Reduced EtOH Intake Research Articles

The serotonin 2C receptor agonist lorcaserin, alone and in combination with the opioid receptor antagonist naltrexone, attenuates binge-like ethanol drinking.

The serotonin (5-HT) system has been implicated in the pathophysiology of alcohol (ethanol; EtOH) use disorders. Lorcaserin, a 5-HT2C receptor agonist, attenuates drug self-administration in animal models. We investigated the effects of lorcaserin on EtOH intake using the drinking-in-the-dark (DID) procedure, an animal model of binge-like drinking. We compared the effects of lorcaserin to those of the Food and Drug Administration (FDA)-approved drug naltrexone and examined the effects of combining lorcaserin and naltrexone. To examine whether effects were specific for EtOH, we examined the effects of lorcaserin and naltrexone, administered alone and in combination, on saccharin intake. Adult male C57BL/6J mice received EtOH access (20% v/v) for 2h in the home-cage during the first 3days of the DID procedure, beginning 3h into the dark cycle. On day 4, mice were injected with lorcaserin, naltrexone, or a combination of lorcaserin and naltrexone prior to a 4-h EtOH access. Intake was measured at 2 and 4h. Lorcaserin reduced EtOH intake in a dose-dependent fashion over the 2- and 4-h measurement periods. Naltrexone also reduced EtOH intake when administered alone, with dose-dependent effects being more pronounced over 2h rather than the full 4-h session. Combining lorcaserin and naltrexone reduced binge-like EtOH drinking to a greater extent than either drug alone. A similar pattern of results was obtained for saccharin intake. These results suggest that lorcaserin and naltrexone can have additive effects on binge-like EtOH drinking. They also support continued research into the therapeutic potential of lorcaserin for alcohol use disorders.

Effects of 5-HT2A receptor agonist 2,5-dimethoxy-4-iodoamphetamine on alcohol consumption in Long-Evans rats.

The objectives of this study were to determine alcohol consumption after administration of (R)(-)-2,5-dimethoxy-4-iodoamphetamine (DOI) or naltrexone in Long-Evans rats, and to assess the effectiveness of these treatments based on individual differences in alcohol consumption. Adult male Long-Evans rats (N = 16) were given opportunities to orally self-administer a 20% (v/v) ethanol (EtOH) solution using an intermittent access, two-bottle (vs. tap water) choice procedure in their home cages. EtOH consumption and preference, total fluid consumption and food intake were measured. Last, we assessed the effects of naltrexone (1 mg/kg; subcutaneous) and (R)(-)-DOI (0.1-1 mg/kg; subcutaneous) on EtOH intake and preference using a quartile analysis. Rats showed stable EtOH (20%) intake and preference after 15 EtOH access sessions. Naltrexone produced a transient decrease in EtOH intake, but an inconsistent effect on EtOH preference, whereas DOI dose-dependently reduced EtOH intake and preference for at least 24 h. Subsequent quartile analyses revealed that rats with the highest EtOH intake during the first 60 min of access to EtOH showed greater reductions in EtOH intake and preference after DOI treatment. This is the first report to show that DOI-elicited reductions in EtOH intake and preference in rats depend on baseline EtOH intake, perhaps supporting a 'baseline dependency' hypothesis of effectiveness with phenethylamine psychedelics on EtOH consumption. If so, individuals with greater potential to develop severe AUDs may be particularly responsive to the positive motivational changes produced by treatment with psychedelics that target the 5-HT2 receptor family.

Apremilast Alters Behavioral Responses to Ethanol in Mice: I. Reduced Consumption and Preference.

Phosphodiesterase type 4 (PDE4) inhibitors produce widespread anti-inflammatory effects and reduce ethanol (EtOH) consumption in several rodent models. These drugs are potential treatments for several diseases, including central nervous system disorders, but clinical use is limited by their emetic activity. Apremilast is a selective PDE4 inhibitor with fewer gastrointestinal side effects that is FDA-approved for the treatment of psoriasis. We measured the acute and chronic effects of apremilast on EtOH consumption in male and female C57BL/6J mice using the continuous and intermittent 24-hour 2-bottle choice drinking models. We also studied the effects of apremilast on preference for sucrose or saccharin, spontaneous locomotor activity, and blood EtOH clearance. Finally, apremilast levels in plasma, liver, and brain were measured 1 or 2hours after injection. In the continuous and intermittent drinking tests, apremilast (15 to 50mg/kg, p.o.) dose dependently reduced EtOH intake and preference in male and female mice. Higher doses of apremilast (30 to 50mg/kg) also reduced total fluid intake in these mice. Chronic administration of apremilast (20mg/kg) produced a stable reduction in EtOH consumption in both drinking tests with no effect on total fluid intake. The drinking effects were reversible after drug treatment was replaced with vehicle administration (saline) for 2 to 4days. Six daily apremilast injections did not alter preference for saccharin or sucrose in male or female mice. Apremilast (20mg/kg) transiently decreased spontaneous locomotor activity and did not alter blood EtOH clearance. The highest levels of apremilast were found in liver followed by plasma and brain. Apremilast produced stable reductions in voluntary EtOH consumption and was rapidly distributed to plasma and tissues (including the brain), suggesting that it may be an improved PDE4 inhibitor for medication development and repurposing efforts to treat alcohol abuse.

