What are the changes that occur when a growth cone turns into a pre-synapse?
- Filopodia retraction & tight junction formation
- Membrane and extracellular glycoproteins added
- Vesicles and all that other shit
Are growth cones the only part of a neuron that can make a synapse?
No – dendrites filopodia grow out to join axons and axons branch
When does synaptogenesis happen?
Varies greatly from region to region
- Most cortical synapses are created after birth
What can induce or inhibit pre-synaptic specialisation?
Guidepost cells (often glia)
What can synapse sites be dictated by?
axon guidance factors secreted from adjacent cells
What localises synapse formation?
Netrin
Name 2 synapse specific cell adhesion molecules (CAMs)
Neurexins (NRXs) and neuroligins (NLS)
What do these cell adhesion molecules allow?
Spacial segregation of different inputs/outputs
What do Purkinje fibres receive input from?
- Parallel fibres
- Molecular layer interneurons
- Climbing fibres
What do climbing fibres synapses move from to?
Some ==> dendrites
What is an IC signal that is triggered by dendrite and axon contact?
Ca flux
What do CAMs e.g. NRXs or NRLs actually cause the recruitment of?
Scaffolding proteins that help form the active zone and post synaptic density
What happens in the neuromuscuklar junction?
In the neuromuscular junction before innervation AChRs are present at low density when innervation arrives this leads to progressive clustering of AChRs under nerve terminal.
What happens in receptor clustering?
- There are preclusters of AChRs post-synaptically which suggests these can direct innervation
- However, MN connection with myotubes at random can induce clustering without pre cluster
- MNs secrete factor called agrin that induces clustering on myotubes
What does agrin bind to?
MuSK (muscle specific kinase) (autophosphorylates)
What does this receptor recruit? (agrin receptor)
Rapsyn which recruits and clusters AChRs
What is neuregulin?
Released by?
Induces what where?
Released by MN growth cones and induces AChR expression in synaptic nuclei
What happens if there is no agrin present?
If there is no agrin present i.e. away from the synapse then it inhibits AChR expression
Are Purkinje fibres plastic?
Yes
