Links for Keyword: Chemical Senses (Smell & Taste)

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By Joanne Silberner Think for a minute about the little bumps on your tongue. You probably saw a diagram of those taste bud arrangements once in a biology textbook — sweet sensors at the tip, salty on either side, sour behind them, bitter in the back. But the idea that specific tastes are confined to certain areas of the tongue is a myth that “persists in the collective consciousness despite decades of research debunking it,” according to a review published this month in The New England Journal of Medicine. Also wrong: the notion that taste is limited to the mouth. The old diagram, which has been used in many textbooks over the years, originated in a study published by David Hanig, a German scientist, in 1901. But the scientist was not suggesting that various tastes are segregated on the tongue. He was actually measuring the sensitivity of different areas, said Paul Breslin, a researcher at Monell Chemical Senses Center in Philadelphia. “What he found was that you could detect things at a lower concentration in one part relative to another,” Dr. Breslin said. The tip of the tongue, for example, is dense with sweet sensors but contains the others as well. The map’s mistakes are easy to confirm. If you place a lemon wedge at the tip of your tongue, it will taste sour, and if you put a bit of honey toward the side, it will be sweet. The perception of taste is a remarkably complex process, starting from that first encounter with the tongue. Taste cells have a variety of sensors that signal the brain when they encounter nutrients or toxins. For some tastes, tiny pores in cell membranes let taste chemicals in. Such taste receptors aren’t limited to the tongue; they are also found in the gastrointestinal tract, liver, pancreas, fat cells, brain, muscle cells, thyroid and lungs. We don’t generally think of these organs as tasting anything, but they use the receptors to pick up the presence of various molecules and metabolize them, said Diego Bohórquez, a self-described gut-brain neuroscientist at Duke University. For example, when the gut notices sugar in food, it tells the brain to alert other organs to get ready for digestion. © 2024 The New York Times Company

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 29336 - Posted: 06.02.2024

Rudi Zygadlo To celebrate our anniversary, my partner and I dine in a trendy London restaurant in Hackney with a Michelin star – my first time in such a place. A crispy little bonbon is introduced to us simply as “Pine, kvass lees and vin brûlé.” I watch my partner light up, the flickering candle in her eyes, as the waiter sets the thing down. The impact of the aroma has already registered on her face. With her first bite she is transported to her childhood in Massachusetts. “Gosh,” she gasps, closing her eyes as a New England virgin pine forest explodes in her mind. When she blinks open, returning to the here and now, she looks at me guiltily. I take a bite and wince. No coniferous wonderland for me. Just unpleasant bitterness, confined very much to the tongue. I am pleased for her, truly. I’m a magnanimous guy. But from that moment on, the whole evening is a bit of a spectator sport and, by the end of it, I have a feeling that she is even playing her enjoyment down, muting her reactions, as if to say, “You’re not missing out.” She finds some dishes prove more successful than others – the sweetness of cherry, an umami-rich mushroom – but I am missing out: on the nuances, the emotions, the memories. The smell. It’s been three years since I lost it. November 2020. I was living with three friends in a flat in Glasgow when we all caught Covid in the pre-vaccine days. Two of us lost our smell and never fully recovered it. We’re in good company. Around 700,000 people in the UK are believed to have total smell loss caused by the virus, with around six million still experiencing some olfactory dysfunction. I estimate mine has returned by about 30%, but it’s inconsistent and often distorted. To summarise my symptoms of anosmia, as total or partial loss of smell is known: some things have a faint odour, some don’t smell as they should and others don’t smell at all. For example: basil smells mild but good, ground coffee and a certain brand of toothpaste smell like fish and, mercifully, shit doesn’t stink at all. Apart from the latter, all bad news.

