Genomewide SNP Screen to Detect Quantitative Trait Loci for Alcohol Preference in the High Alcohol Preferring and Low Alcohol Preferring Mice

Background:  The high and low alcohol preferring (HAP1 and LAP1) mouse lines were selectively bred for differences in alcohol intake. The HAP1 and LAP1 mice are essentially noninbred lines that originated from the outbred colony of HS/Ibg mice, a heterogeneous stock developed from intercrossing 8 inbred strains of mice.
Methods:  A total of 867 informative SNPs were genotyped in 989 HAP1 × LAP1 F2, 68 F1s, 14 parents (6 LAP1, 8 HAP1), as well as the 8 inbred strains of mice crossed to generate the HS/Ibg colony. Multipoint genome wide analyses were performed to simultaneously detect linked QTLs and also fine map these regions using the ancestral haplotypes.
Results:  QTL analysis detected significant evidence of association on 4 chromosomes: 1, 3, 5, and 9. The region on chromosome 9 was previously found linked in a subset of these F2 animals using a whole genome microsatellite screen.
Conclusions:  We have detected strong evidence of association to multiple chromosomal regions in the mouse. Several of these regions include candidate genes previously associated with alcohol dependence in humans or other animal models.     

Pharmacologic Dissociation Between Impulsivity and Alcohol Drinking in High Alcohol Preferring Mice

Background: Impulsivity is genetically correlated with, and precedes, addictive behaviors and alcoholism. If impulsivity or attention is causally related to addiction, certain pharmacological manipulations of impulsivity and/or attention may affect alcohol drinking, and vice versa. The current studies were designed to explore the relationship among impulsivity, drinking, and vigilance in selectively bred High Alcohol Preferring (HAP) mice, a line that has previously demonstrated both high impulsivity and high alcohol consumption. Amphetamine, naltrexone, and memantine were tested in a delay discounting (DD) task for their effects on impulsivity and vigilance. The same drugs and doses were also assessed for effects on alcohol drinking in a 2‐bottle choice test. Methods: HAP mice were subjected to a modified version of adjusting amount DD using 0.5‐second and 10‐second delays to detect decreases and increases, respectively, in impulsive responding. In 2 experiments, mice were given amphetamine (0.4, 0.8, or 1.2 mg/kg), naltrexone (3 and 10 mg/kg), and memantine (1 and 5 mg/kg) before DD testing. Another pair of studies used scheduled access, 2‐bottle choice drinking to assess effects of amphetamine (0.4, 1.2, or 3.0 mg/kg), naltrexone (3 and 10 mg/kg), and memantine (1 and 5 mg/kg) on alcohol consumption. Results: Amphetamine dose‐dependently reduced impulsivity and vigilance decrement in DD, but similar doses left alcohol drinking unaffected. Naltrexone and memantine decreased alcohol intake at doses that did not affect water drinking but had no effects on impulsivity or vigilance decrement in the DD task. Conclusions: Contrary to our hypothesis, none of the drugs tested here, while effective on either alcohol drinking or impulsivity, decreased both behaviors. These findings suggest that the genetic association between drinking and impulsivity observed in this population is mediated by mechanisms other than those targeted by the drugs tested in these studies.     

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.     

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.     

Mouse lines selected for alcohol consumption differ on certain measures of impulsivity

