In mice, a particular type of neuron responds specifically to gentle touch. Stroking skin produces a pleasurable sensation in many mammals, including humans, but until now, it was unclear which neurons detected that stimulus

By Thea Cunningham and Nature magazine

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Picture the expression on your cat’s face when you stroke it. What makes it so happy? The answer lies in a particular type of sensory neuron that responds to pleasant stroking, say scientists at the California Institute of Technology in Pasadena. The neurons, identified in mice, are similar to certain human neurons, which could explain why we enjoy a massage too. 

Stroking skin produces a pleasurable sensation in many mammals, including humans, but until now, it was unclear which neurons detected that stimulus. It is easier to measure responses to pain than to pleasure, so neuroscientists have in general focused their attention on noxious stimulation.

The gentle touch
Writing in this week's Nature, the Caltech team shows that, in mice, a particular type of neuron, identified by molecular markers, responds specifically to stroking. The researchers used a custom-designed brush to pinch, poke or stroke mice on their hind limbs, as seen in the video above, and identified the responding neurons by imaging spots of fluorescence that represent the increase in calcium that occurs when a neuron fires. Another type was identified that was activated by the uncomfortable pinch stimulus but not by stroking.

The team carried out behavioral experiments to confirm that their mice enjoy the sensation produced by a gentle but firm stroke. The animals were genetically engineered in such a way that the 'stroking' neurons could be activated by a drug injection, and in further behavioral tests for 'place preference', the mice showed a preference for the special chamber within their experimental set-up in which the injection had been given.

Activating these neurons also helped to alleviate anxiety symptoms, which might explain why animals enjoy being groomed. Although humans are not as furry as mice, the sensory structures in the stroking neurons in mice resemble those on neurons found in at least parts of our skin (though not on hairless parts, such as the palms of the hands), suggesting that we might respond to stroking using a similar mechanism.

It’s too early to tell whether the results have any therapeutic potential but, with more work, a drug to please our pets is not unthinkable, says neuroscientist David Anderson, head of the Caltech team.

“Imagine smearing something on their skin that makes them feel like they're being stroked and petted even when you're away at work!  It might make your pets feel better and make you feel less guilty for leaving them home alone,” he says.

This article is reproduced with permission from the magazine Nature. The article was first published on January 20, 2013.

http://www.scientificamerican.com/article.cfm?id=mice-have-massage-neurons

http://blogs.scientificamerican.com/observations/2013/01/24/dung-beetles-follow-the-stars/

By Katherine Harmon | January 24, 2013 |  3

Dung beetle on dung ball under the Milky Way; image courtesy of Emily Baird

The humble dung beetle makes its living rolling big balls of excrement to feed its offspring and itself. But this lowly occupation doesn’t mean the insect doesn’t have its eye on the skies—even when the sun goes down.

Recent research has shown that African ball-rolling dung beetles (Scarabaeus satyrus) use strong light cues from the sun and moon to keep traveling in a straight path. But researchers observing these beetles noticed something curious. “Even on clear, moonless nights, many dung beetles still manage to orientate along straight paths,” Marie Dacke, of Lund University in Sweden, said in a prepared statement. What else could the animals be using for guidance? The stars, of course.

“We were sitting out in Vryburg [in South Africa] and the Milky Way was this massive light source,” said Marcus Byrne, of Wits University and co-author on the new study, in a prepared statement. “We thought, they have to be able to use this—they just have to!” Their findings were published online January 24 in Current Biology.

Humans, of course, have long used stars for navigation. And some bird and seal species are thought to do so as well. The use of the Milky Way in particular has been suggested for some insects, spiders and vertebrates, but it has yet to be shown quite as convincingly as the researchers were able to demonstrate for these beetles, which have also recently been shown to engage in complex “dances” to orient themselves on top of their excrement orbs.

Dung beetle in experimental cardboard cap to block view of stars; image courtesy of Marcus Byrne

To see if the starry sky was really serving as such a lofty guide for these little bugs, researchers designed specially crafted cardboard caps for their subjects.

