Oral self-administration of ethanol and not experimenter-administered ethanol facilitates rewarding electrical brain stimulation

Ethanol inhibits dopamine uptake via organic cation transporter 3: Implications for ethanol and cocaine co-abuse

Concurrent cocaine and alcohol use is among the most frequent drug combination, and among the most dangerous in terms of deleterious outcomes. Cocaine increases extracellular monoamines by blocking dopamine (DA), norepinephrine (NE) and serotonin (5-HT) transporters (DAT, NET and SERT, respectively). Likewise, ethanol also increases extracellular monoamines, however evidence suggests that ethanol does so independently of DAT, NET and SERT. Organic cation transporter 3 (OCT3) is an emergent key player in the regulation of monoamine signaling. Using a battery of in vitro, in vivo electrochemical, and behavioral approaches, as well as wild-type and constitutive OCT3 knockout mice, we show that ethanol's actions to inhibit monoamine uptake are dependent on OCT3. These findings provide a novel mechanistic basis whereby ethanol enhances the neurochemical and behavioral effects of cocaine and encourage further research into OCT3 as a target for therapeutic intervention in the treatment of ethanol and ethanol/cocaine use disorders.

The effects of acamprosate on prefrontal cortical function are mimicked by CaCl2 and they are influenced by the history of alcohol exposure

Alcohol use disorder is associated with functional changes in the medial prefrontal cortex (mPFC), which include altered glutamatergic transmission and deficits in executive functions that contribute to relapse. Acamprosate (calcium-bis N-acetylhomotaurinate) reduces alcohol craving and relapse, effects that are thought to be mediated by acamprosate's ability to ameliorate alcohol-induced dysregulation of glutamatergic signaling. Treatment with acamprosate and its active moiety calcium (CaCl2) both improve deficits in cognitive flexibility in postdependent mice following chronic intermittent ethanol (CIE) exposure. Here, we show that mice that self-administered alcohol under goal-directed conditions (i.e., operant responding on a fixed-ratio schedule) also display similar deficits in cognitive flexibility and altered glutamatergic signaling in the mPFC, both of which were improved with acamprosate or CaCl2. However, under conditions shown to bias behavior towards habitual responding (operant self-administration after CIE exposure, or on a variable interval schedule), alcohol-induced changes to glutamatergic transmission were unaffected by either acamprosate or CaCl2 treatment. Together, these findings suggest that the variable effects of acamprosate on synaptic signaling may reflect a shift in mPFC networks related to the loss of behavioral control in habitual alcohol-seeking.

Sex-specific plasticity in CRF regulation of inhibitory control in central amygdala CRF1 neurons after chronic voluntary alcohol drinking

Despite strong preclinical evidence for the ability of corticotropin releasing factor 1 (CRF1) antagonists to regulate alcohol consumption, clinical trials have not yet demonstrated therapeutic effects of these compounds in alcohol use disorder (AUD) patients. Several confounding factors may limit the translation of preclinical CRF1 research to patients, including reliance on experimenter-administered alcohol instead of voluntary consumption, a preponderance of evidence collected in male subjects only and an inability to assess the effects of alcohol on specific brain circuits. A population of particular interest is the CRF1-containing neurons of the central amygdala (CeA). CRF1 CeA neurons are sensitive to ethanol, but the effects of alcohol drinking on CRF signalling within this population are unknown. In the present study, we assessed the effects of voluntary alcohol drinking on inhibitory control of CRF1+ CeA neurons from male and female CRF1:GFP mice using ex vivo electrophysiology and determined the contributions of CRF1 signalling to inhibitory control and voluntary alcohol drinking. Chronic alcohol drinking produced neuroadaptations in CRF1+ neurons that increased the sensitivity of GABA_A receptor-mediated sIPSCs to the acute effects of alcohol, CRF and the CRF1 antagonist R121919, but these adaptations were more pronounced in male versus female mice. The CRF1 antagonist CP-154,526 reduced voluntary alcohol drinking in both sexes and abolished sex differences in alcohol drinking. The lack of alcohol-induced adaptation in the female CRF1 system may be related to the elevated alcohol intake exhibited by female mice and could contribute to the ineffectiveness of CRF1 antagonists in female AUD patients.

Alcohol conditioned contexts enhance positive subjective alcohol effects and consumption

Associations between alcohol and the places it is consumed are important at all stages of alcohol abuse and addiction. However, it is not clear how the associations are formed in humans or how they influence drinking, and there are few effective strategies to prevent their pathological effects on alcohol use. We used a human laboratory model to study the effects of alcohol environments on alcohol consumption. Healthy regular binge drinkers completed conditioned place preference (CPP) with 0 vs. 80 mg/100 mL alcohol (Paired Group). Control participants (Unpaired Group) completed sessions without explicit alcohol-room pairings. After conditioning, participants completed alcohol self-administration in either the alcohol- or no alcohol-paired room. Paired group participants reported greater subjective stimulation and euphoria, and consumed more alcohol in the alcohol-paired room in comparison to the no alcohol-paired room, and controls tested in either room. Moreover, the strength of conditioning significantly predicted drinking; participants who exhibited the strongest CPP consumed the most alcohol in the alcohol-paired room. This is the first empirical evidence that laboratory-conditioned alcohol environments directly influence drinking. The results also confirm the viability of the model to examine the mechanisms by which alcohol environments stimulate drinking and to test strategies to counteract their influence on behavior.

A Circuit-Based Information Approach to Substance Abuse Research

Recent animal research on substance-use disorders (SUDs) has emphasized learning models and the identification of 'addiction-prone' animals. Meanwhile, basic neuroscientific research has elucidated molecular, cellular, and circuit functions with increasing sophistication. However, SUD-related research is hampered by continued arguments over which animal models are more 'addiction like', as well as the facile assignment of behaviors to a given brain region and vice versa. We argue that SUD-related research would benefit from a 'bottom-up' approach including: (i) the characterization of different brain circuits to understand their normal function as well as how they respond to drugs and contribute to SUDs; and (ii) a focus on the use patterns and neurobiological effects of different substances to understand the range of critical SUD-related in vivo phenotypes.

The effects of social instability stress and subsequent ethanol consumption in adolescence on brain and behavioral development in male rats

Excessive drinking in adolescence continues to be a problem, and almost a quarter of young Canadians have reported consuming five or more alcoholic drinks in one occasion in recent surveys. The consequences of such drinking may be more pronounced when commenced in adolescence, given the ongoing brain development during this period of life. Here, we investigated the consequences of 3 weeks' intermittent access to ethanol in mid-adolescence to early adulthood in rats, and the extent to which a stress history moderated the negative consequences of ethanol access. In experiment 1, male rats that underwent adolescent social instability stress (SS; daily 1 h isolation + return to unfamiliar cage partner every day from postnatal day [PND] 30-45) did not differ from control (CTL) rats in intake of 10% ethanol sweetened with 0.1% saccharin (access period; PND 47-66). Ethanol drinking reduced proteins relevant for synaptic plasticity (αCaMKII, βCaMKII, and PSD-95) in the dorsal hippocampus, and in CTL rats only in the prefrontal cortex (αCaMKII and PSD 95), attenuating the difference between CTL and SS rats in the water-drinking group. In experiment 2, ethanol also attenuated the difference between SS and CTL rats in a social interaction test by reducing social interaction in SS rats; CTL rats, however, had a higher intake of ethanol than did SS rats during the access period. Ethanol drinking reduced baseline and fear recall recovery concentrations of corticosterone relative to those exposed only to water, although there was no effect of either ethanol or stress history on fear conditioning. Ethanol drinking did not influence intake after 9 days of withdrawal; however, ethanol-naïve SS rats drank more than did CTL rats when given a 24-h access in adulthood. These results reveal a complex relationship between stress history and ethanol intake in adolescence on outcomes in adulthood.

