Neuroscience

Articles and news from the latest research reports.

Posts tagged neuroscience

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Perceptions trick memory

July 11, 2012

An inflated sense of memory function in people with dementia may influence their likelihood of seeking help, new Flinders University research shows.

As part of her PhD, Flinders research associate Dr. Chris Materne studied the disparity between memory perception and performance in people with dementia.

In the first stage of the project, Dr. Materne analysed data from the Australian Longitudinal Study of Aging which showed that most survey participants believed their memory had remained stable over the 11-year assessment, despite tests showing a decline in memory performance.

She then conducted an intervention with 13 individuals, from a larger group of 23 people with dementia, using spaced retrieval memory training to help them achieve a specific task or activity, such as remembering to lock the front door or keep their glasses in the same spot.

“Spaced retrieval works by helping people remember specific information or tasks by getting them to respond to a prompt question over progressively increasing intervals of time,” Dr. Materne said.

“In one case we helped a man remember to put his glasses in the same place because he was always losing them which made both him and his wife quite distressed,” she said.

“We think the training taps into procedural memory so it becomes habitual rather than explicit memory, such as memory for facts, which tends to decline before procedural memory when you have dementia.”

The technique was conducted once a week for six weeks, with seven out of the 13 participants still able to perform their nominated activity or task after six months.

The 23 participants were also asked to rate their performance based on a specific question, such as how many people they could name in a photo with 10 faces.

While most respondents were initially over-confident in their abilities, with some claiming to be able to name all 10 faces, their perceptions did change over time to more accurately reflect their cognitive function.

About one third of family carers, however, initially considered their loved ones memory to be better than what the person with dementia actually reported.

“In the longitudinal sample people didn’t feel their memory had changed over time because the questions were more general but when we asked specific, detailed questions about memory in the smaller study, the respondents came to recognise their declining performance.”

Dr. Materne said the research highlighted the need for more comprehensive assessments when diagnosing dementia to increase the accuracy of peoples’ perceptions, and therefore their likelihood of seeking help.

Provided by Flinders University

Source: medicalxpress.com

Filed under science neuroscience brain psychology memory perception dementia

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Why the Thrill Is Gone: Potential Target for Treating Major Symptom of Depression

ScienceDaily (July 11, 2012) — Stanford University School of Medicine scientists have laid bare a novel molecular mechanism responsible for the most important symptom of major depression: anhedonia, the loss of the ability to experience pleasure. While their study was conducted in mice, the brain circuit involved in this newly elucidated pathway is largely identical between rodents and humans, upping the odds that the findings point toward new therapies for depression and other disorders.

Additionally, opinion leaders hailed the study’s inventive methodology, saying it may offer a much sounder approach to testing new antidepressants than the methods now routinely used by drug developers.

While as many as one in six Americans is likely to suffer a major depression in their lifetimes, current medications either are inadequate or eventually stop working in as many as 50 percent of those for whom they’re prescribed.

"This may be because all current medications for depression work via the same mechanisms," said Robert Malenka, MD, PhD, the Nancy Friend Pritzker Professor in Psychiatry and Behavioral Sciences. "They increase levels of one or another of two small molecules that some nerve cells in the brain use to signal one another. To get better treatments, there’s a great need to understand in greater detail the brain biology that underlies depression’s symptoms." The study’s first author is Byung Kook Lim, PhD, a postdoctoral scholar in Malenka’s laboratory.

Malenka is senior author of the new study, published July 12 in Nature, which reveals a novel drug target by showing how a hormone known to affect appetite turns off the brain’s ability to experience pleasure when an animal is stressed. This hormone, melanocortin, signals to an ancient and almost universal apparatus deep in the brain called the reward circuit, which has evolved to guide animals toward resources, behaviors and environments — such as food, sex and warmth — that enhance their prospects for survival.

"This is the first study to suggest that we should look at the role of melanocortin in depression-related syndromes," said Eric Nestler, MD, PhD, professor and chair of neuroscience and director of the Friedman Brain Institute at Mount Sinai School of Medicine in New York. Nestler was not involved in the study but is familiar with its contents.

