Involvement of CB1 cannabinoid receptors in emotional behaviour

RATIONALE: Endogenous and exogenous cannabinoids acting through the CB1 cannabinoid receptors are implicated in the control of a variety of behavioural and neuroendocrine functions, including emotional responses, and learning and memory processes. Recently, knockout mice deficient in the CB1 cannabinoid receptor have been generated, and these animals result in an excellent tool to evaluate the neurophysiology of the endogenous cannabinoid system. OBJECTIVES: To establish the role of the CB1 cannabinoid receptor in several emotional-related behavioural responses, including aggressiveness, anxiety, depression and learning models, using CB1 knockout mice. METHODS: We evaluated the spontaneous responses of CB1 knockout mice and wild-type controls under different behavioural paradigms, including the light/dark box, the chronic unpredictable mild stress, the resident-intruder test and the active avoidance paradigm. RESULTS: Our findings showed that CB1 knockout mice presented an increase in the aggressive response measured in the resident-intruder test and an anxiogenic-like response in the light/dark box. Furthermore, a higher sensitivity to exhibit depressive-like responses in the chronic unpredictable mild stress procedure was observed in CB1 knockout mice, suggesting an increased susceptibility to develop an anhedonic state in these animals. Finally, CB1 knockout mice showed a significant increase in the conditioned responses produced in the active avoidance model, suggesting an improvement of learning and memory processes. CONCLUSIONS: Taken together these findings demonstrate that endogenous cannabinoids through the activation of CB1 receptors are implicated in the control of emotional behaviour and participate in the physiological processes of learning and memory.     

Involvement of CB1 cannabinoid receptors in the EDHF-dependent vasorelaxation in rabbits

1. It was recently suggested that an endogenous cannabinoid could represent an endothelium-derived hyperpolarizing factor (EDHF). The aim of the present study was to clarify whether CB1 cannabinoid receptors are involved in the nitric oxide (NO)- and prostanoid-independent vasodilation produced by acetylcholine in rabbits. 2. Pithed rabbits received indomethacin. Noradrenaline was infused to raise blood pressure, and vasodilation was elicited by bolus injections of acetylcholine. The NO-synthase inhibitor Nomega-nitro-L-arginine methylester inhibited the acetylcholine-evoked vasodilation by about 40%. The remaining vasodilation was unaffected by the CB1 cannabinoid receptor antagonist SR141716A, but was inhibited by the potassium channel blocker tetraethylammonium. In addition, the mixed CB1/CB2 cannabinoid receptor agonist WIN55212-2 did not elicit vasodilation. 3. No CB1 cannabinoid receptors were involved in the prostanoid- and NO-independent vasodilation produced by acetylcholine. An exogenous cannabinoid also did not cause vasodilation. Therefore, it is unlikely that an endogenous cannabinoid serves as an EDHF acting at smooth muscle CB1 cannabinoid receptors in the rabbit.     

Enhancement of endocannabinoid neurotransmission through CB1 cannabinoid receptors counteracts the reinforcing and psychostimulant effects of cocaine

Cannabinoids, in contrast to typical drugs of abuse, have been shown to exert complex effects on behavioural reinforcement and psychomotor function. We have shown that cannabinoid agonists lack reinforcing/rewarding properties in the intracranial self-stimulation (ICSS) paradigm and that the CB1 receptor (CB1R) agonist WIN55,212-2 attenuates the reward-facilitating actions of cocaine. We sought to determine the effects of the endocannabinoid neurotransmission enhancer AM-404 (1, 3, 10, 30 mg/kg) on the changes in ICSS threshold and locomotion elicited by cocaine and extend the study of the effects of WIN55,212-2 (0.3, 1, 3 mg/kg) on cocaine-induced hyperlocomotion. AM-404 did not exhibit reward-facilitating properties, and actually increased self-stimulation threshold at the highest dose. Cocaine significantly reduced self-stimulation threshold, without altering maximal rates of responding. AM-404 (10 mg/kg) attenuated this action of cocaine, an effect which was reversed by pretreatment with the selective CB1R antagonist SR141716A. WIN55,212-2 decreased locomotion at the two highest doses, an effect that was blocked by SR141716A; AM-404 had no effect on locomotion. Cocaine caused a significant, dose-dependent increase in locomotion, which was reduced by WIN55,212-2 and AM-404. SR141716A blocked the effects of WIN55,212-2 and AM-404 on cocaine-induced hyperlocomotion. SR141716A alone had no effect on ICSS threshold or locomotion. These results indicate that cannabinoids may interfere with brain reward systems responsible for the expression of acute reinforcing/rewarding properties of cocaine, and provide further evidence that the cannabinoid system could be explored as a potential drug discovery target for the treatment of psychostimulant addiction and pathological states associated with psychomotor overexcitability.     