Electroacupuncture Attenuates Hyperalgesia in Rats Withdrawn from Chronic Alcohol Drinking via Habenular Mu Opioid Receptors.

Hyperalgesia or increased sensitivity to pain is often found in alcoholics during alcohol withdrawal and may contribute to relapse drinking. Alternative therapies such as acupuncture and electroacupuncture (EA), through mechanisms involving opioid receptors, may reduce pain and substance dependence and withdrawal syndromes. The lateral habenula (LHb), an epithalamic structure rich in mu opioid receptors (MORs), is a critical target for both drugs of abuse and pain. We previously observed hyperalgesia in rats withdrawn from chronic ethanol (EtOH) drinking and found that EA at the acupoint Zusanli (ST36) reduced EtOH intake. This raised question of whether EA can alleviate hyperalgesia during alcohol withdrawal and, if so, whether the mechanism involves MORs in the LHb. We trained male rats to drink EtOH using the intermittent access 20% EtOH 2-bottle free-choice drinking paradigm for 8weeks, after which the alcohol supply was discontinued. We measured pain sensitivity using radiant heat (a light beam directed at the hind paw of rats) and compared the paw withdrawal latencies (PWLs) with and without EA at ST36. The PWLs were significantly shorter in rats at 24, 48, and 72hours and 7days after the discontinuation of EtOH when compared to EtOH-naïve rats. After a single administration of 2-Hz EA for 20minutes at ST36, the PWLs at 24hours after the withdrawal of EtOH were significantly greater than those of the sham group (2-Hz EA at the tail). Furthermore, the effect of EA on PWLs was significantly attenuated by bilateral intrahabenula infusion of the MOR antagonist naltrexone. These results suggest that EA can alleviate hyperalgesia during EtOH withdrawal through a mechanism involving MORs in the habenula. Based on this, EA could be of potential value as a therapy for hyperalgesia in alcohol dependence.

Kappa-opioid receptors differentially regulate low and high levels of ethanol intake in female mice.

IntroductionStudies in laboratory animals and humans indicate that endogenous opioids play an important role in regulating the rewarding value of various drugs, including ethanol (EtOH). Indeed, opioid antagonists are currently a front‐line treatment for alcoholism in humans. Although roles for mu‐ and delta‐opioid receptors have been characterized, the contribution of kappa‐opioid receptors (KORs) is less clear. There is evidence that changes in KOR system function can decrease or increase EtOH drinking, depending on test conditions. For example, female mice lacking preprodynorphin – the precursor to the endogenous KOR ligand dynorphin – have reduced EtOH intake. Considering that KORs can regulate dopamine (DA) transmission, we hypothesized that KORs expressed on DA neurons would play a prominent role in EtOH intake in females.MethodsWe used a Cre/loxP recombination strategy to ablate KORs throughout the body or specifically on dopamine uptake transporter (DAT)‐expressing neurons to investigate the role of KORs on preference for and intake of EtOH (2‐bottle choice), the transition from moderate to excessive EtOH drinking (intermittent EtOH access), and binge EtOH drinking (drinking in the dark [DID]).Results KOR deletion decreased preference for EtOH, although this effect was less pronounced when EtOH intake increased beyond relatively low levels.DiscussionOur findings indicate that KOR activation increases EtOH drinking via effects mediated, at least in part, by KORs on DA neurons. While the mechanisms of this regulation remain unknown, previous work suggests that alterations in negative reinforcement processes or sensitivity to the sensory properties of EtOH can affect preference and intake.

Effects of ceftriaxone on ethanol, nicotine or sucrose intake by alcohol-preferring (P) rats and its association with GLT-1 expression

