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Neutral antagonists of GPCRs remain relatively rare—indeed, a large majority of GPCR antagonists are actually inverse agonists. The synthetic cannabinoid receptor agonist (SCRA) EG‐018 was recently reported as a low efficacy cannabinoid receptor agonist. Here we report a comparative characterization of EG‐018 and 13 analogues along with extant putative neutral antagonists of CB1. In HEK cells stably expressing human CB1, assays for inhibition of cAMP were performed by real‐time BRET biosensor (CAMYEL), G protein cycling was quantified by [35S]GTPγS binding, and stimulation of pERK was characterized by AlphaLISA (PerkinElmer). Signaling outcomes for the EG‐018 analogues were highly variable, ranging from moderate efficacy agonism with high potency, to marginal agonism at lower potency. As predicted by differing pathway sensitivities to differences in ligand efficacy, most EG‐018‐based compounds were completely inactive in pERK alone. The lowest efficacy analogue in cAMP assays, 157, had utility in antagonism assay paradigms. Developing neutral antagonists of the CB1 receptor has been a long‐standing research goal, and such compounds would have utility both as research tools and in therapeutics. Although these results emphasize again the importance of system factors in determining signaling outcomes, some compounds characterized in this study appear among the lowest efficacy agonists described to date and therefore suggest that development of neutral antagonists is an achievable goal for CB1. [ABSTRACT FROM AUTHOR]

Abstract: In 2014 and 2015, synthetic cannabinoid receptor agonists NNEI (N‐1‐naphthalenyl‐1‐pentyl‐1H‐indole‐3‐carboxamide) and MN‐18 (N‐1‐naphthalenyl‐1‐pentyl‐1H‐indazole‐3‐carboxamide) were detected in recreationally used and abused products in multiple countries, and were implicated in episodes of poisoning and toxicity. Despite this, the pharmacokinetic profiles of NNEI and MN‐18 have not been characterized. In the present study NNEI and MN‐18 were incubated in rat and human liver microsomes and hepatocytes, to estimate kinetic parameters and to identify potential metabolic pathways, respectively. These parameters and pathways were then examined in vivo, via analysis of blood and urine samples from catheterized male rats following intraperitoneal (3 mg/kg) administration of NNEI and MN‐18. Both NNEI and MN‐18 were rapidly cleared by rat and human liver microsomes, and underwent a range of oxidative transformations during incubation with rat and human hepatocytes. Several unique metabolites were identified for the forensic identification of NNEI and MN‐18 intake. Interestingly, NNEI underwent a greater number of biotransformations (20 NNEI metabolites versus 10 MN‐18 metabolites), yet parent MN‐18 was eliminated at a faster rate than NNEI in vivo. Additionally, in vivo elimination was more rapid than in vitro estimates. These data highlight that even closely related synthetic cannabinoids can possess markedly distinct pharmacokinetic profiles, which can vary substantially between in vitro and in vivo models. [ABSTRACT FROM AUTHOR]

The cannabinoid CB1 receptor is a G protein coupled receptor and plays an important role in many biological processes and physiological functions. A variety of CB1 receptor agonists and antagonists, including endocannabinoids, phytocannabinoids, and synthetic cannabinoids, have been discovered or developed over the past 20 years. In 2005, it was discovered that the CB1 receptor contains allosteric site(s) that can be recognized by small molecules or allosteric modulators. A number of CB1 receptor allosteric modulators, both positive and negative, have since been reported and importantly, they display pharmacological characteristics that are distinct from those of orthosteric agonists and antagonists. Given the psychoactive effects commonly associated with CB1 receptor agonists and antagonists/inverse agonists, allosteric modulation may offer an alternate approach to attain potential therapeutic benefits while avoiding inherent side effects of orthosteric ligands. This review details the complex pharmacological profiles of these allosteric modulators, their structure-activity relationships, and efforts in elucidating binding modes and mechanisms of actions of reported CB1 allosteric modulators. The ultimate development of CB1 receptor allosteric ligands could potentially lead to improved therapies for CB1-mediated neurological disorders. [ABSTRACT FROM AUTHOR]

