Ochratoxin A at nanomolar concentration perturbs the homeostasis of neural stem cells in highly differentiated but not in immature three-dimensional brain cell cultures.

Ochratoxin A (OTA), a fungal contaminant of basic food commodities, is known to be highly cytotoxic, but the pathways underlying adverse effects at subcytotoxic concentrations remain to be elucidated. Recent reports indicate that OTA affects cell cycle regulation. Therefore, 3D brain cell cultures were used to study OTA effects on mitotically active neural stem/progenitor cells, comparing highly differentiated cultures with their immature counterparts. Changes in the rate of DNA synthesis were related to early changes in the mRNA expression of neural stem/progenitor cell markers. OTA at 10nM, a concentration below the cytotoxic level, was ineffective in immature cultures, whereas in mature cultures it significantly decreased the rate of DNA synthesis together with the mRNA expression of key transcriptional regulators such as Sox2, Mash1, Hes5, and Gli1; the cell cycle activator cyclin D2; the phenotypic markers nestin, doublecortin, and PDGFRα. These effects were largely prevented by Sonic hedgehog (Shh) peptide (500ngml(-1)) administration, indicating that OTA impaired the Shh pathway and the Sox2 regulatory transcription factor critical for stem cell self-renewal. Similar adverse effects of OTA in vivo might perturb the regulation of stem cell proliferation in the adult brain and in other organs exhibiting homeostatic and/or regenerative cell proliferation.

Interhemispheric coupling between the posterior sylvian regions impacts successful auditory temporal order judgment.

Accurate perception of the temporal order of sensory events is a prerequisite in numerous functions ranging from language comprehension to motor coordination. We investigated the spatio-temporal brain dynamics of auditory temporal order judgment (aTOJ) using electrical neuroimaging analyses of auditory evoked potentials (AEPs) recorded while participants completed a near-threshold task requiring spatial discrimination of left-right and right-left sound sequences. AEPs to sound pairs modulated topographically as a function of aTOJ accuracy over the 39-77ms post-stimulus period, indicating the engagement of distinct configurations of brain networks during early auditory processing stages. Source estimations revealed that accurate and inaccurate performance were linked to bilateral posterior sylvian regions activity (PSR). However, activity within left, but not right, PSR predicted behavioral performance suggesting that left PSR activity during early encoding phases of pairs of auditory spatial stimuli appears critical for the perception of their order of occurrence. Correlation analyses of source estimations further revealed that activity between left and right PSR was significantly correlated in the inaccurate but not accurate condition, indicating that aTOJ accuracy depends on the functional decoupling between homotopic PSR areas. These results support a model of temporal order processing wherein behaviorally relevant temporal information--i.e. a temporal 'stamp'--is extracted within the early stages of cortical processes within left PSR but critically modulated by inputs from right PSR. We discuss our results with regard to current models of temporal of temporal order processing, namely gating and latency mechanisms.

Dysregulated activation of the CXCR4/CXCL12 Axisand its role in the malignant phenotype of neural crest-derived neuroblastoma tumours

