Big Data Renews Fight Over the Origin of Animals

A new study is the latest in the long-running dispute over which lineage—sponges or comb jellies—is the ancestor to all animals

Big Data Renews Fight Over the Origin of Animals
The debate over which lineage came first — sponges (pictured) or comb jellies — is far from settled.

Evolutionary biologists have battled for years over which animal lineage came first — sponges or comb jellies. The answer could transform how scientists understand the evolution of the human nervous system, digestive system and other complex traits.

A study published on March 16 in Current Biology, sides with the sponges, using an unprecedented array of genetic data to deduce that they were the first to branch off from the animal tree of life1. Sponges are simple creatures that lack a head, nerves and guts, so the conclusion makes intuitive sense. But big data doesn’t necessarily lead to better answers, some researchers warn.

“They’ve got a large data set, but almost certainly this is not the final word,” says David Hillis, an evolutionary biologist at the University of Texas at Austin who was not involved with the project. “This is just such a tough problem to solve.”

Peering back through 600 million years of transformation is hard. It seems that every animal descends from ancestors on one of five branches near the base of the tree. But these five groups look very different from one another today. There are sponges, comb jellies, cnidarians (including sea anenomes, corals and jellyfish), bilaterally symmetrical animals (such as humans and clams) and obscure, microscopic worms called placozoans.

Battle of the branches

For the better part of the past century, zoologists arranged these branches according to their judgements of what was simple and what was complex. Sponges fell to the bottom branch, and bilaterally symmetrical animals resided higher up. But in 2008, a genetic analysis published in Nature put comb jellies, rather than sponges, near the root of the evolutionary tree2.

This arrangement rattled evolutionary biologists because it upended the idea that animal complexity increased over time. It implied that nerves and other characteristics evolved independently in different lineages, and were subsequently lost in sponges. Since then, studies have supported or contradicted the rearrangement, but all have been plagued by problems.

In the most recent study1, the authors attempt to resolve one of the biggest challenges in building evolutionary trees based on DNA comparisons. Some genomes evolve faster than others, and fast-evolving genomes from unrelated animals can converge on a similar sequence. “By chance, lineages accumulate genetic similarities not due to a shared history but due to random change,” explains Michaël Manuel, an evolutionary biologist at the Institute of Biology Paris-Seine, and the study’s senior author.

This problem is called long-branch attraction, because mathematical models depict genetic changes as additional lengths on the branches of the diagrams they produce. Long branches can cluster together on a tree as a result of these convergences, or because their genetic sequences are so unlike others in the tree. Either way, the clustering suggests that two lineages are related when they’re not. Manuel suspects that the long branches of non-animals such as fungi attract the comb-jelly lineage because, for unknown reasons, comb-jelly genomes have accumulated an unusual number of changes over time.


To skirt such long-branch attraction, Manuel and his colleagues analyzed 1,719 genes from an unparalleled range of species. It took computing power from Canada, Germany, Belgium and France to crunch the numbers. The team also tested several mathematical models that accounted for biological phenomena, including the fact that certain genetic changes are more likely than others. They chose a model called CAT, partly because of how well it reproduced sections of the animal tree that have already been confirmed.

The results from the CAT model placed sponges on the earliest branch of the animal family tree. Some other models that the team used had put comb jellies at the base. “The fact that the results flip-flop with different models is a bad sign,” says Hillis, who was not involved with the work.

Casey Dunn, an evolutionary biologist at Brown University in Providence, Rhode Island who also was not involved in the study, agrees. “Unfortunately, this is telling us that adding more species data isn’t moving the needle on the problem.”

In the future, Hillis suggests, biologists should explore genomic data that are less prone to long-branch attraction, because the chance of random convergence is lower. For instance, genes rarely insert themselves into other genes, but it happens. Hillis concedes that finding a solution will not be easy. “But this tree really matters,” he says. “It changes how we understand major things that happened in evolution.”