BACKGROUND: Alcoholics and heavy drinkers score higher on measures of impulsivity than nonalcoholics and light drinkers. This may be due to factors that predate drug exposure (e.g. genetics) or to neuroadaptations associated with exposure to alcohol. The aim of this study was to examine the role of genetics by comparing impulsivity in short-term selected lines of mice bred to voluntarily drink either high (STDRHI2) or low (STDRLO2) amounts of 10% ethanol. METHODS: Independent sets of mice completed 2 experiments designed to measure impulsivity. Using the adjusting amount procedure, we examined preference for smaller, sooner rewards over larger but delayed rewards (delay discounting). This task determines the amount of immediate sucrose equivalent to the discounted value of a 20 microl sucrose reward given following a specific delay (0, 2, 4, 8, or 12 seconds). Using a Go/No-go task, we examined the ability of mice to inhibit nose-poking in response to specific cues. These tasks are commonly used to assess different aspects of impulsive behavior, and provide measures that are not highly correlated. RESULTS: No significant differences were found between STDRHI2 and STDRLO2 mice in delay discounting. In the Go/No-go task, STDRHI2 mice made more responses during the pre-cue period without committing more false alarms, compared with STDRLO2 mice. CONCLUSIONS: The results suggest that short-term selective breeding for high relative alcohol consumption may also select for animals that have impaired response inhibition.     

Delay discounting predicts behavioral sensitization to ethanol in outbred WSC mice

Background: Alcoholic individuals discount the value of future rewards more steeply than social drinkers, which is viewed as symptomatic of higher levels of impulsivity. However, the mechanisms underlying this difference are unknown. This study examined 2 hypotheses about the relationship between discounting and ethanol's effects in mice: (1) steep discounters are less sensitive to the initial stimulant‐like effects of ethanol and (2) steep discounters exhibit greater behavioral adaptation to stimulant effects with repeated ethanol exposure. Methods: An adjusting amount procedure was used to assess discounting as a function of delay in ethanol‐naïve genetically heterogeneous WSC mice. Mice chose between a small amount of sucrose solution delivered immediately and 19.5 μL delivered following a delay (0, 2, 4, 8, or 12 seconds, varied between sessions). Within sessions, the amount (μL) of immediate sucrose was adjusted until animals became indifferent between the immediate and specific delayed reward. Hyperbolic discount functions were fitted to quantify the degree of delay discounting. Then, in a within‐subjects design over 13 days, mice received a pattern of daily injections of saline or ethanol, and after certain treatments their locomotor activity was assessed for 15 minutes. Results: Animals with steeper discount functions (greater impulsivity) tended to exhibit less locomotor stimulation on their initial exposure to ethanol. However, steeper discounting was positively associated with increases in locomotor activity after repeated exposure (sensitization), indicating that steep discounters showed higher levels of sensitization to the stimulating effects of ethanol. Conclusions: These results suggest 2 behavioral effects of ethanol, associated with an increased risk for alcohol abuse, that are associated with variations in delay discounting.     

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.     

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.     

Neural and behavioral mechanisms of impulsive choice in alcohol use disorder

Background: Alcohol dependence has repeatedly been associated with impulsive choice, or the inability to choose large delayed rewards over smaller, but more immediate rewards. However, the neural basis of impulsive choice in alcohol use disorders (AUDs) is not well understood. Methods: One hundred fifty‐one individuals with a range of alcohol use from social drinking to severe alcohol dependence completed a delay discounting task while undergoing functional magnetic resonance imaging. Participants received customized trials designed to ensure an approximately equivalent number of immediate responses. Results: Delaying gratification recruited regions involved in cognitive control, conflict monitoring, and the interpretation of somatic states. Individuals with more severe alcohol use problems showed increased discounting of delayed rewards and greater activation in several regions including supplementary motor area, insula/orbitofrontal cortex, inferior frontal gyrus, and the precuneus. Conclusions: These results suggest that impulsive choice in alcohol dependence is the result of functional anomolies in widely distributed, but interconnected brain regions involved in cognitive and emotional control. Furthermore, our results suggest that the neural mechanisms of impulsive choice in AUD both overlaps with that observed in previous studies, and shows that individuals with AUD recruit additional mechanisms when making intertemporal choices.     

