BIO254:Silent

Introduction

A silent synapse is a special type of excitatory glutamatergic synapse that relies on NMDA receptors to the exclusion of AMPA receptors. The voltage dependency of NMDA receptors causes them to act as logical AND gates, requiring both postsynaptic depolarization and glutamate binding to trigger an excitatory postsynaptic potential (EPSP).

The iGluR channel

Most excitatory synapses in the central nervous system are glutamatergic. In these synapses, glutamate released by the presynaptic cell acts on both metabotropic (mGluR) and ionotropic glutamate receptors (iGluR) in the postsynaptic membrane. Receptors in the iGluR channel can be classified as either NMDA (N-methyl-D-aspartate) or non-NMDA (kainate and AMPA).

Non-NMDA receptors contribute to the early phase of the excitatory postsynaptic current (EPSC) and generate peak current, whereas NMDA receptors contribute to the late phase as a slower component, as can be seen in the image below. This image also shows the effect of APV (see next section) on the EPSC:

NMDA receptors (NMDAR)

NMDA receptors additionally require postsynaptic depolarization to eject a Mg²⁺ ion that blocks the channel during normal operation. As a result, the relative contribution of NMDA receptors to the EPSC depends on the postsynaptic membrane potential.

Also unlike AMPA receptors, open NMDA receptors permit the influx of Ca²⁺, which plays a role in LTP (see below).

The inactivity of an NMDA-only synapse when the postsynaptic cell is polarized below -40 mV gives the silent synapse its name.

NMDA receptors are actively inhibited by APV (R-2-amino-5-phosphonopentanoate), which can thereby regulate silent synapse activity.

Long-term potentiation

BIO254:LTP (LTP) describes the process wherein the synaptic efficacy of two neurons is strengthened over time, in a way that depends on the simultaneity of firing (spike timing dependent plasticity). The best-studied form of this is hippocampal CA3-CA1 LTP, demonstrated by Timothy Bliss and Terje Lomo (1973). Brief high-frequency (tetanic) stimulation of a presynaptic cell can result in long-term enhancement of synaptic transmission. LTP additionally exhibits the following properties:

Cooperativity: The probability of inducing LTP increases with the number of stimulated afferents, and the strength of their stimulation. This reflects a postsynaptic depolarization threshold that must be exceeded in order to induce LTP.

Input specificity: LTP is restricted to the synapses that triggered the process, and does not propagate to nearby synapses.

Associativity: Weak stimulation on one pathway may be insufficient to induce LTP, though when coupled with strong stimulation on another, LTP can be induced on both pathways.

It was found that CA3-CA1 LTP requires both NMDAR and Ca²⁺, and involves depolarization of the postsynaptic cell, activation of NMDA receptors in that cell, the resulting influx of Ca²⁺, and the activation of secondary messengers by Ca²⁺.

The specific expression mechanisms of CA3-CA1 LTP are highly controversial. However, we do know that the expression of LTP is likely to involve both pre- and postsynaptic mechanisms, and that the probability of presynaptic neurotransmitter release is increased after LTP induction. At the postsynaptic cell, AMPA receptors are inserted into the cell membrane, which increases the conductance of the AMPA channel and thereby converts silent synapses into functional ones.

After the early phase of LTP (E-LTP) in which these pre- and post-synaptic changes occur, the late phase (L-LTP) can lead to the formation of new synapses.

Unlike CA3-CA1 LTP, mossy fiber LTP is not dependent on NMDAR, and might be expressed primarily by increased presynaptic neurotransmitter release.

Recent updates to the site

List of abbreviations:

N

This edit created a new page (also see list of new pages)

m

This is a minor edit

b

This edit was performed by a bot

(±123)

The page size changed by this number of bytes

16 April 2024

			10:20		Yarn Microfluidics - Roger Dirth‎‎ 12 changes history +442‎ [Rcostello‎ (12×)]
					10:20 (cur | prev) +41‎ Rcostello talk contribs (→‎Applications)
					10:19 (cur | prev) +36‎ Rcostello talk contribs (→‎Applications)
					10:18 (cur | prev) +36‎ Rcostello talk contribs (→‎Introduction)
					10:17 (cur | prev) +38‎ Rcostello talk contribs (→‎Fabrication)
					10:17 (cur | prev) +38‎ Rcostello talk contribs (→‎Washburn Equation)
					10:16 (cur | prev) +38‎ Rcostello talk contribs (→‎Wicking Rate)
					10:16 (cur | prev) +37‎ Rcostello talk contribs (→‎Introduction)
					10:15 (cur | prev) +36‎ Rcostello talk contribs (→‎Wicking Rate)
					10:14 (cur | prev) +36‎ Rcostello talk contribs (→‎Fabrication)
					10:14 (cur | prev) +34‎ Rcostello talk contribs (→‎Applications)
					10:14 (cur | prev) +36‎ Rcostello talk contribs (→‎Introduction)
					10:13 (cur | prev) +36‎ Rcostello talk contribs (→‎Introduction)

