Increases In Alcohol Self-administration Research Articles

Predator Odor Stressor, 2,3,5-Trimethyl-3-Thiazoline (TMT): Assessment of Stress Reactive Behaviors During an Animal Model of Traumatic Stress in Rats.

Animal models utilizing predator odor stress are important in understanding implications for post-traumatic stress disorder. 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) has been used to measure stress reactive behaviors during TMT exposure, indicative of stress coping behaviors. In addition, long-term consequences of stress including contextual-induced stress memory, anxiety-like and hyperarousal behaviors, and subsequent increases in alcohol self-administration can also be examined after TMT exposure. In this article, we describe the TMT exposure protocol used in our lab and how we measure different stress-reactive behaviors that rats engage in during the TMT exposure. Rats are placed in Plexiglass chambers that contain white bedding on the bottom of the chamber and a metal basket in the top right corner containing a filter paper that 10 µl of TMT is pipetted onto. During the 10 min exposure, rats can move around the chamber freely. Exposures are recorded by a video camera for later analysis. During TMT exposure, rats engage in a variety of stress-reactive behaviors, including digging and immobility behavior. These are two distinctly different types of stress-induced behavioral coping strategies to measure individual differences in stress responsivity. To examine individual differences, we group rats into TMT-subgroups based on time spent engaging in digging or immobility behavior. We calculate a digging/immobility ratio score in which we divide the total time spent digging by the total time spent immobile. A cut-off strategy is used such that rats with a criterion ratio score <1.0 are classified as TMT-1 (i.e., low digging/high immobility; greater passive coping) and rats with a ratio score >1.0 are classified as TMT-2 (i.e., high digging/low immobility; greater active coping). Here, we provide a detailed description of the TMT exposure protocol and step-by-step process in evaluation of stress-reactive behaviors. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Predator odor stressor exposure using TMT Basic Protocol 2: Description of stress-reactive behaviors during TMT exposure and formation of TMT-subgroups.

Sex-related differences in the efficacy of Baclofen enantiomers on self-administered alcohol in a binge drinking pattern and dopamine release in the core of the nucleus accumbens.

Introduction: Clinical studies on the effectiveness of Baclofen in alcohol use disorder (AUD) yielded mixed results possibly because of differential effects of the enantiomers and sex-related differences. Here we examined the effect of the different Baclofen enantiomers on alcohol intake and on evoked dopamine release in the core of the nucleus accumbens (NAcc) in male and female Long Evans rats. Methods: Rats were trained to chronically self-administer 20% alcohol solution in daily binge drinking sessions and were treated with the different forms of Baclofen [RS(±), R(+) and S(-)]. The effects on the evoked dopamine release within the core of the nucleus accumbens were measured in brain slices from the same animals and the alcohol naïve animals using the fast scan cyclic voltammetry technique. Results: RS(±)-Baclofen reduced alcohol intake regardless of sex but more females were non-responders to the treatment. R(+)-Baclofen also reduced alcohol intake regardless of sex but females were less sensitive than males. S(-)-Baclofen did not have any effect on average but in some individuals, especially in the females, it did increase alcohol intake by at least 100%. There were no sex differences in Baclofen pharmacokinetic but a strong negative correlation was found in females with a paradoxical effect of increased alcohol intake with higher blood Baclofen concentration. Chronic alcohol intake reduced the sensitivity to the effect of Baclofen on evoked dopamine release and S(-)-Baclofen increased dopamine release specifically in females. Discussion: Our results demonstrate a sex-dependent effect of the different forms of Baclofen with no or negative effects (meaning an increase in alcohol self-administration) in subgroup of females that could be linked to a differential effect on dopamine release and should warrant future clinical studies on alcohol use disorder pharmacotherapy that will deeply analyze sex difference.

Caffeine increases alcohol self-administration, an effect that is independent of dopamine D2 receptor function.

