Lecture 19 - Circuit Construction III

Question 1

What hampers the ability to study CNS synapses?

Answer 1

The study of CNS synapses is hampered by limited experimental access.

Question 2

True or False?:

There is a diversity of synapse types within the CNS. As such, most studies have focused on the development of inhibitory synapses.

Answer 2

False

There is a diversity of synapse types within the CNS. As such, most studies have focused on the development of excitatory synapses.

Question 3

True or False?:

CNS synapses may continuously change their physiological profile, assemble/disassemble, and change their shape (which is important for motor/sensory output and cognition).

Answer 3

True

Question 4

True or False?:

While the number of synapses per cell continually increases postnatally, the volume of neurons will eventually decrease.

Answer 4

False

The volume per neuron keeps increasing while the number of synapses will eventually start to decrease.

Question 5

The rodent retinocollicular pathway sees many important developmental processes occur. Specifically, we see the generation of RGCs and superior colliculus (SC) neurons, the formation of superficial layers in the SC, RGC axons reaching the SC, the first synapses in the SC, astrocyte formation, oligodendrocyte formation, the main phase of synaptogenesis in the SC, and the first responses to visual stimuli in the SC. Which of these processess occur embryonically and which occur postnatally?

Answer 5

Embryonically: generation of RGCs and superior colliculus (SC) neurons, the formation of superficial layers in the SC, RGC axons reaching the SC, and the first synapses in the SC

Postnatally: astrocyte formation, oligodendrocyte formation, the main phase of synaptogenesis in the SC, and the first responses to visual stimuli in the SC

Question 6

What is the homologus structure to the superior colliculus (SC) in amphibians?

Answer 6

Tectum

Question 7

What are the 3 major steps in central synapse assembly?

Answer 7

• Axo-Dendritic Contact and Initiation
• Induction (Pre-Synaptic and Post-Synaptic Differentiation)
• Synaptic Maturation

Question 8

What adhesive factors are required for axo-dendritic contact and initation?

Answer 8

Cadherins and Protocadherins

Question 9

What do synCAM, ephrin B/ephB-R, neurexin, neuroligin, and neuregulin all have in common?

Answer 9

They are all inductive factors used in pre-synaptic and post-synaptic differentiation.

Question 10

What are the 3 proposed steps in presynaptic differentiation?

Answer 10

• Initial contact is made.
• Soon after, vesicles containing presynaptic proteins are delivered to the sites of contact.
• Active zone is developed and vesicular recycling occurs.

Question 11

How long does it take for functional presynaptic machinery to be established?

Answer 11

Functional presynaptic machinery can be established within an hour of initial contact between the growth cone and the dendritic membrane.

Question 12

What are the 5 stages in the model for presynaptic assembly? What differentiates them from eachother?

Answer 12

Question 13

True or False?:

Presynaptic and postsynaptic contact will lead to the development of a synapse?

Answer 13

False

While apposed membrane contact can lead to the development of a synapse, it is also possible for the migrating cell to retreat and not form a synapse with the cell it encountered.

Question 14

True or False?:

Neuroexin and neuroligin, N-cadherin, and ephrin and eph-R hold together presynaptic and postsynaptic cells.

Answer 14

True

Question 15

How long does it take for postsynaptic sites to develop after contact?

Answer 15

Postsynaptic sites can develop within minutes of contact and detectable vesicle recycling in the presynaptic terminal.

Question 16

Which molecules induce bi-drectional “trans” synaptic adhesion and signalling during postsynaptic assembly?

Answer 16

Sidekicks, cadherins, Eph receptors, SynCAM, neurexins, neuroligins, and TrkC all induce this adhesion and signalling.

Question 17

Adhesion, induction, and maturation all are dependent on molecular factors. What can the factors for each stage be nicknamed?

Answer 17

“Stickies”, “Triggers”, and “Builders”

Question 18

True or False?:

SynCAM and Netrin-G ligands are examples of adhesion factors (“stickies”).

Answer 18

False

SynCAM and Netrin-G ligands are examples of inductive factors (“triggers”)..

Question 19

True or False?:

N-cadherin and P-cadherin are only capable of interacting with other identical cadherins to drive synaptic adhesion.

Answer 19

False

P-cadherin and N-cadherin can interact with eachother as well as identical cadherins.

Question 20

What are the 3 classes of synaptic organizers?

Answer 20

Adhesion Factors, Inductive Factors, and Maturation Factors

Question 21

What is SynCAM?

Answer 21

SynCAM is a synaptic cell adhesion molecule that drive synapse assembly.

Question 22

Is SynCAM found presynaptically or postsynaptically?

Answer 22

Both!

Question 23

What is found when SynCAM C-tail is allowed to interact with neurons? What does this prove?

Answer 23

SynCAM C-tail is part of the SynCAM that will interact with membranes in the way normal SynCAM would, but does not have the functional component of SynCAM that allows for cell adhesion. When the activity of SynCAM is disrupted by the introduction of SynCAM C-tail, there is a significant decrease in the number of synapses formed. This proves that SynCAM is required at the synapse for synapse formation.

Question 24

What happens when non-neuronal cells are modified to express SynCAM?

Answer 24

When non-neuronal cells express SynCAM, they are able to induce the formation of synapses on it from neighbouring neurons.

Question 25

What two components were sufficient to create artificial synapses on a non-neuronal cell?

Answer 25

SynCAM and GluR2

Question 26

What happens when SynCAM is overexpressed or knocked out in mutant mice?

Answer 26

In SynCAM overexpressed mice, there is an increase in the number of excitatory synapses but not change in the number of inhibitory synapses. In knockout mice, there is a decrease in the number of excitatory synapses but no change in the number of inhibitory synapses.

Question 27

True or False?:

Neurexins are found presynaptically while neuroligins are found postsynaptically.

Answer 27

True