Relation of ethanol self-administration to feeding and drinking in a nonrestricted access situation in rats initiated to self-administer ethanol using the sucrose-fading technique

Orexin receptor blockers: A tool for lowering alcohol intake and alcohol addictive behavior in the light of preclinical studies

Alcohol use disorder (AUD) is a severe and globally widespread neurological and psychiatric problem. The treatment with currently used drugs often does not bring the expected effect. New optimization methods or directions in pharmacotherapy are still being sought. The group of bioactive ligands, targeted at neuropeptides called orexins (OXs) and their receptors (OXRs), affects a number of functions including ingestion, sleep-wake regulation, as well as the brain reward system which is the basis of addiction.

The purpose of this paper is to systematize the knowledge in the field of preclinical behavioral studies on rodents (rats and mice) in several models of alcohol consumption using the OXRs antagonists.

The results of the experiments indicated a potential efficacy of particular OXRs antagonists in the AUD treatment, especially those selectively blocking the OX1R. Among them, SB-334867 in the lowest effective dose of 3 mg/kg i.p. was most studied, as shown in the model of two-bottle choice using C57BL/6 mice. Moreover, this compound did not affect the reduction of cognitive functions. GSK1059865 was also involved in the selective reduction of ethanol intake, and simultaneously did not alter the consumption of sugar solution. The other group of selective OX2R antagonists, such as TCS-OX2-29 and LSN2424100, was less efficient.

In summary, the OX1R antagonists proved to have the potential in AUD therapy, not only through the reduction of ethanol consumption but also in the treatment of coexisting behavioral and physiological disorders, such as insomnia and anxiety.

Nicotine and alcohol: the role of midbrain dopaminergic neurons in drug reinforcement

Nicotine and alcohol addiction are leading causes of preventable death worldwide and continue to constitute a huge socio-economic burden. Both nicotine and alcohol perturb the brain's mesocorticolimbic system. Dopamine (DA) neurons projecting from the ventral tegmental area (VTA) to multiple downstream structures, including the nucleus accumbens, prefrontal cortex, and amygdala, are highly involved in the maintenance of healthy brain function. VTA DA neurons play a crucial role in associative learning and reinforcement. Nicotine and alcohol usurp these functions, promoting reinforcement of drug taking behaviors. In this review, we will first describe how nicotine and alcohol individually affect VTA DA neurons by examining how drug exposure alters the heterogeneous VTA microcircuit and network-wide projections. We will also examine how coadministration or previous exposure to nicotine or alcohol may augment the reinforcing effects of the other. Additionally, this review briefly summarizes the role of VTA DA neurons in nicotine, alcohol, and their synergistic effects in reinforcement and also addresses the remaining questions related to the circuit-function specificity of the dopaminergic system in mediating nicotine/alcohol reinforcement and comorbidity.

Ethanol actions on the ventral tegmental area: novel potential targets on reward pathway neurons

The ventral tegmental area (VTA) evaluates salience of environmental stimuli and provides dopaminergic innervation to many brain areas affected by acute and chronic ethanol exposure. While primarily associated with rewarding and reinforcing stimuli, recent evidence indicates a role for the VTA in aversion as well. Ethanol actions in the VTA may trigger neuroadaptation resulting in reduction of the aversive responses to alcohol and a relative increase in the rewarding responses. In searching for effective pharmacotherapies for the treatment of alcohol abuse and alcoholism, recognition of this imbalance may reveal novel strategies. In addition to conventional receptor/ion channel pharmacotherapies, epigenetic factors that control neuroadaptation to chronic ethanol treatment can be targeted as an avenue for development of therapeutic approaches to restore the balance. Furthermore, when exploring therapies to address reward/aversion imbalance in the action of alcohol in the VTA, sex differences have to be taken into account to ensure effective treatment for both men and women. These principles apply to a VTA-centric approach to therapies, but should hold true when thinking about the overall approach in the development of neuroactive drugs to treat alcohol use disorders. Although the functions of the VTA itself are complex, it is a useful model system to evaluate the reward/aversion imbalance that occurs with ethanol exposure and could be used to provide new leads in the efforts to develop novel drugs to treat alcoholism.

Nicotine as a discriminative stimulus for ethanol use

Abused drugs reinforce behavior; i.e., they increase the probability of the behavior preceding their administration. Abused drugs can also act as discriminative stimuli; i.e., they can set the occasion for responding reinforced by another event. Thus, one abused drug could come to set the occasion for the use of another and this functional relationship may play a role in polysubstance abuse, where common patterns of use could result in this relationship. Here we establish nicotine (0.4mg/kg, ip 5-min pre-session) as a discriminative stimulus for behavior reinforced by ethanol (0.1ml 8% w/v po, versus food) and determine the ability of nicotine (0.02-0.4mg/kg), varenicline (0.1-3.0mg/kg), and ethanol (250 and 500mg/kg) to control responding for ethanol. We compare these results to those from rats where nicotine signaled food was available (and ethanol was not). Nicotine came to function as a discriminative stimulus. Nicotine and varenicline produced dose-dependent increases in responding on the nicotine-appropriate lever while ethanol produced responding on the vehicle-appropriate lever. Whether this responding occurred on the lever that produced ethanol or food access depended on the training condition. These results demonstrate that a drug can come to set the occasion for use of another and suggest that this behavioral mechanism could play an important role in the maintenance of and recovery from polysubstance abuse, depending on the pattern of use.

The effects of ethanol on diverse components of choice in the rat: reward discrimination, preference and relative valuation

Alcohol consumption impairs judgment and choice. How alcohol alters these crucial processes is primarily unknown. Choice can be fractionated into different components including reward discrimination, preference and relative valuation that can function together or in isolation depending upon diverse factors including choice context. We examined the diverse components and contextual effects by analyzing the effects of alcohol drinking on choice behavior in a task with a reduced level of temporal and spatial constraints. Rats were trained to drink 10% ethanol during 6 weeks of behavior testing using a combined sucrose-fade and two-bottle free-choice procedure. Two different sucrose pellet outcomes (e.g., constant vs. variable) were presented each week to examine the impact of voluntary drinking on reward-based decision-making. Behavioral contexts of single option, free choice and extinction were examined for each outcome set. Comparisons were made between alcohol and control groups and within the alcohol group over time to inspect choice profiles. Between-group results showed alcohol drinking animals expressed altered place preference and modified sucrose reward approach latencies. The within-group profile showed that alcohol drinking animals can express adequate reward discrimination, preference and incentive contrast during free choice. All of these components were significantly reduced during the context of extinction. Control animals were also impacted by extinction but not as severely. The findings point to a need for a greater focus on the context and the diverse components of choice when examining external and internal factors influencing decision-making during alcohol or other substance of abuse exposure.

Influence of experimental history on nicotine self-administration in squirrel monkeys

RATIONALE

Methods for establishing robust long-term self-administration of intravenous (i.v.) nicotine, the primary psychoactive agent in tobacco, are not well-established in laboratory animals.

OBJECTIVE

Here, we examine the use of a fading procedure to establish robust and consistent i.v. nicotine self-administration under second-order schedule conditions in squirrel monkeys.

