Figure 8. Notch activation induced by odorant mixtures depends on inhibitory cross talk between responding olfactory receptor neurons.

A. 4 day old N-GV UAS.dGFP/+ flies which had been raised on dextrose food were exposed to 1:100 dilutions of odors (for 4 days) or to 5% CO₂ (for 3 days). Seven to twelve flies were assayed for each odor. The fraction of flies with Notch activity in the indicated glomeruli is presented in blue. The activity of the ORNs in response to puffs of the corresponding odor is shown in red. With the exception of 3-octanol this is electrophysiological data (de Bruyne et al., 2001; Hallem and Carlson, 2006) and the height of the red bars reflects spike number. Glomeruli activated by 3-octanol were determined by calcium imaging (Wang et al., 2003). No obvious changes in Notch activation were observed for the following odors: phenethyl acetate, methyl salicylate, cis-vaccenyl acetate, octyl aldehyde.

B–H. N-GV UAS.dGFP/+ flies raised to eclosion and aged for four days on dextrose food were exposed for four days to different concentrations of geranyl acetate and pentyl acetate as indicated, or to paraffin oil alone. Surface plots of Notch activation in an antennal lobe are depicted in B–G, with the height and color of the peaks being proportional to pixel intensity. Orientation of the antennal lobe is depicted in B: M, medial; D, dorsal; L, lateral; V, ventral. Addition of pentyl acetate to geranyl acetate at concentrations of 1:50 and 1:5 caused stepwise reductions in dGFP accumulation in VA6 (asterisk). Conversely, there is an increase in dGFP accumulation in VA3 (arrowhead). Box plots of the fluorescence in VA6 are presented in H, illustrating the reduction in Notch activation in VA6 induced by pentyl acetate (GA, geranyl acetate; PA, pentyl acetate). The number of samples analyzed was: oil, 24; PA 1:50, 24; GA 1:1000, 32; GA 1:1000 PA 1:5, 32; GA 1:1000 PA 1:50, 30.