Chapter 4. The Chemistry of Behavior: Neurotransmitters and Neuropharmacology
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By RONI CARYN RABIN The Food and Drug Administration on Thursday approved a powerful long-acting opioid painkiller, alarming some addiction experts who fear that its widespread use may contribute to the rising tide of prescription drug overdoses. The new drug, Hysingla, and another drug approved earlier this year, Zohydro, contain pure hydrocodone, a narcotic, without the acetaminophen used in other opioids. But Hysingla is to be made available as an “abuse-deterrent” tablet that cannot easily be broken or crushed by addicts looking to snort or inject it. Nearly half of the nation’s overdose deaths involved painkillers like hydrocodone and oxycodone, according to a 2010 study by the Centers for Disease Control and Prevention. More than 12 million people used prescription painkillers for nonmedical reasons that year, according to the study. Prescription opioid abuse kills more adults annually than heroin and cocaine combined, and sends 420,000 Americans to emergency rooms every year, according to the C.D.C. Hysingla, however, will not be not abuse-proof, said officials at the F.D.A. and the drug’s manufacturer, Purdue Pharma. Its extended-release formulation, a pill to be taken once every 24 hours by patients requiring round-the-clock pain relief, will contain as much as 120 milligrams of hydrocodone. The F.D.A. warned that doses of 80 milligrams or more “should not be prescribed to people who have not previously taken an opioid medication,” but officials described the abuse-deterrent formulation as a step forward. © 2014 The New York Times Company
Sara Reardon A technique that makes mouse brains transparent shows how the entire brain responds to cocaine addiction and fear. The findings could uncover new brain circuits involved in drug response. In the technique, known as CLARITY, brains are infused with acrylamide, which forms a matrix in the cells and preserves their structure along with the DNA and proteins inside them. The organs are then treated with a detergent that dissolves opaque lipids, leaving the cells completely clear. To test whether CLARITY could be used to show how brains react to stimuli, neuroscientists Li Ye and Karl Deisseroth of Stanford University in California engineered mice so that their neurons would make a fluorescent protein when they fired. (The system is activated by the injection of a drug.) The researchers then trained four of these mice to expect a painful foot shock when placed in a particular box; another set of mice placed in the box received cocaine, rather than shocks. Once the mice had learned to associate the box with either pain or an addictive reward, the researchers tested how the animals' brains responded to the stimuli. They injected the mice with the drug that activated the fluorescent protein system, placed them in the box and waited for one hour to give their neurons time to fire. The next step was to remove the animals' brains, treat them with CLARITY, and image them using a system that could count each fluorescent cell across the entire brain (see video). A computer combined these images into a model of a three-dimensional brain, which showed the pathways that lit up when mice were afraid or were anticipating cocaine. © 2014 Nature Publishing Group
By Nicholas Bakalar Exposure to secondhand smoke and roadway traffic may be tied to increased body mass index in children and adolescents, a new study suggests. Researchers studied 3,318 children in 12 Southern California communities beginning at an average age of 10, and then followed them through age 18. They used parental questionnaires to establish exposure to smoking, and data on traffic volume and levels of nitrogen dioxide, ozone and particulates to track pollution. The study, in Environmental Health Perspectives, controlled for many other factors: sex, initial B.M.I., asthma, physical activity, insurance status, parental education and income, acres of parks and open space nearby, percentage of people living in poverty in each community. But even after accounting for these issues and more, they found that compared with children exposed to no secondhand smoke or near-roadway air pollution, B.M.I. was 0.80 higher in children exposed to pollution alone, 0.85 higher in those exposed to secondhand smoke alone, and 2.15 higher in those exposed to both. A normal B.M.I. for adults is 18.5 to 24.9. Higher than 25 is considered overweight, and above 30 obese. “It would be interesting to know more about the mechanism,” said the lead author, Dr. Rob McConnell, a professor of preventive medicine at the University of Southern California. “But the finding challenges the view that obesity is due solely to increased caloric intake and reduced physical activity. That’s not the whole story.” © 2014 The New York Times Company
