CNS regulation of body temperature in euthermic and hibernating marmots (Marmota flaviventris) [Régulation de la température corporelle par le système nerveux central chez les marmottes actives et hibernantes (M. flaviventris)].

Résumé

Mise en évidence pendant l'hibernation de l'activité du régulateur hypothalamique de la température corporelle et de ses changements progressifs de thermosensibilité. Hypothalamic thermosensitivity of marmots was characterized during euthermia and hibernation. Hypothalamic temperature (Thy) was manipulated with chronically implanted, water-perfused thermodes while the animal's rate of oxygen consumption was continuously measured. The threshold Thy, for eliciting an increase in metabolic heat production (MHP) and the proportionality constant (alphaMHp) relating rate of MHP to Thy were determined. In four euthermic marmots alphaMHP averaged -1.1 W.kg-1.C-1. During the entrance into hibernation, as body temperature (Tb) declined from 36 to 8°C, the threshold Thy for the MHP response progressively declined and was demonstrable at all times. The Thy of marmots in deep hibernation at an ambient temperature (Ta) of 5°C plateaued near 7.5°C, but theshold Thy for MHP showed a continuous slow decline of 0.2-0.4°C a day, until one day prior to arousal. Proportional regulation of Tb was demonstrable at all times during deep hibernation. The average proportionality constant for the MHP response to hypothalamic cooling during deep hibernation in three marmots was -0.08 W . kg-l . °C-l. These results demonstrate that the hypothalamic regulator of Tb is active throughout hibernation and that there are progressive changes in its thermosensitivity.