Jessica A. Panzer

In Vivo Imaging of Preferential Motor Axon Outgrowth to and Synaptogenesis at Prepatterned Acetylcholine Receptor Clusters in Embryonic Zebrafish Skeletal Muscle

Little is known about the spatial and temporal dynamics of presynaptic and postsynaptic specializations that culminate in synaptogenesis. Here, we imaged presynaptic vesicle clusters in motor axons and postsynaptic acetylcholine receptor (AChR) clusters in embryonic zebrafish to study the earliest events in synaptogenesis in vivo. Prepatterned AChR clusters are present on muscle fibers in advance of motor axon outgrowth from the spinal cord. Motor axon growth cones and filopodia are selectively extended toward and contact prepatterned AChR clusters, followed by the rapid clustering of presynaptic vesicles and insertion of additional AChRs, hallmarks of synaptogenesis. All initially formed neuromuscular synapses contain AChRs that were inserted into the membrane at the time the prepattern is present. Examination of embryos in which AChRs were blocked or clustering is absent showed that neither receptor activity or receptor protein is required for these events to occur. Thus, during initial synaptogenesis, postsynaptic differentiation precedes presynaptic differentiation, and prepatterned neurotransmitter clusters mark sites destined for synapse formation.

Movement disorders in paraneoplastic and autoimmune disease.

PURPOSE OF REVIEW The most relevant advances in immune-mediated movement disorders are described, with emphasis on the clinical--immunological associations, novel antigens, and treatment. RECENT FINDINGS Many movement disorders previously considered idiopathic or degenerative are now recognized as immune-mediated. Some disorders are paraneoplastic, such as anti-CRMP5-associated chorea, anti-Ma2 hypokinesis and rigidity, anti-Yo cerebellar ataxia and tremor, and anti-Hu ataxia and pesudoathetosis. Other disorders such as Sydenhams chorea, or chorea related to systemic lupus erythematosus and antiphospholipid syndrome occur in association with multiple antibodies, are not paraneoplastic, and are triggered by molecular mimicry or unknown mechanisms. Recent studies have revealed a new category of disorders that can be paraneoplastic or not, and associate with antibodies against cell-surface or synaptic proteins. They include anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis, which may cause dyskinesias, chorea, ballismus or dystonia (NMDAR antibodies), the spectrum of Stiff-person syndrome/muscle rigidity (glutamic acid decarboxylase, amphiphysin, GABA(A)-receptor-associated protein, or glycine receptor antibodies), neuromyotonia (Caspr2 antibodies), and opsoclonus--myoclonus--ataxia (unknown antigens). SUMMARY Neurologists should be aware that many movement disorders are immune-mediated. Recognition of these disorders is important because it may lead to the diagnosis of an occult cancer, and a substantial number of patients, mainly those with antibodies to cell-surface or synaptic proteins, respond to immunotherapy.

High prevalence of NMDA receptor IgA/IgM antibodies in different dementia types

To retrospectively determine the frequency of N‐Methyl‐D‐Aspartate (NMDA) receptor (NMDAR) autoantibodies in patients with different forms of dementia.

Mechanisms underlying metabolic and neural defects in zebrafish and human multiple acyl-CoA dehydrogenase deficiency (MADD).

In humans, mutations in electron transfer flavoprotein (ETF) or electron transfer flavoprotein dehydrogenase (ETFDH) lead to MADD/glutaric aciduria type II, an autosomal recessively inherited disorder characterized by a broad spectrum of devastating neurological, systemic and metabolic symptoms. We show that a zebrafish mutant in ETFDH, xavier, and fibroblast cells from MADD patients demonstrate similar mitochondrial and metabolic abnormalities, including reduced oxidative phosphorylation, increased aerobic glycolysis, and upregulation of the PPARG-ERK pathway. This metabolic dysfunction is associated with aberrant neural proliferation in xav, in addition to other neural phenotypes and paralysis. Strikingly, a PPARG antagonist attenuates aberrant neural proliferation and alleviates paralysis in xav, while PPARG agonists increase neural proliferation in wild type embryos. These results show that mitochondrial dysfunction, leading to an increase in aerobic glycolysis, affects neurogenesis through the PPARG-ERK pathway, a potential target for therapeutic intervention.

Gap Junctional Communication Among Motor and Other Neurons Shapes Patterns of Neural Activity and Synaptic Connectivity During Development

We are studying the functional roles of neuronal gap junctional coupling during development, using motor neurons and their synapses with muscle fibers as a model system. At neuromuscular synapses, several studies have shown that the relative pattern of activity among motor inputs competing for innervation of the same target muscle fiber determines how patterns of innervation are sculpted during the first weeks after birth. We asked whether gap junctional coupling among motor neurons modulates the relative timing of motor neuron activity in awake, behaving neonatal mice. We found that the activity of motor neurons innervating the same muscle is temporally correlated perinatally, during the same period that gap junction-mediated electrical and dye coupling are present. In vivo blockade of gap junctions abolished temporal correlations in motor neuron activity, without changing overall motor behavior, motor neuron activity patterns or firing frequency. Together with preliminary studies in mice lacking gap junction protein Cx40, our data suggest that developmentally regulated gap junctional coupling among motor and other neurons affects the activity in nascent neural circuits and thus in turn affects synaptic connectivity. Dynamic monitoring of dye coupling can be used to explore this possibility in normal mice and in mice lacking gap junction proteins during embryonic and neonatal development.

