Effects of periadolescent ethanol exposure on alcohol preference in two BALB substrains

Adolescent alcohol and nicotine exposure alters the adult response to alcohol use

Adolescence through young adulthood is a unique period of neuronal development and maturation. Numerous agents can alter this process, resulting in long-term neurological and biological consequences. In the clinical literature, it is frequently reported that adolescent alcohol consumption increases the propensity to develop addictions, including alcohol use disorder (AUD), during adulthood. A general limitation of both clinical and human pre-clinical adolescent alcohol research is the high rate of co-using/abusing more than one drug during adolescence, such as co-using/abusing alcohol with nicotine. A primary goal of basic research is elucidating neuroadaptations produced by adolescent alcohol exposure/consumption that promote alcohol and other drug self-administration in adulthood. The long-term goal is to develop pharmacotherapeutics for the prevention or amelioration of these neuroadaptations. This review will focus on studies that have examined the effects of adolescent alcohol and nicotine exposure on adult alcohol consumption, the hypersensitivity of the mesolimbic dopaminergic system, and enhanced responses not only to alcohol but also to nicotine during adulthood. Again, the long-term goal is to identify potential cholinergic agents to prevent or ameliorate the consequences of, peri-adolescent alcohol abuse.

Adolescent Intermittent Ethanol Drives Modest Neuroinflammation but Does Not Escalate Drinking in Male Rats

During adolescence, the brain is highly susceptible to alcohol-induced damage and subsequent neuroimmune responses, effects which may enhance development of an alcohol use disorder (AUD). Neuroimmune reactions are implicated in adolescent alcohol exposure escalating adulthood drinking. Therefore, we investigated whether intermittent alcohol exposure in male, adolescent rats (AIE) escalated adult drinking via two-bottle choice (2BC). We also examined the influence of housing environment across three groups: standard (group-housed with enrichment during 2BC), impoverished (group-housed without enrichment during 2BC), or isolation (single-housed without bedding or enrichment throughout). In the standard group immediately after AIE/saline and after 2BC, we also examined the expression of microglial marker, Iba1, reactive astrocyte marker, vimentin, and neuronal cell death dye, FluoroJade B (FJB). We did not observe an escalation of adulthood drinking following AIE, regardless of housing condition. Further, only a modest neuroimmune response occurred after AIE in the standard group: no significant microglial reactivity or neuronal cell death was apparent using this model, although some astrocyte reactivity was detected in adolescence following AIE that resolved by adulthood. These data suggest that the lack of neuroimmune response in adolescence in this model may underlie the lack of escalation of alcohol drinking, which could not be modified through isolation stress.

Assessment of Binge-Like Eating of Unsweetened vs. Sweetened Chow Pellets in BALB/c Substrains

Binge eating disorder (BED) is defined as chronic episodes of consuming large amounts of food in less than 2 h. Binge eating disorder poses a serious public health problem, as it increases the risk of obesity, type II diabetes, and heart disease. Binge eating is a highly heritable trait; however, its genetic basis remains largely unexplored. We employed a mouse model for binge eating that focused on identifying heritable differences between inbred substrains in acute and escalated intake of sucrose-sweetened palatable food vs. unsweetened chow pellets in a limited, intermittent access paradigm. In the present study, we examined two genetically similar substrains of BALB/c mice for escalation in food consumption, incubation of craving after a no-food training period, and compulsive-like food consumption in an aversive context. BALB/cJ and BALB/cByJ mice showed comparable levels of acute and escalated consumption of palatable food across training trials. Surprisingly, BALB/cByJ mice also showed binge-like eating of the unsweetened chow pellets similar to the escalation in palatable food intake of both substrains. Finally, we replicated the well-documented decrease in anxiety-like behavior in BALB/cByJ mice in the light-dark conflict test that likely contributed to greater palatable food intake than BALB/cJ in the light arena. To summarize, BALB/cByJ mice show binge-like eating in the presence and absence of sucrose. Possible explanations for the lack of selectivity in binge-like eating across diets (e.g., novelty preference, taste) are discussed.

Adolescent low-dose ethanol drinking in the dark increases ethanol intake later in life in C57BL/6J, but not DBA/2J mice

Alcohol is the most widely used and abused drug among youth in the United States. Youths aged 12-20 years old drink almost 11% of all alcohol consumed in the United States, and typically these young people are consuming alcohol in the form of binge drinking. Particularly concerning is that the risk of developing an alcohol use disorder over their lifetime increases the younger one begins to drink. Here we investigated the impact of ethanol drinking in early adolescence on adult ethanol intake using C57BL/6J and DBA/2J mice. We modeled low-dose drinking in adolescent mice using a modified Drinking in the Dark (DID) model where the total ethanol intake during adolescence was similar between the strains to specifically ask whether low-dose ethanol exposure in the high-alcohol preferring C57BL/6J strain will also lead to increased ethanol intake in adulthood. Our results show that low-dose ethanol drinking in early adolescence dramatically increases adult intake, but only in the alcohol-preferring C57BL/6J strain. Early adolescent ethanol exposure had no effect on ethanol intake in the alcohol-nonpreferring DBA/2J mice. These data add to the growing evidence that low-dose ethanol exposures, below the pharmacologically relevant dose, can also contribute to increased drinking in adulthood, but the effect may be influenced by genetic background.

Adolescent Ethanol Exposure: Anxiety-Like Behavioral Alterations, Ethanol Intake, and Sensitivity

Adolescence is a developmental period associated with rapid age-specific physiological, neural, and hormonal changes. Behaviorally, human adolescents are characterized by age-typical increases in novelty-seeking and risk-taking, including the frequent initiation of alcohol and drug use. Alcohol use typically begins during early adolescence, and older adolescents often report high levels of alcohol consumption, commonly referred to as high-intensity drinking. Early-onset and heavy drinking during adolescence are associated with an increased risk of developing alcohol use disorders later in life. Yet, long-term behavioral consequences of adolescent alcohol use that might contribute to excessive drinking in adulthood are still not well understood. Recent animal research, however, using different exposure regimens and routes of ethanol administration, has made substantial progress in identifying the consequences of adolescent ethanol exposure that last into adulthood. Alterations associated with adolescent ethanol exposure include increases in anxiety-like behavior, impulsivity, risk-taking, and ethanol intake, although the observed alterations differ as a function of exposure regimens and routes of ethanol administration. Rodent studies have also shown that adolescent ethanol exposure produces alterations in sensitivity to ethanol, with these alterations reminiscent of adolescent-typical ethanol responsiveness. The goal of this mini-review article is to summarize the current state of animal research, focusing on the long-term consequences related to adolescent ethanol exposure, with a special emphasis on the behavioral alterations and changes to ethanol sensitivity that can foster high levels of drinking in adulthood.

Antagonising TLR4-TRIF signalling before or after a low-dose alcohol binge during adolescence prevents alcohol drinking but not seeking behaviour in adulthood

Adolescents frequently engage in risky behaviours such as binge drinking. Binge drinking, in turn, perturbs neurodevelopment reinforcing reward seeking behaviour in adulthood. Current animal models are limited in their portrayal of this behaviour and the assessment of neuroimmune involvement (specifically the role of Toll-like receptor 4 (TLR4)). Therefore, the aims of this project were to develop a more relevant animal model of adolescent alcohol exposure and to characterise its effects on TLR4 signalling and alcohol-related behaviours later life. Balb/c mice received a short (P22-P25), low dose alcohol binge during in early adolescence, and underwent tests to investigate anxiety (elevated plus maze), alcohol seeking (conditioned place preference) and binge drinking behaviour (drinking in the dark) in adulthood. Four doses of alcohol during adolescence increased alcohol-induced conditioned place preference and alcohol intake in adulthood. However, this model did not affect basal elevated plus maze performance. Subsequent analysis of nucleus accumbal mRNA, revealed increased expression of TLR4-related mRNAs in mice who received alcohol during adolescence. To further elucidate the role of TLR4, (+)-Naltrexone, a biased TLR4 antagonist was administered 30 min before or after the adolescent binge paradigm. When tested in adulthood, (+)-Naltrexone treated mice exhibited reduced alcohol intake however, alcohol seeking and anxiety behaviour was unaltered. This study highlights that even a small amount of alcohol, when given during a critical neurodevelopmental period, can potentiate alcohol-related behaviours and TLR4 activation later in life. Interestingly, attenuation of TLR4 before or after adolescent alcohol exposure reduced only binge alcohol intake in adulthood.

