The Reason Flies are Attracted to Foods that Smell Delicious

Professor OZAKI Mamiko and Fellow Researcher MAEDA Toru, Department of Biology at the Graduate School of Science, Kobe University, together with researchers from Nara Women’s University and Fukuoka University, have for the first time identified the reason why flies are attracted to foods that smell delicious. It is due to the fact that two sensory neurons (one controlling the sense of taste and the other controlling the sense of smell) in fly brains are located closely to one another and interact. The research findings were published and highlighted as the top article in Chemical Senses (Volume 39 Issue 5 June 2014), the official chemosensory international journal representing the three academic societies of US, Europe, and Japan. One of the images used in the article made the cover of the journal. The article was also introduced by the editor-in-chief, whose introduction can be found at the Chemical Senses website.

Through taste, smell and tactile information, animals assess, identify, consume nutrients, and avoid harmful poisons. Integrating taste and smell information is important for animals so they can accurately identify which food is better. This is crucial for their survival, and to ensure continuation of their species. However, little is known about their neural mechanisms. For example, flies can associate a food smell with a taste reward yet the neural mechanisms underlying the integration of taste and odor in fly brains, captured by separate sensilla, remain unclear. In flies, it is known that gustatory receptor neurons (GRNs) from the mouth project directly towards the primary gustatory center, known as the subesophageal ganglion (SOG). It is also known that olfactory receptor neurons (ORNs) project directly towards the primary olfactory center, known as the antennal lobes (ALs), which are equivalent to the part of the brain called the olfactory bulb in mammals. Kobe University Ozaki Laboratory research fellow Maeda et al investigated the projections of tactile receptor neurons deriving from the secondary olfactory organs of flies and ORNs through visualization by an anterograde staining method. They confirmed that some of these neurons project towards the primary gustatory center known as SOG. Furthermore, a region of overlapping projections of ORNs and lavellar sensillar GRNs was confirmed (see figure 7), and the possibility of interaction via synapses between GRNs and ORNs was shown. This suggested that external gustatory information was converted into a nerve signal at the peripheral sensilla, carried to the brain via GRNs, and converted into nerve information integrating the context of touch and smell through initial information processing at the SOG (primary olfactory center). Using this mechanism, the published study explains that the fly’s appetite for sucrose increased three times when detecting Tricholoma matsutake-like odorant of 1-octen-3-ol (known as Mushroom Alcohol, which possesses a sewage-like odor when condensed) from the sub-olfactory organ instead of the main-olfactory organ.

Figure 7.

This study explained for the first time the mechanism by which flies are attracted to and ingest foods with delicious smells (to flies). The study is also expected to shed light on universal questions for many animals including human beings about how perception of different types of sensory information are integrated and processed to generate new perception within the brain, and how new perception reflects the behavioral selection of animals.

Figure 7.

This study explained for the first time the mechanism by which flies are attracted to and ingest foods with delicious smells (to flies). The study is also expected to shed light on universal questions for many animals including human beings about how perception of different types of sensory information are integrated and processed to generate new perception within the brain, and how new perception reflects the behavioral selection of animals.

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