Chapter 8. General Principles of Sensory Processing, Touch, and Pain
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By JANE E. BRODY Marijuana has been used medically, recreationally and spiritually for about 5,000 years. Known botanically as cannabis, it has been called a “crude drug”: marijuana contains more than 400 chemicals from 18 chemical families. More than 2,000 compounds are released when it is smoked, and as with tobacco, there are dangers in smoking it. Medical marijuana clinics operate in 20 states and the District of Columbia, and its recreational use is now legal in Colorado and Washington. A Gallup poll conducted last month found that 58 percent of Americans support the legalization of marijuana. Yet researchers have been able to do relatively little to test its most promising ingredients for biological activity, safety and side effects. The main reason is marijuana’s classification by Congress in 1970 as an illegal Schedule I drug, defined as having a potential for abuse and addiction and no medical value. American scientists seeking clarification of marijuana’s medical usefulness have long been stymied by this draconian classification, usually reserved for street drugs like heroin with a high potential for abuse. Dr. J. Michael Bostwick, a psychiatrist at the Mayo Clinic in Rochester, Minn., said the classification was primarily political and ignored more than 40 years of scientific research, which has shown that cellular receptors for marijuana’s active ingredients are present throughout the body. Natural substances called cannabinoids bind to them to influence a wide range of body processes. In a lengthy report entitled “Blurred Boundaries: The Therapeutics and Politics of Medical Marijuana,” published last year in Mayo Clinic Proceedings, Dr. Bostwick noted that the so-called endocannabinoid system has an impact on the “autonomic nervous system, immune system, gastrointestinal tract, reproductive system, cardiovascular system and endocrine network.” Copyright 2013 The New York Times Company
If you were stung by a bark scorpion, the most venomous scorpion in North America, you’d feel something like the intense, painful jolt of being electrocuted. Moments after the creature flips its tail and injects venom into your skin, the intense pain would be joined by a numbness or tingling in the body part that was stung, and you might experience a shortness of breath. The effect of this venom on some people—small children, the elderly or adults with compromised immune systems—can even trigger frothing at the mouth, seizure-like symptoms, paralysis and potentially death. Based solely on its body size, the four-inch-long furry grasshopper mouse should die within minutes of being stung—thanks to the scorpion’s venom, which causes temporary paralysis, the muscles that allow the mouse to breathe should shut down, leading to asphyxiation—so you’d think the rodent would avoid the scorpions at all costs. But if you put a mouse and a scorpion in the same place, the rodent’s reaction is strikingly brazen. If stung, the four-inch-long rodent might jump back for a moment in surprise. Then, after a brief pause, it’ll go in for the kill and devour the scorpion piece by piece: This predatory behavior isn’t the result of remarkable toughness. As scientists recently discovered, the mouse has evolved a particularly useful adaptation: It’s immune to both the pain and paralytic effects that make the scorpion’s venom so toxic. Although scientists long knew that the mouse, native to the deserts of the American Southwest, preys upon a range of non-toxic scorpions, “no one had ever really asked whether they attack and kill really toxic scorpions,” says Ashlee Rowe of Michigan State University, who led the new study published today in Science.