A characterization of approach and avoidance learning in high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats

Background: This study was undertaken as one of a series of experiments designed to examine basic behavioral characteristics present in rats bred specifically for alcohol preference. The basic premise for these experiments has been the idea that alcohol‐preferring and ‐nonpreferring rats may differ in basic activation and inhibition control mechanisms that govern behavior and that different lines of alcohol‐preferring rats may demonstrate differential deficits in behavioral activation and behavioral inhibition tendencies. In the present experiment, conditioned approach and avoidance behaviors were studied in alcohol‐naïve high–alcohol‐drinking (HAD), low–alcohol‐drinking (LAD), and N/NIH rats to evaluate behavioral activation in this line of rats. Methods: High alcohol drinking (HAD1), low alcohol drinking (LAD1), and N/Nih stock rats were trained to press a response bar during a tone signal to avoid a mild foot shock or receive a food reward. In addition, HAD2 and LAD2 rats, independently‐bred replicate lines of the HAD1/LAD1 rats, were trained on the avoidance task. Results: Although the HAD1 rats easily learned the appetitive version of the bar‐pressing task, they did not learn the avoidance response. The LAD1 and N/Nih rats learned both the approach and the avoidance tasks normally. Similar to HAD1 rats, the HAD2 rats did not learn the avoidance response whereas LAD2 rats showed significant avoidance performance levels. Conclusions: The present data demonstrated that both HAD1 and HAD2 rats had a rather specific behavioral activation deficit: although they easily learned to press a bar to receive food reinforcement, they did not learn to press the bar to avoid a foot shock. We speculate that this failure to learn the avoidance response may be related to heightened anxiety in the HAD rats and that this excessive anxiety may lead to the development of high levels of alcohol consumption in these selectively bred rats.     

Inflexible and Indifferent Alcohol Drinking in Male Mice

Background: Alcoholism is characterized by compulsive alcohol intake, but this critical feature of alcoholism is seldom captured in preclinical studies. Here, we evaluated whether alcohol‐preferring C57BL/6J mice develop compulsive alcohol drinking patterns, using adulteration of the alcohol solution with quinine, in a limited access choice paradigm. We assessed 2 independent aspects of compulsive drinking: (i) inflexible alcohol intake by testing whether mice would drink bitter alcohol solutions if this was their only source of alcohol and (ii) indifferent drinking by comparing intake of aversive and nonaversive alcohol solutions. Methods: Male C57BL/6J mice consumed alcohol for 2 or 8 consecutive weeks. The alcohol solution was then adulterated with graded quinine concentrations, and the effect on alcohol intake was determined. Results: C57BL/6J mice rapidly developed compulsive alcohol drinking patterns. Adulteration of the alcohol solution with an aversive quinine concentration failed to reduce intake, indicative of inflexible drinking behavior, after only 2 weeks of alcohol experience, although quinine adulteration did suppress the acquisition of alcohol drinking in naïve mice. After 8 weeks of alcohol consumption, the mice also became indifferent to quinine. They consumed an aversive, quinine‐containing alcohol solution, despite the simultaneous availability of an unadulterated alcohol solution. Prolonged alcohol ingestion did not alter the sensitivity to the bitter taste of quinine itself. Conclusion: These findings demonstrate the staged occurrence in mice of 2 distinct behavioral characteristics of alcoholism, i.e., inflexible and indifferent alcohol drinking.     

Delay Discounting of Reward and Impulsivity in Eating Disorders: From Anorexia Nervosa to Binge Eating Disorder

Evidence points to eating disorder patients displaying altered rates of delay discounting (one's degree of preference for immediate rewards over larger delayed rewards). Anorexia nervosa (AN) patients are believed to have an increased capacity to delay reward, which reflects their ability to override the drive to eat. Contrarily, binge eating disorder (BED) patients are associated with a reduced predisposition to delay gratification. Here, we investigated monetary delay discounting and impulsivity in 80 adult women with EDs (56 AN and 24 BED), diagnosed according to Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria, and 80 healthy controls. AN‐restrictive (AN‐R) subtype patients showed less steep discounting rates than BED and AN‐bingeing/purging subtype patients. Compared with healthy controls and AN‐R patients, BED and AN‐bingeing/purging patients presented higher delay discounting and positive and negative urgency levels. Our findings suggest that restriction in AN‐R patients is associated with disproportionate self‐control, whereas bingeing behaviours could be more driven by emotional states and impulsivity traits. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association.     

