One of the challenges in facilitating repair of the spinal cord after spinal cord injuries has been to get axons to re-grow through the damaged area. Usually the process of axonal re-growth is inhibited by the formation of scar tissue.
But now researchers have discovered a potential new weapon in the treatment of spinal cord injuries – taxol, the same drug that is currently used to inhibit the growth of certain cancers. It turns out that taxol produces “stabilization” of microtubules in damaged areas of the spinal cord, which in turn reduces scarring and reduces the production of certain factors which normally inhibit axonal regeneration. The result is that axons tend to grow more readily through taxol-treated lesion sites.
So far, taxol has only been shown to work in rats. Nevertheless, these encouraging results could pave the way for future clinical trials in humans. Perhaps some day taxol will become part of the normal treatment regimen for spinal cord injuries.
Tampilkan postingan dengan label nervous system. Tampilkan semua postingan
Tampilkan postingan dengan label nervous system. Tampilkan semua postingan
Sabtu, 26 Februari 2011
Kamis, 27 Januari 2011
Reducing Test Anxiety
Some students get so anxious before tests that their test performance falls well below their abilities. The effect is usually greatest on high-stakes tests such as finals and standardized entrance exams. Why do such students “choke under pressure”?
According to current learning theory, anxious thoughts compete for space in the short-term working memory system. If the short-term memory system is concentrating on anxious thoughts, so the theory goes, it can’t focus as well on the information that might be most useful for the test.
If the current learning theory is true, then getting anxious thoughts out of one’s head before the exam might result in improved exam scores. Indeed, in a recent study, students who suffered from test anxiety had better final exam scores in high school biology when they sat down before the exam and wrote their anxious thoughts down, compared to students who didn’t write.
Just 10 minutes of writing was enough to raise the students’ final exam grades from a B- to a B+.
According to current learning theory, anxious thoughts compete for space in the short-term working memory system. If the short-term memory system is concentrating on anxious thoughts, so the theory goes, it can’t focus as well on the information that might be most useful for the test.
If the current learning theory is true, then getting anxious thoughts out of one’s head before the exam might result in improved exam scores. Indeed, in a recent study, students who suffered from test anxiety had better final exam scores in high school biology when they sat down before the exam and wrote their anxious thoughts down, compared to students who didn’t write.
Just 10 minutes of writing was enough to raise the students’ final exam grades from a B- to a B+.
Minggu, 10 Oktober 2010
Cell Phones Can't Cause Cancer?
One of the limitations of the scientific method is that it is virtually impossible to prove that something doesn’t exist or could never happen based on empirical data alone. And if that “something” has the potential for great harm, then common sense would dictate that we should err on the side of caution and continue to assume that it could exist, or might happen. It’s what’s known as the precautionary principle.
Take cell phones and cancer, for example. Despite tens of millions of dollars spent on research, no one has ever proven that mobile phones cause brain cancer. And yet, researchers (and the public) are still unwilling to conclude that they don’t. Even the authors of a major study that once again showed no relationship between cell phones and cancer concluded: “The possible effects of long-term heavy use of mobile phones require further investigation”. Of course, that might mean more funding for their laboratory….
Physicist Bernard Leikind has taken an entirely different approach. He claims that, based on well-accepted physical principles, cell phones cannot cause cancer. He argues that the energy emitted by cell phones is not strong enough to disrupt the chemical bonds in biological molecules, period. Indeed, he claims that if it were possible for radiation energy of this type to disrupt cellular biochemical processes, there would be no life on earth because of natural sources of similar radiation energy in the environment.
Dr. Leikind has taken a lot of heat (no pun intended) from readers – see the reader-response thread after the article. But I have yet to find the flaw in his logic.
Take cell phones and cancer, for example. Despite tens of millions of dollars spent on research, no one has ever proven that mobile phones cause brain cancer. And yet, researchers (and the public) are still unwilling to conclude that they don’t. Even the authors of a major study that once again showed no relationship between cell phones and cancer concluded: “The possible effects of long-term heavy use of mobile phones require further investigation”. Of course, that might mean more funding for their laboratory….