Antigenic and mechanistic characterization of anti-AMPA receptor encephalitis.

Anti‐AMPAR encephalitis is a recently discovered disorder characterized by the presence of antibodies in serum or cerebrospinal fluid against the α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor. Here, we examine the antigenic specificity of anti‐AMPAR antibodies, screen for new patients, and evaluate functional effects of antibody treatment of neurons.

Neural and synaptic defects in slytherin, a zebrafish model for human congenital disorders of glycosylation.

Congenital disorder of glycosylation type IIc (CDG IIc) is characterized by mental retardation, slowed growth and severe immunodeficiency, attributed to the lack of fucosylated glycoproteins. While impaired Notch signaling has been implicated in some aspects of CDG IIc pathogenesis, the molecular and cellular mechanisms remain poorly understood. We have identified a zebrafish mutant slytherin (srn), which harbors a missense point mutation in GDP-mannose 4,6 dehydratase (GMDS), the rate-limiting enzyme in protein fucosylation, including that of Notch. Here we report that some of the mechanisms underlying the neural phenotypes in srn and in CGD IIc are Notch-dependent, while others are Notch-independent. We show, for the first time in a vertebrate in vivo, that defects in protein fucosylation leads to defects in neuronal differentiation, maintenance, axon branching, and synapse formation. Srn is thus a useful and important vertebrate model for human CDG IIc that has provided new insights into the neural phenotypes that are hallmarks of the human disorder and has also highlighted the role of protein fucosylation in neural development.

Antibodies to dendritic neuronal surface antigens in opsoclonus myoclonus ataxia syndrome

Opsoclonus myoclonus ataxia syndrome (OMAS) is an autoimmune disorder characterized by rapid, random, conjugate eye movements (opsoclonus), myoclonus, and ataxia. Given these symptoms, autoantibodies targeting the cerebellum or brainstem could mediate the disease or be markers of autoimmunity. In a subset of patients with OMAS, we identified such autoantibodies, which bind to non-synaptic puncta on the surface of live cultured cerebellar and brainstem neuronal dendrites. These findings implicate autoimmunity to a neuronal surface antigen in the pathophysiology of OMAS. Identification of the targeted antigen(s) could elucidate the mechanisms underlying OMAS and provide a biomarker for diagnosis and response to therapy.

Patterns of cell–cell coupling in embryonic spinal cord studied via ballistic delivery of gap‐junction‐permeable dyes

Intercellular communication mediated by gap junctions is developmentally regulated in many tissues, including the nervous system. In rodent lumbar spinal cord, extensive gap junctional coupling among motor neurons innervating the same muscle is present at birth but is no longer present 1 week later. Little is known about how this motor‐pool‐specific coupling arises during embryonic development. To address this question, we developed a novel method of visualizing patterns of cell–cell coupling that can be applied to a wide range of tissues. Gap‐junction‐permeable dyes adsorbed to metal beads were delivered into individual cells in embryonic cerebral cortex or spinal cord using pressure. Dye diffused off of the bead surface into the cytoplasm, crossed gap junctions, and labeled clusters of coupled cells. For embryonic cerebral cortex, this method revealed patterns of cell–cell coupling similar to those reported with other techniques. In embryonic lumbar spinal cord, cell–cell coupling is widespread in the ventricular zone at E11, and the extent of coupling decreases until birth. In the ventral horn, motor neurons are coupled into clusters at E14, with little change in the extent of coupling at E16, and a similar extent of coupling is present at birth. The cell types within clusters, identified by using antibodies against homeodomain transcription factors, were surprisingly heterogeneous in both the ventricular zone and the motor columns. Taken together, these data suggest that the spatial and temporal patterns of cell–cell coupling are dynamic and that cell‐type‐specific gap junctional coupling arises gradually during spinal cord development. J. Comp. Neurol. 480:273–285, 2004.

Pediatric anti-NMDA receptor encephalitis is seasonal

In the majority of pediatric anti‐N‐methyl‐d‐aspartate receptor encephalitis (NMDARe) cases, the underlying cause of antibody production and subsequent disease remains unknown. We aimed to characterize this poorly understood population, investigating epidemiological factors potentially related to disease etiology, particularly season of onset. In this retrospective case review study, we analyzed data from the 29 pediatric subjects with anti‐NMDAR antibodies and found that symptoms were first reported in the warm months of April–September in 78% of non‐tumor‐related NMDARe (NT‐NMDARe) cases. These findings support further investigation into a possible seasonal trigger of NT‐NMDARe.