Shedding Light on Early Parkinson’s Disease Pathology

In a mouse model of early Parkinson’s disease (PD), animals displayed movement deficits, loss of tyrosine-hydroxylase (TH)-positive fibers in the striatum, and astro-gliosis and micro-gliosis in the substantia nigra (SN), without the loss of nigral dopaminergic neurons. These findings, which may cast light on the molecular processes involved in the initial stages of PD, are available in the current issue of Restorative Neurology and Neuroscience.

“The most intriguing finding of our study was the lack of a significant decrease of TH levels in the SN of the low-dose MPTP-treated mice, suggesting that this treatment does not induce a direct loss of nigral dopaminergic neurons,” says Joost Verhaagen PhD, lead investigator of the study. “These findings appear to support the ‘dying back’ hypothesis of PD, which proposes that the TH-positive terminal loss in the striatum is the first neurodegenerative event in PD, which later induces neuronal degeneration in the SN.” Dr. Verhaagen is Head of the Workgroup on Neuroregeneration at the Netherlands Institute for Neuroscience and Professor at the Free University in Amsterdam.

The neurotoxin MPTP (1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine) was used to induce the degenerative changes. Chronic 5 week administration of 25 mg/kg MPTP combined with probenecid (250 mg/kg), which inhibits MPTP clearance and promotes its crossing of the blood-brain barrier, is known to cause dopaminergic neuron degeneration in the SN and decrease striatal dopaminergic nerve terminals. In the current study, 7 mice were treated with 25 mg/kg MPTP plus probenecid, 6 mice received a lower dose of MPTP (15 mg/kg) plus probenecid, and 8 control mice received saline plus probenecid. A grid test, known to be sensitive to striatal dopaminergic input, was used to detect motor deficits.

Immunohistochemical analysis using TH fluorescence revealed that only the higher dose of MPTP produced significant dopaminergic neuronal cell loss in the SN (65% fluorescence loss, p<0.001). The 15 mg/kg dose produced an 18% decline in fluorescence which was not significantly different than control.

Both dose levels significantly reduced TH immunoreactivity of the striatum. The authors believe that the motor deficits seen at both MPTP dose levels relate to the striatal dopamine depletion.

The study is also the first to report that low-dose MPTP produces astrogliosis and microgliosis in the SN and formation of α-synuclein positive inclusions. “The data suggests that gliosis in the substantia nigra plays a prominent initiating role in the introduction of dopaminergic deficits after MPTP treatment, and may be sufficient to significantly reduce TH levels in the striatum,” says Dr. Korecka, first author and principal investigator of the study and a post-doctoral fellow at the Netherlands Institute for Neuroscience in Amsterdam.

“We are the first to report that this early PD model provides an interesting window of opportunity to study the mechanisms that underlie the early neurodegenerative events that initiate the cellular death of dopaminergic neurons,” write the authors. They suggest that the model can be used to develop potential treatment strategies to counteract early PD cellular changes.

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Our internal clocks can become ticking time bombs for diabetes and obesity

New research in The FASEB Journal using mice suggests that disrupting our internal clocks can lead to a complete absence of 24-hour bodily rhythms and an immediate gain in body weight

If you’re pulling and all-nighter to finish a term paper, a new parent up all night with a fussy baby, or simply can’t sleep like you once could, then you may be snoozing on good health. That’s because new research published in The FASEB Journal used mice to show that proper sleep patterns are critical for healthy metabolic function, and even mild impairment in our circadian rhythms can lead to serious health consequences, including diabetes and obesity.

"We should acknowledge the unforeseen importance of our 24-hour rhythms for health," said Claudia Coomans, Ph.D., a researcher involved in the work from the Department of Molecular Cell Biology in the Laboratory of Neurophysiology at Leiden University Medical Center in Leiden, Netherlands. "To quote Seneca ‘We should live according to nature (secundum naturam vivere).’"

To make this discovery, Coomans and colleagues exposed mice to constant light, which disturbed their normal internal clock function, and observed a gradual degradation of their bodies’ internal clocks until it reached a level that normally occurs when aging. Eventually the mice lost their 24-hour rhythm in energy metabolism and insulin sensitivity, indicating that relatively mild impairment of clock function had severe metabolic consequences.

