Cannabinoid CB1-mediated inhibition of stress-induced gastric ulcers in rats

The effect of cannabinoid drugs (i.p.) on cold/restraint stress-induced gastric ulcers was studied in rats. The cannabinoid receptor agonist (WIN 55,212-2, 0.1-1 mg/kg), but not the less active isomer WIN 55,212-3 (1 mg/kg), reduced gastric ulceration. The protective effect of WIN 55,212-2 (1 mg/kg) was counteracted by the cannabinoid CB1 receptor antagonist SR141716A, but not by the cannabinoid CB2 receptor antagonist SR144528. These results indicate that the antiulcer effect of the cannabinoid receptor agonist WIN 55,212-2 is mediated by cannabinoid CB1 receptors.     

Cannabinoid CB(1) antagonist SR 141716A attenuates reinstatement of heroin self-administration in heroin-abstinent rats

Rats with a previous history of heroin self-administration were studied to assess interactions occurring between cannabinoids and opioids in an animal model of reinstatement of heroin-seeking behaviour. Rats were trained to self-administer heroin and after a long-term extinction were primed with one of the following non-contingent non-reinforced drug administrations: saline (or vehicle), heroin, synthetic cannabinoid CB₁ receptor agonists (WIN 55,212-2 or CP 55,940), opioid antagonist (naloxone) or CB₁ antagonist (SR 141716A), alone or in combination. After primings, lever-pressing activity was recorded and compared to those observed during previous phases of training and extinction. Results of this study showed that (i) priming injections of heroin (0.1 mg/kg) as well as CB₁ agonists WIN 55,212-2 (0.15 or 0.30 mg/kg) and CP 55,940 (0.05 or 0.1 mg/kg) completely restore heroin-seeking behaviour; (ii) primings of naloxone (1 mg/kg) and SR 141716A (0.3 mg/kg) had no effect when administered alone; (iii) heroin-induced reinstatement was fully prevented by pre-treatment with either naloxone or SR 141716A; (iv) pre-treatment with SR 141716A significantly reduced WIN 55,212-2 and CP 55,940 priming effects. These results suggest that cannabinoid CB₁ receptors play an important role in the mechanisms underlying relapse to heroin-seeking and depict CB₁ antagonists as possible therapeutic agents for use in the prevention of relapse to heroin abuse.     

Cannabinoid CB(1) receptor antagonist rimonabant attenuates reinstatement of ketamine conditioned place preference in rats

Recent evidence suggests that cannabinoid CB(1) receptors may represent effective targets for therapeutic agents used to treat cocaine and heroin relapse. However, the role of cannabinoid CB(1) receptors in the potential treatment for other drugs of abuse is still largely unknown. The present study was conducted to determine whether cannabinoid CB(1) receptors play a similar role in relapse to ketamine abuse. To establish a ketamine reinstatement model in the conditioned place preference paradigm, rats were trained to develop place preference conditioned by ketamine, which was subsequently extinguished through daily exposure to the test chambers in the absence of ketamine. On the day following the last extinction session, four groups of rats were injected with ketamine (1, 5, 10 and 15 mg/kg, i.p.) to reinstate previously extinguished conditioned place preference. To investigate the effects of rimonabant, a cannabinoid CB(1) receptor antagonist, on reinstatement of ketamine-induced place preference, different doses of rimonabant (0.1, 0.5 and 3 mg/kg, i.p) were injected 30 min prior to the ketamine (5 and 15 mg/kg, i.p.) priming injection in a separate group of rats. To determine whether rimonabant itself produces conditioned place preference or conditioned place aversion, rats were trained for conditioned place preference or place aversion with rimonabant (0, 0.1, 0.5, 3.0 mg/kg, i.p.). While ketamine priming injections reinstated extinguished place preference, rimonabant administration significantly attenuated the reinstatement of ketamine-induced place preference in a dose-dependent manner. Importantly, rimonabant itself did not produce conditioned place preference or place aversion. Since the reinstatement effects of ketamine administration were inhibited by rimonabant, these findings suggest that a cannabinoid CB(1) receptor antagonist may be useful in preventing relapse to ketamine abuse.     

