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

Maternal deprivation induces cytoskeletal alterations and depressive-like behavior in adult male rats by regulating the AKT/GSK3β/CRMP2 signaling pathway

Early-life adverse events exert persistent effects on brain functions and may increase the risk of psychopathology in adulthood. However, the underlying mechanism remains unclear. The purpose of our study was to study the long-lasting effects of maternal deprivation (MD) on depression-related behaviors and microtubule dynamics, and to illuminate the underlying molecular mechanism. Rat pups were separated from the dams for 360 min (MD) or 15 min (brief maternal separation) each day from postnatal day 4 through 10. Rats with MD experience showed significant depressive-like behaviors in adulthood, while brief maternal separation did not alter the behaviors. Behavioral alterations in the MD group were accompanied by alterations in the AKT/GSK3β/CRMP2 signaling pathway and hyperphosphorylation of CRMP2. CRMP2 interacted and colocalized with the cytoskeleton in the hippocampus, and the overlap of CRMP2 and tubulin staining in the hippocampus of MD rats was decreased. In MD rats, the expression of the α-tubulin isoforms Acet-tubulin and Tyr-tubulin changed, and the ratio of Tyr/Acet-tubulin, which is an important marker of microtubule dynamics, was decreased, indicating decreased microtubule dynamics. Furthermore, regulation of the AKT/GSK3β/CRMP2 signaling pathway by an LY294002 microinjection in the hippocampus resulted in cytoskeletal alterations and depressive-like behaviors in rats. These findings suggest that early-life MD induces depressive-like behaviors and cytoskeletal alterations in adult male rats and that the effects may be partly mediated by the AKT/GSK3β/CRMP2 signaling pathway. An understanding of the mechanism underlying the effect of MD on behaviors is crucial for developing pharmacological and psychological interventions for childhood neglect.

The effects of multiple early life stressors on adolescent alcohol consumption

Alcohol use disorder is pervasive and effects the health of millions. Identifying factors such as early life stress that contribute to the development of alcohol use disorder is therefore critical, especially those that contribute to adolescent drinking, a strong predictor of AUD development. The majority of prior studies have examined early life effects on adult drinking, but have not studied intake during adolescence, and no prior studies have examined how the effects of multiple stressors may be additive. Therefore, this study determined if experiencing individual or multiple stressors increases adolescent alcohol intake. Male Long Evans rats underwent either early or late maternal separation (postnatal day 2-9 or 13-20), early adolescent social defeat (PND 30-40), both, or neither. All rats were then given two-hour access to alcohol, and voluntary intake assessed daily in late adolescence (PND 41-51). In adulthood, sensitivity to alcohol's sedative effects was assessed using loss and regain of righting reflex tests. Results indicate that experiencing maternal separation (at either time point) or social defeat increased adolescent alcohol consumption, but experiencing the combined stressors did not, and that no stressor significantly affected body weight during adolescence or loss and regain of righting reflex in adulthood. Overall, this pattern of effects suggests that experiencing any individual early life stressor may increase adolescent alcohol intake, in agreement with prior literature, but that the combined effects of multiple early life stressors may be more complicated.

Sex-dependent impact of different degrees of maternal separation experience on OFT behavioral performances after adult chronic unpredictable mild stress exposure in rats

Early-life social-environmental factors are important for normal development, and different degrees of early-life stress experience have different impacts on adult behaviors and stress responsiveness. The aim of present study was to investigate the long-term effects of different degrees of maternal separation (MS) on male and female rats and subsequent responsiveness to chronic unpredictable mild stress (CUMS) exposure in adults. Sprague-Dawley (SD) newborn pups were exposed to either 15 min/day of MS (MS15), 360 min/day of MS (MS360) or no separation (NS) during postnatal day (PND)4-PND10. At PND56, behavioral tasks, including sucrose preference test (SPT), forced swimming test (FST) and open field test (OFT), were used to explore depressive and anxiety-like behaviors. Then the rats received a series of CUMS for 28 days, behavioral tasks were recorded after CUMS. Prior to CUMS, the behavioral performances in male and female rats were consistent, MS360 led to increased immobile time in FST and decreased activity in OFT, while MS15 rats exhibited behavioral performances similar to NS group. After CUMS, sexual dimorphism was observed in the OFT behavioral responses to adult stress re-exposure, but no differences in FST were observed. CUMS male rats with MS360 experiences showed the worst behavioral performances in OFT compared to those of the other male rats groups, while CUMS female rats without MS experience showed the worst behavioral performances in OFT compared to those of the other female rats groups. Both CUMS male and female rats with MS15 experiences showed better trend in OFT performances than those of CUMS rats with MS360 experience and without MS experiences. These results suggest that brief MS experiences increase the OFT behavioral resilience of rats to adult stress re-exposure, and prolonged MS promotes OFT behavioral resilience of female rats to adult stress re-exposure, while increases vulnerability of male rats to adult stress re-exposure.

Few long-term consequences after prolonged maternal separation in female Wistar rats

Environmental factors during the early-life period are known to have long-term consequences for the adult phenotype. An intimate interplay between genes and environment shape the individual and may affect vulnerability for psychopathology in a sex-dependent manner. A rodent maternal separation model was here used to study the long-term effects of different early-life rearing conditions on adult behavior, HPA axis activity and long-term voluntary alcohol intake in female rats. Litters were subjected to 15 min (MS15) or 360 min (MS360) of daily maternal separation during postnatal day 1–21. In adulthood, the behavioral profiles were investigated using the multivariate concentric square field™ (MCSF) test or examined for HPA axis reactivity by cat-odor exposure with subsequent characterization of voluntary alcohol intake and associated changes in HPA axis activity. Adult female MS360 offspring showed mostly no, or only minor, effects on behavior, HPA axis reactivity and long-term alcohol intake relative to MS15. Instead, more pronounced effects were found dependent on changes in the natural hormonal cycle or by the choice of animal supplier. However, changes were revealed in corticosterone load after long-term alcohol access, as females subjected to MS360 had higher concentrations of fecal corticosterone. The present findings are in line with and expand on previous studies on the long-term effects of maternal separation in female rats with regard to behavior, HPA axis activity and voluntary alcohol intake. It can also be a window into further studies detailing how early-life experiences interact with other risk and protective factors to impact the adult phenotype and how possible sex differences play a role.