Chronic Ethanol During Adolescence Impacts Corticolimbic Dendritic Spines and Behavior

BACKGROUND

Risk for alcohol use disorders (AUDs) in adulthood is linked to alcohol drinking during adolescence, but understanding of the neural and behavioral consequences of alcohol exposure during adolescence remains incomplete. Here, we examined the neurobehavioral impact of adolescent chronic intermittent EtOH (CIE) vapor exposure in mice.

METHODS

C57BL/6J-background Thy1-EGFP mice were CIE-exposed during adolescence or adulthood and examined, as adults, for alterations in the density and morphology of dendritic spines in infralimbic (IL) cortex, prelimbic (PL) cortex, and basolateral amygdala (BLA). In parallel, adolescent- and adult-exposed C57BL/6J mice were tested as adults for 2-bottle EtOH drinking, sensitivity to EtOH intoxication (loss of righting reflex [LORR]), blood EtOH clearance, and measures of operant responding for food reward.

RESULTS

CIE during adolescence decreased IL neuronal spine density and increased the head width of relatively wide-head IL and BLA spines, whereas CIE decreased head width of relatively narrow-head BLA spines. Adolescents had higher EtOH consumption prior to CIE than adults, while CIE during adulthood, but not adolescence, increased EtOH consumption relative to pre-CIE baseline. CIE produced a tolerance-like decrease in LORR sensitivity to EtOH challenge, irrespective of the age at which mice received CIE exposure. Mice exposed to CIE during adolescence, but not adulthood, required more sessions than AIR controls to reliably respond for food reward on a fixed-ratio (FR) 1, but not subsequent FR3, reinforcement schedule. On a progressive ratio reinforcement schedule, break point responding was higher in the adolescent- than the adult-exposed mice, regardless of CIE. Finally, footshock punishment markedly suppressed responding for reward in all groups.

CONCLUSIONS

Exposure to CIE during adolescence altered dendritic spine density and morphology in IL and BLA neurons, in parallel with a limited set of behavioral alterations. Together, these data add to growing evidence that key corticolimbic circuits are vulnerable to the effects of alcohol during adolescence, with lasting, potentially detrimental, consequences for behavior.

Consequences of adolescent use of alcohol and other drugs: Studies using rodent models

Studies using animal models of adolescent exposure to alcohol, nicotine, cannabinoids, and the stimulants cocaine, 3,4-methylenedioxymethampethamine and methamphetamine have revealed a variety of persisting neural and behavioral consequences. Affected brain regions often include mesolimbic and prefrontal regions undergoing notable ontogenetic change during adolescence, although it is unclear whether this represents areas of specific vulnerability or particular scrutiny to date. Persisting alterations in forebrain systems critical for modulating reward, socioemotional processing and cognition have emerged, including apparent induction of a hyper-dopaminergic state with some drugs and/or attenuations in neurons expressing cholinergic markers. Disruptions in cognitive functions such as working memory, alterations in affect including increases in social anxiety, and mixed evidence for increases in later drug self-administration has also been reported. When consequences of adolescent and adult exposure were compared, adolescents were generally found to be more vulnerable to alcohol, nicotine, and cannabinoids, but generally not to stimulants. More work is needed to determine how adolescent drug exposure influences sculpting of the adolescent brain, and provide approaches to prevent/reverse these effects.

A new Mdr2(-/-) mouse model of sclerosing cholangitis with rapid fibrosis progression, early-onset portal hypertension, and liver cancer

We previously characterized the Mdr2(Abcb4)(-/-) mouse as a reproducible model of chronic biliary liver disease. However, it demonstrates relatively slow fibrosis progression, possibly due to its fibrosis-resistant genetic background. We aimed to improve the model by moving it onto a fibrosis-susceptible background. We generated novel BALB/c.Mdr2(-/-) mouse via genetic backcross onto highly fibrosis-susceptible BALB/c substrain, identified in inbred mouse strain screening. Liver fibrosis, portal pressure, and hepatic tumor burden in BALB/c.Mdr2(-/-) mice were studied up to 1 year of age in direct comparison to parental strain FVB.Mdr2(-/-). BALB/c.Mdr2(-/-) mice developed periductular onion-skin type fibrotic lesions and pronounced ductular reaction starting from 4 weeks of age. Compared to parental strain, BALB/c.Mdr2(-/-) mice demonstrated dramatically accelerated liver fibrosis, with threefold increase in collagen deposition and bridging fibrosis/early signs of cirrhosis at 12 weeks. This was accompanied by early-onset severe portal hypertension and twofold to fourfold increase in profibrogenic transcripts Col1a1 [procollagen α1(I)], Tgfb1, and Timp1. Primary liver cancers in BALB/c.Mdr2(-/-) developed earlier, with greater tumor burden compared to FVB.Mdr2(-/-). BALB/c.Mdr2(-/-) mice have unprecedented degree and rapidity of hepatic fibrosis progression and clinically relevant cirrhosis complications, such as early-onset portal hypertension and primary liver cancers. This new model will facilitate development of antifibrotic drugs and studies into mechanisms of biliary fibrosis progression.

Phenotypic instability between the near isogenic substrains BALB/cJ and BALB/cByJ

Closely related substrains of inbred mice often show phenotypic differences that are presumed to be caused by recent mutations. The substrains BALB/cJ and BALB/cByJ, which were separated in 1935, have been reported to show numerous highly significant behavioral and morphological differences. In an effort to identify some of the causal mutations, we phenotyped BALB/cJ and BALB/cByJ mice as well as their F1, F2, and N2 progeny for behavioral and morphological phenotypes. We also generated whole-genome sequence data for both inbred strains (~3.5× coverage) with the intention of identifying polymorphic markers to be used for linkage analysis. We observed significant differences in body weight, the weight of the heart, liver, spleen and brain, and corpus callosum length between the two substrains. We also observed that BALB/cJ animals showed greater anxiety-like behavior in the open field test, less depression-like behavior in the tail suspension test, and reduced aggression compared to BALB/cByJ mice. Some but not all of these physiological and behavioral results were inconsistent with prior publications. These inconsistencies led us to suspect that the differences were due to, or modified by, non-genetic factors. Thus, we did not perform linkage analysis. We provide a comprehensive summary of the prior literature about phenotypic differences between these substrains as well as our current findings. We conclude that many differences between these strains are unstable and therefore ill-suited to linkage analysis; the source of this instability is unclear. We discuss the broader implications of these observations for the design of future studies.

Chronic alcohol consumption from adolescence-to-adulthood in mice--hypothalamic gene expression changes in the dilated cardiomyopathy signaling pathway

Background

Adolescence is a developmental stage vulnerable to alcohol drinking-related problems and the onset of alcoholism. Hypothalamus is a key brain region for food and water intake regulation, and is one of the alcohol-sensitive brain regions. However, it is not known what would be the alcohol effect on hypothalamus following adolescent alcohol intake, chronically over the adolescent development, at moderate levels.

