Presynaptic actions of endocannabindoids

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Presynaptic actions of endocannabindoids
Bradley E. Alger
2
Acknowledgements
Darrin Brager Greg Carlson Jimok Kim Sergei
Kirov Fiona LeBeau Rob Lenz Masako Isokawa Wade
Morishita Tom Pitler Chris Reich Namita
Varma John Wagner
Paul Luther Jon Lederer Scott Thompson
Catherine Ledent Zoya Katerova Frank Margolis
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Recording ConditionsBrain slice preparation
Extracellular Solution (mM) NaCl 120 KCl 3
MgSO4 2 NaH2PO4 1 Glucose
10 CaCl2 2.5 APV 0.05 NBQX 0.01
Recording Pipette Solution (mM) CsCH3SO3
100 CsCl 50 Hepes
10 CaCl2 0.2/0.1/0 BAPTA 2.0/1.0/0.2
Mg2ATP 2 KCl
1 MgCl2 1 QX314
2 TEACl 10
GABA
Temp 28 30o C Osm 290-310 mOsm pH 7.20 -
7.25
PYR
4
Depolarization-induced Suppression of Inhibition
(DSI)
500 pA
20 s
0
Current (pA)
-1000
-2000
0
100
200
Time (ms)
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Endocannabinoids mediate DSI/DSE
Ca2
2-AG (?)
CB1
Ca2 influx into a principal cell initiates
synthesis and release of an endocannabinoid that
activates CB1 receptors on certain presynaptic
neurons.
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Activation of CB1Rs inhibits exocytosis
2 Hz
1.2
1.0
0.8
Normalized intensity
0.6
0.4
0.2
0.0
0
50
100
150
200
250
300
Time (s)
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The Model
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Presynaptic actions of endocannabinoids
X
3
4
1
IN
2
Post
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Endocannabinoids inhibit presynaptic Ca2 influx
Kreitzer and Regehr, Neuron, March, 2001
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Endocannabinoids inhibit quantal release
Diana and Marty, J. Neuroscience, July, 2003
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Blocking certain K channels blocks DSI
Control
4-AP
D
D
D
D
D
D
sIPSCs
200 pA
20 s
200 pA
50 s


Varma, et al., Neuropharm, Sept., 2002
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Endocannabinoids inhibit neuronal firing
Kreitzer, Carter and Regehr, Neuron, May 2002
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Short-range and long-range actions of
endocannabinoids
IN
Endocannabinoid
From Kreitzer and Regehr, Neuron, May, 2002
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Presynaptic actions of endocannabinoids in DSI/DSE
X
3
4
1
IN
2
Post
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Activation of CB1 can cause long-term depression
(LTD)
CB1-/-
CB1/
(Gerdemann, Ronesi and Lovinger, Nature
Neuroscience, May, 2002)
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Endocannabinoids induce LTD after prolonged CB1R
activation
mGluR stimulation
AM-251
From Chevaleyre and Castillo, Neuron, May, 2003
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Prolonged CB1R activation alone is not sufficient
to cause LTD
Kim and Alger, Soc Neurosci Abstr, Nov 2003
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Summary

• DSI and DSE are produced by short-term retrograde
  action of endocannabinoids on presynaptic cells.
• Endocannabinoids inhibit Ca2 influx, increase K
  efflux and interfere with the quantal release
  process.
• Prolonged activation of CB1Rs can cause long-term
  depression of glutamate or GABA release. (Other
  factor?)

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The Model
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Endocannabinoids and CB1R
Ca2
lipases and diesterases
postsynapticcell interior
degradation
1
5
membrane lipid bilayer
O
O
4
2
O
HO
NH
reuptake
anandamide
2-AG
Synaptic cleft
3
CB1R
presynapticcell interior
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5 Hz
5 Hz
B
C
1.2
Steady-state
Baseline
Fitting
300
1.0
250
0.8
200
Normalized intensity
0.6
Intensity (a.u.)
150
0.4
100
0.2
50
0.0
0
0
50
100
150
200
250
300
0
50
100
150
200
250
300
Time (s)
Time (s)
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Endocannabinoids inhibit Ca2 influx
Diana, Levenes, Mackie, and Marty, J Neurosci,
Jan, 2002
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Baseline
DSI
Recovery
A
350
350
350
n 1625
n 1050
n 1719
300
300
300
250
250
250
of events
200
200
200
Con
150
150
Total of events
150
100
100
100
50
50
50
0
0
0
0
10
20
30
40
50
60
0
10
20
30
40
50
60
0
10
20
30
40
50
60
Total of events
350
350
350
300
300
300
n 546
n 314
n 546
250
250
250
CTX
200
200
200
500 nM
Total of events
150
150
150
Total of events
100
100
100
50
50
50
Total of events
0
0
0
0
10
20
30
40
50
60
0
10
20
30
40
50
60
0
10
20
30
40
50
60
Amplitude (pA)
Amplitude (pA)
Amplitude (pA)