Hyperactivity of the Amygdala Mediates Depressive-Like Phenotypes and Decreased Serotonin Release

Abstract Clinical and preclinical studies have consistently demonstrated a correlation between hyperactivity of the amygdala and the onset of depression. However, the underlying mechanisms influencing serotonin levels a critical neurotransmitter implicated in depression and a primary target for selective serotonin reuptake inhibitors (SSRIs) remain inadequately understood. In this study, we employed a restrained inescapable shock (RIS) model to investigate these mechanisms in mice. The RIS paradigm elicited depressive-like phenotypes, increased c-Fos expression in the amygdala, diminished serotonin levels, and elevated corticosterone concentrations. Notably, chemogenetic inhibition of the amygdala mitigated depressive symptoms, reduced neuronal activity in this region, and restored serotonin levels. Anatomical analyses revealed a significant connectivity between the central amygdala (CeA) and the dorsal raphe nucleus (DRN). Fiber photometry recordings indicated that serotonergic neuronal activity in the DRN decreased in response to aversive stimuli, accompanied by amygdala activation following RIS, with no notable alterations in DRN GABAergic activity. These findings suggest that chronic stress may exacerbate amygdala hyperactivity, which subsequently inhibits serotonin release in the brain, potentially intensifying depressive states. Therefore, targeting amygdala hyperactivity may represent a novel therapeutic strategy for the management of stress-related depressive and anxiety disorders.