CSB332H1 Lecture Notes - Lecture 9: Axon Terminal, Dynamin, Cell Membrane
14 May 2018
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Lecture 9: Vesicle Release & Recovery
Dale’s Law:
• Recently believed that each neuron produces and release one type of neurotransmitter
(i.e. GABAergic neurons only make and release GABA neurotransmitters)
ð New evidence has come that suggests neurons can contain and release
more than one
kind of neurotransmitter (i.e. GABA-Glycine, Dopamine-GABA, Acetylcholine-
Glutamate…)
Presynaptic Structures:
• Synaptic Vesicles:
o Presynaptic sites for neurotransmitter storage
• Active Zones:
o Presynaptic regions characterized by cluster of synaptic vesicles
• Boutons:
o Presynaptic nerve terminal expansion onto nerve cells; site of neurotransmitter release
Neurotransmitter Release – Exocytosis:
• AP travels toward the boutons (axon terminal) to depolarize the highly localized VG-Ca2+
causing an influx of Ca2+ triggering neurotransmitter release
o Increase in [Ca2+] within the synaptic terminal causes release of neurotransmitter
• Ca2+ influx results in the fusion of synaptic vesicles with the plasma membrane of the
axon terminal => neurotransmitters are released by exocytosis
o Neurotransmitter enter a space between pre- and postsynaptic neuron = synaptic cleft
§ Synaptic proteins are found in the axon terminal and synaptic cleft
Overview of Presynaptic Activity:
• Cytomatrix Active Zone (CAZ) is an active region on the presynaptic membrane that has
specific docking sites which are regions localized near VG-Ca2+ channels
o CAZ proteins and SNARE proteins aid in the fusion of synaptic vesicles to the
presynaptic axon terminal following Ca2+ influx
• Presynaptic membrane experiences rapid form of classic endocytosis at specific regions
which is involves GTPase dynamin:
o Dynamin will function to pinch off the endocytosed membrane that is specific; retains
memory and proteins of synaptic vesicle
§ Endocytosed vesicle will be reformed and filled with neurotransmitters again
ð Endocytosis is essential – presynaptic membrane experiences
constant exocytosis causing it to continuously get bigger
o If endocytosis does not occur, presynaptic membrane
will exceed size of postsynaptic membrane not allowing
them to align appropriately
Document Summary
Lecture 9: vesicle release & recovery: recently believed that each neuron produces and release one type of neurotransmitter (i. e. gabaergic neurons only make and release gaba neurotransmitters) New evidence has come that suggests neurons can contain and release more than one kind of neurotransmitter (i. e. gaba-glycine, dopamine-gaba, acetylcholine- Presynaptic structures: synaptic vesicles, presynaptic sites for neurotransmitter storage, active zones, presynaptic regions characterized by cluster of synaptic vesicles, boutons, presynaptic nerve terminal expansion onto nerve cells; site of neurotransmitter release. Synaptic proteins are found in the axon terminal and synaptic cleft. Endocytosed vesicle will be reformed and filled with neurotransmitters again. Endocytosis is essential presynaptic membrane experiences constant exocytosis causing it to continuously get bigger: if endocytosis does not occur, presynaptic membrane will exceed size of postsynaptic membrane not allowing them to align appropriately. Primed position has a 4-helix confirmation: syntaxin (1)/synaptobrevin (1)/snap-25 (2) Complexin is displaced and the fusion of synaptic vesicle with the presynaptic membrane occurs.