Age- and sex-dependent effects of footshock stress on subsequent alcohol drinking and acoustic startle behavior in mice selectively bred for high-alcohol preference

Background: Exposure to stress during adolescence is known to be a risk factor for alcohol‐use and anxiety disorders. This study examined the effects of footshock stress during adolescence on subsequent alcohol drinking in male and female mice selectively bred for high‐alcohol preference (HAP1 lines). Acoustic startle responses and prepulse inhibition (PPI) were also assessed in the absence of, and immediately following, subsequent footshock stress exposures to determine whether a prior history of footshock stress during adolescence would produce enduring effects on anxiety‐related behavior and sensorimotor gating. Methods: Alcohol‐naïve, adolescent (male, n = 27; female, n = 23) and adult (male, n = 30; female, n = 30) HAP1 mice were randomly assigned to a stress or no stress group. The study consisted of 5 phases: (1) 10 consecutive days of exposure to a 30‐minute footshock session, (2) 1 startle test, (3) one 30‐minute footshock session immediately followed by 1 startle test, (4) 30 days of free‐choice alcohol consumption, and (5) one 30‐minute footshock session immediately followed by 1 startle test. Results: Footshock stress exposure during adolescence, but not adulthood, robustly increased alcohol drinking behavior in both male and female HAP1 mice. Before alcohol drinking, females in both the adolescent and adult stress groups showed greater startle in phases 2 and 3; whereas males in the adolescent stress group showed greater startle only in phase 3. After alcohol drinking, in phase 5, enhanced startle was no longer apparent in any stress group. Males in the adult stress group showed reduced startle in phases 2 and 5. PPI was generally unchanged, except that males in the adolescent stress group showed increased PPI in phase 3 and females in the adolescent stress group showed decreased PPI in phase 5. Conclusions: Adolescent HAP1 mice appear to be more vulnerable to the effects of footshock stress than adult mice, as manifested by increased alcohol drinking and anxiety‐related behavior in adulthood. These results in mice suggest that stress exposure during adolescence may increase the risk for developing an alcohol‐use and/or anxiety disorder in individuals with a genetic predisposition toward high alcohol consumption.     

Impulsive responding in alcoholics

BACKGROUND: Impaired decision-making is one diagnostic characteristic of alcoholism. Quantifying decision-making with rapid and robust laboratory-based measures is thus desirable for the testing of novel treatments for alcoholism. Previous research has demonstrated the utility of delay discounting (DD) tasks for quantifying differences in decision-making in substance abusers and normal controls. In DD paradigms subjects choose between a small, immediate reward and a larger, delayed reward. METHODS: We used a novel computerized DD task to demonstrate that abstinent alcoholics (AA, n=14) choose the larger, delayed option significantly less often than control subjects (n=14; p<0.02). This difference in choice tendency was independent of subject age, gender, years of education, or socio-economic status. RESULTS: All subjects discounted as a function of reward delay and amount, with alcoholics demonstrating steeper discounting curves for both variables. This tendency to discount delayed rewards was positively correlated with subjective reports of both alcohol addiction severity (Drug Use Screening Inventory-Revised, Domain 1, p<0.01), and impulsivity (Barratt Impulsivity Scale-11, p<0.004). Novel aspects of this new paradigm include an element of time pressure, an additional experimental condition that evaluated motor impulsivity by assessing the ability to inhibit a pre-potent response, and another control condition to requiring non-subjective choice. CONCLUSIONS: Non-alcoholic controls and alcoholics did not differ on motor impulsivity or non-subjective choice, suggesting that the differing choice behavior of the two groups was due mainly to differences in cognitive impulsivity.     

