Hakim Houchi

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-naïve 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.

A haplotype of the DRD1 gene is associated with alcohol dependence.

BACKGROUNDnThe D1 dopamine receptor has been involved in a number of brain functions, including motor control, inattentive symptoms and reward and reinforcement mechanisms. Indeed, DRD1 antagonists may reduce cocaine-seeking behavior and the acquisition of cocaine-cue associations. The D1.1/r4532 marker of the DRD1 gene has been associated with a large set of phenotypes including addictive behaviors, but none with alcohol dependence per se.nnnMETHODSnWe analyzed a population of 134 patients with alcohol dependence, also assessing more homogeneous (severe) phenotypes, comparing this sample with a healthy control population, assessing two SNPs within the DRD1 gene in order to depict the role of DRD1 polymorphisms and haplotypes.nnnRESULTSnThe T allele of the rs686 polymorphism within DRD1 gene was significantly more frequent in patients with alcohol dependence (p = 0.0008), with a larger excess for patients with severe dependence (p = 6 x 10(-6)), and even more for patients with severe complications such as withdrawal seizures (p = 7 x 10(-7)). A specific haplotype rs686*T-rs4532*G within the DRD1 gene was significantly more precisely associated with alcohol dependence in our sample (p = 5 x 10(-6)).nnnCONCLUSIONSnEven though chance finding cannot be ruled out, convergent evidence is given that the DRD1 gene is a susceptibility gene in alcohol dependence, regarding the fact that relying on more homogeneous phenotypes (i.e., more severe patients) and more informative genetic markers (i.e., haplotypes) reinforce the initial association.

Human and experimental evidence supporting a role for osteopontin in alcoholic hepatitis

We identified, in the transcriptome analysis of patients with alcoholic hepatitis (AH), osteopontin (OPN) as one of the most up‐regulated genes. Here, we used a translational approach to investigate its pathogenic role. OPN hepatic gene expression was quantified in patients with AH and other liver diseases. OPN protein expression and processing were assessed by immmunohistochemistry, western blotting and enzyme‐linked immunosorbent assay. OPN gene polymorphisms were evaluated in patients with alcoholic liver disease. The role of OPN was evaluated in OPN−/− mice with alcohol‐induced liver injury. OPN biological actions were studied in human hepatic stellate cells (HSCs) and in precision‐cut liver slices. Hepatic expression and serum levels of OPN were markedly increased in AH, compared to normal livers and other types of chronic liver diseases, and correlated with short‐term survival. Serum levels of OPN also correlated with hepatic expression and disease severity. OPN was mainly expressed in areas with inflammation and fibrosis. Two proteases that process OPN (thrombin and matrix metalloproteinase 7) and cleaved OPN were increased in livers with AH. Patients with AH had a tendency of a lower frequency of the CC genotype of the +1239C single‐nucleotide polymorphism of the OPN gene, compared to patients with alcohol abuse without liver disease. Importantly, OPN−/− mice were protected against alcohol‐induced liver injury and showed decreased expression of inflammatory cytokines. Finally, OPN was induced by lipopolysaccharide and stimulated inflammatory actions in HSCs. Conclusion: Human and experimental data suggest a role for OPN in the pathogenesis of AH. Further studies should evaluate OPN as a potential therapeutic target. (Hepatology 2013;58:1742–1756)

Fluoxetine, Desipramine, and the Dual Antidepressant Milnacipran Reduce Alcohol Self-Administration and/or Relapse in Dependent Rats

A few clinical studies have shown that dual antidepressants (serotonergic (5-HT) and noradrenergic (NE) transporter inhibitors, SNRIs) may be effective in alcoholism treatment. We studied the effect of the dual antidepressant milnacipran on ethanol operant self-administration in acutely withdrawn ethanol-dependent and in -non-dependent Wistar rats, and used fluoxetine and desipramine to dissect both 5-HT and NE components, respectively, in the effect of milnacipran. Milnacipran was also tested for relapse after protracted abstinence and on ethanol-induced (1.0u2009g/kg) conditioned place preference in control rats and ethanol-induced locomotor sensitization in DBA/2J female mice. Milnacipran dose dependently (5–40u2009mg/kg) attenuated the increased ethanol self-administration observed during early withdrawal and was more potent in preventing reinstatement in dependent rats after protracted abstinence as compared with non-dependent rats. Desipramine and fluoxetine (10u2009mg/kg) blocked ethanol self-administration during early withdrawal, and recovery was delayed in dependent animals, indicating a potent effect. Ethanol self-administration was also reduced 1 day after treatment with desipramine and fluoxetine but not with milnacipran. Finally, milnacipran prevented ethanol-induced place preference in ethanol-naive rats and reduced the magnitude of ethanol-induced sensitization associated with a delayed induction in mice. Desipramine (20u2009mg/kg) countered sensitization development and reduced its expression at 1 week after treatment; fluoxetine (10u2009mg/kg) reduced sensitization expression. Thus, 5-HT and NE transmissions during sensitization expression may mediate the effect of milnacipran on sensitization induction. These results support that SNRIs may have a potential use in alcoholism treatment.

