Effects of long-term episodic access to ethanol on the expression of an alcohol deprivation effect in low alcohol-consuming rats

Background: The alcohol‐preferring (P) and ‐nonpreferring (NP) and high alcohol–drinking (HAD) and low alcohol–drinking (LAD) rats have been selectively bred for divergent preference for ethanol over water. In addition, both P and HAD rats display an alcohol deprivation effect (ADE). This study was undertaken to test whether the NP, LAD‐1, and LAD‐2 lines of rats could display an ADE as well. Method: Adult female NP, LAD‐1, and LAD‐2 rats were given concurrent access to multiple concentrations of ethanol [5, 10, 15% (v/v)] and water in an ADE paradigm involving an initial 6 weeks of 24‐hr access to ethanol, followed by four cycles of 2 weeks of deprivation from and 2 weeks of re‐exposure to ethanol (5, 10, and 15%). A control group had continuous access to the ethanol concentrations (5, 10, and 15%) and water through the end of the fourth re‐exposure period. Results: For NP rats, a preference for the highest ethanol concentration (15%) was evident by the end of the fifth week of access (～60% of total ethanol fluid intake). Contrarily, LAD rats did not display a marked preference for any one concentration of ethanol. All three lines displayed an ADE after repeated cycles of re‐exposure to ethanol, with the general ranking of intake being LAD‐1 > NP > LAD‐2 (e.g., for the first day of reinstatement of the third re‐exposure cycle, intakes were 6.5, 2.9, and 2.4 g/kg/day compared with baseline values of 3.1, 2.0, and 1.3 g/kg/day for each line, respectively). By the 13th week, rats from all three lines, with a ranking of LAD‐1 > NP > LAD‐2, were drinking more ethanol (3.3, 2.2, and 2.0 g/kg/day, respectively) compared with their consumption during the first week of access (～1.1 g/kg/day for all three lines). Conclusion: These data indicate that access to multiple concentrations of ethanol and exposure to multiple deprivation cycles can partially overcome a genetic predisposition of NP, LAD‐1, and LAD‐2 rats for low alcohol consumption. In addition, the findings suggest that genetic control of low alcohol consumption in rats is not associated with the inability to display an ADE.     

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.     

Patterns of Ethanol Intake in Preadolescent, Adolescent, and Adult Wistar Rats Under Acquisition, Maintenance, and Relapse-Like Conditions

Background: Animal behavioral models of voluntary ethanol consumption represent a valuable tool to investigate the relationship between age and propensity to consume alcohol using an experimental methodology. Although adolescence has been considered as a critical age, few are the studies that consider the preadolescence age. This study examines the ethanol consumption/preference and the propensity to show an alcohol deprivation effect (ADE) after a short voluntary ethanol exposure from a developmental perspective. Methods: Three groups of heterogeneous Wistar rats of both sexes with ad libitum food and water were exposed for 10 days to 3 ethanol solutions at 3 different ontogenetic periods: preadolescence (PN19), adolescence (PN28), and adulthood (PN90). Ethanol intake (including circadian rhythm), ethanol preference, water and food consumption, and ADE were measured. Results: During the exposure, the 3 groups differed in their ethanol intake; the greatest amount of alcohol (g/kg) was consumed by the preadolescent rats while the adolescents showed a progressive decrease in alcohol consumption as they approached the lowest adult levels by the end of the assessed period. The pattern of ethanol consumption was not fully explained in terms of hyperphagia and/or hyperdipsia at early ages, and showed a wholly circadian rhythm in adolescent rats. After an abstinence period of 7 days, adult rats showed an ADE measured both as an increment in ethanol consumption and preference, whereas adolescent rats only showed an increment in ethanol preference. Preadolescent rats decreased their consumption and their preference remained unchanged. Conclusions: In summary, using a short period of ethanol exposure and a brief deprivation period the results revealed a direct relationship between chronological age and propensity to consume alcohol, being the adolescence a transition period from the infant to the adult pattern of alcohol consumption. Preadolescent animals showed the highest ethanol consumption level. The ADE was only found in adult animals for both alcohol consumption and preference, whereas adolescents showed an ADE only for preference. No effect of sex was detected in any phase of the experiment.     