Increased Perioculomotor Urocortin 1 Immunoreactivity in Genetically Selected Alcohol Preferring Rats

Introduction: Urocortin 1 (Ucn 1) is an endogenous peptide related to the corticotropin‐releasing factor (CRF). Ucn 1 is mainly expressed in the perioculomotor area (pIII), and its involvement in alcohol self‐administration is well confirmed in mice. In other species, the relationship between the perioculomotor Ucn 1‐containing population of neurons (pIIIu) and alcohol consumption needs further investigation. The pIII also has a significant subpopulation of dopaminergic neurons. Because of dopamine’s (DA) role in addiction, it is important to evaluate whether this subpopulation of neurons contributes to addiction‐related phenotypes. Furthermore, the effects of gender on the relationship between Ucn 1 and tyrosine hydroxylase (TH) in pIII and alcohol preference in rats have not been previously assessed. Methods: To address these issues, we compared 2 Sardinian alcohol‐preferring sublines of rats, a population maintained at the Scripps Research Institute (Scr:sP) and a population maintained at University of Camerino—Marchigian Sardinian preferring rats (msP), to corresponding nonselectively bred Wistar rats of both sexes. Ucn 1‐ and TH‐positive cells were detected on coronal midbrain sections from 6‐ to 8‐week‐old alcohol‐naïve animals using brightfield and fluorescent immunohistochemistry. Ucn 1‐ and TH‐positive cells in pIII were counted in the perioculomotor area, averaged across 2 to 3 sets, and binned into 3 bregma levels. Results: Results demonstrated increased average counts of Ucn 1‐positive cells in the middle bregma level in preferring male rats compared to Wistar controls and no difference in TH‐positive cell counts in pIII. In addition, fluorescent double labeling revealed no colocalization of Ucn 1‐positive and TH‐positive neurons. Ucn 1 but not TH distribution was influenced by gender with female animals expressing more Ucn 1‐positive cells than male animals in the peak bregma level. Conclusions: These findings extend previous reports of increased Ucn 1‐positive cell distribution in preferring lines of animals. They indicate that Ucn1 contributes to increased alcohol consumption across different species and that this contribution could be gender specific. The results also suggest that Ucn1 regulates positive reinforcing rather than aversive properties of alcohol and that these effects could be mediated by CRF₂ receptors, independent of direct actions of DA.     

Alcohol intake in prairie voles is influenced by the drinking level of a peer

Background: Peer interactions can have important effects on alcohol‐drinking levels, in some cases increasing use, and in other cases preventing it. In a previous study, we have established the prairie vole as a model animal for the effects of social relationships on alcohol intake and have observed a correlation of alcohol intake between individual voles housed together as pairs. Here, we investigated this correlated drinking behavior, hypothesizing that 1 animal alters its alcohol intake to match the drinking of its partner. Methods: Adult prairie voles were tested for baseline drinking levels with continuous access to 10% alcohol and water for 4 days. In Experiment 1, high alcohol drinkers (>9 g/kg/d) were paired with low alcohol drinkers (<5 g/kg/d) of the same sex on either side of a mesh divider for 4 days with continuous access to the same 2‐bottle choice test. In Experiment 2, high drinkers were paired with high drinkers and low drinkers paired with low drinkers. In both experiments, animals were again separated following pairing, and drinking was retested in isolation. In Experiment 3, alcohol‐naïve animals were tested for saccharin consumption (0.05%) first in isolation and then in high saccharin drinkers paired with low saccharin drinkers, and then in another isolation period. Results: In Experiment 1, high drinkers paired with low drinkers significantly decreased their alcohol intake and preference from baseline drinking in isolation, and drinking levels remained significantly lower during isolation following pairing. Interestingly, there was variability between pairs in whether the high drinker decreased or the low drinker increased intake. In Experiment 2, high drinkers paired with high drinkers did not significantly change their intake level or preference, nor did low drinkers paired with low drinkers, and no changes occurred during the subsequent isolation. In Experiment 3, there was no change in saccharin intake or preference when high drinkers were paired with high drinkers or low paired with low, or in the subsequent isolation. Conclusions: Alcohol drinking of prairie voles can be altered under social conditions, such that 1 animal changes its alcohol intake to more closely match the intake of the other animal, helping to explain previous findings of correlated alcohol drinking. The effect does not extend to saccharin, a naturally rewarding sweet substance. This behavior can be used to model the peer pressure that can often affect alcohol intake in humans.     

