CX3CR1 and major depressive disorder: Moreover, we evaluated the impact of chronic administration of various antidepressant drugs: tianeptine – an atypical antidepressant, which enhances re-uptake of serotonin; venlafaxine – a serotonin – norepinephrine reuptake inhibitor (SNRI); and fluoxetine – a selective serotonin reuptake inhibitor (SSRI), on the gene expression and protein levels of CX3CL1 and CXCL12 and their receptors CX3CR1, CXCR4, CXCR7 in the hippocampus and the frontal cortex of adult rats in an animal model of depression.