Results

We employed a paradigm of chronic moderate alcohol intake from adolescence-to-adulthood in mice, and analyzed the alcohol effect on both behavioral and hypothalamic gene expression changes. A total of 751 genes were found and subjected to pathway analysis. The dilated cardiomyopathy (DCM) pathway was identified. The changes of ten genes under this pathway were further verified using RT-PCR. Chronic alcohol consumption during adolescence, even at moderate levels, led to a decrease of motor activity in mice, and also a concerted down regulation of signaling pathway initiating factor (SPIF) genes in the DCM signaling pathway, including β1-adrenergic receptor (Adrb1), Gs protein (Gnas), adenylyl cyclase 1 (Adcy1), and dihydropyridine receptor/L-type calcium channel (Cacna1d).

Conclusions

These findings suggest that adolescent alcohol intake may trigger gene expression changes in the CNS that parallel those found in the dilated cardiomyopathy signaling pathway. If such effects also take place in humans, our findings would serve as a warning against alcohol intake in youth, such as by teens and/or college students.

Higher long-lasting ethanol sensitization after adolescent ethanol exposure in mice

RATIONALE

Due to their maturing brain, adolescents are suggested to be more vulnerable to the long-term consequences of chronic alcohol use. Increased sensitization to the stimulant effects of ethanol is a possible consequence of ethanol exposure during adolescence.

OBJECTIVES

The aim of this study was to characterize the long-term alterations in the stimulant effects of ethanol and in the rate of ethanol sensitization in mice pre-exposed to ethanol during adolescence in comparison to mice pre-exposed to ethanol in adulthood.

METHODS

Adolescent and adult female Swiss mice were injected with saline or ethanol (2.5 or 4 g/kg) during 14 consecutive days. After a 3-week period of ethanol abstinence, mice were tested as adults before and after a second exposure to daily repeated ethanol injections.

RESULTS

All mice pre-exposed to ethanol as adults or adolescents showed higher stimulant effects when re-exposed to ethanol 3 weeks later. However, this enhanced sensitivity to the stimulant effects of ethanol was of significantly higher magnitude in mice repeatedly injected with high ethanol doses (4 g/kg) during adolescence. Furthermore, the increased expression of ethanol stimulant effects in these mice was maintained even after a second procedure of ethanol sensitization.

CONCLUSIONS

Adolescence is a critical period for the development of a sensitization to ethanol stimulant properties providing that high intermittent ethanol doses are administered. These results might contribute to explain the relationship between age at first alcohol use and risks of later alcohol problems and highlight the dangers of repeated consumption of high alcohol amounts in young adolescents.

The role of clock in ethanol-related behaviors

Mice with a mutation in the Clock gene (ClockΔ19) exhibit increased preference for stimulant rewards and sucrose. They also have an increase in dopaminergic activity in the ventral tegmental area (VTA) and a general increase in glutamatergic tone that might underlie these behaviors. However, it is unclear if their phenotype would extend to a very different class of drug (ethanol), and if so, whether these systems might be involved in their response. Continuous access voluntary ethanol intake was evaluated in ClockΔ19 mutants and wild-type (WT) mice. We found that ClockΔ19 mice exhibited significantly increased ethanol intake in a two-bottle choice paradigm. Interestingly, this effect was more robust in female mice. Moreover, chronic ethanol experience resulted in a long-lasting decrease in VTA Clock expression. To determine the importance of VTA Clock expression in ethanol intake, we knocked down Clock expression in the VTA of WT mice via RNA interference. We found that reducing Clock expression in the VTA resulted in significantly increased ethanol intake similar to the ClockΔ19 mice. Interestingly, we also discovered that ClockΔ19 mice exhibit significantly augmented responses to the sedative effects of ethanol and ketamine, but not pentobarbital. However, their drinking behavior was not affected by acamprosate, an FDA-approved drug for the treatment of alcoholism, suggesting that their increased glutamatergic tone might underlie the increased sensitivity to the sedative/hypnotic properties of ethanol but not the rewarding properties of ethanol. Taken together, we have identified a significant role for Clock in the VTA as a negative regulator of ethanol intake and implicate the VTA dopamine system in this response.

Chronic tolerance to ethanol-induced sedation: implication for age-related differences in locomotor sensitization

The adolescent brain has been suggested to be particularly sensitive to ethanol-induced neuroadaptations, which in turn could increase the risk of youths for alcohol abuse and dependence. Sensitization to the locomotor stimulant effects of ethanol has often been used as an animal model of ethanol-induced neuroadaptations. Previously, we showed that young mice were more sensitive than adults to the locomotor sensitization induced by high ethanol doses. However, this effect could be due to age-related differences in chronic tolerance to the sedative effects of ethanol. The aim of the present study is to assess chronic tolerance to the sedative effects of ethanol in weaning 21-day-old (P21), adolescent 35-day-old (P35) and adult 63-day-old (P63) female Swiss mice. After a daily injection of saline or 4 g/kg ethanol during 6 consecutive days, all P21, P35 and P63 mice were injected with 4 g/kg ethanol and submitted to the loss of righting reflex procedure. Our results confirm that the sensitivity to the acute sedative effects of ethanol gradually increases with age. Although this schedule of ethanol injections induces significant age-related differences in ethanol sensitization, it did not reveal significant differences between P21, P35 and P63 mice in the development of a chronic ethanol tolerance to its sedative effects. The present results show that age-related differences in the development of ethanol sensitization cannot be explained by differences in chronic ethanol tolerance to its sedative effects. More broadly, they do not support the idea that ethanol-induced sensitization is a by-product of chronic ethanol tolerance.

Time of day influences the voluntary intake and behavioral response to methamphetamine and food reward

The circadian timing system influences a vast array of behavioral responses. Substantial evidence indicates a role for the circadian system in regulating reward processing. Here we explore time of day effects on drug anticipation, locomotor activity, and voluntary methamphetamine (MA) and food intake in animals with ad libitum food access. We compared responses to drug versus a palatable treat during their normal sleep times in early day (zeitgeber time (ZT) 0400) or late day (ZT 1000). In the first study, using a between-subjects design, mice were given daily 1-h access to either peanut butter (PB-Alone) or to a low or high concentration of MA mixed in PB (MA+PB). In study 2, we repeated the experiment using a within-subjects design in which mice could choose between PB-Alone and MA+PB at either ZT 0400 or 1000. In study 3, the effects of MA-alone were investigated by evaluating anticipatory activity preceding exposure to nebulized MA at ZT 0400 vs. ZT 1000. Time of day effects were observed for both drug and palatable treat, such that in the between groups design, animals showed greater intake, anticipatory activity, and post-ingestional activity in the early day. Furthermore, there were differences among mice in the amount of MA ingested but individuals were self-consistent in their daily intake. The results for the within-subjects experiment also revealed robust individual differences in preference for MA+PB or PB-Alone. Interestingly, time of day effects on intake were observed only for the preferred substance. Anticipatory activity preceding administration of MA by nebulization was also greater at ZT 0400 than ZT 1000. Finally, pharmacokinetic response to MA administered intraperitoneally did not vary as a function of time of administration. The results indicate that time of day is an important variable mediating the voluntary intake and behavioral effects of reinforcers.

The effects of abused drugs on adolescent development of corticolimbic circuitry and behavior

Adolescence is a period of significant neurobiological change that occurs as individuals transition from childhood to adulthood. Because the nervous system is in a relatively labile state during this stage of development, it may be especially sensitive to experience-induced plasticity. One such experience that is relatively common to adolescents is the exposure to drugs of abuse, particularly alcohol and psychostimulants. In this review, we highlight recent findings on the long-lasting effects of exposure to these drugs during adolescence in humans as well as in animal models. Whenever possible, our focus is on studies that use comparison groups of adolescent- and adult-exposed subjects as this is a more direct test of the hypothesis that adolescence represents a period of enhanced vulnerability to the effects of drug-induced plasticity. Lastly, we suggest areas of future investigation that are needed and methodological concerns that should be addressed.