Assessing the motivational effects of ethanol in mice using a discrete-trial current-intensity intracranial self-stimulation procedure

BACKGROUND

Alcohol (ethanol) produces both rewarding and aversive effects, and sensitivity to these effects is associated with risk for an alcohol use disorder (AUD). Measurement of these motivational effects in animal models is an important but challenging aspect of preclinical research into the neurobiology of AUD. Here, we evaluated whether a discrete-trial current-intensity intracranial self-stimulation (ICSS) procedure can be used to assess both reward-enhancing and aversive responses to ethanol in mice.

METHODS

Male and female C57BL/6J mice were surgically implanted with bipolar stimulating electrodes targeting the medial forebrain bundle and trained on a discrete-trial current-intensity ICSS procedure. Mice were tested for changes in response thresholds after various doses of ethanol (0.5 g/kg-1.75 g/kg; n = 5-7 per dose), using a Latin square design.

RESULTS

A 1 g/kg dose of ethanol produced a significant reward-enhancement (i.e., lowered response thresholds), whereas a 1.75 g/kg dose produced an aversive effect (elevated response thresholds). Ethanol doses from 1 to 1.75 g/kg increased response latencies as compared to saline treatment.

CONCLUSIONS

The discrete-trial current-intensity ICSS procedure is an effective assay for measuring both reward-enhancing responses to ethanol as well as aversive responses in the same animal. This should prove to be a useful tool for assessing the effects of experimental manipulations on the motivational effects of ethanol in mice.

Sex Differences in Ethanol Reward Seeking Under Conflict in Mice

BACKGROUND

Alcohol use disorders are characterized by inflexible alcohol seeking that occurs despite adverse consequences. Males and females are differentially sensitive to ethanol (EtOH) reward, but it is unclear whether sex differences in EtOH seeking under reward-aversion conflict are present.

METHODS

To investigate sex differences in EtOH seeking under conflict, adult male and female C57BL/6J mice underwent chronic intermittent EtOH (CIE) exposure by vapor inhalation or served as air-exposed controls. After CIE, mice were trained in a modified EtOH conditioned place preference paradigm. During 3 conditioning sessions, 2 g/kg EtOH was administered prior to confinement in the "EtOH-paired" chamber. On alternating days, saline was injected prior to confinement in the "saline-paired" chamber. After conditioning, mice experienced a footshock in the EtOH-paired chamber. EtOH-seeking behavior was assessed before and after footshock.

RESULTS

Control and CIE-exposed males reduced the time spent in and increased latency to enter the reward-paired chamber following footshock. Control females did not alter EtOH-seeking behavior following footshock. CIE-exposed females spent more time in the EtOH-paired chamber at baseline. However, following a footshock, CIE-exposed females significantly reduced the time spent in and increased latency to enter the EtOH-paired chamber.

CONCLUSIONS

Nondependent female mice exhibited aversion-resistant alcohol seeking to a greater degree than males. Chronic EtOH exposure did not impact EtOH seeking in males. In females, CIE enhanced EtOH seeking in the absence of conflict, but reduced EtOH seeking after an aversive experience. While these sex-specific effects of CIE are not present when reward seeking is assessed in the absence of an aversive experience, multiple factors may underlie the differences in reward seeking despite adverse consequences, including reward- and aversion-related learning and decision making under conflict. These data highlight the importance of considering sex as a variable influencing EtOH seeking and provide a greater understanding of how sex interacts with EtOH exposure to alter behavior.

Acute effect of intravenously applied alcohol in the human striatal and extrastriatal D2 /D3 dopamine system

Investigations on the acute effects of alcohol in the human mesolimbic dopamine D₂ /D₃ receptor system have yielded conflicting results. With respect to the effects of alcohol on extrastriatal D₂ /D₃ dopamine receptors no investigations have been reported yet. Therefore we applied PET imaging using the postsynaptic dopamine D₂ /D₃ receptor ligand [¹⁸ F]fallypride addressing the question, whether intravenously applied alcohol stimulates the extrastriatal and striatal dopamine system. We measured subjective effects of alcohol and made correlation analyses with the striatal and extrastriatal D₂ /D₃ binding potential. Twenty-four healthy male μ-opioid receptor (OPRM1)118G allele carriers underwent a standardized intravenous and placebo alcohol administration. The subjective effects of alcohol were measured with a visual analogue scale. For the evaluation of the dopamine response we calculated the binding potential (BP_ND ) by using the simplified reference tissue model (SRTM). In addition, we calculated distribution volumes (target and reference regions) in 10 subjects for which metabolite corrected arterial samples were available. In the alcohol condition no significant dopamine response in terms of a reduction of BP_ND was observed in striatal and extrastriatal brain regions. We found a positive correlation for 'liking' alcohol and the BP_ND in extrastriatal brain regions (Inferior frontal cortex (IFC) (r = 0.533, p = 0.007), orbitofrontal cortex (OFC) (r = 0.416, p = 0.043) and prefrontal cortex (PFC) (r = 0.625, p = 0.001)). The acute alcohol effects on the D₂ /D₃ dopamine receptor binding potential of the striatal and extrastriatal system in our experiment were insignificant. A positive correlation of the subjective effect of 'liking' alcohol with cortical D₂ /D₃ receptors may hint at an addiction relevant trait.

Effects of ethanol on cocaine self-administration in monkeys responding under a second-order schedule of reinforcement

BACKGROUND

Concurrent alcohol use among cocaine abusers is common but the behavioral variables that promote co-abuse are not well understood. The present study examined the effects of intragastric (i.g.) ethanol (EtOH) administration in monkeys responding under a schedule of cocaine reinforcement in which extensive drug seeking was maintained by conditioned stimuli.

METHODS

Four adult male cynomolgus monkeys (Macaca fascicularis) were trained to respond under a second-order fixed-interval (FI) 600s (fixed-ratio (FR) 30:S) schedule of cocaine (0.003-0.56mg/kg/injection) presentation. Sessions ended after 5 injections or 90min had elapsed. Different EtOH doses (0.5-2.0g/kg, i.g.) were administered 30min before the session, typically on Tuesdays and Fridays. Blood ethanol concentrations (BECs) were also assessed. Pattern of FI responding was assessed by determining quarter-life (QL) values.

RESULTS

Cocaine self-administration was characterized as an inverted U-shaped function of dose; QL values increased monotonically with dose. EtOH pretreatments dose-dependently decreased self-administration at several cocaine doses in 3 of 4 monkeys. In one animal, EtOH increased low-dose cocaine-maintained responding. For all monkeys, QL values were increased by EtOH when low- and high-cocaine doses were self-administered, suggesting additive effects of EtOH and cocaine. Furthermore, BECs were not altered following cocaine self-administration.

CONCLUSIONS

The reductions in cocaine self-administration and the increases in QL values following EtOH, suggest that EtOH was enhancing cocaine-related conditioned reinforcement. A better understanding of the behavioral mechanisms that mediate the co-abuse of alcohol and cocaine will lead to improved treatments for both drugs.

