Effects of concurrent access to a single concentration or multiple concentrations of ethanol on the intake of ethanol by male and female periadolescent alcohol-preferring (P) rats

Sex- and age-specific effects on the development of addiction and compulsive-like drinking in rats

BACKGROUND

Biological factors are known to influence disease trajectories and treatment effectiveness in alcohol addiction and preclinical and clinical evidence suggests that sex is an important factor influencing disease dynamics in alcohol dependence. Another critical factor is age at first intoxicating drink, which has been identified as a risk factor for later alcohol binging. Preclinical research allows prospective monitoring of rodents throughout the lifespan, providing very detailed information that cannot be acquired in humans. Lifetime monitoring in rodents can be conducted under highly controlled conditions, during which one can systematically introduce multiple biological and environmental factors that impact behaviors of interest.

METHODS

Here, we used the alcohol deprivation effect (ADE) rat model of alcohol addiction in a computerized drinkometer system, acquiring high-resolution data to study changes over the course of addictive behavior as well as compulsive-like drinking in cohorts of adolescent vs. adult as well as male vs. female rats.

RESULTS

Female rats drank more alcohol than male rats during the whole experiment, drinking much more weak alcohol (5%) and similar amounts of stronger alcohol solutions (10%, 20%); female rats also consumed more alcohol than male rats during quinine taste adulteration. Increased consumption in females compared to males was driven by larger access sizes of alcohol. Differences in circadian patterns of movement were observed between groups. Early age of onset of drinking (postnatal day 40) in male rats had surprisingly little impact on the development of drinking behavior and compulsivity (quinine taste adulteration) when compared to rats that started drinking during early adulthood (postnatal day 72).

CONCLUSIONS

Our results suggest that there are sex-specific drinking patterns, not only in terms of total amount consumed, but specifically in terms of solution preference and access size. These findings provide a better understanding of sex and age factors involved in the development of drinking behavior, and can inform the preclinical development of models of addiction, drug development and exploration of options for new treatments.

Varenicline Reduces Alcohol Intake During Repeated Cycles of Alcohol Reaccess Following Deprivation in Alcohol-Preferring (P) Rats

BACKGROUND

Most alcoholics experience periods of voluntary alcohol abstinence or imposed alcohol deprivation followed by a return to alcohol drinking. This study examined whether varenicline (VAR) reduces alcohol intake during a return to drinking after periods of alcohol deprivation in rats selectively bred for high alcohol drinking (the alcohol preferring or "P" rats).

METHODS

Alcohol-experienced P rats were given 24-hour access to food and water and scheduled access to alcohol (15% and 30% v/v) for 2 h/d. After 4 weeks, rats were deprived of alcohol for 2 weeks, followed by reaccess to alcohol for 2 weeks, and this pattern was repeated for a total of 3 cycles. Rats were fed either vehicle (VEH) or VAR, in doses of 0.5, 1.0, or 2.0 mg/kg BW, at 1 hour prior to onset of the daily alcohol reaccess period for the first 5 days of each of the 3 alcohol reaccess cycles.

RESULTS

Low-dose VAR (0.5 mg/kg BW) reduced alcohol intake during the 5 days of drug treatment in alcohol reaccess cycles 1 and 2. Higher doses of VAR (1.0 mg/kg BW and 2.0 mg/kg BW) reduced alcohol intake during the 5 days of treatment in all 3 alcohol reaccess cycles. The decrease in alcohol intake disappeared with termination of VAR treatment in all alcohol reaccess cycles.

CONCLUSIONS

The results demonstrate that VAR decreases alcohol intake during multiple cycles of alcohol reaccess following alcohol deprivation in rats and suggests that it may prevent a return to heavy alcohol drinking during a lapse from alcohol abstinence in humans with alcohol use disorder.

Rat animal models for screening medications to treat alcohol use disorders

The purpose of this review is to present animal research models that can be used to screen and/or repurpose medications for the treatment of alcohol abuse and dependence. The focus will be on rats and in particular selectively bred rats. Brief introductions discuss various aspects of the clinical picture, which provide characteristics of individuals with alcohol use disorders (AUDs) to model in animals. Following this, multiple selectively bred rat lines will be described and evaluated in the context of animal models used to screen medications to treat AUDs. Next, common behavioral tests for drug efficacy will be discussed particularly as they relate to stages in the addiction cycle. Tables highlighting studies that have tested the effects of compounds using the respective techniques are included. Wherever possible the Tables are organized chronologically in ascending order to describe changes in the focus of research on AUDs over time. In general, high ethanol-consuming selectively bred rats have been used to test a wide range of compounds. Older studies usually followed neurobiological findings in the selected lines that supported an association with a propensity for high ethanol intake. Most of these tests evaluated the compound's effects on the maintenance of ethanol drinking. Very few compounds have been tested during ethanol-seeking and/or relapse and fewer still have assessed their effects during the acquisition of AUDs. Overall, while a substantial number of neurotransmitter and neuromodulatory system targets have been assessed; the roles of sex- and age-of-animal, as well as the acquisition of AUDs, ethanol-seeking and relapse continue to be factors and behaviors needing further study. This article is part of the Special Issue entitled "Alcoholism".

Prazosin Reduces Alcohol Intake in an Animal Model of Alcohol Relapse

BACKGROUND

Many alcoholics and heavy drinkers undergo repeated cycles of alcohol abstinence followed by relapse to alcohol drinking; a pattern that contributes to escalated alcohol intake over time. In rodents, alcohol drinking that is interspersed with periods of alcohol deprivation (imposed abstinence) increases alcohol intake during reaccess to alcohol. This is termed the "alcohol deprivation effect" or "ADE" and is a model of alcohol relapse in humans. We have previously reported that prazosin reduces alcohol drinking during both brief and prolonged treatment in rats selectively bred for alcohol preference ("P" rats). This study explores whether prazosin prevents alcohol "relapse" in P rats, as reflected by a reduced or abolished ADE.

METHODS

Adult male P rats were given 24-hour access to food and water and scheduled access to alcohol (15 and 30% v/v solutions presented concurrently) for 2 h/d. After 5 weeks, rats underwent imposed alcohol deprivation for 2 weeks, followed by alcohol reaccess for 2 weeks, and this pattern was repeated for a total of 3 cycles. Rats were injected with prazosin (0, 0.5, 1.0, or 2.0 mg/kg body weight, intraperitoneally) once a day for the first 5 days of each alcohol reaccess cycle.

RESULTS

Alcohol intake increased on the first day of each alcohol reaccess cycle, demonstrating the formation of an ADE. The ADE was short-lived, lasting only 1 day, during each of the 3 cycles. Prazosin, in all doses tested, prevented the expression of an ADE in all 3 alcohol reaccess cycles.

