Kristin Scott is a professor of Neurobiology. The aim of the Scott Lab's research is to understand how sensory information is processed to produce specific behaviors. They study taste perception in the fruit fly, Drosophila Melanogaster, an excellent model organism with a simple gustatory system and robust gustatory behaviors that is amenable to molecular, genetic and electrophysiological approaches. They are interested in defining taste neural circuits anatomically and functionally to examine how they operate, how they elicit behaviors and how they are modified by sensory experience.
The gustatory system in Drosophila is crucial for detecting food, selecting sites to lay eggs and recognizing mates. Taste neurons are distributed on many parts of the fly's body surface and they recognize familiar taste stimuli: sugars, salts, acids, alcohols and noxious chemicals. They have recently characterized a large family of ~60 candidate gustatory receptor genes (GRs) and found that each gustatory neuron expresses only one or a few receptors. These receptors provide essential molecular markers that they are using to examine taste recognition both in the periphery and in the CNS.
Ligand specificity and behavioral specificity of different gustatory receptors. To understand the function of different gustatory neurons, they are determining the ligands that different taste neurons recognize and the behaviors that they mediate. They are identifying ligands by a combination of genetic cell ablations and receptor misexpression studies, coupled with behavioral paradigms and calcium imaging experiments to assay taste responses. For example, gustatory neurons containing the same receptor gene can be ablated by genetically expressing a toxin and taste defects can be tested by simple behavioral assays, like food choice discrimination measured by food-coloring uptake. They are also expressing calcium-sensitive fluorescent proteins in taste neurons -- this allows them to monitor taste responses in the entire population of gustatory neurons in vivo with single cell resolution. To determine the behaviors that different neurons mediate even in the absence of identifying ligands, inducible activators will be expressed in gustatory neurons, so that each neuron can be stimulated one by one to examine the fly's behavioral response. These studies will allow them to identify a sensory neuron by the stimulus that it recognizes and the response that it generates and will provide a starting point for dissecting taste circuits.
Sensory maps in the brain. In other sensory systems, information from the periphery is mapped in the brain to provide a representation of the external world in the internal wiring. For example, there are tonotopic maps of auditory projections and somatosensory maps of touch projections. The gustatory system of the fly is interesting both because neurons express unique complements of receptors and because neurons are distributed in an orderly array along the body surface. They are using molecular genetic approaches to examine whether gustatory projections are segregated according to the receptor that is expressed in the periphery and whether there is a topographic map of gustatory information. Chemosensory bristles contain one mechanosensory neuron as well as taste neurons, and they are examining how these two different sensory modalities are represented in the brain. Their motivation is to understand the internal representation of gustatory information in the first relay.
Information processing in the brain. The subesophageal ganglion of the fly brain contains both axons of gustatory neurons and dendrites of motor neurons involved in taste behaviors. This suggests that the fly may have simple and localized taste circuits, with few connections between sensory stimulus and motor response. In addition, projection neurons may relay gustatory information to higher brain centers, perhaps for more complex associations. They are interested in mapping the functional and anatomical components of taste circuits using a variety of approaches. Genetic approaches to label subsets of neurons in the brain, behavioral screens for taste mutants, and calcium imaging of taste responses in the brain will help elucidate these circuits. These studies will provide insight into the integration of gustatory cues and the difference between sweet versus bitter, and will set the stage to examine how taste circuits are modified by learning and other sensory stimuli. They plan to study increasingly complex problems of neural integration by examining how different stimuli impinge upon taste circuits.