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Human Sense of Touch Consists of 16 Unique Types of Nerve Cells

The AHA! Team — Fri, 24 Jan 2025 07:50:08 +0000

Linköping University via EurekAlert! – No less than 16 different types of nerve cells have been identified by scientists in a new study on the human sense of touch. Comparisons between humans, mice and macaques show both similarities and significant differences. The study, a collaboration between researchers at Linköping University and Karolinska Institutet in Sweden and the University of Pennsylvania in the USA, has been published in Nature Neuroscience. “Our study provides a landscape view of the human sense of touch. As a next step, we want to make portraits of the different types of nerve cells we have identified,” says Håkan Olausson, Professor at Linköping University, about the study published in Nature Neuroscience. We perceive touch, temperature and pain through the somatic sensation system. A common understanding is that there is a specific type of nerve cell for each type of feeling, such as pain, pleasant touch, or cold. But the findings from the current study challenge that notion and show that bodily sensations are probably much more complicated than that. Much of the knowledge we have today about how the nervous system works comes from research on animals. But how big are the similarities between, for example, a mouse and a human? Many findings in animal studies have not been confirmed in human research. One reason for this may be that our understanding of how it works in humans is inadequate. The researchers behind the current study, therefore, wanted to create a detailed atlas of different types of nerve cells involved in human somatosensation and compare it with those of mice and macaques, a primate species. In the study, a research group at the University of Pennsylvania, led by Associate Professor Wenqin Luo, made detailed analyses of the genes used by individual nerve cells, so-called deep RNA sequencing. Nerve cells that had similar gene expression profiles were grouped together as one sensory nerve cell type. In this way, they identified 16 distinct types of nerve cells in humans. As the researchers analyse more cells, they will likely discover even more distinct types of sensory nerve cells. The nerve cell gene expression analyses provide a picture of what the cellular machinery looks like in the different cell types. The next question was how this relates to nerve cell function. If a nerve cell produces a protein that can detect heat, does that mean that the nerve cell responds to heat? The current study is the first to link gene expression in different types of nerve cells with their actual function. To investigate the function of nerve cells, a research group at Linköping University, led by Saad Nagi and Håkan Olausson, used a method that allows the researchers to listen to the nerve signalling in one nerve cell at a time. Using this method, called microneurography, the researchers can subject skin nerve cells in awake participants to temperature, touch or certain chemicals, and “listen in on” an individual nerve cell to find out if that particular nerve cell is reacting and sending signals to the brain. During these experiments, the researchers made discoveries that would not have been possible, had the mapping of the cellular machinery of different types of nerve cells not given them new ideas to test. One such discovery concerns a type of nerve cell that responds to pleasant touch. The researchers found that this cell type unexpectedly also reacts to heating and capsaicin, the substance that gives chili its heat. Reacting to capsaicin is typical of pain-sensing nerve cells, so it surprised the researchers that touch-sensing nerve cells responded to such stimulation. Further, this nerve cell type also responded to cooling, even though it does not produce the only protein so far known to signal cold perception. This finding cannot be explained by what is known about the cell’s machinery and suggests that there is another mechanism for detection of cold, which has not yet been discovered. The authors speculate that these nerve cells form an integrated sensory pathway for pleasant sensations. “For ten years, we’ve been listening to the nerve signals from these nerve cells, but we had no idea about their molecular characteristics. In this study, we see what type of proteins these nerve cells express as well as what kind of stimulation they can respond to, and now we can link it. It’s a huge step forward”, says Håkan Olausson. Another example is a type of very rapidly conducting pain-sensing nerve cell, which was found to respond to non-painful cooling and menthol. “There’s a common perception that nerve cells are very specific – that one type of nerve cell detects cold, another senses a certain vibration frequency, and a third reacts to pressure, and so on. It’s often talked about in those terms. But we see that it’s a lot more complicated than that,” says Saad Nagi, Associate Professor at Linköping University. And what about the comparison between mice, macaques and humans? How similar are we? Many of the 16 types of nerve cells that the researchers identified in the study are roughly similar between the species. The biggest difference the researchers found was in very rapidly conducting pain-sensing nerve cells that react to stimulation that can cause injury. These were first discovered in humans in 2019 by the same group at Linköping using microneurography. Compared to the mouse, humans have many more pain nerve cells of the type that send pain signals to the brain at high speed. Why this is so, the study cannot answer, but the researchers have a theory: “The fact that pain is signalled at a much higher velocity in humans compared to mice is probably just a reflection of body size. A mouse doesn’t require such rapid nerve signalling. But in humans, the distances are greater, and the signals need to be sent to the brain more rapidly; otherwise, you’d be injured before you even react and withdraw,” says Håkan Olausson. The study is a collaboration between Patrik Ernfors’ research group at Karolinska Institutet, Wenqin Luo’s research group at the University of Pennsylvania and Håkan Olausson and Saad Nagi’s research group at Linköping University. Financial support for the study was provided by the National Institutes of Health, the Swedish Research Council, ALF Grants Region Östergötland, and the Knut and Alice Wallenberg Foundation. Article: Leveraging Deep Single-soma RNA Sequencing to Explore the Neural Basis of Human Somatosensation, Huasheng Yu, Saad S. Nagi, Dmitry Usoskin et al. (2024). Nature Neuroscience, published online November 4 2024, doi: 10.1038/s41593-024-01794-1 Journal Nature Neuroscience DOI 10.1038/s41593-024-01794-1 To read the original article click here.

