Alcohol and gene expression in the central nervous system

Sex-dependent effects of acute stress and alcohol exposure during adolescence on mRNA expression of brain signaling systems involved in reward and stress responses in young adult rats

BACKGROUND

Adolescent stress and alcohol exposure increase the risk of maladaptive behaviors and mental disorders in adulthood, with distinct sex-specific differences. Understanding the mechanisms underlying these early events is crucial for developing targeted prevention and treatment strategies.

METHODS

Male and female Wistar rats were exposed to acute restraint stress and intermittent alcohol during adolescence. We assessed lasting effects on plasma corticosterone (CORT) and adrenocorticotropic hormone (ACTH) levels, and mRNA expression of genes related to corticotropin releasing hormone (CRH), neuropeptide Y (NPY), corticoid, opioid, and arginine vasopressin systems in the amygdala and hypothalamus.

RESULTS

The main findings are as follows: (1) blood alcohol concentrations (BAC) increased after the final alcohol administration, but stressed males had lower BAC than non-stressed males; (2) Males gained significantly more weight than females; (3) Stressed females showed higher ACTH levels than non-stressed females, with no changes in males; (4) Stress increased CORT levels in males, while stressed, alcohol-treated females had lower CORT levels than non-stressed females; (5) CRH: Females had lower Crhr1 levels in the amygdala, while alcohol reduced Crhr2 levels in males but not females. Significant interactions among sex, stress, and alcohol were found in the hypothalamus, with distinct patterns between sexes; (6) NPY: In the amygdala, stress reduced Npy and Npy1r levels in males but increased them in females. Alcohol decreased Npy2r levels in males, with varied effects in females. Similar sex-specific patterns were observed in the hypothalamus; (7) Corticoid system: Stress and alcohol had complex, sex-dependent effects on Pomc, Nr3c1, and Nr3c2 in both brain regions; (8) Opioid receptors: Stress and alcohol blunted the elevated expression of Oprm1, Oprd1, and Oprk1 in the amygdala of males and the hypothalamus of females; (8) Vasopressin: Stress and alcohol interacted significantly to affect Avp and Avpr1a expression in the amygdala, with stronger effects in females. In the hypothalamus, alcohol increased Avp levels in females.

CONCLUSIONS

This study demonstrates that adolescent acute stress and alcohol exposure induce lasting, sex-specific alterations in systems involved in reward and stress responses. These findings emphasize the importance of considering sex differences in the prevention and management of HPA dysfunction and psychiatric disorders.

Alcohol alters IL-6 Signal Transduction in the CNS of Transgenic Mice with Increased Astrocyte Expression of IL-6

Neuroimmune factors, including the cytokine interleukin-6 (IL-6), are important chemical regulators of central nervous system (CNS) function under both physiological and pathological conditions. Elevated expression of IL-6 occurs in the CNS in a variety of disorders associated with altered CNS function, including excessive alcohol use. Alcohol-induced production of IL-6 has been reported for several CNS regions including the cerebellum. Cerebellar actions of alcohol occur through a variety of mechanisms, but alcohol-induced changes in signal transduction, transcription, and translation are known to play important roles. IL-6 is an activator of signal transduction that regulates gene expression. Thus, alcohol-induced IL-6 production could contribute to cerebellar effects of alcohol by altering gene expression, especially under conditions of chronic alcohol abuse, where IL-6 levels could be habitually elevated. To gain an understanding of the effects of alcohol on IL-6 signal transduction, we studied activation/expression of IL-6 signal transduction partners STAT3 (Signal Transducer and Activator of Transcription), CCAAT-enhancer binding protein (C/EBP) beta, and p42/p44 mitogen-activated protein kinase (MAPK) at the protein level. Cerebella of transgenic mice that express elevated levels of astrocyte produced IL-6 in the CNS were studied. Results show that the both IL-6 and chronic intermittent alcohol exposure/withdrawal affect IL-6 signal transduction partners and that the actions of IL-6 and alcohol interact to alter activation/expression of IL-6 signal transduction partners. The alcohol/IL-6 interactions may contribute to cerebellar actions of alcohol, whereas the effects of IL-6 alone may have relevance to cerebellar changes occurring in CNS disorders associated with elevated levels of IL-6.

