Chronic social isolation and chronic variable stress during early development induce later elevated ethanol intake in adult C57BL/6J mice

Cluster and meta-analyses on factors influencing stress-induced alcohol drinking and relapse in rodents

Numerous preclinical studies have focused on the identification of biological and environmental factors that modulate stress and alcohol interactions. Although there is a good qualitative description of the determinants of alcohol consumption in rodents, the magnitude of the variables influencing stress-induced ethanol intake and its dynamics are still poorly understood. We therefore carried out a clustered meta-analysis on stress-induced alcohol consumption in 1520 rats. Two-step clustering of the literature-derived dataset suggests a strong dependency of the experimental outcome on the method used to measure alcohol intake. Free-choice home cage drinking versus operant self-administration is the most critical determinant of stress-induced increases in alcohol consumption in rats. Stress does not typically result in enhanced alcohol consumption in operant self-administration paradigms, whereas it leads to increased home cage drinking. Stress-induced alcohol consumption is age dependent, with adults being more sensitive than adolescents. In addition, foot shock and forced swim stress enhance alcohol intake, while restraint stress does not. In contrast, a meta-analysis of 327 rats on stress-induced reinstatement of alcohol-seeking behavior shows less influence of those modulating factors, and usually foot shock or yohimbine leads to a reinstatement of approximately 300 percent of extinction level responding. Via accurate characterization of the significant factors in the interplay of alcohol consumption, relapse and stress, our quantitative description not only improves the understanding of underlying mechanisms, but also provides an appropriate framework for the optimal experimental design of preclinical studies that more accurately translates to the human condition.

Increased voluntary ethanol consumption and changes in hippocampal synaptic plasticity in isolated C57BL/6J mice

Social isolation (SI) is a notable model of prolonged mild stress, characterized by multiple neurochemical and behavioral alterations, that appears particularly suitable for studying different aspects of the interplay between stress and ethanol (EtOH) consumption in order to characterize potential molecular mechanisms, including changes in the function of inhibitory GABAergic synapses, underlying such interaction. In C57BL/6J mice, SI is associated with an altered hippocampal concentration of the neuroactive steroids 3α-hydroxy-5α-pregnan-20-one (3α-5α-THP), an increased expression of the α4 and δ subunit of γ-aminobutyric acid type A receptors (GABAARs) in the dentate gyrus (DG), and a parallel enhancement of the stimulatory action of 4,5,6,7-tetrahydroisoxazolo[5,4-c] pyridin-3-ol (THIP) on GABAergic tonic currents recorded in voltage-clamped DG granule cells (DGGCs). In addition, SI in C57BL/6J mice determines an increase in voluntary EtOH consumption and EtOH preference when compared to group-housed (GH) control animals. Furthermore, in hippocampal slices of SI mice we also observed a marked reduction of both cellular excitability and long term potentiation (LTP) in pyramidal neurons of the CA1 hippocampal sub-region, effects that were prevented by the long term treatment of SI mice with the neuroactive steroid precursor progesterone. In this article, we summarize some of our recent findings on the effects of SI in C57BL/6J mice on voluntary EtOH intake, regulation of GABAARs gene expression and function and hippocampal long term synaptic plasticity.

Effects of naltrexone on post-abstinence alcohol drinking in C57BL/6NCRL and DBA/2J mice

The present experiment evaluated the effects of naltrexone, a non-selective opioid receptor antagonist, on post-abstinence alcohol drinking in C57BL/6NCRL and DBA/2J male mice. Home cage 2-bottle (alcohol vs. water) free-choice procedures were employed. During the pre-abstinence period, alcohol intake was much lower for the DBA/2J mice relative to the C57BL/6NCRL mice, and this strain difference was observed for groups receiving either 3% or 10% alcohol concentrations. The four-day abstinence period effectively reduced alcohol intakes (i.e., a negative alcohol deprivation effect, negative ADE) in both groups of DBA/2J mice, but had no effect on alcohol intakes in either group of C57BL/6NCRL mice. Both groups trained with 3% alcohol received the second four-day abstinence period, where the effects of acute administration of either naltrexone or saline on post-abstinence alcohol drinking were assessed. Naltrexone was more effective in reducing post-abstinence drinking of 3% alcohol in the DBA/2J mice than in the C57BL/6NCRL mice. In the DBA/2J mice, naltrexone further reduced, relative to saline-injected controls, the low levels of post-abstinence alcohol intake. Thus, the low baseline levels of alcohol drinking in DBA/2J mice were further diminished by the four-day abstinence period (negative ADE), and this suppressed post-abstinence level of alcohol drinking was still further reduced by acute administration of naltrexone. The results indicate that naltrexone is effective in reducing further the low levels of alcohol drinking induced by the negative ADE.