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 29070 - Posted: 12.31.2023

Jon Hamilton If this year's turkey seems over brined, blame your brain. The question of when salty becomes too salty is decided by a special set of neurons in the front of the brain, researchers report in the journal Cell. A separate set of neurons in the back of the brain adjusts your appetite for salt, the researchers showed in a series of experiments on mice. "Sodium craving and sodium tolerance are controlled by completely different types of neurons," says Yuki Oka, an author of the study and a professor of biology at Caltech. The finding could have health implications because salt ingestion is a "major issue" in many countries, including the United States, says Nirupa Chaudhari, a professor of physiology and biology at the University of Miami's Miller School of Medicine. Too much salt can cause high blood pressure and raise the risk for heart disease and stroke, says Chaudhari, who was not involved in the study. Craving, to a point The study sought to explain the complicated relationship that people and animals have with salt, also known as sodium chloride. We are happy to drink sodas, sports drinks, and even tap water that contain a little salt, Oka says. "But if you imagine a very high concentration of sodium like ocean water, you really hate it." This aversion to super salty foods and beverages holds unless your body is really low on salt, something that's pretty rare in people these days. But experiments with mice found that when salt levels plummet, the tolerance for salty water goes up. "Animals start liking ocean water," Oka says. The reason for this change involves at least two different interactions between the body and brain, Oka's team found. When the concentration of sodium in the bloodstream begins to fall below healthy levels, a set of neurons in the back of the brain respond by dialing up an animal's craving for salt. "If you stimulate these neurons, then animals run to a sodium source and start eating," Oka says. Meanwhile, a different set of neurons in the front of the brain monitors the saltiness of any food or water the mice are consuming. And usually, these neurons will set an upper limit on saltiness. © 2023 npr

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell; Chapter 13: Homeostasis: Active Regulation of the Internal Environment
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell; Chapter 9: Homeostasis: Active Regulation of the Internal Environment
Link ID: 29024 - Posted: 11.26.2023

By Hannah Docter-Loeb Paxlovid can prevent severe illness from COVID-19, but it comes with a price: In many users, the antiviral drug leaves a weird, metallic aftertaste that can last for days—a condition nicknamed “Paxlovid mouth.” Now, researchers say they’ve figured out why. A component of Paxlovid activates one of the tongue’s bitter taste receptors even at low levels, which may draw out the yuck factor, the team reports this month in Biochemical and Biophysical Research Communications. The work could lead to ways to alleviate the unpleasant side effect. The study is a “good first step” in teasing apart the mechanism behind Paxlovid mouth, says Alissa Nolden, a sensory scientist at the University of Massachusetts Amherst who was not involved with the research. But she says more work will be needed to truly understand why the metallic taste lingers for so long. Paxlovid is composed of two antivirals: nirmatrelvir and ritonavir. Nirmatrelvir blocks a key protein that SARS-CoV-2 needs to replicate. Ritonavir helps maintain the level of nirmatrelvir in the blood. Scientists have suspected that ritonavir is the primary culprit behind Paxlovid mouth. It was originally used in HIV medications and was known to directly taste bitter. A recent study also demonstrated that the compound acts on several tongue receptors that respond to bitter taste. However, ritonavir’s bitterness is short-lived, says Peihua Jiang, a molecular biologist at the Monell Chemical Senses Center, an independent research institute. So in the new study, he and colleagues looked more closely at nirmatrelvir. They added the antiviral to various groups of cells, each collection with a different member of the 25 human bitter taste receptors. They then identified the receptors that responded most vigorously to the compound by changes in a fluorescence marker in the cells. Nirmatrelvir seemed to hone in on TAS2R1, one of the primary receptors responsible for the bitter aftertaste of antiviral medicines, the researchers found. The compound activated the receptor even when its concentration was relatively low, which could explain why Paxlovid causes a persistent bitter taste.

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 29016 - Posted: 11.22.2023

By Sean Cummings If a bite of dandelion greens or extra-dark chocolate makes you pucker, there’s good reason. Bitterness can indicate the presence of toxins in potential foods, and animals long ago honed the ability to ferret out harsh tastes. But the ability to sense bitterness may be even older than many presumed, a new study finds. It likely first evolved in vertebrates roughly 460 million years ago, when sharks and other cartilaginous fishes separated from bony vertebrates like ourselves, researchers report today in the Proceedings of the National Academy of Sciences. The bitter taste receptor identified in a pair of shark species may mirror a sort of all-purpose bitterness detector that our common ancestor possessed. “Given how quickly taste receptors change, to have this one receptor conserved over 460 million years, that’s pretty astounding,” says Craig Montell, a neurobiologist at the University of California, Santa Barbara who was not involved in the study. “The ability to react to the particular bitter chemicals that activate it must be really important.” Humans and other bony vertebrates experience bitterness thanks to taste 2 receptors, or T2Rs, which are proteins that transmit taste information to the brain. But scientists had never found T2Rs in cartilaginous vertebrates such as sharks and rays. That led many to assume these receptors had evolved after their lineage split from the bony vertebrates. Yet sharks and other cartilaginous fish do have smell receptors closely related to bitter taste receptors. That made Sigrun Korsching, a neurobiologist at the University of Cologne, wonder: Could bitter taste perception be even older than most believed? To find out, she and colleagues examined 17 genomes from various species of sharks, skates, and sawfish. Twelve of these had genes that coded for taste receptors similar to T2Rs, which they dubbed T2R1s. In the lab, the researchers implanted genes for these receptors from two of the species—bamboo sharks and catsharks—into human kidney cells, then exposed them to 94 bitter substances. These included resveratrol, found in foods such as grapes, peanuts, and cranberries, and amarogentin, a compound from the gentian plant considered one of the most astringent tastes in the world.

