revised model of endocannabinoid signaling. cannabinoids medically and traditionally used for...
TRANSCRIPT
![Page 1: Revised Model of Endocannabinoid Signaling. Cannabinoids Medically and traditionally used for thousands of years Active compound of marijuana (D 9 -THC)](https://reader031.vdocuments.mx/reader031/viewer/2022032309/56649d135503460f949e64fb/html5/thumbnails/1.jpg)
Revised Model of Endocannabinoid Signaling
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Cannabinoids
• Medically and traditionally used for thousands of years
• Active compound of marijuana (D9-THC) identified in 1964
• Brain cannabinoid receptor (CB1) identified in 1990.
• CB1 is one of the most abundant G-protein coupled receptors in the brain
• Another receptor (CB2) is absent in brain, but enriched in immune tissues
• Most (but not all) effects of D9-THC are absent in CB1-/- mice
• “CBX” receptor may exist
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Cannabinoids
At central synapses (hippocampus, cerebellum, neocortex), cannabinoids are released in an activity dependent way, and inhibit presynaptic neurotransmitter release
(Depolarization induced Supression of Inhibition/Excitation)
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Depolarization induced suppression of inhibition (DSI)
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The First Problem
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CannabinoidsEndocannabinoids
Synthetic cannabinoids
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Direct modulation of ligand-gated ion channels:
Acetylcholine receptor, Serotonin 5HT3 receptor(frog oocyte experiments)
Receptors
IC50
Reference
AchR - -7
118 nM 2-AG 163 nM Anandamide 1.03 µM CP 55,940 3.2 µM WIN 5521,2
Oz et al., 2004
5-HT3-R 3.7 µM Anandamide Oz et al., 2002
h5-HT3-R >1 µM SR141617A 129.6 nM Anandamide 646,7 nM CP 55,940 103.5 nM WIN 5521,2
Barann et al., 2002
AMPAR GluR-1 GluR-3 GluR-1/3 GluR-2/3
161 µM 143 µM Anandamide 148 µM 241 µM
Akinshola et al., 1999
NMDAR NR1-NR2A
Potentiation
20% 1µM Anandamide max 50% with 10 µM
Hampson et al., 1998
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Direct modulation of ligand-gated ion channels:
Acetylcholine receptor, Serotonin 5HT3 receptor(frog oocyte experiments)
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Research questions
Do cannabinoids modulate GABAergic synaptic transmission by a direct action on
ionotropic GABAA receptors?
If yes, what does this modulation mean for local neuronal circuits
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CB1R agonists modulate currents through recombinant GABAAR
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CB1R agonists modulate currents through recombinant GABAAR
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Cannabinoids show CB1 receptor independent reduction of GABAA mediated response
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Experimental Procedure
Paired recordings from a FS interneuron innervating a pyramidal neuron
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Cannabinoids show CB1 receptor independent reduction of GABAA mediated response
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Cannabinoids show CB1 receptor independent reduction of GABAA mediated response
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Postsynaptic depolarization causes a CB1R-independent suppression of inhibitory synaptic transmission.
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Endocannabinoid synthesis and degradation
Diacylglycerol Lipase (DAGL)Monoacylglycerol Lipase (MAGL)Cyclooxygenase-2 (COX-2)Fatty acid amide hydrolase (FAAH)
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Anandamide synthesis and degradation
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Postsynaptic depolarization causes a CB1R-independent suppression of inhibitory synaptic transmission.
RHC80267 & THL: Diacylglycerol Lipase inhibitorsURB602 Monoacylglycerol Lipase inhibitorNimesulide: Cyclooxygenase-2 inhibitor
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Modulation of microcircuit coupling by cannabinoids
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The effect of CP on hippocampal CCK-positive interneuron to CA1 pyramidal neuron connections in wild-type, CB1R-/- and GABAAR a2
-/- mice.
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Potentiation of extrasynaptic GABAARs by endocannabinoids
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Dual effect of cannabinoids on GABAARs
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Conclusions
These results indicate that:
1. Cannabinoids in addition to the presynaptic (retrograde) mode of action, can suppress inhibition by a direct modulation of postsynaptic GABAA receptors.
2. Suppression of inhibition by a direct modulation of postsynaptic GABAA receptors has a high impact on a neuronal network activity providing a new dimension in cannabinoid signaling.
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Golovko Tatiana Heidelberg University Falconer Caroline Dundee University
Min Rogier Lozovaya Natalia Vrije Universiteit AmsterdamBurnashev Nail Institut de Neurobiologie de la Méditerranée
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Depolarization induced suppression of inhibition (DSI)
R I Wilson, R A Nicoll Science 2002;296:678-682
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Chronic Suppression of Inhibition (CSI)
WT
CB1 KO
Control AM 251
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• Chronic suppression of inhibition (CSI) ?
• Pre- or postsynaptic origin?
• Suitable candidate(s) for mediating the effect ?
• Presynaptic calcium regulation?
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CCK (CB1R +) interneurons
100 msPre
Post100 pA50 mV
CCK
PYR
CCK
Location Firing pattern
Asynchronous release Recording protocol
20 mV200 ms
Vh=-70 mVPost CA1 pyr
20 pA
CCK
PYR
50 ms
Pre CB1 interneuroneVm=-65 mV
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SR/AM
Blocking CB1Rs relieves CSI
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IPSCs potentiated in WT but not CB1 KO mice
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THL
Blocking 2-AG synthesis has no effect on CSI
2AG
THL
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Chelation of presynaptic calcium potentiates IPSCs
CCK CCKCCKPYR PYR PYR
AM251
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A presynaptic calcium-dependent process suppresses IPSCs
AM AMEGTA EGTA
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Half maximal IPSC potentiation with 0.1 mM BAPTA
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Brief extracellular BAPTA application potentiates IPSCs
CCKCCK
BAPTABAPTA
10 mM10 mM
PYRPYR
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CSI time course
AEA/2-AG/CP+
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AEA a potential candidate mediating CSI
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Presynaptic calcium regulation: frequency dependence
CCKCCK
PYRPYR
CB1RCB1R
GABAbRGABAbR
7 s 12 s 30 s 7 s
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What : CSIWhere : PresynapticWho : Anandamide
Why:
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Perisomatic inhibition
Freund T and Katona, Neuron 2007; 56:33-42
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Synaptic inputs
Freund T, TINS 2003; 489-495
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.
When: In vivo firing patterns
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Bolshakov Alex Falconer CarolineCarl Holmgren Dundee University