SLC6A4 and Anxiety: However, the Wistar-Kyoto rats, considered as more anxious, have been reported to have lower levels of 5-HTT binding sites in the hippocampus when compared with the less anxious spontaneously hypertensive rats (Pollier et al., 2000), and animals that are bred for high anxiety-related behaviour in the elevated plus-maze show an increased number of 5-HTT binding sites in the hippocampus (Keck et al., 2005).