Daily patterns of ethanol drinking in adolescent and adult, male and female, high alcohol drinking (HAD) replicate lines of rats

The rationale for our study was to determine the pattern of ethanol drinking by the high alcohol-drinking (HAD) replicate lines of rats during adolescence and adulthood in both male and female rats. Rats were given 30 days of 24 h free-choice access to ethanol (15%, v/v) and water, with ad lib access to food, starting at the beginning of adolescence (PND 30) or adulthood (PND 90). Water and alcohol drinking patterns were monitored 22 h/day with a "lickometer" set-up. The results indicated that adolescent HAD-1 and HAD-2 males consumed the greatest levels of ethanol and had the most well defined ethanol licking binges among the age and sex groups with increasing levels of ethanol consumption throughout adolescence. In addition, following the first week of adolescence, male and female HAD-1 and HAD-2 rats differed in both ethanol consumption levels and ethanol licking behavior. Adult HAD-1 male and female rats did not differ from one another and their ethanol intake or licking behaviors did not change significantly over weeks. Adult HAD-2 male rats maintained a relatively constant level of ethanol consumption across weeks, whereas adult HAD-2 female rats increased ethanol consumption levels over weeks, peaking during the third week when they consumed more than their adult male counterparts. The results indicate that the HAD rat lines could be used as an effective animal model to examine the development of ethanol consumption and binge drinking in adolescent male and female rats providing information on the long-range consequences of adolescent alcohol drinking.

Evidence for possible period 2 gene mediation of the effects of alcohol exposure during the postnatal period on genes associated with maintaining metabolic signaling in the mouse hypothalamus

BACKGROUND

Animals exposed to alcohol during the developmental period develop circadian disturbances and metabolic problems that often persist during their adult period. In order to study whether alcohol and the circadian clock interact to alter metabolic signaling in the hypothalamus, we determined whether postnatal alcohol feeding in mice permanently alters metabolic sensing in the hypothalamus. Furthermore, we evaluated whether the effect of circadian disruption via Period 2 (Per2) gene mutation prevents alcohol's effects on metabolic signaling in the hypothalamus.

METHODS

Per2 mutant and wild-type male and female mice of the same genetic background were given a milk formula containing ethanol (EtOH; 11.34% vol/vol) from postnatal day (PD) 2 to 7 and used for gene expression and peptide level determinations in the hypothalamus at PD7 and PD90.

RESULTS

We report here that postnatal alcohol feeding reduces the expression of proopiomelanocortin (Pomc) gene and production of β-endorphin and α-melanocyte stimulating hormone (α-MSH) in the hypothalamus that persists into adulthood. In addition, expressions of metabolic sensing genes in the hypothalamus were also reduced as a consequence of postnatal alcohol exposure. These effects were not sex-specific and were observed in both males and females. Mice carrying a mutation of the Per2 gene did not show any reductions in hypothalamic levels of Pomc and metabolic genes and β-endorphin and α-MSH peptides following alcohol exposure.

CONCLUSIONS

These data suggest that early-life exposure to alcohol alters metabolic sensing to the hypothalamus possibly via regulating Per2 gene and/or the cellular circadian clock mechanism.

Early exposure to ethanol differentially affects ethanol preference at adult age in two inbred mouse strains

Although the acute effects of ethanol exposure on brain development have been extensively studied, the long term consequences of juvenile ethanol intake on behavior at adult age, regarding especially ethanol consumption, are still poorly known. The aim of this study was to analyze the consequences of ethanol ingestion in juvenile C57BL/6J and DBA/2J mice on ethanol intake and neurobiological regulations at adulthood. Mice were given intragastric ethanol at 4 weeks of age under different protocols and their spontaneous ethanol consumption was assessed in a free choice paradigm at adulthood. Both serotonin 5-HT(1A) and cannabinoid CB1 receptors were investigated using [(35)S]GTP-γ-S binding assay for the juvenile ethanol regimens which modified adult ethanol consumption. In DBA/2J mice, juvenile ethanol ingestion dose-dependently promoted adult spontaneous ethanol consumption. This early ethanol exposure enhanced 5-HT(1A) autoreceptor-mediated [(35)S]GTP-γ-S binding in the dorsal raphe nucleus and reduced CB1 receptor-mediated G protein coupling in both the striatum and the globus pallidus at adult age. In contrast, early ethanol ingestion by C57BL/6J mice transiently lowered spontaneous ethanol consumption and increased G protein coupling of postsynaptic 5-HT(1A) receptors in the hippocampus but had no effect on CB1 receptors at adulthood. These results show that a brief and early exposure to ethanol can induce strain-dependent long-lasting changes in both behavior toward ethanol and key receptors of central 5-HT and CB systems in mice.

Developmental differences in ethanol-induced sensitization using postweanling, adolescent, and adult Swiss mice

RATIONALE

The maturing adolescent brain has been suggested to be more sensitive than the adult brain to ethanol-induced neuroadaptations. In animal studies, sensitization to the stimulant effects of ethanol is used to study the vulnerability to chronic ethanol-induced neurobehavioral alterations.

OBJECTIVES

The aim of the present study was to systematically characterize age-dependent changes in the development and expression of the sensitization to the stimulant effects of a range of ethanol doses in female Swiss mice. Three ages were studied: 21-day-old mice (postweanlings), 35-day-old mice (adolescents), and 63-day-old mice (adults).

METHODS

Postweanling, adolescent, and adult mice were daily injected with saline or various ethanol doses (1.5 to 4 g/kg) for 7 days. They were then tested for acute and sensitized locomotor activity.

RESULTS

Postweanling and adolescent mice were more sensitive than adult mice to the acute stimulant effects of ethanol. In adult mice, daily injections of ethanol at doses between 2.5 and 4 g/kg led to significant sensitization. Higher ethanol doses (3.5 and 4 g/kg) were required to induce sensitization in postweanling and adolescent mice. However, younger mice showed ethanol sensitization of higher magnitude.

CONCLUSIONS

Young mice develop very strong ethanol sensitization at doses that mimic binge drinking in humans. These results might explain why early ethanol drinking during adolescence is related to a higher prevalence of subsequent alcohol disorders.

Investigation of age-specific behavioral and proteomic changes in an animal model of chronic ethanol exposure

Alcohol use during adolescence represents a major health concern given that this is a period in which the brain continues to undergo critical developmental changes. Much behavioral research has been conducted in animal models of alcohol exposure, and a vulnerable period in adolescence has been identified that suggests lasting effects of ethanol exposure during adolescence. However, identification of molecular changes underlying the behavioral outcomes observed as a result from exposure to ethanol during adolescence remains a major technical challenge. In this chapter, we describe a method that allows for assessment of the effects of chronic ethanol exposure during adolescence relative to adulthood through global-scale analysis of protein expression as well as evaluation of behavioral responsivity in adolescent and adult rats. Results from this type of analysis can facilitate identification of age-specific molecular markers associated with behavioral changes following treatment with ethanol or in other animal models of drug abuse.

