Ethanol, endocannabinoids, and the cannabinoidergic signaling system

Striatonigral direct pathway 2-arachidonoylglycerol contributes to ethanol effects on synaptic transmission and behavior

Endocannabinoids (eCB) and cannabinoid receptor 1 (CB1) play important roles in mediating short- and long-term synaptic plasticity in many brain regions involved in learning and memory, as well as the reinforcing effects of misused substances. Ethanol-induced plasticity and neuroadaptations predominantly occur in striatal direct pathway projecting medium spiny neurons (dMSNs). It is hypothesized that alterations in eCB neuromodulation may be involved. Recent work has implicated a role of eCB 2-arachidonoylglycerol (2-AG) in the rewarding effects of ethanol. However, there is insufficient research to answer which cellular subtype is responsible for mediating the 2-AG eCB signal that might be involved in the rewarding properties of ethanol and the mechanisms by which that occurs. To examine the role of dMSN mediated 2-AG signaling in ethanol related synaptic transmission and behaviors, we used conditional knockout mice in which the 2-AG-synthesizing enzyme diacylglycerol lipase α (DGLα) was deleted in dMSNs, DGLαD1-Cre+. Using acute brain slice photometry and a genetically encoded fluorescent eCB sensor, GRABeCB2.0, to assess real-time eCB mediated activity of sensorimotor inputs from primary motor cortices (M1/M2) to the dorsolateral striatum, we showed that DGLαD1-Cre+ mice had blunted evoked eCB-mediated presynaptic eCB signaling compared to littermate controls. Furthermore, ethanol induced eCB inhibition was significantly reduced in DGLαD1-Cre+ deficient mice. Additionally, there was a reduction in the duration of loss of righting reflex (LORR) to a high dose of ethanol in the DGLαD1-Cre+ mice compared to controls. These mice also showed a male-specific decrease in ethanol preference accompanied by an increase in ethanol-induced water consumption in a voluntary drinking paradigm. There were no significant differences observed in sucrose and quinine consumption between the genotypes. These findings reveal a novel role for dMSN mediated 2-AG signaling in modulating ethanol effects on presynaptic function and behavior.

p-Trifluoromethyl- and p-pentafluorothio-substituted curcuminoids of the 2,6-di[(E)-benzylidene)]cycloalkanone type: Syntheses and activities against Leishmania major and Toxoplasma gondii parasites

A series of the title curcuminoids with structural variance in the heteroatom of the cycloalkanone and the p-substituents of the phenyl rings were tested for their activities against Leishmania major and Toxoplasma gondii parasites. The majority of them showed high activities against both parasite forms with EC₅₀ values in the sub-micromolar concentration range. Bis(p-pentafluorothio)-substituted 3,5-di[(E)-benzylidene]piperidin-4-one 1b was not just noticeable antiparasitic, but also exhibited a considerable selectivity for L. major promastigotes over normal Vero cells. While derivatives differing only in the p-phenyl substituents being CF₃ or SF₅ showed similar antiparasitic activities, the cyclic ketone hub was more decisive both for the anti-parasitic activities and the selectivities for the parasites vs. normal cells. QSAR calculations confirmed the observed structure-activity relations and suggested structural variations for a further improvement of the antiparasitic activity. Docking studies based on DFT calculations revealed L. major pteridine reductase 1 as a likely molecular target protein of the title compounds.

Structural, QSAR, machine learning and molecular docking studies of 5-thiophen-2-yl pyrazole derivatives as potent and selective cannabinoid-1 receptor antagonists

We performed a structural study followed by theoretical analysis of the chemical descriptors and biological activity of a series of 5-thiophen-2-yl pyrazole derivatives as potent and selective cannabinoid-1 (CB1) receptor antagonists.

Alcohol Interaction with Cocaine, Methamphetamine, Opioids, Nicotine, Cannabis, and γ-Hydroxybutyric Acid

Millions of people around the world drink alcoholic beverages to cope with the stress of modern lifestyle. Although moderate alcohol drinking may have some relaxing and euphoric effects, uncontrolled drinking exacerbates the problems associated with alcohol abuse that are exploding in quantity and intensity in the United States and around the world. Recently, mixing of alcohol with other drugs of abuse (such as opioids, cocaine, methamphetamine, nicotine, cannabis, and γ-hydroxybutyric acid) and medications has become an emerging trend, exacerbating the public health concerns. Mixing of alcohol with other drugs may additively or synergistically augment the seriousness of the adverse effects such as the withdrawal symptoms, cardiovascular disorders, liver damage, reproductive abnormalities, and behavioral abnormalities. Despite the seriousness of the situation, possible mechanisms underlying the interactions is not yet understood. This has been one of the key hindrances in developing effective treatments. Therefore, the aim of this article is to review the consequences of alcohol's interaction with other drugs and decipher the underlying mechanisms.

Endocannabinoid System and Alcohol Abuse Disorders

Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the primary active component in Cannabis sativa preparations such as hashish and marijuana, signals by binding to cell surface receptors. Two types of receptors have been cloned and characterized as cannabinoid (CB) receptors. CB1 receptors (CB1R) are ubiquitously present in the central nervous system (CNS) and are present in both inhibitory interneurons and excitatory neurons at the presynaptic terminal. CB2 receptors (CB2R) are demonstrated in microglial cells, astrocytes, and several neuron subpopulations and are present in both pre- and postsynaptic terminals. The majority of studies on these receptors have been conducted in the past two and half decades after the identification of the molecular constituents of the endocannabinoid (eCB) system that started with the characterization of CB1R. Subsequently, the seminal discovery was made, which suggested that alcohol (ethanol) alters the eCB system, thus establishing the contribution of the eCB system in the motivation to consume ethanol. Several preclinical studies have provided evidence that CB1R significantly contributes to the motivational and reinforcing properties of ethanol and that the chronic consumption of ethanol alters eCB transmitters and CB1R expression in the brain nuclei associated with addiction pathways. Additionally, recent seminal studies have further established the role of the eCB system in the development of ethanol-induced developmental disorders, such as fetal alcohol spectrum disorders (FASD). These results are augmented by in vitro and ex vivo studies, showing that acute and chronic treatment with ethanol produces physiologically relevant alterations in the function of the eCB system during development and in the adult stage. This chapter provides a current and comprehensive review of the literature concerning the role of the eCB system in alcohol abuse disorders (AUD).

Loren Parsons' contribution to addiction neurobiology

Loren (Larry) H. Parsons passed away at the age of 51. In spite of his premature departure, Larry much contributed to the drug abuse field. Since his graduate studies for the Ph.D. in Chemistry in J.B. Justice lab, microdialysis is the tread that links Larry's research topics, namely, the role of dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), glutamate and endocannabinoids (eCBs) in drug reinforcement and dependence. Larry was the first to show that abstinence from chronic cocaine reduces extracellular DA in the NAc, consistent with the so called 'dopamine depletion hypothesis' of cocaine addiction. Another Larry's major contributions are the studies on 5-HT and 5-HT receptors' role in cocaine stimulant actions, which resulted in the identification of 5-HT1B receptors as a critical substrate of cocaine reinforcement. By applying mass spectrometry to eCBs analysis in brain dialysates, Larry's lab showed that ethanol, heroin, nicotine and cocaine differentially affect anandamide and 2-arachidonoylglicerol overflow in the NAc shell, a critical site of drugs of abuse DA stimulant actions. Larry also applied microdialysis to study GABA and glutamate's role in ethanol dependence and heroin reinforcement, providing in vivo evidence for a sensitization of corticotropin-releasing factor-dependent release of GABA in the central amygdala in withdrawal from chronic ethanol and for a reduction of GABA transmission in the ventral pallidum in heroin but not cocaine intravenous self-administration. Larry showed the wide possibilities of microdialysis as a general purpose methodology for monitoring neurotransmitters and neuromodulators in the brain extracellular compartment. From this viewpoint, he stands as the best advocate for microdialysis.

