5-Hydroxytryptamine (5-HT, also commonly known as serotonin) is synthesized in enterochromaffin cells in the intestine and in serotonergic nerve terminals. In the periphery, 5-HT mediates gastrointestinal motility, platelet aggregation, and contraction of blood vessels. Many functions of the central nervous system are influenced by 5-HT, including sleep, motor activity, sensory perception, arousal, and appetite. A family of 12 GPCRs and one ion channel mediate the biological effects of 5-HT (Hoyer et al., 1994). 5-HT2A which couples to Gq/11 is expressed throughout the central nervous system in the neocortex and olfactory tubercle. 5-HT2A receptor agonists may have important clinical value in the trea™ent of various disorders, such as depression, anxiety, bipolar disorder, and schizophrenia. GenScript's cloned human 5-HT2A–expressing cell line is generated in the CHO-K1 host.