Alcohol and IL-6 Alter Expression of Synaptic Proteins in Cerebellum of Transgenic Mice with Increased Astrocyte Expression of IL-6

Recent studies indicate that neuroimmune factors, including the cytokine interleukin-6 (IL-6), play a role in the CNS actions of alcohol. The cerebellum is a sensitive target of alcohol, but few studies have examined a potential role for neuroimmune factors in the actions of alcohol on this brain region. A number of studies have shown that synaptic transmission, and in particular inhibitory synaptic transmission, is an important cerebellar target of alcohol. IL-6 also alters synaptic transmission, although it is unknown if IL-6 targets are also targets of alcohol. This is an important issue because alcohol induces glial production of IL-6, which could then covertly influence the actions of alcohol. The persistent cerebellar effects of both IL-6 and alcohol typically involve chronic exposure and, presumably, altered gene and protein expression. Thus, in the current studies we tested the possibility that proteins involved in inhibitory and excitatory synaptic transmission in the cerebellum are common targets of alcohol and IL-6. We used transgenic mice that express elevated levels of astrocyte produced IL-6 to model persistently elevated expression of IL-6, as would occur in alcohol use disorders, and a chronic intermittent alcohol exposure/withdrawal paradigm (CIE/withdrawal) that is known to produce alcohol dependence. Multiple cerebellar synaptic proteins were assessed by Western blot. Results show that IL-6 and CIE/withdrawal have both unique and common actions that affect synaptic protein expression. These common targets could provide sites for IL-6/alcohol exposure/withdrawal interactions and play an important role in cerebellar symptoms of alcohol use such as ataxia.

Altered brain activity during withdrawal from chronic alcohol is associated with changes in IL-6 signal transduction and GABAergic mechanisms in transgenic mice with increased astrocyte expression of IL-6

Interleukin-6 (IL-6) is an important neuroimmune factor that is increased in the brain by alcohol exposure/withdrawal and is thought to play a role in the actions of alcohol on the brain. To gain insight into IL-6/alcohol/withdrawal interactions and how these interactions affect the brain, we are studying the effects of chronic binge alcohol exposure on transgenic mice that express elevated levels of IL-6 in the brain due to increased astrocyte expression (IL-6 tg) and their non-transgenic (non-tg) littermate controls. IL-6/alcohol/withdrawal interactions were identified by genotypic differences in spontaneous brain activity in electroencephalogram (EEG) recordings from the mice, and by Western blot analysis of protein activation or expression in hippocampus obtained from the mice after the final alcohol withdrawal period. Results from EEG studies showed frequency dependent genotypic differences in brain activity during withdrawal. For EEG frequencies that were affected by alcohol exposure/withdrawal in both genotypes, the nature of the effect was similar, but differed across withdrawal cycles. Differences between IL-6 tg and non-tg mice were also observed in Western blot studies of the activated form of STAT3 (phosphoSTAT3), a signal transduction partner of IL-6, and subunits of GABA_A receptors (GABA_AR). Regression analysis revealed that pSTAT3 played a more prominent role during withdrawal in the IL-6 tg mice than in the non-tg mice, and that the role of GABA_AR alpha-5 and GABA_AR alpha-1 in brain activity varied across genotype and withdrawal. Taken together, our results suggest that IL-6 can significantly impact mechanisms involved in alcohol withdrawal.

Alcohol consumption increases locomotion in an open field and induces Fos-immunoreactivity in reward and approach/withdrawal-related neurocircuitries

Drug addiction is a chronically relapsing disorder characterized by compulsion to seek and take the drug, loss of control in limiting intake and, eventually, the emergence of a negative emotional state when access to the drug is prevented. Both dopamine and corticotropin-releasing factor (CRF)-mediated systems seem to play important roles in the modulation of alcohol abuse and dependence. The present study investigated the effects of alcohol consumption on anxiety and locomotor parameters and on the activation of dopamine and CRF-innervated brain regions. Male Wistar rats were given a choice of two bottles for 31 days, one containing water and the other a solution of saccharin + alcohol. Control animals only received water and a solution of 0.2% saccharin. On the 31st day, animals were tested in the elevated plus-maze and open field, and euthanized immediately after the behavioral tests. An independent group of animals was treated with ethanol and used to measure blood ethanol concentration. Results showed that alcohol intake did not alter behavioral measurements in the plus-maze, but increased the number of crossings in the open field, an index of locomotor activity. Additionally, alcohol intake increased Fos-immunoreactivity (Fos-ir) in the prefrontal cortex, in the shell region of the nucleus accumbens, in the medial and central amygdala, in the bed nucleus of the stria terminalis, in the septal region, and in the paraventricular and dorsomedial hypothalamus, structures that have been linked to reward and to approach/withdrawal behavior. These observations might be relevant to a better understanding of the behavioral and physiological alterations that follow alcohol consumption.

Eye-specific gene expression following embryonic ethanol exposure in zebrafish: roles for heat shock factor 1

The mechanisms through which ethanol exposure results in developmental defects remain unclear. We used the zebrafish model to elucidate eye-specific mechanisms that underlie ethanol-mediated microphthalmia (reduced eye size), through time-series microarray analysis of gene expression within eyes of embryos exposed to 1.5% ethanol. 62 genes were differentially expressed (DE) in ethanol-treated as compared to control eyes sampled during retinal neurogenesis (24-48 h post-fertilization). The EDGE (extraction of differential gene expression) algorithm identified >3000 genes DE over developmental time in ethanol-exposed eyes as compared to controls. The DE lists included several genes indicating a mis-regulated cellular stress response due to ethanol exposure. Combined treatment with sub-threshold levels of ethanol and a morpholino targeting heat shock factor 1 mRNA resulted in microphthalmia, suggesting convergent molecular pathways. Thermal preconditioning partially prevented ethanol-mediated microphthalmia while maintaining Hsf-1 expression. These data suggest roles for reduced Hsf-1 in mediating microphthalmic effects of embryonic ethanol exposure.