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 29006 - Posted: 11.15.2023

Saima Sidik When the scent of morning coffee wafts past the nose, the brain encodes which nostril it enters, new research shows1. Integrating information from both nostrils might help us to identify the odour. The results were published today in Current Biology. A region of the brain called the piriform cortex, which spans the brain’s two hemispheres, is known to receive and process information about scents. However, scientists were unsure whether the two sides of the piriform cortex react to smells in unison or independently. To investigate this question, researchers recruited people with epilepsy who were undergoing brain surgery to identify the areas of their brains responsible for their seizures. Participants were awake for the surgery, during which the scientists delivered scents to one or both nostrils through tiny tubes that reached roughly one centimetre into each nostril. The authors took advantage of electrodes placed in the study participants’ brains to take readings of activity in the piriform cortex. In reality, scents rarely hit only one nostril. Instead, they’re likely to enter one nostril slightly ahead of the other. “The question to ask is, well, can the brain exploit these potential differences?” says Naz Dikecligil, a neuroscientist at the University of Pennsylvania in Philadelphia and a co-author of the study. The findings suggest that the brain does make use of the different arrival times. When an odour was delivered to a single nostril, the side of the brain closest to that nostril reacted first, and a reaction then followed in the opposite side of the brain. “There seem to be actually two odour representations, corresponding to odour information coming from each nostril,” Dikecligil says. When the researchers provided a scent to both nostrils simultaneously, they saw that both sides of the brain recognized the scent faster than either did when it was delivered through only one nostril. This suggests that the two sides do synergize to some degree, even though one lags behind the other in encoding a scent, Dikecligil says. © 2023 Springer Nature Limited

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28992 - Posted: 11.08.2023

By Tim Vernimmen For humans, division of labor has become a necessity: No person in the world has all the knowledge and skills to perform all the tasks that are required to keep our highly technological societies afloat. This has made us entirely dependent on each other, leaving us individually vulnerable. We really can’t make it on our own. From archaeological findings, we can reconstruct more or less how this situation evolved. Initially, everyone was doing more or less the same thing. But because food was shared among people living in hunter-gatherer groups, some were able to specialize in tasks other than finding food, such as fashioning tools, treating illnesses or cultivating plants. These skills enriched the group but made the specialists even more dependent on others. This further reinforced cooperation among group members and pushed our species to even higher levels of specialization — and prosperity. “Societies that have highly developed task-sharing and division of labor between group members are conspicuous because of their exceptional ecological success,” says Michael Taborsky, a behavioral biologist at the University of Bern in Switzerland. And he doesn’t just mean us: Extensive division of labor also can be seen among many social insects — ants, wasps, bees and termites — in which individuals in large colonies often specialize in particular tasks, making them impressively effective. “It is no exaggeration,” Taborsky says, “to say that societies” — of both humans and social insects — “predominate life on Earth.” But how did this division of labor evolve? Why does it seem to be rare outside of our species and the social insects? Is it, in fact, as rare as it seems? Taborsky, who has studied cooperation in animals for decades, has become increasingly interested in these questions. In March 2023, he and Barbara Taborsky, his wife and colleague, organized a scientific workshop on the topic in Berlin to which they invited a number of other experts. Over the course of two days, the group discussed how division of labor may have evolved over time, and what mechanisms allow it to develop, over and over again, in every colony of certain species. One of the invited scientists was Jennifer Fewell, a social insect biologist at Arizona State University who coauthored an influential overview of division of labor in the Annual Review of Entomology in 2001 and has studied the subject for decades. In social insect colonies, she says, “there is no central controller telling everybody what to do, but instead, the division of labor emerges from the interaction between individuals.” © 2023 Annual Reviews

Related chapters from BN: Chapter 6: Evolution of the Brain and Behavior; Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28944 - Posted: 10.05.2023

