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Taste detection in the periphery: How do flies detect different taste compounds in their environment? Recent work in the lab has characterized different classes of gustatory neurons, the taste stimuli they detect and the molecular basis of detection. These studies have identified four categories of taste cells (sugar-sensing, bitter-sensing, water-sensing and carbon dioxide-sensing) and the receptors that underlie detection. Current work continues to examine taste receptors in the fly, with the aim of a complete description of taste cell categories in the periphery.
Our lab studies the gustatory system in Drosophila melanogaster to understand how sensory information is processed by the brain to give rise to specific behaviors. Drosophila sense many of the same taste stimuli as mammals, including sugars, salts, acids, alcohols and noxious chemicals. These compounds mediate acceptance or avoidance behaviors, and activation of a single sensory neuron is sufficient to produce a behavior. Although innate, taste behaviors may be modified by learning and experience. The simplicity of ligands and behaviors, along with the molecular, genetic, calcium imaging and electrophysiological approaches available in Drosophila, allows us to examine taste processing from sensory input to motor output in a system that can also be modified by learning.
Taste processing in the central nervous system: In the fly gustatory system, sensory neurons, motor neurons driving proboscis extension and feeding, and modulatory neurons all arborize in the same brain region, the subesophageal ganglion (SOG). One attractive hypothesis is that simple circuits mediating taste reflexes might be localized to the SOG, but that in addition, communication between gustatory circuits and higher brain centers may allow for more complex associations. To understand how taste information is processed in the fly, we are delineating taste neural circuits with cellular resolution, using molecular genetic approaches to label, activate and silence neurons, and electrophysiological and calcium imaging approaches to monitor taste-induced activity. These studies aim to examine how the brain processes taste information to allow for stereotyped behavior, behavioral plasticity and individual variation.
Modulation of taste behaviors: For an animal to survive in a constantly changing environment, its behavior must be shaped by the sensory stimuli it detects, its previous experience and its internal state. Although taste behaviors in the fly are relatively simple, with sugars mediating acceptance behavior and bitter compounds avoidance, these behaviors are also plastic and modified by intrinsic and extrinsic cues. How intrinsic cues such as hunger, satiety and thirst and other sensory cues such as odors or noxious stimuli influence taste behaviors is an area of increasing interest in the lab.
A fly extends its proboscis to sucrose
This fly has been engineered to express channelrhodopsin2, a light-gated ion channel, in sugar-sensing neurons. Illumination with blue light produces proboscis extension.
Sensory neuron projections in the SOG. Bitter-sensing neurons are in magenta and sugar-sensing neurons are in green. Note that these two classes of neurons arborize in distinct areas.