Download - Revised Model of Endocannabinoid Signaling
Revised Model of Endocannabinoid Signaling
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
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)
Depolarization induced suppression of inhibition (DSI)
The First Problem
CannabinoidsEndocannabinoids
Synthetic cannabinoids
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
Direct modulation of ligand-gated ion channels:
Acetylcholine receptor, Serotonin 5HT3 receptor(frog oocyte experiments)
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
CB1R agonists modulate currents through recombinant GABAAR
CB1R agonists modulate currents through recombinant GABAAR
Cannabinoids show CB1 receptor independent reduction of GABAA mediated response
Experimental Procedure
Paired recordings from a FS interneuron innervating a pyramidal neuron
Cannabinoids show CB1 receptor independent reduction of GABAA mediated response
Cannabinoids show CB1 receptor independent reduction of GABAA mediated response
Postsynaptic depolarization causes a CB1R-independent suppression of inhibitory synaptic transmission.
Endocannabinoid synthesis and degradation
Diacylglycerol Lipase (DAGL)Monoacylglycerol Lipase (MAGL)Cyclooxygenase-2 (COX-2)Fatty acid amide hydrolase (FAAH)
Anandamide synthesis and degradation
Postsynaptic depolarization causes a CB1R-independent suppression of inhibitory synaptic transmission.
RHC80267 & THL: Diacylglycerol Lipase inhibitorsURB602 Monoacylglycerol Lipase inhibitorNimesulide: Cyclooxygenase-2 inhibitor
Modulation of microcircuit coupling by cannabinoids
The effect of CP on hippocampal CCK-positive interneuron to CA1 pyramidal neuron connections in wild-type, CB1R-/- and GABAAR a2
-/- mice.
Potentiation of extrasynaptic GABAARs by endocannabinoids
Dual effect of cannabinoids on GABAARs
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.
Golovko Tatiana Heidelberg University Falconer Caroline Dundee University
Min Rogier Lozovaya Natalia Vrije Universiteit AmsterdamBurnashev Nail Institut de Neurobiologie de la Méditerranée
Depolarization induced suppression of inhibition (DSI)
R I Wilson, R A Nicoll Science 2002;296:678-682
Chronic Suppression of Inhibition (CSI)
WT
CB1 KO
Control AM 251
• Chronic suppression of inhibition (CSI) ?
• Pre- or postsynaptic origin?
• Suitable candidate(s) for mediating the effect ?
• Presynaptic calcium regulation?
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
SR/AM
Blocking CB1Rs relieves CSI
IPSCs potentiated in WT but not CB1 KO mice
THL
Blocking 2-AG synthesis has no effect on CSI
2AG
THL
Chelation of presynaptic calcium potentiates IPSCs
CCK CCKCCKPYR PYR PYR
AM251
A presynaptic calcium-dependent process suppresses IPSCs
AM AMEGTA EGTA
Half maximal IPSC potentiation with 0.1 mM BAPTA
Brief extracellular BAPTA application potentiates IPSCs
CCK
BAPTA
10 mM
PYR
CSI time course
AEA/2-AG/CP+
AEA a potential candidate mediating CSI
Presynaptic calcium regulation: frequency dependence
CCKPYR
CB1R
GABAbR
7 s 12 s 30 s 7 s
What : CSIWhere : PresynapticWho : Anandamide
Why:
Perisomatic inhibition
Freund T and Katona, Neuron 2007; 56:33-42
Synaptic inputs
Freund T, TINS 2003; 489-495
.When: In vivo firing patterns
Bolshakov Alex Falconer CarolineCarl Holmgren Dundee University