SR141716, a central cannabinoid (CB(1)) receptor antagonist, blocks the motivational and dopamine-releasing effects of nicotine in rats

The mesolimbic dopamine system: the final common pathway for the reinforcing effect of drugs of abuse?

In this review we will critically assess the hypothesis that the reinforcing effect of virtually all drugs of abuse is primarily dependent on activation of the mesolimbic dopamine system. The focus is on five classes of abused drugs: psychostimulants, opiates, ethanol, cannabinoids and nicotine. For each of these drug classes, the pharmacological and physiological mechanisms underlying the direct or indirect influence on mesolimbic dopamine transmission will be reviewed. Next, we evaluate behavioral pharmacological experiments that specifically assess the influence of activation of the mesolimbic dopamine system on drug reinforcement, with particular emphasis on animal experiments using drug self-administration paradigms. There is overwhelming evidence that all five classes of abused drugs increase dopamine transmission in limbic regions of the brain through interactions with a variety of transporters, ionotropic receptors and metabotropic receptors. Behavioral pharmacological experiments indicate that increased dopamine transmission is clearly both necessary and sufficient to promote psychostimulant reinforcement. For the other four classes of abused substances, self-administration experiments suggest that although increasing mesolimbic dopamine transmission plays an important role in the reinforcing effects of opiates, ethanol, cannabinoids and nicotine, there are also dopamine-independent processes that contribute significantly to the reinforcing effects of these compounds.

Cannabinoid CB1 receptors control conditioned drug seeking

Recent developments have implicated cannabinoid CB1 receptors as a novel target for a new class of therapeutic agents used to treat drug addiction. CB1 receptors are expressed in the motivational circuitry of the brain and modulate drug seeking. Blockade of the CB1 receptor is particularly effective in reducing cue-induced reinstatement of drug seeking, an animal analogue of cue-induced relapse in human addicts. These relapse-preventing properties are observed with different classes of abused drug (i.e. psychostimulants, opiates, nicotine and alcohol). In addition, recent evidence indicates a more general role of CB1 receptors in reward-related memories, which is consistent with the proposed role of endocannabinoids in memory-related plasticity. Relapse-preventing actions and inhibitory effects on weight gain were confirmed recently in clinical trials with the CB1 antagonist rimonabant. Collectively, these clinical and preclinical studies suggest that antagonists of CB1 receptors offer a novel approach in the treatment of addictive behaviours.

Transdermal nicotine alters some of marihuana's effects in male and female volunteers

Despite the fact that tobacco and marihuana are often used together, relatively little is known about the effects of this combination. In order to investigate the effects of the principal psychoactive component in tobacco smoke, nicotine, on marihuana-induced intoxication, we conducted a double blind, cross-over experiment using nicotine transdermal patches. Ten male and 10 female participants received either placebo or a 21 mg transdermal nicotine patch 4 h before smoking one of two marihuana cigarettes (1.99 or 3.51% delta-9-tetrahydrocannabinol (Delta(9) THC) content). Measurements of physiological activity (heart rate, blood pressure, and skin temperature) and subjective effects (self-reports of drug effects on visual analog scales (VAS) and the Addiction Research Center Inventory (ARCI)) were made periodically before and for 3h after smoking. Nicotine pre-treatment enhanced several responses to marihuana, in particular, heart rate, reports of "stimulated" on the visual analog scales, and scores on the Amphetamine scale of the ARCI. Male participants reported a more pronounced effect of marihuana that persisted longer than that of the female participants. Compared to the male participants, female participants experienced an attenuated response to marihuana and were less affected by the drug combination. The results of this study show that nicotine can have an important influence on the subjective and physiological effects of smoked marihuana. These effects have implications for the safety and efficacy of marihuana smokers who are self-medicating with the nicotine transdermal patch to manage their tobacco dependence.

Suppression of conditioned nicotine and sucrose seeking by the cannabinoid-1 receptor antagonist SR141716A

The present study shows that the selective cannabinoid CB1 receptor antagonist SR141716A attenuated responding for both nicotine- and sucrose-associated stimuli in a long-term extinction-reinstatement model. The results suggest that endocannabinoids play a general role in modulating cue reactivity or conditioned reinforcement following prolonged abstinence of both drug and natural reinforcers. In line with previous preclinical and recent clinical observations, our results provide a strong rationale for the use of CB1 antagonists in the treatment of addictive behaviors.

Control of the reinforcing effects of nicotine by associated environmental stimuli in animals and humans

Tobacco dependence through cigarette smoking is the leading preventable cause of death in the world and kills nearly 4 million people annually. Nicotine, a psychoactive component of tobacco, is thought to have a major role in tobacco dependence by acting directly as a reinforcer of drug-seeking and drug-taking behavior. However, recent findings obtained with two procedures that are used widely to assess reinforcing effects of drugs in experimental animals, intravenous drug self-administration and conditioned place-preference procedures, demonstrate that environmental factors have a major influence on the reinforcing effects of nicotine. Under some experimental conditions, nicotine is also self-administered reliably by humans. Environmental stimuli that have been associated previously with the self-administration of nicotine can reinstate extinguished drug-seeking behavior in animals and precipitate relapse to smoking behavior in ex-smokers. Innovative medications that target cannabinoid CB(1) and dopamine D(3) receptors and might block specifically the influence of such conditioned environmental stimuli in smokers are in development.

Substituted 5,5'-diphenyl-2-thioxoimidazolidin-4-one as CB1 cannabinoid receptor ligands: synthesis and pharmacological evaluation

A set of 30 substituted 5,5'-diphenyl-2-thioxoimidazolidin-4-one (thiohydantoins) derivatives was synthesized, and their affinity for the human CB(1) cannabinoid receptor has been evaluated. These compounds are derived from the previously described cannabinoid ligands 5,5'-diphenylimidazolidine-2,4-dione (hydantoins). The replacement of the oxygen by a sulfur leads to an increase of the affinity while the function-i.e., inverse agonism-determined by [(35)S]GTPgammaS experiments remains unaffected. Finally, to evaluate the molecular parameters that could influence the affinity of the thiohydantoins, molecular electrostatic potential as well as lipophilicity calculations were undertaken on representative thiohydantoins and hydantoins derivatives. In conclusion, 5,5'-bis-(4-iodophenyl)-3-butyl-2-thioxoimidazolidin-4-one (31) and 3-allyl-5,5'-bis(4-bromophenyl)-2-thioxoimidazolidin-4-one (32) possess the highest affinity for the CB(1) cannabinoid receptor described to date for the hydantoin and thiohydantoins series when compared in a same bioassay.

