IVth International Conference on Dormice (Rodentia, Gliridae)13 - 16 September 1999 EDÝRNE - TURKEY |
INTERMITTENT BREATHING AND APNEIC OXYGENATION DURING HIBERNATION IN FAT DORMICE (GLIS GLIS, L.)
Wilz, M. & Heldmaier, G.
Fachbereich Biologie / Zoologie, Philipps-Universität, D - 35032 Marburg, Germany, e-mail: wilz@mailer.uni-marburg.de
The hibernation period of fat dormice lasts for seven month (September – May), and is composed out of hibernation bouts. The bout length is highly variable and lasts from 2 to 32 days. In the beginning of a hibernation bout the metabolic rate is reduced to a small fraction of basal metabolic rate (MR).Body temperature (Tb) decreases close to ambient temperature (Ta). During the hibernation bouts intermittent breathing appears, with periods of apnea up to one hour. (Wilz M 1999 Dissertation Marburg)
We examined the patterns of intermittent breathing during hibernation at different Ta (0°C – 16°C). We measured six fat dormice in hibernation under controlled conditions in the laboratory. The animals were housed in cages in a climate chamber without food and water ad lib. Tb was measured by telemetry, using implanted temperature sensitive transmitters. Ta was monitored with thermocouples and MR was measured by indirect calorimetry in an open system. Breathing patterns were additionally observed using an infra-red video camera system.
We observed temperature dependent patterns of intermittent breathing. With decreasing Ta from 16°C to 3°C the periods of apnea increased from 8 minutes to 60 minutes. Below 3°C the duration of apnea decreased again. The episodes of breathing separated by periods of apnea also changed with the Ta. At 12°C dormice ventilated 14 times during one breathing episode, at 3°C 30 times. At 0.1°C the intermittent breathing stopped and continuous breathing started again.
During the periods of apnea a significant part of the gas exchange took place without ventilation of the lungs. At 5°C the oxygen consumption was 0.017ml O2*g-1*h-1. 33% of the oxygen was exchanged during the periods of apnea. The total amount of CO2-production was 0.012 ml CO2*g-1*h-1, with 62% of the CO2 excreted during the period of apnea.
The question was now, how a gas exchange without ventilations of the lung could have taken place. Theoretical calculations showed that only a little part of the measured gas exchange can be exchanged by the skin. But if the epiglottis remains open during apnea, the diffusion rate of oxygen and CO2 is high enough to count for the measured gas exchange (Szewczak J M, Jackson D C 1992, J. exp. Biol 173, 217-227). Further influence for the gas exchange might be given by pulsatile gas flow caused by the heart beat (West J B, Hugh-Jones P 1961, J. appl. Physiol. 16, 697-702).
We conclude that intermittent breathing and passive oxygenation are further abilities of the dormice to lower their minimum MR during hibernation and save further energy.