Long-term effects of alcohol drinking on cerebral glucose utilization in alcohol-preferring rats

Experimental models of fatty liver diseases: Status and appraisal

Fatty liver diseases, including alcohol-associated liver disease (ALD) and nonalcoholic fatty liver disease nonalcoholic fatty liver disease (NAFLD), affect a large number of people worldwide and become one of the major causes of end-stage liver disease, such as liver cirrhosis and hepatocellular carcinoma (HCC). Unfortunately, there are currently no approved pharmacological treatments for ALD or NAFLD. This situation highlights the urgent need to explore new intervention targets and discover effective therapeutics for ALD and NAFLD. The lack of properly validated preclinical disease models is a major obstacle to the development of clinical therapies. ALD and NAFLD models have been in the development for decades, but there are still no models that recapitulate the full spectrum of ALD and NAFLD. Throughout this review, we summarize the current in vitro and in vivo models used for research on fatty liver diseases and discuss the advantages and limitations of these models.

Molecular Imaging Studies of Alcohol Use Disorder

Alcohol use disorder (AUD) is a serious public health problem in many countries, bringing a gamut of health risks and impairments to individuals and a great burden to society. Despite the prevalence of a disease model of AUD, the current pharmacopeia does not present reliable treatments for AUD; approved treatments are confined to a narrow spectrum of medications engaging inhibitory γ-aminobutyric acid (GABA) neurotransmission and possibly excitatory N-methyl-D-aspartate (NMDA) receptors, and opioid receptor antagonists. Molecular imaging with positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can open a window into the living brain and has provided diverse insights into the pathology of AUD. In this narrative review, we summarize the state of molecular imaging findings on the pharmacological action of ethanol and the neuropathological changes associated with AUD. Laboratory and preclinical imaging results highlight the interactions between ethanol and GABA A-type receptors (GABAAR), but the interpretation of such results is complicated by subtype specificity. An abundance of studies with the glucose metabolism tracer fluorodeoxyglucose (FDG) concur in showing cerebral hypometabolism after ethanol challenge, but there is relatively little data on long-term changes in AUD. Alcohol toxicity evokes neuroinflammation, which can be tracked using PET with ligands for the microglial marker translocator protein (TSPO). Several PET studies show reversible increases in TSPO binding in AUD individuals, and preclinical results suggest that opioid-antagonists can rescue from these inflammatory responses. There are numerous PET/SPECT studies showing changes in dopaminergic markers, generally consistent with an impairment in dopamine synthesis and release among AUD patients, as seen in a number of other addictions; this may reflect the composite of an underlying deficiency in reward mechanisms that predisposes to AUD, in conjunction with acquired alterations in dopamine signaling. There is little evidence for altered serotonin markers in AUD, but studies with opioid receptor ligands suggest a specific up-regulation of the μ-opioid receptor subtype. Considerable heterogeneity in drinking patterns, gender differences, and the variable contributions of genetics and pre-existing vulnerability traits present great challenges for charting the landscape of molecular imaging in AUD.

A mini-review of the rodent models for alcoholic liver disease: shortcomings, application, and future prospects

Rodents are the most common models in studies of alcoholic liver disease (ALD). Although several rodents ALD models have been established and multiple mechanisms have been elucidated based on them, these models have some non-negligible shortcomings, specifically only inducing early stage (mainly steatosis, slight to moderate steatohepatitis) but not the whole spectrum of human ALD. The resistance of rodents to advanced ALD has been suggested to be due to the physiological differences between rodents and human beings. Previous studies have reported significant interstrain differences in the susceptibility to ethanol-induced liver injury and in the manifestation of ALD (such as different alteration of lipid profiles). Therefore, it would be interesting to characterize the manifestation of ethanol-induced liver damage in various rodents, which may provide a recommendation to investigators of ALD. Furthermore, more severe ALD models need to be established for the study of serious ALD forms, which may be achieved by using genetic modified rodents.

Altered brain functional connectivity and behaviour in a mouse model of maternal alcohol binge-drinking

Prenatal and perinatal alcohol exposure caused by maternal alcohol intake during gestation and lactation periods can have long-lasting detrimental effects on the brain development and behaviour of offspring. Children diagnosed with Foetal Alcohol Spectrum Disorders (FASD) display a wide range of cognitive, emotional and motor deficits, together with characteristic morphological abnormalities. Maternal alcohol binge drinking is particularly harmful for foetal and early postnatal brain development, as it involves exposure to high levels of alcohol over short periods of time. However, little is known about the long-term effects of maternal alcohol binge drinking on brain function and behaviour. To address this issue, we used pregnant C57BL/6 female mice with time-limited access to a 20% v/v alcohol solution as a procedure to model alcohol binge drinking during gestation and lactational periods. Male offspring were behaviourally tested during adolescence (30 days) and adulthood (60 days), and baseline neural metabolic capacity of brain regions sensitive to alcohol effects were also evaluated in adult animals from both groups. Our results show that prenatal and postnatal alcohol exposure caused age-dependent changes in spontaneous locomotor activity, increased anxiety-like behaviour and attenuated alcohol-induced conditioned place preference in adults. Also, significant changes in neural metabolic capacity using cytochrome c oxidase (CCO) quantitative histochemistry were found in the hippocampal dentate gyrus, the mammillary bodies, the ventral tegmental area, the lateral habenula and the central lobules of the cerebellum in adult mice with prenatal and postnatal alcohol exposure. In addition, the analysis of interregional CCO activity correlations in alcohol-exposed adult mice showed disrupted functional brain connectivity involving the limbic, brainstem, and cerebellar regions. Finally, increased neurogenesis was found in the dentate gyrus of the hippocampus of alcohol-exposed offspring, suggesting neuroadaptive effects due to early alcohol exposure. Our results demonstrate that maternal binge-like alcohol drinking causes long-lasting effects on motor and emotional-related behaviours associated with impaired neuronal metabolic capacity and altered functional brain connectivity.

