Prolonged exposure to drugs of abuse, such as cannabinoids and opioids, leads to pharmacological tolerance and receptor desensitization in the nervous system. We found that a similar form of ...functional antagonism was produced by sustained inactivation of monoacylglycerol lipase (MAGL), the principal degradative enzyme for the endocannabinoid 2-arachidonoylglycerol. After repeated administration, the MAGL inhibitor JZL184 lost its analgesic activity and produced cross-tolerance to cannabinoid receptor (CB1) agonists in mice, effects that were phenocopied by genetic disruption of Mgll (encoding MAGL). Chronic MAGL blockade also caused physical dependence, impaired endocannabinoid-dependent synaptic plasticity and desensitized brain CB1 receptors. These data contrast with blockade of fatty acid amide hydrolase, an enzyme that degrades the other major endocannabinoid anandamide, which produced sustained analgesia without impairing CB1 receptors. Thus, individual endocannabinoids generate distinct analgesic profiles that are either sustained or transitory and associated with agonism and functional antagonism of the brain cannabinoid system, respectively.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The serine hydrolase α/β-hydrolase domain 6 (ABHD6) hydrolyzes the most abundant endocannabinoid (eCB) in the brain, 2-arachidonoylglycerol (2-AG), and controls its availability at cannabinoid ...receptors. We show that ABHD6 inhibition decreases pentylenetetrazole (PTZ)-induced generalized tonic-clonic and myoclonic seizure incidence and severity. This effect is retained in Cnr1−/− or Cnr2−/− mice, but blocked by addition of a subconvulsive dose of picrotoxin, suggesting the involvement of GABAA receptors. ABHD6 inhibition also blocked spontaneous seizures in R6/2 mice, a genetic model of juvenile Huntington’s disease known to exhibit dysregulated eCB signaling. ABHD6 blockade retained its antiepileptic activity over chronic dosing and was not associated with psychomotor or cognitive effects. While the etiology of seizures in R6/2 mice remains unsolved, involvement of the hippocampus is suggested by interictal epileptic discharges, increased expression of vGLUT1 but not vGAT, and reduced Neuropeptide Y (NPY) expression. We conclude that ABHD6 inhibition may represent a novel antiepileptic strategy.
•ABHD6 blockade by WWL123 controls PTZ-induced seizures without psychomotor effects•The effect of WWL123is retained in Cnr1−/− and Cnr2−/− mice but blocked by picrotoxin•WWL123 also blocks spontaneous seizures in the R6/2 mouse model of juvenile HD•R6/2 hippocampi feature electrographic abnormalities and profound loss of NPY
Cannabinoids reduce seizure incidence but also induce psychotropic side effects. Here Naydenov and Horne et al. show that seizure incidence is controlled by inhibition of ABHD6, a novel endocannabinoid-degrading enzyme, without producing psychotropic side effects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The endocannabinoid 2-arachidonoylglycerol (2-AG) is a retrograde lipid messenger that modulates synaptic function, neurophysiology, and behavior. 2-AG signaling is terminated by enzymatic ...hydrolysis—a reaction that is principally performed by monoacylglycerol lipase (MAGL). MAGL is broadly expressed throughout the nervous system, and the contributions of different brain cell types to the regulation of 2-AG activity in vivo remain poorly understood. Here, we genetically dissect the cellular anatomy of MAGL-mediated 2-AG metabolism in the brain and show that neurons and astrocytes coordinately regulate 2-AG content and endocannabinoid-dependent forms of synaptic plasticity and behavior. We also find that astrocytic MAGL is mainly responsible for converting 2-AG to neuroinflammatory prostaglandins via a mechanism that may involve transcellular shuttling of lipid substrates. Astrocytic-neuronal interplay thus provides distributed oversight of 2-AG metabolism and function and, through doing so, protects the nervous system from excessive CB1 receptor activation and promotes endocannabinoid crosstalk with other lipid transmitter systems.
