Posts tagged odors
Articles and news from the latest research reports.
Rats’ brains may “remember” odor experienced while under general anesthesia
Rats’ brains may remember odors they were exposed to while deeply anesthetized, suggests research in rats published in the April issue of Anesthesiology.
Previous research has led to the belief that sensory information is received by the brain under general anesthesia but not perceived by it. These new findings suggest the brain not only receives sensory information, but also registers the information at the cellular level while anesthetized without behavioral reporting of the same information after recovering from anesthesia.
In the study, rats were exposed to a specific odor while under general anesthesia. Examination of the brain tissue after they had recovered from anesthesia revealed evidence of cellular imprinting, even though the rats behaved as if they had never encountered the odor before.
“It raises the question of whether our brains are being imprinted during anesthesia in ways we don’t recognize because we simply don’t remember,” said Yan Xu, Ph.D., lead author and vice chairman for basic sciences in the Department of Anesthesiology at the University of Pittsburgh School of Medicine. “The fact that an anesthetized brain can receive sensory information – and distinguish whether that information is novel or familiar during and after anesthesia, even if one does not remember receiving it – suggests a need to re-evaluate how the depth of anesthesia should be measured clinically.”
Researchers randomly assigned 107 rats to 12 different anesthesia and odor exposure paradigms: some were exposed to the same odor during and after anesthesia, some to air before and an odor after, some to familiar odors, others to novel odors, and still others were not exposed to odors at all. After the rats had recovered from the anesthesia, researchers observed their behavior of looking for hidden odors or interacting with scented beads to determine their memory of the smell. Researchers then analyzed the rats’ brains at a cellular level. While the rats had no memory of being exposed to the odor under anesthesia, changes in the brain tissue on a cellular level suggested the rats “remembered” the exposure to the odor under anesthesia and no longer registered the odor as novel.
“This study reveals important new information about how anesthesia affects our brains,” said Dr. Xu. “The results highlight a need for additional research into the effects of general anesthesia on learning and memory.”
Mice can ‘warn’ sons, grandsons of dangers via sperm
Lab mice trained to fear a particular smell can transfer the impulse to their unborn sons and grandsons through a mechanism in their sperm, a study reveals.
The research claims to provide evidence for the concept of animals “inheriting” a memory of their ancestors’ traumas, and responding as if they had lived the events themselves.
It is the latest find in the study of epigenetics, in which environmental factors are said to cause genes to start behaving differently without any change to their underlying DNA encoding.
"Knowing how ancestral experiences influence descendant generations will allow us to understand more about the development of neuropsychiatric disorders that have a transgenerational basis," says study co-author Brian Dias of the Emory University School of Medicine in Atlanta, Georgia.
And it may one day lead to therapies that can soften the memory “inheritance”.
For the study, Dias and co-author Kerry Ressler trained mice, using foot shocks, to fear an odour that resembles cherry blossoms.
Later, they tested the extent to which the animals’ offspring startled when exposed to the same smell. The younger generation had not even been conceived when their fathers underwent the training, and had never smelt the odour before the experiment.
The offspring of trained mice were “able to detect and respond to far less amounts of odour… suggesting they are more sensitive” to it, says Ressler co-author of the study published in the journal Nature Neuroscience.
They did not react the same way to other odours, and compared to the offspring of non-trained mice, their reaction to the cherry blossom whiff was about 200 percent stronger, he says.
The scientists then looked at a gene (M71) that governs the functioning of an odour receptor in the nose that responds specifically to the cherry blossom smell.
Epigenetic marks
The gene, inherited through the sperm of trained mice, had undergone no change to its DNA encoding, the team found.
But the gene did carry epigenetic marks that could alter its behaviour and cause it to be “expressed more” in descendants, says Dias.
This in turn caused a physical change in the brains of the trained mice, their sons and grandsons, who all had a larger glomerulus - a section in the olfactory (smell) unit of the brain.
"This happens because there are more M71 neurons in the nose sending more axons" into the brain, says Dias.
Similar changes in the brain were seen even in offspring conceived with artificial insemination from the sperm of cherry blossom-fearing fathers.
The sons of trained mouse fathers also had the altered gene expression in their sperm.
"Such information transfer would be an efficient way for parents to ‘inform’ their offspring about the importance of specific environmental features that they are likely to encounter in their future environments," says Ressler.
Happening in humans?
Commenting on the findings, British geneticist Marcus Pembrey says they could be useful in the study of phobias, anxiety and post-traumatic stress disorders.
"It is high time public health researchers took human transgenerational responses seriously," he said in a statement issued by the Science Media Centre.
"I suspect we will not understand the rise in neuropsychiatric disorders or obesity, diabetes and metabolic disruptions generally without taking a multigenerational approach."
Wolf Reik, epigenetics head at the Babraham Institute in England, says such results were “encouraging” as they suggested that transgenerational inheritance does exist, but cannot yet be extrapolated to humans.
Genetic Engineering Alters Mosquitoes’ Sense of Smell
In one of the first successful attempts at genetically engineering mosquitoes, HHMI researchers have altered the way the insects respond to odors, including the smell of humans and the insect repellant DEET. The research not only demonstrates that mosquitoes can be genetically altered using the latest research techniques, but paves the way to understanding why the insect is so attracted to humans, and how to block that attraction.
