'One-trial sensitization' to the anxiolytic-like effects of cannabinoid receptor antagonist SR141716A in the mouse elevated plus-maze

Bridging the gap: The endocannabinoid system as a functional fulcrum for benzodiazepines in a novel frontier of anxiety pharmacotherapy

While benzodiazepines have been a mainstay of the pharmacotherapy of anxiety disorders, their short-term efficacy and risk of abuse have driven the exploration of alternative treatment approaches. The endocannabinoid (eCB) system has emerged as a key modulator of anxiety-related processes, with evidence suggesting dynamic interactions between the eCB system and the GABAergic system, the primary target of benzodiazepines. According to the existing literature, the activation of the cannabinoid receptors has been shown to exert anxiolytic effects, while their blockade or genetic deletion results in heightened anxiety-like responses. Moreover, studies have provided evidence of interactions between the eCB system and benzodiazepines in anxiety modulation. For instance, the attenuation of benzodiazepine-induced anxiolysis by cannabinoid receptor antagonism or genetic variations in the eCB system components in animal studies, have been associated with variations in benzodiazepine response and susceptibility to anxiety disorders. The combined use of cannabinoid-based medications, such as cannabinoid receptor agonists and benzodiazepine co-administration, has shown promise in augmenting anxiolytic effects and reducing benzodiazepine dosage requirements. This article aims to comprehensively review and discuss the current evidence on the involvement of the eCB system as a key modulator of benzodiazepine-related anxiolytic effects, and further, the possible mechanisms by which the region-specific eCB system-GABAergic connectivity modulates the neuro-endocrine/behavioral stress response, providing an inclusive understanding of the complex interplay between the eCB system and benzodiazepines in the context of anxiety regulation, to inform future research and clinical practice.

Synergistic interaction between clonidine and ACPA on the modulation of anxiety-like behaviors in non-acute restraint stress and acute restraint stress conditions

The present research examined the possible role of α-2 adrenergic receptor drugs (clonidine, selective α-2 adrenergic receptor agonist, and yohimbine, competitive α-2 adrenoreceptor antagonist,) on the effect of arachidonylcyclopropylamide (ACPA), a cannabinoid CB1 receptor agonist, in non-acute restraint stress (NARS) and acute restraint stress (ARS) mice. The animals were unilaterally implanted with a cannula in the left lateral ventricle. ARS was carried out by movement restraint at a period of 4 h. An elevated plus-maze (EPM) apparatus was used to evaluate anxiety-like behaviors. The results indicated that induction of ARS for 4 h induced anxiogenic-like behavior due to the reduction of %OAT (the percentage of time spent in the open arms) in male mice. Additionally, ARS caused neuronal degeneration in the prefrontal cortex. On the other hand, alone intracerebroventricularly (i.c.v.) infusions of ACPA (0.5 µg/mouse) and clonidine (0.5 µg/mouse) increased %OAT, indicating an anxiolytic-like response in the NARS and ARS mice. In contrast, alone i.c.v. infusions of yohimbine (0.5 µg/mouse) decreased %OAT and %OAE (the percentage of entries to the open arms), proposing an anxiogenic-like effect in the NARS and ARS mice. When the subthreshold dose of ACPA and different doses of clonidine were co-injected, ACPA potentiated the anxiolytic-like behavior produced by clonidine in the ARS mice. On the other hand, when the ineffective dosage of ACPA and different dosages of yohimbine were co-infused, ACPA reversed the anxiogenic-like effect induced by yohimbine in the NARS and ARS mice. Moreover, the results revealed a synergistic effect between ACPA and clonidine upon induction of anxiolytic-like behaviors. It can be concluded that the interaction between clonidine and ACPA modulates the anxiety-like behaviors induced by stress in male mice.

Additive anxiolytic-like effect of citicoline and ACPA in the non-acute restraint stress (NARS) and acute restraint stress (ARS) mice

The cannabinoid system plays a key role in stress-related emotional symptoms such as anxiety. Citicoline is a supplemental substance with neuroprotective properties that alleviates anxiety-related behaviors. There is a relation between the actions of cannabinoids and cholinergic systems. So, we decided to evaluate the effects of intracerebroventricular (i.c.v.) infusion of cannabinoid CB1 receptor agents on citicoline-produced response to anxiety-like behaviors in the non-acute restraint stress (NARS) and acute restraint stress (ARS) mice. For i.c.v. microinjection of drugs, a guide cannula was inserted in the left lateral ventricle. ARS was induced by movement restraint for 4 h. Anxiety-related behaviors were assessed using an elevated plus maze (EPM). The results showed that induction of ARS for 4 h decreased the percentage of time spent in the open arms (%OAT) and the percentage of entries to the open arms (%OAE) without affecting locomotor activity, showing anxiogenic-like behaviors. i.c.v. infusion of ACPA (1 µg/mouse) induced an anxiolytic-like effect due to the enhancement of %OAT in the NARS and ARS mice. Nonetheless, i.c.v. microinjection of AM251 (1 µg/mouse) decreased %OAT in the NARS and ARS mice which suggested an anxiogenic-like response. Intraperitoneal (i.p.) administration of citicoline (80 mg/kg) induced an anxiolytic-like effect by the augmentation of %OAT in the ARS mice. Furthermore, when ACPA and citicoline were co-administrated, ACPA potentiated the anxiolytic-like effect induced by citicoline in the NARS and ARS mice. On the other hand, when AM251 and the citicoline were co-injected, AM251 reversed the anxiolytic-like response induced by the citicoline in the NARS and ARS mice. The results of this research exhibited an additive effect between citicoline and ACPA on the induction of anxiolytic-like response in the NARS and ARS mice. Our results indicated an interaction between citicoline and cannabinoid CB1 receptor drugs on the control of anxiety-like behaviors in the NARS and ARS mice.

Endocannabinoids, cannabinoids and the regulation of anxiety

Cannabis has been used for hundreds of years, with its ability to dampen feelings of anxiety often reported as a primary reason for use. Only recently has the specific role cannabinoids play in anxiety been thoroughly investigated. Here we discuss the body of evidence describing how endocannabinoids and exogenous cannabinoids are capable of regulating the generation and termination of anxiety states. Disruption of the endogenous cannabinoid (eCB) system following genetic manipulation, pharmacological intervention or stress exposure reliably leads to the generation of an anxiety state. On the other hand, upregulation of eCB signaling is capable of alleviating anxiety-like behaviors in multiple paradigms. When considering exogenous cannabinoid administration, cannabinoid receptor 1 (CB1) agonists have a biphasic, dose-dependent effect on anxiety such that low doses are anxiolytic while high doses are anxiogenic, a phenomenon that is evident in both rodent models and humans. Translational studies investigating a loss of function mutation in the gene for fatty acid amide hydrolase, the enzyme responsible for metabolizing AEA, have also shown that AEA signaling regulates anxiety in humans. Taken together, evidence reviewed here has outlined a convincing argument for cannabinoids being powerful regulators of both the manifestation and amelioration of anxiety symptoms, and highlights the therapeutic potential of targeting the eCB system for the development of novel classes of anxiolytics. This article is part of the special issue on 'Cannabinoids'.