By Tom Shroder After more than 30 years in which psychedelics were considered dangerous remnants of the 1960s, the drugs have begun to make a comeback, this time as potential remedies for a host of tough-to-treat maladies. Pilot studies and clinical trials of LSD, psilocybin, ketamine and MDMA have shown that the drugs, often in combination with talk therapy, can be given safely under medical supervision and may help people dealing with opiate and tobacco addiction, alcoholism, anxiety, depression and post-traumatic stress disorder, or PTSD. That these investigations have shown potential is not surprising to many researchers. A generation of scientists and practitioners had used psychedelics successfully with thousands of patients until the research was banned in 1970, after the drugs were embraced by an exploding counterculture that seemed to threaten the status quo. In the panicked reaction, psychedelics were listed along with heroin in the highest rungs of prohibition. Ironically, this failed to stop recreational use but it shut the science down cold. As one researcher put it, “It was as if psychedelic drugs had become undiscovered.” But a small cadre of psychiatrists and researchers, often risking careers and reputations, pushed to bring psychedelics back to the lab and the clinic. Their persistence paid off. Beginning in the 1990s, the Food and Drug Administration approved the first human clinical studies of psychedelic drugs in a quarter of a century. By 2004, the first FDA-approved trial of the medicinal use of a psychedelic drug, in this case a trial of MDMA-assisted therapy for PTSD involving 24 subjects, was underway. Now such studies are proliferating.
|By Bret Stetka The brain is protected by formidable defenses. In addition to the skull, the cells that make up the blood-brain barrier keep pathogens and toxic substances from reaching the central nervous system. The protection is a boon, except when we need to deliver drugs to treat illnesses. Now researchers are testing a way to penetrate these bastions: sound waves. Kullervo Hynynen, a medical physicist at Sunnybrook Research Institute in Toronto, and a team of physicians are trying out a technique that involves giving patients a drug followed by an injection of microscopic gas-filled bubbles. Next patients don a cap that directs sound waves to specific brain locations, an approach called high-intensity focused ultrasound. The waves cause the bubbles to vibrate, temporarily forcing apart the cells of the blood-brain barrier and allowing the medication to infiltrate the brain. Hynynen and his colleagues are currently testing whether they can use the method to deliver chemotherapy to patients with brain tumors. They and other groups are planning similar trials for patients with other brain disorders, including Alzheimer's disease. Physicians are also considering high-intensity focused ultrasound as an alternative to brain surgery. Patients with movement disorders such as Parkinson's disease and dystonia are increasingly being treated with implanted electrodes, which can interrupt problematic brain activity. A team at the University of Virginia hopes to use focused ultrasound to deliver thermal lesions deep into the brain without having patients go under the knife. © 2014 Scientific American
Details of the role of glutamate, the brain’s excitatory chemical, in a drug reward pathway have been identified for the first time. This discovery in rodents — published today in Nature Communications — shows that stimulation of glutamate neurons in a specific brain region (the dorsal raphe nucleus) leads to activation of dopamine-containing neurons in the brain’s reward circuit (dopamine reward system). Dopamine is a neurotransmitter present in regions of the brain that regulate movement, emotion, motivation, and feelings of pleasure. Glutamate is a neurotransmitter whose receptors are important for neural communication, memory formation, and learning. The research was conducted at the Intramural Research Program (IRP) of the National Institute on Drug Abuse (NIDA), which is part of the National Institutes of Health. The research focused on the dorsal raphe nucleus, which has long been a brain region of interest to drug abuse researchers, since nerve cells in this area connect to part of the dopamine reward system. Many of the pathways are rich in serotonin, a neurotransmitter linked to mood regulation. Even though electrical stimulation of the dorsal raphe nucleus promotes reward-related behaviors, drugs that increase serotonin have low abuse potential. As a result, this region of the brain has always presented a seeming contradiction, since it is involved in drug reward but is also abundant in serotonin - a chemical not known for a role in drug reinforcement. This has led researchers to theorize that another neurotransmitter may be responsible for the role that the dorsal raphe nucleus plays in reward.