“The time has come now to do genetics in these important disease-vector insects. I think our new work is a great example that you can do it,” says Leslie Vosshall, an HHMI investigator at The Rockefeller University who led the new research, published May 29, 2013 in the journal Nature.
In 2007, scientists announced the completion of the full genome sequence of Aedes aegypti, the mosquito that transmits dengue and yellow fever. A year later, when Vosshall became an HHMI investigator, she shifted the focus of her lab from Drosophila flies to mosquitoes with the specific goal of genetically engineering the insects. Studying mosquitoes appealed to her because of their importance as disease carriers, as well as their unique attraction to humans.
Vosshall’s first target: a gene called orco, which her lab had deleted in genetically engineered flies 10 years earlier. “We knew this gene was important for flies to be able to respond to the odors they respond to,” says Vosshall. “And we had some hints that mosquitoes interact with smells in their environment, so it was a good bet that something would interact with orco in mosquitoes.”
Vosshall’s team turned to a genetic engineering tool called zinc-finger nucleases to specifically mutate the orco gene in Aedes aegypti. They injected the targeted zinc-finger nucleases into mosquito embryos, waited for them to mature, identified mutant individuals, and generated mutant strains that allowed them to study the role of orco in mosquito biology. The engineered mosquitoes showed diminished activity in neurons linked to odor-sensing. Then, behavioral tests revealed more changes.
When given a choice between a human and any other animal, normal Aedes aegypti will reliably buzz toward the human. But the mosquitoes with orco mutations showed reduced preference for the smell of humans over guinea pigs, even in the presence of carbon dioxide, which is thought to help mosquitoes respond to human scent. “By disrupting a single gene, we can fundamentally confuse the mosquito from its task of seeking humans,” says Vosshall. But they don’t yet know whether the confusion stems from an inability to sense a “bad” smell coming from the guinea pig, a “good” smell from the human, or both.
Next, the team tested whether the mosquitoes with orco mutations responded differently to DEET. When exposed to two human arms—one slathered in a solution containing 10 percent DEET, the active ingredient in many bug repellants, and the other untreated—the mosquitoes flew equally toward both arms, suggesting they couldn’t smell the DEET. But once they landed on the arms, they quickly flew away from the DEET-covered one. “This tells us that there are two totally different mechanisms that mosquitoes are using to sense DEET,” explains Vosshall. “One is what’s happening in the air, and the other only comes into action when the mosquito is touching the skin.” Such dual mechanisms had been discussed but had never been shown before.
Vosshall and her collaborators next want to study in more detail how the orco protein interacts with the mosquitoes’ odorant receptors to allow the insects to sense smells. “We want to know what it is about these mosquitoes that makes them so specialized for humans,” she says. “And if we can also provide insights into how existing repellants are working, then we can start having some ideas about what a next-generation repellant would look like.”
(Source: hhmi.org)
Flies reveal that a sense of smell, like a melody, depends upon timing
The sense of smell remains a mystery in many respects. Fragrance companies, for instance, know it is crucial that chemical compounds in perfumes reach nostrils at different rates to create the desired sensory experience, but it is has been unclear why. Yale researchers decided to interrogate the common fruit fly for answers.
The team of Yale scientist Thierry Emonet, his postdoctoral associate Carlotta Martelli, and his colleague John Carlson systematically recorded both the stimulus reaching the fly and the responses of individual neurons over time. They found that the timing of neuronal response was independent of the concentration of the odor in the air, which in theory might help flies track fluctuating odor stimuli. However, the timing of neuronal response did depend on the identity of the odor.
Different odors elicited tiny delays in neural response. Such odor-dependent delays could be useful to the brain processing complex scents, say the scientists. The research also shows that specific interactions between odors and surfaces can affect the timing of the stimulus and therefore neural response.
Emonet says the findings suggest the world of smell is like music, in which chemical compounds of the scent act as notes and enable recognition of specific odors depending upon when they are played, or processed. For more information on the research, see the April 9 issue of the journal Neuroscience.
Scent Into Action
Ferrero, a neurobiologist from Harvard, was visiting the zoo to gather urine specimens for a study linking odors to instinctual behavior in rodents. Early lab results had hinted that a whiff of a chemical in carnivore pee flashed a sort of billboard message, blinking “DANGER” in neon lights — enough to make animals automatically shrink away in fear.
Ferrero and Harvard neurobiologist Stephen Liberles are among a cadre of researchers trying to understand the basis of instinctual animal behaviors. In the last few years, scientists have made progress by studying smell — unmasking the molecular identities of behavior-triggering odors and charting these odors’ routes to the brain. One early stop, a sensory structure known to spur mice into action when they encounter odors from other mice, can actually rev the rodents up when they run into cats or rats, too.
In fact, studies have shown that odors from different species can spark varying patterns of neural activity in mice. And new evidence from researchers including Ferrero and Liberles suggests behavior-triggering odors don’t always travel to the brain in the way scientists once thought.
Recent research has even revived interest in the once-ridiculed idea that humans also respond instinctually to odors from other humans — though some scientists still think the idea is kooky. No matter who has it right, the new work may hold clues to the brain areas responsible for complex behavior in people.
“We used to think it was beyond the reach of what we could study,” says neurobiologist Lisa Stowers of the Scripps Research Institute in La Jolla, Calif. “There was just too much going on in the brain.”
Human heads are big, complicated and tricky to access, so researchers are zeroing in on rodent brains instead.