Chronic ethanol exposure during adolescence alters the behavioral responsiveness to ethanol in adult mice

Alcohol exposure during early adolescence is believed to durably alter the behavioral properties of ethanol, increasing the likelihood of later alcohol-related disorders. The aim of the present experiments was to characterize changes in the behavioral effects of ethanol in adult female Swiss mice after a chronic ethanol exposure during adolescence, extending from postnatal day 28 to postnatal day 42. After a chronic ethanol exposure during adolescence (daily injections of 0, 2.5 or 4 g/kg ethanol for 14 consecutive days), adult mice were tested at postnatal day 63. The locomotor stimulant effects of ethanol, together with ethanol sensitization were tested in experiment 1. In experiment 2, the sedative effects of ethanol were assessed with the loss of righting reflex procedure. Finally, in experiment 3, the anxiolytic effects of ethanol were tested with the light/dark box test. Adult mice chronically exposed to ethanol during adolescence showed a lower basal locomotor activity, but higher locomotor stimulant effects of ethanol than non-exposed mice. Additionally, these adult mice developed higher rates of ethanol sensitization after chronic re-exposure to ethanol in adulthood. Adult mice exposed to ethanol during adolescence also had a stronger tolerance to the sedative effects of high ethanol doses, although they showed no evidence of changes in the anxiolytic effects of ethanol. These results are in agreement with the thesis that chronic alcohol consumption during adolescence, especially in high amounts, increases the risk of later alcohol-related disorders.

Molecular and behavioral aspects of the actions of alcohol on the adult and developing brain

The brain is one of the major target organs of alcohol actions. Alcohol abuse can lead to alterations in brain structure and functions and, in some cases, to neurodegeneration. Cognitive deficits and alcohol dependence are highly damaging consequences of alcohol abuse. Clinical and experimental studies have demonstrated that the developing brain is particularly vulnerable to alcohol, and that drinking during gestation can lead to a range of physical, learning and behavioral defects (fetal alcohol spectrum disorders), with the most dramatic presentation corresponding to fetal alcohol syndrome. Recent findings also indicate that adolescence is a stage of brain maturation and that heavy drinking at this stage can have a negative impact on brain structure and functions causing important short- and long-term cognitive and behavioral consequences. The effects of alcohol on the brain are not uniform; some brain areas or cell populations are more vulnerable than others. The prefrontal cortex, the hippocampus, the cerebellum, the white matter and glial cells are particularly susceptible to the effects of ethanol. The molecular actions of alcohol on the brain are complex and involve numerous mechanisms and signaling pathways. Some of the mechanisms involved are common for the adult brain and for the developing brain, while others depend on the developmental stage. During brain ontogeny, alcohol causes irreversible alterations to the brain structure. It also impairs several molecular, neurochemical and cellular events taking place during normal brain development, including alterations in both gene expression regulation and the molecules involved in cell-cell interactions, interference with the mitogenic and growth factor response, enhancement of free radical formation and derangements of glial cell functions. However, in both adult and adolescent brains, alcohol damages specific brain areas through mechanisms involving excitotoxicity, free radical formation and neuroinflammatory damage resulting from activation of the innate immune system mediated by TLR4 receptors. Alcohol also acts on specific membrane proteins, such as neurotransmitter receptors (e.g. NMDA, GABA-A), ion channels (e.g. L-type Ca²⁺ channels, GIRKs), and signaling pathways (e.g. PKA and PKC signaling). These effects might underlie the wide variety of behavioral effects induced by ethanol drinking. The neuroadaptive changes affecting neurotransmission systems which are more sensitive to the acute effects of alcohol occur after long-term alcohol consumption. Alcohol-induced maladaptations in the dopaminergic mesolimbic system, abnormal plastic changes in the reward-related brain areas and genetic and epigenetic factors may all contribute to alcohol reinforcement and alcohol addiction. This manuscript reviews the mechanisms by which ethanol impacts the adult and the developing brain, and causes both neural impairments and cognitive and behavioral dysfunctions. The identification and the understanding of the cellular and molecular mechanisms involved in ethanol toxicity might contribute to the development of treatments and/or therapeutic agents that could reduce or eliminate the deleterious effects of alcohol on the brain.

Sex differences in the effects of ethanol pre-exposure during adolescence on ethanol-induced conditioned taste aversion in adult rats

Alcohol use, which typically begins during adolescence and differs between males and females, is influenced by both the rewarding and aversive properties of the drug. One way adolescent alcohol use may modulate later consumption is by reducing alcohol's aversive properties. Here, we used a conditioned taste aversion (CTA) paradigm to determine if pre-exposure to alcohol (ethanol) during adolescence would attenuate ethanol-induced CTA assessed in adulthood in a sex-dependent manner. Male and female Long-Evans rats were given intraperitoneal (i.p.) injections of saline or 3.0g/kg ethanol in a binge-like pattern during postnatal days (PD) 35-45. In adulthood (>PD 100), rats were given access to 0.1% saccharin, followed by saline or ethanol (1.0 or 1.5g/kg, i.p.), over four conditioning sessions. We found sex differences in ethanol-induced CTA, with males developing a more robust aversion earlier in conditioning. Sex differences in the effects of pre-exposure were also evident: males, but not females, showed an attenuated CTA in adulthood following ethanol pre-exposure, which occurred approximately nine weeks earlier. Taken together, these findings indicate that males are more sensitive to the aversive properties of ethanol than females. In addition, the ability of pre-exposure to the ethanol US to attenuate CTA is enhanced in males compared to females.

Adolescent C57BL/6J mice show elevated alcohol intake, but reduced taste aversion, as compared to adult mice: a potential behavioral mechanism for binge drinking

BACKGROUND

Binge alcohol drinking during adolescence is a serious health problem that may increase future risk of an alcohol use disorder. Although there are several different procedures by which to preclinically model binge-like alcohol intake, limited-access procedures offer the advantage of achieving high voluntary alcohol intake and pharmacologically relevant blood alcohol concentrations (BACs). Therefore, in the current study, developmental differences in binge-like alcohol drinking using a limited-access cycling procedure were examined. In addition, as alcohol drinking has been negatively correlated with sensitivity to the aversive properties of alcohol, we examined developmental differences in sensitivity to an alcohol-induced conditioned taste aversion (CTA).

METHODS

Binge-like alcohol consumption was investigated in adolescent (4 weeks) and adult (10 weeks) male C57BL/6J mice for 2 to 4 h/d for 16 days. Developmental differences in sensitivity to an alcohol-induced CTA were examined in adolescent and adult mice, with saline or alcohol (3 or 4 g/kg) repeatedly paired with the intake of a novel tastant (NaCl).

RESULTS

Adolescent mice showed a significant increase in alcohol intake as compared to adults, with adolescents achieving higher BACs and increasing alcohol consumption over successive cycles of the binge procedure. Conversely, adolescent mice exhibited a dose-dependent reduction in sensitivity to the aversive properties of alcohol, as compared to adult mice, with adolescent mice failing to develop a CTA to 3 g/kg alcohol. Finally, extinction of an alcohol CTA was observed following conditioning with a higher dose of alcohol in adolescent, versus adult, mice.

CONCLUSIONS

These results indicate that adolescent mice consume more alcohol, per kilogram body weight, than adults in a binge-like model of alcohol drinking and demonstrate a blunted sensitivity to the conditioned aversive effects of alcohol. Overall, this supports a behavioral framework by which heightened binge alcohol intake during adolescence occurs, in part, via a reduced sensitivity to the aversive properties of alcohol.

Limited access ethanol drinking in the dark in adolescent and adult mice

Adult risk of alcohol dependence increases the younger one first engages in intoxicating consumption. Adolescent mice drink more ethanol than do adults on a gram per kilogram basis, an increase sometimes persisting into adulthood, and this is genotype-dependent. Most studies have used 24 h two-bottle preference, with a choice between ethanol and water. We studied the developmental onset of binge drinking using limited access ethanol drinking in the dark (DID) in male and female mice. To establish age dependence in DID magnitude, we tested HS/Npt mice of 6 ages for DID for 2 weeks, and when they were 9 weeks old, we retested them for 2 weeks vs naïve adult controls. Age groups drank equivalently in their first week; thus, adolescent HS/Npt mice do not show greater DID than adults. Six week old mice drank more ethanol during their second week relative to their other weeks. Ethanol DID during early adolescence (4 weeks) led to increased drinking in adulthood, as did initial DID exposure at 8 weeks. High drinking in the dark-1 (HDID-1) mice (4, 6, 9 weeks old), selectively bred for high blood ethanol after DID, were tested for 9 weeks. Mice beginning at 4 weeks generally drank more ethanol than those of other age groups. Comparison at the same ages showed that 9 week olds initiated at 4 weeks drank more ethanol than did naïve 9 week olds, but all three groups of age-matched mice drank equivalent amounts once they were 10 weeks and older. The DID test is thus sensitive to developmental age. DID intakes by young adolescent HDID-1 mice were greater than intakes by older mice, like those shown by studies with two-bottle preference. Early DID led to increased drinking as adults only in HS/Npt mice. HDID-1 mice provide a useful animal model for exploring whether DID and continuous access preference drinking have parallel consequences when initiated in adolescence.

