Name: synaptic pruning in long-term depression
Uploaded: 2019-03-11T09:21:27.000Z
Duration: 1 min 5 s
Channel: JoVE

- La dépression à long terme, ou DLT,est un processus d'affaiblissement des synapsesqui prend place au fil du tempsentre les connexions neuronales pré- et post-synaptiques. 
L'un des mécanismes d'apparition de la DLTdépend de la quantité d'ions calciumse dirigeant vers le neurone post-synaptiqueaprès une stimulation pré-synaptique. 
Une faible concentration en calciumà cause de stimulations pré-synaptiques peu fréquentespeut initier une cascade de signauxculminant lors de l'endocytose,ou la suppression des récepteurs AMPA de la membrane. 
Résultat : la réponse post-synaptiqueà une même stimulation pré-synaptique sporadiqueest encore plus affaiblie. 
Ainsi, la DLT est importante pour l'apprentissage,car des synapses non ou rarement utiliséessont affaiblies et peuvent même être éliminées,libérant des ressourceset de l'espace utilisable par le neuronepour d'autres fonctions, comme le renforcement de la PLTde synapses plus importantes.

Kukushkin, Nikolay Vadimovich et Thomas James Carew. « La mémoire prend du temps », Neuron 95, n° 2 (19 juillet 2017) : 259-79. [<a href="https://doi.org/10.1016/j.neuron.2017.05.029 » target="__blank">Source</a>]

Lüscher, Christian et Robert C. Malenka. « Potentialisation à long terme dépendante du récepteur NMDA et dépression à long terme (LTP / LTD). » Cold Spring Harbor Perspectives in Biology 4, n° 6 (1er juin 2012) : a005710. [<a href="https://doi.org/10.1101/cshperspect.a005710 » target="__blank">Source</a>]

dépression synaptique à long terme

La dépression à long terme, ou DLT, est l’un des moyens par lesquels la plasticité synaptique — les changements dans la force des synapses chimiques — peut se produire dans le cerveau. La DLT est le processus d’affaiblissement synaptique qui se produit au fil du temps entre les connexions neuronales pré- et postsynaptiques. L’affaiblissement synaptique de la DLT fonctionne en opposition au renforcement synaptique par la potentialisation à long terme (PLT) et, ensemble, ce sont les principaux mécanismes qui sous-tendent l’apprentissage et la mémoire. 
 
 <h4>Le mécanisme de la concentration en ions de calcium</h4>
 
 Si au fil du temps, toutes les synapses étaient renforcées au maximum par la PLT ou un autre mécanisme, le cerveau se stabiliserait au niveau de l’efficacité, rendant l’apprentissage et la formation de nouveaux souvenirs difficiles. La DLT est un moyen d’élaguer les synapses plus faibles, libérant ainsi les ressources et remettant de la flexibilité dans le système nerveux central. Un mécanisme par lequel la DLT se produit dépend du nombre d’ions calcium dans le neurone postsynaptique après la stimulation présynaptique. Des niveaux peu fréquents ou faibles de stimulation présynaptique conduisent à un faible influx d’ions calcium et, par conséquent, à une faible concentration d’ions calcium dans le neurone postsynaptique.
 
 La faible concentration d’ions calcium déclenche une cascade de signalisation qui culmine dans l’endocytose ou l’élimination des récepteurs de glutamate à l’acide α-amino-3-hydroxy-5-méthyl-4-isoxazolepropionique (AMPA) de la membrane plasmique. En conséquence, la réponse postsynaptique à la même stimulation présynaptique sporadique est encore affaiblie, puisqu’il y a moins de canaux pour que les ions chargés positivement entrent et dépolarisent la membrane. Le neurone réutilise les récepteurs AMPA à un moment ultérieur et/ou les sépare en leurs sous-unités constitutives.
 
 La DLT a d'abord été décrite comme se produisant dans l'hippocampe, où elle est censée effacer les vieux souvenirs. Par la suite, il a été montré que la DLT se produit dans beaucoup de régions du cerveau telles que le cervelet, le striatum et le cortex. L’omniprésence de la DLT sous-tend son importance dans le bon fonctionnement du cerveau.
 
 <h4> La DLT et la maladie</h4>
 
 On pense que les mécanismes défectueux de la DLT contribuent à de nombreux troubles neurologiques et cognitifs tels que la toxicomanie, le retard mental et la maladie d’Alzheimer. Des recherches sont en cours pour mieux comprendre les mécanismes de la DLT, comment les troubles neurologiques se produisent, et pour développer des traitements.

Dépression synaptique à long terme

La dépression à long terme, ou DLT, est l’une des façons dont la plasticité synaptique – les changements dans la force des synapses chimiques – peut se produire dans le ...

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Long-term Depression

synaptic pruning in long-term depression

Long-term depression, or LTD, is a form of synaptic plasticity that weakens chemical synapses over time. It acts between presynaptic and postsynaptic neurons. LTD works in opposition to long-term potentiation, or LTP, which strengthens synapses. Together, LTD and LTP are two of the main mechanisms behind learning and memory.

LTD helps the brain avoid staying locked in a fully strengthened state. If synapses were always maximally strengthened, the brain would become less efficient and it would be harder to learn new information or form new memories. By weakening weaker synapses, LTD helps prune connections and restore flexibility to the central nervous system.

One common LTD mechanism depends on calcium ions in the postsynaptic neuron after presynaptic stimulation. When presynaptic activity is infrequent or low, calcium ion influx is also low. This leads to a low calcium ion concentration in the postsynaptic cell. That signal starts a cascade that removes AMPA glutamate receptors from the plasma membrane through endocytosis.

With fewer AMPA receptors on the membrane, the postsynaptic response to the same weak presynaptic signal becomes even smaller. Fewer channels are available for positively charged ions to enter and depolarize the membrane. The neuron can later reuse these AMPA receptors or break them into subunits.

LTD was first described in the hippocampus, where it is thought to help clear old memories. It has also been found in the cerebellum, striatum, and cortex. Because LTD appears in many brain regions, it is an important part of normal brain function. Problems with LTD are thought to play a role in addiction, mental retardation, and Alzheimer’s disease, so researchers continue to study it and possible treatments.

Synaptic Pruning in Long-term Depression

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Long-term potentiation, or LTP, is a form of synaptic strengthening in the brain. It changes the strength of chemical synapses over time between pre- and postsynaptic neurons. LTP works against long-term depression, or LTD, which weakens synapses. Together, LTP and LTD are major mechanisms behind learning and memory. LTP can happen when a presynaptic neuron fires again and again and keeps stimulating a postsynaptic neuron. This is called Hebbian LTP, based on Donald Hebb’s idea that neurons...

long-term depression

Long-term depression, or LTD, is a form of synaptic plasticity that weakens chemical synapses over time. It acts between presynaptic and postsynaptic neurons. LTD works in opposition to long-term potentiation, or LTP, which strengthens synapses. Together, LTD and LTP are two of the main mechanisms behind learning and memory. LTD helps the brain avoid staying locked in a fully strengthened state. If synapses were always maximally strengthened, the brain would become less efficient and it would...

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Learn how long-term depression weakens synapses, removes AMPA receptors, and supports learning, memory, and brain flexibility in high school biology.

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Synaptic Pruning in Long-term Depression

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