A specific region of the brainstem has been identified as a trigger for biological changes that drive up blood pressure, potentially explaining why some patients remain resistant to standard antihypertensive medications. Researchers from the University of São Paulo and the University of Auckland found that the lateral parafacial region (pFL) can cause blood vessels to constrict, contributing to neurogenic hypertension, according to a study published in Circulation Research.
The brainstem’s link between breathing and vascular tone
The pFL is situated in the brainstem, the lowest portion of the brain connecting to the spinal cord. Its primary function is the automatic control of breathing, particularly during forced or voluntary exhalations—the kind associated with coughing, laughter, or physical exertion.
But the pFL does more than manage breath. The research suggests these neurons link breathing rhythms—even those the patient does not consciously perceive—to the sympathetic nervous system. This is the “fight or flight” mechanism that regulates blood pressure during stress. To test this, scientists used genetic engineering in rats to activate and deactivate these neurons, monitoring the immediate impact on arterial pressure and sympathetic nerve activity.
Neural circuits and the failure of standard medication
In hypertensive rats, the pFL neurons acted as a switch for vessel constriction. Mapping of the brainstem revealed that activating the pFL triggered separate cerebral circuits that forced blood pressure upward.
The effect was reversible. Julian Paton, a physiologist and researcher at the University of Auckland, stated that when the team deactivated this specific region in hypertensive rats, the blood pressure returned to normal levels. This “dual role” of pFL neurons—simultaneously controlling respiration and vascular signaling—may be the reason some hypertension remains uncontrolled despite traditional drug therapies.
Targeting the carotid bodies to bypass the blood-brain barrier
Because the pFL is buried deep within the brain, treating it directly would require drugs capable of penetrating the blood-brain barrier. Researchers are instead looking to the neck.
The carotid bodies, small sensory organs located where the carotid arteries bifurcate, act as external sensors that can influence pFL neurons. The University of Auckland team tested pyridoxal 5′-phosphate—the active form of vitamin B6—which blocks the P2X3 receptor. This specific receptor is hyperactive in the carotid bodies of those with hypertension. In hypertensive rats, administering this compound reduced blood pressure by an average of nearly 16 mmHg.
The biological connection to sleep apnea
The discovery offers a concrete biological explanation for the strong correlation between sleep apnea and hypertension. Because the pFL manages the intersection of breathing and vascular tone, the respiratory disruptions typical of sleep apnea may chronically overstimulate the sympathetic nervous system, leading to sustained high blood pressure.
Much of the population suffers from “essential” hypertension, where no specific cause is identified beyond general factors like age, obesity, smoking, high salt intake, and genetics. This research identifies a precise neurological mechanism that may drive the condition for a specific subset of patients.
Human clinical trials must confirm rat model findings
These findings are currently limited to rat models. While scientists believe these circuits function similarly in humans, the mechanism must be confirmed through human clinical trials before treatment can be applied to people.
By targeting the neurological trigger in the brainstem via the carotid bodies, this method seeks to stop the hypertensive signal before it ever reaches the vessels.
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