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yonghyeon
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neruo

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Miller, G.
W., Wang, Y.
M., and Caron, M.
G.
(2000).
Mice lacking
the norepinephrine transporter are supersensitive to psycho-
stimulants.
Nature Neurosci.
3, 465–471.
Zucchi, R., Chiellini, G., Scanlan, T.
S., and Grandy, D.
K.
(2006).
Trace amine-associated receptors and their ligands.
Br.
J.
Phar-
macol.
149, 967–978.
Ariel Y.
Deutch and Robert H.
Why are most synapses chemical?
Chemical synapses are characterized by great fl exibil-
ity.
Chemical
synapses often are modifi ed by prior activity in the
presynaptic neuron.
In
Fundamental Neuroscience, Third Edition 157 © 2008, 2003, 1999 Elsevier Inc.
158 8.
RELEASE OF NEUROTRANSMITTERS
II.
CELLULAR AND MOLECULAR NEUROSCIENCE
D D
E
F F
II.
At a synapse between two neurons, this might
represent the release of 1 to 10 vesicles.
8.1 and 8.2).
(B) Shortly
(5 ms) after stimulation, vesicles were seen to fuse with the plasma
membrane.
Vesicles fuse about 50 nm from rows
of intramembranous particles thought to include Ca2+ channels.
(F) Schematic rendering
of an active zone based on tomographic analysis.
Parts A and B from Heuser (1977); part C from
Heuser et al.
(1979).
Part B reproduced from the Journal of Cell Biology
88, 564–580 (1981).
(D–F) After Harlow et al.
(2001).
Direct recycling
FIGURE 8.2 The life cycle of synaptic vesicles.
Transmitter-fi lled vesicles can be observed in clusters in the vicinity of the active zone.
Some
vesicles are recruited to sites within the active zone in a process called docking.
These vesicles subsequently are primed for release.
Transmitter exits through this fusion pore.
After or
during this recycling process, the vesicle must be refi lled with transmitter.
TRANSMITTER RELEASE IS QUANTAL 159
160 8.
RELEASE OF NEUROTRANSMITTERS
II.
8.1).
8.1; also, see discussion later).
The conse-
quence is the release of about 300 quanta within 1.5 ms.
The anatomy and physiology are somewhat differ-
ent at fast central synapses.
A typical varicosity or bouton contains
one to four active zones.
At any single active zone, an
action potential may release zero, one, or perhaps two
vesicles.
In describing synaptic transmission, two parameters
are particularly important.
These parameters are discussed further
later.
II.
Thus a rise in
intracellular Ca2+ is the essential trigger for vesicle
fusion.
Why then does
transmitter secretion occur only for a millisecond or
so?
8.3).
8.3A and 8.3B).
8.3C).
This signal, some-
times called residual Ca2+, is what is detected by fl uo-
rescent indicator dyes.
8.3).
The on rate must be particularly fast.
RELEASE OF NEUROTRANSMITTERS
II.