The endocannabinoid-alcohol crosstalk: Recent advances on a bi-faceted target

Increasing evidence has focusesed on the endocannabinoid system as a relevant player in the induction of aberrant synaptic plasticity and related addictive phenotype following chronic excessive alcohol drinking. In addition, the endocannabinoid system is implicated in the pathogenesis of alcoholic liver disease. Interestingly, whereas the involvement of CB1 receptors in alcohol rewarding properties is established, the central and peripheral action of CB2 signalling is still to be elucidated. This review aims at giving the input to deepen knowledge on the role of the endocannabinoid system, highlighting the advancing evidence that suggests that CB1 and CB2 receptors may play opposite roles in the regulation of both the reinforcing properties of alcohol in the brain and the mechanisms responsible for cell injury and inflammation in the hepatic tissue. The manipulation of the endocannabinoid system could represent a bi-faceted strategy to counteract alcohol-related dysfunction in central transmission and liver structural and functional disarrangement.

Design, Synthesis, and Biological Evaluation of Novel, Non-Brain-Penetrant, Hybrid Cannabinoid CB1R Inverse Agonist/Inducible Nitric Oxide Synthase (iNOS) Inhibitors for the Treatment of Liver Fibrosis

We report the design, synthesis, and structure-activity relationships of novel dual-target compounds with antagonist/inverse agonist activity at cannabinoid receptor type 1 (CB₁R) and inhibitory effect on inducible nitric oxide synthase (iNOS). A series of 3,4-diarylpyrazolinecarboximidamides were synthesized and evaluated in CB₁ receptor (CB₁R) binding assays and iNOS activity assays. The novel compounds, designed to have limited brain penetrance, elicited potent in vitro CB₁R antagonist activities and iNOS inhibitory activities. Some key compounds displayed high CB₁R binding affinities. Compound 7 demonstrated potent in vivo pharmacological activities such as reduction of food intake mediated by the antagonism of the CB₁Rs and antifibrotic effect in the animal models of fibrosis mediated by iNOS inhibition and CB₁R antagonism.

Effects of Δ9-tetrahydrocannabinol in individuals with a familial vulnerability to alcoholism

BACKGROUND AND AIMS

A family history (FH) of alcoholism accounts for approximately 50% of the risk of developing alcohol problems. Several lines of preclinical evidence suggest that brain cannabinoid receptor (CB1R) function may mediate the effects of alcohol and risk for developing alcoholism including the observations that reduced CB1R function decreases alcohol-related behaviors and enhanced CB1R function increases them. In this first human study, we probed CB1R function in individuals vulnerable to alcoholism with the exogenous cannabinoid Δ(9)-tetrahydrocannabinol (Δ(9)-THC).

DESIGN, SETTING, AND PARTICIPANTS

Healthy volunteers (n = 30) participated in a three test day study during which they received 0.018 and 0.036 mg/kg of Δ(9)-THC, or placebo intravenously in a randomized, counterbalanced order under double-blind conditions.

MEASUREMENTS

Primary outcome measures were subjective "high," perceptual alterations, and memory impairment. Secondary outcome measures consisted of stimulatory and depressant subjective effects, attention, spatial memory, executive function, Δ(9)-THC and 11-hydroxy-THC blood levels, and other subjective effects. FH was calculated using the Family Pattern Density method and was used as a continuous variable.

FINDINGS

Greater FH was correlated with greater "high" and perceptual alterations induced by Δ(9)-THC. This enhanced sensitivity with increasing FH was specific to Δ(9)-THC's rewarding effects and persisted even when FH was calculated using an alternate method.

CONCLUSIONS

Enhanced sensitivity to the rewarding effects of Δ(9)-THC in high-FH volunteers suggests that alterations in CB1R function might contribute to alcohol misuse vulnerability.

Effect of Acetaldehyde Intoxication and Withdrawal on NPY Expression: Focus on Endocannabinoidergic System Involvement

Acetaldehyde (ACD), the first alcohol metabolite, plays a pivotal role in the rewarding, motivational, and addictive properties of the parental compound. Many studies have investigated the role of ACD in mediating neurochemical and behavioral effects induced by alcohol administration, but very little is known about the modulation of neuropeptide systems following ACD intoxication and withdrawal. Indeed, the neuropeptide Y (NPY) system is altered during alcohol withdrawal in key regions for cerebrocortical excitability and neuroplasticity. The primary goal of this research was to investigate the effects of ACD intoxication and withdrawal by recording rat behavior and by measuring NPY immunoreactivity in hippocampus and NAcc, two brain regions mainly involved in processes which encompass neuroplasticity in alcohol dependence. Furthermore, on the basis of the involvement of endocannabinoidergic system in alcohol and ACD reinforcing effects, the role of the selective CB1 receptor antagonist AM281 in modulating NPY expression during withdrawal was assessed. Our results indicate that (i) ACD intoxication induced a reduction in NPY expression in hippocampus and NAcc; (ii) symptoms of physical dependence, similar to alcohol's, were scored at 12 h from the last administration of ACD; and (iii) NPY levels increased in early and prolonged acute withdrawal in both brain regions examined. The administration of AM281 was able to blunt signs of ACD-induced physical dependence, to modulate NPY levels, and to further increase NPY expression during ACD withdrawal both in hippocampus and NAcc. In conclusion, the present study shows that complex plastic changes take place in NPY system during ACD intoxication and subsequent withdrawal in rat hippocampal formation and NAcc. The pharmacological inhibition of CB1 signaling could counteract the neurochemical imbalance associated with ACD, and alcohol withdrawal, likely boosting the setting up of homeostatic functional recovery.

Dorsal hippocampal cannabinoid CB1 receptors mediate the interactive effects of nicotine and ethanol on passive avoidance learning in mice

The present study evaluated the involvement of the dorsal hippocampal cannabinoid CB1 receptors in the combined effect of ethanol and nicotine on passive avoidance learning in adult male mice. The results indicated that pre-training administration of ethanol (1 g/kg, i.p.) impaired memory retrieval. Pre-test administration of ethanol (0.5 and 1 g/kg, i.p.) or nicotine (0.5 and 0.7 mg/kg, s.c.) significantly reversed ethanol-induced amnesia, suggesting a functional interaction between ethanol and nicotine. Pre-test microinjection of a selective CB1 receptor agonist, ACPA (3 and 5 ng/mouse), plus an ineffective dose of ethanol (0.25 g/kg) or nicotine (0.3 mg/kg) improved memory retrieval, while ACPA by itself could not reverse ethanol-induced amnesia. Pre-test intra-CA1 microinjection of a selective CB1 receptor antagonist, AM251 (0.5-2 ng/mouse), did not lead to a significant change in ethanol-induced amnesia. However, pre-test intra-CA1 microinjection of AM251 prevented the ethanol (1 g/kg) or nicotine (0.7 mg/kg) response on ethanol-induced amnesia. In order to support the involvement of the dorsal hippocampal CB1 receptors in nicotine response, the scheduled mixed treatments of AM251 (0.1-1 ng/mouse), ACPA (5 ng/mouse) and nicotine (0.3 mg/kg) were used. The results indicated that AM251 reversed the response of ACPA to the interactive effects of nicotine and ethanol in passive avoidance learning. Furthermore, pre-test intra-CA1 microinjection of the same doses of ACPA or AM251 had no effect on memory retrieval. These findings show that the cannabinoid CB1 receptors of dorsal hippocampus are important in the combined effect of ethanol and nicotine on passive avoidance learning.