Keyword: Drug Abuse
Link ID: 20308 - Posted: 11.13.2014
By Kate Kelland LONDON (Reuters) - British scientists say they have found the best way yet to analyze the effects of smoking on the brain -- by taking functional magnetic resonance imaging (fMRI) scans of people while they puff on e-cigarettes. In a small pilot study, the researchers used electronic cigarettes, or e-cigarettes, to mimic the behavioral aspects of smoking tobacco cigarettes, and say future studies could help scientists understand why smoking is so addictive. E-cigarettes use battery-powered cartridges to produce a nicotine-laced vapor to inhale -- hence the new term "vaping". Their use has rocketed in recent years, but there is fierce debate about the risks and benefits. Some public health experts say they could help millions quit tobacco cigarettes, while others argue they could "normalize" the habit and lure children into smoking. While that argument rages, tobacco kills some 6 million people a year, and the World Health Organization estimates that could rise beyond 8 million by 2030. Matt Wall, an imaging scientist at Imperial College London who led the study using e-cigarettes, said he was not aiming to pass judgment on their rights or wrongs, but to use them to dig deeper into smoking addiction. The fact that other forms of nicotine replacement therapy, such as patches or gum, have had only limited success in getting hardened smokers to quit suggests they are hooked on more than just nicotine, he noted. © 2014 Scientific American
By Jia You Like humans, flies are attracted to alcohol. Fruit flies (Drosophila melanogaster, above) prefer to lay their eggs on rotten food that can contain ethanol in as high as 7% concentration. (That’s 14 proof to you bar hoppers.) And just like people, the insects differ in their ability to hold their drinks. Biologists know that compared with flies from tropical Africa, flies from temperate regions such as Europe survive longer when exposed to ethanol vapors of high concentrations, and they know it has something to do with enzymes on the flies’ second chromosomes, which break down alcohol and are more active in European flies. But now, biologist James Fry of the University of Rochester in New York has pinpointed a missing piece of the story: the role played by the flies’ third chromosomes. After studying flies collected from Vienna and Cameroon, Fry found that the Vienna flies break down alcohol much faster than Cameroon ones, as expected. But when he replaced the third chromosomes in Cameroon flies with those from Vienna, the African flies gained much more resistance, Fry reports online today in The Journal of Experimental Biology. In a specialized population of flies that could not detoxify alcohol, however, the genetic engineering made no difference whatsoever. Fry suggests that’s because the third chromosomes in European flies help them tolerate acetic acid, a byproduct of internal alcohol breakdown that also gives vinegar its sour taste. There’s no telling what the acetic acid does to the flies, but previous studies on mice have found that it may be responsible for hangover headaches, Fry says. © 2014 American Association for the Advancement of Science
By Julia Calderone Antidepressant use among Americans is skyrocketing. Adults in the U.S. consumed four times more antidepressants in the late 2000s than they did in the early 1990s. As the third most frequently taken medication in the U.S., researchers estimate that 8 to 10 percent of the population is taking an antidepressant. But this spike does not necessarily signify a depression epidemic. Through the early 2000s pharmaceutical companies were aggressively testing selective serotonin reuptake inhibitors (SSRIs), the dominant class of depression drug, for a variety of disorders—the timeline below shows the rapid expansion of FDA-approved uses. As the drugs' patents expired, companies stopped funding studies for official approval. Yet doctors have continued to prescribe them for more ailments. One motivating factor is that SSRIs are a fairly safe option for altering brain chemistry. Because we know so little