GABRB3 gene expression increases upon ethanol exposure in human embryonic stem cells

Ionotropic receptors are the target for most mood-defining compounds. Chronic exposure to ethanol (EtOH) alters receptor-mediated responses and the numbers of these channels and specific subunits; as well as induces anxiolytic, sedative, and anesthetic activity in the human brain. However, very little is known regarding the effects of EtOH on ionotropic receptor transcription during early human development (preimplantation). Using two separate human embryonic stem cell lines the study shows that low amounts of EtOH (20 mM) alters transcription of the ionotropic subunit GABRB3. Changes in ionotrophic receptor expression influence the central nervous system development and have been shown to produce brain abnormalities in animal models. These results suggest that low concentrations of EtOH can alter ionotropic receptor transcription during early human development (preimplantation), which may be a contributing factor to the neurological phenotypes seen in fetal alcohol spectrum disorder (FASD).

Molecular genetics of alcohol dependence and related endophenotypes

Alcohol dependence is a worldwide public health problem, and involves both environmental and genetic vulnerability factors. The heritability of alcohol dependence is rather high, ranging between 50% and 60%, although alcohol dependence is a polygenic, complex disorder.

Genome-wide scans on large cohorts of multiplex families, including the collaborative study on genetics of alcoholism (COGA), emphasized the role of many chromosome regions and some candidate genes. The genes encoding the alcohol-metabolizing enzymes, or those involved in brain reward pathways, have been involved. Since dopamine is the main neurotransmitter in the reward circuit, genes involved in the dopaminergic pathway represent candidates of interest. Furthermore, gamma-amino-butyric acid (GABA) neurotransmitter mediates the acute actions of alcohol and is involved in withdrawal symptomatology. Numerous studies showed an association between variants within GABA receptors genes and the risk of alcohol dependence.

In accordance with the complexity of the “alcohol dependence” phenotype, another field of research, related to the concept of endophenotypes, received more recent attention. The role of vulnerability genes in alcohol dependence is therefore re-assessed focusing on different phenotypes and endophenotypes. The latter include brain oscillations, EEG alpha and beta variants and alpha power, and amplitude of P300 amplitude elicited from a visual oddball task.

Recent enhancement on global characterizations of the genome by high-throughput approach for genotyping of polymorphisms and studies of transcriptomics and proteomics in alcohol dependence is also reviewed.

Genetic approaches to alcohol addiction: gene expression studies and recent candidates from Drosophila

Ethanol intake causes gene expression changes resulting in cellular and molecular adaptations that could be associated with a predisposition to alcohol dependence. Recently, several research groups have used high-throughput gene expression profiling to search for alcohol-responsive genes in Drosophila melanogaster. Comparison of data from these studies highlights the functional similarities in their results despite differences in their experimental approach and selection cases. Notably, alcohol-responsive gene sets associated with stress response, olfaction, metabolism, proteases, transcriptional regulation, regulation of signal transduction, nucleic acid binding and cytoskeletal organisation were markedly common to these studies. These data support the view that changes in gene expression in alcoholics are associated with widespread cellular functions.

Glial and glutamatergic markers in depression, alcoholism, and their comorbidity

BACKGROUND

Alteration of glutamatergic neurotransmission in the prefrontal cortex (PFC) may contribute to the pathophysiology of alcoholism and major depressive disorder (MDD). Among glial cells, astrocytes are mostly responsible for recycling synaptic glutamate by uptake through excitatory amino acid transporters 1 and 2 (EAAT1 and EAAT2), and conversion to glutamine with glutamine synthetase (GS). Low density of astrocytes in the PFC of "uncomplicated' alcoholics and MDD subjects may parallel altered glutamate transporters and GS in the PFC.

METHODS

Immunohistochemistry and Western blotting for glutamate transporters, GS and glial fibrillary acidic protein (GFAP) were applied to postmortem tissue of the left orbitofrontal cortex from 13 subjects with MDD, 13 with alcoholism, 10 with comorbid alcoholism plus MDD (MDA), and 13 non-psychiatric controls. Area fraction of immunoreactivity was measured in sections, and protein levels in Western blots.

RESULTS

EAAT2 immunoreactivity was significantly lower in MDD and MDA subjects than in controls. EAAT1 levels were lower in MDA and MDD subjects as compared to controls, while GS levels in MDA were significantly lower than in alcoholics and controls, and lower in MDD subjects than in alcoholics. Area fraction of GFAP was lower in MDD, but not in MDA subjects as compared to controls or alcoholics.