On a starry, moonless evening, researchers released capped-beetles with their dung balls from a central spot. The area was a flat sandy surface surrounded by a one-meter high, circular wall. As a test, other beetles were left uncapped and a third group received transparent plastic caps. The cap-less beetles and those with clear caps had standard, relatively straight paths. But those with the obstructed views meandered far afield and had much longer, inefficient trails.

To make sure the stars were the only guiding landmarks, the researchers designed a second outdoor experiment in an elevated, enclosed arena from which no trees, structures or other objects were visible to the beetles. In this test, beetles were timed to see how long it took them to reach a circular black cloth wall from a central release point in the open-air enclosure. In this case, researchers could hear a “thump” when beetles reached the wall and fell into a slightly lower trough below it. Rolling speeds remained constant for capped bugs as well as those tested in complete darkness. So those sticking to a straight path would reach the wall sooner, whereas those that wandered would take longer.

A moon meant beetles took the most direct route, reaching the edge in an average of just 21 seconds. With a full, starry sky (sans moon) as the main feature to go by, beetles took about 40 seconds. But with a star-obscuring cap, it took the bugs some 125 seconds to roll their balls to the edge, suggesting they took a far less direct route than bugs that had the moon or stars to navigate by. Overcast conditions had a similar effect, resulting in an average time of 117 seconds to reach the edge of the enclosure.

So are these beetles relying on the star scape itself or the swath of the galaxy visible from Earth as the Milky Way stripe? “The vast majority of these stars should be too dim for the tiny compound eyes of the beetle to discriminate,” the researchers noted in their paper. To control the star conditions, the researchers transported their beetle arena to the Johannesburg planetarium, which can project some 4,000 stars and the Milky Way on the domed ceiling.

A close approximation of the night sky, including individual stars and the Milky Way led to the more exacting navigation (about 43 seconds to reach the edge of the enclosure). But if shown the Milky Way—as a diffuse stripe of light, similar to how it might appear to the beetles outside—the beetles still made good time, reaching the outside wall in just 53 seconds. If the researchers took the Milky Way out of the picture, and gave the beetles 18 bright “stars” to navigate by, they didn’t stick to their straight-and-narrow paths so well. It took these bugs some 83 seconds to reach the edge. “This clearly shows that the beetles do not orientate to a single bright ‘lodestar,’ but rather to the band of light that represents the Milky Way,” the researchers noted.

“This finding represents the first convincing demonstration for the use of the starry sky for orientation in insects and provides the first documented use of the Milky Way for orientation in the animal kingdom,” the researchers wrote.

But don’t think that these bugs are going to start creating cross-continental shipping routes or long-distance precision migrations. “The dung beetles don’t care which direction they’re going in; they just need to get away from the bun fight at the poo pile,” Byrne said.

http://www.newscientist.com/article/dn23061-faecal-bacteria-cocktail-treats-superbug-infection.html

Some bugs are good for us (Image: Eye of Science/Science Photo Library)

Feeding faeces to people with chronic infection can cure them, but who wants to eat poo? A synthetic alternative could provide a more palatable option.

Hospital superbug Clostridium difficile can wreak havoc in the guts of vulnerable people, especially those who have lost some of their protective gut flora as a result of antibiotic use. Once it takes hold, the bacteria can cause nasty diarrhoea and in some cases is fatal. The usual treatment for the infection, which affects over half a million people in the US each year, involves a strong course of antibiotics. But the infection returns in about 20 per cent of cases, and some people become chronically infected.

One treatment appears to be remarkably successful. It involves ingesting the faeces of healthy individuals – either via a tube to the stomach or colon – to help repopulate their guts with so-called good bacteria. This boosts defences against reinfection and unpleasant as it may sound, works in around 90 per cent of cases.

"The faecal transplant is fairly disgusting but it works really well," says Emma Allen-Vercoe at the University of Guelph in Ontario, Canada. The therapy is still a little too disgusting for some infected individuals and doctors, though, she adds.

