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

Langzeitdepression oder LTD ist ein allmählicher Prozess der synaptischen Schwächung zwischen prä- und postsynaptischen neuronalen Verbindungen.
 Ein Mechanismus, durch den LTD auftritt, hängt von der Menge von Kalziumionen ab, die nach präsynaptischer Stimulierung in das postsynaptische Neuron fließen.
 Niedrige Kalziumkonzentrationen auf Grund von seltener präsynaptischer Stimulation können eine Signalkaskade auslösen, die in der Endozytose oder Entfernung von AMPA Glutamat-Rezeptoren von der Membran kulminiert.
 In der Folge wird die postsynaptische Antwort auf die gleiche sporadische präsynaptische Stimulierung weiter geschwächt.
 Daher birgt LTD wichtige Erkenntnisse, weil unbenutzte oder selten benutzte Synapsen geschwächt werden und sogar verloren gehen können, womit Resourcen und Raum frei werden, die für das Neuron für andere Funktionen genutzt werden können, wie zum Beispiel LTP-Stärkung von wichtigeren Synapsen.

Kukushkin, Nikolay Vadimovich und Thomas James Carew. "Gedächtnis braucht Zeit." Neuron 95, Nr. 2 (19. Juli 2017): 259–79. [<a href="https://doi.org/10.1016/j.neuron.2017.05.029" target="__blank">Quelle</a>]

Lüscher, Christian und Robert C. Malenka. "NMDA-Rezeptor-abhängige Langzeitpotenzierung und Langzeitdepression (LTP/LTD)." Cold Spring Harbor Perspectives in Biology 4, Nr. 6 (1. Juni 2012): a005710. [<a href="https://doi.org/10.1101/cshperspect.a005710" target="__blank">Quelle</a>]

langzeit-depression

Die Langzeit-Depression oder LTD ist einer der Wege, auf denen synaptische Plastizität im Gehirn auftreten kann. LTD ist der Prozess der synaptischen Depression, die im Laufe der Zeit zwischen prä- und postsynaptischen neuronalen Verbindungen auftritt. Die synaptische Schwächung der LTD wirkt entgegen der synaptischen Verstärkung durch die Langzeit-Potenzierung (LTP). Zusammen sind sie die Hauptmechanismen, die dem Lernen und Gedächtnis zugrunde liegen.
 
 <h4>Mechanismen der Konzentration von Kalzium-Ionen</h4>
 
 Wenn im Laufe der Zeit alle Synapsen durch LTP oder einen anderen Mechanismus maximal verstärkt werden, würde die Gehirnfunktion ein Plateau in der Effizienz erreichen, wobei dann das Lernen und die Bildung neuer Erinnerungen schwierig würde. LTD ist ein Weg, um schwächere Synapsen zu eliminieren, dadurch werden Ressourcen frei und das zentrale Nervensystem erreicht wieder eine gewisse Flexibilität. Ein Weg, der die LTD reguliert, hängt von der Anzahl der Kalzium-Ionen im postsynaptischen Neuron nach präsynaptischer Erregung ab. Seltene oder geringe präsynaptische Erregungen führen zu einem geringem Zufluss der Kalzium-Ionen und damit zu einer niedrigen Kalzium-Ionen-Konzentration im postsynaptischen Neuron.
 
 Die niedrige Konzentration der Kalzium-Ionen initiiert eine Signalkaskade, die schließlich zu der Endozytose oder der Entfernung der α-amino-3-hydroxy-5-methyl-4-isoxazolpropionsäure (AMPA)-Glutamat-Rezeptoren aus der Plasmamembran führt. Dadurch wird die postsynaptische Antwort auf die gleiche sporadische präsynaptische Erregung weiter abgeschwächt, da weniger Kanäle für den Zufluss der positiv geladenen Ionen vorhanden sind, die die Membran depolarisieren. Das Neuron verwendet die AMPA-Rezeptoren zu einem späteren Zeitpunkt wieder und/oder trennt sie in ihre Bestandteile auf.
 
 Erstmals wurde die LTD im Hippocampus beobachtet, wo man vermutet, dass sie alte Erinnerungen löscht. Später wurde gezeigt, dass LTD in vielen Hirnregionen wie dem Kleinhirn, dem Striatum und dem Kortex auftritt. Die allgegenwärtige Präsenz der LTD unterstreicht ihre Bedeutung für die ordnungsgemäße Funktion des Gehirns.
 
 <h4>LTD und Krankheiten</h4>
 
 Fehlerhafte Mechanismen der LTD sollen zu zahlreichen neurologischen und kognitiven Störungen wie Sucht, geistiger Retardierung und Alzheimer beitragen. Die Forschung ist daher bemüht, die Mechanismen der LTD besser zu verstehen. Damit man besser verstehen kann, wie neurologische Störungen auftreten, und dafür Behandlungen entwickeln kann.