Ontogeny of the stimulant and sedative effects of ethanol in male and female Swiss mice: gradual changes from weaning to adulthood

RATIONALE

The adolescent period is characterized by a specific sensitivity to the effects of alcohol, which is believed to contribute to the enhanced risks of alcohol dependence when drinking is initiated early during adolescence. In adolescent rodents, while the reduced sensitivity to the sedative effects of ethanol has been well characterized, its stimulant effects have not yet been extensively studied.

OBJECTIVES

The present study characterized the development of the stimulant and the sedative effects of acute ethanol in male and female Swiss mice from weaning to early adulthood and tested whether both effects are interrelated.

METHODS

In a first experiment, mice aged 21, 28, 35, 42, and 60 days were injected with various ethanol doses and tested for ethanol-induced locomotor activity. In an independent experiment, mice of the same groups of age were injected with 4 g/kg ethanol and ethanol-induced sedation was quantified with the loss of righting reflex procedure.

RESULTS

In male and female mice, the stimulant effects of ethanol gradually decreased, whereas its sedative effects increased with age. When the sedation was statistically controlled using a covariance analysis, the differences between adult and juvenile mice in the locomotor stimulation were significantly reduced.

CONCLUSIONS

From weaning to early adulthood, the acute stimulant and sedative effects of ethanol show gradual changes that are similar in male and female mice. Although the initial tolerance to the sedative effects of ethanol contributes to the changes in ethanol-induced locomotor activity, young mice also show a higher sensitivity to the stimulant effects of ethanol.

The effects of pre-pubertal gonadectomy and binge-like ethanol exposure during adolescence on ethanol drinking in adult male and female rats

The pubertal surge in gonadal hormones that occurs during adolescence may impact the long-term effects of early alcohol exposure and sex differences in drinking behavior in adulthood. We investigated this hypothesis by performing sham or gonadectomy surgeries in Long-Evans rats around post-natal day (P) 20. From P35-45, males and females were given saline or 3.0 g/kg ethanol using a binge-like model of exposure (8 injections total). As adults (P100), they were trained to self-administer ethanol via a sucrose-fading procedure and then given access to different unsweetened concentrations (5-20%, w/v) for 5 days/concentration. We found that during adolescence, ethanol-induced intoxication was similar in males and females that underwent sham surgery. In gonadectomized males and females, however, the level of intoxication was greater following the last injection compared to the first. During adulthood, females drank more sucrose per body weight than males and binge-like exposure to ethanol reduced sucrose consumption in both sexes. These effects were not seen in gonadectomized rats. Ethanol consumption was higher in saline-exposed females compared to males, with gonadectomy reversing this sex difference by increasing consumption in males and decreasing it in females. Exposure to ethanol during adolescence augmented ethanol consumption in both sexes, but this effect was statistically significant only in gonadectomized females. Together, these results support a role for gonadal hormones during puberty in the short- and long-term effects of ethanol on behavior and in the development of sex differences in consummatory behavior during adulthood.

Laboratory models available to study alcohol-induced organ damage and immune variations: choosing the appropriate model

The morbidity and mortality resulting from alcohol-related diseases globally impose a substantive cost to society. To minimize the financial burden on society and improve the quality of life for individuals suffering from the ill effects of alcohol abuse, substantial research in the alcohol field is focused on understanding the mechanisms by which alcohol-related diseases develop and progress. Since ethical concerns and inherent difficulties limit the amount of alcohol abuse research that can be performed in humans, most studies are performed in laboratory animals. This article summarizes the various laboratory models of alcohol abuse that are currently available and are used to study the mechanisms by which alcohol abuse induces organ damage and immune defects. The strengths and weaknesses of each of the models are discussed. Integrated into the review are the presentations that were made in the symposium "Methods of Ethanol Application in Alcohol Model-How Long is Long Enough" at the joint 2008 Research Society on Alcoholism (RSA) and International Society for Biomedical Research on Alcoholism (ISBRA) meeting, Washington, DC, emphasizing the importance not only of selecting the most appropriate laboratory alcohol model to address the specific goals of a project but also of ensuring that the findings can be extrapolated to alcohol-induced diseases in humans.

Withdrawal severity after chronic intermittent ethanol in inbred mouse strains

BACKGROUND

To study withdrawal, ethanol is usually administered chronically without interruption. However, interest has recurred in models of episodic exposure. Increasing evidence suggests that chronic intermittent exposure to ethanol leads to a sensitization effect in both withdrawal severity and ethanol consumption. The goal of the present study was to examine mouse inbred strain differences in withdrawal severity following chronic intermittent exposure using the handling-induced convulsion as the behavioral endpoint. We also sought to compare the withdrawal responses of inbred strains across acute, chronic continuous, and chronic intermittent exposure regimens.

METHODS

Male mice from 15 standard inbred strains were exposed to ethanol vapor for 16 hours each day for 3 days and removed to an air chamber during the intervening 8 hours. Mice in the control groups were handled the same, except that they were exposed only to air. Daily blood ethanol concentrations were averaged for each mouse to estimate total dose of ethanol experienced.

RESULTS

Across strains, mice had an average daily blood ethanol concentration (BEC) of 1.45 +/- 0.02 mg/ml and we restricted the range of this value to 1.00-2.00 mg/ml. To evaluate strain differences, we divided data into two dose groups based on BEC, low dose (1.29 +/- 0.1 mg/ml) and high dose (1.71 +/- 0.02 mg/ml). After the third inhalation exposure, ethanol-exposed and air-exposed groups were tested hourly for handling-induced convulsions for 10 hour and at hour 24 and 25. Strains differed markedly in the severity of withdrawal (after subtraction of air control values) in both dose groups.

CONCLUSION

The chronic intermittent exposure paradigm is sufficient to elicit differential withdrawal responses across nearly all strains. Data from the high-dose groups correlated well with withdrawal data derived from prior acute (single high dose) and chronic continuous (for 72 hours) ethanol withdrawal studies, supporting the influence of common genes on all three responses.

Period 2 gene deletion abolishes beta-endorphin neuronal response to ethanol

BACKGROUND

Ethanol exposure during early life has been shown to permanently alter the circadian expression of clock regulatory genes and the beta-endorphin precursor proopiomelanocortin (POMC) gene in the hypothalamus. Ethanol also alters the stress- and immune-regulatory functions of beta-endorphin neurons in laboratory rodents. Our aim was to determine whether the circadian clock regulatory Per2 gene modulates the action of ethanol on beta-endorphin neurons in mice.

