Discovery sheds new light on marijuana’s anxiety relief effects

An international group led by Vanderbilt University researchers has found cannabinoid receptors, through which marijuana exerts its effects, in a key emotional hub in the brain involved in regulating anxiety and the flight-or-fight response.

This is the first time cannabinoid receptors have been identified in the central nucleus of the amygdala in a mouse model, they report in the current issue of the journal Neuron.

The discovery may help explain why marijuana users say they take the drug mainly to reduce anxiety, said Sachin Patel, M.D., Ph.D., the paper’s senior author and professor of Psychiatry and of Molecular Physiology and Biophysics.

Led by first author Teniel Ramikie, a graduate student in Patel’s lab, the researchers also showed for the first time how nerve cells in this part of the brain make and release their own natural “endocannabinoids.”

The study “could be highly important for understanding how cannabis exerts its behavioral effects,” Patel said. As the legalization of marijuana spreads across the country, more people — and especially young people whose brains are still developing — are being exposed to the drug.
Previous studies at Vanderbilt and elsewhere, Patel said, have suggested the following:

• The natural endocannabinoid system regulates anxiety and the response to stress by dampening excitatory signals that involve the neurotransmitter glutamate.

• Chronic stress or acute, severe emotional trauma can cause a reduction in both the production of endocannabinoids and the responsiveness of the receptors. Without their “buffering” effect, anxiety goes up.

• While marijuana’s “exogenous” cannabinoids also can reduce anxiety, chronic use of the drug down-regulates the receptors, paradoxically increasing anxiety. This can trigger “a vicious cycle” of increasing marijuana use that in some cases leads to addiction.

In the current study, the researchers used high-affinity antibodies to “label” the cannabinoid receptors so they could be seen using various microscopy techniques, including electron microscopy, which allowed very detailed visualization at individual synapses, or gaps between nerve cells.

“We know where the receptors are, we know their function, we know how these neurons make their own cannabinoids,” Patel said. “Now can we see how that system is affected by … stress and chronic (marijuana) use? It might fundamentally change our understanding of cellular communication in the amygdala.”

(Image: Shutterstock)

Worry on the Brain

According to the National Institute of Mental Health, over 18 percent of American adults suffer from anxiety disorders, characterized as excessive worry or tension that often leads to other physical symptoms. Previous studies of anxiety in the brain have focused on the amygdala, an area known to play a role in fear. But a team of researchers led by biologists at the California Institute of Technology (Caltech) had a hunch that understanding a different brain area, the lateral septum (LS), could provide more clues into how the brain processes anxiety. Their instincts paid off—using mouse models, the team has found a neural circuit that connects the LS with other brain structures in a manner that directly influences anxiety.

"Our study has identified a new neural circuit that plays a causal role in promoting anxiety states," says David Anderson, the Seymour Benzer Professor of Biology at Caltech, and corresponding author of the study. "Part of the reason we lack more effective and specific drugs for anxiety is that we don’t know enough about how the brain processes anxiety. This study opens up a new line of investigation into the brain circuitry that controls anxiety."

The team’s findings are described in the January 30 version of the journal Cell.

Led by Todd Anthony, a senior research fellow at Caltech, the researchers decided to investigate the so-called septohippocampal axis because previous studies had implicated this circuit in anxiety, and had also shown that neurons in a structure located within this axis—the LS—lit up, or were activated, when anxious behavior was induced by stress in mouse models. But does the fact that the LS is active in response to stressors mean that this structure promotes anxiety, or does it mean that this structure acts to limit anxiety responses following stress? The prevailing view in the field was that the nerve pathways that connect the LS with different brain regions function as a brake on anxiety, to dampen a response to stressors. But the team’s experiments showed that the exact opposite was true in their system.

In the new study, the team used optogenetics—a technique that uses light to control neural activity—to artificially activate a set of specific, genetically identified neurons in the LS of mice. During this activation, the mice became more anxious. Moreover, the researchers found that even a brief, transient activation of those neurons could produce a state of anxiety lasting for at least half an hour. This indicates that not only are these cells involved in the initial activation of an anxious state, but also that an anxious state persists even after the neurons are no longer being activated.

