The cerebellum is an important structure for accurate control and timing of movement, and Purkinje neurons in the cerebellar cortex are key players in cerebellar motor control. Cerebellar dysfunction can result in ataxia, a disorder characterized by postural instability, gait disturbances and motor incoordination. Cerebellar ataxia is a symptom of a number of conditions, and the emerging evidence that Purkinje neuron dysfunction, in particular, abnormal Purkinje neuron repetitive firing, is a major driver of motor dysfunction in a subset of dominantly inherited ataxias is dicussed. Abnormalities in Purkinje neuron excitability that are observed in mouse models of each of these disorders, and where appropriate describe studies linking particular ion channels to aberrant excitability are also discussed. Common mechanisms of dysfunction and speculate about potential therapeutic targets, suggesting that Purkinje neuron firing abnormalities are a novel target for improving motor dysfunction in patients with some forms of dominantly inherited ataxia are proposed.
atrophy; cerebellum; dominantly inherited ataxia; intrinsic excitability; ion channel; pacemaking; polyglutamine disorder; Purkinje neuron; spinocerebellar ataxia
The article by Lambert et al. reports the identification of 11 novel susceptibility loci for late-onset Alzheimer’s disease. The observations of this study significantly enhance the field since they further disentangle the genetic causes and pathways underlying Alzheimer’s disease by identifying novel disease-associated variants clustering in specific pathways. These pathways include APP processing, lipid metabolism, inflammation/immune response, intracellular trafficking/endocytosis, tau metabolism, synaptic function. All of the newly identified disease-associated variants have small effect sizes with increases in risk of 10–20%. The cumulative population attributable fraction associated with known genetic variants amounts now to approximately 80%. This article also underlines the ongoing value of genome-wide association studies for identification of causative common variants in the era of whole-exome and whole-genome sequencing studies.
Alzheimer’s disease; genes
Of the numerous inherited diseases known to afflict the pediatric population, spinal muscular atrophy (SMA) is among the most common. It has an incidence of approximately one in 10,000 newborns and a carrier frequency of one in 50. Despite its relatively high incidence, SMA remains somewhat obscure among the many neurodegenerative diseases that affect humans. Nevertheless, the last two decades have witnessed remarkable progress in our understanding of the pathology, underlying biology and especially the molecular genetics of SMA. This has led to a genuine expectation within the scientific community that a robust treatment will be available to patients before the end of the decade. The progress made in our understanding of SMA and, therefore, towards a viable therapy for affected individuals is in large measure a consequence of the simple yet fascinating genetics of the disease. Nevertheless, important questions remain. Addressing these questions promises not only to accelerate the march towards a cure for SMA, but also to uncover novel therapies for related neurodegenerative disorders. This review discusses our current understanding of SMA, considers the challenges ahead, describes existing treatment options and highlights state-of-the-art research being conducted as a means to a better, safer and more effective treatment for the disease.
animal models; motor neuron; neurodegeneration; spinal muscular atrophy; survival motor neuron
We are studying the projections from the entorhinal cortex to the hippocampal formation in the mouse. The dentate gyrus is innervated by the lateral entorhinal cortex (lateral perforant path) and medial entorhinal cortex (medial perforant path). The entorhinal cortex also projects to hippocampal areas CA3 and CA1, and to the subiculum. In young transgenic Alzheimer’s disease mouse models (before amyloid-β pathology), the connections are not different from normal mice. In Alzheimer’s disease mice with pathology, two changes occur: first, dystrophic axon endings appear near amyloid-β plaques, and second, there are sparse aberrant axon terminations not in the appropriate area or lamina of the hippocampus. Furthermore, MRI–diffusion tensor imaging analysis indicates a decrease in the quality of the white matter tracts connecting the hippocampus to the brain; in other words, the fimbria/fornix and perforant path. Similar changes in white matter integrity have been found in Alzheimer’s disease patients and could potentially be used as early indicators of disease onset.
entorhinal cortex; hippocampus; limbic system; perforant path; tractography
bariatric surgery; BMI; diet; exercise; headache; migraine; obesity
While the mammalian brain is highly dependent on oxygen, and can withstand only a few minutes without air, there are both vertebrate and invertebrate examples of anoxia tolerance. One example is the freshwater turtle, which can withstand days without oxygen, thus providing a vertebrate model with which to examine the physiology of anoxia tolerance without the pathology seen in mammalian ischemia/reperfusion studies. Insect models such as Drosophila melanogaster have additional advantages, such as short lifespans, low cost and well-described genetics. These models of anoxia tolerance share two common themes that enable survival without oxygen: entrance into a state of deep hypometabolism, and the suppression of cellular injury during anoxia and upon restoration of oxygen. The study of such models of anoxia tolerance, adapted through millions of years of evolution, may thus suggest protective pathways that could serve as therapeutic targets for diseases characterized by oxygen deprivation and ischemic/reperfusion injuries.
