Suprabulbar and bulbar integration of ventilation and ear vascular control during thermoregulation in the rabbit

Suprabulbar and bulbospinal integration of cardiorespiratory responses to cold and heat stress was studied in groups of normal, thalamic and pontine rabbits. The animals sat in an airconditioned environmental chamber in which ambient temperature (TA) was maintained sequentially at 22 degrees C, 12 degrees C, 22 degrees C and 35 degrees C, with an accuracy of +/- 1 degree C. Neither thalamic nor pontine rabbits could maintain core temperature in cold or heat. At TA 35 degrees C, thalamic and pontine animals did not pant, indicating that telencephalic responses were necessary for the integration of mechanisms promoting respiratory heat loss. Thalamic animals, however, could inhibit ear vascular sympathetic tone in the heat, but the response was absent in pontine animals, suggesting diencephalic responses were essential for the integration of mechanisms promoting ear skin heat loss. Thus, the neural adjustments to thermal stress depend on mechanisms of integration distributed longitudinally throughout the central nervous system, and different components of the reflex cardiorespiratory response depend on different sites in the central nervous system for their full expression.