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Ventrolateral medulla and sympathetic chemoreflex in the rat
N Koshiya1, D Huangfu, P G Guyenet
1University of Virginia Health Sciences Center, Department of Pharmacology, Charlottesville 22908.
Brain Research
|April 23, 1993
Summary
The caudal ventrolateral medulla relays the sympathetic baroreflex, while the rostral ventrolateral medulla integrates chemoreceptor and baroreceptor signals for sympathetic control. These reflexes largely follow independent pathways in the brainstem.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
- Autonomic Nervous System Research
Background:
- The sympathetic nervous system regulates crucial cardiovascular functions.
- Understanding the neural pathways of sympathetic reflexes is vital for managing blood pressure and respiration.
- The roles of specific medullary regions in sympathetic baroreflex and chemoreflex pathways require further elucidation.
Purpose of the Study:
- To investigate the distinct roles of the rostral ventrolateral medulla (RVL) and caudal ventrolateral medulla (CVL) in mediating sympathetic baroreflex and chemoreflex.
- To determine the site of integration for baroreceptor and chemoreceptor information in sympathetic vasomotor control.
Main Methods:
- Recording splanchnic sympathetic nerve discharge (SND) and phrenic nerve activity (PND) in urethane-anesthetized rats.
- Stimulating carotid chemoreceptors and manipulating aortic baroreceptors.
- Using microinjections of glutamate receptor antagonist kynurenic acid (Kyn) and GABAA agonist muscimol in RVL and CVL.
Main Results:
- Carotid chemoreceptor stimulation significantly increased SND, mean arterial pressure (MAP), and RVL premotor neuron activity.
- RVL and CVL neurons exhibited respiratory rhythmicity during chemoreceptor activation.
- Kyn in RVL blocked the sympathetic chemoreflex but spared the baroreflex; Kyn or muscimol in CVL blocked the baroreflex but spared the chemoreflex.
Conclusions:
- The CVL is an essential relay for the sympathetic baroreflex but not the sympathetic chemoreflex.
- The RVL contains sympathetic premotor neurons involved in integrating baro- and chemoreceptor inputs.
- Sympathetic baro- and chemoreflexes likely have independent pathways through the medulla, with integration occurring at the premotor neuronal level in the RVL.