Endocannabinoid system: A newer molecular target for the treatment of alcohol-related behaviors

The cannabinoid (CB) receptors, endocannabinoids (eCB) and their synthesizing and catabolizing enzymes and the proteins involved in their transport, constitute what is now recognized as the eCB system. The eCBs are a class of lipids that have been identified as retrograde messengers and produce their effects via presynaptic CB receptors. The major function of the eCBs has been suggested to be that of modulating the release of several neurotransmitters implicated in a number of biological functions that include reward and reinforcement. There is now significant evidence to suggest that the eCB system plays an important role in the development of alcohol tolerance, dependence and relapse. Recent studies suggest that the pharmacological manipulation of the eCB system has the potential not only to block the direct reinforcing properties of alcohol but also alleviate behavioral abnormalities associated with relapse. There is also accumulating evidence that points to the possible utility of the eCB system targeted drugs in the treatment of alcoholism-related behavioral disorders. The agents that block CB1 receptor function or inhibit the synthesis of eCBs are attractive candidate drugs that need to be explored. Further understanding of the role of the eCB system in molecular mechanism/s that underlies alcoholism-related behaviors should lead to a better treatment of this devastating disorder.

A review of the interactions between alcohol and the endocannabinoid system: implications for alcohol dependence and future directions for research

Over the past fifty years a significant body of evidence has been compiled suggesting an interaction between the endocannabinoid (EC) system and alcohol dependence. However, much of this work has been conducted only in the past two decades following the elucidation of the molecular constituents of the EC system that began with the serendipitous discovery of the cannabinoid 1 receptor (CB1). Since then, novel pharmacological and genetic tools have enabled researchers to manipulate select components of the EC system, to determine their contribution to the motivation to consume ethanol. From these preclinical studies, it is evident that CB1 contributes the motivational and reinforcing properties of ethanol, and chronic consumption of ethanol alters EC transmitter levels and CB1 expression in brain nuclei associated with addiction pathways. These results are augmented by in vitro and ex vivo studies showing that acute and chronic treatment with ethanol produces physiologically relevant alterations in the function of the EC system. This report provides a current and comprehensive review of the literature regarding the interactions between ethanol and the EC system. We begin be reviewing the studies published prior to the discovery of the EC system that compared the behavioral and physiological effects of cannabinoids with ethanol in addition to cross-tolerance between these drugs. Next, a brief overview of the molecular constituents of the EC system is provided as context for the subsequent review of more recent studies examining the interaction of ethanol with the EC system. These results are compiled into a summary providing a scheme for the known changes to the components of the EC system in different stages of alcohol dependence. Finally, future directions for research are discussed.

Innate difference in the endocannabinoid signaling and its modulation by alcohol consumption in alcohol-preferring sP rats

The present study was undertaken to examine whether genetically predetermined differences in components of the endocannabinoid system were present in the brain of Sardinian alcohol-preferring (sP) and Sardinian alcohol-non-preferring (sNP) rats, a pair of rat lines selectively bred for opposite alcohol preference. The effects of acquisition and maintenance of alcohol drinking, alcohol withdrawal, and alcohol re-exposure on the endocannabinoid system was also assessed in the striatum of sP rats. The findings revealed significantly higher density of the CB1 receptors and levels of CB1 receptor mRNA, CB1 receptor-mediated G-protein coupling, and endocannabinoids in the cerebral cortex, hippocampus and striatum of alcohol-naive sP rats than sNP rats. A significantly lower expression of mFAAH enzyme was evident in the hippocampus of alcohol-naive sP rats. Alcohol drinking (during both acquisition and maintenance phases) in sP rats resulted in a significant reduction in striatal CB1 receptor-mediated G-protein coupling whereas alcohol withdrawal attenuated this effect. Alcohol consumption was also associated with markedly increased levels of endocannabinoids in the striatum. Co-administration of the CB1 receptor antagonist, rimonabant (SR141716A) reduced alcohol intake, and reversed alcohol-induced changes in CB1 receptor-mediated G-protein activation. These findings provided a new insight into a potential genetic basis of excessive alcohol consumption, suggesting innate differences in the endocannabinoid system might be associated with higher alcohol preference in sP rats. The data also indicate a modulation of CB1 receptor-mediated signaling following alcohol consumption, and further strengthen the potential of the endocannabinoid system as a target for the treatment of alcohol related behaviors.

Critical thoughts on current rodent models for evaluating potential treatments of alcohol addiction and withdrawal

Despite years of neurobiological research that have helped to identify potential therapeutic targets, we do not have a reliable pharmacological treatment for alcoholism. There are a range of possible explanations for this failure, including arguments that alcoholism is a spectrum disorder and that different population subtypes may respond to different treatments. This view is supported by categorisations such as early- and late-onset alcoholism, whilst multifactorial genetic factors may also alter responsivity to pharmacological agents. Furthermore, experience of alcohol withdrawal may play a role in future drinking in a way that may distinguish alcoholism from other forms of addiction. Additionally, our neurobiological models, based largely upon results from rodent studies, may not mimic specific aspects of the human condition and may reflect different underlying phenomena and biological processes from the clinical pattern. As a result, potential treatments may be targeting inappropriate aspects of alcohol-related behaviours. Instead, we suggest a more profitable approach is (a) to identify well-defined intermediate behavioural phenotypes in human experimental models that reflect defined aspects of the human clinical disorder and (b) to develop animal models that are homologous with those phenotypes in terms of psychological processes and underlying neurobiological mechanisms. This review describes an array of animal models currently used in the addiction field and what they tell us about alcoholism. We will then examine how established pharmacological agents have been developed using only a limited number of these models, before describing some alternative novel approaches to achieving homology between animal and human experimental measures.

Structure-activity relationship studies of novel pyrazole and imidazole carboxamides as cannabinoid-1 (CB1) antagonists

The synthesis and biological evaluation of novel pyrazole and imidazole carboxamides as CB1 antagonists are described. As a part of eastern amide SAR, various chemically diverse motifs were introduced on rimonabant template. The central pyrazole core was also replaced with its conformationally constrained motif and imidazole moieties. In general, a range of modifications were well tolerated. Several molecules with low- and sub-nanomolar potencies were identified as potent CB1 receptor antagonists. The in vivo proof of principle for weight loss is demonstrated with a lead compound in DIO mice model.