Negative Affect and Excessive Alcohol Intake Incubate during Protracted Withdrawal from Binge-Drinking in Adolescent, But Not Adult, Mice

Binge-drinking is common in underage alcohol users, yet we know little regarding the biopsychological impact of binge-drinking during early periods of development. Prior work indicated that adolescent male C57BL6/J mice with a 2-week history of binge-drinking (PND28-41) are resilient to the anxiogenic effects of early alcohol withdrawal. Herein, we employed a comparable Drinking-in-the-Dark model to determine how a prior history of binge-drinking during adolescence (EtOH^adolescents) influences emotionality (assayed with the light-dark box, marble burying test, and the forced swim test) and the propensity to consume alcohol in later life, compared to animals without prior drinking experience. For additional comparison, adult mice (EtOH^adults) with comparable drinking history (PND56-69) were subdivided into groups tested for anxiety/drinking either on PND70 (24 h withdrawal) or PND98 (28 days withdrawal). Tissue from the nucleus accumbens shell (AcbSh) and central nucleus of the amygdala (CeA) was examined by immunoblotting for changes in the expression of glutamate-related proteins. EtOH^adults exhibited some signs of hyperanxiety during early withdrawal (PND70), but not during protracted withdrawal (PND98). In contrast, EtOH^adolescents exhibited robust signs of anxiety-l and depressive-like behaviors when tested as adults on PND70. While all alcohol-experienced animals subsequently consumed more alcohol than mice drinking for the first time, alcohol intake was greatest in EtOH^adolescents. Independent of drinking age, the manifestation of withdrawal-induced hyperanxiety was accompanied by reduced Homer2b expression within the CeA and increased Group1 mGlu receptor expression within the AcbSh. The present data provide novel evidence that binge-drinking during adolescence produces a state characterized by profound negative affect and excessive alcohol consumption that incubates with the passage of time in withdrawal. These data extend our prior studies on the effects of subchronic binge-drinking during adulthood by demonstrating that the increase in alcoholism-related behaviors and glutamate-related proteins observed in early withdrawal dissipate with the passage of time. Our results to date highlight a critical interaction between the age of binge-drinking onset and the duration of alcohol withdrawal in glutamate-related neuroplasticity within the extended amygdala of relevance to the etiology of psychopathology, including pathological drinking, in later life.

Ethanol affects limbic and striatal presynaptic glutamatergic and DNA methylation gene expression in outbred rats exposed to early-life stress

Alcohol use disorder is the outcome of both genetic and environmental influences and their interaction via epigenetic mechanisms. The neurotransmitter glutamate is an important regulator of reward circuits and implicated in adaptive changes induced by ethanol intake. The present study aimed at investigating corticolimbic and corticostriatal genetic signatures focusing on the glutamatergic phenotype in relation to early-life stress (ELS) and consequent adult ethanol consumption. A rodent maternal separation model was employed to mimic ELS, and a free-choice paradigm was used to assess ethanol intake in adulthood. Gene expression levels of the Vesicular Glutamate Transporters (Vglut) 1, 2 and 3, as well as two key regulators of DNA methylation, DNA (cytosine-5)-methyltransferase 1 (Dnmt1) and methyl-CpG-binding protein 2 (Mecp2), were analyzed. Brain regions of interest were the ventral tegmental area (VTA), nucleus accumbens (Acb), medial prefrontal cortex (mPFC) and dorsal striatum (dStr), all involved in mediating aspects of ethanol reward. Region-specific Vglut, Dnmt1 and Mecp2 expression patterns were observed. ELS was associated with down-regulated expression of Vglut2 in the VTA and mPFC. Rats exposed to ELS were more sensitive to ethanol-induced changes in Vglut expression in the VTA, Acb, and dStr and in Dnmt1 and Mecp2 expression in the striatal regions. These findings suggest long-term glutamatergic and DNA methylation neuroadaptations as a consequence of ELS, and show an association between voluntary drinking in non-preferring, non-dependent, rodents and different Vglut, Dnmt1 and Mecp2 expression depending on early-life history.

Increased vulnerability to ethanol consumption in adolescent maternal separated mice

The purpose of this study was to evaluate the effects of early life stress on the vulnerability to ethanol consumption in adolescence. To this aim, mice were separated from their mothers for 12 hours/day on postnatal days 8 and 12. Emotional behavior (light-dark box, elevated plus maze and tail suspension tests) and pre-attentional deficit (pre-pulse inhibition) were evaluated in adolescent maternal separated (MS) mice. Alterations of the corticotropin-releasing factor (CRF), glucocorticoid receptor (NR3C1), tyrosine hydroxylase (TH), mu-opioid receptor (MOr), brain-derived neurotrophic factor (BDNF), neuronal nuclei (NeuN), microtubule-associated protein 2 (MAP2) and neurofilament heavy (NF200)-immunoreactive fibers were studied in the paraventricular nucleus of the hypothalamus (PVN), ventral tegmental area (VTA), nucleus accumbens (NAc) or hippocampus (HIP). The effects of maternal separation (alone or in combination with additional stressful stimuli) on ethanol consumption during adolescence were evaluated using the oral ethanol self-administration paradigm. MS mice presented mood-related alterations and pre-attentional deficit. Increased CRF, MOr and TH, and reduced BDNF, NR3C1, NeuN, MAP2 and NF200-immunoreactive fibers were observed in the PVN, NAc and HIP of adolescent MS mice. In the oral ethanol self-administration test, adolescent MS mice presented higher ethanol consumption and motivation. Exposure to additional new stressful stimuli during adolescence significantly increased the vulnerability to ethanol consumption induced by maternal separation. These results clearly demonstrated that exposure to early life stress increased the vulnerability to ethanol consumption, potentiated the effects of stressful stimuli exposure during adolescence on ethanol consumption and modified the expression of key targets involved in the response to stress, ethanol reinforcing properties and cognitive processes.