Read more …

Filed under science neuroscience brain psychology depression

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Using Biomarkers to Identify and Treat Schizophrenia

ScienceDaily (July 11, 2012) — In the current online issue of PLoS ONE, researchers at the University of California, San Diego School of Medicine say they have identified a set of laboratory-based biomarkers that can be useful for understanding brain-based abnormalities in schizophrenia. The measurements, known as endophenotypes, could ultimately be a boon to clinicians who sometimes struggle to recognize and treat the complex and confounding mental disorder.

"A major problem in psychiatry is that there are currently no laboratory tests that aid in diagnosis, guide treatment decisions or help predict treatment response or outcomes," said Gregory A. Light, PhD, associate professor of psychiatry and the study’s first author. "Diagnoses are currently based on a clinician’s ability to make inferences about patients’ inner experiences."

Diagnosing and treating schizophrenia is a particularly troubling challenge. The disorder, which affects about 1 percent of the U.S. population or roughly 3 million people, is characterized by a breakdown of normal thought processes and erratic, sometimes dangerous or harmful, behaviors.

"Schizophrenia is among the most severe and disabling conditions across all categories of medicine," said Light, who also directs the Mental Illness, Research, Education and Clinical Center at the San Diego VA Healthcare System.

The precise cause or causes of schizophrenia are not known, though there is a clear genetic component, with the disorder more common in some families.

Clinicians typically diagnose schizophrenia based upon inferences drawn from the patient’s inner experiences. That is, their ability to describe what’s happening inside their minds.

"But even the best clinicians struggle with diagnostic complexities based on sometimes fuzzy clinical phenomenology," said Light. The clinical challenge is compounded by the fact that "many schizophrenia patients have cognitive and functional impairments," said Light. They may not be able to reasonably explain how or what they think.

Light and colleagues investigated whether a select battery of neurophysiological and neurocognitive biomarkers could provide clinicians with reliable, accurate, long-term indicators of brain dysfunction, even when overt symptoms of the disorder were not apparent. These markers ranged from tests of attention and memory to physiological assessments of basic perceptual processes using scalp sensors to measure brain responses to simple sounds.

The researchers measured the biomarkers in 550 schizophrenia patients, and then re-tested 200 of the patients one year later. They found that most of the markers were significantly abnormal in schizophrenia patients, were relatively stable between the assessments and were not affected by modest fluctuations in clinical status of the patient.

Light said further research is required, including whether the endophenotypes can differentiate other psychiatric disorders, be used to anticipate patient response to different kinds of drugs or non-pharmacological interventions or even be used to predict which subjects are at high risk of developing a psychotic illness.

"We believe this paper is an important step towards validating laboratory-based biomarkers for use in future genomic and clinical treatment studies of schizophrenia," Light said.

Source: Science Daily

Filed under science neuroscience brain psychology schizophrenia

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Is anxiety related to premature aging? A new study by researchers at Brigham and Women’s Hospital (BWH) shows that a common form of anxiety, known as phobic anxiety, was associated with shorter telomeres in middle-aged and older women. The study suggests that phobic anxiety is a possible risk factor for accelerated aging.
Read more: Anxiety Linked to Shortened Telomeres, Accelerated Aging

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Is anxiety related to premature aging? A new study by researchers at Brigham and Women’s Hospital (BWH) shows that a common form of anxiety, known as phobic anxiety, was associated with shorter telomeres in middle-aged and older women. The study suggests that phobic anxiety is a possible risk factor for accelerated aging.

Read more: Anxiety Linked to Shortened Telomeres, Accelerated Aging

Filed under science neuroscience brain psychology anxiety

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Oligodendroglia cells protect neurons against neurodegeneration

July 11, 2012

(Medical Xpress) — Johns Hopkins researchers say they have discovered that the central nervous system’s oligodendroglia cells, long believed to simply insulate nerves as they “fire” signals, are unexpectedly also vital to the survival of neurons. Damage to these insulators appears to contribute to brain injury in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease for the Yankee baseball great who died from the disease.

