Learning alcohol tolerance: the contribution of response expectancies

Alcohol Tolerance in Human Laboratory Studies for Development of Medications to treat Alcohol Use Disorder

AIMS

Human laboratory studies have contributed extensively in the research and development of novel medications to treat alcohol use disorder (AUD). Alcohol tolerance may represent one additional variable that can be utilized to expand the understanding of the AUD wide phenotypic profile and provide support to the medication development process. Tolerance is characterized as an individual's subjective response to alcohol and has been recognized as a predictor of AUD progression. Tolerance can be evaluated both by self-reported response (e.g. assessments) and objective measurements (e.g. motor impairment); as such, it represents an exploitable variable in the field of alcohol research.

METHODS

This Narrative Review focuses on the use of alcohol tolerance, specifically within alcohol laboratory studies, for medication development. It seeks to identify a research gap and a research opportunity in clinical studies to evaluate biobehavioral responses captured in order to develop medications to treat AUD.

RESULTS

Alcohol tolerance may provide additional information on the safety and tolerability of medications to treat AUD, in particular, when novel medications are co-administered with alcohol within the AUD population.

CONCLUSIONS

As such, alcohol tolerance represents an additional outcome that may be included in randomized clinical trial (RCT) protocols designed for developing AUD pharmacotherapies.

Family history of alcoholism interacts with alcohol to affect brain regions involved in behavioral inhibition

RATIONALE

Impulsive behavior is associated with both alcohol use disorders and a family history of alcoholism (FHA). One operational definition of impulsive behavior is the stop-signal task (SST) which measures the time needed to stop a ballistic hand movement.

OBJECTIVE

Employ functional magnetic resonance imaging (fMRI) to study right frontal responses to stop signals in heavy drinking subjects with and without FHA, and as a function of alcohol exposure.

METHODS

Twenty-two family history-positive (FHP; age = 22.7 years, SD = 1.9) and 18 family history-negative (FHN; age = 23.7, SD = 1.8) subjects performed the SST in fMRI in two randomized visits: once during intravenous infusion of alcohol, clamped at a steady-state breath alcohol (BrAC) concentration of 60 mg/dL, and once during infusion of placebo saline. An independent reference group (n = 13, age = 23.7, SD = 1.8) was used to identify a priori right prefrontal regions activated by successful inhibition (Inh) trials, relative to "Go" trials that carried no need for inhibition [Inh > Go].

RESULTS

FHA interacted with alcohol exposure in right prefrontal cortex, where alcohol reduced [Inh > Go] activation in FHN subjects but not in FHP subjects. Within this right frontal cortical region, stop-signal reaction time also correlated negatively with [Inh > Go] activation, suggesting that the [Inh > Go] activity was related to inhibitory behavior.

CONCLUSIONS

The results are consistent with the low level of response theory (Schuckit, J Stud Alcohol 55:149-158, 1980; Quinn and Fromme, Alcohol Clin Exp Res 35:1759-1770, 2011), with FHP being less sensitive to alcohol's effects.

Alcohol and driving: is the 0.05% blood alcohol concentration limit justified?

This paper reviews the findings of experimental and laboratory research to determine whether there is sufficient evidence to support a uniform 0.05% blood alcohol concentration (BAC) as the legal limit for driving. Statistically significant and meaningful decrements in driving-related performance were identified at 0.05% BAC or below in many studies. Younger and inexperienced drinkers and drivers appear to be at greatest risk for alcohol-related traffic crashes. It is concluded that on scientific grounds, there is support for setting the legal limit at 0.05%. The setting of a uniform 0.05% BAC statutory limit should be but one effort within a comprehensive approach including other legal, social, behavioural and environmental strategies to deal with the drink driving problem.