CONCLUSIONS

Prazosin decreases alcohol intake in P rats even in a situation that would be expected to increase alcohol drinking, namely following periods of alcohol deprivation. This suggests that prazosin may be effective in reducing alcohol relapse that often occurs during attempts to achieve permanent alcohol abstinence in treatment-seeking alcoholics and heavy drinkers.

Effects of ceftriaxone on ethanol, nicotine or sucrose intake by alcohol-preferring (P) rats and its association with GLT-1 expression

Increased glutamatergic neurotransmission appears to mediate the reinforcing properties of drugs of abuse, including ethanol (EtOH). We have shown that administration of ceftriaxone (CEF), a β-lactam antibiotic, reduced EtOH intake and increased glutamate transporter 1 (GLT-1) expression in mesocorticolimbic regions of male and female alcohol-preferring (P) rats. In the present study, we tested whether CEF administration would reduce nicotine (NIC) and/or EtOH intake by adult female P rats. P rats were randomly assigned to 4 groups: (a) 5% sucrose (SUC) or 10% SUC [SUC], (b) 5% SUC+0.07mg/ml NIC and 10% SUC+0.14mg/ml NIC [NIC-SUC], 15% EtOH and 30% EtOH [EtOH] and (d) 15% EtOH+0.07mg/ml NIC and 30% EtOH+0.14mg/ml NIC [NIC-EtOH]. After achieving stable intakes (4weeks), the rats were administered 7 consecutive, daily i.p. injections of either saline or 200mg/kg CEF. The effects of CEF on intake were significant but differed across the reinforcers; such that ml/kg/day SUC was reduced by ∼30%, mg/kg/day NIC was reduced by ∼70% in the NIC-SUC group and ∼40% in the EtOH-NIC group, whereas g/kg/day EtOH was reduced by ∼40% in both the EtOH and EtOH-NIC group. The effects of CEF on GLT-1 expression were also studied. We found that CEF significantly increased GLT-1 expression in the prefrontal cortex and the nucleus accumbens of the NIC and NIC-EtOH rats as compared to NIC and NIC-EtOH saline-treated rats. These findings provide further support for GLT-1-associated mechanisms in EtOH and/or NIC abuse. The present results along with previous reports of CEF's efficacy in reducing cocaine self-administration in rats suggest that modulation of GLT-1 expression and/or activity is an important pharmacological target for treating polysubstance abuse and dependence.

The reinforcing properties of ethanol are quantitatively enhanced in adulthood by peri-adolescent ethanol, but not saccharin, consumption in female alcohol-preferring (P) rats

Alcohol drinking during adolescence is associated in adulthood with heavier alcohol drinking and an increased rate of alcohol dependence. Past research in our laboratory has indicated that peri-adolescent ethanol consumption can enhance the acquisition and reduce the rate of extinction of ethanol self-administration in adulthood. Caveats of the past research include reinforcer specificity, increased oral consumption during peri-adolescence, and a lack of quantitative assessment of the reinforcing properties of ethanol. The current experiments were designed to determine the effects of peri-adolescent ethanol or saccharin drinking on acquisition and extinction of oral ethanol self-administration and ethanol seeking, and to quantitatively assess the reinforcing properties of ethanol (progressive ratio). Ethanol or saccharin access by alcohol-preferring (P) rats occurred during postnatal day (PND) 30-60. Animals began operant self-administration of ethanol or saccharin after PND 85. After 10 weeks of daily operant self-administration, rats were tested in a progressive ratio paradigm. Two weeks later, self-administration was extinguished in all rats. Peri-adolescent ethanol consumption specifically enhanced the acquisition of ethanol self-administration, reduced the rate of extinction for ethanol self-administration, and quantitatively increased the reinforcing properties of ethanol during adulthood. Peri-adolescent saccharin consumption was without effect. The data indicate that ethanol consumption during peri-adolescence results in neuroadaptations that may specifically enhance the reinforcing properties of ethanol during adulthood. This increase in the reinforcing properties of ethanol could be a part of biological sequelae that are the basis for the effects of adolescent alcohol consumption on the increase in the rate of alcoholism during adulthood.

Alcohol preferring (P) rats as a model for examining sex differences in alcohol use disorder and its treatment

RATIONALE

Despite epidemiological and clinical data indicating marked gender differences in alcohol use disorders (AUDs), few preclinical studies have examined sex differences in animal models of AUDs.

OBJECTIVE

The purpose of this study was to first characterize sex differences in ethanol consumption and reinforcement in an alcohol preferring (P) rat model of alcoholism, then use this model to screen pharmacological treatments for sex-specific effects.

METHODS

Ethanol consumption was first assessed in male and female P rats under a three-bottle free-choice procedure. Next, ethanol's reinforcing effects were assessed under a fixed-ratio 1 (FR1) schedule followed by a progressive-ratio (PR) schedule. Finally, the effects of two pharmacological treatments for AUDs, naltrexone (1mg/kg) and topiramate (10 or 20mg/kg), alone and in combination, were tested for sex-specific differences in their efficacy at reducing ethanol's reinforcing effects.

RESULTS

Although females initially had higher consumption of and preference for ethanol, male rats increased their consumption and preference over time and rapidly became equal to females. Following prolonged 24-hour/day access, males and females self-administered similar levels of ethanol under FR1 and PR schedules. In response to pharmacological treatment, we observed some sex differences and similarities, most notably, a more robust effect of the combination of naltrexone and topiramate in males as compared to females.

CONCLUSIONS

This model of selectively bred P rats may be useful for understanding sex differences in AUDs and related behavior and their underlying neurobiological mechanisms and treatment.

A snapshot of the hepatic transcriptome: ad libitum alcohol intake suppresses expression of cholesterol synthesis genes in alcohol-preferring (P) rats

Research is uncovering the genetic and biochemical effects of consuming large quantities of alcohol. One prime example is the J- or U-shaped relationship between the levels of alcohol consumption and the risk of atherosclerotic cardiovascular disease. Moderate alcohol consumption in humans (about 30 g ethanol/d) is associated with reduced risk of coronary heart disease, while abstinence and heavier alcohol intake is linked to increased risk. However, the hepatic consequences of moderate alcohol drinking are largely unknown. Previous data from alcohol-preferring (P) rats showed that chronic consumption does not produce significant hepatic steatosis in this well-established model. Therefore, free-choice alcohol drinking in P rats may mimic low risk or nonhazardous drinking in humans, and chronic exposure in P animals can illuminate the molecular underpinnings of free-choice drinking in the liver. To address this gap, we captured the global, steady-state liver transcriptome following a 23 week free-choice, moderate alcohol consumption regimen (∼ 7.43 g ethanol/kg/day) in inbred alcohol-preferring (iP10a) rats. Chronic consumption led to down-regulation of nine genes in the cholesterol biosynthesis pathway, including HMG-CoA reductase, the rate-limiting step for cholesterol synthesis. These findings corroborate our phenotypic analyses, which indicate that this paradigm produced animals whose hepatic triglyceride levels, cholesterol levels and liver histology were indistinguishable from controls. These findings explain, at least in part, the J- or U-shaped relationship between cardiovascular risk and alcohol intake, and provide outstanding candidates for future studies aimed at understanding the mechanisms that underlie the salutary cardiovascular benefits of chronic low risk and nonhazardous alcohol intake.