METHODS

Per2 mutant (mPer2(Brdml)) and wild type (C57BL/6J) mice were used to determine the effect of Per2 mutation on ethanol-regulated beta-endorphin neuronal activity during neonatal period using an in vitro mediobasal hypothalamic (MBH) cell culture model and an in vivo milk formula feeding animal model. The beta-endorphin neuronal activity following acute and chronic ethanol treatments was evaluated by measuring the peptide released from cultured cells or peptide levels in the MBH tissues, using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Per2 mutant mice showed a higher basal level of beta-endorphin release from cultured MBH cells and a moderate increase in the peptide content in the MBH in comparison with control mice. However, unlike wild type mice, Per2 mutant mice showed no stimulatory or inhibitory beta-endorphin-secretory responses to acute and chronic ethanol challenges in vitro. Furthermore, Per2 mutant mice, but not wild type mice, failed to show the stimulatory and inhibitory responses of MBH beta-endorphin levels to acute and chronic ethanol challenges in vivo.

CONCLUSIONS

These results suggest for the first time that the Per2 gene may be critically involved in regulating beta-endorphin neuronal function. Furthermore, the data revealed an involvement of the Per2 gene in regulating beta-endorphin neuronal responses to ethanol.

Reduced alcohol drinking in adult rats exposed to sucrose during adolescence

Intake of sweet-alcoholic drinks during adolescence is believed to favor alcohol abuse and dependence in adulthood. This study examined the influence of early exposure to ethanol with or without sucrose on the consumption of sweet or alcoholic solutions in adulthood. Adolescent rats (from post-natal day 30-46) were given continuous free access to tap water and either 5% sucrose, 5% ethanol or mixed 5% sucrose-5% ethanol. The control group was given access to water only. Upon reaching adulthood (post-natal day 60), rats were tested for saccharin (sweet), quinine (bitter) and ethanol consumption using a two-bottle free-choice paradigm. The results indicated that pre-exposure to ethanol did not alter the intake of sweet or ethanol solutions in adulthood. However, rats exposed to sucrose during adolescence showed a decreased consumption of both sweet and ethanol solutions. Because alcohol has a sweet taste component, an additional group of rats, pre-exposed to either 5% sucrose or water during adolescence, was tested for intravenous ethanol self-administration (preventing oral sensory stimulation) and in a new model of simultaneous access to oral saccharin and intravenous ethanol that results in higher total ethanol intake. Relative to controls, sucrose-exposed rats showed reduced operant self-administration of saccharin, yet no differences were found for intravenous ethanol self-administration. Altogether, these findings indicate that sucrose exposure during adolescence persistently affected the perception of sweet taste reward and thereby alcohol's acceptance in adulthood.

Mechanisms involved in the neurotoxic, cognitive, and neurobehavioral effects of alcohol consumption during adolescence

Studies over the last decade demonstrate that adolescence is a brain maturation period from childhood to adulthood. Plastic and dynamic processes drive adolescent brain development, creating flexibility that allows the brain to refine itself, specialize, and sharpen its functions for specific demands. Maturing connections enable increased communication among brain regions, allowing greater integration and complexity. Compelling evidence has shown that the developing brain is vulnerable to the damaging effects of ethanol. It is possible to infer, therefore, that alcohol exposure during the critical adolescent developmental stages could disrupt the brain plasticity and maturation processes, resulting in behavioral and cognitive deficits. Recent neuroimaging studies have provided evidence of the impact of human adolescent drinking in brain structure and functions. Findings in experimental animals have also given new insight into the potential mechanisms of the toxic effects of ethanol on both adolescent brain maturation and the short- and long-term cognitive consequences of adolescent drinking. Adolescence is also characterized by the rapid maturation of brain systems mediating reward and by changes in the secretion of stress-related hormones, events that might participate in the increasing in anxiety and the initiation pattern of alcohol and drug consumption. Studies in human adolescents demonstrate that drinking at early ages can enhance the likelihood of developing alcohol-related problems. Experimental evidence suggests that early exposure to alcohol sensitizes the neurocircuitry of addiction and affects chromatin remodeling, events that could induce abnormal plasticity in reward-related learning processes that contribute to adolescents' vulnerability to drug addiction. In this article, we review the potential mechanisms by which ethanol impacts brain development and lead to brain impairments and cognitive and behavioral dysfunctions as well as the neurobiological and neurochemical processes underlying the adolescent-specific vulnerability to drug addiction.

Chronic alcohol consumption from adolescence-to-adulthood in mice--effect on growth and social behavior

Experimentation with alcohol is common during adolescence. However the long-term consequences from moderate alcohol use during adolescence development are not clear. Using a two-bottle free-choice paradigm in the home-cage setting, we studied adolescent mice (4 weeks old) across a 6-week time span of the adolescence-to-adulthood development period. Adolescent mice readily reached a steady level of alcohol consumption and maintained this level throughout the 6-week period. Chronic alcohol consumption resulted in reduced growth in adolescent mice, as well as accelerated acclimation to a novel environment. During a social interaction test, similar levels of initial social investigation and subsequent habituation were observed in both the chronic alcohol and the water-only control groups. However, chronic alcohol self-administration resulted in impaired social recognition and decreased social play/fight behavior. Taken together, these results indicated that chronic alcohol consumption across adolescence development negatively impacted both physical growth and social behavior in mice, highlighting the detrimental consequences from prolonged alcohol drinking in adolescence.

Repeated ethanol exposure during adolescence alters the developmental trajectory of dopaminergic output from the nucleus accumbens septi

Individuals who begin using alcohol prior to 14 years of age are 4 times more likely to progress to addiction than those who do not initiate use until 21 years of age. The nucleus accumbens septi undergoes dramatic developmental transitions during the adolescent period, and dopaminergic activity within this region has been identified as a central neurochemical mediator of drug reward, addiction and dependence. Thus, alcohol-induced neurochemical alterations in dopaminergic activity within this brain region likely mediate the heightened vulnerability to addiction observed in adolescent alcohol users. To investigate this idea, Sprague-Dawley rats were exposed to intraperitoneal injections of either saline or ethanol (0.5, 1.0 or 2.0 g/kg) twice daily over four days beginning on postnatal day 21, 31, 41 or 56. Cannulas were implanted toward the nucleus accumbens septi, subsequent in vivo microdialysis was used to collect samples, and both basal and ethanol-stimulated dopamine overflow was measured using high performance liquid chromatography with electrochemical detection. A developmental transition in basal levels of dopamine in the nucleus accumbens septi was apparent with peak levels at postnatal day 45. An ethanol challenge produced unique responses across ages, with greater peak effects relative to baseline in younger animals (postnatal day 25 and 35). Following repeated exposure to ethanol, a significant increase in basal dopamine was apparent for all ages, and when these animals were challenged with ethanol, peak effects relative to baseline were decreased in younger animals, but unchanged in older animals (postnatal day 45 and 60). Results indicate that there is a key developmental transition in the ability of rats to adapt to the effects of repeated ethanol exposure, which occurs between postnatal day 35 and 45. This alteration may explain the increased addiction vulnerability observed in individuals who initiate alcohol use during early adolescence.

Gender and age at drinking onset affect voluntary alcohol consumption but neither the alcohol deprivation effect nor the response to stress in mice

BACKGROUND

Epidemiological studies suggest that initiation of alcohol drinking at an early age is associated with an increased risk of developing an alcohol use disorder later in life. Nevertheless, relatively few studies using animal models have investigated the relationship between age of onset of drinking and ethanol drinking patterns in adulthood. Besides age at drinking onset, other factors such as gender could also affect the pattern of development of alcohol consumption. In rodents, many studies have shown that females drink more than males. However, even if it is assumed that hormonal changes occurring at puberty could explain these differences, only one study performed in rats has investigated the emergence of sex-specific alcohol drinking patterns in adolescence and the transition from adolescence to adulthood. The aim of the present study was to compare the acquisition of voluntary alcohol consumption, relapse-like drinking (the Alcohol Deprivation Effect-ADE) and stress-induced alcohol drinking in male and female outbred mice that acquired alcohol consumption during adolescence or adulthood.

