Summary: Researchers discovered that a specific subpopulation of epinephrine-producing cells, known as C1 neurons, act as master controllers of fear and persistent anxiety. Normally, these cells sound a brief, temporary alarm during highly stressful events. However, the study proved that sustained, heavy activation of this pathway leaves a critical downstream stress hub locked in a permanent “on” position, causing severe anxiety states that linger for many days after a threat has passed.
Key Facts
- The Brainstem Blind Spot Upended: C1 neurons reside nestled inside the rostral ventrolateral medulla (RVLM), a primitive, deep brainstem region traditionally thought to strictly control basic, automatic life functions like breathing rhythms and cardiac processing. Finding cells that direct complex, higher-order emotional behaviors like chronic anxiety within this area completely redefines brainstem biology.
- The PAG Pathway Map: Using an advanced precision-targeting system engineered in the Schwarz lab, investigators isolated C1 neurons from surrounding cells. They unmasked a powerful, direct highway connecting these cells to the periaqueductal gray matter (PAG), a critical command center that coordinates behavioral responses to stress.
- The Week-Long Chronic Pivot: While brief C1 firing helps an animal survive immediate danger, strong, prolonged stimulation triggers a devastating shift. The trial revealed that overactivating this circuit permanently alters downstream PAG signaling, causing severe anxiety behaviors that persist for a full week after the initial trigger.
- The Broken Off-Switch Theory: Neuroscientists hypothesize that under normal conditions, the C1-to-PAG circuit turns off automatically once an environmental stressor disappears. In chronic anxiety disorders, a highly traumatic event can overstimulate these cells, breaking the off-switch and keeping the chemical alarm blaring indefinitely.
- Surgically Blocking Traumatic Stress: In a major therapeutic milestone, researchers tested the effects of chemically silencing these cells. Inhibiting C1 neurons right after a highly traumatic event completely shielded the subjects from developing subsequent, long-term anxiety behaviors.
- Zero Autonomic Interference: Crucially, blocking or activating these cells had absolutely no impact on immediate, real-time behavior or background automatic body functions. This means a future drug targeting C1 neurons could theoretically clear away long-term emotional trauma without causing the grogginess, memory issues, or blood pressure changes associated with standard anti-anxiety medications.
Source: St. Jude Children’s Research Hospital
Anxiety disorders affect more than 300 million people globally. Several brain regions have been linked to anxiety, but how these regions connect has been poorly understood. By exploring these connections, scientists at St. Jude Children’s Research Hospital revealed that epinephrine-producing C1 neurons in mice are modulators of fear and anxiety.
They found that while the activity of these neurons was normally temporarily elevated in times of stress, prolonged activation led to heightened anxiety that could last many days. Inhibition of C1 neurons reduced anxiety-like behaviors, suggesting these neurons may be worth exploring as therapeutic targets for anxiety disorders.
The findings were published today in Neuron.
Anxiety helps us prepare for future threats, but when it is excessive or persistent, it can significantly affect quality of life. Medications exist to alleviate symptoms but can have off-target effects that might discourage long-term use. By identifying C1 neurons as novel modulators of fear and anxiety, Lindsay Schwarz, PhD, Department of Developmental Neurobiology, is hopeful that these cells could serve as a new therapeutic target for anxiety-related disorders.
“C1 neurons appear to promote anxiety without directly affecting autonomic functions,” Schwarz said. “This suggests they may be a better target than broadly affecting signaling across the entire brain and body.”
C1 neurons sound the alarm under stress
C1 neurons reside in the rostral ventrolateral medulla (RVLM), a highly diverse and interconnected brain region that controls breathing and cardiac function. While loosely associated with the stress response, teasing out the individual contributions of neurons in the RVLM had been challenging.
Using a precision-targeting system designed in the Schwarz lab, the researchers selectively interrogated these subpopulations, singling out C1 neurons from other similar cells within the RVLM. The results showed that C1 neuron activation subsequently excited neurons within the periaqueductal grey matter (PAG), an important brain region for regulating physiological and behavioral responses to stress.
“Considering the basic functions that the RVLM controls, it was assumed that neurons controlling complex behaviorssuch as fear and anxiety wouldn’t be found there,” Schwarz said. “Despite being within the RVLM, C1 neurons appear to be doing something different from the neurons around them, suggesting an unappreciated capacity of what these brain regions can do.”