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•Genetic mouse models reveal cellular specificity of 2-AG metabolism•Astrocytes and neurons collaborate to terminate endocannabinoid signaling•Coordinated astrocytic-neuronal metabolism protects against CB1R desensitization•Astrocytes couple 2-AG hydrolysis to neuroinflammatory prostaglandin production
The endocannabinoid 2-arachidonoylglycerol (2-AG) is a retrograde lipid messenger that broadly modulates brain synapses, neurophysiology, and behavior. Viader et al. show that endocannabinoid signaling is regulated by the cooperative, transcellular metabolism of 2-AG, which is shuttled between neurons and astrocytes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The monoacylglycerol lipase (MAGL) inhibitor 4-nitrophenyl 4-(dibenzod1,3dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate (JZL184) produces antinociceptive and anti-inflammatory effects. However, ...repeated administration of high-dose JZL184 (40 mg/kg) causes dependence, antinociceptive tolerance, cross-tolerance to the pharmacological effects of cannabinoid receptor agonists, and cannabinoid receptor type 1 (CB1) downregulation and desensitization. This functional CB1 receptor tolerance poses a hurdle in the development of MAGL inhibitors for therapeutic use. Consequently, the present study tested whether repeated administration of low-dose JZL184 maintains its antinociceptive actions in the chronic constriction injury of the sciatic nerve neuropathic pain model and protective effects in a model of nonsteroidal anti-inflammatory drug-induced gastric hemorrhages. Mice given daily injections of high-dose JZL184 (≥16 mg/kg) for 6 days displayed decreased CB1 receptor density and function in the brain, as assessed in (3)HSR141716A binding and CP55,940 (-)-cis-3-2-hydroxy-4-(1,1-dimethylheptyl)phenyl-trans-4-(3-hydroxypropyl) cyclohexanol-stimulated guanosine 5'-O-(3-(35)Sthio)triphosphate binding assays, respectively. In contrast, normal CB1 receptor expression and function were maintained following repeated administration of low-dose JZL184 (≤8 mg/kg). Likewise, the antinociceptive and gastroprotective effects of high-dose JZL184 underwent tolerance following repeated administration, but these effects were maintained following repeated low-dose JZL184 treatment. Consistent with these observations, repeated high-dose JZL184, but not repeated low-dose JZL184, elicited cross-tolerance to the common pharmacological effects of Δ(9)-tetrahydrocannabinol. This same pattern of effects was found in a rimonabant (5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide)-precipitated withdrawal model of cannabinoid dependence. Taken together, these results indicate that prolonged, partial MAGL inhibition maintains potentially beneficial antinociceptive and anti-inflammatory effects, without producing functional CB1 receptor tachyphylaxis/tolerance or cannabinoid dependence.
2-Arachidonoylglycerol (2-AG) and anandamide are endocannabinoids that activate the cannabinoid receptors CB1 and CB2. Endocannabinoid signaling is terminated by enzymatic hydrolysis, a process that ...for anandamide is mediated by fatty acid amide hydrolase (FAAH), and for 2-AG is thought to involve monoacylglycerol lipase (MAGL). FAAH inhibitors produce a select subset of the behavioral effects observed with CB1 agonists, which suggests a functional segregation of endocannabinoid signaling pathways in vivo. Testing this hypothesis, however, requires specific tools to independently block anandamide and 2-AG metabolism. Here, we report a potent and selective inhibitor of MAGL called JZL184 that, upon administration to mice, raises brain 2-AG by eight-fold without altering anandamide. JZL184-treated mice exhibited a broad array of CB1-dependent behavioral effects, including analgesia, hypothermia and hypomotility. These data indicate that 2-AG endogenously modulates several behavioral processes classically associated with the pharmacology of cannabinoids and point to overlapping and unique functions for 2-AG and anandamide in vivo.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract Co-exposure to opiates and HIV/HIV proteins results in enhanced CNS morphological and behavioral deficits in HIV+ individuals and in animal models. Opiates with abuse liability, such as ...heroin and morphine, bind preferentially to and have pharmacological actions through μ-opioid-receptors (MOR). The mechanisms underlying opiate-HIV interactions are not understood. Exposure to the HIV-1 transactivator of transcription (Tat) protein causes neurodegenerative outcomes that parallel many aspects of the human disease. We have also observed that in vivo exposure to Tat results in apparent changes in morphine efficacy, and thus have hypothesized that HIV proteins might alter MOR activation. To test our hypothesis, MOR-mediated G-protein activation was determined in neuroAIDS-relevant forebrain regions of transgenic mice with inducible CNS expression of HIV-1 Tat. G-protein activation was assessed by MOR agonist-stimulated 35 Sguanosine-5′-O-(3-thio)triphosphate (35 SGTPγS) autoradiography in brain sections, and in concentration-effect curves of MOR agonist-stimulated 35 SGTPγS binding in membranes isolated from specific brain regions. Comparative studies were done using the MOR-selective agonist DAMGO (D-Ala2 , N-MePhe4 , Gly-ol-enkephalin) and a more clinically relevant agonist, morphine. Tat exposure reduced MOR-mediated G-protein activation in an agonist, time, and regionally dependent manner. Levels of the GPCR regulatory protein β-arrestin-2, which is involved in MOR