Keynote review: Medicinal chemistry strategies to CB1 cannabinoid receptor antagonists

The proven clinical efficacy of the CB(1) cannabinoid receptor antagonist rimonabant in both obesity and smoking cessation and its therapeutic potential in other disorders has given a tremendous impetus to the discovery of novel CB(1) antagonists. The number of disclosed patents wherein novel chemical entities having CB(1) antagonistic or inverse agonistic properties have been claimed has exploded. Besides novel compound classes that were identified in screening, rational medicinal chemistry approaches such as conformational constraint and scaffold hopping have been successfully applied. CB(1) receptor modelling has provided insight into crucial receptor-ligand interaction points thereby leading to a general CB(1) inverse agonist pharmacophore model.

Nicotine induces conditioned place preferences over a large range of doses in rats

RATIONALE

Conditioned place preference (CPP) procedures provide one measure of potential rewarding effects of abused drugs. Many attempts to induce CPP with nicotine have been unsuccessful.

OBJECTIVES

To assess the influence of nicotine dose and stimulus assignment procedure on development of nicotine-induced CPP.

METHODS

Initial preferences for one side of a two-compartment apparatus were first determined in Sprague-Dawley rats. In subsequent conditioning trials, the compartment paired with nicotine was the initially preferred side for half of the rats, and the initially non-preferred side for the other half. Rats received either an injection of nicotine (0.01-2 mg/kg SC) before being placed in one compartment (three trials) or saline before being placed in the other compartment (three trials). Control rats had saline injections associated with both compartments. A final test trial with no injection assessed final place preference.

RESULTS

Significant CPP were induced by 0.1-1.4 mg/kg doses of nicotine. Nicotine-induced CPP were only apparent when nicotine was paired with the initially non-preferred side. Moreover, a very high dose of nicotine (2 mg/kg) induced conditioned place aversion when paired with the initially preferred side of the apparatus.

CONCLUSIONS

Nicotine induced significant CPP across a wide range of doses, in accordance with its role as the primary addictive component of tobacco. Small preferences for one side of the apparatus played a major role in the development of nicotine-induced CPP. These findings suggest that biased procedures may be more suitable than unbiased procedures for evaluation of rewarding effects of nicotine using CPP paradigms.

Metabotropic glutamate receptor mGlu5 is a mediator of appetite and energy balance in rats and mice

The metabotropic glutamate receptor subtype mGlu5 modulates central reward pathways. Many transmitter systems within reward pathways affect feeding. We examined the potential role of mGlu5 in body weight regulation using genetic and pharmacological approaches. Adult mice lacking mGlu5, mGluR5-/-, weighed significantly less than littermate controls (mGluR5+/+, despite no difference in ad libitum food intake. After overnight food deprivation, mGluR5-/- mice ate significantly less than their mGluR5+/+ controls when refeeding. When on a high fat diet, mGluR5-/- mice weighed less and had decreased plasma insulin and leptin concentrations. The selective mGlu5 antagonist MTEP [3-[(2-methyl-1,3-thiazol-4-yl)-ethynyl]-pyridine; 15 mg/kg s.c.] reduced refeeding after overnight food deprivation in mGluR5+/+, but not mGluR5-/- mice, demonstrating that feeding suppression is mediated via a mGlu5 mechanism. MTEP (1-10 mg/kg) decreased night-time food intake in rats in a dose-related manner. At 10 mg/kg, MTEP injected at 8.5, 4.5, or 0.5 h before refeeding reduced overnight food intake by approximately approximately 30%. Diet-induced obese (DIO) and age-matched lean rats were treated for 12 days with MTEP (3 or 10 mg/kg/day s.c.), dexfenfluramine (3 mg/kg/day s.c.), or vehicle. Daily and cumulative food intakes were reduced in DIO rats by MTEP and dexfenfluramine. Weight gain was prevented with MTEP (3 mg/kg), and weight and adiposity loss was seen with MTEP (10 mg/kg) and dexfenfluramine. Caloric efficiency was decreased, suggesting increased energy expenditure. In lean rats, similar, although smaller, effects were observed. In conclusion, using genetic and pharmacological approaches, we have shown that mGlu5 modulates food intake and energy balance in rodents.

Adenosine receptor mediates nicotine-induced antinociception in formalin test

In this study, the effect of adenosine receptor agents on nicotine induced antinociception, in formalin test, has been investigated. Intraperitoneal (i.p.) administration of different doses of nicotine (0.1, 1, 10 and 100 microgkg(-1)) induced a dose-dependent antinociception in mice, in the both first and second phases of the test. Adenosine receptor antagonist, theophylline (5, 10, 20 and 80 mgkg(-1), i.p.) also induced antinociception in the both phases, while a dose of the drug (40 mgkg(-1), i.p.) did not induce any response. Theophylline reduced antinociception induced by nicotine in both phases of formalin test. The A(2) receptor agonist, 5'-N-ethylcarboxamide adenosine (NECA; 1 and 5 microgkg(-1), i.p.) also produced antinociception, which was reversed with different doses of theophylline (5, 10, 20 and 40 mgkg(-1), i.p.). But administration of the adenosine receptor agonist, NECA did not potentiate the response of nicotine. It is concluded that adenosine system may be involved in modulation of antinociception induced by nicotine.

