SLC6A4 and Anxiety: In ovariectomized female rhesus monkeys estradiol replacement to mid-follicular levels decreases anxiety-like behaviors in subordinate females in a manner dependent on the polymorphism found in the promoter region of the SLC6A4 gene that encodes the 5HT transporter (5HTT) that has been linked to risk for stress-related psychopathology in humans [57, 72].