Synaptic Adhesion Molecules Regulate the Integration of New Granule Neurons in the Postnatal Mouse Hippocampus and their Impact on Spatial Memory.

Postnatal hippocampal neurogenesis induces network remodeling and may participate to mechanisms of learning. In turn, the maturation and survival of newborn neurons is regulated by their activity. Here, we tested the effect of a cell-autonomous overexpression of synaptic adhesion molecules on the maturation and survival of neurons born postnatally and on hippocampal-dependent memory performances. Families of adhesion molecules are known to induce pre- and post-synaptic assembly. Using viral targeting, we overexpressed three different synaptic adhesion molecules, SynCAM1, Neuroligin-1B and Neuroligin-2A in newborn neurons in the dentate gyrus of 7- to 9-week-old mice. We found that SynCAM1 increased the morphological maturation of dendritic spines and mossy fiber terminals while Neuroligin-1B increased spine density. In contrast, Neuroligin-2A increased both spine density and size as well as GABAergic innervation and resulted in a drastic increase of neuronal survival. Surprisingly, despite increased neurogenesis, mice overexpressing Neuroligin-2A in new neurons showed decreased memory performances in a Morris water maze task. These results indicate that the cell-autonomous overexpression of synaptic adhesion molecules can enhance different aspects of synapse formation on new neurons and increase their survival. Furthermore, they suggest that the mechanisms by which new neurons integrate in the postnatal hippocampus conditions their functional implication in learning and memory

Neuroinflammatory TNFα Impairs Memory via Astrocyte Signaling.

The occurrence of cognitive disturbances upon CNS inflammation or infection has been correlated with increased levels of the cytokine tumor necrosis factor-α (TNFα). To date, however, no specific mechanism via which this cytokine could alter cognitive circuits has been demonstrated. Here, we show that local increase of TNFα in the hippocampal dentate gyrus activates astrocyte TNF receptor type 1 (TNFR1), which in turn triggers an astrocyte-neuron signaling cascade that results in persistent functional modification of hippocampal excitatory synapses. Astrocytic TNFR1 signaling is necessary for the hippocampal synaptic alteration and contextual learning-memory impairment observed in experimental autoimmune encephalitis (EAE), an animal model of multiple sclerosis (MS). This process may contribute to the pathogenesis of cognitive disturbances in MS, as well as in other CNS conditions accompanied by inflammatory states or infections

A Neuron-Glial Perspective for Computational Neuroscience

International audienceThere is growing excitement around glial cells, as compelling evidence point to new, previously unimaginable roles for these cells in information processing of the brain, with the potential to affect behavior and higher cognitive functions. Among their many possible functions, glial cells could be involved in practically every aspect of the brain physiology in health and disease. As a result, many investigators in the field welcome the notion of a Neuron-Glial paradigm of brain function, as opposed to Ramon y Cayal's more classical neuronal doctrine which identifies neurons as the prominent, if not the only, cells capable of a signaling role in the brain. The demonstration of a brain-wide Neuron-Glial paradigm however remains elusive and so does the notion of what neuron-glial interactions could be functionally relevant for the brain computational tasks. In this perspective, we present a selection of arguments inspired by available experimental and modeling studies with the aim to provide a biophysical and conceptual platform to computational neuroscience no longer as a mere prerogative of neuronal signaling but rather as the outcome of a complex interaction between neurons and glial cells

La tuberculose chez les petits ruminants en Algérie

La tuberculose des petits ruminants est une maladie de répartition mondiale qui sévit le plus souvent de façon sporadique. C’est une maladie à évolution progressive, à déclaration obligatoire associée à son aspect zoonotique. Notre étude a consisté à rechercher les lésions suspectes de tuberculose par inspection des carcasses ovines et caprines dans deux abattoirs (Boufarik et Hadjout) d’une part, et à identifier l’agent  pathogène, d’autre part. L’inspection de 966 carcasses de petits ruminants a révélé la présence de lésions suspectes de tuberculose sur 40 carcasses, soit une proportion de 4,14%. Rapportés à chacune des deux espèces animales, les taux de prévalence sont similaires (3,89% et 4,40% respectivement chez les caprins et les ovins). Nous avons pris en   considération deux facteurs qui peuvent influer sur la prévalence de la maladie et qui sont l’âge et le sexe. Nous avons observé que les mâles sont les plus atteints chez les caprins des deux localités alors que chez les ovins, les femelles sont plus touchées dans une des deux localités.  Concernant l’âge, les animaux âgés sont les plus affectés chez les ovins et les caprins. L’examen microscopique direct a détecté 2 cas positifs chez les caprins sur un ensemble de 19 cas suspects, soit 10,5%, et aucun cas chez les ovins. Les résultats de la culture mettent en évidence 8 cas positifs soit 42,1% pour l’espèce caprine et aucun cas positif chez les ovins. L’identification des cultures positives montre que 75% sont des mycobactéries typiques vs 25% de mycobactéries atypiques. On peut en conclure que cette affection est toujours présente sans pouvoir donner de chiffre précis sur sa prévalence en raison de l’absence de dépistage  systématique chez ces espèces, même dans les élevages à effectif important.Mots clés: Petits ruminants, tuberculose, bacilloscopie, culture, abattoir