Novel pyrazole-3-carboxamide derivatives as cannabinoid-1 (CB1) antagonists: journey from non-polar to polar amides

The synthesis and biological evaluation of novel pyrazole-3-carboxamide derivatives as CB1 antagonists are described. As a part of eastern amide SAR, various chemically diverse motifs were introduced. In general, a range of modifications were well tolerated. Several molecules with high polar surface area were also identified as potent CB1 receptor antagonists. The in vivo proof of principle for weight loss is exemplified with a lead compound from this series.

CB1 receptors regulate alcohol-seeking behavior and alcohol self-administration of alcohol-preferring (P) rats

RATIONALE

The endogenous cannabinoid (CB) system mediates a number of behaviors associated with drug-seeking and drug self-administration. In this study the effects of CB1 receptor manipulations on operant ethanol (EtOH) responding during EtOH-seeking, EtOH-relapse as well as on-going EtOH self-administration were determined.

METHODS

Alcohol-preferring (P) rats were trained in 2-lever operant chambers to self-administer 15% EtOH (v/v) and water on a concurrent fixed-ratio 5-fixed-ratio 1 (FR5-FR1) schedule of reinforcement in daily 1-h sessions. After 10 weeks, rats underwent 7 extinction sessions, followed by 2 weeks in their home cages without access to EtOH or operant chambers. Rats were then returned to the operant chambers for testing of EtOH-seeking behavior (no EtOH present) for 4 sessions. After a week in their home cages following the EtOH-seeking test, rats were returned to the operant chambers with access to EtOH and water (relapse). Rats were then maintained in the operant chambers for daily 1-h sessions with access to 15% EtOH and water for several weeks.

RESULTS

The CB1 receptor antagonist (SR141716A), at doses of 1 and 2 mg/kg, i.p. reduced EtOH-seeking and transiently reduced EtOH self-administration during relapse and maintenance. Conversely, treatment with the CB1 receptor agonist CP 55, 940, at doses of 1 and 10 μg/kg i.p., increased EtOH-seeking and EtOH self-administration during relapse.

CONCLUSIONS

The results of this study demonstrate that activation of CB1 receptors are involved in regulating EtOH-seeking as well as the reinforcing effects of EtOH under relapse and on-going self-administration conditions.

Binding of the hemopressin peptide to the cannabinoid CB1 receptor: structural insights

Hemopressin, a bioactive nonapeptide derived from the α1 chain of hemoglobin, was recently shown to possess selective antagonist activity at the cannabinoid CB(1) receptor [Heimann, A. S., et al. (2007) Proc. Natl. Acad. Sci. U.S.A. 104, 20588-20593]. CB(1) receptor antagonists have been extensively studied for their possible therapeutic use in the treatment of obesity, drug abuse, and heroin addiction. In particular, many compounds acting as CB(1) receptor antagonists have been synthesized and subjected to experiments as possible anti-obesity drugs, but their therapeutic application is still complicated by important side effects. Using circular dichroism and nuclear magnetic resonance spectroscopy, this work reports the conformational analysis of hemopressin and its truncated, biologically active fragment hemopressin(1-6). The binding modes of both hemopressin and hemopressin(1-6) are investigated by molecular docking calculations. Our conformational data indicate that regular turn structures in the central portion of hemopressin and hemopressin(1-6) are critical for an effective interaction with the receptor. The results of molecular docking calculations, indicating similarities and differences in comparison to the most accepted CB(1) pharmacophore model, suggest the possibility of new chemical scaffolds for the design of new CB(1) antagonist lead compounds.

Modulation of NMDA and AMPA-mediated synaptic transmission by CB1 receptors in frontal cortical pyramidal cells

Although the endogenous cannabinoid system modulates a variety of physiological and pharmacological processes, the specific role of cannabinoid CB1 receptors in the modulation of glutamatergic neurotransmission and neural plasticity is not well understood. Using whole-cell patch clamp recording techniques, evoked or spontaneous excitatory postsynaptic currents (eEPSCs or sEPSCs) were recorded from visualized, layer II/III pyramidal cells in frontal cortical slices from rat brain. Bath application of the CB1 receptor agonist, WIN 55212-2 (WIN), reduced the amplitude of NMDA receptor-mediated EPSCs in a concentration-dependent manner. When co-applied with the specific CB1 antagonists, AM251 or AM281, WIN did not suppress NMDA receptor-mediated EPSCs. WIN also reduced the amplitude of evoked AMPA receptor-mediated EPSCs, an effect that was also reversed by AM251. Both the frequency and amplitude of spontaneous AMPA receptor-mediated EPSCs were significantly reduced by WIN. In contrast, WIN reduced the frequency, but not the amplitude of miniature EPSCs, suggesting that the suppression of glutamatergic activity by CB1 receptors in the frontal neocortex is mediated by a presynaptic mechanism. Taken together, these data indicate a critical role for endocannabinoid signaling in the regulation of excitatory synaptic transmission in frontal neocortex, and suggest a possible neuronal mechanism whereby THC regulates cortical function.

PKCepsilon regulates behavioral sensitivity, binding and tolerance to the CB1 receptor agonist WIN55,212-2

The cannabinoid CB1 receptor (CB1) is one of the most abundant G protein-coupled receptors in the brain, but little is known about the mechanisms that modulate CB1 receptor signaling. Here, we show that inhibition or null mutation of the epsilon isozyme of protein kinase C (PKCepsilon) selectively enhances behavioral responses to the CB1 agonist WIN55,212-2 in mice, but not to the structurally unrelated CB1 agonist CP55,940. Binding affinity for [(3)H] WIN55,212-2 was increased in brain membranes from PKCepsilon(-/-) mice compared with PKCepsilon(+/+) mice. There was no difference in binding of the inverse agonist [(3)H] SR141716A. In addition, repeated administration of WIN55,212-2 produced greater analgesic and thermal tolerance in PKCvarepsilon(-/-) mice compared with PKCepsilon(+/+)mice. These results indicate that PKCvarepsilon selectively regulates behavioral sensitivity, CB1 receptor binding and tolerance to WIN55,212-2.

Electrophysiological properties of dopamine neurons in the ventral tegmental area of Sardinian alcohol-preferring rats

RATIONALE

Sardinian alcohol-preferring (sP) or -nonpreferring (sNP) rats are one of the few pairs of lines of rats selectively bred for their voluntary alcohol preference or aversion, respectively. Ventral tegmental area (VTA) dopamine (DA) neurons have long been implicated in many drug-related behaviors, including alcohol self-administration. However, the electrophysiological properties of these cells in sP and sNP rats remain unknown.

OBJECTIVES

This study was designed to examine the properties of posterior VTA DA neurons and to unveil functional differences between sP and sNP rats.

MATERIALS AND METHODS

The electrophysiological properties of DA cells were examined performing either single-cell extracellular recordings in anesthetized rats or whole-cell patch-clamp recordings in slices.

RESULTS

Extracellular single-unit recordings revealed an increased spontaneous activity in sP rats. However, a corresponding difference was not found in vitro. Moreover, DA cells of sP and sNP rats showed similar intrinsic properties, suggesting changes at synaptic level. Therefore, inhibitory- and excitatory-mediated currents were studied. A decreased probability of GABA release was found in sP rats. Additionally, sP rats showed a reduced depolarization-induced suppression of inhibition, which is an endocannabinoid-mediated form of short-term plasticity. Additionally, the effect of cannabinoid-type 1 (CB1) receptor agonist WIN55,212-2 on GABAA IPSCs was smaller in sP rats, suggesting either a reduced number or functionality of CB1 receptors in the VTA.

