Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Diverse 'connectomes' hint at genes' limits in the nervous system

Neurons in a small mouse muscle vary markedly in layout and are far longer than expected

Genetics may play a surprisingly small role in determining the precise wiring of the mammalian nervous system, according to painstaking mapping of every neuron projecting to a small muscle mice use to move their ears.

These first-ever mammalian "connectomes," or complete neural circuit diagrams, reveal that neural wiring can vary widely even in paired tissues on the left and right sides of the same animal.

Scientists at Harvard University and the Massachusetts Institute of Technology describe the work this week in the journal PLoS Biology, accompanied by vivid images depicting neurons that are strikingly treelike, but also tremendously varied.

"We had expected to find a great degree of neural symmetry in the same mouse's two interscutularis muscles, but this isn't even close to true," says Jeff W. Lichtman, professor of molecular and cellular biology in Harvard's Faculty of Arts and Sciences.

"It looks like the mammalian nervous system may be a bit like a football game," he adds. "Even when the rules are the same, every single outcome is unique."

Curiously, the connectome of the mouse interscutularis -- a muscle also found in dogs, rats, and other mammals that readily move their ears -- reveals that some of its neurons are as much as 25 percent longer than is necessary. This casts doubt on a longstanding assumption among neuroscientists that neural wiring length is generally minimized to conserve space, energy, and resources.

"This well-known hypothesis that wiring length should be minimized has been in the scientific literature for decades," says Ju Lu, a postdoctoral researcher in molecular and cellular biology at Harvard. "It's very surprising, frankly, to find so much excess wiring in the mammalian nervous system."

Lichtman and Lu's work represents only the second connectome to date, following one for the worm Caenorhabditis elegans. While their task initially appeared manageable -- the entire interscutularis muscle is but a few millimeters in length -- teasing out the muscle's tangle of about 15 intricately branched and intertwined axons proved fiendishly complex.

"It's a bit like taking a giant plate of spaghetti and, without unraveling it, trying to figure out which strand goes where," says Lu. "Except in this case, each strand of spaghetti has up to 37 branches."

Working with mice containing a gene that causes motor neurons to fluoresce, Lichtman and Lu used an automated microscope to gather tens of thousands of images. These images were analyzed with semi-automated tracing tools, although the need for frequent corrections and manual editing by Lu slowed the pace of the mapping to a scant half-millimeter per hour.

Connectomes from a mouse's two interscutularis muscles depict dramatically different neural circuitry even within mirror-image tissues from the same animal.

"Comparison of each neuron and its counterpart on the opposite side of the animal revealed that each connectome was unique," Lichtman says, "demonstrating wiring diagrams that differ substantially in form, even within a common genetic background."

Lichtman says the research suggests the mammalian nervous system is in some ways unexpectedly primitive, its freeform structure lacking the regimentation seen in insects and worms. But, he adds, this seeming randomness may be advantageous.

"This may explain why humans and other mammals can quickly adapt their behaviors to a changing environment," Lichtman says. "We may be less perfected in our genetic evolution, but our flexible neural wiring may allow us to undergo behavioral evolution at a very rapid rate."

Such variation in the nervous system, he adds, could help explain why different humans, each equipped with the same neural building blocks, excel at tasks ranging from dancing to mathematical computations, and from crossword puzzles to bowling.

Steve Bradt | EurekAlert!
Further information:

More articles from Life Sciences:

nachricht Biologists unravel another mystery of what makes DNA go 'loopy'
16.03.2018 | Emory Health Sciences

nachricht Scientists map the portal to the cell's nucleus
16.03.2018 | Rockefeller University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

Im Focus: Radar for navigation support from autonomous flying drones

At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.

Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

International Virtual Reality Conference “IEEE VR 2018” comes to Reutlingen, Germany

08.03.2018 | Event News

Latest News

Wandering greenhouse gas

16.03.2018 | Earth Sciences

'Frequency combs' ID chemicals within the mid-infrared spectral region

16.03.2018 | Physics and Astronomy

Biologists unravel another mystery of what makes DNA go 'loopy'

16.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>