Development of an alcohol deprivation and escalation effect in C57BL/6J mice

BACKGROUND: Relapse-like drinking has been studied through the expression of the alcohol deprivation effect (ADE), which is measured by a pronounced increase in ethanol preference and consumption after imposed abstinence. No studies have characterized the ADE in C57BL/6J (B6) mice. The present study examined the effects of length and number of deprivations on the expression of the ADE in B6 mice. METHODS: Adult male B6 mice received 24-hour continuous access to ethanol and water for 6 weeks (baseline). Experiment 1 determined the ADE in mice receiving weekly access to 15% ethanol (i.e., exposed 1 day a week and deprived during the other 6 days) for a total of 10 weeks. Experiments 2 and 3 determined the ADE after a single 2-week deprivation period in mice receiving a single concentration of 15% ethanol or multiple concentrations of 7.5, 15, and 30% ethanol, respectively, followed by weekly access to their respective ethanol solutions for 10 weeks. Experiment 4 determined the ADE after a single 2-week deprivation period, followed by daily access to 15% ethanol. Mice never deprived of ethanol (i.e., continuous access) were used as age-matched drinking controls. RESULTS: The ADE was observed after the initial 6-day deprivation period and was profoundly enhanced (i.e., escalation of the ADE) following weekly reexposure to 15% ethanol. Compared with a single concentration of 15% ethanol, concurrent access to multiple ethanol concentrations resulted in a near 2-fold increase in baseline ethanol consumption. Regardless of having access to single or multiple concentrations of ethanol, the ADE was not observed immediately after a 2-week deprivation period. The ADE was observed (although to a lesser magnitude and duration) following weekly reexposure to single or multiple concentrations of ethanol. Alternatively, following a 2-week deprivation period, mice receiving daily access to 15% ethanol showed a significant decrease in ethanol intake and preference (i.e., negative ADE). CONCLUSIONS: Short-term deprivations followed by repeated intermittent (weekly) reexposure to ethanol produces a robust ADE in B6 mice. Increasing the initial deprivation length to 2 weeks produces various opposing effects, including erasure of an initial ADE, diminished expression and magnitude of the ADE following weekly exposure, and complete reversal of the ADE following daily exposure to ethanol.     

The effects of gonadectomy on age- and sex-typical patterns of ethanol consumption in Sprague-Dawley rats

Background: Ethanol intake levels characteristic of adult males and females emerge postpubertally. The present set of experiments examined the consequences of prepubertal and adult gonadectomies to explore whether the presence of gonadal hormones at puberty exerts organizational influences and/or plays an activational role in age‐ and sex‐typical patterns of ethanol consumption. Methods: Male and female Sprague–Dawley rats were gonadectomized (GX), received sham gonadectomy (SH), or were left nonmanipulated (NM) at 1 of 2 ages, either prepubertally on postnatal day (P) 23 (early) or postpubertally in adulthood on P70 (late). Early surgery animals were tested for ethanol consumption either during adolescence (P28 to 39) or in adulthood at the same age that late surgery animals were tested (P75 to 86). Voluntary ethanol consumption was indexed using a 2‐hour limited‐access paradigm, with access to 2 bottles: one containing water and the other a sweetened ethanol solution. Results: Age of GX did not impact patterns of ethanol consumption. Removal of testicular hormones in males, regardless of age of removal, elevated consumption levels in adulthood to female‐typical levels. Ovariectomy did not have notable effects on ethanol drinking in females. Ethanol intake and preference of early SH males were significantly greater than those of both late SH and NM males. Removal of the gonads prior to puberty did not influence ethanol drinking or preference during adolescence in either males or females. Conclusions: These results suggest that testicular hormones play an activational role in lowering ethanol intake and preference of adult male rats. Pubertal hormones, in contrast, were found to exert little influence on ethanol drinking or preference during adolescence, although the effect of surgical manipulation itself during development was found to exert a long‐lasting facilitatory effect on ethanol consumption in adulthood.     

