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The area postrema: a cardiovascular control centre at the blood-brain interface?
1Department of Physiology, Queen's University, Kingston, Ont., Canada.
Canadian Journal of Physiology and Pharmacology
|July 1, 1991
Summary
The area postrema (AP), a brain region lacking a blood-brain barrier, plays a key role in cardiovascular regulation. Its neurons respond to various signals and influence blood pressure and heart rate through autonomic pathways.
Area of Science:
- Neuroscience
- Cardiovascular Physiology
- Autonomic Nervous System Research
Background:
- The area postrema (AP) is a circumventricular organ characterized by high vascularization and a lack of a typical blood-brain barrier.
- It receives afferent projections from various brain nuclei and nerves, including the paraventricular nucleus, lateral parabrachial nucleus (l-PBN), nucleus tractus solitarius (NTS), and vagus nerve.
- The AP is densely populated with receptors for peptides like angiotensin II (ANG), atrial natriuretic peptide (ANP), and endothelin (ET).
Purpose of the Study:
- To investigate the role of the area postrema (AP) in cardiovascular regulation.
- To identify the functional properties and afferent/efferent connections of AP neurons.
- To understand how AP neuronal activity influences blood pressure and heart rate.
Main Methods:
- Anatomical tracing studies to map neural projections to and from the AP.
- Receptor localization studies to identify peptide receptor distribution in the AP.
- Electrical stimulation of AP neurons at varying frequencies.
- Extracellular single unit recordings of AP neuronal activity.
- Investigation of afferent inputs from l-PBN and the aortic depressor nerve.
Main Results:
- Electrical stimulation of AP neurons at low frequencies (<15 Hz) decreased blood pressure and heart rate, while high frequencies (>20 Hz) increased blood pressure.
- Two distinct populations of AP neurons were identified: one responsive to ANG and another to blood pressure changes.
- AP neurons are activated by circulating ET, and receive both excitatory and inhibitory inputs from the l-PBN.
- A significant excitatory input to approximately 70% of tested AP neurons originates from the aortic depressor nerve.
Conclusions:
- The area postrema (AP) is a critical neural structure involved in regulating the cardiovascular system.
- The AP integrates various sensory inputs and exerts control over autonomic functions affecting blood pressure and heart rate.
- Distinct neuronal populations and afferent pathways within the AP contribute to its regulatory role.