METHODS

First, self-administration behavior was developed in two groups of male squirrel monkeys using a second-order fixed-interval 5-min schedule with fixed-ratio 5 units (FI 5-min (FR5: S)). Comparable performances were maintained by i.v. cocaine (0.032 mg/kg/injection (inj); group A, n = 3) and the combination of food delivery (20-30 % condensed milk) and 0.01 mg/kg/inj i.v. nicotine (group B, n = 3). Subsequently, the concentration of condensed milk was gradually reduced to zero in the second group and self-administration behavior was maintained by i.v. nicotine alone. Next, self-administration of a range of doses of i.v. nicotine (0.001-0.032 mg/kg/inj) and, in additional experiments, the minor tobacco alkaloid anatabine (0.01-0.18 mg/kg/inj) was studied in both groups.

RESULTS

Results show that nicotine and anatabine had reinforcing effects in both groups. However, optimal doses of nicotine and anatabine maintained significantly higher rates of i.v. self-administration behavior in subjects trained with the fading procedure than in subjects provided with a history of cocaine-maintained responding.

CONCLUSION

These results illustrate conditions under which robust i.v. nicotine self-administration can be established in squirrel monkeys and the influence of prior experimental history in the expression of reinforcing effects of nicotine and anatabine.

Neonatal finasteride administration decreases dopamine release in nucleus accumbens after alcohol and food presentation in adult male rats

Endogenous levels of the neurosteroid (NS) allopregnanolone (AlloP) during neonatal stages are crucial for the correct development of the central nervous system (CNS). In a recent work we reported that the neonatal administration of AlloP or finasteride (Finas), an inhibitor of the enzyme 5α-reductase needed for AlloP synthesis, altered the voluntary consumption of ethanol and the ventrostriatal dopamine (DA) levels in adulthood, suggesting that neonatal NS manipulations can increase alcohol abuse vulnerability in adulthood. Moreover, other authors have associated neonatal NS alterations with diverse dopaminergic (DAergic) alterations. Thus, the aim of the present work is to analyse if manipulations of neonatal AlloP alter the DAergic response in the nucleus accumbens (NAcc) during alcohol intake in rats. We administered AlloP or Finas from postnatal day (PND) 5 to PND9. At PND98, we measured alcohol consumption using a two-bottle free-choice model (ethanol 10% (v/v)+glucose 3% (w/v), and glucose 3% (w/v)) for 12 days. On the last day of consumption, we measured the DA and 3,4-dihydroxyphenylacetic acid (DOPAC) release in NAcc in response to ethanol intake. The samples were obtained by means of in vivo microdialysis in freely moving rats, and DA and DOPAC levels were determined by means of high-performance liquid chromatography analysis (HPLC). The results revealed that neonatal Finas increased ethanol consumption in some days of the consumption phase, and decreased the DA release in the NAcc in response to solutions (ethanol+glucose) and food presentation. Taken together, these results suggest that neonatal NS alterations can affect alcohol rewarding properties.

Ethanol self-administration in mice under a second-order schedule

Long Fixed-Interval (FI) schedules, particularly second-order schedules, can engender substantial responding before drug or ethanol delivery that is uninfluenced by the direct effects of the drug or ethanol. Thus, these schedules can be used to study the effects of medications upon drug- or ethanol-seeking, uninfluenced by the direct effects of the self-administered drug or ethanol. Long FI second-order schedules are frequently used in primates and occasionally in rats. Under second-order schedules, completion of one response requirement, e.g., a Fixed Ratio 10 (FR10:S), produces a brief stimulus presentation, e.g., a 1-s 80-dB 4-kHZ tone, and this FR10:S serves as the response unit under another schedule, e.g., an FI 1800-s. Thus, the first FR10 completed after 1800 s would result in delivery both of the tone and of reinforcement, e.g., 10 × 0.01 mL 16% (w/v) ethanol. To examine if such schedules could be effectively used in mice, which have advantages in neurobiological and genetic studies, we trained eight C57BL/6J mice to respond under the schedule just described. This schedule maintained substantial responding. The temporal pattern of behavior was typical of an FI schedule with responding accelerating across the interval. We also examined the effects of acute and chronic administration of fluvoxamine on this responding, and these were modest. Finally, we examined responding when alcohol and/or tone deliveries were withheld, and found that extinction occurred most rapidly when both were withheld. This work demonstrates that long FI schedules of ethanol delivery may be useful in studying ethanol seeking in mice.

Drug effects on multiple and concurrent schedules of ethanol- and food-maintained behaviour: context-dependent selectivity

BACKGROUND AND PURPOSE

Drugs that more potently or effectively reduce ethanol-maintained behaviour versus an alternative are considered selective and are considered promising pharmacotherapies for alcoholism. Such results are often obtained using separate groups or multiple schedules where ethanol and the alternative are available alone or sequentially. Recently, we observed that when ethanol and food were available sequentially under a multiple schedule, fluvoxamine and varenicline were selective; yet this selectivity disappeared when ethanol and food were concurrently available.

EXPERIMENTAL APPROACH

We examined the generality of these findings by comparing doses of several drugs required to decrease ethanol- and food-maintained responding under a multiple schedule and under a concurrent schedule. Effects were determined for chlordiazepoxide, 2,5-dimethoxy-4-iodoamphetamine (DOI), meta-chlorophenylpiperazine (mCPP), morphine, naltrexone and d-amphetamine.

KEY RESULTS

Under the multiple schedule, ED50 values for decreases in ethanol-maintained responding were significantly different and lower than ED50 s for decreases in food-maintained responding (demonstrating selectivity) for each drug except for chlordiazepoxide (which was equipotent) and naltrexone (which did not affect responding). However, this selectivity vanished or even inverted under the concurrent schedule, such that ED50 values for decreasing ethanol- and food-maintained responding were not different (or, following DOI, the ED50 for food-maintained responding was lower than for ethanol-maintained responding).

CONCLUSIONS AND IMPLICATIONS

Results are consistent with those seen following fluvoxamine and varenicline administration, and suggest that selectivity is assay-dependent. These results indicate the need for careful interpretation of selective drug effects, especially when obtained in situations where ethanol or the alternative is the only programmed reinforcement available.

Early ethanol and water consumption: accumulating experience differentially regulates drinking pattern and bout parameters in male alcohol preferring (P) vs. Wistar and Sprague Dawley rats

Alcohol-preferring (P) rats develop high ethanol intake over several weeks of water/10% ethanol (10E) choice drinking. However, it is not yet clear precisely what components of drinking behavior undergo modification to achieve higher intake. Our concurrent report compared precisely measured daily intake in P vs. non-selected Wistar and Sprague Dawley (SD) rats. Here we analyze their drinking patterns and bouts to clarify microbehavioral components that are common to rats of different genetic backgrounds, vs. features that are unique to each. Under sole-fluid conditions P, Wistar and SD rats all consumed water at a high initial rate followed by a slow maintenance phase, but 10E - in a distinctly different step-like pattern of evenly distributed bouts. During choice period, 10E vs. water patterns for P rat appeared as an overlap of sole-fluid patterns. The SD rat choice patterns resembled sole-fluid patterns but were less regular. Choice patterns in Wistar differed from both P and SD rats, by consisting of intermixed small frequent episodes of drinking both 10E and water. Wistar and SD rats increased choice ethanol intake by elevating the number of bouts. A key finding was that P rat increased choice ethanol intake through a gradual increase of the bout size and duration, but kept bout number constant. This supports the hypothesis that genetic selection modifies microbehavioral machinery controlling drinking bout initiation, duration, and other pattern features. Precision analysis of drinking patterns and bouts allows differentiation between genetic lines, and provides a venue for study of localized circuit and transmitter influences mediating mesolimbic control over ethanol consumption.