Involvement of lateral septum in alcohol's dopamine-elevating effect in the rat

Drugs of abuse share the ability to increase extracellular dopamine (DA) levels in the mesolimbic DA system. This effect has been linked to positive and reinforcing experiences of drug consumption and is presumed to be of importance for continued use, as well as for the development of dependence and addiction. Previous rat studies from our lab have implicated a neuronal circuitry involving glycine receptors in nucleus accumbens (nAc) and, secondarily, nicotinic acetylcholine receptors in the ventral tegmental area (VTA) in ethanol's (EtOH) DA-elevating effect. The work presented here, performed in male Wistar rats, suggests that the lateral septum (LS), which has previously been associated with different aspects of EtOH-related behaviour, is involved as well. In vivo microdialysis methodology demonstrated that blocking the generation of action potentials in LS using tetrodotoxin prevented a DA increase in nAc after accumbal EtOH perfusion. Retrograde tracing and polymerase chain reaction (PCR) were used to identify and characterize cells projecting to VTA from nAc/LS and from LS to nAc. Based on the PCR results, cells projecting from both LS/nAc to anterior VTA and from LS to nAc were mainly GABAergic neurons expressing glycine receptors, and these cells are presumed to be involved in mediating the DA-elevating effect of EtOH. These results provide further evidence implicating LS in the reinforcing effects of EtOH. Additional studies are needed to investigate LS involvement in EtOH consumption behaviour and its potential role in the development of dependence and addiction.

Impact of Alcohol on Glycemic Control and Insulin Action

Alcohol has profound effects on tissue and whole-body fuel metabolism which contribute to the increased morbidity and mortality in individuals with alcohol use disorder. This review focuses on the glucose metabolic effects of alcohol, primarily in the muscle, liver and adipose tissue, under basal postabsorptive conditions and in response to insulin stimulation. While there is a relatively extensive literature in this area, results are often discordant and extrapolating between models and tissues is fraught with uncertainty. Comparisons between data generated in experimental cell and animals systems will be contrasted with that obtained from human subjects as often times results differ. Further, the nutritional status is also an important component of the sometimes divergent findings pertaining to the effects of alcohol on the regulation of insulin and glucose metabolism. This work is relevant as the contribution of alcohol intake to the development or exacerbation of type 2 diabetes remains ill-defined and a multi-systems approach is likely needed as both alcohol and diabetes affect multiple targets within the body.

Animal models of chronic liver diseases

Chronic liver diseases are frequent and potentially life threatening for humans. The underlying etiologies are diverse, ranging from viral infections, autoimmune disorders, and intoxications (including alcohol abuse) to imbalanced diets. Although at early stages of disease the liver regenerates in the absence of the insult, advanced stages cannot be healed and may require organ transplantation. A better understanding of underlying mechanisms is mandatory for the design of new drugs to be used in clinic. Therefore, rodent models are being developed to mimic human liver disease. However, no model to date can completely recapitulate the "corresponding" human disorder. Limiting factors are the time frame required in humans to establish a certain liver disease and the fact that rodents possess a distinct immune system compared with humans and have different metabolic rates affecting liver homeostasis. These features account for the difficulties in developing adequate rodent models for studying disease progression and for testing new pharmaceuticals to be translated into the clinic. Nevertheless, traditional and new promising animal models that mimic certain attributes of chronic liver diseases are established and being used to deepen our understanding in the underlying mechanisms of distinct liver diseases. This review aims at providing a comprehensive overview of recent advances in animal models recapitulating different features and etiologies of human liver diseases.

