New preprint on the sugar taste circuit
We have a new preprint on bioRxiv on how sweet taste elicits different types of behavioral responses!
As we know from daily life, a single sensory cue can elicit different behavioral responses that occur on different timescales or in different contexts. For example, the sound of a fire alarm while working may cause you to initially jump, then look around for a fire, then evacuate the building, but hearing the same sound in a movie would not evoke the same behaviors. In this study, we investigated how the taste of sugar elicits multiple behavioral responses in flies. Sweet taste is well known for its ability to stimulate eating, but it also causes flies to stop moving (so they can feed), encourages them to reside in sugar-containing areas, and serves as a reinforcement cue for learning.
We asked 2 main questions: 1) How are different behavioral responses to sugar modulated by other external and internal cues? 2) At what point does the sweet-sensing circuit diverge into different pathways that mediate different behaviors?
We first asked whether different behavioral responses to sweet taste are coordinately modulated by factors such as hunger, diet, or the presence of an aversive taste. Different behaviors were generally modulated in similar ways, but we also observed some differences that show selective modulation of specific behavioral pathways. These experiments also revealed broader insights into taste modulation: for example, hunger strongly modulates behaviors driven by sweet but not bitter taste, and a high-sugar diet globally suppresses short-term responses to sweet taste.
We then asked at what point the sweet taste circuit diverges into different pathways that drive distinct behaviors.
By individually manipulating interneurons in the sugar circuit, we show that circuits mediating different innate responses to sugar begin to diverge at the level of second- and third-order neurons, whereas circuits for innate versus learned behaviors likely diverge at the first synapse.
Our model is that basic aspects of taste processing occur within second-order neurons, like pooling info across sensory cells, while processing in third-order neurons begins to reflect sensorimotor transformations, and then fourth-order neurons essentially represent premotor pathways. We think this study provides new insights into sweet taste processing, with broader implications on how circuits are organized to elicit diverse behavioral responses to a single cue.
This study was led by Ruby Jacobs (Research Specialist) and Crystal Wang (4th year undergraduate) who now have their very first paper authorships! We also had important contributions from other lab members, including Lam Nguyen (3rd year undergraduate) and Fiorella Lozada-Perdomo (Research Specialist), as well as two former technicians that Dr. Devineni mentored in the Axel lab (Julia Deere and Hannah Uttley). Congratulations to all the authors!!!
