1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in...
-
Upload
jean-mills -
Category
Documents
-
view
216 -
download
2
Transcript of 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in...
![Page 1: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/1.jpg)
1
Bi / CNS 150 Lecture 8
Synaptic inhibition; cable properties of neurons;electrical integration in cerebellum
Wednesday, October 15, 2013
Henry Lester
Chapter 2 (p. 28-35); Chapter 10 (227-232)
![Page 2: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/2.jpg)
Binding region
Membrane region
Cytosolicregion
Colored by secondary
structure
Colored by subunit(chain)
~ 2200 amino acids in 5 chains
(“subunits”),
MW ~ 2.5 x 106
2
Nicotinic ACh, GABAA , and glycine receptors look alike at this resolution (prev. lecture)
![Page 3: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/3.jpg)
The pentameric GABAA and glycine receptors look like ACh receptors;
but they are permeable to anions (mostly Cl-, of course)
1. -amino-butyric acid (GABA) is the principal inhibitory transmitter in the brain.
2. Glycine is the dominant inhibitory transmitter in the spinal cord & hindbrain.
GABAA receptors are more variable than glycine receptors in subunit composition and therefore in kinetic behavior.
. . Cation channels become anion channels with only
one amino acid change per subunit, in this approximate
location
Like a previous lecture
![Page 4: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/4.jpg)
A Synapse “pushes” the Membrane Potential Toward the Reversal Potential (Erev) for the synaptic Channels
4
At Erev , the current through open receptors is zero.
Positive to Erev, current flows
outward
Negative to Erev, current flows inward
ACh and glutamate receptors flux Na+ and K+,
(and in some cases Ca2+),and Erev ~ 0 mV.
-20
-50
-80
-100
-5
+20
+40
+60
+80Membrane potential
Resting potential
EK
ENa
At GABAA and glycine receptors,
Erev is near ECl ~ -70 mV
Like Figure 10-11
![Page 5: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/5.jpg)
5
Benzodiazepines (= BZ below):
Valium (diazepam), (Ambien, Lunesta are derivatives)
Pharmacology of GABAA Receptors: activators
phenobarbital site is unceratin
The natural ligand binds at subunit interfeces
(like ACh at ACh receptors)
![Page 6: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/6.jpg)
The AChBP interfacial “aromatic box” occupied by nicotine (prev. lecture)
Y198C2
Y190C1
Y93A
W149B
non-W55D
(Muscle Nicotinic numbering)6
. . . GABA and glycine also make cation- interactions
![Page 7: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/7.jpg)
GABAA and Glycine blockers bind either at the agonist site or in the channel
Agonist site
Picrotoxin
(GABAA & glycine
receptors)
Strychnine
(glycine receptor)
Bicuculline
(GABAA receptor
![Page 8: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/8.jpg)
How does the receptor transduce binding into channel gating? (prev. lecture)
8
OPENCLOSED
Twist?
Corringer, J
Physiol 2010
Swivel?
Miyazawa, Nature
2003
. . . Both ideas are also in play for
GABA or glycine receptors
![Page 9: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/9.jpg)
We have Completed our Survey of Synaptic Receptors
9
A. ACh, Serotonin 5-HT3, GABA, (invert. GluCl, dopamine, tyrosine)
receptor-channels
Most
^
Figure 10-7
![Page 10: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/10.jpg)
10Like Figure 2-1
(rotated)
Parts of two generalized CNS neurons
synaptic cleft
direction of information flow
apicaldendrites
Excitatoryterminal
cell body
(soma)
nucleus
axon
presynaptic terminal postsynaptic
dendrite
Inhibitoryterminal presynaptic
terminal
axon hillock
neuronPresynaptic
neuronPostsynaptic
basaldendrites
initialsegment
node of Ranvier
myelin
(apex)
(base)
little hill
![Page 11: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/11.jpg)
11
Molecular layer
Purkinje cell layer
Ganule cell layer
Whitematter
Figure 42-4
10% of the neurons in the CNS are
cerebellar granule cells
The cerebellum: a famous circuit in neuroscience.In today’s lecture,
it exemplifies pre- and postsynaptic structures.
![Page 12: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/12.jpg)
12
A plurality of synapses in the CNS (> 1013 ) occur between parallel fiber axons and Purkinje cell dendritic spines
500 nm
Molecular layer
![Page 13: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/13.jpg)
13
Types of synapses
(Don’t mind the Type I, Type II stuff)
Figure 10-3
![Page 14: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/14.jpg)
14
1. TemporalA. Molecular lifetimesB. Capacitive filtering
2. Spatial
3. Excitatory-inhibitory
Types of synaptic integration
![Page 15: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/15.jpg)
15
Concentration of acetylcholine at
NMJ(because of
acetylcholinesterase,turnover time
~ 100 μs)
Number of open channels
ms
0
high closed open
State 1 State 2
k21
all molecules begin here at
t= 0
units: s-1
Synaptic integration 1A.Molecular lifetimes
Previous lecture
![Page 16: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/16.jpg)
16
What causes the ~ δ-function of glutamate & GABA at CNS synapses?
