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3rd Year Biomed > Neuroscience - Classical neurotransmitter storage and release > Flashcards

Neuroscience - Classical neurotransmitter storage and release Flashcards

1
Q

What is a quantal?

A

1 quantum of neurotrasmitter = content of 1 synaptic vesicle

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2
Q

How many molecules approx are in 1 quantal?

A

5-10,000

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3
Q

What does release of a single quantum cause?

A

A mini postsynaptic potential (can be spontaneous) - subthreshold for action potential

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4
Q

What does the simultaneous release of many quanta cause?

A

A larger potential change sufficient to trigger an action potential

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5
Q

What is synaptic delay?

A

Time between stimulation of the presynaptic neuron and the response in the postsynaptic cell

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6
Q

What is the approximate synaptic delay time?

A

approx 0.4-5 milliseconds

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7
Q

What is the quanta release in approx 1.5 milliseconds upon stimulation at the neuromuscular junction?

A

~300 quanta released in ~1.5 milliseconds

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8
Q

How many ionotrophic receptors can each quanta activate?

A

2000 ionotrophic receptors

- permits 70 million ions to enter the post-synapse

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9
Q

300 quanta release causes what kind of potential?

A

Excitatory postsynaptic potential (EPSP) of tens of mV eliciting an action potential

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10
Q

How many quanta are released at central synapses and how many ion channels are activated?

A

~5-10 quanta

30 ion channels

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11
Q

What is the ‘active zone’?

A

Site of neurotransmitter release

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12
Q

What is the basic process of synaptic vesicle trafficking?

A

1) Vesicle release from endosome and neurotransmitter uptake
2) Trafficking to plasma membrane
3) Docking
4) Priming
5) Calcium signal causing exocytosis and neurotransmitter release
6) Endocytosis
7) Fusion to endosome

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13
Q

What was the Nobel prize in Physiology or Medicine given for in 2013?

A

Discoveries of machinery regulating vesicle traffic

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14
Q

What is the most abundant protein on the synaptic vesicle surface?

A

Synaptobrevin (VAMP)

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15
Q

Name some other synaptic vesicle proteins

A
  • Synaptotagmin

- Synapsin

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16
Q

What experimental evidence show SNAREs roles in exocytosis?

A

1) Cleavage by bacterial toxin (botulinum toxin)
2) Loss of or mutations if SNARE proteins

Causes impaired locomotion and defective transmitter release

17
Q

What are the 3 SNARE proteins and where are they found?

A

1) Synaptobrevin (v-SNARE)
- found on the surface of synaptic vesicles

2) SNAP-25 (t-SNARE)
- Anchored to the cytosolic face of the pre-synaptic neuron

3) Syntaxin (t-SNARE)
- transmembrane protein of cytosolic face of pre-synaptic neuron

18
Q

What are the domain structures of the 3 SNARE proteins?

A

Synaptobrevin

  • 1 SNARE motif
  • Transmembrane domain

SNAP-25

  • 2 SNARE motifs
  • Anchored to membrane via palmitoylation of cysteines

Syntaxin

  • 1 SNARE motif
  • A Habc domain
  • Flexible linker in between 2 above domains
  • Transmembrane domain
19
Q

What kind of domains are SNARE motifs?

A

Coiled-coil (alpha helical) domains

20
Q

What are the 3 stages of SNARE complex assembly

A

1) Nucleation
- binding of v-SNARE and t-SNARE

2) Zippering
- Pulling the vesicle close to the membrane
- Induced by Ca2+

3) Fusion
- fusion of the vesicle membrane with the membrane of the pre-synaptic neuron

21
Q

How does membrane fusion occur?

A
  • Energy from v and t SNARE coiling pulls membranes close together
  • Water molecules are displaced from the hydrophilic faces of the membrane
  • Mixing of lipids from from the facing leaflets of neighbouring membranes forms a connecting stalk (STALK FORMATION)
  • The other leaflets of the membranes are pulled apart forming a new bilayer (HEMIFUSION)
  • The force exerted by the fusion complex on the membrane anchors of the SNARE proteins disrupts the bilayer causing fusion
    (FUSION)
22
Q

What is Munc18 and what is its function?

A
  • A SM protein family member
  • Cytosolic protein that regulates fusion by binding to syntaxin in 2 ways
  • Deletion/mutation prevents fusion
23
Q

In what 2 ways does Munc18 bind to syntaxin and what does this cause?

A

1) Binds to closed conformation of syntaxin
- Regulates fusion
- prevents release until appropriate signal

2) Binds to assembling SNARE complex via N-terminus of syntaxin
- essential for fusion

24
Q

What are the 3 active zone proteins and what are their general roles?

A

Munc13, RIM, and Rab3a

Roles in priming vesicles for release and in physically linking vesicles, Ca2+ channels and other presynaptic proteins in the active zone

25
Q

What is the structure of Munc13 and what are its roles?

A
  • MUN domain interacts with SNAREs or SM proteins
  • C2A domain forms homodimer
  • Regulatory region composed of:
    > calmodulin-binding sequence
    > C1 domain
    > C2B domain that binds Ca2+

Essential for vesicle priming, regulated by Ca2+

26
Q

What is the structure and function of RIM?

A
  • 2 alpha-helices that interact with vesicular Rab3a
  • Zinc finger that binds Munc13 C2a domain preventing homodimerisation
  • PDZ domain that binds Ca2+ channels
  • C2B domain

Regulates Munc13 priming
Tethers Ca2+ channels in proximity to docked vesicles
Links various active zone proteins

27
Q

What is the structure and function of Rab3a?

A
  • Small GTPase
  • Cycles between inactive GDP-bound cytosolic form and an active GTP-bound membrane associated form
  • Interacts with RIM and possible Munc18
  • Assembles active zone compartments
  • Promotes vesicle docking by regulating vesicle-cytoskeleton interactions
  • May signal arrival of docked vesicle to RIM-Munc13
28
Q

How is SNARE complex dissembly carried out?

A
  • NSF (an ATPase) binds to alpha-SNAP (A soluble NSF attachment protein
  • NSF uses energy from ATP hydolysis to unravel the coiled-coil interaction between v and t SNARE
29
Q

What occurs to synaptobrevin, SNAP-25 and syntaxin after SNARE dissembly

A

Synaptobrevin is recycled to the vesicle

SNAP-25 and syntaxin remain in plamsa membrane

30
Q

What is the structure of synaptotagmin?

A
  • N terminal integral membrane domain
  • large cytoplasmic domain with 2 C2 domains, C2A and C2B that bind Ca2+
  • Interacts with memvrane phospholipids and SNAREs in a Ca2+ dependant manner
31
Q

What is the structure of complexin?

A
  • small cytoplasmic protein

- central alpha-helical domain that binds to partially assembled SNARE complex

32
Q

Explain the model of synaptotagmin/complexin action

A

1) Complexin clamps partially assembled SNARE complex and superprimes the vesicle
2) Ca2+ bound synaptotagim interacts with SNARE complex and membrane phospholipids releasing complexin clamp
3) Synaptotagmin arrests the docked vesicles
4) Ca2+ binding to synaptotagmin pulls vesicles and membrane into tight apposition, leading to nucleation and zippering
5) Complexin binds and stabilises the SNARE complex

33
Q

What are the roles of the other vesicle protein, synapsin?

A
  • Regulates numbers of vesicles in reserve and releasable pools
  • Implicated in synaptic plasticity and neurodevelopmental disorders

3rd Year Biomed (44 decks)

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