Ionotropic Receptors (IR) expressed in antennal sensory neurons in Drosophila are largely thought to act as odor-responsive ion channels. IRs are a subfamily of ionotropic glutamate receptors that do not bind glutamate. Some only form functional receptors in the presence of coreceptor IRs. The profile of expression of IRs, together with broadly expressed co-receptors underlies the precise odor-responsiveness of subpopulations of antennal neurons. (Adapted from FBrf0222310).