SLC6A4 and depressive disorder: Similarly, constitutive SERT-KO mice, with elevated 5-HT levels, present anxiety-like and depression-like behaviors such as reduced locomotor activity in the open-field, increased latency-to-feed in the novelty-suppressed-feeding test and social-interaction deficits (Lira et al., 2003; Ansorge et al., 2004; Kalueff et al., 2007).