Neuromodulators were discovered through their abilities to regulate physiological BMN 673 order responses in organ or tissue preparations (Langley and Magnus, 1905). This search gained another dimension when peptides were found to belong to this class of transmitters. Then lipid mediators and other small molecules

were found to act as neuromodulators. In parallel, neuromodulator receptors were being defined by pharmacological means. Synthetic ligands were being developed and used to differentiate these receptor identities. A few receptors were even purified and their sequences determined. This culminated with the discovery that the β2-adrenergic receptor and the opsins share a seven transmembrane domains topology (7TMs) and some sequence similarities (Dixon et al., 1986). Since the sole link between these two receptors is the fact that they induce G protein-mediated cellular responses, this discovery suggested that GPCRs may belong to a supergene family. This suggestion was reinforced with the cloning of the first neuropeptide receptor (substance K receptor; Masu et al., 1987) and opened the door to the search for GPCRs by homology screening approaches such as low-stringency hybridization and degenerate polymerase chain reaction (PCR) (Bunzow et al., 1988; Libert et al., 1989). The receptors cloned via these strategies are by definition unmatched to natural ligands. They are “orphan” receptors.

But at that time, some 50 neuromodulators were known to exist but had no cognate cloned receptors. The cloning of the orphan GPCRs offered a solution to this problem. Everolimus mouse The approach was to express orphan GPCRs in cells in culture and to use these heterologous GPCRs as targets for matching to possible neuromodulators. Insights in the orphan GPCR tissue expression profile as well as random testing proved to be successful

in matching the first orphan GPCRs to known neuromodulators. The first deorphanized GPCRs, the 5HT-1A, and the D2 dopamine receptors were reported in 1988 (Bunzow et al., 1988; Fargin et al., 1988). This strategy was rapidly espoused worldwide and is now known as reverse pharmacology (Libert et al., 1991; Mills and Duggan, 1994). During the first part of the 90’s, application of the reverse pharmacology strategy led to the molecular PAK6 identification of many GPCRs (Civelli et al., 2006). These DNA sequences allowed for the determination of their definitive pharmacological profiles as well as for in-depth analyses of their sites of expression. In turn, these receptors DNA probes led to the discovery of sequentially related GPCRs and the blossoming of the GPCR subfamilies. Most often, the cloning of the GPCR genes have greatly extended the diversity of the subfamilies (Civelli et al., 2006). These discoveries have had lasting impact in the fields of pharmacological and pharmaceutical research. Concomitantly, the overall number of orphan GPCRs was steadily increasing due to the mining of the database of expressed sequence tagged cDNAs (Marchese et al.