LIMITATIONS

High variability of protein levels in some groups and effects of antidepressant treatment, although appearing to be limited, cannot be fully evaluated.

CONCLUSIONS

There are differential changes in the expression of glial glutamatergic markers in depression and alcoholism, suggesting a depletion of certain aspects of glutamatergic processing in depression.

Stimulated gene expression profiles as a blood marker of major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a moderately heritable disorder with a high lifetime prevalence. At present, laboratory blood tests to support MDD diagnosis are not available.

METHODS

We used a classifier approach on blood gene expression profiles of a unique set of unmedicated subjects (MDD patients and control subjects) to select genes with expression predictive for disease status. To reveal blood gene expression changes related to major depressive disorder-disease, we applied a powerful ex vivo stimulus to the blood: incubation with lipopolysaccharide (LPS; 10 ng/mL blood).

RESULTS

Based on LPS-stimulated blood gene expression using whole-genome microarrays (primary cohort; 21 MDD patients, 21 healthy control subjects), we identified a set of genes (CAPRIN1, CLEC4A, KRT23, MLC1, PLSCR1, PROK2, ZBTB16) that serves as a molecular signature of MDD. These findings were validated using an independent quantitative polymerase chain reaction method (primary cohort, p = .007). The difference between depressive patients and control subjects was confirmed (p = .019) in a replication cohort of 13 MDD patients and 14 control subjects. The MDD signature score comprised expression levels of seven genes could discriminate depressive patients from control subjects with sensitivity of 76.9% and specificity of 71.8%.

CONCLUSIONS

We have shown for the first time that molecular analysis of stimulated blood cells can be used as an endophenotype for MDD diagnosis, which is a milestone in establishing biomarkers for neuropsychiatric disorders with moderate heritability in general. Our results may provide a new entry point for following and predicting treatment outcome, as well as prediction of severity and recurrence of major depressive disorder.

Ethanol acutely modulates mGluR1-dependent long-term depression in cerebellum

BACKGROUND

Acute and chronic ethanol exposure produces profound impairments in motor functioning. Individuals with lower sensitivity to the acute motor impairing effects of ethanol have an increased risk of developing alcohol dependence and abuse, and infants with subtle delays in motor coordination development may have an increased risk for subsequently developing alcoholism. Thus, understanding the mechanism by which ethanol disrupts motor functioning is very important.

METHODS

Parasagittal slices of the cerebellar vermis (250 microM thick) were prepared from P17 to 20 Sprague-Dawley rats. Whole-cell recordings of Purkinje cells were obtained with an Axopatch 200B amplifier. Parallel fiber-Purkinje cell synaptic currents were sampled at 1 kHz and digitized at 10 kHz, and synaptic long-term depression (LTD) was observed in either external or internal application of ethanol for comparison.

RESULTS

We determined whether ethanol acutely affects parallel fiber LTD using whole-cell patch-clamp recordings from Purkinje cells. Application of ethanol both externally (50 mM) and internally (17 and 10 mM) significantly suppressed mGluR-mediate slow currents. Short-term external ethanol exposure (50 but not 17 mM) during tetanus blocked mGluR-dependent parallel fiber LTD. Furthermore, internal 17 and 10 mM ethanol completely inhibited this LTD.

CONCLUSIONS

The results of the current study demonstrate that ethanol acutely suppresses parallel fiber LTD and may influence the mGluR-mediated slow current intracellularly. This study, plus previous evidence by Carta and colleagues (2006) and Belmeguenai and colleagues (2008), suggests significant actions of ethanol on mGluR-mediated currents and its dependent plasticity in brain.

The regulation of neuronal gene expression by alcohol

In recent years there has been an explosion of interest in how genes regulate alcohol drinking and contribute to alcoholism. This work has been stimulated by the completion of the human and mouse genome projects and the resulting availability of gene microarrays. Most of this work has been performed in drinking animals, and has utilized the extensive genetic variation among different mouse strains. At the same time, a much smaller amount of effort has gone into the in vitro study of the mechanisms underlying the regulation of individual genes by alcohol. These studies at the cellular and sub-cellular level are beginning to reveal the ways in which alcohol can interact with the transcriptional, translational and post-translational events inside the cell. Detailed studies of the promoter regions within several individual alcohol-responsive genes (ARGs) have been performed and this work has uncovered intricate signaling pathways that may be generalized to larger groups of ARGs. In the last few years several distinct ARGs have been identified from 35,000 mouse genes, by both the "top-down" approach (ex vivo gene arrays) and the "bottom-up" methods (in vitro promoter analysis). These divergent methodologies have converged on a surprisingly small number of genes encoding ion channels, receptors, transcription factors and proteins involved in synaptic function and remodeling. In this review we will describe some of the most interesting cellular and microarray work in the field, and will outline specific examples of genes for which the mechanisms of regulation by alcohol are now somewhat understood.

