Expression of Serotonin Transporter in Mice With Ethanol Physical Dependency

Changes in serotonin neurotransmission as assayed by microdialysis after acute, intermittent or chronic ethanol administration and withdrawal

BACKGROUND

The serotonergic neurotransmitter system is involved in many ethanol-induced changes, including many behavioural alterations, as well as contributing to alcohol dependence and its withdrawal.

AIMS

This review has evaluated microdialysis studies where alterations in the serotonin system, that is, serotonin, 5-HT, or its metabolite 5-hydroxyindoleacetic acid, 5-HIAA, have been reported during different ethanol intoxication states, as well as in animals showing alcohol preference or not. Changes in 5-HT receptors and the 5-HT transporter are briefly reviewed to comprehend the significance of changes in microdialysate 5-HT concentrations.

MATERIALS AND METHODS

Changes in 5-HT content following acute, chronic and during ethanol withdrawal states are evaluated. In addition, the serotoninergic system was assessed in animals that have been genetically selected for alcohol preference to ascertain whether changes in this monoamine microdialysate content may contribute to alcohol preference.

RESULTS AND DISCUSSION

Changes occurred in 5-HT signalling in the limbic brain regions, increasing after acute ethanol administration in specific brain regions, particularly at higher doses, while chronic alcohol exposure essentially decreased serotonergic transmission. Such changes may play a pivotal role in emotion-driven craving and relapse. Depending on the dosage, mode of administration and consumption rate, ethanol affects specific brain regions in different ways, enhancing or reducing 5-HT microdialysate content, thereby inducing behavioural and cognitive functions and enhancing ethanol consumption.

CONCLUSION

Microdialysis studies demonstrated that ethanol induces several alterations in 5-HT content as well as its metabolites, 5-HIAA and 5-HTOL, not only in its release from a specific brain region but also in the modifications of its different receptor subtypes and its transporter.

Limosilactobacillus reuteri ATCC 6475 metabolites upregulate the serotonin transporter in the intestinal epithelium

The serotonin transporter (SERT) readily takes up serotonin (5-HT), thereby regulating the availability of 5-HT within the intestine. In the absence of SERT, 5-HT remains in the interstitial space and has the potential to aberrantly activate the many 5-HT receptors distributed on the epithelium, immune cells and enteric neurons. Perturbation of SERT is common in many gastrointestinal disorders as well as mouse models of colitis. Select commensal microbes regulate intestinal SERT levels, but the mechanism of this regulation is poorly understood. Additionally, ethanol upregulates SERT in the brain and dendritic cells, but its effects in the intestine have never been examined. We report that the intestinal commensal microbe Limosilactobacillus (previously classified as Lactobacillus) reuteri ATCC PTA 6475 secretes 83.4 mM ethanol. Consistent with the activity of L. reuteri alcohol dehydrogenases, we found that L. reuteri tolerated various levels of ethanol. Application of L. reuteri conditioned media or exogenous ethanol to human colonic T84 cells was found to upregulate SERT at the level of mRNA. A 4-(4-(dimethylamino) phenyl)-1-methylpyridinium (APP+) uptake assay confirmed the functional activity of SERT. These findings were mirrored in mouse colonic organoids, where L. reuteri metabolites and ethanol were found to upregulate SERT at the apical membrane. Finally, in a trinitrobenzene sulphonic acid model of acute colitis, we observed that mice treated with L. reuteri maintained SERT at the colon membrane compared with mice receiving phosphate buffered saline vehicle control. These data suggest that L. reuteri metabolites, including ethanol, can upregulate SERT and may be beneficial for maintaining intestinal homeostasis with respect to serotonin signalling.

The administration of sertraline plus naltrexone reduces ethanol consumption and motivation in a long-lasting animal model of post-traumatic stress disorder

This study was aimed to evaluate the effects of sertraline (STR) and/or naltrexone (NTX) on ethanol consumption and motivation in an animal model of post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD). Male C57BL/6J mice were submitted to an intermittent and progressively increasing stressful stimuli simulating PTSD behavioural features. Behavioural alterations were explored by the fear conditioning (FC), novelty suppressed feeding test (NSFT) and acoustic startle response (ASR) paradigms. Afterwards, mice were evaluated in the voluntary ethanol consumption (VC) and the oral ethanol self-administration (OEA) paradigms. The effects of STR (10 mg/kg) and/or NTX (0.7 mg/kg) on ethanol consumption and motivation were analysed in the OEA. Furthermore, relative gene expression analyses of tyrosine hydroxylase (Th), mu-opioid receptor (Oprm1) and 5-hydroxitryptamine transporter (Slc6a4) were performed in the ventral tegmental area (VTA), nucleus accumbens (NAcc) and dorsal raphe nucleus (DR), respectively. PTSD-like mice presented increased fear-related memory, anxiety-like behaviours, and startle response, as well as enhanced ethanol consumption and motivation in the VC and OEA paradigms. Interestingly, STR plus NTX combination significantly reduced ethanol intake and motivation in the OEA. Gene expression analyses revealed reduced Th and Oprm1 whereas Slc6a4 gene expression increased in PTSD-like mice. STR and/or NTX modulated Th and Slc6a4 gene expression changes in PTSD-like mice. Furthermore, NTX increased Oprm1 gene expression revealing a synergistic action when combined with STR. These results provide evidence about the efficacy of the STR plus NTX to attenuate ethanol reinforcement and motivation in an animal model of PTSD and AUD dual pathology.