about mental illness, many clinicians reason, we might as well try the pills already on the shelf. Doctors commonly use antidepressants to treat many maladies they are not approved for. In fact, studies show that between 25 and 60 percent of prescribed antidepressants are actually used to treat nonpsychological conditions. The most common and well-supported off-label uses of SSRIs include: Abuse and dependence ADHD (in children and adolescents) Anxiety disorders Autism (in children) Bipolar disorder Eating disorders Fibromyalgia Neuropathic pain Obsessive-compulsive disorder Premenstrual dysphoric disorder © 2014 Scientific American
Link ID: 20300 - Posted: 11.11.2014
By Abby Phillip If you're confused about what marijuana use really does to people who use it, you're not alone. For years, the scientific research on health effects of the drug have been all over the map. Earlier this year, one study suggested that even casual marijuana use could cause changes to the brain. Another found that marijuana use was also associated with poor sperm quality, which could lead to infertility in men. But marijuana advocates point to other research indicating that the drug is far less addictive than other drugs, and some studies have found no relationship between IQ and marijuana use in teens. Researchers at the Center for Brain Health at the University of Texas in Dallas sought to clear up some of the confusion with a study that looked at a relatively large group of marijuana users and evaluated their brains for a slew of different indicators. What they found was complex, but the pattern was clear: The brains of marijuana users were different than those of non-marijuana users. The area of the brain responsible for establishing the reward system that helps us survive and also keeps us motivated was smaller in users than in non-marijuana users. But there was also evidence that the brain compensated for this loss of volume by increasing connectivity and the structural integrity of the brain tissue. Those effects were more pronounced for marijuana users who started young. "The orbitofrontal cortex is one of the primary regions in a network of brain areas called the reward system," explained Francesca Filbey, lead author of the study and an associate professor of the neurogenetics of addictive behavior at the University of Texas in Dallas. "
How Magic Mushrooms Rearrange Your Brain By Brandon Keim A new way of looking at brain activity may give insight into how psychedelic drugs produce their consciousness-altering effects. In recent years, a focus on brain structures and regions has given way to an emphasis on neurological networks: how cells and regions interact, with consciousness shaped not by any given set of brain regions, but by their interplay. Understanding the networks, however, is no easy task, and researchers are developing ever more sophisticated ways of characterizing them. One such approach, described in a new Proceedings of the Royal Society Interface study, involves not simply networks but networks of networks. Perhaps some aspects of consciousness arise from these meta-networks—and to investigate the proposition, the researchers analyzed fMRI scans of 15 people after being injected with psilocybin, the active ingredient in magic mushrooms, and compared them to scans of their brain activity after receiving a placebo. Investigating psychedelia wasn’t the direct purpose of the experiment, said study co-author Giovanni Petri, a mathematician at Italy’s Institute for Scientific Interchange. Rather, psilocybin makes for an ideal test system: It’s a sure-fire way of altering consciousness. “In a normal brain, many things are happening. You don’t know what is going on, or what is responsible for that,” said Petri. “So you try to perturb the state of consciousness a bit, and see what happens.” A representation of that is seen in the image above. Each circle depicts relationships between networks—the dots and colors correspond not to brain regions, but to especially connection-rich networks—with normal-state brains at left, and psilocybin-influenced brains at right. © 2014 Condé Nast.