Discriminative stimulus effects in rats of SR-141716 (rimonabant), a cannabinoid CB1 receptor antagonist

Objective To examine the discriminative stimulus effects of (i) the cannabinoid CB₁ receptor antagonist SR-141716 (SR, 5.6 mg/kg) and vehicle, and (ii) the cannabinoid receptor agonist ⁹-THC (THC, 1.8 mg/kg) and vehicle using a discriminated taste aversion (DTA) procedure.Methods Two groups of rats (n=6) were trained to discriminate between these drugs and vehicle in DTA (t=20 min). The 30-min drinking bout of tap water following drug (SR or THC) treatment was followed by an injection of lithium chloride (LiCl, 120 mg/kg) in the experimental animals. When offered water after vehicle pretreatment, experimental animals subsequently were given IP saline (NaCl, 10 ml/kg). Post-drinking treatment for controls (n=6) was NaCl, irrespective of the pretreatment condition (SR, THC or vehicle). Additional water was provided during the afternoon (30 min) with no other manipulations. Food was available ad lib at all times. When the discriminations were established other doses and drugs were examined (t=20 min). In testing there were no post-drinking treatments.Results The SR-related analog AM-251 (dose range: 1–5.6 mg/kg) substituted for SR, whereas other drugs such as the cannabinoid CB₂ receptor antagonist SR-144528 (3 and 10 mg/kg), THC (1–10 mg/kg), flumazenil (1–10 mg/kg), naloxone (1–10 mg/kg), morphine (10 and 18 mg/kg) and d-amphetamine (1 and 3 mg/kg) did not. There was a dose-related attenuation of SR-induced suppression of drinking when THC (1.8–10 mg/kg) was given together with SR (5.6 mg/kg). In the THC trained rats, SR (1–10 mg/kg), morphine (10 and 18 mg/kg) and d-amphetamine (1 and 3 mg/kg) did not substitute for THC. SR (1 mg/kg) attenuated the THC (1.8 mg/kg) induced suppression of drinking. Together with 3 mg/kg SR and 1.8 mg/kg THC, drinking was roughly equally suppressed in both the experimental group and the controls.Conclusion SR-141716 induces a discriminative stimulus complex in DTA that shows potential for further examination of cannabinoid receptor antagonism.     

Peripheral cannabinoid CB1 receptors inhibit evoked responses of nociceptive neurones in vivo

We investigated the effect of peripheral administration of a selective cannabinoid CB1 receptor agonist arachidonyl-2-choroethylamide (ACEA), on evoked responses of primary afferents in vivo. Extracellular recordings were made from filaments of the saphenous nerve that responded to noxious mechanical stimulation of their receptive fields and effects of ACEA (30 and 50 microg/100 microl, i.a.) were studied. ACEA significantly inhibited evoked responses, effects that were blocked by co-administration of the cannabinoid CB1 receptor antagonist AM251 (30 microg/100 microl). These results demonstrate a cannabinoid CB1 receptor-mediated inhibition of primary afferent nociceptor excitability and provide further support for a peripheral site of action of cannabinoids.     