Association between the Stin2 VNTR polymorphism of the serotonin transporter gene and treatment outcome in alcohol-dependent patients

AIMS

The aim of this study was to investigate the potential association between functional polymorphisms of dopaminergic [dopamine receptor D2 (DRD2), dopamine receptor D3 (DRD3) and dopamine transporter (SLC6A3)] and serotonergic [serotonin 2A receptor (HTR2A) and serotonin transporter (SLC6A4)] genes and treatment outcome in alcohol-dependent patients.

METHODS

A total of 90 Spanish Caucasian alcohol-dependent outpatients (ICD-10 criteria) were enrolled in the study. The association between genotypes and drinking outcomes was measured over 6 months of treatment. Biomarkers of alcohol consumption, as well as alcohol consumption and its consequences, craving, disability and quality of life, were assessed. Based on those measures, we created a composite secondary measure to globally assess treatment outcome in alcoholism.

RESULTS

No association was found between DRD2, DRD3, SLC6A3 or HTR2A gene variants and treatment outcome. However, SLC6A4 STin2 12/12 carriers showed poor 6-month time point treatment outcome [32.8% in the good outcome group versus 64.0% in the poor outcome group, chi(2) (df) = 7.20 (1), corrected P = 0.042, OR (95% CI) = 0.27 (0.10-0.72)]. Nevertheless, independent analysis of each treatment group reveals that the excess of 12/12 carriers in the poor outcome group was only found in the naltrexone-treated group [24.1% versus 64.7% chi(2) (df) = 7.41 (1), corrected P = 0.042, OR (95% CI) = 0.17 (0.05-0.64)]. In the whole sample, the L-10 repeats haplotype (5-HTTLPR-STin2 VNTR) is associated with good outcome (LRT = 3.88, df = 1, P = 0.049).

CONCLUSIONS

Our findings suggest that functional polymorphism of the SLC6A4 gene may have an influence on treatment outcome in alcohol-dependent patients.

Perinatal alcohol exposure leads to prolonged upregulation of hypothalamic GABA A receptors and increases behavioral sensitivity to gaboxadol

Prenatal alcohol exposure (AE) is associated with lasting abnormalities of sleep and motor development, but the underlying mechanisms are unknown. We hypothesized that AE alters development of GABAergic signaling in the hypothalamic regions important for the control of sleep and motor activity. Alcohol (5.25 g/(kg day)) was administered intragastrically to male rats on postnatal days (PD) 4-9, a period of brain development equivalent to the human third trimester (AE group). Control pups were sham-intubated (S group). Motor activity was monitored on PD27 and 28. On PD29 and 30, GABA A receptor subunit mRNA levels and alpha4 and delta subunit proteins were quantified by RT-PCR and immunoblotting, respectively, in the wake- and motor activity-promoting perifornical (PF) region of the posterior hypothalamus and the sleep-promoting ventrolateral preoptic (VLPO) region of the anterior hypothalamus. Then, in 47-52-day-old rats, motor activity was quantified following administration of GABA A receptor agonist, gaboxadol (5 mg/kg s.c.). In the PF region, mRNA and protein levels for the alpha4 and delta subunits were significantly higher and beta3 and gamma2 subunit mRNAs were also increased in the AE group. In the VLPO region, only the delta subunit mRNA was increased. Spontaneous motor activity was lower and suppressed more by gaboxadol in the AE than S group, and the latency to a transient total loss of activity after gaboxadol was shorter in the AE group. Thus, perinatal AE leads to GABA A receptor overexpression in the vigilance- and motor activity-promoting hypothalamic PF region, with the neurochemical and functional outcomes lasting long beyond the period of the insult.

Effects of naltrexone and acamprosate on alcohol-induced NGFI-A expression in mouse brain

In search for the substrate of naltrexone and acamprosate action on alcohol craving, we investigated the effects of ethanol alone and combined with naltrexone or acamprosate on expression of nerve growth factor-inducible clone A (NGFI-A; zif268). In Experiments 1 and 3, alcohol (2 g/kg) alone or in combination with naltrexone (15 mg/kg) or acamprosate (300 mg/kg) was injected intraperitoneally into mice. In Experiment 2, treatment was nor-BNI (0.5 mg/kg) to investigate whether the effect of naltrexone involved blockade of kappa-opioid receptors. Both ethanol and naltrexone alone induced NGFI-A in the central amygdala, but not in several other areas; these effects were additive. However, acamprosate alone or in combination with ethanol had no effect on NGFI-A mRNA, while nor-BNI induced NGFI-A mRNA in the basolateral amygdala. The central amygdala appears to be an important target of both alcohol and naltrexone. Acamprosate may not share the site of action with naltrexone despite being used for the same therapeutic purpose.