Adolescent intermittent ethanol exposure diminishes anhedonia during ethanol withdrawal in adulthood

Adolescent alcohol use may interfere with neurodevelopment, increasing the likelihood of adult alcohol use disorders (AUDs). We investigated whether adolescent intermittent ethanol (AIE) exposure alters the adult reward response to ethanol. Adolescent rats were administered ethanol once (moderate exposure; Cohort 1) or three times per day (severe exposure; Cohort 2) in a 2 days on/2 days off pattern. In adulthood, subjects responded for electrical stimulation directed at the posterior lateral hypothalamus in a discrete-trial intracranial self-stimulation (ICSS) procedure that provides current-intensity thresholds as a measure of brain reward function. The effects of ethanol administration and withdrawal were assessed. Control rats showed dose-dependent threshold elevations after acute ethanol, indicating reward deficits. A majority of moderately AIE-exposed rats (Cohort 1) showed threshold lowering after ethanol, suggesting ethanol-induced reward enhancement in this sub-set of rats. Rats exposed to severe AIE (Cohort 2) showed no threshold elevation or lowering, suggesting a blunted affective ethanol response. Daily ethanol induced threshold elevations 24h after administration in control rats but not in either group of AIE-exposed rats, suggesting decreased sensitivity to the negative affective state of ethanol withdrawal. Withdrawal from a 4-day ethanol binge produced robust and enduring threshold elevations in all rats, although threshold elevations were diminished in rats exposed to severe AIE. These results indicate that AIE exposure diminished reward deficits associated with ethanol intoxication and withdrawal and may have increased ethanol-induced reward enhancement in a sub-set of rats. In humans, enhanced ethanol reward accompanied by reduced withdrawal severity may contribute to the development of AUDs.

The Kv7 potassium channel activator retigabine decreases alcohol consumption in rats

BACKGROUND

Activation of Kv7 potassium channels may decrease the reactivity of mesolimbic dopaminergic neurons that are implicated in mediating the reinforcing effects of ethanol.

OBJECTIVES

The objective of this study was to determine whether the administration of the Kv7 potassium channel opener retigabine would decrease ethanol intake in Long Evans rats.

METHODS

A limited access two-bottle choice model of alcohol (10% solution) consumption was used in this study. A separate group of animals was tested to evaluate the actions of retigabine on sucrose (5% solution) consumption to determine whether this drug might produce non-selective impairment of the ability of rats to drink liquids. Animals were treated with either vehicle or increasing doses (2.5-7.5 mg/kg SC) of retigabine administered over a 3-day period.

RESULTS

Compared to vehicle, retigabine at a dose of 7.5 mg/kg produced a reduction in the amount of ethanol consumed. These effects did not occur in association with significant changes in water consumption. A significant time effect was found for the actions of retigabine in sucrose-drinking rats with a trend for an increase in sucrose intake with the highest dose of retigabine administered.

CONCLUSIONS

These results indicate that the administration of retigabine may produce a decrease in ethanol consumption by rats at doses that do not significantly reduce the drinking of either water or a sucrose solution. These findings are consistent with the hypothesis that activation of Kv7 channels facilitates the reduction of alcohol consumption in the rat.

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

The neurobiology of alcohol consumption and alcoholism: an integrative history

Studies of the neurobiological predisposition to consume alcohol (ethanol) and to transition to uncontrolled drinking behavior (alcoholism), as well as studies of the effects of alcohol on brain function, started a logarithmic growth phase after the repeal of the 18th Amendment to the United States Constitution. Although the early studies were primitive by current technological standards, they clearly demonstrated the effects of alcohol on brain structure and function, and by the end of the 20th century left little doubt that alcoholism is a "disease" of the brain. This review traces the history of developments in the understanding of ethanol's effects on the most prominent inhibitory and excitatory systems of brain (GABA and glutamate neurotransmission). This neurobiological information is integrated with knowledge of ethanol's actions on other neurotransmitter systems to produce an anatomical and functional map of ethanol's properties. Our intent is limited in scope, but is meant to provide context and integration of the actions of ethanol on the major neurobiologic systems which produce reinforcement for alcohol consumption and changes in brain chemistry that lead to addiction. The developmental history of neurobehavioral theories of the transition from alcohol drinking to alcohol addiction is presented and juxtaposed to the neurobiological findings. Depending on one's point of view, we may, at this point in history, know more, or less, than we think we know about the neurobiology of alcoholism.

Alcohol self-administration, anxiety, and cortisol levels predict changes in delta opioid receptor function in the ventral tegmental area

The delta opioid receptor (DOR) agonist DPDPE decreases ethanol (EtOH) consumption when injected into the ventral tegmental area (VTA). We previously showed that DPDPE inhibition of GABAA receptor-mediated inhibitory postsynaptic currents (GABAAR IPSCs) is associated with reduced EtOH consumption. To determine whether self-administration of EtOH is required to change VTA DOR function, we compared the effects of passively administered (gavaged) and self-administered (two-bottle choice) EtOH. Because rats showed variability in DOR regulation of drinking and inhibition of GABAAR IPSCs, we examined whether these changes can be predicted before EtOH exposure by behavioral measures of anxiety or intoxication. Functional DORs were seen with both gavaged and self-administered EtOH, although the magnitude of DPDPE-induced inhibition correlated with behavioral measures only when EtOH was self-administered. Specifically, DPDPE-induced inhibition correlated with predrinking measures of open arm time in the plus maze (n = 19, R = .69, p = .001), with change in maximum fall latency on the rotarod (n = 17, R = .89, p = .000001), and with blood corticosterone (n = 17, R = .66, p = .004) in drinking animals. This DOR-mediated inhibition persisted for at least 14 days after EtOH access was terminated. Together, these findings indicate that anxious animals and those with the greatest EtOH-induced motor impairment have the most robust DPDPE-induced inhibition of GABAAR IPSCs in VTA neurons. These data also extend our understanding of the possible therapeutic value of the DOR for treatment of alcoholism by showing that its relevant synaptic action persists during abstinence.

Intracranial self-stimulation in FAST and SLOW mice: effects of alcohol and cocaine

RATIONALE

Sensitivity to the stimulant and rewarding effects of alcohol may be genetically correlated traits that predispose individuals to develop an alcohol use disorder.

OBJECTIVE

This study aimed to examine the effects of alcohol and cocaine on intracranial self-stimulation (ICSS) in FAST and SLOW mice, which were selectively bred for extremes in alcohol stimulation.

METHODS

Male FAST and SLOW mice were conditioned to respond for reinforcement by direct electrical stimulation of the medial forebrain bundle (i.e., brain stimulation reward). ICSS responses were determined immediately before and after oral gavage with water or alcohol (0.3-2.4 g/kg) or intraperitoneal injection with saline or cocaine (1.0-30.0 mg/kg). In separate FAST and SLOW mice, the locomotor effects of these treatments were measured in activity chambers.

RESULTS

Alcohol dose-dependently lowered the threshold for self-stimulation (θ (0)) and the frequency that maintained 50% of maximal responding (EF50) in FAST mice but did not significantly affect these parameters in SLOW mice. The largest effects of alcohol were after the 1.7- and 2.4-g/kg doses and were about 40% compared to water injection. Alcohol did not affect MAX response rates, but dose-dependently stimulated locomotor activity in FAST mice. Cocaine lowered thresholds equally in FAST and SLOW mice, although cocaine-stimulated locomotor activity was higher in the FAST than in the SLOW mice.