Cannabinoid CB1 receptor antagonists as promising new medications for drug dependence

This review examines the development of cannabinoid CB(1) receptor antagonists as a new class of therapeutic agents for drug addiction. Abused drugs [alcohol, opiates, Delta(9)-tetrahydrocannabinol (Delta(9)-THC), and psychostimulants, including nicotine] elicit a variety of chronically relapsing disorders by interacting with endogenous neural pathways in the brain. In particular, they share the common property of activating mesolimbic dopamine brain reward systems, and virtually all abused drugs elevate dopamine levels in the nucleus accumbens. Cannabinoid CB(1) receptors are expressed in this brain reward circuit and modulate the dopamine-releasing effects of Delta(9)-THC and nicotine. Rimonabant (SR141716), a CB(1) receptor antagonist, blocks both the dopamine-releasing and discriminative and rewarding effects of Delta(9)-THC in animals. Blockade of CB(1) receptor activity by genetic invalidation also decreases rewarding effects of opiates and alcohol in animals. Although CB(1) receptor blockade is generally ineffective in reducing the self-administration of cocaine in rodents and primates, it reduces the reinstatement of extinguished cocaine-seeking behavior produced by cocaine-associated conditioned stimuli and cocaine-priming injections. Likewise, CB(1) receptor blockade is effective in reducing nicotine-seeking behavior induced by re-exposure to nicotine-associated stimuli. Some of these findings have been recently validated in humans. In clinical trials, Rimonabant blocks the subjective effects of Delta(9)-THC in humans and prevents relapse to smoking in exsmokers. Findings from both clinical and preclinical studies suggest that ligands blocking CB(1) receptors offer a novel approach for patients suffering from drug dependence that may be efficacious across different classes of abused drugs.

Suppressing effect of the cannabinoid CB1 receptor antagonist, SR 141716, on alcohol's motivational properties in alcohol-preferring rats

Administration of the cannabinoid CB(1) receptor antagonist, SR 141716 [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide], has been reported to reduce alcohol intake and alcohol self-administration in different models of excessive alcohol consumption, including the selectively bred Sardinian alcohol-preferring (sP) rats. The present study investigated whether SR 141716 was also capable of decreasing, in this rat line, alcohol's motivational properties. Extinction responding for alcohol, defined as the maximal number of lever responses reached in the absence of alcohol in rats trained to lever-press for alcohol, was used as index of alcohol's motivational properties. Rats were initially trained to lever-press for oral alcohol (15%, v/v) under a fixed ratio (FR) schedule of FR4. Once self-administration behavior was established, extinction sessions were conducted. SR 141716 (0, 0.3, 1 and 3 mg/kg; i.p.) was acutely administered before extinction sessions. In order to assess the specificity of SR 141716 action on extinction responding for alcohol, a separate group of sP rats was trained to lever-press for a 3% (w/v) sucrose solution under an FR4 schedule. SR 141716 administration produced a dose-dependent, virtually complete suppression of extinction responding for alcohol. In contrast, extinction responding for sucrose was not significantly altered by treatment with SR 141716. Further to the consummatory aspects, these results also extend the suppressing effect of SR 141716 to the appetitive aspects of alcohol drinking behavior in sP rats. The results also implicate the cannabinoid CB1 receptor in the neural substrate mediating alcohol's motivational properties in this rat line.

Drug Insight: appetite suppressants

The term 'appetite suppressant' is used to denote drugs that act primarily on the neurochemical transmitters of the central nervous system to reduce food intake. In addition to drugs that release or mimic the effect of norepinephrine (noradrenaline), this could include drugs that inhibit: reuptake of norepinephrine or 5-hydroxytryptamine (also known as serotonin); bind to the gamma-aminobutyric acid receptors or the cannabinoid receptors; and some peptides that reduce food intake. The sympathomimetic drugs phentermine, diethylpropion, benzphetamine, and phendimetrazine--so named because they mimic many effects of norepinephrine--are only approved in a few countries, and then only for short-term use. Sibutramine, a norepinephrine-5-hydroxytryptamine reuptake inhibitor, is approved for long-term use. Several new mechanisms for drug action are under investigation. Appetite suppressants should be viewed as useful adjuncts to diet and physical activity and might help selected patients to achieve and maintain weight loss.

Effects of the cannabinoid CB1 receptor antagonist rimonabant in models of emotional reactivity in rodents

BACKGROUND

The endocannabinoid system has been implicated in the modulation of emotional processes.

METHODS

These experiments aimed to investigate the effects of the cannabinoid CB1 receptor antagonist rimonabant (SR141716) in animal models measuring aspects of emotional reactivity and depression.

RESULTS

Rimonabant had weak anxiolytic-like activity in the elevated plus-maze and failed to affect flight and risk assessment activities in the mouse defense test battery (MDTB). It produced clear anxiolytic-like effects in the Vogel conflict test (.3-3 mg/kg intraperitoneal [i.p.]) and on defensive aggression in the MDTB (1 and 10 mg/kg, i.p.). The effects of rimonabant in the MDTB paralleled those observed with CB1 receptor knockout mice in this procedure. In the forced-swimming test in rats and the tonic immobility paradigm in gerbils, rimonabant (3 and 10 mg/kg per os [p.o.]) produced antidepressant-like effects that were comparable to those observed with the reference antidepressant, fluoxetine. In the chronic mild stress model in mice, repeated administration of rimonabant (10 mg/kg, p.o.) for 5 weeks improved the deleterious effects produced by stress.

CONCLUSIONS

These findings point further to a role for the endocannabinoid system in the modulation of emotional processes and suggest that it may be primarily involved in the adaptive responses to unavoidable stressful stimuli.

Bases genéticas del hábito tabáquico

Dependence on tobacco is one of the most important health problems in our society due to the direct relationship with lung cancer. Early studies in twins revealed that genetic factors modify the susceptibility to develop tobacco dependence. Different studies are underway to try to find an association between polymorphisms of genes involved either in nicotine metabolization or in neural transmission and the initiation and maintenance of the dependence on tobacco. Here we review the studies performed so far and discuss new perspectives for future studies.

Treating Tobacco Dependence: State of the Science and New Directions

Despite almost two decades of intensive tobacco control efforts, nearly one quarter of Americans continue to smoke. The two United States Food and Drug Administration–approved medications used to treat tobacco dependence, bupropion and nicotine replacement therapy, are effective for only a fraction of smokers. Investigations of medications approved for affective disorders and other forms of substance abuse, such as fluoxetine and naltrexone, have yielded mixed results as tobacco dependence treatments. A particular challenge in tobacco dependence treatment is the development of effective approaches for smokers with unique needs, such as cancer patients and pregnant women. Despite new developments in these areas, significant gaps in knowledge and practice remain. Basic research in the neurobiologic and genetic basis of nicotine dependence offers promise for the development of novel and more effective treatment approaches. For example, emerging research in pharmacogenetics explores how genetic variation in drug-metabolizing enzymes and drug targets modifies response to pharmacotherapy. These discoveries could someday help practitioners to individualize the type, dosage, and duration of tobacco dependence treatment based on genotype, and maximize the efficacy.