Alcohol regulates gene expression in neurons via activation of heat shock factor 1

Drinking alcohol causes widespread alterations in gene expression that can result in long-term physiological changes. Although many alcohol-responsive genes (ARGs) have been identified, the mechanisms by which alcohol alters transcription are not well understood. To elucidate these mechanisms, we investigated Gabra4, a neuron-specific gene that is rapidly and robustly activated by alcohol (10-60 mM), both in vitro and in vivo. Here we show that alcohol can activate elements of the heat shock pathway in mouse cortical neurons to enhance the expression of Gabra4 and other ARGs. The activation of Gabra4 by alcohol or high temperature is dependent on the binding of heat shock factor 1 (HSF1) to a short downstream DNA sequence, the alcohol response element (ARE). Alcohol and heat stimulate the translocation of HSF1 from the cytoplasm to the nucleus and the induction of HSF1-dependent genes, Hsp70 and Hsp90, in cultured neurons and in the mouse cerebral cortex in vivo. The reduction of HSF1 levels using small interfering RNA prevented the stimulation of Gabra4 and Hsp70 by alcohol and heat shock. Microarray analysis showed that many ARGs contain ARE-like sequences and that some of these genes are also activated by heat shock. We suggest that alcohol activates phylogenetically conserved pathways that involve intermediates in the heat shock cascade and that sequence elements similar to the ARE may mediate some of the changes in gene expression triggered by alcohol intake, which could be important in a variety of pathophysiological responses to alcohol.

The role of acetaldehyde in mediating effects of alcohol on expression of endogenous opioid system genes in a neuroblastoma cell line

Ethanol (EtOH) alters neural activity through interaction with various neurotransmitters and neuromodulators. The endogenous opioid system seems to play a key role in the activities of EtOH, since the opioid antagonist naltrexone (ReVia) attenuates craving. We have investigated the transcriptional regulation of opioid system genes in response to EtOH exposure for up to 96 h in human neuroblastoma SH-SY5Y cells using quantitative real-time polymerase chain reaction. We observed a significant decrease in the expression of opioid peptide precursors (proopiomelanocortin, proenkephalin, and prodynorphin) and of the kappa opioid receptor after 48 and 72 h of EtOH exposure (10 and 40 mM). These alterations were not present when the EtOH metabolism was blocked by 4-methylpyrazole. To evaluate whether the effects evoked by EtOH were possibly due to the first product of EtOH metabolism, cells were exposed to 0.4 mM acetaldehyde. We observed the same pattern of changes for prodynorphin, proenkephalin, and the kappa opioid receptor as after 72 h exposure to EtOH. These results contribute to our understanding of EtOH action at a cellular level and provide evidence of the role of acetaldehyde in mediating some of the EtOH-induced effects.

Ethanol-induced effects on opioid peptides in adult male Wistar rats are dependent on early environmental factors

The vulnerability to develop alcoholism is dependent on both genetic and environmental factors. The neurobiological mechanisms underlying these factors are not fully understood but individual divergence in the endogenous opioid peptide system may contribute. We have previously reported that early-life experiences can affect endogenous opioids and also adult voluntary ethanol intake. In the present study, this line of research was continued and the effects of long-term voluntary ethanol drinking on the opioid system are described in animals reared in different environmental settings. Rat pups were subjected to 15 min (MS15) or 360 min (MS360) of daily maternal separation during postnatal days 1-21. At 10 weeks of age, male rats were exposed to voluntary ethanol drinking in a four-bottle paradigm with 5%, 10% and 20% ethanol solution in addition to water for 2 months. Age-matched controls received water during the same period. Immunoreactive (ir) Met-enkephalin-Arg6Phe7 (MEAP) and dynorphin B (DYNB) peptide levels were thereafter measured in the pituitary gland and several brain areas. In water-drinking animals, lower ir MEAP levels were observed in the MS360 rats in the hypothalamus, medial prefrontal cortex, striatum and the periaqueductal gray, whereas no differences were seen in ir DYNB levels. Long-term ethanol drinking induced lower ir MEAP levels in MS15 rats in the medial prefrontal cortex and the periaqueductal gray, whereas higher levels were detected in MS360 rats in the hypothalamus, striatum and the substantia nigra. Chronic voluntary drinking affected ir DYNB levels in the pituitary gland, hypothalamus and the substantia nigra, with minor differences between MS15 and MS360. In conclusion, manipulation of the early environment caused changes in the opioid system and a subsequent altered response to ethanol. The altered sensitivity of the opioid peptides to ethanol may contribute to the previously reported differences in ethanol intake between MS15 and MS360 rats.