Increased glutamatergic neurotransmission appears to mediate the reinforcing properties of drugs of abuse, including ethanol (EtOH). We have shown that administration of ceftriaxone (CEF), a β-lactam antibiotic, reduced EtOH intake and increased glutamate transporter 1 (GLT-1) expression in mesocorticolimbic regions of male and female alcohol-preferring (P) rats. In the present study, we tested whether CEF administration would reduce nicotine (NIC) and/or EtOH intake by adult female P rats. P rats were randomly assigned to 4 groups: (a) 5% sucrose (SUC) or 10% SUC [SUC], (b) 5% SUC+0.07mg/ml NIC and 10% SUC+0.14mg/ml NIC [NIC–SUC], 15% EtOH and 30% EtOH [EtOH] and (d) 15% EtOH+0.07mg/ml NIC and 30% EtOH+0.14mg/ml NIC [NIC–EtOH]. After achieving stable intakes (4weeks), the rats were administered 7 consecutive, daily i.p. injections of either saline or 200mg/kg CEF. The effects of CEF on intake were significant but differed across the reinforcers; such that ml/kg/day SUC was reduced by ∼30%, mg/kg/day NIC was reduced by ∼70% in the NIC–SUC group and ∼40% in the EtOH–NIC group, whereas g/kg/day EtOH was reduced by ∼40% in both the EtOH and EtOH–NIC group. The effects of CEF on GLT-1 expression were also studied. We found that CEF significantly increased GLT-1 expression in the prefrontal cortex and the nucleus accumbens of the NIC and NIC–EtOH rats as compared to NIC and NIC–EtOH saline-treated rats. These findings provide further support for GLT-1-associated mechanisms in EtOH and/or NIC abuse. The present results along with previous reports of CEF’s efficacy in reducing cocaine self-administration in rats suggest that modulation of GLT-1 expression and/or activity is an important pharmacological target for treating polysubstance abuse and dependence.

Corticotropin Releasing Factor Binding Protein and CRF2 Receptors in the Ventral Tegmental Area: Modulation of Ethanol Binge Drinking in C57BL/6J Mice.

Most studies with corticotropin releasing factor (CRF) and ethanol (EtOH) consumption have focused on CRF type 1 (CRF1 ) receptors; less is known about other components of the CRF system, such as the CRF type 2 (CRF2 ) receptors and the CRF binding protein (CRFBP). In humans, several nucleotide polymorphisms in the CRFBP gene have been associated with EtOH abuse. The role of the CRFBP within the ventral tegmental area (VTA) and the central nucleus of the amygdala (CeA) was investigated in C57BL/6J mice exposed to an EtOH binge drinking paradigm (drinking in the dark [DID]), or to a dependence-producing drinking protocol (2-bottle choice, intermittent access to alcohol [IAA]) for 4 weeks. Potential interactions between VTA CRFBP and CRF2 receptors on EtOH binge drinking were also assessed. Mice were microinjected with the CRFBP antagonist CRF fragment 6-33 (CRF6-33 ) into the VTA or CeA, or with the CRF2 antagonist astressin-2B (A2B) alone or in combination with CRF6-33 into the VTA, and had access to 20% (w/v) EtOH for 4 hours (DID). Separate cohorts of mice received vehicle and doses of CRF6-33 into the VTA or CeA and had access to EtOH/water for 24 hours (IAA). Blood EtOH concentrations (BECs) were measured, and signs of withdrawal by handling-induced convulsions were determined. Intra-VTA CRF6-33 and A2B reduced EtOH intake dose dependently in mice during DID. Furthermore, a combination of a subeffective dose of CRF6-33 and a lower dose of A2B promoted additive effects in attenuating EtOH binge drinking. Intra-VTA CRF6-33 did not affect EtOH consumption in mice given IAA, and intra-CeA CRF6-33 did not change alcohol consumption in both models of drinking. DID and IAA promoted pharmacologically relevant BECs; however, only mice given IAA exhibited convulsive events during withdrawal. These findings suggest that VTA CRFBP is involved in the initial stages of escalated EtOH drinking by mechanisms that may involve CRF2 receptors.

Reduction of alcohol drinking of alcohol-preferring (P) and high-alcohol drinking (HAD1) rats by targeting phosphodiesterase-4 (PDE4).

Phosphodiesterase-4 (PDE4) and neuroimmune signaling have been posited to regulate alcohol drinking. This study evaluated the involvement of PDE4 and Il22ra2 on ethanol (EtOH) intake by alcohol-preferring (P) and high-alcohol-drinking (HAD1) rats. Exp 1 determined the dose-response effects of PDE4 inhibitors, rolipram, and Ro 20-1724, on 2h/day free-choice EtOH intake by adult P and HAD1 rats. Exps 2-3 examined the effects of repeated administration with the PDE4 inhibitors on EtOH or sucrose intake and locomotor behavior. Exp 4 determined Pde4-associated gene expression differences in subregions of the extended amygdala, between high- and low-alcohol-consuming rat lines. Exp 5 evaluated the effects of infusing short hairpin RNA to knock down Il22ra2 in the nucleus accumbens (NAc) shell on a 24-h free-choice EtOH drinking by P rats. Administration of rolipram or Ro 20-1724 reduced EtOH intake by P rats; Ro 20-1724 reduced EtOH intake by HAD1 rats. Repeated rolipram or Ro 20-1724 exposure reduced EtOH intake by P and HAD1 rats. PDE4 inhibition induced motor impairment during the first hour of EtOH intake by P rats. Higher gene expression levels for PDE4A were found in the NAc shell of P vs NP rats. ShRNAs targeting Il22ra2 in the NAc shell significantly reduced chronic EtOH intake. PDE4 and neuroinflammatory/immune signaling pathways could represent molecular targets for the treatment of alcohol use disorders in genetically predisposed subjects. This study underscores the importance of testing compounds over multiple days and rat lines when determining efficacy to disrupt excessive alcohol intake.

