Les astrocytes sont les cellules gliales les plus nombreuses dans le cerveau. Elles utilisent les signaux calciques pour r\u00e9guler leur activit\u00e9 biochimique et communiquer avec les autres cellules du cerveau. Alors que chaque astrocyte est en principe bien plac\u00e9 pour influencer avec une grande dext\u00e9rit\u00e9 les milliers de connexions synaptiques qui se trouvent dans leurs domaines anatomiques respectifs, les signaux calciques astrocytaires ont longtemps \u00e9t\u00e9 consid\u00e9r\u00e9s comme trop lents et diffus pour servir de m\u00e9diateurs \u00e0 tout type d’actions rapides et sp\u00e9cifiques. Cependant, cette id\u00e9e r\u00e9sulte d’\u00e9tudes contraintes par une microscopie \u00e0 faible r\u00e9solution, qui ne peut acc\u00e9der aux signalisations calciques que dans les compartiments cellulaires les plus gros tels que le corps cellulaire et les principaux prolongements \u00e9mergent de celui-ci. Des travaux plus r\u00e9cents ont cependant montr\u00e9 que des signaux calciques rapides et localis\u00e9s pouvaient \u00eatre g\u00e9n\u00e9r\u00e9s dans les prolongements astrocytaires extr\u00eamement fins qui interagissent directement avec les synapses, rappelant ainsi les signaux utilis\u00e9s par les neurones pour op\u00e9rer une communication point-\u00e0-point \u00e0 grande vitesse. Cependant, la base morphologique de ces signaux astrocytaires rapides et localis\u00e9s n\u2019\u00e9tait pas connue, en raison des difficult\u00e9s \u00e0 r\u00e9soudre la morphologie complexe des astrocytes (et des synapses), tout en enregistrant leur activit\u00e9 calcique dans le tissu c\u00e9r\u00e9bral vivant. Pour surmonter ce probl\u00e8me, nous nous sommes tourn\u00e9s vers la microscopie 3D-STED, qui offre une r\u00e9solution spatiale beaucoup plus \u00e9lev\u00e9e que la microscopie optique classique et permet de r\u00e9v\u00e9ler la morphologie des astrocytes et des neurones de mani\u00e8re tr\u00e8s d\u00e9taill\u00e9e. En combinant ce type de microscopie avec l’imagerie confocale calcique permettant de mesurer l’activit\u00e9 calcique, et des exp\u00e9riences de FRAP pour \u00e9valuer les propri\u00e9t\u00e9s biophysiques, nous avons pu \u00e9lucider les bases anatomiques des signaux calciques dans les astrocytes. Nous avons observ\u00e9 que les prolongements astrocytaires forment un r\u00e9seau r\u00e9ticulaire de n\u0153uds et de branches qui s\u2019organisent autour de structures en forme d’anneau. Les n\u0153uds pr\u00e9sentent des signaux calciques spontan\u00e9s, localis\u00e9s la plupart du temps, mais qui peuvent \u00e9galement se propager aux n\u0153uds voisins via des structures en branches. Les exp\u00e9riences de FRAP ont montr\u00e9 que cette organisation permet une signalisation compartiment\u00e9e, mais aussi la propagation du signal \u00e0 travers plusieurs n\u0153uds. La superposition des donn\u00e9es calciques avec la morphologie fine des structures astrocytaires a r\u00e9v\u00e9l\u00e9 que la majorit\u00e9 des signaux calciques sont associ\u00e9s \u00e0 des synapses individuelles, ce qui sugg\u00e8re que les astrocytes sont capables d\u2019engager une communication avec des synapses sp\u00e9cifiques. Notre \u00e9tude apporte donc un nouvel \u00e9clairage sur l’organisation \u00e0 l’\u00e9chelle nanom\u00e9trique des astrocytes dans le tissu c\u00e9r\u00e9bral vivant (tranches organotypiques et aigu\u00ebs et in vivo), en r\u00e9v\u00e9lant une organisation en \u00ab\u00a0n\u0153uds\u00a0\u00bb pouvant r\u00e9guler la communication neuronale \u00e0 l\u2019\u00e9chelle de “synapses tripartites” individuelles.<\/p>\n