Circadian activity rhythms and voluntary ethanol intake in male and female ethanol-preferring rats: effects of long-term ethanol access

Chronic alcohol (ethanol) intake alters fundamental properties of the circadian clock. While previous studies have reported significant alterations in free-running circadian period during chronic ethanol access, these effects are typically subtle and appear to require high levels of intake. In the present study we examined the effects of long-term voluntary ethanol intake on ethanol consumption and free-running circadian period in male and female, selectively bred ethanol-preferring P and HAD2 rats. In light of previous reports that intermittent access can result in escalated ethanol intake, an initial 2-week water-only baseline was followed by either continuous or intermittent ethanol access (i.e., alternating 15-day epochs of ethanol access and ethanol deprivation) in separate groups of rats. Thus, animals were exposed to either 135 days of continuous ethanol access or to five 15-day access periods alternating with four 15-day periods of ethanol deprivation. Animals were maintained individually in running-wheel cages under continuous darkness throughout the experiment to allow monitoring of free-running activity and drinking rhythms, and 10% (v/v) ethanol and plain water were available continuously via separate drinking tubes during ethanol access. While there were no initial sex differences in ethanol drinking, ethanol preference increased progressively in male P and HAD2 rats under both continuous and intermittent-access conditions, and eventually exceeded that seen in females. Free-running period shortened during the initial ethanol-access epoch in all groups, but the persistence of this effect showed complex dependence on sex, breeding line, and ethanol-access schedule. Finally, while females of both breeding lines displayed higher levels of locomotor activity than males, there was little evidence for modulation of activity level by ethanol access. These results are consistent with previous findings that chronic ethanol intake alters free-running circadian period, and show further that the development of chronobiological tolerance to ethanol may vary by sex and genotype.

Reinforcing properties and neurochemical response of ethanol within the posterior ventral tegmental area are enhanced in adulthood by periadolescent ethanol consumption

Alcohol drinking during adolescence is associated with increased alcohol drinking and alcohol dependence in adulthood. Research examining the biologic consequences of adolescent ethanol (EtOH) consumption on the response to EtOH in the neurocircuitry shown to regulate drug reinforcement is limited. The experiments were designed to determine the effects of periadolescent alcohol drinking on the reinforcing properties of EtOH within the posterior ventral tegmental area (pVTA) and the ability of EtOH microinjected into the pVTA to stimulate dopamine (DA) release in the nucleus accumbens shell (AcbSh). EtOH access (24-hour free-choice) by alcohol-preferring rats occurred during postnatal days (PND) 30-60. Animals were tested for their response to EtOH after PND 85. Intracranial self-administration techniques were performed to assess EtOH self-infusion into the pVTA. In the second experiment, rats received microinjections of EtOH into the pVTA, and dialysis samples were collected from the AcbSh. The results indicate that in rats that consumed EtOH during adolescence, the pVTA was more sensitive to the reinforcing effects of EtOH (a lower concentration of EtOH supported self-administration) and the ability of EtOH microinjected into the pVTA to stimulate DA release in the AcbSh was enhanced (sensitivity and magnitude). The data indicate that EtOH consumption during adolescence altered the mesolimbic DA system to be more sensitive and responsive to EtOH. This increase in the response to EtOH within the mesolimbic DA during adulthood could be part of biologic sequelae that are the basis for the deleterious effects of adolescent alcohol consumption on the rate of alcoholism during adulthood.

Chronic ethanol exposure during adolescence in rats induces motor impairments and cerebral cortex damage associated with oxidative stress

Binge drinking is common among adolescents, and this type of ethanol exposure may lead to long-term nervous system damage. In the current study, we evaluated motor performance and tissue alterations in the cerebral cortex of rats subjected to intermittent intoxication with ethanol from adolescence to adulthood. Adolescent male Wistar rats (35 days old) were treated with distilled water or ethanol (6.5 g/kg/day, 22.5% w/v) during 55 days by gavage to complete 90 days of age. The open field, inclined plane and the rotarod tests were used to assess the spontaneous locomotor activity and motor coordination performance in adult animals. Following completion of behavioral tests, half of animals were submitted to immunohistochemical evaluation of NeuN (marker of neuronal bodies), GFAP (a marker of astrocytes) and Iba1 (microglia marker) in the cerebral cortex while the other half of the animals were subjected to analysis of oxidative stress markers by biochemical assays. Chronic ethanol intoxication in rats from adolescence to adulthood induced significant motor deficits including impaired spontaneous locomotion, coordination and muscle strength. These behavioral impairments were accompanied by marked changes in all cellular populations evaluated as well as increased levels of nitrite and lipid peroxidation in the cerebral cortex. These findings indicate that continuous ethanol intoxication from adolescence to adulthood is able to provide neurobehavioral and neurodegenerative damage to cerebral cortex.

High alcohol intake in female Sardinian alcohol-preferring rats

Sardinian alcohol-preferring (sP) rats have been selectively bred for high alcohol preference and consumption. When exposed to the standard, home cage 2-bottle "alcohol (10%, v/v) vs. water" choice regimen with continuous access, male sP rats consume daily approximately 6 g/kg alcohol. Conversely, when exposed to the intermittent (once every other day) access to 2 bottles containing alcohol (20%, v/v) and water, respectively, male sP rats display marked increases in daily alcohol intake and signs of alcohol intoxication and "behavioral" dependence. The present study was designed to assess alcohol intake in female sP rats exposed, under the 2-bottle choice regimen, to (a) 10% (v/v) alcohol with continuous access (CA10%), (b) 10% (v/v) alcohol with intermittent access (IA10%), (c) 20% (v/v) alcohol with continuous access (CA20%), and (d) 20% (v/v) alcohol with intermittent access (IA20%). Male sP rats (exposed to CA10% and IA20% conditions) were included for comparison. Over 20 daily drinking sessions, daily alcohol intake in female CA10% and IA20% rats averaged 7.0 and 9.6 g/kg, respectively. The rank of alcohol intake was IA20% > IA10% = CA20% > CA10%. Conversely, daily alcohol intake in male CA10% and IA20% rats averaged 6.0 and 8.2 g/kg, respectively. Comparison of female and male rats yielded the following rank of alcohol intake: female IA20% > male IA20% > female CA10% ≥ male CA10%. An additional experiment found that alcohol drinking during the first hour of the drinking session produced mean blood alcohol levels of 35-40 mg% and 85-100 mg% in the CA10% and IA20% rats, respectively. These results (a) extend to female sP rats previous data demonstrating the capacity of the IA20% condition to markedly escalate alcohol drinking, and (b) demonstrate that female sP rats consume more alcohol than male sP rats. This sex difference is more evident under the IA20% condition, suggesting that female sP rats are highly sensitive to the promoting effect of the IA20% condition on alcohol drinking. These data contribute to the characterization of sP rats as a model of excessive alcohol consumption.