CONCLUSIONS

Selective breeding for alcohol locomotor stimulation also renders the mice more sensitive to the effects of alcohol, but not cocaine, on ICSS.

Place conditioning with ethanol in rats bred for high (UChB) and low (UChA) voluntary alcohol drinking

The main goal of this study was to investigate the ability of an ethanol dose (1g/kg) administered intraperitoneally to induce conditioned place preference (CPP) and/or conditioned place aversion (CPA) in two lines of rats selectively bred for their high (UChB) or low (UChA) voluntary ethanol intake. It was found that five pairings with ethanol induced CPA in ethanol-naïve rats of both lines, but the magnitude of avoidance was lower in the UChB relative to the UChA rats, indicating that ethanol was less aversive to naïve rats bred for high alcohol drinking. After 2 months of high voluntary ethanol drinking (~6-7g/kg/day), in free choice between 10% ethanol and water, ethanol produced CPP in UChB rats, reflecting that ethanol had become rewarding to these rats. By contrast, the low voluntary ethanol intake (<1g/kg/day) displayed by UChA rats preexposed for 2 months in free choice did not change ethanol-induced CPA. However, preexposure of UChA rats to forced ethanol drinking (~5.7g/kg/day) and the later inhibition of ethanol-derived acetaldehyde by 4-methylpyrazole (10mg/kg intraperitoneal), an inhibitor of the enzyme alcohol dehydrogenase, not only increased their voluntary ethanol intake in free choice, but also had a facilitating effect on the development of CPP. Taken together, these results show that the expression of the reinforcing effects of ethanol required a period of voluntary ethanol intake in UChB rats, whereas in UChA rats, both prior exposure to forced ethanol drinking and reduction of high blood ethanol-derived acetaldehyde were required.

Self-administered and yoked nicotine produce robust increases in blood pressure and changes in heart rate with modest effects of behavioral contingency in rats

Experimenter-administered nicotine produces reliable increases in blood pressure and changes in heart rate. However, an extensive literature demonstrates that the effects of psychoactive drugs are dependent on whether administration is contingent on behavior. The present study assessed the cardiovascular effects of nicotine and whether those effects vary as a function of whether nicotine was self-administered or response-independent. Rats were divided into three groups according to a yoked design. The pattern of infusions for each triad was determined by the animal self-administering nicotine; the other two animals received either yoked nicotine or saline. Heart rate and blood pressure were measured during eighteen daily, 1h drug sessions by radiotelemetry. Each session was preceded and followed by a 20 minute period during which cardiovascular function was monitored in the operant chambers, but drug was not available. Acute exposure to yoked nicotine produced a rapid rise in blood pressure that was larger than the increase observed with self-administered nicotine. Additional infusions during the first session resulted in a similar sustained elevation in blood pressure in the nicotine groups. Over subsequent sessions, self-administered nicotine produced a larger effect on systolic blood pressure particularly early in each session, although for both self-administered and yoked nicotine the hypertensive effects waned partially with repeated test sessions. This decrease was fully accounted for by a pre-session decrease in pressure; relative to pre-session levels the strong hypertensive effects of nicotine persisted. Initial exposure to nicotine produced a short-lived bradycardia that in subsequent sessions was replaced with a longer-lasting nicotine-induced tachycardia; neither effect was related to the behavioral contingency of nicotine delivery. Together, these data provide a rich picture of the cardiovascular effects of nicotine. Effects of behavioral contingency were observed, but differences were limited. Other non-pharmacological factors such as baseline shifts potentially related to nicotine-associated cues deserve further attention.

Adolescent alcohol exposure alters the central brain circuits known to regulate the stress response

Adolescent alcohol exposure (AAE) may exert long-term effects on the adult brain. Here, we tested the hypothesis that the brain regions affected include the rat hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we examined the consequences of AAE [postnatal days (PND) 28-42] on the HPA axis-related brain circuitry of male rats challenged with an intragastric (ig) administration of alcohol in young adulthood (PND 61-62). Adolescent rats were exposed to alcohol vapors, while controls did not receive the drug. The mean blood alcohol level in adolescence on PND 40 was 212.8±5.7 mg %. Using immunohistochemistry and in situ hybridization procedures, we measured signals for c-fos and corticotropin releasing factor (CRF) in the paraventricular nucleus (PVN) of the hypothalamus, as well as signals for c-fos and phenylethanolamine N-methyltransferase (PNMT) in the adrenergic brain stem regions (C1 and C2). PVN CRF mRNA expression was significantly blunted in AAE rats tested at PND 61-62, compared to their controls. These animals also displayed a significant increase in the mean number of PNMT-ir cells/brain stem section in the C2 area. Collectively, these results suggest that exposure to alcohol vapors during adolescence exerts long-term effects on the ability of the PVN to mount a response to an acute alcohol administration in young adulthood, possibly mediated by medullary catecholamine input to the PVN.

Novel apparatus and method for drug reinforcement

Animal models of reinforcement have proven to be useful for understanding the neurobiological mechanisms underlying drug addiction. Operant drug self-administration and conditioned place preference (CPP) procedures are expansively used in animal research to model various components of drug reinforcement, consumption, and addiction in humans. For this study, we used a novel approach to studying drug reinforcement in rats by combining traditional CPP and self-administration methodologies. We assembled an apparatus using two Med Associate operant chambers, sensory stimuli, and a Plexiglas-constructed neutral zone. These modifications allowed our experiments to encompass motivational aspects of drug intake through self-administration and drug-free assessment of drug/cue conditioning strength with the CPP test. In our experiments, rats self-administered cocaine (0.75 mg/kg/inj, i.v.) during either four (e.g., the "short-term") or eight (e.g., the "long-term") alternating-day sessions in an operant environment containing distinctive sensory cues (e.g., olfactory and visual). On the alternate days, in the other (differently-cued) operant environment, saline was available for self-infusion (0.1 ml, i.v.). Twenty-four hours after the last self-administration/cue-pairing session, a CPP test was conducted. Consistent with typical CPP findings, there was a significant preference for the chamber associated with cocaine self-administration. In addition, in animals undergoing the long-term experiment, a significant positive correlation between CPP magnitude and the number of cocaine-reinforced lever responses. In conclusion, this apparatus and approach is time and cost effective, can be used to examine a wide array of topics pertaining to drug abuse, and provides more flexibility in experimental design than CPP or self-administration methods alone.

Reduced alcohol drinking in adult rats exposed to sucrose during adolescence

Intake of sweet-alcoholic drinks during adolescence is believed to favor alcohol abuse and dependence in adulthood. This study examined the influence of early exposure to ethanol with or without sucrose on the consumption of sweet or alcoholic solutions in adulthood. Adolescent rats (from post-natal day 30-46) were given continuous free access to tap water and either 5% sucrose, 5% ethanol or mixed 5% sucrose-5% ethanol. The control group was given access to water only. Upon reaching adulthood (post-natal day 60), rats were tested for saccharin (sweet), quinine (bitter) and ethanol consumption using a two-bottle free-choice paradigm. The results indicated that pre-exposure to ethanol did not alter the intake of sweet or ethanol solutions in adulthood. However, rats exposed to sucrose during adolescence showed a decreased consumption of both sweet and ethanol solutions. Because alcohol has a sweet taste component, an additional group of rats, pre-exposed to either 5% sucrose or water during adolescence, was tested for intravenous ethanol self-administration (preventing oral sensory stimulation) and in a new model of simultaneous access to oral saccharin and intravenous ethanol that results in higher total ethanol intake. Relative to controls, sucrose-exposed rats showed reduced operant self-administration of saccharin, yet no differences were found for intravenous ethanol self-administration. Altogether, these findings indicate that sucrose exposure during adolescence persistently affected the perception of sweet taste reward and thereby alcohol's acceptance in adulthood.

