Acoustic startle at baseline and during acute alcohol withdrawal in replicate mouse lines selectively bred for high or low alcohol preference

BACKGROUND: Previous data in both rat and mouse genetic models suggest that there is a genetic relationship between acute alcohol withdrawal responses and innate alcohol drinking behavior. The purpose of the present study was to examine whether acute alcohol withdrawal responses, as measured by acoustic startle and prepulse inhibition (PPI) of acoustic startle, may be genetically related to innate differences in alcohol preference in 2 mouse lines selectively bred for high (HAP1 and HAP2) or low (LAP1 and LAP2) alcohol preference. Line differences in startle responses at baseline, prior to alcohol or saline treatment, were also measured. METHODS: Alcohol-naive, male and female HAP1 (n = 35) and LAP1 (n = 32) and HAP2 (n = 43) and LAP2 (n = 40) mice were tested under baseline conditions and during withdrawal from a single injection of 4.0 g/kg alcohol or equal volume of saline at 4, 8, and 12 hours post-injection. RESULTS: On most trial types, baseline startle responses and PPI were greater in both HAP lines than in both LAP lines, and startle responses were greater in males than in females. During acute alcohol withdrawal, both male LAP lines, and LAP1 females, showed reduced startle responses at the 4-hour time point during acute alcohol withdrawal. In contrast, both HAP1 males and females showed a trend toward enhanced startle at 4 hours in withdrawal. No clear differences in PPI during withdrawal were evident. CONCLUSIONS: These findings indicate good evidence for a genetic relationship between greater baseline acoustic startle responses and PPI and high alcohol preference. Modest support for a genetic correlation between low alcohol preference and reduced startle responses at 4 hours in withdrawal was found in male mice. The suppression in acoustic startle during acute alcohol withdrawal in male LAP lines but not in male HAP lines suggests that a genetic propensity toward low alcohol preference may be related to greater sensitivity to alcohol as measured by acoustic startle responses during acute alcohol withdrawal.     

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.     

Role of stress in acquisition of alcohol-conditioned place preference in adolescent and adult mice

Background:  Both clinical evidence and findings from animal models demonstrate that there are differences between adolescents and adults in alcohol dependence. As stress plays a critical role in processes of alcohol addiction, we tested whether stress is involved in alcohol vulnerability differently during adolescence and adulthood in mice.
Methods:  To determine whether age differences exist in the acquisition of alcohol-conditioned place preference (CPP) in mice, adolescent and adult mice were trained for CPP with different doses of alcohol (0, 0.5, 1, and 2 g/kg, i.p.). To explore the effects of stress (footshock) on acquisition of alcohol CPP in mice of different ages, adolescent and adult mice underwent acute (1 day) or chronic (1 week) stress before CPP training. Acquisition of CPP was examined after the CPP training.
Results:  Under nonstress conditions, adult mice acquired alcohol CPP when trained with 2 g/kg alcohol, while adolescent mice did not acquire alcohol CPP. After chronic but not acute stress exposure, adolescent mice acquired significant CPP trained with 2 g/kg alcohol that did not produce CPP under nonstress conditions. However, stress did not have significant effect on acquisition of CPP in adult mice trained CPP with 1 g/kg alcohol.
Conclusions:  These results indicate that there is an age difference in acquiring alcohol CPP and adolescent mice are more sensitive than adults to stress.     

Influence of age at drinking onset on long-term ethanol self-administration with deprivation and stress phases