CB1 receptor agonist and heroin, but not cocaine, reinstate cannabinoid-seeking behaviour in the rat

We recently provided evidence for a functional link between cannabinoid and opioid endogenous systems in relapse to heroin-seeking behaviour in rats. In the present study, we aimed at investigating whether the previously observed cross-talk between cannabinoids and opioids could be extended to mechanisms underlying relapse to cannabinoid-seeking behaviour after a prolonged period of abstinence. In rats previously trained to intravenously self-administer the synthetic cannabinoid receptor (CB1) agonist WIN 55,212-2 (12.5 microg kg(-1) inf(-1)) under a fixed ratio (FR1) schedule of reinforcement, noncontingent nonreinforced intraperitoneal (i.p.) priming injections of the previously self-administered CB1 agonist (0.25 and 0.5 mg kg(-1)) as well as heroin (0.5 mg kg(-1)), but not cocaine (10 mg kg(-1)), effectively reinstate cannabinoid-seeking behaviour following 3 weeks of extinction. The selective CB1 receptor antagonist SR 141716A (0.3 mg kg(-1) i.p.) does not reinstate responding when given alone, but completely prevents the cannabinoid-seeking behaviour triggered by WIN 55,212-2 or heroin primings. The nonselective opioid antagonist naloxone (1 mg kg(-1) i.p.) has no effect on operant behaviour per se, but significantly blocks cannabinoid- and heroin-induced reinstatement of cannabinoid-seeking behaviour. These results provide the first evidence of drug-induced reinstatement of cannabinoid-seeking behaviour, and further strengthen previous findings on a cross-talk between the endogenous cannabinoid and opioid systems in relapse mechanisms to drug-seeking.     

Inhibitory effect of the cannabinoid receptor agonist WIN 55,212-2 on pentagastrin-induced gastric acid secretion in the anaesthetized rat

The effect of the cannabinoid (CB) receptor agonist WIN 55,212-2 on gastric acid secretion was studied in the anaesthetized rat after stimulation with pentagastrin. WIN 55,212-2 (0.5-2 mg/kg, i.v.) was inactive on basal secretion but caused a marked inhibition (80%) of the acid secretion stimulated by pentagastrin (10 microg/kg, i.v.). The enantiomer WIN 55,212-3 (1-3 mg/kg, i.v.) did not significantly modify basal or pentagastrin-induced acid secretion. The inhibitory effect of WIN 55,212-2 against pentagastrin was prevented by the administration of the selective cannabinoid CB1 receptor antagonists SR141716A (1 mg/kg, i.v.) and LY320135 (1 mg/kg, i.v.); by contrast, the CB2 receptor antagonist SR144528 (0.3-1 mg/kg, i.v.) was without effect. The selective CB2 receptor agonist JWH-015 (0.1-10 mg/kg, i.v.) was inactive on the increase of acid output stimulated by pentagastrin. These results suggest that the inhibitory effect of WIN 55,212-2 on pentagastrin-stimulated acid secretion in the anaesthetized rat is mediated by specific cannabinoid receptors. Moreover, the antagonism of WIN 55,212-2-induced effects by the selective CB1 receptor antagonists SR141716A and LY320135 together with the ineffectiveness of both the CB2 receptor agonist JWH-015 and the CB2 receptor antagonist SR144528 indicate that CB1 receptor subtypes are predominantly involved in the antisecretory effect of WIN 55,212-2.     

The role of cannabinoid receptors in intestinal motility, defaecation and diarrhoea in rats

