Down-regulation of cannabinoid receptor agonist-stimulated [35S]GTP gamma S binding in synaptic plasma membrane from chronic ethanol exposed mouse

Experience with dronabinol consumption facilitated a stimulant effect of alcohol and affected alcohol-related changes in frontal cortical endocannabinoid levels in male rats

Combined use of cannabis and alcohol is common in adolescents. However, the extent to which such polydrug exposure affects the brain and behaviors remains under-investigated in preclinical studies. This study tested the hypothesis that combined exposure of Δ-9-tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis, and alcohol will have additive effects on cognitive impairments and altered endocannabinoid levels in the hippocampus and frontal cortex. Male Long Evans rats were provided with daily access to cookies laced with oil or dronabinol, a synthetic THC, during adolescence. Three days after discontinuation of edible THC, the effect of orally administered 3 g/kg alcohol on Barnes maze performance was assessed. The results showed that experience with edible THC facilitated the occurrence of increased moving speed on the maze induced by repeated alcohol administration. However, contrasting to the hypothesis, the combined THC and alcohol exposure did not lead to additive deficits in learning and memory on the Barnes maze. While little effect on endocannabinoid levels was observed in the hippocampus, acute abstinence from alcohol significantly reduced endocannabinoid levels in the frontal cortex. In particular, reduction of N-oleoyl ethanolamine (OEA) and N-stearoyl ethanolamine (SEA) were robust and had an interactive effect with discontinuation from edible THC. These findings add to the scarce literature on THC and alcohol associated changes in endocannabinoid levels and provide insights to future investigations on the roles of OEA and SEA on physiology and behaviors following THC and alcohol co-exposure during adolescence.

The Synaptic Interactions of Alcohol and the Endogenous Cannabinoid System

PURPOSE

A growing body of evidence has implicated the endocannabinoid (eCB) system in the acute, chronic, and withdrawal effects of alcohol/ethanol on synaptic function. These eCB-mediated synaptic effects may contribute to the development of alcohol use disorder (AUD). Alcohol exposure causes neurobiological alterations similar to those elicited by chronic cannabinoid (CB) exposure. Like alcohol, cannabinoids alter many central processes, such as cognition, locomotion, synaptic transmission, and neurotransmitter release. There is a strong need to elucidate the effects of ethanol on the eCB system in different brain regions to understand the role of eCB signaling in AUD.

SEARCH METHODS

For the scope of this review, preclinical studies were identified through queries of the PubMed database.

SEARCH RESULTS

This search yielded 459 articles. Clinical studies and papers irrelevant to the topic of this review were excluded.

DISCUSSION AND CONCLUSIONS

The endocannabinoid system includes, but is not limited to, cannabinoid receptors 1 (CB₁), among the most abundantly expressed neuronal receptors in the brain; cannabinoid receptors 2 (CB₂); and endogenously formed CB₁ ligands, including arachidonoylethanolamide (AEA; anandamide), and 2-arachidonoylglycerol (2-AG). The development of specific CB₁ agonists, such as WIN 55,212-2 (WIN), and antagonists, such as SR 141716A (rimonabant), provide powerful pharmacological tools for eCB research. Alcohol exposure has brain region-specific effects on the eCB system, including altering the synthesis of endocannabinoids (e.g., AEA, 2-AG), the synthesis of their precursors, and the density and coupling efficacy of CB₁. These alcohol-induced alterations of the eCB system have subsequent effects on synaptic function including neuronal excitability and postsynaptic conductance. This review will provide a comprehensive evaluation of the current literature on the synaptic interactions of alcohol exposure and eCB signaling systems, with an emphasis on molecular and physiological synaptic effects of alcohol on the eCB system. A limited volume of studies has focused on the underlying interactions of alcohol and the eCB system at the synaptic level in the brain. Thus, the data on synaptic interactions are sparse, and future research addressing these interactions is much needed.

Endocannabinoid signaling in the lateral habenula regulates pain and alcohol consumption

Hyperalgesia, which often occurs in people suffering from alcohol use disorder, may drive excessive drinking and relapse. Emerging evidence suggests that the lateral habenula (LHb) may play a significant role in this condition. Previous research suggests that endocannabinoid signaling (eCBs) is involved in drug addiction and pain, and that the LHb contains core components of the eCBs machinery. We report here our findings in rats subjected to chronic ethanol vapor exposure. We detected a substantial increase in endocannabinoid-related genes, including Mgll and Daglb mRNA levels, as well as monoacylglycerol lipase (MAGL) protein levels, as well as a decrease in Cnr1 mRNA and type-1 cannabinoid receptor (CB1R) protein levels, in the LHb of ethanol-exposed rats. Also, rats withdrawing from ethanol exposure displayed hypersensitivity to mechanical and thermal nociceptive stimuli. Conversely, intra-LHb injection of the MAGL inhibitor JZL184, the fatty acid amide hydrolase inhibitor URB597, or the CB1R agonist WIN55,212-2 produced an analgesic effect, regardless of ethanol or air exposure history, implying that alcohol exposure does not change eCB pain responses. Intra-LHb infusion of the CB1R inverse agonist rimonabant eliminated the analgesic effect of these chemicals. Rimonabant alone elicited hyperalgesia in the air-, but not ethanol-exposed animals. Moreover, intra-LHb JZL184, URB597, or WIN55,212-2 reduced ethanol consumption in both homecages and operant chambers in rats exposed to ethanol vapor but not air. These findings suggest that LHb eCBs play a pivotal role in nociception and facilitating LHb eCBs may attenuate pain in drinkers.

Intermittent ethanol exposure during adolescence impairs cannabinoid type 1 receptor-dependent long-term depression and recognition memory in adult mice

Binge drinking is a significant problem in adolescent populations, and because of the reciprocal interactions between ethanol (EtOH) consumption and the endocannabinoid (eCB) system, we sought to determine if adolescent EtOH intake altered the localization and function of the cannabinoid 1 (CB1) receptors in the adult brain. Adolescent mice were exposed to a 4-day-per week drinking in the dark (DID) procedure for a total of 4 weeks and then tested after a 2-week withdrawal period. Field excitatory postsynaptic potentials (fEPSPs), evoked by medial perforant path (MPP) stimulation in the dentate gyrus molecular layer (DGML), were significantly smaller. Furthermore, unlike control animals, CB1 receptor activation did not depress fEPSPs in the EtOH-exposed animals. We also examined a form of excitatory long-term depression that is dependent on CB1 receptors (eCB-eLTD) and found that it was completely lacking in the animals that consumed EtOH during adolescence. Histological analyses indicated that adolescent EtOH intake significantly reduced the CB1 receptor distribution and proportion of immunopositive excitatory synaptic terminals in the medial DGML. Furthermore, there was decreased binding of [35S]guanosine-5*-O-(3-thiotriphosphate) ([35S] GTPγS) and the guanine nucleotide-binding (G) protein Gαi2 subunit in the EtOH-exposed animals. Associated with this, there was a significant increase in monoacylglycerol lipase (MAGL) mRNA and protein in the hippocampus of EtOH-exposed animals. Conversely, deficits in eCB-eLTD and recognition memory could be rescued by inhibiting MAGL with JZL184. These findings indicate that repeated exposure to EtOH during adolescence leads to long-term deficits in CB1 receptor expression, eCB-eLTD, and reduced recognition memory, but that these functional deficits can be restored by treatments that increase endogenous 2-arachidonoylglycerol.

Distinct functions of endogenous cannabinoid system in alcohol abuse disorders

Δ⁹ -tetrahydrocannabinol, the principal active component in Cannabis sativa extracts such as marijuana, participates in cell signalling by binding to cannabinoid CB₁ and CB₂ receptors on the cell surface. The CB₁ receptors are present in both inhibitory and excitatory presynaptic terminals and the CB₂ receptors are found in neuronal subpopulations in addition to microglial cells and astrocytes and are present in both presynaptic and postsynaptic terminals. Subsequent to the discovery of the endocannabinoid (eCB) system, studies have suggested that alcohol alters the eCB system and that this system plays a major role in the motivation to abuse alcohol. Preclinical studies have provided evidence that chronic alcohol consumption modulates eCBs and expression of CB₁ receptors in brain addiction circuits. In addition, studies have further established the distinct function of the eCB system in the development of fetal alcohol spectrum disorders. This review provides a recent and comprehensive assessment of the literature related to the function of the eCB system in alcohol abuse disorders.

