Positron emission tomography (PET) studies, typically utilizing the selective radiotracer for 5-HT1A receptors, [11C]WAY-100635, have noted lowered levels of 5-HT1A receptor availability (BPND) within these regions in MDD as well as alterations in 5-HT1A availability pre- and post-treatment (Bhagwagar et al., 2004; Drevets et al., 2007; Moses-Kolko et al., 2007; Hirvonen et al., 2008; Kautzky et al., 2017). Here, HTR1A is linked to major depressive disorder.