Alcohol-naïve alcohol-preferring (P) rats exhibit higher local cerebral glucose utilization than alcohol-nonpreferring (NP) and Wistar rats

Background: The present study determined local cerebral glucose utilization (LCGU) rates in alcohol‐naïve alcohol‐preferring (P), alcohol nonpreferring (NP), and outbred Wistar rats to test the hypothesis that innate differences in functional neuronal activity are present in limbic regions as a result of selective breeding for high‐alcohol drinking behavior. Methods: All procedures were conducted during the dark cycle. 2‐[¹⁴C]deoxyglucose ([¹⁴C]2‐DG; 125 μCi/kg) was injected intravenously and timed arterial blood samples were collected during the following 45 min and assayed for glucose and [¹⁴C]2‐DG content. Rats were then decapitated, the brains removed and frozen to ?70°C, and 20 μm coronal sections were prepared for quantitative autoradiographic analysis. Results: Rates of LCGU were determined in 55 regions and subregions, including limbic, cortical, and subcortical structures. LCGU rates were significantly (p < 0.01) higher in several limbic (e.g., ventral tegmental area, nucleus accumbens shell, olfactory tubercle, medial prefrontal cortex, and lateral hypothalamus), cortical (e.g., parietal, temporal, occipital, cingulate, piriform, and entorhinal), and subcortical (e.g., thalamus, habenula, preoptic area, and striatum) regions in P rats, compared with NP and Wistar rats, whereas rates in Wistar rats were higher in a few regions (e.g., CA1 and CA3 regions of the posterior hippocampus) than NP rats. Conclusions: The data suggest that selective breeding for high‐alcohol drinking produces intrinsically higher functional neuronal activity in the central nervous system regions of the high‐alcohol consuming P line compared with low‐alcohol drinking NP or Wistar rats, although these differences may not generalize to other rat lines selectively bred for divergent alcohol drinking.     

Inverse genetic association between alcohol preference and severity of alcohol withdrawal in two sets of rat lines selected for the same phenotype

Background: The purpose of the present study was to determine whether alcohol‐naïve rats selectively bred for alcohol preference or nonpreference differ in alcohol withdrawal severity using two sets of rat lines selectively bred for the same phenotype. Methods: Alcohol‐naïve male rats from the high alcohol drinking (HAD1) and low alcohol drinking (LAD1) rat lines and from the alcohol preferring (P) and nonpreferring (NP) rat lines received an intragastric infusion of alcohol (4.0 g/20.3 ml/kg; 25% v/v) or an equal volume of water once a day for 10 consecutive days. Alcohol withdrawal severity was assessed at using a behavioral rating scale and a radiant heat assay measured analgesia at 10, 12, 14, 16, 18, and 24 hrs following infusion of alcohol or water on days 1, 5, and 10 of treatment. Results: Data were analyzed using body weight as a co‐factor to correct for differences in body weight between the HAD1/LAD1 and P/NP lines. Acute (1 day) but not repeated alcohol treatment (5 or 10 days) produced mild behavioral signs of withdrawal in LAD1 but not in HAD1 rats. HAD1 and LAD1 rats showed alcohol‐induced analgesia after 1 and 5 days of alcohol treatment that disappeared by day 10 in both lines. Repeated alcohol treatment (5 days) produced mild behavioral signs of withdrawal in NP but not in P rats. Neither P nor NP rats showed alcohol‐induced analgesia after 1, 5, or 10 days of alcohol treatment. Conclusions: An inverse genetic association was found between alcohol preference and severity of alcohol withdrawal in two sets of rat lines selected for the same phenotype. The pattern of alcohol withdrawal that emerged over the course of the 10 days of alcohol treatment differed between the two lines selected for low alcohol drinking (LAD1 and NP), suggesting that unique sets of genes may influence alcohol withdrawal severity in the two lines.     