By Hannah Docter-Loeb Growing up, Julian Meeks knew what a life without a sense of smell could look like. He’d watched this grandfather navigate the condition, known as anosmia, observing that he didn’t perceive flavor and only enjoyed eating very salty or meaty foods. The experience influenced him, in part, to study chemosensation, which involves both smell and taste. Meeks, now a professor of neuroscience at the University of Rochester, told Undark that neither gets much attention compared to other senses: “Often, they’re thought of as second or third in order of importance.” The pandemic changed that, at least somewhat, after it left millions of people without a sense of smell, albeit some temporarily. In particular, more researchers started looking at a specific type of condition called acquired anosmia. Common causes include traumatic brain injury, or TBI, neurodegenerative diseases like Parkinson’s or Alzheimer’s, or following a viral infection like Covid-19. Due to the pandemic, “many people found it scientifically interesting to focus their research on smell,” said Valentina Parma, the assistant director of the Monell Chemical Senses Center, a nonprofit research institute in Philadelphia. By one account, NIH funding of anosmia research nearly doubled between 2019 and 2021. But many of the research findings do not apply to those who have lacked the ability to smell since birth: congenital anosmics. And, despite the increased attention to smell loss more broadly, some researchers still face challenges in funding studies. In March 2023, for instance, Meeks received a peer review for a small grant, of less than $275,000, from the National Institutes of Health, with which he had planned to look into anosmia in the context of TBI. For Meeks, the response was frustrating. One expert reviewer in particular “didn’t really understand why there would be any need to establish a preclinical model of anosmia with TBI,” he said, noting that the reviewer also wrote that because anosmia is not a major health problem, the value of the research was low. The comment, Meeks added, was “quite discouraging.”

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28931 - Posted: 09.27.2023

By Amber Dance We’ve all heard of the five tastes our tongues can detect — sweet, sour, bitter, savory-umami and salty. But the real number is actually six, because we have two separate salt-taste systems. One of them detects the attractive, relatively low levels of salt that make potato chips taste delicious. The other one registers high levels of salt — enough to make overly salted food offensive and deter overconsumption. Exactly how our taste buds sense the two kinds of saltiness is a mystery that’s taken some 40 years of scientific inquiry to unravel, and researchers haven’t solved all the details yet. In fact, the more they look at salt sensation, the weirder it gets. Many other details of taste have been worked out over the past 25 years. For sweet, bitter and umami, it’s known that molecular receptors on certain taste bud cells recognize the food molecules and, when activated, kick off a series of events that ultimately sends signals to the brain. Sour is slightly different: It is detected by taste bud cells that respond to acidity, researchers recently learned. In the case of salt, scientists understand many details about the low-salt receptor, but a complete description of the high-salt receptor has lagged, as has an understanding of which taste bud cells host each detector. “There are a lot of gaps still in our knowledge — especially salt taste. I would call it one of the biggest gaps,” says Maik Behrens, a taste researcher at the Leibniz Institute for Food Systems Biology in Freising, Germany. “There are always missing pieces in the puzzle.” A fine balance Our dual perception of saltiness helps us to walk a tightrope between the two faces of sodium, an element that’s crucial for the function of muscles and nerves but dangerous in high quantities. To tightly control salt levels, the body manages the amount of sodium it lets out in urine, and controls how much comes in through the mouth. © 2023 Annual Reviews

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28908 - Posted: 09.16.2023

By David Grimm Apart from Garfield’s legendary love of lasagna, perhaps no food is more associated with cats than tuna. The dish is a staple of everything from The New Yorker cartoons to Meow Mix jingles—and more than 6% of all wild-caught fish goes into cat food. Yet tuna (or any seafood for that matter) is an odd favorite for an animal that evolved in the desert. Now, researchers say they have found a biological explanation for this curious craving. In a study published this month in Chemical Senses, scientists report that cat taste buds contain the receptors needed to detect umami—the savory, deep flavor of various meats, and one of the five basic tastes in addition to sweet, sour, salty, and bitter. Indeed, umami appears to be the primary flavor cats seek out. That’s no surprise for an obligate carnivore. But the team also found these cat receptors are uniquely tuned to molecules found at high concentrations in tuna, revealing why our feline friends seem to prefer this delicacy over all others. “This is an important study that will help us better understand the preferences of our familiar pets,” says Yasuka Toda, a molecular biologist at Meiji University and a leader in studying the evolution of umami taste in mammals and birds. The work could help pet food companies develop healthier diets and more palatable medications for cats, says Toda, who was not involved with the industry-funded study. Cats have a unique palate. They can’t taste sugar because they lack a key protein for sensing it. That’s probably because there’s no sugar in meat, says Scott McGrane, a flavor scientist and research manager for the sensory science team at the Waltham Petcare Science Institute, which is owned by pet food–maker Mars Petcare UK. There’s a saying in evolution, he says: “If you don’t use it, you lose it.” Cats also have fewer bitter taste receptors than humans do—a common trait in uber-carnivores. But cats must taste something, McGrane reasoned, and that something is likely the savory flavor of meat. In humans and many other animals, two genes—Tas1r1 and Tas1r3—encode proteins that join together in taste buds to form a receptor that detects umami. Previous work had shown that cats express the Tas1r3 gene in their taste buds, but it was unclear whether they had the other critical puzzle piece.

