DISCHARGE PATTERNS OF CAROTID BODY CHEMORECEPTORS

The discharge patterns of carotid body chemoreceptors will be
studied. An avian animal model was chosen because avian carotid
body chemoreceptors are nearly identical in structure and
function to mammalian carotid bodies, 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, and
computerized on-line data acquisition to test the physiological
responses of carotid body chemoreceptors 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 pH and
blood pressure. This project will also analyze the temporal
occurrence of action potentials from single chemoreceptors
exposed to different static levels of stimuli cause different
receptor discharge patterns. Pattern differences could be a
neural encoding mechanism for carrying differential stimulus
information to the central respiratory controller, and may
represent fundamental differences in transduction mechanisms for
O2 and CO2. Dynamic oscillations of arterial PCO2 associated with tidal
breathing are hypothesized to cause a feed-forward control signal
via the carotid bodies for ventilatory control during exercise.
This project will use UDV-induced ramp oscillations of arterial
PCO2, and PO2 to test the rate sensitivity of carotid body
chemoreceptors (which would amplify the feed-forward signal in
exercise). UDV-induced sinusoidal oscillations of arterial PO2 and
PCO2 will be used to test the frequency response of the receptors
(determining the receptor response to changes in respiratory
rate), and it will test for phase differences between oscillating
PO2 or PCO2 receptor response (which affects the efficacy of
chemoreceptor discharge arriving at the central controller). Many aspects of the normal dynamic and static carotid body
chemoreceptor sensitivity remain uncertain. It is important to
study these normal physiological responses so that we can define
the roles of carotid body chemoreceptors in the control of
pulmonary ventilation in health and disease.