Peroxisome proliferator-activated receptors α and γ are linked with alcohol consumption in mice and withdrawal and dependence in humans.

Peroxisome proliferator-activated receptor (PPAR) agonists reduce voluntary ethanol (EtOH) consumption in rat models and are promising therapeutics in the treatment for drug addictions. We studied the effects of different classes of PPAR agonists on chronic EtOH intake and preference in mice with a genetic predisposition for high alcohol consumption and then examined human genomewide association data for polymorphisms in PPAR genes in alcohol-dependent subjects. Two different behavioral tests were used to measure intake of 15% EtOH in C57BL/6J male mice: 24-hour 2-bottle choice and limited access (3-hour) 2-bottle choice, drinking in the dark. We measured the effects of pioglitazone (10 and 30mg/kg), fenofibrate (50 and 150mg/kg), GW0742 (10mg/kg), tesaglitazar (1.5mg/kg), and bezafibrate (25 and 75mg/kg) on EtOH intake and preference. Fenofibric acid, the active metabolite of fenofibrate, was quantified in mouse plasma, liver, and brain by liquid chromatography tandem mass spectrometry. Data from a human genome-wide association study (GWAS) completed in the Collaborative Study on the Genetics of Alcoholism (COGA) were then used to analyze the association of single nucleotide polymorphisms (SNPs) in different PPAR genes (PPARA, PPARD, PPARG, and PPARGC1A) with 2 phenotypes: DSM-IV alcohol dependence (AD) and the DSM-IV criterion of withdrawal. Activation of 2 isoforms of PPARs, α and γ, reduced EtOH intake and preference in the 2 different consumption tests in mice. However, a selective PPARδ agonist or a pan agonist for all 3 PPAR isoforms did not decrease EtOH consumption. Fenofibric acid, the active metabolite of the PPARα agonist fenofibrate, was detected in liver, plasma, and brain after 1 or 8days of oral treatment. The GWAS from COGA supported an association of SNPs in PPARA and PPARG with alcohol withdrawal and PPARGC1A with AD but found no association for PPARD with either phenotype. We provide convergent evidence using both mouse and human data for specific PPARs in alcohol action. Reduced EtOH intake in mice and the genetic association between AD or withdrawal in humans highlight the potential for repurposing FDA-approved PPARα or PPARγ agonists for the treatment of AD.

Reduced ethanol consumption by alcohol-preferring (P) rats following pharmacological silencing and deep brain stimulation of the nucleus accumbens shell

There is increasing interest in deep brain stimulation (DBS) for the treatment of addiction. Initial testing must be conducted in animals, and the alcohol-preferring (P) rat meets the criteria for an animal model of alcoholism. This study is composed of 2 experiments designed to examine the effects of 1) pharmacological inactivation and 2) DBS of the nucleus accumbens shell (AcbSh) on the consumption of alcohol by P rats. In the first experiment, the effects of reversible inactivation of the AcbSh were investigated by administering intracranial injections of γ-aminobutyric acid (GABA) agonists. Bilateral microinjections of drug were administered to the AcbSh in P rats (8-10 rats/group), after which the animals were placed in operant chambers containing 2 levers--one used to administer water and the other to administer 15% EtOH--to examine the acquisition and maintenance of oral EtOH self-administration. In the second experiment, a DBS electrode was placed in each P rat's left AcbSh. The animals then received 100 or 200 μA (3-4 rats/group) of DBS to examine the effect on daily consumption of oral EtOH in a free-access paradigm. In the first experiment, pharmacological silencing of the AcbSh with GABA agonists did not decrease the acquisition of EtOH drinking behavior but did reduce EtOH consumption by 55% in chronically drinking rats. Similarly, in the second experiment, 200 μA of DBS consistently reduced EtOH intake by 47% in chronically drinking rats. The amount of EtOH consumption returned to baseline levels following termination of therapy in both experiments. Pharmacological silencing and DBS of the AcbSh reduced EtOH intake after chronic EtOH use had been established in rodents. The AcbSh is a neuroanatomical substrate for the reinforcing effects of alcohol and may be a target for surgical intervention in cases of alcoholism.