HPA Axis Gene Expression and DNA Methylation Profiles in Rats Exposed to Early Life Stress, Adult Voluntary Ethanol Drinking and Single Housing

The neurobiological basis of early life stress (ELS) impact on vulnerability to alcohol use disorder is not fully understood. The effect of ELS, adult ethanol consumption and single housing, on expression of stress and DNA methylation regulatory genes as well as blood corticosterone levels was investigated in the hypothalamus and pituitary of adult out-bred Wistar rats subjected to different rearing conditions. A prolonged maternal separation (MS) of 360 min (MS360) was used to study the effect of ELS, and a short MS of 15 min (MS15) was used as a control. Voluntary ethanol drinking was assessed using a two-bottle free choice paradigm to simulate human episodic drinking. The effects of single housing and ethanol were assessed in conventional animal facility rearing (AFR) conditions. Single housing in adulthood was associated with lower Crhr1 and higher Pomc expression in the pituitary, whereas ethanol drinking was associated with higher expression of Crh in the hypothalamus and Crhr1 in the pituitary, accompanied by lower corticosterone levels. As compared to controls with similar early life handling, rats exposed to ELS displayed lower expression of Pomc in the hypothalamus, and higher Dnmt1 expression in the pituitary. Voluntary ethanol drinking resulted in lower Fkbp5 expression in the pituitary and higher Crh expression in the hypothalamus, independently of rearing conditions. In rats exposed to ELS, water and ethanol drinking was associated with higher and lower corticosterone levels, respectively. The use of conventionally reared rats as control group yielded more significant results than the use of rats exposed to short MS. Positive correlations, restricted to the hypothalamus and ELS group, were observed between the expression of the hypothalamus-pituitary-adrenal receptor and the methylation-related genes. Promoter DNA methylation and expression of respective genes did not correlate suggesting that other loci are involved in transcriptional regulation. Concluding, single housing is a confounding factor to be considered in voluntary ethanol drinking paradigms. ELS and ethanol drinking in adulthood exert independent effects on hypothalamic and pituitary related genes, however, in a manner dependent on the control group used.

Effect of voluntary alcohol consumption on Maoa expression in the mesocorticolimbic brain of adult male rats previously exposed to prolonged maternal separation

Discordant associations between monoamine oxidase A (MAOA) genotype and high alcohol drinking have been reported in human and non-human primates. Environmental influences likely moderate genetic susceptibility. The biological basis for this interplay remains elusive, and inconsistencies call for translational studies in which conditions can be controlled and brain tissue is accessible. The present study investigated whether early life stress and subsequent adult episodic alcohol consumption affect Maoa expression in stress- and reward-related brain regions in the rat. Outbred Wistar rats were exposed to rearing conditions associated with stress (prolonged maternal separation) or no stress during early life, and given free choice between alcohol and/or water in adulthood. Transcript levels of Maoa were assessed in the ventral tegmental area, nucleus accumbens (NAc), medial prefrontal cortex, cingulate cortex, amygdala and dorsal striatum (DS). Blood was collected to assess corticosterone levels. After alcohol consumption, lower blood corticosterone and Maoa expression in the NAc and DS were found in rats exposed to early life stress compared with control rats. An interaction between early life stress and voluntary alcohol intake was found in the NAc. Alcohol intake before death correlated negatively with Maoa expression in DS in high alcohol-drinking rats exposed to early life stress. Maoa expression is sensitive to adulthood voluntary alcohol consumption in the presence of early life stress in outbred rats. These findings add knowledge of the molecular basis of the previously reported associations between early life stress, MAOA and susceptibility to alcohol misuse.

Αlpha 2a-Adrenoceptor Gene Expression and Early Life Stress-Mediated Propensity to Alcohol Drinking in Outbred Rats

Stressful events early in life, later high alcohol consumption and vulnerability to alcohol use disorder (AUD) are tightly linked. Norepinephrine is highly involved in the stress response and the α2A-adrenoceptor, which is an important regulator of norepinephrine signalling, is a putative target in pharmacotherapy of AUD. The aim of the present study was to investigate the effects of early-life stress and adult voluntary alcohol drinking on the α2A-adrenoceptor. The relative expression and promoter DNA methylation of the Adra2a gene were measured in the hypothalamus, a key brain region in stress regulation. A well-characterized animal model of early-life stress was used in combination with an episodic voluntary drinking in adulthood. Alcohol drinking rats with a history of early-life stress had lower Adra2a expression than drinking rats not exposed to stress. Alcohol intake and Adra2a gene expression were negatively correlated in high-drinking animals, which were predominantly rats subjected to early-life stress. The results provide support for a link between early-life stress, susceptibility for high alcohol consumption, and low Adra2a expression in the hypothalamus. These findings can increase our understanding of the neurobiological basis for vulnerability to initiate risk alcohol consumption and individual differences in the response to α2A-adrenoceptor agonists.

Individual differences in risk-related behaviors and voluntary alcohol intake in outbred Wistar rats

Some personality traits and comorbid psychiatric diseases are linked to a propensity for excessive alcohol drinking. The objective of this study was to investigate the association between individual differences in risk-related behaviors, voluntary alcohol intake and preference. Outbred male Wistar rats were tested in a novel open field, followed by assessment of behavioral profiles using the multivariate concentric square field (MCSF) test. Animals were classified into high risk taking and low risk taking on the basis of open-field behavior and into high risk-assessing (HRA) and low risk-assessing (LRA) on the basis of the MCSF profile. Finally, voluntary alcohol intake was investigated using intermittent access to 20% ethanol and water for 5 weeks. Only minor differences in voluntary alcohol intake were found between high risk taking and low risk taking. Differences between HRA and LRA rats were more evident, with higher intake and increased intake over time in HRA relative to LRA rats. Thus, individual differences in risk-assessment behavior showed greater differences in voluntary alcohol intake than risk taking. The findings may relate to human constructs of decision-making and risk taking associated with a predisposition to rewarding and addictive behaviors. Further studies are needed to clarify the relationship between risk-related behaviors, including risk-assessment behavior, and liability for excessive alcohol intake.

Vendor differences in alcohol consumption and the contribution of dopamine receptors to Pavlovian-conditioned alcohol-seeking in Long-Evans rats

RATIONALE

Drug-associated environmental stimuli elicit craving in humans and drug-seeking in animals.

OBJECTIVES

We tested the hypothesis that Pavlovian-conditioned alcohol-seeking is mediated by dopamine, using rats from two vendors.