Ethanol and cannabinoids interact to alter behavior in a zebrafish fetal alcohol spectrum disorder model

BACKGROUND

Recent work suggests that endocannabinoids (eCBs) may signal through the sonic hedgehog signaling pathway. We therefore hypothesized that combined ethanol and eCB exposure during defined stages of zebrafish embryogenesis will produce deficits comparable to human fetal alcohol spectrum disorder (FASD).

METHODS

Zebrafish embryos were exposed to ethanol or cannabinoid agonists alone or in combination at defined developmental stages and assessed for changes in brain morphology or expression of marker genes such as pax6a. Juvenile fish were then assessed for risk-taking/anxiety-like behavior using the novel tank dive test.

RESULTS

Either chronic or acute exposure to high doses of the CB1R agonist ACEA resulted in FASD phenotypes. However, acute subthreshold doses of CB1R agonist alone, or combined with 0.5% ethanol, did not induce morphological phenotypes, but did induce dysmorphogenesis when combined with acute 1% ethanol. Phenotypes were rescued using the CB1R antagonist SR141716A. In addition, JZL195, a dual inhibitor of FAAH and MAGL, two degradative enzymes for eCBs, induced FASD phenotypes in the presence of subthreshold ethanol, confirming the activation of common signaling pathways by ethanol and eCBs. We next analyzed the effects of ethanol and CB1R agonist on juvenile zebrafish behavior and show that ACEA or ethanol alone did not alter behavior, but combined ACEA and ethanol increased risk-taking behavior.

CONCLUSIONS

These studies demonstrate that pathological and behavioral phenotypes associated with FASD are induced by exposure to CB1R agonists and suggest that combined exposure to lower levels of alcohol and marijuana may be capable of inducing FASD-like morphological and behavioral impairments.

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).

Prenatal Ethanol Exposure Persistently Alters Endocannabinoid Signaling and Endocannabinoid-Mediated Excitatory Synaptic Plasticity in Ventral Tegmental Area Dopamine Neurons

Prenatal ethanol exposure (PE) leads to increased addiction risk which could be mediated by enhanced excitatory synaptic strength in ventral tegmental area (VTA) dopamine (DA) neurons. Previous studies have shown that PE enhances excitatory synaptic strength by facilitating an anti-Hebbian form of long-term potentiation (LTP). In this study, we investigated the effect of PE on endocannabinoid-mediated long-term depression (eCB-LTD) in VTA DA neurons. Rats were exposed to moderate (3 g/kg/d) or high (6 g/kg/d) levels of ethanol during gestation. Whole-cell recordings were conducted in male offspring between 4 and 10 weeks old.We found that PE led to increased amphetamine self-administration. Both moderate and high levels of PE persistently reduced low-frequency stimulation-induced eCB-LTD. Furthermore, action potential-independent glutamate release was regulated by tonic eCB signaling in PE animals. Mechanistic studies for impaired eCB-LTD revealed that PE downregulated CB1 receptor function. Interestingly, eCB-LTD in PE animals was rescued by metabotropic glutamate receptor I activation, suggesting that PE did not impair the synthesis/release of eCBs. In contrast, eCB-LTD in PE animals was not rescued by increasing presynaptic activity, which actually led to LTP in PE animals, whereas LTD was still observed in controls. This result shows that the regulation of excitatory synaptic plasticity is fundamentally altered in PE animals. Together, PE leads to impaired eCB-LTD at the excitatory synapses of VTA DA neurons primarily due to CB1 receptor downregulation. This effect could contribute to enhanced LTP and the maintenance of augmented excitatory synaptic strength in VTA DA neurons and increased addiction risk after PE.SIGNIFICANCE STATEMENT Prenatal ethanol exposure (PE) is among many adverse developmental factors known to increase drug addiction risk. Increased excitatory synaptic strength in VTA DA neurons is a critical cellular mechanism for addiction risk. Our results show that PE persistently alters eCB signaling and impairs eCB-LTD at the excitatory synapses, an important synaptic plasticity that weakens synaptic strength. These effects combined with PE-induced anti-Hebbian long-term potentiation reported in a previous study could result in the maintenance of enhanced excitatory synaptic strength in VTA DA neurons, which in turn contributes to PE-induced increase in addiction risk. Our findings also suggest that restoring normal eCB signaling in VTA DA neurons could be a useful strategy for treating behavioral symptoms caused by PE.

Chronic ethanol exposure decreases CB1 receptor function at GABAergic synapses in the rat central amygdala

The endogenous cannabinoids (eCBs) influence the acute response to ethanol and the development of tolerance, dependence and relapse. Chronic alcohol exposure alters eCB levels and Type 1 cannabinoid receptor (CB1 ) expression and function in brain regions associated with addiction. CB1 inhibits GABA release, and GABAergic dysregulation in the central nucleus of the amygdala (CeA) is critical in the transition to alcohol dependence. We investigated possible disruptions in CB1 signaling of rat CeA GABAergic transmission following intermittent ethanol exposure. In the CeA of alcohol-naive rats, CB1 agonist WIN 55,212-2 (WIN) decreased the frequency of spontaneous and miniature GABAA receptor-mediated inhibitory postsynaptic currents (s/mIPSCs). This effect was prevented by CB1 antagonism, but not Type 2 cannabinoid receptor (CB2 ) antagonism. After 2-3 weeks of intermittent ethanol exposure, these WIN inhibitory effects were attenuated, suggesting ethanol-induced impairments in CB1 function. The CB1 antagonist AM251 revealed a tonic eCB/CB1 control of GABAergic transmission in the alcohol-naive CeA that was occluded by calcium chelation in the postsynaptic cell. Chronic ethanol exposure abolished this tonic CB1 influence on mIPSC, but not sIPSC, frequency. Finally, acute ethanol increased CeA GABA release in both naive and ethanol-exposed rats. Although CB1 activation prevented this effect, the AM251- and ethanol-induced GABA release were additive, ruling out a direct participation of CB1 signaling in the ethanol effect. Collectively, these observations demonstrate an important CB1 influence on CeA GABAergic transmission and indicate that the CeA is particularly sensitive to alcohol-induced disruptions of CB1 signaling.

Critical needs in drug discovery for cessation of alcohol and nicotine polysubstance abuse

Polysubstance abuse of alcohol and nicotine has been overlooked in our understanding of the neurobiology of addiction and especially in the development of novel therapeutics for its treatment. Estimates show that as many as 92% of people with alcohol use disorders also smoke tobacco. The health risks associated with both excessive alcohol consumption and tobacco smoking create an urgent biomedical need for the discovery of effective cessation treatments, as opposed to current approaches that attempt to independently treat each abused agent. The lack of treatment approaches for alcohol and nicotine abuse/dependence mirrors a similar lack of research in the neurobiology of polysubstance abuse. This review discusses three critical needs in medications development for alcohol and nicotine co-abuse: (1) the need for a better understanding of the clinical condition (i.e. alcohol and nicotine polysubstance abuse), (2) the need to better understand how these drugs interact in order to identify new targets for therapeutic development and (3) the need for animal models that better mimic this human condition. Current and emerging treatments available for the cessation of each drug and their mechanisms of action are discussed within this context followed by what is known about the pharmacological interactions of alcohol and nicotine. Much has been and will continue to be gained from studying comorbid alcohol and nicotine exposure.