The α5 Neuronal Nicotinic Acetylcholine Receptor Subunit Plays an Important Role in the Sedative Effects of Ethanol But Does Not Modulate Consumption in Mice

Alcohol use disorders (AUDs) are a major public health problem, and the few treatment options available to those seeking treatment offer only modest success rates. There remains a need to identify novel targets for the treatment of AUDs. The neuronal nicotinic acetylcholine receptors (nAChRs) represent a potential therapeutic target in the brain, as recent human genetic studies have implicated gene variants in the α5 nAChR subunit as high risk factors for developing alcohol dependence. Here, we evaluate the role of the α5* nAChR for ethanol (EtOH)-mediated behaviors using male α5+/+ and α5-/- transgenic mice. We characterized the effect of hypnotic doses of EtOH and investigated drinking behavior using an adapted drinking-in-the-dark (DID) paradigm that has been shown to induce high EtOH consumption in mice. We found the α5 subunit to be important in mediating the sedative effects of EtOH. The α5-/- mice showed slower recovery from EtOH-induced sleep, as measured by loss of righting reflex. Additionally, the α5-/- mice showed enhanced impairment to EtOH-induced ataxia. We found the initial sensitivity to EtOH and EtOH metabolism to be similar in both α5+/+ and α5-/- mice. Hence, the enhanced sedation is likely due to a difference in the acute tolerance of EtOH in α5-/- mice. However, the α5 subunit did not play a role in EtOH consumption for EtOH concentrations ranging from 5 to 30% using the DID paradigm. Additionally, varenicline was effective in reducing EtOH intake in α5-/- mice. Together, our data suggest that the α5 nAChR subunit is important for the sedative effects of EtOH but does not play a role in EtOH consumption in male mice. Varenicline can be a treatment option even when there is loss of function of the α5 nAChR subunit.

Environmental Modulation of Alcohol Intake in Hamsters: Effects of Wheel Running and Constant Light Exposure

Alcohol abuse leads to marked disruptions of circadian rhythms, and these disturbances in themselves can increase the drive to drink. Circadian clock timing is regulated by light, as well as by nonphotic influences such as food, social interactions, and wheel running. We previously reported that alcohol markedly disrupts photic and nonphotic modes of circadian rhythm regulation in Syrian hamsters. As an extension of this work, we characterize the hedonic interrelationship between wheel running and ethanol (EtOH) intake and the effects of environmental circadian disruption (long-term exposure to constant light [LL]) on the drive to drink. First, we tested the effect of wheel running on chronic free-choice consumption of a 20% (v/v) EtOH solution and water. Second, the effect of this alcohol drinking on wheel running in alcohol-naive animals was investigated. Third, we assessed the influence of LL, known to suppress locomotor activity and cause circadian rhythm disruption, on EtOH consumption and wheel-running behavior. Inhibitory effects of wheel running on EtOH intake and vice versa were observed. Exposure to LL, while not affecting EtOH intake, induced rhythm splitting in 75% of the animals. Notably, the splitting phenotype was associated with lower levels of EtOH consumption and preference prior to, and throughout, the period of LL exposure. These results are evidence that exercise may offer an efficacious clinical approach to reducing EtOH intake. Also, predisposition for light-induced (or other) forms of circadian disruption may modulate the drive to drink.

Acetaldehyde mediates alcohol activation of the mesolimbic dopamine system

Ethanol (EtOH), the main psychoactive ingredient of alcoholic drinks, is widely considered to be responsible for alcohol abuse and alcoholism through its positive motivational properties, which depend, at least partially, on the activation of the mesolimbic dopaminergic system. However, acetaldehyde (ACD), the first metabolite of EtOH, has been classically considered to be aversive and useful in the pharmacological therapy of alcoholics. Here we show that EtOH-derived ACD is necessary for EtOH-induced place preference, a pre-clinical test with high predictive validity for reward liability. We also found that ACD is essential for EtOH-increased microdialysate dopamine (DA) levels in the rat nucleus accumbens and that this effect is mimicked by intra-ventral tegmental area (VTA) ACD administration. Furthermore, in vitro, ACD enhances VTA DA neuronal firing through action on two ionic currents: reduction of the A-type K+ current and activation of the hyperpolarization-activated inward current. EtOH-stimulating properties on DA neurons are prevented by pharmacological blockade of local catalase, the main metabolic step for biotransformation of EtOH into ACD in the central nervous system. These results provide in-vivo and in-vitro evidence for a key role of ACD in the motivational properties of EtOH and its activation of the mesolimbic DA system. Additionally, these observations suggest that ACD, by increasing VTA DA neuronal activity, would oppose its well-known peripherally originating aversive properties. Careful consideration of these findings could help in devising new effective pharmacological therapies aimed at reducing EtOH intake in alcoholics.

