DISCHARGE PATTERNS OF CAROTID BODY CHEMORECEPTORS

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The discharge patterns of carotid body chemoreceptors will be studied. An avian animal model was chosen because their carotid bodies are nearly identical in structure and function to those of mammals, and because the avian lung offers the powerful experimental advantage of unidirectional ventilation (UDV) for controlling arterial blood gases. Experiments are proposed that combine UDV, on line blood gas measurement, single unit neural recording techniques, measurements of reflex ventilatory responses, and computerized on-line data acquisition to test the physiological responses of carotid bodies in ways difficult or impossible with a mammalian model. Carotid body chemoreceptors are multimodal, responding to arterial PO2, PCO2, and other stimuli. This project will determine the response of single receptors to arterial PO2, PCO2, pH, and blood pressure. This project will also analyze the temporal occurrence of action potential from chemoreceptors exposed to different static level of arterial PO2 and PCO2 (controlled with UDV) to test the hypothesis that the two stimuli cause different receptor discharge patterns. Pattern differences could be a neural encoding mechanism for carrying differential stimulus information centrally, and might be due to difference in transduction mechanisms for oxygen and carbon dioxide. Dynamic oscillations of arterial PCO2 associated with tidal breathing are thought to provide a phasic, centrally gated ventilatory stimulus, and perhaps a feed-forward control signal related to metabolic rate. This project will use precise UDV induced arterial PCO2 oscillations to test the rate sensitivity of carotid boy chemoreceptors (which would amplify their oscillatory signal) and their frequency response. The reflex importance of arterial PCO2 oscillations mediated by carotid body chemoreceptors will also be quantitated. Many aspects of the normal dynamic and static carotid body chemoreceptor sensitivity remain uncertain. It is important to study these normal physiological responses to define the role of the carotid body in the control of pulmonary ventilation in health and disease.