A three-dimensional, reconstructed magnetic resonance image (upper) shows a cavity caused by a spinal injury nearly filled with grafted neural stem cells, colored green. The lower image depicts neuronal outgrowth from transplanted human neurons (green) and development of putative contacts (yellow dots) with host neurons (blue).
An international team led by researchers at the University of California, San Diego School of Medicine reports that a single injection of human neural stem cells produced neuronal regeneration and improvement of function and mobility in rats impaired by an acute spinal cord injury (SCI).
The findings are published in the May 28, 2013 online issue of Stem Cell Research & Therapy.
Martin Marsala, MD, professor in the Department of Anesthesiology, with colleagues at UC San Diego and in Slovakia, the Czech Republic and The Netherlands, said grafting neural stem cells derived from a human fetal spinal cord to the rats’ spinal injury site produced an array of therapeutic benefits – from less muscle spasticity to new connections between the injected stem cells and surviving host neurons.
“The primary benefits were improvement in the positioning and control of paws during walking tests and suppression of muscle spasticity,” said Marsala, a specialist in spinal cord trauma and spinal injury-related disorders. Spasticity – exaggerated muscle tone or uncontrolled spasms – is a serious and common complication of traumatic injury to the spinal cord.
The human stem cells, said the scientists, appeared to vigorously take root at the injury site.
“In all cell-grafted animals, there was robust engraftment, and neuronal maturation of grafted human neurons was noted,” Marsala said. “Importantly, cysts or cavities that can form in or around spinal injuries were not present in any cell-treated animal. The injury-caused cavity was completely filled by grafted cells.”
The rats received the pure stem cell grafts three days after injury (no other supporting materials were used) and were given drugs to suppress an immune response to the foreign stem cells. Marsala said grafting at any time after the injury appears likely to work in terms of blocking the formation of spinal injury cavities, but that more work would be required to determine how timing affects functional neurological benefit.
These photomicrographs depict comparative stained sections of a healthy brain (top) and of patient EP, in which significant structures in the medial temporal lobe are heavily damaged or missing. The letters identify specific brain structures, such as EC and PRC for entorhinal cortex and perirhinal cortex, respectively, both important to memory formation and function.
Gone, But Not Forgotten
UC San Diego scientists recall EP, perhaps the world’s second-most famous amnesiac
An international team of neuroscientists has described for the first time in exhaustive detail the underlying neurobiology of an amnesiac who suffered from profound memory loss after damage to key portions of his brain.
Writing in this week’s Online Early Edition of PNAS, principal investigator Larry R. Squire, PhD, professor in the departments of Neurosciences, Psychiatry and Psychology at the University of California, San Diego School of Medicine and Veteran Affairs San Diego Healthcare System (VASDHS) – with colleagues at UC Davis and the University of Castilla-La Mancha in Spain – recount the case of EP, a man who suffered radical memory loss and dysfunction following a bout of viral encephalitis.
EP’s story is strikingly similar to the more famous case of HM, who also suffered permanent, dramatic memory loss after small portions of his medial temporal lobes were removed by doctors in 1953 to relieve severe epileptic seizures. The surgery was successful, but left HM unable to form new memories or recall people, places or events post-operation.
HM (later identified as Henry Gustav Molaison) was the subject of intense scientific scrutiny and study for the remainder of his life. When he died in 2008 at the age of 82, he was popularized as “the world’s most famous amnesiac.” His brain was removed and digitally preserved at The Brain Observatory, a UC San Diego-based lab headed by Jacopo Annese, PhD, an assistant adjunct professor in the Department of Radiology and a co-author of the PNAS paper.
Like Molaison, EP was also something of a scientific celebrity, albeit purposefully anonymous. In 1992, at the age of 70, he was diagnosed with viral encephalitis. He recovered, but the illness resulted in devastating neurological loss, both physiologically and psychologically.
Not only did he also lose the ability to form new memories, EP suffered a modest impairment in his semantic knowledge – the knowledge of things like words and the names of objects. Between 1994, when he moved to San Diego County, and his death 14 years later, EP was a subject of continued study, which included hundreds of different assessments of cognitive function.