Effect of the cannabinoid CB1 receptor antagonist rimonabant on nociceptive responses and adjuvant-induced arthritis in obese and lean rats

BACKGROUND AND PURPOSE: Obesity is a risk factor for several inflammation-based diseases including arthritis. We investigated the anti-nociceptive and anti-inflammatory effects of the cannabinoid CB1 receptor antagonist rimonabant in lean and diet-induced obese female rats with arthritis induced by complete Freund's adjuvant (CFA) injected in the right hind-paw. EXPERIMENTAL APPROACH: The effect of oral rimonabant was assessed in rat paws on thermal hyperalgesia, mechanical allodynia, oedema, global arthritis score, nitrite/nitrate levels and ankle widths. KEY RESULTS: After 7 but not after 14 days, the inflammatory response to CFA was significantly higher in obese than lean rats; however, the nociceptive response (thermal hyperalgesia and mechanical allodynia) was similar. Oral rimonabant (3 or 10 mg kg-1, once a day for 1 week from day 7 after CFA) only reduced the global arthritic score and joint width in obese rats, with no effect on the paw oedema. It also markedly reduced thermal hyperalgesia and mechanical allodynia in both lean and obese rats, with a greater effect in the latter. CONCLUSION AND IMPLICATIONS: Rimonabant appears to be a potent inhibitor of sensorial hypersensitivity associated with CFA-induced arthritis in obese rats, in which the inflammatory reaction is more severe than in lean rats. It may thus have therapeutic potential in obesity-associated inflammatory diseases, particularly in the treatment of the pain associated with arthritis.     

CB1 cannabinoid receptors mediate anxiolytic effects: convergent genetic and pharmacological evidence with CB1-specific agents

Cannabinoids are known to modulate GABAergic and glutamatergic transmission in cortical areas, the former via CB1 and the latter via a novel receptor. Pharmacological data demonstrate that several widely used cannabinoid ligands bind to both receptors, which may explain the inconsistencies in their behavioural effects. Earlier we showed that the cannabinoid antagonist SR-141716A affected behaviour in both CB1 knockout and wild-type animals, and its effect (anxiolysis) was different from that of CB1 gene disruption (anxiogenesis). In the present experiments, we studied the effects of the CB1 antagonist AM-251, and the cannabinoid agonist WIN-55,212-2 in wild-type as well as in CB1 knockout mice. CB1 knockout mice showed higher scores of anxiety-like behaviour than the wild-type animals in the elevated plus-maze. Selective blockade of CB1 receptors by AM-251 (0.3, 1 and 3 mg/kg) increased anxiety-like behaviour dose-dependently in the wild-type mice but had no effect in the knockouts. In wild types, the cannabinoid agonist WIN-55,212-2 (1 and 3 mg/kg) caused a decrease in anxiety-like behaviour, which was abolished by the CB1-selective antagonist AM-251 (3 mg/kg). The same agonist did not change plus-maze behaviour in CB1 knockout animals. These data demonstrate at the behavioural level that AM-251 and, at low concentrations, WIN-55,212-2, are selective ligands of the CB1 cannabinoid receptor in mice. Our studies on the behavioural effects of the cannabinoid antagonist SR-141716A and the CB1 antagonist AM-251 show that the CB1 and the novel cannabinoid receptor mediate anxiolytic and anxiogenic effects, respectively. This suggests that agonists of the former, or antagonists of the latter, are promising new compounds in the pharmacotherapy of anxiety.     

