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Flashcards in Synaptogenesis] Deck (18)
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What word can be used to describe synapse formation

Competitive - not all nerves/axons make synapses - not all synapses persist


What is an example of a cell that is present before sensory innervation

Merkel cells - specialised epithelium overlaying free nerve endings forming Merkel discs


What are the morphological changes that occur in synaptogenesis

Growth cone turns into a pre-synapse
The post synapse develops specializations


What is interesting about the cat visual cortex in early infants

At around day 10 - number of synapses/neurons increase as this is when the kitten first opens its eyes
Shows the synapse requires sensory input in order to differentiate


How might the site availability for a synapse be restricted

Astrocytes may cover the length of the cell body - only some dendrites are free for synaptogenesis


How might post-synaptic cells be specialised for synapse formation

May have pre-prepared sites e.e cadherin/other adhesion molecules


How does the neuromuscular junction form

Initially - receptors are diffusely distributed across the muscle cell
Agrin (a secreted proteoglycan) is produced by motor axons and released from their terminals - These are thought to induce clustering of AchR on the surface of the cell directly below the incoming motor axon terminal
Expression of genes encoding AchR subunits increases at the location underlying the terminal - simultaneously these genes are suppressed in the remaining area of the cell
Newly synthesised receptors are then incorporated
All this creates localisation


What is the difference between the motor neurons innervating pectoral muscle and motor neurons innervating the cutaneous maximus and latissimus dorsi

Neurons innervating pectoral muscles develop monosynaptic connections whereas cutaneous maximus and lats receive polysynaptic input from interneurons


How is the difference in innervation between pecs and lats controlled

Controlled by GDNF secreted from the cutaneous maximus and latissimus dorsi which turns on the transcription factor Pea3 in the motor neurons


What happens when there is a loss of Pea3

Motor neurons innervating cutaneous maximus and latissimus dorsi have the dendritic morphology of pectoral muscle (monosynaptic) innervating motor neurons and incorrect proprioceptive connections


What happens when there is a lack of synaptic input causing a loss of target neurons and the neuron synthesis neurotrophins

Anterograde transport of the neurotrophins
Trophic support not only for the targets in the periphery but there are complex interacions going on in the CNS


What is the primary determinant for synaptic survival

Co-ordinated synaptic activity pre and post synaptically


How does altering activity lead to changes in NMJ survival

Initially - multiple motor neurons innervate a single muscle fibre
Changes - one motor neuron fires and causes the muscle fibre to contract
This causes trophin release that supports that neuron so it survives - others die


What induces receptor clustering

Ach receptor inducing activity (ARIA)
Released by motor neurons - increases AchR subunit mRNA - especially e subunit which replaces the y subunit in the mature receptor


What role does ARIA have in the CNS

Member of the neuregulin family
multiple members of the family found in the CNS
Can upregulate NMDA receptors in the developing cerebellum


What is the role of Torpedo californica

Used to investigate clustering factor
Tissues with high expression of subunits allow for production of an electric organ capable of 50V discharge to stun prey/predator


What is the mechanism of agrin action

Binds to muscle specific kinase (MUSK)
Engages with the receptors via rapsyn
MUSK KO mice are agrin insensitive


What is the role of rapsyn

Clustering needs rapsyn
AchR alone - no clustering
AchR and rapsyn = clustering