Chronic childhood adversity and stages of substance use involvement in adolescents

BACKGROUND

Studies have shown that those who experience chronic childhood adversity have a greater likelihood of substance abuse and dependence. However, substance use disorders are first preceded by substance use, and substance use is preceded by substance use opportunities. This study aims to estimate the association of chronic adversity with different stages of substance involvement: opportunities, use given the opportunity and abuse or dependence given use.

METHODS

3005 adolescents aged 12-17 were interviewed in a stratified multistage general population probability survey of Mexico City, Mexico. Substance involvement and chronic childhood adversities were assessed with the World Mental Health Composite International Diagnostic Interview Adolescent Version (WMH-CIDI-A). Discrete-time survival models were performed; their survival coefficients and standard errors were exponentiated, and reported as odds-ratios (ORs).

RESULTS

Childhood adversities were associated with alcohol opportunity, alcohol use and alcohol abuse/dependence with significant ORs for individual adversities ranging from 1.4 to 4.1. Childhood adversities were also associated with illicit drug opportunity, drug use and drug abuse/dependence with significant ORs for individual adversities ranging from 1.6 to 17.3. Having more adversities was associated with greater incremental odds of substance involvement, particularly drug use given the opportunity.

CONCLUSIONS

While adversities are mostly related to transitioning into use and disorder, a few are related to substance opportunities, particularly those which were likely to make substances available through parents. Attending to the needs of youth living in adversity, particularly adversities related to parental dysfunction and child abuse should be integral to addiction prevention efforts.

Effects of the kappa opioid receptor antagonist, nor-binaltorphimine, on ethanol intake: impact of age and sex

The kappa opioid receptor (KOR) antagonist, nor-binaltorphimine (nor-BNI), was used to investigate the role of the KOR system in mediating ethanol intake. On P25 (adolescent) or P67 (adult) male and female rats were individually housed and given ad libitum access to food and water. The experimental procedure was initiated on P28 or P70: animals were given 30 min/day access to a 10% ethanol/supersaccharin solution every other day (3 baseline exposures). On the day after the final baseline test, rats were injected with nor-BNI (0, 2.5, 5, 10 mg/kg), with testing initiated 24 hr later (30-min access every other day, 3 test exposures). Nor-BNI (10 mg/kg) increased ethanol intake in adult males, whereas the same dose decreased intake in adult females, suggesting pronounced sex differences in KOR-associated mediation of ethanol intake in adulthood. There was no impact of nor-BNI in adolescent animals of either sex, suggesting that the KOR may play less of a role in modulating ethanol intake during adolescence.

Transient increase in alcohol self-administration following a period of chronic exposure to corticosterone

Stressful life events and chronic stressors have been associated with escalations in alcohol drinking. Stress exposure leads to the secretion of glucocorticoids (cortisol in the human; corticosterone (CORT) in the rodent). To model a period of heightened elevations in CORT, the present work assessed the effects of chronic exposure to the stress hormone CORT on alcohol self-administration. Male Long Evans rats were trained to self-administer a sweetened alcohol solution (2% sucrose/15% alcohol) resulting in moderate levels of daily alcohol intake (0.5-0.7 g/kg). Following stable baseline operant self-administration, rats received CORT in the drinking water for 7 days. A transient increase in alcohol self-administration was observed on the first self-administration session following CORT exposure, and behavior returned to control levels by the second session. Control experiments determined that this increase in alcohol self-administration was specific to alcohol, unrelated to general motor activation, and functionally dissociated from decreased CORT levels at the time of testing. These results indicate that repeated exposure to heightened levels of stress hormone (e.g., as may be experienced during stressful episodes) has the potential to lead to exacerbated alcohol intake in low to moderate drinkers. Given that maladaptive drinking patterns, such as escalated alcohol drinking following stressful episodes, have the potential to put an individual at risk for future drinking disorders, utilization of this model will be important for examination of neuroadaptations that occur as a consequence of CORT exposure in order to better understand escalated drinking following stressful episodes in nondependent individuals.