Integrating Endocannabinoid Signaling and Cannabinoids into the Biology and Treatment of Posttraumatic Stress Disorder

Exposure to stress is an undeniable, but in most cases surmountable, part of life. However, in certain individuals, exposure to severe or cumulative stressors can lead to an array of pathological conditions including posttraumatic stress disorder (PTSD), characterized by debilitating trauma-related intrusive thoughts, avoidance behaviors, hyperarousal, as well as depressed mood and anxiety. In the context of the rapidly changing political and legal landscape surrounding use of cannabis products in the USA, there has been a surge of public and research interest in the role of cannabinoids in the regulation of stress-related biological processes and in their potential therapeutic application for stress-related psychopathology. Here we review the current state of knowledge regarding the effects of cannabis and cannabinoids in PTSD and the preclinical and clinical literature on the effects of cannabinoids and endogenous cannabinoid signaling systems in the regulation of biological processes related to the pathogenesis of PTSD. Potential therapeutic implications of the reviewed literature are also discussed. Finally, we propose that a state of endocannabinoid deficiency could represent a stress susceptibility endophenotype predisposing to the development of trauma-related psychopathology and provide biologically plausible support for the self-medication hypotheses used to explain high rates of cannabis use in patients with trauma-related disorders.

Pharmacological comparison of traditional and non-traditional cannabinoid receptor 1 blockers in rodent models in vivo

Cannabinoid receptor 1 (CB1R) antagonists have been proven to be effective anti-obesity drugs; however, psychiatric side effects have halted their pharmaceutical development worldwide. Despite the emergence of next generation CB1R blockers, a preclinical head to head comparison of the anti-obesity and psychiatric side effect profiles of the key compounds has not been performed. Here, we compared classical CB1R antagonists (rimonabant, taranabant, otenabant, ibipinabant, and surinabant) and non-traditional CB1R blockers (the partial agonist O-1269, the neutral antagonists VCHSR and LH-21 and the peripherally acting inverse agonist JD-5037) using an in vivo screening cascade. First, the potencies of these compounds to reduce CB1R agonist-induced hypothermia and decrease fasting-induced food intake were determined. Then, equipotent doses of the non-toxic compounds were compared in a diet-induced obesity (DIO) test, which includes measurements of metabolic syndrome markers. Psychiatric side effects were assessed by measuring anxiogenicity in an ultrasonic vocalization test. All classical CB1R blockers were centrally acting appetite suppressants and decreased body weight and food intake in an obesity-dependent manner, with only slight effects on metabolic syndrome markers. In addition, all classical CB1R blockers increased ultrasonic vocalization. Surprisingly, none of the non-classical CB1R blockers was eligible for the DIO comparison and side effect profiling. O-1269 and LH-21 induced convulsive behavior, whereas VCHSR and JD-5037 were devoid of any in vivo activity. The classical CB1R blockers displayed similar therapeutic and side effect profiles in vivo, whereas the available non-traditional CB1R blockers were not appropriate tools for testing the therapeutic potential of alternative CB1R inhibitors.

Time-dependent sensitization of antipsychotic effect in adolescent male and female rats

Many behavioral and biological effects of a psychoactive drug often undergo time-dependent change following even one single drug exposure. The present study examined whether one or two exposures of haloperidol, olanzapine or clozapine would also induce a time-dependent change in their behavioral effects in adolescent rats, and whether such a change vary between sexes. Adolescent Sprague-Dawley rats (<40days old) were first treated with one single injection of haloperidol (0.05 and 0.1mg/kg, sc), clozapine (10.0 and 20.0mg/kg, sc), 2 injections of olanzapine (1.0 and 2.0mg/kg, sc) or vehicle, and tested in a conditioned avoidance response (CAR) model or a PCP (3.20mg/kg, sc)-induced hyperlocomotion model to assess the drug's antipsychotic-like behavioral effects. One or three weeks later, rats were challenged with the drug and their avoidance responses and the PCP-induced hyperlocomotion were re-assessed. One-trial haloperidol and 2-trial olanzapine induced a sensitization, while 1-trial clozapine induced a tolerance effect. The 1-trial haloperidol sensitization was significantly higher at the 3-week time point than at 1-week point, especially in the females. Clozapine tolerance in the conditioned avoidance response model also exhibited the time-dependent increase in both sex groups. Olanzapine sensitization in the PCP model showed a time-dependent change in a sex-dependent fashion. Overall, the time-dependent antipsychotic sensitization and tolerance can be demonstrated in adolescent animals. Many pharmacological (e.g. specific drugs, drug doses), individual (e.g. male versus female) and environmental (e.g. specific behavioral models) factors play a role in the modulation of the strength of antipsychotic sensitization and tolerance.

Endocannabinoids and Mental Disorders

Preclinical and clinical data fully support the involvement of the endocannabinoid system in the etiopathogenesis of several mental diseases. In this review we will briefly summarize the most common alterations in the endocannabinoid system, in terms of cannabinoid receptors and endocannabinoid levels, present in mood disorders (anxiety, posttraumatic stress disorder, depression, bipolar disorder, and suicidality) as well as psychosis (schizophrenia) and autism. The arising picture for each pathology is not always straightforward; however, both animal and human studies seem to suggest that pharmacological modulation of this system might represent a novel approach for treatment.

Micromolar concentrations of rimonabant directly inhibits delta opioid receptor specific ligand binding and agonist-induced G-protein activity

WHAT IS KNOWN

There is a growing number of evidence showing, that the cannabinoid receptor 1 (CB1) antagonist rimonabant has many non-cannabimimetic actions, such as affecting the opioid system. The direct effect of rimonabant on opioid receptors has been studied so far mainly on μ-opioid receptors. However recently the δ-opioid receptor (DOR) receives much more attention as before, due to its potential therapeutic applications, such as nociception or treatment for psychiatric disorders.

OBJECTIVES

To investigate the direct effect of rimonabant on DOR specific ligand binding and on the DOR mediated G-protein activation.

RESULTS

Micromolar concentrations of rimonabant directly inhibited the DOR specific agonist binding in radioligand competition binding experiments using Chinese hamster ovary cells stably transfected with mouse DOR (CHO-mDOR). However the inhibition occurred also in the subnanomolar range during DOR specific antagonist binding in similar experimental conditions. In functional [(35)S]GTPγS binding assays rimonabant significantly decreased the basal receptor activity in CHO-mDOR but also in parental CHO cell membranes. During DOR agonist stimulation, micromolar concentration of rimonabant attenuated the DOR G-protein activation and the potency of the activator ligand in [(35)S]GTPγS binding assays performed in CHO-mDOR, in wild type and also in CB1/CB2 double knock-out mouse forebrain membranes. Yet again this inhibitory action was DOR specific, since it did not occur during other specific GPCR agonist mediated G-protein activation.

CONCLUSION

Rimonabant directly inhibited DOR function in the micromolar concentrations. The inhibitory actions indicate an antagonistic behavior towards DOR which was established by the followings: (i) rimonabant inhibited DOR antagonist binding more effectively than agonist binding, (ii) the inverse agonistic, agonistic effect of the compound can be excluded, and (iii) additionally according to previous findings the allosteric mechanism can also be foreclosed.