desensitization, were found to be elevated in only one affected brain region, the amygdala; amygdalar β-arrestin-2 also showed a significantly increased association with MOR by co-immunoprecipitation, suggesting decreased availability of MOR. Interestingly, this correlated with changes in anxiety and fear-conditioned extinction, behaviors that have substantial amygdalar input. We propose that HIV-1 Tat alters the intrinsic capacity of MOR to signal in response to agonist binding, possibly via a mechanism involving altered expression and/or function of β-arrestin-2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The immunomodulatory prodrug 2-amino-2-(2-4-octylphenylethyl)-1,3-propanediol (FTY720), which acts as an agonist for sphingosine-1-phosphate (S1P) receptors (S1PR) when phosphorylated, is proposed as ...a novel pain therapeutic. In this study, we assessed FTY720-mediated antinociception in the radiant heat tail-flick test and in the chronic constriction injury (CCI) model of neuropathic pain in mice. FTY720 produced antinociception and antiallodynia, respectively, and these effects were dose-dependent and mimicked by the S1PR1-selective agonist CYM-5442. Repeated administration of FTY720 for 1 week produced tolerance to acute thermal antinociception, but not to antiallodynia in the CCI model. S1PR-stimulated
SGTP
S autoradiography revealed apparent desensitization of G protein activation by S1P or the S1PR1 agonist 5-4-phenyl-5-(trifluoromethyl)-2-thienyl-3-3-(trifluoromethyl)phenyl-1,2,4-oxadiazole (SEW-2871) throughout the brain. Similar results were seen in spinal cord membranes, whereby the E
value of S1PR-stimulated
SGTP
S binding was greatly reduced in repeated FTY720-treated mice. These results suggest that S1PR1 is a primary target of FTY720 in alleviating both acute thermal nociception and chronic neuropathic nociception. Furthermore, the finding that tolerance develops to antinociception in the tail-flick test but not in chronic neuropathic pain suggests a differential mechanism of FTY720 action between these models. The observation that repeated FTY720 administration led to desensitized S1PR1 signaling throughout the central nervous system suggests the possibility that S1PR1 activation drives the acute thermal antinociceptive effects, whereas S1PR1 desensitization mediates the following: 1) tolerance to thermal antinociceptive actions of FTY720 and 2) the persistent antiallodynic effects of FTY720 in neuropathic pain by producing functional antagonism of pronociceptive S1PR1 signaling.
Four sets of diastereomeric C9-alkenyl 5-phenylmorphans, varying in the length of the C9-alkenyl chain, were designed to examine the effect of these spatially distinct ligands on opioid receptors. ...Functional activity was obtained by forskolin-induced cAMP accumulation assays and several compounds were examined in the 35SGTPgS assay and in an assay for respiratory depression. In each of the four sets, similarities and differences were observed dependent on the length of their C9-alkenyl chain and, most importantly, their stereochemistry. Three MOR antagonists were found to be as or more potent than naltrexone and, unlike naltrexone, none had MOR, KOR, or DOR agonist activity. Several potent MOR full agonists were obtained, and, of particular interest partial agonists were found that exhibited less respiratory depression than that caused by morphine. The effect of stereochemistry and the length of the C9-alkenyl chain was also explored using molecular modeling. The MOR antagonists were found to interact with the inactive (4DKL) MOR crystal structures and agonists were found to interact with the active (6DDF) MOR crystal structures. The comparison of their binding modes at the mouse MOR was used to gain insight into the structural basis for their stereochemically induced pharmacological differences.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
9.
Essential Role for RGS9 in Opiate Action Zachariou, Venetia; Georgescu, Dan; Sanchez, Nick ...
Proceedings of the National Academy of Sciences - PNAS,
11/2003, Volume:
100, Issue:
23
Journal Article
Peer reviewed
Open access
Regulators of G protein signaling (RGS) are a family of proteins known to accelerate termination of effector stimulation after G protein receptor activation. RGS9-2, a brain-specific splice variant ...of the RGS9 gene, is highly enriched in striatum and also expressed at much lower levels in periaqueductal gray and spinal cord, structures known to mediate various actions of morphine and other opiates. Morphine exerts its acute rewarding and analgesic effects by activation of inhibitory guanine nucleotide-binding regulatory protein-coupled opioid receptors, whereas chronic morphine causes addiction, tolerance to its acute analgesic effects, and profound physical dependence by sustained activation of these receptors. We show here that acute morphine administration increases expression of RGS9-2 in NAc and the other CNS regions, whereas chronic exposure decreases RGS9-2 levels. Mice lacking RGS9 show enhanced behavioral responses to acute and chronic morphine, including a dramatic increase in morphine reward, increased morphine analgesia with delayed tolerance, and exacerbated morphine physical dependence and withdrawal. These findings establish RGS9 as a potent negative modulator of opiate action in vivo, and suggest that opiate-induced changes in RGS9 levels contribute to the behavioral and neural plasticity associated with chronic opiate administration.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
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