The endocannabinoid system:A new approach to control cardiovascular disease

The endocannabinoid (EC) system consists of 2 types of G-protein-coupled cannabinoid receptors--cannabinoid type 1 (CB1) and cannabinoid type 2 (CB2)--and their natural ligands. The EC system plays a key role in the regulation of food intake and fat accumulation, as well as glucose and lipid metabolism. When overactivated, the EC system triggers dyslipidemia, thrombotic and inflammatory states, and insulin resistance. Blocking CB1 receptors centrally and peripherally in adipose tissue can help normalize an overactivated EC system. CB1 blockade helps regulate food intake and adipose tissue metabolism, contributing to improved insulin sensitivity and other features of the metabolic syndrome. Visceral adipose tissue is most closely associated with the metabolic syndrome, which is a constellation of conditions that place people at high risk for coronary artery disease. Targeting the EC system represents a new approach to treating visceral obesity and reducing cardiovascular risk factors.

Endogenous cannabinoids are not involved in cocaine reinforcement and development of cocaine-induced behavioural sensitization

The endogenous cannabinoid system is a relatively novel discovered system consisting of cannabinoid CB1 receptors, which are expressed both in the periphery and in the central nervous system, peripheral cannabinoid CB2 receptors and endogenous cannabinoids, which are anandamide and 2-arachidonyl glycerol. The cannabinoid CB1 receptors have recently been implicated in rewarding aspects of not only the cannabinoid drug Delta9-tetrahydrocannabinol (Delta9-THC), but also of other drugs of abuse, including cocaine. The present study was designed to further investigate the role of CB1 receptors in reward-related effects of cocaine. Using the CB1 receptor selective antagonist SR141716A, the involvement of CB1 receptors in cocaine reinforcement was determined by intravenous cocaine self-administration. In addition, the effects of the CB1 receptor selective antagonist SR141716A upon the development of cocaine-induced behavioural sensitization were investigated. SR141716A did not affect cocaine reinforcement nor did it affect the development of behavioural sensitization to the locomotor stimulant effects of cocaine. These findings suggest that CB1 receptors are not involved in acute cocaine reinforcement nor in cocaine-induced behavioural sensitization.

Nicotine-associated cues maintain nicotine-seeking behavior in rats several weeks after nicotine withdrawal: reversal by the cannabinoid (CB1) receptor antagonist, rimonabant (SR141716)

Conditioned stimuli are important for nicotine dependence and may trigger craving and relapse after prolonged nicotine abstinence. However, little is known about the pharmacology of this process. Among the systems that have been shown to play a role in drug-seeking behavior is the endocannabinoid transmission. Therefore, the present study examined the resistance to extinction of drug-seeking behavior elicited by nicotine-associated environmental stimuli and the effects of the selective CB1 cannabinoid antagonist rimonabant (SR141716) on the reinforcing effects of nicotine-related stimuli. Rats were trained to self-administer nicotine (0.03 mg/kg/injection, i.v.) under conditions in which responding was reinforced jointly by response-contingent nicotine injections and stimuli (light and tone). After self-administration acquisition, nicotine was withdrawn and lever pressing was only reinforced by contingent presentation of the audiovisual stimuli. Under such a condition, responding persisted for 3 months, following which nonpresentation of the cues produced a progressive extinction of responding. As expected, rats trained to lever-press for saline injections paired with the audiovisual stimuli did not acquire the self-administration. These findings indicate that the cues required learned association with nicotine to acquire reinforcing properties and to function as conditioned reinforcers. When administered 1 month following nicotine withdrawal, rimonabant (1 mg/kg, i.p.) decreased conditioned behavior. These results showing the persistence of a nicotine-conditioned behavior are congruent with the role of nicotine-related environmental stimuli in nicotine craving in abstinent smokers. Rimonabant, which has been shown previously to reduce nicotine self-administration, may be effective not only as an aid for smoking cessation but also in the maintenance of abstinence.

Changes in endocannabinoid levels in a rat model of behavioural sensitization to morphine

The opioid and cannabinoid systems co-operate to regulate physiological processes such as nociception and reward. The endocannabinoid system may be a component of the brain reward circuitry and thus play a role not only in cannabinoid tolerance/dependence, but also in dependence/withdrawal for other misused drugs. We provide evidence of a cannabinoid mechanism in an animal model of morphine drug-seeking behaviour, referred to as behavioural sensitization. The present study was designed to test the effects of the CB1 cannabinoid receptor antagonist SR141716A in two different phases of morphine sensitization (induction and expression) and to measure the brain contents of arachidonoylethanolamide (anandamide, AEA) and 2-arachidonoylglycerol (2-AG), the two main endogenous ligands for cannabinoid receptors in the different phases of morphine sensitization. The cannabinoid antagonist modified the signs of morphine sensitization when administered in the expression phase, whereas co-administration of SR141716A and morphine in the induction phase only slightly affected the behavioural responses, suggesting that CB1 receptor blockade attenuates the behavioural manifestations of morphine sensitization but not its development. AEA and 2-AG were affected differently by morphine during the two phases of behavioural sensitization. The alterations were in opposite directions and specific for the cerebral area analysed (caudate putamen, nucleus accumbens, hippocampus and prefrontal cortex). The results suggest that the endocannabinoid system undergoes profound changes during the different phases of sensitization to morphine in rats, providing a possible neurochemical basis for the previously observed cross-sensitization between opiates and cannabinoids.