We have studied the effects of the cannabinoid receptor agonists (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, 0. 3-5 mg/kg, i.p.) and (-)-cis-3-[2-hydroxy-4-(1, 1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol) (CP 55,940, 0.03-1 mg/kg, i.p.), the cannabinoid CB(1) receptor antagonist (N-piperidin-1-yl)-5-(4-chlorophenyl)-1-2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A, 0. 3-5 mg/kg, i.p.) and the cannabinoid CB(2) receptor antagonist N-[-(1S)-endo-1,3,3-trimethyl bicyclo [2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazo le- 3-carboxamide (SR144528, 1 mg/kg, i.p.) on intestinal motility, defaecation and castor-oil (1 ml/100 g rat, orally)-induced diarrhoea in the rat. SR141716A, but not SR144528, increased defaecation and upper gastrointestinal transit, while WIN 55,212-2 and CP 55,940 decreased upper gastrointestinal transit but not defaecation. WIN 55,212-3 (5 mg/kg), the less active enantiomer of WIN 55,212-2, was without effect. A per se non-effective dose of SR141716A (0.3 mg/kg), but not of SR144528 (1 mg/kg) or the opioid receptor antagonist, naloxone (2 mg/kg i.p.), counteracted the inhibitory effect of both WIN 55,212-2 (1 mg/kg) and CP 55,940 (0.1 mg/kg) on gastrointestinal motility. WIN 55,212-2 did not modify castor-oil-induced diarrhoea, while CP 55,940 produced a transient delay in castor-oil-induced diarrhoea at the highest dose tested (1 mg/kg), an effect counteracted by SR141715A (5 mg/kg). These results suggest that (i) intestinal motility and defaecation could be tonically inhibited by the endogenous cannabinoid system, (ii) exogenous activation of cannabinoid CB(1) receptors produces a reduction in intestinal motility in the upper gastrointestinal tract but not in defaecation, (iii) endogenous or exogenous activation of cannabinoid CB(2) receptors does not affect defaecation or intestinal motility and (iv) the cannabinoid receptor agonist, CP 55, 940, possesses a weak and transient antidiarrhoeal effect while the cannabinoid receptor agonist, WIN 55,212-2, does not possess antidiarrhoeal activity.     

Calcium-dependent mechanisms of the reinstatement of nicotine-conditioned place preference by drug priming in rats

Reinstatement of drug-seeking behaviour in animals is relevant to relapse to drug taking in humans. We used the conditioned place preference version of the reinstatement model to investigate the establishment, extinction, reinstatement and cross-reinstatement of nicotine-induced place conditioning in rats. Nicotine produced a place preference to the compartment paired with its injections during conditioning (0.5 mg/kg, i.p., three drug sessions). Once established, nicotine place preference was extinguished by repeated training. Following this extinction phase, nicotine-experienced rats were challenged with nicotine (0.5 mg/kg, i.p.), a cannabinoid receptor agonist WIN55,212-2 (0.5 mg/kg, i.p.), ethanol (0.5 g/kg, i.p.) or d-amphetamine (2 mg/kg, i.p.). The priming injections of nicotine, WIN55,212-2 and ethanol, but not of d-amphetamine renewed a preference for the compartment previously paired with nicotine. Finally, we examined the influence of the calcium channel antagonists, nimodipine (5 and 10 mg/kg, i.p.) and flunarizine (5 and 10 mg/kg, i.p.), on the reinstatement of nicotine place conditioning induced by WIN55,212-2 and ethanol. It was shown that the calcium channel blockers attenuated the reinstatement of nicotine-conditioned response induced by both drugs. As reinstatement of drug-seeking is a factor for the development of dependence, the L-type calcium channel antagonists may be useful in the relapse-prevention phase of addiction treatment, including cannabinoid, ethanol, and/or nicotine dependence.     

Inverse relationship of cannabimimetic (R+)WIN 55, 212 on behavior and seizure threshold during the juvenile period