METHODS

Separate groups of naïve female and male WSC-1 mice aged +/- 28 days (adolescents) or +/-70 days (adults) were given ad libitum access to water and 6% ethanol solution for 8 weeks (1st to 8th week) before undergoing a 2-week deprivation phase (9th and 10th week). After the deprivation period, 2-bottle preference testing (ethanol vs. water) resumed for 3 weeks (11th to 13th). During the 13th week, all animals were subjected to restraint stress for 2 consecutive days.

RESULTS

Over the entire time course of the experiment, ethanol intake and preference increased in females (both adults and adolescents). Adolescent animals (both females and males) showed a transient increase in alcohol consumption and preference compared to adults. However, by the end of continuous alcohol exposure (when all mice were adults), ethanol intake was not affected by age at drinking onset. A deprivation phase was followed by a rise in ethanol intake (ADE) that was not affected by sex or age. Finally, stress did not alter alcohol self-administration either during or after its occurrence.

CONCLUSIONS

Emergence of greater alcohol consumption in adult females does not seem to be limited to a specific developmental period (i.e., puberty). Age of voluntary drinking onset (adolescence vs. adulthood) does not affect eventual alcohol intake in adult WSC-1 mice and does not modify the transient increase in ethanol consumption after alcohol deprivation.

Effects of chronic swim stress on EtOH-related behaviors in C57BL/6J, DBA/2J and BALB/cByJ mice

There is a strong clinical relationship between stress and stress-related disorders and the incidence of alcohol abuse and alcoholism, and this relationship appears to be partly genetic in origin. There are marked strain differences in ethanol (EtOH)-related behaviors and reactivity to stress, but little investigation of the interaction between the two. The present study assessed the effects of chronic exposure to swim stress on EtOH-related behavior in three common inbred strains of mice, C57BL/6J, DBA/2J and BALB/cByJ. After establishing baseline (10%) EtOH self-administration in a two-bottle free choice test, mice were exposed to daily swim stress for 14 consecutive days and EtOH consumption was measured as a percent of baseline both during stress and for 10 days afterwards. A separate experiment examined the effects of 14 days of swim stress on sensitivity to the sedative/hypnotic effects of an acute injection of 4g/kg EtOH. Results showed that stress produced a significant decrease in EtOH consumption, relative to pre-stress baseline, in DBA/2J and BALB/cByJ, but not C57BL/6J mice. By contrast, stress increased sensitivity to the sedative/hypnotic effects of EtOH in all three strains. These findings demonstrate that chronic swim stress produces reductions in EtOH self-administration in a strain-dependent manner, and that these effects may be restricted to strains with a pre-existing aversion to EtOH. Present data also demonstrates a dissociation between effects of this stressor on EtOH self-administration and sensitivity to EtOH's sedative/hypnotic effects. In conclusion, strain differences, that are likely in large part genetic in nature, modify the effects of this stressor on EtOH's effects in a behavior-specific manner.

Time course of elevated ethanol intake in adolescent relative to adult rats under continuous, voluntary-access conditions

BACKGROUND

Adolescence is a period of elevated alcohol consumption in humans as well as in animal models. Previous studies in our laboratory have shown that adolescent Sprague-Dawley rats consume approximately 2 times more ethanol on a gram per kilogram basis than adult animals in a 2-bottle choice free-access situation. The purpose of the present study was to examine the time course and pattern of elevated ethanol intake during adolescence and the adolescent-to-adult transition, contrast this intake with ontogenetic patterns of food and water intake, and determine whether adolescent access to ethanol elevates voluntary consumption of ethanol in adulthood.

METHODS

Adolescent [postnatal day (P)27-28] and adult (P69-70) male Sprague-Dawley rats were singly housed with continuous access to both water and 1 of 3 experimental solutions in ball-bearing-containing sipper tubes: unsweetened ethanol (10% v/v), sweetened ethanol (10% v/v+0.1% w/v saccharin), and saccharin alone (0.1% w/v).

RESULTS

Ethanol consumption plateaued at approximately 7.5 g/kg/d during the first 2 weeks of measurement (i.e., P28-39) in early adolescence, before declining sharply at approximately P40 to levels that were only modestly elevated compared with adult-typical consumption patterns that were reached by approximately P70. In contrast, intake of food and total calories showed a more gradual decline into adulthood with no distinguishable plateaus in early adolescence. When adolescent-initiated and adult-initiated animals were tested at the same chronological age in adulthood, animals drank similar amounts regardless of the age at which they were first given voluntary access to ethanol.

CONCLUSIONS

Taken together, these data suggest that the elevated ethanol intake characteristic of early-to-mid adolescence is not simply a function of adolescent-typical hyperphagia or hyperdipsia, but instead may reflect age-related differences in neural substrates contributing to the rewarding or aversive effects of ethanol, as well as possible modulatory influences of ontogenetic differences in sensitivity to novelty or in ethanol pharmacokinetics. Voluntary home cage consumption of ethanol during adolescence, however, was not found to subsequently elevate ethanol drinking in adulthood.

An investigation of the behavioral actions of ethanol across adolescence in mice

RATIONALE

The transition from adolescence into adulthood is characterized by rapid maturation of brain systems mediating reward and by increasing experimentation with drugs of abuse including ethanol (EtOH). Previous studies have found marked differences in sensitivity to the behavioral effects of EtOH in adolescent rats as compared to adults, but relatively few studies have been conducted in mice.

OBJECTIVES

The present study examined sensitivity to various behavioral effects of EtOH in C57BL/6J mice at various stages of adolescence/adulthood (4, 6, 8 weeks old). Ages were compared for locomotor stimulant (open field), anxiolytic-like (elevated plus-maze), memory-impairing (Pavlovian fear conditioning) and ataxic (accelerating rotarod) effects of EtOH, and the sedative/hypnotic (sleep time) effects of EtOH and pentobarbital. EtOH self-administration was compared using a two-bottle choice paradigm. Measures of EtOH metabolism were also obtained.

RESULTS

Early adolescent mice exhibited increased sensitivity to locomotor stimulant (1.5 g/kg), anxiolytic-like (1.5 g/kg) and ataxic (1.5-2.5 g/kg), but not memory impairing (2.0 g/kg), effects of EtOH relative to adults. Early adolescent, and to some extent peri-adolescent, mice were less sensitive than adults to the sedative/hypnotic effects of EtOH (3.5-4.5 g/kg), but not pentobarbital (40-50 mg/kg). Early adolescent mice showed lower EtOH preference, but not EtOH consumption, than adults. Blood EtOH concentrations were higher at early time points and lower at later time points after (3.0 g/kg) EtOH injection in early and peri-adolescents relative to adults.

CONCLUSIONS

Present data demonstrate that sensitivity to the acute intoxicating effects of EtOH changes across mouse adolescent development in a behavior-dependent manner.

Use of A Standard Strain for External Calibration in Behavioral Phenotyping

The present paper evaluates the inclusion of a standard strain or outbred stock in multi-strain behavioral phenotyping protocols to perform the same role as the external standard in biochemical assay procedures. As potential standards, the F344 inbred strain and an outbred stock of Long Evans were tested with three other inbred strains. To evaluate the influence of rearing conditions on phenotype stability, one group of F344s was born at the University of Tsukuba, another, bred elsewhere and delivered to Tsukuba at 4 weeks of age. All animals were tested in open-field (OF), runway emergence (RE) and digging tests as adults. The results showed no influence of breeding or transportation history on OF and RE behavior of the two F344 groups, while there was evidence that digging behavior may be affected by the different rearing experience. The inclusion of a 'standard strain or stock' in phenotyping protocols involving multiple inbred strains or lines of rats, mice and flies has obvious advantages by providing a reference point for inter-laboratory comparisons. The properties of inbred strains and outbred stocks favorable to their use as standards are discussed.