The role of context on responding to an alcohol-predictive cue in female and male rats

Impact of satiety on palatable food associative learning and consumption in male and female adult rats

Hedonic and memory mechanisms can stimulate food cravings and consumption in sated individuals, promoting binge eating and obesity. Despite that, how satiety impacts learning and memory about cues for palatable food in males and females remains unclear. This is the first study to directly compare food associative learning, extinction, and memory renewal between hungry and sated subjects of both sexes. Food-restricted and sated male and female adult Sprague Dawley rats were trained in Pavlovian cue-food conditioning sessions, followed by cue-only presentations during extinction in a different context. They were then tested for renewal of conditioned responding to the food cue by return to the conditioning context. Conditioned responding was assessed through foodcup approach behavior. These rats were also tested for consumption of palatable food and chow before and after the learning and memory protocol. Sated rats demonstrated learning, extinction, and renewal of conditioned responding, indicating that physiological hunger is not required for learning and memory of palatable food cues. There were differences during cue-food acquisition, food-deprived rats learned faster and reached a plateau in conditioned responding sooner than sated rats. However, there were no differences after the fourth session, when sated rats reached the same level of responding as the food-deprived rats. There were sex differences during early acquisition under sated but not hungry states. Sated females had higher conditioned responding than sated males, while food-deprived rats of both sexes responded similarly. Extinction and renewal tests showed that both hungry and sated rats successfully decreased and subsequently renewed their conditioned responses. These results demonstrate the durability of learning and persistence of food-cue memory regardless of hunger state. Consumption tests found that all rats prefer palatable food compared to chow. Females, particularly when sated, consumed more palatable food compared to males. Higher palatable food consumption and learning in females suggest an enhanced sensitivity to palatable rewards. Correlation analyses found a positive relation between the amounts of food rats consumed and their conditioned responding in both sexes. These results demonstrate robust associative learning and memory under satiety and add evidence of sex differences in hedonic food motivation.

Differential reductions in alcohol consumption and cue-induced alcohol-seeking behavior following mGlu5 receptor inhibition in the prelimbic vs. infralimbic subregions of the rat prefrontal cortex

Glutamatergic signaling is one of the primary targets of actions of alcohol in the brain, and dysregulated excitatory transmission in the prefrontal cortex (PFC) may contribute problematic drinking and relapse. A prominent component of glutamate signaling is the type 5 metabotropic glutamate (mGlu5) receptor. However, little is known about the role of this receptor type in subregions of the PFC that regulate either alcohol intake or alcohol-seeking behavior. Here we examined the effects of microinfusions of the selective mGlu5 inhibitor 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP) into either the prelimbic (PL) or infralimbic (IL) regions of the PFC on alcohol intake or cue-evoked reinstatement of alcohol-seeking behavior. Adult male Wistar rats were trained to self-administer 10 % alcohol in the presence of compound discriminative stimuli (SD) signaling alcohol availability (S+) or non-availability (S-). In one group of animals, effects of locally administered MTEP (0, 0.5 or 1 μg/μl) into either the PL or IL on active alcohol intake were examined. MTEP was without effect on alcohol self-administration when infused into the PL, but decreased alcohol intake at both doses tested when infused into the IL. In separate groups of animals, we examined effects of locally administered MTEP (0, 0.5 or 1 μg/μl) into either the PL or IL on reinstatement of alcohol seeking elicited by alcohol predictive stimuli (S+). When infused into the PL, MTEP attenuated cue-induced reinstatement only at the higher dose tested (1 μg/μl), but when infused into the IL, MTEP reduced cue-induced reinstatement at both doses tested (0.5 μg/μl and 1 μg/μl). Together, these results suggest a largely preferential role for mGlu5 signaling in the IL vs. PL in regulating both alcohol self-administration behavior and cue-elicited alcohol seeking. Neuromodulatory approaches aimed at reducing mGlu5 signaling in the IL may therefore be of potential therapeutic value in problematic alcohol use.