Identification of neurotransmitter receptor genes involved in alcohol self-administration in the rat prefrontal cortex, hippocampus and amygdala

About half of the risk to develop alcoholism is related to genetic background and it is well known that alcohol consumption is highly individualized. In this study, we investigated how individual alcohol consumption behaviour in Wistar rats correlated with mRNA expression of 20 genes in the prefrontal cortex, hippocampus and amygdala. We found that the long-term alcohol consumption of an individual could be estimated by the mean of its consumption on Day 2 and 3. This short exposure minimized changes in gene expression induced by alcohol itself. We found a positive correlation in the prefrontal cortex of GABA(A) alpha5 (r=0.96), GABA(B1) (r=0.96), AMPA GluR1 (r=0.93), 5-HT(3A) (r=0.93) and the alpha adrenoceptors (alpha(1A)r=1.00, alpha(1B)r=0.93, alpha(2A)r=0.93) with consumption. In the hippocampus, we found negative correlations with the NMDA NR2A subunit (r=-0.86), the alpha(1A) adrenoceptor (r=-0.89) and the glucocorticoid receptor (r=-0.86). Finally, in the amygdala there was a negative correlation to NMDA NR2A (r= -0.79) and a positive correlation with serotonin 5-HT(2C) (r=0.79). In conclusion, we have used qPCR to identify specific genes in the brain that correlated to alcohol self-administration of an individual animal. This study suggests that alcohol consumption in the early stages of acquisition depends on the genetic background of the individual and that the prefrontal cortex is particularly important in this behaviour.

Time-Dependent Alterations in Ethanol Intake in Male Wistar Rats Exposed to Short and Prolonged Daily Maternal Separation in a 4-Bottle Free-Choice Paradigm

BACKGROUND

Previous studies have shown that maternal separation can be used in animal studies of early environmental influence on adult ethanol intake. These studies have shown that short daily separations result in low ethanol intake, whereas prolonged separations relate to an enhanced risk for a high ethanol intake. The aim of the present study was to further examine the long-term effects of early-life events on ethanol intake.

METHODS

Rat pups were exposed to 15 minutes (MS15) or 360 minutes (MS360) of daily maternal separation during postnatal days 1 to 21 or kept under normal animal facility rearing (AFR) conditions. In adulthood, male rats were given free access to 5, 10, and 20% ethanol, in addition to water, in a 4-bottle-choice paradigm.

RESULTS

No differences in total ethanol intake or preference between the 3 experimental groups were found. The 54-day drinking period was divided into acquisition, stabilization, and maintenance phases for analysis of time and group differences. The MS15 rats increased ethanol intake over time; they mostly consumed 5% ethanol and had a low intake of 20% ethanol throughout the experiment. MS360 rats increased ethanol intake, changed preference from 5% to 20% ethanol, and had a higher increase in intake of 20% ethanol over time. The ethanol intake and preference in the AFR rats were more similar to that of the MS360 rats.

CONCLUSIONS

Time-dependent changes were observed in the preferred choice of low versus high ethanol concentrations in MS15 and MS360 rats. The results support previous findings suggesting that MS15 can be used as a model for environmental protective factors and that MS360 represents a risk environment for acquisition of a high adult ethanol intake.

Candidate genes, pathways and mechanisms for alcoholism: an expanded convergent functional genomics approach

We describe a comprehensive translational approach for identifying candidate genes for alcoholism. The approach relies on the cross-matching of animal model brain gene expression data with human genetic linkage data, as well as human tissue data and biological roles data, an approach termed convergent functional genomics. An analysis of three animal model paradigms, based on inbred alcohol-preferring (iP) and alcohol-non-preferring (iNP) rats, and their response to treatments with alcohol, was used. A comprehensive analysis of microarray gene expression data from five key brain regions (frontal cortex, amygdala, caudate-putamen, nucleus accumbens and hippocampus) was carried out. The Bayesian-like integration of multiple independent lines of evidence, each by itself lacking sufficient discriminatory power, led to the identification of high probability candidate genes, pathways and mechanisms for alcoholism. These data reveal that alcohol has pleiotropic effects on multiple systems, which may explain the diverse neuropsychiatric and medical pathology in alcoholism. Some of the pathways identified suggest avenues for pharmacotherapy of alcoholism with existing agents, such as angiotensin-converting enzyme (ACE) inhibitors. Experiments we carried out in alcohol-preferring rats with an ACE inhibitor show a marked modulation of alcohol intake. Other pathways are new potential targets for drug development. The emergent overall picture is that physical and physiological robustness may permit alcohol-preferring individuals to withstand the aversive effects of alcohol. In conjunction with a higher reactivity to its rewarding effects, they may able to ingest enough of this nonspecific drug for a strong hedonic and addictive effect to occur.