anoxia; brain; Drosophila melanogaster; heat shock protein; hypometabolism; neuroprotection; oxidative stress; PKG; potassium channel; Trachemys scripta
Brain metabolism declines with age and do so in an accelerated manner in neurodegenerative disorders. Noninvasive neuroimaging techniques have played an important role to identify the metabolic biomarkers in aging brain. Particularly, PET with fluorine-18 (18F)-labeled 2-fluoro-2-deoxy-d-glucose tracer and proton magnetic resonance spectroscopy (MRS) have been widely used to monitor changes in brain metabolism over time, identify the risk for Alzheimer’s disease (AD) and predict the conversion from mild cognitive impairment to AD. Novel techniques, including PET carbon-11 Pittsburgh compound B, carbon-13 and phosphorus-31 MRS, have also been introduced to determine Aβ plaques deposition, mitochondrial functions and brain bioenergetics in aging brain and neurodegenerative disorders. Here, we introduce the basic principle of the imaging techniques, review the findings from 2-fluoro-2-deoxy-d-glucose-PET, Pittsburgh compound B PET, proton, carbon-13 and phosphorus-31 MRS on changes in metabolism in normal aging brain, mild cognitive impairment and AD, and discuss the potential of neuroimaging to identify effective interventions and treatment efficacy for neurodegenerative disorders.
Aβ plaques; aging; Alzheimer’s disease; APOE4; glucose metabolism; magnetic resonance spectroscopy; mild cognitive impairment; mitochondrial function; PET
The formation of cerebral aneurysms and their rupture propensity is of immediate clinical importance. Current management includes observation with expectant management, microsurgical clipping and/or endovascular coiling. The surgical options are invasive and are not without increased risk despite the technological advances. Recent human and animal studies have shown that inflammation plays a critical role in aneurysm formation and progression to rupture. Modulating this inflammatory process may prove to be clinically significant. This review will discuss cerebral aneurysm pathogenesis with a focus on current and future research of potential use of pharmaceutical agents that attenuate inflammation in the aneurysm wall leading to decreased risk of aneurysm rupture.
cerebral aneurysm; ferumoxytol; inflammation; macrophages; subarachnoid hemorrhage
The revised ‘expanded’ neurovascular unit (eNVU) is a physiological and functional unit encompassing endothelial cells, pericytes, smooth muscle cells, astrocytes and neurons. Ischemic stroke and traumatic brain injury are acute brain injuries directly affecting the eNVU with secondary damage, such as blood–brain barrier (BBB) disruption, edema formation and hypoperfusion. BBB dysfunctions are observed at an early postinjury time point, and are associated with eNVU activation of proteases, such as tissue plasminogen activator and matrix metalloproteinases. BBB opening is accompanied by edema formation using astrocytic AQP4 as a key protein regulating water movement. Finally, nitric oxide dysfunction plays a dual role in association with BBB injury and dysregulation of cerebral blood flow. These mechanisms are discussed including all targets of eNVU encompassing endothelium, glial cells and neurons, as well as larger blood vessels with smooth muscle. In fact, the feeding blood vessels should also be considered to treat stroke and traumatic brain injury. This review underlines the importance of the eNVU in drug development aimed at improving clinical outcome after stroke and traumatic brain injury.
aquaporin-4; blood–brain barrier; cerebral blood flow; edema; expanded neurovascular unit; ischemic stroke; matrix metalloproteinases; nitric oxide; tissue plasminogen activator; traumatic brain injury
Modern approaches to the investigation of the molecular mechanisms underlying human cognitive disease often include multidisciplinary examination of animal models engineered with specific mutations that spatially and temporally restrict expression of a gene of interest. This approach not only makes possible the development of animal models that demonstrate phenotypic similarities to their respective human disorders, but has also allowed for significant progress towards understanding the processes that mediate synaptic function and memory formation in the nondiseased state. Examples of successful mouse models where genetic manipulation of the mouse resulted in recapitulation of the symptomatology of the human disorder and was used to significantly expand our understanding of the molecular mechanisms underlying normal synaptic plasticity and memory formation are discussed in this article. These studies have broadened our knowledge of several signal transduction cascades that function throughout life to mediate synaptic physiology. Defining these events is key for developing therapies to address disorders of cognitive ability.