Operant ethanol self-administration behaviors do not predict sex differences in continuous access home cage drinking

Understanding sex differences in disease prevalence is critical to public health, particularly in the context of alcohol use disorder (AUD). The goal of this study was to understand sex differences in ethanol drinking behavior and define the precise conditions under which sex differences emerge. Consistent with prior work, C57BL/6J females drank more than males under continuous access two-bottle choice conditions. However, using ethanol self-administration - where an operant response results in access to an ethanol sipper for a fixed time period - we found no sex differences in operant response rates or ethanol consumption (volume per body weight consumed, as well as lick behavior). This remained true across a wide range of parameters including acquisition, when the ethanol sipper access period was manipulated, and when the concentration of the ethanol available was scaled. The only sex differences observed were in total ethanol consumption, which was explained by differences in body weight between males and females, rather than by sex differences in motivation to drink. Using dimensionality reduction approaches, we found that drinking behavior in the operant context did not cluster by sex, but rather clustered by high and low drinking phenotypes. Interestingly, these high and low drinking phenotypes in the operant context showed no correlation with those same categorizations in the home cage context within the same animals. These data underscore the complexity of sex differences in ethanol consumption, highlighting the important role that drinking conditions/context plays in the expression of these differences.

Sex and gender in alcohol use disorder and alcohol-associated liver disease in the United States: A narrative review

Over the last 20 years, there has been an alarming increase in alcohol use and AUD prevalence among women, narrowing the historical gender gap. Concurrently, there has also been a significant rise in alcohol-associated liver disease (ALD) prevalence, severity, and mortality among women. Despite this, there are no recent reviews that have sought to evaluate both sex and gender differences at the intersection of AUD and ALD. In this narrative review, we address the escalating rates of ALD and AUD in the United States, with a specific focus on the disproportionate impact on women. Sex and gender play an important and well-known role in the pathogenesis and epidemiology of ALD. However, sex and gender are also implicated in the development and prevalence of AUD, as well as in the treatment of AUD, all of which have important consequences on the approach to the treatment of patients with ALD and AUD. A better understanding of sex and gender differences in AUD, ALD, and the intersection of the 2 is essential to enhance prevention, diagnosis, and management strategies. These data underscore the urgent need for awareness and preventive efforts to mitigate the potential long-term health consequences.

Animal models of compulsion alcohol drinking: Why we love quinine-resistant intake and what we learned from it

Alcohol Use Disorder (AUD) ranks among the most prevalent mental disorders, extracting ~$250 billion/year in the US alone and producing myriad medical and social harms. Also, the number of deaths related to problem drinking has been increasing dramatically. Compulsive alcohol drinking, characterized by intake that persists despite negative consequences, can be particularly important and a major obstacle to treatment. With the number of people suffering from AUD increasing during the past years, there is a critical need to understand the neurobiology related to compulsive drives for alcohol, as well as the development of novel AUD pharmacological therapies. Here we discuss rodent compulsion-like alcohol drinking (CLAD) models, focusing on the two most widely used adverse stimuli to model rodent compulsion-like responding, quinine adulteration of alcohol and footshook-resistant alcohol intake. For both cases, the goal is to uncover behavior patterns and brain circuits that underlie drive for alcohol even in the face of negative consequences. We discuss caveats, benefits, and potential brain mechanisms, of models for consequence-resistant responding for alcohol more generally, and especially highlight some advantages of quinine-resistance over footshook-resistance. Further, since this review contributes to a Special issue focused on Molecular Aspects of Compulsive Drug Use, we discuss our new findings showing how the noradrenergic system is related to CLAD responding. In particular, we comment on the importance of α1 and β adrenergic receptors (ARs) as potential targets for treating AUD.

Interaction of stress and alcohol on discriminating fear from safety and reward in male and female rats

RATIONALE

Stressful events can have lasting and impactful effects on behavior, especially in terms of appropriate fear regulation and reward seeking. Our prior work in rats has shown baseline sex differences in fear expression and sucrose seeking in a discriminative reward-fear-safety conditioning task.

OBJECTIVES

The objectives of the current study were to determine how prior stress may affect alcohol consumption across a reward-fear-safety learning task, and how prior alcohol history may interact with stress to impact learning in this task.

METHODS

Male and female Long Evans rats were given home cage intermittent 24 h access to both water and alcohol for 5 weeks. A subset of rats then received exposure to stress (15 unsignaled footshocks), while remaining unstressed rats received context exposure without shock. One week later, all rats were trained on the same reward-fear-safety cue task while having continuous home cage access to both water and alcohol.