The rising popularity of alcohol mixed with energy drinks (AmEDs) has become a significant public health concern, with AmED users reporting higher levels of alcohol intake than non-AmED users. One mechanism proposed to explain this heightened level of alcohol intake in AmED users is that the high levels of caffeine found in energy drinks may increase the positive reinforcing properties of alcohol, an effect that may be dependent on interactions between adenosine receptor signaling pathways and the dopamine D2 receptor. Therefore, the purpose of the current study was to confirm whether caffeine does increase the positive reinforcing effects of alcohol using both fixed ratio (FR) and progressive ratio (PR) designs, and to investigate a potential role of the dopamine D2 receptor to caffeine-induced increases in alcohol self-administration. Male Long-Evans rats were trained to self-administer a sweetened alcohol solution (10% v/v alcohol+2% w/v sucrose) on an FR2 schedule of reinforcement, and the effects of caffeine (0, 5, 10, and 20mg/kg, i. p. [intraperitoneally]) on the maintenance of alcohol self-administration and alcohol break point were examined. Parallel experiments in rats trained to self-administer sucrose (0.8% w/v) were conducted to determine whether caffeine's reinforcement-enhancing effects extended to a non-drug reinforcer. Caffeine pretreatment (5-10mg/kg) significantly increased sweetened alcohol self-administration and motivation for a sweetened alcohol reinforcer. However, similar increases in self-administration of a non-drug reinforcer were not observed. Contrary to our hypothesis, the D2 receptor antagonist eticlopride did not block a caffeine-induced increase in sweetened alcohol self-administration, nor did it alter caffeine-induced increases in motivation for a sweetened alcohol reinforcer. Taken together, these results support the hypothesis that caffeine increases the positive reinforcing effects of alcohol, which may explain caffeine-induced increases in alcohol intake. However, the reinforcement-enhancing effects of caffeine appear to be independent of D2 receptor function.

Stress vulnerability and alcohol use and consequences: From human laboratory studies to clinical outcomes

It is well known that vulnerability to stress is a risk factor for alcohol use disorder (AUD). Chronic alcohol use can result in neuroadaptations in cortico-striatal pathways and hypothalamic pituitary adrenal (HPA) axis function that are manifested in altered behavioral and cognitive control functions contributing to alcohol craving, compulsive motivation, consumption, and consequences. This symposium brings together studies utilizing novel approaches to help improve our understanding of stress - past, acute, and chronic - on alcohol seeking and consumption and related outcomes using a combination of human laboratory models, neuroimaging, and clinical measures. Examining factors that determine vulnerability as well as resilience to stress are of particular interest in the study of AUD because, in addition to increasing our understanding of the risk factors for AUD, such knowledge can be used to develop more effective treatments. Dr. Stangl presented a novel human experimental model that demonstrates, for the first time, stress-induced increases in alcohol self-administration in binge drinkers using a guided imagery paradigm combined with intravenous alcohol self-administration (IV-ASA). Dr. Blaine presented data demonstrating that glucocorticoid response to stress drives compulsive alcohol motivation and intake in binge/heavy drinkers. Dr. Plawecki presented data examining sex differences in the effect of two distinct stress paradigms - mood induction and abstinence - on IV-ASA in moderate drinkers. Dr. Schwandt presented clinical data providing a new perspective on the relationship between childhood trauma and AUD by suggesting possible underlying mechanisms that confer resilience, rather than vulnerability, to severe early life stress exposure.

