evidence from animal models of depression that hippocampal neurogenesis is decreased during the behavioral syndrome, that antidepressants increase neurogenesis, and that BDNF has antidepressant-like properties in these animal models (25). BDNF expression is increased in animals by treatment with antidepressants or lithium, and BDNF SNPs have repeatedly been implicated in genetic risk for BD, although the effect size is quite limited, e.g. odds ratio of 1.1 (26-29).