Early ethanol and water intake: choice mechanism and total fluid regulation operate in parallel in male alcohol preferring (P) and both Wistar and Sprague Dawley rats

The goal of this study was to clarify similar and distinctly different parameters of fluid intake during early phases of ethanol and water choice drinking in alcohol preferring P-rat vs. non-selected Wistar and Sprague Dawley (SD) rats. Precision information on the drinking amounts and timing is needed to analyze micro-behavioral components of the acquisition of ethanol intake and to enable a search for its causal activity patterns within individual CNS circuits. The experiment followed the standard ethanol-drinking test used in P-rat selective breeding, with access to water, then 10% ethanol (10E) as sole fluids, and next to ethanol/water choice. The novelty of the present approach was to eliminate confounding prandial elevations of fluid intake, by time-separating daily food from fluid access. P-rat higher initial intakes of water and 10E as sole fluids suggest adaptations to ethanol-induced dehydration in P vs. Wistar and SD rats. P-rat starting and overall ethanol intake during the choice period were the highest. The absolute extent of ethanol intake elevation during choice period was greatest in Wistar and their final intake levels approached those of P-rat, contrary to the hypothesis that selection would produce the strongest elevation of ethanol intake. The total daily fluid during ethanol/water choice period was strikingly similar between P, Wistar and SD rats. This supports the hypothesis for a universal system that gauges the overall intake volume by titrating and integrating ethanol and water drinking fluctuations, and indicates a stable daily level of total fluid as a main regulated parameter of fluid intake across the three lines in choice conditions. The present findings indicate that a stable daily level of total fluid comprises an independent physiological limit for daily ethanol intake. Ethanol drinking, in turn, stays under the ceiling of this limit, driven by a parallel mechanism of ethanol/water choice.

Acetaldehyde involvement in ethanol's postabsortive effects during early ontogeny

Clinical and biomedical studies sustains the notion that early ontogeny is a vulnerable window to the impact of alcohol. Experiences with the drug during these stages increase latter disposition to prefer, use or abuse ethanol. This period of enhanced sensitivity to ethanol is accompanied by a high rate of activity in the central catalase system, which metabolizes ethanol in the brain. Acetaldehyde (ACD), the first oxidation product of ethanol, has been found to share many neurobehavioral effects with the drug. Cumulative evidence supports this notion in models employing adults. Nevertheless very few studies have been conducted to analyze the role of ACD in ethanol postabsorptive effects, in newborns or infant rats. In this work we review recent experimental literature that syndicates ACD as a mediator agent of reinforcing aspects of ethanol, during early ontogenetic stages. We also show a meta-analytical correlational approach that proposes how differences in the activity of brain catalase across ontogeny, could be modulating patterns of ethanol consumption.

Effects of varenicline on ethanol- and food-maintained responding in a concurrent access procedure

BACKGROUND

Varenicline has been reported to reduce drinking in smokers and to selectively decrease responding for ethanol (EtOH) versus alternatives in preclinical studies. Such selectivity may reflect potential therapeutic effects and the involvement of nicotinic receptors in EtOH reinforcement. However, these studies have been conducted with EtOH and an alternative available in isolation or in separate groups, and selectivity can depend on the context in which reinforcement occurs. Whether varenicline selectivity is maintained when EtOH and an alternative are concurrently available has not been reported. To examine the effects of varenicline on EtOH self-administration when an alternative is concurrently available, male Lewis rats (n = 5) were trained to respond for EtOH and food under a concurrent FR5 FRX schedule where the fixed ratio (FR) for food was adjusted (FR = 25 or 35 for each subject) to provide similar numbers of EtOH and food deliveries during a 30-minute session.

METHODS

Doses of varenicline (0.56 to 5.6 mg/kg, i.p.) or vehicle were administered 30 minutes before sessions. Effects of varenicline on responding across the session and during each tenth of the session were compared to responding following vehicle treatment.

RESULTS

Lower doses (0.56 to 1.0 mg/kg) of varenicline increased responding for EtOH without affecting responding for food. Higher doses disrupted responding for EtOH and food similarly.

CONCLUSIONS

Previous reports of varenicline selectivity on EtOH-maintained responding do not generalize to other experimental conditions such as a concurrent schedule. The increase in responding for EtOH following lower doses might be due to enhanced EtOH reinforcement, decreased food reinforcement, rate dependency, or greater perseverance on the initial, EtOH response.

Effects of removing food on maintenance of drinking initiated by pairings of sipper and food

Two experiments evaluated the effects of removing food presentations on the maintenance of drinking induced by experience with sipper - food pairings. In Exp 1, ethanol drinking was induced in non-deprived Long-Evans rats by Pavlovian conditioning procedures employing an ethanol sipper as conditioned stimulus (CS) and food pellet as unconditioned stimulus (US). The Paired/Ethanol group received presentations of the ethanol sipper CS followed immediately by the response-independent presentation of the food pellet US. The Random/Ethanol group received the ethanol sipper CS and food US randomly with respect to one another. For both groups, the concentration of ethanol in the sipper CS [(3%, 4%, 6%, 8% (vol./vol.)] was increased across sessions, and, as in previous studies employing low concentrations of ethanol in non-deprived rats (i.e., maintained with free access to food in their home cages), the two procedures induced comparable levels of sipper CS-directed ethanol drinking. Removing food US presentations had no effect on sipper CS-directed ethanol drinking in either group. In Exp 2, groups of non-deprived Long-Evans rats were trained either with water or ethanol in the sipper CS paired with food US. Removing food US presentations had no effect on ethanol drinking in the Paired/Ethanol group, but water drinking in the Paired/Water group declined systematically across sessions. Results indicate that food US presentations contribute to the maintenance of water drinking but not to the maintenance of ethanol drinking. Implications for accounts of ethanol drinking based on Pavlovian sign-tracking, behavioral economics and intermittent sipper procedures are considered.

Effect of topiramate treatment on ethanol consumption in rats

RATIONALE

Results from clinical studies have shown that topiramate effectively reduces alcohol consumption in a population of heavy-drinking alcohol-dependent humans.

OBJECTIVES

We undertook this preclinical study in order to establish topiramate's efficacy in a rodent model and to determine whether topiramate's efficacy may vary with level of drinking and/or genetic background.

METHODS

The effects of acutely administered topiramate (0, 5, and 10 mg/kg) on ethanol consumption were examined in a large group of ethanol-preferring (P) rats (N = 20) in order to assess the relationship between level of consumption and treatment effect using a two-bottle free-choice paradigm (10% ethanol versus water). We also evaluated the effects of topiramate in two groups of Wistar rats that were given access to ethanol under either the standard two-bottle free-choice paradigm or under conditions that are known to produce higher levels of daily ethanol consumption (i.e. three-bottle free choice).

RESULTS

Topiramate treatment produced a modest, but persistent (average of 5 days), reduction in ethanol consumption in P rats, and this effect did not vary with level of consumption. Topiramate did not affect ethanol consumption in either group of Wistar rats.

CONCLUSIONS

The results from this study establish in a rodent model that topiramate effectively and persistently reduces ethanol consumption and suggests that its efficacy may depend on genetic vulnerability but not level of drinking.