Résumé: Le neuroblastome (NB) est un néoplasme dévastateur de la petite enfance, pour lequel il n'existe pas encore de traitement efficace. Les chimiokines et leurs récepteurs ont été impliqués dans la croissance des tumeurs et la formation de métastases, et en particulier, il a été rapporté que l'axe CXCR4/CXCL12 dirigeait le guidage, ainsi que l'invasion des cellules cancéreuses vers des organes spécifiques. Notre étude avait pour objectif d'analyser le rôle de CxCR4 exogène dans le comportement malin du NB, en étudiant la croissance des cellules tumorales, leur capacité de survie, de migration et d'invasion in vitro et en validant ces résultats grâce à un modèle orthotopique murin de la progression tumorale du NB in vivo. La surexpression de CXCR4 dans les cellules faiblement métastatiques IGR-NB8 n'exprimant pas CXCR4, a augmenté la mobilité des cellules vers CXCL12 in vitro. De plus, les cellules surexprimant CXCR4 ont été moins affectées par la privation de sérum que les cellules contrôles. Le volume des tumeurs chez les animaux greffés de manière orthotopique avec les cellules NB8-CXCR4-C3 était significativement plus élevé que celui des tumeurs issues des cellules contrôles NB8-E6 au moment du sacrifice des animaux. Cependant, aucune induction des métastases n'a été observée. La lignée cellulaire IGR-N91, aux propriétés invasives et métastatiques in vivo, exprime constitutivement des quantités modérées de CXCR4. La surexpression du récepteur dans cette lignée a accéléré la croissance tumorale in vivo, mais n'a pas augmenté pas l'occurrence des métastases. Les cellules IGR-N91, dans lesquelles l'expression de CXCR4 a été éteinte, suite à l'introduction de shRNA stable contre CXCR4, a présenté une croissance cellulaire plus lente, in vitro et in vivo. Afin d'identifier les gènes et les voies de signalisation impliqués dans les effets dépendants de CXCR4-CXCL12 dans le NB, des analyses du profil d'expression des gènes ont été effectuées sur les lignées cellulaires transfectées ou non (contrôle). Trois clones contrôles ont été comparés à 3 clones surexprimant CXCR4 pour chacune des lignées (IGR-NB8 et IGR-N91). Les analyses biostatiques ont identifié 10 gènes induits, dont CXCR4, et 31 gènes réprimés, communs entre tous les clones surexprimant CXCR4. Ces observations démontrent que la surexpression de CXCR4 dans le NB stimule la croissance, la survie et la migration chémotactique des cellules tumorales, mais est insuffisante pour induire ou augmenter leurs capacités invasives et métastatiques. Les voies de signalisation activées suite à la surexpression de CXCR4 et identifiées à travers le profil global de l'expression des gènes pourraient être des cibles intéressantes pour le développement de drogues capables d'inhiber la croissance tumorale. Abstact: Neuroblastoma (NB) is a devastating childhood neoplasm for which there is not yet an efficient treatment. Chemokines and their receptors have been involved in tumour growth and metastasis, and in particular the CXCR4/CXCL12 axis has been reported to mediate organ-specific cancer cells homing and invasion. The purpose of the study was to investigate the role of ectopic CXCR4 in the malignant behaviour of NB by studying tumour cell growth, survival, migration, and invasion in vitro and by validating these results using a murine orthotopic model of NB tumour progression in vivo. CXCR4 overexpression in the low metastatic, CXCR4-negative IGR-NB8 cells resulted in CXCL12-mediated chemotaxis in vitro. Furthermore, CXCR4 overexpressing cells were less affected by serum deprivation than mock-transduced cells. In vivo studies revealed that, at sacrifice, volumes of tumours developing in mice with orthotopically implanted NB8-CXCR4-C3 cells, were significantly increased compared to NB8-E6 control tumours. However, no induction of metastases was observed. The in vivo invasive and metastatic cell line IGR-N91 cell line constitutively expresses moderate levels of CXCR4. Overexpression of CXCR4 enhanced in vivo tumour growth but did not increase the occurrence of metastases. IGR-N91 cells where CXCR4 has been knocked-down by stable shRNA grew slower in vitro and in vivo. To identify genes and pathways involved in the CXCR4/CXCL12-mediated effects in NB expression, profiles analyses (Affymetrix) were performed on transduced and control cell lines. Three mock-transduced clones were compared to three CXCR4 overexpressing clones of either cell line IGR-NB8 and IGR-N91. Biostatistical analysis identified 10 commonly upregulated genes (including CXCR4) and 31 downregulated genes common to all CXCR4 overexpressing clones. These observations demonstrate that overexpression of CXCR4 in NB stimulates tumour cell growth, survival, and chemotactic migration but is not sufficient to induce or enhance invasive and metastatic capacities. Activated pathways upon CXCR4 overexpression, identified through global gene expression profiling may be interesting targets for drugs inhibiting tumour growth.

Left temporal lobe epilepsy revealing left posterior cortical atrophy due to Alzheimer's disease.

Seizures can be an early symptom of Alzheimer's disease (AD) and can precede cognitive decline. Early epilepsy in AD can mimic transient epileptic amnesic syndrome (TEAS) or epileptic amnesic syndrome. We report the case of a patient who started a cerebrospinal fluid (CSF)-proven AD with partial seizures and TEAS that secondarily became a cortical posterior atrophy syndrome. CSF biomarkers showed a high amyloid production, amyloidopathy, and high level of total tau and p-Tau. This observation adds data to the complex AD-early epilepsy interactions and illustrates that atypical AD can cause a TEAS. Possible red flags for an underlying neurodegenerative process in TEAS are discussed.

Neural detection of complex sound sequences in the absence of consciousness.