Increase in Alcohol Intake,Reduced Flexibility of Alcohol Drinking,and Evidence of Signs of Alcohol Intoxication in Sardinian Alcohol‐Preferring Rats Exposed to Intermittent Access to 20% Alcohol

Background: This study assessed in Sardinian alcohol‐preferring (sP) rats a procedure known to promote alcohol drinking and based on the intermittent (once every other day) access to 2 bottles containing alcohol (20%, v/v) and water, respectively (Wise, 1973). Methods: To this end, sP rats were exposed – under the 2‐bottle choice regimen – to: (i) 10% (v/v) alcohol with continuous access (CA10%; i.e., the procedure under which sP rats had been selectively bred); (ii) 10% (v/v) alcohol with intermittent access (IA10%); (iii) 20% (v/v) alcohol with continuous access (CA20%); (iv) 20% (v/v) alcohol with intermittent access (IA20%; the “Wise” condition) (Experiment 1). Additional experiments assessed the influence of (i) adulteration with quinine of the alcohol solution (Experiment 2) and (ii) concurrent presentation of a saccharin solution (Experiment 3) on alcohol drinking under the CA10% and IA20% conditions. Finally, it was assessed whether alcohol drinking under the CA10% and IA20% conditions resulted in motor incoordination at the Rota‐Rod task, as a possible sign of alcohol intoxication (Experiment 4). Results: Daily alcohol intake markedly escalated in rats exposed to the IA20% condition, averaging 9.0 g/kg (in comparison with the average intake of 6.5 g/kg in the CA10% rat group). CA20% and IA10% rats displayed intermediate values of daily alcohol intake between those of CA10% and IA20% rats. Alcohol intake was virtually abolished by addition of quinine or by concurrent presentation of the saccharin solution in CA10% rats; conversely, alcohol intake in IA20% rats was only partially affected by gustatory aversion or concurrent presentation of an alternative reinforcer. Finally, alcohol intake in IA20%, but not in CA10%, rats resulted in clear motor‐incoordinating effects. Conclusions: These data suggest that the “Wise” procedure is effective in inducing marked increases in alcohol intake in sP rats. These increases are associated with a reduced flexibility of alcohol drinking (suggesting the development of “behavioral” dependence) and produce signs of alcohol intoxication that are not detected when sP rats are exposed to the more conventional CA10% condition.     

Effects of measurement methods on the relationship between smoking and delay reward discounting

Aims Delay reward discounting (DRD) measures the degree to which a person prefers smaller rewards soon or larger rewards later. People who smoke have been shown to have higher DRD. There are several ways of measuring DRD, and the method used might influence the association between smoking and DRD. The key differences are the order in which the items are presented, the delays used and the magnitude of the delayed amount. Setting An international online study running from September 2010 to June 2011. Participants A total of 9454 individuals; 38% male, mean age = 23.1 years. Design and measurements Users completed a multi‐item DRD task. They were randomly presented the immediate rewards in an ascending, descending or randomized order. The delays were between 1 week and 5 years. The delayed amounts were $1000 for all delays, and $100 for 1 month. Users also self‐reported their smoking status. Findings A hyperbolic DRD function fitted better than an exponential function. There were differences in the derived DRD function based on methodology used; items presented in a randomized order, longer delays and smaller rewards showed steeper discounting. However, these did not interact with smoking status, as for all methodologies used daily smokers showed the steepest discounting, followed by non‐daily smokers, then non‐smokers. Conclusions Smokers discount future consequences more than non‐smokers, irrespective of which measurement is used, but variations in method lead to different estimates that are not comparable between experiments.