Abstract
The neural control of sugar consumption is critical for normal metabolism. In contrast to sugar-sensing taste neurons that promote consumption, we identify a taste neuron that limits sucrose consumption in Drosophila. Silencing of the neuron increases sucrose feeding; optogenetic activation decreases it. The feeding inhibition depends on the IR60b receptor, as shown by behavioral analysis and Ca2+ imaging of an IR60b mutant. The IR60b phenotype shows a high degree of chemical specificity when tested with a broad panel of tastants. An automated analysis of feeding behavior in freely moving flies shows that IR60b limits the duration of individual feeding bouts. This receptor and neuron provide the molecular and cellular underpinnings of a new element in the circuit logic of feeding regulation. We propose a dynamic model in which sucrose acts via IR60b to activate a circuit that inhibits feeding and prevents overconsumption.
Highlights
Feeding regulation is a critical problem in animal life (Morton et al, 2006)
The analysis reveals a new element in the circuit logic of feeding regulation: sugar-sensing taste neurons that act to prevent overconsumption
IR60b is expressed in the labral sense organ (LSO) in sensillum 7 (Figure 1A–C), which houses eight neurons (Gendre et al, 2004)
Summary
Feeding regulation is a critical problem in animal life (Morton et al, 2006). The initiation of feeding has been studied in the model genetic system Drosophila, whose taste system has many parallels to that of mammals (Liman et al, 2014). A variety of molecular and cellular mechanisms must operate for feeding to be initiated. Receptors sensitive to sugars signal the presence of nutrients (Dahanukar et al, 2007; Freeman et al, 2014; Jiao et al, 2008; Wisotsky et al, 2011); receptors sensitive to bitter-tasting compounds signal the danger of toxins (Lee et al, 2009, 2015; Shim et al, 2015; Weiss et al, 2011). If nutrient levels are sufficiently high and toxin levels sufficiently low, the animal begins to feed (French et al, 2015)
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