Alzheimer’s disease; Angelman syndrome; autism; hippocampus; knockout mouse; neurofibromatosis type 1; Reelin; Rubinstein-Taybi syndrome; secretin; synaptic plasticity
Fragile X-associated disorders (FXD) are a group of disorders caused by expansion of non-coding CGG repeat elements in the fragile X (FMR1) gene. One of these disorders, fragile X syndrome (FXS), is the most common heritable cause of intellectual disability, and is caused by large CGG repeat expansions (>200) resulting in silencing of the FMR1 gene. An increasingly recognized number of neuropsychiatric FXD have recently been identified that are caused by ‘premutation’ range expansions (55-200). These disorders are characterized by a spectrum of neuropsychiatric manifestations ranging from an increased risk of neurodevelopmental, mood and anxiety disorders to neurodegenerative phenotypes such as the fragile X-associated tremor ataxia syndrome (FXTAS). Here, we review advances in the clinical understanding of neuropsychiatric disorders in premutation carriers across the lifespan and offer guidance for the detection of such disorders by practicing psychiatrists and neurologists.
FMR1; Fragile X Syndrome; Fragile X Premutation; Fragile X-associated Tremor Ataxia Syndrome; FXTAS; Depression; Anxiety; Autism; ASD; ADHD
Astrocytes are the predominant glial cell type in the CNS. Although astrocytes are electrically nonexcitable, their excitability is manifested by their Ca2+ signaling, which serves as a mediator of neuron–glia bidirectional interactions via tripartite synapses. Studies from in vivo two-photon imaging indicate that in healthy animals, the properties of spontaneous astrocytic Ca2+ signaling are affected by animal species, age, wakefulness and the location of astrocytes in the brain. Intercellular Ca2+ waves in astrocytes can be evoked by a variety of stimulations. In animal models of some brain disorders, astrocytes can exhibit enhanced Ca2+ excitability featured as regenerative intercellular Ca2+ waves. This review first briefly summarizes the astrocytic Ca2+ signaling pathway and the procedure of in vivo two-photon Ca2+ imaging of astrocytes. It subsequently summarizes in vivo astrocytic Ca2+ signaling in health and brain disorders from experimental studies of animal models, and discusses the possible mechanisms and therapeutic implications underlying the enhanced Ca2+ excitability in astrocytes in brain disorders. Finally, this review summarizes molecular genetic approaches used to selectively manipulate astrocyte function in vivo and their applications to study the role of astrocytes in synaptic plasticity and brain disorders.
Alzheimer's disease; G-protein coupled receptors; in vivo imaging; intercellular Ca2+ waves; IP3 receptor; molecular genetics; photothrombosis; spontaneous Ca2+ signaling; status epilepticus; traumatic brain injury; two-photon microscopy
In this article, the authors aim to introduce the nonradiologist to
diffusion tensor imaging (DTI) and its applications to both clinical and
research aspects of tuberous sclerosis complex. Tuberous sclerosis complex is a
genetic neurocutaneous syndrome with variable and unpredictable neurological
comorbidity that includes refractory epilepsy, intellectual disability,
behavioral abnormalities and autism spectrum disorder. DTI is a method for
modeling water diffusion in tissue and can noninvasively characterize
microstructural properties of the brain. In tuberous sclerosis complex, DTI
measures reflect well-known pathological changes. Clinically, DTI can assist
with detecting the epileptogenic tuber. For research, DTI has a putative role in
identifying potential disease biomarkers, as DTI abnormalities of the white
matter are associated with neurocognitive morbidity including autism. If indeed
DTI changes parallel phenotypical changes related to the investigational
treatment of epilepsy, cognition and behavior with mTOR inhibitors, it will
facilitate future clinical trials.
autism spectrum disorders; behavior; cognition; diffusion tensor imaging; epilepsy; MRI; mTOR serine–threonine kinases; tuberous sclerosis complex
Few specific therapeutic targets exist to manage brain injury, despite
the prevalence of stroke or traumatic brain injury. With traumatic brain injury,
characteristic neuronal changes include axonal swelling and degeneration, and
the loss of synapses, the sites of communication between neurons. This is
followed by axonal sprouting and alterations in synaptic markers in recovery.
