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First published online March 21, 2005
Journal of Experimental Biology 208, 1373-1383 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01546

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Cardiorespiratory and metabolic reactions during entrance into torpor in dormice, Glis glis

Ralf Elvert^1,* and Gerhard Heldmaier^1,2

¹ GSF National Research Center for Environment and Health, GMC – German Mouse Clinic – Metabolic Screen, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany
² Department of Biology, Karl von Frisch Strasse, Philipps University Marburg, 35043 Marburg, Germany

View larger version (33K): [in a new window]   Fig. 1. Experimental setup for measuring body temperature (Tb), heart rate (fH), electrocardiogram (ECG) and metabolic rate (O2). For measuring ventilation frequency (fV) the nesting box was replaced by a total body plethysmograph and a differential pressure transducer. On top of the nesting box an infra red camera was fixed for observing the dormice. The receiver was placed below the nesting box or the plethysmograph, respectively. For further information see text.

View larger version (39K): [in a new window]   Fig. 2. (A) Entry into torpor in a dormouse (#R4S, BW=120 g) at 15°C Ta. Body temperature (Tb, black filled circles), metabolic rate (O2, solid black line) and heart rate (fH, thick solid black line) were recorded simultaneously. The different phases of entries into torpor are shown in a 4 day sample recording, broken after the first day, from 1–5 August, 2000. Four different phases were defined: phase I (P I) as a resting phase, phase II as the pre-torpor phase, phase III was defined as the period lasting from the initial peak through 90% of transition towards values reached in steady state of torpor. Dotted lines indicate beginning and end of single phases. The end of P III is determined by 90% reduction value of RMR during P I. The 90% decrease time of fV, fH and Tb are calculated separately. Phase IV is defined as the phase of lethargy. (B) The same entry into torpor as in Fig. 2A, but additionally the ventilation frequency (fV, gray circles) and the oxygen pulse for ventilation are shown (compare Fig. 5B). Note the high ventilatory frequency and the simultaneous low oxygen pulse occuring prior to entrance into torpor.

View larger version (29K): [in a new window]   Fig. 3. Effect of Ta on fV, O2 and fH during the different phases (I–III). Top: change of fV, individual dormice are marked with symbols: circles #R4S, squares #L6S, triangles #R13G, diamonds #R3S. Open symbols indicate phase I (N=5, n=31, r2=0.33, P<0.001), black symbols indicate phase II (N=3, n=11, r2=0.37, P<0.05), dark grey symbols indicate phase III (N=3, n=11, r2=0.013, P>0.05); middle: change of O2, light grey symbols in phase I of O2 and fH (middle and bottom, N=4, n=125, r2=0.468, P<0.001) indicate values measured in the thermoneutral zone; phase II (N=4, n=146, r2=0.27, P<0.001), phase III (N=4, n=107, r2=0.571, P<0.001); bottom: change of fH, phase I (N=4, n=121, r2=0.58, P<0.001), phase II (N=4, n=141, r2=0.567, P<0.001), phase III (N=4, n=105, r2=0.574, P<0.001).

View larger version (44K): [in a new window]   Fig. 4. Monitoring of fH and change of ventilation during the entrance into torpor in the different phases. While phase I–III have the same time scale, it is enlarged in phase IV, due to the intermittent breathing pattern during deep torpor.

View larger version (33K): [in a new window]   Fig. 5. (A) Sample recording at Ta=5°C of dormouse #L6S from 22.01.2001, BW=118 g. Tb (black filled circles), O2 (solid black line) and fH (thick solid black line) were recorded simultaneously. The inset diagram further shows the oxygen pulse for ventilation, calculated from fV and oxygen consumption. Note the change in scaling for fV and O2 compared with Fig. 2. Scaling is adapted to show the consistence of congruent decline of O2 and fH during entrance into torpor at different Ta. (B) The same entry into torpor as in Fig. 5A, but additionally the ventilation frequency (fV, gray circles) and the oxygen pulse for ventilation are shown (compare Fig. 2B). Note the high ventilatory frequency and the simultaneous low oxygen pulse occuring prior to entrance into torpor.

View larger version (23K): [in a new window]   Fig. 6. Minimum values of deep torpor (phase IV) correlated with Tb (N=95). Top: minimum O2, bottom: minimum fH. Individual dormice are marked with symbols: circles #R4S, squares #L6S, triangles #R13G, diamonds #R3S.

View larger version (17K): [in a new window]   Fig. 7. Mean values of phase I and phase II preceeding entries into torpor of a sample dormouse #R3S at different ambient temperature. To elucidate the temporal delay between both phases the values of phase II are slightly displaced.

View larger version (30K): [in a new window]   Fig. 8. The plot shows Tb (solid circles), fH (thin solid line) and Ta (thick solid line). A sample peak in fH during entrance into torpor is framed, indicating arrhythmia with extra systoles shown in the ECG plots above. Regular heart beats are interrupted by additional beats (ES). At the time of the snapshot the Tb was at 24.5°C.

View larger version (22K): [in a new window]   Fig. 9. The cardiac cycle length expressed as PT-duration as a function of Tb (top) and Ta (bottom) during normothermia (filled symbols, N=3, n=32) and hypothermia (open symbols, N=3, n=76). Individual dormice are marked with different symbols: squares #L6S, triangles #R13G, diamonds #R3S.