Translational evidence for the involvement of the endocannabinoid system in stress-related psychiatric illnesses

Accumulating evidence over the past decade has highlighted an important role of the endocannabinoid (eCB) system in the regulation of stress and emotional behavior across divergent species, from rodents to humans. The general findings from this work indicate that the eCB system plays an important role in gating and buffering the stress response, dampening anxiety and regulating mood. Work in rodents has allowed researchers to determine the neural mechanisms mediating this relationship while work in human populations has demonstrated the possible importance of this system in stress-related psychiatric diseases, such as post-traumatic stress disorder, generalized anxiety and major depression. These stress-protective effects of eCB signaling appear to be primarily mediated by their actions within corticolimbic structures, particularly the amygdala and the prefrontal cortex. The aim of this review is to provide an up-to-date discussion of the current level of knowledge in this field, as well as address the current gaps in knowledge and specific areas of research that require attention.

Discovery of novel anxiolytic agents--the trials and tribulations of pre-clinical models of anxiety

Anxiety disorders are the most common class of mental disorders present in the general population with an estimated lifetime prevalence of any anxiety disorder being approximately 15%, while the 12-month prevalence is more than 10%. They are classified into simple phobias, social phobias, obsessive-compulsive disorder (OCD) and panic attacks. Anxiety disorders are more prevalent in females than males and respond to pharmacological and non-pharmacological (behavioral) treatments. Anxiety disorders are complex with genetic and environmental factors interacting to produce the final psychopathology. There are many tests used to detect behaviors that indicate heightened anxiety in rodents however there are few pathological models of anxiety in rodents. Most compound testing is performed on naive, non-pathologically anxious, male animals which is a potential limitation to current strategies since these animals do not reflect the anxious patient. This article briefly describes some of the most common anxiety tests used in rodent research and concludes with a short perspective on areas the field could concentrate on to improve the understanding and successful translation of novel targets into new therapies in the clinic.

Orexin-1 receptor antagonism fails to reduce anxiety-like behaviour in either plus-maze-naïve or plus-maze-experienced mice

Although several lines of evidence have recently implicated orexins and their receptors in fear and anxiety, there is also a growing number of apparently inconsistent and/or negative findings. In the present study, we have used ethological methods to comprehensively profile the behavioural effects of the orexin-1 receptor antagonist SB-334867 (3-30 mg/kg) in mice exposed to the elevated plus-maze. Two experiments were performed, the first involving test-naïve animals and the second using prior undrugged experience of the maze to induce a qualitatively different emotional response to that seen on first exposure. In Experiment 1, a reference benzodiazepine (chlordiazepoxide, CDP, 15 mg/kg) produced a robust anxioselective profile comprising substantial increases in open arm exploration and reduced risk assessment without any signiifcant change in general activity levels. In contrast, SB-334867 failed to produce any behavioural effects over the dose range tested. In Experiment 2, 5 min undrugged experience of the maze 24h prior to testing increased open arm avoidance and abolished the anxiolytic efficacy of CDP. Despite this altered baseline, SB-334867 again failed to alter plus-maze behaviour. These findings agree with several recent reports that orexin receptor antagonists, such as SB-334867 and almorexant, do not alter basal anxiety levels in rats but markedly contrast with the anxiolytic-like effects of the same agents when anxiety levels have been exacerbated by fear conditioning, drug challenge or hypercapnia. This unique pattern of activity suggests that orexin receptor antagonists may have therapeutic value in those clinical anxiety disorders characterised by intense emotional arousal.

Effect of chronic exposure to rimonabant and phytocannabinoids on anxiety-like behavior and saccharin palatability

The acute effects of cannabinoid compounds have been investigated in animal models of anxiety-like behavior and palatability processing. However, the chronic effects of cannabinoids in such models are poorly understood. Experiment 1 compared the effects of both acute and chronic (14 days) exposure to the CB(1) receptor inverse agonist/antagonist, rimonabant, and the cannabis-derived CB(1) receptor neutral antagonist, tetrahydrocannabivarin (THCV), on: 1) time spent in the open, lit box in the Light-Dark (LD) immersion model of anxiety-like behavior and 2) saccharin hedonic reactions in the taste reactivity (TR) test of palatability processing. Experiment 2 compared the effects of chronic administration of cannabis-derived Δ(9)-tetrahydrocannabinol (Δ(9)-THC), cannabidiol (CBD) and cannabigerol (CBG) in these models. Tests were administered on Days 1, 7 and 14 of drug administration. In Experiment 1, rimonabant, but not THCV, produced an anxiogenic-like reaction in the LD immersion test and reduced saccharin palatability in the TR test; both of these effects occurred acutely and were not enhanced by chronic exposure. In Experiment 2, Δ(9)-THC also produced an acute anxiogenic-like reaction in the LD immersion test, without enhancement by chronic exposure. However, Δ(9)-THC enhanced saccharin palatability in the TR test on Day 1 of drug exposure only. CBD and CBG did not modify anxiety-like responding, but CBG produced a weak enhancement of saccharin palatability on Day 1 only. The results suggest that the anxiogenic-like reactions and the suppression of hedonic responding produced by rimonabant, are mediated by inverse agonism of the CB(1) receptor and these effects are not enhanced with chronic exposure.

Nicotine-induced anxiety-like behavior in a rat model of the novelty-seeking phenotype is associated with long-lasting neuropeptidergic and neuroplastic adaptations in the amygdala: effects of the cannabinoid receptor 1 antagonist AM251

A rat model of the novelty-seeking phenotype predicts vulnerability to the expression of behavioral sensitization to nicotine, where locomotor reactivity to novelty is used to screen experimentally-naïve rats for high (HR) versus low (LR) responders. The present study examines the long-term neuropeptidergic and neuroplastic adaptations associated with the expression of locomotor sensitization to a low dose nicotine challenge and social anxiety-like behavior following chronic intermittent nicotine exposure during adolescence in the LRHR phenotype. Our data show that the expression of behavioral sensitization to nicotine and abstinence-related anxiety are detected in nicotine pre-exposed HRs even across a long (3 wks) abstinence. Moreover, these behavioral effects of nicotine are accompanied by a persistent imbalance between neuropeptide Y and corticotrophin releasing factor systems, and a persistent increase in brain-derived neurotrophic factor (BDNF) and spinophilin mRNA levels in the amygdala. Furthermore, treatment with the cannabinoid receptor 1 antagonist, AM251 (5 mg/kg) during a short (1 wk) abstinence is ineffective in reversing nicotine-induced anxiety, fluctuations in BDNF and spinophilin mRNAs, and the neuropeptidergic dysregulations in the amygdala; although this treatment is effective in reversing the expression of locomotor sensitization to challenge nicotine even after a long abstinence. Interestingly, the identical AM251 treatment administered during the late phase of a long abstinence further augments anxiety and associated changes in BDNF and spinophilin mRNA in the basolateral nucleus of the amygdala in nicotine pre-exposed HRs. These findings implicate long-lasting neuropeptidergic and neuroplastic changes in the amygdala in vulnerability to the behavioral effects of nicotine in the novelty-seeking phenotype.

