Why does a fly fly?

Hepeng Jia / Beijing, China

Chinese scientists have deciphered the complicated value-based decision-making process of the fruit fly, Drosophila. Their findings reveal a key role for the neurotransmitter dopamine and a region of the insect brain called the mushroom bodies. Dopamine is known to be involved in the transmission of reward or punishment signals in the nervous system, while the mushroom bodies have been linked to learning and memory.

Guo Aike at the Shanghai-based Institute of Neuroscience, Chinese Academy of Sciences, and colleagues trained Drosophila in a ’flight simulator’. This gave the flies different positional and colour cues. The animals were subjected to varying degrees of heat when flying in response to different cues. 

Training flies to make decisions

Drosophila in the simulator had to decide how to balance the degree of punishment (heat) against the various cues.

The researchers created Drosophila mutants by inserting genes involved in the function of the nervous system. The system was tweaked so that, when the temperature of the flies’ surroundings was higher than 30 degrees Celsius, those proteins blocked the function of the dopamine system and the function of the mushroom bodies. 

The researchers compared the flight of genetically modified Drosophila with that of wild-type counterparts. They found that when the mutant flies were first introduced to a new set of cues, they were unable to make ’rational’ decisions. This changed once the animals were used to their conditions.

’We found that coordinated functions of the dopamine system and the mushroom bodies play a crucial role at the early stages of Drosophila value-based decision making,’ lead researcher Guo told Chemistry World, ’but at the later stage, which we call an execution stage, the two are no longer needed.’

The researchers then took Drosophila that had reached the execution stage of a decision-making process and exposed them to conflicting cues. Genetic analysis revealed that the dopamine system and the mushroom bodies were once again activated to help the animals make new decisions.

Quick change

’Drosophila can rapidly make new complicated decisions,’ said Guo. ’The conclusion further increases our understanding of the complexity and delicacy of Drosophila’s decision making.’

The findings will be helpful to biological chemists, he added, as they shed further light on the complexity of the dopamine system, a system that has long attracted the pharmaceutical industry.

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