"The good news is that some of us can ‘sleep it off’ to avoid obesity and diabetes," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. "The bad news is that we can all get the metabolic doldrums when our normal day/night cycle is disrupted."

Should I trust my intuition?

Do we always make better decisions when we take more time to think? Or are there decisions where more time doesn’t really help?

A study led by Zachary Mainen, Director of the Champalimaud Neuroscience Programme, and published in the scientific journal, Neuron, reports that when rats were challenged with a series of perceptual decision problems, their performance was just as good when they decided rapidly as when they took a much longer time to respond. Despite being encouraged to slow down and try harder, the subjects of this study achieved their maximum performance in less than 300 milliseconds.

'There are many kinds of decisions, and for some, having more time appears to be of no help. In these cases, you'd better go with your intuition, and that's what our subjects did', explains Zachary Mainen, the neuroscientist who led this study, while an Associate Professor at CSHL, in the USA.

This study suggests that rats can be used as an animal model to investigate what is happening in the human brain when ‘intuitive’ decisions are being made. ‘Decision-making is not a well-understood process, but it appears to be surprisingly similar among species. This study provides a basis to begin to take apart one type of decision and see how it really works’, the author adds.

(Image: Kristen Dold | Thinkstock)

Rats’ brains are more like ours than scientists previously thought

Neuroscientists face a multitude of challenges in their efforts to better understand the human brain. If not for model organisms such as the rat, they might never know what really goes on inside our heads.

The brain is a phenomenal processor that in a year’s time can generate roughly 300,000 petabytes of data — 30,000 times the amount generated by the Large Hadron Collider. Trying to decipher its signals is a daunting prospect.

But particularly for individuals who have lost a limb or been partially or fully paralyzed, such research has potentially life-changing results because it can enable such biotechnological advances as the development of a brain-computer interface for controlling prosthetic limbs.

Such devices require a detailed understanding of the motor cortex, a part of the brain that is crucial in issuing the neural commands that execute behavioral movements. A recent paper published in the journal Frontiers in Neural Circuits by Jared Smith and Kevin Alloway, researchers at the Penn State Center for Neural Engineering and affiliates of the Huck Institutes of the Life Sciences, details their discovery of a parallel between the motor cortices of rats and humans that signifies a greater relevance of the rat model to studies of the human brain than scientists had previously known.

"The motor cortex in primates is subdivided into multiple regions, each of which receives unique inputs that allow it to perform a specific motor function," said Alloway, professor of neural and behavioral sciences. "In the rat brain, the motor cortex is small and it appeared that all of it received the same type of input. We know now that sensory inputs to the rat motor cortex terminate in a small region of the motor cortex that is distinct from the larger region that issues the motor commands. Our work demonstrates that the rat motor cortex is parcellated into distinct subregions that perform specific functions, and this result appears to be similar to what is seen in the primate brain."

"You have to take into account the animal’s natural behaviors to best understand how its brain is structured for sensory and motor processing," said Jared Smith, graduate student in the Huck Institutes’ neuroscience program and the first author of the paper. "For primates like us, that means a strong reliance on visual information from the eyes, but for rats it’s more about the somatosensory inputs from their whiskers."

In fact, nearly a third of the rat’s sensorimotor cortex is devoted to processing whisker-related information, even though the whiskers’ occupy only one-third of one percent of the rat’s total body surface. In humans, nearly 40 percent of the entire cortex is devoted to processing visual information even though the eyes occupy a very tiny portion of our body’s surface.

To understand the structure and function of the rat motor cortex, Smith and Alloway conducted a series of experiments focused on the medial agranular region, which responds to whisker stimulation and elicits whisker movements when stimulated.

"Our research," said Smith, "was conducted in two stages to investigate the functional organization of the brain: first tracing the neuronal connectivity, and then measuring how the circuits behave in terms of their electrophysiology. Just like in any electrical circuit, the first thing you need to do is trace the wires to see how the different components are connected. Then you can use this information to make sense of the activity going on at any particular node. In the end, you can step back and see how all the circuits work together to achieve something more complex, such as motor control."