“The work was long-term,” said Squire, a Career Research Scientist at the VASDHS. “We probably visited his house 200 times. We knew his family.” In a 2000 paper, Squire and colleagues described EP as a 6-foot-2, 192-pound affable fellow with a fascination for the computers used in his testing. He was always agreeable and pleasant. “He had a sense of humor,” said Squire.
Schwann cells (colored purple) forming myelin sheathes (green) around axons (brown). Image courtesy of David Furness, Wellcome Images.
Pinning Down the Pain
Schwann cell protein plays major role in neuropathic pain
An international team of scientists, led by researchers at the University of California, San Diego School of Medicine, says a key protein in Schwann cells performs a critical, perhaps overarching, role in regulating the recovery of peripheral nerves after injury. The discovery has implications for improving the treatment of neuropathic pain, a complex and largely mysterious form of chronic pain that afflicts over 100 million Americans.
The findings are published in the March 27, 2013 issue of the Journal of Neuroscience.
Neuropathic pain occurs when peripheral nerve fibers (those outside of the brain and spinal cord) are damaged or dysfunctional, resulting in incorrect signals sent to the brain. Perceived pain sensations are frequently likened to ongoing burning, coldness or “pins and needles.” The phenomenon also involves changes to nerve function at both the injury site and surrounding tissues.
Not surprisingly, much of the effort to explain the causes and mechanisms of neuropathic pain has focused upon peripheral nerve cells themselves. The new study by principal investigator Wendy Campana, PhD, associate professor in UC San Diego’s Department of Anesthesiology, with colleagues at UC San Diego and in Japan, Italy and New York, points to a surprisingly critical role for Schwann cells – a type of glial support cell.
Schwann cells promote the growth and survival of neurons by releasing molecules called trophic factors, and by supplying the myelin used to sheathe neuronal axons. Myelination of axons helps increase the speed and efficacy of neural impulses, much as plastic insulation does with electrical wiring.
“When Schwann cells are deficient they can’t perform these functions,” said Campana. “Impaired neurons remain impaired and acute damage may transition to become chronic damage, which can mean lasting neuropathic pain for which there is currently no effective treatment.”
Specifically, the scientists investigated a protein called LRP1, which Campana and colleagues had first identified in 2008 as a potential basis for new pain-relieving drugs due to its signal-blocking, anti-inflammatory effects.
The researchers found that mice genetically engineered to lack the gene that produces LRP1 in Schwann cells suffered from abnormalities in axon myelination and in Remak bundles – multiple non-myelinated pain transmitting axons grouped together by Schwann cells. In both cases, one result was neuropathic pain, even in the absence of an actual injury.
Moreover, injured mice lacking the LRP1 gene showed accelerated cell death and poor neural repair compared to controls, again resulting in significantly increased and sustained neuropathic pain and loss of motor function.
“LRP1 helps mediate normal interactions between Schwann cells and axons and, when peripheral nerves have been injured, plays a critical role in regulating the steps that lead to eventual nerve regeneration,” said Campana. “When LRP1 is deficient, defects and problems become worse. They may go from acute to chronic, with increasing levels of pain.”
Campana and others are now pursuing development of a small molecule drug that can mimic LRP1, binding to receptors in Schwann cells to improve their health and ability to repair damaged nerve cells. “By targeting Schwann cells and LRP1, I think we can improve cells’ response to injury, including reducing or eliminating chronic neuropathic pain.”
Rewriting a Receptor’s Role
Synaptic molecule works differently than thought; may mean new therapeutic targets for treating Alzheimer’s disease
In a pair of new papers, researchers at the University of California, San Diego School of Medicine and the Royal Netherlands Academy of Arts and Sciences upend a long-held view about the basic functioning of a key receptor molecule involved in signaling between neurons, and describe how a compound linked to Alzheimer’s disease impacts that receptor and weakens synaptic connections between brain cells.
The findings are published in the Feb. 18 early edition of the Proceedings of the National Academy of Sciences.
