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  • 1
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Chronic exposure of golden hamsters to a gas mixture containing 5% CO2, 21% O2, and 74% N2 favors entry into hibernation. In the hibernating golden hamster, however, chronic CO2 exposure facilitates arousal.
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  • 2
    ISSN: 1432-2013
    Keywords: Thermoregulation ; Non-shivering thermogenesis ; Corticosteroids ; Metopirone ditartrate ; Hedgehog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract 1. Non-shivering thermogenesis (NST) was studied in 8 hedgehogs before and after a single injection of metopirone ditartrate (150–450 mg/kg, i.p.) at a thermoneutral chamber temperature (Ta) of 28°C and during cold exposure (Ta=8°C for 20 min). 2. An average metabolic increase of 149% of the standard metabolic rate (SMR) was observed 12–26 min after an injection of metopirone ditartrate at thermoneutral chamber temperature. Average temperatures simultaneously increased by 2.1°C in the brown adipose tissue (BAT) and 2.0°C in the deep colon. This initial effect lasted for 40±8 min. 3. In a period of 3–48 h after injection of metopirone ditartrate, cold-induced NST was reduced by 89% of SMR (av.). Concomitant exposure to cold caused average temperatures to decrease by 1.0°C in the BAT and 1.1°C in the colon relative to control experiments. 4. Our results suggest the participation of corticosteroids in the control of NST in the hedgehog. As metopirone blocks enzymatic 11 β-hydroxylation in the steroid ring, there is a pronounced increase of endogenous 11-deoxycorticosteroids, such as deoxycorticosterone (DOC). An injection of DOC (3 mg/kg, i.m.) increases NST at thermoneutrality similar to the initial metabolic effect elicited by metopirone ditartrate. The reduced response to cold exposure after several hours may be explained by competitive inhibition of glucocorticoid receptors since there is also an increased production of other 11-deoxycorticosteroids.
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  • 3
    ISSN: 1432-2013
    Keywords: Temperature Regulation ; Control of Shivering ; Central Thermosensitive Structures ; Spinal Cord ; Diencephalon ; Temperaturregulation ; Steuerung des Kältezitterns ; zentrale thermosensitive Strukturen ; Rückenmark ; Zwischenhirn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In young guinea pigs the ascending pathways from the spinal thermosensitive region were studied by means of 1. microelectrode recording and 2. micro-electrocoagulation. In the first series of studies, impulse frequency was recorded from single units of the spinothalamic tract which responded to a temperature rise in the spinal segments C5-T2 with an increase of discharge frequency. At a spinal cord temperature of 38–39° C these units showed a firing rate of 1–5 imp./sec; local heating of the spinal cord (dT/dt=0.1° C/sec) to 40–41° C caused an increase in discharge frequency to 20–25 imp./sec. The mean static impulse frequency was 3 imp./sec at a spinal cord temperature of 39° C, and 10 imp./sec at a spinal cord temperature of 42.5° C. In the second series of studies bilateral RF-coagulations were carried out in different sites of the diencephalon. These experiments showed that the ascending fibres from the spinal thermosensitive region connect the thermosensitive spinal region with a hypothalamic “temperature control centre”.
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  • 4
    ISSN: 1432-2013
    Keywords: Temperature Regulation ; Spinal Thermosensitive Structures ; Hypothalamus ; EEG ; Cold Adaptation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary EEG activity of various parts of the hypothalamus was recorded in unanaesthetized guinea pigs during thermal stimulation of the spinal cord. In the anterior hypothalamus fast waves became more prominent when the spinal cord temperature (T sc ) was raised from 40° to 42° C, resulting in an increase of the mean frequency by about 50%. The electrical activity remained unaffected whenT sc was raised from 38° to 40° C. In the posterior hypothalamus, spinal cord heating from 39.5° to 42° C led to a decrease of the mean frequency by about 30%, while temperature changes from 38° to 39.5° C were less effective. Corresponding studies in cold-adapted animals showed that the EEG response to spinal cord heating is modified by thermal adaptation. In this group of animals electrical activity of the posterior hypothalamus could be influenced clearly by heating the spinal cord from 38° to 39.5° C, while a temperature change in this range was nearly ineffective in animals reared at 20° C.
