Nicolas Gaspard

An intrinsic mechanism of corticogenesis from embryonic stem cells

The cerebral cortex develops through the coordinated generation of dozens of neuronal subtypes, but the mechanisms involved remain unclear. Here we show that mouse embryonic stem cells, cultured without any morphogen but in the presence of a sonic hedgehog inhibitor, recapitulate in vitro the major milestones of cortical development, leading to the sequential generation of a diverse repertoire of neurons that display most salient features of genuine cortical pyramidal neurons. When grafted into the cerebral cortex, these neurons develop patterns of axonal projections corresponding to a wide range of cortical layers, but also to highly specific cortical areas, in particular visual and limbic areas, thereby demonstrating that the identity of a cortical area can be specified without any influence from the brain. The discovery of intrinsic corticogenesis sheds new light on the mechanisms of neuronal specification, and opens new avenues for the modelling and treatment of brain diseases.

American Clinical Neurophysiology Society's Standardized Critical Care EEG Terminology: 2012 version.

Continuous EEG Monitoring is becoming a commonly used tool in assessing brain function in critically ill patients. However, there is no uniformly accepted nomenclature for EEG patterns frequently encountered in these patients such as periodic discharges, fluctuating rhythmic patterns, and combinatio

Pyramidal Neurons Derived from Human Pluripotent Stem Cells Integrate Efficiently into Mouse Brain Circuits In Vivo

The study of human cortical development has major implications for brain evolution and diseases but has remained elusive due to paucity of experimental models. Here we found that human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), cultured without added morphogens, recapitulate corticogenesis leading to the sequential generation of functional pyramidal neurons of all six layer identities. After transplantation into mouse neonatal brain, human ESC-derived cortical neurons integrated robustly and established specific axonal projections and dendritic patterns corresponding to native cortical neurons. The differentiation and connectivity of the transplanted human cortical neurons complexified progressively over several months in vivo, culminating in the establishment of functional synapses with the host circuitry. Our data demonstrate that human cortical neurons generated in vitro from ESC/iPSC can develop complex hodological properties characteristic of the cerebral cortex in vivo, thereby offering unprecedented opportunities for the modeling of human cortex diseases and brain repair.

Intravenous ketamine for the treatment of refractory status epilepticus: A retrospective multicenter study

To examine patterns of use, efficacy, and safety of intravenous ketamine for the treatment of refractory status epilepticus (RSE).

Mechanisms of neural specification from embryonic stem cells.

While embryonic stem (ES) cells have been used for several years to generate specific populations of neural cells in a translational perspective, they have also emerged as a promising approach in developmental neurobiology, by providing reductionist models of neural development. Here we review recent work that indicates that ES-based models are not only able to mimic normal brain development, but also provide novel tools to dissect the relative contribution of intrinsic and extrinsic mechanisms of neural specification. These have thus not only revealed insights on early steps such as neural induction and regional patterning, but also temporal specification of distinct neuronal subtypes, as well as the later acquisition of more complex features such as cytoarchitecture and hodological properties.

New-onset refractory status epilepticus Etiology, clinical features, and outcome

Objectives: The aims of this study were to determine the etiology, clinical features, and predictors of outcome of new-onset refractory status epilepticus. Methods: Retrospective review of patients with refractory status epilepticus without etiology identified within 48 hours of admission between January 1, 2008, and December 31, 2013, in 13 academic medical centers. The primary outcome measure was poor functional outcome at discharge (defined as a score >3 on the modified Rankin Scale). Results: Of 130 cases, 67 (52%) remained cryptogenic. The most common identified etiologies were autoimmune (19%) and paraneoplastic (18%) encephalitis. Full data were available in 125 cases (62 cryptogenic). Poor outcome occurred in 77 of 125 cases (62%), and 28 (22%) died. Predictors of poor outcome included duration of status epilepticus, use of anesthetics, and medical complications. Among the 63 patients with available follow-up data (median 9 months), functional status improved in 36 (57%); 79% had good or fair outcome at last follow-up, but epilepsy developed in 37% with most survivors (92%) remaining on antiseizure medications. Immune therapies were used less frequently in cryptogenic cases, despite a comparable prevalence of inflammatory CSF changes. Conclusions: Autoimmune encephalitis is the most commonly identified cause of new-onset refractory status epilepticus, but half remain cryptogenic. Outcome at discharge is poor but improves during follow-up. Epilepsy develops in most cases. The role of anesthetics and immune therapies warrants further investigation.