Additive effects of cannabinoid CB1 receptors blockade and cholecystokinin on feeding inhibition

Cannabinoid CB1 receptor and cholecystokinin-1 (CCK₁) receptors are located in peripheral nerve terminals of the gut, where they mediate satiety signals. Here we describe a detailed analysis of the interaction of both receptors in the control of feeding of food-deprived rats. Male Wistar rats were deprived for food 24 h before testing. Rats were pre-treated with SR141716A (Rimonabant) or WIN 55,212-2 before CCK-8 sulphated administration and tested for food intake 60, 120 and 240 min after last drug injection. In parallel, the effect of Lorglumide - a CCK₁ receptor antagonist - pre-treatment was evaluated on feeding behaviour after SR141716A administration. Results show that SR141716A activates c-Fos expression in brainstem areas receiving vagal inputs. Blockade of CB1 receptors with SR141716A (1 mg/kg) reduces feeding and display additive satiety induction with the CCK₁ receptor agonist CCK-8 sulphated (5, 10, 25 μg/kg). The effect of SR141716A is not blocked by Lorglumide (10 mg/kg), indicating independent sites of action. Conversely, the administration of the CB1 agonist WIN 55,212-2 (2 mg/kg) reduced satiety induced by CCK-8. In conclusion, these results report additive anorectic actions for CCK1 activation and peripheral CB1 receptor blockade providing a framework for combined therapies in the treatment of eating disorders.     

Assessment of the role of CB1 receptors in cannabinoid anticonvulsant effects.

The cannabinoid CB1 receptor has been shown to be the primary site of action for cannabinoid-induced effects on the central nervous system. Activation of this receptor has proven to dampen neurotransmission and produce an overall reduction in neuronal excitability. Cannabinoid compounds like delta9-tetrahydrocannabinol and cannabidiol have been shown to be anticonvulsant in maximal electroshock, a model of partial seizure with secondary generalization. However, until now, it was unknown if these anticonvulsant effects are mediated by the cannabinoid CB1 receptor. Likewise, (R)-(+)-[2,3-Dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN 55,212-2), a cannabimimetic compound that has been shown to decrease hyperexcitability in cell culture models via the cannabinoid CB1 receptor, has never been evaluated for anticonvulsant activity in an animal seizure model. We first show that the cannabinoid compounds delta9-tetrahydrocannabinol (ED50 = 42 mg/kg), cannabidiol (ED50 = 80 mg/kg), and WIN 55,212-2 (ED50 = 47 mg/kg) are anticonvulsant in maximal electroshock. We further establish, using the cannabinoid CB1 receptor specific antagonist N-(piperidin-1-yl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride (SR141716A) (AD50 = 2.5 mg/kg), that the anticonvulsant effects of delta9-tetrahydrocannabinol and WIN 55,212-2 are cannabinoid CB1 receptor-mediated while the anticonvulsant activity of cannabidiol is not. This study establishes a role for the cannabinoid CB1 receptor in modulating seizure activity in a whole animal model.     

Alterations in behavioral flexibility by cannabinoid CB1 receptor agonists and antagonists

Rationale Cannabinoid CB₁ receptors are expressed in the prefrontal cortex, but their role in mediating executive functions such as behavioral flexibility is unclear.Objective The present study examined the effect of pharmacological activation or blockade of the cannabinoid CB₁ receptors on behavioral flexibility using a strategy set-shifting task conducted on a cross maze.Materials and methods In experiment 1, rats initially were trained to turn left or right while ignoring the visual cue to obtain a food; on the second test day, rats had to inhibit the previously learned rule and approach the cue to obtain the food. In experiment 2, the order of discrimination training was reversed.Results Administration of the cannabinoid CB₁ receptor agonist HU-210 before the set-shift on day 2 elicited dose-dependent effects on performance. A 20-μg/kg dose of HU-210 increased perseverative errors, whereas the effects of a lower, 5-μg/kg dose caused differential effects depending on whether rats were required to shift from a response to a visual-cue discrimination strategy or vice versa. Conversely, administration of a 2-mg/kg, but not a 5-mg/kg dose of the CB₁ receptor antagonist AM251 reduced perseverative errors.Conclusions These data demonstrate a biphasic and dose-sensitive role for the cannabinoid system in behavioral flexibility, which in turn may have clinical implications for the role of the endocannabinoid system in psychiatric disorders where behavioral flexibility is compromised.     

