Department of Entomology, Center for Chemical Ecology, 105 Chemical Ecology Laboratory, Penn State University, University Park, PA 16802, USA.
Chem Senses. 2012 May;37(4):299-313. doi: 10.1093/chemse/bjr122. Epub 2012 Jan 9.
We are proposing that the "relative" abundances of the differently tuned pheromone-component-responsive olfactory receptor neurons (ORNs) on insect antennae are not a result of natural selection working to maximize absolute sensitivity to individual pheromone components. Rather, relative abundances are a result of specifically tuned sensillum-plus-ORN units having been selected to accurately transduce and report to the antennal lobe the maximal ranges of molecular flux imparted by each pheromone component in every plume strand. To not reach saturating stimulus flux levels from the most concentrated plume strands of a pheromone blend, the dendritic surface area of the ORN type that is tuned to the most abundant component of a pheromone blend is increased in dendritic diameter in order to express a greater number of major pheromone component-specific odorant receptors. The increased ability of these enlarged dendrite, major component-tuned ORNs to accurately report very high flux of its component results in a larger working range of stimulus flux able to be accurately transduced by that type of ORN. However, the larger dendrite size and possibly other high-flux adjustments in titers of pheromone-binding proteins and degrading enzymes cause a decrease in absolute sensitivity to lower flux levels of the major component in lower concentration strands of the pheromone blend. In order to restore the ability of the whole-antenna major pheromone component-specific channel to accurately report to its glomerulus the abundance of the major component in lower concentration strands, the number of major component ORNs over the entire antenna is adjusted upward, creating a greater proportion of major component-tuned ORNs than those tuned to minor components. Pheromone blend balance reported by the whole-antennal major and minor component channels in low plume-flux strands is now restored, and the relative fluxes of the 2 components occurring in both low- and high-flux strands are thereby accurately reported to the component-specific glomeruli. Thus, we suggest that the 2 phenomena, dendrite size and relative numbers of differentially tuned ORNs are linked, and both are related to wide disparities in molecular flux ranges occurring for the more abundant and less abundant components in the pheromone blend plume strands.
我们提出，昆虫触角上不同调谐的信息素成分响应嗅觉受体神经元（ORNs）的“相对”丰度不是自然选择的结果，旨在最大限度地提高对单个信息素成分的绝对敏感性。相反，相对丰度是特定调谐的感觉器官加-ORN 单元被选择的结果，以准确地转导和向触角叶报告每个信息素成分在每个羽流束中赋予的最大分子通量范围。为了不从信息素混合物中最浓缩的羽流束达到饱和刺激通量水平，对信息素混合物中最丰富成分调谐的 ORN 类型的树突表面积通过增加树突直径而增大，以表达更多的主要信息素成分特异性气味受体。这些增大的树突、主要成分调谐的 ORN 准确报告其成分的非常高通量的能力增加，导致能够由该类型的 ORN 准确转导的刺激通量的工作范围更大。然而，较大的树突尺寸和可能的其他高流量调整，如信息素结合蛋白和降解酶的滴度，导致对信息素混合物中较低浓度羽流束中主要成分较低通量水平的绝对敏感性降低。为了恢复整个触角主要信息素成分特异性通道准确报告其小球体内主要成分在较低浓度羽流束中的丰度的能力，整个触角上的主要成分 ORN 数量向上调整，从而创造了比调谐次要成分的 ORN 更大比例的主要成分调谐 ORN。在低羽流通量羽流中，整个触角的主要和次要成分通道报告的信息素混合物平衡现在得以恢复，并且在低通量和高通量羽流中发生的两种成分的相对通量被准确报告给特定成分的小球体。因此，我们认为，这两种现象，树突大小和差异调谐 ORN 的相对数量是相关的，并且都与信息素混合物羽流束中更丰富和较不丰富成分的分子通量范围的巨大差异有关。