Physicist Bernard Leikind has taken an entirely different approach. He claims that, based on well-accepted physical principles, cell phones cannot cause cancer. He argues that the energy emitted by cell phones is not strong enough to disrupt the chemical bonds in biological molecules, period. Indeed, he claims that if it were possible for radiation energy of this type to disrupt cellular biochemical processes, there would be no life on earth because of natural sources of similar radiation energy in the environment.
Dr. Leikind has taken a lot of heat (no pun intended) from readers – see the reader-response thread after the article. But I have yet to find the flaw in his logic.
Minggu, 08 Agustus 2010
Rapid Eye Movement (REM) Sleep
Humans go through several stages of sleep during a typical night. One of them is the period during which we have complex dreams, called rapid eye movement (REM) sleep. During REM sleep our eyes move about rapidly beneath closed eyelids, even though our bodies typically remain completely motionless.
The explanation for rapid eye movement during REM sleep has always remained somewhat of a mystery - until now. In the June issue of Brain, researchers report that the most likely explanation is that our eyes are trying to follow the action in our dreams. They came to this conclusion after studying the direction of eye movements in a group of subjects who have a particular sleep disorder in which they physically act out their dreams while sleeping. The patients’ eye movements tracked their physical actions with a consistency of nearly 90%. The eye movements in these patients were no different than in normal subjects who did not move physically during sleep, leading the authors to suggest that the “follow-the-dream-action” explanation for REM activity may hold for normal subjects as well.
The explanation for rapid eye movement during REM sleep has always remained somewhat of a mystery - until now. In the June issue of Brain, researchers report that the most likely explanation is that our eyes are trying to follow the action in our dreams. They came to this conclusion after studying the direction of eye movements in a group of subjects who have a particular sleep disorder in which they physically act out their dreams while sleeping. The patients’ eye movements tracked their physical actions with a consistency of nearly 90%. The eye movements in these patients were no different than in normal subjects who did not move physically during sleep, leading the authors to suggest that the “follow-the-dream-action” explanation for REM activity may hold for normal subjects as well.
Minggu, 01 Agustus 2010
First Human Stem Cell Therapy Trial
The first clinical trial of a therapy based on human stem cells has received final approval from the Food and Drug Administration (FDA) and will get underway shortly, according to a press release from Geron Corporation, the company sponsoring the research. During the first phase of the trial, researchers will inject precursor cells to neural support cells called oligodendrocytes into the spinal cords of patients who have suffered recent spinal cord injuries and who have almost no chance of recovery of function otherwise. The hope is that the precursor cells will differentiate into mature oligodendrocytes (the cells that produce myelin) and that the myelin will form new sheaths around damaged nerves.
The trial was planned several years ago but held up by the FDA over concerns that the therapy could increase the risk of tumors forming in the spinal cord if the injected cells were not free of embryonic stem cells. The first phase of the trial is designed to test the safety of the procedure. It will be years before the technique becomes widely available for the repair of spinal cord injuries, even if it does eventually prove to be both safe and effective.
Stem cell researchers will be holding their breath. A failure in this first approved trial could set back the whole field of stem cell therapy research for years.
The trial was planned several years ago but held up by the FDA over concerns that the therapy could increase the risk of tumors forming in the spinal cord if the injected cells were not free of embryonic stem cells. The first phase of the trial is designed to test the safety of the procedure. It will be years before the technique becomes widely available for the repair of spinal cord injuries, even if it does eventually prove to be both safe and effective.
Stem cell researchers will be holding their breath. A failure in this first approved trial could set back the whole field of stem cell therapy research for years.
Selasa, 13 Juli 2010
Heritable, Non-Genetic Behavioral Patterns
Why do abused children grow up to be abusive parents? Why do people raised in lower socio-economic environments tend to have more long-term health problems? Why is it so hard for drug addicts to kick their habit?
For possible answers, behavioral neuroscientists are turning to a hot new field called behavioral epigenetics. Behavioral epigenetics is the study of inherited changes in behavior or gene expression that are caused by factors other than changes in DNA, i.e., that are epi- (Greek: over, above) genetics.
