Wipe out a single memory

Drug can clear away one fearful memory while leaving another intact.

Kerri Smith

A single frightening thought can be erased from a rat's mind. Alamy

A single, specific memory has been wiped from the brains of rats, leaving other recollections intact.

The study adds to our understanding of how memories are made and altered in the brain, and could help to relieve sufferers of post-traumatic stress disorder (PTSD) of the fearful memories that disrupt their lives. The results are published in Nature Neuroscience¹.

The brain secures memories by transferring them from short-term to long-term storage, through a process called reconsolidation. It has been shown before that this process can be interrupted with drugs. But Joseph LeDoux of the Center for Neural Science at New York University and his colleagues wanted to know how specific this interference was: could the transfer of one specific memory be meddled with without affecting others?

"Our concern was: would you do something really massive to their memory network?" says LeDoux.

Scary music

To find out, they trained rats to fear two different musical tones, by playing them at the same time as giving the rats an electric shock. Then, they gave half the rats a drug known to cause limited amnesia (U0126, which is not approved for use in people), and reminded all the animals, half of which were still under the influence of the drug, of one of their fearful memories by replaying just one of the tones.

When they tested the rats with both tones a day later, untreated animals were still fearful of both sounds, as if they expected a shock. But those treated with the drug were no longer afraid of the tone they had been reminded of under treatment. The process of re-arousing the rats' memory of being shocked with the one tone while they were drugged had wiped out that memory completely, while leaving their memory of the second tone intact.

LeDoux's team also confirms the idea that a part of the brain called the amygdala is central to this process - communication between neurons in this part of the brain usually increases when a fearful memory forms, but it decreases in the treated rats. This shows that the fearful memory is actually deleted, rather than simply breaking the link between the memory and a fearful response.

Greg Quirk, a neurophysiologist from the Ponce School of Medicine in Puerto Rico, thinks that psychiatrists working to treat patients with conditions such as PTSD will be encouraged by the step forward. "These drugs would be adjuncts to therapy," he says. "This is the future of psychiatry - neuroscience will provide tools to help it become more effective."
http://www.nature.com/news/2007/070305/full/070305-17.html

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article en Français du CNRS : http://www2.cnrs.fr/presse/communique/1052.htm

http://www.nature.com/news/2007/070312/full/070312-1.html

Commonly used anaesthetic alters mouse brains

Study adds to concerns over drug link to Alzheimer's.

Michael Hopkin

Breathe deep: inhaled anaesthetics can do funny things to mouse brains. Corbis

Exposure to widely used anaesthetic drugs increases production of a brain protein thought to cause Alzheimer's disease, a study of mice has shown. The research feeds concern that general anaesthesia may be linked to dementia in humans.

Inhaled doses of halothane, one of a class of drugs called volatile anaesthetics, increase the amount of a protein called amyloid beta in mouse brains, researchers at the University of Pennsylvania in Philadelphia have found.

Some 60 million people worldwide are given volatile anaesthetics each year. The drugs are known to cause 'post-operative cognitive decline' in many cases, which can last for days, weeks or years.

If these drugs boost production of amyloid beta, they may also be linked to long-term dementias such as Alzheimer's. The brains of Alzheimer's patients contain high levels of amyloid beta, although the molecule's links with disease are still unknown.

There are no data on whether the effect occurs in humans. Until such information is gathered, it will be difficult to say whether anaesthetists should stop using volatile anaesthetics, including halothane and the related isoflurane, the most widely used of the group.

Nevertheless, it adds to a growing pool of evidence that these drugs can damage the brain. "This creates a little more concern than before," says Roderic Eckenhoff, one of the researchers, who report the study in Neurobiology of Aging¹. "But if you need surgery you should get your surgery."

 

Méditerranée : Posidonia ocanica, famille des Alismatales (groupe de l'arum)

Atlantique : Zoostera marina, famille des Zoostéracées

Antilles : Thalassia testidunum « l'herbe à tortues »

Mer Rouge : Halophila stipulacea

Le terme batholite (du grec « bathos » : profondeur et « lithos » : roche) désigne une masse de roches ignées [feu] intrusives (aussi appelées roches plutoniques) qui se forme lorsque le magma se refroidit à l'intérieur de l'écorce terrestre. http://fr.wikipedia.org/wiki/Batholite

Parc d'Augrabies, Afrique du sud

Cette maladie se caractérise par la prolifération des cellules myéloïdes maintenant leur capacité de maturation jusqu'à une phase pré-terminale généralement courte (survie de 3 mois après son déclenchement) où ces cellules perdent cette capacité et restent myéoblastiques, ce qui conduit à une leucémie aiguë très résistante à la chimiothérapie.
D'un point de vue cytogénétique la LMC se caractérise par une altération chromosomique typique : une translocation réciproque entre les chromosomes 9 et 22 formant ce qu'on appelle le chromosome Philadelphie.
On peut observer sur l'image des chromosomes en 24 couleurs qu'un fragment du chromosome 22 est transloqué sur le chromosome 9.
Cette translocation a pour conséquence la fusion de l'oncogène c-abl du chromosome 9 avec ls séquences du chromosome 22 proche de la région de rupture (breakpoint cluster region ou bcr) aboutissant à la formation d'un gène fusionné bcr-abl, s'exprimant, produit une protéine de fusion. Le gène c-abl code habituellement pour une tyrosine kinase non liée aux récepteurs. La protéine de fusion bcr-abl code pour une grande quantité de cette tyrosinekinase ce qui accroît le transport d'ATP sur les protéines de prolifération cellulaire et explique le pouvoir cancérigène.

http://acces.inrp.fr/acces/equipes/dyna/travaux/dynacell%20plone/cancer/html/glivec.htm