Chronic stress-induced dendritic reorganization and abundance of synaptosomal PKA-dependent CP-AMPA receptor in the basolateral amygdala in a mouse model of depression

Chronic stress is a precipitating factor for disorders including depression. The basolateral amygdala (BLA) is a critical substrate that interconnects with stress-modulated neural networks to generate emotion- and mood-related behaviors. The current study shows that 3 h per day of restraint stress for 14 days caused mice to exhibit long-term depressive behaviors, manifested by disrupted sociality and despair levels, which were rescued by fluoxetine. These behavioral changes corresponded with morphological and molecular changes in BLA neurons, including chronic stress-elicited increases in arborization, dendritic length, and spine density of BLA principal neurons. At the molecular level, calcium-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (CP-AMPARs) within the synaptosome exhibited an increased GluR1:GluR2 subunit ratio. We also observed increased GluR1 phosphorylation at Ser 845 and enhanced cyclic AMP-dependent protein kinase (PKA) activity in the BLA. These molecular changes reverted to the basal state post-treatment with fluoxetine. The expression of synaptophysin (SYP) and postsynaptic density protein 95 (PSD-95) at BLA neuronal synapses was also enhanced by chronic stress, which was reversed post-treatment. Finally, chronic stress-provoked depressive behavior was overcome by local blockage of CP-AMPARs in the BLA via stereotaxic injection (IEM-1460). Chronic stress-elicited depressive behavior may be due to hypertrophy of BLA neuronal dendrites and increased of PKA-dependent CP-AMPAR levels in BLA neurons. Furthermore, fluoxetine can reverse chronic stress-triggered cytoarchitectural and functional changes of BLA neurons. These findings provide insights into depression-linked structural and functional changes in BLA neurons.