The discovery, described online in the journal Nature, suggests that a previously unknown — and unexpected — function of these cells is to supply nutrition to the principal brain cells, neurons. This new pathway may prove to be an important and novel therapeutic target for ALS, the researchers say, and potentially other diseases that attack the body’s nerve fibers, such as multiple sclerosis.

"More than 100 years after their discovery, we have now found a fundamentally new property in the way oligodendroglia work in the brain, laying the foundation for a new approach to try to treat debilitating neurodegenerative diseases,” says Jeffrey D. Rothstein, M.D., Ph.D., a professor of neurology and neuroscience at the Johns Hopkins University School of Medicine, and the study’s leader. “We’ve added a whole new category to what they do in the brain.”

The cells responsible for the transfer of information and electrical impulses around the body, neurons work by transferring electrical charges from neuron to neuron. Axons, the wire-like extensions of the neurons, help move the messages, in some cases over many feet, from cell to cell. Oligodendroglia insulate axons, like rubber coating around an electrical wire, to speed up the conduction of information. Axonal death is a hallmark of ALS and most other neurodegenerative disorders, Rothstein says.

Rothstein and his colleagues say the other principal brain cells, the astroglia, were believed to be primarily responsible for providing energy to neurons in the form of glucose, but their experiments show that oligodendroglia are surprisingly crucial in feeding neurons — in the form of less energy-rich lactate, without which neurons and their axons die. Lactate has long been seen as a minor player in this process, but the Johns Hopkins team says it appears to be far more important to nerve cell survival. Moreover, they found that the protein MCT1, the dominant transporter of lactate in the brain, is only found in oligodendroglia.

Rothstein says their discovery was rooted in experiments during which scientists, using mice, knocked out the gene that makes the MCT1 protein and saw axons begin to die, even though they were still getting plenty of glucose.

As part of these experiments, the researchers engineered mice whose cells would light up if they were expressing MCT1. The scientists then determined that only oligodendroglia cells lit up, showing that MCTI is located on this type of cell alone. They also knocked out the MCT1 in cell cultures and found that neurons would begin to die, but would recover when fed lactate, proving the importance of MCT1 in providing this nutritional compound. They conducted the same experiments in mice and got similar results.

Finally, the researchers turned their attention to ALS, a disease where they had recently uncovered abnormalities related to oligodendroglia. In ALS mice, they found that MCT1 was missing in brain cells well before the disease developed, and they found similar results in ALS patients. Rothstein says the findings suggest that oligodendroglia injury — specifically injury to the mechanism that produces MCT1 — may be an important event in the onset and progression of ALS.

Rothstein, who is director of the Johns Hopkins University School of Medicine’s Brain Science Institute, says he hopes further research can establish that the activation of MCT1 in people will protect axons in those with ALS and other degenerative diseases.

Provided by Johns Hopkins University School of Medicine

Source: medicalxpress.com

Filed under science neuroscience brain psychology neuron neurodegenerative disorders

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Two proteins offer a ‘clearer’ way to treat Huntington’s disease

July 11, 2012

In a paper published in the July 11 online issue of Science Translational Medicine, researchers at the University of California, San Diego School of Medicine have identified two key regulatory proteins critical to clearing away misfolded proteins that accumulate and cause the progressive, deadly neurodegeneration of Huntington’s disease (HD).

This is a human neuron. UC San Diego scientists have identified a pair of proteins that help clear away other misfolded proteins responsible for the progressive degeneration of brain cells in Huntington’s disease. Credit: UC San Diego School of Medicine

The findings explain a fundamental aspect of how HD wreaks havoc within cells and provides “clear, therapeutic opportunities,” said principal investigator Albert R. La Spada, MD, PhD, professor of cellular and molecular medicine, chief of the Division of Genetics in the Department of Pediatrics and associate director of the Institute for Genomic Medicine at UC San Diego.

