Habitual alcohol seeking: modeling the transition from casual drinking to addiction

A role for the dorsolateral striatum in prospective action control

The dorsolateral striatum (DLS) is important for performing actions persistently, even when it becomes suboptimal, reflecting a function that is reflexive and habitual. However, there are also ways in which persistent behaviors can result from a more prospective, planning mode of behavior. To help tease apart these possibilities for DLS function, we trained animals to perform a lever press for reward and then inhibited the DLS in key test phases: as the task shifted from a 1-press to a 3-press rule (upshift), as the task was maintained, as the task shifted back to the one-press rule (downshift), and when rewards came independent of pressing. During DLS inhibition, animals always favored their initially learned strategy to press just once, particularly so during the free-reward period. DLS inhibition surprisingly changed performance speed bidirectionally depending on the task shifts. DLS inhibition thus encouraged habitual behavior, suggesting it could normally help adapt to changing conditions.

Repeated Binge Alcohol Drinking Leads to Reductions in Corticostriatal Theta Coherence in Female but not Male Mice

Decreased functional connectivity between the striatum and frontal cortex is observed in individuals with alcohol use disorder (AUD), and predicts the probability of relapse in abstinent individuals with AUD. To further our understanding of how repeated alcohol (ethanol; EtOH) consumption impacts the corticostriatal circuit, extracellular electrophysiological recordings (local field potentials; LFPs) were gathered from the nucleus accumbens (NAc) and prefrontal cortex (PFC) of C57BL/6J mice voluntarily consuming EtOH or water using a 'drinking-in-the-dark' (DID) procedure. Following a three-day acclimation period wherein only water access was provided during DID, mice were given 15 consecutive days of access to EtOH. Each session consisted of a 30-minute baseline period where water was available and was followed immediately by a 2-hour period where sippers containing water were replaced with new sippers containing either unsweetened 20% (v/v) EtOH (days 4-18; DID) or water (days 1-3; acclimation). Our analyses focused primarily on theta coherence during bouts of drinking, as differences in this band are associated with several behavioral markers of AUD. Both sexes displayed decreases in theta coherence during the first day of binge EtOH consumption. However, only females displayed further decreases in theta coherence on the 14th day of EtOH access. No differences in theta coherence were observed between the first and final bout on any EtOH drinking days. These results provide additional support for decreases in the functional coupling of corticostriatal circuits as a consequence of alcohol consumption and suggests that female mice are uniquely vulnerable to these effects following repeated EtOH drinking.

Astrocytic GABAergic Regulation in Alcohol Use and Major Depressive Disorders

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). Most GABAergic neurons synthesize GABA from glutamate and release it in the synaptic cleft in the CNS. However, astrocytes can also synthesize and release GABA, activating GABA receptors in the neighboring neurons in physiological and pathological conditions. As the primary homeostatic glial cells in the brain, astrocytes play a crucial role in regulating GABA homeostasis and synaptic neurotransmission. Accumulating evidence demonstrates that astrocytic GABA dysregulation is implicated in psychiatric disorders, including alcohol use disorder (AUD) and major depressive disorder (MDD), the most prevalent co-occurring psychiatric disorders. Several current medications and emerging pharmacological agents targeting GABA levels are in clinical trials for treating AUD and MDD. This review offers a concise summary of the role of astrocytic GABA regulation in AUD and MDD. We also provide an overview of the current understanding and areas of debate regarding the mechanisms by which astrocytes regulate GABA in the CNS and their potential significance in the molecular basis of AUD and MDD, paving the way toward future research directions and potential therapeutic target areas within this field.

Aberrant functional brain network organization is associated with relapse during 1-year follow-up in alcohol-dependent patients

Alcohol dependence (AD) is a debilitating disease associated with high relapse rates even after long periods of abstinence. Thus, elucidating neurobiological substrates of relapse risk is fundamental for the development of novel targeted interventions that could promote long-lasting abstinence. In the present study, we analysed resting-state functional magnetic resonance imaging (rsfMRI) data from a sample of recently detoxified patients with AD (n = 93) who were followed up for 12 months after rsfMRI assessment. Specifically, we employed graph theoretic analyses to compare functional brain network topology and functional connectivity between future relapsers (REL, n = 59), future abstainers (ABS, n = 28) and age- and gender-matched controls (CON, n = 83). Our results suggest increased whole-brain network segregation, decreased global network integration and overall blunted connectivity strength in REL compared with CON. Conversely, we found evidence for a comparable network architecture in ABS relative to CON. At the nodal level, REL exhibited decreased integration and decoupling between multiple brain systems compared with CON, encompassing regions associated with higher-order executive functions, sensory and reward processing. Among patients with AD, increased coupling between nodes implicated in reward valuation and salience attribution constitutes a particular risk factor for future relapse. Importantly, aberrant network organization in REL was consistently associated with shorter abstinence duration during follow-up, portending to a putative neural signature of relapse risk in AD. Future research should further evaluate the potential diagnostic value of the identified changes in network topology and functional connectivity for relapse prediction at the individual subject level.

Consequences of adolescent drug use

Substance use in adolescence is a known risk factor for the development of neuropsychiatric and substance use disorders in adulthood. This is in part due to the fact that critical aspects of brain development occur during adolescence, which can be altered by drug use. Despite concerted efforts to educate youth about the potential negative consequences of substance use, initiation remains common amongst adolescents world-wide. Additionally, though there has been substantial research on the topic, many questions remain about the predictors and the consequences of adolescent drug use. In the following review, we will highlight some of the most recent literature on the neurobiological and behavioral effects of adolescent drug use in rodents, non-human primates, and humans, with a specific focus on alcohol, cannabis, nicotine, and the interactions between these substances. Overall, consumption of these substances during adolescence can produce long-lasting changes across a variety of structures and networks which can have enduring effects on behavior, emotion, and cognition.

Chronic alcohol consumption shifts learning strategies and synaptic plasticity from hippocampus to striatum-dependent pathways

Introduction

The hippocampus and striatum have dissociable roles in memory and are necessary for spatial and procedural/cued learning, respectively. Emotionally charged, stressful events promote the use of striatal- over hippocampus-dependent learning through the activation of the amygdala. An emerging hypothesis suggests that chronic consumption of addictive drugs similarly disrupt spatial/declarative memory while facilitating striatum-dependent associative learning. This cognitive imbalance could contribute to maintain addictive behaviors and increase the risk of relapse.

Methods

We first examined, in C57BL/6 J male mice, whether chronic alcohol consumption (CAC) and alcohol withdrawal (AW) might modulate the respective use of spatial vs. single cue-based learning strategies, using a competition protocol in the Barnes maze task. We then performed in vivo electrophysiological studies in freely moving mice to assess learning-induced synaptic plasticity in both the basolateral amygdala (BLA) to dorsal hippocampus (dCA1) and BLA to dorsolateral striatum (DLS) pathways.

Results

We found that both CAC and early AW promote the use of cue-dependent learning strategies, and potentiate plasticity in the BLA → DLS pathway while reducing the use of spatial memory and depressing BLA → dCA1 neurotransmission.

Discussion

These results support the view that CAC disrupt normal hippocampo-striatal interactions, and suggest that targeting this cognitive imbalance through spatial/declarative task training could be of great help to maintain protracted abstinence in alcoholic patients.

Task history dictates how the dorsolateral striatum controls action strategy and vigor

The dorsolateral striatum (DLS) is linked to the learning and honing of action routines. However, the DLS is also important for performing behaviors that have been successful in the past. The learning function can be thought of as prospective, helping to plan ongoing actions to be efficient and often optimal. The performance function is more retrospective, helping the animal continue to behave in a way that had worked previously. How the DLS manages this all is curious. What happens when a learned behavior becomes sub-optimal due to environment changes. In this case, the prospective function of the DLS would cause animals to (adaptively) learn and plan more optimal actions. In contrast, the retrospective function would cause animals to (maladaptively) favor the old behavior. Here we find that, during a change in learned task rules, DLS inhibition causes animals to adjust less rapidly to the new task (and to behave less vigorously) in a 'maladaptive' way. Yet, when the task is changed back to the initially learned rules, DLS inhibition instead causes a rapid and vigorous adjustment of behavior in an 'adaptive' way. These results show that inhibiting the DLS biases behavior towards initially acquired strategies, implying a more retrospective outlook in action selection when the DLS is offline. Thus, an active DLS could encourage planning and learning action routines more prospectively. Moreover, the DLS control over behavior can appear to be either advantageous/flexible or disadvantageous/inflexible depending on task context, and its control over vigor can change depending on task context.