METHODS

Male, Long-Evans rats (220-240 g) from Charles River (St-Constant, QC, Canada) and Harlan Laboratories (Indianapolis, IN, USA) received 21 sessions of intermittent, 24-h access to ethanol (15 %, v/v) and water in the home-cage. Subsequently, rats were trained to discriminate between one conditioned stimulus (CS+) that was paired with ethanol (0.2 ml per CS+) and a second stimulus (CS-) that was not. Entries into a fluid port where ethanol was delivered were recorded. Next, rats were exposed to a different context where cues and ethanol were withheld. At test, responding to the CS+ and CS- without ethanol was assessed in the second, non-alcohol context. Injections (1 ml/kg; s.c.) of the dopamine D1-receptor antagonist SCH 23390 (0, 3.33, and 10 μg/kg) or dopamine D2-receptor antagonist eticlopride (0, 5, and 10 μg/kg) were administered before test.

RESULTS

Home-cage alcohol consumption was higher in Harlan rats than Charles River rats. At test, saline-treated rats responded more to the alcohol-predictive CS+ than the CS-. While SCH 23390 attenuated CS+ responding in rats from both vendors, eticlopride reduced CS+ responding in Harlan rats only. Subsequently, SCH 23390 but not eticlopride attenuated CS+ responding when the CS+ was again paired with ethanol.

CONCLUSIONS

These results indicate important differences in alcohol consumption in Long-Evans rats from different suppliers, and highlight a novel role for dopamine in Pavlovian-conditioned alcohol-seeking.

Effects of rearing conditions on behaviour and endogenous opioids in rats with alcohol access during adolescence

Causal links between early-life stress, genes and later psychiatric diagnoses are not possible to fully address in human studies. Animal models therefore provide an important complement in which conditions can be well controlled and are here used to study and distinguish effects of early-life stress and alcohol exposure. The objective of this study was to investigate the impact of rearing conditions on behaviour in young rats and if these changes could be followed over time and to examine interaction effects between early-life environment and adolescent alcohol drinking on behaviour and immunoreactive levels of the opioid peptides dynorphin B, met-enkephalin-Arg(6)Phe(7) and beta-endorphin. We employed a rodent model, maternal separation, to study the impact of rearing conditions on behaviour, voluntary alcohol consumption and alcohol-induced effects. The consequences of short, 15 min (MS 15), and long, 360 min (MS 360), maternal separation in combination with adolescent voluntary alcohol consumption on behaviour and peptides were examined. A difference in the development of risk taking behaviour was found between the MS15 and MS360 while the development of general activity was found to differ between intake groups. Beta-endorphin levels in the pituitary and the periaqueductal gray area was found to be higher in the MS15 than the MS360. Adolescent drinking resulted in higher dynorphin B levels in the hippocampus and higher met-enkephalin-Arg(6)Phe(7) levels in the amygdala. Amygdala and hippocampus are involved in addiction processes and changes in these brain areas after adolescent alcohol drinking may have consequences for cognitive function and drug consumption behaviour in adulthood. The study shows that individual behavioural profiling over time in combination with neurobiological investigations provides means for studies of causality between early-life stress, behaviour and vulnerability to psychiatric disorders.

Is the rodent maternal separation model a valid and effective model for studies on the early-life impact on ethanol consumption?

RATIONALE

Early-life events can cause long-term neurobiological and behavioural changes with a resultant effect upon reward and addiction processes that enhance risk to develop alcohol use disorders. Maternal separation (MS) is used to study the mediating mechanisms of early-life influences in rodents. In MS studies, the pups are exposed to maternal absence during the first postnatal weeks. The outcome of MS experiments exhibits considerable variation and questions have been raised about the validity of MS models.

OBJECTIVES

This short review aims to provide information about experimental conditions that are important to consider when assessing the impact of early-life environment on voluntary ethanol consumption.

RESULTS

The results from currently used MS protocols are not uniform. However, studies consistently show that longer separations of intact litters predispose for higher ethanol consumption and/or preference in adult male rats as compared to shorter periods of MS. Studies using individual pup MS paradigms, other controls, low ethanol concentrations, adult females or examining adolescent consumption reported no differences or inconsistent results.

CONCLUSIONS

There is no "a rodent MS model", there are several models and they generate different results. The compiled literature shows that MS is a model of choice for analysis of early-life effects on voluntary ethanol consumption but there are examples of MS paradigms that are not suitable. These studies emphasize the importance to carefully designed MS experiments to supply the optimal conditions to definitely test the research hypothesis and to be particulate in the interpretation of the outcome.

Individual differences and social influences on the neurobehavioral pharmacology of abused drugs

The interaction of drugs with biologic targets is a critical area of research, particularly for the development of medications to treat substance use disorders. In addition to understanding these drug-target interactions, however, there is a need to understand more fully the psychosocial influences that moderate these interactions. The first section of this review introduces some examples from human behavioral pharmacology that illustrate the clinical importance of this research. The second section covers preclinical evidence to characterize some of the key individual differences that alter drug sensitivity and abuse vulnerability, related primarily to differences in response to novelty and impulsivity. Evidence is presented to indicate that critical neuropharmacological mechanisms associated with these individual differences involve integrated neurocircuits underlying stress, reward, and behavioral inhibitory processes. The third section covers social influences on drug abuse vulnerability, including effects experienced during infancy, adolescence, and young adulthood, such as maternal separation, housing conditions, and social interactions (defeat, play, and social rank). Some of the same neurocircuits involved in individual differences also are altered by social influences, although the precise neurochemical and cellular mechanisms involved remain to be elucidated fully. Finally, some speculation is offered about the implications of this research for the prevention and treatment of substance abuse.

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.

Neuropeptides as mediators of the early-life impact on the brain; implications for alcohol use disorders

The brain is constantly exposed to external and internal input and to function in an ever-changing environment we are dependent on processes that enable the brain to adapt to new stimuli. Exposure to postnatal environmental stimuli can interfere with vital adaption processes and cause long-term changes in physiological function and behavior. Early-life alterations in brain function may result in impaired ability to adapt to new situations, in altered sensitivity to challenges later in life and thereby mediate risk or protection for psychopathology such as alcohol use disorders (AUD). In clinical research the studies of mechanisms, mediators, and causal relation between early environmental factors and vulnerability to AUD are restricted and attempts are made to find valid animal models for studies of the early-life influence on the brain. This review focuses on rodent models and the effects of adverse and naturalistic conditions on peptide networks within the brain and pituitary gland. Importantly, the consequences of alcohol addiction are not discussed but rather neurobiological alterations that can cause risk consumption and vulnerability to addiction. The article reviews earlier results and includes new data and multivariate data analysis with emphasis on endogenous opioid peptides but also oxytocin and vasopressin. These peptides are vital for developmental processes and it is hypothesized that early-life changes in peptide networks may interfere with neuronal processes and thereby contribute the individual vulnerability for AUD. The summarized results indicate a link between early-life rearing conditions, opioids, and ethanol consumption and that the ethanol-induced effects and the treatment with opioid antagonists later in life are dependent on early-life experiences. Endogenous opioids are therefore of interest to further study in the early-life impact on individual differences in vulnerability to AUD and treatment outcome.

