A low dose alcohol drug discrimination in social drinkers: relationship with subjective effects

Substitution therapy for patients with alcohol dependence: Mechanisms of action and efficacy

New approaches for the treatment of alcohol dependence (AD) may improve patient outcomes. Substitution maintenance therapy is one of the most effective treatment options for opioid and nicotine use disorders. So far, there has been little attention to substitution therapy for the treatment of AD. Here, we explain the mechanistic foundations of alcohol substitution maintenance therapy. Alcohol has many primary targets in the brain (and other organs) and the physical interaction of ethanol molecules with these specific ethanol-sensitive sites on a variety of ionotropic receptors (e.g. GABA-A, NMDA, and nicotinic acetylcholine (nACh) receptors) and ion channels provides the rationale for substitution. As such, a variety of compounds can interact with those ethanol-sensitive sites and can thus substitute for some of the effects of alcohol. For some of these compounds, alcohol discrimination studies have shown their substitution potential. Accordingly, potential substitution treatments include agonists acting at GABA receptors such as sodium oxybate, baclofen and benzodiazepines, NMDA receptor antagonists such as ketamine and memantine, or nAChRs agonists such as varenicline. All these compounds are already approved for other indications and we present clinical evidence for these drugs in the treatment of alcohol withdrawal syndrome (AWS) and in the long-term treatment of AD, and outline future steps for their acceptance as substitution treatment in AD. Finally, we discuss the substitution approach of managed alcohol programs for the most severely affected homeless populations. Results showed that sodium oxybate is probably the closest to a substitution therapy for AD and is already approved for the treatment of AWS and in the long-term treatment of AD in some countries. In conclusion, we argue that better AD treatment can be provided if substitution maintenance treatments for alcohol are implemented at a similar scale as for opioid and nicotine use disorder.

Cross-Species Translational Findings in the Discriminative Stimulus Effects of Ethanol

The progress on understanding the pharmacological basis of ethanol's discriminative stimulus effects has been substantial, but appears to have plateaued in the past decade. Further, the cross-species translational efforts are clear in laboratory animals, but have been minimal in human subject studies. Research findings clearly demonstrate that ethanol produces a compound stimulus with primary activity through GABA and glutamate receptor systems, particularly ionotropic receptors, with additional contribution from serotonergic mechanisms. Further progress should capitalize on chemogenetic and optogenetic techniques in laboratory animals to identify the neural circuitry involved in mediating the discriminative stimulus effects of ethanol. These infrahuman studies can be guided by in vivo imaging of human brain circuitry mediating ethanol's subjective effects. Ultimately, identifying receptors systems, as well as where they are located within brain circuitry, will transform the use of drug discrimination procedures to help identify possible treatment or prevention strategies for alcohol use disorder.

Threshold dose for discrimination of nicotine via cigarette smoking

RATIONALE

The lowest nicotine threshold "dose" in cigarettes discriminated from a cigarette containing virtually no nicotine may help inform the minimum dose maintaining dependence.

OBJECTIVES

Spectrum research cigarettes (from NIDA) differing in nicotine content were used to evaluate a procedure to determine discrimination thresholds.

METHODS

Dependent smokers (n = 18; 13 M, 5 F) were tested on ability to discriminate cigarettes with nicotine contents of 11, 5, 2.4, and 1.3 mg/g, one per session, from the "ultralow" cigarette with 0.4 mg/g, after having discriminated 16 mg/g from 0.4 mg/g (all had 9-10 mg "tar"). Exposure to each was limited to 4 puffs/trial. All subjects were abstinent from smoking overnight prior to each session, and the number of sessions was determined by the participant's success in discrimination behavior on >80 % of trials. Subjective perceptions and behavioral choice between cigarettes were also assessed and related to discrimination behavior.

RESULTS

The median threshold was 11 mg/g, but the range was 2.4 to 16 mg/g, suggesting wide variability in discrimination threshold. Compared to the ultralow, puff choice was greater for the subject's threshold dose but only marginal for the subthreshold (next lowest nicotine) cigarette. Threshold and subthreshold also differed on subjective perceptions but not withdrawal relief.

CONCLUSIONS

Under these testing conditions, threshold content for discriminating nicotine via cigarettes may be 11 mg/g or greater for most smokers, but some can discriminate nicotine contents one-half or one-quarter this amount. Further study with other procedures and cigarette exposure amounts may identify systematic differences in nicotine discrimination thresholds.