ABSTRACT The role of kappa-opioid receptors (KOR) in the regulation of alcohol-related behaviors is not completely understood. For example, alcohol consumption has been reported to increase following treatment with KOR antagonists in rats, but was decreased in mice with genetic deletion of KOR. Recent studies have further suggested that KOR antagonists may selectively decrease alcohol self-administration in rats following a history of dependence. We assessed the effects of the KOR antagonist JDTic on alcohol self-administration, reinstatement of alcohol seeking induced by alcohol-associated cues or stress, and acute alcohol withdrawal-induced anxiety ('hangover anxiety'). JDTic dose-dependently reversed hangover anxiety when given 48 hours prior to testing, a time interval corresponding to the previously demonstrated anxiolytic efficacy of this drug. In contrast, JDTic decreased alcohol self-administration and cue-induced reinstatement of alcohol seeking when administered 2 hours prior to testing, but not at longer pre-treatment times. For comparison, we determined that the prototypical KOR antagonist nor-binaltorphimine can suppress self-administration of alcohol at 2 hours pre-treatment time, mimicking our observations with JDTic. The effects of JDTic were behaviorally specific, as it had no effect on stress-induced reinstatement of alcohol seeking, self-administration of sucrose, or locomotor activity. Further, we demonstrate that at a 2 hours pre-treatment time JDTic antagonized the antinociceptive effects of the KOR agonist U50,488H but had no effect on morphine-induced behaviors. Our results provide additional evidence for the involvement of KOR in regulation of alcohol-related behaviors and provide support for KOR antagonists, including JDTic, to be evaluated as medications for alcoholism. [ABSTRACT FROM AUTHOR]

Background and Purpose: Disruption of the substantial re-organization of the brain during adolescence may be induced by persistent abuse of marijuana. The aim of this study was to determine whether adolescent and adult rats exhibit differential adaptation of brain cannabinoid (CB(1)) receptors after repeated exposure to Delta(9)-tetrahydrocannabinol (THC).Experimental Approach: Rats of both ages and sexes were dosed with 10 mg kg(-1) THC or vehicle twice daily for 9.5 days. Subsequently, CB(1) receptor function and density were assessed.Key Results: In all brain regions, THC treatment produced desensitization and down-regulation of CB(1) receptors. While the magnitude of down-regulation did not differ across groups, greater desensitization was evident in the brains of THC-treated female adolescent rats for most regions. Adolescent females showed greater desensitization than adult females in the prefrontal cortex, hippocampus, periaqueductal gray (PAG) and ventral midbrain. In contrast, adolescent males exhibited less desensitization in the prefrontal cortex, hippocampus and PAG, an effect opposite to that seen in females. With the exception of the PAG, sex differences were seen only in adolescents, with greater desensitization in the prefrontal cortex, striatum, hippocampus, PAG, and ventral midbrain of females.Conclusions and Implications: These results suggest that the brains of adolescent females may be particularly vulnerable to disruption of CB(1) receptor signalling by marijuana abuse. Alternatively, increased desensitization may reflect protective adaptation. Given the extensive re-organization of the brain during adolescence, this disruption has potential long-term consequences for maturation of the endocannabinoid system. [ABSTRACT FROM AUTHOR]