BACKGROUND: Onset of alcohol use during adolescence has potentially long-lasting consequences, e.g., prospective alcohol dependence. To obtain new insight into the effects of early chronic ethanol consumption, we compared the drinking behavior of two adult male Wistar rat groups: one that initiated alcohol consumption during adolescence (adolescent group) and the other that initiated their drinking during adulthood (adult group) in a model of long-term alcohol self-administration. We investigated the magnitude of the effects of deprivation and stress on alcohol intake and the influence of these events on the alcohol drinking behavior across time. METHODS: Heterogeneous Wistar rats aged 31 days (adolescents) and 71 days (adults) were given ad libitum access to water, as well as 5% and 20% ethanol solutions during an observation period of 30 wk. A deprivation phase of 14 days was instituted after eight wk of access to alcohol. After 16 and 26 wk of alcohol access, all animals were subjected for three consecutive days to forced swimming and electric foot shocks, respectively. RESULTS: At the onset of drinking, adolescent animals consumed less alcohol and showed lower preference than adults. The deprivation phase was followed by increased intake of highly concentrated ethanol solution without appreciable differences between age groups. Repeated swim stress produced a slight increase in ethanol consumption in both animal groups; however, alcohol intake was not significantly different between groups, whereas the foot shock stress-induced increase in alcohol intake was significantly higher in the animal group that initiated alcohol consumption during adolescence. After swim stress, the drinking behavior of the adolescent group resembled that of the adult group. In particular, the adolescent group increased their preference for 20% ethanol solution for the remainder of the experiment. CONCLUSIONS: Age of voluntary alcohol drinking onset does not appear to be a strong predictor for prospective alcohol intake and relapse-like drinking behavior under the present experimental conditions. However, male Wistar rats that initiated alcohol consumption during adolescence seem to be more susceptible to acute stressor-specific effects in terms of alcohol consumption.     

Implicit and explicit alcohol cognitions and observed alcohol consumption: three studies in (semi)naturalistic drinking settings

Aims Dual‐process models imply that alcohol use is related to implicit as well as explicit cognitive processes. Few studies have tested whether both types of processes are related to ad libitum drinking. In a series of three studies, we tested whether both implicit and explicit alcohol‐related cognitions predicted the amount of alcohol consumed in an ad libitum (semi)naturalistic drinking situation. Design Two experimental studies used trained confederates (same‐sex peers) who consumed either alcoholic or non‐alcoholic beverages, while observing participants' drinking behaviour in a 30‐minute session. The third study involved observations of participants' alcohol use during a 45‐minute session in which participants spent time with five to seven friends. Setting A (semi)naturalistic drinking setting, a laboratory bar. Participants Participants were undergraduates recruited at Radboud University (study 1: n = 115; study 2: n = 121; study 3: n = 200). Measurements We used coding of drinking behaviour from observations, questionnaire data on positive alcohol expectancies and alcohol use patterns and implicit association tests to assess alcohol associations. Findings Implicit associations were not related to observed alcohol use, whereas explicit positive expectancies were related positively to observed alcohol use in study 1 and study 2. Conclusions Among undergraduate students in (semi)naturalistic drinking settings with peers, implicit alcohol‐related cognitions do not predict the amount of alcohol consumed.     

Genetic correlation between innate alcohol preference and fear-potentiated startle in selected mouse lines

Background: There is a high rate of co‐occurrence between anxiety and alcohol‐use disorders in humans that may arise from the inheritance of common genes that increase the risk for both psychiatric disorders. The purpose of this study was to investigate whether a genetic relationship exists between innate alcohol preference and propensity to develop learned fear, using the fear‐potentiated startle (FPS) paradigm, in 2 mouse lines selectively bred for high or low alcohol preference. Methods: Alcohol‐naïve, male, and female mice from replicate pairs of lines selectively bred for high alcohol preference and low alcohol preference were randomly assigned to a fear‐conditioned or control group. Mice in the fear‐conditioned group received 20 pairings of a light stimulus and footshock; the control group received the same number of exposures to light and footshock, except that these stimuli were explicitly unpaired. During testing for FPS, acoustic stimuli were presented both in the presence and in the absence of the light stimulus. Results: In both replicate pairs of lines, mice selectively bred for high alcohol preference showed greater FPS than mice selectively bred for low alcohol preference. No sex differences in FPS were found in any line. Control groups did not show FPS. Conclusion: These findings suggest that common genes mediate both innate alcohol preference and propensity to develop learned fear in these selected mouse lines.     