Involvement of Dopamine D2 Autoreceptors in the Ventral Tegmental Area on Alcohol and Saccharin Intake of the Alcohol‐Preferring P Rat

The ventral tegmental area (VTA) dopamine (DA) system is considered to be involved in mediating the actions of ethanol (EtOH). The objective of the present study was to examine the role of VTA DA D2 receptors in regulating EtOH intake of alcohol-preferring P rats. EtOH (10% v/v) and saccharin (SACC, 0.0125% g/v) intake during 2 hr of limited access was assessed after microinjections of the D2 agonist quinpirole and the D2 antagonist sulpiride into the anterior VTA (AVTA) of female P rats. Both EtOH-SACC alternate-day-access conditions and daily availability of EtOH and SACC solutions to separate groups of subjects were used. A second D2 agonist, quinelorane, and coadministration of 2.0 microg sulpiride with 2.0 microg quinpirole were tested in animals given limited access to EtOH. Finally, the effects of quinpirole injected 2 mm dorsal to the VTA and within the posterior VTA (PVTA) were assessed under EtOH-SACC alternate-day-access conditions. Microinjections of 2.0-6.0 microg quinpirole into the AVTA dose dependently decreased EtOH intake 40-80% during the first 30 min of the limited access sessions but did not alter SACC intake. Injections of 2.0-4.0 microg quinelorane into the AVTA also reduced EtOH intake in the first 30 min. Administration of 0.5-2.0 microg sulpiride into the AVTA had no effect on either EtOH or SACC intakes but did attenuate the effects of quinpirole on reducing EtOH intake. Injections of 2.0-4.0 quinpirole 2 mm dorsal to the VTA did not alter EtOH or SACC intakes. Posterior VTA injections of quinpirole decreased EtOH and SACC intakes approximately 25-30% and 60-70%, respectively, in the first 30 min. None of the treatments altered intakes during the 30-120 min period. The data suggest that DA neuronal activity within the AVTA may be important for maintaining EtOH drinking in P rats, whereas DA neuronal activity within the PVTA may be involved in regulating general drinking and/or motivational behaviors. Overall, the results confirm the involvement of mesolimbic DA in EtOH self-administration and suggest that there is functional heterogeneity within the VTA regulating drinking behavior of the P rat.

Comparison of the Effects of the Selective Serotonin-Reuptake Inhibitors Fluoxetine, Paroxetine, Citalopram and Fluvoxamine in Alcohol-Preferring cAA Rats

Clinical studies indicate that selective serotonin-reuptake inhibitors (SSRIs) may decrease alcohol intake and craving in particular subgroups of alcoholics. The aim of the present study was to compare the behavioral profile of various SSRIs in alcohol-preferring cAA rats, a genetic model of alcoholism. The effects of acute IP administration of fluoxetine (doses in mg/kg 1–10), citalopram (3–30), fluvoxamine (3–30) and paroxetine (1–10) on ethanol (EtOH) intake and preference, as well as food and total fluid intake, were determined in a 12-h access, water vs. 10% v/v EtOH two-bottle choice paradigm. Each compound reduced EtOH intake [Minimal Effective Doses (MEDs) 5, 10, 30 and 1 mg/kg for fluoxetine, citalopram, fluvoxamine, and paroxetine, respectively]. The degree of selectivity, that is, the extent to which reductions in EtOH intake could be separated from reductions in food and/or total fluid intake varied across the compounds. Thus, whereas EtOH intake was more markedly affected than food intake by fluoxetine, both parameters were equally affected by citalopram, and food intake was more markedly affected than EtOH intake by fluvoxamine and paroxetine. The anti-alcohol effect also differed with respect to specificity, that is, the degree to which effects on EtOH intake coincided with effects on EtOH preference. Whereas fluoxetine showed the highest level of specificity, followed by citalopram and fluvoxamine, the effect of paroxetine was nonspecific. The observed variation in the degree of selectivity and specificity of the anti-alcohol effect of SSRIs suggests that reductions in EtOH intake are not merely a consequence of a general suppressive effect on consummatory behavior. It is hypothesized that differences between the behavioral profiles of these compounds reflect a differential involvement of 5-HT receptor subtypes.

