Operant Self-administration Procedure Research Articles

Sex Differences in Home-Cage Ethanol Drinking and Operant Self-Administration in C57BL/6J Mice with Equivalent Regulation by Glutamate AMPAR Activity.

Considering sex as a biological variable (SABV) in preclinical research can enhance understanding of the neurobiology of alcohol use disorder (AUD). However, the behavioral and neural mechanisms underlying sex-specific differences remain unclear. This study aims to elucidate SABV in ethanol (EtOH) consumption by evaluating its reinforcing effects and regulation by glutamate AMPA receptor activity in male and female mice. C57BL/6J mice (male and female) were assessed for EtOH intake under continuous and limited access conditions in the home cage. Acute sensitivity to EtOH sedation and blood clearance were evaluated as potential modifying factors. Motivation to consume EtOH was measured using operant self-administration procedures. Sex-specific differences in neural regulation of EtOH reinforcement were examined by testing the effects of a glutamate AMPA receptor antagonist on operant EtOH self-administration. Female C57BL/6J mice exhibited a time-dependent escalation in EtOH intake under both continuous and limited access conditions. They were less sensitive to EtOH sedation and had lower blood levels post-EtOH administration (4 g/kg) despite similar clearance rates. Females also showed increased operant EtOH self-administration and progressive ratio performance over a 30-day baseline period compared to males. The AMPAR antagonist GYKI 52466 (0-10 mg/kg, IP) dose-dependently reduced EtOH-reinforced lever pressing in both sexes, with no differences in potency or efficacy. These findings confirm that female C57BL/6J mice consume more EtOH than males in home-cage conditions and exhibit reduced acute sedation, potentially contributing to higher EtOH intake. Females demonstrated increased operant EtOH self-administration and motivation, indicating higher reinforcing efficacy. The lack of sex differences in the relative effects of GYKI 52466 suggests that AMPAR activity is equally required for EtOH reinforcement in both sexes.

Intermittent-access operant alcohol self-administration promotes binge-like drinking and drinking despite negative consequences in male and female heterogeneous stock rats

The study of Alcohol Use Disorders (AUD) in preclinical models is hampered by difficulty in training rodents to voluntarily consume high levels of alcohol. The intermittency of alcohol access/exposure is well known to modulate alcohol consumption (e.g., alcohol deprivation effect, intermittent-access two-bottle-choice) and recently, intermittent access operant self-administration procedures have been used to produce more intense and binge-like self-administration of intravenous psychostimulant and opioid drugs. In the present study, we sought to systematically manipulate the intermittency of operant self-administered alcohol access to determine the feasibility of promoting more intensified, binge-like alcohol consumption. To this end, 24 male and 23 female NIH Heterogeneous Stock rats were trained to self-administer 10% w/v ethanol, before being split into three different-access groups. Short Access (ShA) rats continued receiving 30-min training sessions, Long Access (LgA) rats received 16-h sessions, and Intermittent Access (IntA) rats received 16-h sessions, wherein the hourly alcohol-access periods were shortened over sessions, down to 2 min. IntA rats demonstrated an increasingly binge-like pattern of alcohol drinking in response to restriction of alcohol access, while ShA and LgA rats maintained stable intake. All groups were tested on orthogonal measures of alcohol-seeking and quinine-punished alcohol drinking. The IntA rats displayed the most punishment-resistant drinking. In a separate experiment, we replicated our main finding, that intermittent access promotes a more binge-like pattern of alcohol self-administration using 8 male and 8 female Wistar rats. In conclusion, intermittent access to self-administered alcohol promotes more intensified self-administration. This approach may be useful in developing preclinical models of binge-like alcohol consumption in AUD.

Sex-specific decision-making impairments and striatal dopaminergic changes after binge drinking history in rats.