Birds Can See Earth’s Magnetic Fields, And We Finally Know How That’s Possible

The mystery behind how birds navigate might finally be solved: it’s not the iron in their beaks providing a magnetic compass, but a newly discovered protein in their eyes that lets them “see” Earth’s magnetic fields.

main article image

These findings come courtesy of two new papers – one studying robins, the other zebra finches.

The fancy eye protein is called Cry4, and it’s part of a class of proteins called cryptochromes – photoreceptors sensitive to blue light, found in both plants and animals. These proteins play a role in regulating circadian rhythms.

There’s also been evidence in recent years that, in birds, the cryptochromes in their eyes are responsible for their ability to orient themselves by detecting magnetic fields, a sense called magnetoreception.

We know that birds can only sense magnetic fields if certain wavelengths of light are available – specifically, studies have shown that avian magnetoreception seems dependent on blue light.

This seems to confirm that the mechanism is a visual one, based in the cryptochromes, which may be able to detect the fields because of quantum coherence.

To find more clues on these cryptochromes, two teams of biologists set to work. Researchers from Lund University in Sweden studied zebra finches, and researchers from the Carl von Ossietzky University Oldenburg in Germany studied European robins.

The Lund team measured gene expression of three cryptochromes, Cry1, Cry2 and Cry4, in the brains, muscles and eyes of zebra finches. Their hypothesis was that the cryptochromes associated with magnetoreception should maintain constant reception over the circadian day.

They found that, as expected for circadian clock genes, Cry1 and Cry2 fluctuated daily – but Cry4 expressed at constant levels, making it the most likely candidate for magnetoreception.

This finding was supported by the robin study, which found the same thing.

“We also found that Cry1a, Cry1b, and Cry2 mRNA display robust circadian oscillation patterns, whereas Cry4 shows only a weak circadian oscillation,” the researchers wrote.

But they made a couple of other interesting findings, too. The first is that Cry4 is clustered in a region of the retina that receives a lot of light – which makes sense for light-dependent magnetoreception.

The other is that European robins have increased Cry4 expression during the migratory season, compared to non-migratory chickens.

Both sets of researchers caution that more research is needed before Cry4 can be declared the protein responsible for magnetoreception.

The evidence is strong, but it’s not definitive, and both Cry1 and Cry2 have also been implicated in magnetoreception, the former in garden warblers and the latter in fruit flies.

Observing birds with non-functioning Cry4 could help confirm the role it seems to play, while other studies will be needed to figure Cry1’s role.

bird visionThis is how a bird might see magnetic fields. (Theoretical and Computational Biophysics/UofI)

So what does a bird actually see? Well, we can’t ever know what the world looks like through another species’ eyes, but we can take a very strong guess.

According to researchers at the Theoretical and Computational Biophysics group at the University of Illinois at Urbana-Champaign, whose researcher Klaus Schulten first predicted magnetoreceptive cryptochromes in 1978, they could provide a magnetic field “filter” over the bird’s field of view – like in the picture above.

The zebra finch study was published in the Journal of the Royal Society Interface, and the robin study was published in Current Biology.

Researchers Find More Than 100,000 of Borneo’s Orangutans Have Been Wiped Out

There’s no excuse.

Bornean orangutans, the largest tree-dwellers on the planet, are vanishing. The population of these great apes was halved between 1999 and 2015, per an estimate published Thursday in the journal Current Biology.

A survey of orangutan nests, coupled with a statistical analysis of habitat changes, indicates that more than 100,000 animals were lost in the last 16 years.

It is a dramatic drop for the animals who, because their genomes and unique physical characteristics so resemble ours, are among the closest living relatives to humans.

Orangutans’ exact numbers are uncertain. They are intelligent and shy and prefer thick forests.

You could walk by an orangutan hiding in the canopy and never know the 4-foot-tall (1.2 metre tall) animal was there, said Maria Voigt, an expert in sustainability and ape habitat at the Max Planck Institute for Evolutionary Anthropology in Germany.