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28885 - Posted: 08.26.2023

By Aara'L Yarber When the pandemic began, losing your sense of smell was considered a key indicator of covid-19, and the condition affected about half of those who tested positive for the coronavirus. However, a new study reveals that the chance of smell loss from the latest omicron variants has dropped dramatically since the early days of the pandemic. “So now, three people out of 100 getting covid presumably may lose their sense of smell, which is far, far less than it was before,” said study leader Evan Reiter, the medical director of Virginia Commonwealth University Health’s Smell and Taste Disorders Center. The findings, published in the journal Otolaryngology — Head and Neck Surgery, mean that losing smell and, by association, your sense of taste is no longer a reliable sign that someone has a covid infection, Reiter said. Advertisement “Now, the chance of you having [smell loss from] covid as opposed to another virus, like different cold and flu bugs, is about the same,” he said. Although it is unclear why the frequency of smell loss has decreased over time, vaccinations and preexisting immunity could be playing a role, the researchers said. Doctors have had difficulty explaining the cause of smell loss, but some research suggests it is due to covid triggering a prolonged immune assault on olfactory nerve cells. These cells sit at the top of the nasal cavity and help send smell signals from the nose to the brain. It is possible that over time this attack causes a decline in the number of olfactory cells. But if you’ve already been infected or vaccinated, the time the virus has to inflict this kind of damage is dramatically reduced, said Benjamin tenOever, a professor of microbiology and medicine at New York University who was not involved in the study.

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28866 - Posted: 08.05.2023

By Wynne Parry For the first time, researchers have determined how a human olfactory receptor captures an airborne scent molecule, the pivotal chemical event that triggers our sense of smell. Whether it evokes roses or vanilla, cigarettes or gasoline, every scent starts with free-floating odor molecules that latch onto receptors in the nose. Multitudes of such unions produce the perception of the smells we love, loathe or tolerate. Researchers therefore want to know in granular detail how smell sensors detect and respond to odor molecules. Yet human smell receptors have resisted attempts to visualize how they work in detail — until now. In a recent paper published in Nature, a team of researchers delineated the elusive three-dimensional structure of one of these receptors in the act of holding its quarry, a compound that contributes to the aroma of Swiss cheese and body odor. “People have been puzzled about the actual structure of olfactory receptors for decades,” said Michael Schmuker, who uses chemical informatics to study olfaction at the University of Hertfordshire in England. Schmuker was not involved in the study, which he describes as “a real breakthrough.” He and others who study our sense of smell say that the reported structure represents a step toward better understanding how the nose and brain jointly wring from airborne chemicals the sensations that warn of rotten food, evoke childhood memories, help us find mates and serve other crucial functions. The complexity of the chemistry that the nose detects has made olfaction particularly difficult to explain. Researchers think that human noses possess about 400 types of olfactory receptors, which are tasked with detecting a vastly larger number of odoriferous “volatiles,” molecules that vaporize readily, from the three-atom, rotten-egg-smelling hydrogen sulfide to the much larger, musky-scented muscone. (One recent estimate put the number of possible odor-bearing compounds at 40 billion or more.) == All Rights Reserved © 2023