RESULTS

All rats increased consumption (g/kg/24 h) across the 5 weeks of intermittent access, with females showing higher consumption levels. Stress exposure did not alter alcohol consumption in the week following stress, but did increase home cage alcohol consumption during later reward-fear-safety cue learning. Stress in both sexes also elevated freezing levels to the reward cue resulting in decreased sucrose seeking and was positively correlated with home cage alcohol consumption.

CONCLUSIONS

While stress increased drinking in both males and females, the effects of stress were particularly pronounced in females, indicating our results could be capturing a higher propensity for females to display stress-induced drinking.

Learning processes in relapse to alcohol use: lessons from animal models

RATIONALE

Alcohol use is reliably preceded by discrete and contextual stimuli which, through diverse learning processes, acquire the capacity to promote alcohol use and relapse to alcohol use.

OBJECTIVE

We review contemporary extinction, renewal, reinstatement, occasion setting, and sex differences research within a conditioning framework of relapse to alcohol use to inform the development of behavioural and pharmacological therapies.

KEY FINDINGS

Diverse learning processes and corresponding neurobiological substrates contribute to relapse to alcohol use. Results from animal models indicate that cortical, thalamic, accumbal, hypothalamic, mesolimbic, glutamatergic, opioidergic, and dopaminergic circuitries contribute to alcohol relapse through separable learning processes. Behavioural therapies could be improved by increasing the endurance and generalizability of extinction learning and should incorporate whether discrete cues and contexts influence behaviour through direct excitatory conditioning or occasion setting mechanisms. The types of learning processes that most effectively influence responding for alcohol differ in female and male rats.

CONCLUSION

Sophisticated conditioning experiments suggest that diverse learning processes are mediated by distinct neural circuits and contribute to relapse to alcohol use. These experiments also suggest that gender-specific behavioural and pharmacological interventions are a way towards efficacious therapies to prevent relapse to alcohol use.

Reinstatement of Pavlovian responses to alcohol cues by stress

RATIONALE

Stress may contribute to relapse to alcohol use in part by enhancing reactivity to cues previously paired with alcohol. Yet, standard models of stress-induced reinstatement generally use contingent presentations of alcohol-paired cues to reinforce instrumental behaviors, making it difficult to isolate the ability of cues to invigorate alcohol-seeking.

OBJECTIVE

Here we sought to test the impact of stress on behavioral responses to alcohol-paired cues, using a model of stress-induced reinstatement of Pavlovian conditioned approach, inspired by Nadia Chaudhri's work on context-induced reinstatement.

METHODS

Long Evans rats were trained to associate one auditory cue with delivery of alcohol or sucrose and an alternative auditory cue with no reward. Following extinction training, rats were exposed to a stressor prior to being re-exposed to the cues under extinction conditions. We assessed the effects of yohimbine, intermittent footshock and olfactory cues paired with social defeat on responses to alcohol-paired cues and the effects of yohimbine on responses to sucrose-paired cues.

RESULTS

The pharmacological stressor, yohimbine, enhanced alcohol seeking in a Pavlovian setting, but not in a cue-selective manner. Intermittent footshock and social defeat cues did not enhance alcohol seeking in this paradigm.

CONCLUSIONS

While yohimbine elicited reinstatement of reward-seeking in a Pavlovian setting, these effects may be unrelated to activation of stress systems or to interactions with specific cues.

Supplementary dataset of context-dependent conditioned responding to an alcohol-predictive cue in female and male rats

This supplementary dataset is supportive of the research article entitled ‘The role of context on responding to an alcohol-predictive cue in female and male rats’ [1]. This article describes the raw data pertaining to the behaviour of male and female rats during intermittent to ethanol and Pavlovian conditioning training and testing procedures. Specifically, the dataset describes the alcohol consumption and ingested-dose of ethanol during home-cage ethanol exposure, as well as the conditioned responding during Pavlovian discrimination training, a test assessing the effect of context on responding to an alcohol-predict cue in the absence of alcohol, and a reinstatement test assessing the effect of context on conditioned responding to an extinguished alcohol-predictive cue.