Have you ever stood in a high place and felt the instinctive drive to step back and find safety? Researchers studying the brains of mice may have found the neurons responsible for such deep-seated anxieties.
In a study published Jan. 31 in Neuron, a team of scientists at UC San Francisco and Columbia University Medical Center report discovering previously unknown “anxiety cells” in the mouse hippocampus.
The hippocampus is known for forming new memories of events and places, but recent research has shown that parts of the hippocampus also play a powerful role in our emotional lives as well.
In the new study, experiments using live imaging of the brains of freely moving mice revealed neurons in the hippocampus that respond strongly when mice wander into exposed regions of an elevated maze or open field, areas that typically triggers strong anxiety in rodents.
The scientists then showed that these “anxiety neurons” are connected directly to regions of another brain region called the hypothalamus that trigger avoidance behavior in animals. To test the function of these neural projections, the team used a technology called optogenetics to allow them to control signals flowing from the anxiety neurons to the hypothalamus using beams of light while observing the animals’ behavior.
They found that suppressing the anxiety neuron pathway made animals more comfortable spending time in environments that usually frighten them, while stimulating the same neural connections made mice behave with anxiety even in safely enclosed spaces.
“This is exciting because it represents a direct, rapid pathway in the brain that lets animals respond to anxiety-provoking places without needing to go through the higher-order brain regions,” said Mazen Kheirbek, PhD, an assistant professor of psychiatry and member of the UCSF Weill Institute for Neurosciences, whose lab conducted the study in collaboration with neuroscientist René Hen, PhD, of Columbia University Medical Center.
The researchers say that this new discovery of hard-wired anxiety circuits that don’t depend on learning or higher brain functions could help researchers hoping to understand anxiety disorders in humans, and potentially lead to new targeted therapies in the future.