Guidelines on nicotine dose selection for in vivo research

RATIONALE

This review provides insight for the judicious selection of nicotine dose ranges and routes of administration for in vivo studies. The literature is replete with reports in which a dosaging regimen chosen for a specific nicotine-mediated response was suboptimal for the species used. In many cases, such discrepancies could be attributed to the complex variables comprising species-specific in vivo responses to acute or chronic nicotine exposure.

OBJECTIVES

This review capitalizes on the authors' collective decades of in vivo nicotine experimentation to clarify the issues and to identify the variables to be considered in choosing a dosaging regimen. Nicotine dose ranges tolerated by humans and their animal models provide guidelines for experiments intended to extrapolate to human tobacco exposure through cigarette smoking or nicotine replacement therapies. Just as important are the nicotine dosaging regimens used to provide a mechanistic framework for acquisition of drug-taking behavior, dependence, tolerance, or withdrawal in animal models.

RESULTS

Seven species are addressed: humans, nonhuman primates, rats, mice, Drosophila, Caenorhabditis elegans, and zebrafish. After an overview on nicotine metabolism, each section focuses on an individual species, addressing issues related to genetic background, age, acute vs chronic exposure, route of administration, and behavioral responses.

CONCLUSIONS

The selected examples of successful dosaging ranges are provided, while emphasizing the necessity of empirically determined dose-response relationships based on the precise parameters and conditions inherent to a specific hypothesis. This review provides a new, experimentally based compilation of species-specific dose selection for studies on the in vivo effects of nicotine.

The mGluR5 antagonist MPEP selectively inhibits the onset and maintenance of ethanol self-administration in C57BL/6J mice

RATIONALE

Many of the biochemical, physiological, and behavioral effects of ethanol are known to be mediated by ionotropic glutamate receptors. Emerging evidence implicates metabotropic glutamate receptors (mGluRs) in the biobehavioral effects of ethanol and other drugs of abuse, but there is little information regarding the role of mGluRs in the reinforcing effects of ethanol.

MATERIALS AND METHODS

Male C57BL/6J mice were trained to lever-press on a concurrent fixed ratio 1 schedule of ethanol (10% v/v) vs water reinforcement during 16-h sessions. Effects of mGluR1, mGluR2/3, and mGluR5 antagonists were then tested on parameters of ethanol self-administration behavior.

RESULTS

The mGluR5 antagonist MPEP (1-10 mg/kg, i.p.) dose-dependently reduced ethanol-reinforced responding but had no effect on concurrent water-reinforced responding. Analysis of the temporal pattern of responding showed that MPEP reduced ethanol-reinforced responding during peak periods of behavior occurring during the early hours of the dark cycle. Further analysis showed that MPEP reduced the number of ethanol response bouts and bout-response rate. MPEP also produced a 13-fold delay in ethanol response onset (i.e., latency to the first response) with no corresponding effect on water response latency or locomotor activity. The mGluR1 antagonist CPCCOEt (1-10 mg/kg, i.p.) or the mGluR2/3 antagonist LY 341495 (1-30 mg/kg, i.p.) failed to alter ethanol- or water-reinforced responding.

CONCLUSIONS

These data indicate that mGlu5 receptors selectively regulate the onset and maintenance of ethanol self-administration in a manner that is consistent with reduction in ethanol's reinforcement function.

Effects of fluvoxamine on a multiple schedule of ethanol- and food-maintained behavior in two rat strains

RATIONALE

Previous studies show that selective serotonin reuptake inhibitors (SSRIs), including fluvoxamine, have a greater effect on ethanol-maintained responding compared with an alternative reinforcer. However, none of these studies matched baseline responding for reinforcers. Because behavioral effects of many drugs depend on the baseline response rate, the preferential effects of SSRIs may be due to different baseline response rates.

OBJECTIVES

Fluvoxamine effects on ethanol- and food-maintained responding were compared using a multiple schedule of behavior, providing matched baseline responding and allowing within-subject analysis in two strains of rats.

METHODS

The multiple schedule consisted of three consecutive 5-min, fixed-ratio five components (Food1, Ethanol, Food2). Fluvoxamine (3-30 mg/kg, i.p.) was administered 30 min presession. In Lewis rats, fluvoxamine effects were determined at several available ethanol concentrations [8, 16, 32, and 8% (w/v) redetermination]. In Sprague-Dawley rats, fluvoxamine effects were determined when the available ethanol concentration was 8% (w/v).

RESULTS

Baseline responding was stable and well matched under all conditions except 32% ethanol, when responding for ethanol was lower than for food. After the administration of 17.8 mg/kg fluvoxamine, ethanol-maintained responding was 15-33% lower than food-maintained responding in four of the five conditions tested. Breath ethanol assessments indicated that rats had blood ethanol levels of 33 mg/dl following responding for 8% ethanol.

CONCLUSIONS

These results are in agreement with previous findings that SSRIs preferentially reduce ethanol-maintained responding and suggest this is not likely due to different baseline levels of responding between the comparison conditions. Further, these results support the hypothesis that alteration of synaptic serotonin can modulate ethanol reinforcement.

A procedure to produce high alcohol intake in mice

RATIONALE

While prolonged access to ethanol (EtOH), or deprivations, or their combination have occasionally been shown to yield high levels of voluntary self-administration, in almost all cases, rodents do not self-administer alcohol to the degree that they will develop substantial, intoxicating blood alcohol levels and then continue to self-administer at these levels.

OBJECTIVES

The purpose of the present series of experiments was to modify a fluid restriction procedure to demonstrate consistent, high EtOH consumption.

METHODS

Male and female mice from an alcohol preferring inbred strain (C57BL/6J; B6) as well as from a genetically heterogeneous strain (WSC) were given varying periods of access to fluid, ranging from 90 min to 10 h per day, for 12-21 days. Every 3rd or 4th day, separate groups of mice were offered a 5, 7 or 10% EtOH solution for either 10 min or 30 min, followed by water for the remainder of the time.

RESULTS

In all studies, stable high EtOH doses were consumed by both B6 and WSC mice across the EtOH sessions, exceeding 2 g/kg in a 30-min session. Mean blood EtOH concentration exceeded 1 mg/ml (i.e. 100 mg%), with values in individual animals ranging from 0.6 mg/ml to 3.4 mg/ml. Notably, mice receiving 10 h of fluid/day continued to consume 2 g/kg doses of EtOH. While this procedure did not produce subsequent preference for EtOH in WSC mice, consumption remained high in some animals.

CONCLUSIONS

These data indicate that scheduling fluid intake produces high, stable EtOH consumption and BEC in male and female B6 and WSC mice.

Failure of a schedule-induction procedure to increase ethanol intake in an established limited-access self-administration condition

Determining mechanisms that can increase ethanol consumption during a single drinking bout is central to understanding alcohol abuse. When rodents are used as models to study excessive drinking, most often limited and transient increases in bout size are found with various manipulations. In a variety of studies, investigators have reported that schedule-induced drinking can result in excessive consumption of either water or alcohol (ethanol) during a single drinking period in food-restricted rats. The question examined in this experiment was, Could a schedule-induction paradigm increase bout size in nondeprived rats already self-administering ethanol? After the rats were trained to self-administer a 10% (volume/volume) ethanol solution in a fixed daily drinking session, non-response-contingent presentation of a 10% (weight/volume) sucrose solution, on a fixed-time, 120-s schedule, was used to determine whether additional ethanol consumption could be induced. This was followed by the use of a fixed-time, 300-s schedule and then, by using the fixed-time, 120-s schedule, with the presentation of a 2% (weight/volume) sucrose solution. None of these conditions induced an increase in ethanol self-administration. The results indicate that factors that control ethanol bout size in the nondeprived rat are such that the standard schedule-induction condition seems to be ineffective if an ethanol bout has occurred in the recent past.

