A transcriptomic axis predicts state modulation of cortical interneurons

Transcriptomics has revealed that cortical inhibitory neurons exhibit a great diversity of fine molecular subtypes1-6, but it is not known whether these subtypes have correspondingly diverse patterns of activity in the living brain. Here we show that inhibitory subtypes in primary visual cortex (V1) have diverse correlates with brain state, which are organized by a single factor: position along the main axis of transcriptomic variation. We combined in vivo two-photon calcium imaging of mouse V1 with a transcriptomic method to identify mRNA for 72 selected genes in ex vivo slices. We classified inhibitory neurons imaged in layers 1-3 into a three-level hierarchy of 5 subclasses, 11 types and 35 subtypes using previously defined transcriptomic clusters3. Responses to visual stimuli differed significantly only between subclasses, with cells in the Sncg subclass uniformly suppressed, and cells in the other subclasses predominantly excited. Modulation by brain state differed at all hierarchical levels but could be largely predicted from the first transcriptomic principal component, which also predicted correlations with simultaneously recorded cells. Inhibitory subtypes that fired more in resting, oscillatory brain states had a smaller fraction of their axonal projections in layer 1, narrower spikes, lower input resistance and weaker adaptation as determined in vitro7, and expressed more inhibitory cholinergic receptors. Subtypes that fired more during arousal had the opposite properties. Thus, a simple principle may largely explain how diverse inhibitory V1 subtypes shape state-dependent cortical processing

Intrinsic Neuronal Activity during Migration Controls the Recruitment of Specific Interneuron Subtypes in the Postnatal Mouse Olfactory Bulb

International audienceNeuronal activity has been identified as a key regulator of neuronal network development, but the impact of activity on migration and terminal positioning of interneuron subtypes is poorly understood. The absence of early subpopulation markers and the presence of intermingled migratory and postmigratory neurons make the developing cerebral cortex a difficult model to answer these questions. Postnatal neurogenesis in the subventricular zone (SVZ) offers a more accessible and compartmentalized model. Neural stem cells regionalized along the border of the lateral ventricle produce two main subtypes of neural progenitors, granule cells and periglomerular neurons that migrate tangentially in the rostral migratory stream (RMS) before migrating radially in the olfactory bulb (OB) layers. Here, we used targeted postnatal electroporation to compare the migration of these two populations in male and female mice. We do not observe any obvious differences regarding the mode of tangential or radial migration between these two subtypes. However, we find a striking increase of intrinsic calcium activity in granule cell precursors (GC-Ps) when they switch from tangential to radial migration. By decreasing neuronal excitability in GC-Ps, we find that neuronal activity has little effect on migration but is required for normal positioning and survival of GC-Ps in the OB layers. Strikingly, decreasing activity of periglomerular neuron precursors (PGN-Ps) did not impact their positioning or survival. Altogether these findings suggest that neuronal excitability plays a subtype specific role during the late stage of migration of postnatally born OB interneurons

Rapid quantification of muscle fat content and subcutaneous adipose tissue in fish using MRI

International audienceThe potentiality of MRI to quantify fat content in flesh and subcutaneous fat in fish cutlets was investigated. Low measurement time was aimed at in a view to handling large number of samples needed in selective breeding programs for example. Results on fresh and frozen-thawed cutlets were compared to assess this way of conservation. As MRI generates unwanted spatial variations of the signal, a correction method was developed enabling the measurement on several cutlets simultaneously in less than 3 min per sample. For subcutaneous fat, the results were compared with vision measurements. High correlations between both techniques were found (R2 = 0.77 and 0.87 for the ventral and dorsal part). Fat in flesh was validated vs NMR measurements. No statistical difference was found between fresh and frozen-thawed cutlets. RMSE was respectively 0.8% and 0.89%. These results confirmed the potentiality of MRI for fat measurement in fish particularly for a large number of samples

Direct and efficient transfection of mouse neural stem cells and mature neurons by in vivo mRNA electroporation

International audienceIn vivo brain electroporation of DNA expression vectors is a widely used method for lineage and gene function studies in the developing and postnatal brain. However, transfection efficiency of DNA is limited and adult brain tissue is refractory to electroporation. Here, we present a systematic study of mRNA as a vector for acute genetic manipulation in the developing and adult brain. We demonstrate that mRNA electroporation is far more efficient than DNA electroporation, and leads to faster and more homogeneous protein expression in vivo Importantly, mRNA electroporation allows the manipulation of neural stem cells and postmitotic neurons in the adult brain using minimally invasive procedures. Finally, we show that this approach can be efficiently used for functional studies, as exemplified by transient overexpression of the neurogenic factor Myt1l and by stably inactivating Dicer nuclease in vivo in adult born olfactory bulb interneurons and in fully integrated cortical projection neurons