The alcohol-preferring (P) and high-alcohol-drinking (HAD) rats--animal models of alcoholism

The objective of this article is to review the literature on the utility of using the selectively bred alcohol-preferring (P) and high-alcohol-drinking (HAD) lines of rats in studies examining high alcohol drinking in adults and adolescents, craving-like behavior, and the co-abuse of alcohol with other drugs. The P line of rats meets all of the originally proposed criteria for a suitable animal model of alcoholism. In addition, the P rat exhibits high alcohol-seeking behavior, demonstrates an alcohol deprivation effect (ADE) under relapse drinking conditions, consumes amounts of ethanol during adolescence equivalent to those consumed in adulthood, and co-abuses ethanol and nicotine. The P line also exhibits excessive binge-like alcohol drinking, attaining blood alcohol concentrations (BACs) of 200 mg% on a daily basis. The HAD replicate lines of rats have not been as extensively studied as the P rats. The HAD1,2 rats satisfy several of the criteria for an animal model of alcoholism, e.g., these rats will voluntarily consume ethanol in a free-choice situation to produce BACs between 50 and 200 mg%. The HAD1,2 rats also exhibit an ADE under repeated relapse conditions, and will demonstrate similar levels of ethanol intake during adolescence as seen in adults. Overall, the P and HAD1,2 rats have characteristics attributed to an early onset alcoholic, and can be used to study various aspects of alcohol use disorders.

Scheduled access alcohol drinking by alcohol-preferring (P) and high-alcohol-drinking (HAD) rats: modeling adolescent and adult binge-like drinking

Binge alcohol drinking continues to be a public health concern among today's youth and young adults. Moreover, an early onset of alcohol use, which usually takes the form of binge drinking, is associated with a greater risk for developing alcohol use disorders. Given this, it is important to examine this behavior in rat models of alcohol abuse and dependence. Toward that end, the objective of this article is to review findings on binge-like drinking by selectively bred alcohol-preferring (P) and high-alcohol-drinking (HAD) lines of rats. As reviewed elsewhere in this special issue, the P line meets all, and the HAD line meets most, of the proposed criteria for an animal model of alcoholism. One model of binge drinking is scheduled ethanol access during the dark cycle, which has been used by our laboratory for over 20 years. Our laboratory has also adopted a protocol involving the concurrent presentation of multiple ethanol concentrations. When this protocol is combined with limited access, ethanol intake is maximized yielding blood ethanol levels (BELs) in excess, sometimes greatly in excess, of 80 mg%. By extending these procedures to include multiple scheduled ethanol access sessions during the dark cycle for 5 consecutive days/week, P and HAD rats consume in 3 or 4 h as much as, if not more than, the amount usually consumed in a 24 h period. Under certain conditions, using the multiple scheduled access procedure, BELs exceeding 200 mg% can be achieved on a daily basis. An overview of findings from studies with other selectively bred, inbred, and outbred rats places these findings in the context of the existing literature. Overall, the findings support the use of P and HAD rats as animal models to study binge-like alcohol drinking and reveal that scheduled access procedures will significantly increase ethanol intake by other rat lines and strains as well.

Therapeutic and prophylactic ethanol lock therapy in patients with bleeding disorders

Obtaining a reliable venous access is a limiting factor for early initiation of clotting factor prophylaxis and immune tolerance induction. To circumvent this issue, central venous access devices (CVADs) are increasingly being used. Catheter-related infections (CRIs) remain the primary complication of insertion of CVAD. Thus, newer strategies for treatment and prevention of CRI are needed. Ethanol lock therapy (ELT) has been used to treat and prevent CRI in non-bleeding disorder patients. The aim of this study was to assess the efficacy of ELT in treating and preventing CRI in bleeding disorder patients. The medical charts of patients with bleeding disorders who underwent ELT for antimicrobial resistant CRIs were reviewed and data were analysed. ELT was effective in catheter salvage in 87% of patients with antimicrobial resistant CRI by a wide variety of pathogens. Prophylactic therapy with ethanol lock was associated with catheter dysfunction especially in mediports. ELT should be considered prior to removal of catheters in bleeding disorder patients with resistant CRIs. Further studies are needed for using prophylactic ethanol lock in prevention of CRIs in bleeding disorder patients.

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

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

A mouse model for adolescent alcohol abuse: stunted growth and effects in brain

BACKGROUND

Adolescent alcohol abuse remains a serious public health concern, with nearly a third of high school seniors reporting heavy drinking in the previous month.

METHODS

Using the high ethanol-consuming C57BL/6J mouse strain, we examined the effects of ethanol (3.75 g/kg, IP, daily for 45 days) on body weight and brain region mass (cerebral cortex, cerebellum, corpus callosum) during peri-adolescence (postnatal day [P]25 to 70) or adulthood (P180 to 225) of both males and females.

RESULTS

In control peri-adolescent animals, body weight gain was greater in males compared with females. In the peri-adolescent exposure group, ethanol significantly reduced body weight gain to a similar extent in both male and female mice (82 and 84% of controls, respectively). In adult animals, body weight gain was much less than that of the peri-adolescent mice, with ethanol having a small but significant effect in males but not females. Between the control peri-adolescent and adult cohorts (measurements taken at P70 and 225, respectively), there were no significant differences in the mass of the cerebral cortex or the cerebellum from either male or female mice, although the rostro-caudal length of the corpus callosum increased slightly but significantly (6.1%) between these time points.

CONCLUSIONS

Ethanol treatment significantly reduced the mass of the cerebral cortex in peri-adolescent (-3.1%), but not adult, treated mice. By contrast, ethanol significantly reduced the length of the corpus callosum in adult (-5.4%), but not peri-adolescent, treated mice. Future studies at the histological level may yield additional details concerning ethanol and the peri-adolescent brain.