Cannabinoids have anti-convulsant effects in both in vivo and in vitro models of status epilepticus. Since the development of spontaneous seizures and neuronal vulnerability are age-dependent, we hypothesized that the anti-convulsant effects of cannabimimetics are also age-dependent. We administered a single injection of varied doses of (R+)WIN 55,212 (0.5, 1, 5 mg/kg) to postnatal (P) day 20 rats 90 min prior to induction of kainate (KA)-induced status epilepticus. The highest dose of (R+)WIN 55,212 (5 mg/kg) resulted in rapid onset of behavioral stupor, loss of balance, stiffening and immobility while standing on hind legs or laying flat in prone position; lower doses had minimal or no behavioral effect. After KA administration, seizure scores and electroencephalography (EEG) recordings were inversely related to (R+)WIN 55,212 dosage whereby higher doses were associated with high seizures scores and synchronous epileptiform activity and low doses with low seizure scores and diminished spiking in the EEG. Immunohistochemistry revealed a dose-dependent reduction in CB1 receptor expression with increasing concentrations of (R+)WIN 55,212 in presence or absence of KA seizures. Nissl and NeuN staining showed hippocampal injury was attenuated only when seizures were mild following low doses of WIN 55,212 (0.5, 1 mg/kg), consistent with the level of CB1 expression. Since low doses abolished seizures without psychotropic side-effects further study may facilitate a groundbreaking cannabamimetic therapeutic strategy to treat early-life seizures. Higher doses had adverse effects on behavior and failed to prevent seizures and protect CA1 neurons possibly due to inactivation or loss of CB1 receptors.     

Central mediation of the cannabinoid cue: activity of a selective CB1 antagonist, SR 141716A

Active cannabimimetic drugs are known to bind to two receptor subtypes: one, called CB1, is mainly localised in the central nervous system while the other (CB2) is expressed preferentially in the immune system. SR 141716A has been demonstrated to have a nanomolar affinity for CB1 receptor subtypes and a micromolar affinity for CB2 receptors. Moreover, it is an effective antagonist at these receptors both in vitro (antagonism of cannabinoid activity in vas deferens) and in vivo (suppression of the hypothermia elicited by WIN 55,212-2). The present experiments were thus undertaken to investigate the role of CB1 receptors in cannabinoid discrimination. Rats were trained to discriminate WIN 55,212-2 (0.3mg/kg s.c.) from saline in a standard operant (FR10) food rewarded discrimination procedure. Acquisition of the discrimination required 16 days on average and the ED(50) of WIN 55,212-2 was 0.032mg/kg s.c. CP55,940 and delta-9-tetrahydrocannabinol (Delta(9)-THC) generalised to the WIN 55,212-2 stimulus with the respective ED(50)s of 0.007mg/kg (s.c.) and 0.64mg/kg (p.o.). Pretreatment with SR 141716A antagonised the cue elicited by WIN 55,212-2 (ED(50) = 1.6mg/kg) as well as the generalisation to CP 55,940 (ED(50) = 0.08mg/kg) and to Delta(9)-THC (ED(50) = 0.15mg/kg). SR 140098 is a CB1 antagonist as potent as SR 141716A in vitro. This compound is unlikely to pass into the brain since it failed to displace [(3)H]-CP55, 940 from rat brain membranes ex vivo, and to reverse WIN 55,212-2-induced hypothermia. SR 140098, in contrast to SR 141716A, did not antagonise the WIN 55,212-2 stimulus. Taken together, the present results demonstrate that the brain CB1 receptor subtype mediates the cannabinoid cue.     

Effects of pharmacological manipulations of cannabinoid receptors on severity of dystonia in a genetic model of paroxysmal dyskinesia

Previous studies have shown beneficial effects of the cannabinoid CB(1)/CB(2) receptor agonist (R)-4,5-dihydro-2-methyl-4-(4-morpholinylmethyl)-1-(1-naphthalenylcarbonyl)-6H-pyrrolo [3,2,1-ij]quinolin-6-one mesylate (WIN 55,212-2) in dt(sz) mutant hamsters, a model of idiopathic paroxysmal dystonia (dyskinesia). To examine the pathophysiological significance of the cannabinergic system in the dystonic syndrome, the effect of the cannabinoid CB(1) receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide (SR 141716A) on severity of dystonia was investigated in dt(sz) mutants which exhibit episodes of dystonic and choreoathetotic disturbances in response to mild stress. SR 141716A (5 and 10 mg/kg i.p.) failed to exert any effects on the severity of dystonia. While the antidystonic efficacy of WIN 55,212-2 (5 mg/kg i.p.) was confirmed, cannabidiol (which has low affinity to cannabinoid receptors) tended to delay the progression of dystonia only at a high dose (150 mg/kg i.p.). The antidystonic and cataleptic effects of WIN 55,212-2 (5 mg/kg i.p.) were completely antagonized by pretreatment with SR 141716A at doses of 2.5 mg/kg (catalepsy) and 10 mg/kg (antidystonic efficacy). These data indicate that the antidystonic efficacy of WIN 55,212-2 is selectively mediated via CB(1) receptors. The lack of prodystonic effects of SR 141716A together with only moderate antidystonic effects of WIN 55,212-2 suggests that reduced activation of cannabinoid CB(1) receptors by endocannabinoids is not critically involved in the dystonic syndrome. In view of previous pathophysiological findings in mutant hamsters, the antidystonic efficacy of WIN 55,212-2 can be explained by modulation of different neurotransmitter systems within the basal ganglia.     