"We discovered different sensory input regions that were distinct from the region that issued the motor commands to move the whiskers," said Alloway. "In this respect, we were fortunate to have Patrick Drew [assistant professor of engineering science and mechanics and neurosurgery at Penn State] help us analyze the EMG signals produced by microstimulation because this showed that the sensory input region was significantly less effective in evoking whisker movements."

As a result of Smith and Alloway’s discovery, previously published data on the rat motor cortex can be revisited with a new degree of specificity, and more similarities between the brains and neural processes of rats and humans may eventually come to light, perhaps even informing studies of other model organisms. This discovery is also likely to advance the study of the human brain.

"This study opens up avenues for studying some very complex neural processes in rodents that are more like our own than we had previously thought," said Smith. "The tools now available for studying activity in the rodent brain are improving at a remarkable pace, and the findings are even more interesting as we discover just how similar these mammalian relatives are to us. This is a very exciting time in neuroscience."

Researchers discover the brain origins of variation in pathological anxiety

New findings from nonhuman primates suggest that an overactive core circuit in the brain, and its interaction with other specialized circuits, accounts for the variability in symptoms shown by patients with severe anxiety. In a brain-imaging study published in the Proceedings of the National Academy of Sciences (PNAS), researchers from the University of Wisconsin School of Medicine and Public Health describe work that for the first time provides an understanding of the root causes of clinical variability in anxiety disorders.

Using a well-established nonhuman primate model of childhood anxiety, the scientists identified a core circuit that is chronically over-active in all anxious individuals, regardless of their particular pattern of symptoms. They also identified a set of more specialized circuits that are over- or under-active in individuals prone to particular symptoms, such as chronically high levels of the stress-hormone cortisol.

“These findings provide important new insights into altered brain functioning that explains why people with anxiety have such different symptoms and clinical presentations, and it also gives us new ideas, based on an understanding of altered brain function, for helping people with different types of anxiety,’’ says Ned Kalin, senior author, chair of Psychiatry and director of the HealthEmotions Research Institute.

“There is a large need for new treatment strategies, because our current treatments don’t work well for many anxious adults and children who come to us for help.”

In the study, key anxiety-related symptoms were measured in 238 young rhesus monkeys using behavioral and hormonal measurement procedures similar to those routinely used to assess extreme shyness in children. Young monkeys are ideally suited for these studies because of their similarities in brain development and social behavior, Kalin notes. Variation in brain activity was quantified in the monkeys using positron emission tomography (PET) imaging, a method that is also used in humans.

Combining behavioral measures of shyness, physiological measures of the stress-hormone cortisol, and brain metabolic imaging, co-lead authors Alexander Shackman, Andrew Fox and their collaborators showed that a core neural system marked by elevated activity in the central nucleus of the amygdala was a consistent brain signature shared by young monkeys with chronically high levels of anxiety. This was true despite striking differences across monkeys in the predominance of particular anxiety-related symptoms.

The Wisconsin researchers also showed that young monkeys with particular anxiety profiles, such as high levels of shyness, showed changes in symptom-specific brain circuits. Finally, Shackman, Fox and colleagues uncovered evidence that the two kinds of brain circuits, one shared by all anxious individuals, the other specific to those with particular symptoms, work together to produce different presentations of pathological anxiety.

The new study builds upon earlier work by the Kalin laboratory demonstrating that activity in the amygdala is strongly shaped by early-life experiences, such as parenting and social interactions. They hypothesize that extreme anxiety stems from problems with the normal maturation of brain systems involved in emotional learning, which suggests that anxious children have difficulty learning to effectively regulate brain anxiety circuits. Taken together, this line of research sets the stage for improved strategies for preventing extreme childhood anxiety from blossoming into full-blown anxiety disorders.

“This means the amygdala is an extremely attractive target for new, broad-spectrum anxiety treatments,’’ says Shackman. “The central nucleus of the amygdala is a uniquely malleable substrate for anxiety, one that can help to trigger a wide range of symptoms.”