Significant Statement

Basal ganglia networks aid behavioral learning (a prospective planning function) but also favor the use of old behaviors (a retrospective performance function), making it unclear what happens when learned behaviors become suboptimal. Here we inhibit the dorsolateral striatum (DLS) as animals encounter a change in task rules, and again when they shift back to those learned task rules. DLS inhibition reduces adjustment to new task rules (and reduces behavioral vigor), but it increases adjustment back to the initially learned task rules later (and increases vigor). Thus, in both cases, DLS inhibition favored the use of the initially learned behavioral strategy, which could appear either maladaptive or adaptive. We suggest that the DLS might promote a prospective orientation of action control.

Discriminating goal-directed and habitual cocaine seeking in rats using a novel outcome devaluation procedure

Habits are theorized to play a key role in compulsive cocaine seeking, yet there is limited methodology for assessing habitual responding for intravenous (IV) cocaine. We developed a novel outcome devaluation procedure to discriminate goal-directed from habitual responding in cocaine-seeking rats. This procedure elicits devaluation temporarily and requires no additional training, allowing repeated testing at different time points. After training male rats to self-administer IV cocaine, we devalued the drug outcome via experimenter-administered IV cocaine (a "satiety" procedure) prior to a 10-min extinction test. Many rats were sensitive to outcome devaluation, a hallmark of goal-directed responding. These animals reduced responding when given a dose of experimenter-administered cocaine that matched or exceeded satiety levels during self-administration. However, other rats were insensitive to experimenter-administered cocaine, suggesting their responding was habitual. Importantly, reinforcement schedules and neural manipulations that produce goal-directed responding (i.e., ratio schedules or dorsolateral striatum lesions) caused sensitivity to outcome devaluation, whereas reinforcement schedules and neural manipulations that produce habitual responding (i.e., interval schedules or dorsomedial striatum lesions) caused insensitivity. Satiety-based outcome devaluation is an innovative new tool to dissect the neural and behavioral mechanisms underlying IV cocaine-seeking behavior.

Effectiveness of a practice change intervention in reducing alcohol consumption in pregnant women attending public maternity services

Background

The aim of this study was to examine the effect of a practice change intervention to support the implementation of guideline-recommended care for addressing alcohol use in pregnancy on self-reported alcohol use during pregnancy.

Methods

A randomized, stepped-wedge controlled trial in three clusters (sectors) within the Hunter New England Local Health District (NSW, Australia). We evaluated a practice change intervention that supported the introduction of a new model of care for reducing alcohol use in pregnancy, consistent with local and international guidelines, and implemented in random order across the sectors. Each week throughout the study period, pregnant women who attended any public antenatal services within the previous week, for a 27–28 or 35–36 week gestation visit, were randomly sampled and invited to participate in the survey. The intended intervention for all women was Brief advice (to abstain from alcohol and information about potential risks). Women identified as medium-risk alcohol consumers using the Alcohol Use Disorder Identification Test-Consumption (AUDIT-C) were to be offered referral to a phone coaching service, and women identified as high-risk were to be offered referral to a Drug and Alcohol Service. Rates of self-reported alcohol use (AUDIT-C risk level and special occasion drinking) were summarized and compared in groups of women pre-intervention and post-intervention using multivariable logistic regression.

Results

Surveys were completed by 1309 women at pre-intervention and 2540 at post-intervention. The majority of women did not drink during pregnancy (pre-intervention: 89.68%; post-intervention: 90.74%). There was no change in the proportion of women classified as No risk from drinking (AUDIT-C score = 0) or Some risk from drinking (AUDIT-C score ≥ 1) pre- or post-intervention (p = 0.08). However, a significant reduction in special occasion drinking was observed (pre-intervention: 11.59%; post-intervention: 8.43%; p < 0.001).

Conclusions

Special occasion drinking was reduced following implementation of guideline-recommended care. Failure to change other patterns of alcohol use in pregnancy may reflect barriers to implementing the model of care in antenatal care settings and the need to address other social determinants of alcohol use.

Trial registration

Australian and New Zealand Clinical Trials Registry (registration number: ACTRN12617000882325; date: 16 June 2017).

Effects of chronic alcohol exposure on motivation-based value updating

Dysfunctional decision-making has been observed in alcohol dependence. However, the specific underlying processes disrupted have yet to be identified. Important to goal-directed decision-making is one's motivational state, which is used to update the value of actions. As ethanol dependence disrupts decision-making processes, we hypothesized that ethanol dependence could alter sensitivity to motivational state and/or value updating, thereby reducing the capability for adaptive behavior. Here we employed a sequential instrumental learning task to examine this hypothesis. In two experiments, mice underwent chronic intermittent ethanol (CIE) or air (Air) vapor exposure and repeated withdrawal procedures to induce ethanol dependence. Mice were then trained on a sequence of distal and proximal lever pressing for sucrose under either mild or more severe food restriction. Half of all Air and CIE mice then underwent a motivational shift to a less hungry state and effects of this motivational shift were evaluated across three days. First, mice were re-exposed to sucrose, and effects of food restriction state and CIE exposure on lick and consummatory behavior were examined in the absence of lever pressing. Over the next two days, mice underwent a brief non-rewarded test and then a rewarded test where the ability to retrieve and infer sucrose value to guide lever pressing was measured. In the sucrose re-exposure session, prior CIE exposure altered sucrose-seeking in mice with a history of mild but not more severe food restriction, suggesting altered motivational sensitivity. During lever press testing, CIE mice were insensitive to decreases in motivational state and did not reduce proximal lever pressing regardless of food restriction state. Mildly restricted CIE mice, but not severely restricted CIE mice, also did not reduce distal pressing to the same degree as Air mice following a downshift in motivational state. Our findings suggest that ethanol dependence may disrupt motivational processes supporting value updating that are important for decision-making.

Evaluating habit formation across pairs of female and male selectively bred alcohol-preferring and non-preferring rats

Some individuals with alcohol use disorder (AUD) continue to drink because they have developed a habit where they do not consider the consequences of their actions. Genetically selected lines of alcohol-preferring and non-preferring rats allow for exploration of how specific endophenotypes, such as tendency to form habits, may be risk factors that interact with a genetic predisposition of AUD. While high alcohol drinking (HAD) and alcohol-preferring (P) rats were selectively bred to consume high amounts of freely available ethanol, they exhibit differences in alcohol-seeking behaviors as well as impulsive behaviors, and may represent different behavioral models of AUD. The goal of the current study was to compare the tendency to develop habitual behaviors across female and male HAD1, HAD2, and P rats and their respective alcohol non-preferring counterparts. Alcohol-naïve rats were trained on a variable interval schedule using a non-ethanol reinforcer and were then tested in two extinction sessions, one prior to a reinforcer devaluation (conditioned taste aversion) procedure and one after. There were no differences in total lever presses between P and alcohol non-preferring (NP) rats, but there were differences between HAD and low-alcohol drinking (LAD) rats. All six strains decreased lever pressing after reinforcer devaluation. However, P and NP females did not increase latency to first lever press after devaluation, suggesting some inclination toward habitual behavior that was not apparent in either the HAD or LAD lines. Selective breeding for alcohol preference does not seem to influence the tendency to form habits, whereas background strain and sex may have an influence on this behavior.

Dynamic structural equation modeling of the relationship between alcohol habit and drinking variability

BACKGROUND

A hyper-engaged habit system may be common in alcohol use disorders (AUDs). Regarding drinking patterns, habit may be expressed as higher levels of drinking autoregression, where previous day drinking is correlated with next day drinking. This study utilized dynamic structural equation models (DSEM) with intensive longitudinal data to understand whether alcohol habit relates to drinking autoregression and variable levels of alcohol consumption.

METHODS

Participants were adult drinkers (N = 313) who completed baseline self-report assessments of past 30-day alcohol consumption and alcohol habit. Alcohol habit was measured by the Self Report Habit Index (SRHI). Thirty-day coding of the Timeline Followback assessed total daily drinking and any daily heavy drinking.

