Researchers retrieve “lost” memories

Retrograde amnesia is the inability to recall established memories. In humans, amnesia is associated with traumatic brain injury, Alzheimer’s disease, and other neurological conditions. Whether memories lost to amnesia are completely erased or merely unable to be recalled remains an open question. Now, in a finding that casts new light on the nature of memory, published in Science, researchers from the RIKEN-MIT Center for Neural Circuit Genetics demonstrated in mice that traces of old memories do remain in the amnestic brain, and that the cellular pathways underlying them can be reactivated, allowing lost memories to be found.

The research team, led by Susumu Tonegawa, Director of the RIKEN Brain Science Institute in Saitama, Japan, was interested in how stable memories are formed in the brain and whether memories whose storage was disrupted by chemically inducing retrograde amnesia, could still be recalled. “Brain researchers have been divided for decades on whether amnesia is caused by an impairment in the storage of a memory, or in its recall,” said Tonegawa.

To make mice amnestic, they were first trained to associate a mild foot shock with a specific environment, chamber A, eliciting a typical “freezing” behavior. Eventually, trained mice would freeze in chamber A even without the shock. Neurons activated during memory formation were genetically labeled to allow their visualization and reactivation. Then, some mice were given a chemical, anisomycin, which inhibits new protein synthesis and prevents increases in synaptic strength important for memory encoding, thus inducing retrograde amnesia. Other mice received saline as a control. As expected, amnestic mice returned to chamber A did not freeze, indicating that they could not recall the memory for the specific association of the chamber and the mild foot shock.

Next, to investigate whether the stored memory from the foot shock training in chamber A was absent from the amnestic mice or remained present but was not retrievable, the researchers used optogenetic technology to selectively activate neurons that were genetically labelled during their training in chamber A with a blue light-sensitive protein, channel rhodopsin, but this time while the mice were in a novel, neutral environment, chamber B. Surprisingly, during activation of the cells involved in the foot shock memory, collectively called a “memory engram”, with blue light pulses, the amnestic mice froze just as much as the control mice, indicating that they remembered that they had acquired the memory, even though they could not recall it when placed in chamber A.

To explain how the “lost” memory was recalled during light stimulation of the memory engram, despite the induction of retrograde amnesia, the authors suggest that different processes may control memory encoding and recall. For example, during the training period, brain connections between unique memory engrams in neighbouring brain structures may be strengthened and once this has occurred, may not require an increase in synaptic strength in order to store, but not recall, the contextual fear memory and would be preserved in the amnestic state. Indeed, they observed that connectivity was enhanced between memory engram cells in the fear memory-holding amygdala and context memory-holding hippocampus of amnestic mice, even though synaptic changes remained stable.

“Our conclusion,” says Tonegawa, “is that in retrograde amnesia, past memories may not be erased, but could simply be lost and inaccessible for recall. These findings provide striking insight into the fleeting nature of memories, and will stimulate future research on the biology of memory and its clinical restoration.”

doi: 10.1126/science.aaa5542

Nanorobotic agents open blood-brain barrier, offering hope for new brain treatments

Magnetic nanoparticles can open the blood-brain barrier and deliver molecules directly to the brain, say researchers from the University of Montreal, Polytechnique Montréal, and CHU Sainte-Justine. This barrier runs inside almost all vessels in the brain and protects it from elements circulating in the blood that may be toxic to the brain. The research is important as currently 98% of therapeutic molecules are also unable to cross the blood-brain barrier.

“The barrier is temporary opened at a desired location for approximately 2 hours by a small elevation of the temperature generated by the nanoparticles when exposed to a radio-frequency field,” explained first author and co-inventor Seyed Nasrollah Tabatabaei.

“Our tests revealed that this technique is not associated with any inflammation of the brain. This new result could lead to a breakthrough in the way nanoparticles are used in the treatment and diagnosis of brain diseases,” explained the co-investigator, Hélène Girouard.

“At the present time, surgery is the only way to treat patients with brain disorders. Moreover, while surgeons are able to operate to remove certain kinds of tumours, some disorders are located in the brain stem, amongst nerves, making surgery impossible,” added collaborator and senior author Anne-Sophie Carret.