Abstract: The recent upsurge of research on adolescent rats raises the issue of the extent to which different methods of rodent procurement might affect results. Here, we examined the effects of acute and repeated dosing with two antipsychotics, haloperidol and clozapine, and Δ9-tetrahydrocannabinol [Experiments 1 and 2, respectively] in adolescent rats of both sexes that differed in shipping status (i.e., shipped from a commercial breeder at weaning or bred in-house). In each experiment, test drugs produced effects that were characteristic for their respective classes in previous studies with adult rodents. Both haloperidol and clozapine produced catalepsy and haloperidol decreased locomotion in shipped and bred rats of both sexes, with sensitization to haloperidol-induced catalepsy developing with repeated dosing. The most prominent between-status difference in this experiment was greater sensitivity of the shipped rats to haloperidol-induced changes in locomotor activity over a wider dose range, an effect that was especially evident in females. In Experiment 2, vehicle levels of motor activity were decreased in bred rats (which did not occur in Experiment 1), resulting in flattening of the Δ9-tetrahydrocannabinol dose–effect curve for this measure in bred rats of each sex. Acutely, Δ9-tetrahydrocannabinol produced antinociception, hypothermia and catalepsy in both groups of rats, with tolerance developing after repeated dosing. Status-related differences were sex-dependent. Whereas bred female rats were more sensitive to Δ9-tetrahydrocannabinol''s antinociceptive effects, shipped male rats were more sensitive to its antinociceptive effects as well as to its hypothermic and cataleptic effects. Together, the results of these descriptive experiments suggest that between-status differences tend to be quantitative rather than qualitative. Further, these results suggest that careful attention to issues related to rodent procurement during adolescence is warranted and may help to account for divergent findings in different labs. [Copyright &y& Elsevier]

Lifelong substance abuse is often initiated during adolescence; yet, most pre-clinical research in this area has been conducted in adult animals. Substantial evidence exists that the brain development that continues throughout adolescence may result in pharmacological responses that differ in a crucial manner from those of adults. The goal of this study was to evaluate age differences in motor activity following acute and repeated administration of drugs that are commonly abused by adolescents, including cocaine, Δ9-tetrahydrocannabinol (Δ9-THC), and the club drugs, ketamine and 3,4-methylenedioxymethamphetamine (MDMA). Adolescent and adult male rats were injected once daily with saline or with a dose of one of the test drugs for two 5-day dosing periods, separated by a 2-day drug holiday during which they remained in their home cages. Following each injection, rats were placed in a locomotor chamber for a 20-minute session. The potencies of cocaine, ketamine and MDMA for producing motor stimulation were less in male adolescents than in male adults. Furthermore, sensitization to the club drug, ketamine, developed after repeated dosing in adults, but not adolescents. In contrast, adolescents were initially more sensitive to the stimulatory effects of low doses of Δ9-THC than were adults, although rapid tolerance occurred. These results suggest that adolescents are less sensitive to the acute and repeated stimulant effects of some, but not all, of the drugs that are preferentially abused by this age group. This differential sensitivity may contribute to the different patterns of use that have been noted in adolescent versus adult drug abusers. [ABSTRACT FROM AUTHOR]

We previously reported that the compound O-2093 is a selective inhibitor of the reuptake of the endocannabinoid anandamide (AEA). We have now re-examined the activity of O-2093 in vivo and synthesized four structural analogs (O-2247, O-2248, O-3246, and O-3262), whose activity was assessed in: (a) binding assays carried out with membranes from cells overexpressing the human CB1 and CB2 receptors; (b) assays of transient receptor potential of the vanilloid type-1 (TRPV1) channel functional activity (measurement of [Ca2+]i); (c) [14C]AEA cellular uptake and hydrolysis assays in rat basophilic leukaemia (RBL-2H3) cells; (d) the mouse ‘tetrad’ tests (analgesia on a hot plate, immobility on a ‘ring’, rectal hypothermia and hypolocomotion in an open field); and (e) the limb spasticity test in chronic relapsing experimental allergic encephalomyelitis (CREAE) mice, a model of multiple sclerosis (MS).O-2093, either synthesized by us or commercially available, was inactive in the ‘tetrad’ up to a 20 mg kg−1 dose (i.v.). Like O-2093, the other four compounds exhibited low affinity in CB1 (Ki from 1.3 to >10 μM) and CB2 binding assays (1.3i< 8 μM), low potency and efficacy in a TRPV1 functional assay (EC50>10 μM), very low potency as fatty acid amide hydrolase (FAAH) inhibitors (IC50>25 μM) and were inactive in the ‘tetrad’ up to a 30 mg kg−1 dose (i.v.).While O-2247 and O-2248 were poor inhibitors of [14C]AEA cellular uptake (IC50>40 μM), O-3246 and O-3262 were quite potent in this assay. O-3246, which exhibits only a very subtle structural difference with O-2093, is the most potent inhibitor of AEA uptake reported in vitro under our experimental conditions (IC50=1.4 μM) and is 12-fold more potent than O-2093.When injected intravenously O-3246 and O-3262, again like O-2093 and unlike O-2247 and O-2248, significantly inhibited limb spasticity in mice with CREAE.These data confirm the potential utility of selective AEA uptake inhibitors as anti-spasticity drugs in MS and, given the very subtle chemical differences between potent and weak inhibitors of uptake, support further the existence of a specific mechanism for this process.British Journal of Pharmacology (2006) 147, 83–91. doi:10.1038/sj.bjp.0706418; published online 14 November 2005 [ABSTRACT FROM AUTHOR]