The neural response to a violation of sequences of identical sounds is a typical example of the brain's sensitivity to auditory regularities. Previous literature interprets this effect as a pre-attentive and unconscious processing of sensory stimuli. By contrast, a violation to auditory global regularities, i.e. based on repeating groups of sounds, is typically detectable when subjects can consciously perceive them. Here, we challenge the notion that global detection implies consciousness by testing the neural response to global violations in a group of 24 patients with post-anoxic coma (three females, age range 45-87 years), treated with mild therapeutic hypothermia and sedation. By applying a decoding analysis to electroencephalographic responses to standard versus deviant sound sequences, we found above-chance decoding performance in 10 of 24 patients (Wilcoxon signed-rank test, P < 0.001), despite five of them being mildly hypothermic, sedated and unarousable. Furthermore, consistently with previous findings based on the mismatch negativity the progression of this decoding performance was informative of patients' chances of awakening (78% predictive of awakening). Our results show for the first time that detection of global regularities at neural level exists despite a deeply unconscious state.

Neural Circuits: Male Mating Motifs.

Characterizing microcircuit motifs in intact nervous systems is essential to relate neural computations to behavior. In this issue of Neuron, Clowney et al. (2015) identify recurring, parallel feedforward excitatory and inhibitory pathways in male Drosophila's courtship circuitry, which might explain decisive mate choice.

Cognitive anatomy of the temporal lobe: Effect of personality in population with mild cognitive impairment & Functional specialization for memory systems in healthy individuals.