"The counterintuitive feature of these neurons is that even though activating them causes more anxiety, the neurons are actually inhibitory neurons, meaning that we would expect them to shut off other neurons in the brain," says Anderson, who is also an investigator with the Howard Hughes Medical Institute (HHMI).

So, if these neurons are shutting off other neurons in the brain, then how can they increase anxiety? The team hypothesized that the process might involve a double-inhibitory mechanism: two negatives make a positive. When they took a closer look at exactly where the LS neurons were making connections in the brain, they saw that they were inhibiting other neurons in a nearby area called the hypothalamus. Importantly, most of those hypothalamic neurons were, themselves, inhibitory neurons. Moreover, those hypothalamic inhibitory neurons, in turn, connected with a third brain structure called the paraventricular nucleus, or PVN. The PVN is well known to control the release of hormones like cortisol in response to stress and has been implicated in anxiety.

This anatomical circuit seemed to provide a potential double-inhibitory pathway through which activation of the inhibitory LS neurons could lead to an increase in stress and anxiety. The team reasoned that if this hypothesis were true, then artificial activation of LS neurons would be expected to cause an increase in stress hormone levels, as if the animal were stressed. Indeed, optogenetic activation of the LS neurons increased the level of circulating stress hormones, consistent with the idea that the PVN was being activated. Moreover, inhibition of LS projections to the hypothalamus actually reduced the rise in cortisol when the animals were exposed to stress. Together these results strongly supported the double-negative hypothesis.

"The most surprising part of these findings is that the outputs from the LS, which were believed primarily to act as a brake on anxiety, actually increase anxiety," says Anderson.

Knowing the sign—positive or negative—of the effect of these cells on anxiety, he says, is a critical first step to understanding what kind of drug one might want to develop to manipulate these cells or their molecular constituents. If the cells had been found to inhibit anxiety, as originally thought, then one would want to find drugs that activate these LS neurons, to reduce anxiety. However, since the group found that these neurons instead promote anxiety, then to reduce anxiety a drug would have to inhibit these neurons.

"We are still probably a decade away from translating this very basic research into any kind of therapy for humans, but we hope that the information that this type of study yields about the brain will put the field and medicine in a much better position to develop new, rational therapies for psychiatric disorders," says Anderson. "There have been very few new psychiatric drugs developed in the last 40 to 50 years, and that’s because we know so little about the brain circuitry that controls the emotions that go wrong in a psychiatric disorder like depression or anxiety."

The team will continue to map out this area of the brain in greater detail to understand more about its role in controlling stress-induced anxiety.

"There is no shortage of new questions that have been raised by these findings," Anderson says. "It may seem like all that we’ve done here is dissect a tiny little piece of brain circuitry, but it’s a foothold onto a very big mountain. You have to start climbing someplace."

Study reveals how ecstasy acts on the brain and hints at therapeutic uses

Brain imaging experiments have revealed for the first time how ecstasy produces feelings of euphoria in users.

Results of the study at Imperial College London, parts of which were televised in Drugs Live on Channel 4 in 2012, have now been published in the journal Biological Psychiatry.

The findings hint at ways that ecstasy, or MDMA, might be useful in the treatment of anxiety and post-traumatic stress disorder (PTSD).

MDMA has been a popular recreational drug since the 1980s, but there has been little research on which areas of the brain it affects. The new study is the first to use functional magnetic resonance imaging (fMRI) on resting subjects under its influence.

Twenty-five volunteers underwent brain scans on two occasions, one after taking the drug and one after taking a placebo, without knowing which they had been given.

The results show that MDMA decreases activity in the limbic system – a set of structures involved in emotional responses. These effects were stronger in subjects who reported stronger subjective experiences, suggesting that they are related.

Communication between the medial temporal lobe and medial prefrontal cortex, which is involved in emotional control, was reduced. This effect, and the drop in activity in the limbic system, are opposite to patterns seen in patients who suffer from anxiety.

MDMA also increased communication between the amygdala and the hippocampus. Studies on patients with PTSD have found a reduction in communication between these areas.

The project was led by David Nutt, the Edmond J. Safra Professor of Neuropsychopharmacology at Imperial College London, and Professor Val Curran at UCL.