Counting the shaggy orange creatures by sight would be a very difficult task.

Instead, surveyors tally orangutan nests. Orangutans, before they sleep, bend long branches into structures that look like leafy baskets. The nests are so large that researchers can use helicopters to spot them.

Since 1999, surveyors have covered a total of 500 square miles in Borneo looking for their nests.

One nest does not equal one ape. Some orangutans, especially infants and mothers, may crowd together into the same nest. Researchers must also account for abandoned nests, too. But extrapolating population counts from the nests is possible.

When the study began, surveyors found 22 nests per every kilometer traveled. By 2015, they found 10 nests in the same distance.

Voigt and her co-authors, an international team of ecologists, biodiversity experts, conservationists and others, created a mathematical model to track the ape population.

They bundled the decreasing number of nests together with human population density, deforestation and rates at which orangutans are hunted and killed.

By the researchers’ best estimate, there were 148,500 more orangutans in 1999 than in 2015. Some experts were shocked to see such a precipitous decline. Others doubted that there were so many orangutans in 1999.

Voigt summarised their responses: “That can’t be, that’s too much, we don’t think there are so many left.”

But the findings are on par with other declines in great ape populations, she said. Grauer’s gorilla populations have dropped by 80 percent in 20 years. The western chimpanzee population dropped by 80 percent in 25 years.

The researchers estimate there are 17,000 to 100,000 Bornean orangutans left, Voigt said. Looking to 2050, a business-as-usual model suggested a less dramatic decline – a loss of 45,300 animals from habitat destruction.

Demand for wood, palm oil and other natural resources harvested in Borneo has fractured the island’s forests. Plantations replaced orangutan habitats in some areas.

But those plantations can become “steppingstones,” Voigt said, that enable the apes to travel between fragmented forests.

The new research suggests that in places where valuable trees are selectively logged but the rest of the forest remains intact, orangutans will return. “If the fruit trees are left intact, then the disturbance is minimal,” Voigt said.

What had been widely underestimated, Voigt said, was the number of orangutans hunted for meat or otherwise killed by humans. Voigt said she suspected conservationists might have been reluctant to point to humans for the population decline.

“People have hunted orangutans since they coexisted,” Voigt said. But there is nuance amid the conflict – even the word “conflict,” she said, suggests the involvement of two equal partners, which is not the case when one party has a gun.

Bornean hunters target orangutans only as a last resort, she said, and prefer pigs and deer. Others might kill orangutans out of surprise, if “an orangutan and human meet and the human gets scared,” she said.

Interviews with people who live near orangutans suggest orangutan deaths per village are low. Perhaps a village will report that one orangutan was killed in the past few years, Voigt said.

But multiplied over many villages in forest area, and the deaths add up: As little as one orangutan killed out of 100 each year can cause the species to decline. Orangutans are slow to reproduce, having at most a newborn every six years.

But there is hope for this species, Voigt said. Humans can be taught to live in peace with orangutans. “We have relatively stable populations in national parks. We see that they can coexist with humans,” she said.

“If we stop the killing they could even bound back.”

Brain scans of one-handed people are completely changing our understanding of the brain.

“The implications, if this interpretation is correct, are massive.”

 Scans taken of people born with only one hand have revealed areas of the brain typically associated with the ‘missing hand’ are taken over by other parts of the body, radically changing our thinking on how our brain operates.

Whether it’s an arm or a foot, other limbs seem to fill in for the missing hand. In other words, rather than being responsible for specific parts of the body, as previously thought, different sections of the brain could be responsible for specific functions.

 The team of researchers say their findings could prompt a fundamental shift in our understanding of the brain and the way it’s able to manage certain tasks with different parts of the body.

“Scientifically, I think one way to put our results in context is to say, what if the hand area is not the hand area per se, but just the part of the brain in charge of function ‘normally’ carried by that hand?” says one of the researchers, Tamar Makin from University College London in the UK.

