Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Caltech scientists find emotion-like behaviors, regulated by dopamine, in fruit flies

27.11.2009
Finding may provide new insights into the neurological basis of ADHD, learning deficits, and more

Scientists at the California Institute of Technology (Caltech) have uncovered evidence of a primitive emotion-like behavior in the fruit fly, Drosophila melanogaster.

Their findings, which may be relevant to the relationship between the neurotransmitter dopamine and attention deficit hyperactivity disorder (ADHD), are described in the December issue of the journal Neuron.

The Drosophila brain contains only about 20,000 neurons and has long been considered a powerful system with which to study the genetic basis of behaviors such as learning and courtship, as well as memory and circadian rhythms. What hasn't been clear is whether the Drosophila brain also could be used to study the genetic basis of "emotional" behaviors.

"Such studies are important," says David Anderson, Caltech's Seymour Benzer Professor of Biology and a Howard Hughes Medical Institute investigator, "because it's believed that abnormalities in these types of behaviors may underlie many psychiatric disorders."

Most of the genes found in the fruit fly—more accurately referred to as the vinegar fly—are found in humans as well, including those neurons that produce brain chemicals like dopamine and serotonin, which have been implicated in psychiatric disorders.

In their Neuron paper, the Caltech team—led by postdoctoral fellow Tim Lebestky—found that a series of brief but brisk air puffs, delivered in rapid succession, caused flies to run around their test chamber in what Anderson calls a "frantic manner." This behavior persisted for several minutes after the last of the puffs.

"Even after the flies had 'calmed down,'" he adds, "they remained hypersensitive to a single air puff."

To quantify the flies' behavior, Anderson's group collaborated with Pietro Perona, the Allen E. Puckett Professor of Electrical Engineering at Caltech. Together with his students, Perona developed an automated machine-vision-based system to track the movement of the flies, and derived a simple mathematical model to fit the movement data and to extract metrics that described various aspects of the flies' responses under different conditions.

The researchers used this test to search for flies with an abnormally exaggerated hyperactivity response; genetic studies of these flies revealed that a mutation in a dopamine receptor (a mutation that eliminates the receptor) produced the aberrant behavior. Flies with this dopamine-receptor mutation were hypersensitive to the air puffs, and took much longer to calm down than did "normal" flies without the mutation.

What is surprising about this result, notes Lebestky, "is that previous studies in both flies and vertebrates had suggested that dopamine promotes activity, but our experiments uncovered a function of dopamine in the opposite direction." Because removing the receptor causes hypersensitivity to the air puffs, these results "suggested that dopamine actively inhibits the hyperactivity response," Lebestky says.

This observation suggested a possible link to ADHD, a behavioral disorder characterized by impulsivity, hyperactivity, and short attention span. Humans with the disorder often take drugs, such as Ritalin, that increase levels of brain dopamine in order to reduce hyperactivity.

The ways the mutant flies respond to the air puffs is, moreover, "reminiscent of the way in which individuals with ADHD display hypersensitivity to environmental stimuli and are more easily aroused by such influences," says Anderson. Importantly, ADHD has been genetically linked to abnormalities of the dopamine system in humans, further strengthening the analogy between the mutant flies and this psychiatric disorder.

There is also another possible link: some individuals with ADHD display learning disabilities. Similarly, researchers from Pennsylvania State University—who collaborated on the Neuron study—have shown previously that flies with the same dopamine receptor mutation are unable to learn to associate a particular odor with an electric shock, and do not avoid the odor when subsequently tested. (Flies without the mutation quickly learn to make the association.)

It is often assumed that because individuals with ADHD are hyperactive and easily distracted, they have difficulty learning. The Caltech group showed, however, that hyperactivity and learning disabilities are not causally related in flies bearing the dopamine receptor mutation, thereby disproving the theory—at least in flies.

"We could separately 'rescue' the hyperactivity and learning deficits in a completely independent manner," says Anderson, "by genetically restoring the dopamine receptor to different regions of the fly's brain."

Thus, in dopamine-receptor-mutant flies, hyperactivity does not seem to cause learning deficits. Instead, these two "symptoms" reflect independent effects of the mutation that manifest themselves in distinct brain regions. "Being able to observe and manipulate the different neural substrates for learning and arousal will hopefully give us a unique method for identifying new molecular pathways that could be investigated and validated in higher organisms," says Lebestky.

This finding in flies, notes Anderson, raises the possibility that hyperactivity and learning deficits also may not be causally linked in humans with ADHD. If so, he says, it ultimately may prove more effective to develop drugs to treat these two symptoms separately, rather than trying to cure them both with the broad-spectrum pharmaceuticals currently available, which have many undesirable side effects.

"The finding that flies exhibit emotion-like behaviors that are controlled by some of the same brain chemicals as in humans opens up the possibility of applying the powerful genetics of this 'model organism' to understanding how these chemicals influence behavior through their actions on specific brain circuits," says Anderson. "While the specific details of where and how this occurs are likely to be different in flies and in humans, the basic principles are likely to be evolutionarily conserved, and may aid in our understanding of what goes wrong in disorders such as ADHD."

In addition to Lebestky, Anderson, and Perona, other researchers on the Neuron paper, "Two Different Forms of Arousal in Drosophila are Oppositely Regulated by the Dopamine D1 Receptor Ortholog DopR via Distinct Neural Circuits," are Jung-Sook Chang, Heiko Dankert, and Lihi Zelnik from Caltech; Young-Cho Kim and Kyung-An Han from Pennsylvania State University; and Fred Wolf from the University of California, San Francisco. Their work was funded by grants from the National Science Foundation and the Howard Hughes Medical Institute.

Lori Oliwenstein | EurekAlert!
Further information:
http://www.caltech.edu
http://media.caltech.edu

More articles from Life Sciences:

nachricht At last, butterflies get a bigger, better evolutionary tree
16.02.2018 | Florida Museum of Natural History

nachricht New treatment strategies for chronic kidney disease from the animal kingdom
16.02.2018 | Veterinärmedizinische Universität Wien

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

Im Focus: Autonomous 3D scanner supports individual manufacturing processes

Let’s say the armrest is broken in your vintage car. As things stand, you would need a lot of luck and persistence to find the right spare part. But in the world of Industrie 4.0 and production with batch sizes of one, you can simply scan the armrest and print it out. This is made possible by the first ever 3D scanner capable of working autonomously and in real time. The autonomous scanning system will be on display at the Hannover Messe Preview on February 6 and at the Hannover Messe proper from April 23 to 27, 2018 (Hall 6, Booth A30).

Part of the charm of vintage cars is that they stopped making them long ago, so it is special when you do see one out on the roads. If something breaks or...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Fingerprints of quantum entanglement

16.02.2018 | Information Technology

'Living bandages': NUST MISIS scientists develop biocompatible anti-burn nanofibers

16.02.2018 | Health and Medicine

Hubble sees Neptune's mysterious shrinking storm

16.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>