The expression of an alcohol deprivation effect in the high-alcohol-drinking replicate rat lines is dependent on repeated deprivations

BACKGROUND: The alcohol deprivation effect (ADE) is a temporary increase in the ratio of alcohol/total fluid intake and voluntary intake of ethanol (EtOH) solutions over baseline drinking conditions when EtOH access is reinstated after a period of alcohol deprivation. The ADE has been posited to be an animal model for alcohol craving. In the current study, we examined the effects of initial deprivation length and number of deprivation exposures on the ADE in the replicate lines of the high-alcohol-drinking (HAD) rats. METHODS: Adult male HAD-1 and HAD-2 rats received 24 hr free-choice access to 10% (v/v) EtOH and water for 6 weeks. Rats were then assigned to groups deprived of EtOH for 0 (control), or 2 to 8 weeks. All deprived groups were then given 24 hr access to EtOH for 2 weeks before being deprived of EtOH for another 2 weeks. This cycle of 2 weeks of access and 2 weeks of deprivation was carried out for a total of four deprivations. RESULTS: After the initial EtOH deprivation period, EtOH consumption in HAD-1 and HAD-2 rats returned to baseline levels but failed to exhibit either an early onset ADE (initial 2 hr) or prolonged ADE (24 hr). An ADE was observed in two of the four deprived groups for the HAD-1 rats (2 week and 6 week groups) and in all deprived groups for the HAD-2 rats after a second deprivation, and in all deprived groups of both lines after a third deprivation. In the HAD-2 line, but not in the HAD-1 line, the duration of the ADE was prolonged into the second reinstatement day after the fourth deprivation. CONCLUSIONS: The expression of an ADE was observed only after repeated deprivation periods in the HAD lines. The duration of the ADE was prolonged in the HAD-2 line, but not in the HAD-1 line, with repeated deprivations, which suggests a dissociation between selection for alcohol preference and the effects of repeated deprivations on the duration of the ADE.     

Central nervous system mechanisms in alcohol relapse

BACKGROUND: Alcohol relapse is a major problem in the treatment of alcohol abuse and alcoholism. Understanding the long-term neuronal alterations that promote relapse of alcohol drinking is critical for the development of pharmacotherapies to treat alcoholism and alcohol abuse. The major objectives of this workshop were to present recent findings, by using rodent models, on behavioral and neurobiological factors that may underlie alcohol relapse and the results of clinical and pharmacological treatment strategies for preventing relapse. METHODS: Prolonged ethanol drinking and repeated periods of alcohol deprivation were studied in nonselected rats and in rats selectively bred for high alcohol preference (P rat). The expression of a robust alcohol deprivation effect (ADE) was used as a model for alcohol relapse in rodents. Operant techniques were used to examine responding for ethanol after deprivation in both rats and C57BL/6J mice. Environmental cues and stress were used to assess their effects on reinstatement of alcohol responding. Microdialysis and [14C]-2-deoxyglucose techniques were used to examine neuronal alterations associated with alcohol relapse. RESULTS: Prolonged free-choice ethanol drinking followed by deprivation produced an ADE in both stock and P rats. These rats demonstrated loss of control on reinstatement after chronic drinking and after prolonged deprivation. Acamprosate and naltrexone effectively reduced the ADE in stock rats. Stress reinstated operant responding for alcohol, and rats trained to associate a cue with ethanol presentation increased responding on the ethanol-associated lever in the absence of ethanol. After repeated deprivations, P rats shifted their preference toward drinking higher concentrations of ethanol, which increased the magnitude and duration of the ADE. Stock rats also shifted their preference toward solutions with higher ethanol concentrations and demonstrated a loss of control after prolonged ethanol drinking and deprivation. Long-lasting alterations in neuronal activity, serotonin-3 receptor function, and dopamine neurotransmission within the mesolimbic system were evident after chronic drinking that followed a prolonged deprivation period. CONCLUSIONS: The ADE is a useful model for studying alcohol relapse in both rats and mice. The potential validity of this model is supported by the findings that acamprosate and naltrexone are effective in preventing the ADE in rodents, and both compounds have gained recognition for their therapeutic effects in clinical populations. Genetics, stress, and environmental cues are all important factors that influence alcohol relapse. Long-term alterations in neuronal activity within the mesolimbic system, which possibly involve dopamine and serotonin, may underlie alcohol relapse.     

