Implanted Neurons Integrate Into Brain Circuitry

Here is some awesome news via PhysOrg: neurons made from human embryonic stem cells in a lab were transplanted into mice and formed functional connections. They adopted the activity patterns of their area and could apparently modify their neighbouring cells through their behaviour too. 

Neurons are specialized, impulse conducting cells that are the most elementary functional unit of the central nervous system. The 100 billion or so neurons in the human brain are constantly sending and receiving the signals that govern everything from walking and talking to thinking. The work represents a crucial step toward deploying customized cells to repair damaged or diseased brains, the most complex human organ…

The Wisconsin team tested the ability of their lab grown neurons to integrate into the brain’s circuitry by transplanting the cells into the adult mouse hippocampus, a well-studied region of the brain that plays a key role in processing memory and spatial navigation. The capacity of the cells to integrate was observed in live tissue taken from the animals that received the cell transplants.

Weick and colleagues also reported that the human neurons adopted the rhythmic firing behavior of many brain cells talking to one another in unison. And, perhaps more importantly, that the human cells could modify the way the neural network behaved.

If human neurons could integrate in and work with mouse neurons, one would hope they can do the same in humans. There are plenty of diseases that involve the loss of neurons (neurodegenerative diseases), so this could possibly be a step towards better treatment for the many millions of people affected. 

They also describe how they modulated the implanted neurons’ behaviour using light, the basic mechanism of which I explained in the context of heart muscle cells earlier.

A critical tool that allowed the UW group to answer this question was a new technology known as optogenetics, where light, instead of electric current, is used to stimulate the activity of the neurons.

“Previously, we’ve been limited in how efficiently we could stimulate transplanted cells. Now we have a tool that allows us to specifically stimulate only the transplanted human cells, and lots of them at once in a non-invasive way,” says Weick.

Weick explains that the capacity to modulate the implanted cells was a necessary step in determining the function of implanted cells because previous technologies were too imprecise and unreliable to accurately determine what transplanted neurons were doing…

The new study opens the door to the potential for clinicians to deploy light-based stimulation technology to manipulate transplanted tissue and cells. “The marriage between stem cells and optogenetics has the potential to assist in the treatment of a number of debilitating neurodegenerative disorders,” notes Su-Chun Zhang, a UW-Madison professor of neuroscience and an author of the new PNAS report. “You can imagine that if the transplanted cells don’t behave as they should, you could use this system to modulate them using light.”

The idea of having brain cells implanted into me that can be externally manipulated by light is a bit eerie, but I guess flying through the air at super speeds in a big metal vehicle used to be weird too. 

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