Effects of prenatal and postnatal maternal ethanol on offspring response to alcohol and psychostimulants in long evans rats

An important factor that may influence addiction liability is exposure during the early life period. Exposure to ethanol, early in life, can have long-lasting implications on brain function and drugs of abuse response later in life. In the present study we investigated the behavioral responses to ethanol and to psychostimulants in Long Evans rats that have been exposed to pre- and postnatal ethanol. Since a relationship between heightened drug intake and susceptibility to drug-induced locomotor activity/sensitization has been demonstrated, we tested these behavioral responses, in control and early life ethanol-exposed animals. The young adult male and female progeny were tested for locomotor response to alcohol, cocaine and d-amphetamine. Sedative, rewarding effects of alcohol and alcohol consumption were measured. Our results show that early life ethanol exposure behaviorally sensitized animals to subsequent ethanol and psychostimulants exposure. Ethanol-exposed animals were also more sensitive to the hyperlocomotor effects of all drugs of abuse tested and to those of the dopamine receptor agonist apomorphine. Locomotor sensitization to repeated injections of cocaine was facilitated in ethanol-exposed animals. Ethanol-induced conditioned place preference was also facilitated in ethanol-exposed animals. Ethanol consumption and preference were increased after early life ethanol exposure and this was associated with decreased sensitivity to the sedative effects of ethanol. The altered behavioral responses to drugs of abuse were associated with decreased striatal dopamine transporter and hippocampal NMDAR binding. Our results outline an increased vulnerability to rewarding and stimulant effects of ethanol and psychostimulants and support the epidemiological and clinical data that suggested that early chronic exposure to ethanol may increase the propensity for later self-administration of ethanol or other substances.

Involvement of A2A receptors in anxiolytic, locomotor and motivational properties of ethanol in mice

We have shown previously that mice lacking the adenosine A2A receptor (A2AR) generated on a CD1 background self‐administer more ethanol and exhibit hyposensitivity to acute ethanol. We aimed to investigate if the increased propensity of A2A−/− mice to consume ethanol is associated with an altered sensitivity in the motivational properties of ethanol in the conditioned place preference (CPP) and conditioned taste aversion (CTA) paradigms and with an altered development of sensitization to the locomotor effects of ethanol. We also tested their sensitivity to the anxiolytic effects of ethanol. Our results show that A2A−/− mice produced on a CD1 background displayed a reduced ethanol‐induced CPP and an increased sensitivity to the anxiolytic and locomotor‐stimulant effects of ethanol, but they did not show alteration in ethanol‐induced CTA and locomotor sensitization. Ethanol‐induced CPP, ethanol consumption and the locomotor effects of ethanol were also tested in A2A−/− mice produced on a C57BL/6J background. Our results emphasized the importance of the genetic background because alteration in ethanol consumption and preference, ethanol‐induced CPP and locomotor‐stimulant effects were not found in knockout mice produced on the alcohol‐preferring C57BL/6J genetic background. Finally, the A2AR agonist, 2‐p‐(2‐carboxyethyl)‐phenylethylamino‐5′‐N‐ethylcarboxamidoadenosine hydrochloride (CGS 21680), reduced ethanol consumption and preference in C57BL/6J mice. In conclusion, A2AR deficiency in mice generated on a CD1 background leads to high ethanol consumption that is associated with an increased sensitivity to the locomotor‐stimulant/anxiolytic effects of ethanol and a decrease in ethanol‐induced CPP.

Blunted response to low oxygen of rat respiratory network after perinatal ethanol exposure: involvement of inhibitory control

Acute ethanol depresses respiration, but little is known about chronic ethanol exposure during gestation and breathing, while the deleterious effects of ethanol on CNS development have been clearly described. In a recent study we demonstrated that pre‐ and postnatal ethanol exposure induced low minute ventilation in juvenile rats. The present study analysed in juvenile rats the respiratory response to hypoxia in vivo by plethysmography and the phrenic (Phr) nerve response to ischaemia in situ. Glycinergic neurotransmission was assessed in situ with strychnine application and [3H]strychnine binding experiments performed in the medulla. After chronic ethanol exposure, hyperventilation during hypoxia was blunted in vivo. In situ Phr nerve response to ischaemia was also impaired, while gasping activity occurred earlier and recovery was delayed. Strychnine applications in situ (0.05–0.5 μm) demonstrated a higher sensitivity of expiratory duration in ethanol‐exposed animals compared to control animals. Moreover, [3H]strychnine binding density was increased after ethanol and was associated with higher affinity. Furthermore, 0.2 μm strychnine in ethanol‐exposed animals restored the low basal Phr nerve frequency, but also the Phr nerve response to ischaemia and the time to recovery, while gasping activity appeared even earlier with a higher frequency. Polycythaemia was present after ethanol exposure whereas lung and heart weights were not altered. We conclude that chronic ethanol exposure during rat brain development (i) induced polycythaemia to compensate for low minute ventilation at rest; (ii) impaired the respiratory network adaptive response to low oxygen because of an increase in central glycinergic tonic inhibitions, and (iii) did not affect gasping mechanisms. We suggest that ethanol exposure during early life can be a risk factor for the newborn respiratory adaptive mechanisms to a low oxygen environment.