The study looked at 17 people born with just one hand and 24 two-handed controls, who were video recorded while carrying out five everyday tasks, including handling money and wrapping presents.

Participants were also asked to move different parts of their body, and all the while their brains were being scanned via MRI.

The researchers found that when congenital one-handers used something to replace their missing hand in a task – like an elbow or a foot – that body part lit up the same part of the brain as the missing hand would in a two-handed person.

We should point out that this is just a small sample of people, and the scientists aren’t certain why this is happening, but they have a hypothesis: that areas of the brain aren’t organised by body parts, but by what those body parts are doing.

 “If true, this means we’ve been misinterpreting brain organisation based on body part, rather than based on function,” says Makin.

“It’s kind of mind-blowing for me to think we could have been getting this wrong for so long. The implications, if this interpretation is correct, are massive.”

For now, it’s still just a hypothesis, but it’s a hypothesis that could lead to a rethink on how our brain is organised. Maybe the brain is more flexible and adaptable than we thought.

There are already studies that indicate people with missing senses, such as sight, can recruit parts of the brain usually responsible for other tasks, such as performing calculations or processing language.

We have understood for some time that the brain can rewire itself following a limb amputation to make use of the real estate, sometimes causing painful ‘phantom sensations‘, but this new discovery could potentially cast existing research in a new light.

With about 86 billion neurons firing in all directions, the brain is an incredibly complex organ that scientists are still trying to properly understand.

While we’re making progress in smarter AI, working out the fundamentals of copying human movement in robots continues to prove tricky – by the age of two, humans can control their hands better than the most advanced robots.

With that in mind, the findings could eventually help us to understand how the brain compensates for the loss of a limb, and improve prosthetic replacements which could be attached to the right part of the brain and controlled with our minds.

This new research could help push all those efforts further forward.

“If we, as neuroscientists, could harness this process, we could provide a really powerful tool to better healthcare and society,” adds Makin.

“By learning how this occurs spontaneously in one-handers, we can get a handle on what we might be able to achieve.”

Source: Current Biology.

Key mechanism behind brain connectivity and memory revealed

Key mechanism behind brain connectivity and memory revealed
Schematic of mice with dysfunctional and functional Wnt signaling. 

Memory loss in mice has been successfully reversed following the discovery of new information about a key mechanism underlying the loss of nerve connectivity in the brain, say UCL researchers.

Published today in Current Biology, the study funded by Alzheimer’s Research UK, Parkinson’s UK, Wellcome, MRC and the EU investigated the mechanism driving communication breakdown in – specifically, the loss of connections between in the hippocampus, an area of the that controls learning and memory. The team found Wnt proteins play a key role in the maintenance of nerve connectivity in the adult brain and could become targets for new treatments that prevent and restore brain function in.

The breakdown of connections between nerve cells is an early feature of diseases like Alzheimer’s and is known to cause like memory and thinking decline, but the biological processes behind it are poorly understood. Nerve cells are connected at communication points called synapses and the slow degeneration of these connections is an important area of study for researchers looking to slow or stop Alzheimer’s disease.

Lead author, Professor Patricia Salinas (UCL Cell & Developmental Biology), said: “Synapses are absolutely critical to everything that our brains do. When these important communication points are lost, nerve cells cannot exchange information and this leads to symptoms like memory and thinking problems. The Wnt pathway is emerging as a key player in the regulation of the formation, maintenance and function of synapses, and we have provided strong evidence that the Wnt proteins are also critical for memory.

“Understanding the role of Wnts in Alzheimer’s disease is an important next step, as there is potential we could target this chain of events with drugs. Preventing or reversing the disruptions in connectivity and communication between nerve cells in Alzheimer’s would be a huge step forward.”