Lack of CB1 cannabinoid receptor impairs cocaine self-administration.

Acute rewarding properties are essential for the establishment of cocaine addiction, and multiple neurochemical processes participate in this complex behavior. In the present study, we used the self-administration paradigm to evaluate the role of CB1 cannabinoid receptors in several aspects of cocaine reward, including acquisition, maintenance, and motivation to seek the drug. For this purpose, both CB1 receptor knockout mice and wild-type littermates were trained to intravenously self-administer cocaine under different schedules. Several cocaine training doses (0.32, 1, and 3.2 mg/kg/infusion) were used in the acquisition studies. Only 25% of CB1 knockout mice vs 75% of their wild-type littermates acquired a reliable operant responding to self-administer the most effective dose of cocaine (1 mg/kg/infusion), and the number of sessions required to attain this behavior was increased in knockout mice. Animals reaching the acquisition criteria were evaluated for the motivational strength of cocaine as a reinforcer under a progressive ratio schedule. The maximal effort to obtain a cocaine infusion was significantly reduced after the genetic ablation of CB1 receptors. A similar result was obtained after the pharmacological blockade of CB1 receptors with SR141716A in wild-type mice. Moreover, the cocaine dose-response curve was flattened in the knockout group, suggesting that the differences observed between genotypes were related to changes in the reinforcing efficacy of the training dose of cocaine. Self-administration for water and food was not altered in CB1 knockout mice in any of the reinforcement schedules used, which emphasizes the selective impairment of drug reinforcement in these knockout mice. Finally, cocaine effects on mesolimbic dopaminergic transmission were evaluated by in vivo microdialysis in these mice. Acute cocaine administration induced a similar enhancement in the extracellular levels of dopamine in the nucleus accumbens of both CB1 knockout and wild-type mice. This work clearly demonstrates that CB1 receptors play an important role in the consolidation of cocaine reinforcement, although are not required for its acute effects on mesolimbic dopaminergic transmission.     

CNS effects of CB2 cannabinoid receptors: beyond neuro-immuno-cannabinoid activity

There are two well characterized cannabinoid receptors (CBRs), CB1-Rs and CB2-Rs, with other candidates, such as GPR55, PPARs and vanilloid TRPV1 (VR1) receptors, which are either activated by cannabinoids and/or endocannabinoids (eCBs). The neuronal and functional expression of CB2-Rs in the brain has been much less well characterized in comparison with the expression of the ubiquitous CB1-Rs. CB2-Rs were previously thought to be predominantly expressed in immune cells in the periphery and were traditionally referred to as peripheral CB2-Rs. We and others have now demonstrated the expression of CB2-Rs in neuronal, glial and endothelial cells in the brain, and this warrants a re-evaluation of the CNS effects of CB2-Rs. In the present review we summarize our current understanding of CNR2 genomic structure, its polymorphic nature, subtype specificity, from mice to human subjects, and its variants that confer vulnerabilities to neuropsychiatric disorders beyond neuro-immuno-cannabinoid activity.     

Involvement of central cannabinoid (CB1) receptors in the establishment of place conditioning in rats

The involvement of cannabinoid processes in positive reinforcement was studied using an unbiased, one-compartment, conditioned place preference (CPP) procedure in rats. This was achieved by examining the ability of the selective antagonist of the CB₁ cannabinoid receptor subtype, SR 141716, to counteract the CPP supported by classical reinforcers. The acquisition of CPP induced by cocaine (2 mg/kg), morphine (4 mg/kg) and food (standard chow and sucrose pellets) was dose-dependently blocked by pre-pairing administration of SR 141716 (0.03–3 mg/kg). However, SR 141716 (up to 10 mg/kg) did not significantly counteract the expression of cocaine-induced CPP. On the other hand, the synthetic CB receptor agonist, WIN 55212-2 (0.3–1 mg/kg), established a robust place aversion (CPA), as already described with other agonists, and CPP was never observed, even at 100-fold lower doses. The aversive effect of WIN 55212-2 was reversed by SR 141716 (0.3–1 mg/kg), suggesting that it was accounted for by the stimulation of CB₁ receptors. These findings indicate that, on their own, CB receptor agonists are unable to generate the processes necessary to induce a pleasurable state in animals, as assessed in place conditioning procedures. Nevertheless, a cannabinoid link may be involved in the neurobiological events, allowing the perception of the rewarding value of various kinds of reinforcers. However, a permanent endogenous cannabinoid tone seems unlikely to be necessary to ensure the organism a basal hedonic level since, given alone, SR 141716 supported neither CPP nor CPA. Received: 14 March 1997 / Final version: 28 July 1997     