Endocannabinoid system and psychiatry: in search of a neurobiological basis for detrimental and potential therapeutic effects

Public concern on mental health has noticeably increased given the high prevalence of neuropsychiatric disorders. Cognition and emotionality are the most affected functions in neuropsychiatric disorders, i.e., anxiety disorders, depression, and schizophrenia. In this review, most relevant literature on the role of the endocannabinoid (eCB) system in neuropsychiatric disorders will be presented. Evidence from clinical and animal studies is provided for the participation of CB1 and CB2 receptors (CB1R and CB2R) in the above mentioned neuropsychiatric disorders. CBRs are crucial in some of the emotional and cognitive impairments reported, although more research is required to understand the specific role of the eCB system in neuropsychiatric disorders. Cannabidiol (CBD), the main non-psychotropic component of the Cannabis sativa plant, has shown therapeutic potential in several neuropsychiatric disorders. Although further studies are needed, recent studies indicate that CBD therapeutic effects may partially depend on facilitation of eCB-mediated neurotransmission. Last but not least, this review includes recent findings on the role of the eCB system in eating disorders. A deregulation of the eCB system has been proposed to be in the bases of several neuropsychiatric disorders, including eating disorders. Cannabis consumption has been related to the appearance of psychotic symptoms and schizophrenia. In contrast, the pharmacological manipulation of this eCB system has been proposed as a potential strategy for the treatment of anxiety disorders, depression, and anorexia nervosa. In conclusion, the eCB system plays a critical role in psychiatry; however, detrimental consequences of manipulating this endogenous system cannot be underestimated over the potential and promising perspectives of its therapeutic manipulation.

Characterization of a novel, brain-penetrating CB1 receptor inverse agonist: metabolic profile in diet-induced obese models and aspects of central activity

Pharmacologic antagonism of cannabinoid 1 receptors (CB1 receptors) in the central nervous system (CNS) suppresses food intake, promotes weight loss, and improves the metabolic profile. Since the CB1 receptor is expressed both in the CNS and in peripheral tissues, therapeutic value may be gained with CB1 receptor inverse agonists acting on receptors in both domains. The present report examines the metabolic and CNS actions of a novel CB1 receptor inverse agonist, compound 64, a 1,5,6-trisubstituted pyrazolopyrimidinone. Compound 64 showed similar or superior binding affinity, in vitro potency, and pharmacokinetic profile compared to rimonabant. Both compounds improved the metabolic profile in diet-induced obese (DIO) rats and obese cynomolgus monkeys. Weight loss tended to be greater in compound 64-treated DIO rats compared to pair-fed counterparts, suggesting that compound 64 may have metabolic effects beyond those elicited by weight loss alone. In the CNS, reversal of agonist-induced hypothermia and hypolocomotion indicated that compound 64 possessed an antagonist activity in vivo. Dosed alone, compound 64 suppressed extinction of conditioned freezing (10 mg/kg) and rapid eye movement (REM) sleep (30 mg/kg), consistent with previous reports for rimonabant, although for REM sleep, compound 64 was greater than threefold less potent than for metabolic effects. Together, these data suggested that (1) impairment of extinction learning and REM sleep suppression are classic, centrally mediated responses to CB1 receptor inverse agonists, and (2) some separation may be achievable between central and peripheral effects with brain-penetrating CB1 receptor inverse agonists while maintaining metabolic efficacy. Furthermore, chronic treatment with compound 64 contributes to evidence that peripheral CB1 receptor blockade may yield beneficial outcomes that exceed those elicited by weight loss alone.

Pharmacological characterization of AM1710, a putative cannabinoid CB2 agonist from the cannabilactone class: antinociception without central nervous system side-effects

Cannabinoid CB(2) agonists produce antinociception without central nervous system (CNS) side-effects. This study was designed to characterize the pharmacological and antinociceptive profile of AM1710, a CB(2) agonist from the cannabilactone class of cannabinoids. AM1710 did not exhibit off-target activity at 63 sites evaluated. AM1710 also exhibited limited blood brain barrier penetration. AM1710 was evaluated in tests of antinociception and CNS activity. CNS side-effects were evaluated in a modified tetrad (tail flick, rectal temperature, locomotor activity and rota-rod). Pharmacological specificity was established using CB(1) (SR141716) and CB(2) (SR144528) antagonists. AM1710 (0.1-10mg/kg i.p.) produced antinociception to thermal but not mechanical stimulation of the hindpaw. AM1710 (5mg/kg i.p.) produced a longer duration of antinociceptive action than the aminoalkylindole CB(2) agonist (R,S)-AM1241 (1mg/kg i.p.) at maximally antinociceptive doses. Antinociception produced by the low (0.1mg/kg i.p.) dose of AM1710 was blocked selectively by the CB(2) antagonist SR144528 (6mg/kg i.p.), whereas antinociception produced by the high dose of AM1710 (5mg/kg i.p.) was blocked by either SR144528 (6mg/kg i.p.) or SR141716 (6mg/kg i.p.). AM1710 did not produce hypoactivity, hypothermia, tail flick antinociception, or motor ataxia when evaluated in the tetrad at any dose. In conclusion, AM1710, a CB(2)-preferring cannabilactone, produced antinociception in the absence of CNS side-effects. Thus, any CB(1)-mediated antinociceptive effects of this compound may be attributable to peripheral CB(1) activity. The observed pattern of pharmacological specificity produced by AM1710 is consistent with limited blood brain barrier penetration of this compound and absence of CNS side-effects.

Anxiety-like effects of SR141716-precipitated delta9-tetrahydrocannabinol withdrawal in mice in the elevated plus-maze

Marijuana discontinuation has been recently reported to be anxiogenic in humans, which may predict relapse. Limited animal research has been carried out to model this withdrawal-associated negative affect. The current study sought to investigate the potential anxiety-like effects of cannabinoid withdrawal in mice. Male ICR mice were injected s.c. with delta9-tetrahydrocannabinol (THC) at 10mg/kg or vehicle once daily for 10 days. To precipitate withdrawal, the cannabinoid CB1 antagonist SR141716 (0.3, 1.0, or 3.0mg/kg) or vehicle was administrated i.p. 4h following the last THC or vehicle treatment. Thirty minutes later, mice were tested on the elevated plus-maze (EPM) for 5min. SR141716 did not significantly change EPM behaviors in vehicle-treated mice. In contrast, SR141716 precipitated a reduction in exploration of the open arms of EPM in mice repeatedly treated with THC vs vehicle. At 3.0mg/kg, SR141716 significantly reduced % open arm entries of the total arm entries, % open arm time of total time in arms, and the absolute time spent in open arms. No significant differences in the number of closed or total arm entries were observed, indicating that the behavioral changes were not due to altered motor activity. Collectively, the present results constitute the first evidence that cannabinoid withdrawal produces anxiety-like effects in mice. This animal model may help to identify the mechanisms that contribute to adaptations in the neuronal circuitry of the brain that are expressed as emotional symptoms of cannabinoid withdrawal.

