SLC6A4 and Anxiety: The mid-rostrocaudal DRD is considered a stress- and anxiety-responsive subregion of the DR (Lowry et al., 2005, 2008; Donner et al., 2016, 2018, 2020; Hassell et al., 2017), and previous studies have demonstrated that single or “two hit” stressors increase both Tph2 and Slc6a4 mRNA expression in this region (Gardner et al., 2009a,b; Donner et al., 2018).