Characterization of the effects of inhaled perchloroethylene on sustained attention in rats performing a visual signal detection task

The aliphatic hydrocarbon perchloroethylene (PCE) has been associated with neurobehavioral dysfunction including reduced attention in humans. The current study sought to assess the effects of inhaled PCE on sustained attention in rats performing a visual signal detection task (SDT). Due to its similarities in physiological effect to toluene and trichloroethylene (TCE), two other commonly used volatile organic compounds (VOCs) known to reduce attention in rats, we hypothesized (1) that acute inhalation of PCE (0, 500, 1000, 1500 ppm) would disrupt performance of the SDT in rats; (2) that impaired accuracy would result from changes in attention to the visual signal; and (3) that these acute effects would diminish upon repetition of exposure. PCE impaired performance of the sustained attention task as evidenced by reduced accuracy [P(correct): 500 to 1500 ppm], elevated response time [RT: 1000 and 1500 ppm] and reduced number of trials completed [1500 ppm]. These effects were concentration-related and either increased (RT and trial completions) or remained constant [P(correct)] across the 60-min test session. The PCE-induced reduction in accuracy was primarily due to an increase in false alarms, a pattern consistent with reduced attention to the signal. A repeat of the exposures resulted in smaller effects on these performance measures. Thus, like toluene and TCE, inhaled PCE acutely impaired sustained attention in rats, and its potency weakened upon repetition of the exposure.

Differential effects of alcohol and alcohol expectancy on risk-taking during simulated driving

This study examined the separate and combined effects of alcohol (0.0 or 0.5 g/kg) and alcohol expectancies (none or 2-3 standard drinks) on risk-taking using a simulated-driving lane choice task. In this task, risk-taking was operationalized as choosing a cone-defined lane with a higher relative probability of hitting a cone. When alcohol was received but not expected, the probability of a risky lane choice increased compared with when alcohol was neither expected nor received. However, when subjects both expected and received alcohol, the probability of a risky lane choice was significantly decreased compared with when alcohol was neither expected nor received. These findings suggest that the knowledge of dose received can differentially influence the pharmacological effect of alcohol on decision-making.

Ethanol effects on three strains of zebrafish: model system for genetic investigations

The effects of acute and chronic ethanol administration on the wild-type (WT), long-fin striped (LFS), and blue long-fin (BLF) strains of zebrafish were investigated. In the LFS strain, acute exposure to 0.25% (v/v) ethanol inhibited the startle reaction and increased both the area occupied by a group of subjects and the average distance between each fish and its nearest neighbor. Similar effects were found in the WT fish although higher concentrations of ethanol were required. No effects on the behavior of the BLF fish were observed with up to 1.0% (v/v) ethanol. Brain alcohol levels were comparable among the three strains precluding a pharmacokinetic explanation for the behavioral results. In LFS zebrafish, behavioral tolerance was observed after 1 week of continual exposure to ethanol. Conversely, chronic ethanol exposure of the WT fish for up to 2 weeks did not result in the development of tolerance, but rather appeared to increase the disruptive action of the drug. The present results suggest the observed strain differences in the effects of ethanol reflect genotypic differences in both the response of the central nervous system (CNS) to ethanol as well as the ability of the CNS to adapt to ethanol exposure. Although preliminary, the present study indicates that the zebrafish is an excellent model system to investigate the genetic determinants involved in regulating the responses to ethanol.

D3 dopamine receptor, behavioral sensitization, and psychosis

Behavioral sensitization is a progressive, enduring enhancement of behaviors that develops following repeated stimulant administration. It is mediated in part by dopaminergic pathways that also modulate a number of psychiatric conditions including the development of psychosis. We propose that down-regulation of D3 dopamine receptor function in critical brain regions contributes to sensitization. Rodent locomotion, a sensitizable behavior, is regulated by the opposing influence of dopamine receptor subtypes, with D3 stimulation opposing concurrent D1 and D2 receptor activation. The D3 dopamine receptor has a 70-fold greater affinity for dopamine than D1 or D2 dopamine receptors. This imbalance in ligand affinity dictates greater occupancy for D3 than D1 or D2 receptors at typical dopamine concentrations following stimulant drug administration, resulting in differences in the relative tolerance at D3 vs D1 and D2 receptors. Sensitization may therefore result in part from accommodation of the inhibitory D3 receptor 'brake' on D1/D2 mediated behaviors, leading to a progressive locomotion increase following repeated stimulant exposure. The requirement for differential tolerance at D3 vs D1 and D2 receptors may explain the observed development of sensitization following application of cocaine, but not amphetamine, directly into nucleus accumbens. If correct, the 'D3 Dopamine Receptor Hypothesis' suggests D3 antagonists could prevent sensitization, and may interrupt the development of psychosis when administered during the prodromal phase of psychotic illness. Additional study is needed to clarify the role of the D3 dopamine receptor in sensitization and psychosis.

