Molecular neurophysiology of neural mechanisms of taste reception in Drosophila

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(1) We showed that a G-protein gamma subunit is partially required for sugar taste reception in Drosophila. The gene for the G-protein gamma subunit is expressed mainly in one of the gustatory receptor neurons. Behavioral and electrophysiological responses of the flies to sucrose were reduced by the targeted neural suppression of Gel gamma subunit-expressing cells utilizing Ga14/UAS system. We also demonstrated that responses to sugars were lowered in Gcl gamma null mutant.(2) Insects have specialized gustatory cells responding to water. We found a Ga14 enhancer trap strain in which GAL4 is expressed in a single taste receptor cell in each sensillum on the labellum. The neural function of these cells was blocked by expressing shibire [ts1] and behavioral tests and electrophysiological recordings indicated that they are the water taste cells. We show that axons of the water receptor cells project to a specific region in the subesophageal ganglion.(3) Sex pheromones are volatile or non-volatile in Drosophila. Volatile pheromones are sensed by olfactory neurons and we found that labellar Gr66a-expressing taste neurons respond to a male specific non-volatile pheromone, 7-tricosene. This was done by a newly developed tungsten electrode recording method. 7-Tricosene is probably sensed by tarsal taste sensilla during courtship and we observed projection patterns from Gr66a-expressing neurons in tarsi. By using a Flp-out technique, we generated mosaic flies in which only a few Gr66a-expressing neurons can be labeled and observed their projection patterns. Results showed that projection patterns of Gr66a-expressing neurons from sensilla that might sense the sex-pheromone and those from other sensilla that are involved in feeding behavior are different. We suggest that information from Gr66a-expressing neurons is sent to a different region depending on their related behavior.