Differential expression of hippocampal EphA4 and ephrinA3 in anhedonic-like behavior, stress resilience, and antidepressant drug treatment after chronic unpredicted mild stress

- Rats were exposed to 3 weeks stress and treated by 4 weeks fluoxetine administration.
- Hippocampal expression of EphA4 and ephrinA3 was dysregulated in stress susceptible rats but not in resilient rats.
- Fluoxetine restored dysregulation of EphA4 and ephrinA3 in drug response rats but not drug non-response rats.
- EphA4 and ephrinA3 were involved in stress regulation and antidepressant response.

Stress exposure is one of the major risk factors of depression, but the mechanism is not understood. While some individuals show resilience to stress exposure, antidepressants only partially reduce stress-induced depression in both humans and rodents. Stress could dysregulate the remodeling of neuronal dendrites and spines in hippocampus while antidepressants could recover the deficiency induced by stress. EphA4 and its ligand ephrinA3 are critical in the remodeling of neuronal dendrites and spines, but the relationship between ephrinA3/EphA4, stress-induced depression and antidepressants treatment is largely unknown. Based on a rat chronic unpredicted mild stress (CUMS) model, we investigated ephrinA3/EphA4 expression in stress susceptibility, stress resilience, treatment response and treatment resistance in rats. CUMS led to downregulation of EphA4 expression and upregulation of ephrinA3 expression in the hippocampus of stress-susceptible rats, but not in stress-resilient rats. Dysregulated EphA4 and ephrinA3 can be rescued by fluoxetine administration in drug responders, but not in fluoxetine resistant rats. These data provide insights into the potential role of EphA4 and ephrinA3 after stressor exposure, stress adaptation, fluoxetine response and drug treatment refraction.