Dr Robin Carhart-Harris from the Department of Medicine at Imperial, who performed the research, said: “We found that MDMA caused reduced blood flow in regions of the brain linked to emotion and memory. These effects may be related to the feelings of euphoria that people experience on the drug.”

Professor Nutt added: “The findings suggest possible clinical uses of MDMA in treating anxiety and PTSD, but we need to be careful about drawing too many conclusions from a study in healthy volunteers. We would have to do studies in patients to see if we find the same effects.”

MDMA has been investigated as an adjunct to psychotherapy in the treatment of PTSD, with a recent pilot study in the US reporting positive preliminary results.

As part of the Imperial study, the volunteers were asked to recall their favourite and worst memories while inside the scanner. They rated their favourite memories as more vivid, emotionally intense and positive after MDMA than placebo, and they rated their worst memories less negatively. This was reflected in the way that parts of the brain were activated more or less strongly under MDMA. These results were published in the International Journal of Neuropsychopharmacology.

Dr Carhart-Harris said: “In healthy volunteers, MDMA seems to lessen the impact of painful memories. This fits with the idea that it could help patients with PTSD revisit their traumatic experiences in psychotherapy without being overwhelmed by negative emotions, but we need to do studies in PTSD patients to see if the drug affects them in the same way.”

Erasing traumatic memories

Nearly 8 million Americans suffer from posttraumatic stress disorder (PTSD), a condition marked by severe anxiety stemming from a traumatic event such as a battle or violent attack.

Many patients undergo psychotherapy designed to help them re-experience their traumatic memory in a safe environment so as to help them make sense of the events and overcome their fear. However, such memories can be so entrenched that this therapy doesn’t always work, especially when the traumatic event occurred many years earlier.

MIT neuroscientists have now shown that they can extinguish well-established traumatic memories in mice by giving them a type of drug called an HDAC2 inhibitor, which makes the brain’s memories more malleable, under the right conditions. Giving this type of drug to human patients receiving psychotherapy may be much more effective than psychotherapy alone, says Li-Huei Tsai, director of MIT’s Picower Institute for Learning and Memory.

“By inhibiting HDAC2 activity, we can drive dramatic structural changes in the brain. What happens is the brain becomes more plastic, more capable of forming very strong new memories that will override the old fearful memories,” says Tsai, the senior author of a paper describing the findings in the Jan. 16 issue of Cell.

The new study also reveals the molecular mechanism explaining why older memories are harder to extinguish. Lead authors of the paper are former Picower Institute postdoc Johannes Graff and Nadine Joseph, a technical assistant at the Picower Institute.

Genes and memories

Tsai’s lab has previously shown that when memories are formed, neurons’ chromatin — DNA packaged with proteins — undergoes extensive remodeling. These chromatin modifications make it easier to activate the genes necessary to create new memories.

In this study, the researchers focused on chromatin modifications that occur when previously acquired memories are extinguished. To do this, they first trained mice to fear a particular chamber — by administering a mild foot shock — and then tried to recondition the mice so they no longer feared it, which was done by placing the mice in the chamber where they received the shock, without delivering the shock again.

This training proved successful in mice that had experienced the traumatic event only 24 hours before the reconditioning. However, in mice whose memories were 30 days old, it was impossible to eliminate the fearful memory.

The researchers also found that in the brains of mice with 24-hour-old memories, extensive chromatin remodeling occurred during the reconditioning. For several hours after the mice were placed back in the feared chamber, there was a dramatic increase in histone acetylation of memory-related genes, caused by inactivation of the protein HDAC2. That histone acetylation makes genes more accessible, turning on the processes needed to form new memories or overwrite old ones.

In mice with 30-day-old memories, however, there was no change in histone acetylation. This suggests that re-exposure to a fearful memory opens a window of opportunity during which the memory can be altered, but only if the memory has recently been formed, Tsai says.

“If you do something within this window of time, then you have the possibility of modifying the memory or forming a new trace of memory that actually instructs the animal that this is not such a dangerous place,” she says. “However, the older the memory is, the harder it is to really change that memory.”

Based on this finding, the researchers decided to treat mice with 30-day-old memories with an HDAC2 inhibitor shortly after re-exposure to the feared chamber. Following this treatment, the traumatic memories were extinguished just as easily as in the mice with 24-hour-old memories.