Time-Specific Effects of Spindle Positioning on Embryonic Progenitor Pool Composition and Adult Neural Stem Cell Seeding

International audienceThe developmental mechanisms regulating the number of adult neural stem cells (aNSCs) are largely unknown. Here we show that the cleavage plane orientation in murine embryonic radial glia cells (RGCs) regulates the number of aNSCs in the lateral ganglionic eminence (LGE). Randomizing spindle orientation in RGCs by overexpression of Insc or a dominant-negative form of Lgn (dnLgn) reduces the frequency of self-renewing asymmetric divisions while favoring symmetric divisions generating two SNPs. Importantly, these changes during embryonic development result in reduced seeding of aNSCs. Interestingly, no effects on aNSC numbers were observed when Insc was overexpressed in postnatal RGCs or aNSCs. These data suggest a new mechanism for controlling aNSC numbers and show that the role of spindle orientation during brain development is highly time and region dependent

Positive impact of moderate food restriction on reproductive success of the rainbow trout Oncorhynchus mykiss

Rainbow trout (Oncorhynchus mykiss) egg production is a key sector for aquaculture. This industry relies on well-controlled reproductive cycles and the extensive use of photoperiod control to obtain year-round egg production. However, feed management practices are very diverse among producers and not always designed to optimize egg production. Among these different practices, feed restriction is of major interest due to its direct impact on the reduction of egg production costs. It is however not always used under optimal conditions. The aim of the present study was to evaluate the impact of moderate feed restriction on reproductive performances and egg quality in rainbow trout. For that purpose, two feeding strategies were implemented during the last five months before the second reproduction. Females were either fed (1) ad libitum, or (2) 80% of ad libitum (i.e. restricted) with a commercial diet. An artificial photoperiod was applied to trigger reproduction during the summer. As expected, feed restriction resulted in smaller females in comparison to those fed ad libitum whereas gonado-somatic index was significantly higher in restricted females. In addition, hatching rate was significantly higher for eggs from originating from restricted females. Feed restriction led to the production of bigger eggs with less size variability and lower number of non-viable eggs. These restricted females also exhibited lower viscero-somatic index suggesting an impact of feed restriction on the allocation of reserves. However, lipid content in eggs and muscle were not different between groups, while fatty acid profile of eggs presented some differences. PUFA analysis revealed that proportions of ALA, AA and EPA were higher in eggs from restricted females, a feature possibly linked to higher egg quality. Together, these results demonstrate that feed intake of female rainbow trout broodstock can be reduced by at least 20% without any negative impact on egg production and egg quality

"Qualitytruite" : l'IRM comme méthode de quantification rapide du gras intramusculaire et du tissu adipeux sous cutané des darnes de truite arc-en-ciel (Oncorhynchus mykiss)

Le but du projet était d’évaluer chez la truite arc-en-ciel la faisabilité du dosage de la teneur en lipides intramusculaires et de la surface de gras sous cutané par Imagerie en Résonance Magnétique (IRM) sur des darnes entières après décongélation. La possibilité d’analyser plusieurs darnes simultanément dans l’IRM a été validée en utilisant un support spécifique pour disposer les darnes au sein de l’imageur. Un modèle de correction du signal permet de pallier l’inhomogénéité du signal dans l’espace de mesure. La comparaison de la teneur en lipides de darnes fraîches et décongelées avec un dosage RMN met en évidence de très bonnes corrélations avec une erreur moyenne de 0.8 et 0.89% respectivement. Ce qui démontre que la congélation ne dégrade pas la précision du dosage. La surface de gras sous cutané mesurée en IRM et en vision numérique présente de bonnes corrélations R²=0.77 et 0.87 respectivement pour les tissus adipeux ventraux et dorsaux

Impact positif d’une restriction alimentaire modérée sur les performances de reproduction de la truitearc en ciel Oncorhynchus mykiss

Session : Reproductio

Impact positif d’une restriction alimentaire modérée sur les performances de reproduction de la truitearc en ciel Oncorhynchus mykiss

Session : Reproductio

Seven generations of divergent selection for muscle lipid content in rainbow trout: main impacts on lipid distribution and metabolism

International audienc