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.     

Effects of alcohol deprivation on alcohol consumption using a sipper-tube procedure

BACKGROUND: When rats with prior experience drinking ethanol solutions are deprived of ethanol for various time periods, a transitory increase in alcohol consumption is observed when ethanol solutions are again made available. This has been termed the alcohol deprivation effect (ADE). The ADE has been observed in limited-access operant procedures in which small dippers of ethanol are presented following completion of a lever press requirement. However, it has not been determined if the effect occurs in an operant model of ethanol self-administration that separates the ethanol-seeking responding from the consummatory drinking (the sipper procedure). METHODS: Rats were initiated to drink ethanol from a sipper tube using the sucrose-substitution procedure. Once initiated, the rats had to make 30 lever presses to gain access to a sipper-tube containing the ethanol solution for 20 min. The effects of 2-3 days, 7 days, and 14 days of ethanol deprivation were examined on ethanol consumption and extinction responding (seeking response). RESULTS: There were no effects of deprivation on intake at any deprivation period examined. Contrary to expectations, the alcohol-seeking response as measured by extinction responding was decreased after 7 and 14 days of deprivation. CONCLUSIONS: The data from this study and others using the limited access operant procedures suggest that the ADE may be more related to consummatory control (i.e., loss of control) and not to ethanol-seeking behaviors (i.e., craving).     

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.     

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.     

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.     

Free-choice alcohol consumption in mice after application of the appetite regulating peptide leptin

BACKGROUND: Leptin has been shown to regulate food intake and energy expenditure. Very recently, associations of elevated leptin plasma levels during alcohol withdrawal with alcohol craving have been observed in humans. Therefore, we tested the hypothesis that the application of exogenous leptin modulates voluntary alcohol consumption in mice. METHODS: Sixteen mice (129/Sv x C57BL/6J) were habituated to ethanol consumption over a time period of 3 months. After a basal 2-week free-choice drinking phase, mice were separated into two groups (n = 8) according to weight and alcohol consumption. They received recombinant leptin (1 mg/kg) versus saline intraperitoneally daily for 10 days. After 4 days of free-choice consumption of ethanol (16% v/v) versus water, ethanol was withdrawn at day 4 and replaced at day 6 to test the occurrence of an alcohol deprivation effects. Fluid intake was evaluated by controlling the weight of the drinking tubes daily. RESULTS: Free-choice ethanol consumption after withdrawal was significantly elevated in mice after intraperitoneal injection of 1 mg/kg leptin (alcohol deprivation effect), but not during basal drinking. CONCLUSION: We suggest that leptin may enhance motivation for alcohol consumption in habituated mice after alcohol withdrawal.     

Persistent escalation of alcohol drinking in C57BL/6J mice with intermittent access to 20% ethanol

