Comparison of High and Low Affinity Serotonin 1A Receptors by PET In Vivo in Nonhuman Primates

Serotonin (5-HT) 1A receptors exist in high and low affinity states. Agonist ligands bind preferentially to the high affinity state receptors, providing a more functionally relevant measure than antagonist binding. We now report comparison of 5-HT1A binding in vivo using both [11C]CUMI-101 (agonist) and [11C]WAY100635 (antagonist) in nonhuman primates. PET studies show that both tracers bind to known 5-HT1A receptor (5-HT1AR)-rich regions of baboon brain. The binding (BPF) of [11C]CUMI-101 was lower on an average of 55% across the regions of interest (ROIs) compared to [11C]WAY100635. This ratio is consistent with the in vitro binding data of agonist and antagonist 5-HT1AR ligands previously reported. Keywords:: 5-HT1A receptor (5-HT1AR), positron emission tomography, brain imaging