Presynaptic gain control drives sweet and bitter taste integration in Drosophila.

The sense of taste is critical in determining the nutritional suitability of foods. Sweet and bitter are primary taste modalities in mammals, and their behavioral relevance is similar in flies. Sweet taste drives the appetitive response to energy sources, whereas bitter taste drives avoidance of potential toxins and also suppresses the sweet response [1, 2]. Despite their importance to survival, little is known about the neural circuit mechanisms underlying integration of sweet and bitter taste. Here, we describe a presynaptic gain control mechanism in Drosophila that differentially affects sweet and bitter taste channels and mediates integration of these opposing stimuli. Gain control is known to play an important role in fly olfaction, where GABAB receptor (GABABR) mediates intra- and interglomerular presynaptic inhibition of sensory neuron output [3-5]. In the taste system, we find that gustatory receptor neurons (GRNs) responding to sweet compounds express GABABR, whereas those that respond to bitter do not. GABABR mediates presynaptic inhibition of calcium responses in sweet GRNs, and both sweet and bitter stimuli evoke GABAergic neuron activity in the vicinity of GRN axon terminals. Pharmacological blockade and genetic reduction of GABABR both lead to increased sugar responses and decreased suppression of the sweet response by bitter compounds. We propose a model in which GABA acts via GABABR to expand the dynamic range of sweet GRNs through presynaptic gain control and suppress the output of sweet GRNs in the presence of opposing bitter stimuli.

Chu B ，Chui V ，Mann K ，Gordon MD ... -  《-》

Starvation-Induced Depotentiation of Bitter Taste in Drosophila.

LeDue EE ，Mann K ，Koch E ，Chu B ，Dakin R ，Gordon MD ... -  《-》

Multimodal stimulus coding by a gustatory sensory neuron in Drosophila larvae.

van Giesen L ，Hernandez-Nunez L ，Delasoie-Baranek S ，Colombo M ，Renaud P ，Bruggmann R ，Benton R ，Samuel ADT ，Sprecher SG ... -  《Nature Communications》

Behavioral Analysis of Bitter Taste Perception in Drosophila Larvae.

Insect larvae, which recognize food sources through chemosensory cues, are a major source of global agricultural loss. Gustation is an important factor that determines feeding behavior, and the gustatory receptors (Grs) act as molecular receptors that recognize diverse chemicals in gustatory receptor neurons (GRNs). The behavior of Drosophila larvae is relatively simpler than the adult fly, and a gustatory receptor-to-neuron map was established in a previous study of the major external larval head sensory organs. Here, we extensively study the bitter taste responses of larvae using 2-choice behavioral assays. First, we tested a panel of 23 candidate bitter compounds to compare the behavioral responses of larvae and adults. We define 9 bitter compounds which elicit aversive behavior in a dose-dependent manner. A functional map of the larval GRNs was constructed with the use of Gr-GAL4 lines that drive expression of UAS-tetanus toxin and UAS-VR1 in specific gustatory neurons to identify bitter tastants-GRN combinations by suppressing and activating discrete subsets of taste neurons, respectively. Our results suggest that many gustatory neurons act cooperatively in larval bitter sensing, and that these neurons have different degrees of responsiveness to different bitter compounds.

Kim H ，Choi MS ，Kang K ，Kwon JY ... -  《-》

Molecular basis of fatty acid taste in Drosophila.

Ahn JE ，Chen Y ，Amrein H 《eLife》