Individual differences in elevated plus-maze exploration predicted higher ethanol consumption and preference in outbred mice

Psychiatric illnesses, such as anxiety, are highly comorbid with drug use disorders in general and alcohol abuse in particular. Unfortunately, the causal role of anxiety in ethanol addiction is still unclear. We asked the question whether high anxiety predicts predilection of mice to voluntarily consume more alcohol than water. In the current study, we used the voluntary alcohol intake in two bottle choice drinking paradigm to explore whether high anxiety predicts higher alcohol preference and intake in outbred Tuck-Ordinary "TO" mice. To this end, mice were tested for their anxiety-like behavior using the elevated plus maze, open field and the marble burying test prior to voluntary continuous access to increasing concentrations of alcohol solutions. To assess their taste discrimination, mice had access to saccharin and quinine solutions. Results showed that compared to low-anxious mice (LAM), high-anxious mice (HAM) showed greater consumption and preference for ethanol but not for saccharin and quinine suggesting alterations in the rewarding effects of alcohol. Taken together, these findings suggest a correlative link between trait anxiety and the behavioral responses to ethanol.

Epigenetic Modulation of Mood Disorders

BACKGROUND

Mood disorders are expressed in many heterogeneous forms, varying from anxiety to severe major clinical depression. The disorders are expressed in individual variety through manifestations governed by co-morbidities, symptom frequency, severity, and duration, and the effects of genes on phenotypes. The underlying etiologies of mood disorders consist of complex interactive operations of genetic and environmental factors. The notion of endophenotypes, which encompasses the markers of several underlying liabilities to the disorders, may facilitate efforts to detect and define, through staging, the genetic risks inherent to the extreme complexity of disease state.

AIMS

This review evaluates the role of genetic biomarkers in assisting clinical diagnosis, identification of risk factors, and treatment of mood disorders.

METHODS

Through a systematic assessment of studies investigating the epigenetic basis for mood disorders, the present review examines the interaction of genes and environment underlying the pathophysiology of these disorders.

RESULTS

The majority of research findings suggest that the notion of endophenotypes, which encompasses the markers of several underlying liabilities to the disorders, may facilitate efforts to detect and define, through staging, the genetic risks inherent to the extreme complexity of the disease states. Several strategies under development and refinement show the propensity for derivation of essential elements in the etiopathogenesis of the disorders affecting drug-efficacy, drug metabolism, and drug adverse effects, e.g., with regard to selective serotonin reuptake inhibitors. These include: transporter gene expression and genes encoding receptor systems, hypothalamic-pituitary-adrenal axis factors, neurotrophic factors, and inflammatory factors affecting neuroimmune function. Nevertheless, procedural considerations of pharmacogenetics presume the parallel investment of policies and regulations to withstand eventual attempts at misuse, thereby ensuring patient integrity.

CONCLUSIONS

Identification of genetic biomarkers facilitates choice of treatment, prediction of response, and prognosis of outcome over a wide spectrum of symptoms associated with affective states, thereby optimizing clinical practice procedures. Epigenetic regulation of primary brain signaling, e.g., serotonin and hypothalamic-pituitary-adrenal function, and factors governing their metabolism are necessary considerations. The participation of neurotrophic factors remains indispensable for neurogenesis, survival, and functional maintenance of brain systems.

Emotional valence and context of social influences on drug abuse-related behavior in animal models of social stress and prosocial interaction

RATIONALE

Social factors are important determinants of drug dependence and relapse.

OBJECTIVES

We reviewed pre-clinical literature examining the role of social experiences from early life through the development of drug dependence and relapse, emphasizing two aspects of these experiences: (1) whether the social interaction is appetitive or aversive and (2) whether the social interaction occurs within or outside of the drug-taking context.

METHODS

The models reviewed include neonatal care, isolation, social defeat, chronic subordination, and prosocial interactions. We review results from these models in regard to effects on self-administration and conditioned place preference established with alcohol, psychostimulants, and opiates.

RESULTS

We suggest that in general, when the interactions occur outside of the drug-taking context, prosocial interactions are protective against drug abuse-related behaviors, whereas social stressors facilitate these behaviors. By contrast, positive or negative social interactions occurring within the drug-taking context may interact with other risk factors to enhance or inhibit these behaviors.

CONCLUSIONS

Despite differences in the nature and complexity of human social behavior compared to other species, the evolving animal literature provides useful models for understanding social influences on drug abuse-related behavior that will allow for research on the behavioral and biological mechanisms involved. The models have contributed to understanding social influences on initiation and maintenance of drug use, but more research is needed to understand social influences on drug relapse.

