Ventilatory and metabolic responses to cold and hypoxia in conscious rats with discrete hypothalamic lesions

We tested the hypothesis that hypothalamic nuclei involved in thermoregulatory control could represent a site of integration of the metabolic and ventilatory response to cold and hypoxia. Electrolytic lesions were performed bilaterally under stereotaxic guide, either within the anterior or posterior hypothalamic areas of adult rats. One week later, oxygen consumption (VO2) and ventilation (VE) were measured in the conscious animals during warm (27 degrees C) or cold (12 degrees C) conditions, in normoxia (21% O2) or hypoxia (10% O2), and compared to measurements obtained in control rats, which were either intact or sham-operated. VO2, VE, and body temperature did not differ between lesioned and control rats during warm normoxia. In cold and hypoxia, singly or combined, VE/VO2 was higher in the lesioned rats, because of higher VE. The differences in the cold were mostly confined to rats with anterior lesions, whereas differences in hypoxia were mostly in rats with posterior lesions. We conclude that the integrity of the anterior and posterior hypothalamic areas is important for the proper coupling of metabolism and ventilation during cold or hypoxic stimuli.