Probable gustatory receptor which mediates acceptance or avoidance behavior, depending on its substrates (By similarity). Atypical expression suggests also nongustatory roles in the nervous system and tissues involved in proprioception, hygroreception, and other sensory modalities. It is also possible that it has chemosensory roles in the detection of internal ligands. Isoforms A and E have taste neuron-specific expression restricted to the labial palps, the internal taste organs in the pharynx, and the legs. In addition to expression in a large number of taste neurons, isoform A is also expressed in a few nonchemosensory neurons, including the campaniform sensilla of the wing, leg stretch receptors, and multiple dendritic neurons in the abdomen. Isoform B is the only receptor not expressed in gustatory receptor neurons in the labellum. We observe expression of this receptor in a single large cell at the base of each maxillary palp, in campaniform sensilla of the wing, and multiple dendritic neurons in the abdomen. Isoform C is expressed by many gustatory receptor neurons in the labial palps, the pharyngeal taste clusters, and taste neurons in the legs. In addition, isoform C expressed in a single cell at the base of the maxillary palps, neurons in the Johnston's organ (JO), campaniform sensilla of the wing, stretch receptors and the femoral chordotonal organ of the legs, and multiple dendritic neurons in the abdomen.Isoform D is expressed in a small number of gustatory receptor neurons in the labial palps, the ventral cibarial sense organ (VCSO), and legs. Atypical expression is observed in three neurons in the arista, campaniform sensilla of the wing, stretch and femoral chordotonal organ receptors in the legs, and multiple dendritic neurons in the abdomen. In larvae, Isoform A is expressed in neurons of the terminal external chemosensory organ and the dorsal external chemosensory organ; and isoform E is expressed in neurons of the terminal external chemosensory organ. Belongs to the insect chemoreceptor superfamily. Gustatory receptor (GR) family. Gr66a subfamily.