Binge drinking (BD) is a harmful behavior for health and is a predictive factor for the development of alcohol addiction. Weak decision-making (DM) capacities could play a role in the vulnerability to BD which in turn would lead to DM impairments, thus perpetuating BD. Longitudinal preclinical studies are however lacking and necessary to understand this complex relationship. Both DM and BD are influenced by sex and involve dopamine release in the core of the nucleus accumbens, a central mechanism regulated by dopamine D2/3 autoreceptors. In this context, we used an operant self-administration procedure of BD in male and female rats, and longitudinally assessed DM capacity, memory and anxiety-like behavior. To better understand the mechanisms potentially involved in the relationship between DM and BD, ex vivo dopamine transmission was assessed short term after the end of the binge exposure in the core of the nucleus accumbens (NAc) using the fast-scan cyclic voltammetry (FSCV) technique and the D2/3 agonist quinpirole. We found important basal sex differences in DM, with female rats showing better performances at baseline. Choice processes were impaired exclusively in males after BD history, associated with a decrease in impulse control in both sexes, while memory and anxiety-like behavior were not affected. Our neurobiological results demonstrate that BD did not affect basal dopamine signaling in the NAc core, regardless of the sex, but reveal changes in the sensitivity to the inhibitory effects of quinpirole in females. DM impairments were neither associated with changes in basal dopamine signaling nor pre-synaptic D2 activity. Overall, our findings show that BD affects both DM processes and dopamine transmission in the core of the NAc in a sex-related manner, further suggesting that these effects may play a role in the vicious cycle leading to BD perpetuation and the early onset of AUD. Our results may inform novel strategies for therapeutic and prevention interventions.

Activation of peroxisome proliferator-activated receptor γ reduces alcohol drinking and seeking by modulating multiple mesocorticolimbic regions in rats.

Peroxisome proliferator-activated receptor γ (PPARγ) is an intracellular transcription factor whose signaling activation by the selective agonist pioglitazone reduces alcohol drinking and alcohol-seeking behavior in rats. The present study utilized the two-bottle choice and operant self-administration procedures to investigate neuroanatomical substrates that mediate the effects of PPARγ agonism on alcohol drinking and seeking in msP rats. Bilateral infusions of pioglitazone (0, 5, and 10 μg/μl) in the rostromedial tegmental nucleus (RMTg) decreased voluntary alcohol drinking and alcohol self-administration. Microinjections of pioglitazone in the ventral tegmental area (VTA), central amygdala (CeA), and nucleus accumbens (NAc) shell had no such effect. Notably, water, food, and saccharin consumption was unaltered by either treatment. The yohimbine-induced reinstatement of alcohol seeking was prevented by infusions of pioglitazone (0, 2.5, 5, and 10 μg/μl) in the CeA, VTA, and RMTg but not in the NAc shell. These results emphasize the involvement of mesocorticolimbic circuitries in mediating the effects of PPARγ agonists on alcohol drinking and seeking. These results will facilitate future studies that investigate the pathophysiological role of PPARγ in alcohol use disorder and help clarify the mechanisms by which the activation of this receptor decreases the motivation for drinking.

S03-3vulnerability to voluntary binge drinking in rats using an operant self-administration procedure

S03-3vulnerability to voluntary binge drinking in rats using an operant self-administration procedure

Stroke triggers nigrostriatal plasticity and increases alcohol consumption in rats

Excessive alcohol consumption is a known risk factor for stroke, but the effect of stroke on alcohol intake is unknown. The dorsomedial striatum (DMS) and midbrain areas of the nigrostriatal circuit are critically associated to stroke and alcohol addiction. Here we sought to explore the influence of stroke on alcohol consumption and to uncover the underlying nigrostriatal mechanism. Rats were trained to consume alcohol using a two-bottle choice or operant self-administration procedure. Retrograde beads were infused into the DMS or midbrain to label specific neuronal types, and ischemic stroke was induced in the dorsolateral striatum (DLS). Slice electrophysiology was employed to measure excitability and synaptic transmission in DMS and midbrain neurons. We found that ischemic stroke-induced DLS infarction produced significant increases in alcohol preference, operant self-administration, and relapse. These increases were accompanied by enhanced excitability of DMS and midbrain neurons. In addition, glutamatergic inputs onto DMS D1-neurons was potentiated, whereas GABAergic inputs onto DMS-projecting midbrain dopaminergic neurons was suppressed. Importantly, systemic inhibition of dopamine D1 receptors attenuated the stroke-induced increase in operant alcohol self-administration. Our results suggest that the stroke-induced DLS infarction evoked abnormal plasticity in nigrostriatal dopaminergic neurons and DMS D1-neurons, contributing to increased post-stroke alcohol-seeking and relapse.