Ethanol locks to prevent catheter-related bloodstream infections in parenteral nutrition: a meta-analysis

OBJECTIVE

Patients with pediatric intestinal failure (IF) depend on parenteral nutrition for growth and survival, but are at risk for complications, such as catheter-related bloodstream infections (CRBSIs). CRBSI prevention is crucial, as sepsis is an important cause of IF-associated liver disease and mortality. We aim to estimate the pooled effectiveness and safety of ethanol locks (ELs) in comparison with heparin locks (HLs) with regard to CRBSI rate and catheter replacements for pediatric IF patients with chronic parenteral nutrition dependence.

METHODS

A systematic review without language restriction was performed on Medline (1948-2010), Embase (1980-2010), and conference programs and trial registries up to December 2010. Search terms included "Catheter-Related Infections," "Catheter," "Catheters, Indwelling," "alcohol," "ethanol," and "lock." Two authors identified 4 retrospective studies for the pediatric IF population. Double, independent data extraction using predefined data fields and risk of bias assessment (Newcastle-Ottawa scale) was performed.

RESULTS

In comparison with HLs, ELs reduced the CRBSI-rate per 1000 catheter days by 7.67 events and catheter replacements by 5.07. EL therapy decreased the CRBSI rate by 81% and replacements by 72%. One hundred eight to 150 catheter days of EL exposure were necessary to prevent 1 CRBSI and 122 to 689 days of exposure avoided 1 catheter replacement. Adverse events were rare and included thrombotic events.

CONCLUSIONS

In pediatric patients with IF, EL is a more effective alternative to HL. Adverse events include thrombotic events.

Modeling binge-like ethanol drinking by peri-adolescent and adult P rats

Alcohol binge-drinking, especially among adolescents and young adults, is a serious public health concern. The present study examined ethanol binge-like drinking by peri-adolescent [postnatal days (PNDs 30-72)] and adult (PNDs 90-132) alcohol-preferring (P) rats with a drinking-in-the-dark-multiple-scheduled-access (DID-MSA) procedure used by our laboratory. Male and female P rats were provided concurrent access to 15% and 30% ethanol for three 1-h sessions across the dark cycle 5 days/week. For the 1st week, adolescent and adult female P rats consumed 3.4 and 1.6g/kg of ethanol, respectively, during the 1st hour of access, whereas for male rats the values were 3.5 and 1.1g/kg of ethanol, respectively. Adult intakes increased to ~2.0 g/kg/h and adolescent intakes decreased to ~2.5 g/kg/h across the 6 weeks of ethanol access. The daily ethanol intake of adult DID-MSA rats approximated or modestly exceeded that seen in continuous access (CA) rats or the selection criterion for P rats (≥5 g/kg/day). However, in general, the daily ethanol intake of DID-MSA peri-adolescent rats significantly exceeded that of their CA counterparts. BELs were assessed at 15-min intervals across the 3rd hour of access during the 4th week. Ethanol intake was 1.7 g/kg vs. 2.7 g/kg and BELs were 57 mg% vs. 100mg% at 15- and 60-min, respectively. Intoxication induced by DID-MSA in female P rats was assessed during the 1st vs. 4th week of ethanol access. Level of impairment did not differ between the 2 weeks (106 vs. 97 s latency to fall, 120 s criterion) and was significant (vs. naïve controls) only during the 4th week. Overall, these findings support the use of the DID-MSA procedure in rats, and underscore the presence of age- and sex-dependent effects mediating ethanol binge-like drinking in P rats.

The emergence of gonadal hormone influences on dopaminergic function during puberty

Adolescence is the developmental epoch during which children become adults-intellectually, physically, hormonally and socially. Brain development in critical areas is ongoing. Adolescents are risk-taking and novelty-seeking and they weigh positive experiences more heavily and negative experiences less than adults. This inherent behavioral bias can lead to risky behaviors like drug taking. Most drug addictions start during adolescence and early drug-taking is associated with an increased rate of drug abuse and dependence. The hormonal changes of puberty contribute to physical, emotional, intellectual and social changes during adolescence. These hormonal events do not just cause maturation of reproductive function and the emergence of secondary sex characteristics. They contribute to the appearance of sex differences in non-reproductive behaviors as well. Sex differences in drug use behaviors are among the latter. The male predominance in overall drug use appears by the end of adolescence, while girls develop the rapid progression from first use to dependence (telescoping) that represent a female-biased vulnerability. Sex differences in many behaviors including drug use have been attributed to social and cultural factors. A narrowing gap in drug use between adolescent boys and girls supports this thesis. However, some sex differences in addiction vulnerability reflect biologic differences in brain circuits involved in addiction. The purpose of this review is to summarize the contribution of sex differences in the function of ascending dopamine systems that are critical to reinforcement, to briefly summarize the behavioral, neurochemical and anatomical changes in brain dopaminergic functions related to addiction that occur during adolescence and to present new findings about the emergence of sex differences in dopaminergic function during adolescence.

Effects of repeated light-dark phase shifts on voluntary ethanol and water intake in male and female Fischer and Lewis rats

Several lines of evidence implicate reciprocal interactions between excessive alcohol (ethanol) intake and dysregulation of circadian biological rhythms. Thus, chronic alcohol intake leads to widespread circadian disruption in both humans and experimental animals, while in turn, chronobiological disruption has been hypothesized to promote or sustain excessive alcohol intake. Nevertheless, the effects of circadian disruption on voluntary ethanol intake have not been investigated extensively, and prior studies have reported both increased and decreased ethanol intake in rats maintained under "shift-lag" lighting regimens mimicking those experienced by shift workers and transmeridian travelers. In the present study, male and female inbred Fischer and Lewis rats were housed in running wheel cages with continuous free-choice access to both water and 10% (vol/vol) ethanol solution and exposed to repeated 6-h phase advances of the daily light-dark (LD) cycle, whereas controls were kept under standard LD 12:12 conditions. Shift-lag lighting reduced overall ethanol and water intake, and reduced ethanol preference in Fischer rats. Although contrary to the hypothesis that circadian disruption would increase voluntary ethanol intake, these results are consistent with our previous report of reduced ethanol intake in selectively bred high-alcohol-drinking (HAD1) rats housed under a similar lighting regimen. We conclude that chronic circadian disruption is a form of chronobiological stressor that, like other stressors, can either increase or decrease ethanol intake, depending on a variety of poorly understood variables.