Alcohol, cocaine, and brain stimulation-reward in C57Bl6/J and DBA2/J mice

BACKGROUND

Pleasure and reward are critical features of alcohol drinking that are difficult to measure in animal studies. Intracranial self-stimulation (ICSS) is a behavioral method for studying the effects of drugs directly on the neural circuitry that underlies brain reward. These experiments had 2 objectives: first, to establish the effects of alcohol on ICSS responding in the C57Bl6/J (C57) and DBA2/J (DBA) mouse strains; and second, to compare these effects to those of the psychostimulant cocaine.

METHODS

Male C57 and DBA mice were implanted with unipolar stimulating electrodes in the lateral hypothalamus and conditioned to spin a wheel for reinforcement by the delivery of rewarding electrical stimulation (i.e., brain stimulation-reward or BSR). Using the curve-shift method, the BSR threshold (theta(0)) was determined immediately before and after oral gavage with alcohol (0.3, 0.6, 1.0, 1.7 g/kg) or water. Blood alcohol concentration (BAC) was measured to determine the influence of alcohol metabolism on BSR threshold. Separately, mice were administered cocaine (1.0, 3.0, 10.0, 30.0 mg/kg) or saline intraperitoneally.

RESULTS

In C57 mice, the 0.6 g/kg dose of alcohol lowered BSR thresholds by about 20%, during the rising (up to 40 mg/dl), but not falling, phase of BAC. When given to the DBA mice, alcohol lowered BSR thresholds over the entire dose range; the largest reduction was by about 50%. Cocaine lowered BSR thresholds in both strains. However, cocaine was more potent in DBA mice than in C57 mice as revealed by a leftward shift in the cocaine dose-response curve. For both alcohol and cocaine, effects on BSR threshold were dissociable from effects on operant response rates.

CONCLUSIONS

In C57 and DBA mice, reductions in BSR threshold reflect the ability of alcohol to potentiate the neural mechanisms of brain reward. The DBA mice are more sensitive to the reward-potentiating effects of both alcohol and cocaine, suggesting that there are mouse strain differences in the neural mechanisms of brain reward that can be measured with the ICSS technique.

Alcoholism: A Systems Approach From Molecular Physiology to Addictive Behavior

Alcohol consumption is an integral part of daily life in many societies. The benefits associated with the production, sale, and use of alcoholic beverages come at an enormous cost to these societies. The World Health Organization ranks alcohol as one of the primary causes of the global burden of disease in industrialized countries. Alcohol-related diseases, especially alcoholism, are the result of cumulative responses to alcohol exposure, the genetic make-up of an individual, and the environmental perturbations over time. This complex gene × environment interaction, which has to be seen in a life-span perspective, leads to a large heterogeneity among alcohol-dependent patients, in terms of both the symptom dimensions and the severity of this disorder. Therefore, a reductionistic approach is not very practical if a better understanding of the pathological processes leading to an addictive behavior is to be achieved. Instead, a systems-oriented perspective in which the interactions and dynamics of all endogenous and environmental factors involved are centrally integrated, will lead to further progress in alcohol research. This review adheres to a systems biology perspective such that the interaction of alcohol with primary and secondary targets within the brain is described in relation to the behavioral consequences. As a result of the interaction of alcohol with these targets, alterations in gene expression and synaptic plasticity take place that lead to long-lasting alteration in neuronal network activity. As a subsequent consequence, alcohol-seeking responses ensue that can finally lead via complex environmental interactions to an addictive behavior.

Responding for brain stimulation reward in the bed nucleus of the stria terminalis in alcohol-preferring rats following alcohol and amphetamine pretreatments

The bed nucleus of the stria terminalis (BNST) has been reported to release increased levels of extracellular dopamine (DA) following the systemic administration of abused drugs in outbred rats. This study examined the BNST as a novel locus for supporting operant responding for brain stimulation reward (BSR) in rats bred for alcohol preference while determining any potentiating effects of ethanol (EtOH) (0.125-1.25 g/kg, i.p.) and amphetamine (0.25-1.60 mg/kg, i.p.) on BSR within the BNST. Also examined was the capability of D1 receptor blockade to attenuate any observed potentiation. Following surgical implantation, alcohol-preferring (P) and non-preferring (NP) rats responded to a range of descending frequencies (300-20 Hz) as evaluated by a rate-frequency paradigm. The results revealed that the BNST was capable of supporting BSR in P but not NP rats. Also, amphetamine pretreatment produced a significant leftward shift in the rate-frequency function in P rats with significant reductions observed in three other measures of reward threshold, while EtOH only lowered the minimum frequency needed to produce responding. The effects of systemic amphetamine were successfully attenuated by the unilateral infusion of the D1 receptor antagonist SCH 23390 (5.0 microg) into the contralateral nucleus accumbens. The results suggest the BNST is capable of supporting BSR performance in P, but not NP rats, possibly due to increased sensitivity to the electrical stimulation-induced DA release of BSR in the innately DA "deficient" limbic system of P rats.

Comparing the physiological and subjective effects of self-administered vs yoked cocaine in humans

RATIONALE

Studies with laboratory animals demonstrating different effects of self- vs experimenter-administered drug suggest that the ability to control or predict drug delivery may be an important determinant of drug action.

OBJECTIVE

This study assessed whether self-administered and yoked cocaine injections produce different effects in humans.

METHODS

Ten inpatient volunteers with experience in using cocaine participated in a double-blind, yoked design during which four experimental test sessions were conducted. During two sessions, participants controlled if and when up to six 40 mg/70 kg i.v. cocaine injections were given. During two sessions, participants received noncontingent exposure to the same pattern of injections given during the preceding session (i.e., yoked) under blind conditions. Sessions followed a fixed-order, ABAB design. Measures of subjective and physiological response to cocaine were taken throughout each session.

RESULTS

Cardiovascular safety parameters were exceeded in some individuals after yoked, but not self-administered, cocaine resulting in some scheduled injections being delayed or withheld. Mean systolic and diastolic blood pressures were higher following yoked compared to self-administered cocaine. In contrast, analysis of the subjective effects revealed only small and generally nonsignificant differences in the effects of self-administered vs yoked cocaine.

CONCLUSIONS

These results suggest that under the laboratory methods employed, control over the schedule of drug delivery may not alter the subjective effects of cocaine in humans. In contrast, the cardiovascular effects of cocaine appear to be greater when the drug is administered noncontingently.

