Using magnets to turn on neurons

A newly designed ion channel allows scientists to use magnetic fields to force neurons to fire in animals’ brains. The channel joins a growing number of tools that are helping researchers map neural circuits and understand the roles different cells play in the brain.

To tease apart the daunting complexity of the brain, neuroscientists have developed techniques to activate or silence specific neurons. One such method, optogenetics, controls neurons with light but requires fiber optics to be inserted into animals’ brains or spinal cords.

Because magnetic fields can penetrate into tissue, Ali D. Güler of the University of Virginia and colleagues think their ion channel, which they call Magneto, provides a noninvasive means of manipulating groups of neurons in animals.

To design Magneto, they added the protein ferritin to the C-terminus of an ion channel called TRPV4. Ferritin binds iron and is paramagnetic. That means it is attracted to applied magnetic fields. So ferritin serves as a handle that allows magnetic fields to tug open the channels. When Magneto opens while sitting on a neuron’s surface, sodium and calcium ions flow through the channel and into the cell, triggering the neuron to fire.

In one experiment involving mice, they delivered Magneto’s DNA to neurons in reward circuits of the animals’ brains (Nat. Neurosci. 2016, DOI: 10.1038/nn.4265). These genetic instructions enabled the cells to express Magneto. When placed in a chamber with two arms, the mice preferred hanging out in the arm with neodymium magnets inserted in the walls, showing that the magnetic field activated reward-signaling cells.