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New Technology Restores Sense of Touch to Damaged Nerves

AHA Publisher — Tue, 13 Jul 2021 07:06:18 +0000

Nicky Blackburn via Israel21c – A groundbreaking technology that can restore the sense of touch to nerves damaged as a result of amputation or injury has been developed by a team of scientists in Israel. The technology, developed at Tel Aviv University and tested so far only in animals, involves a tiny sensor implanted in the nerve of the injured limb, and connected directly to a healthy nerve. Every time the limb touches an object, the sensor – which does not require electricity, wires or batteries — is activated and conducts an electric current to the functioning nerve, recreating the sense of touch. “Loss of sensation can result from a very wide range of injuries, from minor wounds – like someone chopping a salad and accidentally cutting himself with the knife – to very serious injuries,” said Ben Maoz from the Department of Biomedical Engineering, Fleischman Faculty of Engineering, and one of the leaders of the research. Work on the sensor began after a chance meeting between Maoz and a surgeon, Dr. Amir Arami, from the Sackler School of Medicine and the Microsurgery Unit in the Department of Hand Surgery at Sheba Medical Center. “We were talking about the challenges we face in our work and Dr. Arami shared with me the difficulty he experiences in treating people who have lost tactile sensation in one organ or another as a result of injury,” said Maoz. “Even if the wound can be healed and the injured nerve can be sutured, in many cases the sense of touch remains damaged. People lacking tactile sensation cannot feel if their finger is being crushed, burned or frozen.” “We decided to tackle this challenge together, and find a solution that will restore tactile sensation to those who have lost it,” he added. The researchers, working with a team of five other scientists, developed a sensor that can be implanted on a damaged nerve under the tip of the finger and connected to another nerve that functions properly. The device consists of two tiny plates less than half a centimeter by half a centimeter in size. When these plates come into contact with each other, they release an electric charge that is transmitted to the undamaged nerve. A Normal Sensation of Touch When the injured finger touches something, the touch releases tension corresponding to the pressure applied to the device – weak tension for a weak touch and strong tension for a strong touch – just like in a normal sense of touch. Unlike existing technologies that use sensors to replace damaged nerves, batteries and electricity are not required to power the new sensor, the scientists explained, as it works on frictional force – whenever the device senses friction, it charges itself. The device can be implanted in a simple process anywhere in the body where tactile sensation needs to be restored, and bypasses damaged sensory organs. It is developed from biocompatible material that is safe to use in the human body, does not require maintenance and is not visible externally. “We tested our device on animal models, and the results were very encouraging,” said Maoz, adding that the team will continue animal trials before they move to clinical trials. “At a later stage [we will] implant our sensors in the fingers of people who have lost the ability to sense touch. Restoring this ability can significantly improve people’s functioning and quality of life, and more importantly, protect them from danger.” The study was published in the journal ACS Nano. Other scientists involved in the sensor development include Iftach Shlomy, Shay Divald, and Yael Leichtmann-Bardoogo from the Department of Biomedical Engineering, Fleischman Faculty of Engineering, and Keshet Tadmor from the Sagol School of Neuroscience. To read the original article click here. For more information from Israel21c click here.

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New Therapy Provides Relief in Patients with Chronic Low Back Pain

AHA Publisher — Tue, 23 Jun 2020 07:00:27 +0000

University of Rochester Medical Center via News-Medical Net – A new study has found that tanezumab, a monoclonal antibody that inhibits nerve activity, provides relief in patients with chronic low back pain, one of the leading reasons why people seek medical care and the number one cause of disability worldwide. “This demonstration of efficacy is a major breakthrough in the global search to develop non-opioid treatments for chronic pain,” said John Markman, M.D., director of the Translational Pain Research Program in the University of Rochester Medical Center (URMC) Department of Neurosurgery and lead author of the study which appears in the journal Pain. “There were also improvements in function linked to the reduction in pain severity.” This is the first study that shows long-term relief for chronic low back pain with a single dose of tanezumab delivered under the skin once every two months. The study was conducted in 191 sites across eight countries in North America, Europe, and Asia. Researchers are increasingly finding that certain proteins circulating in the bloodstream heighten the sensitivity of cells in the nervous system to pain. One of these proteins, called nerve growth factor (NGF), may explain why some individuals experience more intense and chronic back pain. Tanezumab is an NGF inhibitor. The patients with chronic low back pain enrolled in this study did not previously have relief with at least three different types of pain medication, including opioids, and were considered “difficult-to-treat.” Patients with symptoms, signs, and x-ray evidence of moderate-to-severe osteoarthritis, a disorder commonly found in older patients with chronic low back pain, were excluded from the study. Tanezumab has not been associated with the often serious adverse side effects seen with opioids or nonsteroidal anti-inflammatory drugs (NSAIDs), which are often used to treat low back pain. However, this class of drugs has been linked to joint problems, which are sometimes serious enough to require joint replacement. Because of this concern, the researchers followed participants for an extended period and determined there was a low rate of serious joint problems requiring joint replacement. “In the future, clinicians may have to weigh the different risks of lumbar fusion surgery, chronic opioid use, or NSAIDs against the unique risks of a rare but rapidly progressive form of joint problem associated with blocking nerve growth factor. I expect that that the tradeoffs between benefit and risk will be different for osteoarthritis than for chronic low back pain.” John Markman, M.D., Director of the Translational Pain Research Program in the University of Rochester Medical Center (URMC) Department of Neurosurgery. To read the original article click here.

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