It takes three to tango: the tripartite synapse revealed by super-resolution microscopy<\/strong><\/p>\n Astrocytes, which are the most numerous glial cells in the brain, use Ca2+ signals to regulate their biochemical activity and communication with other brain cells. While single astrocytes are in principle well positioned to influence thousands of neuronal synapses that lie within their anatomical domain with great dexterity, astrocytic Ca2+ signals have long been thought to be too sluggish and sprawling for mediating any type of fast and specific actions. However, this view has come from low-resolution studies that have looked at the soma and major branches of the astrocytes. More recent work on the tiny but relevant astrocytic processes that actually contact synapses suggests that the situation may be similar to neurons, where fast and local synaptic Ca2+ signals mediate high-speed point-to-point communication. However, the anatomical basis of such specific signaling by astrocytes has remained unclear, owing to difficulties in resolving the complex morphology of astrocytes (and synapses), while also recording their Ca2+ activity in live brain tissue. <\/p>\n Reference:<\/strong><\/p>\n Structural basis of astrocytic Ca2+ signals at tripartite synapses Contact chercheur:<\/strong><\/p>\n Valentin N\u00e4gerl, IINS, valentin.nagerl@u-bordeaux.fr<\/p>\n","protected":false},"excerpt":{"rendered":" Les astrocytes sont les cellules gliales les plus nombreuses dans le cerveau. Elles utilisent les signaux calciques pour r\u00e9guler leur activit\u00e9 biochimique et communiquer avec les autres cellules du cerveau. Alors que chaque astrocyte est en principe bien plac\u00e9 pour influencer avec une grande dext\u00e9rit\u00e9 les milliers de connexions synaptiques qui se trouvent dans leurs […]<\/p>\n","protected":false},"author":4,"featured_media":13546,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[25],"tags":[31],"class_list":["post-13550","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-actualite-en"],"publishpress_future_action":{"enabled":false,"date":"2026-04-24 10:47:27","action":"change-status","newStatus":"draft","terms":[],"taxonomy":"category"},"publishpress_future_workflow_manual_trigger":{"enabledWorkflows":[]},"_links":{"self":[{"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/posts\/13550","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/comments?post=13550"}],"version-history":[{"count":1,"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/posts\/13550\/revisions"}],"predecessor-version":[{"id":13551,"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/posts\/13550\/revisions\/13551"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/media\/13546"}],"wp:attachment":[{"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/media?parent=13550"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/categories?post=13550"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.neurosciences.asso.fr\/en\/wp-json\/wp\/v2\/tags?post=13550"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\nTo overcome this problem, we turned to 3D-STED microscopy, which offers a much higher spatial resolution than regular light microscopy and can reveal the morphology of astrocytes and neurons in great detail. By combining it with confocal Ca2+ imaging to monitor Ca2+ activity, and FRAP experiments to assess biophysical properties, we could elucidate the anatomical basis of Ca2+ signals in astrocytes. We observed that astrocytic processes form a reticular meshwork of nodes and shafts that formed ring-like structures. The nodes exhibited spontaneous Ca2+ signals that stayed local most of the time, but could also spread to neighboring nodes via the shafts. FRAP experiments established that the astrocytic node\/shaft structure generally supports compartmentalized signaling, yet also permits signal propagation across multiple nodes. Mapping the Ca2+ data onto the STED images of the morphology, showed that the majority of astrocytic Ca2+ signals were associated with single synapses suggesting that astrocytes are capable of engaging in synapse-specific communication.
\nAltogether, our study shines new light on the nanoscale organization of astrocytes in live brain tissue (organotypic and acute brain slices and in vivo), identifying astrocytic nodes as the elusive anatomical structure that may regulate neuronal communication at single \u2018tripartite synapses\u2019.<\/p>\n
\nMisa Arizono, V. V. G. Krishna Inavalli, Aude Panatier, Thomas Pfeiffer, Julie Angibaud, Florian Levet, Mirelle J. T. Ter Veer, Jillian Stobart, Luigi Bellocchio, Katsuhiko Mikoshiba, Giovanni Marsicano, Bruno Weber, St\u00e9phane H. R. Oliet & U. Valentin N\u00e4gerl
\nNature Communications volume 11, Article number: 1906 (2020)
\nhttps:\/\/www.nature.com\/articles\/s41467-020-15648-4<\/p>\n