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

- [Anlatıcı] Uzun dönem depresyon ya da UDD, presinaptik ve postsinaptik nöron bağlantıları arasında zaman içinde oluşan bir sinaptik zayıflama sürecidir.
 UDD'yi meydana getiren mekanizma, presinaptik stimülasyon sonrasında postsinaptik nörona ulaşan kalsiyum iyonlarının miktarına bağlıdır.
 Sık olmayan presinaptik stimülasyondan kaynaklı düşük kalsiyum yoğunluğu, endositozla sonuçlanan bir sinyaller serisini başlatabilir ya da membrandaki AMPA glutamatlarının yok olmasıyla sonuçlanabilir.
Aynı düzensiz presinaptik stimülasyona yönelik postsinaptik tepki daha da zayıflar.
 Bu yüzden UDD öğrenme açısından önemlidir çünkü kullanılmayan ya da nadiren kullanılan sinapslar zayıflar ve hatta törpülenebilir.
 Nöron tarafından UDD'nin daha önemli sinapsları güçlendirmesi gibi başka işlevler için kaynakların ve alanın serbest bırakılması gerekir.

Kukushkin, Nikolay Vadimovich ve Thomas James Carew. "Hafıza zaman alır." Neuron 95, hayır. 2 (19 Temmuz 2017): 259–79. [<a href="https://doi.org/10.1016/j.neuron.2017.05.029" target="__blank">Kaynak</a>]

Lüscher, Christian ve Robert C. Malenka. "NMDA Reseptörüne Bağlı Uzun Süreli Güçlendirme ve Uzun Süreli Depresyon (LTP / LTD)." Biyolojide Cold Spring Harbor Perspektifleri 4, no. 6 (1 Haziran 2012): a005710. [<a href="https://doi.org/10.1101/cshperspect.a005710" target="__blank">Kaynak</a>]

uzun süreli depresyon

Uzun süreli depresyon veya LTD, beyinde sinaptik plastisitenin (kimyasal sinapsların gücündeki değişiklikler) ortaya çıkmasının yollarından biridir. LTD, pre ve postsinaptik nöronal bağlantılar arasında zaman içinde meydana gelen sinaptik zayıflama sürecidir. LTD'nin sinaptik zayıflaması, uzun vadeli güçlendirme (LTP) ile sinaptik güçlenmeye karşı çalışır ve birlikte öğrenme ve hafızanın altında yatan ana mekanizmalardır.

<h4>Kalsiyum İyon Konsantrasyon Mekanizması</h4>

 Zamanla, tüm sinapslar LTP veya başka bir mekanizma ile mümkün olduğunca güçlendirilirse, beyin öğrenme ve yeni anılar oluşturma konusunda zorlanmaya başlayacak, plato evresine girecektir. LTD, daha zayıf sinapsları yok etmenin, böylece kaynakları serbest bırakmanın ve merkezi sinir sistemine esneklik kazandırmanın bir yoludur. LTD'nin meydana geldiği mekanizmalardan biri, presinaptik stimülasyondan sonra postsinaptik nörondaki kalsiyum iyonlarının sayısına bağlıdır. Seyrek veya düşük presinaptik stimülasyon seviyeleri, düşük kalsiyum iyonu akışına ve sonuç olarak postsinaptik nöronda düşük kalsiyum iyonu konsantrasyonuna yol açar.

Düşük kalsiyum iyonu konsantrasyonu, endositoz veya &alfa;-amino-3-hidroksi-5-metil-4-izoksazolepropiyonik asit (AMPA) glutamat reseptörlerinin plazma membranından çıkarılmasıyla sonuçlanan bir sinyal kaskadını başlatır. Sonuç olarak, aynı sporadik presinaptik stimülasyona postsinaptik yanıt daha da zayıflar, çünkü pozitif yüklü iyonların membrana girmesi ve depolarize edilmesi için daha az kanal vardır. Nöron, AMPA reseptörlerini daha sonra yeniden kullanır ya da bunları kurucu alt birimlerine parçalar.

LTD’nin ilk olarak eski anıları temizlediğine inanılan hipokampusta meydana geldiği tanımlandı. Daha sonra, beyincik, striatum ve korteks gibi birçok beyin bölgesinde meydana geldiği gösterilmiştir. LTD'nin her yerde bulunması, beynin düzgün işleyişindeki öneminin kalbinde yer almaktadır.

<h4>LTD ve Hastalık</h4>

LTD'nin hatalı işlev mekanizmalarının bağımlılık, mental retardasyon ve Alzheimer hastalığı gibi çok sayıda nörolojik ve bilişsel bozukluğa katkıda bulunduğu düşünülmektedir. LTD'nin mekanizmalarını, nörolojik bozuklukların nasıl ortaya çıktığını ve tedavilerin nasıl geliştirilebileceği konusunda araştırmalar devam etmektedir.

Uzun Süreli Depresyon

Uzun süreli depresyon veya LTD, sinaptik plastisitenin (kimyasal sinapsların gücündeki değişiklikler) meydana gelebileceği yollardan biridir.

Education

JoVE Core

Biology

Biyoloji

Human Biology

İnsan Biyolojisi

Nervous System

Sinir Sistemi

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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

JoVE Core serisi, biyolojinin ana konseptlerini açıklayan 300 adet kısa ve kolay anlaşılabilir olan video dersleriyle ve günümüz laboratuvarlarında yürütülen gerçek araştırmaları gösteren 150'den fazla \"bilim insanları iş başında\" videolarıyla biyolojiye hayat vermektedir.

myJoVE Corporation

Synaptic Pruning in Long-term Depression

Description

Transcript

Tags