Background: Intermittent access (IA) to drugs of abuse, as opposed to continuous access, is hypothesized to induce a kindling‐type transition from moderate to escalated use, leading to dependence. Intermittent 24‐hour cycles of ethanol access and deprivation can generate high levels of voluntary ethanol drinking in rats. Methods: The current study uses C57BL/6J mice (B6) in an IA to 20% ethanol protocol to escalate ethanol drinking levels. Adult male and female B6 mice were given IA to 20% ethanol on alternating days of the week with water available ad libitum. Ethanol consumption during the initial 2 hours of access was compared with a short‐term, limited access “binge” drinking procedure, similar to drinking‐in‐the‐dark (DID). B6 mice were also assessed for ethanol dependence with handling‐induced convulsion, a reliable measure of withdrawal severity. Results: After 3 weeks, male mice given IA to ethanol achieved high stable levels of ethanol drinking in excess of 20 g/kg/24 h, reaching above 100 mg/dl blood ethanol concentrations, and showed a significantly higher ethanol preference than mice given continuous access to ethanol. Also, mice given IA drank about twice as much as DID mice in the initial 2‐hour access period. B6 mice that underwent the IA protocol for longer periods of time displayed more severe signs of alcohol withdrawal. Additionally, female B6 mice were given IA to ethanol and drank significantly more than males (ca. 30 g/kg/24 h). Discussion: The IA method in B6 mice is advantageous because it induces escalated, voluntary, and preferential per os ethanol intake, behavior that may mimic a cardinal feature of human alcohol dependence, though the exact nature and site of ethanol acting in the brain and blood as a result of IA has yet to be determined.     

Role of Fyn tyrosine kinase in ethanol consumption by mice

BACKGROUND: Mice deficient for the intracellular protein Fyn tyrosine kinase (fynZ/fynZ mice) have been reported to show increased alcohol sensitivity and lack of tolerance to the effects of ethanol. To further study the involvement of Fyn in neurobehavioral effects of alcohol, we examined ethanol consumption and relapse drinking behavior in fynZ/fynZ mice. METHODS: FynZ/fynZ and wild-type mice were given a free choice between water and increasing concentrations of ethanol (2-16%). Once a stable baseline of 16% ethanol consumption was established, access to ethanol was withdrawn for 2 weeks and then reinstated, to measure the alcohol deprivation effect (ADE). Forced swim stress was performed thereafter on 2 consecutive days. In a final experiment we studied alcohol sensitivity by measuring ethanol-induced loss of righting reflex (LORR). RESULTS: The concentration of available ethanol had a significant effect on ethanol consumption and preference; however, there was no significant effect of genotype on these measures. Deprivation from ethanol led to a significant increase in ethanol consumption by all mice with no significant impact of genotype on ethanol consumption or water consumption during the ADE. Two consecutive days of forced swim stress led to a significant increase in ethanol consumption; again however, genotype had no effect on stress-associated ethanol consumption. Surprisingly, however, FynZ/fynZ mice showed no differences in alcohol sensitivity when compared to wild-type animals, in contrast to previously reported results ( Miyakawa et al., 1997). CONCLUSIONS: Deletion of the Fyn tyrosine kinase gene may be involved in ethanol sensitivity but this effect may depend on a gene-environment interaction. Fyn does not influence ethanol consumption, neither under basal conditions nor following a deprivation period or stress. This finding indicates that phosphorylation and activation of N-methyl-D-aspartate (NMDA) receptors through Fyn is not a critical mechanism in alcohol drinking or relapse behavior.     

The influence of selection for ethanol withdrawal severity on traits associated with ethanol self-administration and reinforcement

Background: Several meta‐analyses indicate that there is an inverse genetic correlation between ethanol preference drinking and ethanol withdrawal severity, but limited work has characterized ethanol consumption in 1 genetic animal model, the Withdrawal Seizure‐Prone (WSP) and‐Resistant (WSR) mouse lines selected for severe or mild ethanol withdrawal, respectively. Methods: We determined whether line differences existed in: (i) operant self‐administration of ethanol during sucrose fading and under different schedules of reinforcement, followed by extinction and reinstatement of responding with conditioned cues and (ii) home cage drinking of sweetened ethanol and the development of an alcohol deprivation effect (ADE). Results: Withdrawal Seizure‐Prone‐1 mice consumed more ethanol than WSR‐1 mice under a fixed ratio (FR)‐4 schedule as ethanol was faded into the sucrose solution, but this line difference dissipated as the sucrose was faded out to yield an unadulterated 10% v/v ethanol solution. In contrast, WSR‐1 mice consumed more ethanol than WSP‐1 mice when a schedule was imposed that procedurally separated appetitive and consummatory behaviors. After both lines achieved the extinction criterion, reinstatement was serially evaluated following oral ethanol priming, light cue presentation, and a combination of the 2 cues. The light cue produced maximal reinstatement of responding in WSP‐1 mice, whereas the combined cue was required to produce maximal reinstatement of responding in WSR‐1 mice. There was no line difference in the home cage consumption of a sweetened ethanol solution over a period of 1 month. Following a 2‐week period of abstinence, neither line developed an ADE. Conclusions: Although some line differences in ethanol self‐administration and reinstatement were identified between WSP‐1 and WSR‐1 mice, the absence of consistent divergence suggests that the genes underlying these behaviors do not reliably overlap with those that govern withdrawal severity.     