Acute and chronic ethanol exposure differentially regulate CB1 receptor function at glutamatergic synapses in the rat basolateral amygdala

The endogenous cannabinoid (eCB) system has been suggested to play a key role in ethanol preference and intake, the acute effects of ethanol, and in the development of withdrawal symptoms following ethanol dependence. Ethanol-dependent alterations in glutamatergic signaling within the lateral/basolateral nucleus of the amygdala (BLA) are critical for the development and expression of withdrawal-induced anxiety. Notably, the eCB system significantly regulates both glutamatergic and GABAergic synaptic activity within the BLA. Chronic ethanol exposure significantly alters eCB system expression within regions critical to the expression of emotionality and anxiety-related behavior, including the BLA. Here, we investigated specific interactions between the BLA eCB system and its functional regulation of synaptic activity during acute and chronic ethanol exposure. In tissue from ethanol naïve-rats, a prolonged acute ethanol exposure caused a dose dependent inhibition of glutamatergic synaptic activity via a presynaptic mechanism that was occluded by CB1 antagonist/inverse agonists SR141716a and AM251. Importantly, this acute ethanol inhibition was attenuated following 10 day chronic intermittent ethanol vapor exposure (CIE). CIE exposure also significantly down-regulated CB1-mediated presynaptic inhibition at glutamatergic afferent terminals but spared CB1-inhibition of GABAergic synapses arising from local inhibitory-interneurons. CIE also significantly elevated BLA N-arachidonoylethanolamine (AEA or anandamide) levels and decreased CB1 receptor protein levels. Collectively, these data suggest a dynamic regulation of the BLA eCB system by acute and chronic ethanol.

Cannabinoid Ligands and Alcohol Addiction: A Promising Therapeutic Tool or a Humbug?

The vast therapeutic potential of cannabinoids of both synthetic and plant-derived origins currently makes these compounds the focus of a growing interest. Although cannabinoids are still illicit drugs, their possible clinical usefulness, including treatment of acute or neuropathic pain, have been suggested by several studies. In addition, some observations indicate that cannabinoid receptor antagonists may be useful for the treatment of alcohol dependence and addiction, which is a major health concern worldwide. While the synergism between alcohol and cannabinoid agonists (in various forms) creates undesirable side effects when the two are consumed together, the administration of CB1 antagonists leads to a significant reduction in alcohol consumption. Furthermore, cannabinoid antagonists also mitigate alcohol withdrawal symptoms. Herein, we present an overview of studies focusing on the effects of cannabinoid ligands (agonists and antagonists) during acute or chronic consumption of ethanol.

Effects of Chronic Alcohol Exposure on the Modulation of Ischemia-Induced Glutamate Release via Cannabinoid Receptors in the Dorsal Hippocampus

BACKGROUND

Chronic alcohol consumption is a critical contributing factor to ischemic stroke, as it enhances ischemia-induced glutamate release, leading to more severe excitotoxicity and brain damage. But the neural mechanisms underlying this phenomenon are poorly understood.

METHODS

We evaluated the effects of chronic alcohol exposure on the modulation of ischemia-induced glutamate release via CB1 and CB2 cannabinoid receptors during middle cerebral artery occlusion, using in vivo microdialysis coupled with high-performance liquid chromatography, in alcohol-naïve rats or rats after 1 or 30 days of withdrawal from chronic ethanol intake (6% v/v for 14 days).

RESULTS

Intra-dorsal hippocampus (DH) infusions of ACEA or JWH133, selective CB1 or CB2 receptor agonists, respectively, decreased glutamate release in the DH in alcohol-naïve rats in a dose-dependent manner. Such an effect was reversed by co-infusions of SR141716A or AM630, selective CB1 or CB2 receptor antagonists, respectively. After 30 days, but not 1 day of withdrawal, ischemia induced an enhancement in glutamate release in the DH, as compared with non-alcohol-treated control group. Intra-DH infusions of JWH133, but not ACEA, inhibited ischemia-induced glutamate release in the DH after 30 days of withdrawal. Finally, 1 day of withdrawal did not alter the protein level of CB1 or CB2 receptors in the DH, as compared to non-alcohol-treated control rats. Whereas 30 days of withdrawal robustly decreased the protein level of CB1 receptors, but failed to alter the protein level of CB2 receptors, in the DH, as compared to non-alcohol-treated control rats.

CONCLUSIONS

Together, these findings suggest that loss of expression/function of CB1 receptors, but not CB2 receptors in the DH, is correlated with the enhancement of ischemia-induced glutamate release after prolonged alcohol withdrawal.

A review on alcohol: from the central action mechanism to chemical dependency

SummaryIntroduction:alcohol is a psychotropic depressant of the central nervous system (CNS) that promotes simultaneous changes in several neuronal pathways, exerting a profound neurological impact that leads to various behavioral and biological alterations.Objectives:to describe the effects of alcohol on the CNS, identifying the signaling pathways that are modified and the biological effects resulting from its consumption.Methods:a literature review was conducted and articles published in different languages over the last 15 years were retrieved.Results:the studies reviewed describe the direct effect of alcohol on several neurotransmitter receptors (gamma-aminobutyric acid [GABA], glutamate, endocannabinoids AEA and 2-AG, among others), the indirect effect of alcohol on the limbic and opioid systems, and the effect on calcium and potassium channels and on proteins regulated by GABA in the hippocampus.Discussion and conclusion:the multiple actions of alcohol on the CNS result in a general effect of psychomotor depression, difficulties in information storage and logical reasoning and motor incoordination, in addition to stimulating the reward system, a fact that may explain the development of addiction. Knowledge on the neuronal signaling pathways that are altered by alcohol allows the identification of effectors which could reduce its central action, thus, offering new therapeutic perspectives for the rehabilitation of alcohol addicts.

Ethanol exposure induces neonatal neurodegeneration by enhancing CB1R Exon1 histone H4K8 acetylation and up-regulating CB1R function causing neurobehavioral abnormalities in adult mice

BACKGROUND

Ethanol exposure to rodents during postnatal day 7 (P7), which is comparable to the third trimester of human pregnancy, induces long-term potentiation and memory deficits. However, the molecular mechanisms underlying these deficits are still poorly understood.

METHODS

In the present study, we explored the potential role of epigenetic changes at cannabinoid type 1 (CB1R) exon1 and additional CB1R functions, which could promote memory deficits in animal models of fetal alcohol spectrum disorder.

RESULTS

We found that ethanol treatment of P7 mice enhances acetylation of H4 on lysine 8 (H4K8ace) at CB1R exon1, CB1R binding as well as the CB1R agonist-stimulated GTPγS binding in the hippocampus and neocortex, two brain regions that are vulnerable to ethanol at P7 and are important for memory formation and storage, respectively. We also found that ethanol inhibits cyclic adenosine monophosphate response element-binding protein (CREB) phosphorylation and activity-regulated cytoskeleton-associated protein (Arc) expression in neonatal and adult mice. The blockade or genetic deletion of CB1Rs prior to ethanol treatment at P7 rescued CREB phosphorylation and Arc expression. CB1R knockout mice exhibited neither ethanol-induced neurodegeneration nor inhibition of CREB phosphorylation or Arc expression. However, both neonatal and adult mice did exhibit enhanced CREB phosphorylation and Arc protein expression. P7 ethanol-treated adult mice exhibited impaired spatial and social recognition memory, which were prevented by the pharmacological blockade or deletion of CB1Rs at P7.

CONCLUSIONS

Together, these findings suggest that P7 ethanol treatment induces CB1R expression through epigenetic modification of the CB1R gene, and that the enhanced CB1R function induces pCREB, Arc, spatial, and social memory deficits in adult mice.

Chronic ethanol alters network activity and endocannabinoid signaling in the prefrontal cortex

Chronic use of alcohol is associated with structural and functional alterations in brain areas that subserve cognitive processes. Of particular importance is the prefrontal cortex (PFC) that is involved in higher order behaviors such as decision making, risk assessment and judgment. Understanding the mechanisms that underlie alcohol's effects on PFC function is important for developing strategies to overcome the cognitive deficits that may predispose individuals to relapse. Our previous studies showed that acutely applied ethanol inhibits network activity in slices of prefrontal cortex and that exogenous and endogenous cannabinoids modulate up-state dynamics. In the present study, we examined the effects of repeated alcohol exposure on cannabinoid regulation of up-states in slice cultures of the prefrontal cortex. Compared to controls, up-state duration, but not amplitude was enhanced when measured 4 days after a 10 day ethanol exposure (44 mM ethanol; equivalent to 0.2% blood ethanol). Administration of the CB1 agonist WIN 55,212-2 enhanced the amplitude of up-states in control cultures but not in those treated previously with ethanol. This lack of effect occurred in the absence of any noticeable change in CB1 receptor protein expression. Chronic ethanol treatment and withdrawal also blunted WIN's inhibition of electrically evoked GABA IPSCs in layer II/III pyramidal neurons but not those in layer V/VI. WIN inhibited the amplitude of spontaneous GABA IPSCs in both layers and the magnitude of this effect was not altered by ethanol treatment. However, in layer V/VI neurons, WIN's effect on sIPSC frequency was greater in ethanol treated cultures. WIN also inhibited electrically evoked NMDA EPSCs in both layer II/III and V/VI neurons but this action was unaffected by ethanol treatment and withdrawal. Overall, these results suggest that ethanol's down-regulation of cannabinoid signaling results in altered network activity in the prefrontal cortex.