CONCLUSIONS

Our findings suggest that both decreased GABA release and endocannabinoid transmission in the VTA play a role in the increased impulse activity of DA cells and, ultimately, in alcohol preference displayed by sP rats.

Effects of a short-term exposure to alcohol in rats on FAAH enzyme and CB1 receptor in different brain areas

Acute alcohol exposure in rats (8% ethanol in the liquid diet for a period of 24 h) is associated with a decrease in the levels of endocannabinoids (anandamide and 2-arachidonoyl-glycerol) as well as in various N-acylethanolamines, in different brain regions. In the present study, we wanted to further explore: (i) whether these decreases might be caused by an increase in fatty acid amide hydrolase (FAAH), the enzyme involved in the degradation of N-acylethanolamines including anandamide, and (ii) whether the changes in endocannabinoid levels are accompanied by parallel changes in the major cannabinoid receptor type, the CB(1) receptor, activated by these ligands in the brain. Our data proved that FAAH activity did not increase in any of the four regions analyzed, even it was reduced in the hypothalamus and the prefrontal cortex. Paradoxically, FAAH levels increased in the hypothalamus and, to a lesser extent, in the prefrontal cortex and the amygdala, but not in the caudate-putamen. By contrast, the levels of CB(1) receptors were markedly reduced in the amygdala and prefrontal cortex of these rats, although no changes were seen in the hypothalamus and the caudate-putamen. These results suggest that reductions in the levels of endocannabinoids and related N-acylethanolamines caused by acute alcohol exposure are not originated by an enhanced degradation by FAAH enzyme, but they are associated with low levels of the receptors activated by these ligands, although this parallelism did not occur in all brain regions analyzed. In any case, these observations would support the notion of a general reduction in the activity of the cannabinoid signaling system by acute alcohol exposure.

[Neuropsychopharmacology of delta-9-tetrahydrocannabinol]

Today, the main route of introduction of tetrahydrocannabinol (THC), the main active substance of cannabis, into the human body is via the lungs, from smokes produced by combustion of a haschich-tobacco mixture. The use of a water pipe (nargileh-like) intensifies its fast supply to the body. THC reaches the brain easily where it stimulates CB1 receptors; their ubiquity underlies a wide variety of effects. THC disappears from extracellular spaces by dissolving in lipid rich membranes, and not by excretion from the body. This is followed by a slow release, leading to long lasting effects originating from brain areas containing a large proportion of spare receptors ("reserve receptors"). Far from mimicking the effects of endocannabinoids, THC caricatures and disturbs them. It induces both psychical and physical dependencies, but the perception of withdrawal is weak on account of its very slow elimination. THC disturbs cognition. Acutely, it develops anxiolytic- and antidepressant-like effects, which causes a lot of users to abuse THC, thus leading to a tolerance (desensitization of CB1 receptors) making anxiety and depression to reappear more intensely than originally. THC has close relationships with schizophrenia. It incites to tobacco, alcohol and heroine abuses.

Cannabinoid CB1 receptor antagonists in therapeutic and structural perspectives

The observed antiobesity effect of rimonabant (1) in a pharmacological rodent model 10 years ago has led to a surge in the search for novel cannabinoid CB1 antagonists as a new therapeutic target for the treatment of obesity. Rimonabant showed clinical efficacy in the treatment of obesity and also improved cardiovascular and metabolic risk factors. Cannabinoid CB1 receptor antagonists have also good prospects in other therapeutic areas, including smoking and alcohol addiction as well as cognitive impairment. Solvay's research achievements in this fast-moving field are reported in relation with the current state of the art. Several medicinal chemistry strategies have been pursued. The application of the concept of conformational constraint led to the discovery of more rigid analogs of the prototypic CB1 receptor antagonist rimonabant. Replacement of the central heterocyclic pyrazole ring in rimonabant yielded imidazoles, triazoles, and thiazoles as selective CB1 receptor antagonists. Dedicated medium-throughput screening efforts delivered one 3,4-diarylpyrazoline hit. Its poor pharmacokinetic properties were successfully optimized which led to the discovery of orally active and highly CB1/CB2 receptor selective analogs in this series. Regioisomeric 1,5-diarylpyrazolines, 1,2-diarylimidazolines, and water-soluble imidazoles have been designed as novel CB1 receptor antagonist structure classes.

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

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

Endocannabinoid system involvement in brain reward processes related to drug abuse

Cannabis is the most commonly abused illegal drug in the world and its main psychoactive ingredient, delta-9-tetrahydrocannabinol (THC), produces rewarding effects in humans and non-human primates. Over the last several decades, an endogenous system comprised of cannabinoid receptors, endogenous ligands for these receptors and enzymes responsible for the synthesis and degradation of these endogenous cannabinoid ligands has been discovered and partly characterized. Experimental findings strongly suggest a major involvement of the endocannabinoid system in general brain reward functions and drug abuse. First, natural and synthetic cannabinoids and endocannabinoids can produce rewarding effects in humans and laboratory animals. Second, activation or blockade of the endogenous cannabinoid system has been shown to modulate the rewarding effects of non-cannabinoid psychoactive drugs. Third, most abused drugs alter brain levels of endocannabinoids in the brain. In addition to reward functions, the endocannabinoid cannabinoid system appears to be involved in the ability of drugs and drug-related cues to reinstate drug-seeking behavior in animal models of relapse. Altogether, evidence points to the endocannadinoid system as a promising target for the development of medications for the treatment of drug abuse.

Short-term exposure to alcohol in rats affects brain levels of anandamide, other N-acylethanolamines and 2-arachidonoyl-glycerol

Chronic alcohol exposure leads to significant changes in the levels of endocannabinoids and their receptors in the brains of humans and laboratory animals, as well as in cultured neuronal cells. However, little is known about the effects of short-term periods of alcohol exposure. In the present study, we examined the changes in endocannabinoid levels (anandamide and 2-arachidonoylglycerol), as well as four additional N-acylethanolamines, in four brain regions of rats exposed to alcohol through the liquid diet for a period of 24h. The levels of N-acylethanolamines were diminished 24h after the onset of alcohol exposure. This was particularly evident for anandamide in the hypothalamus, amygdala and caudate-putamen, for N-palmitoylethanolamine in the caudate-putamen, for N-oleoylethanolamine in the hypothalamus, caudate-putamen and prefrontal cortex, and for N-stearoylethanolamine in the amygdala. The only exception was N-linoleoylethanolamine for which the levels increased in the amygdala after the exposure to alcohol. The levels of the other major endocannabinoid, 2-arachidonoylglycerol, were also reduced with marked effects in the prefrontal cortex. These results support the notion that short-term alcohol exposure reduces endocannabinoid levels in the brain accompanied by a reduction in several related N-acylethanolamines.

