Controlling Muscles with Light: Neuroscientists Inhibit Muscle Contractions

Can you imagine controlling muscles with light? MIT neuroscientists have shown that they can do just that by applying optogenetics, a technique that allows them to control neurons' electrical impulses with light.

The researchers wanted to explore the function of inhibitory interneurons, which form circuits with many other neurons in the spinal cord. These circuits execute commands from the brain, with additional input from sensory information from the limbs. In previous studies, scientists used electrical stimulation or pharmacological intervention to control neurons' activity. Yet the scientists decided to take a different approach, in this case.

Optogenetics allow scientists to control specific types of neurons by genetically programming them to express light-sensitive proteins. These proteins, called opsins, then act as ion channels or pumps that regulate neurons' electrical activity.

In order to study the function of inhibitory neurons, the scientists examined mice in which all inhibitory spinal neurons were engineered to suppress an opsin called channelrhodopsin 2. This opsin stimulates neural activity when exposed to blue light. Then, the scientists shone light at different points along the spine.

"The spinal location where we found this complete suppression was completely new," said Vittorio Caggiano, one of the researchers, in a news release. "It has not been shown by any other scientists that there is this front-to-back suppression that affects only motor behavior without affecting sensory behavior."

Now that the researchers have found that optogenetics are useful in this sort of study, they plant to explore the roles of other types of spinal cord neurons.

"There's huge interest in trying to extend these studies and dissect these circuits because we tackled only the inhibitory system in a very global way," said Caggiano. "Further studies will highlight the contribution of single populations of neurons in the spinal cord for the control of limbs and control of movement."

The findings are published in the journal PLOS One.