed-rectifier K channels of mammalian nerve fibres. Most of the K+ current was carried by intermediate (KI) and fast (KF) K channels. Dendrotoxin block indicated that "approximate"55% of the K+ current was due to KI channels, with no significant difference amongst the three groups of animals tested. The Arrhenius plot of the time constant of K+ current activation, "tau"n, yielded a mean Q10 of 3.3 at -40 mV (4. 0 at + 60 mV). No significant differences of the channel kinetics between rats, warm-adapted hamsters and cold-adapted hamsters were detected. We observed, however, a significant decrease of the Na channel density in the paranodal region of cold-adapted hamsters.
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PMID:Kinetic parameters of the ionic currents in myelinated axons: characterization of temperature effects in a hibernator and a nonhibernator. 892 6

We investigated the process of rewarming from torpor with respect to respiratory and circulatory oxygen transport properties in the smallest mammal, the Etruscan shrew Suncus etruscus. In seven adult Etruscan shrews with a mean body mass of 2.4g, torpor was induced by deprivation of food and a cold environment. During arousal from torpor at an ambient temperature of 22 degrees C, the shrews actively rewarmed from the lowest mean (+/- S.D.) body temperature (Tb) of 12.1 +/- 1.2 degrees C to 20 degrees C at a rate of 0.43 +/- 0.14 degree C min-1, from 20 to 24 degrees C at a rate of 0.8 degree C min-1, and from 24 to 36 degrees C at a rate of 1.1 +/- 0.1 degrees C min-1. The mean rate from 12 degrees C to normothermia amounted to 0.83 degree C min-1, which is among the highest values recorded in mammals. During rewarming, the heart rate increased exponentially (Q10 = 2.2) from 100 to 800-1200 min-1, whereas the respiratory rate increased linearly from 50 to 600-800 min-1. These rates are higher than the heart and respiratory rates reported for other small mammals at the same Tb. The fraction of brown adipose tissue (BAT) was 9.2 +/- 1.6% of body mass, which is higher than in any other mammal. Up to a body temperature of approximately 17 degrees C, the heat for rewarming was mainly produced in the BAT; above this value, considerable activity of the skeletal muscles enhanced thermogenesis. Estimation of the mixed venous oxygen partial pressure showed that, at the tissue level, the rewarming process corresponds to heavy work conditions. The ventilatory system is adapted such that during rewarming, in addition to the appropriate oxygen transport capacity, there is also a capacity for hyperventilation.
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PMID:Rates of rewarming, heart and respiratory rates and their significance for oxygen transport during arousal from torpor in the smallest mammal, the Etruscan shrew Suncus etruscus. 919 97


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