By Elizabeth Pennisi It’s not such a stretch to think that humans can catch the Ebola virus from monkeys and the flu virus from pigs. After all, they are all mammals with fundamentally similar physiologies. But now researchers have discovered that even a virus found in the lowly algae can make mammals its home. The invader doesn’t make people or mice sick, but it does seem to slow specific brain activities. The virus, called ATCV-1, showed up in human brain tissue several years ago, but at the time researchers could not be sure whether it had entered the tissue before or after the people died. Then, it showed up again in a survey of microbes and viruses in the throats of people with psychiatric disease. Pediatric infectious disease expert Robert Yolken from Johns Hopkins University School of Medicine in Baltimore, Maryland, and his colleagues were trying to see if pathogens play a role in these conditions. At first, they didn't know what ATCV-1 was, but a database search revealed its identity as a virus that typically infects a species of green algae found in lakes and rivers. The researchers wanted to find out if the virus was in healthy people as well as sick people. They checked for it in 92 healthy people participating in a study of cognitive function and found it in 43% of them. What’s more, those infected with the virus performed 10% worse than uninfected people on tests requiring visual processing. They were slower in drawing a line connecting a sequence of numbers randomly placed on a page, for example. And they seemed to have shorter attention spans, the researchers report online today in the Proceedings of the National Academy of Sciences. The effects were modest, but significant. © 2014 American Association for the Advancement of Science
Link ID: 20258 - Posted: 10.29.2014
By ABIGAIL SULLIVAN MOORE The gray matter of the nucleus accumbens, the walnut-shaped pleasure center of the brain, was glowing like a flame, showing a notable increase in density. “It could mean that there’s some sort of drug learning taking place,” speculated Jodi Gilman, at her computer screen at the Massachusetts General Hospital-Harvard Center for Addiction Medicine. Was the brain adapting to marijuana exposure, rewiring the reward system to demand the drug? Dr. Gilman was reviewing a composite scan of the brains of 20 pot smokers, ages 18 to 25. What she and fellow researchers at Harvard and Northwestern University found within those scans surprised them. Even in the seven participants who smoked only once or twice a week, there was evidence of structural differences in two significant regions of the brain. The more the subjects smoked, the greater the differences. Moderate marijuana use by healthy adults seems to pose little risk, and there are potential medical benefits, including easing nausea and pain. But it has long been known that, with the brain developing into the mid-20s, young people who smoke early and often are more likely to have learning and mental health problems. Now researchers suggest existing studies are no longer sufficient. Much of what’s known is based on studies conducted years ago with much less powerful pot. Marijuana samples seized by the federal Drug Enforcement Agency show the concentration of THC, the drug’s psychoactive compound, rising from a mean of 3.75 percent in 1995 to 13 percent in 2013. Potency seesaws depending on the strain and form. Fresh Baked, which sells recreational marijuana in Boulder, Colo., offers “Green Crack,” with a THC content of about 21 percent, and “Phnom Pen,” with about 8 percent. The level in a concentrate called “Bubble Hash” is about 70 percent; cartridges for vaporizers, much like e-cigarettes, range from 15 to 30 percent THC. © 2014 The New York Times Company
Sarah Boseley, health editor A record haul of “smart” drugs, sold to students to enhance their memory and thought processes, stay awake and improve concentration, has been seized from a UK website by the medicines regulator, which is alarmed about the recent rise of such sites. The seizure, worth £200,000, illustrates the increasing internet trade in cognitive enhancement drugs and suggests people who want to stay focused and sharp are moving on from black coffee and legally available caffeine tablets. Most of the seized drugs are medicines that should only be available on a doctor’s prescription. One, Sunifiram, is entirely experimental and has never been tested on humans in clinical trials. Investigators from the Medicines and Healthcare Products Regulatory Authority (MHRA) are worried at what they see as a new phenomenon – the polished, plausible, commercial website targeting students and others who are looking for a mental edge over the competition. In addition to Ritalin, the drug that helps young people with attention deficit disorder (ADD) focus in class and while writing essays, and Modafinil (sold as Provigil), licensed in the US for people with narcolepsy, they are also offering experimental drugs and research chemicals. MHRA head of enforcement, Alastair Jeffrey, said the increase in people buying cognitive-enhancing drugs or “nootropics” is recent and very worrying. “The idea that people are willing to put their overall health at risk in order to attempt to get an intellectual edge over others is deeply troubling,” he said. © 2014 Guardian News and Media Limited
A drug being studied as a fast-acting mood-lifter restored pleasure-seeking behavior independent of — and ahead of — its other antidepressant effects, in a National Institutes of Health trial. Within 40 minutes after a single infusion of ketamine, treatment-resistant depressed bipolar disorder patients experienced a reversal of a key symptom — loss of interest in pleasurable activities — which lasted up to 14 days. Brain scans traced the agent’s action to boosted activity in areas at the front and deep in the right hemisphere of the brain. “Our findings help to deconstruct what has traditionally been lumped together as depression,” explained Carlos Zarate, M.D., of the NIH’s National Institute of Mental Health. “We break out a component that responds uniquely to a treatment that works through different brain systems than conventional antidepressants — and link that response to different circuitry than other depression symptoms.” This approach is consistent with the NIMH’s Research Domain Criteria project, which calls for the study of functions – such as the ability to seek out and experience rewards – and their related brain systems that may identify subgroups of patients in one or multiple disorder categories. Zarate and colleagues reported on their findings Oct. 14, 2014 in the journal Translational Psychiatry. Although it’s considered one of two cardinal symptoms of both depression and bipolar disorder, effective treatments have been lacking for loss of the ability to look forward to pleasurable activities, or anhedonia. Long used as an anesthetic and sometimes club drug, ketamine and its mechanism-of-action have lately been the focus of research into a potential new class of rapid-acting antidepressants that can lift mood within hours instead of weeks.