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28766 - Posted: 05.03.2023

Sara Reardon Octopuses and squids both use the suckers on their limbs to grapple with their prey and to taste their quarry at the same time. Now, a pair of studies describes how these animals ‘taste by touching’ — and how evolution has equipped them with the perfect sensory ability for their lifestyles1,2. The papers were published in Nature on 12 April. The research details the structure of the receptors that stud the animals’ suckers. These receptors transmit information that enables the creature to taste chemicals on a surface independently from those floating in the water. Armed with brains Cephalopods — the group that includes octopuses and squids — have long fascinated neuroscientists because their brains and sensory systems are unlike those found in any other animals. Octopuses, for instance, have more neurons in their arms than in their central brain: a structure that allows each arm to function independently as if it has its own brain3. And researchers have long known that the hundreds of suckers on each arm can both feel the environment and taste it4. Molecular biologist Nicholas Bellono at Harvard University in Cambridge, Massachusetts, and his group were studying the California two-spot octopus (Octopus bimaculoides) when they came across a distinctive structure on the surface of the animal’s tentacle cells. Bellono suspected that this structure acted as a receptor for chemicals in the octopus’s environment. He contacted neurobiologist Ryan Hibbs at the University of California San Diego, who studies receptors that are architecturally similar to the octopus structures found by Bellono’s team: both types consist of five barrel-like proteins clustered to form a hollow tube. When the researchers looked at the octopus genome, they found 26 genes for these barrel-shaped proteins, which could be shuffled to create millions of distinct five-part combinations that detect various tastes1. The researchers found that the octopus receptors tend to bind to ‘greasy’ molecules that don’t dissolve in water, suggesting that they are optimized for detecting chemicals on surfaces such as a fish’s skin, the sea floor or the octopus’s own eggs. © 2023 Springer Nature Limited

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28741 - Posted: 04.15.2023

By Bethany Brookshire Cockroaches are changing up their sex lives, and it’s all our fault. Faced with sweet poisoned bait, roaches first ended up with a mutation that made them hate sweets, hindering their mating strategies. Now, more roach mutations are emerging, showing you can’t keep a good pest down. Like many animals, cockroaches have a sweet tooth, and that preference for sugar plays a central role in their reproductive activities. When a male roach targets a female roach, he will back up to her, secreting a solution called a nuptial gift from the tergal gland under his wings. The solution is full of proteins, fats and sugars, what some researchers call the chocolate of roach food. The female cockroach will crawl up on his back to take a sample, and while she is occupied, the male will whip out a hooked penis to latch onto her reproductive tract. They will then turn back to back and do the deed for about 90 minutes. Humans have aimed to exploit this love of sweet stuff to push cockroaches — particularly the German cockroaches that turn up in American homes — out of our spaces. For decades, people used poisoned roach baits baited with solutions containing glucose. Cockroaches took the bait. But some time in the late 20th century, a new mutation arose — glucose aversion. No one knows how many roaches now hate the sweet stuff, but Coby Schal, an evolutionary biologist at North Carolina State University, suspects the mutation is very common. “There are more and more papers being published on the fact that a whole suite of baits don’t work so well,” he said. This lack of a sweet tooth saved cockroaches from death, but it hurt their sex lives. The gift that normal males secrete contains maltose, a sugar that cockroach saliva transforms into glucose. But if females had the glucose averse mutation, they did not find the male secretions sexy and turned away before the male could hook on. © 2023 The New York Times Company

Related chapters from BN: Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases; Chapter 6: Evolution of the Brain and Behavior
Related chapters from MM:Chapter 8: Hormones and Sex
Link ID: 28722 - Posted: 03.29.2023

Miryam Naddaf It is thanks to proteins in the nose called odour receptors that we find the smell of roses pleasant and that of rotting food foul. But little is known about how these receptors detect molecules and translate them into scents. Now, for the first time, researchers have mapped the precise 3D structure of a human odour receptor, taking a step forwards in understanding the most enigmatic of our senses. The study, published in Nature on 15 March1, describes an olfactory receptor called OR51E2 and shows how it ‘recognizes’ the smell of cheese through specific molecular interactions that switch the receptor on. “It’s basically our first picture of any odour molecule interacting with one of our odour receptors,” says study co-author Aashish Manglik, a pharmaceutical chemist at the University of California, San Francisco. Smell mystery The human genome contains genes encoding 400 olfactory receptors that can detect many odours. Mammalian odour-receptor genes were first discovered in rats by molecular biologist Richard Axel and biologist Linda Buck in 19912. Researchers in the 1920s estimated that the human nose could discern around 10,000 smells3, but a 2014 study suggests that we can distinguish more than one trillion scents4. Each olfactory receptor can interact with only a subset of smelly molecules called odorants — and a single odorant can activate multiple receptors. It is “like hitting a chord on a piano”, says Manglik. “Instead of hitting a single note, it’s a combination of keys that are hit that gives rise to the perception of a distinct odour.” Beyond this, little is known about exactly how olfactory receptors recognize specific odorants and encode different smells in the brain. Technical challenges in producing mammalian olfactory-receptor proteins using standard laboratory methods have made it difficult to study how these receptors bind to odorants. © 2023 Springer Nature Limited