Transient increase in alcohol self-administration following a period of chronic exposure to corticosterone

Stressful life events and chronic stressors have been associated with escalations in alcohol drinking. Stress exposure leads to the secretion of glucocorticoids (cortisol in the human; corticosterone (CORT) in the rodent). To model a period of heightened elevations in CORT, the present work assessed the effects of chronic exposure to the stress hormone CORT on alcohol self-administration. Male Long Evans rats were trained to self-administer a sweetened alcohol solution (2% sucrose/15% alcohol) resulting in moderate levels of daily alcohol intake (0.5–0.7 g/kg). Following stable baseline operant self-administration, rats received CORT in the drinking water for 7 days. A transient increase in alcohol self-administration was observed on the first self-administration session following CORT exposure, and behavior returned to control levels by the second session. Control experiments determined that this increase in alcohol self-administration was specific to alcohol, unrelated to general motor activation, and functionally dissociated from decreased CORT levels at the time of testing. These results indicate that repeated exposure to heightened levels of stress hormone (e.g., as may be experienced during stressful episodes) has the potential to lead to exacerbated alcohol intake in low to moderate drinkers. Given that maladaptive drinking patterns, such as escalated alcohol drinking following stressful episodes, have the potential to put an individual at risk for future drinking disorders, utilization of this model will be important for examination of neuroadaptations that occur as a consequence of CORT exposure in order to better understand escalated drinking following stressful episodes in nondependent individuals.

Transient increase in alcohol self-administration following a period of chronic exposure to corticosterone

Transient increase in alcohol self-administration following a period of chronic exposure to corticosterone

Enhanced AMPA receptor activity increases operant alcohol self‐administration and cue‐induced reinstatement

Long-term alcohol exposure produces neuroadaptations that contribute to the progression of alcohol abuse disorders. Chronic alcohol consumption results in strengthened excitatory neurotransmission and increased α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPA) receptor signaling in animal models. However, the mechanistic role of enhanced AMPA receptor activity in alcohol-reinforcement and alcohol-seeking behavior remains unclear. This study examined the role of enhanced AMPA receptor function using the selective positive allosteric modulator, aniracetam, in modulating operant alcohol self-administration and cue-induced reinstatement. Male alcohol-preferring (P-) rats, trained to self-administer alcohol (15%, v/v) versus water were pre-treated with aniracetam to assess effects on maintenance of alcohol self-administration. To determine reinforcer specificity, P-rats were trained to self-administer sucrose (0.8%, w/v) versus water, and effects of aniracetam were tested. The role of aniracetam in modulating relapse of alcohol-seeking was assessed using a response contingent cue-induced reinstatement procedure in P-rats trained to self-administer 15% alcohol. Aniracetam pre-treatment significantly increased alcohol-reinforced responses relative to vehicle treatment. This increase was not attributed to aniracetam-induced hyperactivity as aniracetam pre-treatment did not alter locomotor activity. AMPA receptor involvement was confirmed because 6,7-dinitroquinoxaline-2,3-dione (AMPA receptor antagonist) blocked the aniracetam-induced increase in alcohol self-administration. Aniracetam did not alter sucrose-reinforced responses in sucrose-trained P-rats, suggesting that enhanced AMPA receptor activity is selective in modulating the reinforcing function of alcohol. Finally, aniracetam pre-treatment potentiated cue-induced reinstatement of alcohol-seeking behavior versus vehicle-treated P-rats. These data suggest that enhanced glutamate activity at AMPA receptors may be key in facilitating alcohol consumption and seeking behavior, which could ultimately contribute to the development of alcohol abuse disorders.

Cocaine reverses the naltrexone-induced reduction in operant ethanol self-administration: The effects on immediate-early gene expression in the rat prefrontal cortex

