develops from expresses sends synaptic output throughout has sensory dendrite in Gr63a Gr21a antennal lobe glomerulus V eo neuron antennal olfactory receptor neuron precursor Nbb adult antennal lobe receptor neuron unilateral antennal lobe receptor neuron antennal basiconic sensillum ab1 adult olfactory receptor neuron Gr21a/63a FlyBrain_NDB:10391 Adult unilateral odorant receptor neuron that expresses Gr21a and Gr63a (Couto et al., 2005; Kwon et al., 2007; Kaur et al., 2019; Benton et al., 2025). It responds to CO2 levels (Suh et al., 2004; Kwon et al., 2007). Its dendrite transduces signals from antennal basiconic sensillum ab1 and sends output to antennal glomerulus V (Benton et al., 2025). It develops from an Nbb precursor (Benton et al., 2025). There are around 30-40 of these cells on each side (Grabe et al., 2016; Benton et al., 2025). FBbt:00067064 fly_anatomy.ontology olfactory receptor neuron V ORN (Gr21a) DoOR:Gr21a.Gr63a FlyBrain_NDB:10390 Gr21a and Gr63a are only found in one ORN type and they are co-expressed (Kwon et al., 2006). ORN_V VFB:FBbt_00067064 adult olfactory receptor neuron Gr21a ORN ab1C ORN_V adult ORN Gr21a FBbt:00100336 carbon dioxide sensitive neuron