Generation of cortical neurons from mouse embryonic stem cells

Embryonic stem cells (ESCs) constitute a tool of great potential in neurobiology, enabling the directed differentiation of specific neural cell types. We have shown recently that neurons of the cerebral cortex can be generated from mouse ESCs cultured in a chemically defined medium that contains no morphogen, but in the presence of the sonic hedgehog inhibitor cyclopamine. Corticogenesis from ESCs recapitulates the most important steps of cortical development, leading to the generation of multipotent cortical progenitors that sequentially produce cortical pyramidal neurons displaying distinct layer-specific identities. The protocol provides a most reductionist cellular model to tackle the complex mechanisms of cortical development and function, thereby opening new perspectives for the modeling of cortical diseases and the design of novel neurological treatments, while offering an alternative to animal use. In this protocol, we describe a method by which millions of cortical neurons can be generated in 2–3 weeks, starting from a single frozen vial of ESCs.

Interrater agreement for Critical Care EEG Terminology

The interpretation of critical care electroencephalography (EEG) studies is challenging because of the presence of many periodic and rhythmic patterns of uncertain clinical significance. Defining the clinical significance of these patterns requires standardized terminology with high interrater agreement (IRA). We sought to evaluate IRA for the final, published American Clinical Neurophysiology Society (ACNS)–approved version of the critical care EEG terminology (2012 version). Our evaluation included terms not assessed previously and incorporated raters with a broad range of EEG reading experience.

From stem cells to neural networks: recent advances and perspectives for neurodevelopmental disorders.

Embryonic or induced pluripotent stem cells, available in mouse and human, have emerged as powerful tools to address complex questions in neurobiology. This review focuses on major advances relating to brain development and developmental disorders. Stem cells can differentiate into many different neuronal subtypes using in vitro models mimicking relevant in vivo developmental processes, and the underlying molecular and cellular mechanisms. Disease–specific human embryonic stem cells (ESCs) and induced pluripotent stem (iPS) cells are now available and allow for the study in vitro of the pathophysiology of degenerative and neurodevelopmental hereditary and sporadic disorders, including in the near future those of the human cortex. Finally, some recent studies have shown that stem cell‐derived neural progenitors and neurons could help to rebuild damaged brain circuitry, opening the possibility of cell therapy.

Temporal regulation of ephrin/Eph signalling is required for the spatial patterning of the mammalian striatum

Brain structures, whether mature or developing, display a wide diversity of pattern and shape, such as layers, nuclei or segments. The striatum in the mammalian forebrain displays a unique mosaic organization (subdivided into two morphologically and functionally defined neuronal compartments: the matrix and the striosomes) that underlies important functional features of the basal ganglia. Matrix and striosome neurons are generated sequentially during embryonic development, and segregate from each other to form a mosaic of distinct compartments. However, the molecular mechanisms that underlie this time-dependent process of neuronal segregation remain largely unknown. Using a novel organotypic assay, we identified ephrin/Eph family members as guidance cues that regulate matrix/striosome compartmentalization. We found that EphA4 and its ephrin ligands displayed specific temporal patterns of expression and function that play a significant role in the spatial segregation of matrix and striosome neurons. Analysis of the striatal patterning in ephrin A5/EphA4 mutant mice further revealed the requirement of EphA4 signalling for the proper sorting of matrix and striosome neuronal populations in vivo. These data constitute the first identification of genes involved in striatal compartmentalization, and reveal a novel mechanism by which the temporal control of guidance cues enables neuronal segregation, and thereby the generation of complex cellular patterns in the brain.