1 Marijuana's appetite-increasing effects have long been known. Recent research suggests that the CB(1) cannabinoid receptor antagonist SR141716A may suppress appetite. This study represents a further, systematic investigation of the role of CB(1) cannabinoid receptors in the pharmacological effects of cannabinoids on food intake. 2 Mice were food-restricted for 24 h and then allowed access to their regular rodent chow for 1 h. Whereas the CB(1) antagonist SR141716A dose-dependently decreased food consumption at doses that did not affect motor activity, Delta(9)-tetrahydrocannabinol (Delta(9)-THC) increased food consumption at doses that had no effect on motor activity. O-3259 and O-3257, structural analogs of SR141716A, produced effects similar to those of the parent compound. 3 Amphetamine (a known anorectic) and diazepam (a benzodiazepine and CNS depressant) decreased food consumption, but only at doses that also increased or decreased motor activity, respectively. The CB(2) cannabinoid receptor antagonist SR144528 and the nonpsychoactive cannabinoid cannabidiol did not affect food intake nor activity. 4 SR141716A decreased feeding in wild-type mice, but lacked pharmacological activity in CB(1) knockout mice; however, basal food intake was lower in CB(1) knockout mice. Amphetamine decreased feeding in both mouse genotypes. 5 These results suggest that SR141716A may affect the actions of endogenous cannabinoids in regulating appetite or that it may have effects of its own aside from antagonism of cannabinoid effects (e.g., decreased feeding behavior and locomotor stimulation). In either case, these results strongly suggest that CB(1) receptors may play a role in regulation of feeding behavior. [ABSTRACT FROM AUTHOR]

Abusers of inhaled solvents may show impaired cognitive functioning as reflected in problems with short-term memory and attention. In the present study, we examined the effects of the abused solvents toluene, m-xylene and 1,1,1-trichloroethane in an acoustic startle paradigm which included tests for pre-pulse inhibition (PPI). This procedure has been used to model sensorimotor reactivity and gating, pre-attentional processes that may be disrupted by mental illness, substance abuse or drug withdrawal. Following exposure to an inhalant vapor or to air, rats were placed in startle chambers in which they were exposed to loud: [120 dB] acoustic pulses presented alone or preceded by a less intense pre-pulse: [85 dB]. Results were compared to those obtained with the depressants ethanol, pentobarbital and methoxyflurane, which have many acute behavioral effects in common with those of abused solvents. As expected, these depressants only decreased startle amplitudes during pulse alone trials and had no effect on PPI. Although solvent vapors also had no effect on PPI, they did not decrease startle amplitudes in pulse alone trials, at least at the concentrations tested. In fact, toluene robustly increased startle amplitude. The lack of effect of the abused solvents on PPI does not provide support for an hypothesis that acute effects of vapors on attention and early information processing is a basis for cognitive deficits in solvent abusers. [ABSTRACT FROM AUTHOR]