The lack of CB1 receptors prevents neuroadapatations of both NMDA and GABAA receptors after chronic ethanol exposure

As the contribution of cannabinoid (CB1) receptors in the neuroadaptations following chronic alcohol exposure is unknown, we investigated the neuroadaptations induced by chronic alcohol exposure on both NMDA and GABAA receptors in CB1−/− mice. Our results show that basal levels of hippocampal [3H]MK‐801 ((1)‐5‐methyl‐10,11‐dihydro‐5Hdibenzo[a,d]cyclohepten‐5,10‐imine) binding sites were decreased in CB1−/− mice and that these mice were also less sensitive to the locomotor effects of MK‐801. Basal level of both hippocampal and cerebellar [3H]muscimol binding was lower and sensitivity to the hypothermic effects of diazepam and pentobarbital was increased in CB1−/− mice. GABAAα1, β2, and γ2 and NMDA receptor (NR) 1 and 2B subunit mRNA levels were altered in striatum of CB1−/− mice. Our results also showed that [3H]MK‐801 binding sites were increased in cerebral cortex and hippocampus after chronic ethanol ingestion only in wild‐type mice. Chronic ethanol ingestion did not modify the sensitivity to the locomotor effects of MK‐801 in both genotypes. Similarly, chronic ethanol ingestion reduced the number of [3H]muscimol binding sites in cerebral cortex, but not in cerebellum, only in CB1+/+ mice. We conclude that lifelong deletion of CB1 receptors impairs neuroadaptations of both NMDA and GABAA receptors after chronic ethanol exposure and that the endocannabinoid/CB1 receptor system is involved in alcohol dependence.

The adenosine A2A receptor agonist CGS 21680 decreases ethanol self-administration in both non-dependent and dependent animals

There is emerging evidence that the adenosinergic system might be involved in drug addiction and alcohol dependence. We have already demonstrated the involvement of A2A receptors (A2AR) in ethanol‐related behaviours in mice. Here, we investigated whether the A2AR agonist CGS 21680 can reduce ethanol operant self‐administration in both non‐dependent and ethanol‐dependent Wistar rats. To rule out a potential involvement of the A1R in the effects of CGS 21680, we also tested its effectiveness to reduce ethanol operant self‐administration in both heterozygous and homozygous A1R knockout mice. Our results demonstrated that CGS 21680 (0.065, 0.095 and 0.125u2009mg/kg, i.p.) had a bimodal effect on 10% ethanol operant self‐administration in non‐dependent rats. The intermediate dose was also effective in reducing 2% sucrose self‐administration. Interestingly, the intermediate dose reduced 10% ethanol self‐administration in dependent animals more effectively (75% decrease) when compared with non‐dependent animals (57% decrease). These results suggest that the A2AR are involved in CGS 21680 effects since the reduction of ethanol self‐administration was not dependent upon the presence of A1R in mice. In conclusion, our findings demonstrated the effectiveness of the A2AR agonist CGS 21680 in a preclinical model of alcohol addiction and suggested that the adenosinergic pathway is a promising target to treat alcohol addiction.

Memantine reduces alcohol drinking but not relapse in alcohol-dependent rats.

Alcoholism is a chronic relapsing disorder with consequences on health and that requires more effective treatments. Among alternative therapies, the therapeutic potential of the non‐competitive N‐methyl‐D‐aspartate receptor antagonist memantine has been suggested. Despite promising results, its efficiency in the treatment of alcoholism remains controversial. Currently, there is no pre‐clinical data regarding its effects on the motivation for ethanol in post‐dependent (PD) animals exposed to intermittent ethanol vapor, a validated model of alcoholism. Thus, the objectives of this study were to evaluate the effects of acute injections of memantine (0, 12.5, 25 and 50u2009mg/kg) on operant ethanol self‐administration in non‐dependent (ND) and PD rats tested either during acute withdrawal or relapse after protracted abstinence. Our results showed that memantine (25u2009mg/kg) abolished ethanol self‐administration in ND rats and reduced by half the one of PD rats during acute withdrawal. While this effect was observed only 6u2009hours after treatment in ND rats, it was long lasting in PD rats (at least 30u2009hours after injection). Furthermore, our results indicated that memantine did not modify the breaking point for ethanol. This suggests that memantine probably act by potentiating the pharmacological effect of ethanol but not by reducing motivation for ethanol. Finally, memantine was also ineffective in reducing relapse after protracted abstinence. Altogether, our pre‐clinical results highlighted a potential therapeutic use of memantine that may be used as a replacement therapy drug but not as relapse‐preventing drug.