Langzeit-Depression

Die Langzeitdepression (LTD) ist eine der Möglichkeiten, wie synaptische Plastizität – Veränderungen in der Stärke chemischer Synapsen – in der ...

Education

Lehre

JoVE Core

Biology

Biologie

Human Biology

Humanbiologie

Nervous System

Nervensystem

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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

what is a nervous system?

Nervous System Parts and Control

The nervous system is a network of specialized cells that keeps the body working and helps it respond to the world around it. It controls essential functions such as heart rate and breathing. It also supports movement that helps an organism escape danger. In vertebrates, the nervous system has two major parts: the central nervous system, or CNS, and the peripheral nervous system, or PNS. The CNS includes the brain, spinal cord, and retina, which is the sensory tissue of the visual system. The...

the parasympathetic nervous system

Rest and Digest: Parasympathetic Control

The parasympathetic nervous system helps the body stay calm and return to a rested state. It is one of the two major divisions of the autonomic nervous system, which controls many unconscious functions such as heart rate and digestion. Its neurons are found in the brain and the peripheral nervous system, and they send axons to muscles, organs, and glands. This system is often called the “rest and digest” system because it supports body processes that restore homeostasis. It is most active...

the sympathetic nervous system

Sympathetic Stress Response and Body Changes

The sympathetic nervous system helps the body respond to stress and danger. It is one of the two main divisions of the autonomic nervous system. When it turns on, it prepares the body for action and puts lower-priority functions, such as digestion, on hold. This response is often called the fight-or-flight system. A surprise exam can trigger it, and students may notice a tight stomach, a dry mouth, and a fast heartbeat. In a real threat, the system shifts blood away from the digestive system...

the blood-brain barrier

How the Blood-Brain Barrier Works

The blood-brain barrier is a specialized system of blood vessels that helps control what enters the brain. It delivers nutrients from the blood while tightly regulating ions, molecules, pathogens, and other substances. This semipermeable barrier protects the brain and also makes it harder to deliver some therapies. The blood-brain barrier includes several cellular parts, especially endothelial cells and astrocytes. These cells share a common basement membrane and regulate movement between the...

neuron structure

How Neurons Send Signals

Neurons send signals through a clear set of structures that let them receive, process, and pass on information. They are the main cells of the nervous system and use electrochemical signals to communicate. Neurons also talk to other cells through neurotransmitters at junctions called synapses. Most neurons share three main parts: a cell body, also called the soma, dendrites, and an axon. The soma holds the nucleus and other organelles needed for cell function. Dendrites usually receive...

glial cells

Glial Cells and Nervous System Support

Glial cells support the nervous system and work alongside neurons. They are one of the two main cell types in the nervous system. Unlike neurons, glia do not send electrical signals, but they help with nearly every other part of nervous system function. In humans, glial cells are about as numerous as neurons in the brain. In the central nervous system, glia include astrocytes, oligodendrocytes, microglia, and ependymal cells. Astrocytes are the most common glial cells. They form organized,...

action potentials

How Nerve Signals Travel in Axons

Neurons send signals through action potentials, the rapid electrical changes that move along the axon. These signals lead to neurotransmitter release at axon terminals, which passes information through the nervous system. An action potential is an all-or-none change in membrane potential, the voltage across a cell membrane. A neuron usually has a resting membrane potential of about -70 millivolts. When it receives signals from neurotransmitters or sensory input, the membrane can become more...

the resting membrane potential

How Neurons Keep a Negative Resting Charge

Neurons keep a negative resting charge across their membrane. This electrical difference, called the membrane potential, comes from how ions move and how the membrane lets them pass. In a resting neuron, the inside is typically around -70 millivolts and is more negative than the outside, so the cell is polarized. Two main factors create this resting state. First, the membrane is selectively permeable, which means most ions and molecules cannot cross the lipid bilayer without help from ion...

long-term potentiation

Synaptic Strengthening in Learning and Memory

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...

the synapse

How Neurons Signal at Synapses

Neurons communicate through synapses, the points where two neurons meet to pass on signals. At a synapse, the sending neuron is the presynaptic cell, and the receiving neuron is the postsynaptic cell. Most neurons can serve in both roles because they send and receive information. Electrical synapses move signals directly between cells. The presynaptic and postsynaptic cells are linked by gap junctions, which are proteins that physically connect them. This type of synapse can pass electrical...

key terms and concepts

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

Synaptic Pruning in Long-term Depression | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

Die JoVE-Serie erweckt die Biologie durch über 300 prägnante und leicht verständliche animierte Video-Lektionen zum Leben, die Schlüsselkonzepte der Biologie erklären, sowie durch mehr als 150 Videos von Wissenschaftlern in der Praxis, die aktuelle Forschungsexperimente in den Labors von heute zeigen.

myJoVE Corporation

Synaptic Pruning in Long-term Depression

Description

Transcript

Tags