"We think the implications are significant," said La Spada. "It’s a lead we can vigorously pursue, not just for Huntington’s disease, but also for similar neurodegenerative conditions like Parkinson’s disease and maybe even Alzheimer’s disease.”

In HD, an inherited mutation in the huntingtin (htt) gene results in misfolded htt proteins accumulating in certain central nervous system cells, leading to progressive deterioration of involuntary movement control, cognitive decline and psychological problems. More than 30,000 Americans have HD. There are no effective treatments currently to either cure the disease or slow its progression.

La Spada and colleagues focused on a protein called PGC-1alpha, which helps regulate the creation and operation of mitochondria, the tiny organelles that generate the fuel required for every cell to function.

"It’s all about energy," La Spada said. "Neurons have a constant, high demand for it. They’re always on the edge for maintaining adequate levels of energy production. PGC-1alpha regulates the function of transcription factors that promote the creation of mitochondria and allow them to run at full capacity.”

Previous studies by La Spada and others discovered that the mutant form of the htt gene interfered with normal levels and functioning of PGC-1alpha. “This study confirms that,” La Spada said. More surprising was the discovery that elevated levels of PGC-1alpha in a mouse model of HD virtually eliminated the problematic misfolded proteins.

Specifically, PGC-1alpha influenced expression of another protein vital to autophagy – the process in which healthy cells degrade and recycle old, unneeded or dangerous parts and products, including oxidative, damaging molecules generated by metabolism. For neurons, which must last a lifetime, the self-renewal is essential to survival.

"Mitochondria get beat up and need to be recycled," La Spada said. "PGC-1alpha drives this pathway through another protein called transcription factor EB or TFEB. We were unaware of this connection before, because TFEB is a relatively new player, though clearly emerging as a leading actor. We discovered that even without PGC-1alpha induction, TFEB can prevent htt aggregation and neurotoxicity."

In their experiments, HD mice crossbred with mice that produced greater levels of PGC-1alpha showed dramatic improvement. Production of misfolded proteins was essentially eliminated and the mice behaved normally. “Degeneration of brain cells is prevented. Neurons don’t die,” said La Spada.

PGC-1alpha and TFEB provide two new therapeutic targets for Huntington’s disease, according to La Spada. “If you can induce the bioenergetics and protein quality control pathways of nervous system cells to function properly, by activating the PGC-1alpha pathway and promoting greater TFEB function, you stand a good chance of maintaining neural function for an extended period of time. If we could achieve the level of increased function necessary to eliminate misfolded proteins, we might nip the disease process in the bud. That would go a long way toward treating this devastating condition.”

Provided by University of California - San Diego

Source: medicalxpress.com

Filed under science neuroscience brain psychology huntington protein

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Alzheimer’s plaques in PET brain scans identify future cognitive decline

July 11, 2012

Among patients with mild or no cognitive impairment, brain scans using a new radioactive dye can detect early evidence of Alzheimer’s disease that may predict future decline, according to a multi-center study led by researchers at Duke University Medical Center.

PET images using florbetapir dye to highlight beta-amyloid plaques show (A), a cognitively normal subject; (B) an amyloid-positive patient with Alzheimer’s disease; (C) a patient with mild cognitive impairment; and (D) a patient with mild cognitive impairment who progressed to dementia during the study. Credit: Slide courtesy of the journal Neurology.

The finding is published online July 11, 2012, in the journal Neurology, the medical journal of the American Academy of Neurology. It expands on smaller studies demonstrating that early detection of tell-tale plaques could be a predictive tool to help guide care and treatment decisions for patients with Alzheimer’s disease.

"Even at a short follow-up of 18 months we can see how the presence of amyloid plaques affects cognitive function," said P. Murali Doraiswamy, M.D., professor of psychiatry at Duke who co-led the study with R. Edward Coleman, M.D., professor of radiology at Duke . "Most people who come to the doctor with mild impairment really want to know the short-term prognosis and potential long-term effect."

