Warm nanoparticles stimulate the brain 18.03.2015

Nanoparticles heated by a magnetic field can replace conventional brain implants with electrodes and external power sources.

Many have heard about the methods of transcranial brain stimulation, when a particular area of ​​the cerebral cortex is affected by a magnetic field or a weak electric current without any surgical intervention. Last year, an article was published in Science stating that using an external magnetic field can improve memory, and in 2013, researchers from Ben-Gurion University were able to use it to rid several smokers of their bad habit - at least for six months. .

But purely transcranial methods are not highly specific. On the other hand, there are invasive methods, when we implant electrodes in the brain that selectively act on certain groups of cells. With the help of such electrodes, it is possible, for example, to suppress muscle tremor in patients with Parkinson's syndrome, but the inconvenience of this method is obvious: surgical intervention plus the need for an external power source.

Polina Anikeeva of the Massachusetts Institute of Technology and her lab have developed an ingenious method that eliminates the need for a permanent brain implant while still providing stimulation specificity. Its essence is that iron oxide nanoparticles are introduced into the brain, which do not carry any drugs, but can be heated in a magnetic field. When heated, they stimulate capsaicin receptors on cell membranes. Capsaicin is an alkaloid that provides a burning taste to capsicum, receptor proteins for it (TRPV1) are found in different cells, including some brain neurons. However, in the absence of receptors, it is possible to force the cell to synthesize them by genetic engineering methods - which was done in this case.

Proteins sensitive to capsaicin react to heated nanoparticles and open an ion channel in the membrane, as a result, the cell is excited and generates an impulse. Usually, such hot nanoparticles are considered as an antitumor agent that allows them to kill cancer cells, but this time the researchers were interested in just exciting the cells without killing them. By adjusting the strength of the magnetic field, you can achieve the desired temperature of the particles and the desired effect. They themselves, being chemically completely inert with respect to living tissue, can remain for quite a long time where they were introduced. As the authors of the work write in their article in Science, their method made it possible to stimulate an area of ​​the midbrain in mice called the ventral tegmental region (which, by the way, is involved in the reinforcement system and is involved in the formation of drug addiction) for a month.

In the future, nanoparticles with a magnetic field can be used as a wireless and "long-playing" neuron stimulator, which would allow solving a variety of research and medical problems. Of course, practical application is still far away, but we have a fundamental proof that such a method is possible and works - and this is already quite a lot.