Mu Opioid Receptors in Gamma-Aminobutyric Acidergic Forebrain Neurons Moderate Motivation for Heroin and Palatable Food

BackgroundMu opioid receptors (MORs) are central to pain control, drug reward, and addictive behaviors, but underlying circuit mechanisms have been poorly explored by genetic approaches. Here we investigate the contribution of MORs expressed in gamma-aminobutyric acidergic forebrain neurons to major biological effects of opiates, and also challenge the canonical disinhibition model of opiate reward. MethodsWe used Dlx5/6-mediated recombination to create conditional Oprm1 mice in gamma-aminobutyric acidergic forebrain neurons. We characterized the genetic deletion by histology, electrophysiology, and microdialysis; probed neuronal activation by c-Fos immunohistochemistry and resting-state functional magnetic resonance imaging; and investigated main behavioral responses to opiates, including motivation to obtain heroin and palatable food. ResultsMutant mice showed MOR transcript deletion mainly in the striatum. In the ventral tegmental area, local MOR activity was intact, and reduced activity was only observed at the level of striatonigral afferents. Heroin-induced neuronal activation was modified at both sites, and whole-brain functional networks were altered in live animals. Morphine analgesia was not altered, and neither was physical dependence to chronic morphine. In contrast, locomotor effects of heroin were abolished, and heroin-induced catalepsy was increased. Place preference to heroin was not modified, but remarkably, motivation to obtain heroin and palatable food was enhanced in operant self-administration procedures. ConclusionsOur study reveals dissociable MOR functions across mesocorticolimbic networks. Thus, beyond a well-established role in reward processing, operating at the level of local ventral tegmental area neurons, MORs also moderate motivation for appetitive stimuli within forebrain circuits that drive motivated behaviors.

Oxycodone physical dependence and its oral self-administration in C57BL/6J mice

Abuse of prescription opioids, such as oxycodone, has markedly increased in recent decades. While oxycodone's antinociceptive effects have been detailed in several preclinical reports, surprisingly few preclinical reports have elaborated its abuse-related effects. This is particularly surprising given that oxycodone has been in clinical use since 1917. In a novel oral operant self-administration procedure, C57BL/6J mice were trained to self-administer water before introducing increasing concentrations of oxycodone (0.056–1.0mg/ml) under post-prandial conditions during daily, 3-h test sessions. As the concentration of oxycodone increased, the numbers of deliveries first increased, then decreased in an inverted U-shape fashion characteristic of the patterns of other drugs self-administered during limited access conditions. After post-prandial conditions were removed, self-administration at the highest concentration was maintained suggesting oral oxycodone served as a positive reinforcer. In other mice, using a novel regimen of physical dependence, mice were administered increasing doses of oxycodone (9.0–33.0mg/kg, s.c.) over 9 days, challenged with naloxone (0.1–10.0mg/kg, s.c.), and then observed for 30min. Naloxone dose-dependently increased the observed number of somatic signs of withdrawal, suggesting physical dependence of oxycodone was induced under this regimen. This is the first report demonstrating induction of oral operant self-administration of oxycodone and dose-dependent precipitations of oxycodone withdrawal in C57BL/6J mice. The use of oral operant self-administration as well as the novel physical dependence regimen provides useful approaches to further examine the abuse- and dependence-related effects of this highly abused prescription opioid.

The Small G Protein H-Ras in the Mesolimbic System Is a Molecular Gateway to Alcohol-Seeking and Excessive Drinking Behaviors