Long the object of study, the NMDA receptor is located at neuronal synapses – the multitudinous junctions where brain cells trade electrical and chemical messages. In particular, NMDA receptors are ion channels activated by glutamate, a major “excitatory” neurotransmitter associated with cognition, learning and memory.
“NMDA receptors are well known to allow the passage of calcium ions into cells and thereby trigger biochemical signaling,” said principal investigator Roberto Malinow, MD, PhD professor of neurosciences at UC San Diego School of Medicine.
The new research, however, indicates that NMDA receptors can also operate independent of calcium ions. “It turns upside down a view held for decades regarding how NMDA receptors function,” said Malinow, who holds the Shiley-Marcos Endowed Chair in Alzheimer’s Disease Research in Honor of Dr. Leon Thal (a renowned UC San Diego Alzheimer’s disease researcher who died in a single-engine airplane crash in 2007).
Specifically, Malinow and colleagues found that glutamate binding to the NMDA receptor caused conformational changes in the receptor that ultimately resulted in a weakened synapse and impaired brain function.
They also found that beta amyloid – a peptide that comprises the neuron-killing plaques associated with Alzheimer’s disease – causes the NMDA receptor to undergo conformational changes that also lead to the weakening of synapses.
“These new findings overturn commonly held views regarding synapses and potentially identify new targets in the treatment of Alzheimer’s disease,” said Malinow.
Using serial block face scanning electron microscopy and other technologies, researchers created three-dimensional images of the neocortex of transgenic mice engineered to over-express the human protein, alpha-synuclein, and noted massively enlarged nerve terminals. In this image, an over-sized terminal (green) forms a synapse (red) with a dendritic spine (golden). A normal and smaller terminal (blue) forms a synapse with an adjacent spine on the same dendrite. Image courtesy of the National Center for Microscopy and Imaging Research, UC San Diego.
Excess Protein Linked to Development of Parkinson’s Disease
Accumulation appears to progressively disrupt neuronal function and viability
Researchers at the University of California, San Diego School of Medicine say overexpression of a protein called alpha-synuclein appears to disrupt vital recycling processes in neurons, starting with the terminal extensions of neurons and working its way back to the cells’ center, with the potential consequence of progressive degeneration and eventual cell death.
The findings, published in the February 6, 2013 issue of The Journal of Neuroscience, have major implications for more fully understanding the causes and mechanisms of Parkinson’s disease (PD), a neurodegenerative movement disorder that affects an estimated one million Americans.
“This is an important new insight. I don’t think anybody realized just how big a role alpha-synuclein played in managing the retrieval of worn-out proteins from synapses and the role of alterations in this process in development of PD,” said principal investigator Mark H. Ellisman, PhD, professor of neurosciences and bioengineering and director of the National Center for Microscopy and Imaging Research (NCMIR), based at UC San Diego.
Parkinson’s disease is characterized by the gradual destruction of select brain cells that produce dopamine, a neurotransmitter involved in regulating movement and emotion. Symptoms include increasing loss of muscle and movement control. While most cases are sporadic – that is, their causes are unknown – there are also inherited forms of PD linked to specific gene mutations and modifications.
The UC San Diego researchers, with colleagues at the University of Illinois, Urbana, focused upon one of those gene products: alpha-synuclein. Using a variety of leading-edge imaging technologies, including a new fluorescent tagging technique developed for electron microscopy by UC San Diego Nobel laureate Roger Tsien’s lab and colleagues at NCMIR, the scientists created three-dimensional maps of alpha-synuclein distribution both in cultured neurons and in the neurons of mice engineered to over-express the human protein.
They found that excess levels of alpha-synuclein accumulated in the presynaptic terminal – part of the junction where axons and dendrites of brain cells meet to exchange chemical signals.
“The over-expression of alpha-synuclein caused hypertrophy in these terminals,” said Daniela Boassa, PhD, a research scientist at NCMIR and the study’s first author. “The terminals were enlarged, filled with structures we normally don’t see.”