The resulting changes in neuronal connectivity are likely to contribute to the
effects of traumatic brain injury on cognitive functions and the underlying
mechanisms may represent points of therapeutic intervention. In agreement,
animal studies implicate adhesion and signaling molecules that organize synapses
as molecular players in neuronal recovery. In this article, the authors focus on
the role of cell surface interactions in the recovery after brain injury in
humans and animals. The authors review cellular and synaptic alterations that
occur with injury and how changes in cell adhesion, protein expression and
modification may be involved in recovery. The changes in neuronal surface
interactions as potential targets and their possible value for the development
of therapeutics are also discussed.
brain injury; cellular adhesion; dendritic spines; neuronal adhesion proteins; recovery; repair; synapse organizing proteins; synapses; traumatic brain injury
The Second Muscular Dystrophy Association Scientific Meeting was held on 21–24 April 2013 in Washington (DC, USA). The meeting provided an opportunity for research scientists, clinicians, government agencies and industry experts to highlight and discuss different aspects of therapy development for neuromuscular diseases, including novel targets, biomarkers, therapeutic approaches, animal models and clinical trials. With 500 participants, 66 presentations and 200 abstracts, the 3-day conference has become a central focus for scientists interested in translational research and moving potential therapies forward from the bench to the bedside. Key issues covered by the meeting included the need to identify new drugs to treat patients with neuromuscular diseases and the importance of establishing collaborations between government, academic and industry sectors toward an efficient and rigorous translational path for neuromuscular diseases.
CD200 and its receptor, CD200 receptor (CD200R), have uniaue roles in controlling damaging inflammatory processes. At present, the only identified function for CD200 is as a ligand for CD200R. These proteins interact resulting in the activation of anti-inflammatory signaling by CD200R-expressing cells. When this interaction becomes deficient with aging or disease, chronic inflammation occurs, Experimental animal studies have demonstrated the consequences of disrupting CD200–CD200R interactions in the brain, but there have been few studies in human brains. Deficiency in neuronal CD200 may explain the chronic inflammation in human neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis; however, deficits in the microglial expression of CD200R may also be of functional significance. The purpose of this review is to assess the data regarding the role of CD200–CD200R interactions in relation to the brain in order to determine if this could be a therapeutic target for human brain diseases with inflammatory components, and what additional studies are needed.
aging; alternative activation; anti-inflammatory signaling; cell surface protein; endogenous inflammatory regulator; inflammation; neurodegenerative disease; neuropathology
progressive hearing loss; age-related hearing loss; deafness; DNFB77; hair cells; LOXHD1; stereocilia; PLAT domain
Huntington disease (HD) is a devastating illness, although its autosomal dominant genetic transmission allows a unique opportunity to study apparently healthy individuals before manifest disease. Attempts to study early disease are not unique in neurology (e.g., Mild Cognitive Impairment, Vascular Cognitive Impairment), but studying otherwise-healthy appearing individuals who will go on with nearly 99% certainty to manifest the symptoms of brain disease does provide distinct but valuable information about the true natural history of the disease. The field has witnessed an explosion of research examining possible early indicators of HD during what is now referred to as the “prodrome” of HD. A NIH study in its ninth year (PREDICT-HD) has offered a glimpse into the transition from an apparently healthy state to an obviously diseased state, and can serve as a model for many other genetic diseases, both neurological and non-neurological.
Huntington disease; diagnosis; detection; prevention; biomarkers; clinical endpoints; clinical trials
Synaptic communication is highly regulated process of contact between cells allowing information to be stored and modified. Synaptic formation and maturation is the result of interactions between intrinsic genetic/molecular factors and the external environment to establish the communication in the brain. One disorder associated with faulty synapse communication is Rett Syndrome (RTT). RTT is the leading form of severe MR in females, affecting approximately 1:10,000 females worldwide, without predisposition to any particular racial or ethnic group. Mutations in MECP2, the gene encoding methyl-CpG-binding protein-2, have been identified in more than 95% of individuals with RTT. Birth and the milestones of early development appear to be normal in individuals with RTT until approximately 6–18 months when in the subsequent months and years that follows, physical, motor, and social-cognitive development enter a period of regression. The clinical management of these individuals is extremely multifaceted, relying on collaborations of specialists and researchers from many different fields. In this critical literature review, we provide an overview of Rett Syndrome, from patient to pathophysiology with a therapeutic summary of clinical trials in RTT and preclinical studies using mouse and cell models of RTT.
