Secondary taste neurons that convey sweet taste and starvation in the Drosophila brain.

The gustatory system provides vital sensory information to determine feeding and appetitive learning behaviors. Very little is known, however, about higher-order gustatory circuits in the highly tractable model for neurobiology, Drosophila melanogaster. Here we report second-order sweet gustatory projection neurons (sGPNs) in the Drosophila brain using a powerful behavioral screen. Silencing neuronal activity reduces appetitive behaviors, whereas inducible activation results in food acceptance via proboscis extensions. sGPNs show functional connectivity with Gr5a(+) sweet taste neurons and are activated upon sucrose application to the labellum. By tracing sGPN axons, we identify the antennal mechanosensory and motor center (AMMC) as an immediate higher-order processing center for sweet taste. Interestingly, starvation increases sucrose sensitivity of the sGPNs in the AMMC, suggesting that hunger modulates the responsiveness of the secondary sweet taste relay. Together, our results provide a foundation for studying gustatory processing and its modulation by the internal nutrient state.

Kain P ，Dahanukar A 《-》

Representations of Taste Modality in the Drosophila Brain.

Gustatory receptors and peripheral taste cells have been identified in flies and mammals, revealing that sensory cells are tuned to taste modality across species. How taste modalities are processed in higher brain centers to guide feeding decisions is unresolved. Here, we developed a large-scale calcium-imaging approach coupled with cell labeling to examine how different taste modalities are processed in the fly brain. These studies reveal that sweet, bitter, and water sensory cells activate different cell populations throughout the subesophageal zone, with most cells responding to a single taste modality. Pathways for sweet and bitter tastes are segregated from sensory input to motor output, and this segregation is maintained in higher brain areas, including regions implicated in learning and neuromodulation. Our work reveals independent processing of appetitive and aversive tastes, suggesting that flies and mammals use a similar coding strategy to ensure innate responses to salient compounds.

Harris DT ，Kallman BR ，Mullaney BC ，Scott K ... -  《-》

A gustatory second-order neuron that connects sucrose-sensitive primary neurons and a distinct region of the gnathal ganglion in the Drosophila brain.

Miyazaki T ，Lin TY ，Ito K ，Lee CH ，Stopfer M ... -  《-》

Starvation-induced elevation of taste responsiveness and expression of a sugar taste receptor gene in Drosophila melanogaster.

Nishimura A ，Ishida Y ，Takahashi A ，Okamoto H ，Sakabe M ，Itoh M ，Takano-Shimizu T ，Ozaki M ... -  《-》

Neural architecture of the primary gustatory center of Drosophila melanogaster visualized with GAL4 and LexA enhancer-trap systems.

Miyazaki T ，Ito K 《-》