Sour has been studied almost exclusively as an aversive taste modality. Yet recent work in Drosophila demonstrates that specific carboxylic acids are attractive at ecologically relevant concentrations. Here, we demonstrate that lactic acid is an appetitive and energetic tastant, which stimulates feeding through activation of sweet gustatory receptor neurons (GRNs). This activation displays distinct, mechanistically separable stimulus onset and removal phases. Ionotropic receptor 25a (IR25a) primarily mediates the onset response, which shows specificity for the lactate anion and drives feeding initiation through proboscis extension. Conversely, sweet gustatory receptors (Gr64a-f) mediate a non-specific removal response to low pH that primarily impacts ingestion. While mutations in either receptor family have marginal impacts on feeding, lactic acid attraction is completely abolished in combined mutants. Thus, specific components of lactic acid are detected through two classes of receptors to activate a single set of sensory neurons in physiologically distinct ways, ultimately leading to robust behavioral attraction.

酸几乎完全被研究为一种厌恶的味道形式。然而，最近在果蝇中的工作表明特定的羧酸在生态相关浓度下具有吸引力。在这里，我们证明乳酸是一种食欲和精力充沛的促味剂，它通过激活甜味觉受体神经元 (GRN) 来刺激进食。这种激活显示了不同的、机械上可分离的刺激开始和消除阶段。离子型受体 25a (IR25a) 主要介导起效反应，它显示出对乳酸阴离子的特异性，并通过长鼻延伸来驱动进食开始。相反，甜味觉受体 (Gr64a-f) 介导对低 pH 值的非特异性去除反应，主要影响摄入。虽然任一受体家族的突变对摄食有边际影响，但乳酸吸引在组合突变体中完全消除。因此，