Changes in cerebral CB1 receptor availability after acute and chronic alcohol abuse and monitored abstinence

Involvement of the type 1 cannabinoid receptor (CB1R) in the effects of alcohol on the brain is supported by animal experiments, but how in vivo CB1R levels are altered in alcoholic patients is still unclear. To assess the short-time effects of a binge drinking episode on CB1R availability, 20 healthy social drinkers underwent [(18)F]MK-9470-positron emission tomography (PET) at baseline and after intravenous ethanol administration (ALC ACU). Moreover, 26 alcoholic patients underwent sequential CB1R PET after chronic heavy drinking (ALC CHR) and after 1 month of abstinence (ALC ABST). Seventeen healthy subjects served as controls. Compared with baseline, ALC ACU resulted in a global increase of CB1R availability (+15.8%). In contrast, a global decreased CB1R availability was found in ALC CHR patients (-16.1%) compared with controls, which remained unaltered after abstinence (-17.0%). Voxel-based analysis showed that ALC CHR patients had reduced CB1R availability, especially in the cerebellum and parieto-occipital cortex. After abstinence, reduced CB1R availability extended also to other areas such as the ventral striatum and mesotemporal lobe. In conclusion, whereas the acute alcohol effect is an increase in CB1R availability, chronic heavy drinking leads to reduced CB1R availability that is not reversible after 1 month of abstinence. Longer follow-up is required to differentiate whether this is a compensatory effect of repeated endocannabinoid overstimulation or an enduring trait-like feature. An enhanced CB1R signaling may offer a new therapeutic direction for treatment of the negative affective state produced by alcohol withdrawal and abstinence, which is critical for the maintenance of alcohol addiction.

Elevation of endogenous anandamide impairs LTP, learning, and memory through CB1 receptor signaling in mice

In rodents, many exogenous and endogenous cannabinoids, such as anandamide (AEA) and 2-arachidonyl glycerol (2-AG), have been shown to play an important role in certain hippocampal memory processes. However, the mechanisms by which endogenous AEA regulate this processes are not well understood. Here the effects of AEA on long-term potentiation (LTP), hippocampal-dependent learning and memory tasks, pERK1/2, pCaMKIV, and pCREB signaling events in both cannabinoid receptor type 1 (CB1R) wild-type (WT) and knockout (KO) mice were assessed following administration of URB597, an inhibitor of the fatty acid amide hydrolase (FAAH). Acute administration of URB597 enhanced AEA levels without affecting the levels of 2-AG or CB1R in the hippocampus and neocortex as compared to vehicle. In hippocampal slices, URB597 impaired LTP in CB1R WT but not in KO littermates. URB597 impaired object recognition, spontaneous alternation and spatial memory in the Y-maze test in CB1R WT mice but not in KO mice. Furthermore, URB597 enhanced ERK phosphorylation in WT without affecting total ERK levels in WT or KO mice. URB597 impaired CaMKIV and CREB phosphorylation in WT but not in KO mice. CB1R KO mice have a lower pCaMKIV/CaMKIV ratio and higher pCREB/CREB ratio as compared to WT littermates. Our results indicate that pharmacologically elevated AEA impair LTP, learning and memory and inhibit CaMKIV and CREB phosphorylation, via the activation of CB1Rs. Collectively, these findings also suggest that pharmacological elevation of AEA beyond normal concentrations is also detrimental for the underlying physiological responses.

Care and feeding of the endocannabinoid system: a systematic review of potential clinical interventions that upregulate the endocannabinoid system

Background

The “classic” endocannabinoid (eCB) system includes the cannabinoid receptors CB₁ and CB₂, the eCB ligands anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and their metabolic enzymes. An emerging literature documents the “eCB deficiency syndrome” as an etiology in migraine, fibromyalgia, irritable bowel syndrome, psychological disorders, and other conditions. We performed a systematic review of clinical interventions that enhance the eCB system—ways to upregulate cannabinoid receptors, increase ligand synthesis, or inhibit ligand degradation.

Methodology/Principal Findings

We searched PubMed for clinical trials, observational studies, and preclinical research. Data synthesis was qualitative. Exclusion criteria limited the results to 184 in vitro studies, 102 in vivo animal studies, and 36 human studies. Evidence indicates that several classes of pharmaceuticals upregulate the eCB system, including analgesics (acetaminophen, non-steroidal anti-inflammatory drugs, opioids, glucocorticoids), antidepressants, antipsychotics, anxiolytics, and anticonvulsants. Clinical interventions characterized as “complementary and alternative medicine” also upregulate the eCB system: massage and manipulation, acupuncture, dietary supplements, and herbal medicines. Lifestyle modification (diet, weight control, exercise, and the use of psychoactive substances—alcohol, tobacco, coffee, cannabis) also modulate the eCB system.

Conclusions/Significance

Few clinical trials have assessed interventions that upregulate the eCB system. Many preclinical studies point to other potential approaches; human trials are needed to explore these promising interventions.

Chronic alcohol produces neuroadaptations to prime dorsal striatal learning

Drug addictions including alcoholism are characterized by degradation of executive control over behavior and increased compulsive drug seeking. These profound behavioral changes are hypothesized to involve a shift in the regulation of behavior from prefrontal cortex to dorsal striatum (DLS). Studies in rodents have shown that ethanol disrupts cognitive processes mediated by the prefrontal cortex, but the potential effects of chronic ethanol on DLS-mediated cognition and learning are much less well understood. Here, we first examined the effects of chronic EtOH on DLS neuronal morphology, synaptic plasticity, and endocannabinoid-CB1R signaling. We next tested for ethanol-induced changes in striatal-related learning and DLS in vivo single-unit activity during learning. Mice exposed to chronic intermittent ethanol (CIE) vapor exhibited expansion of dendritic material in DLS neurons. Following CIE, DLS endocannabinoid CB1 receptor signaling was down-regulated, and CB1 receptor-dependent long-term depression at DLS synapses was absent. CIE mice showed facilitation of DLS-dependent pairwise visual discrimination and reversal learning, relative to air-exposed controls. CIE mice were also quicker to extinguish a stimulus-reward instrumental response and faster to reduce Pavlovian approach behavior under an omission schedule. In vivo single-unit recording during learning revealed that CIE mice had augmented DLS neuronal activity during correct responses. Collectively, these findings support a model in which chronic ethanol causes neuroadaptations in the DLS that prime for greater DLS control over learning. The shift to striatal dominance over behavior may be a critical step in the progression of alcoholism.

Temporal and behavioral variability in cannabinoid receptor expression in outbred mice submitted to ethanol-induced locomotor sensitization paradigm

BACKGROUND

There is a close relationship between the endocannabinoid system and alcoholism. This study investigated possible differential expression of cannabinoid receptors CB1 (CB1R) and CB2 (CB2R) in an outbred mice strain displaying behavioral variability to ethanol (EtOH)-induced locomotor sensitization.

METHODS

Male adult Swiss mice treated chronically with EtOH (2 g/kg, i.p., daily for 21 days) were classified as "EtOH_High" or "EtOH_Low" according to their locomotor activity after the 21st EtOH injection. A control group was similarly injected with saline. Temporal analysis of CB1R and CB2R immunoreactivity was performed in 3 different occasions: (i) at the end of chronic EtOH treatment, (ii) on the fifth day of EtOH withdrawal, and (iii) after EtOH challenge.