Who would win in a fight: a bark scorpion or a grasshopper mouse? It seems like an easy call. The bark scorpion (Centruroides sculpturatus) delivers one of the most painful stings in the animal kingdom—human victims have compared the experience to being branded. The 25-gram grasshopper mouse (Onychomys torridus) is, well, a mouse. But as you can see in the video above, grasshopper mice routinely kill and eat bark scorpions, blissfully munching away even as their prey sting them repeatedly (and sometimes right in the face). Now, scientists have discovered why the grasshopper mice don’t react to bark scorpion stings: They simply don’t feel them. Evolutionary neurobiologist Ashlee Rowe at the University of Texas, Austin, has been studying the grasshopper mice’s apparent superpower since she was in graduate school. For the new study, she milked venom from nearly 500 bark scorpions and started experimenting. When she injected the venom into the hind paws of regular laboratory mice, the mice furiously licked the site for several minutes. But when she injected the same venom into grasshopper mice, they licked their paws for just a few seconds and then went about their business, apparently unfazed. In fact, the grasshopper mice appeared to be more irritated by injections of the saline solution Rowe used as a control. Rowe knew that grasshopper mice weren’t entirely impervious to pain—they reacted to injections of other painful chemicals such as formalin, just not the bark scorpion venom. To find out what was going on, she and her team decided to determine how the venom affects the grasshopper mouse’s nervous system, in particular the parts responsible for sensing pain. © 2013 American Association for the Advancement of Science
by Alyssa Botelho A sense of touch lets you connect with loved ones, makes your limbs feel your own, and helps you to interact with your surroundings. But people who are paraplegics or have lost limbs have to navigate the world without this most fundamental of sensory inputs. Sliman Bensmaia at the University of Chicago, Illinois, is working to change that with a new model for transmitting a sense of touch to the brain that bypasses regular routes. He hopes it will be a blueprint for constructing prosthetics that convey touch in the same way that natural limbs do. To start, Bensmaia and his colleagues trained rhesus macaques to focus their gaze in different directions depending on whether their index finger or fourth finger were being prodded. Microelectrodes were then placed in an area of the brain called the primary somatosensory cortex. This area represents an entire map of the body, with each neuron responsible for sensing when a different part of the skin is touched. Microelectrodes record the activity pattern of neurons. They can also be used in reverse – to deliver electrical stimulation to make neurons fire. Fourth finger exercise Next, the team recorded what activity occurred and where it registered in the somatosensory cortex when a monkey had its index or fourth finger poked. Then they stimulated the brain using the same pattern of activity. The monkeys reacted as if they had been touched – fixing their gaze in the direction they been taught in response to a poke. © Copyright Reed Business Information Ltd.
By Stephen L. Macknik and Susana Martinez-Conde Dennis Rogers is an unassuming guy. He's on the short side. And though muscular, he doesn't come across as the kind of towering Venice Beach, muscle-bound Arnold that you might expect from someone billed as the World's Strongest Man. Rather he has the kind of avuncular intensity you find in a great automobile mechanic—a mechanic who happens to be able to lift an engine with one hand while using the fingertips of the other hand to wrench the spark plugs out. Like it's nothing. Rogers, who has been known to keep two U.S. Air Force fighter planes from blasting away in opposite directions by holding them back with his bare hands, performed at the most recent Gathering for Gardner—a conference that celebrates the interests of one of Scientific American's greatest columnists, the late mathemagician Martin Gardner. We asked Rogers about the source of his incredible powers after the show, and we were surprised to learn that he did not know. Bill Amonette of the University of Houston–Clear Lake found that Rogers could recruit an abnormally high number of muscle fibers. But was this ability because of a freak genetic mutation? Another possibility, which Rogers thinks is more likely, is the way he processes pain when he strains those muscles. What if, instead of superpowered muscles, Rogers has a normal—though extremely well exercised—body, and his abilities arise because he can withstand more pain than most mere mortals? He claims that he does feel pain and is actually scared of dentists. In fact, during one stunt in which he held back four souped-up Harley motorbikes with straps, he bit down so hard he split a tooth from top to bottom. Rather than taking his chances at the dentist, he reached into his mouth, clamped his viselike fingertips onto the broken tooth, and extracted it, root and all. Rogers reasons that, unlike in the dentist's office—where he has no control over the pain that is inflicted on him—he has direct executive control over pain that he inflicts on himself. “I know it's coming, I have an idea of what to expect and I can decide to ignore it,” he says. © 2013 Scientific American