RESULTS

The DSEM model for daily drinking found a weak but significant autoregressive data structure. Alcohol habit was related to increased mean drinking but did not strengthen the autoregressive effect of drinks per day. Higher alcohol habit was associated with higher levels of drinks per day person-specific variability. This pattern was replicated with the DSEM model for heavy drinking. Alcohol habit did not impact the autoregressive effect of heavy drinking but was associated with higher levels of heavy drinking.

CONCLUSIONS

While both drinks per day and heavy drinking showed a significant autoregressive structure, evidence of alcohol habit did not strengthen this effect. Alcohol habit did impact drinking variability; higher alcohol habit is associated with greater levels of drinking variability and higher mean drinking. Strategies to regulate drinking variability, including heavier drinking occasions, could target AUD habit.

Transdiagnostic phenotypes of compulsive behavior and associations with psychological, cognitive, and neurobiological affective processing

Compulsivity is a poorly understood transdiagnostic construct thought to underlie multiple disorders, including obsessive-compulsive disorder, addictions, and binge eating. Our current understanding of the causes of compulsive behavior remains primarily based on investigations into specific diagnostic categories or findings relying on one or two laboratory measures to explain complex phenotypic variance. This proof-of-concept study drew on a heterogeneous sample of community-based individuals (N = 45; 18-45 years; 25 female) exhibiting compulsive behavioral patterns in alcohol use, eating, cleaning, checking, or symmetry. Data-driven statistical modeling of multidimensional markers was utilized to identify homogeneous subtypes that were independent of traditional clinical phenomenology. Markers were based on well-defined measures of affective processing and included psychological assessment of compulsivity, behavioral avoidance, and stress, neurocognitive assessment of reward vs. punishment learning, and biological assessment of the cortisol awakening response. The neurobiological validity of the subtypes was assessed using functional magnetic resonance imaging. Statistical modeling identified three stable, distinct subtypes of compulsivity and affective processing, which we labeled "Compulsive Non-Avoidant", "Compulsive Reactive" and "Compulsive Stressed". They differed meaningfully on validation measures of mood, intolerance of uncertainty, and urgency. Most importantly, subtypes captured neurobiological variance on amygdala-based resting-state functional connectivity, suggesting they were valid representations of underlying neurobiology and highlighting the relevance of emotion-related brain networks in compulsive behavior. Although independent larger samples are needed to confirm the stability of subtypes, these data offer an integrated understanding of how different systems may interact in compulsive behavior and provide new considerations for guiding tailored intervention decisions.

On the interrelation between alcohol addiction-like behaviors in rats

RATIONALE

Alcohol use disorder (AUD) is a complex, heterogeneous disorder that only occurs in a minority of alcohol users. Various behavioral constructs, including excessive intake, habit formation, motivation for alcohol and resistance to punishment have been implicated in AUD, but their interrelatedness is unclear.

OBJECTIVE

The aim of this study was therefore to explore the relation between these AUD-associated behavioral constructs in rats. We hypothesised that a subpopulation of animals could be identified that, based on these measures, display consistent AUD-like behavior.

METHODS

Lister Hooded rats (n = 47) were characterised for alcohol consumption, habit formation, motivation for alcohol and quinine-adulterated alcohol consumption. The interrelation between these measures was evaluated through correlation and cluster analyses. In addition, addiction severity scores were computed using different combinations of the behavioral measures, to assess the consistency of the AUD-like subpopulation.

RESULTS

We found that the data was uniformly distributed, as there was no significant tendency of the behavioral measures to cluster in the dataset. On the basis of multiple ranked addiction severity scores, five animals (~ 11%) were classified as displaying AUD-like behavior. The composition of the remaining subpopulation of animals with the highest addiction severity score (9 rats; ~ 19%) varied, depending on the combination of measures included.

CONCLUSION

Consistent AUD-like behavior was detected in a small proportion of alcohol drinking rats. Alcohol consumption, habit formation, motivation for alcohol and punishment resistance contribute in varying degrees to the AUD-like phenotype across the population. These findings emphasise the importance of considering the heterogeneity of AUD-like behavior.

Neurobiological mechanisms of control in alcohol use disorder - moving towards mechanism-based non-invasive brain stimulation treatments

Alcohol use disorder (AUD) is characterized by excessive habitual drinking and loss of control over alcohol intake despite negative consequences. Both of these aspects foster uncontrolled drinking and high relapse rates in AUD patients. Yet, common interventions mostly focus on the phenomenological level, and prioritize the reduction of craving and withdrawal symptoms. Our review provides a mechanistic understanding of AUD and suggests alternative therapeutic approaches targeting the mechanisms underlying dysfunctional alcohol-related behaviours. Specifically, we explain how repeated drinking fosters the development of rigid drinking habits and is associated with diminished cognitive control. These behavioural and cognitive effects are then functionally related to the neurobiochemical effects of alcohol abuse. We further explain how alterations in fronto-striatal network activity may constitute the neurobiological correlates of these alcohol-related dysfunctions. Finally, we discuss limitations in current pharmacological AUD therapies and suggest non-invasive brain stimulation (like TMS and tDCS interventions) as a potential addition/alternative for modulating the activation of both cortical and subcortical areas to help re-establish the functional balance between controlled and automatic behaviour.

Impaired cognitive flexibility and heightened urgency are associated with increased alcohol consumption in rodent models of excessive drinking

Alcohol use disorder (AUD) is characterized by impairments in decision-making that can exist as stable traits or transient states. Cognitive inflexibility reflects an inability to update information that guides decision-making and is thought to contribute to the inability to abstain from drinking. While several studies have reported evidence of impaired cognitive flexibility following chronic alcohol exposure, evidence that a pre-existing impairment in cognitive flexibility is a heritable risk factor for AUD is scarce. Here, we found that cognitive flexibility was impaired in rodents selectively bred for excessive alcohol consumption (alcohol preferring (P) rats), on the attentional set-shifting task (ASST). Further, the degree of impairment is predictive of future ethanol consumption, thus suggesting that cognitive inflexibility is a stable trait capable of predisposing one for drinking. In a second set of experiments, we observed an impairment in the ability of P rats to use a previously learned rule to guide foraging in a simple discrimination task. Convergence across several behavioral measures suggested that this impairment reflected a state of heightened urgency that interfered with decision-making. A similar impairment on a simple discrimination task was observed in Wistar rats with a history of alcohol consumption. These findings indicate how trait and state variables-in this case, impaired cognitive flexibility and heightened urgency, respectively-may influence the risk for excessive drinking. Furthermore, our results suggest that cognitive inflexibility and urgency can exist as both risk factors for and the result of alcohol exposure.

Alcohol intoxication, but not hangover, differentially impairs learning and automatization of complex motor response sequences

Behavioral automatization usually makes us more efficient and less error-prone, but may also foster dysfunctional behavior like alcohol abuse. Yet, it has remained unclear whether alcohol itself causes the shift from controlled to habitual behavior commonly observed in alcohol use disorder (AUD). We thus investigated how the acute and post-acute effects of binge drinking affect the automatization of motor response sequences and the execution of automated vs. controlled motor response sequences. N = 70 healthy young men performed a newly developed automatization paradigm once sober and once after binge drinking (half of them intoxicated and half of them hungover). While we found no significant effects of alcohol hangover, acute intoxication (~ 1.2 ‰) had two dissociable effects: Firstly, it impaired the automatization of complex motor response sequence execution. Secondly, it eliminated learning effects in response selection and pre-motor planning processes. The results suggest that alcohol hangover did not affect controlled or automated processes, and disprove the assumption that alcohol intoxication generally spares or facilitates motor response sequence automatization. As these effects could be specific to the investigated explicit learning context, acute intoxication might potentially still improve the execution of pre-existing automatisms and/or the implicit acquisition of motor response sequence automatisms.

