Researchers find that interneurons are not all created equally

Sep 08, 2010 by Deborah Halber

(PhysOrg.com) -- A type of neuron that, when malfunctioning, has been tied to epilepsy, autism and schizophrenia is much more complex than previously thought, researchers at MIT's Picower Institute for Learning and Memory report in the Sept. 9 issue of Neuron.

The majority of are called excitatory because they ramp up the action of target cells. In contrast, inhibitory cells called interneurons put the brakes on unbridled activity to maintain order and control. , as well as symptoms of autism and , have been tied to dysfunctional inhibitory cells.

"Too much activity and you run the risk of uncontrolled activity, while too little leads to cognitive and behavioral deficits," said Mriganka Sur, Paul E. Newton Professor of , whose laboratory carried out the study. "Normal brain development and function hinges on the delicate balance between excitation and inhibition."

For a long time, interneurons, which make up only one-fifth of brain cells, were thought to be a kind of generic, homogenous shutdown agent. The MIT study points to a new view: At least some interneurons have very precise responses and form specific connections and circuits.

"If these cells are targeted in brain disorders, then these disorders must arise from precise dysfunction in specific circuits," said Sur, head of the MIT Department of Brain and Cognitive Sciences. "This study sheds light on precisely what is going on in these circuits that may be targeted for future treatments."

Inhibitory cells are diverse: researchers are only starting to discern distinct electrophysiological profiles, shapes and molecular signatures among the 20 or more known types.

But all interneurons fall into two clear subtypes: those that target the cell body, or soma, of their target cells and those that target the branchlike dendrites. The soma-targeting type expresses a protein called parvalbumin and has been linked to and circuit development. This type of interneuron was thought to dampen activity uniformly across the cortex. "Our paper overturns this view," Sur said.

"These neurons had been thought to have only broad response features that would nonspecifically dampen their target cells. Our finding indicates that they have well-defined properties and functions," he said.

MIT graduate student Caroline Runyan and postdoctoral fellows James Schummers, Audra Van Wart and Nathan Wilson used cutting-edge techniques to examine the properties of parvalbumin-expressing inhibitory .

With the help of mice genetically engineered to have just these cells fluoresce red in their visual cortex, the researchers used a sophisticated technique called two-photon imaging to identify and record the activity of these cells in living animals.

They found that parvalbumin-expressing interneurons have a range of response features. Many of these cells have precisely tuned responses. Some only respond to very specific signals and locations in space.

"These cells are components of and contributors to highly specific networks that shape the selectivity of neuronal responses," Runyan said. "They need to be defined by a combination of features, including structure, connections, gene expression profiles, electrophysiological properties and response types.

"This study supports the idea that individual cell classes may provide specific forms of inhibition and serve unique functions," she said.

Explore further: Researchers show EEG's potential to reveal depolarizations following TBI

More information: "Response features of parvalbumin-expressing interneurons suggest precise roles for subtypes of inhibition in visual cortex" by TK TK. Neuron, 9 Sept. 2010.

Related Stories

Rare cell prevents rampant brain activity

Mar 02, 2007

One of the mysteries of the brain is how it avoids ending up in a state of chaos, something which happens only on exceptional occasions, when it can lead to epileptic fits. Scientists at Karolinska Institutet have now uncovered ...

Trigger for brain plasticity identified

Aug 07, 2008

Researchers have long sought a factor that can trigger the brain's ability to learn – and perhaps recapture the "sponge-like" quality of childhood. In the August 8 issue of the journal Cell, neuroscientists at Children's Hospit ...

Recommended for you

Obama's BRAIN initiative gets more than $300 million

3 hours ago

President Barack Obama's initiative to study the brain and improve treatment of conditions like Alzheimer's and autism was given a boost Tuesday with the announcement of more than $300 million in funds.

US aims for traumatic brain injury clinical trial success

15 hours ago

An unprecedented, public-private partnership funded by the Department of Defense (DoD) is being launched to drive the development of better-run clinical trials and may lead to the first successful treatments for traumatic ...

User comments : 0