Strong emotions such as fear and anxiety tend to be accompanied and reinforced by measurable bodily changes including increased blood pressure, heart rate and respiration, and dilation of the eyes’ pupils. These so-called “physiological arousal responses” are often abnormally high or low in psychiatric illnesses such as anxiety disorders and depression. Now scientists at the UNC School of Medicine have identified a population of brain cells whose activity appears to drive such arousal responses.
The scientists, whose study is published in Cell Reports, found that artificially forcing the activity of these brain cells in mice produced an arousal response in the form of dilated pupils and faster heart rate, and worsened anxiety-like behaviors.
The finding helps illuminate the neural roots of emotions, and point to the possibility that the human-brain counterpart of the newly identified population of arousal-related neurons might be a target of future treatments for anxiety disorders and other illnesses involving abnormal arousal responses.
“Focusing on arousal responses might offer a new way to intervene in psychiatric disorders,” said first author Jose Rodríguez-Romaguera, PhD, assistant professor in the UNC Department of Psychiatry and member of the UNC Neuroscience Center, and co-director of the Carolina Stress Initiative at the UNC School of Medicine.
Rodríguez-Romaguera and co-first author Randall Ung, PhD, an MD-PhD student and adjunct assistant professor in the Department of Psychiatry, led this study when they were members of the UNC laboratory of Garret Stuber, PhD, who is now at the University of Washington.
“This work not only identifies a new population of neurons implicated in arousal and anxiety, but also opens the door for future experiments to systematically examine how molecularly defined cell types contribute to complex emotional and physiological states,” Stuber said. “This will be critical going forward for developing new treatments for neuropsychiatric disorders.”
Anxiety disorders, depression, and other disorders featuring abnormally high or low arousal responses affect a large fraction of the human population, including tens of millions of adults in the United States alone. Treatments may alleviate symptoms, but many have adverse side effects, and the root causes of these disorders generally remain obscure.
Untangling these roots amid the complexity of the brain has been an enormous challenge, one that laboratory technology has only recently begun to surmount.
Rodríguez-Romaguera, Ung, Stuber and colleagues examined a brain region within the amygdala called the BNST (bed nucleus of the stria terminalis), which has been linked in prior research to fear and anxiety-like behaviors in mice.
Increasingly, scientists view this region as a promising target for future psychiatric drugs. In this case, the researchers zeroed in on a set of BNST neurons that express a neurotransmitter gene, Pnoc, known to be linked to pain sensitivity and more recently to motivation.
The team used a relatively new technique called two-photon microscopy to directly image BNST Pnoc neurons in the brains of mice while the mice were presented with noxious or appealing odors — stimuli that reliably induce fear/anxiety and reward behaviors, respectively, along with the appropriate