08:11

3D Printing Overview‎ diffhist +422‎ Michele Caggioni talk contribs

15 April 2024

			23:43		User:Yanbin Huang‎‎ 2 changes history +170‎ [Yanbin Huang‎ (2×)]
					23:43 (cur | prev) 0‎ Yanbin Huang talk contribs (→‎Granted Patents)
					23:43 (cur | prev) +170‎ Yanbin Huang talk contribs (→‎Granted Patents)

			22:11		The paper that launched microfluidics - Xi Ning‎‎ 14 changes history +9,705‎ [Xning098‎ (14×)]
					22:11 (cur | prev) −6‎ Xning098 talk contribs (→‎Summary)
					22:07 (cur | prev) −12‎ Xning098 talk contribs (→‎Synthesis)
					22:06 (cur | prev) 0‎ Xning098 talk contribs
					22:06 (cur | prev) +1‎ Xning098 talk contribs
					22:05 (cur | prev) 0‎ Xning098 talk contribs
					22:03 (cur | prev) +630‎ Xning098 talk contribs
					22:01 (cur | prev) +3,189‎ Xning098 talk contribs
					21:44 (cur | prev) +688‎ Xning098 talk contribs (→‎Separation and quantification)
					21:33 (cur | prev) +306‎ Xning098 talk contribs
					21:29 (cur | prev) −2‎ Xning098 talk contribs (→‎Electrokinetic effect)
					21:28 (cur | prev) −1‎ Xning098 talk contribs (→‎Separation and quantification)
					21:27 (cur | prev) +398‎ Xning098 talk contribs (→‎Separation and quantification)
					21:24 (cur | prev) +2,812‎ Xning098 talk contribs
					21:06 (cur | prev) +1,702‎ Xning098 talk contribs

			21:45		(Upload log)‎ [Xning098‎ (4×)]
					21:45 Xning098 talk contribs uploaded File:Figure 4 Tdesign.png ‎
					21:30 Xning098 talk contribs uploaded File:Figure 3 Set-up3.png ‎
					21:24 Xning098 talk contribs uploaded File:Figure 2 Set-up1.png ‎
					21:09 Xning098 talk contribs uploaded File:Figure 1 electroosmotic flow.png ‎

			18:16		Multilayer Paper Microfluidics - Madyson Redder‎‎ 15 changes history +4,948‎ [Mredder‎ (15×)]
					18:16 (cur | prev) +540‎ Mredder talk contribs (→‎Fabrication Methods)
					18:07 (cur | prev) +822‎ Mredder talk contribs (→‎Fabrication Methods)
					17:58 (cur | prev) +1,223‎ Mredder talk contribs (→‎Fabrication Methods)
					17:47 (cur | prev) −47‎ Mredder talk contribs (→‎Motivation for Multilayer Paperfluidics)
					17:46 (cur | prev) +2‎ Mredder talk contribs (→‎Advantages)
					17:46 (cur | prev) +1,094‎ Mredder talk contribs (→‎Advantages)
					17:37 (cur | prev) +24‎ Mredder talk contribs (→‎Materials)
					17:37 (cur | prev) +619‎ Mredder talk contribs (→‎Materials)
					17:19 (cur | prev) +18‎ Mredder talk contribs (→‎Uses)
					17:19 (cur | prev) +7‎ Mredder talk contribs (→‎Uses)
					17:18 (cur | prev) −19‎ Mredder talk contribs (→‎Developing Countries and Travel)
					17:18 (cur | prev) +15‎ Mredder talk contribs (→‎Uses)
					17:16 (cur | prev) 0‎ Mredder talk contribs (→‎Uses)
					17:16 (cur | prev) +1,103‎ Mredder talk contribs (→‎Uses)
					17:14 (cur | prev) −453‎ Mredder talk contribs (→‎Motivation for Multilayer Paperfluidics)