Urocortins: CRF's siblings and their potential role in anxiety, depression and alcohol drinking behavior

It is widely accepted that stress, anxiety, depression and alcohol abuse-related disorders are in large part controlled by corticotropin-releasing factor (CRF) receptors. However, evidence is accumulating that some of the actions on these receptors are mediated not by CRF, but by a family of related Urocortin (Ucn) peptides Ucn1, Ucn2 and Ucn3. The initial narrow focus on CRF as the potential main player acting on CRF receptors appears outdated. Instead it is suggested that CRF and the individual Ucns act in a complementary and brain region-specific fashion to regulate anxiety-related behaviors and alcohol consumption. This review, based on a symposium held in 2011 at the research meeting on "Alcoholism and Stress" in Volterra, Italy, highlights recent evidence for regulation of these behaviors by Ucns. In studies on stress and anxiety, the roles of Ucns, and in particular Ucn1, appear more visible in experiments analyzing adaptation to stressors rather than testing basal anxiety states. Based on these studies, we propose that the contribution of Ucn1 to regulating mood follows a U-like pattern with both high and low activity of Ucn1 contributing to high anxiety states. In studies on alcohol use disorders, the CRF system appears to regulate not only dependence-induced drinking, but also binge drinking and even basal consumption of alcohol. While dependence-induced and binge drinking rely on the actions of CRF on CRFR1 receptors, alcohol consumption in models of these behaviors is inhibited by actions of Ucns on CRFR2. In contrast, alcohol preference is positively influenced by actions of Ucn1, which is capable of acting on both CRFR1 and CRFR2. Because of complex distribution of Ucns in the nervous system, advances in this field will critically depend on development of new tools allowing site-specific analyses of the roles of Ucns and CRF.

The impact of chronic cigarette smoking on recovery from cortical gray matter perfusion deficits in alcohol dependence: longitudinal arterial spin labeling MRI

BACKGROUND

Neuroimaging studies reported cerebral perfusion abnormalities in individuals with alcohol use disorders. However, no longitudinal magnetic resonance imaging (MRI) studies of cerebral perfusion changes during abstinence from alcohol have been reported.

METHODS

Arterial spin labeling MRI was used to evaluate cortical gray matter perfusion changes in short-term abstinent alcohol dependent individuals in treatment and to assess the impact of chronic cigarette smoking on perfusion changes during abstinence. Seventy-six patients were scanned at least once. Data from 19 non-smoking (17 males, 2 females) and 22 smoking (21 males, 1 female) patients scanned at 1 and 5 weeks of abstinence were used to assess perfusion changes over time. Twenty-eight age-equated healthy controls (25 males, 3 females) were scanned for cross-sectional comparison, 13 of them were scanned twice. Given the age range of the cohort (28 to 68 years), age was used as a covariate in the analyses. Mean perfusion was measured in voxels of at least 80% gray matter in the frontal and parietal lobes and related to neurocognitive and substance use measures.

RESULTS

At 1 week of abstinence, frontal and parietal gray matter perfusion in smoking alcoholics was not significantly different from that in non-smoking alcoholics, but each group's perfusion values were significantly lower than in controls. After 5 weeks of abstinence, perfusion of frontal and parietal gray matter in non-smoking alcoholics was significantly higher than that at baseline. However, in smoking alcoholics, perfusion was not significantly different between the time-points in either region. The total number of cigarettes smoked per day was negatively correlated with frontal gray matter perfusion measured at 5 weeks of abstinence. Lobar perfusion measures did not correlate significantly with drinking severity or cognitive domain measures at either time-point.

CONCLUSION

Although cerebral perfusion in alcohol dependent individuals shows improvement with abstinence from alcohol, cigarette smoking appears to hinder perfusion improvement.

Effects of concurrent access to multiple ethanol concentrations and repeated deprivations on alcohol intake of high-alcohol-drinking (HAD) rats

High-alcohol-drinking rats, given access to 10% ethanol, expressed an alcohol deprivation effect (ADE) only after multiple deprivations. In alcohol-preferring (P) rats, concurrent access to multiple ethanol concentrations combined with repeated cycles of EtOH access and deprivation produced excessive ethanol drinking. The current study was undertaken to examine the effects of repeated alcohol deprivations with concurrent access to multiple concentrations of ethanol on ethanol intake of HAD replicate lines of rats. HAD-1 and HAD-2 rats received access to 10, 20 and 30% (v/v) ethanol for 6 weeks. Rats from each replicate line were assigned to: (1) a non-deprived group; (2) a group initially deprived of ethanol for 2 weeks; or (3) a group initially deprived for 8 weeks. Following the restoration of the ethanol solutions, cycle of 2 weeks of ethanol exposure and 2 weeks of alcohol deprivation was repeated three times for a total of four deprivations. Following the initial ethanol deprivation period, deprived groups significantly increased ethanol intakes during the initial 24-hour re-exposure period. Multiple deprivations increased ethanol intakes, shifted preference to higher ethanol concentrations and prolonged the duration of the elevated ethanol intakes for up to 5 days. In addition, repeated deprivations increased ethanol intake in the first 2-hour re-exposure period as high as 5-7 g/kg (which are equivalent to amounts consumed in 24 hours by HAD rats), and produced blood ethanol levels in excess of 150 mg%. The results indicate that HAD rats exhibit 'loss-of-control' of alcohol drinking with repeated deprivations when multiple ethanol concentrations are available.