Human factors in the causation of road traffic crashes

Road traffic crashes (RTCs) are responsible for a substantial fraction of morbidity and mortality and are responsible for more years of life lost than most of human diseases. In this review, we have tried to delineate behavioral factors that collectively represent the principal cause of three out of five RTCs and contribute to the causation of most of the remaining. Although sharp distinctions are not always possible, a classification of behavioral factors is both necessary and feasible. Thus, behavioral factors can be distinguished as (i) those that reduce capability on a long-term basis (inexperience, aging, disease and disability, alcoholism, drug abuse), (ii) those that reduce capability on a short-term basis (drowsiness, fatigue, acute alcohol intoxication, short term drug effects, binge eating, acute psychological stress, temporary distraction), (iii) those that promote risk taking behavior with long-term impact (overestimation of capabilities, macho attitude, habitual speeding, habitual disregard of traffic regulations, indecent driving behavior, non-use of seat belt or helmet, inappropriate sitting while driving, accident proneness) and (iv) those that promote risk taking behavior with short-term impact (moderate ethanol intake, psychotropic drugs, motor vehicle crime, suicidal behavior, compulsive acts). The classification aims to assist in the conceptualization of the problem that may also contribute to behavior modification-based efforts.

Alcohol tolerance and nicotine cross-tolerance in adolescent mice

The present experiment was designed to evaluate the development of tolerance to alcohol and cross-tolerance to nicotine in adolescent mice. C57BL/6J mice (30-40 days old) were injected IP with alcohol (2.5 g/kg) for 4 consecutive days. A control group received four saline injections. On the test day, all subjects received an alcohol injection. Tolerance to alcohol's hypothermic effect was observed. Mice (male and female) exposed to alcohol for the 4 previous days showed less hypothermic response to an alcohol challenge than animals injected for 4 days with saline and then challenged with alcohol. Tolerance to alcohol's motor incoordinating effects and differences in blood alcohol concentrations were not observed. Thirty days following alcohol treatment, the same mice received a single nicotine injection (1 mg/kg) to assess cross-tolerance. Nicotine's effect on locomotor activity (open field test) and rectal temperature varied as a function of prior adolescent alcohol exposure and gender. Specifically, female mice who had been exposed to alcohol administrations were more resistant to nicotine's effect on locomotion and temperature than saline-treated animals. In summary, these data demonstrate that adolescent mice develop tolerance to some, but not all, alcohol-induced responses, and that female mice are cross-tolerant to nicotine's effects on temperature and activity.

Differential effects of a dihydropyridine calcium channel antagonist on the components of ethanol tolerance

The dihydropyridine calcium channel antagonist, nimodipine, was found to decrease the extent of tolerance that developed to the ataxic action of ethanol in experimental designs in which the tolerance was not context-specific, when ethanol was given by liquid diet. When ethanol was given by injection, so that cues were present for the effects of ethanol during the chronic treatment, tolerance to the ataxic actions of ethanol was unaffected. Nimodipine, however, decreased the tolerance to the hypothermic actions of ethanol, when the ethanol was given by injection. When the rats were given practice sessions on the motor task while under the influence of the ethanol, during the chronic treatment, nimodipine did not affect tolerance to the ataxic actions of ethanol. When nimodipine was given before the motor task learning and ethanol after the practice sessions, the tolerance to the ataxic effect of ethanol was increased. A similar schedule of drug treatment with the NMDA antagonist CGP37849 given before the practice sessions, and ethanol afterwards, resulted in decreased tolerance to ethanol. It is suggested that these changes in ethanol tolerance may be explained by dual actions of nimodipine in, firstly, decreasing the form of tolerance to ethanol that is not dependent on contextual cues and, secondarily, in increasing the learning of a motor task.