5-HT2A and 5-HT2C/5-HT1B Receptors Are Differentially Involved in Alcohol Preference and Consummatory Behavior in cAA Rats

The present study aimed to investigate the role of serotonin 5-HT2A and 5-HT2C receptors in the control of alcohol preference and consummatory behavior in alcohol-preferring cAA rats. Effects of the 5-HT2A/2C receptor agonist, DOI, the 5-HT2C/1B receptor agonist, mCPP, the 5-HT2A/2C receptor antagonist, ritanserin, and the 5-HT2A receptor antagonist, MDL 100,907, on ethanol (EtOH, 10% v/v) preference and intake, as well as total fluid and food intake were evaluated in a 12-h limited-access two-bottle paradigm. DOI (0.3–3 mg/kg, IP) reduced EtOH intake and preference, but not total fluid or food intake; whereas mCPP (1–10 mg/kg, SC) reduced EtOH, total fluid, and food intake. Therefore, it is concluded that DOI induces a specific and selective antialcohol effect, whereas mCPP rather induces a general suppressive effect on consummatory behavior. Ritanserin (1–10 mg/kg, IP) did not affect EtOH intake and preference, nor total fluid and food consumption. MDL 100,907 (0.1–1 mg/kg, IP) induced only a small reduction of food intake at the highest dose tested. Pretreatment with ritanserin (3 mg/kg, IP) and MDL 100,907 (0.3 mg/kg, IP) blocked the effects of DOI (3 mg/kg, IP), but not those of mCPP (10 mg/kg, IP). It is suggested that activation of 5-HT2C and/or 5-HT1B receptors results in a general decrease of consummatory behavior, whereas activation of 5-HT2A receptors selectively decreases EtOH intake and preference, as assessed in the cAA rat model of alcoholism.

Blocking GABA A receptors in the anterior ventral tegmental area attenuates ethanol intake of the alcohol-preferring P rat

The effect of blocking the A subtype of gamma-aminobutyric acid (GABA(A)) receptors in the anterior ventral tegmental area (VTA) on ethanol (EtOH; 10% v/v) and saccharin (SACC; 0.0125%) consumption was investigated in alcohol-preferring P rats. Picrotoxin (0.005, 0.01, 0.05 and 0.10 microg/0.5 microl) was injected into the VTA, and consumption of EtOH and SACC was assessed in two 2-h limited-access drinking paradigms (concurrent EtOH/SACC access, and alternate-day-access to EtOH and SACC). Under concurrent-access conditions, the picrotoxin microinjections resulted in a 55 and 84% decrease in EtOH consumption at the 0.05 and 0.10 microg doses, respectively, compared with consumption following microinjections of vehicle solution (P<0.05). Saccharin intake was not significantly altered by picrotoxin. Under alternate-day-access drinking conditions, the picrotoxin microinjections resulted in dose-dependent decreases in EtOH consumption of 37-68%, with significant decreases following the 0.005, 0.05 and 0.10 microg doses (P<0.04). Saccharin intake was significantly reduced only at the 0.05 microg dose. The decrease in EtOH consumption after 0.10 microg picrotoxin was attenuated by co-administration of 0.01 microg muscimol. This dose of muscimol had no effect on EtOH consumption when injected alone. Intra-VTA injections of bicuculline (0.04 microg), another GABA(A) antagonist, reduced EtOH intake, comparable to the reduction following 0.10 microg picrotoxin. Microinjections of 0.10 microg picrotoxin in regions outside the VTA failed to decrease EtOH intake. These results suggest that anterior VTA mechanisms regulating alcohol drinking behavior are under tonic GABA inhibition, mediated by GABA(A) receptors. The results also suggest that different neural mechanisms are regulating voluntary EtOH and SACC drinking behaviors.

Stimulus properties of the L-type calcium channel agonist BAY k 8644 in rats.

Calcium (Ca(2+)) channels appear to be involved in the regulation of ethanol (EtOH) intake, as indicated by the effectiveness of both L-type Ca(2+) channel antagonists and agonists in reducing EtOH intake in animals. The present study was aimed to investigate rewarding/aversive and discriminative stimulus effects of the Ca(2+) channel agonist BAY k 8644, a compound showing pronounced anti-alcohol effects in rats. Therefore, a series of conditioned taste aversion (CTA), conditioned place preference (CPP) and two-lever drug discrimination (DD) experiments were conducted in Wistar rats, with (+/-)-BAY k 8644 and its enantiomers. After i.p. application, (+/-)-BAY k 8644 (0.0625-1mg/kg), (-)-BAY k 8644 (0.125-1mg/kg) and (+)-BAY k 8644 (2.5-20mg/kg) all induced a dose-dependent CTA. The minimal effective doses (MED) for (+/-)-, (-)- and (+)-BAY k 8644 were 0.25, 0.25 and 10mg/kg, respectively. In a CPP study, however, (+/-)-BAY k 8644 (0.25-2mg/kg, i.p.) showed neither aversive nor rewarding stimulus properties. Rats were trained to discriminate (-)-BAY k 8644 (0.3mg/kg, i.p.), the enantiomer acting as a high potency Ca(2+) channel agonist, from vehicle, in a two-lever DD procedure (ED(50)) value: 0.05mg/kg); full generalisation: 0.1mg/kg). The (-)-BAY k 8644 cue dose-dependently generalized to (+/-)-BAY k 8644 and (+)-BAY k 8644, the enantiomer acting as a low potency Ca(2+) channel antagonist, with ED(50) values of 0.06 and 0.28mg/kg, respectively. Both (+/-)- and (+)-BAY k 8644 produced full generalization at 1mg/kg, the latter compound showing an inverted U-shaped curve (i.e., this was the only dose showing >80% drug lever selection). The stimulus patterns of BAY k 8644 and its enantiomers appear to resemble the anti-alcohol profiles of these compounds. Therefore, commonalities between the stimulus properties of the agonistic and antagonistic enantiomers might provide a clue for the mechanism underlying the anti-alcohol effects of L-type Ca(2+) channel antagonists and agonists.