Confocal micrograph of a primary human fibroblast cell grown in culture stained blue for actin, a highly abundant protein that makes up the cytoskeleton of cells. Energy-producing mitochondria are shown in green. Image courtesy of Matthew Daniels, University of Oxford and Wellcome Images.
Regulating Single Protein Prompts Fibroblasts to Become Neurons
Repression of a single protein in ordinary fibroblasts is sufficient to directly convert the cells – abundantly found in connective tissues – into functional neurons. The findings, which could have far-reaching implications for the development of new treatments for neurodegenerative diseases like Huntington’s, Parkinson’s and Alzheimer’s, will be published online in advance of the January 17 issue of the journal Cell.
In recent years, scientists have dramatically advanced the ability to induce pluripotent stem cells to become almost any type of cell, a major step in many diverse therapeutic efforts. The new study focuses upon the surprising and singular role of PTB, an RNA-binding protein long known for its role in the regulation of alternative RNA splicing.
In in vitro experiments, scientists at University of California, San Diego School of Medicine and Wuhan University in China describe the protein’s notable regulatory role in a feedback loop that also involves microRNA – a class of small molecules that modulate the expression of up to 60 percent of genes in humans. Approximately 800 miRNAs have been identified and characterized to various degrees.
One of these miRNAs, known as miR-124, specifically modulates levels of PTB during brain development. The researchers found that when diverse cell types were depleted of PTB, they became neuronal-like cells or even functional neurons – an unexpected effect. The protein, they determined, functions in a complicated loop that involves a group of transcription factors dubbed REST that silences the expression of neuronal genes in non-neuronal cells.
According to principal investigator Xiang-Dong Fu, PhD, professor of cellular and molecular medicine at UC San Diego, it’s not known which neuronal signal or signals turn on the loop, which in principle can happen at any point in the circle. But the ability to artificially manipulate PTB levels in cells, inducing them to become neurons, offers tantalizing possibilities for scientists seeking new treatments for an array of neurodegenerative diseases.
It is estimated that over a lifetime, one in four Americans will suffer from a neurodegenerative disease, from Alzheimer’s and Parkinson’s to multiple sclerosis and amyotrophic lateral sclerosis (Lou Gehrig’s disease).
“All of these diseases are currently incurable. Existing therapies focus on simply trying to preserve neurons or slow the rate of degeneration,” said Fu. “People are working with the idea of replacing lost neurons using embryonic stem cells, but there are a lot of challenges, including issues like the use of foreign DNA and the fact that it’s a very complex process with low efficiency.”
How the Nose Knows
Whether we’re awake or asleep, and whether an odor is familiar or new, appears to determine our response to smells. Since we know that smells are highly evocative as well as serving to warn us of danger like smoke or spoiled foods, how the brain perceives odors is of interest to scientists.
Researchers at the University of California, San Diego School of Medicine wondered how sensory representations, in this case the sense of smell, are shaped by the state of an animal and its history. They studied this question in the mouse olfactory bulb, the part of the brain involved in the perception of odors.
Their major conclusion is that the way in which sensory information such as odor is represented isn’t fixed or static, but highly dynamic and flexible. It is modulated by brain state such as wakefulness, experience, even by simple sensory exposure to smells. According to the researchers, his could be the basis of why novel or unfamiliar odors are such noticeable stimuli for humans, compared to familiar odors.
Using a powerful means for monitoring the activity of brain neurons in mammals – called two-photon calcium imaging – the UC San Diego team, headed by Takaki Komiyama, PhD, assistant professor in the UCSD Department of Neurosciences, recorded the activity of specific neuronal cell types in mice, following the activity of the same set of neurons over days, weeks and months.
With this technique, the researchers explored how wakefulness and odor experience modulate the activity of two neuron types in the olfactory bulb, namely mitral cells – the principal neurons of the bulb – and granule cells, very small brain cells that account for nearly half of the neurons in the central nervous system. Granule cells are the major class of interneurons that inhibit mitral cells.
