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EXERCISE AND RESPIRATORY PHYSIOLOGY

Cold stimulates the behavioral response to hypoxia in newborn mice

¹INSERM, UMR676, Robert-Debré Teaching Hospital, Paris, France; ²University of Leuven, Laboratory of Biological Psychology, Leuven, Belgium; ³University of Paris 7, Faculty of Medicine Denis Diderot, Paris, France; ⁴University of Amiens, Faculty of Medicine, Amiens, France; ⁵Raymond Poincaré Hospital, Department of Physiology, Garches, France; ⁶University of Leuven, Research Group on Health Psychology, Leuven, Belgium

Submitted 8 July 2008 ; accepted in final form 11 March 2009

In newborns, hypoxia elicits increased ventilation, arousal followed by defensive movements, and cries. Cold is known to affect the ventilatory response to hypoxia, but whether it affects the arousal response remains unknown. The aim of the present study was to assess the effects of cold on the ventilatory and arousal responses to hypoxia in newborn mice. We designed an original platform measuring noninvasively and simultaneously the breathing pattern by whole body plethysmography, body temperature by infrared thermography, as well as motor and ultrasonic vocal (USV) responses. Six-day-old mice were exposed twice to 10% O₂ for 3 min at either cold temperature (26°C) or thermoneutrality (33°C). At 33°C, hypoxia elicited a marked increase in ventilation followed by a small ventilatory decline, small motor response, and almost no USVs. Body temperature was not influenced by hypoxia, and oxygen consumption (O₂) displayed minimal changes. At 26°C, hypoxia elicited a slight increase in ventilation with a large ventilatory decline and a large drop of O₂. This response was accompanied by marked USV and motor responses. Hypoxia elicited a small decrease in temperature after the return to normoxia, thus precluding any causal influence on the motor and USV responses to hypoxia. In conclusion, cold stimulated arousal and stress responses to hypoxia, while depressing hypoxic hyperpnea. Arousal is an important defense mechanism against sleep-disordered breathing. The dissociation between ventilatory and behavioral responses to hypoxia suggests that deficits in the arousal response associated with sleep breathing disorders cannot be attributed to a depressed hypoxic response.

arousal; chemosensitivity; control of breathing