Ventral pallidum roles in reward and motivation

In recent years the ventral pallidum has become a focus of great research interest as a mechanism of reward and incentive motivation. As a major output for limbic signals, the ventral pallidum was once associated primarily with motor functions rather than regarded as a reward structure in its own right. However, ample evidence now suggests that ventral pallidum function is a major mechanism of reward in the brain. We review data indicating that (1) an intact ventral pallidum is necessary for normal reward and motivation, (2) stimulated activation of ventral pallidum is sufficient to cause reward and motivation enhancements, and (3) activation patterns in ventral pallidum neurons specifically encode reward and motivation signals via phasic bursts of excitation to incentive and hedonic stimuli. We conclude that the ventral pallidum may serve as an important 'limbic final common pathway' for mesocorticolimbic processing of many rewards.

Acute ethanol effects on local cerebral glucose utilization in select central nervous system regions of adolescent alcohol-preferring (P) and alcohol-nonpreferring (NP) rats

BACKGROUND

Alcohol abuse among adolescents is a major health and developmental problem. The 2-[(14)C]deoxyglucose (2-DG) technique allows for the in vivo quantification of local cerebral glucose utilization (LCGU) as a measure of functional neuronal activity.

METHODS

Local cerebral glucose utilization rates were examined after acute ethanol administration within selected brain regions of adolescent alcohol-preferring (P) and -nonpreferring (NP) rats. Postnatal day 45 male P and NP rats were injected with saline or 1.0 g/kg ethanol, i.p., 10 minutes prior to an intravenous bolus of [(14)C]-2-deoxyglucose (125 microCi/kg). Image densities were determined using quantitative autoradiography and LCGU values calculated.

RESULTS

Acute ethanol injection significantly decreased LCGU rates in select brain regions including the olfactory tubercles, the frontal cortex (Fr), and subregions of the posterior hippocampus (pCA1 and pCA3). Acute ethanol had no significant effects on LCGU rates in any region of the adolescent NP rats. Significant basal LCGU rate differences were apparent between the rat lines in a nearly global fashion with adolescent P rats having much higher basal LCGU rates compared with adolescent NP rats.

CONCLUSIONS

These findings suggest that the adolescent P and NP rats are less sensitive to the effects of acute ethanol than their adult counterparts. The adolescent P rat is relatively more sensitive to the initial effects of acute ethanol in select brain regions as compared with the adolescent NP rat. Additionally, the innate hyper-excited state of the adolescent P central nervous system is a likely factor in the development of their high alcohol drinking behaviors.

Longitudinal brain magnetic resonance imaging study of the alcohol-preferring rat. Part II: effects of voluntary chronic alcohol consumption

BACKGROUND

Tracking the dynamic course of human alcoholism brain pathology can be accomplished only through naturalistic study and without opportunity for experimental manipulation. Development of an animal model of alcohol-induced brain damage, in which animals consume large amounts of alcohol following cycles of alcohol access and deprivation and are examined regularly with neuroimaging methods, would enable hypothesis testing focused on the degree, nature, and factors resulting in alcohol-induced brain damage and the prospects for recovery or relapse.

METHODS

We report the results of longitudinal magnetic resonance imaging (MRI) studies of the effects of free-choice chronic alcohol intake on the brains of 2 cohorts of selectively bred alcohol-preferring (P) rats. In the companion paper, we described the MRI acquisition and analysis methods, delineation of brain regions, and growth patterns in total brain and selective structures of the control rats in the present study. Both cohorts were studied as adults for about 1 year and consumed high doses of alcohol for most of the study duration. The paradigm involved a 3-bottle choice with 0, 15 (or 20%), and 30% (or 40%) alcohol available in several different exposure schemes: continuous exposure, cycles of 2 weeks on followed by 2 weeks off alcohol, and binge drinking in the dark.

RESULTS

Brain structures of the adult P rats in both the alcohol-exposed and the water control conditions showed significant growth, which was attenuated in a few measures in the alcohol-exposed groups. The region with the greatest demonstrable effect was the corpus callosum, measured on midsagittal images.

CONCLUSION

The P rats showed an age-alcohol interaction different from humans, in that normal growth in selective brain regions that continues in adult rats was retarded.

Neuroadaptations of Cdk5 in cholinergic interneurons of the nucleus accumbens and prefrontal cortex of inbred alcohol-preferring rats following voluntary alcohol drinking

BACKGROUND

Neurobiological studies have identified brain areas and related molecular mechanisms involved in alcohol abuse and dependence. Specific cell types in these brain areas and their role in alcohol-related behaviors, however, have not yet been identified. This study examined the involvement of cholinergic cells in inbred alcohol-preferring rats following 1 month of alcohol drinking. Cyclin-dependent kinase 5 (Cdk5) immunoreactivity (IR), a marker of neuronal plasticity, was examined in cholinergic neurons of the nucleus accumbens (NuAcc) and prefrontal cortex (PFC) and other brain areas implicated in alcohol drinking, using dual immunocytochemical (ICC) procedures. Single Cdk5 IR was also examined in several brain areas implicated in alcohol drinking.

