Study in Fruit Flies Shows that Epilepsy Drug Target May Have Implications for Brain Disorder Sleep Disruption

A new study in a mutant fruitfly called sleepless (sss) confirmed that the enzyme GABA transaminase, which is the target of some epilepsy drugs, contributes to sleep loss. The findings, published online in Molecular Psychiatry, were led by Amita Sehgal, PhD, head of the Chronobiology Program at the University of Pennsylvania’s Perelman School of Medicine. The findings shed light on mechanisms that may be shared between sleep disruption and some neurological disorders. A better understanding of this connection could enable treatments that target both types of symptoms and perhaps provide better therapeutic efficacy.

“Epilepsy is essentially an increase-in-firing disorder of the brain and maybe a decrease in activity of the neurotransmitter GABA, too,” says Sehgal, who is also a professor of Neuroscience and an investigator with the Howard Hughes Medical Institute (HHMI). “This connects our work to drugs that inhibit GABA transaminase. Changes in GABA transaminase activity are implicated in epilepsy and some other psychiatric disorders, which may account for some of the associated sleep problems.”

The team looked at the proteomics of the sss mutant brain – a large-scale study of the structure and function of related proteins — and found that GABA transaminase is increased in the sss brain compared to controls. This enzyme breaks down GABA, so GABA is decreased in the sss brain. Because GABA promotes sleep, there is a decrease in sleep in the sss mutant fly, as the name implies.  

The relationship between the SSS protein and GABA is not fully understood. The SSS protein controls neural activity, and its absence results in increased neural firing, which likely uses up a lot of energy, says Sehgal. GABA transaminase works in the mitochondria, the energy-production organelle in the glial cells of the brain, which provide fuel for neurons. The large energy demand created by the increased neural firing in sss brains probably alters mitochondrial metabolism, including GABA transaminase function in glia.

In the sss mutant fly, there is a stream of connections that leads to its signature loss of sleep: The sss mutant has increased neuron firing caused by downregulation of a potassium channel protein called Shaker. Recently, the Sehgal lab showed that SSS also affects activity of acetylcholine receptors. Both of these actions may directly cause an inability to sleep. In addition, increased energy demands on glia, which increase GABA transaminase and decrease GABA, may further contribute to sleep loss. On the other hand, if GABA is increased, then sleep is increased, as in flies that lack GABA transaminase.

A gene mutation for excessive alcohol drinking found

Researchers have discovered a gene that regulates alcohol consumption and when faulty can cause excessive drinking. They have also identified the mechanism underlying this phenomenon.

The study showed that normal mice show no interest in alcohol and drink little or no alcohol when offered a free choice between a bottle of water and a bottle of diluted alcohol.

However, mice with a genetic mutation to the gene Gabrb1 overwhelmingly preferred drinking alcohol over water, choosing to consume almost 85% of their daily fluid as drinks containing alcohol - about the strength of wine.

The consortium of researchers from five UK universities – Newcastle University, Imperial College London,  Sussex University, University College London and University of Dundee – and the MRC Mammalian Genetics Unit at Harwell, funded by the Medical Research Council (MRC), Wellcome Trust and ERAB, publish their findings today in Nature Communications.

Dr Quentin Anstee, Consultant Hepatologist at Newcastle University, joint lead author said: “It’s amazing to think that a small change in the code for just one gene can have such profound effects on complex behaviours like alcohol consumption.

“We are continuing our work to establish whether the gene has a similar influence in humans, though we know that in people alcoholism is much more complicated as environmental factors come into play. But there is the real potential for this to guide development of better treatments for alcoholism in the future.”

Identifying the gene for alcohol preference

Working at the MRC Mammalian Genetics Unit, a team led by Professor Howard Thomas from Imperial College London introduced subtle mutations into the genetic code at random throughout the genome and tested mice for alcohol preference. This led the researchers to identify the gene Gabrb1 which changes alcohol preference so strongly that mice carrying either of two single base-pair point mutations in this gene preferred drinking alcohol (10% ethanol v/v - about the strength of wine), over water.

The group showed that mice carrying this mutation were willing to work to obtain the alcohol-containing drink by pushing a lever and, unlike normal mice, continued to do so even over long periods. They would voluntarily consume sufficient alcohol in an hour to become intoxicated and even have difficulty in coordinating their movements.

The cause of the excessive drinking was tracked down to single base-pair point mutations in the gene Gabrb1, which codes for the beta 1 subunit, an important component of the GABAA receptor in the brain. This receptor responds to the brain’s most important inhibitory chemical messenger (GABA) to regulate brain activity. The researchers found that the gene mutation caused the receptor to activate spontaneously even when the usual GABA trigger was not present.