By NICHOLAS BAKALAR Black and Hispanic children who go to an emergency room with stomach pain are less likely than white children to receive pain medication, a new study reports, and more likely to spend long hours in the emergency room. The analysis, published in the October issue of Pediatrics, examined the records of 2,298 emergency room visits by people under 21, a nationally representative sample from a large survey conducted by the Centers for Disease Control and Prevention. About 53 percent were white, 24 percent non-Hispanic black, 21 percent Hispanic, and the rest from other ethnic or racial groups. Over all, 27.1 percent of white children with severe pain received analgesics, but only 15.8 percent of blacks, 18.9 percent of Hispanics and 7.1 percent of children of other races did. Black children were about 68 percent more likely than white children to spend longer than six hours in the emergency room, although there were no statistically significant differences among races in results for any diagnostic test. “This data set will not answer the question of why,” said the lead author, Dr. Tiffani J. Johnson, an instructor at the University of Pennsylvania School of Medicine. “It could be that white parents are more likely to ask for pain meds, or that minority patients are likely to get care in E.R.’s that have longer wait times. And it could be racial bias.” Copyright 2013 The New York Times Company
The Conservative government is launching a $1.3-billion free market in medical marijuana on Tuesday, eventually providing an expected 450,000 Canadians with quality weed. Health Canada is phasing out an older system on Monday that mostly relied on small-scale, homegrown medical marijuana of varying quality, often diverted illegally to the black market. In its place, large indoor marijuana farms certified by the RCMP and health inspectors will produce, package and distribute a range of standardized weed, all of it sold for whatever price the market will bear. The first sales are expected in the next few weeks, delivered directly by secure courier. "We're fairly confident that we'll have a healthy commercial industry in time," Sophie Galarneau, a senior official with the department, said in an interview. "It's a whole other ball game." The sanctioned birth of large-scale, free-market marijuana production comes as the Conservatives pillory Liberal Leader Justin Trudeau's campaign to legalize recreational marijuana. Health Canada is placing no limits on the number of these new capital-intensive facilities, which will have mandatory vaults and security systems. Private-dwelling production will be banned. Imports from places such as the Netherlands will be allowed. Already 156 firms have applied for lucrative producer and distributor status since June, with the first two receiving licences just last week. © CBC 2013
by Michael Slezak How do you convince someone that a finger they can't see or feel – one they don't even know is there – is actually part of their body? Turns out it's all in the wrist. The technique is a spin on the rubber hand illusion, developed almost 15 years ago. To perform the original trick, sit someone at a table and somehow hide one of their hands from their view. Then put a corresponding rubber hand on the table in front of them and stroke it while also stroking the real hand unseen. Bizarrely, they will often feel that the rubber hand is their own. Besides being a cool party trick, this illusion revealed a novel insight into how the brain develops its sense of "owning" body parts. It quickly led to treatments for conditions in which that sense is disrupted, such as phantom limb syndrome. Since then, the illusion has been tested thoroughly to find exactly what is needed for it to occur. We now know that the trick works using a rubber hand with a different colour skin to the participant and even without a rubber hand at all. You can do it just by making a person think you're going to stroke their hand. It's even been done in virtual reality. The theory emerging from these experiments is that if two different senses – like sight and touch – both suggest a rubber hand is yours, then your brain is convinced. © Copyright Reed Business Information Ltd.