The team imaged the activity of mitral and granule cell populations in awake mice, and subsequently anesthetized the mice to find out how odor representations differ between the awake and anesthetized state. They found that anesthesia increases odor responses of mitral cells. In contrast, granule cell activity is dramatically reduced with anesthesia. These results suggest that, in awake animals, mitral cell odor representations are made sparse by the action of local inhibitory circuits, and that studies in anaesthetized animals may have underestimated the actions of granule cells.
Next, the researchers looked at how mitral cell odor representations in awake mice are shaped by experience. By monitoring the response of same sets of mitral cells to a panel of odors, they found that repeated odor experience causes a gradual lessening of mitral cell responses which accumulates across days. This change is odor-specific – the same mitral cells still respond strongly to other smells. The plasticity, or ability of the neuronal connection to change in strength, recovers gradually over months.
“Intriguingly, this plasticity is not expressed when the mouse is tested under anesthesia, indicating that wakefulness plays a key role in the dynamic nature of mitral cell odor representations,” Komiyama said.
“All available evidence from comparative genetics and neuroanatomy suggests that mouse and human olfactory systems function similarly,” he added. “We have many reasons to believe that what we found in this study in mice directly translates to the perception of odors in humans.”
We as a bird
Almost 50 years ago, UC San Diego neuro-psychiatrist Harvey J. Karten, MD, then 30 years old and working at Massachusetts Institute of Technology, and colleagues discovered that a region of the avian brain (he was studying auditory and visual pathways, in particular) was surprisingly similar to a distinctly different looking region of the mammalian brain, including humans.
Notably, they reported that neural inputs and outputs into the dorsal ventricular ridge (DVR), a cluster of neurons found in bird (and reptile) brains, was strikingly similar to the functioning of the neocortex in mammalian brains.
Here’s the kicker: The neocortex is a part of the brain’s outer layer where higher-order processing is thought to occur. Research at the time posited that the neocortex was unique to mammals, and perhaps responsible for their presumed greater cognitive powers. Karten’s findings threatened to upend that notion of singularity. More importantly, it suggested a shared evolutionary history with mammalian cortex, one that predated the evolutionary separation of mammals and birds. And it proposed a mechanism of cortical development in mammals that was clearly at odds with the prevailing notions.
Ever since, the debate over similarities (and their significance) between the brains of mammalian and non-mammalian vertebrates has rumbled along. Karten has steadfastly pursued it, most recently in a 2010 PNAS paper that demonstrated that the microcircuitry in the region of the avian brain that processes auditory signals (hearing) is similar to the region of the mammalian brain responsible for the same function.
Final confirmation that Karten and colleagues were right, however, may have come earlier this month with the report (also in PNAS) by researchers at the University of Chicago, who tested Karten’s 47 -year-old hypothesis by using new molecular markers capable of identifying specific neuron types in the mammalian cortex, then looking to see if the same marker genes were expressed in DVR nuclei in the brains of chickens and zebra finch.
They were. The neurons of the avian DVR are homologous to those of the mammalian neocortex.
“Here was a completely different line of evidence,” said Clifton Ragsdale, PhD, an associate professor of neurobiology and senior author of the study. “There were molecular makers that picked out specific layers of cortex; whereas the original Karten theory was based just on connections, and some people dismissed that. But in two very different birds, all of the gene expression fits together very nicely with the connections.
It’s welcome, if expected, news for Karten.
“I recall that my mentor, the distinguished neuroanatomist Walle J. H. Nauta, cautioned me about not hoping for much of an enthusiastic reception. He said that for really novel, iconoclastic ideas, it can take 40 years before they are accepted. This is closer to 50 years! The most exciting part of the story will be watching how this may serve as a foundation for exciting new research into the evolution and development of the mammalian cortex by the next generation of bright young scientists.”
Confirming functional similarities between avian and mammalian brains does more than just end an old argument. It opens up new avenues of investigation for neuroscientists, who now have another animal model to study. They can compare developmental steps between more, diverse organisms. They can look at how neurons take different form to provide the same function and how their differences impact behaviors and abilities, notably communication skills.
More fundamentally, scientists are slightly closer to addressing the ultimate question of evolution: How did humans get from there to here?
Part of the answer, it now appears, lies in the part of your brain that behaves like a bird’s.