Uncontrolled consumption of alcohol is a hallmark of alcohol abuse disorders; however, the central molecular mechanisms underlying excessive alcohol consumption are still unclear. Here, we report that the GTP binding protein, H-Ras in the nucleus accumbens (NAc) plays a key role in neuroadaptations that underlie excessive alcohol-drinking behaviors. Specifically, acute (15 min) systemic administration of alcohol (2.5 g/kg) leads to the activation of H-Ras in the NAc of mice, which is observed even 24 h later. Similarly, rat operant self-administration of alcohol (20%) also results in the activation of H-Ras in the NAc. Using the same procedures, we provide evidence suggesting that the exchange factor GRF1 is upstream of H-Ras activation by alcohol. Importantly, we show that infection of mice NAc with lentivirus expressing a short hairpin RNA that targets the H-Ras gene produces a significant reduction of voluntary consumption of 20% alcohol. In contrast, knockdown of H-Ras in the NAc of mice did not alter water, quinine, and saccharin intake. Furthermore, using two-bottle choice and operant self-administration procedures, we show that inhibiting H-Ras activity by intra-NAc infusion of the farnesyltransferase inhibitor, FTI-276, produced a robust decrease of rats' alcohol drinking; however, sucrose consumption was unaltered. Finally, intra-NAc infusion of FTI-276 also resulted in an attenuation of seeking for alcohol. Together, these results position H-Ras as a central molecular mediator of alcohol's actions within the mesolimbic system and put forward the potential value of the enzyme as a novel target to treat alcohol use disorders.

18-Methoxycoronaridine blocks context-induced reinstatement following cocaine self-administration in rats

Numerous studies utilizing drug self-administration have shown the importance of conditioned cues in maintaining and reinstating addictive behaviors. However, most used simple cues that fail to replicate the complexity of cues present in human craving and addiction. We have recently shown that music can induce behavioral and neurochemical changes in rats following classical conditioning with psychostimulants. However, such effects have yet to be characterized utilizing operant self-administration procedures, particularly with regard to craving and relapse. The goal of the present study was to validate the effectiveness of music as a contextual conditioned stimulus using cocaine in an operant reinstatement model of relapse. Rats were trained to lever press for cocaine with a musical cue, and were subsequently tested during reinstatement sessions to determine how musical conditioning affected drug seeking behavior. Additionally, in vivo microdialysis was used to determine basolateral amygdala involvement during reinstatement. Lastly, tests were conducted to determine whether the putative anti-addictive agent 18-methoxycoronaridine (18-MC) could attenuate cue-induced drug seeking behavior. Our results show that music-conditioned animals exhibited increased drug seeking behaviors when compared to controls during reinstatement test sessions. Furthermore, music-conditioned subjects exhibited increased extracellular dopamine in the basolateral amygdala during reinstatement sessions. Perhaps most importantly, 18-MC blocked musical cue-induced reinstatement. Thus, music can be a powerful contextual conditioned cue in rats, capable of inducing changes in both brain neurochemistry and drug seeking behavior during abstinence. The fact that 18-MC blocked cue-induced reinstatement suggests that α3β4 nicotinic receptors may be involved in the mechanism of craving, and that 18-MC may help prevent relapse to drug addiction in humans.

Microinjection of Glycine into the Ventral Tegmental Area Selectively Decreases Ethanol Consumption

The mechanisms of ethanol addiction are not completely understood. The mesolimbic dopaminergic system is involved in many drug-related behaviors, including ethanol self-administration. The dopaminergic neurons in this system originate in the ventral tegmental area (VTA) and are under the control of GABAergic transmission. Our previous in vitro electrophysiological data indicate that glycine receptors (GlyRs) exist on the GABAergic terminals, which make synapses on VTA dopaminergic neurons, and activation of these GlyRs reduces GABAergic transmission and increases the activity of VTA dopaminergic neurons. In the current study, we tested the hypothesis that the activation of the presynaptic GlyRs in the VTA might interfere with ethanol self-administration. Glycine and strychnine, the selective antagonist of GlyRs, were injected, either alone or in combination, into the VTA of rats. Ethanol self-administration by rats was evaluated by using three different drinking models: intermittent access, continuous access, and operant self-administration. We found that the infusion of glycine into the VTA selectively reduced the intake of ethanol but not sucrose or water in rats chronically exposed to ethanol under the intermittent-access and continuous-access procedures and decreased lever-press responding for ethanol under an operant self-administration procedure. The effects of glycine probably were mediated by strychnine-sensitive GlyRs, because the coinjection of glycine and strychnine reduced neither ethanol intake in the home cages nor lever-press responding for ethanol in the operant chambers. Thus, GlyRs in the VTA may play a critical role in ethanol self-administration in animals chronically exposed to ethanol. Therefore, drugs targeting GlyRs may be beneficial for alcoholics.

