Most natural odors are complex mixtures of volatile components, competing to bind odorant receptors (ORs) expressed in olfactory sensory neurons (OSNs) of the nose. To date, surprisingly little is known about how OR antagonism shapes neuronal representations in the detection layer of the olfactory system. Here, we investigated its prevalence, the degree to which it disrupts OR ensemble activity, and its conservation across phylogenetically related ORs. Calcium imaging microscopy of dissociated OSNs revealed significant inhibition, often complete attenuation, of responses to indole—a commonly occurring volatile associated with both floral and fecal odors—by a set of 36 tested odorants. To confirm an OR mechanism for the observed inhibition, we performed single-cell transcriptomics on OSNs exhibiting specific response profiles to a diagnostic panel of odorants and identified three paralogous receptors—Olfr740, Olfr741, and Olfr743—which, when tested in vitro, recapitulated OSN responses. We screened ten ORs from the Olfr740 gene family with ∼800 perfumery-related odorants spanning a range of chemical scaffolds and functional groups. Over half of these compounds (430) antagonized at least one of the ten ORs. OR activity fitted a mathematical model of competitive receptor binding and suggests normalization of OSN ensemble responses to odorant mixtures is the rule rather than the exception. In summary, we observed OR antagonism occurred frequently and in a combinatorial manner. Thus, extensive receptor-mediated computation of mixture information appears to occur in the olfactory epithelium prior to transmission of odor information to the olfactory bulb.

大多数天然气味是挥发性成分的复杂混合物，它们竞争结合鼻子嗅觉感觉神经元（OSN）中表达的气味受体（OR）。迄今为止，令人惊讶的是，人们对 OR 拮抗如何塑造嗅觉系统检测层中的神经元表征知之甚少。在这里，我们调查了它的流行程度、它破坏 OR 整体活动的程度，以及它在系统发育相关 OR 中的保守性。解离的 OSN 的钙成像显微镜显示，一组 36 种测试的气味剂对吲哚（一种与花香和粪便气味相关的常见挥发物）的反应有显着的抑制作用，通常是完全减弱。为了确认所观察到的抑制的 OR 机制，我们对 OSN 进行了单细胞转录组学，这些 OSN 对气味剂诊断组表现出特定的反应特征，并鉴定了三种旁系同源受体——Olfr740、Olfr741 和 Olfr743——在体外测试时，它们重现了OSN回应。我们从 Olfr740 基因家族中筛选了 10 个 OR，其中包含约 800 种香水相关气味剂，涵盖一系列化学支架和官能团。超过一半的这些化合物 (430) 拮抗十种 OR 中的至少一种。OR 活性符合竞争性受体结合的数学模型，表明 OSN 整体对气味混合物的反应标准化是规则而不是例外。总之，我们观察到 OR 拮抗作用频繁且以组合方式发生。因此，在气味信息传输到嗅球之前，嗅觉上皮细胞中似乎发生了广泛的受体介导的混合物信息计算。