The Alcohol Deprivation Effect in C57BL/6J Mice is Observed Using Operant Self-Administration Procedures and is Modulated by CRF-1 Receptor Signaling

Background: The alcohol deprivation effect (ADE) is characterized by transient excessive alcohol consumption upon reinstatement of ethanol following a period of ethanol deprivation. While this phenomenon has been observed in rats using both bottle drinking (consummatory behavior) and operant self‐administration (consummatory and appetitive “ethanol‐seeking” behavior) procedures, ADE studies in mice have primarily relied on bottle drinking measures. Furthermore, the neurochemical pathways that modulate the ADE are not well understood. Therefore, we determined whether the ADE can be observed in C57BL/6J mice using operant self‐administration procedures and if expression of the ADE is modulated by the corticotropin releasing factor‐1 (CRF‐1) receptor. Methods: C57BL/6J mice were trained in a 2‐hour operant self‐administration paradigm to lever press for 10% ethanol or water on separate response keys. Between operant sessions, mice had access to ethanol in their homecage. Once stable responding occurred, mice were deprived of ethanol for 4 days and were then retested with ethanol in the operant paradigm for 3 consecutive days. Next, to assess the role of the CRF‐1 receptor, mice were given intraperitoneal (i.p.) injection (0, 10, or 20 mg/kg) of the CRF‐1 receptor antagonist CP‐154,526 30 minutes before ADE testing. Additional experiments assessed (i) ADE responding in which the alternate response lever was inactive, (ii) the effects of CP‐154,526 on self‐administration of a 1% sucrose solution following 4 days of deprivation, and (iii) ADE responding in which mice did not received i.p. injections throughout the experiment. Results: Mice exhibited a significant increase in postdeprivation lever responding for ethanol with either a water reinforced or inactive alternate lever. Interestingly, i.p. injection of a 10 mg/kg dose of CP‐154,526 protected against the ADE while not affecting lever responding for a sucrose solution. Finally, baseline and deprivation‐induced increases of ethanol reinforced lever responding were greater in mice not given i.p. injections. Conclusions: The ADE in C57BL/6J mice can be modeled using the operant self‐administration paradigm and increased ethanol self‐administration associated with the ADE is modulated by CRF‐1 receptor signaling.     

Blockade of the leptin-sensitive pathway markedly reduces alcohol consumption in mice

BACKGROUND: The neuropeptide leptin links adipose stores with hypothalamic centers and serves as an endocrine signal involved in the regulation of appetite (and possibly in the endorphinergic modulation of the drug reward system). Increased plasma leptin has been observed at the onset of alcohol withdrawal in humans, and ethanol consumption after withdrawal was increased by injection of leptin in mice. We addressed the role of leptin in alcohol-related behaviors by studying ethanol consumption in two strains of spontaneously mutant mice that lack leptin (ob/ob) or the leptin receptor (db/db). METHODS: Two strains of mutant leptin-deficient (ob/ob) or leptin-resistant (db/db) mice were tested in a two-bottle-choice paradigm and were compared with wild-type (C57BL/6 inbred strain) mice. The effects of leptin injection on voluntary ethanol intake have been investigated in ob/ob and C57BL/6 mice. RESULTS: Males and females of both mutant strains showed a significantly lower preference for alcohol in a two-bottle-choice paradigm compared with wild-type mice. Male ob/ob mice demonstrated slightly higher avoidance of bitter taste, and females of the both mutant strains showed a reduced preference for saccharin solutions. Administration of leptin (1 mg/kg intraperitoneally, daily for 8 days) altered body weight but failed to increase the preference for ethanol in ob/ob mice; i.e., we could not correct the effects of leptin deficiency on alcohol consumption by the injection of leptin. Also, there were no differences between the effects of leptin (1 mg/kg intraperitoneally, daily for 8 days) and saline injections on alcohol consumption in C57BL/6 mice. CONCLUSIONS: These data show that blockade of the leptin pathway markedly decreases the preference for alcohol intake, but this decrease may be the result of compensatory or developmental changes in other systems rather than a more direct effect of leptin on alcohol consumption.     