Rett Syndrome; MeCP2; Neurodevelopmental Disorders; Clinical Trials
Autism spectrum disorders are neurodevelopmental disorders characterized by significant deficits in reciprocal social interactions, impaired communication and restricted, repetitive behaviors. As autism spectrum disorders are among the most heritable of neuropsychiatric disorders, much of autism research has focused on the search for genetic variants in protein-coding genes (i.e., the ‘trees’). However, no single gene can account for more than 1% of the cases of autism spectrum disorders. Yet, genome-wide association studies have often identified statistically significant associations of genetic variations in regions of DNA that do not code for proteins (i.e., intergenic regions). There is increasing evidence that such noncoding regions are actively transcribed and may participate in the regulation of genes, including genes on different chromosomes. This article summarizes evidence that suggests that the research spotlight needs to be expanded to encompass far-reaching gene-regulatory mechanisms that include a variety of epigenetic modifications, as well as noncoding RNA (i.e., the ‘forest’). Given that noncoding RNA represents over 90% of the transcripts in most cells, we may be observing just the ‘tip of the iceberg’ or the ‘edge of the forest’ in the genomic landscape of autism.
autism spectrum disorder phenotypes; ‘dark matter’ RNA; epigenetics; future therapeutic options; gene–environment interaction; genetics; new research paradigm
Treatment of visual hallucinations in neurodegenerative disorders is not well advanced. The complexity of underlying mechanisms presents a number of potential avenues for developing treatments, but also suggests that any single one may be of limited efficacy. Reducing medication, with the careful introduction of antidementia medication if needed, is the mainstay of current management. Antipsychotic medication leads to excessive morbidity and mortality and should only be used in cases of high distress that do not otherwise respond. Education, reduction of risk factors and psychological treatments have limited evidence of efficacy, but are unlikely to cause harm.
Alzheimer’s disease; amyloidopathy; Lewy body; Parkinson’s disease; synucleinopathy; tauopathy; treatment; visual hallucination
Our elderly population is growing and declines in cognitive abilities, such as memory, can be costly, because it can interfere with a person’s ability to live independently. The NMDA receptor is very important for many different forms of memory and this receptor is negatively affected by aging. This review examines the progress that has been made recently in characterizing selective vulnerabilities of different subunits and splice variants of the NMDA receptor to normal aging in C57BL/6 mice. Evidence is also presented for changes in the relationships of NMDA receptors to plasticity across aging. Recent interventions show that enhancing NMDA receptors in aged individuals is associated with improvements in memory, but mouse models of neurodegenerative diseases suggest that finding the right balance between too little and too much NMDA receptor activity will be the key to enhancing memory without inducing pathology.
frontal cortex; GluN1 (NR1; ζ1) subunit; GluN2B (NR2B; ε2) subunit; glutamate receptor; hippocampus; splice variants
In this article, we will describe the malignant synaptic growth hypothesis of Alzheimer’s disease. Originally presented in 1994, the hypothesis remains a viable model of the functional and biophysical mechanisms underlying the development and progression of Alzheimer’s disease. In this article, we will refresh the model with references to relevant empirical support that has been generated in the intervening two decades since it’s original presentation. We will include discussion of its relationship, in terms of points of alignment and points of contention, to other models of Alzheimer’s disease, including the cholinergic hypothesis and the tau and β-amyloid models of Alzheimer’s disease. Finally, we propose several falsifiable predictions made by the malignant synaptic growth hypothesis and describe the avenues of treatment that hold the greatest promise under this hypothesis.
β amyloid; acetylcholine; Alzheimer’s; computational model; dementia; excitotoxicity; long-term potentiation; neurofibrillary tangles; plasticity; tau
Current treatments for epilepsy suffer from significant limitations, including medical intractability and lack of disease-modifying or anti-epileptogenic actions. As most current seizure medications modulate ion channels and neurotransmitter receptors, more effective therapies likely need to target completely different mechanisms of action. The mammalian target of rapamycin (mTOR) pathway represents a potential novel therapeutic target for epilepsy. mTOR inhibitors can suppress seizures and prevent epilepsy in animal models of certain genetic epilepsies, such as tuberous sclerosis complex. mTOR inhibitors may also be effective in some models of acquired epilepsy related to brain injury, but these effects are more variable and dependent on a number of factors. Some clinical data suggest that mTOR inhibitors decrease seizures in tuberous sclerosis complex patients, but controlled trials are lacking and no clinical data on potential anti-epileptogenic actions exist. Future basic and clinical research will help to determine the full potential of mTOR inhibitors for epilepsy.
epilepsy; rapamycin; seizure; tuberous sclerosis