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell; Chapter 8: General Principles of Sensory Processing, Touch, and Pain
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell; Chapter 5: The Sensorimotor System
Link ID: 28710 - Posted: 03.18.2023

By Dana Mackenzie On October 2, 2022, four days after Hurricane Ian hit Florida, a search-and-rescue Rottweiler named Ares was walking the ravaged streets of Fort Myers when the moment came that he had been training for. Ares picked up a scent within a smashed home and raced upstairs, with his handler trailing behind, picking his way gingerly through the debris. They found a man who had been trapped inside his bathroom for two days after the ceiling caved in. Some 152 people died in Ian, one of Florida’s worst hurricanes, but that lucky man survived thanks to Ares’ ability to follow a scent to its source. We often take for granted the ability of a dog to find a person buried under rubble, a moth to follow a scent plume to its mate or a mosquito to smell the carbon dioxide you exhale. Yet navigating by nose is more difficult than it might appear, and scientists are still working out how animals do it. “What makes it hard is that odors, unlike light and sound, don’t travel in a straight line,” says Gautam Reddy, a biological physicist at Harvard University who coauthored a survey of the way animals locate odor sources in the 2022 Annual Review of Condensed Matter Physics. You can see the problem by looking at a plume of cigarette smoke. At first it rises and travels in a more or less straight path, but very soon it starts to oscillate and finally it starts to tumble chaotically, in a process called turbulent flow. How could an animal follow such a convoluted route back to its origin? Over the last couple of decades, a suite of new high-tech tools, ranging from genetic modification to virtual reality to mathematical models, have made it possible to explore olfactory navigation in radically different ways. The strategies that animals use, as well as their success rates, turn out to depend on a variety of factors, including the animal’s body shape, its cognitive abilities and the amount of turbulence in the odor plume. One day, this growing understanding may help scientists develop robots that can accomplish tasks that we now depend on animals for: dogs to search for missing people, pigs to search for truffles and, sometimes, rats to search for land mines. © 2023 Annual Reviews

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28692 - Posted: 03.08.2023

By Erin Garcia de Jesús A female giraffe has a great Valentine’s Day gift for potential mates: urine. Distinctive anatomy helps male giraffes get a taste for whether a female is ready to mate, animal behaviorists Lynette and Benjamin Hart report January 19 in Animals. A pheromone-detecting organ in giraffes has a stronger connection to the mouth than the nose, the researchers found. That’s why males scope out which females to mate with by sticking their tongues in a urine stream. Animals such as male gazelles will lick fresh urine on the ground to track if females are ready to mate. But giraffes’ long necks and heavy heads make bending over to investigate urine on the ground an unstable and vulnerable position, says Lynette Hart, of the University of California, Davis. The researchers observed giraffes (Giraffa giraffa angolensis) in Etosha National Park in Namibia in 1994, 2002 and 2004. Bull giraffes nudged or kicked the female to ask her to pee. If she was a willing participant, she urinated for a few seconds, while the male took a sip. Then the male curled his lip and inhaled with his mouth, a behavior called a flehmen response, to pull the female’s scent into two openings on the roof of the mouth. From the mouth, the scent travels to the vomeronasal organ, or VNO, which detects pheromones. The Harts say they never saw a giraffe investigate urine on the ground. Unlike many other mammals, giraffes have a stronger oral connection — via a duct — to the VNO, than a nasal one, examinations of preserved giraffe specimens showed. One possible explanation for the difference could be that a VNO-nose link helps animals that breed at specific times of the year detect seasonal plants, says Benjamin Hart, a veterinarian also at the University of California, Davis. But giraffes can mate any time of year, so the nasal connection may not matter as much. © Society for Science & the Public 2000–2023.