Promoter variants of the cannabinoid receptor 1 gene (CNR1) in interaction with 5-HTTLPR affect the anxious phenotype

Anxiety is a polygenic condition, and the recently discovered Endocannabinoid System (ECS) is one plausible candidate. Experimental data suggest that the ECS can modulate several neurotransmitter systems, including the serotonergic system, which itself plays a significant role in anxiety. However, to date there is no evidence of gene-gene interactions; indeed genetic studies focusing separately on the two systems provide conflicting data. Thus, the aim of our study was to analyze the interaction of the promoter regions of the serotonin transporter (SLC6A4) and cannabinoid receptor 1 (CNR1) genes on anxiety. We genotyped 706 individuals for the 5-HTTLPR in the SLC6A4 promoter and 4 SNPs located in the CNR1 promoter region. Anxiety was measured by the State-Trait Anxiety Inventory (STAI-S, STAI-T), the anxiety subscale of TEMPS-A (TEMPS-Anx), and the Brief Symptom Inventory (BSI-Anx). Significant 5-HTTLPR x CNR1 promoter-promoter interaction was observed using STAI-T (P = 0.0006) and TEMPS-Anx (P = 0.0013). The risk of high anxiety scores on BSI-Anx was 4.6-fold greater in homozygous 'GG' rs2180619 in combination with homozygous 'SS' 5-HTTLPR (P = 0.0005) compared to other genotypes. The effect of previously described "TGC" haplotype in the alternative promoter of CNR1 depended both on the conventional promoter polymorphism and the 5-HTTLPR. Our haplotype and putative transcription binding profile analyses strongly suggest that certain constellations of CB1-receptor and 5-HTT promoters yield extremely high or low synaptic 5-HT concentrations, and these are associated with an anxious phenotype. In conclusion, genetically determined serotonergic and endocannabinoid dysfunctions could lead to a vulnerability causing anxiety disorders and possibly depression.

Relations between open-field, elevated plus-maze, and emergence tests in C57BL/6J and BALB/c mice injected with GABA- and 5HT-anxiolytic agents

Two 5HT(1A) receptor agonists and chlordiazepoxide were examined in open-field, elevated plus maze, and emergence tests. At doses with no effect in the open-field, chlordiazepoxide increased open and open/total arm visits as well as open arm duration in the elevated plus maze, whereas 5HT(1A) receptor agonists showed an anxiolytic response on a single measure. The anxiolytic action of chlordiazepoxide was limited to the less active BALB/c strain. Unlike the 5HT(1A) receptor agonists, chlordiazepoxide was also anxiolytic in the emergence test, once again only in BALB/c and not C57BL/6J mice. Significant correlations were found between emergence latencies and specific indicators of anxiety in the elevated plus-maze in chlordiazepoxide-treated but not in mice treated with buspirone and 8-OH-DPAT. These results indicate that elevated plus-maze and emergence tests depend on benzodiazepine receptors. In contrast, 5HT(1A) receptor agonists were ineffective in the emergence test and no correlation was found between emergence latencies and specific indicators of anxiety in the elevated plus-maze. Though superficially similar, the emergence test seems to tap into a partially separate facet of anxiety.

Interactions between environmental aversiveness and the anxiolytic effects of enhanced cannabinoid signaling by FAAH inhibition in rats

RATIONALE

Since the discovery of endogenous cannabinoid signaling, the number of studies exploring its role in health and disease has increased exponentially. Fatty acid amide hydrolase (FAAH), the enzyme responsible for degradation of the endocannabinoid anandamide, has emerged as a promising target for anxiety-related disorders. FAAH inhibitors (e.g., URB597) increase brain levels of anandamide and induce anxiolytic-like effects in rodents. Recent findings, however, questioned the efficacy of URB597 as an anxiolytic.

OBJECTIVES

We tested here the hypothesis that conflicting findings are due to variations in the stressfulness of experimental conditions employed in various studies.

RESULTS

We found that URB597 (0.1-0.3 mg/kg) did not produce anxiolytic effects when the aversiveness of testing procedures was minimized by handling rats daily before experimentation, by habituating them to the experimental room, or by employing low illumination during testing. In contrast, URB597 had robust anxiolytic effects when the aversiveness of the testing environment was increased by eliminating habituation to the experimental room or by employing bright lighting conditions. Unlike URB597, the benzodiazepine chlordiazepoxide (5 mg/kg) had anxiolytic effects under all testing conditions. The anxiolytic effects of URB597 were abolished by the cannabinoid CB1-receptor antagonist AM251, showing that they were mediated by CB1 receptors. Close inspection of experimental conditions employed in earlier reports suggests that conflicting findings with URB597 can be explained by different testing conditions, such as those manipulated in the present study.

CONCLUSIONS

Our findings show that FAAH inhibition does not affect anxiety under mildly stressful circumstances but protects against the anxiogenic effects of aversive stimuli.

Role of endocannabinoid signaling in anxiety and depression

Cannabinoid receptors and their endogenous ligands are located throughout the limbic, or "emotional," brain, where they modulate synaptic neurotransmission. Converging preclinical and clinical data suggest a role for endogenous cannabinoid signaling in the modulation of anxiety and depression. Augmentation of endocannabinoid signaling (ECS) has anxiolytic effects, whereas blockade or genetic deletion of CB₁ receptors has anxiogenic properties. Augmentation of ECS also appears to have anti-depressant actions, and in some assays blockade and genetic deletion of CB₁ receptors produces depressive phenotypes. These data provide evidence that ECS serves in an anxiolytic, and possibly anti-depressant, role. These data suggest novel approaches to treatment of affective disorders which could include enhancement of endogenous cannabinoid signaling, and warrant cautious use of CB₁ receptor antagonists in patients with pre-existing affective disorders.

Chronic delta 9-tetrahydrocannabinol during adolescence provokes sex-dependent changes in the emotional profile in adult rats: behavioral and biochemical correlates

Few and often contradictory reports exist on the long-term neurobiological consequences of cannabinoid consumption in adolescents. The endocannabinoid system plays an important role during the different stages of brain development as cannabinoids influence the release and action of different neurotransmitters and promote neurogenesis. This study tested whether long-lasting interference by cannabinoids with the developing endogenous cannabinoid system during adolescence caused persistent behavioral alterations in adult rats. Adolescent female and male rats were treated with increasing doses of Delta(9)-tetrahydrocannabinol (THC) for 11 days (postnatal day (PND) 35-45) and left undisturbed until adulthood (PND 75) when behavioral and biochemical assays were carried out. CB1 receptor level and CB1/G-protein coupling were significantly reduced by THC exposure in the amygdala (Amyg), ventral tegmental area (VTA) and nucleus accumbens (NAc) of female rats, whereas male rats had significant alterations only in the amygdala and hippocampal formation. Neither female nor male rats showed any changes in anxiety responses (elevated plus maze and open-field tests) but female rats presented significant 'behavioral despair' (forced swim test) paralleled by anhedonia (sucrose preference). In contrast, male rats showed no behavioral despair but did present anhedonia. This different behavioral picture was supported by biochemical parameters of depression, namely CREB alteration. Only female rats had low CREB activity in the hippocampal formation and prefrontal cortex and high activity in the NAc paralleled by increases in dynorphin expression. These results suggest that heavy cannabis consumption in adolescence may induce subtle alterations in the emotional circuit in female rats, ending in depressive-like behavior, whereas male rats show altered sensitivity to rewarding stimuli.