Optogenetic induction of orbitostriatal long-term potentiation in the dorsomedial striatum elicits a persistent reduction of alcohol-seeking behavior in rats

Uncontrolled drug-seeking and -taking behaviors are generally driven by maladaptive corticostriatal synaptic plasticity. The orbital frontal cortex (OFC) and its projections to the dorsomedial striatum (DMS) have been extensively implicated in drug-seeking and relapse behaviors. The influence of the synaptic plasticity of OFC projections to the DMS (OFC→DMS) on drug-seeking and -taking behaviors has not been fully characterized. To investigate this, we trained rats to self-administer 20% alcohol and then delivered an in vivo optogenetic protocol designed to induce long-term potentiation (LTP) selectively at OFC→DMS synapses. We selected LTP induction because we found that voluntary alcohol self-administration suppressed OFC→DMS transmission and LTP may normalize this transmission, consequently reducing alcohol-seeking behavior. Importantly, ex vivo slice electrophysiology studies confirmed that this in vivo optical stimulation protocol resulted in a significant increase in excitatory OFC→DMS transmission strength on day two after stimulation, suggesting that LTP was induced in vivo. Rat alcohol-seeking and -taking behaviors were significantly reduced on days 1-3, but not on days 7-11, after LTP induction. Striatal synaptic plasticity is modulated by several critical neurotransmitter receptors, including dopamine D1 receptors (D1Rs) and adenosine A2A receptors (A2ARs). We found that delivery of in vivo optical stimulation in the presence of a D1R antagonist abolished the LTP-associated decrease in alcohol-seeking behavior, whereas delivery in the presence of an A2AR antagonist may facilitate this LTP-induced behavioral change. These results demonstrate that alcohol-seeking behavior was negatively regulated by the potentiation of excitatory OFC→DMS neurotransmission. Our findings provide direct evidence that the OFC exerts "top-down" control of alcohol-seeking behavior via the DMS.

Rats exposed to intermittent ethanol during late adolescence exhibit enhanced habitual behavior following reward devaluation

The brain undergoes substantial maturation during adolescence, and repeated exposure to ethanol at this time has been shown to result in long-lasting behavioral and neural consequences. During the broad period of adolescence, different neuronal populations and circuits are refined between early and late adolescence, suggesting the possibility that ethanol exposure at these differing times may lead to differential outcomes. The goal of the current study was to evaluate the impact of adolescent intermittent ethanol (AIE) during early and late adolescence on the formation of goal-directed and habitual behavior in adulthood. Male and female Sprague-Dawley rats were exposed to ethanol via intragastric gavage (4.0 g/kg, 25% v/v) every other day from postnatal day (P) 25-45 or P45-65, considered early and late adolescence, respectively. In adulthood (~P70 early or ~ P90 late), rats were gradually food-restricted and began operant training on a fixed ratio 1 schedule. Rats were then transitioned onto random interval schedules and eventually underwent a sensory-specific satiation procedure as a model of reward devaluation. Few differences as a result of adolescent ethanol exposure were found during instrumental training. Following reward devaluation, rats exposed to water and ethanol during early adolescence exhibited reductions in lever pressing, suggestive of a goal-directed response pattern. In contrast, late AIE males and females demonstrated persistent responding following both devalued and non-devalued trials, findings representative of a habitual behavior pattern. The shifts from goal-directed to habitual behavior noted only following late AIE contribute to the growing literature identifying specific behavioral consequences as a result of ethanol exposure during distinct developmental periods within adolescence. More work is needed to determine whether the greater habit formation following late AIE is also associated with elevated habitual ethanol consumption.

The effects of fatty acid amide hydrolase inhibition and monoacylglycerol lipase inhibition on habit formation in mice

Emerging data indicate that endocannabinoid signaling is critical to the formation of habitual behavior. Previous work demonstrated that antagonism of cannabinoid receptor type 1 (CB1R) with AM251 during operant training impairs habit formation, but it is not known if this behavioral effect is specific to disrupted signaling of the endocannabinoid ligands anandamide or 2-arachidonoyl glycerol (2-AG). Here, we used selective pharmacological compounds during operant training to determine the impact of fatty acid amide hydrolase (FAAH) inhibition to increase anandamide (and other n-acylethanolamines) or monoacylglycerol lipase (MAGL) inhibition to increase 2-AG levels on the formation of habitual behaviors in mice using a food-reinforced contingency degradation procedure. We found, contrary to our hypothesis, that inhibition of FAAH and of MAGL disrupted the formation of habits. Next, AM251 was administered during training to verify that impaired habit formation could be assessed using contingency degradation. AM251-exposed mice responded at lower rates during training and at higher rates in the test. To understand the inconsistency with published data, we performed a proof-of-principle dose-response experiment to compare AM251 in our vehicle-solution to the published vehicle-suspension on response rates. We found consistent reductions in response rate with increasing doses of AM251 in solution and an inconsistent dose-response relationship with AM251 in suspension. Together, our data suggest that further characterization of the role of CB1R signaling in the formation of habitual responding is warranted and that augmenting endocannabinoids may have clinical utility for prophylactically preventing aberrant habit formation such as that hypothesized to occur in substance use disorders.

Drinking and responses to antidrinking messages among young adults: An fMRI study

Young adults consume most of their alcohol by binge drinking, and more than one-third report binge drinking in the past month. Some will transition out of excessive drinking, while others will maintain or increase alcohol use into adulthood. Public health campaigns depicting negative consequences of drinking have shown some efficacy at reducing this behavior. However, substance use in dependent individuals is governed in part by automatic or habitual responses to drug cues rather than the consequences. This study used functional magnetic resonance imaging to measure neural responses to drinking cues and drinking cues paired with antidrinking messages among young adults who binge drink (N = 30). This study also explored responses to smoking cues and antismoking messages. Neural responses were also compared between drinking/smoking and neutral cues. Self-reported drinking and smoking were collected at baseline, postscan, and 1 month. Results indicate that activity in the ventral striatum-implicated in reward processing-was lower for drinking cues paired with antidrinking messages than drinking cues. This difference was less pronounced in young adults who reported greater baseline past month drinking quantity. Past month drinking quantity decreased from baseline to 1 month. Further, young adults who showed higher activity during antidrinking messages in the medial prefrontal cortex-implicated in processing message self-relevance- reported a greater decrease in past month drinking frequency from baseline to 1 month. Findings may help to identify young adults who are at risk for continued heavy drinking in adulthood and inform interventions aimed to reduce drinking and reward in young adults.

Saracatinib Fails to Reduce Alcohol-Seeking and Consumption in Mice and Human Participants

More effective treatments to reduce pathological alcohol drinking are needed. The glutamatergic system and the NMDA receptor (NMDAR), in particular, are implicated in behavioral and molecular consequences of chronic alcohol use, making the NMDAR a promising target for novel pharmacotherapeutics. Ethanol exposure upregulates Fyn, a protein tyrosine kinase that indirectly modulates NMDAR signaling by phosphorylating the NR2B subunit. The Src/Fyn kinase inhibitor saracatinib (AZD0530) reduces ethanol self-administration and enhances extinction of goal-directed ethanol-seeking in mice. However, less is known regarding how saracatinib affects habitual ethanol-seeking. Moreover, no prior studies have assessed the effects of Src/Fyn kinase inhibitors on alcohol-seeking or consumption in human participants. Here, we tested the effects of saracatinib on alcohol consumption and craving/seeking in two species, including the first trial of an Src/Fyn kinase inhibitor to reduce drinking in humans. Eighteen male C57BL/6NCrl mice underwent operant conditioning on a variable interval schedule to induce habitual responding for 10% ethanol/0.1% saccharin. Next, mice received 5 mg/kg saracatinib or vehicle 2 h or 30 min prior to contingency degradation to measure habitual responding. In the human study, 50 non-treatment seeking human participants who drank heavily and met DSM-IV criteria for alcohol abuse or dependence were randomized to receive 125 mg/day saracatinib (n = 33) or placebo (n = 17). Alcohol Drinking Paradigms (ADP) were completed in a controlled research setting: before and after 7-8 days of treatment. Each ADP involved consumption of a priming drink of alcohol (0.03 mg%) followed by ad libitum access (3 h) to 12 additional drinks (0.015 g%); the number of drinks consumed and craving (Alcohol Urge Questionnaire) were recorded. In mice, saracatinib did not affect habitual ethanol seeking or consumption at either time point. In human participants, no significant effects of saracatinib on alcohol craving or consumption were identified. These results in mice and humans suggest that Fyn kinase inhibition using saracatinib, at the doses tested here, may not reduce alcohol consumption or craving/seeking among those habitually consuming alcohol, in contrast to reports of positive effects of saracatinib in individuals that seek ethanol in a goal-directed manner. Nevertheless, future studies should confirm these negative findings using additional doses and schedules of saracatinib administration.