Not only does C1 neuron activation induce an instant anxiety response in mice, but persistent activation also prolongs the response up to a week later. “Signaling from these neurons to the PAG is very powerful in producing long-lasting anxiety,” Schwarz said. “C1 neuron activation increases PAG activity in stressful situations, but normally, we think this circuit turns off when the stress has passed. We found that strong activation may keep it on too long, leading to prolonged anxiety.”
Finally, the researchers tested whether blocking C1 neuron activation alleviated anxiety. Notably, inhibition was most effective at reducing anxiety felt after experiencing a highly stressful event.
“When we blocked these neurons during a period of heightened stress, the mice were less affected by subsequent stressful events. This suggests C1 neurons play a key role in regulating anxiety over time,” Schwarz said. “Importantly, blocking these neurons doesn’t affect behavior in the moment. So, targeting them therapeutically may be an effective strategy without causing issues otherwise.”
Authors and funding
The study’s first author is Carlos Fernández-Peña, formerly of St. Jude, now at the University of Nebraska Medical Center. The study’s other authors are Rachel Pace, Lourds Fernando, Heather Sheppard, and Brittany Pittman, St. Jude.
Funding: The study was supported by the Brain & Behavior Research Foundation, the National Institutes of Health (1DP2NS115764), and the American Lebanese Syrian Associated Charities (ALSAC), the fundraising and awareness organization of St. Jude.
Key Questions Answered:
A: For decades, psychiatric research has focused almost entirely on the brain’s higher-order “thinking” centers, like the amygdala and prefrontal cortex, when exploring anxiety and fear. The lower brainstem, particularly the medulla, was written off as a simple, automated computer responsible only for basic survival tasks like keeping your heart beating and your lungs inflating. Discovering that a tiny cluster of cells tucked inside this primitive engine can single-handedly dictate complex, long-lasting emotional trauma fundamentally challenges our understanding of brain architecture.
A: It comes down to a broken neurological off-switch. Under normal conditions, your C1 neurons sound a loud, temporary alarm to help you navigate a crisis, and then they immediately quiet down. But Dr. Lindsay Schwarz’s team discovered that if the initial trauma is too intense or prolonged, it overstimulates these cells. This heavy firing keeps the downstream periaqueductal gray (PAG) pathway jammed open. Even when you are completely safe, the broken circuit keeps pumping out stress signals, keeping the brain locked in a state of high anxiety for days or weeks.
A: Amazingly, no. This is what makes the St. Jude discovery such an exciting blueprint for future psychiatric medicine. When the researchers blocked these specialized neurons, it didn’t change the subjects’ immediate, in-the-moment behavior during a crisis, nor did it alter their vital heart or breathing rates. Instead, silencing the cells simply prevented the acute stress from hardening into long-term, chronic anxiety later on. This suggests that targeting these cells therapeutically could create a highly precise medication that cures persistent trauma without numbing a patient’s natural emotions or disrupting their body’s health.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this anxiety and neuroscience research news
Author: Chelsea Bryant
Source: St. Jude Children’s Research Hospital
Contact: Chelsea Bryant – St. Jude Children’s Research Hospital
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Autonomic C1 neurons promote anxiety via activation of vlPAG” by Brittany G. Pittman, Carlos Fernández-Peña, Heather Sheppard, Lindsay A. Schwarz, Lourds M. Fernando, Rachel L. Pace. Neuron
DOI:10.1016/j.neuron.2026.06.012
Abstract
Autonomic C1 neurons promote anxiety via activation of vlPAG
Anxiety is an emotional state triggered by the anticipation of a threat. While acute anxiety favors survival by increasing preparedness against future danger, anxiety disorders impair health and negatively impact quality of life.
Despite extensive research, the etiology of anxiety disorders remains unresolved, limiting the improvement of therapeutic strategies to alleviate anxiety-related symptoms with increased specificity and efficacy.
Here, we applied intersectional tools to elucidate that activation of a small population of autonomic adrenergic neurons in the brainstem, named C1 cells, promotes anxiety-related behaviors. Calcium-based imaging revealed that these cells are activated in stressful situations, while inhibition of C1 neurons reduced fear responses and prevented enhancement of anxiety.
These findings implicate C1 neurons as a key brain-body hub for the promotion of anxiety-related behaviors and suggest that targeted inhibition of this circuit could be therapeutically advantageous.