Regulation of brain anandamide by acute administration of ethanol

The endogenous cannabinoid acylethanolamide AEA (arachidonoylethanolamide; also known as anandamide) participates in the neuroadaptations associated with chronic ethanol exposure. However, no studies have described the acute actions of ethanol on AEA production and degradation. In the present study, we investigated the time course of the effects of the intraperitoneal administration of ethanol (4 g/kg of body mass) on the endogenous levels of AEA in central and peripheral tissues. Acute ethanol administration decreased AEA in the cerebellum, the hippocampus and the nucleus accumbens of the ventral striatum, as well as in plasma and adipose tissue. Parallel decreases of a second acylethanolamide, PEA (palmitoylethanolamide), were observed in the brain. Effects were observed 45-90 min after ethanol administration. In vivo studies revealed that AEA decreases were associated with a remarkable inhibition of the release of both anandamide and glutamate in the nucleus accumbens. There were no changes in the expression and enzymatic activity of the main enzyme that degrades AEA, the fatty acid amidohydrolase. Acute ethanol administration did not change either the activity of N-acyltransferase, the enzyme that catalyses the synthesis of the AEA precursor, or the expression of NAPE-PLD (N-acylphosphatidylethanolamine-hydrolysing phospholipase D), the enzyme that releases AEA from membrane phospholipid precursors. These results suggest that receptor-mediated release of acylethanolamide is inhibited by the acute administration of ethanol, and that this effect is not derived from increased fatty acid ethanolamide degradation.

The lack of CB1 receptors prevents neuroadapatations of both NMDA and GABA(A) receptors after chronic ethanol exposure

As the contribution of cannabinoid (CB1) receptors in the neuroadaptations following chronic alcohol exposure is unknown, we investigated the neuroadaptations induced by chronic alcohol exposure on both NMDA and GABA(A) receptors in CB1-/- mice. Our results show that basal levels of hippocampal [(3)H]MK-801 ((1)-5-methyl-10,11-dihydro-5Hdibenzo[a,d]cyclohepten-5,10-imine) binding sites were decreased in CB1-/- mice and that these mice were also less sensitive to the locomotor effects of MK-801. Basal level of both hippocampal and cerebellar [(3)H]muscimol binding was lower and sensitivity to the hypothermic effects of diazepam and pentobarbital was increased in CB1-/- mice. GABA(A)alpha1, beta2, and gamma2 and NMDA receptor (NR) 1 and 2B subunit mRNA levels were altered in striatum of CB1-/- mice. Our results also showed that [(3)H]MK-801 binding sites were increased in cerebral cortex and hippocampus after chronic ethanol ingestion only in wild-type mice. Chronic ethanol ingestion did not modify the sensitivity to the locomotor effects of MK-801 in both genotypes. Similarly, chronic ethanol ingestion reduced the number of [(3)H]muscimol binding sites in cerebral cortex, but not in cerebellum, only in CB1+/+ mice. We conclude that lifelong deletion of CB1 receptors impairs neuroadaptations of both NMDA and GABA(A) receptors after chronic ethanol exposure and that the endocannabinoid/CB1 receptor system is involved in alcohol dependence.

The alcohol-preferring AA and alcohol-avoiding ANA rats: neurobiology of the regulation of alcohol drinking

The AA (alko, alcohol) and ANA (alko, non-alcohol) rat lines were among the earliest rodent lines produced by bidirectional selection for ethanol preference. The purpose of this review is to highlight the strategies for understanding the neurobiological factors underlying differential alcohol-drinking behavior in these lines. Most early work evaluated functioning of the major neurotransmitter systems implicated in drug reward in the lines. No consistent line differences were found in the dopaminergic system either under baseline conditions or after ethanol challenges. However, increased opioidergic tone in the ventral striatum and a deficiency in endocannabinoid signaling in the prefrontal cortex of AA rats may comprise mechanisms leading to increased ethanol consumption. Because complex behaviors, such as ethanol drinking, are not likely to be controlled by single factors, system-oriented molecular-profiling strategies have been used recently. Microarray based expression analysis of AA and ANA brains and novel data-mining strategies provide a system biological view that allows us to formulate a hypothesis on the mechanism underlying selection for ethanol preference. Two main factors appear active in the selection: a recruitment of signal transduction networks, including mitogen-activated protein kinases and calcium pathways and involving transcription factors such as Creb, Myc and Max, to mediate ethanol reinforcement and plasticity. The second factor acts on the mitochondrion and most likely provides metabolic flexibility for alternative substrate utilization in the presence of low amounts of ethanol.

Increased ethanol consumption and preference and decreased ethanol sensitivity in female FAAH knockout mice

Previous studies have shown that mice lacking cannabinoid (CB1) receptor gene consume markedly reduced levels of ethanol. Mice lacking the enzyme fatty acid amidohydrolase (FAAH) are severely impaired in their ability to degrade anandamide (AEA) and therefore represent a unique animal model in which to examine the function of AEA in vivo on ethanol-drinking behavior. In the current study, FAAH(-/-) mice were tested for ethanol, saccharin or quinine consumption and preference. Ethanol-induced hypothermia, and sleep time were used to evaluate the sensitivity to acute effects of ethanol. Ethanol intake and preference were increased only in female FAAH(-/-) mice. No significant difference in saccharin or quinine consumption or preference was observed between genotypes. Female FAAH(-/-) mice were less sensitive to the hypothermic and sedative/hypnotic effects of acute ethanol. Supersensitivity to exogenous AEA was noted in both male and female FAAH(-/-) mice. Following voluntary ethanol consumption, CB1 receptor levels and function were down-regulated in male FAAH(+/+), FAAH(-/-), and female FAAH(+/+) mice but not in female FAAH(-/-) mice. Our results suggest that absence of an effect in male mice indicates a sex-linked mechanism that is secondary (or modulatory) to FAAH function. Thus, the data suggest that FAAH may be indirectly related to ethanol intake and sensitivity and central endocannabinoidergic-mediated pathways may regulate ethanol consumption.

Tricyclic pyrazoles. 3. Synthesis, biological evaluation, and molecular modeling of analogues of the cannabinoid antagonist 8-chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide

A series of analogues of 8-chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide 4a (NESS 0327) (Ruiu, S.; Pinna, G. A.; Marchese, G.; Mussinu, J. M.; Saba, P.; Tambaro, S.; Casti, P.; Vargiu, R.; Pani, L. Synthesis and Characterization of NESS 0327: A Novel Putative Antagonist of CB1 Cannabinoid Receptor. J. Pharmacol. Exp. Ther. 2003, 306, 363-370) was synthesized and evaluated for their affinity to cannabinoid receptors. Depending on the chemical modification of the lead structure that was chosen, compounds 4b, 4c, 4i, 4l, and 4m still proved to be potent binders of the CB1 receptor. Moreover, several analogues (4c, 4d, 4e, and 4m) demonstrated superior CB2 receptor binding affinities compared to the parent ligand. Compounds 4b, 4c, 4i, and 4l displayed the most promising pharmacological profiles, having the highest selectivity for CB1 receptors with Ki(CB2) to Ki(CB1) ratios of 11,250, 2000, 3330 and 4625, respectively. Compound 4c increased the intestinal propulsion in mice and antagonized the effect induced by the CB1 receptor agonist WIN 55,212-2. Finally, molecular modeling studies were carried out on a set of tricyclic pyrazoles (2a-4a) and on rimonabant 1 (SR141716A), indicating that high CB1 receptors affinities were consistent for the tricyclic derivatives, both with a nonplanar geometry of the tricyclic cores and with a precise orientation of the substituent (chlorine) on this ring system.

Pharmacological manipulation of CB1 receptor function alters development of tolerance to alcohol

AIMS

The current study investigated the efficacy of CB1 receptor-targeted drugs on the development and expression of tolerance to alcohol (EtOH).