AKT Signaling Pathway in the Nucleus Accumbens Mediates Excessive Alcohol Drinking Behaviors

Neuroadaptations within the nucleus accumbens (NAc) have been implicated in molecular mechanisms underlying the development and/or maintenance of alcohol abuse disorders. We recently reported that the activation of mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in the NAc of rodents, after exposure to alcohol, contributes to alcohol drinking behaviors. The kinase AKT is a main upstream activator of the mTORC1 pathway. We therefore hypothesized that the activation of AKT in the NAc in response to alcohol exposure plays an important role in mechanisms that underlie excessive alcohol consumption. Western blot analysis was used to assess the phosphorylation levels of enzymes. Acute exposure of mice to alcohol was achieved by the administration of 2 g/kg alcohol intraperitoneally (i.p.). Two-bottle choice and operant self-administration procedures were used to assess drinking behaviors in rats. We found that acute systemic administration of alcohol and recurring cycles of excessive voluntary consumption of alcohol and withdrawal result in the activation of AKT signaling in the NAc of rodents. We show that inhibition of AKT or its upstream activator, phosphatidylinositol-3-kinase (PI3K), within the NAc of rats attenuates binge drinking as well as alcohol but not sucrose operant self-administration. Our results suggest that the activation of the AKT pathway in the NAc in response to alcohol exposure is an important contributor to the molecular mechanisms underlying alcohol-drinking behaviors. AKT signaling pathway inhibitors are therefore potential candidates for drug development for the treatment of alcohol use and abuse disorders.

Assessment of GABA-B, metabotropic glutamate, and opioid receptor involvement in an animal model of binge drinking

Drinking to intoxication or binge drinking is a hallmark characteristic of alcohol abuse. Although hard to model in rodents, the scheduled high alcohol consumption (SHAC) procedure generates high, stable ethanol intake and blood ethanol concentrations in mice to levels consistent with definitions of binge drinking. The purpose of the present studies was to determine the effects of pharmacological manipulation of the opioidergic, glutamatergic, and γ-aminobutyric acid (GABA)ergic systems on binge drinking with the SHAC procedure. Parallel manipulations were conducted in mice trained in operant self-administration of either sucrose or ethanol. For the SHAC procedure, genetically heterogeneous Withdrawal Seizure Control mice were given varying periods of fluid access, with a 30-min ethanol session every third day (total of seven). Mice were pretreated intraperitoneally with naltrexone (0, 0.6, or 1.25 mg/kg), baclofen (0, 2.5, or 5.0 mg/kg), or 2-methyl-6-(phenylethynyl)-pyridine (MPEP; 0, 3.0, or 10.0 mg/kg) before each ethanol session. For the operant self-administration procedure, separate groups of C57BL/6 mice were trained to complete a single response requirement (16 presses on the active lever) to gain 30 min of access to an ethanol or a sucrose solution. Mice received pretreatments of the same doses of naltrexone, MPEP, or baclofen before the self-administration sessions, with saline injections on intervening days. Naltrexone produced a dose-dependent decrease in binge drinking, and the highest dose also significantly decreased operant self-administration of ethanol and sucrose. Both doses of baclofen significantly decreased binge alcohol consumption, but the higher dose also tended to decrease water intake. The highest dose of baclofen also significantly decreased operant self-administration of sucrose. MPEP (10 mg/kg) significantly decreased binge alcohol consumption and sucrose self-administration. These results indicate that manipulation of the opioidergic, glutamatergic, and GABAergic systems significantly decreased binge drinking.

Operant Self‐Administration Models for Testing the Neuropharmacological Basis of Ethanol Consumption in Rats

Operant self-administration procedures are used to assess the neural basis of ethanol-seeking behavior under a wide range of experimental conditions. In general, rats do not spontaneously self-administer ethanol in pharmacologically meaningful amounts. This unit provides a step-by-step guide for training rats to self-administer quantities of ethanol that produce moderate to high blood-alcohol content. Different protocols are used for rats that are genetically heterogeneous versus rats that are selectively bred for high alcohol preference. Also, these protocols have different sets of advantages and disadvantages in terms of the ability to control for caloric intake and taste of solutions in operant testing. Basic self-administration protocols can also be altered to focus on different aspects of the motivational properties of ethanol (for example, those related to dependence). This unit provides multiple protocols that lead to alcohol intake in rats, which can be pharmacologically probed relative to a variety of control conditions.

