A human hair follicle (pink) surrounded by a sensory nerve ending (green). Credit: Julia Agramunt
Key points:
- New research in cell cultures shows that cells within hair follicles are able to detect sensation.
- Researchers found that the hair follicle cells release histamine and serotonin in response to touch.
- The findings could help researchers better understand histamine’s role in inflammatory skin diseases like eczema.
Previously, touch was thought to be detected only by nerve endings present within the skin and surrounding hair follicles. But now, a team of researchers at Imperial College of London have discovered a hidden mechanism within hair follicles that allow people to feel touch.
The researchers also found that hair follicle cells release the neurotransmitters histamine and serotonin in response to touch—results that could shed light on skin diseases like eczema.
For the study, published in Science Advances, researchers established co-cultures of human hair follicle cells and sensory nerves, then mechanically stimulated the hair follicle cells, finding that this led to activation of the adjacent sensory nerves. Then, they used a technique known as fast scan cyclic voltammetry to analyze the cells in culture, discovering that the hair follicle cells were releasing serotonin and histamine in response to touch.
When they blocked the receptor for these neurotransmitters on the sensory neurons, the neurons no longer responded to the hair follicle cell stimulation. Similarly, when they blocked synaptic vesicle production by hair follicle cells, they were no longer able to signal to the sensory nerves.
The researchers also conducted the same experiments with cells from the skin instead of the hair follicle. The cells responded to light touch by releasing histamine, but they didn’t release serotonin.
“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,” said lead author Claire Higgins, professor of bioengineering at Imperial. “Our work uncovers a new role for skin cells in the release of histamine, with potential applications for eczema research.”
Since the experiments were performed in cell cultures, the next step will be to replicate the findings in living organisms. The researchers say they also want to determine if the hair follicles are activating specific types of sensory nerves. Since C-LTMRs are only present within hairy skin, they are interested to see if hair follicles have a unique mechanism to signal to these nerves—one that we have yet to uncover.