High- and low-alcohol-preferring mice show differences in conditioned taste aversion to alcohol

Background: Genetic differences in sensitivity to the aversive effects of alcohol may contribute to alcohol drinking behavior. The present study examined the development of conditioned taste aversion (CTA) to various doses of alcohol in two pairs of mouse lines selectively bred for high (HAP) and low (LAP) alcohol preference. Methods: Alcohol‐naïve, male and female HAP and LAP mice from both replicate 1 (HAP n= 29; LAP n= 28) and replicate 2 (HAP n= 34; LAP n= 35) were adapted to a 2‐hr per day water restriction regimen. During five conditioning trials at 48 hr intervals, mice received an intraperitoneal injection of saline or 2 g/kg or 4 g/kg alcohol immediately following 1 hr of access to a 0.20 M NaCl solution. Results: LAP mice of both replicates showed a significantly greater magnitude of CTA to both 2 g/kg and 4 g/kg alcohol compared with HAP mice of both replicates. There were no line differences in consumption of the NaCl solution in the saline control groups. Conclusions: These data suggest that mice selectively bred for low alcohol preference are more sensitive to the development of alcohol CTA than mice selectively bred for high alcohol preference. The present findings indicate that common genes mediate both alcohol preference and the aversive effects of alcohol as measured in the CTA paradigm.     

Age-dependent variation in behavior following acute ethanol administration in male and female adolescent rhesus macaques (Macaca mulatta)

Background: There has been considerable focus on the adolescent stage of development in the study of alcohol use and the etiology of alcohol‐related problems. Because adolescence is a process of dynamic change rather than a discrete or static stage of development, it is important to consider ontogenetic changes in the response to ethanol within the adolescent time period. In rodents, levels of ethanol‐induced motor impairment have been shown to increase from early to late adolescence. This study investigated associations between behavior following acute ethanol administration and age, rearing condition (mother‐reared vs nursery‐reared), and serotonin transporter (rh5‐HTTLPR) genotype in a sample of alcohol‐naïve adolescent rhesus macaques. Methods: Rhesus macaques (n=97; 41 males, 56 females), ranging in age from 28 to 48 months, were administered intravenous (IV) doses of ethanol (2.2 g/kg for males, 2.0 g/kg for females) twice in 2 separate testing sessions. A saline/ethanol group (n=16; 8 males, 6 females) was administered saline in 1 testing session and ethanol in the second session. Following each IV injection, subjects underwent a 30‐minute general motor behavioral assessment. Behavior in the saline/ethanol group was compared between the saline and ethanol‐testing sessions using analysis of variance. Behavioral data for the larger study sample were averaged between the 2 testing sessions and summarized using factor analysis. Rotated factor scores were used as dependent variables in multiple regression analyses to test for relationships between behavior and age, rearing condition, and rh5‐HTTLPR genotype. Results: During the ethanol‐testing session, behaviors indicative of motor impairment (stumbles, falls, sways, bumping the wall, and unsuccessful jumps) were frequently observed in the saline/ethanol group, while they did not occur under the saline‐testing session. Factor analysis of behavior following ethanol administration in the larger study sample yielded 3 factors: Ataxia, Impaired Jumping Ability, and Stimulation. Significant negative correlations between age and Ataxia were found for both males and females. Females also exhibited positive correlations between age and Impaired Jumping Ability and age and Stimulation. No significant correlations were found with either rearing condition or rh5‐HTTLPR genotype. Conclusions: These findings suggest that ontogenetic changes during adolescence in the behavioral response to ethanol differ between rodents and primates. Furthermore, sex differences in the behavioral response to ethanol appear to develop during adolescence.     

Differential effects of acute alcohol on prepulse inhibition and event-related potentials in adolescent and adult Wistar rats