Cannabinoid physiology and pharmacology: 30 years of progress

Delta9-Tetrahydrocannabinol from Cannabis sativa is mimicked by cannabimimetic analogs such as CP55940 and WIN55212-2, and antagonized by rimonabant and SR144528, through G-protein-coupled receptors, CB1 in the brain, and CB2 in the immune system. Eicosanoids anandamide and 2-arachidonoylglycerol are the "endocannabinoid" agonists for these receptors. CB1 receptors are abundant in basal ganglia, hippocampus and cerebellum, and their functional activity can be mapped during behaviors using cerebral metabolism as the neuroimaging tool. CB1 receptors couple to G(i/o) to inhibit cAMP production, decrease Ca2+ conductance, increase K+ conductance, and increase mitogen-activated protein kinase activity. Functional activation of G-proteins can be imaged by [35S]GTPgammaS autoradiography. Post-synaptically generated endocannabinoids form the basis of a retrograde signaling mechanism referred to as depolarization-induced suppression of inhibition (DSI) or excitation (DSE). Under circumstances of sufficient intracellular Ca2+ (e.g., burst activity in seizures), synthesis of endocannabinoids releases a diffusible retrograde messenger to stimulate presynaptic CB1 receptors. This results in suppression of gamma-aminobutyric acid (GABA) release, thereby relieving the post-synaptic inhibition. Tolerance develops as neurons adjust both receptor number and cellular signal transduction to the chronic administration of cannabinoid drugs. Future therapeutic drug design can progress based upon our current understanding of the physiology and pharmacology of CB1, CB2 and related receptors. One very important role for CB1 antagonists will be in the treatment of craving in the disease of substance abuse.

Nicotine-induced changes in neurotransmitter levels in brain areas associated with cognitive function

Nicotine, one of the most widespread drugs of abuse, has long been shown to impact areas of the brain involved in addiction and reward. Recent research, however, has begun to explore the positive effects that nicotine may have on learning and memory. The mechanisms by which nicotine interacts with areas of cognitive function are relatively unknown. Therefore, this paper is part of an ongoing study to evaluate regional effects of nicotine enhancement of cognitive function. Nicotine-induced changes in the levels of three neurotransmitters, dopamine (DA), serotonin (5-HT), norepinepherine (NE), their metabolites, homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA), and their precursor, L-DOPA, were evaluated in the ventral and dorsal hippocampus (VH and DH), prefrontal and medial temporal cortex (PFC and MTC), and the ventral tegmental area (VTA) using in vivo microdialysis in awake, freely moving, male Sprague-Dawley rats. The animals were treated with acute nicotine (0.5 mg/kg, s.c.) halfway through the 300-min experimental period. The reuptake blockers, desipramine (100 microM) and fluoxetine (30 microM), were given to increase the levels of NE and 5-HT so that they could be detected. Overall, a nicotine-induced DA increase was found in some areas, and this increase was potentiated by desipramine and fluoxetine. The two DA metabolites, HVA and DOPAC, increased in all the areas throughout the experiments, both with and without the inhibitors, indicating a rapid metabolism of the released DA. The increase in these metabolites was greater than the increase in DA. 5-HT was increased in the DH, MTC, and VTA in the presence of fluoxetine; its metabolite, 5-HIAA, was increased in the presence and absence of fluoxetine. Except in the VTA, NE levels increased to a similar extent with desipramine and fluoxetine. Overall, nicotine appeared to increase the release and turnover of these three neurotransmitters, which was indicated by significant increases in their metabolites. Furthermore, DA, and especially HVA and DOPAC, increased for the 150 min following nicotine administration; 5-HT and NE changes were shorter in duration. As gas chromatography experiments showed that nicotine levels in the brain decreased by 75% after 150 min, this may indicate that DA is more susceptible to lower levels of nicotine than 5-HT or NE. In conclusion, acute nicotine administration caused alterations in the levels of DA, 5-HT, and NE, and in the metabolism of DA and 5-HT, in brain areas that are involved in cognitive processes.

Modulation of morphine-induced Fos-immunoreactivity by the cannabinoid receptor antagonist SR 141716

A growing body of evidence suggests the existence of a functional interaction between opioid and cannabinoid systems. The present study further investigated this functional interaction by examining the combined effects of morphine and the cannabinoid receptor antagonist SR 141716 on Fos-immunoreactivity (Fos-IR), a marker for neural activation. Male albino Wistar rats were treated with SR 141716 (3 mg/kg, intraperitoneally), morphine HCl (10 mg/kg, subcutaneously), vehicle, or SR 141716 and morphine combined (n = 6 per group). Rats were injected with morphine or its vehicle 30-min after administration of SR 141716 or its vehicle and perfused 3 h later. Locomotor activity and body temperature were both increased in the morphine-treated group and SR 141716 significantly inhibited these effects. Morphine increased Fos-IR in several brain regions including the caudate-putamen (CPu), cortex (cingulate, insular and piriform), nucleus accumbens (NAS) shell, lateral septum (LS), bed nucleus of the stria terminalis (BNST), median preoptic nucleus (MnPO), medial preoptic nucleus (MPO), hypothalamus (paraventricular, dorsomedial and ventromedial), paraventricular thalamic nucleus (PV), amygdala (central and basolateral nuclei), dorsolateral periaqueductal gray, ventral tegmental area (VTA), and Edinger-Westphal nucleus. SR 141716 alone increased Fos-IR in the cortex (cingulate, insular and piriform), NAS (shell), LS, BNST, hypothalamus (paraventricular, dorsomedial and ventromedial), PV, amygdala (central, basolateral and medial nuclei), VTA, and Edinger-Westphal nucleus. SR 141716 attenuated morphine-induced Fos-IR in several regions including the CPu, cortex, NAS (shell), LS, MnPO, MPO, paraventricular and dorsomedial hypothalamus, PV, basolateral amygdala, VTA, and Edinger-Westphal nucleus (EW). These results provide further support for functional interplay between the cannabinoid and opioid systems. Possible behavioural and physiological implications of the interactive effects of SR 141716 on morphine-induced Fos-IR are discussed.

