Most people who were stung with a needle know the drill: first the puncture, then the sharp, burning pain and the urge to withdraw or at least flinch. The exact circuitry behind this near-universal response has not been fully elucidated, but scientists may have just found one important piece of the puzzle: a hitherto unknown sensory organ in the skin.
This structure is referred to as a nociceptive glio-neuronal complex much like the typical picture of a complex organ such as heart or spleen. Instead, it is a simple organ made up of a network of cells, called glial cells, that are known to surround and support the nerve cells of the body. In this case, the glial cells form a reticular structure between the outer and inner skin layers, with filamentous projections extending into the outer skin layer. (Also find out about a kind of simple organ that has recently been found in humans, the so-called interstitium.)
As reported by the study team today in the journal Science this modest organ seems to play a key role in the perception of mechanical pain to play – complaints of pressure, stinging and other effects on the skin. So far, individual cells, so-called nociceptive fibers, have been considered as the main starting points for this type of pain.
"Probably for a hundred years, we have thought that the pain emanates from nerves in the skin," says study co-author Patrik Ernfors, a molecular neurobiologist at Karolinska Institutet in Sweden. "What we are now showing is that pain can also be triggered in these glial cells."
The team first identified this new organ in mice and tested its functionality by measuring rodent responses to different responses Types of pain. When the cells in the organ were turned off by gene editing, the animals responded normally to thermal pain or discomfort caused by heat or cold. However, all mice showed a reduced response to mechanical pain when the glial complex was deactivated.
The results change the way scientists think about the onset and progression of pain – at least in mice. The scientists have not yet checked whether the organ is present in humans, but Ernfors says that the likelihood is high.
"Considering that all other previously known sensory organs in [mice] are also present in humans, it is possible, if not likely, that this is the case. Sensory organ is also present in our skin," he says.
In this case, the work can help find treatments for a variety of neuropathic pain disorders, which affect an estimated 10 percent of the US population and between 7 and 10 percent of the European population, says Ernfors. For example, if you're looking for ways to change this cell network, you may be able to help people with allodynia. In this condition, the skin becomes so sensitive that even light touches or brushes can be unbearable. (Also, be aware of the prevalence of the eczema syndrome, the misconception that insects bite or crawl on or under the skin.)
University of Maryland School of Medicine, which was not involved in the study. "It's exciting to know that there is a system that is much more than the nociceptive fibers we impart to our students."