RESULTS

Overall, no differences were seen between experimental groups regarding the CB1R at the end of acquisition. However, there were decreases in CB2R in the prefrontal cortex and the hippocampus in EtOH_Low mice. On the fifth day of withdrawal, only EtOH_High mice presented increase in CB1R. Nonetheless, CB2R up-regulation was observed in both EtOH_High and EtOH_Low mice. EtOH challenge counteracted CB1R and CBR2 up-regulation, mainly in the EtOH_High, in structures related to emotionality, such as prefrontal cortex, ventral tegmental area, amygdala, striatum, and hippocampus.

CONCLUSIONS

There are different patterns of cannabinoid receptor expression during locomotor sensitization paradigm, at both temporal and behavioral perspectives. We hypothesize that CB2R down-regulation might be related to resilience to develop locomotor sensitization, while CB1R up-regulation relates to withdrawal aspects in sensitized mice.

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.

Tolerance to cannabinoid-induced behaviors in mice treated chronically with ethanol

RATIONALE

Chronic ethanol (EtOH) treatment decreases the motor-impairing effects of cannabinoids and downregulates the cannabinoid type 1 (CB1) receptor. However, these studies have been limited to measures of ataxia and analysis of CB1 expression from whole-brain or hippocampal preparations.

OBJECTIVE

To more fully assess the interactions between ethanol and cannabinoids, a tetrad of four well-characterized cannabinoid-induced behaviors (hypolocomotion, antinociception, hypothermia, and catalepsy) was measured in mice following EtOH treatment. Additionally, immunoblotting assessed CB1 protein in tissue from nine brain regions associated with these behaviors and the addiction neurocircuitry.

MATERIALS AND METHODS

Male C57Bl/6J mice were administered EtOH (0, 2, or 4 g/kg; intraperitoneally (i.p.)) twice daily for 10 days. Tetrad behaviors induced by the CB1 agonist WIN 55212-2 (3 mg/kg, i.p.) were measured in subjects 1 or 10 days following the last EtOH injection. In a separate group of animals, tissue was collected at the same time points for immunoblot analysis.

RESULTS

EtOH-treated mice were less sensitive to the hypothermic, hypolocomotive, and antinociceptive effects of WIN, and this effect reversed to control levels over a 10-day abstinence period. EtOH treatment did not affect WIN-induced catalepsy. CB1 protein expression was significantly altered in several brain areas including the hypothalamus, periaqueductal gray, ventral tegmental area, and cerebellum.

CONCLUSIONS

These results show that chronic EtOH treatment significantly affects the behavioral sensitivity to cannabinoid drugs and alters CB1 expression in several brain regions. Furthermore, these effects are selective as some behaviors and brain regions display an altered response while others do not.

Acute ethanol suppresses glutamatergic neurotransmission through endocannabinoids in hippocampal neurons

Ethanol exposure during fetal development is a leading cause of long-term cognitive impairments. Studies suggest that ethanol exposure have deleterious effects on the hippocampus, a brain region that is important for learning and memory. Ethanol exerts its effects, in part, via alterations in glutamatergic neurotransmission, which is critical for the maturation of neuronal circuits during development. The current literature strongly supports the growing evidence that ethanol inhibits glutamate release in the neonatal CA1 hippocampal region. However, the exact molecular mechanism responsible for this effect is not well understood. In this study, we show that ethanol enhances endocannabinoid (EC) levels in cultured hippocampal neurons, possibly through calcium pathways. Acute ethanol depresses miniature post-synaptic current (mEPSC) frequencies without affecting their amplitude. This suggests that ethanol inhibits glutamate release. The CB1 receptors (CB1Rs) present on pre-synaptic neurons are not altered by acute ethanol. The CB1R antagonist SR 141716A reverses ethanol-induced depression of mEPSC frequency. Drugs that are known to enhance the in vivo function of ECs occlude ethanol effects on mEPSC frequency. Chelation of post-synaptic calcium by EGTA antagonizes ethanol-induced depression of mEPSC frequency. The activation of CB1R with the selective agonist WIN55,212-2 also suppresses the mEPSC frequency. This WIN55,212-2 effect is similar to the ethanol effects and is reversed by SR141716A. In addition, tetani-induced excitatory post-synaptic currents (EPSCs) are depressed by acute ethanol. SR141716A significantly reverses ethanol effects on evoked EPSC amplitude in a dual recording preparation. These observations, taken together, suggest the participation of ECs as retrograde messengers in the ethanol-induced depression of synaptic activities.

The cannabinoid receptor agonist CP-55,940 and ethyl arachidonate interfere with [(3)H]batrachotoxinin A 20 alpha-benzoate binding to sodium channels and inhibit sodium channel function

Recent investigations in our laboratory showed that voltage-gated sodium channels (VGSCs) in brain are sensitive to inhibition by various synthetic cannabinoids and endocannabinoids. The present experiments examined the effects of the cannabinoid-1 (CB1) receptor agonist CP-55,940 and ethyl arachidonate on [(3)H]batrachotoxinin A 20 alpha-benzoate ([(3)H]BTX-B]) binding and VGSC-dependent depolarization of the nerve membrane in synaptoneurosomes isolated from mouse whole brain. CP-55,940 acted as a full inhibitor of [(3)H]BTX-B binding and its IC(50) was established at 22.3 microM. At its maximum effect concentration, ethyl arachidonate achieved partial (approximately 70%) inhibition and was less effective than CP-55,940 as an inhibitor of binding (IC(50)=262.7 microM). The potent CB1 receptor antagonist AM251 (2 microM) had no significant effect on the displacement of [(3)H]BTX-B by either compound (P>0.05). Scatchard analyses showed that CP-55,940 and ethyl arachidonate reduce the binding of [(3)H]BTX-B by lowering its B(max) but ethyl arachidonate also increased the K(d) of radioligand binding. In kinetic experiments, CP-55,940 and ethyl arachidonate were found to boost the dissociation of [(3)H]BTX-B from VGSCs to rates that exceed the maximum velocity achievable by veratridine, indicating they operate as allosteric inhibitors of [(3)H]BTX-B binding. Neither compound was effective at changing the initial rate of association of [(3)H]BTX-B with sodium channels. CP-55,940 and ethyl arachidonate inhibited veratridine-dependent (TTX-suppressible) depolarization of the plasma membrane of synaptoneurosomes with IC(50)s of 3.2 and 50.1 microM respectively. These inhibitory effects were again not influenced by 2 microM AM251. Our data demonstrate that the potent cannabinoid receptor agonist CP-55,940 and the ethyl ester of arachidonic acid have the ability to associate with VGSCs and inhibit their function independently of effects on CB1 receptors. Binding data comparisons using mouse brain preparations indicate CP-55,940 is approximately 10,000 times more potent as a CB1 receptor ligand than a sodium channel ligand while ethyl arachidonate shows a much smaller differential. Ethyl arachidonate has been shown previously to be the principal metabolite of ethanol in the brains of intoxicated individuals and effects of this ester on VGSCs and CB1 receptors may contribute to the depressant effects of alcohol.

Cannabinoid receptor 1 blocker rimonabant (SR 141716) for treatment of alcohol dependence: results from a placebo-controlled, double-blind trial

Multiple lines of evidence suggest that the endocannabinoid system is implicated in the development of alcohol dependence. In addition, in animal models, the cannabinoid receptor 1 blocker rimonabant was found to decrease alcohol consumption, possibly by indirect modulation of dopaminergic neurotransmission. This was a 12-week double-blind, placebo-controlled, proof-of-concept study to assess the possible efficacy of the cannabinoid receptor 1 antagonist rimonabant 20 mg/d (2 x 10 mg) in the prevention of relapse to alcohol in recently detoxified alcohol-dependent patients. A total of 260 patients were included, 258 were exposed to medication, and 208 (80.6%) were men. Patients had an alcohol history of 15 years on average. More patients in the rimonabant group (94/131 [71.8%]) completed treatment compared with the placebo group (79/127 [62.2%]). Although there was a modest effect of rimonabant with respect to relapse rate, there were no statistically significant differences between treatment groups. Approximately 41.5% of the rimonabant group had relapsed to drinking at the end of the study compared with 47.7% of the placebo group (obtained from Kaplan-Meier-curve). Differences were more marked but not statistically significant in patients who relapsed to heavy drinking: 27.7% versus 35.6%, respectively. Safety and tolerance of the drug were good. Similar rates of adverse events were reported between the 2 groups; less patients experienced serious events or discontinued the treatment with rimonabant compared with placebo. Rates of depression-related events were low (3.8% with rimonabant compared with 1.6% with placebo). Patients on rimonabant lost weight (Mean, -1.7 kg) compared with baseline, whereas there was no such change in the placebo group. Weight loss was more pronounced in patients with a higher body mass index. In addition, there was a significant decrease in leptin levels in the rimonabant group compared with baseline. Lack of efficacy in this study may be explained by a very high response rate in the placebo group and a relatively short treatment duration. Taking the substantial numbers of animal studies suggesting a possible role of CB1 antagonists for the treatment of alcohol dependence into account, it seems worthwhile to further test cannabinoid blockers in the treatment of alcoholism.