METHODS

An EtOH-inhalation model was used to induce tolerance, as measured by EtOH-induced sedation and hypothermia after a 24 h withdrawal period. Two drug treatment procedures, (i) co-treatment with EtOH and (ii) acute drug administration following chronic EtOH treatment, were used to test the efficacy of CB1 receptor manipulations on EtOH tolerance.

RESULTS

The effects of the CB1 receptor agonist CP-55,940 varied depending on paradigm and behavioural measure. Chronic CP-55,940 co-treatment blocked tolerance to EtOH-induced hypothermia but not to the sedative effect (sleep time) in EtOH-exposed mice. However, chronic CP-55,940 administration alone resulted in tolerance to the sedative effect of a challenge dose of EtOH in control mice. Acute CP-55,940 administration after chronic alcoholization blocked the development of tolerance to EtOH-induced sedation compared to the EtOH alone exposed group, but induced tolerance to the hypothermic effects of EtOH in control mice. Chronic blockade of CB1 receptor function by SR141716A resulted in tolerance to both the sedative and hypothermic effects of EtOH in control mice, but had no effect on EtOH-exposed mice.

CONCLUSIONS

The data support a role for the endocannabinoid (EC) system in EtOH tolerance/dependence and suggest that drugs targeted against EC system could be therapeutically useful in treating alcohol-related disorders.

Development of medications for alcohol use disorders: recent advances and ongoing challenges

During the past decade, efforts to develop medications for alcoholism have burgeoned. Three agents, disulfiram, naltrexone and acamprosate, are now approved in a large number of countries. Although many patients have benefited from existing medications, their effects are moderate, and some alcoholics fail to respond to them. A host of new agents are currently under active investigation. Critical barriers must be overcome to ensure that future efforts in the development of medications for alcohol use disorders reach full fruition. These challenges include: establishing key targets for drug discovery; validating animal and human screening models; and developing biomarkers to help predict treatment success. In addition, it is important to formulate methodological and statistical strategies to efficiently conduct alcohol pharmacotherapy trials; to specify genetic and phenotypic patient characteristics associated with efficacy and safety for lead compounds; to forge productive alliances among governmental agencies, the pharmaceutical industry and academic researchers to further drug development; and, ultimately and perhaps most difficult, to engage the practitioner community to incorporate medications into the alcohol treatment process.

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.

Cannabinoid CB1 receptor antagonism reduces conditioned reinstatement of ethanol-seeking behavior in rats

The endocannabinoid system is involved in a variety of effects of drugs of misuse, and blockade of the cannabinoid CB1 receptor by selective antagonists elicits marked reductions in opioid and alcohol self-administration. The present study was designed to extend our knowledge of the role of the cannabinoid CB1 receptor in the modulation of alcohol misuse vulnerability in rats. Accordingly, using nonselected Wistar rats and genetically selected Marchigian Sardinian alcohol-preferring (msP) rats, we investigated the effect of the CB1 antagonist SR141716A on operant alcohol self-administration and on reinstatement of alcohol-seeking behavior by environmental conditioning factors. In addition, in situ hybridization studies in both strains were performed to measure cannabinoid CB1 receptor mRNA in different brain areas of these animals. Results showed that intraperitoneal administration of SR141716A (0.03, 1.0 and 3.0 mg/kg) markedly inhibits ethanol self-administration and conditioned reinstatement of ethanol-seeking behavior in both strains of rats. ED50 analysis showed significantly higher sensitivity (P < 0.05) to the effect of SR141716A in msP rats than in heterogeneous Wistar rats. In situ hybridization studies revealed that, compared with Wistar rats, msP animals have consistently greater cannabinoid CB1 receptor mRNA expression in a number of brain areas, including the frontoparietal cortex, caudate-putamen and hippocampus (CA1 and dentate gyrus areas). In conclusion, we provide clear evidence that blockade of CB1 receptors reduces both ethanol self-administration and conditioned reinstatement of alcohol-seeking behavior in rats. In addition, current pharmacological and neuroanatomical data suggest that an altered function of the CB1 receptor system exists between genetically selected alcohol-preferring msP rats and a heterogeneous animal population.

Elevated levels of endocannabinoids and CB1 receptor-mediated G-protein signaling in the prefrontal cortex of alcoholic suicide victims

BACKGROUND

Alcoholism is often comorbid with mood disorders and suicide. We recently reported an upregulation of CB(1) receptor-mediated signaling in the dorsolateral prefrontal cortex (DLPFC) of subjects with major depression who died by suicide. In the present study, we sought to determine whether the changes in depressed suicides would also be present in alcoholic suicides and whether the endocannabinoid (EC) system plays a role in suicide in alcoholism.

METHODS

The density of CB(1) receptor and its mediated [(35)S]GTP gamma S signaling were measured in the DLPFC of alcoholic suicides (AS) (n = 11) and chronic alcoholics (CA) (n = 11). The levels of ECs were measured by a liquid chromatograph/mass spectrometry.

RESULTS

The CB(1) receptor density was higher in AS compared with the CA group in the DLPFC. Western blot analysis confirmed a greater immunoreactivity of the CB(1) receptor in AS. The CB(1) receptor-mediated [(35)S]GTP gamma S binding indicated a greater signaling in AS. Higher levels of N-arachidonyl ethanolamide and 2-arachidonylglycerol were observed in the DLPFC of AS.

CONCLUSIONS

The elevated levels of ECs, CB(1) receptors, and CB(1) receptor-mediated [(35)S]GTP gamma S binding strongly suggest a hyperactivity of endocannabinoidergic signaling in AS. EC system may be a novel therapeutic target for the treatment of suicidal behavior.

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.

CB1 receptor knockout mice display reduced ethanol-induced conditioned place preference and increased striatal dopamine D2 receptors

Cannabinoids and ethanol activate the same reward pathways, and recent advances in the understanding of the neurobiological basis of alcoholism suggest that the CB1 receptor system may play a key role in the reinforcing effects of ethanol and in modulating ethanol intake. In the present study, male CB1 receptors knockout mice generated on a CD1 background displayed decreased ethanol-induced conditioned place preference (CPP) compared to wild-type (CB1(+/+)) mice. Ethanol (0.5, 1.0, 1.5, and 2.0 g/kg) induced significant CPP in CB1(+/+) mice at all doses tested, whereas it induced significant CPP only at the highest dose of ethanol (2.0 g/kg) in CB1(-/-) mice. However, there was no genotypic difference in cocaine (20 mg/kg)-induced CPP. There was also no genotypic difference, neither in cocaine (10-50 mg/kg) nor in D-amphetamine (1.2-5 mg/kg)-induced locomotor effects. In addition, mutant and wild-type mice did not differ in sensitivity to the anxiolytic effects of ethanol (1.5 g/kg) when tested using the elevated plus maze. Interestingly, this decrease in ethanol efficacy to induce CPP in CB1(-/-) mice was correlated with an increase in D2/D3 receptors, as determined by [3H]raclopride binding, whereas there was no difference in D1-like receptors, as determined by [3H]SCH23390 binding, measured in the striatum from drug-naive mice. This increase in D2/D3 binding sites observed in CB1 knockout mice was associated with an altered locomotor response to the D2/D3 agonist quinpirole (low doses 0.02-0.1 mg/kg) but not to an alteration of quinpirole (0.1-1.0 mg/kg)-induced CPP compared to wild-type mice. Altogether, the present results indicate that lifelong deletion of CB1 receptors reduced ethanol-induced CPP and that these reduced rewarding effects of ethanol are correlated to an overexpression of striatal dopamine D2 receptors.