These changes were particularly strong in the region of the brain that controls pleasurable emotions and reward, the nucleus accumbens, as Dr Anstee explains: “The mutation of the beta1 containing receptor is altering its structure and creating spontaneous electrical activity in the brain in this pleasure zone, the nucleus accumbens. As the electrical signal from these receptors increases, so does the desire to drink to such an extent that mice will actually work to get the alcohol, for much longer than we would have expected.”

Professor Howard Thomas said: “We know from previous human studies that the GABA system is involved in controlling alcohol intake. Our studies in mice show that a particular subunit of GABAA receptor has a significant effect and most importantly the existence of these mice has allowed our collaborative group to investigate the mechanism involved. This is important when we come to try to modify this process first in mice and then in man.”

Leading to a treatment for alcohol addiction

Initially funded by the MRC, the 10-year project aimed to find genes affecting alcohol consumption. Professor Hugh Perry, Chair of the MRC’s Neurosciences and Mental Health Board, said: “Alcohol addiction places a huge burden on the individual, their family and wider society. There’s still a great deal we don’t understand about how and why consumption progresses into addiction, but the results of this long-running project suggest that, in some individuals, there may be a genetic component. If further research confirms that a similar mechanism is present in humans, it could help us to identify those most at risk of developing an addiction and ensure they receive the most effective treatment.”

A Sleep Aid Without the Side Effects

Insomniacs desperate for some zzzs may one day have a safer way to get them. Scientists have developed a new sleep medication that has induced sleep in rodents and monkeys without apparently impairing cognition, a potentially dangerous side effect of common sleep aids. The discovery, which originated in work explaining narcolepsy, could lead to a new class of drugs that help people who don’t respond to other treatments.

Between 10% and 15% of Americans chronically struggle with getting to or staying asleep. Many of them turn to sleeping pills for relief, and most are prescribed drugs, such as zolpidem (Ambien) and eszopiclone (Lunesta), that slow down the brain by binding to receptors for GABA, a neurotransmitter that’s involved in mood, cognition, and muscle tone. But because the drugs target GABA indiscriminately, they can also impair cognition, causing amnesia, confusion, and other problems with learning and memory, along with a number of strange sleepwalking behaviors, including wandering, eating, and driving while asleep. This has led many researchers to seek out alternative mechanisms for inducing sleep.

Neuroscientist Jason Uslaner of Merck Research Laboratories in West Point, Pennsylvania, and colleagues decided to tap into the brain’s orexin system. Orexin (also known as hypocretin) is a protein that controls wakefulness and is missing in people with narcolepsy. Past studies successfully induced sleep by inhibiting orexin, but had not looked into its effects on cognition. The researchers developed a new orexin-inhibiting compound called DORA-22 and confirmed that it could induce sleep in rats and rhesus monkeys as effectively as the GABA-modulating drugs.

Then the researchers went about testing the drugs’ effects on the animals’ cognition. They measured the rats’ cognition and memory by assessing the rodents’ ability to recognize objects. They presented the rats with a new object—say, a cone or a sphere—that the rats then sniffed and explored. Then they took the object away for an hour. After that hour, the rats were exposed to a new object and the one they’d already gotten to know; if the rats remembered, they spent less time checking out the familiar object. With the primates, Uslaner’s team tested their ability to match colors on a touchscreen and to pay attention to and identify the origin of a flashing light. In all the cases, the researchers found the GABA-modulating sleeping pills caused both the rats and the primates to respond more slowly and less accurately. Monkeys taking the memory and attention tests, for example, were 20% less accurate on the highest dose of each of the GABA-modulating drugs. But DORA-22 had no such effect on cognition, the team reports today in Science Translational Medicine.

"We were very excited," Uslaner says. "Folks who take sleep medications need to be able to perform cognitive tasks when they awake, and this [compound] could help them do so without impairment."

Although DORA-22 has not yet been tested in humans, it holds tremendous promise for helping people suffering from sleep disorders, says Emmanuel Mignot, a sleep researcher with the Stanford University School of Medicine in Palo Alto, California. “This study is encouraging and exciting, because there’s good reason to believe it would work differently from what we’ve used in the past,” says Mignot, who helped discover the link between orexin (or its absence) and narcolepsy. “Not every drug works for everyone, so it’s really, really good news to have a potential new drug on the horizon.”