Involvement of the sigma 1 receptor in the motivational effects of ethanol in mice

In the present study, we examined the involvement of the sigma(1) (sigma(1)) receptor in several behavioral manifestations of ethanol addiction. Administration of ethanol (0.5, 1, and 2 g/kg) in Swiss mice dose-dependently induced locomotor stimulation, conditioned place preference, and conditioned taste aversion, which are considered as behavioral index of drug-induced reward. Pretreatment with the selective sigma(1) receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047, 3-30 mg/kg) dose-dependently blocked ethanol (1 g/kg)-induced hyperlocomotion and taste aversion and ethanol (2 g/kg)-induced place preference. Pretreatment with the selective sigma(1) receptor agonist 2-(4-morpholino)ethyl 1-phenylcyclohexane-1-carboxylate (PRE-084, 1-10 mg/kg) before ethanol (0.5 g/kg) failed to affect the resulting locomotor stimulation, but dose-dependently enhanced the conditioned place preference. Each sigma(1) receptor ligand was devoid of behavioral effect by itself. These observations show that activation of the sigma(1) receptor is a necessary component of ethanol-induced motivational effects and suggest a new pharmacological target for alleviating ethanol addiction.

Motivational effects of ethanol in DARPP-32 knock-out mice

DARPP-32 (dopamine and adenosine 3',5'-monophosphate-regulated phosphoprotein, 32 kDa) is an important component of dopaminergic function in brain areas thought to be important for drug and alcohol addiction. The present experiments characterized the acquisition of ethanol-induced conditioned taste aversion, ethanol-induced conditioned place preference, and ethanol self-administration in DARPP-32 knock-out (KO) mice compared to wild-type (WT) controls. For taste conditioning, KO and WT mice received access to 0.2 m NaCl solution followed immediately by intraperitoneal injection of 0-4 gm/kg ethanol. Ethanol produced dose-dependent conditioned taste aversion that was the same in both genotypes. For place conditioning, KO and WT mice received eight pairings of a tactile stimulus with ethanol (2 gm/kg, i.p.), and a different stimulus with saline. Ethanol produced increases in locomotor activity during conditioning, with KO mice showing higher activity levels after ethanol compared to WT mice. WT mice, but not KO mice, acquired conditioned preference for the ethanol-paired stimulus. In the self-administration procedure, KO and WT mice were trained to lever press for access to 10% v/v ethanol. Subsequently, the mice had 23 hr/d access to food, ethanol, and water. Response patterns were determined using 0-30% v/v ethanol concentrations. WT mice displayed concentration-dependent responding for ethanol. Responding on the ethanol lever by KO mice did not change as a function of ethanol concentration. Saccharin (0.2% w/v) was subsequently added to the ethanol mixture, and responding was examined at 0, 5, 10, and 20% ethanol concentrations. Ethanol responding increased in both genotypes, although WT mice showed higher rates at all concentrations.

Effects of prior ethanol exposure on ethanol self-administration in a continuous access situation using retractable drinking tubes

To examine whether exposure to ethanol influences subsequent ethanol consumption using a continuous access procedure, two groups of rats were given differing initial exposure to ethanol. One group underwent a sucrose-substitution initiation procedure. The second group received abbreviated initiation consisting of one-session exposure to each ethanol/sucrose combination used in standard initiation. The animals were then provided with 23 h/day access to ethanol (10%, v/v) from a retractable drinking tube. Food pellets were available following a single-lever press, and water was available from a sipper tube. After 5 weeks, the data indicated that few significant differences existed between the groups on total ethanol (g/kg), food or water consumed. The overall intake (g/kg/day), number of ethanol bouts per day, and amount consumed per bout (g/kg/bout) were substantially lower than observed in previous research using ethanol presented in a dipper. However, differences in g/kg per ethanol bout did differ significantly between the two groups with the group receiving standard initiation showing more ethanol consumed per bout. These data agree with our previous work indicating that initiation results in larger drinking bouts.

Chronic ethanol self-administration in a continuous-access operant situation: the use of a sucrose/ethanol solution to increase daily ethanol intake

The addition of sucrose to an ethanol solution increases both limited- and continuous-access ethanol consumption. The present study examined if the increased intakes in a continuous-access condition could produce withdrawal signs indicating physical dependence on ethanol. Rats were maintained in a continuous-access operant situation in which one lever press on one lever resulted in the presentation of a food pellet, whereas one lever press on a second lever presented 0.1 ml of fluid in a dipper. Water was available from a drinking spout. Ten rats received a 10% sucrose/20% ethanol mixture in the dipper and six rats 10% sucrose. After 30 days the animals were tested for withdrawal signs after 8 h without ethanol using an activity test and response to key shaking. They were then given an additional 30 days of access to the solutions and retested for withdrawal. This was followed by a final 30 days of access and a third withdrawal test. Over the 90 days, the sucrose/ethanol group consumed 8-10 g of ethanol per kilogram of body weight per day. Over this time both groups gained weight. At the third withdrawal test, a significant reduction in activity occurred in the ethanol-drinking group, compared with the sucrose group. No severe withdrawal effects were observed to the key shake test. The results suggest that the higher ethanol intakes previously observed using this sucrose/ethanol solution can be maintained over long periods of time. Although this intake was not sufficient to produce severe withdrawal signs, the results suggest that longer exposure might result in more severe ethanol dependence.

Oral operant ethanol self-administration in 5-HT1b knockout mice

The present experiment examined oral ethanol self-administration in 5-HT1b knockout (KO) mice and 5-HT1b wide-type (WT) control mice using a continuous access operant procedure. After lever press training, adult 5-HT1b KO and 5-HT1b WT mice were placed in operant chambers on a 23 h per day basis with access to food (FR1), 10% v/v ethanol (FR4), and water from a sipper tube. KO mice displayed higher rates of responding on the ethanol-associated lever compared to WT mice. KO mice also consumed greater amounts of water. Food responding was the same in both genotypes. Following 30 sessions, ethanol concentration was altered every 5 days. Response patterns were determined using 0, 5, and 20% v/v ethanol concentrations. Ethanol responding (0, 5, 10, and 20% v/v) was also examined after the addition of 0.15% saccharin. KO mice and WT mice showed similar response rates for all ethanol concentrations. Since KO mice showed greater levels of ethanol responding only for unsweetened 10% v/v ethanol, and showed modest ethanol self-administration overall, the present results are not consistent with the notion that 5-HT1b KO have a generally greater preference for ethanol than 5-HT1b WT mice.