Posted by Rachel Dolhun, MD, The ability to quit smoking, especially “cold turkey” or on the first attempt, has been heralded as a marker of strong willpower and determination. But could the ease with which one eschews cigarettes also serve as an early sign of Parkinson’s disease (PD)? This is the conclusion drawn by Beate Ritz, MD, PhD, and colleagues from the University of California, Los Angeles in a recent study published in Neurology. Researchers compared lifelong tobacco use, use of nicotine substitutes, and individual’s rating of their difficulty in trying to quit tobacco among 1,808 Danish people with PD and 1,876 control volunteers. They found that those with PD were less inclined to ever pick up the smoking habit, but, even if they did, they were less likely to need nicotine replacement therapies and able to more effortlessly stop smoking cigarettes. Therefore, ease of quitting smoking may be a sign of early PD. This joins a short list of other symptoms — smell loss, constipation and REM sleep behavior disorder — that usually predate diagnosis and are strongly associated with PD. Physicians rely heavily on such information to help confirm the diagnosis of Parkinson’s, given that biomarkers, objective measurements of disease, are currently lacking. Research led by The Michael J. Fox Foundation is ongoing to identify biological markers of PD, which could help diagnose and treat people earlier. In the meantime, doctors must look for symptoms and behaviors to help identify Parkinson’s. Researchers have long known that tobacco use was linked to a lower risk of PD. An ongoing Foundation-funded study is investigating whether nicotine might guard against or slow the progression of PD.
|By Brian Bienkowski and Environmental Health News Babies born to mothers with high levels of perchlorate during their first trimester are more likely to have lower IQs later in life, according to a new study. The research is the first to link pregnant women's perchlorate levels to their babies’ brain development. It adds to evidence that the drinking water contaminant may disrupt thyroid hormones that are crucial for proper brain development. Perchlorate, which is both naturally occurring and manmade, is used in rocket fuel, fireworks and fertilizers. It has been found in 4 percent of U.S. public water systems serving an estimated 5 to 17 million people, largely near military bases and defense contractors in the U.S. West, particularly around Las Vegas and in Southern California. “We would not recommend action on perchlorate levels from this study alone, although our report highlights a pressing need for larger studies of perchlorate levels from the general pregnant population and those with undetected hypothyroidism,” the authors from the United Kingdom, Italy and Boston wrote in the study published in The Journal of Clinical Endocrinology & Metabolism. The Environmental Protection Agency for decades has debated setting a national drinking water standard for perchlorate. The agency in 2011 announced it would start developing a standard, reversing an earlier decision. In the meantime, two states, California and Massachusetts, have set their own standards. © 2014 Scientific American
By Jennifer Cutraro and Michael Gonchar Marijuana is illegal in the United States. Yet 35 states and the District of Columbia permit some form of marijuana consumption for medical purposes, and, as of this year, two states now allow its recreational use. As national policy evolves on this issue, the New York Times editorial board this summer published a six-part series calling for legalization. In this lesson, we pull together those opinion pieces as well as many other Times articles, graphics and videos to offer starting points for science, social studies and English teachers aiming to use the debate as an opportunity for learning, research and discussion. Like other crops, marijuana is largely cultivated — legally and illegally — in greenhouse-type “grow houses” and on farms. And like other crops, marijuana comes from a plant — cannabis, originally found in the wild and cultivated over thousands of years. Have students research the history of cannabis, from its origins in South and Central Asia to its introduction to the Americas. How have people used the