Martine Daoust

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.

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.

Ethanol-sensitive brain regions in rat and mouse: a cartographic review, using immediate early gene expression.

BACKGROUND Ethanol addiction has been conceptualized as a progression from occasional, impulsive use to compulsive behavior. Ethanol-dependence is a chronic pathology with repeated cycles of withdrawal, craving, and relapse. Specific molecular and cellular mechanisms underlie these transition stages. METHODS This review aimed at elucidating whether there are also adaptations in the pattern of brain regions responding to ethanol. This paper reviews the evidence in rodents for activation of specific brain regions, assessed by induction of IEG expression, following acute and chronic ethanol exposure. RESULTS The review sheds light on the specific patterns of response in regions of the brain to different types of ethanol exposure and shows that activation of specific brain regions may occur in particular phases of the development of ethanol addiction. Some brain regions respond consistently following acute or chronic treatments or withdrawal: the prefrontal cortex; nucleus accumbens; lateral septum; hippocampus; perioculomotor urocortin-containing cells population (pIIIu), also known as Edinger-Westphal nucleus; central nucleus of the amygdala; and the paraventricular nucleus of hypothalamus. The two last brain areas are particularly activated by relapse-inducing stressors. It is of interest that the amygdala, hippocampus, and prefrontal cortex, which belong to the reward system, are activated by cue-induced relapse to ethanol self-administration in rodents and humans, while activation of these regions is reversed with anti-craving compounds. Following chronic exposure, IEG induction desensitizes while withdrawal reactivates these regions. DISCUSSION Some responding regions are implicated in reward related processes (VTA, extended amygdala, hypothalamus, hippocampus, prelimbic cortex, ventral part of lateral septum) and some others in aversive-related processes (area postrema, nucleus of solitary tract). CONCLUSION A better understanding of the neural circuits affected by ethanol and their adaptations during the development of ethanol addiction will provide new opportunities for developing appropriate therapies.

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

BACKGROUND The 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. METHODS We 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. RESULTS The 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)). CONCLUSIONS Even 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.

Long-term alterations in vulnerability to addiction to drugs of abuse and in brain gene expression after early life ethanol exposure

Exposure to ethanol early in life can have long-lasting implications on brain function and drug of abuse response later in life. The present study investigated in rats, the long-term consequences of pre- and postnatal (early life) ethanol exposure on drug consumption/reward and the molecular targets potentially associated with these behavioral alterations. Since a relationship has been demonstrated between heightened drugs intake and susceptibility to drugs-induced locomotor activity/sensitization, anxiolysis, we tested these behavioral responses, depending on the drug, in control and early life ethanol-exposed animals. Our results show that progeny exposed to early life ethanol displayed increased consumption of ethanol solutions and increased sensitivity to cocaine rewarding effects assessed in the conditioned place preference test. Offspring exposed to ethanol were more sensitive to the anxiolytic effect of ethanol and the increased sensitivity could, at least in part, explain the alteration in the consumption of ethanol for its anxiolytic effects. In addition, the sensitivity to hypothermic effects of ethanol and ethanol metabolism were not altered by early life ethanol exposure. The sensitization to cocaine (20 mg/kg) and to amphetamine (1.2 mg/kg) was increased after early life ethanol exposure and, could partly explain, an increase in the rewarding properties of psychostimulants. Gene expression analysis revealed that expression of a large number of genes was altered in brain regions involved in the reinforcing effects of drugs of abuse. Dopaminergic receptors and transporter binding sites were also down-regulated in the striatum of ethanol-exposed offspring. Such long-term neurochemical alterations in transmitter systems and in the behavioral responses to ethanol and other drugs of abuse may confer an increased liability for addiction in exposed offspring.

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.

Biphasic effect of acamprosate on NMDA but not on GABAA receptors in spontaneous rhythmic activity from the isolated neonatal rat respiratory network.

