Scientists have identified a specific brain circuit that appears to play a major role in anxiety, depression-like behaviors, and social withdrawal. Even more striking, they found that restoring balance within this circuit was enough to reverse several of these behaviors in mice.
The research was led by Juan Lerma and his team at the Synaptic Physiology laboratory at the Institute for Neurosciences (IN), a joint center of the Spanish National Research Council (CSIC) and Miguel Hernández University (UMH) of Elche. Their findings were published in iScience.
A Key Brain Region Linked to Emotional Disorders
The study focused on the amygdala, a region of the brain that helps regulate emotions such as fear and anxiety. Researchers discovered that a particular group of neurons within this area can have a powerful influence on emotional and social behavior.
“We already knew the amygdala was involved in anxiety and fear, but now we’ve identified a specific population of neurons whose imbalanced activity alone is sufficient to trigger pathological behaviors,” explains Lerma.
To investigate, the team used genetically engineered mice that produced unusually high levels of the Grik4 gene. This change increased the number of GluK4 glutamate receptors, making certain neurons more excitable than normal.
The mouse model was originally developed by the same laboratory in 2015. These animals display behaviors resembling anxiety and social withdrawal, traits often associated with conditions such as autism and schizophrenia.
Restoring Balance Reversed Anxiety
The scientists then targeted neurons in a part of the amygdala known as the basolateral amygdala. By normalizing Grik4 gene activity in this region, they restored communication with inhibitory neurons in the centrolateral amygdala called regular firing neurons.
The effects were dramatic.
“That simple adjustment was enough to reverse anxiety-related and social deficit behaviors, which is remarkable,” says Álvaro García, first author of the study.
To measure the impact, the team combined electrophysiological recordings with behavioral tests commonly used to assess anxiety, depression, and social interaction in rodents. These tests examine behaviors such as willingness to explore open spaces and interest in unfamiliar mice.
Using genetic engineering techniques and modified viruses, the researchers selectively corrected the neural imbalance in the basolateral amygdala. They then observed improvements in both brain activity and behavior.
Findings Extend Beyond a Single Genetic Model
The researchers also wanted to know whether the same mechanism might be involved in anxiety more broadly.
To test this, they applied the same intervention to wild-type mice that naturally displayed elevated anxiety levels. The treatment reduced anxiety in those animals as well.
“This validates our findings and gives us confidence that the mechanism we identified is not exclusive to a specific genetic model, but may represent a general principle for how these emotions are regulated in the brain,” Lerma adds.
The result suggests that the neural pathway identified in the study may be part of a more universal system involved in emotional regulation.
New Possibilities for Targeted Treatments
Not every symptom improved after the intervention. The mice continued to show deficits in object recognition memory, indicating that additional brain regions may contribute to certain aspects of these disorders.
The researchers point to areas such as the hippocampus as possible contributors that were not affected by the treatment.
Even so, the findings offer a promising direction for future therapies.
“Targeting these specific neural circuits could become an effective and more localized strategy to treat affective disorders,” the researcher concludes.
The study was supported by funding from the Spanish State Research Agency (AEI) — Spanish Ministry of Science, Innovation and Universities, the Severo Ochoa Excellence Program for Research Centers at the Institute for Neurosciences CSIC-UMH, the European Regional Development Fund (ERDF), and the Generalitat Valenciana through the PROMETEO and CIPROM programs.