different parts of the plant throughout history? Then, have students work in groups to annotate a map of the world, tracing the history of marijuana cultivation. Marijuana is best known for its psychoactive properties. But how does marijuana bring about these sensations and how else does it behave in the body? To answer these questions, students might research how the active compounds in marijuana affect the body at the level of the cell, and draw parallels with how other drugs act in the body. As is the case with many other drugs — from legal, over-the-counter medications to illegal street drugs, like heroin — the active compounds interact with locations on the surfaces of cells called receptors. Cell surface receptors provide a means for cells to receive information and input from the environment; when a molecule attaches, or binds, to a cell surface receptor, it triggers a series of events inside the cell, like the release of hormones, neurotransmitters or other molecules. A discussion about marijuana’s effects on the body might dovetail nicely with a broader class discussion or review of cell biology, the makeup and function of the cell membrane, and the function of neurotransmitters. © 2014 The New York Times Company
Keyword: Drug Abuse
Link ID: 20118 - Posted: 09.27.2014
|By Simon Makin The Claim Casual cannabis use harms young people's brains. The Facts A study found differences in the brains of users and nonusers, but it did not establish that marijuana use caused the variations or that they had any functional significance. The Details Researchers at Northwestern University and Harvard Medical School conducted MRI scans of two groups of 20 young adults ages 18 to 25. One group reported using marijuana at least once a week, smoking 11 joints a week on average, whereas the other had used it less than five times total and not at all during the last year. Neither group had any psychiatric disorders, and the users were psychiatrically assessed as not dependent on the drug. The study focused on two brain regions involved in processing rewards, the nucleus accumbens and the amygdala. These areas create pleasurable experiences of things such as food and sex, as well as the high associated with drugs, and have been shown to change in animals given THC, the main psychoactive component of cannabis. The researchers found that cannabis users had more gray matter density in the left nucleus accumbens and left amygdala, as well as differences in the shape of the left nucleus accumbens and right amygdala. The left nucleus accumbens also tended to be slightly larger in users. They concluded that recreational cannabis use might be associated with abnormalities in the brain's reward system. News reports have proclaimed that scientists have shown that even casual cannabis use harms young people's brains. The Caveats The most obvious problem with leaping to that conclusion is that the scans were conducted at only one point. © 2014 Scientific American
|By Victoria Stern Many studies show that teens who use marijuana face a greater risk of later developing schizophrenia or symptoms of it, especially if they have a genetic predisposition. For instance, one 15-year study followed more than 45,000 Swedes who initially had no psychotic symptoms. The researchers determined that subjects who smoked marijuana by age 18 were 2.4 times more likely to be diagnosed with schizophrenia than their nonsmoking peers, and this risk increased with the frequency of cannabis use. The connection still held when researchers accounted for participants' use of other drugs. Yet despite these results and an uptick in marijuana use in the 1970s and 1980s, other researchers have not uncovered an increase in the incidence of schizophrenia in the general Swedish population—suggesting that perhaps people who were going to develop schizophrenia anyway were more likely to use marijuana. Another study, conducted in Australia over a 30-year period, also found no increase in schizophrenia diagnoses among the general population, despite rising rates of teen marijuana use. These authors concluded that although cannabis most likely does not cause schizophrenia, its use might trigger psychosis in vulnerable people or exacerbate an existing condition. © 2014 Scientific American