Operant ethanol reward in C57BL/6 mice: influence of gender and procedural variables

Food-deprived C57BL/6 (C57) mice of either sex responded for oral ethanol rewards delivered on ratio schedules of reinforcement, thus extending to female C57 mice effects previously reported only for male members of the strain. Lever responding for ethanol reward was influenced by thirst motivation (post- vs. preprandial tests), time of access to ethanol reward, ethanol concentration, and reinforcement schedule. A particularly high response output for 12% ethanol delivered on a PR2 schedule (e.g., approximately 1400/15 min test session) indicates its efficacy as a reinforcer for C57 mice. Estimated consumption of ethanol differed from lever responding when reward access time was relatively long (10 s) and response demand of the reinforcement schedule was low, but paralleled lever responding when reward access time was restricted (3 s) and response demands were greater. Gender influenced lever responding for ethanol reward and its consumption, the difference depending upon reward access time and reinforcement schedule. When the response demands were low and the reward access time long, females tended to respond more than males for ethanol reward; with greater response demands and shorter reward access time, males tended to respond more. In conjunction with our companion report, the present study helps define the behavioral conditions under which ethanol is rewarding for C57 mice and establish the conditions under which ethanol reward differs for male and female mice.

Ethanol consumption by C57BL/6 mice: influence of gender and procedural variables

Both sexes of C57BL/6 (C57) mice consumed substantial quantities of ethanol without food or water deprivation whether access was continuous or limited. Food deprivation increased the amount of ethanol consumed, and the amount consumed depended upon when the animals were tested with reference to their daily food allotment. Ethanol consumption was greater if the mice were tested postprandially, high thirst motivation, rather than preprandially (approximately 10 vs. approximately 4.5 g/kg/30 min). Preference for ethanol over water, however, was greater when mice were under low thirst motivation (i.e., tested preprandially or with water available during the test). Compared to males, female mice consumed more of a high-ethanol concentration solution (10%) when access was continuous or limited to the first hour of the dark (active) phase of the circadian cycle. Also, in contrast to males, female mice exhibited increased ethanol consumption across days of drinking experience. Finally, although ethanol consumption under the food deprivation conditions of this experiment did not differ according to sex, females had higher blood ethanol concentrations than male C57 mice, a finding not previously reported for rodents but common to humans.

Mouse strain differences in oral operant ethanol reinforcement under continuous access conditions

The present experiment examined ethanol self-administration in C57BL/6J (C57) and DBA/2J (DBA) mice using a continuous access operant procedure. Adult male C57 and DBA mice were initially trained to perform a lever press response to obtain access to 10% w/v sucrose solution. Subsequently, the mice were placed in operant chambers on a continuous (23 hr/day) basis with access to food (FR1), 10% v/v ethanol (FR4), and water from a sipper tube. C57 mice displayed greater rates of responding on the ethanol-associated lever compared with DBA mice. Responding on the food lever was the same in both strains, but DBA mice consumed greater amounts of water. C57 mice consistently displayed both prandial and nonprandial episodes (bouts) of ethanol responding. DBA mice did not respond for ethanol in bouts. Following 50 consecutive sessions, ethanol concentration was altered every 5 days. Response patterns were determined using 0, 5, 10, 20, and 30% v/v ethanol concentrations. C57 mice displayed concentration-dependent responding on the ethanol lever showing that ethanol was functioning as an effective reinforcer in this strain. In contrast, responding on the ethanol lever by DBA mice did not change as a function of ethanol concentration. Saccharin (0.2% w/v) was subsequently added to the ethanol mixture, and responding was examined at 0, 5, 10, and 20% ethanol concentrations. Overall, ethanol lever responding was increased in both strains. As before, C57 mice showed higher levels of ethanol responding, compared with DBA mice. C57 mice also showed higher responding for saccharin alone. These results are consistent with findings that suggest orally administered ethanol is a more effective reinforcer in C57 mice than in DBA mice. Furthermore, C57 mice engage in ethanol-reinforced responding over a broader range of conditions than DBA mice.

Effects of sucrose-substitution initiation on patterns of drinking by Lewis rats during continuous alcohol access

Initiation of alcohol drinking using the sucrose-substitution procedure was studied in inbred Lewis rats. One group of animals was initiated to self-administer alcohol prior to being placed in the continuous-access condition, whereas the second group of animals did not undergo initiation. During the continuous-access period, the animals were housed in operant chambers where they had continuous access to alcohol (10% v/v), food, and water during daily 23-h experimental sessions. After 5 weeks of baseline conditions, the response, requirement for food was increased over weeks. This was followed by weekly increases in the ethanol response requirement with the food response requirement returned to baseline conditions. In the continuous-access condition, both groups consumed similar amounts of alcohol by the end of the 4-week baseline period and showed similar numbers of dippers presented per alcohol bout and number of alcohol bouts per day. During the food response requirement manipulation, alcohol consumption increased for both groups but intake increased significantly more for the noninitiated group. The difference between groups was accounted for by a larger number of alcohol drinking bouts per day for the noninitiated group. Alcohol consumption decreased at each increase in ethanol reinforcement response requirement for both groups. Alcohol-reinforced responding per session increased for the noninitiated animals but remained unchanged for the initiated group during this condition. Responding increased substantially for both groups when the alcohol reinforcement response requirement was returned to baseline conditions. These results suggest that alcohol may serve more as a food source for noninitiated animals during the food reinforcement manipulation and that initiation may result in more resistance to change during the alcohol reinforcement manipulation. These data show that the type of initial exposure to alcohol can impact future drinking patterns.

Absence of tolerance to the aversive stimulus properties of ethanol following oral ethanol self-administration

Depending on the situation, ethanol can serve as a reinforcer in one paradigm and an aversive stimulus in another. The relationships between the two stimuli are not clear, particularly the behavioural adaptation following chronic ethanol exposure. We report on two experiments using an oral-self administration (OSA) paradigm and a conditioned taste aversion (CTA) paradigm. Male Wistar rats were exposed to ethanol using either the OSA or the CTA paradigm, and the consequences were examined in the same groups of rats by performing the other corresponding experiment. Thus, sensitisation or tolerance to the respective stimulus properties of ethanol would be detectable. For OSA experiments, rats were presented, under a free-choice setting, tap water and an ascending series of ethanol concentrations (2-10%) for up to 4 days per concentration. The amounts of ethanol and water consumed in 23-h sessions were measured. For CTA, a two-bottle procedure was employed. Distinctively flavoured solutions (saccharin or saline) were paired with IP injections of either ethanol (1.5 g/kg) or saline (1 ml/kg). Tests for aversion were made after two pairings, when both solutions were presented simultaneously for 10 min. At low concentrations of ethanol, drinking solution consumption was high, decreasing gradually with increasing concentrations; however, daily intake of orally self-administered ethanol remained stable. No significant differences could be established between the two groups tested. Ethanol preference [EtOH/EtOH + H2O] was attenuated in rats experienced with the CTA procedure before the OSA experiment. Injections of ethanol produced marked CTAs, even in rats that had consumed ethanol in the OSA experiment. The absence of tolerance to the aversive stimulus effects suggests that this stimulus property may not play a significant role in the consumption of ethanol.

Patterns of ethanol consumption in a continuous access situation: the effect of adding a sweetener to the ethanol solution

The effect of the addition of sucrose to an ethanol solution upon daily intake patterns was examined in a continuous-access operant situation with Wistar rats. Rats were first initiated to self-administer orally a 10% ethanol (v/v) solution using the sucrose-substitution procedure in 30-min limited-access conditions. When then studied in a continuous-access operant situation (23 hr ethanol access), substantial increases in ethanol consumption were found when varying concentrations of sucrose were added to the ethanol solutions presented. This increased consumption was found to be a complex function of both an increase in the number of drinking occurrences each day and in the size of each drinking occurrence. When 2% sucrose was compared with 2% sucrose/10% ethanol, the consumption of the sweetened ethanol was greater than consumption of the sweetener alone, suggesting that the ethanol added to the ability of the solution to maintain behavior beyond that of the sucrose alone. This study supports the use of sweetened ethanol solutions for the study of ethanol drinking patterns, and as a model system for examining factors involved in the regulation of ethanol consumption.