Time dependent alterations on tyrosine hydroxylase, opioid and cannabinoid CB1 receptor gene expressions after acute ethanol administration in the rat brain

The aim of this study was to examine the differential regulation after acute ethanol administration on tyrosine hydroxylase, proenkephalin and cannabinoid CB(1) receptor gene expressions in selected areas of the rat brain. Rats received an intragastric administration of 3 g/kg ethanol and were killed by decapitation at 1, 2, 4, 8 and 24 h. The results showed an activation of tyrosine hydroxylase gene expression in the ventral tegmental area and the substantia nigra, increased proenkephalin gene expression in the caudate-putamen, nucleus accumbens core and shell, central and medial amygdala, ventromedial hypothalamic nucleus and the paraventricular hypothalamic nucleus. In contrast, a significant decrease in the cannabinoid CB1 receptor gene expression was found in caudate-putamen, central amygdala and ventromedial hypothalamic nucleus. In conclusion, the results suggest that an acute dose of ethanol induces neuroplastic alterations in proenkephalin, tyrosine hydroxylase and cannabinoid CB1 receptor gene expressions that may contribute to trigger the rewarding effects of ethanol consumption.

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.

Alcohol inhibits spontaneous activity of basolateral amygdala projection neurons in the rat: involvement of the endocannabinoid system

BACKGROUND

A large body of evidence indicates that the limbic system is involved in the neural processing underlying drug addiction. Among limbic regions, the basolateral nucleus of amygdala (BLA) is implicated in some aspects of the neurobiological mechanisms of drugs of abuse, including alcohol and cannabinoids. It is recently emerging that the endocannabinoid system is involved in many pharmacological and behavioral effects of alcohol. The BLA possesses a very high density of CB1 cannabinoid receptors, and endocannabinoids modulate forms of synaptic plasticity in this region. The aims of our study were first to investigate in vivo the sensitivity of BLA pyramidal neurons to alcohol and second to determine the role of the endocannabinoid system in the acute effects of alcohol.

METHODS

We utilized extracellular single cell recordings in urethane anesthetized rats from BLA principal neurons, antidromically identified from their projection site in the nucleus accumbens.

RESULTS

Alcohol (0.25 to 2.0 g/kg i.v.) induced a marked decrease in the spontaneous firing rate of BLA projecting neurons (51.1 +/- 16% of baseline at 0.5 g/kg alcohol, p < 0.0001). The involvement of the endogenous cannabinoid system was investigated by administering the CB1 receptor antagonist SR141716A (rimonabant, SR) (1.0 mg/kg i.v.) before alcohol. SR per se did not significantly affect firing rate of BLA neurons, but it prevented the inhibition produced by alcohol (98 +/- 18% of baseline firing at 0.5 g/kg alcohol, p < 0.01). Then, we studied the actions of alcohol following a chronic treatment with the CB1 agonist WIN55212-2 (WIN). Animals were administered WIN for 6.5 days (2.0 mg/kg, i.p. twice daily) and alcohol dose-response curves were carried out on firing rate of BLA neurons 24 hours following the last injection of the cannabinoid agonist. In WIN-treated animals the inhibitory effect of alcohol was significantly reduced as compared with controls (95 +/- 16% of baseline firing at 0.5 g/kg, p < 0.05).

CONCLUSIONS

Our results provide evidence of the involvement of the endocannabinoid system in the effects of alcohol on BLA projection neurons. They also further point to the endocannabinoid system as a possible molecular target in the treatment of alcoholism.

Role of endocannabinoids in regulating drug dependence

This review will discuss the latest knowledge of how the endocannabinoid system might be involved in treating addiction to the most common illicit drugs. Experimental models are providing increasing evidence for the pharmacological management of endocannabinoid signaling not only to block the direct reinforcing effects of cannabis, opioids, nicotine and ethanol, but also for preventing relapse to the various drugs of abuse, including opioids, cocaine, nicotine, alcohol and metamphetamine. Preclinical and clinical studies suggest that the endocannabinoid system can be manipulated by the CB1 receptor antagonist SR141716A, that might constitute a new generation of compounds for treating addiction across different classes of abused drugs.

The role of the cannabinoid type 1 receptor and down-stream cAMP/DARPP-32 signal in the nucleus accumbens of methamphetamine-sensitized rats

Blockade of the cannabinoid type 1 (CB(1)) receptor could suppress methamphetamine self-administration; however, the cellular mechanism remains unclear. In this study, we intended to investigate the significance of brain CB(1) receptors on the development of behavioral sensitization to methamphetamine. Male Sprague-Dawley rats treated with chronic methamphetamine (4 mg/kg, i.p.) for either 7 or 14 days developed behavioral sensitization to methamphetamine (1 mg/kg) at withdrawal day 7. A progressive decrease in numbers of CB(1) receptor (both Bmax and mRNA) but increase in binding affinity (Kd) was noticed during withdrawal days 3 to 7. Microinjection of CB(1) antagonist [5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-4-ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide] into the nucleus accumbens (NAc) at withdrawal day 7, significantly suppressed the behavioral sensitization to methamphetamine. In NAc brain slices preparation, acute incubation with CB(1) agonist (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP 55940) dose-dependently enhanced cAMP accumulation in sensitized rats; no change was noticed in control groups. Consequently, treatment of CP 55940 induced a dose-dependent (10 nmol/L-10 micromol/L) phosphorylation on down-stream dopamine and cAMP-regulated phosphoprotein of Mr 32 000 (DARPP-32)/Thr34 in sensitized rats, while only 10 micromol/L CP 55940 was able to enhance the phosphoDARPP-32/T34 in control groups. Alternatively, both basal activity of calcineurin (PP-2B) and CP 55940-induced changes in the amount of PP-2B in the NAc were both decreased in sensitized rats, but not in controls. Overall, we demonstrated that brain CB(1) receptor and its down-stream cAMP/DARPP-32/T34/PP-2B signaling are profoundly altered in methamphetamine-sensitized animals.

Cortico-limbic circuitry for conditioned nicotine-seeking behavior in rats involves endocannabinoid signaling

RATIONALE

The endocannabinoid system plays an important role in conditioned drug seeking, but the neuronal mechanisms involved in this behavior are unclear.

OBJECTIVES

Here, we evaluate the role of endogenous cannabinoids in the cortico-limbic circuitry in cue-induced nicotine-seeking behavior in rats.

METHODS

Animals were first trained to self-administer nicotine (0.03 mg/kg/injection, IV) under conditions in which responding was reinforced jointly by response-contingent nicotine injections and audiovisual stimuli. During subsequent sessions, nicotine was withdrawn and responding was reinforced by contingent presentation of the stimuli only. One month after nicotine removal, the cannabinoid CB1 receptor antagonist, rimonabant, was injected bilaterally into the shell of the nucleus accumbens (ShNAcc, 0.3, 3, or 30 ng/0.5 microl), the basolateral amygdala (BLA, 30 ng/0.5 microl), or the prelimbic cortex (PLCx, 30 ng/0.5 microl).

RESULTS

Rimonabant injected into the ShNAcc dose-dependently reduced nicotine-seeking behavior without modifying spontaneous locomotor activity. Similar results were obtained when the drug (30 ng) was injected into the BLA or the PLCx. The anatomical specificity was confirmed in a control experiment using [(3)H]rimonabant. Fifteen minutes after drug injection, when the behavioral effects of rimonabant were already achieved, radioactivity was detected at the site of injection and had not diffused to adjacent regions.