Contribution of early environmental stress to alcoholism vulnerability

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

Long-term risk preference and suboptimal decision making following adolescent alcohol use

Individuals who abused alcohol at an early age show decision-making impairments. However, the question of whether maladaptive choice constitutes a predisposing factor to, or a consequence resulting from, alcohol exposure remains open. To examine whether a causal link exists between voluntary alcohol consumption during adolescence and adult decision making the present studies used a rodent model. High levels of voluntary alcohol intake were promoted by providing adolescent rats with access to alcohol in a palatable gel matrix under nondeprivation conditions. A probability-discounting instrumental response task offered a choice between large but uncertain rewards and small but certain rewards to assess risk-based choice in adulthood either 3 weeks or 3 months following alcohol exposure. While control animals' performance on this task closely conformed to a predictive model of risk-neutral value matching, rats that consumed high levels of alcohol during adolescence violated this model, demonstrating greater risk preference. Evidence of significant risk bias was still present when choice was assessed 3 months following discontinuation of alcohol access. These findings provide evidence that adolescent alcohol exposure may lead to altered decision making during adulthood and this model offers a promising approach to the investigation of the neurobiological underpinnings of this link.

Differential effects of chronic ethanol consumption and withdrawal on homer/glutamate receptor expression in subregions of the accumbens and amygdala of P rats

BACKGROUND

Homer proteins are constituents of scaffolding complexes that regulate the trafficking and function of central Group1 metabotropic glutamate receptors (mGluRs) and N-methyl-d-aspartate (NMDA) receptors. Research supports the involvement of these proteins in ethanol-induced neuroplasticity in mouse. In this study, we examined the effects of short versus long-term withdrawal from chronic ethanol consumption on Homer and glutamate receptor protein expression within striatal and amygdala subregions of selectively bred, alcohol-preferring P rats.

METHODS

For 6 months, male P rats had concurrent access to 15% and 30% ethanol solutions under intermittent (IA: 4 d/wk) or continuous (CA: 7 d/wk) access conditions in their home cage. Rats were killed 24 hours (short withdrawal: SW) or 4 weeks (long withdrawal: LW) after termination of ethanol access, subregions of interest were micropunched and tissue processed for detection of Group1 mGluRs, NR2 subunits of the NMDA receptor and Homer protein expression.

RESULTS

Within the nucleus accumbens (NAC), limited changes in NR2a and NR2b expression were detected in the shell (NACsh), whereas substantial changes were observed for Homer2a/b, mGluRs as well as NR2a and NR2b subunits in the core (NACc). Within the amygdala, no changes were detected in the basolateral subregion, whereas substantial changes, many paralleling those observed in the NACc, were detected in the central nucleus (CeA) subregion. In addition, most of the changes observed in the CeA, but not NACc, were present in both SW and LW rats.

CONCLUSIONS

Overall, these subregion specific, ethanol-induced increases in mGluR/Homer2/NR2 expression within the NAC and amygdala suggest changes in glutamatergic plasticity had taken place. This may be a result of learning and subsequent memory formation of ethanol's rewarding effects in these brain structures, which may, in part, mediate the chronic relapsing nature of alcohol abuse.

Decreased sensitivity to ethanol reward in adolescent mice as measured by conditioned place preference

BACKGROUND

Many preclinical studies have demonstrated age-related differential sensitivity to various effects of ethanol between adolescent and adult animals. However, published data addressing possible differences in ethanol's motivational effects are sparse, particularly in mice. The present study examined age-related differences in the conditioned rewarding effects of ethanol in DBA/2J mice.

METHODS

In the first experiment an unbiased place conditioning procedure was used to determine the rewarding effects of 2 g/kg ethanol in adult and adolescent DBA/2J mice. In a subsequent place conditioning experiment, the effects of 2 and 4 g/kg were assessed in adolescent mice.

RESULTS

Adolescents demonstrated a place preference with the high dose of 4 g/kg but not with a more moderate dose of 2 g/kg. In contrast, 2 g/kg was sufficient to produce place preference in adult mice.

CONCLUSIONS

Adolescents are less sensitive than adults to the rewarding effects of ethanol but can experience reward with high doses. These results extend the current literature on ethanol's effects in adolescent animals.

Effects of different concentrations of sugarcane alcohol on food intake and nutritional status of male and female periadolescent rats

The present study evaluated the effects of food and alcohol intake on the nutritional and metabolic status of male and female periadolescent rats submitted to single (15%) and multiple (10%, 20%, 30%) concentrations of hydroalcoholic solutions of sugar-based alcohol associated with a feed mixture. Thirty-six periadolescent Wistar rats were used and randomly arranged into three groups: Group A (control; 0% ethanol; six males and six females), Group B (15% ethanol; six males and six females), and Group C (10%, 20%, and 30% ethanol; six males and six females). Food consumption, body weight, water intake (mL), ethanol intake (g/kg/day), ethanol preference in relation to water and different concentrations, and serum biochemical dosages (glucose, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein (HDL) cholesterol, very low-density lipoprotein fraction, triglycerides, cholesterol/HDL [CT/HDL], albumin) were analyzed. Males from Group C ingested more feed than females, which consumed reducing amounts throughout the weeks studied. Males also had heavier body weight, which increased throughout the experimental period. The animals ingested more water (females ingested more than males) in the first experimental week. Group C had a higher ethanol intake and greater preference for ethanol over water in both genders than Group B, which decreased over the subsequent weeks. Serum glucose was lower in Group A, whereas the CT/HDL ratio was lower in Group C. These findings allow the conclusion that nutritional and metabolic impact resulting from alcohol intake is different between genders and between the different forms in which the drug is offered. It is important to warn the population about the concentrations of alcohol intake, which may influence the growth and development of adolescents, thereby compromising their quality of life.

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.

