Pain Sensing Could Involve Previously Unknown Cells

An organ that was previously unknown has been discovered by scientists. This finding is hoped to lead to the development of new pain killing drugs.

The research published in Science claims to have discovered special cells that surround the nerve cells that sense pain. These special cells extend into the outer layer of skin and are involved in sensing pain—a discovery that points to a new organ behind the feeling of pain.

The scientists believe that the findings provide new insight into pain and can answer longstanding confusion in the field of pain research. Patrik Ernfors, co-author of the study from the Karolinska Institute, Sweden, said: “The major question for us now is whether these cells are actually the cause for certain kinds of chronic pain disorders”.

The specialised cells reside in the skin and have been largely overlooked for their role. These are a kind of Schwann cells that wrap around nerve cells and keep them alive. The study revealed that these Schwann cells have an octopus-like shape and after examining tissues, the researchers found that the cells reside below the outer layer of the skin and also have long extensions that wrap the pain sensing nerve cells. The pain sensing nerve cells also extend up to the epidermis, the outer layer of the skin.

The finding is said to be path-breaking for understanding the neurobiological base of pain sensing. Till now it has been thought that the endings of the nerve cells in the epidermis are bare or unwrapped. In the field of pain research, scientists talk about free nerve endings that are responsible for the sensation of pain.

But the wrapping of the pain sensing nerve cells by the Schwann cells is not the big deal. What makes the findings outstanding is that the Schwann cells themselves can sense pain and then signal it to the brain via the nerve cells that they wrap.

For the research, the scientists used the technique of optogenetics. This technique involved a genetic modification of mice Schwann cells in the skin of their feet. The genetic modification produced a light absorbing protein in the Schwann cells.

When light falls on the cells, the light absorbing protein produced due to the genetic modification, the cells get stimulated—light affects the membrane and there is a shift in the cells’ electrical charge. Light- stimulated Schwann cells made the mice lift their feet. The mice also showed behaviour expressed in pain sensing—licking, shaking, guarding their paws. These indicated that stimulation of the Schwann cells caused pain in the mice.

When the pulses of light were increased in duration, the firing of the nearby nerve cells also increased. This suggests that the Schwann cells send a signal that carries the sensation of pain to the brain through the nerve cells.

The scientists also exposed the feet of the mice to heat, cold and pinpricks and observed their behaviour. Then they compared the behaviour with the response of the animal when light was used to activate the Schwann cells slightly to activate or deactivate them. The results showed that for all three kinds of stimuli, the mice showed a stronger pain response after the cells were activated by light. The work has to be replicated in humans.

The findings suggest that Schwann cells in the epidermis are important in pain sensing. The Schwann cells and the nerve cells they engulf, form a mesh like network and thus is a discovery of a new pain sensing organ, the scientists argue.