Synaptogenesis

Question 1

3 stages of development in synaptogenesis

Answer 1

1) synapse formation and differentiation (forms pre/post synaptic cells)
2) circuit refinement
3) synaptic growth and maintenance (columnar organisation occurs after refinement)

Question 2

synapse density

Answer 2

number of synapses created and the number of synapses removed
turnover

Question 3

developmental changes in the synapse

Answer 3

birth - 6months (synaptic contact > pruning)
6 months - 3 years (ASD feature detection)
3 years onwards - synaptic pruning > contact

15-20 yrs have large scale changes

Question 4

what does the postsynaptic density contain

Answer 4

clustered receptors (few nm wide)
e.g. AChR (coded receptors), codes 4 aspects of the stimulus (modality/intensity/location/duration)

Question 5

Transgenic mice expressing fluorescent proteins (CFP/YFP)

Young et al., 2003

Answer 5

in-vivo innervation
a-bungarotoxin - snake venom blocks AChR function and labels post-synaptic membrane (permanent- forms synapse)
each MN innervates many target muscles

Question 6

NMJ adult vs embryonic

Answer 6

MN growth cone releases ACh before myotube contraction - transmission at NMJ is weak/subthreshold (embryogenesis)
terminal, broad AP in adult pre-terminal axons are myelinated

Question 7

post synaptic differentiation in NMJ

Answer 7

spontaneous AChR clusters form on muscle (absence of light)
neurites synapse on AChR (cause further clustering)
spontaneous clusters remain even if no nerve is present
Receptors not hit by clusters disappear
innervation causes synthesis of new AChR

Question 8

what is agrin

Answer 8

secreted factor
induces AChR clustering in cultured myotubes (C2C12 muscle cells)

Question 9

agrin KO

Answer 9

impairs postsynaptic function
no clusters/no axon guidance

Question 10

what do clusters activates

Answer 10

MuSK (muscle specific kinase) (TRK) - agrin R
Rapsyn (binds to AChR) downstream effector of MuSK

Question 11

Musk/rapsyn/agrin mutants

Answer 11

musk mutant - no NMJ/no clustering/agrin signalling required for clustering
rapsyn mutant - needed for clustering/diffuse clusters
agrin mutant - needed for maintenance/growth/clusters formed but not sustained

Question 12

how does NT release suppress AChR clustering

Misgeld et al., 2005

Answer 12

ChAT -> choline acetyltransferase (enzyme used in ACh synthesis)
ACh prevents AChR expression
agrin prevents ACh release, causes AChR clusters

Chat-/- clustering
agrn-/- declustering, no synapses

Question 13

molecules involved in synaptic maturation

Answer 13

agrin (frog/mouse) - increase AChR clustering/Musk activation
ACh - decreases AChR synthesis/clustering

both ACh and agrin are post synaptic

Question 14

what are boutons

Answer 14

presynaptic terminals which form synapses

Question 15

3 factors needed for synapse formation

Answer 15

1) priming factors - neuronal(FGF/wnt) glial (cholesterol/TSP)

2) adhesive factors - cadherins/protocadherins inductive factors - Syn CAM/NXN/NLG/narp/EphrinB/EphBR

3) de/stabilising factors - activity/ubiquitination for pruning

Question 16

is agrin essential for CNS synaptogenesis and why

Answer 16

no

Agrin -/- causes no change in PSD-95 quantity

Question 17

types of synapses

Answer 17

excitatory (glutamate synapses) on spine
inhibitory (GABAergic) on shaft

neurexin is common in both

Question 18

Priming diffusable factors

Terauchi et al., 2010

Answer 18

FGF 7/22 released post synaptically and binds presynaptically
VGLUT - measures excitatory synapses VGAT - measures inhibitory synapses

FGF22 KO in CA3 neurons - decreased vGLUT/decreases excitatory synapses/decreases stochastic events
FGF7 KO - decreased VGAT/decreases inhibitory synapses

Question 19

cell adhesion factors (transmembrane proteins)

Answer 19

NRX
NLG
CASK

Question 20

neurexin beads

Answer 20

neurexin has no concept of identity

Question 21

neuroligins (1-4)

Answer 21

NLG1/3 - induces glutamatergic synapse formation (co-localised with PSD-95)
NLG 2 - induces GABAergic synapse formation (co-localised with gephyrin)

Question 22

NLG triple KO (1/2/3)

Answer 22

still forms synapses
no significant changes in PSD length/synaptic cleft width/no. of docked vesicles

Question 23

NLG-1 competition

Answer 23

co-culture Nlg1-/- and Nlg+/+ causes an imbalance

Question 24

glutamate uncaging

Answer 24

caged glutamate is inert and cannot interact with the receptor
UV light releases Glutamate
new spine formed which matures
in young networks - glutamate acts at a distance

Question 25

GABA uncaging

Answer 25

GABA is excitatory and causes depolarisation (early in development)
at site of uncaging - GABA forms inhibitory postsynaptic receptors and new spines
spine activation formed inhibitory synapses

Question 26

pruning

Answer 26

many neurons compete for 1 postsynaptic receptor

occurs in: NMJ/visual system/cerebellum

Question 27

synapse elimination

Answer 27

occurs in first 2 weeks post-natal
occupies less synaptic space

inverse correlation between relative motor unit size (competition sites) and synaptic occupancy

Question 28

competition between axons

Answer 28

synaptically active axons out-compete silent axons
synapses with no NT are retracted e.g. AChRs

Question 29

axon thickness and ACh

Answer 29

ChAT+/+ - ACh release and thicker axons
ChAT-/- - no release and thinner axons
no ACh release - similar diameter

Question 30

CNS refinement at the retinogeniculate synapse

Answer 30

LGN receives input from RGCs
axon recruitment : if little current - fewer axons recruited if increased current - more axon excitation, bigger postsynaptic response - graded