METHODS

The experimental group self-administered alcohol using a 2-bottle-choice test paradigm with unlimited access to 10% (v/v) alcohol and water for 23 h/d for 1 month. An average of 6 g/kg alcohol was consumed daily. Control animals received identical treatment, except that both bottles contained water. Rats were perfused and brain sections were processed for ICC procedures.

RESULTS

Alcohol drinking resulted in a 51% increase in Cdk5 IR cholinergic interneurons in the shell NuAcc, while in the PFC there was a 51% decrease in the percent of Cdk5 IR cholinergic interneurons in the infralimbic region and a 46% decrease in Cdk5 IR cholinergic interneurons in the prelimbic region. Additionally, single Cdk5 IR revealed a 42% increase in the central nucleus of the amygdala (CNA).

CONCLUSIONS

This study identified Cdk5 neuroadaptation in cholinergic interneurons of the NuAcc and PFC and in other neurons of the CNA following 1 month of alcohol drinking. These findings contribute to our understanding of the cellular and molecular basis of alcohol drinking and toward the development of improved region and cell-specific pharmacotherapeutic and behavioral treatment programs for alcohol abuse and alcoholism.

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.

Glutamate and dopamine synaptic terminals in extended amygdala after 14-week chronic alcohol drinking in inbred alcohol-preferring rats

Alcohol has been shown to affect glutamate (GLU) and dopamine (DA) release and their correlated receptors in the key reward center--extended amygdala--which includes the shell of nucleus accumbens (sNAc) and central nucleus of amygdala (cAmg). It is unclear to date whether there is an alteration in the number of presynaptic GLU/DA nerve terminals. In this study, we investigated the number of GLU and DA terminals in the extended amygdala of alcohol-preferring (P) rats that chronically drank ethanol. P rats have a propensity to drink ethanol to intoxication and develop an alcohol dependency. The P rats were divided into (1) Water group given ad libitum chow and water for 14 weeks; (2) Continuous alcohol group (C-Alc) given ad libitum chow and choice of 15 or 30% (v/v) ethanol or water for 14 weeks; and (3) Repeated deprivation (RD-Alc) group given the same choice of ethanol or water for 6 weeks, followed by a twice repeated cycle of 2 weeks without ethanol followed by 2 weeks with ethanol. Two subpopulations of GLU terminals were labeled by immunostaining for the vesicular GLU transporter 1 (vGLUT1) and vesicular GLU transporter 2 (vGLUT2). DA terminals were labeled by immunostaining for tyrosine hydroxylase (TH). The GLU and DA immunostained (im) varicosities were quantified and analyzed using stereological methods. We found that chronic alcohol did not alter the number of TH-im terminals in the extended amygdala in either the C-Alc or RD-Alc drinking paradigms. Thus, the increases in extracellular levels of DA previously reported following chronic alcohol are likely due to a change in the efficiency of DA release rather than a change in the number of DA terminals. The number of vGLUT1-im terminals was also unchanged in the extended amygdala; however, the number of vGLUT2-im terminals, which represent the greater population of GLU terminals, was increased in the sNAc of the RD-Alc group compared to the Water group. Chronic alcohol is known to affect GLU release, and our findings indicate that repeated alcohol deprivation may preferentially increase GLU terminals in the sNAc bearing the vGLUT2, which are primarily afferents from the thalamus. Our results further indicate that repeated deprivation of alcohol can change the ratio of GLU to DA innervation in the sNAc, a key region of the reward circuitry.

Adolescent alcohol drinking and its long-range consequences. Studies with animal models

This chapter reviews findings, mainly obtained from the selectively bred alcohol-preferring (P) line of rats, on (a) the development of alcohol drinking during the peri-adolescent period, (b) neurobiological factors that may contribute to adolescent drinking, (c) interventions to prevent alcohol drinking during adolescence, and (d) some long-lasting consequences of adolescent alcohol drinking. The findings indicate that P rats readily initiate alcohol drinking during the early post-weaning, adolescent and peri-adolescent periods of development. The early age-of-onset of alcohol drinking in the P compared to the NP line is associated with (a) higher densities of serotonin-1A (5-HT1A) receptors in cerebral cortical and hippocampal regions; (b) lower densities of dopamine (DA) D2 receptors in the ventral tegmental area (VTA); (c) higher functional activity in several limbic, cortical and hippocampal regions; and (d) sensitivity to the low-dose stimulating effect of ethanol. Conditioned taste aversion (CTA) training during adolescence produces long-term effects on preventing high alcohol drinking behavior of P rats. Alcohol drinking during peri-adolescence by P rats produces long-lasting effects that increase the acquisition of ethanol self-administration in adulthood, and, in addition, increase craving-like behavior and the potential for alcohol relapse. With suitable animal models, a better understanding of the mechanisms underlying adolescent alcohol drinking and its long-range consequences can be attained.