To get around these issues, Allen-Vercoe, together with Elaine Petrof at Queens University in Kingston, Ontario, and their colleagues attempted to create an alternative version of the faecal transplant – a concoction that contains only the good gut bacteria found in faeces.

The first step – getting hold of the faeces of a healthy person – was the hardest, says Allen-Vercoe. "We wanted someone with no chronic disease and a good body mass index who doesn't drink, smoke, take drugs and had never been exposed to antibiotics," she says.

The team's closest match was a woman who was born and raised in rural India. The group then set about identifying the bacteria within her faeces, isolating the individual species and attempting to cultivate them.

Culturing bacteria is a tricky process as the bugs do not survive well in lab conditions. So far, Allen-Vercoe's team have been able to culture 10 per cent of the bacteria they isolated. This should be enough for therapy, says Allen-Vercoe. "There's an awful lot of redundancy and you don't need everything to get a functional ecosystem."

To find out if the cultures could be used therapeutically, the team gave a suspension of their cultured bacteria to two people with recurrent C. difficile infection. The bacteria cocktail was effectively "drizzled" along the inside of each person's large intestine using a colonic tube. Both people avoided C. difficile infections for the six months they were monitored.

Early promise

While the synthetic stool therapy will need to be trialled in more people, the early results are promising, says Allen-Vercoe. And it offers another important advantage.

"Faecal transplants have been heralded as a wonderful thing… but we don't know what the long-term consequences are," she says. There's always a chance that there'll be a pathogen lurking in faeces, for example. The benefit of using a synthetic stool therapy is that you know exactly what is in it, and can ensure that no dangerous bacteria or antibiotic-resistant strains are present, she says.

Vincent Young, a microbiologist at the University of Michigan, Ann Arbor, agrees. "It's a move in the right direction," he says.

Young cautions that more research is needed before therapies that target gut bacteria become more common. For recurrent C. difficile infections, you cannot argue with the success of the treatment, he says. "But at the same time, gut bacteria has been linked to diabetes, obesity, allergies… the list goes on." Gut bacteria that make one person healthy might cause health problems in another, he says.

Journal reference: Microbiome, DOI: 10.1186/2049-2618-1-3

http://www.pourlascience.fr/ewb_pages/a/actualite-l-addiction-a-internet-frappe-les-jeunes-30765.php

L’addiction à Internet concerne 17 pour cent des adolescents en Chine, 25 pour cent aux États-Unis, et représenterait de l’ordre de six pour cent en population générale. En Allemagne sont dénombrés 1 million d’addicts ; des études chiffrées manquent en France.

De quoi s’agit-il ? La dépendance à Internet est une dépendance comparable à celle que l’on peut observer avec les drogues, l’alcool ou le jeu. On y range plusieurs composantes :

• le temps passé sur Internet, 
• les modifications de l’humeur, 
• la tolérance ou besoin d’augmenter les doses, 
• le syndrome de manque ressenti après un arrêt, et 
• la tendance aux rechutes.

Les principales études réalisées récemment ont été chinoises. En 2011, une première étude sur le cerveau d’addicts montrait une atrophie de certaines zones cérébrales tel le cortex préfrontal, ce qui suggére que la pratique pathologique d’internet réduit les capacités de contrôle inhibiteur (savoir patienter, résister à une stimulation, ne pas agir de façon impulsive). En janvier 2012, une autre étude chinoise révélait une réduction de la substance blanche dans le cerveau, c’est–à-dire des câbles neuronaux qui permettent aux différentes zones cérébrales d’interagir, là encore pour le raisonnement planifié et le contrôle des impulsions.

Ces études anatomiques prédisaient donc des signes d’impulsivité et de manque de contrôle inhibiteur chez les patients. C’est ce que viennent d’observer d’autres chercheurs chinois, dans des tests de comportements sur des jeunes dépendants à Internet et spécialement aux jeux en ligne, qui y consacrent en moyenne 11 heures par jour. Dans des tâches de décision où il faut appuyer sur un bouton pour faire la différence entre un élément de jeu en ligne et un objet quelconque, ces personnes réagissent trop vite, n’arrivent pas à refréner leurs impulsions, et commettent beaucoup d’erreurs, confondant des objets courants avec des objets de jeux en ligne.