Although the technology was developed using murine models and has not yet been tested in humans, the researchers are confident that future research will enable its use in people.

“Building on earlier findings and drawing on the global effort of an interdisciplinary team of researchers, this technology proposes a modern version of the vision described almost 40 years ago in the movie Fantastic Voyage, where a miniature submarine navigated in the vascular network to reach a specific region of the brain,” said principal investigator Sylvain Martel. In earlier research, Martel and his team had managed to manipulate the movement of nanoparticles through the body using the magnetic forces generated by magnetic resonance imaging (MRI) machines. To open the blood-brain barrier, the magnetic nanoparticles are sent to the surface of the blood-brain barrier at a desired location in the brain. Although it was not the technique used in this study, the placement could be achieved by using the MRI technology described above.

Then, the researchers generated a radiofrequency field. The nanoparticles reacted to the radio-frequency field by dissipating heat thereby creating a mechanical stress on the barrier. This allows a temporary and localized opening of the barrier for diffusion of therapeutics into the brain. The technique is unique in many ways.

“The result is quite significant since we showed in previous experiments that the same nanoparticles can also be used to navigate therapeutic agents in the vascular network using a clinical MRI scanner,” Martel remarked. “Linking the navigation capability with these new results would allow therapeutics to be delivered directly to a specific site of the brain, potentially improving significantly the efficacy of the treatment while avoiding systemic circulation of toxic agents that affect healthy tissues and organs,” Carret added. “While other techniques have been developed for delivering drugs to the blood-brain barrier, they either open it too wide, exposing the brain to great risks, or they are not precise enough, leading to scattering of the drugs and possible unwanted side effect,” Martel said.

Although there are many hurdles to overcome before the technology can be used to treat humans, the research team is optimistic. “Although our current results are only proof of concept, we are on the way to achieving our goal of developing a local drug delivery mechanism that will be able to treat oncologic, psychiatric, neurological and neurodegenerative disorders, amongst others,” Carret concluded.

doi: 10.1016/j.jconrel.2015.02.027

Re-inflating balloon after carotid stenting doubles risk of stroke and death

After reviewing outcomes from thousands of cases, researchers at Johns Hopkins report that patients with blocked neck arteries who undergo carotid stenting to prop open the narrowed blood vessels fare decidedly worse if their surgeons re-inflate a tiny balloon in the vessel after the mesh stent is in place.

Although the overall risk of stroke and death is low in patients who undergo carotid stenting, the common practice of “ballooning” the vessel after the wire mesh is inserted can double the risk of death and stroke during or shortly after the procedure, according to findings published online May 30 in the Journal of Vascular Surgery. “Ballooning after placing the stent appears to cause the very complication it’s intended to prevent,” says study senior author Mahmoud Malas, M.D., M.H.S., an associate professor of surgery at the Johns Hopkins University School of Medicine. “Surgeons should avoid doing it. Period.”

The carotid arteries, which run on both sides of the neck and ferry oxygen-rich blood from the heart to the brain, can become narrowed and stiff from build-up of fat and calcium deposits over time. The condition, known as carotid stenosis, is responsible for half of the nearly 800,000 strokes that occur in the United States each year, according to the Centers for Disease Control and Prevention.

Patients with severe blockages typically undergo surgery to scrape off the fatty deposits from the walls of the vessel, the preferred approach that carries notably lower stroke risk but is not recommended for people too sick to withstand traditional surgery. Such patients are often offered minimally invasive stent placement to flatten and stabilize the built up debris inside the clogged vessels.

To place the stent, surgeons thread a catheter through the groin and up into the neck artery. Once inside, surgeons typically insert a tiny surgical balloon and inflate it to compress the fatty deposits, open up the vessel, and make room for the stent. Once the stent is in place, however, it is common practice to re-inflate the balloon to expand the wire mesh and firm up its position against the artery walls. But the new Johns Hopkins study shows re-inflating the balloon once the stent is in place fuels stroke risk.

A previous study led by Malas showed post-stent ballooning could cause another serious complication marked by a precipitous drop in blood pressure and breathing problems.