Home-cage ethanol consumption and motor activity: lack of relation to either initial activity or amphetamine-induced locomotion

In two separate studies, the relationship between home-cage, two bottle ethanol/water consumption and both initial motor reactivity to a novel environment and amphetamine induced motor activity was determined in nonselected Wistar rats. In neither study was any correlation found. While home-cage ethanol consumption may not be an accurate measure of ethanol self-administration, the studies suggest that unlike reports for other drugs of abuse, there does not appear to be a simple relationship between alcohol preference and motor activity.

Effects of continuous versus limited access to ethanol on ethanol self-administration

Eight male, experimentally naive Long-Evans rats were housed in operant chambers 23 h per day following initiation to self-administer ethanol. While housed in the chambers, the animals had continuous access to food pellets according to a fixed ratio 1 schedule of reinforcement, 10% ethanol (v/v) according to a fixed ratio 4 schedule of reinforcement and water in a drinking tube with licks recorded via a drinkometer. Over a series of experimental phases, daily availability of the ethanol solution was limited to 16, 6, 4, 2, or 1 30-min period per day. The 1 30-min period access was examined during the 12th hour or the second hour of the daily sessions. Over the course of the experiment, total responses on the lever that operated the dipper, g/kg per day and number of ethanol drinking bouts per day decreased significantly as the number of daily access periods decreased. On the other hand, the number of dippers presented per ethanol bout, g/kg per ethanol bout and ethanol bout duration increased, with significant increases in dippers per bout occurring when one 30-min access period per day was provided. These data indicate that the size of a single ethanol drinking bout can be increased somewhat by limiting the opportunity to obtain ethanol reinforcement and agrees with earlier research that has shown similar effects.

Effects of manipulating food availability on ethanol self-administration by P rats in a continuous access situation

Male rats from the alcohol-preferring (P) line were housed in operant chambers in which food, water, and ethanol (10% v/v) were available continuously 23 hr per day. Over a period of weeks, the fixed ratio (FR) requirement for food reinforcement was gradually increased from FR 1 to FR 64. The response requirements for water and ethanol remained constant throughout the experiment. As the FR requirement for food reinforcement increased, the total number of food-reinforced responses increased significantly, whereas the total number of food pellets delivered per day and total calories per day decreased significantly. Conversely, ethanol intake (g/kg) and the percentage of total calories from ethanol increased significantly as the response requirement for food reinforcement increased. The increase in ethanol intake was accounted for largely by an increase in the number of ethanol drinking bouts per day rather than an increase in the number of dippers presented per bout. The results support the hypothesis that the manipulation of environmental variables, such as FR requirement for food reinforcement, can influence the ethanol self-administration of P rats; an effect observed previously with nonselected Long-Evans rats.

Ethanol self-administration by alcohol-nonpreferring (NP) rats in a continuous access situation

Male rats, from the alcohol nonpreferring (NP) line, were studied in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 h/d. The NP rats consumed less ethanol per day following 7 weeks under these conditions than did either alcohol-preferring (P) rats or Long-Evans (LE) studied previously under the same conditions for 4 weeks. The NP rats consumed 0.2 g/kg per day during the first week of the experiment, 0.72 g/kg per day during the fourth week, and 1.03 g/kg per day during the seventh week compared to 2.2 g/kg per day for LE rats and 4.8 g/kg per day for P rats following 4 weeks. These data indicate that NP rats will slowly initiate ethanol self-administration under continuous access conditions, but to a lesser extent and at a slower rate than other lines of rats studied previously.

Effects of ethanol concentration and fixed-ratio requirement on ethanol self-administration by P rats in a continuous access situation

Rats, from the alcohol preferring (P) line, were placed in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 hr/day. During Experiment 1, the effects of changing ethanol concentration and response requirement for ethanol were examined. Ten percent and 20% ethanol (v/v) were available on two fixed ratio (FR) schedules, FR 1 and FR 4, for 2 weeks each. During Experiment 2, the effects of increasing the response requirement for ethanol were investigated. Starting with FR 4, the FR requirement for ethanol doubled during 2-week intervals until FR 32 was in effect. For the final phase of these studies, water was placed in the dipper for 1 week followed by a return to 10% ethanol in the dipper. The results from Experiment 1 indicated that when the FR requirement was decreased from FR 4 to FR 1, ethanol-reinforced responding decreased but total daily intake increased. Lowering the FR requirement did not affect the number of ethanol bouts per day but bout size increased. Ethanol concentration had no effect on bout size but the number of bouts per day decreased when the concentration was increased to 20%. Since bout size was unchanged by increasing the ethanol concentration, intake per bout increased at 20% ethanol. The results from Experiment 2 indicated that increasing the response requirement for ethanol decreases ethanol intake. When water was placed in the dipper, responding decreased to the lowest levels observed in the experiment. When ethanol was returned to the dipper, responding returned to baseline levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol and circadian rhythms in the Syrian hamster: effects on entrained phase, reentrainment rate, and period

Wheel-running rhythms were examined in male hamsters with access to 28% ethanol in lieu of water. One group was recorded in a light-dark (LD) cycle that was phase advanced by 8 h on three occasions separated by 23-27 days. On two of the three occasions, hamsters were subjected to a 2- to 3-h cage change procedure designed to stimulate wheel running, which accelerates the rate of reentrainment to 8-h advances. Ethanol and control hamsters showed no group differences in rhythm amplitude, entrained phase, or reentrainment rate. Both groups showed faster reentrainment in the cage change condition. A second group of hamsters recorded in constant dim showed a small but significant lengthening of the free-running period of their wheel-running rhythm when provided with a 28% ethanol solution. Wheel running decreased during ethanol access in this group. Voluntary ethanol consumption evidently can slow the circadian pacemaker regulating activity rhythms in hamsters but has no measurable effect on photic entrainment or pacemaker response to LD shifts or nonphotic manipulations (stimulated activity). Period lengthening may be secondary to decreased activity, but other period-activity correlations obtained did not reveal a strong association between these two variables.

Ethanol drinking patterns in a continuous-access operant situation: effects of ethanol concentration and response requirements

Rats, initiated to self-administer ethanol with either a sucrose-substitution procedure or a secondary-conditioning procedure, were maintained in a continuous-access environmental system in which operant lever press responses were required to receive 10% ethanol and food reinforcement. Water available from a drinking tube was electronically monitored to detect licks. Total daily consumption and patterns of food, water, and ethanol responding were analyzed under conditions in which the concentration of ethanol presented as a reinforcer was either 10% or 20%, and the response requirement for ethanol reinforcement was either a fixed ratio 4 schedule or a fixed ratio 1 schedule. Either increasing the ethanol concentration or decreasing the response requirement resulted in an increase in total daily ethanol intake. There was no significant difference between initiation procedures. These results are similar to observations in studies using a limited-access operant situation. This increased ethanol intake resulted from a complex alteration in the daily ethanol drinking pattern. The greatest ethanol intakes were observed when both the ethanol concentration was increased and response requirement was decreased. This was predominantly the result of increasing the number of ethanol drinking bouts per day when the response requirement was decreased, and by decreasing individual bout size by less than half when the ethanol concentration was doubled. These studies indicate that concentration of the ethanol presented as the reinforcer and the response cost required for reinforcement are involved in regulating ethanol consumption in the continuous-access condition. Type of initiation did not appear to interact with these variables.