Background: Previous studies have demonstrated that adolescent and adult rats show differential sensitivity to many of the acute effects of alcohol. We recently reported evidence of developmental differences in the effects of acute alcohol on the cortical electroencephalogram. However, it is unclear whether developmental differences are also observed in other neurophysiological and neurobehavioral measurements known to be sensitive to alcohol exposure. The present study determined the age‐related effects of acute alcohol on behavioral and event‐related potential (ERP) responses to acoustic startle (AS) and prepulse inhibition (PPI). Methods: Male adolescent and adult Wistar rats were implanted with cortical recording electrodes. The effects of acute alcohol (0.0, 0.75, and 1.5 g/kg) on behavioral and ERP responses to AS and PPI were assessed. Results: Acute alcohol (0.75 and 1.5 g/kg) significantly reduced the behavioral and electrophysiological response to AS in adolescent and adult rats. Both 0.75 and 1.5 g/kg alcohol significantly enhanced the behavioral response to PPI in adolescent, but not in adult rats. During prepulse + pulse trials, 1.5 g/kg alcohol significantly increased the N10 pulse response in the adolescent frontal cortex. Acute alcohol (0.75 and 1.5 g/kg) also increased the N1 ERP pulse response to prepulse stimuli in frontal and parietal cortices in adult rats, but not in adolescent rats. Conclusions: These data suggest that alcohol’s effect on behavioral and electrophysiological indices of AS do not differ between adults and adolescents whereas developmental stage does appear to significantly modify alcohol‐influenced response to PPI.     

Prazosin effects on stress- and cue-induced craving and stress response in alcohol-dependent individuals: preliminary findings

Background: Stress, alcohol cues, and dysregulated stress responses increase alcohol craving and relapse susceptibility, but few pharmacologic agents are known to decrease stress‐ and cue‐induced alcohol craving and associated stress dysregulation in humans. Here we report findings from a preliminary efficacy study of the alpha‐1 receptor antagonist, prazosin, in modulating these relapse‐relevant factors in alcohol‐dependent individuals. Methods: Seventeen early abstinent, treatment‐seeking alcohol‐dependent individuals (12 men and 5 women) were randomly assigned to receive either placebo or 16 mg daily prazosin in a double‐blind, placebo‐controlled manner over 4 weeks. During week 4, all patients participated in a 3‐day laboratory experiment involving 5‐minute guided imagery exposure to stress, alcohol cue, and neutral‐relaxing/control conditions, 1 exposure per day, on consecutive days in a random, counterbalanced order. Alcohol craving, anxiety, negative emotion, cardiovascular measures, and plasma hypothalamic–pituitary–adrenal (HPA; cortisol, adenocorticotropic hormone) were assessed repeatedly in each session. Results: The prazosin group (n = 9) versus the placebo group (n = 8) showed significantly lower alcohol craving, anxiety, and negative emotion following stress exposure. The placebo group also showed significantly increased stress‐ and cue‐induced alcohol craving, anxiety, negative emotion, and blood pressure (BP), as well as a blunted HPA response relative to the neutral condition, while the prazosin group showed no such increases in craving, anxiety, negative emotion, and BP, and no blunted HPA response to stress and alcohol cue exposure. Conclusions: Prazosin appears efficacious in decreasing stress‐ and cue‐induced alcohol craving and may normalize the stress dysregulation associated with early recovery from alcoholism. Further research to assess the efficacy of prazosin in reducing alcohol craving and stress‐related relapse risk is warranted.     

Adolescent binge drinking linked to abnormal spatial working memory brain activation: differential gender effects

Background: Binge drinking is prevalent during adolescence, and its effect on neurocognitive development is of concern. In adult and adolescent populations, heavy substance use has been associated with decrements in cognitive functioning, particularly on tasks of spatial working memory (SWM). Characterizing the gender‐specific influences of heavy episodic drinking on SWM may help elucidate the early functional consequences of drinking on adolescent brain functioning. Methods: Forty binge drinkers (13 females, 27 males) and 55 controls (24 females, 31 males), aged 16 to 19 years, completed neuropsychological testing, substance use interviews, and an SWM task during functional magnetic resonance imaging. Results: Significant binge drinking status × gender interactions were found (p < 0.05) in 8 brain regions spanning bilateral frontal, anterior cingulate, temporal, and cerebellar cortices. In all regions, female binge drinkers showed less SWM activation than female controls, while male bingers exhibited greater SWM response than male controls. For female binge drinkers, less activation was associated with poorer sustained attention and working memory performances (p < 0.025). For male binge drinkers, greater activation was linked to better spatial performance (p < 0.025). Conclusion: Binge drinking during adolescence is associated with gender‐specific differences in frontal, temporal, and cerebellar brain activation during an SWM task, which in turn relate to cognitive performance. Activation correlates with neuropsychological performance, strengthening the argument that blood oxygen level–dependent activation is affected by alcohol use and is an important indicator of behavioral functioning. Females may be more vulnerable to the neurotoxic effects of heavy alcohol use during adolescence, while males may be more resilient to the deleterious effects of binge drinking. Future longitudinal research will examine the significance of SWM brain activation as an early neurocognitive marker of alcohol impact to the brain on future behaviors, such as driving safety, academic performance, and neuropsychological performance.     