Naltrexone is a clinically approved medication for alcoholism. We aimed to investigate the effectiveness of naltrexone co-administered with cocaine and the association of these substances with immediate-early gene expression in the rat prefrontal cortex. We used chronic operant ethanol self-administration and oral treatments prescribed for alcoholism and available in pharmacies to maximise the predictive validity in humans. We performed real-time PCR analysis to determine gene expression levels in the prefrontal cortex. Only the highest dose of naltrexone (1, 3, and 10 mg/kg, p.o.) reduced the response to ethanol. Cocaine increased ethanol self-administration in a dose-dependent manner (2.5, 10, 20 mg/kg, i.p.) and reversed the naltrexone-induced reduction. Naltrexone failed to prevent the cocaine-induced increase in locomotor activity observed in these animals. Chronic self-administration of ethanol reduced the expression of the C-fos gene 4- to 12-fold and increased expression of the COX-2 (up to 4-fold) and Homer1a genes in the rat prefrontal cortex. Chronic ethanol self-administration is prevented by naltrexone, but cocaine fully reverses this effect. This result suggests that cocaine may overcome naltrexone's effectiveness as a treatment for alcoholism. The ethanol-induced reduction in C-fos gene expression in the prefrontal cortex reveals an abnormal activity of these neurons, which may be relevant in the compulsive consumption of ethanol, the control of reward-related areas and the behavioural phenotype of ethanol addiction.

Increased expression of protein kinase A inhibitor α (PKI-α) and decreased PKA-regulated genes in chronic intermittent alcohol exposure

Intermittent models of alcohol exposure that mimic human patterns of alcohol consumption produce profound physiological and biochemical changes and induce rapid increases in alcohol self-administration. We used high-density oligonucleotide microarrays to investigate gene expression changes during chronic intermittent alcohol exposure in three brain regions that receive mesocorticolimbic dopaminergic projections and that are believed to be involved in alcohol's reinforcing actions: the medial prefrontal cortex, the nucleus accumbens and the amygdala. An independent replication of the experiment was used for RT-PCR validation of the microarray results. The protein kinase A inhibitor α (PKI-α, Pkia), a member of the endogenous PKI family implicated in reducing nuclear PKA activity, was found to be increased in all three regions tested. Conversely, we observed a downregulation of the expression of several PKA-regulated transcripts in one or more of the brain regions studied, including the activity and neurotransmitter-regulated early gene (Ania) - 1, -3, -7, -8, the transcription factors Egr1 and NGFI-B (Nr4a1) and the neuropeptide NPY. Reduced expression of PKA-regulated genes in mesocorticolimbic projection areas may have motivational significance in the rapid increase in alcohol self-administration induced by intermittent alcohol exposure.

Role of alpha-2 adrenoceptors in stress-induced reinstatement of alcohol seeking and alcohol self-administration in rats

Alpha-2 adrenoceptors are known to be involved in stress-induced reinstatement of heroin and cocaine seeking in laboratory animals. Here, we studied the involvement of these receptors in stress-induced reinstatement of alcohol seeking by using an agonist (lofexidine) and an antagonist (yohimbine) of these receptors, which inhibit and activate, respectively, noradrenaline transmission. We also tested the effect of lofexidine and yohimbine on alcohol self-administration. Lofexidine is used clinically for treating opiate withdrawal symptoms and yohimbine induces stress-like responses in humans and non-humans. Rats were trained to self-administer alcohol (12% w/v, 1 h/day) and after extinction of the alcohol-reinforced behavior, they were tested for the effect of lofexidine (0, 0.05 and 0.1 mg/kg, IP) on reinstatement of alcohol seeking induced by intermittent footshock stress (10 min, 0.8 mA) or for the effect of yohimbine (0, 1.25 and 2.5 mg/kg, IP) on reinstatement of alcohol seeking. Other rats were trained to self-administer alcohol, and after stable responding, the effects of lofexidine and yohimbine on alcohol self-administration were determined. Pretreatment with lofexidine (0.05 mg/kg and 0.1 mg/kg) attenuated stress-induced reinstatement of alcohol seeking and also decreased alcohol self-administration. In contrast, yohimbine pretreatment potently reinstated alcohol seeking after extinction and also induced a profound increase in alcohol self-administration. Results indicate that activation of alpha-2 adrencoceptors is involved in both stress-induced reinstatement of alcohol seeking and alcohol self-administration. To the degree that the present results are relevant to human alcoholism, alpha-2 adrencoceptor agonists should be considered in the treatment of alcohol dependence.