Study shows how fruit flies beat the heat (and cold)

Study shows how fruit flies beat the heat (and cold)

Monday, November 23, 2015

NIH-funded research suggests how sensory information is read in the brain

Humans aren’t the only ones that take shelter when the weather turns unpleasant. A team of researchers at Northwestern University’s Department of Neurobiology has mapped the neural circuits that allow flies to avoid uncomfortable temperatures. Their research, funded in part by the NIH’s National Institute of Neurological Disorders and Stroke (NINDS) and published in the journal Nature, suggests that the brain works like a mixing table in a music studio, combining different “tracks” that convey specific information about temperature.

“The question is how the brain turns simple sensations into directed behavior,” said Marco Gallio, Ph. D., the study’s senior author and an assistant professor in Northwestern’s Department of Neurobiology, Evanston, IL. “Although individual neurons respond to very specific features of a temperature change, when they work together they provide a complex picture of what is happening in the outside world.”

Dr. Gallio’s previous research had shown that, like human skin, a fly’s antennae contain one set of neurons that detects heat and another that detects cold. These neurons send information to two distinct but adjacent areas in a part of the fly brain called the posterior antennal lobe (PAL). In this study, he and his colleagues mapped the set of brain circuits that receive sensory signals from the PAL and showed how those regions control a fly’s reaction to temperature changes.

Dominic Frank, a graduate student in the Gallio Lab, traced two parallel pathways from the PAL to neurons in the fly brain activated only by either heating or cooling. However, within these two systems, some cell types responded transiently to changes in temperature while others showed a longer-lasting response that varied based on the intensity of the heat or cold. To their surprise, Dr. Gallio’s team also found neurons that were activated by both heating and cooling. All these pathways largely converged onto the same regions in the fly brain.

“This study shows that sensing temperature may be more complex than we thought,” said NINDS program director Jim Gnadt, Ph.D. “Using a simple model system like the fly nervous system offers insight into how our brain circuits might process temperature and other everyday senses.”

To see how the neurons influenced behavior, Dr. Gallio’s team put flies in a cage containing floor tiles set at various temperatures. Normally, flies spend the most time on tiles at room temperature and actively avoid hotter or colder tiles.

“Flies are small, cold-blooded animals, so if they like a temperature they stay and if they don’t like it they run away,” Dr. Gallio said.

But when the scientists silenced the neurons that responded only to cold, the flies spent more time on the cold tiles. Similarly, when they silenced the cells that responded to both hot and cold, the flies tolerated warmer and cooler temperatures. Dr. Gallio believes this second set of neurons signals the general hazard posed by extreme temperatures.

“This rich repertoire of responses that comes from the different cell types allows the flies to respond to different temperatures in specific ways,” Dr. Gallio said. He speculates that fly and mammalian brains may use similar processes to interpret sensations.

The study provides insight into how simple information is broken down and put back together by the brain to create a vibrant sensory experience.

This work was supported by grants from the National Institute of Neurological Disorders (NS086859) and National Institute of Mental Health (MH067564).

 – by Brandon Levy

References:

Frank et al. “Temperature representation in the Drosophila brain.” Nature, March 4, 2015. DOI: 10.1038/nature14284.

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The NINDS (http://www.ninds.nih.gov) is the nation’s leading funder of research on the brain and nervous system. The mission of NINDS is to seek fundamental knowledge about the brain and nervous system and to use that knowledge to reduce the burden of neurological disease.

About the National Institute of Mental Health (NIMH): The mission of the NIMH is to transform the understanding and treatment of mental illnesses through basic and clinical research, paving the way for prevention, recovery and cure. For more information, visit the NIMH website.

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.

Scientist map out temperature in a fly brain
Marco Gallio, Ph.D., discusses results from a study he lead showing how fly brains sense temperature. results from a study he lead showing how fly brains sense temperature. Video courtesy of NINDS.

image of temperature-taking brain circuits

Temperature-taking brain circuits
Scientists mapped the brain circuits that allow flies to react to temperature changes. Courtesy of Gallio lab, Northwestern University Department of Neurobiology, Evanston, IL