For the new study, the team analyzed stroke and death risk in more than 3,700 patients, ages 19 to 89, who had carotid stenting between 2005 and 2014 in hospitals across the United States and whose outcomes were reported in the Vascular Quality Initiative, a national repository of vascular surgery outcomes. One group of patients had pre-stent ballooning only, another was treated with post-stent ballooning only, and a third had the combination technique involving balloon use both before and after stent placement.

While the overall risk of stroke and death was relatively low – 2.4% of patients had a stroke within 30 days of treatment and less than 1% died – those treated with combination pre and poststent ballooning were twice as likely to suffer a stroke or die. Those who had post-stent ballooning alone also had an elevated risk but in the final analysis, the difference did not reach statistical significance. The researchers believe that repeat ballooning after stent placement causes stroke by driving the stent deeper into the fragile vessel walls and disturbing the fatty plaque that is built up atop the walls. This, they say, can cause splinters of plaque to chip off and make their way to the brain.

“The main goal of carotid stenting is not so much to restore blood flow as to contain and stabilize preexisting plaque,” Malas says. “Our message is clear: Once inside the artery, leave the stent alone.” Unlike the more common heart stenting where the main goal is to open the heart’s arteries and restore blood flow to the cardiac muscle, stenting the carotid arteries is done with the brain in mind.

“Carotid stenting is unique,” says study author Tammam Obeid, M.B.B.S., a surgery fellow at the Johns Hopkins University School of Medicine. “It is the only stenting procedure where the end target is not muscle but the far more delicate tissue of the brain.”

Other investigators involved in the study were Dean Arnaoutakis, Isibor Arhuidese, Umair Qazi, Christopher Abularrage, James Black and Bruce Perler, all of Johns Hopkins.

doi: 10.1016/j.jvs.2015.03.069

Chinese herbal remedy shown to reduce fatigue in cancer patients

Cancer patients suffering from moderate to severe fatigue reported significantly less fatigue within 2-3 weeks of treatment with the traditional Chinese medicine herbal mixture Ren Shen Yangrong Tang (RSYRT), a soup containing 12 herbs. The safety and efficacy of RSYRT in a Phase I/II trial are presented in an article in The Journal of Alternative and Complementary Medicine. The article is available online – doi:10.1089/acm.2014.0211.

Yichen Xu, MD, Yanzhi Chen, MD, and Pingping Li, MD, Peking University School of Oncology (Beijing, China) and Xin Shelley Wang, MD, MPH, The University of Texas MD Anderson Cancer Center (Houston) assessed the level of fatigue in cancer patients before and after RSYRT therapy. Patients took RSYRT twice a day for 6 weeks. Fatigue is one of the major challenges in oncology care. According to traditional Chinese medicine, fatigue is characterized by a deficiency in Qi, a physical life force related to the energy flow of the body. RSYRT is intended to improve Qi deficiency.

In the article “Ren Shen Yangrong Tang for Fatigue in Cancer Survivors: A Phase I/II Open-Label Study, the authors report that RSYRT was safe, with no evidence of toxicity in any of the patients treated.

Mutated gene leads to insensitivity to pain with drastic consequences

A rare congenital genetic mutation means that those affected do not feel pain. However, what seems, at first sight, to be a blessing, can have serious consequences. It means that injuries or diseases can go undetected for a long time. The affected gene was identified by an international research team from MedUni Vienna, the University of Munich and the University of Cambridge.

The starting point for this discovery was two unrelated children with a very rare and unusual disease: they had not been able to feel any pain since birth. But what sounds like a blessing can have serious consequences. “The affected children usually come to our attention when their baby teeth start to erupt because they start to bite their own tongue, lips and fingers and, in some cases, even bite bits of them off. They are also susceptible to bone fractures, which can go unnoticed for a long time because they cannot feel pain,” explains Michaela Auer-Grumbach of the University Department of Orthopaedics at the Medical University of Vienna, lead author of the study together with Ya-Chun Chen of the University of Cambridge. Because they cannot perceive pain, over the course of their lives, sufferers can sustain injuries, burns and bone fractures, which, because there is no pain warning, are often discovered late and do not heal well. Without appropriate medical care these complications can even prove fatal.