Alcohol self-administration in a nonrestricted access situation with alcohol-preferring (P) rats

Genetic variables have been implicated as contributing factors in the development of alcoholic behavior. Rats bred selectively for alcohol preference have been used in laboratory studies to investigate the role of such variables. In the present study, rats from the alcohol preferring (P) line were placed in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 hr/day. Food pellets (45 mg) were presented on an FR 1 schedule of reinforcement, while ethanol was presented in a 0.1 ml dipper on an FR 4 schedule of reinforcement. Water was available in a drinking tube with licks monitored by a drinkometer. Data were analyzed in terms of both total daily intakes and computer defined bouts. The P rats showed greater daily ethanol intakes compared with Long-Evans (LE) animals previously studied under similar access conditions. The major difference in intake was a result of the P rats having a greater number of daily ethanol drinking bouts, while having only a slight increase in individual bout size. These data indicate that genetic selection for ethanol preference may result in the regulation of ethanol intake by means of changes in the frequency of ethanol drinking bouts but not by changes in bout size.

Effect of drugs influencing 5-HT function on ethanol drinking and feeding behaviour in rats: studies using a drinkometer system

In the present study, we have investigated how various 5-HT agonists (m-chlorophenylpiperazine (mCPP) (0.1-1 mg/kg), 8-hydroxy 2-(di-N-propylamino) tetralin (8-OH DPAT) (0.125-2 mg/kg) and 5-HT (0.5-2 mg/kg)), the 5-HT uptake blocker sertraline (1-10 mg/kg), and the 5-HT uptake blocker and releaser dexfenfluramine (0.5-2.5 mg/kg), affect ethanol intake in a continual access paradigm using Wistar rats. By means of a drinkometer system the effect of each drug on microdrinking parameters (e.g., drink latency, number, and duration of drinking bouts) was assessed. The effect of various 5-HT antagonists (metergoline, ritanserin, ondansetron, and xylamidine) against the dexfenfluramine-induced suppression was studied. Furthermore, threshold doses for the anorectic and the suppressant effects of mCPP, sertraline and dexfenfluramine on ethanol intake were identified. From these studies, it seemed that similar mechanisms may be responsible for the suppressant effects of the various 5-HT agonists studied (direct and indirect) on ethanol and food intake. The 5-HT3 receptor antagonist, ondansetron, also reduced ethanol (but not food) intake. However, the profile of this effect may suggest an alternative means by which 5-HT3 receptors regulate ethanol intake in the rat by comparison to the various 5-HT agonists studied.

The effects of ethanol initiation procedures on ethanol reinforced behavior in the alcohol-preferring rat

Rats from the alcohol preferring (P) line developed at Indiana University were initiated to self-administer ethanol orally without food or water restriction using either a sucrose-fading or a secondary-conditioning procedure. Following initiation, they were tested under a variety of operant conditions to examine the ability of ethanol to reinforce lever pressing behavior. Regardless of initiation procedure, the animals maintained lever pressing behavior with ethanol reinforcement, even at ethanol concentrations as high as 40% (v/v). Slightly higher daily session intakes (g/kg) were found at the higher ethanol concentrations following the secondary-conditioning initiation procedure compared with the sucrose-fading technique. When both ethanol and water were concurrently available, the rats showed a high preference for ethanol reinforcement. When varying concentrations of sucrose were substituted for water, the amount of ethanol ingested decreased as the concentration of the alternative sucrose increased. However, if the response requirement for the sucrose was substantially greater than that for ethanol, the rats shifted their responding to the lever associated with ethanol presentation. The results are discussed in relation to prior work using similar procedures with Long-Evans non-selected rats and with the alcohol non-preferring (NP) rat line.

Ethanol self-administration in a nonrestricted access situation: effect of ethanol initiation

Two groups of rats (male, Long-Evans) were studied in a continuous access situation, in which ethanol, food and water intake patterns were monitored, 23 h/day. One group of rats was initiated to lever press for ethanol prior to study in the continuous access situation by use of a secondary-conditioning procedure. The other group had no prior initiation. It was found that the ethanol self-administration pattern of the initiated rats was similar to a previous study using another initiation procedure. After four weeks, the noninitiated group also demonstrated an ethanol intake pattern similar to initiated animals. However, the specific nature of individual ethanol drinking bouts in the noninitiated animals was found to be different, suggesting that initiation resulted in larger and more ethanol-drinking bouts. In addition, the noninitiated animals failed to show any home-cage shift in ethanol preference, which is observed after the use of the initiation procedures. The only major difference found between the sucrose-substitution initiation procedure and the secondary-conditioning procedure occurred when response requirements to obtain food were increased. In this situation, ethanol intake increased only in the sucrose-substitution initiated animals. The relation of this finding to the underlying theoretical basis for each type of initiation procedure is discussed.

Lead attenuates the antipunishment effects of ethanol

Adult male rats were exposed to a diet containing no added chemicals, or a diet containing 500 ppm added lead (as lead acetate), for 70 days. On Day 71 (training day), after 24 h of water deprivation, all animals were placed in a test apparatus and permitted to make 220 licks for a 5.5 percent (v/v) sucrose in water solution. On Day 72 (test day), all animals received conditioned punishment training where electric shock was delivered to the tongue following every 20 licks of the sucrose and water solution. Prior to commencing punishment training on Day 72, half the animals for the control diet condition (Group Control-Diet-Saline), and half the animals for the lead diet condition (Group Lead-Diet-Saline), received IP injections of saline. Conversely, the remaining half of the animals (Groups Control-Diet-Ethanol and Lead-Diet-Ethanol) received IP injections of 1.5 g/kg ethanol. The results of the conditioned punishment test revealed that animals exposed to a control diet and administered ethanol (Group Control-Diet-Ethanol) engaged in more punished licking and received more shocks than their lead-treated counterparts (Group Lead-Diet-Ethanol). Both of the groups exhibited more punished licking and received more shocks than either of the groups that received saline injections. The possibility that lead contamination may reduce the pharmacologic impact of ethanol is noted.

Differential reinforcement and diurnal rhythms of lever pressing for ethanol in AA and Wistar rats

High-drinking AA (Alko, Alcohol) and moderate-drinking Wistar rats, after ethanol drinking experience in their home cages, were housed continually in operant chambers with free access to water and food. Ethanol and water could be obtained by lever pressing on a concurrent FR1:FR1 schedule. The AA rats readily learned the operant response for oral ethanol, responded significantly more for ethanol than water, and increased ethanol responding when the fixed-ratio schedule for it was increased from FR1 to FR2 and FR4. This indicates that ethanol was serving as a reinforcer for the AAs. In contrast, the Wistars showed little evidence for ethanol reinforcement. Both AAs and Wistars had a three-peak pattern of ethanol responding during the dark phase, but peaks for the Wistars preceded those for the AAs by 1 or 2 hr. The patterns were similar when on an FR4 schedule, which greatly reduced the amount of alcohol, suggesting that they are not controlled by blood alcohol levels. The difference between the AA and Wistar patterns may, however, be related to the differential ethanol reinforcement.