The work also suggests more specific brain targets for different symptom profiles. Such therapies could range from new, more selectively targeted medications to intensive therapies that seek to re-train the amygdala, ranging from conventional cognitive-behavioral therapies to training in mindfulness and other techniques, Shackman noted. To further understand the clinical significance of these observations, the laboratory is conducting a parallel study in young children suffering from anxiety disorders.

Innate ability to vocalize: Deaf or not, courting male mice make same sounds

Scientists have long thought mice might be a model for how humans learn to vocalize. But new research led by scientists at Washington State University Vancouver has found that, unlike humans and songbirds, mice do not learn to vocalize.

The results, published in the Journal of Neuroscience, point the way to a more finely focused, genetic tool for teasing out the mysteries of speech and its disorders.

To see if mice learn to vocalize, WSU neurophysiologist Christine Portfors destroyed the ear hair cells in more than a dozen newborn male mice. The cells convert sound waves into electrical signals processed by the brain, making hearing possible.

The deaf mice were then raised with hearing mice in a normal social environment.

Portfors and her fellow researchers, including WSU graduate student Elena Mahrt, used males because they are particularly exuberant vocalizers in the presence of females.

"We can elicit vocalization behavior in males really easily by just putting them with a female,” Portfors said. "They vocalize like crazy.”

And it turned out that it didn’t matter if the mouse was deaf or not. The researchers catalogued essentially the same suite of ultrasonic sounds from both the deaf and hearing mice. “It means that they don’t need to hear to be able to produce their sounds, their vocalizations,” Portfors said. “Basically, they don’t need to hear themselves. They don’t need auditory feedback. They don’t need to learn.”

The finding means mice are out as a model to study vocal learning. However, scientists can now focus on the mouse to learn the genetic mechanism behind communication disorders.

"If you don’t have learning as a variable, you can look at the genetic control of these things,” Portfors said. "You can look at the genetic control of the output of the signal. It’s not messed up by an animal that’s been in a particular learning situation.”

(Image: Fotolia)

Research Provides Clues to Alcohol Addiction Vulnerability

A Wake Forest Baptist Medical Center team studying alcohol addiction has new research that might shed light on why some drinkers are more susceptible to addiction than others.

Jeff Weiner, Ph.D., professor of physiology and pharmacology at Wake Forest Baptist, and colleagues used an animal model to look at the early stages of the addiction process and focused on how individual animals responded to alcohol. Their findings may lead not only to a better understanding of addiction, but to the development of better drugs to treat the disease as well, Weiner said.

"We know that some people are much more vulnerable to alcoholism than others, just like some people have a vulnerability to cancer or heart disease," Weiner said. "We don’t have a good understanding of what causes this vulnerability, and that’s a big question. But if we can figure it out, we may be able to better identify people at risk, as well as gain important clues to help develop better drugs to treat the disease."

The findings are published in the March 13 issue of the Journal of Neuroscience. Weiner, who directs the Translational Studies on Early-Life Stress and Vulnerability to Alcohol Addiction project at Wake Forest Baptist, said the study protocol was developed by the first author of the paper, Karina Abrahao, a graduate student visiting from the collaborative lab of Sougza-Formigoni, Ph.D, of the Department of Psychobiology at the Federal University of Sao Paulo, Brazil.

Weiner said the study model focused on how individual animals responded to alcohol. Typically, when a drug like alcohol is given to a mouse every day, the way the animals respond increases - they become more stimulated and run around more. “In high doses, alcohol is a depressant, but in low doses, it can have a mellowing effect that results in greater activity,” he said. “Those low dose effects tend to increase over time and this increase in activity in response to repeated alcohol exposure is called locomotor sensitization.”

Prior studies with other drugs, such as cocaine and amphetamine, have suggested that animals that show the greatest increases in locomotor sensitization are also the animals most likely to seek out or consume these drugs. However, the relationship between locomotor sensitization and vulnerability to high levels of alcohol drinking is not as well established, Weiner said.

Usually when researchers are studying a drug, they give it to one test group while the other group gets a control solution, and then they look for behavioral differences between the two, Weiner said. But in this study, the researchers focused on individual differences in how each animal responded to the alcohol. A control group received a saline injection while another was injected with the same amount of alcohol every day for three weeks. Weiner said they used mice bred to be genetically variable like humans to make the research more relevant.