The expected drug and its expected effect interact to determine placebo responses to alcohol and caffeine

This study tested placebo responses in psychomotor performance when caffeine or alcohol was expected. Fifty male university students were assigned to one of four placebo groups or to a no-treatment control group. Two groups received placebo caffeine and two received placebo alcohol. Subjects performed 12 trials on a pursuit rotor task and performance was measured by the percent time on target. Then they received information about the expected drug effect on the task. One caffeine placebo group (C+) and one alcohol placebo group (A+) were led to expect enhanced performance on the task. The other caffeine placebo group (C-) and alcohol placebo group (A-) were led to expect impaired performance. Subjects subsequently performed 12 trials on the task. An interaction was obtained between the expected type of effect and the expected type of drug. The C+ group displayed superior performance compared to the C- group, and the reverse relationship was observed between the A+ and A- group. In addition, subjects led to expect alcohol-induced impairment (A-) performed better than subjects led to expect caffeine-induced impairment (C-). Subjects also reported greater motivation to resist impairment when they expected alcohol rather than caffeine. The research indicates that understanding and predicting placebo responses may require consideration of the drug that is expected as well as its expected effect.

A quantitative theory of acute tolerance to alcohol

A theory of acute tolerance to alcohol is proposed that includes two assumptions: 1) acute tolerance is a linear process with time, and 2) the slope of the line is a measure of the magnitude of the acute tolerance effect. Evidence that supports the validity of the theory is presented both from studies in which blood alcohol level (BAL) was manipulated experimentally and from studies based on the one-dose method that is common in human research. The slope of the acute tolerance line defined by this theory is a measure of the percent decrement in maximum alcohol effect per unit time. Thus, quantitative comparisons can be made of acute tolerance effects obtained under different environmental conditions or experimental treatments, including comparisons of different drugs. Limitations of the proposed theory and the relation of this theory to other theories of tolerance to alcohol are discussed.

Impairment and recovery under repeated doses of alcohol: effects of response-outcomes

This research examined the behavioral effect of alcohol during rising and declining blood alcohol concentrations (BACs) when the dose was repeated three times (mean peak BAC = 78 mg/100 ml). A total of 36 male social drinkers learned a complex psychomotor task and subsequently performed it at intervals after alcohol was received. Subjects performed under one of two conditions: an experimental (E) treatment associated drug-compensatory (nonimpaired) task performance with a positively reinforcing outcome or a control (C) treatment associated no environmental consequence with performance. E treatment diminished impairment at all positions on the BAC curve and carried over to result in progressively less impairment when the dose was repeated. In contrast, C treatment tended to increase impairment around the BAC curve with repeated doses. The rate of recovery during declining BACs remained stable across sessions and was not altered by the treatments. The results imply that impairment under a dose of alcohol is governed by two processes: response-outcome associations that determine the amount of impairment displayed under a dose and some adaptive process that determines the rate of recovery with time during exposure to a dose.

Neurobiology of alcohol abuse

Excessive consumption of beverage alcohol (ethanol) is a major health concern worldwide. Understanding the mechanisms by which ethanol affects neural functioning, after both acute and chronic exposure, has become a major goal in the study of alcoholism. With such an understanding, we should be able to institute more effective treatments and preventative measures for alcohol abuse problems. Recent studies have found, contrary to earlier assumptions, that ethanol has selective, dose-dependent effects on various neurotransmitter systems within the CNS. These effects are observed at all levels of analysis, from molecular to behavioral. This review by Herman Samson and Adron Harris covers these recent findings, with the intent of generating questions that will focus further research efforts.