Na+ -coupled transporters for glutamate & GABA
are present at densities of > 1000 / μm2 near each synapse,
probably high enough to sequester each transmitter molecule
as it leaves a receptor
(more in a few slides).
At the nerve-muscle synapse, acetylcholinesterase is present
at densities of > 1000 / μm2 near each synapse,
high enough to destroy each transmitter molecule
as it leaves a receptor
![Page 17: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/17.jpg)
17
Synaptic Integration 1B. Capacitive filtering
CC ICVdTdVCI ;
Figure 9-6
![Page 18: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/18.jpg)
18
1B. Temporal Summation 2. Spatial summation
Recording Recording
SynapticCurrent
SynapticPotential
Long time constant(100 ms)
Short time constant(20 ms)
Axon Axon
SynapticCurrent
SynapticPotential
Long length constant(1 mm)
Short length constant(0.33 mm)
Vm
Vm
2 mV25 ms
Improved from Figure 10-14
~ 100 pA
CC ICVdTdVCI ;
![Page 19: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/19.jpg)
19
1. If dendrites were passive, they would act like leaky cables . . .
Gulledge & Stuart (2005) J. Neurobiol 64:75,
V
EPSP measured in soma
V
EPSP measured in dendrite
Excitatory synapses
![Page 20: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/20.jpg)
20
. . . and passively integrate inputs . . .
Gulledge & Stuart (2005) J. Neurobiol 64:75,
Δt = 0
Simultaneous,colocalized
EPSPs(two individual trials)
V
Nearly simultaneous,colocalized
EPSPs(two individual trials)
V
Δt = 5 ms
Simultaneous,Spatially distinct
EPSPs
V
Δt = 0
Prolonged rising phase
http://www.neuron.yale.edu/neuron/static/about/stylmn.html
Inspect the simulation, and run the movie, at
![Page 21: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/21.jpg)
21
. . . but two-photon microscopes allow
researchers to visualize patch-clamped dendrites in
living animals . . .
Gulledge & Stuart (2005) J. Neurobiol 64:75,
![Page 22: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/22.jpg)
22
immunocytochemistry
25 μm Whitaker, Brain Res, 2001
Magee & Johnston, J Physiol (1995)
Now break the patch, to fill the cell with dye:
Averaged traces * = axon hillock
. . . dendrites are not passive. They have Na channels
![Page 23: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/23.jpg)
23
. . . voltage-gated Na+ and Ca2+ channels
in dendrites
lead to
partial “backpropagation”
of
action potentials,
implying
that parts of cells
can process signals
semi-independently.
Stay tuned!
Gulledge & Stuart (2005) J. Neurobiol 64:75,
brain slice
![Page 24: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/24.jpg)
24
3. Excitatory-inhibitory integration:
The “veto principle” of inhibitory transmission
Inhibitory synapses work best when they are “near“ the excitatory event they will inhibit.
“Near” means < one cable length.
A. Inhibitory synapses on dendrites
do a good job of inhibiting EPSPs on nearby spines
B. Inhibitory synapses on cell bodies and initial segments
do a good job of inhibiting spikes
![Page 25: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/25.jpg)
25
“Veto” inhibition at the axon initial segment:Schematic of a GABAergic “chandelier cell” in
human cerebral cortex
Ch terminals
from Felipe et al, Brain (1999) 122, 1807
Ch. axon
InhibitoryChandelier
Cell
Ch terminals
PyramidalCells
![Page 26: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/26.jpg)
26
Molecular layer
Purkinje cell layer
Ganule cell layer
Whitematter
Now we localize the inhibitory “vetos” of cerebellar Purkinje cells
by “pinceaux” (paintbrushes) of basket cells
Figure 42-4
![Page 27: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/27.jpg)
27
NH2
A fusion protein: GABA transporter (GAT1)-GFP
How to localize and quantify inhibitory synapses
![Page 28: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/28.jpg)
28
cerebellum
![Page 29: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/29.jpg)
29
Molecular layer (basket cells stain)
Purkinje cell layer“pinceux” (paintbrushes)stain heavily
Granule cell layer
<ImmunocytochemistryFor GABA transporter
![Page 30: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/30.jpg)
30
Molecular layer (basket cells stain)
Purkinje cell layer“pinceaux” stain heavily, showing soma-hillock “veto”
Granule cell layer
mGAT1 GFP knock-in fluorescence >
<ImmunocytochemistryFor GABA transporter
![Page 31: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/31.jpg)
31
GAT1-GFP expression in cerebellum: basket cell terminals in molecular layer,Showing dendritic “veto”GABA transporter density is ~1000/(μm2)
50 m
![Page 32: 1 Bi / CNS 150 Lecture 8 Synaptic inhibition; cable properties of neurons; electrical integration in cerebellum Wednesday, October 15, 2013 Henry Lester.](https://reader037.fdocuments.in/reader037/viewer/2022110103/5697bfaf1a28abf838c9d343/html5/thumbnails/32.jpg)
32
End of Lecture 8