"We found large variations in the development of locomotor sensitization to alcohol in these mice, with some showing robust sensitization and others showing no more of a change in locomotor activity than control mice given daily saline injections," Weiner said. "Surprisingly, when all of the alcohol-exposed mice were given an opportunity to voluntarily drink alcohol, those that had developed sensitization drank more than those that did not. In fact, the alcohol-treated mice that failed to develop sensitization drank no more alcohol than the saline-treated control group."

The authors also conducted a series of neurobiological studies and discovered that mice that showed robust locomotor sensitization had deficits in a form of brain neuroplasticity - how experiences reorganize neural pathways in the brain - that has been linked with cocaine addiction in other animal models.

"We found that this loss of the ability of brain cells to change the way that they communicate with each other only occurred in the animals that showed the behavioral response to alcohol," he said. "What this suggests for the first time in the alcohol addiction field is that this particular deficit may represent an important brain correlate of vulnerability to alcoholism. It’s a testable hypothesis. That’s why I think it’s an important finding."

DNA damage occurs as part of normal brain activity

Scientists at the Gladstone Institutes have discovered that a certain type of DNA damage long thought to be particularly detrimental to brain cells can actually be part of a regular, non-harmful process. The team further found that disruptions to this process occur in mouse models of Alzheimer’s disease—and identified two therapeutic strategies that reduce these disruptions.

Scientists have long known that DNA damage occurs in every cell, accumulating as we age. But a particular type of DNA damage, known as a double-strand break, or DSB, has long been considered a major force behind age-related illnesses such as Alzheimer’s. Today, researchers in the laboratory of Gladstone Senior Investigator Lennart Mucke, MD, report in Nature Neuroscience that DSBs in neuronal cells in the brain can also be part of normal brain functions such as learning—as long as the DSBs are tightly controlled and repaired in good time. Further, the accumulation of the amyloid-beta protein in the brain—widely thought to be a major cause of Alzheimer’s disease—increases the number of neurons with DSBs and delays their repair.

"It is both novel and intriguing team’s finding that the accumulation and repair of DSBs may be part of normal learning," said Fred H. Gage, PhD, of the Salk Institute who was not involved in this study. "Their discovery that the Alzheimer’s-like mice exhibited higher baseline DSBs, which weren’t repaired, increases these findings’ relevance and provides new understanding of this deadly disease’s underlying mechanisms."

In laboratory experiments, two groups of mice explored a new environment filled with unfamiliar sights, smells and textures. One group was genetically modified to simulate key aspects of Alzheimer’s, and the other was a healthy, control group. As the mice explored, their neurons became stimulated as they processed new information. After two hours, the mice were returned to their familiar, home environment.

The investigators then examined the neurons of the mice for markers of DSBs. The control group showed an increase in DSBs right after they explored the new environment—but after being returned to their home environment, DSB levels dropped.

"We were initially surprised to find neuronal DSBs in the brains of healthy mice," said Elsa Suberbielle, DVM, PhD, Gladstone postdoctoral fellow and the paper’s lead author. "But the close link between neuronal stimulation and DSBs, and the finding that these DSBs were repaired after the mice returned to their home environment, suggest that DSBs are an integral part of normal brain activity. We think that this damage-and-repair pattern might help the animals learn by facilitating rapid changes in the conversion of neuronal DNA into proteins that are involved in forming memories."

The group of mice modified to simulate Alzheimer’s had higher DSB levels at the start—levels that rose even higher during neuronal stimulation. In addition, the team noticed a substantial delay in the DNA-repair process.

To counteract the accumulation of DSBs, the team first used a therapeutic approach built on two recent studies—one of which was led by Dr. Mucke and his team—that showed the widely used anti-epileptic drug levetiracetam could improve neuronal communication and memory in both mouse models of Alzheimer’s and in humans in the disease’s earliest stages. The mice they treated with the FDA-approved drug had fewer DSBs. In their second strategy, they genetically modified mice to lack the brain protein called tau—another protein implicated in Alzheimer’s. This manipulation, which they had previously found to prevent abnormal brain activity, also prevented the excessive accumulation of DSBs.