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.

Cues that signal the alcohol content of a beverage and their effectiveness at altering drinking rates in young social drinkers

AIMS

The aim of this study was to assess the impact of cues that signal the alcoholic strength of a beverage on drinking rate in young social drinkers.

METHODS

In Experiment 1, two groups of young social drinkers (n=20 per group) consumed a lager-based drink containing either 3% or 7% alcohol-by-volume. The pattern of drinking behaviour was observed, and drinking time was recorded. Self-reported mood was measured across the session, and participants also provided ratings of the drinks' sensory and hedonic properties. Experiment 2 replicated Experiment 1, but used a within-subjects design (n=12).

RESULTS

In both experiments, participants took significantly longer to consume the 7% drink compared with the 3% drink, and the total inter-sip interval was longer for the 7% drink. These effects were most closely related to the participants' changing estimates of alcohol strength across the test session, alongside concomitant changes in various aspects of self-reported mood. Sensory and hedonic evaluations of the drinks did not affect drinking behaviour in either experiment.

CONCLUSIONS

The findings suggest that the consumption rate of an alcoholic beverage can be modulated by its alcohol content, and that the perceived pharmacological effect of the alcohol serves as an effective signal to alter drinking behaviour.

Effects of dose and time on the ability of alcohol to prime social drinkers

Interoceptive drug cues, through associations with the drug's reinforcing properties, may act as conditioned stimuli and elicit conditioned responses. For instance, a dose of alcohol, given to alcohol-experienced people, can lead to an enhancement of alcohol drinking, a phenomenon known as the priming effect. The present study aimed to investigate the alcohol priming effect in non-dependent social drinkers with respect to the dose of alcohol preload and the time of testing after preload. Fifteen social drinkers participated in five daily consecutive sessions. On days 1 and 2 (training sessions), participants consumed a 500 ml beverage of either 0.6 g/kg of alcohol or placebo (50 ml aliquots) presented in 10 colour-coded cups. During days 3, 4 and 5 (testing sessions), a preload of placebo, 0.3 or 0.6 g/kg of alcohol was given (in randomized sequence) in 10 opaque colourless cups. Thirty, 60 and 90 min following the preload, participants responded to an imagery script referring to the drinks sampled at training including a question on the number of aliquots participants would consume from each of the drinks if given the opportunity (hypothetical choice). Participants completed questionnaires evaluating mood and alcohol desires at baseline (before the beverages were given) and after the hypothetical choice. The hypothetical choice showed significant interactions between dose and time: the greatest number of alcohol aliquots were wanted 30 min following the 0.6 g/kg dose of alcohol preload. Ratings from the Desires for Alcohol Questionnaire also showed that alcohol desires peaked 30 min following the 0.6 g/kg of alcohol preload. These data support previous evidence that priming with alcohol can occur and indicate that dose of, and time after preload might affect the strength of, the priming effect for alcohol-related behaviours.

Effect of duration and pattern of chronic ethanol exposure on tolerance to the discriminative stimulus effects of ethanol in C57BL/6J mice

This study was conducted to examine whether amount and/or pattern (intermittent or continuous) of chronic ethanol exposure subsequently alters sensitivity to the discriminative stimulus effects of ethanol. Adult male C57BL/6J mice were trained to discriminate between 1.5 g/kg ethanol and saline in a two-lever food-reinforced operant procedure. Once ethanol discrimination was successfully acquired, generalization testing was conducted using a cumulative dosing procedure to generate a baseline dose-response function (0-2.5 g/kg ethanol). Discrimination training was then suspended while mice received chronic ethanol vapor or air exposure in inhalation chambers. The total amount of ethanol exposure was systematically increased, but it was delivered in an intermittent or continuous manner. At 24 or 16 h after inhalation treatment, ethanol discriminability was reassessed using the same generalization testing procedures. Results indicated that discrimination performance in control (air-exposed) mice was similar to baseline. However, sensitivity to the discriminative cue of ethanol following chronic ethanol treatment was reduced (as evidenced by rightward shifts in the dose-response functions and increased ED(50) values). The magnitude of this tolerance effect increased as a function of the number of chronic ethanol exposures as well as the total duration of ethanol exposure. In addition, tolerance was more robust when generalization testing was conducted earlier (16 versus 24 h) after chronic ethanol treatment was halted (2- to 3-fold increase in ED(50) values). These results may have important clinical implications, because blunted sensitivity to the discriminative cue of ethanol may contribute to enhanced ethanol self-administration behavior observed in these mice following similar chronic ethanol treatment.