Effects of concurrent access to multiple ethanol concentrations and repeated deprivations on alcohol intake of alcohol-preferring rats

BACKGROUND: The alcohol deprivation effect (ADE) is a temporary increase in the voluntary intake of ethanol solutions following a period of alcohol deprivation. Multiple deprivations can prolong the expression of an ADE. This study examined the effects of initial deprivation length, concurrent exposure to multiple ethanol concentrations, and number of deprivation exposures on the magnitude and duration of the ADE in alcohol-preferring (P) rats. METHODS: Adult female P rats received 24-hr free-choice access to 10, 20, and 30% ethanol and water for 6 weeks. Rats were then randomly assigned to three groups; one group served as a nondeprived control, whereas the other two groups were initially deprived of ethanol for 2 or 8 weeks. The ethanol solutions were restored to both deprived groups for 2 weeks before the groups were deprived of ethanol for another 2 weeks. This cycle was repeated three times for a total of four deprivations. RESULTS: After the initial ethanol deprivation period, both deprived groups displayed a similar 2-fold increased ethanol intake (g/Kg/day) during the initial 24-hr period when ethanol was restored. Both deprived groups showed greater than 2-fold increases in intake of the 20 and 30% ethanol solutions after re-exposure. Ethanol consumption returned to baseline levels within 2 weeks, before the subsequent deprivation period. Multiple deprivations increased the magnitude of the ADE over that observed in the first deprivation during the initial 24-hr period of re-exposure and prolonged the duration of the ADE. In addition, repeated deprivations increased ethanol intake in the first 2-hr period of re-exposure and produced blood ethanol levels in excess of 150 mg/100 ml. CONCLUSIONS: Alterations in the reinforcing and/or aversive effects of alcohol occurred after a single prolonged deprivation and were enhanced with repeated deprivations.     

Age of onset of drinking and the use of alcohol in adulthood: a follow-up study from age 8-42 for females and males

Aim To investigate longitudinally for both genders the relation between the age of onset of drinking and several indicators of alcohol use. Design and setting In the Finnish Jyväskylä Longitudinal Study of Personality and Social Development, data have been collected by interviews, inventories, and questionnaires. Data on alcohol consumption was gathered at ages 14, 20, 27, 36 and 42 years; behavioural data at age 8. Participants A total of 155 women and 176 men; 90.4% of the original sample consisting of 12 complete school classes in 1968. Measurements The age of onset of drinking was determined based on participants’ responses that were closest to the actual age of onset of drinking. Four indicators of the adult use of alcohol were used: frequency of drinking, binge drinking, Cut‐down, Annoyed, Guilt, Eye‐opener (CAGE) and Malmö modified Michigan Alcoholism Screening Test (Mm‐MAST). Socio‐emotional behaviour at age 8 was assessed using teacher ratings and peer nominations. Findings Early onset of drinking was related to the four indicators of the use of alcohol in adulthood both in men and women. The level of adult alcohol use and alcohol problems was significantly higher in men. The risk for heavy drinking was highest in men and women if drinking was started at less than age 16 years. Socio‐emotional behaviour and school success at age 8 did not predict the age of onset of drinking. Conclusions Delaying the initiation of drinking from early adolescence to late adolescence is an important goal for prevention efforts. No clear risk group for early initiators of drinking could be identified on the basis of preceding behaviour among 8‐year‐olds.