A Frontal Neuropsychological Profile in Fitness to Drive

Traffic accidents are a global concern due to the elevated mortality rates of both drivers and pedestrians. The World Health Organization declared 2011-2020 as the Decade of Action for Road Safety, endorsing initiatives to reduce traffic-related deaths. Yet, despite these incentives, fatal accidents still occur. Different studies have linked deficits in executive functions to risky driving attitudes and crashes. The present study focuses on demographic, cognitive and personality factors, related to the prefrontal cortex, that are characteristic of drivers prone to risky behavior behind the wheel. The penalty Points System was used to classify drivers as "safe", with no point loss over a two-year period, or "risky", with full point loss during the same interval. A neuropsychological assessment of prefrontal cognitive functions was carried out on each group to identify variables associated with safe and risky behavior. Neuropsychological indexes were obtained from a continuous performance task without cue (Simple Attention), a continuous performance task with cue (Conditioned Attention), the Tower of Hanoi test and the Neurologically-related Changes in Personality Inventory (NECHAPI). A Discriminant Analysis (DA) found that education level, reaction times in Simple and Conditioned Attention, learning errors in the Tower of Hanoi and vulnerability in the personality test, best predicted whether drivers were likely to be in the safe or risky group. Finally, a cross-validation analysis performed on the same sample correctly classified 87.5% of the drivers. These data suggest that prefrontal dysfunction contributes to risky behavior behind the wheel. The inclusion of cognitive programs to identify and train drivers with this propensity could reduce risky driving, and consequently, save lives on the road.

Additive influences of acute early life stress and sex on vulnerability for aversion-resistant alcohol drinking

Acute early life stress (ELS) alters stress system functioning in adulthood and increases susceptibility to posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD). The current study assessed the effects of acute, infant ELS on alcohol drinking, including aversion-resistant drinking, in male and female Long Evans rats. Acute ELS was induced using a stress-enhanced fear learning (SEFL) protocol that consisted of 15 footshocks delivered on postnatal day (PND) 17. Alcohol drinking during adolescence and adulthood was measured with a two-bottle choice intermittent alcohol access paradigm. Aversion-resistant drinking was assessed in adulthood by adding quinine (0.01, 0.1, and 1.0 g/L) to the alcohol bottle after 5 to 6 weeks and 11 to 12 weeks of drinking. ELS had minimal influences on adolescent and adult alcohol consumption and preference. However, ELS, sex, and alcohol exposure history all influenced aversion-resistant alcohol drinking in an additive fashion. Higher concentrations of quinine were tolerated in females, ELS-exposed rats, and after 11 to 12 weeks of drinking. Tests of quinine sensitivity in a separate cohort of animals found that rats can detect concentrations of quinine as low as 0.001 g/L in water and that quinine sensitivity is not influenced by sex or ELS exposure. These results agree with reports of sex differences in aversion-resistant drinking and are the first to demonstrate an influence of ELS on this behavior. Our results also suggest that a single traumatic stress exposure in infancy may be a promising model of comorbid PTSD and AUD and useful in studying the interactions between ELS, sex, and alcohol dependence.

Selective Deficits in Contingency-Driven Ethanol Seeking Following Chronic Ethanol Exposure in Male Mice

BACKGROUND

People with alcohol use disorders exhibit an overreliance on habitual response strategies which may result from a history of chronic alcohol exposure. Although habits are defined by behavior that persists despite changes in outcome value and in action-outcome relationships, most research investigating the effects of ethanol exposure on habits has focused only on outcome devaluation. A clear understanding of the effects of chronic alcohol exposure on the ability to flexibly update behavior may provide insight into the behavioral deficits that characterize alcohol use disorders.

METHODS

To dissociate the effects of chronic intermittent ethanol (CIE) exposure on contingency-mediated sucrose versus ethanol seeking, adult male C57Bl/6J mice were assigned to 2 separate experiments. In the first experiment, mice were trained to self-administer ethanol prior to 2 cycles of interleaved CIE exposure by vapor inhalation. In a second experiment, mice were trained to self-administer sucrose and ethanol in separate training sessions prior to 4 cycles of interleaved CIE. The use of contingencies to mediate reward seeking was assessed using a contingency degradation paradigm.

RESULTS

In mice trained to self-administer only ethanol, 2 weeks of CIE resulted in escalated self-administration. At this time point, CIE-exposed mice, but not air-exposed controls, exhibited ethanol seeking that was insensitive to changes in action-outcome contingency, consistent with habitual ethanol seeking. In mice trained to self-administer ethanol and sucrose rewards in sequential sessions, no escalation in self-administration across 4 weeks of CIE was observed. Under these conditions, neither Air- nor CIE-exposed mice reduced ethanol seeking in response to contingency degradation. In contrast, sucrose seeking remained goal-directed.

CONCLUSIONS

Our results suggest that chronic ethanol exposure impairs contingency-driven ethanol seeking more readily than sucrose-seeking behavior. Further, these findings indicate that the transition from contingency-mediated ethanol seeking occurs more rapidly than for sucrose seeking under similar ethanol exposure conditions.

Behavioral, neurobiological, and neurochemical mechanisms of ethanol self-administration: A translational review

Alcohol use disorder has multiple characteristics including excessive ethanol consumption, impaired control over drinking behaviors, craving and withdrawal symptoms, compulsive seeking behaviors, and is considered a chronic condition. Relapse is common. Determining the neurobiological targets of ethanol and the adaptations induced by chronic ethanol exposure is critical to understanding the clinical manifestation of alcohol use disorders, the mechanisms underlying the various features of the disorder, and for informing medication development. In the present review, we discuss ethanol's interactions with a variety of neurotransmitter systems, summarizing findings from preclinical and translational studies to highlight recent progress in the field. We then describe animal models of ethanol self-administration, emphasizing the value, limitations, and validity of commonly used models. Lastly, we summarize the behavioral changes induced by chronic ethanol self-administration, with an emphasis on cue-elicited behavior, the role of ethanol-related memories, and the emergence of habitual ethanol seeking behavior.

Involvement of the rodent prelimbic and medial orbitofrontal cortices in goal-directed action: A brief review

Goal-directed action refers to selecting behaviors based on the expectation that they will be reinforced with desirable outcomes. It is typically conceptualized as opposing habit-based behaviors, which are instead supported by stimulus-response associations and insensitive to consequences. The prelimbic prefrontal cortex (PL) is positioned along the medial wall of the rodent prefrontal cortex. It is indispensable for action-outcome-driven (goal-directed) behavior, consolidating action-outcome relationships and linking contextual information with instrumental behavior. In this brief review, we will discuss the growing list of molecular factors involved in PL function. Ventral to the PL is the medial orbitofrontal cortex (mOFC). We will also summarize emerging evidence from rodents (complementing existing literature describing humans) that it too is involved in action-outcome conditioning. We describe experiments using procedures that quantify responding based on reward value, the likelihood of reinforcement, or effort requirements, touching also on experiments assessing food consumption more generally. We synthesize these findings with the argument that the mOFC is essential to goal-directed action when outcome value information is not immediately observable and must be recalled and inferred.

Brain region-specific neuromedin U signalling regulates alcohol-related behaviours and food intake in rodents

Albeit neuromedin U (NMU) attenuates alcohol‐mediated behaviours, its mechanisms of action are poorly defined. Providing that the behavioural effects of alcohol are processed within the nucleus accumbens (NAc) shell, anterior ventral tegmental area (aVTA), and laterodorsal tegmental area (LDTg), we assessed the involvement of NMU signalling in the aforementioned areas on alcohol‐mediated behaviours in rodents. We further examined the expression of NMU and NMU receptor 2 (NMUR2) in NAc and the dorsal striatum of high compared with low alcohol‐consuming rats, as this area is of importance in the maintenance of alcohol use disorder (AUD). Finally, we investigated the involvement of NAc shell, aVTA and LDTg in the consumption of chow and palatable peanut butter, to expand the link between NMU and reward‐related behaviours. We demonstrated here, that NMU into the NAc shell, but not aVTA or LDTg, blocked the ability of acute alcohol to cause locomotor stimulation and to induce memory retrieval of alcohol reward, as well as reduced peanut butter in mice. In addition, NMU into NAc shell decreased alcohol intake in rats. On a molecular level, we found increased NMU and decreased NMUR2 expression in the dorsal striatum in high compared with low alcohol‐consuming rats. Both aVTA and LDTg, rather than NAc shell, were identified as novel sites of action for NMU's anorexigenic properties in mice based on NMU's ability to selectively reduce chow intake when injected to these areas. Collectively, these data indicate that NMU signalling in different brain areas selectively modulates different behaviours.