Acamprosate (calcium acetylhomotaurinate) has been shown to be effective in attenuating relapse in human alcoholics. The precise mechanism for acamprosate has been yet to be determined as there may be multiple sites of action for this drug. We investigated the mechanism of action of acamprosate on a spontaneous rhythmic activity recorded from hypoglossal nerve rootlet (XII) in neonatal rat brainstem slices. At 30 microM, acamprosate reversibly increased burst amplitude and reduced burst frequency, whereas at higher concentrations (100-400 microM) it induced a reversible and concentration-dependent inhibition of this activity. Interestingly, acamprosate (30 microM) enhanced the effects of low NMDA-induced excitation (1.5 microM), but inhibited higher NMDA-induced excitation (2.5, 5 microM) by 50-70%, demonstrating a differential effect on NMDA-induced excitation. Blockade of GABAA receptors did not affect the increase in amplitude of 30 microM acamprosate and partially abolished the inhibitory effects of 200 microM acamprosate. At 200 microM, acamprosate reduced high NMDA-induced excitation and abolished NMDA-evoked excitatory tonic phase, suggesting that excitatory effect of low concentrations of acamprosate mainly involved NMDA receptors, while the inhibitory effects at higher concentration included an increase in GABAA-mediated inhibition with a reduction of NMDA-mediated excitation. Consequently, combined blockade of both receptors abolished all effects of acamprosate tested at all concentrations. These results show that the effects of acamprosate are mediated via both GABAA and NMDA receptors and suggest a partial co-agonist role on NMDA receptors, at the level of a spontaneously active network.

Ethanol potentiates lipopolysaccharide- or interleukin-1 β-induced nitric oxide generation in RBE4 cells

Our present study investigated the effects of ethanol treatment on inducible nitric oxide (NO) synthase pathway from lipopolysaccharide- or interleukin-1 beta-treated cultured rat blood-brain barrier cell line (rat brain endothelial 4 cells: RBE4 cells). Cells were lipopolysaccharide- or interleukin-1 beta-treated with or without ethanol (50, 100 or 200 mM) for 16 or 24 h. Inducible NO synthase activity and mRNA expression were measured using Griess reaction and reverse transcription-polymerase chain reaction (RT-PCR) respectively. In the absence of lipopolysaccharide or interleukin-1 beta, ethanol treatments failed to stimulate inducible NO synthase gene expression. Lipopolysaccharide or interleukin-1 beta increased nitrite production and inducible NO synthase mRNA levels, and ethanol potentiated this effect. We concluded that ethanol could aggravate the consequences of NO generation by RBE4 cells after inducible NO synthase induction following inflammation or sepsis. This ethanol action on NO generation could contribute to circulatory failure associated with shock due to sepsis or hemorrhage, and alter blood-brain barrier permeability.

Perinatal alcohol exposure in rat induces long-term depression of respiration after episodic hypoxia.

RATIONALE Little is known about the effects of alcohol exposure during pregnancy, which is responsible for fetal alcohol syndrome and the respiratory network functions, especially respiratory network plasticity (e.g., long-term facilitation) elicited after repeated short-lasting hypoxic episodes. The mechanism of induction of respiratory long-term facilitation involves 5-HT(2A/2C) receptors, which also participate in the response to hypoxia. Because fetal alcohol exposure is known to reduce serotonin centrally, and synaptic plasticity in the hippocampus, we hypothesized that alcohol exposure during gestation might impair respiratory long-term facilitation after hypoxic episodes. OBJECTIVES To analyze the effects of prenatal and postnatal alcohol exposure on respiratory long-term facilitation in 5- to 7-day-old rats. METHODS Respiratory frequency and amplitude were measured in vivo and in an in vitro rhythmic medullary slice before and after three hypoxia episodes or three applications of a 5-HT(2A/2C) receptor agonist in vitro. 5-HT(2A/2C) receptor mRNA was measured from the slice. MEASUREMENTS AND MAIN RESULTS Alcohol exposure impaired respiratory long-term facilitation and induced long-term depression of respiration in both in vivo and in vitro models. Alcohol altered 5-HT(2A/2C) mRNA expression, although 5-HT(2A/2C) agonist efficacy was not altered in increasing rhythmic activity in slices. However, a higher concentration of 5-HT(2A/2C) agonist was necessary to induce transient facilitation in slices from ethanol-exposed animals, suggesting disturbances in induction and maintenance mechanisms of respiratory long-term facilitation. CONCLUSIONS Respiratory facilitation after repeated hypoxia was converted to long-term depression in rats treated with alcohol in utero. Alcohol exposure during pregnancy may therefore induce long-term maladaptive behavior of the respiratory system in neonates.