Brain reward deficits accompany withdrawal (hangover) from acute ethanol in rats

Withdrawal from an acute bolus injection of ethanol produces affective or emotional signs that include anxiogenic-like behavior and conditioned place aversion. This study assessed whether brain reward deficits that accompany withdrawal from chronic ethanol dependence are also observed upon withdrawal from acute intoxication. Rats were implanted with stimulating electrodes aimed at the medial forebrain bundle in the lateral hypothalamus and trained on a discrete-trial current-intensity brain stimulation reward threshold paradigm. Ethanol intoxication was produced by bolus intraperitoneal injections of ethanol (1.0, 1.5, or 2.0 g/kg). Brain reward thresholds were monitored periodically following the bolus injection (3, 6, 9, 12, 24, 48, 72, 96 h postethanol). Blood samples taken at various intervals postethanol revealed that peak blood alcohol levels (BAL) at all doses tested were reached within 10 min of injection. Following doses of 1.0, 1.5, and 2.0 g/kg ethanol, BAL had declined to undetectable levels within 3-6h postinjection. Withdrawal from a single injection of ethanol resulted in a significant but transient increase in brain reward thresholds only with the highest ethanol dose tested (2.0 g/kg). When acute intoxication and withdrawal episodes were repeated two additional times at weekly intervals, the peak magnitude and duration of threshold elevation increased significantly at the 2.0 g/kg dose of ethanol. A significant but transient increase in thresholds was also seen in the group treated with 1.5 g/kg ethanol during the third and final week of testing. Results indicate that withdrawal from a single exposure to an intoxicating dose of ethanol produces significant brain reward deficits in addition to other affective disturbances previously reported, and that repeated weekly intoxication and withdrawal results in a progressive increase in magnitude and duration of the reward deficit.

Effects of ethanol on locomotor and anxiety-like behaviors and the acquisition of ethanol intake in Lewis and spontaneously hypertensive rats

The purpose of the present study was to investigate whether Lewis (LEW) and spontaneously hypertensive rats (SHR), characterized in numerous behavioral tests as strains with high-anxiety and low-anxiety, respectively, could differ in their sensitivity to the effects of ethanol in the elevated plus maze (EPM) and the open field (OF), two classical models of anxiety/emotionality, as well as in the acquisition of ethanol drinking behavior. It was also of interest to examine the relationship between sweet and bitter fluids preference and ethanol intake. SHR and LEW rats were given saline or ethanol injections (0.6 or 1.2 g/kg, ip.) and tested in the EPM and OF. Subsequently the same animals were given continuous free choice between water and ethanol solution (2-8%). Additional groups of animals were exposed to a free-choice regimen between saccharin (0.002-0.09%) or quinine (0.0001-0.0015%) and water. The low dose of ethanol (0.6 g/kg) induced anxiolytic-like effects and intensive locomotor activation mainly in SHR rats tested in the OF arena. Overall, LEW counterparts were unaffected in OF test. In oral self-administration paradigm, SHR rats consumed significantly more ethanol than LEW rats. Concerning other solutions, SHR rats consumed large amounts of saccharin compared with LEW rats. These data indicate that the SHR preference for ethanol intake may be positively related to their differential sensitivity to the anxiolytic/stimulant effects of ethanol and to the sensitivity of this strain for saccharin reinforcement. In addition, these findings provide evidence that the SHR strain may represent a useful genetic and pharmacological tool to investigate ethanol drinking traits.

Development of Individual Alcohol Inhalation Chambers for Mice: Validation in a Model of Prenatal Alcohol

BACKGROUND

The purpose of this work was first to develop a system of individual chambers through which controlled delivery of alcohol vapors allows us to target specific blood alcohol levels (BALs) in mice without requiring the administration of an alcohol dehydrogenase inhibitor. As a proof of concept, we demonstrated that this new system could be used to expose pregnant BALB/c or C57BL/6 mice to alcohol and that the hypothalamic-pituitary-adrenal (HPA) axis of their mature offspring exhibited the well-known hyperactivity that has been previously documented in rats.

METHODS

A first series of experiments was designed to establish the parameters that resulted in specific BALs in nonpregnant adult male and female BALB/c as well as C57BL/6 mice that were exposed to various alcohol flow rates. Using information gathered from these experiments, we then chose a regimen of 6 hr of daily vapor exposure in pregnant mice to determine whether this regimen would alter the HPA axis activity of their mature offspring. Control dams were maintained in similar chambers but without alcohol. We first used control mice to assess plasma ACTH levels as a function of shock intensity as well as total duration of the shock session. The most suitable protocol was then used to measure shock-induced ACTH release in 2-month-old male and female offspring that were exposed to alcohol prenatally or not.

RESULTS

BALs increased as a function of the alcohol flow rates and remained within an acceptable range of homogeneity, consistency, and reproducibility over the desired periods of time. There were no sex differences in BALs while vapors were delivered. However, there was a strain difference in that BALB/c mice displayed slightly higher BALs than C57BL/6. Female mice also exhibited a slightly more pronounced decrease in BALs, compared with male mice, once removed from the drug. Measurement of plasma ACTH levels as a function of the intensity and duration of the shock sessions indicated that 0.3 mA intensity, 1-sec duration shocks at the rate of 2 shocks/min for 20 min provided the most reliable protocol. We then used the alcohol model in pregnant mice. Alcohol exposure did not interfere with maternal weights during gestation. When offspring were tested at 8 to 9 weeks of age, male and female BALB/c as well as female C57BL/6 mice that were exposed to alcohol vapors prenatally exhibited significantly higher shock-induced plasma ACTH levels, compared with controls of the same strain.

CONCLUSIONS

Collectively, our results indicate that the individual alcohol chamber system that we have developed offers a reliable means of exposing mice to alcohol so that they reach predetermined BALs in the absence of the pharmacological manipulations often used to influence alcohol metabolism in this species. This system, which is compatible with normal weight gains, was used to provide evidence that as previously demonstrated in rats, adult murine offspring of alcohol-treated dams exhibit a hyperactive HPA axis. The development of protocols for use in mice offers the possibility of investigating the influence of alcohol in mutant animals with manipulations of specific genes of interest.

Neuroadaptive effects of active versus passive drug administration in addiction research

Increasing knowledge of the genome sequences of several organisms and the development of genome-wide, high-throughput screening techniques for gene expression are likely to generate a vast amount of data aimed at elucidating the molecular mechanisms of addiction. These findings are likely to have potential for future addiction pharmacotherapies. However, it is important to employ animal models that dissociate the molecular and cellular consequences of the direct pharmacological effects of addictive drugs from those that result from the cognitive processes associated with self-administration of these drugs. In this article, we suggest that the short-term and long-term neuroadaptive effects of addictive drugs in the brain depend crucially on the drug-exposure paradigm used [i.e. passive (non-contingent) drug exposure and active (contingent) self-administration]. This has important ramifications for future molecular and cellular studies of drug addiction.

Brain-stimulation reward, morphine-induced oral stereotypy, and sensitization: implications for abuse

Early professionals believed that it was unlikely that anyone but the emotionally unstable received pleasure and became addicted to narcotic drugs. This position was well entrenched and influenced much of the thinking well into the latter half of the last century. Although the discovery of a brain reward system was made early in the 1950's it was not until 20 years later that this discovery was applied to the study of the mechanisms involved in the rewarding aspects of abused substances. Along this vein results will be shown in which opiate antagonist block the dopamine agonist activation of the brain reward system as well as the corollary. Sensitization of the reward system suggests that a driving force for drug use is 'liking' and not just 'wanting.' Basal changes in cerebral metabolic rates of glucose are seen in the presence of cues associated with morphine experience, giving evidence for the role of drug related cues in craving. Finally we asked the question 'Do old rats have as much fun as young rats?'