Disruptions in serotonergic regulation of cortical glutamate release in primate insular cortex in response to chronic ethanol and nursery rearing

Early-life stress has been shown to increase susceptibility to anxiety and substance abuse. Disrupted activity within the anterior insular cortex (AIC) has been shown to play a role in both of these disorders. Altered serotonergic processing is implicated in controlling the activity levels of the associated cognitive networks. We therefore investigated changes in both serotonin receptor expression and glutamatergic synaptic activity in the AIC of alcohol-drinking rhesus monkeys. We studied tissues from male rhesus monkeys raised under two conditions: Male rhesus monkeys (1) "mother reared" (MR) by adult females (n=9) or (2) "Nursery reared" (NR), that is, separated from their mothers and reared as a separate group under surrogate/peer-reared conditions (n=9). The NR condition represents a long-standing and well-validated nonhuman primate model of early life stress. All monkeys were trained to self-administer ethanol (4% w/v) or an isocaloric maltose-dextrin control solution. Subsets from each rearing condition were then given daily access to ethanol, water, or maltose-dextrin for 12 months. Tissues were collected at necropsy and were further analyzed. Using real time RT-PCR we found that ethanol-naive, NR monkeys had lower AIC levels of 5-HT(1A) and 5-HT(2A) receptor mRNA compared with ethanol-naive, MR animals. Although NR monkeys consumed more ethanol over the 12-month period compared with MR animals, both MR and NR animals expressed greater 5-HT(1A) and 5-HT(2A) receptor mRNA levels following chronic alcohol self-administration. The interaction between nursery-rearing conditions and alcohol consumption resulted in a significant enhancement of both 5-HT(1A) and 5-HT(2A) receptor mRNA levels such that lower expression levels observed in nursery-rearing conditions were not found in the alcohol self-administration group. Using voltage clamp recordings in the whole cell configuration we recorded excitatory postsynaptic currents in both ethanol-naive and chronic self-administration groups of NR and MR monkeys. Both groups that self-administered ethanol showed greater glutamatergic activity within the AIC. This AIC hyperactivity in MR alcohol-consuming monkeys was accompanied by an increased sensitivity to regulation by presynaptic 5-HT(1A) receptors that was not apparent in the ethanol-naive, MR group. Our data indicate that chronic alcohol consumption leads to greater AIC activity and may indicate a compensatory upregulation of presynaptic 5-HT(1A) receptors. Our results also indicate that AIC activity may be less effectively regulated by 5-HT in ethanol-naive NR animals than in NR monkeys in response to chronic ethanol self-administration. These data suggest possible mechanisms for increased alcohol seeking and possible addiction potential among young adults who had previously experienced early-life stress that include disruptions in both AIC activity and serotonin system dynamics.

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.

Differences in voluntary ethanol consumption in Wistar rats from five different suppliers

Understanding the mechanism of action of ethanol and the neurobiological substrates for alcohol use disorders is challenging. In search of this knowledge, it is imperative to use valid animal experimental models. The Wistar rat is one example of a commonly used strain that also exert foundation stock for several rat lines selectively bred for high and low voluntary ethanol intake. Different studies report varying ethanol intake in Wistar rats posing the question of whether this is because of the methodological differences or the rat strain. The purpose of this study was therefore to compare voluntary ethanol intake in Wistar rats from five different suppliers. Rats from B&K Universal, UK (BK); Charles River, Germany; Harlan Laboratories, IN (Hsd); Harlan Laboratories, The Netherlands (RccHan™); and Taconic, Denmark were exposed to a three-bottle free-choice paradigm with intermittent 24 h access to 5 and 20% ethanol and water three times per week for 6 weeks. A general finding was that the RccHan™ rats differed significantly from the other groups. At the end of the experiment, the RccHan™ group had the highest median ethanol intake of 3.85 g/kg/24 h, whereas the BK rats had the lowest intake of 1.84 g/kg/24 h. The preference for ethanol was also different throughout the experiment. At the end of the experiment, the RccHan™ rats had the highest preference of approximately 80%, whereas the BK rats had the lowest preference around 25%. During the 6-week drinking period, only the Hsd rats increased their ethanol intake, as evidenced by a significant increase of 5% ethanol intake. Although all rats are of Wistar origin, they display profound differences in voluntary ethanol consumption depending on the supplier. The choice of Wistar can therefore have implications for the outcome and make comparisons between studies difficult. The present findings highlight the supplier as an important parameter to consider when planning and performing preclinical animal studies in the field of alcohol research.

Ethanol-induced effects on the dopamine and serotonin systems in adult Wistar rats are dependent on early-life experiences

Some individuals control their ethanol consumption throughout life, but others escalate their intake to levels that increase the risk for addiction. The early environment influences the individual response to ethanol and affects the underlying physiological processes that lead to a transition from a voluntary to a compulsive use of ethanol. However, the neurobiological substrates for these processes are not understood. The present study aimed to test the hypothesis that early environmental experiences affect the neurobiological effects that are induced by voluntary ethanol consumption. Rat pups were subjected to three different rearing environments: conventional animal facility rearing or separation from dam and littermates for either 15 or 360min. In adulthood, the rats were exposed to a two-bottle free choice between ethanol and water for seven weeks. Tissue levels of dopamine, 5-hydroxytryptamine (5-HT) and their metabolites were measured in brain areas that have been implicated in reward and addiction processes. Differences in ethanol-induced effects were noted in 5-HT-related measurements in the nucleus accumbens and ventral tegmental area and in dopamine-related measurements in the dorsal raphe nucleus (DRN). These results provided evidence of an early environmental impact on interactive neuronal circuits between the DRN and reward pathways. The amygdala, a key area in addiction processes, was particularly sensitive to early-life conditions. The animals that experienced the longest separation differed from the others; they had low basal 5-HT levels and responded with an increase in 5-HT after ethanol. These altered responses to initial ethanol consumption as a result of early environmental factors may affect the transition from habitual to compulsive drinking and contribute to individual vulnerability or resilience to addiction.