Doraiswamy said such knowledge also has some pitfalls. There is no cure for Alzheimer’s disease, which afflicts 5.4 million people in the United States and is the sixth-leading cause of death among U.S. adults. But he said numerous drugs are being investigated, and identifying earlier disease would improve research into their potential benefits and speed new discoveries, while also enhancing care and treatment of current patients.

In the Neurology study, 151 people who had enrolled in a multi-center test of a new radioactive dye called florbetapir (Amyvid) were recruited to participate in a 36-month analysis. Of those participants, 69 had normal cognitive function at the start of the study, 51 had been diagnosed with mild impairment, and 31 had Alzheimer’s dementia.

All completed cognitive tests and underwent a brain scan using Positron Emission Tomography, or PET imaging. The technology uses radioactive tracers designed to highlight specific tissue to create a three-dimensional picture of an organ or a biological function.

The dye used in the study, florbetapir, was recently approved by the U.S. Food and Drug Administration for PET imaging of the brain to estimate beta-amyloid plaque density in patients who are being evaluated for cognitive impairment. It binds to the amyloid plaques that characterize Alzheimer’s disease, providing a window into the brain to see if the plaques have formed, and how extensively.

Patients in the study were reassessed with additional cognitive exams at 18 months and 36 months. At the 18-month point, patients with mild cognitive impairment who had PET evidence of plaque at the trial’s start worsened to a great degree on cognitive tests than patients who had no evidence of plaque at the trial’s start. Twenty-nine percent of the plaque-positive patients in this group developed Alzheimer’s dementia, compared to 10 percent who started with no plaque.

Cognitively normal patients with a plaque-positive PET scan at the start of the study also showed more mental decline at 18 months compared to those who were negative for plaque.

The study additionally found that people with negative scans reversed from minimally impaired to normal more often than people with positive PET scan, suggesting test anxiety or concentration problems could have affected their initial performance.

"For the most part we have been blind about who would progress and who wouldn’t, so this approach is a step toward having a biomarker that predicts risk of decline in people who are experiencing cognitive impairment," Doraiswamy said.

He said the study’s results provide initial data that needs to be verified by additional research. Final, 36-month data from the study has been completed and will be presented at the Alzheimer’s Association International Conference this week in Vancouver, Canada. Doraiswamy also cautioned that florbetapir is currently not approved to predict the development of dementia or other neurologic conditions and stressed that it should not be used as a screening tool in otherwise normal or minimally impaired people. Likewise, a positive scan is not necessarily diagnostic for Alzheimer’s by itself.

Provided by Duke University Medical Center

Source: medicalxpress.com

Filed under science neuroscience brain psychology alzheimer neuroimaging

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Individual differences in altruism explained by brain region involved in empathy

July 11, 2012

What can explain extreme differences in altruism among individuals, from Ebenezer Scrooge to Mother Teresa? It may all come down to variation in the size and activity of a brain region involved in appreciating others’ perspectives, according to a study published in the July 12th issue of the journal Neuron. The findings also provide a neural explanation for why altruistic tendencies remain stable over time.

The junction (yellow) between the parietal and the temporal lobes, in which the relative proportion of gray matter is significantly positively correlated with the propensity for altruistic behavior. Credit: University of Zurich

"This is the first study to link both brain anatomy and brain activation to human altruism,” says senior study author Ernst Fehr of the University of Zurich. “The findings suggest that the development of altruism through appropriate training or social practices might occur through changes in the brain structure and the neural activations that we identified in our study.”

Individuals who excel at understanding others’ intents and beliefs are more altruistic than those who struggle at this task. The ability to understand others’ perspectives has previously been associated with activity in a brain region known as the temporoparietal junction (TPJ). Based on these past findings, Fehr and his team reasoned that the size and activation of the TPJ would relate to individual differences in altruism.

In the new study, subjects underwent a brain imaging scan and played a game in which they had to decide how to split money between themselves and anonymous partners. Subjects who made more generous decisions had a larger TPJ in the right hemisphere of the brain compared with subjects who made stingy decisions.