The researchers also found that HDAC2 inhibitor treatment turns on a group of key genes known as immediate early genes, which then activate other genes necessary for memory formation. They also saw an increase in the number of connections among neurons in the hippocampus, where memories are formed, and in the strength of communication among these neurons.

“Our experiments really strongly argue that either the old memories are permanently being modified, or a new much more potent memory is formed that completely overwrites the old memory,” Tsai says.

“This could be a very promising way to bring older memories back, process them in the hippocampus, and then extinguish them with the correct paradigm,” says Jelena Radulovic, a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine who was not part of the research team.

Treating anxiety

Some HDAC2 inhibitors have been approved to treat cancer, and Tsai says she believes it is worth trying such drugs to treat PTSD. “I hope this will convince people to seriously think about taking this into clinical trials and seeing how well it works,” she says.

Such drugs might also be useful in treating people who suffer from phobias and other anxiety disorders, she adds.

Tsai’s lab is now studying what happens to memory traces when re-exposure to traumatic memories occurs at different times. It is already known that memories are formed in the hippocampus and then transferred to the cortex for longer-term storage. It appears that the HDAC2 inhibitor treatment may somehow restore the memory to the hippocampus so it can be extinguished, Tsai says.

Want a good night’s sleep in the new year? Quit smoking

As if cancer, heart disease and other diseases were not enough motivation to make quitting smoking your New Year’s resolution, here’s another wake-up call: New research published in the January 2014 issue of The FASEB Journal suggests that smoking disrupts the circadian clock function in both the lungs and the brain. Translation: Smoking ruins productive sleep, leading to cognitive dysfunction, mood disorders, depression and anxiety.

"This study has found a common pathway whereby cigarette smoke impacts both pulmonary and neurophysiological function. Further, the results suggest the possible therapeutic value of targeting this pathway with compounds that could improve both lung and brain functions in smokers," said Irfan Rahman, Ph.D., a researcher involved in the work from the Department of Environmental Medicine at the University of Rochester Medical Center in Rochester, N.Y. "We envisage that our findings will be the basis for future developments in the treatment of those patients who are suffering with tobacco smoke-mediated injuries and diseases.

Rahman and colleagues found that tobacco smoke affects clock gene expression rhythms in the lung by producing parallel inflammation and depressed levels of brain locomotor activity. Short- and long- term smoking decreased a molecule known as SIRTUIN1 (SIRT1, an anti-aging molecule) and this reduction altered the level of the clock protein (BMAL1) in both lung and brain tissues in mice. A similar reduction was seen in lung tissue from human smokers and patients with chronic obstructive pulmonary disease (COPD). They made this discovery using two groups of mice which were placed in smoking chambers for short-term and long-term tobacco inhalation. One of the groups was exposed to clean air only and the other was exposed to different numbers of cigarettes during the day. Researchers monitored their daily activity patterns and found that these mice were considerably less active following smoke exposure.

Scientists then used mice deficient in SIRT1 and found that tobacco smoke caused a dramatic decline in activity but this effect was attenuated in mice that over expressed this protein or were treated with a small pharmacological activator of the anti-aging protein. Further results suggest that the clock protein, BMAL1, was regulated by SIRT1, and the decrease in SIRT1 damaged BMAL1, resulting in a disturbance in the sleep cycle/molecular clock in mice and human smokers. However, this defect was restored by a small molecule activator of SIRT1.

"If you only stick to one New Year’s resolution this year, make it quitting smoking," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. “Only Santa Claus has a list longer than that of the ailments caused or worsened by smoking. If you like having a good night’s sleep, then that’s just another reason to never smoke.”

Biofeedback-based horror game challenges players to deal with fear

While traditional horror video games seek to provide an exciting thrill, Nevermind is a biofeedback-enhanced horror game that has greater ambitions. It requires you to manage your anxiety in alarming scenarios – the more stressed you feel, the harder the game becomes. The aim, says Erin Reynolds, its creator, is for players to learn how to not let their fears get the best of them in nerve-wracking situations and hopefully carry over their gameplay-acquired skills into the real world.