Alcohol expectancies and behavioral and emotional responses to placebo versus alcohol administration

Forty normal drinking males were recruited for a study of "responses to alcohol." Following the completion of an alcohol use questionnaire that included measures of expectancies of alcohol effects, subjects were randomly assigned to either receive the actual 0.6 g/kg dose of ethanol to bring their peak blood alcohol concentration (BAC) to near 0.075 g/dl or to receive a placebo dose. Neither the subject nor the tester was aware of the condition to which the subject has been assigned. Prior to dosing and at repeated 1/2-hr intervals following dosing, subjects were tested on a battery of motor coordination, perceptual speed, reaction time, and mood measures. Significant alcohol effects were found for several measures, but the only significant interaction of individual differences in expectancies of alcohol effects with alcohol dosing occurred for self-perceived intoxication. Subjects who expected more disinhibition after alcohol dosing and who were administered alcohol reported more intoxication than those expecting less disinhibition, while no expectancy effect was found for subjects administered the placebo.

Context-drug pairings enhance tolerance to ethanol-induced disruption of operant responding

Much of the research implicating learning in the development of tolerance to ethanol-induced impairment has used an experimental design in which different groups receive drug either before or after an opportunity to perform an instrumental or operant task. The stronger tolerance observed in subjects who perform while intoxicated is most often attributed to the reinforced practice of a learned compensatory response. Using an experimental procedure modeled after Chen (1979), the present study examined an alternative theoretical basis for tolerance in the before-versus-after design. Specifically, the effects of Pavlovian context-drug pairings were assessed under circumstances that precluded reinforced practice of the operant response. Three groups of food-deprived rats were initially trained to barpress for sucrose on an FR15 schedule. After 30 sessions, the bar was retracted and the dipper was covered for a 3-day tolerance acquisition phase. During this phase, each group received an IP injection 15 min before and 45 min after each session. The Paired group received ethanol (1.2 g/kg) before and saline after the session, thus pairing ethanol with cues of the test chamber. The Unpaired group received saline before and ethanol after the session, while the No-Drug group always received saline. During a final test phase, all groups received ethanol (1.5 g/kg) before access to sucrose on the FR schedule. The Paired group completed the first FR15 sequence more rapidly than either control group, indicating that context-ethanol pairings enhanced tolerance to the drug's disruptive effect on the initiation of operant responding.(ABSTRACT TRUNCATED AT 250 WORDS)

Expected effect of caffeine on motor performance predicts the type of response to placebo

Two experiments (N = 56) investigated the relationship between subjects' expectancies concerning the effect of caffeine on a motor skill, and the type of placebo response. Male subjects were assigned to four groups. Three groups expected to receive caffeine but received a placebo. Prior to the placebo, two of the groups received information about the effect of caffeine on a motor skill task which led one group E(+) to expect enhanced performance, and the other E(-) to expect impairment. The third placebo group received no information E(?). A control group E(0) received no beverage, so neither caffeine nor any effect on performance was expected. The expected type of effect predicted the type of placebo response displayed. Group E(+) displayed greater improvement under placebo than did group E(0), and group E(-) performed more poorly than those in group E(0). No placebo response was observed in group E(?). Placebo effects on mood were correlated with subjects' predictions about the effect of caffeine on mood. The role of expectancies in response to placebos and psychoactive drugs is discussed.