Maternal care alterations induced by repeated ethanol leads to heightened consumption of the drug and motor impairment during adolescence: a dose-response analysis

Maternal ethanol exposure during lactation induces behavioral alterations in offspring, including disruptions in motor skills and heightened ethanol ingestion during adolescence. These behavioral outcomes appear to partially depend on ethanol-induced disruptions in maternal care. The present study assessed motor skills and ethanol intake in adolescent rats raised by dams that had been repeatedly given ethanol during lactation. Female rats (postpartum days [PDs] 3-13) were administered ethanol (0.5, 1.5, or 2.5 g/kg) or vehicle every other day and allowed to freely interact with their pups. During adolescence, the offspring were evaluated for motor coordination (accelerating rotarod test) and oral ethanol self administration. The lowest maternal ethanol dose (0.5 g/kg) mildly affected motor performance, whereas the higher doses (1.5 and 2.5 g/kg) resulted in motor coordination impairment and greater ethanol intake. Maternal care behavior was affected by ethanol in a dose-dependent fashion. These results indicate that early experience with ethanol during lactation, even when the drug dosage is kept relatively low, leads to long-term consequences in offspring. Dose-response effects on maternal care behavior (i.e., nest building, crouching) may underlie disruptions in motor development and greater ethanol intake resulting from these early ethanol experiences.

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.

Early environmental factors differentially affect voluntary ethanol consumption in adolescent and adult male rats

BACKGROUND

Previous studies using the maternal separation (MS) model have shown that environmental factors early in life affect adult ethanol consumption. Prolonged MS is related to enhanced propensity for high adult ethanol intake when compared to short MS. Less is known about the environmental impact on adolescent ethanol intake. In this study, the aim was to compare establishment of voluntary ethanol consumption in adolescent and adult rats subjected to different rearing conditions.

METHODS

Wistar rat pups were separated from their mother 0 minutes (MS0), 15 minutes (MS15), or 360 minutes (MS360) daily during postnatal days (PNDs) 1 to 20. After weaning, the male rats were divided into two groups; rats were given free access to water, 5 and 20% ethanol at either PND 26 or 68. Ethanol was provided in 24-hour sessions three times per week for 5 weeks.

RESULTS

MS resulted in altered ethanol consumption patterns around the pubertal period but otherwise the rearing conditions had little impact on ethanol consumption in adolescents. In adults, the establishment of ethanol consumption was dependent on the rearing condition. The adult MS0 and MS15 rats had a stable ethanol intake, whereas the MS360 rats increased both their ethanol intake and preference over time.

CONCLUSIONS

With the use of intermittent access to ethanol, new data were provided, which confirm the notion that MS360 represents a risk environment related to higher ethanol intake compared to MS15. The adolescent rats had higher ethanol intake than adult rats but the consumption was independent of rearing condition. Experiences during the first three postnatal weeks thus affect the establishment of voluntary ethanol consumption differently in adolescent and adult rats. Further studies are now warranted to examine the consequences of a combination of early environmental influence and high adolescent ethanol intake.

Short- and long-term consequences of different early environmental conditions on central immunoreactive oxytocin and arginine vasopressin levels in male rats

Numerous studies have provided evidence for an important role for the neuropeptides oxytocin (OT) and arginine vasopressin (AVP) in establishment of social behaviour early in life, such as mother-pup interactions. However, there are few reports examining the consequences of early-life experiences on OT and AVP in male offspring. We have used the maternal separation (MS) model to study the effect of different early environmental conditions in rats. The purpose was to study OT and AVP in rats subjected to prolonged daily MS (360 min, MS360), short daily MS (15 min, MS15) and conventional animal facility rearing (AFR) during postnatal days 1-21. In addition, the influence of the presence or absence of littermates during MS, i.e. litter-wise (l) or individual (i) MS, was assessed. The immunoreactive (ir) peptide levels were measured in the hypothalamus, amygdala and pituitary gland of 3 and 10 weeks old male rats. Assessment in 3-week-old rats revealed that MS15 was associated with low ir OT levels in the hypothalamus and amygdala and high levels in the pituitary gland compared with the MS360 and AFR condition. In the amygdala, differences between groups were also detected in adulthood. MS studies commonly use either MS15 or AFR as a control for prolonged MS. The present results show differences in MS360 rats as compared to MS15 but not AFR rats. Consequently, comparisons between prolonged MS with either short periods of MS or AFR will generate divergent results, hence, making the outcome of MS difficult to compare between studies. Moreover, the different early environments had no effect on ir AVP levels. In conclusion, OT in the amygdala was most sensitive to MS. Besides both short- and long-term consequences, distinct effects were seen after litter and individual separation, respectively. We propose that environmentally induced alterations in OT transmission due to disrupted mother-pup interactions early in life may cause altered susceptibility to challenges later in life.

Does the transcription factor AP-2beta have an impact on the genetic and early environmental influence on ethanol consumption?

Genes involved in alcoholism have consensus sites for the transcription factor activator protein (TFAP) 2β. In the present study, we investigated TFAP-2β protein levels in the ethanol-preferring alko, alcohol (AA) and the ethanol-avoiding alko, non-alcohol (ANA) rat lines. Furthermore, basal and ethanol-induced TFAP-2β levels were examined in Wistar rats exposed to different early postnatal environments that are known to affect later ethanol consumption. Taken together, we found differences in brainstem TFAP-2β protein between the AA and ANA rats.