Anandamide induces overeating: mediation by central cannabinoid (CB1) receptors

  Rationale: Central cannabinoid systems have been implicated in appetite regulation by the respective hyperphagic actions of exogenous cannabinoids, such as Δ9-THC, and hypophagic effects of selective cannabinoid receptor antagonists. Objective: This study examined whether an endogenous cannabinoid, anandamide, could induce overeating, via a specific action at central (CB1) cannabinoid receptors. Methods: Pre-satiated male rats (n=18), received subcutaneous injections of anandamide (0.5, 1.0, 5.0, 10.0 mg/kg) before 3-h, nocturnal food intake tests. In a second series of intake tests (n=8), anandamide injection (1.0 mg/kg) was preceded by injection of the specific CB1 receptor antagonist, SR141716 (0.1, 0.5, 1.0 mg/kg SC). Results: All doses of anandamide induced significant overeating, with 1.0 mg/kg being most potent. Additionally, hyperphagia induced by 1.0 mg/kg anandamide was dose-dependently attenuated by SR141716 pretreatment. Conclusion: This first demonstration of anandamide-induced, CB1-mediated, overeating provides important evidence for the involvement of a central cannabinoid system in the normal control of eating. Received: 10 November 1998 / Final version: 13 January 1999     

2-Arachidonylglycerol acting on CB1 cannabinoid receptors mediates delayed cardioprotection induced by nitric oxide in rat isolated hearts

Endocannabinoids have been implicated in protective effects in the heart and brain, but the mechanism of possible infarct-size-reducing effects remains controversial. Using a model of delayed preconditioning (PC), rats received the nitric oxide (NO) donor nitroglycerin (0.15 mg/h/kg) for 24 hours via transdermal application. Two days later, rat isolated perfused hearts were subjected to global, no-flow ischemia (20 min), and reperfusion (120 min). Cannabinoid receptor antagonists were given before no-flow throughout the protocol. Endocannabinoids were detected by liquid chromatography and mass spectrometry. NO-induced PC reduced the left ventricular infarct size from 40.9 +/- 3.9% to 27.5 +/- 3.8% (P < 0.05). Treatment with the specific CB1 cannabinoid receptor antagonist AM-251 (0.3 microM) prevented the protective effect of PC on infarct size (40.2 +/- 4.7%, P > 0.05 vs. controls). On the contrary, the specific CB2 receptor antagonist AM-630 (0.3 microM) did not alter infarct size (31.6 +/- 6.3%, P > 0.05 vs. PC alone). Recovery of left ventricular developed pressure and coronary flow was incomplete in control and NO-pretreated hearts and not consistently altered by cannabinoid receptor antagonists. PC increased the heart tissue content of the endocannabinoid 2-arachidonylglycerol (2-AG) from 4.6 +/- 1.0 nmol/g in controls to 12.0 +/- 2.1 nmol/g (P < 0.05). Tissue levels of the endocannabinoid arachidonylethanolamide (anandamide) remained unchanged (19.8 +/- 3.9 pmol/g vs. 19.5 +/- 4.8 pmol/g). 2-AG (1 microM) or its metabolically stable derivative noladinether (0.1 microM), given 30 minutes before ischemia/reperfusion in unpreconditioned hearts, mimicked the cardioprotective effects of PC and reduced infarct size. We conclude that delayed PC through transdermal nitroglycerin application increases the production of the endocannabinoid 2-AG which elicits protective effects against myocardial infarction via CB1 cannabinoid receptors which represents one new mechanism of NO-mediated PC.     