Keyword: Pain & Touch
Link ID: 18700 - Posted: 09.25.2013
By NICHOLAS BAKALAR Many people use copper bracelets and magnetic wrist straps to alleviate the pain of arthritis, but a new randomized, double-blinded, placebo-controlled study concludes they do not work. British researchers randomized 65 patients with rheumatoid arthritis to receive one of four treatments: wearing a powerful magnetic wrist strap, a weak magnetic strap, a non-magnetic strap and a copper bracelet. Each patient wore each device for five weeks and completed pain surveys. The study appears in the September issue of PLoS One. The patients reported pain levels using a visual scale, ranging from “no pain” to “worst pain ever,” and recorded how often their joints felt tender and swollen. Researchers used questionnaires to assess physical limitations, and tested for inflammation by measuring blood levels of C-reactive protein and plasma viscosity. There was no statistically significant difference in any of these measures regardless of which type of device patients were wearing. Stewart J. Richmond, a researcher at the University of York who led the study, acknowledged that the devices may have some benefits as a placebo. “People swear by these things,” he said. “Is it ethically correct to allow patients to live in blissful ignorance? Or is it better to provide them with the facts? We can’t deceive patients. We have to be honest with them.” Copyright 2013 The New York Times Company
Keyword: Pain & Touch
Link ID: 18695 - Posted: 09.24.2013
By JOHN SCHWARTZ Candace Pert, a neuroscientist who helped discover a fundamental element of brain chemistry as a graduate student and went on to become a major proponent of alternative medicine, died on Sept. 12 at her home in Potomac, Md. She was 67. The cause was cardiac arrest, said her sister, Deane Beebe. Dr. Pert was working at the Johns Hopkins University School of Medicine in the 1970s when a team she was on found one of the most sought-after objects in brain research: the receptor in the brain that opiates like morphine fit into, like a key in a lock, allowing the drug’s effects to work. The discovery of the opioid receptor would, in 1978, earn the coveted Albert Lasker Award, often a precursor to the Nobel Prize. The award went to Solomon H. Snyder, who headed the lab. Neither Dr. Pert nor any of the other lab assistants was cited. Such omissions are common in the world of science; the graduate student in the lab rarely gets credit beyond being the first name on the papers describing the research. But Dr. Pert did something unusual: she protested, sending a letter to the head of the foundation that awards the prize, saying she had “played a key role in initiating the research and following it up” and was “angry and upset to be excluded.” Her letter caused a sensation in the field. Some saw her exclusion as an example of the burdens and barriers women face in science careers. In a 1979 article about Dr. Pert in the The Washington Post, Dr. Snyder, who had lauded Dr. Pert’s contributions in his Lasker acceptance speech, argued that “that’s the way the game is played,” adding that today’s graduate students will be tomorrow’s lab chiefs, and that “when they have students, it will be the same.” © 2013 The New York Times Company
Keyword: Pain & Touch
Link ID: 18685 - Posted: 09.21.2013
By William Saletan In much of this country, over the last three years, pro-lifers have banned abortions 20 weeks after fertilization. They’ve justified these bans by asserting—contrary to the most authoritative studies—that fetuses at this stage of development can feel pain. Their assertions, in turn, are based on research by several doctors. But the doctors don’t buy the pro-lifers’ conclusions. They say their research doesn’t support the bans. The 12 state bans (several of which have been blocked or limited by courts) begin with legislative “findings.” The findings parrot a 33-page report posted by the National Right to Life Committee and other pro-life organizations. The report cites the work of a number of researchers. Pam Belluck, an enterprising New York Times correspondent, contacted the researchers and asked them about the abortion bans. It turns out there’s a big gap between the science and the legislation. The pro-life report cites Dr. Nicholas Fisk, a former president of the