Intermittent (every-other-day) drinking induces rapid escalation of ethanol intake and preference in adolescent and adult C57BL/6J mice

Background: Using adult C57BL/6J (B6) mice, we previously developed a procedure that causes a progressive increase in ethanol intake and preference (i.e., alcohol escalation effect) following weekly (intermittent) access to ethanol ( Melendez et al., 2006 ). A limitation of this procedure is that it requires many weeks of testing, which limits its use to study ethanol escalation (i.e., binge‐like drinking) during adolescence. Previous studies have shown that intermittent every‐other‐day (EOD) access to ethanol is sufficient to induce ethanol escalation in rats. The objective of this study was to verify whether EOD access is sufficient to induce escalated levels of ethanol intake and preference in adult and adolescent B6 mice. Methods: Male B6 mice received free‐choice 24‐hour access to 15% ethanol and water on an EOD or daily basis for 2 weeks. Food and water were available at all times. Using adult mice, Experiment 1 characterized the induction of ethanol escalation following EOD access at 6 (i.e., drinking in the dark) and 24‐hour intervals, whereas Experiment 2 determined whether daily drinking reverses escalation induced by EOD drinking. Experiment 3 compared ethanol‐drinking capacity following daily versus EOD drinking in adolescent (P30‐45) and adult (P70‐85) mice. Results: Experiment 1 revealed that EOD drinking leads to a significant (nearly 2‐fold) increase in ethanol intake and preference over mice given daily access. Experiment 2 demonstrated that EOD‐elicited escalation is blocked and subsequently reversed following daily drinking. Experiment 3 revealed that ethanol drinking was greater in adolescent mice compared with adults following daily drinking and EOD (escalated) drinking. Although the escalated levels of ethanol intake were greater in adolescent mice, the rate or onset of escalation was comparable between both age‐groups. Conclusions: This study is the first to demonstrate that EOD drinking leads to escalation of ethanol intake and preference in adolescent and adult mice. Moreover, our results indicate that daily ethanol reverses ethanol escalation induced by intermittent drinking. The study also revealed that adolescent mice have a greater capacity to drink ethanol under both daily (controlled) and EOD (escalated) conditions, which further supports the notion of adolescent’s susceptibility to heavy drinking.     

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.     

Enhanced prepulse inhibition following adolescent ethanol exposure in Sprague-Dawley rats

OBJECTIVES: Recent studies have demonstrated that ethanol exposure differentially affects adolescents and adults. The current studies were designed to compare the effects of 2-week exposure to ethanol during adolescence or adulthood on the acoustic startle response (ASR) and prepulse inhibition (PPI) METHODS: Male Sprague-Dawley rats were exposed to ethanol vapor 12 hr/d (on from 6 pm to 6 am) for 14 days during adolescence or adulthood. Six days after the cessation of ethanol vapor exposure, the ASR and PPI were assessed. RESULTS: During ethanol treatment, overall blood alcohol levels averaged 230 to 250 mg/dl in the adolescent and adult treatment groups. Assessment of the ASR revealed that latency to startle was more rapid in adolescents than in adults, but ASR latency was not altered by ethanol exposure. In addition, ASR magnitude was lower in adolescents and was decreased in ethanol-exposed rats on startle trials. Ethanol exposure significantly enhanced PPI, but only after adolescent exposure CONCLUSIONS: These data further demonstrate a differential sensitivity of adolescents and adults to the effects of ethanol exposure. Specifically, a 2-week period of ethanol exposure during adolescence selectively enhanced PPI, a neurobehavioral index of sensorimotor gating. However, ASR magnitude was decreased by ethanol exposure regardless of age. On the basis of previous studies, the effects of ethanol exposure on PPI data could indicate that adolescent rats exposed to ethanol are more likely to exhibit behavioral inflexibility and that ethanol exposure acts as a more potent physical stressor in adolescent rats.     

