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Cervical preganglionic sympathetic nerve activity and chemoreflexes in the cat
Journal of Applied Physiology (Bethesda, Md. : 1985)
|April 1, 1987
Summary
The carotid body chemoreflex quickly impacts sympathetic nerve activity. However, a moderate drop in oxygen also directly excites the sympathetic nervous system, suggesting intrinsic O2 sensitivity.
Area of Science:
- Cardiovascular Physiology
- Autonomic Nervous System Regulation
- Respiratory Control
Background:
- Chemoreceptors in the carotid body and central nervous system regulate sympathetic nerve activity.
- Understanding the interplay between these chemoreceptors and sympathetic output is crucial for physiological regulation.
Purpose of the Study:
- To investigate the role of carotid body and central chemoreceptors in controlling cervical preganglionic sympathetic nerve (PSN) activity.
- To differentiate the contributions of peripheral and central chemoreflexes to sympathetic responses during hypoxia.
Main Methods:
- Simultaneous recording of PSN activity, respiratory parameters (tidal volume, PO2, PCO2), and blood pressure in anesthetized cats.
- Pharmacological stimulation with cyanide, nicotine, and dopamine before and after carotid sinus nerve (CSN) section.
- Assessment of PSN and ventilatory responses to transient and steady-state changes in arterial PO2 and PCO2.
Main Results:
- CSN section increased baseline PSN activity and abolished responses to pharmacological stimuli but not to hypoxia.
- PSN responses to hypoxia were diminished after CSN section, while ventilatory responses were abolished.
- A portion of the PSN response to hypoxia was independent of peripheral chemoreflex and respiratory drive.
Conclusions:
- The carotid body chemoreflex mediates rapid PSN responses to hypoxia.
- A moderate decrease in arterial PO2 directly excites the sympathetic nervous system, indicating O2 chemosensitivity.
- The sympathetic nervous system may initiate chemoreflex responses independently of peripheral chemoreceptors.