Effects of ethanol drinking on central nervous system functional activity of alcohol-preferring rats

The [(14)C]-2-deoxyglucose (2-DG) technique was used to assess the rates of local cerebral glucose utilization (LCGU) in key limbic, cerebral cortical, hippocampal, basal ganglionic, and subcortical regions of alcohol-preferring (P) rats following chronic 24-h free-choice ethanol drinking. Adult male P rats were submitted to (1) 8 continuous weeks of two-bottle access to 15% ethanol and water (E-C group); (2) 8 weeks of identical two-bottle access followed by 2 weeks of ethanol deprivation (E-D group); (3) cycles of 2 weeks of two-bottle ethanol access and 2 weeks of deprivation, repeated for four cycles (E-RD group); or (4) water only treatment [ethanol-naive group (E-N group)]. A single pulse of [(14)C]-2-DG (125 microCi/kg) was administered via a venous catheter, and timed arterial blood samples were collected over 45 min and later assayed for plasma glucose and [(14)C]-2-DG concentrations. Quantitative autoradiography was used to determine [(14)C] densities, and LCGU values were calculated. With the exception of a few small differences in the hippocampus, no significant differences were found in any of the central nervous system (CNS) regions examined among the four experimental groups of P rats. Animals in the E-D group had lower LCGU rates in the anterior hippocampal CA1 subregion than animals in the E-N, E-C, and E-RD groups. In the anterior hippocampal CA3 subregion and the anterior hippocampal dentate gyrus, the E-D group had significantly lower LCGU rates than the E-RD group. Overall, the results of this study indicate that 24-h ethanol-drinking experience has little effect on CNS functional neuronal activity in P rats.

Effects of acute administration of ethanol on cerebral glucose utilization in adult alcohol-preferring and alcohol-nonpreferring rats

Local cerebral glucose utilization (LCGU) rates, as determined by the [(14)C]-2-deoxyglucose (2-DG) technique, were examined after acute ethanol administration within selected brain regions of alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. Adult male P and NP rats were injected with saline, 0.25 g/kg, or 1.0 g/kg ethanol, intraperitoneally (ip), 10 min before an intravenous bolus of [(14)C]2-DG (125 microCi/kg). Timed arterial blood samples were collected over 45 min and assayed for plasma glucose, ethanol, and [(14)C]2-DG levels. Image densities were determined using quantitative autoradiography and LCGU values calculated. Data were collected from several key limbic, basal ganglionic, cortical, and subcortical structures. Low-dose ethanol (0.25 g/kg) significantly decreased LCGU rates in several brain regions including the medial prefrontal cortex, olfactory tubercles, and the CA1 subregion of the hippocampus of P rats. Low-dose ethanol had no significant effects on LCGU rates in the NP rats. Moderate-dose ethanol (1.0 g/kg) also significantly lowered LCGU rates in many brain regions of P rats, including key limbic structures, such as the medial prefrontal cortex, olfactory tubercles, ventral tegmental area, basolateral nucleus of the amygdala, lateral septum, and ventral pallidum. Moderate-dose ethanol also significantly lowered LCGU rates in the medial prefrontal cortex as well as in the habenula of NP rats. All other regions were unaffected in the NP rats. These findings support the suggestion that certain central nervous system regions of P rats may be more sensitive than those of NP rats to the effects of low to intermediate doses of ethanol.

Effects of Long-Term Episodic Access to Ethanol on the Expression of an Alcohol Deprivation Effect in Low Alcohol???Consuming Rats

BACKGROUND

The alcohol-preferring (P) and -nonpreferring (NP) and high alcohol-drinking (HAD) and low alcohol-drinking (LAD) rats have been selectively bred for divergent preference for ethanol over water. In addition, both P and HAD rats display an alcohol deprivation effect (ADE). This study was undertaken to test whether the NP, LAD-1, and LAD-2 lines of rats could display an ADE as well.

METHOD

Adult female NP, LAD-1, and LAD-2 rats were given concurrent access to multiple concentrations of ethanol [5, 10, 15% (v/v)] and water in an ADE paradigm involving an initial 6 weeks of 24-hr access to ethanol, followed by four cycles of 2 weeks of deprivation from and 2 weeks of re-exposure to ethanol (5, 10, and 15%). A control group had continuous access to the ethanol concentrations (5, 10, and 15%) and water through the end of the fourth re-exposure period.

RESULTS

For NP rats, a preference for the highest ethanol concentration (15%) was evident by the end of the fifth week of access (approximately 60% of total ethanol fluid intake). Contrarily, LAD rats did not display a marked preference for any one concentration of ethanol. All three lines displayed an ADE after repeated cycles of re-exposure to ethanol, with the general ranking of intake being LAD-1 > NP > LAD-2 (e.g., for the first day of reinstatement of the third re-exposure cycle, intakes were 6.5, 2.9, and 2.4 g/kg/day compared with baseline values of 3.1, 2.0, and 1.3 g/kg/day for each line, respectively). By the 13th week, rats from all three lines, with a ranking of LAD-1 > NP > LAD-2, were drinking more ethanol (3.3, 2.2, and 2.0 g/kg/day, respectively) compared with their consumption during the first week of access (approximately 1.1 g/kg/day for all three lines).

