Neuronal Assemblies In The Amygdala Are Correlated To Resilience And Vulnerability To Chronic Stress For Major Depression

Background: Chronic stressful life is thought to be main etiology for major depression that is featured by persistent negative mood.Many individuals demonstrate a resistance to chronic stress with no suffering from depression,i.e.,resilience.Endogenous cellular mechanisms underlying resilience versus major depression remain unknown.As the amygdala is believed to regulate negative mood,we propose to examine the functional change of neuronal circuits in the amygdala in major depression versus resilience mice that are treated by chronic stress.Methods: Mice were treated by the chronic unpredictable mild stress(CUMS)for three weeks.Their expressions of depression-like behaviors or resilience was confirmed by seeing whether their emotion-related behaviors are altered significantly in sucrose preference,Y-maze and forced swimming tests.Mice from depression,resilience and control were studied in terms of glutamatergic and GABAergic neuronal activities in the central and lateral amygdala by cell electrophysiology.Results: GABAergic neurons in the central amygdala from CUMS-induced depressionlike mice show the increases of excitability and excitatory inputs from the lateral amygdala as well as a decrease of their interaction,compared to those in control mice.Although excitatory input and inhibitory input are similar in CUMS-induced depression and resilience mice,GABAergic neurons in resilience mice show an up-down regulation in encoding ability.In addition,glutamatergic and GABAergic neurons in the lateral amygdala from CUMS-induced depression-like mice express the increase of excitability,in comparison with those in control mice.Conclusions: An upregulated neuronal function in CUMS-induced depression-like mice may cause the strengthened outputs of GABAergic neurons in the central amygdala,whose inhibitory projection toward other areas in the limbic system leads to negative mood.The up-down regulation in the output of amygdala GABAergic neurons in resilience mice may permit the disappearance of their inhibitory output in high neuronal activity,i.e.,a turnover of depression to resilience.