Researchers from Imperial College London have uncovered a previously unknown method by which humans perceive light touches through hair follicles.
It was conventionally believed that only nerve endings within the skin and around hair follicles were responsible for transmitting such sensations. The study focused on the detection of touch within hair follicles, challenging the prior assumption that it was solely reliant on nerve endings within the skin.
The research, conducted on cell cultures, demonstrated that cells within hair follicles, the structures surrounding hair fibers, possess the ability to sense touch.
Moreover, the scientists observed that these hair follicle cells release neurotransmitters, namely histamine and serotonin, in response to touch. These findings hold potential implications for understanding the role of histamine in inflammatory skin conditions like eczema.
Processing Light Touch of Humans
Dr. Claire Higgins, the lead author of the study and affiliated with Imperial's Department of Bioengineering, expressed her surprise at this discovery.
The team is now focused on unraveling why hair follicle cells play this role in processing light touch, particularly given the abundance of sensory nerve endings within the follicle.
Their objective is to ascertain if hair follicles activate specific types of sensory nerves through an unidentified mechanism. Human touch perception involves multiple mechanisms.
Sensory nerve endings in the skin play a crucial role in detecting touch and transmitting signals to the brain. Additionally, richly innervated hair follicles are adept at detecting the movement of hair fibers.
There are also specialized sensory nerves known as C-LTMRs, exclusive to hairy skin, which process emotional or "feel-good" touch, according to the researchers.
The study employed single-cell RNA sequencing data from both human skin and hair follicles to discern the higher percentage of touch-sensitive receptors in hair follicle cells compared to their counterparts in the skin.
Through co-cultures of human hair follicle cells and sensory nerves, the researchers mechanically stimulated the hair follicle cells, resulting in the activation of adjacent sensory nerves.
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Analyzing Cells in Culture
Further investigation delved into understanding how the hair follicle cells communicate with sensory nerves. The team utilized a technique called fast-scan cyclic voltammetry to analyze cells in culture.
They observed that hair follicle cells release the neurotransmitters serotonin and histamine in response to touch. Blocking the receptors for these neurotransmitters on sensory neurons led to a cessation of response to hair follicle cell stimulation.
Similarly, blocking synaptic vesicle production by hair follicle cells hindered their ability to signal to the sensory nerves. A notable observation was made when the same experiments were conducted using cells from the skin rather than the hair follicles.
These cells released histamine in response to light touch but did not release serotonin. The researchers underscored that their experiments were conducted in cell cultures, emphasizing the need for replication in living organisms to validate the findings.
They also expressed interest in determining if hair follicles activate specific types of sensory nerves, particularly in light of the exclusive presence of C-LTMRs in hairy skin.
This aspect warrants further exploration to unveil the unique mechanism through which hair follicles communicate with these nerves. The findings of the study were published in the journal Science Advances.
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