O-1-8 - Cannabis withdrawal syndrome: Laboratory artifact or clinically important?

Clinical studies indicate that selective serotonin-reuptake inhibitors (SSRIs) may decrease alcohol intake and craving in particular subgroups of alcoholics. The aim of the present study was to compare the behavioral profile of various SSRIs in alcohol-preferring cAA rats, a genetic model of alcoholism. The effects of acute IP administration of fluoxetine (doses in mg/kg 1–10), citalopram (3–30), fluvoxamine (3–30) and paroxetine (1–10) on ethanol (EtOH) intake and preference, as well as food and total fluid intake, were determined in a 12-h access, water vs. 10% v/v EtOH two-bottle choice paradigm. Each compound reduced EtOH intake [Minimal Effective Doses (MEDs) 5, 10, 30 and 1 mg/kg for fluoxetine, citalopram, fluvoxamine, and paroxetine, respectively]. The degree of selectivity, that is, the extent to which reductions in EtOH intake could be separated from reductions in food and/or total fluid intake varied across the compounds. Thus, whereas EtOH intake was more markedly affected than food intake by fluoxetine, both parameters were equally affected by citalopram, and food intake was more markedly affected than EtOH intake by fluvoxamine and paroxetine. The anti-alcohol effect also differed with respect to specificity, that is, the degree to which effects on EtOH intake coincided with effects on EtOH preference. Whereas fluoxetine showed the highest level of specificity, followed by citalopram and fluvoxamine, the effect of paroxetine was nonspecific. The observed variation in the degree of selectivity and specificity of the anti-alcohol effect of SSRIs suggests that reductions in EtOH intake are not merely a consequence of a general suppressive effect on consummatory behavior. It is hypothesized that differences between the behavioral profiles of these compounds reflect a differential involvement of 5-HT receptor subtypes.

Benzodiazepine receptor ligands with different intrinsic efficacies alter ethanol intake in alcohol-nonpreferring (NP) rats

Benzodiazepine (BDZ) receptor ligands with varying intrinsic efficacies [RO19-4603, 0.02-0.15 mg/kg; FG 7142 1-16 mg/kg; DMCM, 1-8 mg/kg; RO16-6028 (bretazenil), 8-32 mg/kg] in modulating GABAergic activity were examined for the ability to alter palatability-induced ethanol (EtOH) intake in the alcohol-nonpreferring (NP) line of rats. NP rats on a 22-hour fluid-deprivation schedule were given 2-hour daily access to a 10% (v/v) EtOH/3% (g/v) polycose solution and water. Average EtOH intake was 2.1 +/- 0.2 g/kg/2 hours, and water intake was 17.1 +/- 0.9 ml/2 hours. During the initial 15 minutes of the 2-hour session, RO19-4603, the imidazothienodiazepine partial inverse agonist reduced EtOH intake to 19% of control values at 0.04 mg/kg and completely suppressed drinking of the EtOH solution at 0.15 mg/kg. Twenty-four-hour postdrug administration, the 0.08-mg/kg dose of RO19-4603 completely suppressed drinking of the EtOH solution at the 60-minute interval, and the 0.15-mg/kg dose reduced intake to 20% of control levels at the 15-minute interval. FG 7142, the partial beta-carboline inverse agonist reduced EtOH drinking at the 60-minute interval with the 1-mg/kg dose, and the 16-mg/kg dose reduced water intake at the 15-minute interval. DMCM, the full beta-carboline inverse agonist, significantly reduced water intake at 15 minutes (4 and 8 mg/kg), and the same doses caused a substantial increase in EtOH drinking at the 120-minute interval. The anxiolytic agent bretazenil (16 and 32 mg/kg) increased EtOH consumption during the initial 15 minutes to 270% to 425% of control levels, and water intake increased by the end of the 2-hour session to as much as 210% of control following administration of the 32-mg/kg dose. These findings support existing evidence suggesting that BDZ receptor ligands may modify neuronal processes that mediate some reinforcing and/or aversive properties of alcohol. They further demonstrate a potential importance of the GABAA-BDZ receptor complex in mediating palatability- (environmentally) induced EtOH drinking even in rats selectively bred for low alcohol preference.