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  • 5
    ISSN: 1432-2013
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Bei Meerschweinchen im Alter von 0 Tagen bis durchschnittlich 11 Monaten wurde die Altersabhängigkeit des maximalen Ausmaßes der zitterfreien Thermogenese mit folgenden Methoden bestimmt: 1. Mit dem Noradrenalintest, das ist Bestimmung der O2-Aufnahmesteigerung nach Noradrenalininjektion, 2. mit dem „Blockadetest“, d.h. durch quantitative Erfassung der Beziehung zwischen elektrischer Muskelaktivität und O2-Aufnahme vor und nach Blockade der zitterfreien Thermogenese mit einem β-Receptorenblocker. Die zitterfreie Thermogenese betrug beim neugeborenen Meerschweinchen rund 250% des Grundumsatzes. Bei Aufzucht in warmer Umgebung nahm sie im Verlauf von 4 Wochen bis auf 10 bis 15% ab. Bei Aufzucht in kalter Umgebung (+3° C) bzw. vierwöchiger Adaptation an + 3° C nach vorheriger Aufzucht in wärmerer Umgebung betrug die zitterfreie Thermogenese im Alter von 3 Monaten noch ca. 60%, im Alter von 9 Monaten nur noch 40% des Grundumsatzes. Bei tieferer Adaptationstemperatur, wurden keine höheren, sondern sogar geringere Werte erhalten. Der Abbau der zitterfreien Thermogenese war von einem Schwund an braunem Fettgewebe begleitet.
    Notes: Summary In guinea pigs, 0 days to, on the average, 11 months of age, the age-dependency was determined of the maximum extent of non-shivering thermogenesis, using the following methods: 1. The noradrenaline-test: measurement of the increase in oxygen uptake on a noradrenaline injection. 2. The “blocking test”: quantitative evaluation of the relationship between electrical activity of the musculature and oxygen uptake before and after blockade of non-shivering thermogenesis by a β-receptor blocking agent. In the newborn guinea pig non-shivering thermogenesis amounted to 250% of the basal metabolic rate. It decreased to 10–15% within four weeks in animals which were reared in a warm environment. In animals reared in the cold or adapted to a cold environment (+3° C) after having been reared in a warm environment the non-shivering thermogenesis amounted to about 60% at the age of 3 months and to no more than 40% at the age of 9 months. With lower adaptation temperatures no larger but smaller amounts of non-shivering thermogenesis were obtained. The loss of non-shivering thermogenesis was accompanied by a reduction of the brown adipose tissue.
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  • 6
    ISSN: 1432-2013
    Keywords: Temperature regulation ; Hibernation ; Preoptic region ; Temperature-responsive units ; Thermal stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Thermosensitivity of preoptic units was studied at hypothalamic temperatures (T hy) ranging from 8–43°C in golden hamsters in a non-hibernating state as well as in guinea pigs. In golden hamsters 2 types of thermoresponsive preoptic neurones were found: 1. Neurones sensitive toT hy ranging from 10–42°C with an exponential characteristic and very high spontaneous firing rates (29–59 imp/s) atT hy 36–37°C. 2. Neurones with a bell-shaped temperature-firing rate characteristic, a negative temperature coefficient atT hy 40–30°C, a maximal activity atT hy 20–30°C and a positive temperature coefficient (+0.8 to +4 imp/s·°C) even atT hy close to 10°C. In guinea pigs thermoresponsive preoptic units became inactive or insensitive to thermal stimulation as soon asT hy fell below 30°C. These results suggest that in hibernators central nervous structures involved in temperature regulation are adapted to maintain their function over the wide range of core temperatures which occur during the different phases of hibernation.
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  • 7
    ISSN: 1432-2013
    Keywords: Temperature regulation ; Hibernation ; Preoptic region ; Thermosensitive neurones ; Skin temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of ambient temperature on the thermosensitivity of preoptic neurones was studied in euthermic golden hamsters. At skin temperatures (Tsk) of 20°C, preoptic units were still responsive to hypothalamic temperatures (Thy) below 10°C, while at Tsk=36°C these neurones became inactive at Thy=15°C on the average. These studies suggest that thermoreceptive preoptic neurones, influenced by a high activity of cutaneous cold-receptors, are capable of sensing core temperatures even in deep hibernation.
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  • 8
    ISSN: 1432-1912
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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