Activate or deactivate certain cells, it is possible. Researchers have succeeded in stimulating proteins in the brain using light pulses. Hope for certain neurological diseases.
What if it was possible to control brain activity? This is the principle of optogenetics, developed for several decades. It consists in inserting, in the membrane of neurons, proteins which are activated only in the presence of light. This first allowed us to observe how electricity circulates in the brain. A team from the Stanford School of Medicine (California, United States), described this April 24 in Science an innovative method, which activates or deactivates certain brain cells.
Open a “channel” in the cell
At the moment, optogenetics is focusing on animal models. As in gene therapy, researchers inject proteins capable of reacting to light stimulation, the opsins. The neurons which receive them assimilate them, and end up producing them on their own at the level of their membrane. When light stimulation is sent to the brain, via an optical fiber inserted into the examination area, the opsins are activated.
The Stanford team has succeeded in acting on cells, via proteins, by stimulating or inhibiting them. “This is something that we, and other researchers in this field, have tried to do for a very long time,” says lead author of the study, Prof. Karl Deisseroth. Depending on the type of light pulse, it is possible to send a flow of positive ions (stimulators) or negative (inhibitors). Thanks to them, researchers control the behavior of cells.
Concretely, the stimulating light pushes the opsins to open a channel in the membrane of the cells. The type of protein used is slightly modified, so as to remain active even in the absence of light. This allows light to be sent from outside the brain, without implanting an optical fiber. Inhibitory light only worked in the presence of light: the channel closed in its absence. Stanford researchers managed to keep it open by changing the action of cells: a positively charged channel opens and attracts negative ions.
Towards a treatment of neurological disorders
Optogenetics currently allow us to observe how the brain works, more particularly how electrical messages are transmitted. Activating or deactivating certain neurons is therefore an opportunity to understand what roles they play, especially in emotions. But in the future, such a technique could become a treatment, underlines Dr Merab Kokaia, of the university hospital of Lund (Sweden), who took part in the study. “These tools could be much more useful in behavioral studies in animals, but they could also become an effective therapeutic alternative for neurological disorders that drugs do not treat – such as certain forms of severe epilepsy or other disorders. ‘hyperexcitability’, enthuses this researcher.
The method has already made it possible to better understand the functioning of Parkinson’s disease in 2009. If it is erected at the treatment stage, it could go as far as stimulating neuronal links damaged by this type of degeneration.
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