Amygdala Neural Encoding Of Anxiety In Mouse Brain

Anxiety is a normal emotional response to potential threats or stresses. While excessive anxiety is a kind of psychological disease. Amygdala plays a key role in arising and mediating anxiety. Recently, basolateral amygdala (BLA) has been studied as one of the critical components in the neural circuitry medicating anxiety-related states and behaviors. Anxiety-related physiological and behavioral responses will change, when BLA activation increases or decreases. However, the neural mechanisms that mediate anxiety states and behaviors remain unclear in the BLA.To investigate the role of BLA in anxiety-related behaviors, we carried out multi-channel in vivo recordings in the BLA of freely behaving mice combining the anxiety behavior tests. In the open field test mice showed anxiety-like behaviors including thigmotaxis, jump and defecation. While recording BLA activity simultaneously, we found a group of neurons fire tonically in the open field test. The firing patterns of these neurons displayed a characteristic slow onset and progressively firing rates. The firing rate decreased quickly when mice were taken out of the open field test environment. Moreover, the change of firing rates of these neurons was similar with anxiety-like behaviors. Mice did not show anxiety-like behavior and the firing rate remained a low level in the enriched box test as a control. In addition, these BLA neurons can be invoked by any open field-like environment and suppressed by introduced external stimuli. More importantly, results revealed that excitability of BLA anxiety-related neurons increased progressively during repeated exposures to the open field test environment, which was consistent with the increase of anxiety-like behaviors.To further investigate the relationship between the group of BLA neurons and anxiety-like behavior, we exploited drugs to enhance or inhibit the mice anxiety level in open field test and observed the activity of BLA anxiety-related neurons. It has been reported that drugs enhancing GABAA receptor in the central nervous system (midazolam) can inhibit anxiety-like behaviors, while drugs blocking GABAA receptor (picrotoxin) can promote anxiety-like behaviors. In the midazolam tests, we found two BLA anxiety-related neurons exhibit differential responses. One neuron showed the change in firing rate in open field test. The other displayed an altered firing pattern.These results demonstrate that there is a type of BLA neurons, whose activities are highly correlated with anxiety-like behaviors induced by open field test.