A Garmin cardio chest strap akin to the ones gym-goers use to monitor their workout acts as a sensor, relaying the player’s heart rate information to the game through an ANT+ USB stick. The game calculates the player’s Heart Rate Variability (HRV), measuring the change in the duration between their heartbeats to figure out when their “fight or flight” response has kicked in and adjusts the gameplay accordingly. While Nevermind can’t zero in on specific stressful emotions like frustration or upset, it’s able to detect the intensity of the player’s feelings and gauge how deeply they feel stress at any point during the game.

Instead of having fanged horrors and hordes of zombies jump out from around corners, which might need a learning curve, the game is more subtle in inducing fear and is designed to appeal to non-gamers too. It creates a warped chaotic atmosphere where the creepiness factor is slowly dialed up, with huge screaming heads, blood-spattered doors and thrashing body bags.

Assuming the role of a newly hired Neruroprober at the Neurostalgia Institute, players boldly dive into the troubled minds of traumatized patients who are repressing their most horrific memories. To root out the cause of their suffering, players will need to solve puzzles and be willing to face a host of unimaginable terrors before the patient’s subconscious is ready to release its painful memories.

"This psychological phenomenon is based on how some people cope with severe psychological trauma in real life," Reynolds tells Gizmag. "These are individuals who experienced an event so terrible at some point in their lives that their conscious minds locked all memories of that event away completely. Although the patients can’t recall exactly what, if anything, happened to them, the repressed memories end up festering within their subconscious and create immense challenges in their attempts to live a normal life."

The sensor detects how scared or stressed the player gets as they move through the patient’s subconscious, recovering ten Polaroid photographs that each represent a distressful memory. Once all the photographs have been collected, they’ll have to differentiate the false memories from the five true ones and reconstruct the traumatizing memory. If they start to feel more fear, which the game sets out to trigger, the gameplay becomes perceptibly difficult. While some situations impact players more than others, they are all designed to push the player’s buttons.

For example, in the “car maze” section players follow the guiding sound of a blaring car horn through a twisting cave-like maze of crashed and wrecked cars full of disorienting imagery. As the player’s fear levels rise, the visuals become increasingly distorted until they are barely able to see what’s ahead of them.

"Some players become anxious over the car horn, others over the complexity of the maze, some over the imagery – there are a whole host things in this area that can rile up one’s nerves," says Reynolds. "The player needs to have a good grasp on how to calm down by this point in the game as it’s a nearly impossible challenge to escape the maze while scared or stressed."

In another scenario, the player explores a grotesque kitchen to find an ambiguous writhing mass in an oven and a giant bloodied refrigerator buzzing with flies that offers a puzzle. If the player gets rattled trying to solve the puzzle in this disturbing setting, milk starts flooding the room, pouring in from all over. Sloshing around in the waist-high milk makes it harder to move and the more anxious the player feels, the more milk floods in until it drowns them. If they are able to calm down in time the milk stops pouring in and drains out. If not, they drown and the game pulls them out of the room, returning them to the peaceful surroundings of the Institute until they feel ready again.

Making the game tougher as the player’s fear increases might seem counter-intuitive, but its developers were very clear about designing it that way. “We wanted players to become aware in a very real way of when their anxiety levels were starting to become elevated and reward them for being able to manage that anxiety on the fly,” Reynolds tells us. “We knew making the environment change so significantly that it would impact what the player was doing would get their attention.”

Developed as part of a Master of Fine Arts (MFA) thesis project within the University of Southern California’s Interactive Media and Games Division, Nevermind took about a year to build and presently exists as a “proof of concept game.” It has one level with one patient’s subconscious mind connected to a hub area that’s built to support the minds of 10 more patients. A play through takes about an hour. Reynolds plans to get a Kickstarter project going and launch the game with a variety of disturbed patients in late 2014. The team also plans to conduct thorough studies of the game’s impact on players and explore its use in therapy.

Will playing the game have us reacting to freaky situations with a Yoda-like serene gaze? Its developers hope it will help.

“Nevermind draws players in with the promise of a fun, exciting horror game that uses some spiffy new technology, but I hope it ultimately leaves them better equipped to take on the world more bravely and confidently than ever before,” Reynolds tells us. “In a way, it’s the biggest puzzle in the game – how do you solve your gut, knee-jerk reactions to unpleasant scenarios? If you can figure it out in the game, you’ll find success. If you can figure it out in life, you’ll find success there too.”