Endocannabinoid contributions to alcohol habits and motivation: Relevance to treatment

Individuals with alcohol use disorder exhibit compulsive habitual behaviors that are thought to be, in part, a consequence of chronic and persistent use of alcohol. The endocannabinoid system plays a critical role in habit learning and in ethanol self-administration, but the role of this neuromodulatory system in the expression of habitual alcohol seeking is unknown. Here, we investigated the role of the endocannabinoid system in established alcohol habits using contingency degradation in male C57BL/6 mice. We found that administration of the novel diacyl glycerol lipase inhibitor DO34, which decreases the biosynthesis of the endocannabinoid 2-arachidonoyl glycerol (2-AG), reduced habitual responding for ethanol and ethanol approach behaviors. Moreover, administration of the endocannabinoid transport inhibitor AM404 or the cannabinoid receptor type 1 antagonist AM251 produced similar reductions in habitual responding for ethanol and ethanol approach behaviors. Notably, AM404 was also able to reduce ethanol seeking and consumption in mice that were insensitive to lithium chloride-induced devaluation of ethanol. Conversely, administration of JZL184, a monoacyl glycerol lipase inhibitor that increases levels of 2-AG, increased motivation to respond for ethanol on a progressive ratio schedule of reinforcement. These results demonstrate an important role for endocannabinoid signaling in the motivation to seek ethanol, in ethanol-motivated habits, and suggest that pharmacological manipulations of endocannabinoid signaling could be effective therapeutics for treating alcohol use disorder.

A study on the correlates of habit-, reward-, and fear-related motivations in alcohol use disorder

OBJECTIVE

We assessed self-reported drives for alcohol use and their impact on clinical features of alcohol use disorder (AUD) patients. Our prediction was that, in contrast to "affectively" (reward or fear) driven drinking, "habitual" drinking would be associated with worse clinical features in relation to alcohol use and higher occurrence of associated psychiatric symptoms.

METHODS

Fifty-eight Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) alcohol abuse patients were assessed with a comprehensive battery of reward- and fear-based behavioral tendencies. An 18-item self-report instrument (the Habit, Reward and Fear Scale; HRFS) was employed to quantify affective (fear or reward) and non-affective (habitual) motivations for alcohol use. To characterize clinical and demographic measures associated with habit, reward, and fear, we conducted a partial least squares analysis.

RESULTS

Habitual alcohol use was significantly associated with the severity of alcohol dependence reflected across a range of domains and with lower number of detoxifications across multiple settings. In contrast, reward-driven alcohol use was associated with a single domain of alcohol dependence, reward-related behavioral tendencies, and lower number of detoxifications.

CONCLUSION

These results seem to be consistent with a shift from goal-directed to habit-driven alcohol use with severity and progression of addiction, complementing preclinical work and informing biological models of addiction. Both reward-related and habit-driven alcohol use were associated with lower number of detoxifications, perhaps stemming from more benign course for the reward-related and lack of treatment engagement for the habit-related alcohol abuse group. Future work should further explore the role of habit in this and other addictive disorders, and in obsessive-compulsive related disorders.

The Fyn kinase inhibitor, AZD0530, suppresses mouse alcohol self-administration and seeking

Fyn is a member of the Src family of protein tyrosine kinases (PTKs) that plays an important role not only in normal synaptic functions but also in brain pathologies including alcohol use disorder. We previously reported that repeated cycles of binge drinking and withdrawal activate Fyn in the dorsomedial striatum (DMS) of rodents, and that Fyn signaling in the DMS contributes to rat alcohol intake and relapse. Here, we used AZD0530, a CNS penetrable inhibitor of Src PTKs developed for the treatment of Alzheimer disease and cancer and tested its efficacy to suppress alcohol-dependent molecular and behavioral effects. We show that systemic administration of AZD0530 prevents alcohol-induced Fyn activation and GluN2B phosphorylation in the DMS of mice. We further report that a single dose of AZD0530 reduces alcohol operant self-administration and promotes extinction of alcohol self-administration without altering basal and dopamine D1 receptor-dependent locomotion. Together, our findings suggest that AZD0530, through its inhibitory actions on Fyn kinase, dampens alcohol seeking and drinking.

Adolescent intermittent ethanol impairs behavioral flexibility in a rat foraging task in adulthood

Alcohol exposure is linked to behavioral flexibility deficits in humans, but it is unclear when the critical exposure occurred or if alcohol exposure alone is sufficient to produce behavior deficits. Increasing evidence shows that binge levels of alcohol during adolescence are particularly harmful to the brain, producing physiological and behavioral effects that can persist into adulthood. The present study determined whether adolescent intermittent ethanol (AIE) in rats impaired action selection in a discriminative stimulus task using a foraging response. Rats were exposed to ethanol during adolescence (5 g/kg/day, IG, 2-days-on/2-days-off, postnatal day 25-54). In adulthood, they learned to dig for food reward buried in one of two media, cued with one of two odors. AIE and control rats both learned to discriminate between olfactory cues, but AIE rats were impaired when reversing that learned association (first intra-dimensional reversal). However, AIE rats were faster to reinstate the original odor discrimination rule (second reversal), suggesting perseverative behavior. Next, the reward location was cued by digging media rather than odor. Both groups learned this extra-dimensional shift; however, control rats were slower to reach criterion. These findings are consistent with studies of people with substance abuse disorder, who learn new stimulus-response associations similarly to, or better than, control subjects, but perseverate when attempting to replace a well-learned association. These data suggest that adolescent binge-alcohol exposure contributes to behavioral flexibility deficits observed in adulthood.

Light and heavy drinking in jurisdictions with different alcohol policy environments

BACKGROUND

A basic, yet untested tenet underlying alcohol control policies is that they should affect both light and heavy drinking, thereby shifting the entire population in a favourable direction. The aim of this study was to test this assumption in young Swiss men.

METHODS

Cross-sectional self-reported data - from 5755 young Swiss men participating in the Cohort Study on Substance Use Risk Factors (C-SURF), a large cohort study on young men living within 21 jurisdictions across Switzerland - were analysed via nested logistic regression. With this approach, a set of increasingly-heavy drinking patterns was broken down into a set of nested regression models, each one estimating the probability of heavier drinking, conditional on the lighter drinking pattern. Drinking patterns relating to heavy episodic drinking (HED), heavy volume drinking (HVD) on weekends, and workweek drinking, as well as alcohol use disorder (AUD) were examined. The explanatory variable was a previously-used alcohol policy environment index (APEI) reflecting the number of alcohol control policies implemented in each jurisdiction. Conventional and multilevel logistic regression models were tested, adjusted for age, education, linguistic region, urban/rural status, attention-deficit/hyperactivity disorder, depression, sensation seeking, antisocial personality disorder, and unobserved heterogeneity between jurisdictions.

RESULTS

For HED, weekend HVD, and AUD, negative relationships with the APEI were found, such that with a higher APEI the probability of lighter drinking patterns was increased while the probability of heavier patterns was reduced, including a reduced probability of the heaviest patterns. These relationships were non-linear, however, and tapered off towards the heavy end of the drinking spectrum. No relationship was identified between the APEI and workweek drinking patterns.

CONCLUSION

Among young Swiss men, stricter alcohol policy environments were associated with a global shift towards lighter drinking, consistent with the basic tenet behind the universal prevention approach.

Low cognitive flexibility as a risk for heavy alcohol drinking in non-human primates

Chronic alcohol abuse is frequently considered a habitual or inflexible behavior; however, measures of pre-existing cognitive flexibility prior to initiation of alcohol use are usually not available. This study used rhesus monkeys and an attentional set-shifting task to investigate whether pre-existing cognitive flexibility would predict increased risk for heavy alcohol drinking. As previously reported, monkeys were given 30 daily set-shifting sessions prior to alcohol access. These sessions consisted of the same sequence of eight unique visual discriminations (sets) of two objects that varied on two dimensions (shapes and colors). The ratio of errors per trials, session duration, and maximum set reached were primary dependent variables from each session and were used to compose a session performance index (PI) that ranged from a low performance PI of 31 to an optimal performance PI of 247. Here, animals underwent an alcohol induction period followed by 22 weeks of daily (22-h) self-administration sessions with free access to water and alcohol. Based on average daily alcohol intake during 22 weeks of 22-h/day access, the monkeys were categorized as non-heavy (mean = 2.0 ± 0.3 g/kg/day; n = 3) and heavy (mean = 3.3 ± 0.5 g/kg/day; n = 6) drinkers. The two groups diverged in performance on the set-shifting task across the 30 pre-alcohol sessions, and at the end of the pre-alcohol testing, the group average PI was 216 ± 27 and 137 ± 71 for the future non-heavy and heavy drinkers, respectively. The data show that low cognitive flexibility assessed with a set-shifting procedure was predictive of future classification as a heavy alcohol drinker. The data highlight individual differences in both cognitive flexibility and in alcohol self-administration in this population of rhesus monkeys.