International Fetal Medicine and Surgery Society, 27 times. According to the report, Fisk’s work shows fetal “stress responses” that imply sensitivity to pain. But Fisk tells Belluck that he doesn’t buy the inference from stress hormones and cerebral blood flow to pain. Neural studies, he says, have persuaded him that until 24 weeks gestation—the current abortion limit in many states—fetal pain “is not possible at all.” The report also cites Dr. Mark Rosen, a fetal anesthesia pioneer, 16 times. Rosen’s work, the report suggests, shows that painkillers and anesthesia are common during fetal surgery because unborn children can feel pain. But Rosen tells Belluck that the real purpose of such drugs during fetal surgery is to minimize dangerous movement and harmful stress hormones, thereby facilitating recovery. The drugs don’t signify medical belief in fetal pain. Dr. Scott Adzick, another fetal surgery expert cited in the pro-life report, makes the same point. © 2013 The Slate Group, LLC
By William Skaggs At the level of personal experience, there is nothing that seems easier to understand than pain. When I jam my finger in a doorway, I have no difficulty at all recognizing the sensation that results. But this superficial simplicity covers up a world of complexity at the level of brain mechanisms, and the complexities are even greater when we try to identify pain in other people or other species of animals. Some of the complexities are purely scientific, but others are caused by moral or philosophical issues getting mixed up with scientific issues. My provocation for writing this post was a blog post called Do Octopuses Feel Pain?, by Katherine Harmon, who writes the blog Octopus Chronicles, It’s basically a nice article—there’s nothing objectionable about it—but it pressed one of my buttons. She made a number of important points, and altogether what she wrote is well worth reading, but nevertheless the result left me with a feeling of dissatisfaction, as do most scientific discussions about pain in animals. I’d like to try to explain where that discomfort comes from. In her blog post, Harmon listed three elements that are involved in feeling pain: (1) nociception, that is, having mechanisms in the body that are capable of detecting damage and transmuting it into neural signals; (2) the experience of pain; (3) the ability to communicate pain information from sensation to perception. I’m not sure I understand the third aspect, but I take it to mean the ability to transform nociception into experience. In any case, the essence of pain as most people understand it is aspect 2. Most people think of pain as a particular type of experience—as something that happens inside our minds and can only be observed by ourselves. © 2013 Scientific American
Keyword: Pain & Touch
Link ID: 18679 - Posted: 09.21.2013
The structure of the brain may predict whether a person will suffer chronic low back pain, according to researchers who used brain scans. The results, published in the journal Pain, support the growing idea that the brain plays a critical role in chronic pain, a concept that may lead to changes in the way doctors treat patients. The research was supported by the National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health. “We may have found an anatomical marker for chronic pain in the brain,” said Vania Apkarian, Ph.D., a senior author of the study and professor of physiology at Northwestern University Feinberg School of Medicine in Chicago. Chronic pain affects nearly 100 million Americans and costs the United States up to $635 billion per year to treat. According to the Institute of Medicine, an independent research organization, chronic pain affects a growing number of people. “Pain is becoming an enormous burden on the public. The U.S. government recently outlined steps to reduce the future burden of pain through broad-ranging efforts, including enhanced research,” said Linda Porter, Ph.D, the pain policy advisor at NINDS and a leader of NIH’s Pain Consortium. “This study is a good example of the kind of innovative research we hope will reduce chronic pain which affects a huge portion of the population.” Low back pain represents about 28 percent of all causes of pain in the United States; about 23 percent of these patients suffer chronic, or long-term, low back pain.