Adolescent binge drinking disrupts normal trajectories of brain functional organization and personality maturation

Adolescent binge drinking has been associated with higher risks for the development of many health problems throughout the lifespan. Adolescents undergo multiple changes that involve the co-development processes of brain, personality and behavior; therefore, certain behavior, such as alcohol consumption, can have disruptive effects on both brain development and personality maturation. However, these effects remain unclear due to the scarcity of longitudinal studies. In the current study, we used multivariate approaches to explore discriminative features in brain functional architecture, personality traits, and genetic variants in 19-year-old individuals (n = 212). Taking advantage of a longitudinal design, we selected features that were more drastically altered in drinkers with an earlier onset of binge drinking. With the selected features, we trained a hierarchical model of support vector machines using a training sample (n = 139). Using an independent sample (n = 73), we tested the model and achieved a classification accuracy of 71.2%. We demonstrated longitudinally that after the onset of binge drinking the developmental trajectory of improvement in impulsivity slowed down. This study identified the disrupting effects of adolescent binge drinking on the developmental trajectories of both brain and personality.

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History of binge drinking could be identified by multivariate features at age 19.

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Adolescent binge drinking disrupted frontal connectivity maturation in the brain.

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Impulsivity improvement slowed down after the onset of adolescent binge drinking.

Effects of monoamines on the intrinsic excitability of lateral orbitofrontal cortex neurons in alcohol-dependent and non-dependent female mice

Changes in brain reward and control systems of frontal cortical areas including the orbitofrontal cortex (OFC) are associated with alcohol use disorders (AUD). The OFC is extensively innervated by monoamines, and drugs that target monoamine receptors have been used to treat a number of neuropsychiatric diseases, including AUDs. Recent findings from this laboratory demonstrate that D2, α2-adrenergic and 5HT_1A receptors all decrease the intrinsic excitability of lateral OFC (lOFC) neurons in naïve male mice and that this effect is lost in mice exposed to repeated cycles of chronic intermittent ethanol (CIE) vapor. As biological sex differences may influence an individual's response to alcohol and contribute to the propensity to engage in addictive behaviors, we examined whether monoamines have similar effects on lOFC neurons in control and CIE exposed female mice. Dopamine, norepinephrine and serotonin all decreased spiking of lOFC neurons in naïve females via activation of G_iα-coupled D2, α2-adrenergic and 5HT_1A receptors, respectively. Firing was also inhibited by the direct GIRK channel activator ML297, while blocking these channels with barium eliminated the inhibitory actions of monoamines. Following CIE treatment, evoked spiking of lOFC neurons from female mice was significantly enhanced and monoamines and ML297 no longer inhibited firing. Unlike in male mice, the enhanced firing of neurons from CIE exposed female mice was not associated with changes in the after-hyperpolarization and the small-conductance potassium channel blocker apamin had no effect on current-evoked tail currents from either control or CIE exposed female mice. These results suggest that while CIE exposure alters monoamine regulation of OFC neuron firing similarly in males and female mice, there are sex-dependent differences in processes that regulate the intrinsic excitability of these neurons.

Changes in the methylation status of DAT, SERT, and MeCP2 gene promoters in the blood cell in families exposed to alcohol during the periconceptional period

BACKGROUND

Alcohol exposure has been shown to cause devastating effects on neurobehavioral development in numerous animal and human studies. The alteration of DNA methylation levels in gene-specific promoter regions has been investigated in some studies of human alcoholics. This study was aimed to investigate whether social alcohol consumption during periconceptional period is associated with epigenetic alteration and its generational transmission in the blood cells.

METHODS

We investigated patterns of alcohol intake in a prospective cohort of 355 pairs of pregnant women and their spouses who reported alcohol intake during the periconceptional period. A subpopulation of 164 families was established for the epigenetic study based on the availability of peripheral blood and cord blood DNA. The relative methylation changes of dopamine transporter (DAT), serotonin transporter (SERT), and methyl CpG binding protein 2 (MeCP2) gene promoters were analyzed using methylation-specific endonuclease digestion followed by quantitative real-time polymerase chain reaction.