Response expectancies affect the acquisition and display of behavioral tolerance to alcohol

Two experiments demonstrated that a learned expectation of a favourable consequence for drug-compensatory performance enhanced behavioral tolerance to alcohol, and when the expectancy was trained, the subsequent display of tolerance depended upon its consequence. Both experiments involved each of four groups of six male social drinkers each, who drank 0.62 g/kg alcohol on four sessions, and a placebo on a fifth session. Experiment 1 provided two groups with the opportunity to learn the response expectancy by performing a motor task under alcohol with either an informative consequence (IO) or information plus money contingent upon drug-compensatory performance (MI). Two control groups performed with either no outcome (N), or with money for compensatory performance but no information about earnings until the experiment concluded (MO). The effects of learning history were evident on sessions 4 and 5 when the same consequence was contingent upon the performance of all groups. Compared to controls, the groups that had received response expectancy training (MI and IO) displayed significantly more alcohol tolerance and greater compensatory facilitation of performance under placebo. In Experiment 2, all groups received the same response expectancy training, and the effect of the consequence of compensatory performance was demonstrated during subsequent test sessions 4 and 5. An informative consequence (MI or IO) enhanced tolerance and the compensatory response to placebo, whereas performance with no response contingent information (N or MO), revealed little tolerance or compensatory response to placebo. Theoretical and practical implications of the findings were discussed.

Situational specificity of tolerance to decreased operant responding by morphine and l-nantradol

In one experiment, key pressing of rats was maintained under a fixed-ratio schedule of food presentation in a first daily session in one environmental situation, and interruption of a photobeam was maintained under a continuous shock avoidance schedule in a second daily session in another environmental situation. After receiving acute injections of the cannabinoid l-nantradol (0.01-0.3 mg/kg), rats received daily administration of a rate-decreasing dose of the drug after the second session, then before the second session, and then before the first session. Tolerance that developed to decreased avoidance responding in the second daily session did not extend to decreased fixed-ratio responding in the first daily session, but was specific to circumstances coinciding with the pharmacological actions of l-nantradol. In a second experiment lever pressing of squirrel monkeys was maintained under an identical fixed-interval schedule of food delivery in two separate daily sessions in different experimental situations. After receiving once-weekly acute injections of morphine (0.3-3.0 mg/kg), monkeys received daily administration of a rate-decreasing dose of morphine in a counter-balanced order before each session. Just as for experiment 1, tolerance that developed in the environment coinciding with the pharmacological actions of morphine did not immediately generalize to operants in the other environmental situation. Instead, tolerance depended on both pharmacologic action as well as concurrently operating behavioral processes.

Learned tolerance to alcohol: mental rehearsal with imagined consequences

Two experiments tested the hypothesis that the acquisition of a new response is enhanced by mental rehearsal which includes the imagined consequence of mental performance. A total of 48 males participated in the research. Experiment 1 tested drug-free learning of a motor skill task. Experiment 2 used the same task to test the acquisition of a drug-compensatory response (i.e., tolerance) under alcohol. Subjects in each experiment were randomly assigned to one of three treatments: mental rehearsal with imagined consequences (C), mental rehearsal with no imagined consequences (N), and rest (R). Both experiments confirmed the hypothesis. C treatment yielded superior drug-free performance, and a greater tolerance. The effect of N treatment was intermediate, and R treatment was least effective. It was concluded that incorporating an imagined consequence of mental performance enhances the learning of alcohol tolerance and the acquisition of a motor skill. Factors that may have contributed to the marginal efficacy of N treatment were discussed, and research implications were considered.

Resistance to alcohol impairment of visual-motor performance. II: Effects for attentional set and self-reported concentration

There has been little or no direct inquiry into the feasibility of nonbiological processes for attenuating alcohol effects. In an initial study, we found that an instructional Set (to concentrate) presented at each trial facilitated visual-motor performance among moderately intoxicated subjects. We extended this work in the present study by varying density of the Set presentation across trials, by varying Set onset and offset, and by assessing self-reported concentration levels. After dosing, subjects participated in two pairs of performance trials separated by a rest period. Six groups of subjects differed with respect to the number and sequence of Set presentations received across the postbeverage trials. We found that more Set presentations yielded better performance. Also, onset of Set presentation led to improved or sustained performance, whereas offset led to diminished performance. Finally, consistent with the possibility that concentration serves as a mediating variable, self-reported concentration correlated with performance. Implications of the obtained effects are discussed in the context of tolerance research and practical considerations.