Endocannabinoid modulation of fear responses: learning and state-dependent performance effects

Recently, disruption of the endogenous cannabinoid (endocannabinoid, eCB) system was found to impair extinction in delay and contextual fear conditioning models. However, conditioning procedures used in that work precluded investigation of possible eCB effects on acquisition of learned fear. We therefore examined the role of eCBs in modulating fear responses using multiple-trial versions of trace (hippocampal-dependent) and delay (amygdala-dependent) Pavlovian fear conditioning. By administering the CB1 receptor antagonist AM251 (5 mg/kg, i.p) to C57/Bl/6 mice at various times, we systematically identified the stages of learning and memory (i.e. acquisition, consolidation, recall and extinction) that are modulated by eCB signaling. During tone (CS) - footshock (US) conditioning, AM251 enhanced acquisition of freezing behavior for both trace- and delay-conditioning protocols. CB1 antagonism also enhanced generalized fear (baseline freezing) and cued (CS) freezing during memory recall tests in a state-dependent manner for both trace and delay conditioned animals. Furthermore, in trace-conditioned animals, AM251 impaired extinction performance of both cued and generalized fear. CB1 antagonism did not affect short-term memory (STM) or long-term memory (LTM) consolidation processes. Together, these results suggest that during acquisition and recall of aversive learning, eCBs prevent the expression and retention of inappropriate generalized and learned responses. These findings have important implications for the therapeutic use of CB1 antagonists.

Cat odour-induced anxiety--a study of the involvement of the endocannabinoid system

RATIONALE

Recent evidence suggests the involvement of the endocannabinoid (EC) system in the regulation of anxiety.

OBJECTIVES

The aim of present work was to study the role of the EC system in cat odour-induced anxiety in rats. Materials and methods Male Wistar rats were exposed to cat odour in home and motility cages. Exposure of rats to elevated zero-maze was used to determine changes in anxiety. Effect of rimonabant (0.3-3 mg/kg), antagonist of CB1 receptors, was studied on cat odour-induced alterations in exploratory behaviour. Real-time PCR was used to determine gene expression levels of EC-related genes in the brain.

RESULTS

Anxiogenic-like action of cat odour was evident in the elevated zero-maze. Cat odour increased the expression of FAAH, the enzyme responsible for the degradation of anandamide, in the mesolimbic area. By contrast, in the amygdala and periaqueductal grey (PAG) levels of NAPE-PLD, the enzyme related to the synthesis of anandamide, and FAAH were remarkably decreased. Cat odour also decreased the expression of enzymes related to metabolism of 2-archidonoyl-glycerol in the amygdala and PAG. Pre-treatment of rats with rimonabant (0.3-3 mg/kg) reduced the exploratory behaviour of rats, but did not affect cat odour-induced changes.

CONCLUSION

Exposure to cat odour induces anxiogenic-like effect on the behaviour in rats. Cat odour also causes moderate increase in expression of EC-related genes in the mesolimbic area, whereas significant down-regulation is established in the amygdala and PAG. Relation of predator odour-induced anxiety to the inhibition of the EC system in the amygdala and PAG is supported by behavioural studies where blockade of CB1 receptors by rimonabant induces anxiogenic-like action.

The endocannabinoid system: emotion, learning and addiction

The identification of the cannabinoid receptor type 1 (CB1 receptor) was the milestone discovery in the elucidation of the behavioural and emotional responses induced by the Cannabis sativa constituent Delta(9)-tetrahydrocannabinol. The subsequent years have established the existence of the endocannabinoid system. The early view relating this system to emotional responses is reflected by the fact that N-arachidonoyl ethanolamine, the pioneer endocannabinoid, was named anandamide after the Sanskrit word 'ananda', meaning 'bliss'. However, the emotional responses to cannabinoids are not always pleasant and delightful. Rather, anxiety and panic may also occur after activation of CB1 receptors. The present review discusses three properties of the endocannabinoid system as an attempt to understand these diverse effects. First, this system typically functions 'on-demand', depending on environmental stimuli and on the emotional state of the organism. Second, it has a wide neuro-anatomical distribution, modulating brain regions with different functions in responses to aversive stimuli. Third, endocannabinoids regulate the release of other neurotransmitters that may have even opposing functions, such as GABA and glutamate. Further understanding of the temporal, spatial and functional characteristics of this system is necessary to clarify its role in emotional responses and will promote advances in its therapeutic exploitation.

CB1 receptor blockade reduces the anxiogenic-like response and ameliorates the neurochemical imbalances associated with alcohol withdrawal in rats

There is strong evidence that blocking CB1 receptors may reduce alcohol intake in alcohol-dependent individuals. However, there is still limited evidence that CB1 receptor antagonists may also be beneficial in the attenuation of alcohol withdrawal syndrome, even though alcohol withdrawal appears to be milder in CB1 receptor knockout mice. Here we have examined whether the CB1 receptor antagonist rimonabant (SR141716) can alleviate the behavioral symptoms and revert the neurochemical imbalance elicited by a 3-h interruption of chronic alcohol exposure (7.2% in the drinking water for 10 days) in male Wistar rats. Administration of rimonabant attenuated the strong anxiogenic traits of the animals that developed when regular alcohol intake was interrupted. This may reflect the correction of the GABA/glutamate imbalances developed by the animals that received rimonabant in various brain regions involved in emotional (e.g. prefrontal cortex) and motor (e.g. caudate-putamen and globus pallidus) responses. In addition, rimonabant also affected the dopamine deficits generated by alcohol abstinence in the amygdala and ventral-tegmental area, albeit to a lesser extent. However, this antagonist was unable to correct the impairment caused by alcohol abstinence in serotonin and neuropeptide Y. The endocannabinoid activity in the brain of alcohol-abstinent rats indicated that the behavioral and neurochemical improvements caused by rimonabant were not related to the attenuation of a possible increase in this activity generated by alcohol withdrawal. Conversely, the density of CB1 receptors was reduced in alcohol-abstinent animals (e.g. globus pallidus, substantia nigra), as were the levels of endocannabinoids and related N-acylethanolamines (e.g. amygdala, caudate-putamen). Thus, rimonabant possibly enhances an endogenous response generated by interrupting the regular use of alcohol. In summary, rimonabant might attenuate withdrawal symptoms associated with alcohol abstinence, an effect that was presumably due to the normalization of GABA and glutamate, and to a lesser extent, dopamine transmission in emotion- and motor-related areas.

Role in anxiety behavior of the endocannabinoid system in the prefrontal cortex

In the present study we explored with a multidisciplinary approach, the role of anandamide (AEA) in the modulation of anxiety behavior at the level of the prefrontal cortex (PFC). Low doses of the metabolically stable AEA analog, methanandamide, microinjected into the PFC, produced an anxiolytic-like response in rats, whereas higher doses induced anxiety-like behaviors. Pretreatment with the selective antagonist of CB1 or TRPV1 receptors (AM251 and capsazepine, respectively) suggested that the anxiolytic effect evoked by AEA might be due to the interaction with the CB1 cannabinoid receptor, whereas vanilloid receptors seem to be involved in AEA anxiogenic action. When AEA contents in the PFC were increased by microinjecting the selective inhibitor of fatty acid amide hydrolase (FAAH), URB597, we observed an anxiolytic response only at low doses of the compound and no effect or even an anxiogenic profile at higher doses. In line with this, a marked decrease of AEA levels in the PFC, achieved by lentivirus-mediated local overexpression of FAAH, produced an anxiogenic response. These findings support an anxiolytic role for physiological increases in AEA in the PFC, whereas more marked increases or decreases of this endocannabinoid might lead to an anxiogenic response due to TRPV1 stimulation or the lack of CB1 activation, respectively.

