The microarray and ethanol startle data presented above suggested that olfactory sensory acuity may be reduced during the development of rapid ethanol tolerance. Bilateral surgical removal of the third antennal segment that houses the majority of the olfactory sensory neurons was previously shown to block the ethanol olfactory startle response (Wolf et al., 2002), but we found that it also reduced ethanol absorption by an unknown mechanism (not shown), confounding this direct analysis of olfactory input to rapid tolerance. Or83b is an OR present in approximately 70% of all olfactory neurons that is required for both the localization to dendrites and function of co-expressed ORs as heteromeric ion channels (Benton et al., 2006; Sato et al., 2008). Or83b expression levels were markedly reduced by ethanol exposure (Fig. 5A). Surprisingly, flies harboring a targeted deletion of Or83b (Or83b1) exhibited a normal ethanol-induced olfactory startle response (PS for Berlin: 5.9 ± 0.46 mm/s, Or83b1: 5.1 ± 0.90 mm/s, p = 0.471, paired t-test, n = 6), suggesting that ethanol odor is detected by Or83b-independent means, presumably by the 30% of OR neurons
