As science progresses we are constantly learning new things about the human body, from finding differences in voice prints between people who have diabetes and the general population, to noticing whole new organs inside the human head.
Add to that list a new sense of touch, which we weren’t aware of before. Humans sense touch mainly through receptors in the top layer of skin, and in the skin surrounding hair follicles detecting the movement of your hair. However, a team analyzing single cell RNA sequencing data of human skin and hair follicles found that hair follicles themselves contain a higher than expected percentage of touch-sensitive receptors.
This was intriguing, so next the team, from Imperial College London, created co-cultures of human hair follicle cells and sensory nerve cells. They then stimulated the hair follicle cells, and found that this activated the adjacent sensory nerve cells. After being stimulated, the cells were passing on a signal to the nerve cells, but the team didn’t know how. Analyzing the hair follicle cells in culture, they found that they were releasing the neurotransmitters serotonin and histamine.
“The release of different signaling molecules is likely to facilitate interaction and communication with different sensory neurons surrounding the follicle,” the team explained in their paper, “leading to a variety of physical and emotive effects within the nervous system and brain.”
When the receptors for these transmitters were blocked in the sensory nerve cells, they no longer responded when the adjacent follicle cells were stimulated, suggesting that this was indeed how hair follicles were passing on a sense of touch.
“This is a surprising finding as we don’t yet know why hair follicle cells have this role in processing light touch,” senior author Dr Claire Higgins said in a statement. “Since the follicle contains many sensory nerve endings, we now want to determine if the hair follicle is activating specific types of sensory nerves for an unknown but unique mechanism.”
Repeating the same experiments on skin cells, the team found that they released histamine but not serotonin. This discovery has applications in its own right.
“This is interesting as histamine in the skin contributes to inflammatory skin conditions such as eczema, and it has always been presumed that immune cells called mast cells release all the histamine,” Higgins added. “Our work uncovers a new role for skin cells in the release of histamine, with potential applications for eczema research.”
The study is published in Science Advances.