A way to link unconnected neurons in the brain and change an organism’s behaviour, dubbed neural engineering, could one day help treat spinal injuries.
There is already a technique for manipulating neurons with light, known as optogenetics, that been used for a variety of purposes, such as controlling the (Caenorhabditis elegans). But using this method in vertebrates, including humans, requires invasive surgical procedures so the light can reach specific brain cells.
at the Institute of Photonic Sciences (ICFO) in Spain wanted to devise a non-invasive alternative, using light as a neurotransmitter. In a typical brain, neurotransmitters are chemicals that are secreted into the gap between two neurons, also known as a synapse, allowing them to communicate.
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Krieg and his colleagues figured out a way to do this using particles of light, called photons, in some of the synapses of a nematode worm.
To do this, the researchers genetically engineered some of the worm’s neurons so that they didn’t produce any neurotransmitters when activated. They also modified two types of protein present on either side of a synapse, called the presynapse and postsynapse, that normally send and receive neurotransmitters.
The genetically engineered presynapse produced an enzyme that releases photons when activated, while the modified postsynapse produced a protein that responds to photons and fires a second neuron.
To show that their method worked, the researchers took advantage of the worm’s natural attraction to a chemical compound called diacetyl, which smells like a food source and so is normally attractive to the creatures.
Using their neural engineering technique, the researchers were able to instead make the worms scurry away from diacetyl. They linked the neurons that register the smell of the compound to the neuronal circuit that triggers avoidant behaviour, allowing them to communicate. These circuits aren’t connected to each other in a typical nematode, says Krieg.
“There are not a lot of methods available by which you can connect two neurons that are not in direct physical connection,” he says. “Photons can bridge that gap.”
Krieg says the biggest limitation of the method is the fact the enzymes in the presynapse don’t produce many photons and so don’t always activate ion channels in the postsynapse, making it unreliable. But this should improve with more research, he says.
The team hopes that the method could one day be used to treat spinal injuries in which neurons struggle to communicate with each other using neurotransmitters.
“In the long term, this could lead to the design of artificial neural networks that reconnect broken connections found in the physical disc of a spinal cord injury,” says Krieg. “You could functionally connect neurons in the spinal cord using photons that are quite far from one another – but such work is still a very long way away.”
“I think this is a very exciting study,” says at Keele University in the UK. “This is a new way of controlling signalling between neurons, but I think the therapeutic applications are a way off.”
Nature Methods