High-Alcohol Preferring Mice Are More Impulsive Than Low-Alcohol Preferring Mice as Measured in the Delay Discounting Task

Background: Repeated studies have shown that high impulsivity, when defined as the tendency to choose small immediate rewards over larger delayed rewards, is more prevalent in drug addicts and alcoholics when compared with nonaddicts. Assessing whether impulsivity precedes and potentially causes addiction disorders is difficult in humans because they all share a history of drug use. In this study, we address this question by testing alcohol‐naïve mice from lines showing heritable differences in alcohol intake. Methods: Replicated selected lines of outbred high‐alcohol preferring (HAP) mice were compared to a low‐alcohol preferring (LAP) line as well as the low‐drinking progenitor line (HS/Ibg) on an adjusting amount delay discounting (DD) task. The DD task employs 2 levers to present subjects with a choice between a small, immediate and a large, delayed saccharin reward. By adjusting the quantity of the immediate reward up and down based on choice behavior, the task allows an estimate of how the subjective value of the delayed reinforcer decreases as delays increase. Latency to respond was also measured for each trial. Results: Both HAP2 and HAP1 lines of mice were more impulsive than the LAP2 and HS/Ibg lines, respectively. Hyperbolic curve‐fitting confirmed steeper discounting in the high‐alcohol drinking lines. In addition, the high‐alcohol drinking lines demonstrated greater within‐session increases in reaction times relative to the low‐alcohol drinking lines. No other differences (consumption of saccharin, total trials completed) consistently mapped onto genetic differences in alcohol drinking. Conclusions: Alcohol‐naïve outbred mice selected for high‐alcohol drinking were more impulsive with saccharin reinforcers than low‐alcohol drinkers. These data are consistent with results seen using inbred strain descendents of high‐alcohol drinking and low‐alcohol drinking rat lines, and suggest that impulsivity is a heritable difference that precedes alcoholism.     

Limited Access Alcohol Drinking in High- and Low-Alcohol Preferring Selected Lines of Mice

BACKGROUND: Selection studies and genetic analyses of drinking behavior in rodents often involved unlimited access to alcohol over a period of weeks, with water and food freely available. Most studies investigating the pharmacology of alcohol drinking, on the other hand, use procedures in which access to alcohol is limited to a particular time each day. Reconciliation of findings between these two conditions likely depends on their sharing common genetic mechanisms as indicated, for example, by covariation in response to selection. To this end, high- and low-alcohol preferring (HAP and LAP, respectively) mice, selected for differences in 24-hr access alcohol drinking over a 4-week period, were subjected to a limited access alcohol drinking protocol. METHODS: During 2-hr sessions, mice had access to various concentrations of alcohol (7-15%, v/v) in the home cage for 2 hr a day, with ad libitum access to food and water. Additional sessions were conducted with no food present. RESULTS: Although both strains consumed alcohol and water during these sessions, HAP mice drank far more alcohol than did LAP mice. HAP but not LAP mice drank alcohol at a high rate early in the session compared with later in the session. Additionally, HAP mice responded to changes in alcohol concentration, whereas LAP mice did not. Removal of food did not influence alcohol drinking, although water drinking decreased following food removal. HAP mice reached appreciable blood alcohol concentrations after limited access. CONCLUSIONS: These findings indicate that in these selectively bred mice, alcohol drinking during limited and unlimited access may be genetically related, and that drinking during limited access sessions in HAP mice is likely for the pharmacological properties of alcohol.     