Increasing evidence suggests that deficiency in Wnt function contributes to disruption of brain connectivity in Alzheimer’s disease and therefore resulting in memory loss. The team studied the impact of a protein called Dkk1, known to block the action of Wnts and found at higher levels in people with Alzheimer’s, in brain circuits and memory.

Genetically modified mice in which Dkk1 can be switched on, disrupting the action of Wnts and its downstream chain of events were used. To avoid any disruption to normal brain development driven by Wnts and Dkk1, the researchers waited until the mice were adults before switching on Dkk1 in an area of the brain important for the formation of new memories.

When Dkk1 was switched on in the adult mice, the researchers found the mice had memory problems, and that this coincided with the presence of fewer synapses between nerve cells, indicating a communication breakdown. However, when the researchers switched Dkk1 back off, the mice no longer had memory problems, the number of synapses increased back to normal levels and brain circuits were restored.

Dr Simon Ridley, Director of Research at Alzheimer’s Research UK, said: “This study in mice adds further weight to a growing body of evidence implicating Wnts and its related proteins to nerve cell connectivity and memory. By understanding mechanisms driving healthy nerve cells, we can best unpick what happens when these processes go so wrong.

“This research sets a solid foundation for future work to explore the role of Wnts in diseases like Alzheimer’s, and this biological process is already a key target being explored by expert teams in the Alzheimer’s Research UK Drug Discovery Alliance. Researchers are taking huge steps forward in their understanding of what happens in the brain in health and disease, and we must now capitalise on these discoveries to deliver effective treatments that can transform lives.”


Youngest born ‘perceived as shorter’

girls legs

Mothers perceive their youngest children as shorter than they actually are, a study suggests.

This “baby illusion” applies regardless of the number of children a mother has, Current Biology reports.

Mothers underestimated the height of their youngest child by an average of 7.5cm (3in), yet accurately judged the height of any older children they had.

The study authors believe this is an adaptive mechanism – to nurture and protect most vulnerable offspring.

Always the baby

The Australian researchers surveyed 747 mothers, asking them if they remembered experiencing a sudden shift in their youngest son or daughter’s size immediately after the birth of a new baby.

More than two-thirds (70%) said they did.

This perceptual shift primarily relates to the former “baby” of the family – mothers were less likely to report any height difference in other siblings.

This is not just because the older child looks so big compared with a baby, the researchers say.

It actually happens because all along the parents were under an illusion their child was smaller than he or she really was. When the new baby is born, the spell is broken and parents now see their older child as he or she really is, they say.

The researchers asked 70 mothers to estimate – by putting a mark on a wall – the height of each of their children.

The mothers consistently underestimated the height of their only or youngest children (aged two to six).

Yet many were good at estimating the height of their older children and everyday objects, such as the bathroom sink or kitchen counter.

Lead researcher Jordy Kaufman, of Swinburne University of Technology, said: “Our research potentially explains why the ‘baby of the family’ never outgrows that label. To the parents, the baby of the family may always be ‘the baby’.”

Plastic fibre a ‘major pollutant’

Tiny pieces of plastic and man-made fibres are causing contamination of the world’s oceans and beaches, the journal Science has reported.

Even remote and apparently pristine layers of sand and mud are now composed partly of this microscopic rubbish, broken down from discarded waste.

Plastic bottles on a beach, Science

This is the first assessment of plastic fragments accumulating in sediments and in the water column itself.

It is not yet known what the long term effects of this pollution may be.

A team led by scientists at the universities of Plymouth and Southampton took samples from 17 beaches and estuaries around the UK, and analysed particles which did not appear to be natural.

The researchers found that most samples included evidence of a range of plastics or polymers including nylon, polyester and acrylic.


It suggests to us that the problem is really quite ubiquitous

They also found that when creatures such as lugworms and barnacles fed on the sediments, the plastics turned up inside their bodies within a few days.

To test whether this contamination was getting worse, the scientists analysed plankton samples taken from survey ships between Scotland and Iceland since the 1960s – and found that the plastic content had increased significantly over time.

