NEUS 609 - Neurotransmitter Release

synaptic vesicle-associated proteins

proteins embedded in vesicular membrane regulating vesicles’ life cycle

• about 200 per vesicles

synaptic vesicle cycle

1. vesicle loading

2. movement into reserve poll and mobilization

3. docking t presynaptic membrane

4. priming

5. fusion (NT release)

6. endocytosis and recycling

vesicle loading

process of loading NTs into vesicles against their concentration gradients using respective transporters

glutamate

aka GLU

small molecule NT synthesized from glutamine from astrocytes, transported into vesicles by VGLUT transporters, reuptake in minor

Gamma-aminobutyric acid

aka GABA

small molecule NT synthesized from glutamine from astrocytes, transported into vesicles, 80% recycled

Catecholamines

Ex: dopamine (DA), norepinephrine (NE), epinephrine (E)

small molecule NT synthesized by tyrosine hydroxylase in terminal, E and NE can be derived from DA by vesicular enzymes. Majority of them is recycled.

Serotonin

small molecule NT synthesized from tryptophan and packaged into vesicles. Reuptake is a major route of termination.

Acetylcholine

aka ACh

synthesized in terminal, termination by hydrolysis in synaptic cleft via acetylcholinesterase

neuropeptides

vesicular loading step only applies to small molecule NTs, as ___ are derived from cell body and arrived prefilled and ready for release.

reserve pool

___ is AWAY FOM ACTIVE ZONE, and is made of microfilaments and synapsin proteins

non-phosphorylated

__ synapsins cluster vesicles together with actin filaments into reserve pool creating caged-vesicles

phophorylated

___ synapsins release vesicles from reserve pool, allowing them to move to active zone of presynaptic terminal

PKA

synapsin proteins in reserve pool are phosphorylated by calcium-mediated kinases like ___

cAMP

calcium influx causes increased levels of ___ which activates PKA and phosphorylates synapsins

Rab3

when docking at the presynaptic membrane, vesicles associate with ___ and bind GTP

RIM, Munc13

GTP-bound Rab 3 recruits __ (Rab 3 interacting molecule) and __ both of which anchor vesicles to presynaptic membrane

DOCKED

after vesicles anchored to presynaptic membrane ala ___, Rab3 is released and priming starts

priming

hold vesicle in close apposition to the presynaptic membrane using the SNARE complex proteins

SNARE protein complex

3 proteins interacting to hold vesicles to presynaptic membrane

snap25

• target snare protein

• on cytoplasmic side of presynaptic membrane

• associate with the zipper domain formed by syntaxin and synaptobrevin

syntaxin

• target snare protein

• transmembrane protein on presynaptic membrane

• associate with synaptobrevin to form zipper domain

synaptobrevin

• vesicular snare protein

• transmembrane protein on vesicular membrane

• associate with syntaxin to form the zipper domain

SM proteins

example: Munc 18

required for exocytosis by facilitating “clasping” of SNARE proteins

C2, ,synaptotagmin

When vesicles fuse with presynaptic membrane, it is when calcium binds to the __ domains on __ which causes conformational changes and forces the vesicles into the membrane

clathrin, dynamin, clathrin

Endocytosis and recycling

1. __ is recruited and initiates inward bending of membrane and endocytosis

2. ___ pinches off budding membrane to create vesicles

3. ___ is released and new vesicle joins reserve pool

quantal unit

clathrin is the reason for the __ of neurotransmission as all the vesicles need to be the same size

expand

without clathrin to induce endocytosis, the presynaptic membrane would __ and presynaptic terminal would run out of vesicles at some point

60

__ seconds is the time is takes to go through the whole vesicle cycle

• loading and endocytosis are the rate limiting steps, thus the need for a reserve pool