Tph2-/- mice have also been reported to have altered behaviors such as increased conditioned fear responses, aggression, depression-like behaviors, and impairment of maternal care (Savelieva et al., 2008; Alenina et al., 2009; Mosienko et al., 2012; for review, see Lesch et al., 2012). This evidence concerns the gene TPH2 and major depressive disorder.