Endocannabinoid system and synaptic plasticity: implications for emotional responses

The endocannabinoid system has been involved in the regulation of anxiety, and proposed as an inhibitory modulator of neuronal, behavioral and adrenocortical responses to stressful stimuli. Brain regions such as the amygdala, hippocampus and cortex, which are directly involved in the regulation of emotional behavior, contain high densities of cannabinoid CB1 receptors. Mutant mice lacking CB1 receptors show anxiogenic and depressive-like behaviors as well as an altered hypothalamus pituitary adrenal axis activity, whereas enhancement of endocannabinoid signaling produces anxiolytic and antidepressant-like effects. Genetic and pharmacological approaches also support an involvement of endocannabinoids in extinction of aversive memories. Thus, the endocannabinoid system appears to play a pivotal role in the regulation of emotional states. Endocannabinoids have emerged as mediators of short- and long-term synaptic plasticity in diverse brain structures. Despite the fact that most of the studies on this field have been performed using in vitro models, endocannabinoid-mediated plasticity might be considered as a plausible candidate underlying some of the diverse physiological functions of the endogenous cannabinoid system, including developmental, affective and cognitive processes. In this paper, we will focus on the functional relevance of endocannabinoid-mediated plasticity within the framework of emotional responses. Alterations of the endocannabinoid system may constitute an important factor in the aetiology of certain neuropsychiatric disorders, and, in turn, enhancers of endocannabinoid signaling could represent a potential therapeutical tool in the treatment of both anxiety and depressive symptoms.

Correlated species differences in the effects of cannabinoid ligands on anxiety and on GABAergic and glutamatergic synaptic transmission

Cannabinoid ligands show therapeutic potential in a variety of disorders including anxiety. However, the anxiety-related effects of cannabinoids remain controversial as agonists show opposite effects in mice and rats. Here we compared the effects of the cannabinoid agonist WIN-55,212 and the CB1 antagonist AM-251 in CD1 mice and Wistar rats. Special attention was paid to antagonist–agonist interactions, which had not yet been studied in rats. In mice, WIN-55,212 decreased whereas AM-251 increased anxiety. The antagonist abolished the effects of the agonist. In contrast, WIN-55,212 increased anxiety in rats. Surprisingly, the antagonist potentiated this effect. Cannabinoids affect both GABAergic and glutamatergic functions, which play opposite roles in anxiety. We hypothesized that discrepant findings resulted from species differences in the relative responsiveness of the two transmitter systems to cannabinoids. We investigated this hypothesis by studying the effects of WIN-55,212 on evoked hippocampal inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs). IPSCs were one order of magnitude more sensitive to WIN-55,212 in mice than in rats. In mice, IPSCs were more sensitive than EPSCs to WIN-55,212. This is the first study showing that the relative cannabinoid sensitivity of GABA and glutamate neurotransmission is species-dependent. Based on behavioural and electrophysiological findings, we hypothesize that WIN-55,212 reduced anxiety in mice by affecting GABA neurotransmission whereas it increased anxiety in rats via glutamatergic mechanisms. In rats, AM-251 potentiated this anxiogenic effect by inhibiting the anxiolytic GABAergic mechanism. We suggest that the anxiety-related effects of cannabinoids depend on the relative cannabinoid responsiveness of GABAergic and glutamatergic neurotransmission.

CB1 receptor stimulation in specific brain areas differently modulate anxiety-related behaviour

There is a general consensus that the effects of cannabinoid agonists on anxiety seem to be biphasic, with low doses being anxiolytic and high doses ineffective or possibly anxiogenic. Besides the behavioural effects of cannabinoids on anxiety, very few papers have dealt with the neuroanatomical sites of these effects. We investigated the effect on rat anxiety behavior of local administration of THC in the prefrontal cortex, basolateral amygdala and ventral hippocampus, brain regions belonging to the emotional circuit and containing high levels of CB1 receptors. THC microinjected at low doses in the prefrontal cortex (10 microg) and ventral hippocampus (5 microg) induced in rats an anxiolytic-like response tested in the elevated plus-maze, whilst higher doses lost the anxiolytic effect and even seemed to switch into an anxiogenic profile. Low THC doses (1 microg) in the basolateral amygdala produced an anxiogenic-like response whereas higher doses were ineffective. All these effects were CB1-dependent and closely linked to modulation of CREB activation. Specifically, THC anxiolytic activity in the prefrontal cortex and ventral hippocampus was paralleled by an increase in CREB activation, whilst THC anxiogenic response in the basolateral amygdala was paralleled by a decrease in CREB activation. Our results suggest that while a mild activation of CB1 receptors in the prefrontal cortex and ventral hippocampus attenuates anxiety, a slight CB1 receptor stimulation in the amygdala results in an anxiogenic-like response. The molecular underpinnings of these effects involve a direct stimulation of CB1 receptors ending in pCREB modulation and/or a possible alteration in the fine tuning of local neuromodulator release.

Evaluation of fatty acid amide hydrolase inhibition in murine models of emotionality

RATIONALE

Manipulations of the endocannabinoid/fatty acid amide hydrolase (FAAH) signaling systems result in conflicting and paradoxical effects in rodent models of emotional reactivity.

OBJECTIVES

In the present study, we tested the hypothesis that the inhibition of FAAH would elicit significant effects in murine models used to screen anxiolytic and antidepressant drugs.

MATERIALS AND METHODS

FAAH (-/-) mice and wild-type mice treated with FAAH inhibitors (URB597 and OL-135) were evaluated in standard behavioral screening models for antidepressant (i.e., tail suspension and forced-swim tests) and anxiolytic (i.e., elevated plus maze) agents. The doses of URB597 and OL-135 selected were based on their ability to augment the pharmacological effects (i.e., analgesia, catalepsy, and hypothermia) of exogenously administered anandamide.

RESULTS

FAAH (-/-) mice, anandamide-injected FAAH (-/-) mice, or wild-type mice injected with FAAH inhibitors or anandamide failed to exhibit significant effects in standard tests of emotional reactivity, although the antidepressant desipramine and the anxiolytic agent midazolam were active in the appropriate assays. FAAH- (-/-) and URB597-treated mice finally displayed significant effects in the tail suspension test when substantial methodological changes were made (i.e., altered ambient light and increased sample sizes).

CONCLUSIONS

Although FAAH suppression can elicit significant effects under some instances in which consequential procedural modifications are made, the present results indicate that the pharmacological inhibition or genetic deletion of FAAH is ineffective in standard mouse models of emotional reactivity. It remains to be established whether the effects of FAAH inhibition in these modified tasks are predictive of their efficacy in treating emotional disorders.