The influence of mecamylamine on ethanol and sucrose self-administration

Neuronal nicotinic acetylcholine receptors (nAChRs) are believed to be critically involved in ethanol-related behaviors as well as in neurochemical responses to ethanol. However, discernment of nAChR contribution to ethanol reinforcement and consumption remains incomplete. The current studies examined the influence of the nAChR antagonist mecamylamine (MEC) on operant ethanol self-administration using a procedure that independently assessed appetitive and consumptive processes, and compared these findings to effects of MEC on sucrose self-administration. Male C57BL/6J (B6) mice were trained to respond for 30-min access to a retractable drinking tube containing either 10% v/v ethanol (10E) or 5% w/v sucrose (5S). Once trained, mice were habituated to saline injection and then treated with a series of MEC doses (0–8 mg/kg; i.p.) in a within-subject design. In a separate cohort, MEC was evaluated for its influence on locomotor activity. MEC dose-dependently reduced 10E and 5S self-administration. The suppression in ethanol intake was attributable to a reduction in bout frequency, whereas the attenuation in sucrose intake was due to a decrease in bout size. Doses of MEC (6–8 mg/kg) that altered drinking patterns were also found to impair locomotor activity. Although MEC non-selectively reduced 10E and 5S intakes in mice, there was some specificity in alterations of the underlying drinking pattern for each reinforcer. Assessment of drinking topography within an operant self-administration procedure may provide useful insights regarding the role of nAChR function in the regulation of ethanol consumption.

The Alcohol Deprivation Effect (ADE) in C57BL/6J mice is observed using operant self-administration procedures and is modulated by CRF-1 receptor signaling

The Alcohol Deprivation Effect (ADE) in C57BL/6J mice is observed using operant self-administration procedures and is modulated by CRF-1 receptor signaling

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

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

Relationship Between Ethanol’s Acute Locomotor Effects and Ethanol Self‐Administration in Male Long‐Evans Rats

Human studies have suggested an important relationship between ethanol sensitivity and risk of alcoholism. These studies have led some to hypothesize that a low initial sensitivity to ethanol's depressant effects and/or an elevated response to ethanol's stimulant effects may represent important risk factors associated with the development of abusive drinking behavior. Unfortunately, elucidating neurobiologic mechanisms that may underlie these relationships between ethanol sensitivity and ethanol drinking have been hampered by difficulties in modeling some of these interactions in animals. In this study, we re-examined some of these relationships in an outbred strain of rats using continuous access two-bottle choice drinking and a limited-access operant procedure that engenders pharmacologically relevant levels of ethanol intake and permits the discrete assessment of appetitive and consummatory measures of ethanol drinking behavior. Twenty-three male Long-Evans rats were habituated to a locomotor activity box and then tested for their response to a stimulant (0.5 g/kg) and depressant (1.5 g/kg) ethanol dose. Rats were then trained to complete a lever pressing requirement to gain access to 10% ethanol for 20-minute sessions conducted 5 d/wk for 5 weeks. Appetitive behavior was assessed after 2.5 and 4.5 weeks using 20-minute extinction trials in which ethanol was not presented and lever responses were recorded. Home-cage ethanol preference was also assessed prior to and immediately following the 5-week self-administration regimen using a continuous access, two-bottle choice procedure. A significant increase in home-cage ethanol preference was observed following the self-administration procedure, however, neither measure of ethanol preference correlated with average daily ethanol intake during the operant self-administration sessions or with initial sensitivity to ethanol's stimulant or depressant effects. Notably, a significant negative correlation was observed between sensitivity to ethanol's locomotor depressant effect and daily intake during the operant self-administration sessions. No significant relationships were noted between sensitivity to ethanol's locomotor effects and extinction responding. The results of these studies suggest that the well-established relationship between a low level of response to ethanol and increased ethanol consumption reported in human studies can be observed in an outbred rodent strain using a limited-access operant self-administration procedure, but not with home-cage ethanol drinking.

