Acid taste detection in Drosophila. Sandhya Charlu¹, Zev Wisotsky², Adriana Medina³, Anupama Dahanukar^1,2,3. 1) Biomedical Sciences Graduate Program, UC Riverside; 2) Interdepartmental Neuroscience Program, UC RIverside; 3) Department of Entomology, IIGB, UC Riverside.

   The taste system acts as the first line of defense against ingestion of harmful substances. Stimuli that could cause damage to internal organs are usually signaled as aversive by the taste system. Acids, which are often present in spoilt or unpalatable foods, are perceived as sour by humans but little is understood about their detection by the Drosophila taste system. Here we identify the behavioral and cellular responses of the fly to acid tastants. Using two independent behavioral assays we find that acid tastants inhibit behavioral responses to sucrose, suggesting that they are recognized as deterrents. Recordings from individual taste hairs in the labellum reveal that a subset of bitter taste neurons is activated by acidic pH. Correspondingly, flies in which bitter taste neurons are genetically silenced show reduced aversion to mixtures of acids with sucrose. Nevertheless, such flies still retain the ability to reject high concentrations of acids. We therefore investigated the effect of acids on the activity of sweet taste neurons, and found that sucrose response is inhibited in a pH-dependent manner. Sucrose response inhibition occurs directly on sweet taste neurons and does not rely on the presence of functional bitter taste neurons. The inhibitory effect can be alleviated by an increase in the concentration of sucrose, suggesting that sweet taste neurons can calibrate information about the sugar content as well as the pH of a food substrate. Together, our results reveal two independent cellular pathways for sensing and responding to acid tastants. Currently, we are investigating the molecular mechanisms that underlie acid detection by taste neurons.