According to epigenetics theory, environmental factors such as the degree of nurturing (or lack of it) by one’s parents early in life can alter the chemical structure of DNA (specifically, the degree of methylation of DNA and its associated histones). This in turn affects how and when certain genes are turned on and off. In theory, such chemical alterations in DNA could last for multiple generations (i.e., be heritable) even though the nucleotide sequence of the genes themselves hasn’t changed.
So far, there’s very little evidence to suggest that epigenetic mechanisms influence human behavior, mostly because human brain tissue is not readily available for research. However, laboratory studies show that rats raised by less-nurturing mothers tend to be more prone to stress as adults and to exhibit increased methylation of certain genes. It’s worth keeping an eye on this developing field to see where it leads.
For possible answers, behavioral neuroscientists are turning to a hot new field called behavioral epigenetics. Behavioral epigenetics is the study of inherited changes in behavior or gene expression that are caused by factors other than changes in DNA, i.e., that are epi- (Greek: over, above) genetics.
According to epigenetics theory, environmental factors such as the degree of nurturing (or lack of it) by one’s parents early in life can alter the chemical structure of DNA (specifically, the degree of methylation of DNA and its associated histones). This in turn affects how and when certain genes are turned on and off. In theory, such chemical alterations in DNA could last for multiple generations (i.e., be heritable) even though the nucleotide sequence of the genes themselves hasn’t changed.
So far, there’s very little evidence to suggest that epigenetic mechanisms influence human behavior, mostly because human brain tissue is not readily available for research. However, laboratory studies show that rats raised by less-nurturing mothers tend to be more prone to stress as adults and to exhibit increased methylation of certain genes. It’s worth keeping an eye on this developing field to see where it leads.
Jumat, 02 Juli 2010
Studying Human Behavior
What drives human behavior? In a provocative paper published online in Behavioral and Brain Sciences last week, it is argued that much of what we believe we know about human behavior is skewed by the fact that most psychological studies are performed on WIERDs – subjects from Western, Educated, Industrialized, Rich, Democratic societies. Indeed, most human subjects used in psychological studies are from the United States, according to an article published several years ago in American Psychologist by Jeffrey Arnett. And most of the subjects are psychology undergraduate students – hardly representative of the world’s cultures as a whole.
How might this affect the results? Take for example, perception of self. Textbooks generally describe people has having a tendency to rate their own abilities as above average and to be motivated to maintain a positive image of themselves. But this may not necessarily be true for non-WEIRD cultures, who may place more emphasis on family relationships and less on personal choice or ability.
There’s nothing inherently wrong with studying WEIRDs, of course, as long as it is understood that the conclusions may not generalize to all cultures.
Reference: Henrich, Joseph et al. The Weirdest People in the World? Behavioral and Brain Sciences 33 pp. 61-83.
How might this affect the results? Take for example, perception of self. Textbooks generally describe people has having a tendency to rate their own abilities as above average and to be motivated to maintain a positive image of themselves. But this may not necessarily be true for non-WEIRD cultures, who may place more emphasis on family relationships and less on personal choice or ability.
There’s nothing inherently wrong with studying WEIRDs, of course, as long as it is understood that the conclusions may not generalize to all cultures.
Reference: Henrich, Joseph et al. The Weirdest People in the World? Behavioral and Brain Sciences 33 pp. 61-83.
Minggu, 21 Maret 2010
Potential Alzheimer's Drug Flames Out
A closely-watched drug that was supposed to offer hope to Alzheimer’s sufferers failed miserably in Phase III trials this month, according to a press release from Pfizer, one of the pharmaceutical companies involved in its development. In all likelihood all further research on the drug will stop.
It wasn’t supposed to end like this, although looking back it may not be as surprising as it sounds. The drug, called Dimebon, was actually an antihistamine previously sold only in Russia. The Phase I and Phase II trials (efficacy in animals and limited safety tests in humans) were performed in Russia, and then the drug was patented and brought to the United States for Phase III trials and future marketing as an Alzheimer’s treatment. Apparently it doesn’t work.
Although people sometimes complain (rightly) that the drug approval process in the United States is expensive and time-consuming, there’s a good reason for the process. It protects us all.