Age differences in the spontaneous acquisition of nicotine self-administration in male Wistar and Long–Evans rats

Epidemiological evidence suggests that adolescents may exhibit a unique susceptibility to the motivational effects of nicotine compared to adults. In contrast to the hypothesis of an enhanced vulnerability to nicotine during adolescence, we have observed that nicotine is less reinforcing in adolescent compared to adult rats using a progressive ratio reinforcement schedule in an operant self-administration procedure, although prior operant conditioning experience may have masked differences in initial sensitivity to nicotine. This study examined the spontaneous acquisition of nicotine self-administration in adolescent (postnatal day (PD) 31) and adult (PD87) male Wistar and Long-Evans rats. Rats self-administered nicotine (0.015 or 0.03 mg/kg/infusion, i.v.) during 2-h operant conditioning sessions under fixed-ratio-1 (FR1) and FR3 reinforcement schedules for six sessions each. A subset of rats (adolescents: PD42, adults: PD98) underwent extinction of responding and nicotine priming-induced reinstatement (0.15 mg/kg, s.c.). In a separate group of rats, saccharin self-administration (0.1 ml of 0.2% w/v) was tested to determine the specificity of our findings with nicotine. A greater proportion of adult compared to adolescent rats acquired self-administration of 0.015 mg/kg/infusion nicotine, but both age groups readily acquired self-administration of 0.03 mg/kg/infusion nicotine and saccharin. Age differences in extinction of responding for nicotine or saccharin depended upon strain, but priming-induced reinstatement was similar across age and strain. The current findings are consistent with those obtained under a more demanding progressive ratio reinforcement schedule and suggest that adolescents, compared to adults, may not be as sensitive to the reinforcing effects of nicotine.

Increased Consumption but Not Operant Self‐administration of Ethanol in Mice Lacking the RIIβ Subunit of Protein Kinase A

Accumulating evidence indicates that adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is involved in the neurobiological responses to ethanol. Previous reports indicate that mice lacking the RIIbeta subunit of PKA (RIIbeta(-/-)) voluntarily consume more ethanol than wild-type controls (RIIbeta(+/+)) using 2-bottle testing procedures. Although such procedures primarily measure consummatory behavior, operant self-administration procedures allow analysis of consummatory as well as appetitive or "ethanol-seeking" behavior (i.e., lever pressing is required to gain access to the ethanol solution). Therefore, we determined whether the high ethanol consumption characteristic of RIIbeta(-/-) mice would be complemented by increased appetitive ethanol-seeking behavior in an operant paradigm. RIIbeta(-/-) (n=8) and RIIbeta(+/+) (n=8) mice were initially sucrose-faded until they were lever responding for nonsweetened ethanol (10, 14, and 18%). Following the self-administration testing, RIIbeta(+/+) and RIIbeta(-/-) mice were given access to 2 bottles, one containing water and the other ethanol to replicate the voluntary ethanol drinking data previously from our laboratory. Finally, immediately after voluntary consumption all mice were again tested for self-administration of 10% ethanol. Alterations in the reinforcement schedule were also explored as RIIbeta(+/+) and RIIbeta(-/-) mice were tested for self-administration of 10% ethanol at FR-3 and FR-5 schedules. The RIIbeta(-/-) mice displayed lower operant responding for ethanol and food reinforcement compared with RIIbeta(+/+) controls. However, this effect was driven by a significant increase in lever responses made by female RIIbeta(+/+) mice. When the excessive lever responses of the female RIIbeta(+/+) mice are accounted for, the RIIbeta(-/-) mice show ethanol lever responses comparable to controls. Following operant self-administration testing, RIIbeta(-/-) mice of both sexes consumed more ethanol solution compared with RIIbeta(+/+) mice during 2-bottle testing. Increased ingestion of ethanol by RIIbeta(-/-) mice is likely the result of altered PKA activity within neuronal pathways that control ethanol-consummatory behaviors. Conversely, the RIIbeta subunit of PKA appears not to play a critical role in neuronal pathways that regulate appetitive behaviors directed at obtaining ethanol. Finally, increased operant self-administration of food and ethanol by female wild-type mice was absent in female RIIbeta(-/-) mice, suggesting that normal PKA signaling may be part of a general, and sex-dependent, mechanism involved with reinforcement-seeking behavior.