Keyword: Pain & Touch
Link ID: 18663 - Posted: 09.18.2013
By PAM BELLUCK It is a new frontier of the anti-abortion movement: laws banning abortion at 20 weeks after conception, contending that fetuses can feel pain then. Since 2010, a dozen states have enacted them, most recently Texas. Nationally, a bill passed the Republican-dominated House of Representatives in June. The science of fetal pain is highly complex. Most scientists who have expressed views on the issue have said they believe that if fetuses can feel pain, the neurological wiring is not in place until later, after the time when nearly all abortions occur. Several scientists have done research that abortion opponents say shows that fetuses can feel pain at 20 weeks after conception. One of those scientists said he believed fetuses could likely feel pain then, but he added that he believed the few abortions performed then could be done in ways to avoid pain. He and two other scientists said they did not think their work or current evidence provided scientific support for fetal-pain laws. Some scientists’ views have evolved as more research has been done. Dr. Nicholas Fisk, a senior maternal-fetal medicine specialist at Royal Brisbane and Women’s Hospital in Australia, said he once considered early fetal pain “a major possibility” after finding that fetuses receiving blood transfusions produced increased stress hormones and blood flow to the brain, and that painkillers lowered those levels. But Dr. Fisk, a former president of the International Fetal Medicine and Surgery Society, said neurological research has convinced him that pain “is not possible at all” before 24 weeks. © 2013 The New York Times Company
by Andy Coghlan A girl who does not feel physical pain has helped researchers identify a gene mutation that disrupts pain perception. The discovery may spur the development of new painkillers that will block pain signals in the same way. People with congenital analgesia cannot feel physical pain and often injure themselves as a result – they might badly scald their skin, for example, through being unaware that they are touching something hot. By comparing the gene sequence of a girl with the disorder against those of her parents, who do not, Ingo Kurth at Jena University Hospital in Germany and his colleagues identified a mutation in a gene called SCN11A. This gene controls the development of channels on pain-sensing neurons. Sodium ions travel through these channels, creating electrical nerve impulses that are sent to the brain, which registers pain. Overactivity in the mutated version of SCN11A prevents the build-up of the charge that the neurons need to transmit an electrical impulse, numbing the body to pain. "The outcome is blocked transmission of pain signals," says Kurth. To confirm their findings, the team inserted a mutated version of SCN11A into mice and tested their ability to perceive pain. They found that 11 per cent of the mice with the modified gene developed injuries similar to those seen in people with congenital analgesia, such as bone fractures and skin wounds. They also tested a control group of mice with the normal SCN11A gene, none of which developed such injuries. © Copyright Reed Business Information Ltd.
Amanda Fiegl What's the difference between a spicy meal and being tickled? Not much, from your lips' perspective. A new study reports that Szechuan pepper activates the same nerves that respond to a light physical touch. Researchers at the University College London Institute of Cognitive Neuroscience found that people experienced the same sensation when either Szechuan pepper—a spice used in many types of Asian cuisine—or a machine vibrating at a particular frequency was placed on their lips. "The pepper is sending the same information to the brain as having a buzzer on your lips," the study's lead author, Nobuhiro Hagura, said in an email. The study, published today in Proceedings of the Royal Society B with the wry headline "Food Vibrations," delves into the little-known field of psychophysics, which "describes the relation between physical reality and what we actually perceive," Hagura said. "Our research shows just one interesting example of a case where we perceive something quite different than what is actually there," he said. "In many cases, the difference between perception and reality can be explained by understanding how the nervous system transmits information about the outside world to the brain." Previous studies have shown that other spicy ingredients, such as chili peppers and mustard oils, activate the nerve fibers associated with pain and physical heat. And studies in animals indicated that the spicy chemical in Szechuan pepper—sanshool—acts on the nervous system's "light touch" fibers. So Hagura and his colleagues wanted to find out whether sanshool produces a conscious sensation of touch in humans. © 1996-2013 National Geographic Society.
