Do endocannabinoids (eCBs) participate in long-term synaptic plasticity in the brain? Using pharmacological approaches and genetically altered mice, we show that stimulation of prelimbic cortex afferents at naturally occurring frequencies causes a longterm depression of nucleus accumbens glutamatergic synapses mediated by eCB release and presynaptic CB1 receptors. Translation of glutamate synaptic transmission into eCB retrograde signaling involved metabotropic glutamate receptors and postsynaptic intracellular Ca 2؉ stores. These findings unveil the role of the eCB system in activity-dependent long-term synaptic plasticity and identify a mechanism by which marijuana can alter synaptic functions in the endogenous brain reward system. E xogenous cannabinoids, such as the active component of Cannabis sativa L, (Ϫ)-transdelta9-tetrahydrocannabinol, as well as endocannabinoids (eCBs; anandamide and 2-arachidonoyl-glycerol) share the same target in the central nervous system: a Gi͞Go-coupled receptor named CB1 (1, 2). Activation of CB1 receptors inhibits both inhibitory and excitatory synaptic transmission in the hippocampus (3, 4), substantia nigra pars compacta (5), the cerebellum (6), the prefrontal cortex (7), and the nucleus accumbens (NAc) (8, 9). Both eCBs and CB1 have been involved in a short-lasting form of synaptic regulation: the ''depolarization-induced suppression'' of both inhibitory (10-15) and excitatory transmission (16). However, the involvement of eCB in long-lasting activity-dependent synaptic plasticity remained to be documented. The mesocorticolimbic dopaminergic system, and particularly the NAc, is essential to the reinforcing properties of addictive drugs (17, 18). Cannabinoids activate mesolimbic dopamine neurons (19) and increase NAc dopamine levels (20), similarly to other drugs of abuse. Our finding that CB1 are localized at the excitatory afferents to the NAc where exogenous cannabimimetics inhibit glutamatergic synaptic transmission (9) raised two questions: how does synaptic activity lead to the production of eCBs in the NAc, and what are the physiological correlates of eCB release on synaptic transmission? Methods Slice Preparation and Electrophysiology. Whole-cell patch-clamp and extracellular field recordings were made from medium spiny neurons in parasagittal slices of mouse NAc. These methods have been described in detail previously (9). In brief, mice (male C57BL6, 4-6 weeks) were anesthetized with isoflurane and decapitated. The brain was sliced (300-400 m) in the parasagittal plane by using a vibratome and maintained in physiological saline at 4°C. Slices containing the NAc were stored at least 1 h at room temperature before being placed in the recording chamber and superfused (2 ml͞min) with artificial cerebrospinal fluid that contained (in mM): 126 NaCl, 2.5 KCl, 1.2 MgCl 2 , 2.4 CaCl 2, 18 NaHCO 3 , 1.2 NaH 2 PO 4 , and 11 glucose, and was equilibrated with 95% O 2 ͞5% CO 2 . All experiments were done at room temperature. The superfusion medium contained picrotoxin (100 M) to...

The endocannabinoid 2-arachidonoylglycerol (2-AG) regulates neurotransmission and neuroinflammation by activating CB 1 cannabinoid receptors on neurons and CB 2 cannabinoid Correspondence should be addressed to N.S. (nstella@uw.edu). 11 These authors contributed equally to this work.Note: Supplementary information is available on the Nature Neuroscience website. Competing Financial Interests:The authors declare no competing financial interests.Reprints and permissions information is available online at http://www.nature.com/reprintsandpermissions/. NIH Public Access Author ManuscriptNat Neurosci. Author manuscript; available in PMC 2011 February 1. Published in final edited form as:Nat Neurosci. 2010 August ; 13(8): 951-957. doi:10.1038/nn.2601. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript receptors on microglia. Enzymes that hydrolyze 2-AG, such as monoacylglycerol lipase, regulate the accumulation and efficacy of 2-AG at cannabinoid receptors. We found that the recently described serine hydrolase α-β-hydrolase domain 6 (ABHD6) also controls the accumulation and efficacy of 2-AG at cannabinoid receptors. In cells from the BV-2 microglia cell line, ABHD6 knockdown reduced hydrolysis of 2-AG and increased the efficacy with which 2-AG can stimulate CB 2 -mediated cell migration. ABHD6 was expressed by neurons in primary culture and its inhibition led to activitydependent accumulation of 2-AG. In adult mouse cortex, ABHD6 was located postsynaptically and its selective inhibition allowed the induction of CB 1 -dependent long-term depression by otherwise subthreshold stimulation. Our results indicate that ABHD6 is a rate-limiting step of 2-AG signaling and is therefore a bona fide member of the endocannabinoid signaling system.In the nervous system, the endocannabinoids (eCBs) arachidonoylethanolamide (anandamide) and 2-AG are produced and inactivated by neurons and glia 1,2 . The production of eCBs increases in response to specific stimuli, including membrane receptor activation, ion channel opening and calcium influx 2 . eCBs are inactivated by cellular uptake followed by intracellular enzymatic hydrolysis 3,4 . The balance between this production and inactivation dictates the levels of extracellular eCB accumulation and the ensuing activation of CB 1 receptors expressed by neurons (regulating neurotransmitter release) and CB 2 receptors expressed by microglia (regulating their motility and ability to produce immunomodulators) [4][5][6][7] . Thus, the enzymatic steps that control the production and inactivation of eCBs constitute promising molecular targets for indirectly modulating CB 1 and CB 2 receptor activity, and thereby controlling neurotransmission and neuroinflammation.Of all the steps that control the accumulation of eCBs, the hydrolytic enzymes that inactivate anandamide and 2-AG represent the most promising pharmacological and genetic targets for fine-tuning the local accumulation of these lipid transmitters. Inhibition of fatty acid amide hydrolase (FAAH) increases...

Chronic exposure to drugs of abuse induces countless modifications in brain physiology. However, the neurobiological adaptations specifically associated with the transition to addiction are unknown. Cocaine self-administration rapidly suppresses long-term depression (LTD), an important form of synaptic plasticity in the nucleus accumbens. Using a rat model of addiction, we found that animals that progressively develop the behavioral hallmarks of addiction have permanently impaired LTD, whereas LTD is progressively recovered in nonaddicted rats maintaining a controlled drug intake. By making drug seeking consistently resistant to modulation by environmental contingencies and consequently more and more inflexible, a persistently impaired LTD could mediate the transition to addiction.