Metabolic mapping of the effects of cocaine during the initial phases of self-administration in the nonhuman primate

Because most human studies of the neurobiological substrates of the effects of cocaine have been performed with drug-dependent subjects, little information is available about the effects of cocaine in the initial phases of drug use before neuroadaptations to chronic exposure have developed. The purpose of the present study, therefore, was to define the substrates that mediate the initial effects of cocaine in a nonhuman primate model of cocaine self-administration using the 2-[14C]deoxyglucose method. Rhesus monkeys were trained to self-administer 0.03 mg/kg per injection (N = 4) or 0.3 mg/kg per injection (N = 4) cocaine and compared with monkeys trained to respond under an identical schedule of food reinforcement (N = 4). Monkeys received 30 reinforcers per session, and metabolic mapping was conducted at the end of the fifth self-administration session. Cocaine self-administration reduced glucose utilization in the mesolimbic system, including the ventral tegmental area, ventral striatum, and medial prefrontal cortex. In addition, metabolic activity was increased in the dorsolateral and dorsomedial prefrontal cortex, as well as in the mediodorsal nucleus of the thalamus. These latter effects are distinctly different from those seen after the noncontingent administration of cocaine, suggesting that self-administration engages circuits beyond those engaged merely by the pharmacological actions of cocaine. The involvement of cortical areas subserving working memory suggests that strong associations between cocaine and the internal and external environment are formed from the very outset of cocaine self-administration. The assessment of the effects of cocaine at a time not readily evaluated in humans provides a baseline from which the effects of chronic cocaine exposure can be investigated.

Ethanol preexposure attenuates the interaction of ethanol and cocaine in taste aversion learning

Although the potentiating effects of ethanol and cocaine have been well documented, little has been reported regarding the effects of ethanol or cocaine history on this interaction. In the present study, female Long-Evans rats received five exposures to ethanol (3.5 g/kg ip) or vehicle prior to taste aversion conditioning in which a novel saccharin solution was paired with either ethanol (0.56 g/kg ip), cocaine (25 mg/kg sc) or the combination (or the drugs' vehicle) for a total of five conditioning trials. Nonpreexposed subjects conditioned with the ethanol/cocaine combination displayed aversions, drinking levels significantly less than nonpreexposed subjects conditioned with either drug alone. Further, the aversions produced by the combination were greater than the sum of the aversions produced by ethanol and cocaine, alone. Ethanol-preexposed animals conditioned with the combination displayed an attenuated aversion, drinking significantly greater amounts of saccharin than nonpreexposed conditioned subjects and not differing from controls. Although the basis for the attenuation by ethanol of the aversions induced by the drug combination is not known, the present findings may have implications for the use and abuse of the combination in that alcohol history may reduce the subsequent toxicity of the combination that in turn may affect its acceptability.

Cue dependency of nicotine self-administration and smoking

A paradox exists regarding the reinforcing properties of nicotine. The abuse liability associated with smoking equals or exceeds that of other addictive drugs, yet the euphoric, reinforcing and other psychological effects of nicotine, compared to these other drugs, are more subtle, are manifest under more restricted conditions, and do not readily predict the difficulty most smokers experience in achieving abstinence. One possible resolution to this apparent inconsistency is that environmental cues associated with drug delivery become conditioned reinforcers and take on powerful incentive properties that are critically important for sustaining smoking in humans and nicotine self-administration in animals. We tested this hypothesis by using a widely employed self-administration paradigm in which rats press a lever at high rates for 1 h/day to obtain intravenous infusions of nicotine that are paired with two types of visual stimuli: a chamber light that when turned on signals drug availability and a 1-s cue light that signals drug delivery. We show that these visual cues are at least as important as nicotine in sustaining a high rate of responding once self-administration has been established, in the degree to which withdrawing nicotine extinguishes the behavior, and in the reinstatement of lever pressing after extinction. Additional studies demonstrated that the importance of these cues was manifest under both fixed ratio and progressive ratio (PR) schedules of reinforcement. The possibility that nicotine-paired cues are as important as nicotine in smoking behavior should refocus our attention on the psychology and neurobiology of conditioned reinforcers in order to stimulate the development of more effective treatment programs for smoking cessation.

Differential effects of response-contingent and response-independent nicotine in rats

Passive administration of nicotine activates the hypothalamic-pituitary-adrenocortical axis and sympathetic nervous system. However, little is known about the effects of self-administered nicotine. Drug-naive rats were trained to respond for food reinforcement and then tested in one, 1-h session in which they received response-contingent i.v. nicotine or response-independent i.v. nicotine or saline. Blood draws were taken immediately prior to the session, 15 min after the first infusion and immediately after the session. Both response-contingent and response-independent nicotine (RI/N) increased corticosterone within 15 min, however, corticosterone levels returned to baseline in animals receiving response-contingent nicotine (RC/N) by the end of the session while remaining elevated in those receiving RI/N. Furthermore, only RI/N increased plasma epinephrine and norepinephrine levels; RC/N produced no effect. These differences indicate that nicotine's acute effects are powerfully modified by the presence of a contingency relationship between drug administration and the animal's behavior and that this relationship develops very rapidly.

Brain ethanol levels after voluntary ethanol drinking in AA and Wistar rats

Brain ethanol was monitored in the nucleus accumbens with one minute microdialysis and headspace gas chromatography in male Wistar and alcohol preferring AA (Alko Alcohol) rats after voluntary limited access consumption without food restriction. The rats drank 0.93 +/- 0.14 (Wistar) and 0.73 +/- 0.07 g/kg (AA), with a resulting mean maximal brain ethanol level of 15.9 mM and 14.1 mM, respectively. Maximum brain ethanol levels for individual AA rats were in the range 9.4-33.6 mM, median 15.5 mM and for the individual Wistar rats in the range 2.5-35.2 mM, median 17.8 mM. There was a significant but not perfect correlation between the amount ethanol drunk and the resulting ethanol level in the nucleus accumbens, probably because of the rats not being food deprived before the experiment. The results show that rats drink pharmacologically meaningful doses in a voluntary limited access situation and that blood samples can give us a hint about the level attained in the brain, but to know the early brain concentration after drinking, microdialysis is an excellent tool.

Brain imaging. Functional consequences of ethanol in the central nervous system

In recent years, sophisticated methods have been developed to view structure and function within the living brain. Functional imaging methods are used to visualize dynamic chemical processes that are linked to brain activity. Increased neural activity, for example, leads to greater glucose and oxygen consumption and greater regional rates of blood flow to meet elevated energy demands. Mapping these changes provides quantitative visual descriptions of localized changes in brain activity that result from behavioral or pharmacological manipulations. This chapter first describes several current methods and how they are used to study the effects of alcohol on brain function. In the second part, the effects of acute intoxication are discussed with emphasis on the complex nature of alcohol's effects in the central nervous system, which depend on dose, time since administration, and environmental context. In the final part, the functional consequences of long-term exposure to alcohol as well as diseases associated with chronic alcoholism are reviewed.

Genetic selection of alcohol preference can be countered by conditioning processes

Twenty-four P rats and 24 NP rats were conditioned to consume 10% w/v alcohol in daily 0.5-h limited access periods using a modified version of Samson's sucrose fading procedure. Both P and NP rats demonstrated a strikingly similar day-to-day pattern of alcohol intakes. For the most part, P rats drank more than NP rats, but by the middle of the fourth month of drinking, P and NP rats were drinking equivalent amounts of alcohol. Both P and NP rats consumed alcohol in amounts similar to two outbred strains of rats (Wistar and Sprague-Dawley) previously conditioned to drink alcohol in this laboratory.