Résumé: L'impact de la maladie d'Alzheimer (MA) est dévastateur pour la vie quotidienne de la personne affectée, avec perte progressive de la mémoire et d'autres facultés cognitives jusqu'à la démence. Il n'existe toujours pas de traitement contre cette maladie et il y a aussi une grande incertitude sur le diagnostic des premiers stades de la MA. La signature anatomique de la MA, en particulier l'atrophie du lobe temporal moyen (LTM) mesurée avec la neuroimagerie, peut être utilisée comme un biomarqueur précoce, in vivo, des premiers stades de la MA. Toutefois, malgré le rôle évident du LMT dans les processus de la mémoire, nous savons que les modèles anatomiques prédictifs de la MA basés seulement sur des mesures d'atrophie du LTM n'expliquent pas tous les cas cliniques. Au cours de ma thèse, j'ai conduit trois projets pour comprendre l'anatomie et le fonctionnement du LMT dans (1) les processus de la maladie et dans (2) les processus de mémoire ainsi que (3) ceux de l'apprentissage. Je me suis intéressée à une population avec déficit cognitif léger (« Mild Cognitive Impairment », MCI), à risque pour la MA. Le but du premier projet était de tester l'hypothèse que des facteurs, autres que ceux cognitifs, tels que les traits de personnalité peuvent expliquer les différences interindividuelles dans le LTM. De plus, la diversité phénotypique des manifestations précliniques de la MA provient aussi d'une connaissance limitée des processus de mémoire et d'apprentissage dans le cerveau sain. L'objectif du deuxième projet porte sur l'investigation des sous-régions du LTM, et plus particulièrement de leur contribution dans différentes composantes de la mémoire de reconnaissance chez le sujet sain. Pour étudier cela, j'ai utilisé une nouvelle méthode multivariée ainsi que l'IRM à haute résolution pour tester la contribution de ces sous-régions dans les processus de familiarité (« ou Know ») et de remémoration (ou « Recollection »). Finalement, l'objectif du troisième projet était de tester la contribution du LTM en tant que système de mémoire dans l'apprentissage et l'interaction dynamique entre différents systèmes de mémoire durant l'apprentissage. Les résultats du premier projet montrent que, en plus du déficit cognitif observé dans une population avec MCI, les traits de personnalité peuvent expliquer les différences interindividuelles du LTM ; notamment avec une plus grande contribution du neuroticisme liée à une vulnérabilité au stress et à la dépression. Mon étude a permis d'identifier un pattern d'anormalité anatomique dans le LTM associé à la personnalité avec des mesures de volume et de diffusion moyenne du tissu. Ce pattern est caractérisé par une asymétrie droite-gauche du LTM et un gradient antéro-postérieur dans le LTM. J'ai interprété ce résultat par des propriétés tissulaires et neurochimiques différemment sensibles au stress. Les résultats de mon deuxième projet ont contribué au débat actuel sur la contribution des sous-régions du LTM dans les processus de familiarité et de remémoration. Utilisant une nouvelle méthode multivariée, les résultats supportent premièrement une dissociation des sous-régions associées aux différentes composantes de la mémoire. L'hippocampe est le plus associé à la mémoire de type remémoration et le cortex parahippocampique, à la mémoire de type familiarité. Deuxièmement, l'activation correspondant à la trace mnésique pour chaque type de mémoire est caractérisée par une distribution spatiale distincte. La représentation neuronale spécifique, « sparse-distributed», associée à la mémoire de remémoration dans l'hippocampe serait la meilleure manière d'encoder rapidement des souvenirs détaillés sans interférer les souvenirs précédemment stockés. Dans mon troisième projet, j'ai mis en place une tâche d'apprentissage en IRM fonctionnelle pour étudier les processus d'apprentissage d'associations probabilistes basé sur le feedback/récompense. Cette étude m'a permis de mettre en évidence le rôle du LTM dans l'apprentissage et l'interaction entre différents systèmes de mémoire comme la mémoire procédurale, perceptuelle ou d'amorçage et la mémoire de travail. Nous avons trouvé des activations dans le LTM correspondant à un processus de mémoire épisodique; les ganglions de la base (GB), à la mémoire procédurale et la récompense; le cortex occipito-temporal (OT), à la mémoire de représentation perceptive ou l'amorçage et le cortex préfrontal, à la mémoire de travail. Nous avons également observé que ces régions peuvent interagir; le type de relation entre le LTM et les GB a été interprété comme une compétition, ce qui a déjà été reporté dans des études récentes. De plus, avec un modèle dynamique causal, j'ai démontré l'existence d'une connectivité effective entre des régions. Elle se caractérise par une influence causale de type « top-down » venant de régions corticales associées avec des processus de plus haut niveau venant du cortex préfrontal sur des régions corticales plus primaires comme le OT cortex. Cette influence diminue au cours du de l'apprentissage; cela pourrait correspondre à un mécanisme de diminution de l'erreur de prédiction. Mon interprétation est que cela est à l'origine de la connaissance sémantique. J'ai également montré que les choix du sujet et l'activation cérébrale associée sont influencés par les traits de personnalité et des états affectifs négatifs. Les résultats de cette thèse m'ont amenée à proposer (1) un modèle expliquant les mécanismes possibles liés à l'influence de la personnalité sur le LTM dans une population avec MCI, (2) une dissociation des sous-régions du LTM dans différents types de mémoire et une représentation neuronale spécifique à ces régions. Cela pourrait être une piste pour résoudre les débats actuels sur la mémoire de reconnaissance. Finalement, (3) le LTM est aussi un système de mémoire impliqué dans l'apprentissage et qui peut interagir avec les GB par une compétition. Nous avons aussi mis en évidence une interaction dynamique de type « top -down » et « bottom-up » entre le cortex préfrontal et le cortex OT. En conclusion, les résultats peuvent donner des indices afin de mieux comprendre certains dysfonctionnements de la mémoire liés à l'âge et la maladie d'Alzheimer ainsi qu'à améliorer le développement de traitement. Abstract: The impact of Alzheimer's disease is devastating for the daily life of the affected patients, with progressive loss of memory and other cognitive skills until dementia. We still lack disease modifying treatment and there is also a great amount of uncertainty regarding the accuracy of diagnostic classification in the early stages of AD. The anatomical signature of AD, in particular the medial temporal lobe (MTL) atrophy measured with neuroimaging, can be used as an early in vivo biomarker in early stages of AD. However, despite the evident role of MTL in memory, we know that the derived predictive anatomical model based only on measures of brain atrophy in MTL does not explain all clinical cases. Throughout my thesis, I have conducted three projects to understand the anatomy and the functioning of MTL on (1) disease's progression, (2) memory process and (3) learning process. I was interested in a population with mild cognitive impairment (MCI), at risk for AD. The objective of the first project was to test the hypothesis that factors, other than the cognitive ones, such as the personality traits, can explain inter-individual differences in the MTL. Moreover, the phenotypic diversity in the manifestations of preclinical AD arises also from the limited knowledge of memory and learning processes in healthy brain. The objective of the second project concerns the investigation of sub-regions of the MTL, and more particularly their contributions in the different components of recognition memory in healthy subjects. To study that, I have used a new multivariate method as well as MRI at high resolution to test the contribution of those sub-regions in the processes of familiarity and recollection. Finally, the objective of the third project was to test the contribution of the MTL as a memory system in learning and the dynamic interaction between memory systems during learning. The results of the first project show that, beyond cognitive state of impairment observed in the population with MCI, the personality traits can explain the inter-individual differences in the MTL; notably with a higher contribution of neuroticism linked to proneness to stress and depression. My study has allowed identifying a pattern of anatomical abnormality in the MTL related to personality with measures of volume and mean diffusion of the tissue. That pattern is characterized by right-left asymmetry in MTL and an anterior to posterior gradient within MTL. I have interpreted that result by tissue and neurochemical properties differently sensitive to stress. Results of my second project have contributed to the actual debate on the contribution of MTL sub-regions in the processes of familiarity and recollection. Using a new multivariate method, the results support firstly a dissociation of the subregions associated with different memory components. The hippocampus was mostly associated with recollection and the surrounding parahippocampal cortex, with familiarity type of memory. Secondly, the activation corresponding to the mensic trace for each type of memory is characterized by a distinct spatial distribution. The specific neuronal representation, "sparse-distributed", associated with recollection in the hippocampus would be the best way to rapidly encode detailed memories without overwriting previously stored memories. In the third project, I have created a learning task with functional MRI to sudy the processes of learning of probabilistic associations based on feedback/reward. That study allowed me to highlight the role of the MTL in learning and the interaction between different memory systems such as the procedural memory, the perceptual memory or priming and the working memory. We have found activations in the MTL corresponding to a process of episodic memory; the basal ganglia (BG), to a procedural memory and reward; the occipito-temporal (OT) cortex, to a perceptive memory or priming and the prefrontal cortex, to working memory. We have also observed that those regions can interact; the relation type between the MTL and the BG has been interpreted as a competition. In addition, with a dynamic causal model, I have demonstrated a "top-down" influence from cortical regions associated with high level cortical area such as the prefrontal cortex on lower level cortical regions such as the OT cortex. That influence decreases during learning; that could correspond to a mechanism linked to a diminution of prediction error. My interpretation is that this is at the origin of the semantic knowledge. I have also shown that the subject's choice and the associated brain activation are influenced by personality traits and negative affects. Overall results of this thesis have brought me to propose (1) a model explaining the possible mechanism linked to the influence of personality on the MTL in a population with MCI, (2) a dissociation of MTL sub-regions in different memory types and a neuronal representation specific to each region. This could be a cue to resolve the actual debates on recognition memory. Finally, (3) the MTL is also a system involved in learning and that can interact with the BG by a competition. We have also shown a dynamic interaction of « top -down » and « bottom-up » types between the pre-frontal cortex and the OT cortex. In conclusion, the results could give cues to better understand some memory dysfunctions in aging and Alzheimer's disease and to improve development of treatment.