Lack of CB1 cannabinoid receptors modifies nicotine behavioural responses,but not nicotine abstinence

Cannabis is the most widely consumed illicit drug and its consumption is currently associated with tobacco, which contains another psychoactive compound, namely nicotine. Interactions between cannabinoids and other drugs of abuse, such as opioids, have been previously reported. The aim of the present study was to evaluate the possible role of CB1 cannabinoid receptor in responses induced by acute and repeated nicotine administration by using knockout mice lacking the CB1 cannabinoid receptor and their wild-type littermates. Acute nicotine (0.5, 1, 3 and 6 mg/kg, sc) administration decreased locomotor activity and induced antinociceptive responses in the tail-immersion and the hot-plate test, in wild-type animals. The antinociceptive effects in the tail-immersion test were significantly enhanced in CB1 knockout mice. In wild-type mice nicotine (0.5 mg/kg, sc) produced a significant rewarding effect, as measured by a conditioned place preference paradigm. This response was absent in CB1 knockout mice. Finally, a model of mecamylamine-induced abstinence in chronic nicotine-treated mice (10 mg/kg/day, sc) was developed. Mecamylamine (1 and 2 mg/kg, sc) precipitated several somatic signs of nicotine withdrawal in wild-type dependent mice. However, no difference in the severity of nicotine withdrawal was observed in CB1 knockout mice. These results demonstrate that some acute effects and motivational responses elicited by nicotine can be modulated by the endogenous cannabinoid system and support the existence of a physiological interaction between these two systems.     

Acute administration of the cannabinoid CB1 antagonist rimonabant impairs positive affective memory in healthy volunteers

Background  Emotional processing measures are sensitive to acute administration of clinically useful antidepressant drugs. We wished to test the hypothesis that these models would also be able to detect agents likely to cause depression as an adverse effect. The anti-obesity drug and cannabinoid type 1 receptor antagonist, rimonabant, is associated with significant rates of depression and anxiety in clinical use. Materials and methods  Thirty healthy adult volunteers were randomly assigned to receive a single dose of rimonabant (20 mg) or lactose placebo in a double-blind, between-groups design. Three hours after medication administration, subjects undertook an emotional processing test battery including facial emotion recognition, emotional word attentional dot probe, self-relevant word classification, emotional and declarative memory and the emotion-potentiated acoustic startle response. Subjective state was assessed via self-report measures. Results  A single dose of rimonabant did not alter subjective mood. However, rimonabant selectively reduced incidental recall of positive self-relevant adjectives, an effect contrary to that seen following the administration of antidepressants. There were no effects of rimonabant on the other measures of emotional processing. Conclusions  These results suggest that a single dose of rimonabant decreases positive emotional memory in the absence of changes in subjective state. Further studies are required to examine whether rimonabant might produce a wider range of negative emotional biases with repeated treatment.     

Involvement of sigma receptors in the behavioral effects of cocaine: evidence from novel ligands and antisense oligodeoxynucleotides

Pharmacological and molecular biological tools were used to validate the involvement of σ receptors in the actions of cocaine. Radioligand binding studies demonstrated significant levels of σ receptors in the brain and heart, where cocaine interacts preferentially with the σ₁ subtype. In behavioral pharmacological studies using mice, nine novel σ receptor antagonists significantly attenuated cocaine-induced convulsions, while structural analogs with weak interactions with σ receptors were ineffective. In contrast to the protection provided by the antagonists, a classical σ receptor agonist exacerbated the convulsive effects of cocaine. The antagonists also attenuated cocaine-induced lethality, with the best compound protecting against death even when administered as a post-treatment. At doses where the antagonists had no effect on baseline locomotor activity, they significantly attenuated the locomotor stimulatory effects of cocaine, suggesting their ability to block the psychomotor as well as the toxic effects of cocaine. To further validate that the anti-cocaine effects were achieved by interfering with cocaine’s access to σ receptors, antisense oligodeoxynucleotides against σ₁ receptors were shown to attenuate the convulsive and locomotor stimulatory effects of cocaine. Together, the studies support the involvement of σ receptors, particularly the σ₁ subtype, in the behavioral effects of cocaine.     