It wasn’t supposed to end like this, although looking back it may not be as surprising as it sounds. The drug, called Dimebon, was actually an antihistamine previously sold only in Russia. The Phase I and Phase II trials (efficacy in animals and limited safety tests in humans) were performed in Russia, and then the drug was patented and brought to the United States for Phase III trials and future marketing as an Alzheimer’s treatment. Apparently it doesn’t work.
Although people sometimes complain (rightly) that the drug approval process in the United States is expensive and time-consuming, there’s a good reason for the process. It protects us all.
Selasa, 05 Januari 2010
Combating Motion Sickness
What causes motion sickness? The main reason is that during certain kinds of involuntary motions the brain receives conflicting neural signals from visual receptors in the eyes, positional receptors in the inner ears and in muscles and tendons, and gravity receptors in the stomach. These conflicting signals confuse the brain, and nausea ensues.
Recently, researchers learned that the severity of motion sickness caused by a slow, cyclic motion can be reduced by deliberately breathing out of sync with the motion. Breathing either faster or slower than the cyclic motion allows the diaphragm to counteract the heaving movements of the stomach, thereby minimizing the neural disconnect between stomach gravity sensors and other motion and position receptors. The worst thing you can do is to take a breath with each heaving motion, although it’s the natural thing to do.
Reference: Denise, P. et al. Effect of temporal relationship between respiration and body motion on motion sickness. Autonomic Neuroscience 151:142-146, 2009.
Recently, researchers learned that the severity of motion sickness caused by a slow, cyclic motion can be reduced by deliberately breathing out of sync with the motion. Breathing either faster or slower than the cyclic motion allows the diaphragm to counteract the heaving movements of the stomach, thereby minimizing the neural disconnect between stomach gravity sensors and other motion and position receptors. The worst thing you can do is to take a breath with each heaving motion, although it’s the natural thing to do.
Reference: Denise, P. et al. Effect of temporal relationship between respiration and body motion on motion sickness. Autonomic Neuroscience 151:142-146, 2009.
Kamis, 10 Desember 2009
Prion-like Activity in Neurodegenerative Disorders
Could misfolded human proteins with prion-like activity contribute to the progression of certain chronic diseases such as Alzheimer’s, Parkinsons, and Huntington’s disease? A common feature of all three of these diseases is the presence of abnormal accumulations of certain misfolded proteins in or around nerve cells in the brain. Eventually these protein accumulations become so extensive that they choke off nerve cell function.
No one is saying that these diseases are infectious, like mad cow disease. But according to the latest thinking, once an endogenous protein "goes rogue" and misfolds, it might then cause nearby normal proteins to misfold as well. Once the process starts it could become self-propagating, from one region of the brain to the next.
No one is saying that these diseases are infectious, like mad cow disease. But according to the latest thinking, once an endogenous protein "goes rogue" and misfolds, it might then cause nearby normal proteins to misfold as well. Once the process starts it could become self-propagating, from one region of the brain to the next.
Minggu, 18 Januari 2009
Young Adults Turn to Sleeping Pills
Prescriptions for sleep medications increased nearly 50% in adults under the age of 45 between 1998 and 2006, according to a report in The New York Times. Among young adults aged 18-24, the use of heavily-advertised prescription sleep medications such as Ambien CR and Lunesta nearly tripled. These drugs truly are safer than older, benzodiazepine-based products, so there would seem to be little reason not to use them to get a good night's sleep.
However, in some cases these drugs may be prescribed too readily. Many of these prescriptions are written when the patient is being seen for something other than a sleep disorder, such as a general medical examination or a menstrual disorder. The worry is not the safety of the drugs per se, but that patients may not be receiving much-needed medical workups to eliminate potential underlying psychiatric disorders before prescriptions are written.
If all you want is a good night's sleep, what about adjusting your behavior or environment a little? You might just get a good night's rest if you were to move out of that noisy dorm and stop drinking 6 cups of coffee a day! Just a thought.