The synthetic cannabinoid WIN55,212-2 attenuates hyperalgesia and allodynia in a rat model of neuropathic pain

The analgesic properties of the synthetic cannabinoid WIN55,212-2 were investigated in a model of neuropathic pain. In male Wistar rats, bilateral hind limb withdrawal thresholds to cold, mechanical and noxious thermal stimuli were measured. Following this, unilateral L5 spinal nerve ligation was performed. Seven days later, sensory thresholds were reassessed and the development of allodynia to cold and mechanical stimuli and hyperalgesia to a noxious thermal stimulus confirmed. The effect of WIN55,212-2 (0.1 - 5.0 mg kg(-1), i.p.) on the signs of neuropathy was then determined; there was a dose related reversal of all three signs of painful neuropathy at doses which did not generally alter sensory thresholds in the contralateral unligated limb. This effect was prevented by co-administration of the CB(1) receptor antagonist SR141716a, but not by co-administration of the CB(2) receptor antagonist SR144528, suggesting this action of WIN55,212-2 is mediated via the CB(1) receptor. Administration of SR141716a alone had no affect on the observed allodynia and hyperalgesia, which does not support the concept of an endogenous analgesic tone. These data indicate that cannabinoids may have therapeutic potential in neuropathic pain, and that this effect is mediated through the CB(1) receptor.     

Stimulation of voluntary ethanol intake by cannabinoid receptor agonists in ethanol-preferring sP rats

RATIONALE: Recent studies have shown that the cannabinoid CB1 receptor antagonist, SR 141716, is capable of reducing voluntary ethanol intake in rodents, suggesting the involvement of the CB1 receptor in the neural circuitry mediating the positive reinforcing properties of ethanol. OBJECTIVES: The present study extended to the agonists the investigation on the pharmacological manipulation of ethanol intake by cannabinoid agents. METHODS: Selectively bred, Sardinian alcohol-preferring (sP) rats were offered ethanol and water under the two-bottle free choice procedure with unlimited access for 24 h/day. RESULTS: The acute administration of WIN 55,212-2 (0.5-2 mg/kg; IP) and CP 55,940 (3-30 microg/kg; IP) induced a significant, dose-dependent increase in ethanol intake. Conversely, water consumption and intake of regular food and a highly palatable sucrose solution were not affected by treatment with WIN 55,212-2 and CP 55,940. The stimulatory effect of WIN 55,212-2 and CP 55,940 on ethanol intake was completely prevented by administration of SR 141716 (0.3 mg/kg; IP) and the opioid receptor antagonist, naloxone (0.1 mg/kg; IP). CONCLUSIONS: Administration of WIN 55,212-2 and CP 55,940 promoted voluntary ethanol intake in sP rats. This effect was mediated by stimulation of the cannabinoid CB1 receptor and required the activation of the endogenous opioid system. The results of the present study add further support to the hypothesis that the cannabinoid CB1 receptor is part of the neural substrate regulating ethanol intake. These results are also discussed in terms of WIN 55,212-2 and CP 55,940 administration possibly fixing to a higher level the hedonic set-point mechanism regulating ethanol drinking behavior in sP rats.     

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     

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.     