Bidirectional interactions between acute psychosocial stress and acute intravenous alcohol in healthy men

Background: The biological mechanisms by which acute stress increases alcohol consumption are unclear. One potential mechanism is that stress acts by altering the pharmacological and subjective effects of alcohol. Acute stress produces a cascade of physiological and psychological effects, each with a distinctive time course. In this study, we investigated whether different phases of response to an acute stress alter the subjective effects of intravenous alcohol, by administering the drug at 2 different times after the stress. Methods: Healthy men (n = 25) participated in 2 sessions: 1 with the Trier Social Stress Test and the other with a nonstressful control task, each followed by infusions of intravenous alcohol (targeting 40 mg% in 5 minutes) and placebo. One group of participants received alcohol within 1 minute of completing the tasks (Alc0, n = 11), followed by placebo 30 minutes later. In the other group (Alc30, n = 14), the order of alcohol and placebo infusions was reversed. Subjective effects (i.e., anxiety, stimulation, want more) and physiological measures (heart rate, blood pressure, salivary cortisol) were measured before and at repeated intervals after the tasks and infusions. Results: Stress did not change the subjective effects of alcohol in either group. However, when individual differences in alcohol responses were considered, stress differentially altered the stimulant‐like and sedative effects of alcohol. Among individuals who exhibited predominantly stimulant responses to alcohol in the nonstressful condition, stress decreased the stimulant‐like effects of alcohol and “wanting more.” By contrast, among participants who did not report stimulation after alcohol in the control session, stress decreased the sedative effects and increased “want more.” In addition, alcohol administered immediately after the Trier Social Stress Test dampened cortisol responses yet prolonged negative subjective responses to the stress. Conclusions: These findings demonstrate that there are bidirectional relationships between alcohol and stress. Alcohol influences responses to stress, and stress changes reactions to alcohol, depending on an individual’s pattern of response to alcohol. This study highlights the fact that stress–alcohol interactions vary among individual drinkers, suggesting that the effects of stress on motivation to drink alcohol may also differ between individuals.     

Adolescent C57BL/6J (but not DBA/2J) Mice Consume Greater Amounts of Limited‐Access Ethanol Compared to Adults and Display Continued Elevated Ethanol Intake into Adulthood

Background: Alcohol use is common during the adolescent period, a time at which a number of crucial neurobiological, hormonal, and behavioral changes occur ( Spear, 2000 ). In order to more fully understand the complex interaction between alcohol use and these age‐typical neurobiological changes, animal models must be utilized. Rodents experience a developmental period similar to that of adolescence. Although rat models have shown striking adolescent‐specific differences in sensitivity to ethanol, little work has been done in mice despite the fact that the C57BL/6J (B6) and DBA2/J (D2) mice have been shown to markedly differ in ethanol preference drinking and exhibit widely different sensitivities to ethanol. Methods: The current study examined ethanol intake in adolescent and adult B6 and D2 mice using a limited access alcohol exposure paradigm called Drinking in the Dark (DID). Additionally, the effect of adolescent (or adult) ethanol exposure on subsequent adult ethanol intake was examined by re‐exposing the mice to the same paradigm once the adolescents reached adulthood. We hypothesized that adolescent (P25–45) mice would exhibit greater binge‐like alcohol intake compared to adults (P60–80), and that B6 mice would exhibit greater binge‐like alcohol intake compared to D2 mice. Moreover, we predicted that relative difference in binge‐like alcohol intake between adolescents and adults would be greater in D2 mice. Results: Adolescent B6 mice consumed more ethanol than adults in the DID model. There was no difference between adolescent and adult D2 mice. Conclusions: This work adds to the literature suggesting that adolescents will consume more ethanol than adults and that this exposure can result in altered adult intake. However, this effect seems largely dependent upon genotype. Future work will continue to examine age‐related differences in ethanol intake, preference, and sensitivity in inbred mouse strains.     