However, in some cases these drugs may be prescribed too readily. Many of these prescriptions are written when the patient is being seen for something other than a sleep disorder, such as a general medical examination or a menstrual disorder. The worry is not the safety of the drugs per se, but that patients may not be receiving much-needed medical workups to eliminate potential underlying psychiatric disorders before prescriptions are written.
If all you want is a good night's sleep, what about adjusting your behavior or environment a little? You might just get a good night's rest if you were to move out of that noisy dorm and stop drinking 6 cups of coffee a day! Just a thought.
Senin, 08 Desember 2008
Alzheimer's Disease Linked to a Virus
Alzheimer’s disease is a debilitating disorder of the elderly characterized by severe, progressive loss of memory, confusion, irritability, and withdrawal. The disease develops because amyloid plaques accumulate in the brain, interfering with neural transmission. But why do these plaques develop in some elderly persons but not others?
A recent paper in the Journal of Pathology (217:131-138, Jan. 2009) offers some tantalizing clues. It appears that two factors may be involved; 1) a genetic predisposition to Alzheimer’s disease, and 2) chronic infection of the brain with the same virus that causes cold sores; Herpes simplex type 1. The herpes virus is present in the brains of a high proportion of elderly persons. In the absence of the genetic predisposition to Alzheimer’s the virus doesn’t seem to do much. But in elderly patients with the genetic risk factor for Alzheimer’s, the virus is associated with amyloid plaque accumulation and may in fact be the cause of the plaque formation. If this turns out to be correct, Alzheimer’s disease may some day be preventable with a vaccine.
I am reminded of another chronic disease - peptic ulcers - that turned out to be caused by an infection, in this case by a bacterium called Helicobacter pylori (see Human Biology, 5th ed., p. 328).
A recent paper in the Journal of Pathology (217:131-138, Jan. 2009) offers some tantalizing clues. It appears that two factors may be involved; 1) a genetic predisposition to Alzheimer’s disease, and 2) chronic infection of the brain with the same virus that causes cold sores; Herpes simplex type 1. The herpes virus is present in the brains of a high proportion of elderly persons. In the absence of the genetic predisposition to Alzheimer’s the virus doesn’t seem to do much. But in elderly patients with the genetic risk factor for Alzheimer’s, the virus is associated with amyloid plaque accumulation and may in fact be the cause of the plaque formation. If this turns out to be correct, Alzheimer’s disease may some day be preventable with a vaccine.
I am reminded of another chronic disease - peptic ulcers - that turned out to be caused by an infection, in this case by a bacterium called Helicobacter pylori (see Human Biology, 5th ed., p. 328).
Rabu, 19 November 2008
Ginkgo Doesn't Prevent Dementia
According to a study in the Journal of the American Medical Association, daily doses of the popular herbal antioxidant Ginkgo biloba neither prevent nor delay the onset of dementia (cognitive impairment). The most common type of dementia is Alzheimer’s disease.
Herbal extracts of Ginkgo remain popular as a memory enhancer, even though previous scientific evidence showed that Ginkgo just doesn’t enhance memory. So don't expect this latest finding regarding dementia to put much of a dent in Ginkgo’s annual sales of over $200 million. Good marketing apparently trumps good science.
Herbal extracts of Ginkgo remain popular as a memory enhancer, even though previous scientific evidence showed that Ginkgo just doesn’t enhance memory. So don't expect this latest finding regarding dementia to put much of a dent in Ginkgo’s annual sales of over $200 million. Good marketing apparently trumps good science.
Minggu, 06 Juli 2008
Your Cell Phone's Radiation Emission
Does the radiation emitted by cell phones cause brain cancers? Although most of the scientific evidence suggests that it doesn’t, the media always seems to find a physician or a patient or even a scientist who is willing to talk about it. The debate has been going on since cell phones first came out, and it’s not likely to go away any time soon.
Are you concerned? How much radiation does your cell phone emit, anyway – a lot, or a little? The Federal Trade Commission sets an upper limit of 1.6 W/kg (watts per kilogram) for certification, but commercial phones on the market vary all the way from 1.6 down to 0.14 – more than a 10-fold difference.
For a complete listing of the radiation output of all current phone models, go to http://reviews.cnet.com, go to “Cell phone reviews”, then click on “Cell phone radiation charts.”