ROLE OF THE ENDOCANNABINOID SYSTEM IN THE DEVELOPMENT OF TOLERANCE TO ALCOHOL

The present review evaluates the evidence that the endocannabinoid system plays in the development of tolerance to alcohol. The identification of a G-protein-coupled receptor, namely, the cannabinoid receptor (CB(1) receptor), which was activated by Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the major psychoactive component of marijuana, led to the discovery of endogenous cannabinoid agonists. Until now, four fatty acid derivatives identified to be arachidonylethanolamide (AEA), 2-arachidonylglycerol (2-AG), 2-arachidonylglycerol ether (noladin ether) and virodhamine have been isolated from both nervous and peripheral tissues. Both AEA and 2-AG have been shown to mimic the pharmacological and behavioural effects of Delta(9)-THC. The role of the endocannabinoid system in the development of tolerance to alcohol was not known until recently. Recent studies from our laboratory have implicated for the first time a role for the endocannabinoid system in development of tolerance to alcohol. Chronic alcohol treatment has been shown to down-regulate CB(1) receptors and its signal transduction. The observed downregulation of CB(1) receptor function results from the persistent stimulation of the receptors by AEA and 2-AG, the synthesis of which has been shown to be increased by chronic alcohol treatment. The enhanced formation of endocannabinoids may subsequently influence the release of neurotransmitters. It was found that the DBA/2 mice, known to avoid alcohol intake, have significantly reduced CB(1) receptor function in the brain, consistent with other studies in which the CB(1) receptor antagonist SR 141716A has been shown to block voluntary alcohol intake in rodents. Similarly, activation of the CB(1) receptor system promoted alcohol craving, suggesting a role for the CB(1) receptor gene in excessive alcohol drinking behaviour and development of alcoholism. Ongoing investigations may lead to a better understanding of the mechanisms underlying the development of tolerance to alcohol and to develop therapeutic strategies to treat alcoholism.

Delta9-tetrahydrocannabinol decreases somatic and motivational manifestations of nicotine withdrawal in mice

The possible interactions between Delta9-tetrahydrocannabinol (Delta9-THC) and nicotine remain unclear in spite of the current association of cannabis and tobacco in humans. The aim of the present study was to explore the interactions between these two drugs of abuse by evaluating the consequences of Delta9-THC administration on the somatic manifestations and the aversive motivational state associated with nicotine withdrawal in mice. Acute Delta9-THC administration significantly decreased the incidence of several nicotine withdrawal signs precipitated by mecamylamine or naloxone, such as wet-dog-shakes, paw tremor and scratches. In both experimental conditions, the global withdrawal score was also significantly attenuated by acute Delta9-THC administration. This effect of Delta9-THC was not due to possible adaptive changes induced by chronic nicotine on CB1 cannabinoid receptors, as the density and functional activity of these receptors were not modified by chronic nicotine administration in the different brain structures investigated. We also evaluated the consequences of Delta9-THC administration on c-Fos expression in several brain structures after chronic nicotine administration and withdrawal. c-Fos was decreased in the caudate putamen and the dentate gyrus after mecamylamine precipitated nicotine withdrawal. However, acute Delta9-THC administration did not modify c-Fos expression under these experimental conditions. Finally, Delta9-THC also reversed conditioned place aversion associated to naloxone precipitated nicotine withdrawal. Taken together, these results indicate that Delta9-THC administration attenuated somatic signs of nicotine withdrawal and this effect was not associated with compensatory changes on CB1 cannabinoid receptors during chronic nicotine administration. In addition, Delta9-THC also ameliorated the aversive motivational consequences of nicotine withdrawal.

SR147778 [5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-4-ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide], a new potent and selective antagonist of the CB1 cannabinoid receptor: biochemical and pharmacological characterization

Based on binding, functional, and pharmacological data, this study introduces SR147778 [5-(4-bromophenyl)-1-(2,4-dichloro-phenyl)-4-ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide] as a highly potent, selective, and orally active antagonist for the CB1 receptor. This compound displays nanomolar affinity (Ki = 0.56 and 3.5 nM) for both the rat brain and human CB1 recombinant receptors, respectively. It has low affinity (Ki = 400 nM) for both the rat spleen and human CB2 receptors. Furthermore, it shows no affinity for any of the over 100 targets investigated (IC50 > 1 microM). In vitro, SR147778 antagonizes the inhibitory effects of CP 55,940 [(1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol] on both the mouse vas deferens contractions (pA2 value = 8.1) and on forskolin-stimulated adenylyl cyclase activity in the U373 MG cell lines (pA2 value = 8.2) but not in Chinese hamster ovary (CHO) cells permanently expressing the human peripheral cannabinoid receptor (hCB2). SR147778 is able to block the mitogen-activated protein kinase activity induced by CP 55,940 in the CHO cell line expressing human brain cannabinoid receptor (IC50 = 9.6 nM) but was inactive in cells expressing hCB2. After oral administration, SR147778 displaced the ex vivo [3H]-CP 55,940 binding to mouse brain membranes (ED50 = 3.8 mg/kg) with a long duration of action, whereas it did not interact with the CB2 receptor expressed in the mouse spleen. Using different routes of administration, SR147778 (0.3-3 mg/kg) is shown to antagonize pharmacological effects (hypothermia, analgesia, and gastrointestinal transit) induced by R-(+)-(2,3-dihydro-5-methyl-3-[[4-morpholinyl]methyl] pyrol [1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl) methanone in mice. Finally, per se, SR147778 (0.3-10 mg/kg) is able to reduce ethanol or sucrose consumption in mice and rats and food intake in fasted and nondeprived rats.

Rats on the grog: novel pharmacotherapies for alcohol craving

Current pharmacotherapies for alcohol dependence in humans (e.g., naltrexone, acamprosate) are meeting with only limited therapeutic success. The development of novel pharmacotherapies is urgently needed but is reliant upon the screening of large numbers of candidate "anticraving" drugs using appropriate animal models. The development of animal models is complex because (1) laboratory animals are often reluctant to consume large quantities of alcohol, (2) inducing a state of alcohol dependence, analogous to the human condition, may require many months of alcohol exposure, (3) concluding that a given drug selectively reduces alcohol craving requires very carefully controlled experiments, and (4) false positives and false negatives may result from the sometimes distinct physiology and psychology of the alcohol-addicted human and rat. To address some of these problems, our laboratory has recently developed the "beer model" of alcohol dependence and craving. Rats, like humans, have a prodigious appetite for beer and will drink much more beer than equivalent ethanol solutions in water. Beer consumption in rats leads to clear signs of intoxication, anxiety reduction, and signs of withdrawal when beer access is suddenly denied. We have found that beer craving in rats is selectively reduced by the cannabinoid receptor antagonist SR 141716 and the opioid receptor antagonist naltrexone. Combining these two drugs appears to have a synergistic anticraving effect. Other promising pharmacotherapies for the future are discussed.

