Introduction to Synaptic Plasticity

Question 1

Some aspects of integration are activity-dependent. This means ?

Answer 1

They are influenced

by the past activity of the neuron

Question 2

Briefly explain Short-term synaptic plasticity ?

Answer 2

• Different forms, including facilitation, PTP and depression

Question 3

Briefly explain Long-term synaptic plasticity ?

Answer 3

• Significant among these is the phenomenon called long-term potentiation
• a long-lasting, activity-dependent change in synaptic efficacy

Question 4

Long-term plasticity can bidirectionally modify ?

Answer 4

Synaptic strength, either:

• Enhancing (LTP, long-term potentiation)
• Depressing (LTD, long-term depression)

Question 5

What is meant Facilitation ?

Answer 5

An increase in the amplitude of postsynaptic responses as a result of repetitive activation

Question 6

Transmitter release is triggered by ?

Answer 6

The level of presynaptic Ca2+

Question 7

What is a simple explanation for facilitation ?

Answer 7

That the initial stimulus leaves some ‘residual’ Ca2+ within the presynaptic terminal (perhaps because facilitating synapses do not bind or remove Ca2+ quickly)

Question 8

In some synapses, activity leads to a ?

Answer 8

Reduced synaptic release, that is, the amount of neurotransmitter released by an action potential reduces with time during sustained firinh

Question 9

What is a reason for synaptic depression ?

Answer 9

A limited vesicle pool

- At some presynaptic terminals, vesicle numbers are small

Question 10

Some synapses appear totally immune to depression. Give examples and why this could possibly be ?

Answer 10

• Eg. crayfish NMJs and
  chick ciliary ganglion
• Appear to have very fast vesicle pool replenishment and presumably this is functionally important to sustain reliable signalling

Question 11

What are some other mechanisms of depression ?

Answer 11

1. Inactivation of release sites
   - Fusion of one vesicle inhibits fusion of other available vesicles for several seconds
   - Clearance of vesicle proteins is thought to be a key factor

Question 12

What is another mechanism of depression ?

Answer 12

2. Calcium-inhibition of calcium influx
   - Calcium-sensing proteins such as calmodulin can actually interact with calcium channels to change presynaptic calcium entry – for example in Calyx of Held

Question 13

What is the last mechanism of depression ?

Answer 13

3. Autoreceptor-activation induced depression
   - In some systems, short-term depression arises because transmitters act on metabotropic receptors on the presynaptic terminal from which they were released (‘autoreceptors’)

Question 14

What are some examples of short-lasting presynaptic memories ?

Answer 14

Facilitation, PTP and Depression

Question 15

What can residual Ca2+ as the memory trace allow to happen?

Answer 15

• The presynaptic terminal
  can store information about its previous activity history
• This biochemical information can then be used to change presynaptic function for
  a short period of time

Question 16

What did Donald Hebb predict?

Answer 16

How synapses might strengthen to support storage of learned associations

Question 17

What can long-term potentiation (LTP) involve ?

Answer 17

LTP can involve presynaptic and postsynaptic

changes

Question 18

What are the classifications of long-term memory ?

Answer 18

Implicit (nondeclarative) and Explicit (declarative)

Question 19

Explain Implicit (nondeclarative) memory ?

Answer 19

Subconscious
Types of learning include:
1. Procedural learning (e.g. skills)
2. Nonassociative learning 
(e.g. habituation/sensitization)

Question 20

Explain Explicit (declarative) ?

Answer 20

Conscious
Types of memory encoded:
1. Semantic (e.g. facts)   
2. Episodic (e.g. events) 
- Information about context: 
what, where and when?
3. Spatial (e.g. navigation)

Question 21

What is the Hippocampus?

Answer 21

Part of the medical temporal lobe

Question 22

Effect of bilateral removal of the hippocampus ?

Answer 22

• Catastrophic effect on memory
• His procedural memory and working memory remained intact
• H.M. could not convert short-term explicit memory into long-term memory

Question 23

What leads to LTP ?

Answer 23

It is the simultaneous activation of the presynaptic and postsynaptic neuron during the
tetanus
- This is the essence of the associative nature of long-term potentiation

Question 24

Name three types of ionotropic glutamate receptor?

Answer 24

• AMPA
• NMDA
• Kainate

Question 25

What are NMDA dependent on?

Answer 25

It is both glutamate-dependent AND voltage-dependent

Question 26

CA3-CA1 LTP depnds on ?

Answer 26

NMDAR activation

Question 27

To allow Ca2+ to enter the postsynaptic neuron, two conditions must therefore be met:

Answer 27

1. presynaptic neuron must be active and release glutamate

2. postsynaptic neuron must be strongly depolarized to remove Mg2+ from the NMDA pore

Question 28

Example demonstrating link between NMDAR activation and learning ?

Answer 28

Blocking hippocampal NMDA
receptors with AP-5 inhibits
spatial learning in rats