Are you concerned? How much radiation does your cell phone emit, anyway – a lot, or a little? The Federal Trade Commission sets an upper limit of 1.6 W/kg (watts per kilogram) for certification, but commercial phones on the market vary all the way from 1.6 down to 0.14 – more than a 10-fold difference.
For a complete listing of the radiation output of all current phone models, go to http://reviews.cnet.com, go to “Cell phone reviews”, then click on “Cell phone radiation charts.”
Jumat, 11 Januari 2008
Thimerosal and Autism
The results of a study by researchers at the Department of Public Health in California do not support the hypothesis that autism is caused by thimerosal, a preservative containing ethylmercury that was once used in childhood vaccines. The researchers found that the incidence of autism rose steadily in California from 1995 to 2007, even though thimerosal was removed from most childhood vaccines in 2001. If thimerosal were responsible for causing autism there should have been a sharp decline in new cases of autism after 2004. The new findings and a commentary about them are published in The Archives of General Psychiatry.
It is doubtful that the study will do much to reassure parents, however, some of whom continue to believe passionately that their child's autism was a direct consequence of childhood vaccinations despite research findings to the contrary.
Selasa, 17 Juli 2007
Antidepressants and Childhood/Adolescent Suicide
One of the most basic rules of medicine is expressed in the Latin phrase primum no nocere – first do no harm. So here’s an real-life ethical dilemma for you; if antidepressants such as Prozac have the potential to cause harm to some patients, is it still okay for a physician to prescribe them if, in the balance, the drugs help more patients than they harm? That, apparently, is the dilemma now faced by the Food and Drug Administration (FDA).
Several years ago a careful analysis of trials of antidepressants reported that Prozac and the other drugs in its class (known as selective serotonin reuptake inhibitors, or SSRIs) increase the risk of spontaneously reported suicide-related events in children and adolescents. Accordingly, in 2003 the FDA issued a health-advisory that children and adolescents on Prozac might be at “increased risk of suicidal thinking and behavior”, and ordered that a black box warning be placed on all prescriptions. (The label is called a “black-box” warning because of its black border).
Physicians and parents took the warning seriously. From 2003 to 2005 the number of prescriptions for SSRIs for childhood and adolescent depression fell by 50%. This should have been a good thing, right? Perhaps not. New data shows that after 10 years of decline, the suicide rate in children and adolescents increased 18% in 2004, the most recent year for which there are data (Annual Summary of Vital Statistics: 2005. Pediatrics 119:345-360, 2007).
The data support the hypothesis that the risk of not prescribing Prozac for child and adolescent depression may, in fact, be more harmful than prescribing it. But we need to be careful to not over-interpret the data, for correlation does not prove causation. Now at least we know what the question is. Careful attention to study protocols will be needed to sort this one out, because suicidal thinking and behavior are difficult to classify at best.
Several years ago a careful analysis of trials of antidepressants reported that Prozac and the other drugs in its class (known as selective serotonin reuptake inhibitors, or SSRIs) increase the risk of spontaneously reported suicide-related events in children and adolescents. Accordingly, in 2003 the FDA issued a health-advisory that children and adolescents on Prozac might be at “increased risk of suicidal thinking and behavior”, and ordered that a black box warning be placed on all prescriptions. (The label is called a “black-box” warning because of its black border).
Physicians and parents took the warning seriously. From 2003 to 2005 the number of prescriptions for SSRIs for childhood and adolescent depression fell by 50%. This should have been a good thing, right? Perhaps not. New data shows that after 10 years of decline, the suicide rate in children and adolescents increased 18% in 2004, the most recent year for which there are data (Annual Summary of Vital Statistics: 2005. Pediatrics 119:345-360, 2007).
The data support the hypothesis that the risk of not prescribing Prozac for child and adolescent depression may, in fact, be more harmful than prescribing it. But we need to be careful to not over-interpret the data, for correlation does not prove causation. Now at least we know what the question is. Careful attention to study protocols will be needed to sort this one out, because suicidal thinking and behavior are difficult to classify at best.
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