Effects of the cannabinoid CB1 receptor antagonist AM 251 on the reinstatement of nicotine-conditioned place preference by drug priming in rats

Tobacco and cannabis are among the most widely abused drugs in humans, and recently, the functional interaction between nicotine and cannabinoids has been reported. The aim of the present studies is to evaluate the role of CB1 cannabinoid receptors in the reinstatement of nicotine-induced conditioned place preference. Nicotine-induced conditioned place preference was established (threeday nicotine sessions, 0.5 mg/kg), extinguished and reinstated by a priming dose of nicotine. It was shown that the CB1 receptor antagonist AM 251 (0.25 and 0.5 mg/kg) in a dose-dependent manner attenuates the reinstatement of nicotine place conditioning. These studies suggest a role for CB1 cannabinoids receptors in preventing the reinstatement of nicotine addiction.     

Rewarding effects and reinstatement of MDMA-induced CPP in adolescent mice.

Although the rewarding effects of 3,4-methylenedioxy-metamphetamine (MDMA) have been demonstrated in self-administration and conditioned place preference (CPP) procedures, its addictive potential (ie, the vulnerability to relapse, measured by its ability to induce reinstatement of an extinguished response), remains poorly understood. In this study, the effects of MDMA (5, 10, and 20 mg/kg) on the acquisition, extinction and reinstatement of CPP were evaluated in mice, using two different protocols during acquisition of CPP. In the first experiment, animals were trained using a two-session/day schedule (MDMA and saline for 4 consecutive days), whereas in the second experiment, they were trained using an alternating day schedule (MDMA and saline each 48 h). After extinction, the ability of drug priming to reinstate CPP was evaluated. In Experiment 1, MDMA did not significantly increase the time spent in the drug-paired compartment during the post-conditioning (Post-C) test, although the preference was evident a week afterwards, lasting between 2 and 21 weeks. No reinstatement was observed after MDMA priming. In Experiment 2, all doses produced CPP in Post-C, which lasted between 1 and 4 weeks. MDMA induces reinstatement at doses up to 4 times lower than those used in conditioning. The analyses of brain monoamines revealed that the daily schedule of treatment induces a non-dose-dependent decrease in dopamine and serotonin (5-HT) in the striatum, whereas the alternating schedule produces a dose-dependent decrease of 5-HT in the cortex. These results demonstrate that MDMA produces long-lasting rewarding effects and reinstatement after extinction, suggesting the susceptibility of this drug to induce addiction.     

Role of different brain structures in the behavioural expression of WIN 55,212-2 withdrawal in mice

We have evaluated several responses induced by the cannabinoid agonist WIN 55,212-2 related to its addictive properties, including rewarding effects and the development of physical dependence in mice. Moreover, we have studied the specific involvement of several brain regions with high density of CB1 cannabinoid receptors, such as striatum, hippocampus, amygdala and cerebellum, in the behavioural expression of SR 141716A-precipitated WIN 55,212-2 withdrawal. The systemic administration of the CB1 receptor antagonist SR 141716A (10 mg kg(-1), s.c.) precipitated behavioural signs of withdrawal in mice chronically treated with WIN 55,212-2 (1 and 2 mg kg(-1), intraperitoneal (i.p.)), revealing the development of physical dependence. The microinjection of SR 141716A (1.5 and 3 micrograms) into the cerebellum induced severe manifestations of abstinence in mice dependent on WIN 55,212-2 (1 mg kg(-1), i.p.). Out of 10 signs evaluated, seven were statistically significant: wet dog shakes, body tremor, paw tremor, piloerection, mastication, genital licks and sniffing. When the cannabinoid antagonist was administered into the hippocampus and the amygdala, a moderate but significant withdrawal syndrome was also observed. However, no signs of abstinence were induced when SR 141716A was microinjected into the striatum. WIN 55,212-2 produced rewarding effects in the place-conditioning paradigm in mice pre-exposed to a priming injection of the drug. These results show a reliable behavioural model to reveal rewarding effects and physical dependence induced by the repeated administration of WIN 55,212-2 in mice. The cerebellum and to a lesser extent the hippocampus and the amygdala participate in the behavioural expression of cannabinoid withdrawal.     