By Michele Solis Like truth and beauty, pain is subjective and hard to pin down. What hurts one moment might not register the next, and our moods and thoughts color the experience of pain. According to a report in April in the New England Journal of Medicine, however, researchers may one day be able to measure the experience of pain by scanning the brain—a much needed improvement over the subjective ratings of between one and 10 that patients are currently asked to give. Led by neuroscientist Tor Wager of the University of Colorado at Boulder, researchers used functional MRI on healthy participants who were given heated touches to their arm, some pleasantly warm, others painfully hot. During the painful touches, a scattered group of brain regions consistently turned on. Although these regions have been previously associated with pain, the new study detected a striking and consistent jump in their activity when people reported pain, with much greater accuracy than previous studies had attained. This neural signature appeared in 93 percent of subjects reporting to feel painful heat, ramping up as pain intensity increased and receding after participants took a painkiller. The researchers determined that the brain activity specifically marked physical pain rather than a generally unpleasant experience, because it did not emerge in people shown a picture of a lover who had recently dumped them. Although physical pain and emotional pain involve some of the same regions, the study showed that fine-grained differences in activation separate the two conditions. © 2013 Scientific American
by Nancy Shute It was hard to ignore those headlines saying that people with migraine have brain damage, even if you're not among the 12 percent or so who do suffer from these painful, recurring headaches. Don't panic, says the neurologist whose work sparked those alarming headlines. "It's still not something to stay up nights worrying about," says Dr. Richard Lipton, director of the Montefiore Headache Center in New York. But knowing about the brain anomalies that Lipton and his colleagues found might help people reduce their stroke risk. Some people who get do have a slightly . And some of the brain changes identified in the study look like mini-strokes. "On the MRI they look like very tiny strokes," Lipton tells Shots. But the people aren't having any stroke symptoms. Still, Lipton is convinced that the process is the same. "We now know it's a risk factor for these very small silent strokes," he says. The scientists evaluated data from 19 studies in which people with migraine headaches got MRI scans of their brains. Just about everybody is going to have some abnormalities show up in a scan. But the people who had migraines were more likely to have two common abnormalities: white matter abnormalities and infarct-like lesions. The were published in the journal Neurology. ©2013 NPR
By Katherine Harmon The past couple posts have described some pretty severe experiments on octopuses, including: showing how octopus arms can grow back after inflicted damage and how even severed octopus arms can react to stimuli. (For the record, animals in the studies were anesthetized and euthanized, respectively.) Without getting too far into the woods (or reefs) of animal treatment ethics, the question remains: How much pain and distress can these relatively short-lived invertebrates experience? Luckily for us, a new paper deals with that very question. Researchers from Europe, the UK and Japan teamed up to explore what we know about pain, perception and cognition in octopuses. The findings are described in the special “Cephalopod Research” issue of September’s Journal of Experimental Marine Biology and Ecology. And the issue is not just philo-scientific cloud (or wave) gazing. Starting this year the European Union asks researchers to make similarly humane accommodations for cephalopods as they do for vertebrates (Directive 2010/63/EU, pdf). But, do octopuses experience would-be painful experiences the same way mice do? As the researchers note in their paper, we know very little about whether cephalopods recognize pain or experience suffering and distress in a similar way that we humans—or even we vertebrates—do. Previous (as well as much current) research has looked largely to behavioral clues as an indication to an octopus’s internal state. For example, researchers have observed an octopus’s color changing and activity patterns and looked for any self-inflicted harm (swimming into the side of a tank or eating its own arms) to judge whether the animal is “stressed.” And to tell whether an animal has “gone under” anesthesia, they often look for movements, lack of response, posture change or, at the most, measure heart rate and breathing. © 2013 Scientific American
By Cristy Gelling Bacteria can directly trigger the nerves that sense pain, suggesting that the body’s own immune reaction is not always to blame for the extra tenderness of an infected wound. In fact, mice with staph-infected paws showed signs of pain even before immune cells had time to arrive at the site, researchers report online August 21 in Nature. “Most people think that when they get pain during infection it’s due to the immune system,” says coauthor Isaac Chiu of Boston Children’s Hospital and Harvard Medical School. Indeed, immune cells do release pain-causing molecules while fighting off invading microbes. But in recent years scientists have started uncovering evidence that bacteria can also cause pain. Chiu and his colleagues stumbled on this idea when they grew immune cells and pain-sensing cells together in a dish. The researchers were trying to activate the immune cells by adding bacteria to the mix but were surprised to see an immediate response in the nerve cells instead. This made them suspect that nerve cells were sensing the bacteria directly. To take a closer look at a real infection, the team injected the back paws of mice with Staphylococcus aureus, a bacterium that causes painful sores in humans. The researchers measured how tender the infected area was by poking it with flexible filaments of plastic. If the mouse didn’t like being prodded, it would lift its paw, giving a sensitive measure of each infection’s ouch factor. © Society for Science & the Public 2000 - 2013