Moreover, activity in the TPJ reflected each subject’s specific cutoff value for the maximal cost the subject was willing to endure to increase the partner’s payoff. Activity in the TPJ was higher during hard decisions—when the personal cost of an altruistic act was just below the cutoff value—than during easy decisions associated with a very low or very high cost.

"The structure of the TPJ strongly predicts an individual’s setpoint for altruistic behavior, while activity in this brain region predicts an individual’s acceptable cost for altruistic actions," says study author Yosuke Morishima of the University of Zurich. "We have elucidated the relationship between the hardware and software of human altruistic behavior."

Provided by Cell Press

Source: medicalxpress.com

Filed under science neuroscience brain psychology empathy emotion

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H1N1 Vaccine Associated With Small but Significant Risk of Guillain-Barre Syndrome

July 10th, 2012

Guillain-Barre syndrome (GBS) is usually characterized by rapidly developing motor weakness and areflexia (the absence of reflexes). “The disease is thought to be autoimmune and triggered by a stimulus of external origin.

In 1976-1977, an unusually high rate of GBS was identified in the United States following the administration of inactivated ‘swine’ influenza A(H1N1) vaccines. In 2003, the Institute of Medicine (IOM) concluded that the evidence favored acceptance of a causal relationship between the 1976 swine influenza vaccines and GBS in adults.

Studies of seasonal influenza vaccines administered in subsequent years have found small or no increased risk,” according to background information in the article. “In a more recent assessment of epidemiologic studies on seasonal influenza vaccines, experimental studies in animals, and case reports in humans, the IOM Committee to Review Adverse Effects of Vaccines concluded that the evidence was inadequate to accept or reject a causal relationship.”

Analysis of recent H1N1 vaccination data indicated a small but significant risk of GBS following influenza A(H1N1) vaccinations.

Philippe De Wals, M.D., Ph.D., of Laval University, Quebec City, Canada and colleagues conducted a study to assess the risk of GBS following pandemic influenza vaccine administration. In fall 2009 in Quebec an immunization campaign was launched against the 2009 influenza A(H1N1) pandemic strain. By the end of the year, 4.4 million residents had been vaccinated. The study included follow-up over the 6-month period of October 2009 through March 2010 for suspected and confirmed GBS cases reported by physicians, mostly neurologists, during active surveillance or identified in the provincial hospital summary discharge database. Immunization status was verified.

Over the 6-month period, 83 confirmed GBS cases were identified. Twenty-five confirmed cases had been vaccinated against 2009 influenza A(H1N1) 8 or fewer weeks before disease onset, with most (19/25) vaccinated 4 or fewer weeks before onset. Analysis of data indicated a small but significant risk of GBS following influenza A(H1N1) vaccination. The number of cases attributable to vaccination was approximately 2 per 1 million doses. The excess risk was observed only in persons 50 years of age or older.

“In Quebec, the individual risk of hospitalization following a documented influenza A(H1N1) infection was 1 per 2,500 and the risk of death was 1/73,000. The H1N1 vaccine was very effective in preventing infections and complications. It is likely that the benefits of immunization outweigh the risks,” the authors write.

Source: Neuroscience News

Filed under science neuroscience disease guillain-barre H1N1

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Potential Cause of HIV-Associated Dementia Revealed

ScienceDaily (July 10, 2012) — Researchers at Georgetown University Medical Center appear to have solved the mystery of why some patients infected with HIV, who are using antiretroviral therapy and show no signs of AIDS, develop serious depression as well as profound problems with memory, learning, and motor function. The finding might also provide a way to test people with HIV to determine their risk for developing dementia.

They say the answer, published in the July 11 issue of the Journal of Neuroscience, may ultimately lead to a therapeutic solution that helps these patients as well as others suffering from brain ailments that appear to develop through the same pathway, including those that occur in the aged.