Ce syndrome fait donc apparaître une attraction automatique vers le monde virtuel, et une tendance à l’impulsivité, notamment une difficulté à prendre son temps pour réfléchir et optimiser ses décisions , le tout étant corrélé au nombre d’années d’addiction. Nous sommes donc en face d’un nouveau type d’addiction, qu’il est question d’introduire dans la nouvelle version du manuel diagnostic des maladies mentales, à paraître en 2013.

Z. Zhou et al., Cognitive biases toward internet game-related pictures and executive deficits in individuals with an internet game addiction, PLOS ONE, vol.7, e48961, 2012.

Cerveau et psycho N°7 septembre - novembre 2004 Les dépendances sans drogues

Les cellules du pancréas qui produisent l’insuline peuvent être endommagées si l’on traite un cancer par radiothérapie, selon une étude sur 2500 personnes. Plus tard, cela facilite le développement du diabète.

François Pattou est spécialiste du diabète à l’Université Lille-Nord de France.

Une équipe franco-britannique révèle que les enfants traités par radiothérapie ont plus de risques de développer un diabète à l’âge adulte. Comment a-t-elle procédé ?

F.P. : Pilotée par Florent de Vathaire, épidémiologiste à l’Inserm, cette étude a porté sur 2 500 adultes. Durant l’enfance, tous avaient contracté un cancer. Il s’agissait soit d’une une tumeur solide située par exemple dans un rein, dans l’abdomen… ; soit d’un « lymphome », un cancer affectant les vaisseaux lymphatiques par lesquels les globules blancs circulent dans l’organisme. Certains avaient alors été traités par radiothérapie, d’autres pas. L’étude révèle qu’à l’âge de 45 ans, 6,6 % des volontaires traités par radiothérapie avaient développé un diabète, contre seulement 2,3 % pour les autres [1].

Comment expliquer ce phénomène ?

F.P. : On sait que lors d’une radiothérapie, le pancréas peut être plus ou moins irradié, même si ce n’est pas l’organe visé. Parallèlement, on sait que le diabète est provoqué par la perte ou l’altération des cellules pancréatiques productrices d’insuline. Or, précisément, l’étude montre que le risque de diabète à l’âge adulte est proportionnel à la dose d’irradiation reçue par la queue du pancréas où l’on trouve beaucoup de ces cellules. Ainsi, à l’âge de 45 ans, le taux de diabétiques atteignait 16,3 % chez les sujets ayant reçu plus de 10 gray [2] au niveau de cette zone. Et pour les doses faibles et modérées, les résultats montrent que chaque gray reçu au niveau de la queue du pancréas augmente de 65 % le risque de diabète ultérieur, accréditant un lien de cause à effet.

Quels enseignements en tirer ?

F.P. : La radiothérapie semble donc augmenter le risque de diabète en altérant à long terme ces cellules productrices d’insuline. Or, actuellement, le pancréas est l’un des rares organes jugé sans risque de complications après une radiothérapie. Parallèlement, de plus en plus d’études indiquent qu’il n’est pas si « inerte » que cela : même à l’âge adulte, le pancréas aurait une certaine capacité de régénération, probablement conférée par des cellules souches. Cette étude suggère que la radiothérapie altèrerait aussi cette plasticité. Il semble donc qu’il faille désormais considérer le pancréas comme un organe critique en limitant au maximum son irradiation, en particulier chez les enfants.

Propos recueillis par Jean-Philippe Braly

[1] F. de Vathaire et al., The Lancet Oncology, 13, 1002,2012.

[2] Le gray est l'unité de mesure de la dose de radiation absorbée par le corps.

Sur ce thème, La Recherchea publié :

> Détourner des cellules pour soigner le diabète, La Recherche, 437, janvier 2010.

> Le rôle ambigu des cellules pancréatiques, La Recherche, 431, juin 2009.