In 2007, Braun et al. found expression of 4 ORs: OR5D18 (OR73), OR1A1 (hOR17-7/11), OR1G1 (hOR17-209), OR1E3 (hOR17-219) in microdissected human mucosal enterochromaffin cells and in a cell line derived from human enterochromaffin cells. Their studies revealed that the OR activation by the identified odorants cause Ca 2+ influx, elevation of intracellular free Ca 2+ levels, and, consequently, serotonin release, which stimulates the submucosal sensory branch of the enteric nervous system and, via inter- and motor neurons, control gut motility and chloride secretion by enterocytes. The odorant ligands of the identified ORs, OR1G1 and OR1E3, had already been deorphanized by Matarazzo et al. (2005) but Braun et al. were the first ones reporting agonists for the OR5D18 and OR1A1. They reported that OR1G1 is activated by thymol, geraniol, β-ionone, isoamyl acetate, and acetophenone, OR5D18 is activated by eugenol, OR1A1 is activated by geraniol, bourgeonal, and helional and OR1D2 is activated by bourgeonal ( Braun et al. 2007 ).