Autonomic activation associated with ethanol self-administration in adult female P rats

The present study examined changes in heart rate (HR) prior to and during limited access ethanol drinking in adult female P rats. P rats were implanted with radio-telemetric transmitters to measure HR. Daily testing involved a 90-min pre-test period (water only available) and a subsequent 90-min test period [either water (W) or ethanol available]. After a week of habituation, one ethanol group had access to ethanol for 7 weeks (CE), and another ethanol group had access for 4 weeks, was deprived for 2 weeks and then had access for a final week (DEP). Analyses of HR revealed that CE and DEP rats had significantly higher HR than W rats during test periods that ethanol was present and that DEP rats displayed higher HR during the early test period of the ethanol deprivation interval, as well. These data indicate that ethanol drinking induces HR activation in adult female P rats, and that this activation can be conditioned to the test cage environment, paralleling reports on contextual conditioning and cue-reactivity in alcoholics exposed to alcohol-associated stimuli. Therefore, this behavioral test may prove advantageous in screening pharmacotherapies for reducing craving and relapse, which are associated with cue-reactivity in abstinent alcoholics.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effects of short deprivation and re-exposure intervals on the ethanol drinking behavior of selectively bred high alcohol-consuming rats

Alcoholics generally display cycles of excessive ethanol intake, abstinence and relapse behavior. Using an animal model of relapse-like drinking, the alcohol deprivation effect (ADE), our laboratory has shown that repeated 2-week cycles of ethanol deprivation and re-exposure, following an initial 6-week access period, result in a robust ADE by alcohol-preferring (P) and high alcohol-drinking (HAD-1 and HAD-2) rats. These rat lines have been selectively bred to prefer a 10% ethanol solution over water. The present study examined whether P and HAD rats would display an ADE using much shorter ethanol deprivation and re-exposure intervals. Rats were given either continuous or periodic concurrent access to multiple concentrations (10%, 20%, and 30% [vol/vol]) of ethanol. The periodic protocol involved access to ethanol for 12 days followed by four cycles of 4 days of deprivation and 4 days of re-exposure to ethanol access. High-alcohol-drinking rats displayed a robust 24-h ADE upon first re-exposure (HAD-1: approximately 5 vs. 8g/kg/day; HAD-2: approximately 6 vs. 9g/kg/day, baseline vs. re-exposure), whereas P rats ( approximately 7 vs. 8g/kg/day) displayed a modest, nonsignificant, increase in 24-h intake. In a separate group of rats, ethanol intake and blood alcohol concentrations after the first hour of the fourth re-exposure cycle were HAD-1: 2.0g/kg and 97 mg%, HAD-2: 2.3g/kg and 73 mg%, and P: 1.2g/kg and 71 mg%; with all three lines displaying a robust first hour ADE. These findings suggest that (a) an ADE may be observed with short ethanol deprivation and re-exposure intervals in HAD rats, and (b) the genetic make-up of the P and HAD rats influences the expression of this ADE.

Longitudinal brain magnetic resonance imaging study of the alcohol-preferring rat. Part II: effects of voluntary chronic alcohol consumption

BACKGROUND

Tracking the dynamic course of human alcoholism brain pathology can be accomplished only through naturalistic study and without opportunity for experimental manipulation. Development of an animal model of alcohol-induced brain damage, in which animals consume large amounts of alcohol following cycles of alcohol access and deprivation and are examined regularly with neuroimaging methods, would enable hypothesis testing focused on the degree, nature, and factors resulting in alcohol-induced brain damage and the prospects for recovery or relapse.

METHODS

We report the results of longitudinal magnetic resonance imaging (MRI) studies of the effects of free-choice chronic alcohol intake on the brains of 2 cohorts of selectively bred alcohol-preferring (P) rats. In the companion paper, we described the MRI acquisition and analysis methods, delineation of brain regions, and growth patterns in total brain and selective structures of the control rats in the present study. Both cohorts were studied as adults for about 1 year and consumed high doses of alcohol for most of the study duration. The paradigm involved a 3-bottle choice with 0, 15 (or 20%), and 30% (or 40%) alcohol available in several different exposure schemes: continuous exposure, cycles of 2 weeks on followed by 2 weeks off alcohol, and binge drinking in the dark.

RESULTS

Brain structures of the adult P rats in both the alcohol-exposed and the water control conditions showed significant growth, which was attenuated in a few measures in the alcohol-exposed groups. The region with the greatest demonstrable effect was the corpus callosum, measured on midsagittal images.

CONCLUSION

The P rats showed an age-alcohol interaction different from humans, in that normal growth in selective brain regions that continues in adult rats was retarded.

The alcohol-preferring P rat and animal models of excessive alcohol drinking

The alcohol-preferring, P, rat was developed by selective breeding to study ethanol drinking behavior and its consequences. Characterization of this line indicates the P rat meets all of the criteria put forth for a valid animal model of alcoholism, and displays, relative to their alcohol-non-preferring, NP, counterparts, a number of phenotypic traits associated with alcohol abuse and alcoholism. Behaviorally, compared with NP rats, P rats are less sensitive to the sedative and aversive effects of ethanol and more sensitive to the stimulatory effects of ethanol. Neurochemically, research with the P line indicates the endogenous dopaminergic, serotonergic, GABAergic, opiodergic, and peptidergic systems may be involved in a predisposition for alcohol abuse and alcoholism. Paralleling the clinical literature, genetically selected P rats display levels of ethanol intake during adolescence comparable to that seen during adulthood. Binge drinking has been associated with an increased risk for health and other problems associated with ethanol abuse. A model of binge-like drinking during the dark cycle indicates that P rats will consume 6 g/kg/day of ethanol in as little as three 1-hour access periods/day, which approximates the 24-hour intake of P rats with free-choice access to a single concentration of ethanol. The alcohol deprivation effect (ADE) is a transient increase in ethanol intake above baseline values upon re-exposure to ethanol access after an extended period of deprivation. The ADE has been proposed to be an animal model of relapse behavior, with the adult P rat displaying a robust ADE after prolonged abstinence. Overall, these findings indicate that the P rat can be effectively used in models assessing alcohol-preference, a genetic predisposition for alcohol abuse and/or alcoholism, and excessive drinking using protocols of binge-like or relapse-like drinking.

Daily patterns of ethanol drinking in peri-adolescent and adult alcohol-preferring (P) rats

Alcohol abuse among adolescents continues to be a major health problem for our society. Our laboratory has used the peri-adolescent alcohol-preferring, P, rat as an animal model of adolescent alcohol abuse. Even though peri-adolescent P rats consume more alcohol (g/kg/day) than their adult counterparts, it is uncertain whether their drinking is sufficiently aggregated to result in measurable blood ethanol concentrations (BECs). The objectives of this study were to examine daily alcohol drinking patterns of adolescent and adult, male and female P rats, and to determine whether alcohol drinking episodes were sufficiently aggregated to result in meaningful BECs. Male and female P rats were given 30 days of 24 h free-choice access to alcohol (15%, v/v) and water, with ad lib access to food, starting at the beginning of adolescence (PND 30) or adulthood (PND 90). Water and alcohol drinking patterns were monitored 22 h/day with a "lickometer" set-up. The results indicated that (a) peri-adolescent P rats consumed more water and total fluids than adult P rats, (b) female P rats consumed more water and total fluids than male P rats, (c) there were differences in alcohol, and water, licking patterns between peri-adolescent and adult and female and male P rats, (d) individual licking patterns revealed that alcohol was consumed in bouts often exceeding the amount required to self-administer 1 g/kg of alcohol, and (e) BECs at the end of the dark cycle, on the 30th day of alcohol access, averaged 50 mg%, with alcohol intakes during the last 1 to 2 h averaging 1.2 g/kg. Overall, these findings indicate that alcohol drinking patterns differ across the age and sex of P rats. This suggests that the effectiveness of treatments for reducing excessive alcohol intake may vary depending upon the age and/or sex of the subjects being tested.