CONCLUSIONS

These findings demonstrate that increased endocannabinoid transmission critically triggers conditioned nicotine-seeking behavior in key cortico-limbic regions.

Role of endocannabinoids in alcohol consumption and intoxication: studies of mice lacking fatty acid amide hydrolase

Endocannabinoid signaling plays the important role in regulation of ethanol intake. Fatty acid amide hydrolase (FAAH) is a key membrane protein for metabolism of endocannabinoids, including anandamide, and blockade of FAAH increases the level of anandamide in the brain. To determine if FAAH regulates ethanol consumption, we studied mutant mice with deletion of the FAAH gene. Null mutant mice showed higher preference for alcohol and voluntarily consumed more alcohol than wild-type littermates. There was no significant difference in consumption of sweet or bitter solutions. To determine the specificity of FAAH for ethanol intake, we studied additional ethanol-related behaviors. There were no differences between null mutant and wild-type mice in severity of ethanol-induced acute withdrawal, conditioned taste aversion to alcohol, conditioned place preference, or sensitivity to hypnotic effect of ethanol. However, null mutant mice showed shorter duration of loss of righting reflex induced by low doses of ethanol (3.2 and 3.4 g/kg) and faster recovery from motor incoordination induced by ethanol. All three behavioral phenotypes (increased preference for ethanol, decreased sensitivity to ethanol-induced sedation, and faster recovery from ethanol-induced motor incoordination) seen in mutant mice were reproduced in wild-type mice by injection of a specific inhibitor of FAAH activity--URB597. These data suggest that increased endocannabinoid signaling increased ethanol consumption owing to decreased acute ethanol intoxication.

Role of cannabinoidergic mechanisms in ethanol self-administration and ethanol seeking in rat adult offspring following perinatal exposure to Delta9-tetrahydrocannabinol

The present study evaluated the consequences of perinatal Delta(9)-tetrahydrocannabinol (Delta(9)-THC) treatment (5 mg/kg/day by gavage), either alone or combined with ethanol (3% v/v as the only fluid available), on ethanol self-administration and alcohol-seeking behavior in rat adult offspring. Furthermore, the effect of the selective cannabinoid CB(1) receptor antagonist, SR-141716A, on ethanol self-administration and on reinstatement of ethanol-seeking behavior induced either by stress or conditioned drug-paired cues was evaluated in adult offspring of rats exposed to the same perinatal treatment. Lastly, microarray experiments were conducted to evaluate if perinatal treatment with Delta(9)-tetrahydrocannabinol, ethanol or their combination causes long-term changes in brain gene expression profile in rats. The results of microarray data analysis showed that 139, 112 and 170 genes were differentially expressed in the EtOH, Delta(9)-THC, or EtOH+Delta(9)-THC group, respectively. No differences in alcohol self-administration and alcohol seeking were observed between rat groups. Intraperitoneal (IP) administration of SR-141716A (0.3-3.0 mg/kg) significantly reduced lever pressing for ethanol and blocked conditioned reinstatement of alcohol seeking. At the same doses SR-141716A failed to block foot-shock stress-induced reinstatement of alcohol seeking. The results reveal that perinatal exposure to Delta(9)-THC ethanol or their combination results in evident changes in gene expression patterns. However, these treatments do not significantly affect vulnerability to ethanol abuse in adult offspring. On the other hand, the results obtained with SR-141716A emphasize that endocannabinoid mechanisms play a major role in ethanol self-administration, as well as in the reinstatement of ethanol-seeking behavior induced by conditioned cues, supporting the idea that cannabinoid CB(1) receptor antagonists may represent interesting agents for the pharmacotherapy of alcoholism.

Neuropharmacology of the endocannabinoid signaling system-molecular mechanisms, biological actions and synaptic plasticity

The endocannabinoid signaling system is composed of the cannabinoid receptors; their endogenous ligands, the endocannabinoids; the enzymes that produce and inactivate the endocannabinoids; and the endocannabinoid transporters. The endocannabinoids are a new family of lipidic signal mediators, which includes amides, esters, and ethers of long-chain polyunsaturated fatty acids. Endocannabinoids signal through the same cell surface receptors that are targeted by Delta(9)-tetrahydrocannabinol (Delta(9)THC), the active principles of cannabis sativa preparations like hashish and marijuana. The biosynthetic pathways for the synthesis and release of endocannabinoids are still rather uncertain. Unlike neurotransmitter molecules that are typically held in vesicles before synaptic release, endocannabinoids are synthesized on demand within the plasma membrane. Once released, they travel in a retrograde direction and transiently suppress presynaptic neurotransmitter release through activation of cannabinoid receptors. The endocannabinoid signaling system is being found to be involved in an increasing number of pathological conditions. In the brain, endocannabinoid signaling is mostly inhibitory and suggests a role for cannabinoids as therapeutic agents in central nervous system (CNS) disease. Their ability to modulate synaptic efficacy has a wide range of functional consequences and provides unique therapeutic possibilities. The present review is focused on new information regarding the endocannabinoid signaling system in the brain. First, the structure, anatomical distribution, and signal transduction mechanisms of cannabinoid receptors are described. Second, the synthetic pathways of endocannabinoids are discussed, along with the putative mechanisms of their release, uptake, and degradation. Finally, the role of the endocannabinoid signaling system in the CNS and its potential as a therapeutic target in various CNS disease conditions, including alcoholism, are discussed.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

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.

Endocannabinoid lipids and mediated system: implications for alcoholism and neuropsychiatric disorders

Several natural lipids have emerged as candidate modulators of central nervous system (CNS) functions. Fatty acid amides and their coupled signaling pathways are known to regulate several physiological and behavioral processes. Recent studies from our laboratory and others also have implicated endogenous marijuana-like brain constituents, endocannabinoids (ECs), and cannabinoid-1 (CB1) receptors in the neural circuitry that mediate drug addiction and neuropsychiatric disorders. Neuroadaptation to chronic ethanol (EtOH) has been shown to involve changes in the EC system. These changes include alterations in the synthesis of EC, their precursors, as well as density and coupling efficacy of CB1 receptors. The evidence for the participation of the EC system in the pathophysiology of various neuropsychiatric disorders is just beginning to evolve. It is of great interest to explore the components of EC system in different areas of the CNS for further understanding of its role in health and disease. This article presents a comprehensive overview of the currently available literature pertaining to the role of the EC system in alcoholism, schizophrenia, depression and/or suicide.

Involvement of the endogenous cannabinoid system in the effects of alcohol in the mesolimbic reward circuit: electrophysiological evidence in vivo

RATIONALE

Several lines of evidence indicate that the endogenous cannabinoid system is involved in the pharmacological and behavioural effects of alcohol. The mesolimbic dopaminergic (DA) system and the nucleus accumbens (NAc) process rewarding properties of drugs of abuse, including alcohol and cannabinoids, whereas endocannabinoids in these regions modulate synaptic function and mediate short- and long-term forms of synaptic plasticity.

OBJECTIVES

The present study was designed to investigate the contribution of the endogenous cannabinoid system in alcohol electrophysiological effects in the mesolimbic reward circuit.

METHODS

We utilized extracellular single cell recordings from ventral tegmental area (VTA) DA and NAc neurons in anesthetized rats. DA neurons were antidromically identified as projecting to the shell of NAc, whereas NAc putative medium spiny neurons were identified by their evoked responses to basolateral amygdala (BLA) stimulation.

RESULTS

Alcohol stimulated firing rate of VTA DA neurons and inhibited BLA-evoked NAc neuron spiking responses. The cannabinoid type-1 receptor (CB1) antagonist rimonabant (SR141716A) fully antagonized alcohol effect in both regions. In the NAc, either inhibition of the major catabolic enzyme of the endocannabinoid anandamide, the fatty-acid amyd hydrolase, with URB597 or a pretreatment with the CB1 receptor agonist WIN55212-2 significantly depressed alcohol-induced effects in the NAc.

CONCLUSIONS

These results corroborate the notion of the involvement of endocannabinoids and their receptors in the actions of alcohol and highlight the endocannabinoid system as a valuable target in the therapy for alcoholism.

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.