Inhibitory effect of cannabinoid agonists on gastric emptying in the rat

We have studied the effect of WIN 55,212-2 (a psychoactive cannabinoid agonist), cannabinol (a nonpsychoactive cannabinoid agonist), SR141716A, a cannabinoid CB1 antagonist, and SR144528, a cannabinoid CB2 antagonist, on gastric emptying in the rat. WIN 55,212-2 (0.1-5 mg/kg, i.p.) and cannabinol (0.1-25 mg/kg, i.p.) dose-dependently delayed gastric emptying while SR141716A (1 mg/kg and 5 mg/kg) and SR144528 (1 mg/kg) were without effect. SR141716A (1 mg/kg), but not SR144528 (1 mg/kg), counteracted the inhibitory effect of the two cannabinoid agonists. These results suggest that cannabinoid agonists delay gastric emptying through activation of cannabinoid CB1 receptors, while the endogenous cannabinoid system does not seem to modulate gastric motility.     

Intravenous self-administration of the cannabinoid CB1 receptor agonist WIN 55,212-2 in rats

RATIONALE: Delta9-tetrahydrocannabinol (Delta9-THC), the main psychoactive ingredient of marijuana, as well as synthetic cannabinoid (CB1) receptor agonists, has led to negative or equivocal results when tested with the intravenous self-administration procedure, the best validated behavioural model for evaluating abuse liability of drugs in experimental animals. We recently reported, however, that the synthetic CB1 receptor agonist WIN 55,212-2 is intravenously self-administered by drug-naive mice and that its self-administration is blocked by the cannabinoid CB1 receptor antagonist SR 141716A. OBJECTIVE: To assess a reliable model of cannabinoid intravenous self-administration in rats. Long Evans male rats were allowed the opportunity to self-administer WIN 55,212-2 at doses ranging from 6.25 to 50 microg/kg per injection, under a fixed-ratio 1 (FR1) schedule of reinforcement and nose-pokes as the operant responses. The effect of either a change in the unit drug dose available or a pretreatment with the specific CB1 receptor antagonist SR 141716A were then investigated (maintenance phase). Finally, the extinction of the self-administration behaviour was evaluated. RESULTS: Response rate depended on the drug dose available, with maximum rates occurring at 12.5 microg/kg per injection. Response rate increased following pretreatment with the specific CB1 receptor antagonist, SR 141716A. Moreover, operant behaviour rapidly extinguished following both the substitution of saline or vehicle for cannabinoid and the disconnection of the drug delivery pumps. CONCLUSION: Rats will intravenously self-administer the synthetic CB1 receptor agonist WIN 55,212-2 under specific experimental conditions, thus allowing further investigation of the neurobiological mechanisms underlying cannabinoid-taking behaviour.     

Cannabidiol inhibits the hyperphagia induced by cannabinoid-1 or serotonin-1A receptor agonists

Δ9-THC is a component of Cannabis sativa that increases food intake in animals and humans, an effect prevented by selective CB1 receptor antagonists. Cannabidiol (CBD) is another constituent of this plant that promotes several opposite neuropharmacological effects compared to Δ9-THC. CBD mechanisms of action are still not clear, but under specific experimental conditions it can antagonize the effects of cannabinoid agonists, block the reuptake of anandamide and act as an agonist of 5-HT1A receptors. Since both the cannabinoid and serotoninergic systems have been implicated in food intake control, the aim of the present work was to investigate the effects caused by CBD on hyperphagia induced by agonists of CB1 or 5-HT1A receptors. Fed or fasted Wistar rats received intraperitoneal (i.p.) injections of CBD (1, 10 and 20 mg/kg) and food intake was measured 30 min later for 1 h. Moreover, additional fed or fasted groups received, after pretreatment with CBD (20 mg/kg) or vehicle, i.p. administration of vehicle, a CB1 receptor agonist WIN55,212-2 (2 mg/kg) or a 5-HT1A receptor agonist 8-OH-DPAT (1 mg/kg) and were submitted to the food intake test for 1 h. CBD by itself did not change food intake in fed or fasted rats. However, it prevented the hyperphagic effects induced by WIN55,212-2 or 8-OH-DPAT. These results show that CBD can interfere with food intake changes induced by a CB1 or 5-HT1A receptor agonist, suggesting that its role as a possible food intake regulator should be further investigate.