Bi-directional modulation of food habit expression by the endocannabinoid system

The compulsive, habitual behaviors that have been observed in individuals diagnosed with substance use disorders may be due to disruptions in the neural circuits that mediate goal-directed actions. The endocannabinoid system has been shown to play a critical role in habit learning, but the role of this neuromodulatory system in habit expression is unclear. Here, we investigated the role of the endocannabinoid system in established habitual actions using contingency degradation in male C57BL/6 mice. We found that administration of the endocannabinoid transport inhibitor AM404 reduced habitual responding for food and that antagonism of cannabinoid receptor type 1 (CB1), but not transient receptor potential cation subfamily V (TRPV1), receptors produced a similar reduction in habitual responding. Moreover, pharmacological stimulation of CB1 receptors increased habitual responding for food. Co-administration of an enzyme inhibitor that selectively increases the endocannabinoid 2-arachidonoyl glycerol (2-AG) with AM404 partially restored habitual responding for food. Together, these findings demonstrate an important role for the endocannabinoid system in the expression of habits and provide novel insights into potential pharmacological strategies for reducing habitual behaviors in mental disorders.

Inactivation of ventral hippocampus projections promotes sensitivity to changes in contingency

The loss of behavioral flexibility is common across a number of neuropsychiatric illnesses. This may be in part due to the loss of the ability to detect or use changes in action–outcome contingencies to guide behavior. There is growing evidence that the ventral hippocampus plays a critical role in the regulation of flexible behavior and reward-related decision making. Here, we investigated the role of glutamatergic projections from the ventral hippocampus in the expression of contingency-mediated reward seeking. We demonstrate that selectively silencing ventral hippocampus projections can restore the use of action–outcome contingencies to guide behavior, while sparing cue-guided behavior and extinction learning. Our findings further indicated that the ability of the ventral hippocampus to promote habitual response strategies may be in part mediated by selective projections from the ventral hippocampus to the nucleus accumbens shell. Together these results implicate glutamatergic projections from the ventral hippocampus in the regulation of behavioral flexibility and suggest that alterations in ventral hippocampus function may contribute to overreliance on habitual response strategy observed in neuropsychiatric illnesses including addiction and obsessive–compulsive disorder.

Action-Outcome Knowledge Dissociates From Behavior in Obsessive-Compulsive Disorder Following Contingency Degradation

BACKGROUND

In obsessive-compulsive disorder (OCD), actions persist despite being inappropriate to the situation and without relationship to the overall goal. Dysfunctional beliefs have traditionally been postulated to underlie this condition. More recently, OCD has been characterized in terms of an imbalance between the goal-directed and the habit systems. To test these competing hypotheses, we used a novel experimental task designed to test subjective action-outcome knowledge of the effectiveness of actions (i.e., instrumental contingency), together with the balance between goal-directed and habitual responding.

METHODS

Twenty-seven patients with OCD and 27 healthy control subjects were tested on a novel task involving the degradation of an action-outcome contingency. Sensitivity to instrumental contingency and the extent to which explicitly reported action-outcome knowledge guided behavior were probed by measuring response rate and subjectively reported judgments.

RESULTS

Patients with OCD responded more than healthy control subjects in situations in which an action was less causally related to obtaining an outcome. However, patients showed intact explicit action-outcome knowledge, as assessed by self-report. In patients, the relationship between causality judgment and responding was altered; therefore, their actions were dissociated from explicit action-outcome knowledge.

CONCLUSIONS

These findings indicate reduced sensitivity to instrumental contingency in OCD, reinforcing the notion of a deficient goal-directed system in this disorder. By showing a dissociation between subjectively reported action-outcome knowledge and behavior, the data provide experimental evidence for the ego-dystonic nature of OCD.

The Action Representation Elicited by Different Types of Drug-Related Cues in Heroin-Abstinent Individuals

Drug related cue-induced reactivity plays a significant role in maintaining drug use and relapse in addicted individuals. The activation of Dorsolateral striatum-Sensorimotor system (DLS-SM) has been suggested as an important route through which drug cues may induce automatic drug using behavior. The current study used fMRI to investigate the reactivity of heroin abstinent individuals to different types of cues, to clarify the characteristics of the cues that induce the activation of the sensorimotor area. Forty heroin-dependent abstinent individuals and 29 healthy subjects were recruited to perform the heroin cue-reactivity task during fMRI. The participants’ subjective craving and physical signs were evaluated before and after scanning. Whole-brain analysis showed that compared to drug use tool and drug cues, cues related to drug use action were more likely to activate posterior central gyrus, para-hippocampus, supra marginal gyrus, superior parietal lobule (SPL) and inferior parietal lobule (IPL). These areas are involved in motor preparation and output, indicating that the sensorimotor area is also an important neural basis of craving and automatic drug using behavior, and may mediate craving and drug seeking behavior. Our findings thus suggest that cues related to drug using action may induce automatic drug seeking behavior more than cues related only to the drug itself.

Enhanced Striatal Dopamine Release to Expectation of Alcohol: A Potential Risk Factor for Alcohol Use Disorder

BACKGROUND

We used positron emission tomography imaging with [¹¹C]raclopride to examine the effects of consumption of alcohol or placebo beverage by participants with alcohol use disorder (AUD) compared with healthy participants with and without family history of AUD. We sought to assess dopamine release following alcohol exposure in relation to AUD risk.

METHODS

Three groups were enrolled: participants with AUD (n = 15) and healthy participants with family history negative (n = 34) or positive (n = 16) for AUD. Participants consumed a placebo (n = 65) or alcohol (n = 63) beverage in counterbalanced order before positron emission tomography scanning (128 scans). Binding potential (BP_ND) in the two drink conditions and the percent change in BP_ND between conditions were evaluated across striatal subregions. Subjective effects of beverage consumption were rated. Effects of group, drink order, and sex were evaluated.

RESULTS

Alcohol resulted in greater dopamine release than did placebo in the ventral striatum (p < .001). There were no main effects of group, drink order, or sex on ventral striatum BP_ND or percent change in BP_ND. However, there was a drink order-by-group interaction (p = .02) whereby family history-positive participants who received placebo first had both lower placebo BP_ND and less difference between placebo and alcohol BP_ND than all other groups, consistent with expectation of alcohol powerfully evoking dopamine release in this group. Subjective responses showed the same order-by-group interaction.

CONCLUSIONS

Hyper-responsivity of the dopaminergic system in family history-positive participants to expectation of alcohol may contribute to the expression of familial risk for AUD.

Synaptic adaptations to chronic ethanol intake in male rhesus monkey dorsal striatum depend on age of drinking onset

One in 12 adults suffer with alcohol use disorder (AUD). Studies suggest the younger the age in which alcohol consumption begins the higher the probability of being diagnosed with AUD. Binge/excessive alcohol drinking involves a transition from flexible to inflexible behavior likely involving the dorsal striatum (caudate and putamen nuclei). A major focus of this study was to examine the effect of age of drinking onset on subsequent chronic, voluntary ethanol intake and dorsal striatal circuitry. Data from rhesus monkeys (n = 45) that started drinking as adolescents, young adults or mature adults confirms an age-related risk for heavy drinking. Striatal neuroadaptations were examined using whole-cell patch clamp electrophysiology to record AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs) and GABAA receptor-mediated miniature inhibitory postsynaptic currents (mIPSCs) from medium-sized spiny projection neurons located in the caudate or putamen nuclei. In controls, greater GABAergic transmission (mIPSC frequency and amplitude) was observed in the putamen compared to the caudate. With advancing age, in the absence of ethanol, an increase in mIPSC frequency concomitant with changes in mIPSC amplitude was observed in both regions. Chronic ethanol drinking decreased mIPSC frequency in the putamen regardless of age of onset. In the caudate, an ethanol drinking-induced increase in mIPSC frequency was only observed in monkeys that began drinking as young adults. Glutamatergic transmission did not differ between the dorsal striatal subregions in controls. With chronic ethanol drinking there was a decrease in the postsynaptic characteristics of rise time and area of mEPSCs in the putamen but an increase in mEPSC frequency in the caudate. Together, the observed changes in striatal physiology indicate a combined disinhibition due to youth and ethanol leading to abnormally strong activation of the putamen that could contribute to the increased risk for problem drinking in younger drinkers.