The role of corticosteroids in nicotine's physiological and behavioral effects

This paper reviews evidence indicating that adrenal corticosteroids modulate the responsiveness of mice and rats to nicotine. Adrenalectomy increases, and both acute and chronic corticosteroid administration decrease, some of the physiological and behavioral effects of nicotine. One function of adrenal steroids may be to regulate stress-induced changes in nicotine sensitivity. Another is to mediate the development of chronic tolerance when nicotine is given intermittently, and when the resulting tolerance has a learned component. A role of glucocorticoids in the development of tolerance to nicotine is suggested by the findings that a conditioned elevation of plasma corticosterone, which anticipates nicotine delivery, accompanies the development of chronic tolerance and that environmental cues evoke a conditioned corticosterone response, but only after they have become associated with nicotine delivery. The mechanisms by which adrenal steroids modulate nicotine sensitivity are not known, although recent in vitro evidence suggests that steroids can rapidly and reversibly reduce nicotinic receptor function. While most of the data are consistent with the hypothesis that corticosteroids reduce nicotine responsiveness, and thus promote a learned form of tolerance, there are new findings that corticosteroids increase the development of sensitization to the locomotor-activating effects of nicotine. These data suggest that formulations postulating a unidirectional effect of corticosteroids on nicotine's actions (e.g. decreased sensitivity) must be revised to take into account interacting variables such as the specific nicotine effect being studied and whether that effect normally exhibits tolerance or sensitization. Finally, research is presented which indicates that the corticosterone-elevating effects of nicotine, previously reported for experimenter-administered drug, are also produced when nicotine administration is contingent on an operant response, and at a dose which sustains the development of nicotine self-administration in rats. These findings highlight the feasibility of using self-administration models in future explorations of the relationship between adrenal steroids and nicotine function.

The paradoxical hedonic valence of acute ethanol withdrawal (hangover) states in rats: place and taste conditioning

The hedonic valence of EtOH's delayed effects, usually referred to as "hangover," was assessed 18 h after a 4 g/kg injection using both place and taste learning tasks. In the place conditioning task two CS-,CS+ intervals were used (48 h and 144 h); within each treatment interval, experimentally induced "hangover" was paired with the initially nonpreferred conditioning compartment for half of the experimental group (N = 10 rats) and with the initially preferred conditioning compartment for the half (N = 10 rats). Saline injections were paired with placement in the alternate conditioning compartment. A third group (N = 10 rats) was conditioned with milliliter equivalent volumes of saline on both sides. A conditioned place preference was conditioned with the hangover state-induced interoceptive stimuli. Attempts were made to taste condition 24 rats with the interoceptive stimulus attributes of hangover. Experimentally induced hangover was associated with an adipsogenic state, defined as a significant decline in voluntary intake of both saccharin and water, which prevented taste conditioning.

Effect of prior ethanol experience on dopamine overflow in accumbens of AA and ANA rats

The purpose of this study was to investigate the effect of repeated ethanol administration on dopamine overflow in the nucleus accumbens of alcohol-preferring AA (Alko Alcohol) and alcohol-avoiding ANA (Alko Nonalcohol) rats. Dopamine is a possible mediator of the reinforcing effects of ethanol, but it has previously been shown that ethanol-naïve alcohol-preferring AA and alcohol-nonpreferring ANA rats do not differ in their dopaminergic reaction to an intraperitoneal ethanol injection (0.5-2.0 g/kg), as assessed by measuring extracellular dopamine in the nucleus accumbens with in vivo microdialysis. Here a group of AA rats drank 10% (v/v) ethanol voluntarily-continual access for 5-15 days, limited access for 3 weeks-while a yoked group of AA rats and a yoked group of ANA rats received the same amount intragastrically by intubation. The rats were implanted with guide cannulas on the fourth week of limited access. Dopamine overflow was monitored in the microdialysis perfusate after 1 g/kg i.p. ethanol. The AA and the ANA rats that received ethanol non-contingently showed the same dopaminergic response to this as naïve animals have before. The group that had ingested the ethanol voluntarily showed, however, a significantly smaller increase in dopamine after 1 g/kg ethanol i.p. This suggests that the active behavior associated with obtaining the contingent drug may have an important impact on the reactions of the dopamine system to the drug, producing different results than when the same drug is administered by other routes. The hypothesis that dopamine mediates ethanol reinforcement in AA rats is not supported by the results.

Ethanol self-administration restores withdrawal-associated deficiencies in accumbal dopamine and 5-hydroxytryptamine release in dependent rats

Basal forebrain dopamine (DA) and 5-HT neurotransmission has been implicated in the mediation of the acute reinforcing actions of ethanol. Neuroadaptation theories predict that compensatory changes in neurochemical systems that are activated by alcohol acutely may underlie symptoms of withdrawal after chronic administration. To test this hypothesis, the release of DA and 5-HT was monitored by microdialysis in the nucleus accumbens of dependent male Wistar rats at the end of a 3-5 week ethanol (8.7% w/v) liquid diet regimen, during 8 hr of withdrawal, and during renewed availability of ethanol involving (1) the opportunity to operantly self-administer ethanol (10% w/v) for 60 min, followed by (2) unlimited access to the ethanol-liquid diet. Results were compared to control groups pair-fed with ethanol-free liquid diet and trained to self-administer either ethanol or water. In nondependent rats, operant ethanol self-administration increased both DA and 5-HT release in the NAC. Withdrawal from the chronic ethanol diet produced a progressive suppression in the release of these transmitters over the 8 hr withdrawal period. Self-administration of ethanol reinstated and maintained DA release at prewithdrawal levels but failed to completely restore 5-HT efflux. 5-HT levels recovered rapidly, however, within 1 hr of reexposure to ethanol liquid diet. These findings suggest that deficits in accumbal monoamine release may contribute to the negative affective consequences ethanol withdrawal and, thereby, motivate ethanol-seeking behavior in dependent subjects.

Decreased brain reward produced by ethanol withdrawal

Abstinence from chronic administration of various drugs of abuse such as ethanol, opiates, and psychostimulants results in withdrawal syndromes largely unique to each drug class. However, one symptom that appears common to these withdrawal syndromes in humans is a negative affective/motivational state. Prior work in rodents has shown that elevations in intracranial self-stimulation (ICSS) reward thresholds provide a quantitative index that serves as a model for the negative affective state during withdrawal from psychostimulants and opiates. The current study sought to determine whether ICSS threshold elevations also accompany abstinence from chronic ethanol exposure sufficient to induce physical dependence. Rats prepared with stimulating electrodes in the lateral hypothalamus were trained in a discrete-trial current-intensity ICSS threshold procedure; subsequently they were subjected to chronic ethanol administration in ethanol vapor chambers (average blood alcohol level of 197 mg/dl). A time-dependent elevation in ICSS thresholds was observed following removal from the ethanol, but not the control, chambers. Thresholds were significantly elevated for 48 hr after cessation of ethanol exposure, with peak elevations observed at 6-8 hr. Blood alcohol levels were directly correlated with the magnitude of peak threshold elevation. Ratings of traditional overt signs of withdrawal showed a similar time course of expression and resolution. The results suggest that decreased function of reward systems (elevations in reward thresholds) is a common element of withdrawal from chronic administration of several diverse classes of abused drugs.