Rimonabant, a CB1 antagonist, blocks nicotine-conditioned place preferences

The effects of Rimonabant (SR141716), an antagonist at cannabinoid CB1 receptors, were evaluated in animal models for subjective and rewarding effects of nicotine. Acute administration of 1 or 3 mg/kg SR141716 blocked expression of nicotine-induced conditioned place preferences. SR141716 (0.3-3 mg/kg) was also studied in rats trained to discriminate nicotine from saline under a fixed-ratio schedule of food delivery. In contrast to nicotine replacement therapy and bupropion, SR141716 did not have nicotine-like discriminative effects and did not alter the dose-response curve for nicotine discrimination. These findings support the proposed use of SR141716 for smoking cessation and indicate that it would selectively reduce the influence of environmental stimuli that contribute to persistent smoking behavior, without affecting subjective responses to nicotine.

Cannabinoid antagonist SR-141716 inhibits endotoxic hypotension by a cardiac mechanism not involving CB1 or CB2 receptors

Endocannabinoids and CB1 receptors have been implicated in endotoxin (LPS)-induced hypotension: LPS stimulates the synthesis of anandamide in macrophages, and the CB1 antagonist SR-141716 inhibits the hypotension induced by treatment of rats with LPS or LPS-treated macrophages. Recent evidence indicates the existence of cannabinoid receptors distinct from CB1 or CB2 that are inhibited by SR-141716 but not by other CB1 antagonists such as AM251. In pentobarbital-anesthetized rats, intravenous injection of 10 mg/kg LPS elicited hypotension associated with profound decreases in cardiac contractility, moderate tachycardia, and an increase in lower body vascular resistance. Pretreatment with 3 mg/kg SR-141716 prevented the hypotension and decrease in cardiac contractility, slightly attenuated the increase in peripheral resistance, and had no effect on the tachycardia caused by LPS, whereas pretreatment with 3 mg/kg AM251 did not affect any of these responses. SR-141716 also elicited an acute reversal of the hypotension and decreased contractility when administered after the response to LPS had fully developed. The LPS-induced hypotension and its inhibition by SR-141716 were similar in pentobarbital-anesthetized wild-type, CB1(-/-), and CB1(-/-)/CB2(-/-) mice. We conclude that SR-141716 inhibits the acute hemodynamic effects of LPS by interacting with a cardiac receptor distinct from CB1 or CB2 that mediates negative inotropy and may be activated by anandamide or a related endocannabinoid released during endotoxemia.

Blockade by the cannabinoid CB1 receptor antagonist, rimonabant (SR141716), of the potentiation by quinelorane of food-primed reinstatement of food-seeking behavior

It has been shown previously that the selective cannabinoid CB1 receptor antagonist, rimonabant (SR141716), reduced the intake of palatable food as well as the self-administration of several drugs of abuse, suggesting that endocannabinoid systems play a role in brain reward function. The present study investigated whether a cannabinoid step was involved in food-seeking behavior induced by explicit stimuli, using an operant reinstatement procedure in rats. Experimental sessions consisted of a 15-min food rewarded period, followed by a 45-min extinction period. Rimonabant did not affect the response reinstatement induced by noncontingent delivery of food pellets, but prevented (0.03-0.3 mg/kg) the potentiation by quinelorane, a dopamine D3 receptor-preferring agonist, of food-seeking behavior. A possible link between cannabinoid processes and D3- and/or D2-mediated dopaminergic transmission was further investigated by studying Fos protein expression in cortico-limbic structures in D3 (D3-/-) and D2 (D2-/-) knockout mice. Rimonabant (10 mg/kg) increased Fos immunoreactivity in the prefrontal cortex (pFCortex) and in the shell but not the core of the nucleus accumbens (NAcc). Fos induction by this dose of rimonabant was not seen in mice lacking CB1 receptors, providing clear evidence for the involvement of CB1 receptors. In the NAcc shell, the effect of rimonabant was suppressed in D3-/-, but remained unchanged in D2-/- mice. In contrast, Fos expression by rimonabant in the pFCortex was impervious to D2 or D3 receptor deletion. In conclusion, these data indicate first that rimonabant prevented the enhancement by quinelorane of the appetitive value of food pellets unexpectedly delivered during extinction and second that rimonabant effects might involve D3 receptor-mediated processes. Overall, these results are consistent with the notion that endocannabinoid functions control brain reward processes and in particular the capacity of explicit stimuli to precipitate food-seeking behavior.

The endocannabinoid system in the basal ganglia and in the mesolimbic reward system: implications for neurological and psychiatric disorders

To date, N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol are the best studied endocannabinoids and are thought to act as retrograde messengers in the central nervous system (CNS). By activating presynaptic cannabinoid CB1 receptors, they can reduce glutamate release in dorsal and ventral striatum (nucleus accumbens) and alter synaptic plasticity, thereby modulating neurotransmission in the basal ganglia and in the mesolimbic reward system. In this review, we will focus on the role of the endocannabinoid system within these neuronal pathways and describe its effect on dopaminergic transmission and vice versa. The endocannabinoid system is unlikely to directly affect dopamine release, but can modify dopamine transmission trough trans-synaptic mechanisms, involving gamma-aminobutyric acid (GABA)-ergic and glutamatergic synapses, as well as by converging signal transduction cascades of the cannabinoid and dopamine receptors. The dopamine and endocannabinoid systems exert a mutual control on each other. Cannabinergic signalling may lead to release of dopamine, which can act via dopamine D1-like receptors as a negative feedback mechanism to counteract the effects of activation of the cannabinoid CB1 receptor. On the other hand, dopaminergic signalling via dopamine D2-like receptors may lead to up-regulation of cannabinergic signalling, which is likely to represent a negative feedback on dopaminergic signalling. The consequences of these interactions become evident in pathological conditions in which one of the two systems is likely to be malfunctioning. We will discuss neurological and psychiatric disorders such as Parkinson's and Huntington's disease, drug addiction and schizophrenia. Furthermore, the possible role of the endocannabinoid system in disorders not necessarily depending on the dopaminergic system, such as eating disorders and anxiety, will be described.