Long-lasting increase of alcohol relapse by the cannabinoid receptor agonist WIN 55,212-2 during alcohol deprivation

Alcoholism is characterized by successive relapses. Recent data have shown a cross-talk between the cannabinoid system and ethanol. In this study, male Wistar rats with a limited (30 min sessions), intermittent, and extended background of alcohol operant self-administration were used. The relapse to alcohol after 1 week of alcohol deprivation was evaluated. Two weeks later, the animals were treated with the cannabinoid agonist WIN 55,212-2 (R-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate) (0, 0.4, 2.0, and 10.0 mg/kg, s.c.) during a similar alcohol deprivation period, and alcohol relapse during 2 weeks was assessed. A conditioned place preference (CPP) paradigm was used to study the rewarding properties of the cannabinoid agonist. Locomotor activity was also recorded. All doses of WIN 55,212-2 produced aversion in the CPP paradigm. The doses of 2.0 and 10.0 mg/kg resulted in an important suppression of spontaneous locomotor activity and a progressive weight loss during the next 2 weeks. The single alcohol deprivation was followed by a transient increase in their responding for alcohol from a range of 20-24 lever presses at baseline to a range of 38-48 responses in the first and second days (alcohol deprivation effect). However, the administration of WIN 55,212-2 during ethanol deprivation produced similar increased responses for alcohol but in a long-term way (at least over 2 weeks). These findings suggest that noncontingent chronic exposure to cannabinoids during alcohol deprivation can potentiate the relapse into alcohol use, indicating that functional changes in the cannabinoid brain receptor may play a key role in ethanol relapse.

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.

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.

INTERACTIONS BETWEEN CANNABINOID AND OPIOID RECEPTOR SYSTEMS IN THE MEDIATION OF ETHANOL EFFECTS

Over the past few years, advances in the investigation of the neurochemical circuits involved in the development and treatment of alcohol dependence have identified peptides and receptors as potential key targets in the treatment of problems related to alcohol consumption. The endogenous opioid system is modified by alcohol intake in areas of the brain related to reward systems, and differential basal levels of opioid gene expression are found in rodents with a high preference for ethanol. This suggests a greater vulnerability to alcohol consumption in relation to differences in genetic background. Further evidence of the involvement of opioid peptides in alcohol dependence is the ability of the opioid antagonist naltrexone to reduce alcohol intake in animal models of dependence and in alcohol-dependent patients. Abundant evidence indicates that the activation of cannabinoid receptors stimulates the release of opioid peptides, therefore the cannabinoid receptor antagonists may presumably alter opioid peptide release, thus facilitating the reduction of ethanol consumption. However, little is known about the effects of ethanol on the endogenous cannabinoid system, the vulnerability of cannabinoid receptors to alcohol intake or their neurochemical implications in reducing consumption of alcohol. In this paper, we review the role of opioid and cannabinoid receptor systems, their vulnerability to alcohol intake and the development of dependence, and the targeting of these systems in the treatment of alcoholism.

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.

Changes in endocannabinoid contents in reward-related brain regions of alcohol-exposed rats, and their possible relevance to alcohol relapse

1. Chronic alcohol exposure modifies endocannabinoid levels in different brain regions, while pharmacological targeting of the endocannabinoid system has been reported to influence ethanol intake in laboratory animals. 2. The present study was aimed at evaluating the pattern of changes of endocannabinoids and their receptors, with emphasis on reward-related brain areas, in Wistar rats subjected to consecutive phases of alcoholization, alcohol deprivation (abstinence), and voluntary consumption of alcohol (relapse). 3. We observed that, in the limbic forebrain, anandamide (AEA) and 2-arachidonoylglycerol (2-AG) contents increased after 7 days of alcoholization, then to dramatically decrease after 48 h of alcohol deprivation and, in the case of 2-AG, to further decrease when rats were allowed to relapse to alcohol consumption. By contrast, in the midbrain, there was a marked reduction in AEA, but not 2-AG, content, after alcoholization. This decrease was not affected during alcohol abstinence, but both AEA and 2-AG contents were then significantly reduced when rats were allowed to relapse to alcohol consumption. 4. Based on these data, we examined whether pharmacological activation/blockade of endocannabinoid transmission might influence ethanol intake in rats allowed to relapse to alcohol consumption after subsequent periods of alcoholization and alcohol deprivation. 5. Treatment with either Delta(9)-tetrahydrocannabinol or CP55,940, two cannabinoid agonists, reduced both total liquid and ethanol intake but did not affect ethanol preference. Treatment with SR141716, a selective cannabinoid CB(1) receptor antagonist, also produced a significant reduction in both total liquid and ethanol intake without affecting ethanol preference. Accordingly, none of these effects on ethanol intake were accompanied by changes in dopamine and GABA in limbic structures. 6. In summary, the levels of endocannabinoids underwent significant changes in reward-related areas during alcoholization, alcohol deprivation, and relapse, showing the lowest values in this latter phase. Treatment with cannabinoid agonists or a selective CB(1) receptor antagonist resulted in a reduction of ethanol intake by rats allowed to relapse to alcohol consumption after periods of alcoholization and alcohol deprivation, but these effects did not appear to be due to changes in neurobiological substrates currently involved in alcohol reinforcement/relapse.

Role of Endocannabinoids and Cannabinoid CB1 Receptors in Alcohol-Related Behaviors

This review presents the remarkable research during the past several years indicating that some of the pharmacological and behavioral effects of alcohol, including alcohol drinking and alcohol-preferring behavior, are mediated through one of the most abundant neurochemical systems in the central nervous system, the endocannabinoid signaling system. The advances, with the discovery of specific receptors and the existence of naturally occurring cannabis-like substances in the mammalian system and brain, have helped in understanding the neurobiological basis for drugs of abuse, including alcoholism. The cDNA and genomic sequences encoding G-protein-coupled cannabinoid receptors (CB1 and CB2) from several species have now been cloned. This has facilitated discoveries of endogenous ligands (endocannabinoids). To date, two fatty acid derivatives characterized to be arachidonylethanolamide and 2-arachidonylglycerol have been isolated from both nervous and peripheral tissues. Both these compounds have been shown to mimic the pharmacological and behavioral effects of Delta9-tetrahydrocannabinol, the psychoactive component of marijuana. The involvement of the endocannabinoid signaling system in tolerance development to drugs of abuse, including alcohol, were unknown until recently. Studies from our laboratory demonstrated for the first time the downregulation of CB1 receptor function and its signal transduction by chronic alcohol. The observed downregulation of CB1 receptor binding and its signal transduction results from the persistent stimulation of receptors by the endogenous CB1 receptor agonists arachidonylethanolamide and 2-arachidonylglycerol, the synthesis of which is increased by chronic alcohol treatment. The deletion of CB1 receptor has recently been shown to block voluntary alcohol intake in mice, which is consistent with our previous findings where the DBA/2 mice known to avoid alcohol intake had significantly reduced brain CB1 receptor function. These findings suggest a role for the CB1 receptor gene in excessive alcohol drinking behavior and development of alcoholism. Ongoing investigations may lead to the development of potential therapeutic agents to modulate the endocannabinoid signaling system, which will be helpful for the treatment of alcoholism.

Decreased alcohol self-administration and increased alcohol sensitivity and withdrawal in CB1 receptor knockout mice

Recent advances in the understanding of the neurobiological basis of alcohol dependence suggest that the endocannabinoid system may play a key role in the reinforcing effects of ethanol. In the present study, disruption of CB1 receptors in mice generated on a CD1 background decreased both ethanol consumption and preference. This decreased ethanol self-administration was associated with increased sensitivity to the acute intoxicating effects of ethanol. Mutant mice were more sensitive to the hypothermic and sedative/hypnotic effects of acute ethanol administration (1.5-4.0 g/kg), although plasma ethanol concentrations did not differ from those of controls. Moreover, wild-type mice exhibited normal locomotor activation caused by 1.0-2.5 g/kg injection of ethanol, whereas mutant mice displayed sedation in response to the injection of the same ethanol doses. The severity of alcohol withdrawal-induced convulsions was also increased in CB1(-/-) mice. Our results suggest that CB1 receptors participate in the regulation of ethanol drinking and demonstrate that their disruption lead to increased ethanol sensitivity and withdrawal severity.