Diuretic Drug Offers Latest Hope for Autism Treatment

A drug used for decades to treat high blood pressure and other conditions has shown promise in a small clinical trial for autism. The drug, bumetanide, reduced the overall severity of behavioral symptoms after 3 months of daily treatment. The researchers say that many parents of children who received the drug reported that their children were more “present” and engaged in social interactions after taking it. The new findings are among several recent signs that treatments to address the social deficits at the core of autism may be on the horizon.

Several lines of evidence suggest that autism interferes with the neurotransmitter GABA, which typically puts a damper on neural activity. Bumetanide may enhance the inhibitory effects of GABA, and the drug has been used safely as a diuretic to treat a wide range of heart, lung, and kidney conditions. In the new study, researchers led by Yehezkel Ben-Ari at the Mediterranean Institute of Neurobiology in Marseille, France, recruited 60 autistic children between the ages of 3 and 11 and randomly assigned them to receive either a daily pill of bumetanide or a placebo. (Neither the children’s parents nor the researchers who assessed the children knew who received the actual drug).

As a group, those who got bumetanide improved by 5.6 points on a 60-point scale that’s often used to assess behaviors related to autism, the researchers report today in Translational Psychiatry. That was enough to nudge the group average just under the cutoff for severe autism and into the mild to medium category. The study did not look directly at whether the drug improved all symptoms equally or some more than others. “We have some indications that the symptoms particularly ameliorated with bumetanide are the genuine core symptoms of autism, namely communication and social interactions,” Ben-Ari says. More work will be needed to verify that impression. Ben-Ari says his team is now preparing for a larger, multicenter trial in Europe.

New research investigates how the common ‘cat parasite’ gets into the brain

The Toxoplasma gondii parasite causes toxoplasmosis. The parasite is common and infects between 30 and 50 per cent of the global population. It also infects animals, especially domestic cats. Human infection is contracted by eating poorly cooked (infected) meat and handling cat feces. Toxoplasmosis first appears with mild flu-like symptoms in adults and otherwise healthy people before entering a chronic and dormant phase, which has previously been regarded as symptom-free. But when the immune system is weakened toxoplasmosis in the brain can be fatal. The fetus can be infected through the mother and because of this risk, pregnant women are recommended to avoid contact with cat litter boxes. Surprisingly, several studies in humans and mice have suggested that even in the dormant phase, the parasite can influence increasing risk taking and infected people show higher incidence of schizophrenia, anxiety and depression, which are broader public health concerns.

In their recent study Fuks et al. showed for the first time how the parasite enters the brain and increases the release of a neurotransmitter called GABA (gaba-Aminobutyric acid), that, amongst other effects, inhibits the sensation of fear and anxiety. In one laboratory experiment, human dendritic cells were infected with toxoplasma. After infection, the cells, which are a key component of the immune defense, began actively releasing GABA), In another experiment on live mice, the team was able to trace the movement of infected dendritic cells in the body after introducing the parasite into the brain, from where it spread and continued to affect the GABA system.

"For toxoplasma to make cells in the immune defense secrete GABA was as surprising as it was unexpected, and is very clever of the parasite," says Antonio Barragan, researcher at the Center for Infectious Medicine at Karolinska Institute and the Swedish Institute for Communicable Disease Control. "It would now be worth studying the links that exist between toxoplasmosis, the GABA systems and major public health threats."

New clues to how the brain and body communicate to regulate weight

Maintaining a healthy body weight may be difficult for many people, but it’s reassuring to know that our brains and bodies are wired to work together to do just that—in essence, to achieve a phenomenon known as energy balance, a tight matching between the number of calories consumed versus those expended. This careful balance results from a complex interchange of neurobiological crosstalk within regions of the brain’s hypothalamus, and when this “conversation” goes awry, obesity or anorexia can result.

Given the seriousness of these conditions, it’s unfortunate that little is known about the details of this complex interchange. Now research led by investigators at Beth Israel Deaconess Medical Center (BIDMC) provides new insights that help bring order to this complexity. Described in the October 26 issue of the journal Cell, the findings demonstrate how the GABA neurotransmitter selectively drives energy expenditure, and importantly, also help explain the neurocircuitry underlying the fat-burning properties of brown fat.

"Our group has built up a research program with the overall goal of unraveling the ‘wiring diagram’ by which the brain controls appetite and the burning of calories," says senior author Bradford Lowell, MD, PhD, a Professor of Medicine in BIDMC’s Division of Endocrinology and Harvard Medical School. "To advance our understanding to this level, we need to know the function of specific subsets of neurons, and in addition, the upstream neurons providing input to, and the downstream neurons receiving output from, these functionally defined neurons. Until recently, such knowledge in the hypothalamus has been largely unobtainable."