Further, in the chronic, unpredictable, mild stress model of depression, increased levels of CXCL1 mRNA and protein in the hippocampus [118] and protein in cerebrospinal fluid [119], respectively, and increased expression of its cognate receptor CXCR2 [119], coincided with decreased sucrose preference that was reversed by the selective serotonin reuptake inhibitor (SSRI) fluoxetine [119]. This evidence concerns the gene CXCR2 and depressive disorder.