Effects of forced alcohol intake associated with chronic stress on the severity of periodontitis: an animal model study

This study histometrically evaluated the effect of forced alcohol intake by stressed animals on the severity of ligature-induced periodontitis in rats. Thirty-two rats were randomly divided in four groups: group GAL—alcohol and ligature; group GASL—alcohol, chronic physical stress, and ligature; GNC—negative control; GPC—positive control. GAL and GASL received 20% ethanol ad libitum, and GNC received water ad libitum for 60 days. After 24 hours of exposition to alcohol intake—by GAL and GASL—immobilization was applied as a chronic stressor in the GASL group for a two-month period, six times a week, in random hours. The means of the respective groups were statistically compared (Analysis of Variance and Tukey tests, P < 0.05). The most severe periodontal breakdown was observed in nonstressed animals which drank alcohol (GAL), followed by stressed animals exposed to alcohol (GASL). GASL did not differ from the positive control group (GPC). The negative control group showed the lowest values of periodontal breakdown (P < 0.05). Conclusions. Non-stressed alcohol consumer animals showed the most severe pattern of periodontal breakdown. Although stressed animals which were forced to drink alcohol showed poorer periodontal status than the negative controls, their results were similar to those of positive controls.

Effects of stress on alcohol drinking: a review of animal studies

RATIONALE

While stress is often proposed to play a significant role in influencing alcohol consumption, the relationship between stress and alcohol is complex and poorly understood. Over several decades, stress effects on alcohol drinking have been studied using a variety of animal models and experimental procedures, yet this large body of literature has generally produced equivocal results.

OBJECTIVES

This paper reviews results from animal studies in which alcohol consumption is evaluated under conditions of acute/sub-chronic stress exposure or models of chronic stress exposure. Evidence also is presented indicating that chronic intermittent alcohol exposure serves as a stressor that consequently influences drinking.

RESULTS

The effects of various acute/sub-chronic stress procedures on alcohol consumption have generally been mixed, but most study outcomes suggest either no effect or decreased alcohol consumption. In contrast, most studies indicate that chronic stress, especially when administered early in development, results in elevated drinking later in adulthood. Chronic alcohol exposure constitutes a potent stressor itself, and models of chronic intermittent alcohol exposure reliably produce escalation of voluntary alcohol consumption.

CONCLUSIONS

A complex and dynamic interplay among a wide array of genetic, biological, and environmental factors govern stress responses, regulation of alcohol drinking, and the circumstances in which stress modulates alcohol consumption. Suggestions for future directions and new approaches are presented that may aid in developing more sensitive and valid animal models that not only better mimic the clinical situation, but also provide greater understanding of mechanisms that underlie the complexity of stress effects on alcohol drinking.

Altered anxiety-like behavior and long-term potentiation in the bed nucleus of the stria terminalis in adult mice exposed to chronic social isolation, unpredictable stress, and ethanol beginning in adolescence

Alcohol and chronic stress exposure, especially during adolescence, can lead to an increased risk in adulthood of developing alcohol use disorders. To date, however, no study has assessed the potential long-term effects of chronic intermittent and unpredictable ethanol (EtOH) exposure in mice chronically stressed beginning in adolescence on brain function and anxiety-like behaviors in adulthood. In particular, alterations in function of the bed nucleus of the stria terminalis (BNST), a brain region heavily implicated in anxiety-related behaviors and altered plasticity following EtOH exposure, may play a key role in the pathological responses to chronic stress and EtOH. In the present study, adolescent and adult C57Bl/6J mice were exposed to a regimen of chronic social isolation and unpredictable stressors and EtOH (or air [sham]; CSI-CUS-EtOH and CSI-CUS-Sham, respectively) for 8-10 weeks. In adulthood, mice were tested for altered anxiety-like behavior (elevated plus maze [EPM] and modified social interaction [SI] test). Following behavioral testing, mice were reexposed to CSI-CUS-EtOH (and CSI-CUS-Sham for controls) for an additional 3 days. Four to six hours following the final EtOH (or air) exposure, field potential recordings of the dorsal-lateral (dl)BNST were performed. Mice first exposed during adolescence to CSI-CUS-EtOH displayed lower levels of anxiety-like behavior on the EPM compared with mice first exposed to CSI-CUS-EtOH during adulthood and control mice only exposed to CSI-CUS-Sham, regardless of age of first exposure. However, mice first exposed to CSI-CUS-EtOH during adulthood displayed lower levels of anxiety-like behavior on the SI test compared with mice first exposed during adolescence and control CSI-CUS-Sham mice. CSI-CUS-EtOH exposure, regardless of age, produced blunted expression of long-term potentiation (LTP) in the dlBNST compared with CSI-CUS-Sham mice. This study demonstrates age-dependent effects of chronic unpredictable ethanol exposure in chronically stressed mice on anxiety-like behaviors during adulthood. Further, CSI-CUS-EtOH exposure results in blunted LTP expression in the adult dlBNST.