Patterns of gene expression in the frontal cortex discriminate alcoholic from nonalcoholic individuals

Alcohol dependence is characterized by tolerance, physical dependence, and craving. The neuroadaptations underlying these effects of chronic alcohol abuse are likely due to altered gene expression. Previous gene expression studies using human post-mortem brain demonstrated that several gene families were altered by alcohol abuse. However, most of these changes in gene expression were small. It is not clear if gene expression profiles have sufficient power to discriminate control from alcoholic individuals and how consistent gene expression changes are when a relatively large sample size is examined. In the present study, microarray analysis (approximately 47,000 elements) was performed on the superior frontal cortex of 27 individual human cases (14 well characterized alcoholics and 13 matched controls). A partial least squares statistical procedure was applied to identify genes with altered expression levels in alcoholics. We found that genes involved in myelination, ubiquitination, apoptosis, cell adhesion, neurogenesis, and neural disease showed altered expression levels. Importantly, genes involved in neurodegenerative diseases such as Alzheimer's disease were significantly altered suggesting a link between alcoholism and other neurodegenerative conditions. A total of 27 genes identified in this study were previously shown to be changed by alcohol abuse in previous studies of human post-mortem brain. These results revealed a consistent re-programming of gene expression in alcohol abusers that reliably discriminates alcoholic from non-alcoholic individuals.

Microarray analysis of the effects of a gamma-protein kinase C null mutation on gene expression in striatum: a role for transthyretin in mutant phenotypes

A constitutive null mutation of the neural-specific isotype of protein kinase C (gamma-PKC) in mice produces alterations in behavioral traits and responses to ethanol suggesting that gamma-PKC-mediated phosphorylation is essential for regulation of some behaviors. However, it is possible that some of the effects of gamma-PKC gene deletion also may be due to altered gene expression. To examine alterations in gene expression, microarray analyses were performed on striatal tissue from wild types and mutants. A total of 143 genes and ESTs were identified as potential candidates related to differences between null mutants and wild types. Confirmation studies using qRT-PCR indicated that the expression of transthyretin was increased about 8-fold in striatum of naïve mutants compared to wild types. The effect of chronic ethanol treatment on transthyretin expression was analyzed because gamma-PKC mutants do not develop tolerance to chronic ethanol treatment. Ethanol treatment of mutants reversed the dramatic increase in transthyretin expression seen in naïve and control-diet treated mutants, but did not affect transthyretin expression in wild types.

Integrative strategies to identify candidate genes in rodent models of human alcoholism

The search for genes underlying alcohol-related behaviours in rodent models of human alcoholism has been ongoing for many years with only limited success. Recently, new strategies that integrate several of the traditional approaches have provided new insights into the molecular mechanisms underlying ethanol's actions in the brain. We have used alcohol-preferring C57BL/6J (B6) and alcohol-avoiding DBA/2J (D2) genetic strains of mice in an integrative strategy combining high-throughput gene expression screening, genetic segregation analysis, and mapping to previously published quantitative trait loci to uncover candidate genes for the ethanol-preference phenotype. In our study, 2 genes, retinaldehyde binding protein 1 (Rlbp1) and syntaxin 12 (Stx12), were found to be strong candidates for ethanol preference. Such experimental approaches have the power and the potential to greatly speed up the laborious process of identifying candidate genes for the animal models of human alcoholism.

Transcriptome analysis of frontal cortex in alcohol-preferring and nonpreferring rats

Although it is widely accepted that alcohol abuse and alcoholism have a significant genetic component of risk, the identities of the genes themselves remain obscure. To illuminate such potential genetic contributions, DNA macroarrays were used to probe for differences in normative cortical gene expression between rat strains genetically selected for alcohol self-administration preference, AA (Alko, alcohol) and P (Indiana, preferring), or avoidance, ANA (Alko, nonalcohol) and NP (Indiana, nonpreferring). Among 1,176 genes studied, six demonstrated confirmable, differential expression following comparison of ethanol-naive AA and ANA rats. Specifically, the mRNA level for metabotropic glutamate receptor 3 (mGluR3) was down-regulated in the AA vs. ANA lines. In contrast, calcium channel subunit alpha2delta1 (cacna2d1), vesicle-associated membrane protein 2 (VAMP2), syntaxin 1 (both syntaxin 1a and 1b; STX1a and STX1b), and syntaxin binding protein (MUNC-18) mRNAs were found to be increased in frontal cortex following comparison of AA with ANA animals. Bioinformatic analysis of these molecular targets showed that mGluR3 and cacna2d1 fall within chromosomal locations reported to be alcohol-related by the Collaborative Study on the Genetics of Alcoholism (COGA) as well as quantitative trait loci (QTL) studies. To determine further whether these differences were strain specific, the above-mentioned genes were compared in ethanol-preferring (P) and -nonpreferring (NP) selected lines. VAMP2 was the only gene that displayed statistically different mRNA levels in a comparison of P and NP rats. In conclusion, the altered cortical gene expression illuminated here would have the effect of altering neurotransmitter release in AA rats (compared with ANA rats). Such alterations, however, might not be a universal characteristic of all animal models of alcohol abuse and will also require further investigation in post-mortem human samples.