The scientists analyzed the whole exome of the patients, that is to say all sections of the genetic material, which encode proteins. In both cases they identified mutations in gene PRDM12. “Identification of mutations in the same gene in two people from different families but with a very similar clinical picture was a strong indication that we had discovered the gene responsible,” says Jan Senderek of the Friedrich Baur Institute at the University of Munich. Definitive proof was then provided by the results of the working group led by Geoffrey Woods at the University of Cambridge: they also identified PRDM12 mutations in patients with congenital analgesia. Together with colleagues at home and abroad, the scientists went on to examine more patients with congenital pain perception disorders and came across further mutations. The results of the study are published in Nature Genetics.

“By discovering the cause of the disorder, we are able to provide appropriate genetic diagnosis and counselling for affected patients and their families,” says Michaela Auer-Grumbach in summary. Even though no treatment is currently available, we can reduce the risk of serious injury and complications by means of supportive measures, information and training for sufferers and their families. The study authors hope that the publication will make doctors and geneticists more aware of this very rare and little known clinical picture.

In order to understand the mechanism of the disorder, the scientists worked with the developmental biologists Tatsuo Michiue and Shinya Matsukawa from the University of Tokyo to investigate the function of PRDM12 in tadpoles. In these tadpoles the loss of PRDM12 resulted in the defective development of nerve cells or neurons, which are important for pain perception. The PRDM12 gene contains the information for a factor that establishes the activity of other genes and hence the development of cells and tissue. This suggests that the absence of PRDM12 results in a malfunction of as yet unknown target genes, which are necessary for the development of the nervous system and effective pain perception.

The association between the congenital inability to feel pain and the defective development and function of the nervous system had already been demonstrated in earlier studies. These studies showed that mutations affected special sodium channels of pain receptors and signalling pathways for nerve growth factors. The discovery that disruptions to factors, which – like PRDM12 – control the genetic material, can result in insensitivity to pain, is new and provides insights into the development of the nervous system and the functional principle of pain perception. “Further investigations will show what significance the findings regarding PRDM12 have for pain research and the development of new pain medication,” says Michaela Auer-Grumbach.

doi: 10.1038/ng.3308.

Researchers develop surgical clip that dissolves

Kobe University, Japan, has developed a safe surgical clip that dissolves and is absorbed by the body over time. Clinical use of this clip is expected because it can reduce the rate of postoperative complications and minimize problems associated with diagnostic imaging.

The clip was developed as a collaboration between the Division of Mechanics and Physics of Materials at the Kobe University Graduate School of Engineering and the Division of Hepato-Biliary-Pancreatic Surgery at the Kobe University Graduate School of Medicine.

Most surgical clips are currently made of titanium, and as many as 30 to 40 clips may be used during a single surgical procedure. They remain inside the patient’s body after the wounds are healed. Retained clips lead to diminished quality of CT and MRI images around the wound and may cause complications. The newly developed clip is 5mm in size and made of a magnesium alloy. The alloy also contains calcium and zinc to improve its microstructure, ensuring fastening ability and formability, qualities required of materials to make clips.

The safety and functionality of the clip were evaluated in vivo studies. To evaluate the safety, an implantation study was conducted in a subcutaneous mouse model. Very little gas was produced as the clip dissolved and there was no inflammation of the surrounding tissues after 1 to 12 weeks. These results suggest that the clip is associated with very few adverse effects. Blood testing revealed that levels of magnesium and other substances in the blood were in the normal range after 12 weeks. The volume of the implanted clip was reduced by almost half after 12 weeks. Therefore, the clip is likely to dissolve and exit the body within 1 year.

To evaluate its functionality, it was tested in a rat model in which the biliary duct, portal vein, hepatic artery, and hepatic vein were occluded with the clip and a partial liver was removed. The rat had no problems during a monitoring period of 8 weeks, suggesting that the clip functioned properly. Micro CT scanning of the mouse and rat revealed that the quality of images was not degraded and organs can be observed.

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