"We believe we have discovered a general mechanism of neuronal decline that even explains what happens in some elderly folks," says the study’s lead investigator, Italo Mocchetti, Ph.D., professor and vice chair of the department of neuroscience at Georgetown University Medical Center. "The HIV-infected patients who develop this syndrome are usually quite young, but their brains act old."

The research team found that even though HIV does not infect neurons, it tries to stop the brain from producing a protein growth factor — mature brain derived neurotrophic factor (mature BDNF) — that Mocchetti says acts like “food” for brain neurons. Reduced mature BDNF results in the shortening of the axons and their branches that neurons use to connect to each other, and when they lose this communication, the neurons die.

"The loss of neurons and their connections is profound in these patients," Mocchetti says. HIV-associated dementia occurs in two to three percent of HIV-infected patients using retroviral therapies, all of who appear to be otherwise healthy, and in 30 percent of HIV-positive patients who are not on medication.

Mocchetti believes that HIV stops production of mature BDNF because that protein interferes with the ability of the virus to attack other brain cells. It does this through the potent gp120 envelope protein that sticks out from the viral shell — the same protein that hooks on to brain macrophages and microglial cells to infect them. “In earlier experiments, when we dumped gp120 into neuronal tissue culture, there was a 30-40 percent loss of neurons overnight. That makes gp120 a remarkable neurotoxin.”

This study is the product of years of work that has resulted in a string of publications. It began when Mocchetti and his colleagues were given a grant from the National Institutes on Drug Abuse to determine whether there was a connection between the use of cocaine and morphine, and dementia. (A substantial number of HIV-positive patients have been or currently are intravenous drugs users.)

They found that it was the virus that was responsible for the dementia, not the drugs, and so they set out to discover how the virus was altering neuronal function.

Their scientific break came when the researchers were able to study the blood of 130 women who were enrolled in the 17 year-old, nationwide WIHS (Women’s Interagency HIV Study, directed at Georgetown by Mary Young, M.D.), which has focused on the effects of HIV in infected females. In one seminal discovery, Mocchetti and colleagues found that when there was less BDNF in the blood, patients were at risk of developing brain abnormalities. He published this finding in 2011 in the May 15 issue of AIDS.

In this study, Mocchetti, Alessia Bachis, Ph.D., and their colleagues studied the brains of HIV-positive patients who had died, and who had developed HIV-associated dementia. They also found that neurons had shrunk, and that mature BDNF had substantially decreased.

He and his colleagues then worked out the mechanism responsible for this destruction of neurons.

Normally, neurons release a long form of BDNF known as proBDNF, and then certain enzymes, including one called furin, cleave proBDNF to produce mature BDNF, which then nurtures brain neurons. When uncut, proBDNF is toxic, leading to “synaptic simplification,” or the shortening of axons. It does this by binding to a receptor, p75NTR, that contains a death domain.

"HIV interferes with that normal process of cleaving proBDNF, resulting in neurons primarily secreting a toxic form of BDNF," Mocchetti says. The same imbalance between mature BDNF and proBDNF occurs as we age, he says, although no one knows how that happens. "The link between depression and lack of mature BDNF is also known, as is the link to issues of learning and memory. That’s why I say HIV-associated dementia resembles the aging brain."

Loss of mature BDNF has also been suggested to be a risk factor in chronic diseases such as Parkinson’s and Huntington’s diseases, Mocchetti says.

The findings suggest a possible therapeutic intervention, he adds. “One way would be to use a small molecule to block the p75NTR receptor that proBDNF uses to kill neurons. A small molecule like that could get through the blood-brain barrier.

"If this works in HIV-dementia, it may also work in other brain issues caused by proBDNF, such as aging," Mocchetti adds.

The finding also suggests that measuring proBDNF in HIV-positive patients may provide a biomarker of risk for development of dementia, he adds.

"This finding is extremely important for both basic scientists and physicians, because it suggests a new avenue to understand, and treat, a fairly widespread cause of dementia," Mocchetti says.

Source: Science Daily

Filed under science neuroscience brain psychology HIV dementia

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