Voluntary Ethanol Consumption Induced by Social Isolation Reverses the Increase of α(4)/δ GABA(A) Receptor Gene Expression and Function in the Hippocampus of C57BL/6J Mice

Post-weaning social isolation (SI) is a model of prolonged mild stress characterized by behavioral and neurochemical alterations. We used SI in C57BL/6J mice to investigate the effects of ethanol (EtOH) in the free-choice drinking paradigm on gene expression and function of γ-aminobutyric acid type A receptors (GABA_ARs) and the role of neuroactive steroids in the actions of EtOH in the hippocampus. SI stress induced a marked reduction in hippocampal 3α-hydroxy-5α-pregnan-20-one (3α,5α-TH PROG) and was associated with molecular and functional changes of the GABA_AR. The gene expression of the α₄ and δ subunits was increased in the hippocampus of SI C57BL/6J mice; the expression of the γ₂ subunit was decreased whereas that of the α₁ did not change. Patch-clamp recordings in dentate gyrus (DG) granule cells obtained from SI C57BL/6J mice revealed a greater enhancement of tonic currents induced by α-(4,5,6,7-tetrahydroisoxazolo[5,4-c] pyridin-3-ol (THIP) compared to that in control C57BL/6J mice. These neurochemical, molecular and functional changes observed in SI C57BL/6J mice were associated with an increased EtOH intake and EtOH preference. Nevertheless, the increase in EtOH consumption did not restore the reduction in hippocampal 3α,5α-TH PROG induced by SI. EtOH self-administration blocked the changes in gene expression of the α₄ subunit but not those of the δ and γ₂ subunits induced by SI. In addition, EtOH self-administration did not block the SI-induced changes in GABA_AR-mediated tonic inhibition in hippocampal granule cells but increased the frequency of basal GABAergic sIPSCs in DG granule cells. We conclude that self-administration of EtOH selectively abolishes the increase of α₄ subunit but not other neurochemical, molecular, and functional modifications induced by SI prolonged mild stress.

Epigenetics of early child development

Comprehensive clinical studies show that adverse conditions in early life can severely impact the developing brain and increase vulnerability to mood disorders later in life. During early postnatal life the brain exhibits high plasticity which allows environmental signals to alter the trajectories of rapidly developing circuits. Adversity in early life is able to shape the experience-dependent maturation of stress-regulating pathways underlying emotional functions and endocrine responses to stress, such as the hypothalamo-pituitary-adrenal (HPA) system, leading to long-lasting altered stress responsivity during adulthood. To date, the study of gene-environment interactions in the human population has been dominated by epidemiology. However, recent research in the neuroscience field is now advancing clinical studies by addressing specifically the mechanisms by which gene-environment interactions can predispose individuals toward psychopathology. To this end, appropriate animal models are being developed in which early environmental factors can be manipulated in a controlled manner. Here we will review recent studies performed with the common aim of understanding the effects of the early environment in shaping brain development and discuss the newly developing role of epigenetic mechanisms in translating early life conditions into long-lasting changes in gene expression underpinning brain functions. Particularly, we argue that epigenetic mechanisms can mediate the gene-environment dialog in early life and give rise to persistent epigenetic programming of adult physiology and dysfunction eventually resulting in disease. Understanding how early life experiences can give rise to lasting epigenetic marks conferring increased risk for mental disorders, how they are maintained and how they could be reversed, is increasingly becoming a focus of modern psychiatry and should pave new guidelines for timely therapeutic interventions.

The Varied Uses of Conditioned Place Preference in Behavioral Neuroscience Research: An Investigation of Alcohol Administration in Model Organisms

Place conditioning procedures have been used to study human addiction to alcohol for the past several years. This experimental resource has been utilized successfully due to the fact that investigators can carefully manipulate the experimental design in order to explore specific hypotheses. Only three choices exist regarding animal response to place conditioning: aversion, preference, or no change. This review provides an in-depth analysis of five variables commonly adjusted or changed in place conditioning experiments with ethanol. These include: apparatus design, administration methods, choice of model organism, age of model organism, and model paradigms. It is suggested that the two-chamber design, the intragastric administration, the mouse model, the adolescent age group, and the pre-exposure to stress paradigm are the best current options available in place conditioning experiments with ethanol. The basis for evaluation used throughout this review is that investigators should adjust the variables employed in place conditioning experiments in a manner that most accurately represents and models complex human addiction to alcohol.