RESULTS

The relative methylation level of the DAT gene promoter was decreased in the group of mothers reporting above moderate drinking (p = 0.029) and binge drinking (p = 0.037) during pregnancy. The relative methylation level of the DAT promoter was decreased in the group of fathers reporting heavy binge drinking (p = 0.003). The relative methylation levels of the SERT gene promoter were decreased in the group of newborns of light drinking mothers before pregnancy (p = 0.012) and during pregnancy (p = 0.003). The methylation level in the MeCP2 promoter region of babies whose mothers reported above moderate drinking during pregnancy was increased (p = 0.02). In addition, methylation pattern in the DAT promoter region of babies whose fathers reported heavy binge drinking was decreased (p = 0.049).

CONCLUSIONS

These findings suggest that periconceptional alcohol intake may cause epigenetic changes in specific locus of parental and newborn genomes as follows: Alcohol consumption decreases the methylation level of the DAT promoter region of the parent themselves, maternal alcohol drinking during the periconceptional period decreases the methylation level of the SERT promoter region of newborns, and maternal alcohol consumption increases the methylation level of the MeCP2 promoter region of newborns.

Dopamine D1 receptor signaling system regulates ryanodine receptor expression in ethanol physical dependence

BACKGROUND

Ryanodine receptors (RyRs) amplifying activity-dependent calcium influx via calcium-induced calcium release play an important role in central nervous system functions including learning, memory, and drug abuse. In this study, we investigated the role and the regulatory mechanisms of RyR expression under continuous exposure of mice to ethanol (EtOH) vapor for 9 days.

METHODS

The model of EtOH physical dependence was prepared as follows: 8-week-old male ddY mice were exposed to EtOH vapor for 9 days. Protein and mRNA of RyR-1, RyR-2, and RyR-3 in the frontal cortex and limbic forebrain were determined by Western blot and real-time RT-PCR analysis, respectively.

RESULTS

Exposure of mice to EtOH vapor for 9 days induced significant withdrawal signs when estimated with withdrawal score, which was dose-dependently suppressed by intracerebroventricular administration of dantrolene, an RyR antagonist. Protein levels of RyR-1 and RyR-2 in the frontal cortex and limbic forebrain significantly increased during EtOH vapor exposure for 9 days with increased expression of their mRNA, whereas that of RyR-3 in these 2 brain regions showed no changes. Increased proteins and mRNA of RyR-1 and RyR-2 were completely abolished by SCH23390, a selective antagonist of dopamine D1 receptors (D1DRs), but not by sulpiride, a selective antagonist of D2DRs.

CONCLUSIONS

RyRs play a critical role in the development of EtOH physical dependence and that the up-regulation of RyRs in the brain of mouse, showing EtOH physical dependence is regulated by D1DRs.

Alcohol-induced plasticity in the dynorphin/kappa-opioid receptor system

Alcoholism is a chronic relapsing disorder characterized by continued alcohol use despite numerous adverse consequences. Alcohol has been shown to interact with numerous neurotransmitter systems to exert its pharmacological effects. The endogenous opioid system (EOS) has been strongly implicated in the positive and negative reinforcing effects of alcohol. Traditionally recognized as dysphoric/anhedonic in nature, the dynorphin/kappa-opioid receptor (DYN/KOR) system has recently received considerable attention due to evidence suggesting that an upregulated DYN/KOR system may be a critical contributor to the complex factors that result in escalated alcohol consumption once dependent. The present review will discuss alcohol-induced plasticity in the DYN/KOR system and how these neuroadaptations could contribute to excessive alcohol seeking and consumption.

The effects of chronic ethanol self-administration on hippocampal serotonin transporter density in monkeys

Evidence for an interaction between alcohol consumption and the serotonin system has been observed repeatedly in both humans and animal models yet the specific relationship between the two remains unclear. Research has focused primarily on the serotonin transporter (SERT) due in part to its role in regulating extracellular levels of serotonin. The hippocampal formation is heavily innervated by ascending serotonin fibers and is a major component of the neurocircuitry involved in mediating the reinforcing effects of alcohol. The current study investigated the effects of chronic ethanol self-administration on hippocampal SERT in a layer and field specific manner using a monkey model of human alcohol consumption. [(3)H]Citalopram was used to measure hippocampal SERT density in male cynomolgus macaques that voluntarily self-administered ethanol for 18 months. Hippocampal [(3)H]citalopram binding was less dense in ethanol drinkers than in controls, with the greatest effect observed in the molecular layer of the dentate gyrus. SERT density was not correlated with measures of ethanol consumption or blood ethanol concentrations, suggesting the possibility that a threshold level of consumption had been met. The lower hippocampal SERT density observed suggests that chronic ethanol consumption is associated with altered serotonergic modulation of hippocampal neurotransmission.