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell; Chapter 12: Sex: Evolutionary, Hormonal, and Neural Bases
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell; Chapter 8: Hormones and Sex
Link ID: 28664 - Posted: 02.15.2023

By Chris Gorski At first glance, saliva seems like pretty boring stuff, merely a convenient way to moisten our food. But the reality is quite different, as scientists are beginning to understand. The fluid interacts with everything that enters the mouth, and even though it is 99 percent water, it has a profound influence on the flavors — and our enjoyment — of what we eat and drink. “It is a liquid, but it’s not just a liquid,” says oral biologist Guy Carpenter of King’s College London. Scientists have long understood some of saliva’s functions: It protects the teeth, makes speech easier and establishes a welcoming environment for foods to enter the mouth. But researchers are now finding that saliva is also a mediator and a translator, influencing how food moves through the mouth and how it sparks our senses. Emerging evidence suggests that interactions between saliva and food may even help to shape which foods we like to eat. The substance is not very salty, which allows people to taste the saltiness of a potato chip. It’s not very acidic, which is why a spritz of lemon can be so stimulating. The fluid’s water and salivary proteins lubricate each mouthful of food, and its enzymes such as amylase and lipase kickstart the process of digestion. This wetting also dissolves the chemical components of taste, or tastants, into saliva so they can travel to and interact with the taste buds. Through saliva, says Jianshe Chen, a food scientist at Zhejiang Gongshang University in Hangzhou, China, “we detect chemical information of food: the flavor, the taste.” © 2023 Annual Reviews

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28637 - Posted: 01.25.2023

Miryam Naddaf Researchers have made transgenic ants whose antennae glow green under a microscope, revealing how the insects’ brains process alarming smells. The findings identify three unique brain regions that respond to alarm signals. In these areas, called glomeruli, the ants’ nerve endings intersect. The work was posted on the bioRxiv preprint server on 29 December 20221 and has not yet been peer reviewed. “Ants are like little walking chemical factories,” says study co-author Daniel Kronauer, a biologist at the Rockefeller University in New York City. Previous research has focused on identifying the chemicals that ants release or analysing the insects’ behavioural responses to these odours, but “how ants can actually smell the pheromones is really only now becoming a little bit clearer”, says Kronauer. “This is the first time that, in a social insect, a particular glomerulus has been associated very strongly with a particular behaviour,” he adds. Smelly signals Ants are social animals that communicate with each other by releasing scented chemicals called pheromones. The clonal raider ants (Ooceraea biroi) that the researchers studied are blind. “They basically live in a world of smells,” says Kronauer. “So the vast amount of their social behaviour is regulated by these chemical compounds.” When an ant perceives danger, it releases alarm pheromones from a gland in its head to warn its nestmates. Other ants respond to this signal by picking up their larvae and evacuating the nest. “Instead of having dedicated brain areas for face recognition or language processing, ants have a massively expanded olfactory system,” says Kronauer. The researchers created transgenic clonal raider ants by injecting the insects’ eggs with a vector carrying a gene for a green fluorescent protein combined with one that expresses a molecule that indicates calcium activity in the brain. © 2023 Springer Nature Limited

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28632 - Posted: 01.18.2023

By Kelsey Ables Persistent loss of smell has left some covid-19 survivors yearning for the scent of their freshly bathed child or a waft of their once-favorite meal. It’s left others inured to the stink of garbage and accidentally drinking spoiled milk. “Anosmia,” as experts call it, is one of long covid’s strangest symptoms — and researchers may be one step closer to figuring it out what causes it and how to fix it. A small study published online on Wednesday in Science Translational Medicine and led by researchers at Duke University, Harvard and the University of California San Diego offers a theory, and new insight, into lingering smell loss. Scientists analyzed samples of olfactory epithelial tissue — where smell cells live — from 24 biopsies, nine of which were from post-covid patients struggling with persistent loss of smell. Although the sample was small, the results suggest that the sensory deficit is linked to an ongoing immune attack on cells responsible for smell — which endures even after the virus is gone — and a decline in the number of olfactory nerve cells. Bradley Goldstein, associate professor in Duke’s Department of Head and Neck Surgery and Communication Sciences and the Department of Neurobiology, an author on the paper, called the results “striking” and said in a statement, “It’s almost resembling a sort of autoimmune-like process in the nose.” While there has been research that looks at short-term smell loss and uses animal models, the new study is notable because it focuses on persistent smell loss and uses high-tech molecular analysis on human tissue. The study reflects enduring interest in the mysterious symptom. In July, researchers estimated that at least 5.6 percent of covid-19 patients develop chronic smell problems. That study, published in the peer-reviewed medical trade publication BMJ, also suggested that women as well as those who had more severe initial dysfunction were less likely to recover their sense of smell. Seniors are also especially vulnerable, The Post has reported.

Related chapters from BN: Chapter 9: Hearing, Balance, Taste, and Smell
Related chapters from MM:Chapter 6: Hearing, Balance, Taste, and Smell
Link ID: 28613 - Posted: 12.28.2022