Understanding how the brain perceives alcohol: neurobiological basis of ethanol discrimination

Understanding the neurobiological mechanisms that regulate how the brain perceives the intoxicating effects of alcohol is highly relevant to understanding the development and maintenance of alcohol addiction. The basis for the subjective effects of intoxication can be studied in drug discrimination procedures in which animals are trained to differentiate the presence of internal stimulus effects of a given dose of ethanol (EtOH) from its absence. Research on the discriminative stimulus effects of psychoactive drugs has shown that these effects are mediated by specific receptor systems. In the case of alcohol, action mediated through ionotropic glutamate, gamma-aminobutyric acid, and serotonergic receptors concurrently produce complex, or multiple, basis for the discriminative stimulus effects of EtOH. These receptor systems may contribute differentially to the discriminative stimulus effects of EtOH based on the EtOH dose, species differences, physiological states, and genetic composition of the individual. An understanding of the receptor mechanisms that mediate the discriminative stimulus effects of EtOH can be used to develop medications aimed at decreasing the subjective effects associated with repeated intoxication. The goal of this symposium was to present an overview of recent findings that highlight the neurobiological mechanisms of EtOH's subjective effects and to suggest the relevance of these discoveries to both basic and clinical alcohol research.

Gender differences in response to lorazepam in a human drug discrimination study

Gender differences in the discriminative stimulus properties of drugs of abuse have sometimes been reported, although we have previously found no differences in subjective or discriminative responses in human subjects acquiring an alcohol discrimination. The aim of the present work was to determine if there were gender differences in the effects of lorazepam, a benzodiazepine-receptor agonist which substituted for the alcohol stimulus in trained social drinkers. Volunteers who had already acquired an alcohol (0.2g/kg) placebo discrimination were administered (double-blind) either placebo (nine females, nine males) or lorazepam 2mg (six females, six males). They then sampled a series of five drinks and rated each one for likeness to the training stimulus (the generalization response). In addition they completed rating scales for subjective effects and the Digit Symbol Substitution Test (DSST). Lorazepam substituted for the alcohol stimulus equally in both sexes and increased associated scores for lightheadedness. Females however, showed a much greater DSST performance impairment following lorazepam, compared with males. This effect was independent of body weight differences and sedation. These results are discussed in the light of current knowledge of gender differences in response to drugs of abuse and suggest that the stimulus and cognitive effects of benzodiazepine-receptor agonists are modulated by different brain mechanisms.

Effects of alcohol and lorazepam during extinction of alcohol self-administration in rats

Systemic injections of alcohol have previously been reported to 'prime' or to reinstate self-administration of alcohol in rats, and it has been suggested that the priming effects of drugs are related to their stimulus properties. We tested this hypothesis by investigating the effects of lorazepam, which cross-generalizes with alcohol in animal drug-discrimination studies, in rats trained to self-administer 7% alcohol in an operant paradigm. Once animals were trained, extinction tests were carried out twice weekly, before which rats were injected with either vehicle, alcohol (0.063-0.5 g/kg, i.p.) or lorazepam (0.03-0.25 mg/kg, i.p.). Alcohol did not increase responding for alcohol during extinction. Doses of 0.25 and 0.5 g/kg reduced alcohol-appropriate lever pressing (p < 0.05 versus 0 g/kg), with the largest dose also suppressing general activity (p < 0.02 versus 0 g/kg). Lorazepam also reduced alcohol-appropriate responding, in a behaviourally specific manner; doses of 0.03 mg/kg and above decreased lever pressing (p < 0.05 versus 0 mg/kg), whereas general activity was depressed at 0.06 mg/kg and larger doses (p < 0.05 versus 0 mg/kg). Although lorazepam mimicked the effect of alcohol at doses predicted to do so on the basis of their relative potency in drug discrimination studies, neither alcohol nor lorazepam primed rats to respond for alcohol. By contrast, the pattern of results suggested that, in this model, they 'satiated' or substituted for alcohol, resulting in a reduced motivation to respond.