Role of dorsal hippocampal cannabinoid receptors and nitric oxide in anxiety like behaviours in rats using the elevated plus-maze test

1. The important role of the cannabinoid system in the modulation of anxiety like behaviours in clinical and experimental studies has been proposed. However, investigations into this effect of cannabinoids has produced contradictory results. It has been reported that different neurotransmitters, such as nitric oxide (NO), are involved in the behavioural effects of cannabinoids. The hippocampus is also an important brain region in the modulation of anxiety in which CB1 receptors are densely expressed. The present study was designed to evaluate the interactions between cannabinoid and NO systems in the CA1 brain region of the rats using the plus-maze test. 2. Rats were anaesthetized with ketamine and xylazine and special cannulas were inserted stereotaxically into the CA1 region of the dorsal hippocampus. After 1 week recovery, the effects of intra-CA1 administration of WIN55212-2 (1, 2.5 and 5 microg/rat), AM251 (2, 10 and 50 ng/rat), L-arginine (0.01, 0.1 and 1 microg/rat) and N(G)-nitro-L-arginine methyl ester (L-NAME; 1, 10 and 100 ng/rat) on percentage open arm time (%OAT) and percentage open arm entries (%OAE) were determined. Moreover, the effects of pretreatment with AM251 (2 ng/rat), L-arginine (0.01 microg/rat) and L-NAME (1 ng/rat) on the response induced by intra-CA1 administration of WIN55212-2 were also assessed. 3. The administration of either L-arginine or L-NAME into the CA1 region produced significant anxiogenic-like responses, whereas administration of AM251 induced anxiolytic effects. Intra-CA1 injection of WIN55212-2 produced a significant anxiogenic-like effect that was reversed by AM251 and was also altered by L-NAME, but not by L-arginine. 4. These data imply that cannabinoids may have anxiogenic-like effects in the CA1 region of the hippocampus in which CB1 receptors and NO may be involved.

Antidepressant-induced undesirable weight gain: Prevention with rimonabant without interference with behavioral effectiveness

Antidepressant pharmacotherapy has dramatically improved the quality of life for many patients. However, prolonged use may induce weight gain, resulting in enhanced risk for treatment noncompliance. Cannabinoid CB(1) receptor antagonists decrease food intake and body weight, but may also affect mood. We investigated in female Sabra mice first, whether acute treatment with the cannabinoid receptor antagonist rimonabant (5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide, SR141716, 5 mg/kg) interfered with the tricyclic antidepressant desipramine (15 mg/kg) or the selective serotonin reuptake inhibitor fluoxetine (20 mg/kg) in the Porsolt forced swimming test. Second, whether chronic treatment (3 months) with desipramine (5 mg/kg) enhanced weight gain and whether cotreatment with rimonabant (2 mg/kg), prevented the excessive weight gain, while retaining antidepressant effectiveness. Motor activity and anxiety-like behavior were also investigated. The acute studies indicated that rimonabant did not influence 'antidepressant' activity of desipramine or fluoxetine. In the chronic studies, desipramine enhanced weight gain, despite the observation that the injection procedure reduced weight gain. The enhanced weight gain continued at least 35 days after treatment ended. Rimonabant reduced weight gain to which no tolerance developed and which persisted at least 30 days beyond treatment. Mice cotreated with rimonabant and desipramine had body weights closer to controls or to those receiving rimonabant alone than to those treated with desipramine alone. The antidepressant effects of desipramine were maintained throughout treatment; this was not altered by the chronic rimonabant treatment at any time, although rimonabant together with desipramine transiently enhanced anxiety-like behavior. These observations suggest that combined treatment with antidepressants and cannabinoid CB(1) receptor antagonist to prevent undesirable weight gain, should be further investigated.

Cannabinoid-1 receptor: a novel target for the treatment of neuropsychiatric disorders

G-protein-coupled receptor (GPCR)-mediated signalling is the most widely used signalling mechanism in cells, and its regulation is important for various physiological functions. The cannabinoid-1 (CB(1)) receptor, a GPCR, has been shown to play a critical role in neural circuitries mediating motivation, mood and emotional behaviours. Several recent studies have indicated that impairment of CB(1) receptor-mediated signalling may play a critical role in the pathophysiology of various neuropsychiatric disorders. In this article, the authors briefly review literature relating to the role played by the endocannabinoid system in various neuropsychiatric disorders, and the CB(1) receptor as a potential therapeutic target for the treatment of alcoholism, depression, anxiety and schizophrenia.

Antiobesity effects of the novel in vivo neutral cannabinoid receptor antagonist 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-3-hexyl-1H-1,2,4-triazole – LH 21

The present study evaluates the pharmacological profile of the new neutral cannabinoid CB1 receptor antagonist 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-3-hexyl-1H-1,2,4-triazole -LH-21- on feeding behavior and alcohol self-administration in rats, two behaviors inhibited by cannabinoid CB1 receptor antagonists. Administration of LH-21 (0.03, 0.3 and 3 mg/kg) to food-deprived rats resulted in a dose-dependent inhibition of feeding. Subchronic administration of LH-21 reduced food intake and body weight gain in obese Zucker rats. Acute effects on feeding were not associated with anxiety-like behaviors, or induction of complex motor behaviors such as grooming or scratching sequences, usually observed after central administration of cannabinoid receptor blockers with inverse agonist properties. LH-21 did not markedly reduce alcohol self-administration (30% reduction observed only at a high dose of 10 mg/kg). This pharmacological pattern partially overlaps that of the reference cannabinoid CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide, SR141716A, (0.3, 1 and 3 mg/kg) that reduced feeding and alcohol self-administration with similar efficacy. In vitro analysis of blood-brain barrier permeability using a parallel artificial membrane permeation assay demonstrated that LH-21 has lower permeation through membranes than SR141716A. That was confirmed in vivo by studies showing lower potency of peripherally injected LH-21 when compared to SR141716A to antagonize motor depression induced by intracerebroventricular administration of the CB1 agonist CP55,940. The neutral antagonist profile and the lower penetration into the brain of LH-21 favour this class of antagonists with respect to reference inverse agonists for the treatment of obesity because they potentially will display reduced side effects.

Pharmacological evaluation of cannabinoid receptor ligands in a mouse model of anxiety: further evidence for an anxiolytic role for endogenous cannabinoid signaling

Extracts of Cannabis sativa have been used for their calming and sedative effects for centuries. Recent developments in drug discovery have suggested that modulation of neuronal endogenous cannabinoid signaling systems could represent a novel approach to the treatment of anxiety-related disorders while minimizing the adverse effects of direct acting cannabinoid receptor agonists. In this study, we evaluated the effects of direct cannabinoid receptor agonists and antagonists and endocannabinoid-modulating drugs on anxiety-like behavior in mice using the elevated-plus maze. We found that the direct CB1 receptor agonists (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP 55,940) (0.001-0.3 mg/kg) and 2,3-dihydro-5-methyl-3[(4-morpholinyl)methyl]pyrrolo [1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate) (WIN 55212-2) (0.3-10 mg/kg) increased time spent on the open arms (To) at low doses only. At the highest doses tested, both compounds altered overall locomotor activity. In contrast, Delta9-tetrahydrocannabinol (0.25-10 mg/kg) produced a dose-dependent reduction in To. The endocannabinoid uptake/catabolism inhibitor 4-hydroxyphenylarachidonylamide (AM404) (0.3-10 mg/kg) produced an increase in To at low doses and had no effect at the highest dose tested. The fatty acid amide hydrolase inhibitor cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB597) (0.03-0.3 mg/kg) produced a monophasic, dose-dependent increase in To. The CB1 receptor antagonists N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl (SR141716) (1-10 mg/kg) and N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) (1-10 mg/kg) produced dose-related decreases in To. These data indicate that activation of CB1 cannabinoid receptors reduces anxiety-like behaviors in mice and further support an anxiolytic role for endogenous cannabinoid signaling. These results suggest that pharmacological modulation of this system could represent a new approach to the treatment of anxiety-related psychiatric disorders.