TAAR9 is a trace amine-associated receptor predominantly expressed in olfactory epithelium neurons, where it functions as a G protein-coupled receptor detecting volatile amine odorants 1. In humans, TAAR9 is one of six functional TAAR isoforms and represents part of a genomic cluster on chromosome 6 2. The receptor selectively binds trace amines including β-phenylethylamine and N,N-dimethylcyclohexylamine, but notably does not respond to triethylamine, cadaverine, or spermidine in human orthologs, unlike rodent homologs 3. Structurally, TAAR9 possesses two distinct entry tunnels with vestibular binding pockets, a feature that challenges previous single-tunnel models of olfactory receptors 4. Upon amine binding, TAAR9 activates adenylate cyclase through G protein coupling (GNAL in mature neurons, GNAS in immature neurons), triggering cAMP signaling and membrane depolarization to transmit odorant signals [UniProt]. Beyond olfaction, emerging evidence indicates TAAR9 has broader physiological roles. TAAR9 knockout in rats increased hippocampal serotonin levels and altered grooming behavior microstructure, suggesting involvement in monoaminergic regulation 5. Additionally, TAAR9 expression is detected in pancreatic islets, potentially contributing to metabolic regulation 6, and the receptor is expressed in immune cells, indicating possible immunomodulatory functions 7.