Low-dose stimulatory effects of ethanol during adolescence in rat lines selectively bred for high alcohol intake

Abstract : Background: The low‐dose stimulatory effect of ethanol (EtOH) in rats has been hypothesized to reflect its hedonic effects and to be associated with a genetic predisposition toward high alcohol preference. To test the hypothesis that phenotypes associated with high alcohol preference in adulthood are also present in adolescent rats at the time of onset of alcohol drinking, the current study examined the effects of EtOH on locomotor activity (LMA) during adolescence in lines of rats selectively bred for divergent alcohol intakes. Methods: Subjects were adolescent (31–40 days of age) rats from the alcohol‐preferring (P) and ‐nonpreferring (NP) lines and from the high–alcohol‐drinking (HAD) and low–alcohol‐drinking (LAD) replicate lines. On day 1, all subjects (n= 8–10/line/gender/dose) received intraperitoneal saline injections and were placed in the activity monitor for 30 min. On day 2, subjects received intraperitoneal saline or 0.25, 0.50, 0.75, 1.0, or 1.5 g EtOH/kg. Results: The LMA of male and female P rats was increased with low doses (0.25–0.75 g/kg) and decreased at the highest dose (1.5 g/kg) of EtOH. Similar effects were observed with low doses of EtOH on the LMA of HAD‐1 and HAD‐2 rats. None of the EtOH doses stimulated LMA in the NP, LAD‐1, or LAD‐2 rats, although all of the low–alcohol‐intake lines of rats showed decreased LMA at the highest dose of EtOH. Only the P rats among the high–alcohol‐consuming lines of rats showed decreased LMA at the highest dose of EtOH. Conclusion: Selective breeding for high alcohol consumption seems to be associated with increased sensitivity to the low‐dose stimulating effects of EtOH and reduced sensitivity to the high‐dose motor‐impairing effects of ethanol. The expression of these phenotypes emerges during adolescence by the age of onset of alcohol‐drinking behavior.     

Development of ethanol withdrawal-related sensitization and relapse drinking in mice selected for high- or low-ethanol preference

Background: Previous studies have shown that high alcohol consumption is associated with low withdrawal susceptibility, while at the same time, other studies have shown that exposure to ethanol vapor increases alcohol drinking in rats and mice. In the present studies, we sought to shed light on this seeming contradiction using mice selectively bred for High‐ (HAP) and Low‐ (LAP) Alcohol Preference, first, assessing these lines for differences in signs of ethanol withdrawal and second, for differences in the efficacy of intermittent alcohol vapor exposure on elevating subsequent ethanol intake. Methods: Experiment 1 examined whether these lines of mice differed in ethanol withdrawal‐induced CNS hyperexcitability and the development of sensitization to this effect following intermittent ethanol vapor exposure. Adult HAP and LAP lines (replicates 1 and 2), and the C3H/HeNcr inbred strain (included as a control genotype for comparison purposes) received intermittent exposure to ethanol vapor and were evaluated for ethanol withdrawal‐induced seizures assessed by scoring handling‐induced convulsions (HIC). Experiment 2 examined the influence of chronic intermittent ethanol exposure on voluntary ethanol drinking. Adult male and female HAP‐2 and LAP‐2 mice, along with male C57BL/6J (included as comparative controls) were trained to drink 10% ethanol using a limited access (2 h/d) 2‐bottle choice paradigm. After stable baseline daily intake was established, mice received chronic intermittent ethanol vapor exposure in inhalation chambers. Ethanol intake sessions resumed 72 hours after final ethanol (or air) exposure for 5 consecutive days. Results: Following chronic ethanol treatment, LAP mice exhibited overall greater withdrawal seizure activity compared with HAP mice. In Experiment 2, chronic ethanol exposure/withdrawal resulted in a significant increase in ethanol intake in male C57BL/6J, and modestly elevated intake in HAP‐2 male mice. Ethanol intake for male control mice did not change from baseline levels of intake. In contrast, HAP‐2 female and LAP‐2 mice of both sexes did not show changes in ethanol intake as a consequence of intermittent ethanol exposure. Conclusions: Overall, these results indicate that the magnitude of ethanol withdrawal‐related seizures is inversely related to inherited ethanol intake preference. Additionally, intermittent ethanol vapor exposure appears more likely to affect high‐drinking mice (C57BL/6J and HAP‐2) than low drinkers, although these animals are less affected by ethanol withdrawal.