HTR1A and major depressive disorder: 11C-WAY-100635 (N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl)-cyclohexane carboxamide) and 18F-MPPF (2'-Methoxyphenyl-(N-2'-pyridinyl)-p-18F-fluoro-benzamidoethylpiperazine) are antagonistic radioligands for 5-HT1A receptors and have been employed in positron emission tomography (PET) evaluation of in vivo 5-HT1A availability in patients with depression (Aznavour and Zimmer, 2007; Pillai et al., 2018; Langenecker et al., 2019; Buchecker et al., 2020).