Typically, it’s thought that we perceive harmful sensations on our skin entirely through the very sensitive endings of certain nerve cells. These nerve cells aren’t coated by a protective layer of myelin, as other types are. Nerve cells are kept alive by and connected to other cells called glia; outside of the central nervous system, one of the two major types of glia are called Schwann cells.
The authors of the new study, published Thursday in Science, say they were studying these helper cells near the skin’s surface in the lab when they came across something strange—some of the Schwann cells seemed to form an extensive “mesh-like network” with their nerve cells, differently than how they interact with nerve cells elsewhere. When they ran further experiments with mice, they found evidence that these Schwann cells play a direct, added role in pain perception, or nociception.
One experiment, for instance, involved breeding mice with these cells in their paws that could be activated when the mice were exposed to light. Once the light came on, the mice seemed to behave like they were in pain, such as by licking themselves or guarding their paws. Later experiments found that these cells—since dubbed nociceptive Schwann cells by the team—respond to mechanical pain, like being pricked or hit by something, but not to cold or heat.
Because these cells are spread throughout the skin as an intricately connected system, the authors argue that the system should be considered an organ.
“Our study shows that sensitivity to pain does not occur only in the skin’s nerve [fibers], but also in this recently discovered pain-sensitive organ,” said senior study author Patrik Ernfors, a pain researcher at Sweden’s Karolinska Institute, in a release from the university.