Comparison of hippocampal metabotropic glutamate receptor 7 (mGlu7) mRNA levels in two animal models of depression

There is increasing evidence to suggest that metabotropic glutamate (mGlu) receptors including mGlu(7) receptor are important in the pathophysiology of stress-related psychiatric disorders such as anxiety and major depression. mGlu(7) receptor is highly expressed in the hippocampus, a key region involved in the modulation of depression-related behaviour. Moreover, mice deficient in mGlu(7) receptor have an antidepressant-like behaviour and altered stress response. To our knowledge there is little information as to whether stressful phenotypes can influence hippocampal mGlu(7) receptor levels. To this end, we examined hippocampal mGlu(7) receptor mRNA expression in two models of depression, the stress-sensitive Wistar Kyoto (WKY) and the maternally separated model of early-life stress. In situ hybridization analysis revealed that the WKY, but not the maternally separated (MS) rats displayed selective increases in mGlu(7) receptor mRNA expression in subregions of the hippocampus compared to relevant controls. These data suggest that higher levels of this receptor could affect the behaviour in response to stressful conditions and may play a role in WKY animal's susceptibility to stress-related disorders. However, the data in maternally separated animals confirm that whilst hippocampal mGlu(7) receptors maybe involved in certain aspects of stress biology, an increased expression is not necessary for the manifestation of depression-related phenotype per se.

Maternal deprivation induces depressive-like behaviours only in female rats

Maternal deprivation (MD) has been developed to study the effects of early adverse experiences on behaviour and neurobiology. It has been proposed to represent a potential animal model of major depression. The purpose of our study was to examine the responses induced by MD in male and female adult Long-Evans rats in tasks designed to explore depressive-like behaviours (forced swimming test (FST), repeated open space swim test (OSST), sucrose solution consumption) and in the novel object recognition and object location tasks. A consistent sexual dimorphism was observed in the responses of male and female rats that underwent MD. In male rats, MD led to increased transitions between behaviours in the FST and increased consumption and preference for sucrose (1%) in comparison with non-deprived rats. In female rats, MD induced a decreased swimming activity on the second day of the OSST and reduced the cognitive performance in an object location task. In both sexes, MD did not alter the swimming activity in the FST and the performance in a novel object recognition task. These divergent responses in male and female rats can be related to the gender differences which exist in depression. However, due to the low amplitude of responses obtained in our study, the MD model in Long-Evans rats does not seem to mimic symptoms of major depression. In contrast, our present results suggest the use of the MD model, especially in females, as a model of the dysthymia, a mild chronic-depressive condition, which has been related to poorer maternal relationship.

Contribution of early environmental stress to alcoholism vulnerability

The most problematic aspects of alcohol abuse disorder are excessive alcohol consumption and the inability to refrain from alcohol consumption during attempted abstinence. The root causes that predispose certain individuals to these problems are poorly understood but are believed to be produced by a combination of genetic and environmental factors. Early environmental trauma alters neurodevelopmental trajectories that can predispose an individual to a number of neuropsychiatric disorders, including substance abuse. Prenatal stress (PNS) is a well-established protocol that produces perturbations in nervous system development, resulting in behavioral alterations that include hyperresponsiveness to stress, novelty, and psychomotor stimulant drugs (e.g., cocaine, amphetamine). Moreover, PNS animals exhibit enduring alterations in basal and cocaine-induced changes in dopamine and glutamate transmission within limbic structures, which exhibit pathology in drug addiction and alcoholism, suggesting that these alterations may contribute to an increased propensity to self-administer large amounts of drugs of abuse or to relapse after periods of drug withdrawal. Given that cocaine and alcohol have actions on common limbic neural substrates (albeit by different mechanisms), we hypothesized that PNS would elevate the motivation for, and consumption of, alcohol. Accordingly, we have found that male C57BL/6J mice subject to PNS exhibit higher operant responding and consume more alcohol during alcohol reinforcement as adults. Alterations in glutamate and dopamine neurotransmission within the forebrain structures appear to contribute to the PNS-induced predisposition to high alcohol intake and are induced by excessive alcohol intake. Accordingly, we are exploring the interactions between neurochemical changes produced by PNS and changes induced by consumption of alcohol in adulthood to model the biological bases of high vulnerability to alcohol abuse.

Two repeated maternal separation procedures differentially affect brain 5-hydroxytryptamine transporter and receptors in young and adult male and female rats

Early environment is a known determinant for individual differences in vulnerability for adult psychopathology, e.g., ethanol addiction. One underlying mechanism could be dysfunction in serotonergic neurotransmission. This study focused on the methodological considerations regarding an animal model for studying effects of early environment, maternal separation (MS), using two different paradigms. Age- and sex-specific effects on brain stem 5-hydroxytryptamine (5-HT) transporter and receptors were examined. Male and female rat pups were assigned to either litter-wise MS for 15 or 360 min (MS15l or MS360l) or individual MS for 15 or 360 min (MS15i or MS360i) daily during postnatal days 1-21. Normal animal facility reared rats were used as controls. Analyses were performed in young and adult rats. As compared to the other males, MS15l males had lower 5-HT(1A) and 5-HT(2C) receptor mRNA expression at both ages, lower 5-HT(2A) receptor mRNA when young and lower 5-HTT mRNA expression when adult. In contrast, adult MS15l females had higher 5-HT(2C) receptor mRNA expression than other female rats. The strong impact of MS15l on 5-HT-related genes was either transient or persistent depending on sex and fewer effects on gene expression were observed in females than in males. This study shows the importance of tactile contact for the consequences of short but not prolonged MS, as evidenced by major differences between MS15l and MS15i. The results suggest that MS15i is less suitable than MS15l to simulate a protective environment in studies of, for instance, ethanol addiction processes.

Maternal separation stress in male mice: long-term increases in alcohol intake

RATIONALE

In rodents, prolonged maternal separation has been used as a model of developmentally early environmental stress to influence adult drug intake.

OBJECTIVES

The aim of the present study was to evaluate the long-term effects of prolonged maternal separation on alcohol consumption using two different self-administration procedures in mice: operant alcohol self-administration vs. three-bottle choice.

MATERIALS AND METHODS

From postnatal day (PND) 1 to 14, pups were separated from the dam (maternal separation, MS) daily for 180 min or were left undisturbed, only handled during cage cleaning (animal facility rearing, AFR). On PND 60, they were assigned to one of two experimental manipulations: either a three-bottle choice or operant oral alcohol self-administration. In the three-bottle choice procedure, mice were given access to 6% or 10% alcohol or 0.05% saccharin solution for 2 h/day for 10 days. In the second experiment, mice were reinforced for nose poking by delivery of oral alcohol (6% or 10% in saccharin) or 0.05% saccharin solutions during daily 30-min sessions. Following the acquisition phase, "break points" were determined. Later, mice were allowed 1 h access to the reinforcing solution with no dosage limitation.