Effects of naltrexone on the acquisition of alcohol intake in male and female periadolescent and adult alcohol-preferring (P) rats

The objective of this study was to compare the effects of naltrexone (NTX) on the acquisition of alcohol drinking, during periadolescence and adulthood in rats using a rodent model of alcoholism. Periadolescent and adult alcohol-preferring (P) rats of both sexes were given access to water and 15% (v/v) alcohol 24-hr/day for 45 days. Alcohol access started at 1200 hr on post-natal day (PND) 30 for the periadolescent rats and approximately PND 90 for the adult rats. Subcutaneous (SC) injections of NTX (0, 5, 10, 20, and 30 mg/kg) were administered daily between 1600-1700 hr to separate groups of animals during the first 10 days of alcohol access. During the treatment period, differential effects on alcohol intake were seen between periadolescent and adult animals: (a) lower doses of NTX were more effective in the periadolescent than the adult P rats, and (b) greater tolerance to repeated dosing was displayed by adult, compared with periadolescent, rats. By the 20h day of alcohol access there were no significant differences between the NTX dose groups. Additionally, there were no sex of animal differences at the ages tested. These findings indicate that the endogenous opioid system(s) mediating alcohol intake are developmentally present in periadolescent P rats, such that NTX not only interfered with the acquisition of alcohol intake by adolescent P rats but appeared to also have a greater effect than that observed in adult P rats. Therefore, NTX may serve as an effective treatment in reducing alcohol abuse and dependence in genetically, and perhaps environmentally, at-risk youth.

Adolescent vulnerabilities to chronic alcohol or nicotine exposure: findings from rodent models

This article presents an overview of the proceedings from a symposium entitled "Is adolescence special? Possible age-related vulnerabilities to chronic alcohol or nicotine exposure," organized by Susan Barron and Linda Spear and held at the 2004 Research Society on Alcoholism Meeting in Vancouver, British Columbia. This symposium, co-sponsored by the Fetal Alcohol Syndrome Study Group and the Neurobehavioral Teratology Society, focused on our current knowledge regarding the long-term consequences of ethanol and/or nicotine exposure during adolescence with the emphasis on data from rodent models. The support from these two societies represents the understanding by these research groups that adolescence represents a unique developmental stage for the effects of chronic drug exposure and also marks an age in which many risky behaviors including alcohol consumption and smoking typically begin. The speakers included (1) Aaron White, who presented data on the effects of adolescent ethanol exposure on subsequent motor or cognitive response to an ethanol challenge in adulthood; (2) Richard Bell, who presented data suggesting that genetic differences could play a role in adolescent vulnerability to ethanol; (3) Craig Slawecki, who presented data looking at the effects of chronic exposure to alcohol or nicotine on neurophysiologic and behavioral end points; and (4) Ed Levin, who presented data on acute and long-term consequences of adolescent nicotine exposure. Finally, Linda Spear provided some summary points and recommendations regarding unresolved issues and future directions.

Glycyl-glutamine in nucleus accumbens reduces ethanol intake in alcohol preferring (P) rats

Opioid peptides and glycyl-glutamine (Gly-Gln) have been implicated in the control of ethanol consumption. A recognized beta-endorphin cleavage product, Gly-Gln, inhibits voluntary alcohol consumption when microinjected into the nucleus accumbens (AcbSh) of P rats. To evaluate the site-specific efficacy of Gly-Gln on ethanol consumption following AcbSh application, ethanol preferring (P) rats were allowed to establish individual baseline ethanol/water consumption utilizing a voluntary self-administration paradigm. Subsequent to baseline ethanol consumption being established, bilateral guide cannulae were stereotaxically implanted +1 mm dorsal to the AcbSh for subsequent Gly-Gln (100 nmol/microl) or saline vehicle (1 microl) injections. Alcohol intake, body weight, and water intake were measured at 24 h post-injection intervals. Unilateral Gly-Gln injections reduced ethanol consumption 35.6% (P < 0.05) from pre-established baseline consumption (6.24 +/- 0.64 g/kg to 4.06 +/- 0.28 g/kg). Bilateral Gly-Gln injections further reduced consumption to 51.9% (6.4 +/- 1.0 g/kg to 3.08 +/- 0.65 g/kg at 24 h (P < 0.01) below established baseline values within 24 h without significant changes in body weight or water consumption. Also, the amino acid constituents of the dipeptide had no influence on ethanol consumption behavior; however, Gly-Gln efficacy was shown to be comparable to central beta-endorphin-(1-27) or intraperitoneal (i.p.) naltrexone-induced suppression of ethanol intake. These data indicate that the AcbSh exhibits a site-specific sensitivity to the suppressive actions of Gly-Gln or beta-endorphin-(1-27) injections that modulate voluntary ethanol consumption in P rats. These findings support the broader concept that select forebrain opioid-responsive neural sites may influence the development or expression of alcohol abuse syndromes in animal models or humans.

Adolescent alcohol drinking and its long-range consequences. Studies with animal models

This chapter reviews findings, mainly obtained from the selectively bred alcohol-preferring (P) line of rats, on (a) the development of alcohol drinking during the peri-adolescent period, (b) neurobiological factors that may contribute to adolescent drinking, (c) interventions to prevent alcohol drinking during adolescence, and (d) some long-lasting consequences of adolescent alcohol drinking. The findings indicate that P rats readily initiate alcohol drinking during the early post-weaning, adolescent and peri-adolescent periods of development. The early age-of-onset of alcohol drinking in the P compared to the NP line is associated with (a) higher densities of serotonin-1A (5-HT1A) receptors in cerebral cortical and hippocampal regions; (b) lower densities of dopamine (DA) D2 receptors in the ventral tegmental area (VTA); (c) higher functional activity in several limbic, cortical and hippocampal regions; and (d) sensitivity to the low-dose stimulating effect of ethanol. Conditioned taste aversion (CTA) training during adolescence produces long-term effects on preventing high alcohol drinking behavior of P rats. Alcohol drinking during peri-adolescence by P rats produces long-lasting effects that increase the acquisition of ethanol self-administration in adulthood, and, in addition, increase craving-like behavior and the potential for alcohol relapse. With suitable animal models, a better understanding of the mechanisms underlying adolescent alcohol drinking and its long-range consequences can be attained.

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

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.