In mouse models for depression (such as mice with mutations in serotonin receptor 5HT1A or mice treated with unpredictable chronic mild stress or chronic corticosterone), alterations in hippocampal neurogenesis were not consistently observed (Santarelli et al., 2003; Surget et al., 2008; David et al., 2009); neither was an elevation in neurogenesis associated with an antidepressant effect (Fuss et al., 2010; Sahay et al., 2011). This evidence concerns the gene HTR1A and major depressive disorder.