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Revised Model of Endocannabinoid Signaling. Cannabinoids Medically and traditionally used for thousands of years Active compound of marijuana ( D 9 -THC) identified in 1964 Brain cannabinoid receptor (CB1) identified in 1990.
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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
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)
Cannabinoids Endocannabinoids Synthetic cannabinoids
Direct modulation of ligand-gated ion channels: Acetylcholine receptor, Serotonin 5HT3 receptor (frog oocyte experiments)
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
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)
Postsynaptic depolarization causes a CB1R-independent suppression of inhibitory synaptic transmission. RHC80267 & THL: Diacylglycerol Lipase inhibitors URB602 Monoacylglycerol Lipase inhibitor Nimesulide: Cyclooxygenase-2 inhibitor
The effect of CP on hippocampal CCK-positive interneuron to CA1 pyramidal neuron connections in wild-type, CB1R-/- and GABAAR a2-/-mice.
Conclusions These results indicate that: 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 VrijeUniversiteit Amsterdam • Burnashev 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 Control AM 251 CB1 KO
Chronic suppression of inhibition (CSI) ? • Pre- or postsynaptic origin? • Suitable candidate(s) for mediating the effect ? • Presynaptic calcium regulation?
CCK (CB1R +) interneurons Location Firing pattern CCK 20 mV 200 ms PYR CCK Asynchronous release Recording protocol PYR CCK
Blocking 2-AG synthesis has no effect on CSI THL 2AG THL
Chelation of presynaptic calcium potentiates IPSCs AM251 CCK CCK CCK PYR PYR PYR
A presynaptic calcium-dependent process suppresses IPSCs EGTA AM EGTA AM
Brief extracellular BAPTA applicationpotentiates IPSCs 10 mM BAPTA CCK PYR
CSI time course + AEA/2-AG/CP
Presynaptic calcium regulation: frequency dependence CB1R CCK PYR GABAbR 7 s 12 s 30 s 7 s
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 Caroline • Carl Holmgren Dundee University