Flies' Taste Similar to Human's

Ever wonder why flies have an annoying habit of landing in your food, especially the really tasty food? Researchers at UC Berkeley have discovered that fruit flies can sense taste in much the same way that humans can.

"The reason that we're interested in these fruit flies is that we want to understand how simple neural circuits work," said Kristin Scott, an assistant professor of molecular and cell biology at UC Berkeley. "Understanding the brain of a fruit fly may help understand how more complex brains work."

Researchers found that the fruit fly, Drosophila melanogaster, detects sweet and bitter foods similar to the way that humans do. The fly is attracted to the sweet foods and avoids the bitter ones.

"It turns out that flies, just like mammals, have some taste cells that are tuned to sugars and others that recognize bitter compounds," Scott said.

In order to discover how these taste cells, called neurons, work, researchers put toxins into various taste cells of the fruit fly.

With a particular taste cell killed, the researchers tested to see how the flies responded to bitter and sweet foods.

Drosophilia is often used by geneticists because of its extremely quick reproductive cycle, allowing scientists to observe several generations in a relatively short period of time. It also has a completely mapped genome, which allowed resarchers to identify which genes are responsible for taste.

Flies have the ability to sense taste through a number of different organs, including their feet. In order to determine if a fly was able to taste a sweet compound, the fly's foot was placed into a dish of sugar water. If the fly sensed the sugar, it reacted by extending its trunk-like proboscis in an effort to drink up the sweet water.

Using this process the team was able to identify which neurons were connected to which sense of taste.

Researchers also used a fluorescent protein to show that different parts of the fly's brain processed tastes that were picked up from different parts of the body. The team tracked where the protein traveled after leaving the neuron and found that it would enter different parts of the fly's brain depending on where the fly detected the flavor.

For example, if the fly is tasting something sweet on its leg, it might perceive the flavor on the back of its brain rather than the front. This allows the fly to have some form of a spatial map of where it is detecting different tastes. This allows the fly to know exactly where its food is.

Currently, Scott and her team only have the ability to kill two out of the four types of fruit fly taste neurons. She speculates that the other taste neurons might detect the flavors salty and sour.

"In the future we would like to know how flies can detect salt and sour as well as how taste is processed in the brain," Scott said.

The team hopes to learn exactly how the detection of a particular flavor affects fly behavior.

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