After using the elevated plus maze—certain sections of which are difficult for mice to interpret—the team opted for a successive alleys test, which offers a linear progression toward increasingly aversive compartments. In this test, astrocyte calcium activity gradually increased as the rodents moved forward, reflecting their growing perception of the threat.
“Some didn’t get very far, others stopped halfway, and others made it all the way to the end,” explained Ciaran Murphy-Royal, also an assistant professor in the Department of Neuroscience at the Faculty of Medicine at University of Montreal. “The most anxious mice reach their maximum activity level much sooner, and as soon as they do, they stop exploring. In fact, these mice exhibit consistently high levels of anxiety in various tests, which corresponds to what is known in humans as trait anxiety.”
The team then studied how the brain reacts when a new element is introduced into an environment that has become familiar. The astrocytes adapted very quickly. After a single exploration, the warning signal disappears as soon as the environment is no longer perceived as threatening, suggesting that astrocytes are fast and dynamic. In the basolateral amygdala, their anxiety-related calcium activity proved to be more precise than that of the neurons, despite the neurons being highly active.
They then used this signal to train a decoder capable of determining whether a mouse was in an anxiogenic area. Notably, the astrocyte signal outperformed neuronal signals in predicting the mice’s location in another maze. By directly manipulating astrocyte calcium activity, Murphy-Royal’s team demonstrated a causal relationship: when calcium levels were increased, the mice exhibited markedly more anxious behaviour.