RESULTS

In the three-bottle choice procedure, MS mice showed higher alcohol intake than AFR at the 10% alcohol concentration. In the operant alcohol self-administration, MS mice achieved higher alcohol intake than AFR at the concentrations 6% and 10% during the 1-h session.

CONCLUSIONS

The results demonstrate the long-term consequences of MS on alcohol intake in male mice, suggesting early life stress as a risk factor for alcohol consumption and abuse.

Desperately driven and no brakes: developmental stress exposure and subsequent risk for substance abuse

Adverse life events are associated with a wide range of psychopathology, including an increased risk for substance abuse. In this review, we focus on the inter-relationship between exposure to adversity and brain development, and relate this to enhanced windows of vulnerability. This review encompasses clinical and preclinical data, drawing evidence from epidemiological studies, morphometric and functional imaging studies, and molecular biology and genetics. The interaction of exposure during a sensitive period and maturational events produces a cascade that leads to the initiation of substance use at younger ages, and increases the likelihood of addiction by adolescence or early adulthood. A stress-incubation/corticolimbic dysfunction model is proposed based on the interplay of stress exposure, development stage, and neuromaturational events that may explain the seeking of specific classes of drugs later in life. Three main factors contribute to this age-based progression of increased drug use: (1) a sensitized stress response system; (2) sensitive periods of vulnerability; and (3) maturational processes during adolescence. Together, these factors may explain why exposure to early adversity increases risk to abuse substances during adolescence.

Early life programming of hemispheric lateralization and synchronization in the adult medial prefrontal cortex

Neonatal maternal separation (MS) in the rat increases the vulnerability to stressors later in life. In contrast, brief handling (H) in early life confers resilience to stressors in adulthood. Early life programming of stress reactivity may involve the medial prefrontal cortex (mPFC), a region which modulates various stress responses. Moreover, hemispheric specialization in mPFC may mediate adaptive coping responses to stress. In the present study, neuronal activity was examined simultaneously in left and right mPFC in adult rats previously subjected to MS, H or animal facility rearing (AFR). In vivo electrophysiology, under isoflurane anesthesia, was used to conduct acute recordings of unit and local field potential (LFP) activity in response to systemic administration of N-methyl-beta-carboline-3-carboxamide (FG-7142), a benzodiazepine receptor partial inverse agonist which mimics various stress responses. MS decreased basal unit activity selectively in right mPFC. Basal LFP activity was reduced with MS in left and right mPFC, compared to AFR and H, respectively. Hemispheric synchronization of basal LFP activity was also attenuated by MS at lower frequencies. FG-7142 elicited lateralized effects on mPFC activity with different early rearing conditions. Activity in left mPFC was greater with AFR and MS (AFR>MS), whereas activity was predominantly greater with H in right mPFC. Finally, compared to AFR, MS reduced and H enhanced hemispheric synchronization of LFP activity with FG-7142 treatment in a dose-dependent manner. These results indicate that functionally-relevant alterations in mPFC GABA transmission are programmed by the early rearing environment in a hemisphere-dependent manner. These findings may model the hemispheric specialization of mPFC function thought to mediate adaptive coping responses to stressors. They also suggest the possibility that early environmental programming of hemispheric functional coupling in mPFC is involved in conferring vulnerability or resilience to stressors later in life.

The impact of postnatal environment on opioid peptides in young and adult male Wistar rats

Early environmental influences can change the neuronal development and thereby affect behavior in adult life. The aim in the present study was to thoroughly examine the impact of early environmental factors on endogenous opioids by using a rodent maternal separation (MS) model. The endogenous opioid peptide system is not fully developed at birth, and short- and/or long-term alterations may occur in these neural networks in animals exposed to manipulation of the postnatal environment. Rat pups were subjected to one of five rearing conditions; 15 min (MS15) litter (l) or individual (i), 360 min (MS360) l or i daily MS, or housed under normal animal facility rearing (AFR) conditions during postnatal days 1-21. Measurements of immunoreactive (ir) Met-enkephalin-Arg6Phe7 (MEAP) and dynorphin B (DYNB) peptide levels in the pituitary gland and in a number of brain areas, were performed at three and 10 weeks of age, respectively. MS-induced changes were more pronounced in ir MEAP levels, especially in individually separated rats at three weeks of age and in litter-separated rats at 10 weeks of age. The enkephalin and dynorphin systems have different developmental patterns, dynorphin appearing earlier, which may point at a more sensitive enkephalin system during the early postnatal weeks. The results provide evidence that opioid peptides are sensitive for early environmental factors and show that the separation conditions are critical and also result in changes manifesting at different time points. MS-induced effects were observed in areas related to stress, drug reward and dependence mechanisms. By describing effects on opioid peptides, the study addresses the possible role of a deranged endogenous opioid system in the previously described behavioral consequences of MS.

Early maternal separation and sex differences in the aversive effects of amphetamine in adult rats

Early life stress increases vulnerability to psychostimulant abuse, sometimes in a sex-dependent manner. These effects are presumably produced by modulation of neurobiological reward mechanisms; however, drug intake is also influenced by sensitivity to the drug's aversive properties, and little is known about the effects of early life stress on stimulant aversion. To assess this possibility, Sprague-Dawley rat litters experienced daily separation from the dam for 3 h (MS) or 15 min (H) on post-natal days 2-14; control litters (AFR) experienced twice-weekly routine animal facility care only. As adults, the animals were tested for conditioned taste aversions (CTA) induced by 1.5, 2.0 or 3.0 mg/kg d-amphetamine administered intraperitoneally over three acquisition trials followed by six drug-free extinction trials (n=7-8/sex/dose/rearing group). All groups acquired significant aversions compared to their vehicle-treated controls, but differential rearing had no effect on CTA acquisition or extinction. Collapsed across rearing groups, females exhibited significantly stronger aversions and slower extinction than their male counterparts at the low 1.5 mg/kg dose, and unlike the males, failed to fully extinguish relative to their vehicle controls at 1.5 and 2.0 mg/kg. These data underscore the importance of sex differences in assays of stimulant abuse liability, and further support the hypothesis that the effects of post-natal stress on the reinforcing efficacy of psychostimulants may be predominantly due to modulation of reward mechanisms.

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.