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

OBJECTIVE

To examine the discriminative stimulus effects of (i) the cannabinoid CB(1) receptor antagonist SR-141716 (SR, 5.6 mg/kg) and vehicle, and (ii) the cannabinoid receptor agonist Delta(9)-THC (THC, 1.8 mg/kg) and vehicle using a discriminated taste aversion (DTA) procedure.

METHODS

Two groups of rats ( n=6) were trained to discriminate between these drugs and vehicle in DTA ( t'=20 min). The 30-min drinking bout of tap water following drug (SR or THC) treatment was followed by an injection of lithium chloride (LiCl, 120 mg/kg) in the experimental animals. When offered water after vehicle pretreatment, experimental animals subsequently were given IP saline (NaCl, 10 ml/kg). Post-drinking treatment for controls ( n=6) was NaCl, irrespective of the pretreatment condition (SR, THC or vehicle). Additional water was provided during the afternoon (30 min) with no other manipulations. Food was available ad lib at all times. When the discriminations were established other doses and drugs were examined ( t'=20 min). In testing there were no post-drinking treatments.

RESULTS

The SR-related analog AM-251 (dose range: 1-5.6 mg/kg) substituted for SR, whereas other drugs such as the cannabinoid CB(2) receptor antagonist SR-144528 (3 and 10 mg/kg), THC (1-10 mg/kg), flumazenil (1-10 mg/kg), naloxone (1-10 mg/kg), morphine (10 and 18 mg/kg) and d-amphetamine (1 and 3 mg/kg) did not. There was a dose-related attenuation of SR-induced suppression of drinking when THC (1.8-10 mg/kg) was given together with SR (5.6 mg/kg). In the THC trained rats, SR (1-10 mg/kg), morphine (10 and 18 mg/kg) and d-amphetamine (1 and 3 mg/kg) did not substitute for THC. SR (1 mg/kg) attenuated the THC (1.8 mg/kg) induced suppression of drinking. Together with 3 mg/kg SR and 1.8 mg/kg THC, drinking was roughly equally suppressed in both the experimental group and the controls.

CONCLUSION

SR-141716 induces a discriminative stimulus complex in DTA that shows potential for further examination of cannabinoid receptor antagonism.

Nicotine in alcohol deprivation increases alcohol operant self-administration during reinstatement

Tobacco and alcohol are highly co-abused by humans. Most experimental studies have evaluated ethanol consumption in animals exposed concomitantly to nicotine. However, little is known regarding the effects of nicotine administered during periods of alcohol deprivation. In the present study, adult male Wistar rats with an extended background of operant self-administration of ethanol were alcohol-deprived and treated with nicotine (0.1, 0.2, 0.4 and 0.8 mg/kg) or saline during five consecutive days in one chamber of a place conditioning apparatus. Nicotine-induced changes in locomotion were monitored daily, whereas the expression of place conditioning was studied the day after the last nicotine injection. Forty-eight hours after testing for conditioning, the animals resumed operant self-administration of ethanol and their alcohol intake was evaluated during the next 14 days. We observed that alcohol consumption was increased in animals treated with nicotine at doses of 0.2, 0.4 and 0.8 mg/kg but not in animals treated with the dose of 0.1 mg/kg or saline. Additionally, the dose of 0.8 mg/kg of nicotine not only induced persistent changes in alcohol self-administration but also produced conditioned place aversion and depressed locomotor activity. These results indicate that nicotine administration during the ethanol deprivation period can exacerbate the maintenance of alcohol consumption.

THE ENDOCANNABINOID SYSTEM: PHYSIOLOGY AND PHARMACOLOGY

The endogenous cannabinoid system is an ubiquitous lipid signalling system that appeared early in evolution and which has important regulatory functions throughout the body in all vertebrates. The main endocannabinoids (endogenous cannabis-like substances) are small molecules derived from arachidonic acid, anandamide (arachidonoylethanolamide) and 2-arachidonoylglycerol. They bind to a family of G-protein-coupled receptors, of which the cannabinoid CB(1) receptor is densely distributed in areas of the brain related to motor control, cognition, emotional responses, motivated behaviour and homeostasis. Outside the brain, the endocannabinoid system is one of the crucial modulators of the autonomic nervous system, the immune system and microcirculation. Endocannabinoids are released upon demand from lipid precursors in a receptor-dependent manner and serve as retrograde signalling messengers in GABAergic and glutamatergic synapses, as well as modulators of postsynaptic transmission, interacting with other neurotransmitters, including dopamine. Endocannabinoids are transported into cells by a specific uptake system and degraded by two well-characterized enzymes, the fatty acid amide hydrolase and the monoacylglycerol lipase. Recent pharmacological advances have led to the synthesis of cannabinoid receptor agonists and antagonists, anandamide uptake blockers and potent, selective inhibitors of endocannabinoid degradation. These new tools have enabled the study of the physiological roles played by the endocannabinoids and have opened up new strategies in the treatment of pain, obesity, neurological diseases including multiple sclerosis, emotional disturbances such as anxiety and other psychiatric disorders including drug addiction. Recent advances have specifically linked the endogenous cannabinoid system to alcoholism, and cannabinoid receptor antagonism now emerges as a promising therapeutic alternative for alcohol dependence and relapse.

ETHANOL INDUCES HIGHER BEC IN CB1 CANNABINOID RECEPTOR KNOCKOUT MICE WHILE DECREASING ETHANOL PREFERENCE

AIMS

Previous studies have shown that CB(1) cannabinoid receptors are involved in the behavioural effects induced by chronic ethanol administration in Wistar rats by using SR 141716, a CB(1) cannabinoid receptor antagonist. These studies have now been extended to investigate the effect of acute and chronic alcoholization on blood ethanol concentration (BEC) and ethanol preference in CB(1) knockout (-/-) mice.

METHODS

BEC was monitored for a period of 8 h in both CB(1)(-/-) male mice and CB(1) male wild-type (+/+) mice, which had received an acute i.p. injection of ethanol in 1, 3 or 5 g/kg doses. Ethanol preference was assayed in both groups of male mice in non-forced ethanol administration and forced chronic pulmonary alcohol administration for 14 and 39 days, respectively.

RESULTS

After an acute intraperitoneal ethanol injection of 5 g/kg, CB(1)(-/-) mice showed a significant higher BEC during the ethanol elimination stage than the CB(1)(+/+) mice. However, those in the 1 and 3 g/kg groups showed no significant difference. A 2-3 fold increase in BEC was observed in CB(1)(-/-) mice on days 10 and 11 after commencement of forced chronic pulmonary alcoholization in comparison with CB(1)(+/+) mice, although comparable BEC values were assayed in both groups on day 12. In addition, these CB(1)(-/-) mice showed a significantly lower preference for ethanol than CB(1)(+/+) mice.

CONCLUSIONS

The studies on CB(1)(-/-) and CB(1)(+/+) mice have clearly confirmed the involvement of CB(1) receptor on ethanol induced behavioural effects and also revealed that CB(1) receptors may be implicated in ethanol absorption/distribution, particularly after administration of high ethanol doses.