Non-nicotinic neuropharmacological strategies for nicotine dependence: beyond bupropion

Smoking is a major health problem and is propelled, at least in part, by the addictive properties of nicotine. Two types of pharmacological therapies have been approved for smoking cessation by the US Food and Drug Administration. The first therapy consists of nicotine replacement, substituting the nicotine from cigarettes with safer nicotine formulations. The second therapy is bupropion (Zyban), an atypical antidepressant, whose use has raised much debate as to how a non-nicotine-based agent can aid in smoking cessation. This review focuses on recent advances that could lead to the development of improved novel pharmacological treatments. These strategies focus on altering reward processes in the brain by modulating various neurotransmitter systems: the most promising include dopamine D(3) receptor antagonists, noradrenaline reuptake inhibitors, GABA(B) receptor agonists, metabotropic glutamate 5 (mGluR5) receptor antagonists, cannabinoid CB1 receptor antagonists, and corticotropin releasing factor (CRF) 1 receptor antagonists.

SSR591813, a novel selective and partial alpha4beta2 nicotinic receptor agonist with potential as an aid to smoking cessation

(5aS,8S,10aR)-5a,6,9,10-Tetrahydro,7H,11H-8,10a-methanopyrido[2',3':5,6]pyrano[2,3-d]azepine (SSR591813) is a novel compound that binds with high affinity to the rat and human alpha4beta2 nicotinic acetylcholine receptor (nAChR) subtypes (Ki = 107 and 36 nM, respectively) and displays selectivity for the alpha4beta2 nAChR (Ki, human alpha3beta4 > 1000, alpha3beta2 = 116; alpha1beta1deltagamma > 6000 nM and rat alpha7 > 6000 nM). Electrophysiological experiments indicate that SSR591813 is a partial agonist at the human alpha4beta2 nAChR subtype (EC50 = 1.3 micro M, IA =19% compared with the full agonist 1,1-dimethyl-4-phenyl-piperazinium). In vivo findings from microdialysis and drug discrimination studies confirm the partial intrinsic activity of SSR591813. The drug increases dopamine release in the nucleus accumbens shell (30 mg/kg i.p.) and generalizes to nicotine or amphetamine (10-20 mg/kg i.p.) in rats, with an efficacy approximately 2-fold lower than that of nicotine. Pretreatment with SSR591813 (10 mg/kg i.p.) reduces the dopamine-releasing and discriminative effects of nicotine. SSR591813 shows activity in animal models of nicotine dependence at doses devoid of unwanted side effects typically observed with nicotine (hypothermia and cardiovascular effects). The compound (10 mg/kg i.p.) also prevents withdrawal signs precipitated by mecamylamine in nicotine-dependent rats and partially blocks the discriminative cue of an acute precipitated withdrawal. SSR591813 (20 mg/kg i.p.) reduces i.v. nicotine self-administration and antagonizes nicotine-induced behavioral sensitization in rats. The present results confirm important role for alpha4beta2 nAChRs in mediating nicotine dependence and suggest that SSR591813, a partial agonist at this particular nAChR subtype, may have therapeutic potential in the clinical management of smoking cessation.

The cannabinoid CB1 antagonist N-piperidinyl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl) -4-methylpyrazole-3-carboxamide (SR-141716A) differentially alters the reinforcing effects of heroin under continuous reinforcement, fixed ratio, and progressive ratio schedules of drug self-administration in rats

Activation or blockade of cannabinoid CB1 receptors markedly alters many effects of opioids. In the present study, we investigated whether the cannabinoid antagonist (N-piperidinyl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide (SR-141716A) could alter the reinforcing effects of heroin in rats. A Delta9-tetrahydrocannabinol (THC) drug-discrimination procedure was first used to determine effective CB1 antagonist doses of SR-141716A and optimal pretreatment times for self-administration studies. Subsequently, Sprague-Dawley rats learned to self-administer heroin under three different schedules of intravenous drug injection: a continuous reinforcement schedule [fixed ratio (FR)1], a five-response, fixed ratio schedule (FR5), and a progressive ratio schedule. Then, SR-141716A (1 mg/kg i.p.) was administered 60 min before the start of the session for three consecutive daily sessions. SR-141716A markedly decreased heroin self-administration under the progressive ratio schedule at heroin doses ranging from 12.5 to 100 micro g/kg/injection. In contrast, SR-141716A had no effect on heroin self-administration under the FR1 schedule at heroin doses of 50 or 100 micro g/kg/injection, but produced small decreases in self-administration at lower doses (25 and 12.5 micro g/kg/injection). Consistent with a behavioral economics evaluation, SR-141716A produced a small but significant decrease in self-administration of the higher 50 micro g/kg/injection dose of heroin when the fixed ratio requirement was raised to five (FR5). Thus, blockade of CB1 receptors differentially decreased the reinforcing efficacy of heroin depending on the number of responses required for each injection (price). These findings indicate a facilitatory modulation of opioid reward by endogenous cannabinoid activity and provide support for the use of cannabinoid CB1 antagonists as medications for heroin addiction.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Cannabis and alcohol--a close friendship

Cannabinoids and alcohol activate the same reward pathways, and the cannabinoid CB(1) receptor system plays an important role in regulating the positive reinforcing properties of alcohol. Indeed, both cannabinoids and alcohol cause the release of dopamine in the nucleus accumbens. Recent research suggests that ethanol preference, which is dependent on CB(1) receptors, is higher in young mice than in old mice, and higher in female mice than in male mice.

Cannabinoid CB1 receptor knockout mice exhibit markedly reduced voluntary alcohol consumption and lack alcohol-induced dopamine release in the nucleus accumbens

The mechanisms underlying predisposition to alcohol abuse and alcoholism are poorly understood. In this study, we evaluated the role of cannabinoid (CB1) receptors in (i) voluntary alcohol consumption, and (ii) acute alcohol-induced dopamine (DA) release in the nucleus accumbens, using mice that lack the CB1 receptor gene (CB1-/-). CB1-/- mice exhibited dramatically reduced voluntary alcohol consumption, and completely lacked alcohol-induced DA release in the nucleus accumbens, as compared to wild-type mice. The gender difference, with female mice consuming significantly more alcohol than wild-type male mice, was observed in wild-type mice, whereas this gender difference was nonexistent in CB1 mutant male and female mice. There was also a significant gender difference, with the wild-type, heterozygous, and mutant females consuming significantly more liquid and food than wild-type, heterozygous and mutant males. However, the total volume of fluid consumption and food intake did not differ between wild-type, heterozygous, and mutant mice. These results strongly suggest that the CB1 receptor system plays an important role in regulating the positive reinforcing properties of alcohol.