CONCLUSION

These data indicate that access to multiple concentrations of ethanol and exposure to multiple deprivation cycles can partially overcome a genetic predisposition of NP, LAD-1, and LAD-2 rats for low alcohol consumption. In addition, the findings suggest that genetic control of low alcohol consumption in rats is not associated with the inability to display an ADE.

Microarray analysis of mouse brain gene expression following acute ethanol treatment

Alterations in gene expression are thought to help mediate certain effects of alcohol in the brain. We have analyzed the expression of approximately 24,000 genes using oligonucleotide microarrays to examine the brain expression profiles in two strains of inbred mice, C57BL/6J and DBA/2J, following exposure to an acute dose of ethanol. Our screen identified 61 genes responding to the ethanol treatment beyond a 1.5-fold threshold, with 46 genes altered in both mouse strains and 15 altered in only one strain. Approximately 25% of the genes were selected for confirmation by reverse transcriptase polymerase chain reaction with an 87% success rate. The genes identified have roles in cell signaling, gene regulation, and homeostasis/stress response. Although some of the genes were previously known to be ethanol responsive, we have for the most part identified novel genes involved in the acute murine brain response to ethanol. Such genes have the potential to represent candidate genes in the search to elucidate the molecular pathways mediating ethanol's effects in the brain.

Ethanol Drinking and Deprivation Alter Dopaminergic and Serotonergic Function in the Nucleus Accumbens of Alcohol-Preferring Rats

The alcohol deprivation effect is a temporary increase in the intake of, or preference for, ethanol after a period of deprivation that may result from persistent changes in key limbic regions thought to regulate alcohol drinking, such as the nucleus accumbens. The present study tested the hypothesis that chronic alcohol drinking under continuous 24-h free-choice conditions alters dopamine and serotonin neurotransmission in the nucleus accumbens and that these alterations persist in the absence of alcohol. Using the no-net-flux microdialysis method, the steady-state extracellular concentration (point of no-net-flux) for dopamine was approximately 25% higher in the adult female alcohol-preferring P rats given prior access to 10% ethanol, even after 2 weeks of ethanol abstinence, compared with the P rats gives access only to water. However, the extracellular concentration of serotonin was approximately 35% lower in animals given 8 weeks of continuous access to ethanol compared with water controls and animals deprived of ethanol for 2 weeks. The effect of local perfusion with 100 microM sulpiride (D(2) receptor antagonist) and 35 microM 1-(m-chlorophenyl)-biguanide (5-hydroxytryptamine(3) receptor agonist) on dopamine overflow were reduced approximately 33% in both groups of ethanol-exposed P rats compared with water controls. Free-choice alcohol drinking by P rats alters dopamine and serotonin neurotransmission in the nucleus accumbens, and many of these effects persist for at least 2 weeks in the absence of ethanol, suggesting that these underlying persistent changes may be in part responsible for increased ethanol drinking observed in the alcohol-deprivation effect.

Interaction of aging and intermittent ethanol exposure on brain cytochrome c oxidase activity levels

The effects of chronic, intermittent ethanol exposure on brain cytochrome c oxidase (CO) activity levels were studied in young (3- to 4-month-old) and aged (29- to 30-month-old) male Wistar rats. The rats were given highly intoxicating doses of ethanol three times a day by intragastric intubation for four successive days, followed by a 3-day ethanol-withdrawal period. This 4-day ethanol-exposure with 3-day ethanol-withdrawal cycle was repeated five times to simulate the binge drinking of human alcoholics. The histochemical demonstration of CO showed a markedly decreased activity level in the medial prefrontal cortex (especially layer V pyramids and neuropil) of the ethanol-exposed rats of both age groups compared with findings for the respective controls. In the cerebellar vermis, CO activity level was decreased in the Purkinje neurons of the aged ethanol-exposed rats and in the granule cells of both young and aged ethanol-exposed rats. The CO activity level in the locus coeruleus was decreased in both young and old ethanol-exposed rats, but the decrease was more pronounced in the young ethanol-exposed group. Aging per se did not markedly change CO histochemical findings in either prefrontal or cerebellar cortex, but CO activity levels were increased in the locus coeruleus. In summary, results of the current study support our conclusion that CO activity levels were decreased in the cerebral and cerebellar cortices as well as in the locus coeruleus-CNS regions known to be negatively affected by chronic ethanol exposure. Defective energy metabolism due to decreased CO activity levels might compromise neuronal energy stores and thereby contribute to ethanol-induced brain dysfunction and irreversible CNS degeneration.