Toxic chemicals

Because the team only sampled particles which looked different from natural sediments, it is believed that the true level of plastic contamination could be much higher.

The lead author of the study, Dr Richard Thompson, said: “Given the durability of plastics and the disposable nature of many plastic items, this type of contamination is likely to increase.


Rocket casing on a beach, Thompson/Science

This rocket casing is one of the more unusual pieces of litter on the world’s beaches

“Our team is now working to identify the possible environmental consequences of this new form of contamination.”

One concern is that toxic chemicals could attach themselves to the particles which would then help to spread them up the food chain.

That research is for the future, but this study suggests that practically everything really is made of plastic these days – even the oceans.

“We’ve found this microscopic plastic material at all of the sites we’ve examined,” Dr Thompson said.

“Interestingly, the abundance is reasonably consistent. So, it suggests to us that the problem is really quite ubiquitous.”

Accumulating ‘microplastic’ threat to shores.

Debris on shoreline (Image: AP)
Concentrations of microplastic were greatest near coastal urban areas, the study showed

Microscopic plastic debris from washing clothes is accumulating in the marine environment and could be entering the food chain, a study has warned.

Researchers traced the “microplastic” back to synthetic clothes, which released up to 1,900 tiny fibres per garment every time they were washed.

Earlier research showed plastic smaller than 1mm were being eaten by animals and getting into the food chain.

The findings appeared in the journal Environmental Science and Technology.

“Research we had done before… showed that when we looked at all the bits of plastic in the environment, about 80% was made up from smaller bits of plastic,” said co-author Mark Browne, an ecologist now based at the University of California, Santa Barbara.

“This really led us to the idea of what sorts of plastic are there and where did they come from.”

Dr Browne, a member of the US-based research network National Center for Ecological Analysis and Synthesis, said the tiny plastic was a concern because evidence showed that it was making its way into the food chain.

“Once the plastics had been eaten, it transferred from [the animals’] stomachs to their circulation system and actually accumulated in their cells,” he told BBC News.

In order to identify how widespread the presence of microplastic was on shorelines, the team took samples from 18 beaches around the globe, including the UK, India and Singapore.

“We found that there was no sample from around the world that did not contain pieces of microplastic.”

Scanning microscope image of nylon fibres
The smallest fibres could end up causing huge problems worldwide

Dr Browne added: “Most of the plastic seemed to be fibrous.

“When we looked at the different types of polymers we were finding, we were finding that polyester, acrylic and polyamides (nylon) were the major ones that we were finding.”

The data also showed that the concentration of microplastic was greatest in areas near large urban centres.

In order to test the idea that sewerage discharges were the source of the plastic discharges, the team worked with a local authority in New South Wales, Australia.

“We found exactly the same proportion of plastics,” Dr Browne revealed, which led the team to conclude that their suspicions had been correct.

As a result, Dr Browne his colleague Professor Richard Thompson from the University of Plymouth, UK carried out a number of experiments to see what fibres were contained in the water discharge from washing machines.

“We were quite surprised. Some polyester garments released more than 1,900 fibres per garment, per wash,” Dr Browne observed.

“It may not sound like an awful lot, but if that is from a single item from a single wash, it shows how things can build up.

“It suggests to us that a large proportion of the fibres we were finding in the environment, in the strongest evidence yet, was derived from the sewerage as a consequence from washing clothes.”

Plastic ‘a threat’ to biodiversity

Microplastics ‘pose toxic threat to marine biodiversity’

Micro plastic
An estimated 150 million tonnes of plastic is “lost” each year

Tiny particles of waste plastic that are ingested by shoreline “eco-engineer” worms may be negatively affecting biodiversity, a study says.

So-called microplastics may be able to transfer toxic pollutants and chemicals into the guts of lugworms, reducing the animals’ functions.

An estimated 150 million tonnes vanishes from the global waste-stream each year.