The team’s findings suggest that restoring proper neuronal communication is important for staving off the effects of Alzheimer’s—perhaps by maintaining the delicate balance between DNA damage and repair.

"Currently, we have no effective treatments to slow, prevent or halt Alzheimer’s, from which more than 5 million people suffer in the United States alone," said Dr. Mucke, who directs neurological research at Gladstone and is a professor of neuroscience and neurology at the University of California, San Francisco, with which Gladstone is affiliated. "The need to decipher the causes of Alzheimer’s and to find better therapeutic solutions has never been more important—or urgent. Our results suggest that readily available drugs could help protect neurons against some of the damages inflicted by this illness. In the future, we will further explore these therapeutic strategies. We also hope to gain a deeper understanding of the role that DSBs play in learning and memory—and in the disruption of these important brain functions by Alzheimer’s disease."

(Image courtesy: Lulu Qian, Erik Winfree & Jehoshua Bruck | California Institute of Technology)

Wireless, implanted sensor broadens range of brain research

A compact, self-contained sensor recorded and transmitted brain activity data wirelessly for more than a year in early stage animal tests, according to a study funded by the National Institutes of Health. In addition to allowing for more natural studies of brain activity in moving subjects, this implantable device represents a potential major step toward cord-free control of advanced prosthetics that move with the power of thought. The report is in the April 2013 issue of the Journal of Neural Engineering.

“For people who have sustained paralysis or limb amputation, rehabilitation can be slow and frustrating because they have to learn a new way of doing things that the rest of us do without actively thinking about it,” said Grace Peng, Ph.D., who oversees the Rehabilitation Engineering Program of the National Institute of Biomedical Imaging and Bioengineering (NIBIB), part of NIH. “Brain-computer interfaces harness existing brain circuitry, which may offer a more intuitive rehab experience, and ultimately, a better quality of life for people who have already faced serious challenges.”

Recent advances in brain-computer interfaces (BCI) have shown that it is possible for a person to control a robotic arm through implanted brain sensors linked to powerful external computers. However, such devices have relied on wired connections, which pose infection risks and restrict movement, or were wireless but had very limited computing power.

Building on this line of research, David Borton, Ph.D., and Ming Yin, Ph.D., of Brown University, Providence, R.I., and colleagues surmounted several major barriers in developing their sensor. To be fully implantable within the brain, the device needed to be very small and completely sealed off to protect the delicate machinery inside the device and the even more delicate tissue surrounding it. At the same time, it had to be powerful enough to convert the brain’s subtle electrical activity into digital signals that could be used by a computer, and then boost those signals to a level that could be detected by a wireless receiver located some distance outside the body. Like all cordless machines, the device had to be rechargeable, but in the case of an implanted brain sensor, recharging must also be done wirelessly.

The researchers consulted with brain surgeons on the shape and size of the sensor, which they built out of titanium, commonly used in joint replacements and other medical implants. They also fitted the device with a window made of sapphire, which electromagnetic signals pass through more easily than other materials, to assist with wireless transmission and inductive charging, a method of recharging also used in electronic toothbrushes. Inside, the device was densely packed with the electronics specifically designed to function on low power to reduce the amount of heat generated by the device and to extend the time it could work on battery power.

Testing the device in animal models — two pigs and two rhesus macaques — the researchers were able to receive and record data from the implanted sensors in real time over a broadband wireless connection. The sensors could transmit signals more than three feet and have continued to perform for over a year with little degradation in quality or performance.

The ability to remotely record brain activity data as an animal interacts naturally with its environment may help inform studies on muscle control and the movement-related brain circuits, the researchers say. While testing of the current devices continues, the researchers plan to refine the sensor for better heat management and data transmission, with use in human medical care as the goal.

“Clinical applications may include thought-controlled prostheses for severely neurologically impaired patients, wireless access to motorized wheelchairs or other assistive technologies, and diagnostic monitoring such as in epilepsy, where patients currently are tethered to the bedside during assessment,” said Borton.