The monoamine 5-hydroxytryptamine (serotonin, 5-HT) is a neurotransmitter, which acts via seven families of serotonin receptors. All of these, except 5-HT3, are G protein-coupled receptors. We have been focusing on studying 5-HT1A receptor, which is the most widespread of all serotonin receptors. We have found that fluorescently labelled serotonergic ligand NAN-190 is suitable for the characterization of ligand binding to 5-HT1A receptors in budded baculovirus particles. Our experiments have also shown that co-expression of 5-HT1A and αi+βγ is possible in a baculovirus display system and we can use this to study the effects of Mn2+ and guanine nucleotides on high affinity ligand binding to these signaling complexes (Tõntson et al. 2014).