The findings have been published in the academic journal Current Biology.

“We are losing a large volume of plastic and we know it is going into the environment and the assumption being made by policymakers is that this material is non-hazardous, it has got the same ranking as scraps of food,” explained co-author Mark Browne, an ecologist from the US-based National Center for Ecological Analysis and Synthesis.

“The research we have done really challenges that,” Dr Browne added, referring to the findings of lab work carried out by colleagues at Plymouth University, UK, led by co-author Prof Richard Thompson.

“Our findings show that the plastic itself can be a problem and can affect organisms.

“Also, when particles of plastic go into the environment what you find is that they accumulate large quantities of pollutants that are banned. So you have these particles themselves but also a load of nasty chemicals.”

Important role

The team found that the tiny bits of plastic, which measure 1mm or smaller, transferred pollutants and additive chemicals – such as flame-retardants – into the guts of lugworms (Arenicola marina).

This process results in the chemical reaching the creatures’ tissue, causing a range of biological effects such as thermal stress and the inability to consume as much sediment.

Dr Browne explained that this had consequences for the surrounding ecosystem.

“If the animals are not able to eat as much then there is a change in the function of the organisms and there is an impact on the semblance of the species found in an area,” he said.

He added that the worms had earned the nickname “eco-engineers” as a result of their ability to eat organic matter from the sediment and prevent the build-up of silt.

“Through that process, it produces burrows and changes the whole assemblage of animals that live around it,” Dr Browne observed.

“This is quite considerable because if you look at the total biomass of a shoreline, about 32% can be made up from these organisms.”

He told BBC News that it was the first study of its kind to highlight the toxic risk posed by microplastics to marine organisms.

“For about 40 or 50 years, we have been finding very large concentrations of chemicals in animals. Then they started to find animals with larger concentrations of pollutants and plastics, so researchers began to establish this correlation.

“But no-one had actually shown whether chemicals could transfer from plastic when they are eaten by animals and accumulate in their bodies and reduce important functions that maintain their health.”

Nicotine withdrawal traced to very specific group of brain cells.

Nicotine withdrawal might take over your body, but it doesn’t take over your brain. The symptoms of nicotine withdrawal are driven by a very specific group of neurons within a very specific brain region, according to a report in Current Biology, a Cell Press publication, on November 14. Although caution is warranted, the researchers say, the findings in mice suggest that therapies directed at this group of neurons might one day help people quit smoking.

“We were surprised to find that one population of neurons within a single brain region could actually control physical nicotine withdrawal behaviors,” says Andrew Tapper of the Brudnick Neuropsychiatric Research Institute at the University of Massachusetts Medical School.

Tapper and his colleagues first obtained mice addicted to nicotine by delivering the drug to mice in their water for a period of 6 weeks. Then they took the nicotine away. The mice started scratching and shaking in the way a dog does when it is wet. Close examination of the animals’ brains revealed abnormally increased activity in neurons within a single region known as the interpeduncular nucleus.

When the researchers artificially activated those neurons with light, animals showed behaviors that looked like nicotine withdrawal, whether they had been exposed to the drug or not. The reverse was also true: treatments that lowered activity in those neurons alleviated nicotine withdrawal symptoms.

That the interpeduncular nucleus might play such a role in withdrawal from nicotine makes sense because the region receives connections from other areas of the brain involved in nicotine use and response, as well as feelings of anxiety. The interpeduncular nucleus is also densely packed with nicotinic acetylcholine receptors that are the molecular targets of nicotine.

It is much less clear whether the findings related to nicotine will be relevant to other forms of addiction, but there are some hints that they may.

“Smoking is highly prevalent in people with other substance-use disorders, suggesting a potential interaction between nicotine and other drugs of abuse,” Tapper says. “In addition, naturally occurring mutations in genes encoding the nicotinic receptor subunits that are found in the interpeduncular nucleus have been associated with drug and alcohol dependence.”

Source: Cell Press
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