Sorting Out Stroking Sensations: Caltech biologists find individual neurons in the skin that react to massage

The skin is a human being’s largest sensory organ, helping to distinguish between a pleasant contact, like a caress, and a negative sensation, like a pinch or a burn. Previous studies have shown that these sensations are carried to the brain by different types of sensory neurons that have nerve endings in the skin. Only a few of those neuron types have been identified, however, and most of those detect painful stimuli. Now biologists at the California Institute of Technology (Caltech) have identified in mice a specific class of skin sensory neurons that reacts to an apparently pleasurable stimulus.

More specifically, the team, led by David J. Anderson, Seymour Benzer Professor of Biology at Caltech, was able to pinpoint individual neurons that were activated by massage-like stroking of the skin. The team’s results are outlined in the January 31 issue of the journal Nature.

Why Our Backs Can’t Read Braille: Scientists map sensory nerves in mouse skin

Johns Hopkins scientists have created stunning images of the branching patterns of individual sensory nerve cells. Their report, published online in the journal eLife on Dec. 18, details the arrangement of these branches in skin from the backs of mice. The branching patterns define ten distinct groups that, the researchers say, likely correspond to differences in what the nerves do and could hold clues for pain management and other areas of neurological study.

Each type of nerve cell that the team studied was connected at one end to the spinal cord through a thin, wire-like projection called an axon. On the other side of the cell’s “body” was another axon that led to the skin. The axons branched in specific patterns, depending on the cell type, to reach their targets within the skin. “The complexity and precision of these branching patterns is breath-taking,” says Jeremy Nathans, M.D., Ph.D., a Howard Hughes researcher and professor of molecular biology and genetics at the Institute for Basic Biomedical Sciences at the Johns Hopkins School of Medicine.

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Stanford’s touch-sensitive plastic skin heals itself

Nobody knows the remarkable properties of human skin like the researchers struggling to emulate it. Not only is our skin sensitive – sending the brain precise information about pressure and temperature – but it also heals efficiently to preserve a protective barrier against the world. Combining these two features in a single synthetic material presented an exciting challenge for Stanford chemical engineering Professor Zhenan Bao and her team.

Now, they have succeeded in making the first material that can both sense subtle pressure and heal itself when torn or cut. Their findings will be published Nov. 11 in the journal Nature Nanotechnology.

In the last decade, there have been major advances in synthetic skin, said Bao, the study’s principal investigator, but even the most effective self-healing materials had major drawbacks. Some had to be exposed to high temperatures, making them impractical for day-to-day use. Others could heal at room temperature, but repairing a cut changed their mechanical or chemical structure, so they could heal themselves only once. Most important, no self-healing material was a good bulk conductor of electricity, a crucial property.

"To interface this kind of material with the digital world, ideally you want it to be conductive," said Benjamin Chee-Keong Tee, a researcher on the project.

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Using ultrasound waves, MIT engineers have found a way to enhance the permeability of skin to drugs, making transdermal drug delivery more efficient. This technology could pave the way for noninvasive drug delivery or needle-free vaccinations, according to the researchers.

“This could be used for topical drugs such as steroids — cortisol, for example — systemic drugs and proteins such as insulin, as well as antigens for vaccination, among many other things,” says Carl Schoellhammer, an MIT graduate student in chemical engineering and one of the lead authors of a recent paper on the new system.

Ultrasound — sound waves with frequencies greater than the upper limit of human hearing — can increase skin permeability by lightly wearing away the top layer of the skin, an effect that is transient and pain-free.

In a paper appearing in the Journal of Controlled Release, the research team found that applying two separate beams of ultrasound waves — one of low frequency and one of high frequency — can uniformly boost permeability across a region of skin more rapidly than using a single beam of ultrasound waves.