Ethanol effects on local cerebral glucose utilization in high-alcohol-drinking and low-alcohol-drinking rats

Divergent ethanol-drinking behavior in rats selectively bred for high- or low-ethanol-drinking behavior could be related to differences in the sensitivity of the CNS to ethanol. In the current study, we examined the effects of acute (i.e., single injection) ethanol administration on local cerebral glucose utilization (LCGU) within selected brain regions of high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats. Adult, male, HAD and LAD rats from replicate line 2 were injected intraperitoneally with saline, or ethanol, at doses of 0.25 g/kg or 1.0 g/kg, during their dark cycle; 10 min later, [14C]-2-deoxyglucose ([14C]-2-DG; 125 microCi/kg) was injected into the femoral vein. Timed arterial blood samples were collected over 45 min and assayed for plasma glucose, ethanol, and [14C]-2-DG levels. Rats were then decapitated, and their brains were quickly extracted and frozen in isopentane at -50 degrees C. Coronal brain sections were prepared and apposed to x-ray film for 2 days, and image densities were determined by using quantitative autoradiography. Data were collected from several key limbic (nucleus accumbens, ventral tegmental area, olfactory tubercle, amygdala, hippocampus, ventral pallidum, and septum), basal ganglia, cortical (medial prefrontal, frontal, parietal, temporal, occipital, entorhinal, piriform, and cingulate), and subcortical (thalamus, habenula, and superior colliculus) structures. After administration of both low (0.25 g/kg) and moderate (1.0 g/kg) doses of ethanol, LCGU values were lower, relative to those for saline controls, in several CNS regions (lateral septum; posterior cingulate, frontal, parietal, and temporal cortices; dorsomedial striatum; and dorsomedial thalamus) of LAD but not HAD rats. These findings may indicate that certain CNS regions of LAD-2 rats are more sensitive than regions of HAD-2 rats to the effects of low-to-intermediate doses of ethanol.

Local cerebral glucose utilization after relapse in ethanol drinking in alcohol-preferring (P) rats

The [(14)C]-2-deoxyglucose ([(14)C]-2-DG) quantitative autoradiographic technique was used to determine rates of local cerebral glucose utilization (LCGU) in discrete brain regions of adult, male alcohol-preferring (P) rats after 2 weeks of ethanol deprivation (E-D), 3 and 14 days of ethanol-relapse drinking (E-R3; E-R14), and in P rats, which were chronically drinking ethanol (E-C) for 8 weeks during daily 3-h scheduled-access sessions to 15% (vol./vol.) ethanol and water, or were ethanol-naive (E-N). The hypothesis to be tested was that ethanol-relapse drinking is initiated to restore changes in functional activity back to their chronic ethanol-exposed state. The LCGU rates were measured 1 h before the scheduled-access session. Mean ethanol intake did not differ among the groups. The LCGU rates were decreased in 41 of 57 regions or subregions examined in E-C rats compared with findings for E-N rats, including subregions of the cerebral cortex, hippocampus, and structures in the mesocorticolimbic and nigrostriatal systems. After 2 weeks of deprivation, LCGU values tended to return toward control values (E-N) in most CNS regions and did not differ significantly from control values in 12 regions or subregions (e.g., parts of the limbic system, cerebral cortex). Compared with LCGU values that recovered toward control levels in the E-D group, ethanol-relapse drinking was associated with decreased LCGU values in (1) 4 of 10 limbic structures, (2) all 6 cerebral cortical regions, (3) 1 of 4 basal ganglia regions, (4) 2 of 7 hippocampus subregions, and (5) 1 of 6 thalamic nuclei. The present results indicate that ethanol-relapse drinking was associated with reduced LCGU rates in most CNS regions that recovered toward control values and suggested to us that ethanol-relapse drinking may be initiated to restore neuronal function to its prior chronic ethanol-exposure state.

Central nucleus of the amygdala and the effects of alcohol and alcohol-drinking behavior in rodents

This article will review key literature on the effects of alcohol on the amygdala and the involvement of the amygdala in regulating alcohol drinking in mice and rats. Special emphasis will be placed on the central nucleus of the amygdala (CeA) because this nucleus is a major component of the extended amygdala, which has been implicated in regulating alcohol-drinking behavior. Immunocytochemical and in situ hybridization studies indicate that acute high-dose ethanol administration increases c-fos expression in GABAergic neurons within the CeA of the rat, suggesting activation of these neurons by ethanol. A similar high-dose (4 g/kg ethanol) effect on c-fos expression in the CeA of C57 mice was also observed, whereas the DBA mice showed increased c-fos expression in the CeA in the dose range of 1.25-4.0 g/kg. Studies with DBA x C57 F2 intercross mice suggest that there may be a relationship between the neuronal activating effects of ethanol in the CeA and the locomotor stimulating effects of ethanol. Studies with rats examining the effects of acute ethanol or chronic alcohol drinking on local cerebral glucose utilization (LCGU) rates (as a measure of synaptic activity) indicated that (a) acute ethanol (0.25-2.0 g/kg) had little effect on LCGU rates in the CeA; (b) basal LCGU rates were reduced in the CeA as a result of chronic alcohol drinking; and (c) oral self-administration of ethanol increased LCGU values within the CeA. Microdialysis studies demonstrated that acute ethanol (2 g/kg) injection increased dopamine (DA) and serotonin (5-HT) release in the CeA. Microinjection studies indicate that GABA(A) receptors within the CeA are involved in oral ethanol self-administration. Overall, the findings from the various studies support a role for the CeA in mediating the stimulating actions of alcohol in mice and regulating alcohol-drinking behavior in mice and rats.