Programming Hippocampal Neural Stem/Progenitor Cells into Oligodendrocytes Enhances Remyelination in the Adult Brain after Injury.

Demyelinating diseases are characterized by a loss of oligodendrocytes leading to axonal degeneration and impaired brain function. Current strategies used for the treatment of demyelinating disease such as multiple sclerosis largely rely on modulation of the immune system. Only limited treatment options are available for treating the later stages of the disease, and these treatments require regenerative therapies to ameliorate the consequences of oligodendrocyte loss and axonal impairment. Directed differentiation of adult hippocampal neural stem/progenitor cells (NSPCs) into oligodendrocytes may represent an endogenous source of glial cells for cell-replacement strategies aiming to treat demyelinating disease. Here, we show that Ascl1-mediated conversion of hippocampal NSPCs into mature oligodendrocytes enhances remyelination in a diphtheria-toxin (DT)-inducible, genetic model for demyelination. These findings highlight the potential of targeting hippocampal NSPCs for the treatment of demyelinated lesions in the adult brain.

Galanin pathogenic mutations in temporal lobe epilepsy.

Temporal lobe epilepsy (TLE) is a common epilepsy syndrome with a complex etiology. Despite evidence for the participation of genetic factors, the genetic basis of TLE remains largely unknown. A role for the galanin neuropeptide in the regulation of epileptic seizures has been established in animal models more than two decades ago. However, until now there was no report of pathogenic mutations in GAL, the galanin-encoding gene, and therefore its role in human epilepsy was not established. Here, we studied a family with a pair of monozygotic twins affected by TLE and two unaffected siblings born to healthy parents. Exome sequencing revealed that both twins carried a novel de novo mutation (p.A39E) in the GAL gene. Functional analysis revealed that the p.A39E mutant showed antagonistic activity against galanin receptor 1 (GalR1)-mediated response, and decreased binding affinity and reduced agonist properties for GalR2. These findings suggest that the p.A39E mutant could impair galanin signaling in the hippocampus, leading to increased glutamatergic excitation and ultimately to TLE. In a cohort of 582 cases, we did not observe any pathogenic mutations indicating that mutations in GAL are a rare cause of TLE. The identification of a novel de novo mutation in a biologically-relevant candidate gene, coupled with functional evidence that the mutant protein disrupts galanin signaling, strongly supports GAL as the causal gene for the TLE in this family. Given the availability of galanin agonists which inhibit seizures, our findings could potentially have direct implications for the development of anti-epileptic treatment.