Evaluation of the role of striatal cannabinoid CB1 receptors on movement activity of parkinsonian rats induced by reserpine

It has been observed cannabinoid CB₁ receptor signalling and the levels of endocannabinoid ligands significantly increased in the basal ganglia and cerebrospinal fluids of Parkinson’s disease (PD) patients. These evidences suggest that the blocking of cannabinoid CB₁ receptors might be beneficial to improve movement disorders as a sign of PD. In this study, a dose–response study of the effects of intrastriatal injection of a cannabinoid CB₁ receptor antagonist, AM251 and agonist, ACPA, on movement activity was performed by measuring the catalepsy of reserpinized and non-PD (normal) rats with bar test. Also the effect of co-administration the most effective dose of AM251 and several doses of ACPA were assessed. AM251 decreases the reserpine induced catalepsy in dose dependent manner and ACPA causes catalepsy in normal rats in dose dependant manner as well. AM251 significantly reverse the cataleptic effect in all three groups (1, 10, 100 ng/rat) that received ACPA. These results support this theory that cannabinoid CB₁ receptor antagonists might be useful to alleviate movement disorder in PD. Also continuance of ACPA induced catalepsy in rats after AM251 injection can indicate that other neurotransmitters or receptors interfere in ACPA induced catalepsy. Based on the present finding there is an incomplete overlapping between cannabinoid CB₁ receptor agonist and antagonist effects.     

The cannabinoid CB1 receptor antagonists rimonabant (SR141716) and AM251 directly potentiate GABA(A) receptors

BACKGROUND AND PURPOSE

Rimonabant (SR141716) and the structurally related AM251 are widely used in pharmacological experiments as selective cannabinoid receptor CB₁ antagonists / inverse agonists. Concentrations of 0.5–10 µM are usually applied in in vitro experiments. We intended to show that these drugs did not act at GABA_A receptors but found a significant positive allosteric modulation instead.

EXPERIMENTAL APPROACH

Recombinant GABA_A receptors were expressed in Xenopus oocytes. Receptors were exposed to AM251 or rimonabant in the absence and presence of GABA. Standard electrophysiological techniques were used to monitor the elicited ionic currents.

KEY RESULTS

AM251 dose-dependently potentiated responses to 0.5 µM GABA at the recombinant α₁β₂γ₂ GABA_A receptor with an EC₅₀ below 1 µM and a maximal potentiation of about eightfold. The Hill coefficient indicated that more than one binding site for AM251 was located in this receptor. Rimonabant had a lower affinity, but a fourfold higher efficacy. AM251 potentiated also currents mediated by α₁β₂, α_xβ₂γ₂ (x = 2,3,5,6), α₁β₃γ₂ and α₄β₂δ GABA_A receptors, but not those mediated by α₁β₁γ₂. Interestingly, the CB₁ receptor antagonists {"type":"entrez-nucleotide","attrs":{"text":"LY320135","term_id":"1257555575","term_text":"LY320135"}}LY320135 and O-2050 did not significantly affect α₁β₂γ₂ GABA_A receptor-mediated currents at concentrations of 1 µM.

CONCLUSIONS AND IMPLICATIONS

This study identified rimonabant and AM251 as positive allosteric modulators of GABA_A receptors. Thus, potential GABAergic effects of commonly used concentrations of these compounds should be considered in in vitro experiments, especially at extrasynaptic sites where GABA concentrations are low.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7