A paradigm for examining stress effects on alcohol-motivated behaviors in participants with alcohol use disorder

Although epidemiological research has shown an increase in drinking following stressors and trauma, limited paradigms have been validated to study the relationship between stress and drinking in the human laboratory. The current study developed a progressive ratio (PR) operant procedure to examine the effects of psychosocial stress on alcohol craving and several alcohol-motivated behaviors in persons with alcohol use disorder. Current heavy, nontreatment-seeking drinkers (N = 30) were media-recruited and completed a comprehensive assessment of recent drinking, mood and health. Participants were admitted to the clinical research unit and underwent 4-day, physician-monitored alcohol abstinence. On days 4 and 5, participants underwent the Trier Social Stress Test or a neutral session in random order followed by the alcohol-motivated response (AMR) procedure in which subjects worked for money or alcohol under a PR operant procedure. Subjects received earned money vouchers or alcohol at the conclusion of the session. The Trier Social Stress Test increased alcohol craving and rate of responding and decreased the number of changeovers between alcohol versus money reinforcers on the PR schedule. There was a positive relationship between alcohol craving and drinks earned during the stress session. This novel paradigm provides an experimental platform to examine motivation to drink without confounding by actual alcohol ingestion during the work session, thereby setting the stage for future studies of alcohol interventions.

Habitual Behavior Is Mediated by a Shift in Response-Outcome Encoding by Infralimbic Cortex

The ability to flexibly switch between goal-directed actions and habits is critical for adaptive behavior. The infralimbic prefrontal cortex (IfL-C) has been consistently identified as a crucial structure for the regulation of response strategies. To investigate the role of the IfL-C, the present study employed two validated reinforcement schedules that either promote habits or goal-directed actions in mice. The results reveal that information about action-outcome relationships is differentially encoded in the IfL-C during actions and habits as evidenced by encoding of behavioral outcomes during goal-directed actions that is lost during habits. Optogenetic inhibition of the IfL-C selectively at press during habitual behavior (when firing rates are reduced during unreinforced goal-directed actions) resulted in restoration of sensitivity to change of action-outcome contingency. These results reveal a novel functional mechanism by which IfL-C promotes habitual behavior, and provide insight into strategies for the treatment and prevention of pathological, inflexible behavior common in neuropsychiatric illness.

Sleep Deprivation Promotes Habitual Control over Goal-Directed Control: Behavioral and Neuroimaging Evidence

Sleep is one of the most fundamental processes of life, playing an important role in the regulation of brain function. The long-term lack of sleep can cause memory impairments, declines in learning ability, and executive dysfunction. In the present study, we evaluated the effects of sleep deprivation on instrumental learning behavior, particularly goal-directed and habitual actions in humans, and investigated the underlying neural mechanisms. Healthy college students of either gender were enrolled and randomly divided into sleep deprivation group and sleep control group. fMRI data were collected. We found that one night of sleep deprivation led to greater responsiveness to stimuli that were associated with devalued outcomes in the slips-of-action test, indicating a deficit in the formation of goal-directed control and an overreliance on habits. Furthermore, sleep deprivation had no effect on the expression of acquired goal-directed action. The level of goal-directed action after sleep deprivation was positively correlated with baseline working memory capacity. The neuroimaging data indicated that goal-directed learning mainly recruited the ventromedial PFC (vmPFC), the activation of which was less pronounced during goal-directed learning after sleep deprivation. Activation of the vmPFC during goal-directed learning during training was positively correlated with the level of goal-directed action performance. The present study suggests that people rely predominantly on habits at the expense of goal-directed control after sleep deprivation, and this process involves the vmPFC. These results contribute to a better understanding of the effects of sleep loss on decision-making.SIGNIFICANCE STATEMENT Understanding the cognitive consequences of sleep deprivation has become extremely important over the past half century, given the continued decline in sleep duration in industrialized societies. Our results provide novel evidence that goal-directed action may be particularly vulnerable to sleep loss, and the brain mechanism underlying this effect was explored. Elucidation of the effects of sleep deprivation on decision-making will deepen our understanding of the function of sleep, emphasizing the role of sleep in cognitive impairments and mental health.

Convergent Neuronal Plasticity and Metaplasticity Mechanisms of Stress, Nicotine, and Alcohol

Stress and tobacco smoking are risk factors for alcoholism, but the underlying neural mechanisms are not well understood. Although stress, nicotine, and alcohol have broad, individual effects in the brain, some of their actions converge onto the same mechanisms and circuits. Stress and nicotine augment alcohol-related behaviors, in part via modulation of alcohol-evoked neuronal plasticity and metaplasticity mechanisms. Stress modulates alcohol-evoked plasticity via the release of signaling molecules that influence synaptic transmission. Nicotine also activates some of the same signaling molecules, cells, and circuits, producing a convergence of both stress and nicotine onto common plasticity mechanisms that influence alcohol self-administration. We describe several forms of alcohol-induced plasticity, including classic Hebbian plasticity at glutamatergic synapses, and we highlight less appreciated forms, such as non-Hebbian and GABAergic synaptic plasticity. Risk factors such as stress and nicotine initiate lasting neural changes that modify subsequent alcohol-induced synaptic plasticity and increase the vulnerability to alcohol addiction.

Sex differences in incentive motivation and the relationship to the development and maintenance of alcohol use disorders

Despite considerable evidence of higher rates of alcohol use disorders (AUDs) in men than in women, there is a dearth of research into the underlying causes of this disparity. As the gap in high risk drinking between men and women closes, it is critical to disentangle the biological factors that may place men and women at different risk for the development of AUDs as well as AUD-associated health problems. While sex differences in alcohol drinking have been reported in animal models and in human alcoholics, it increasingly seems that consummatory behavior may be dissociated from propensity toward inflexible and cue-elicited drug seeking and taking that characterize alcohol use disorders. While much of this work was initially performed in males a growing, yet limited, body of literature suggests that there are sex differences in both cue reactivity, and further, the relationship between cue reactivity and the maintenance of addictive behavior, indicating that males may be at greater risk for the development of a subset of addiction-related behaviors independent of alcohol consumption. Here, we will review the current literature on sex effects on the relationship between incentive motivation and addictive behavior and discuss unanswered questions that we expect will inform the development of individualized and sex-specific treatment and prevention strategies for AUDs. We believe that a greater understanding of how sex interacts with in cue reactivity to independently mediate the drug taking and risk for the development of uncontrolled drug or alcohol-seeking and -taking will inform the development of individualized treatment and prevention strategies for addiction.

Rat animal models for screening medications to treat alcohol use disorders

The purpose of this review is to present animal research models that can be used to screen and/or repurpose medications for the treatment of alcohol abuse and dependence. The focus will be on rats and in particular selectively bred rats. Brief introductions discuss various aspects of the clinical picture, which provide characteristics of individuals with alcohol use disorders (AUDs) to model in animals. Following this, multiple selectively bred rat lines will be described and evaluated in the context of animal models used to screen medications to treat AUDs. Next, common behavioral tests for drug efficacy will be discussed particularly as they relate to stages in the addiction cycle. Tables highlighting studies that have tested the effects of compounds using the respective techniques are included. Wherever possible the Tables are organized chronologically in ascending order to describe changes in the focus of research on AUDs over time. In general, high ethanol-consuming selectively bred rats have been used to test a wide range of compounds. Older studies usually followed neurobiological findings in the selected lines that supported an association with a propensity for high ethanol intake. Most of these tests evaluated the compound's effects on the maintenance of ethanol drinking. Very few compounds have been tested during ethanol-seeking and/or relapse and fewer still have assessed their effects during the acquisition of AUDs. Overall, while a substantial number of neurotransmitter and neuromodulatory system targets have been assessed; the roles of sex- and age-of-animal, as well as the acquisition of AUDs, ethanol-seeking and relapse continue to be factors and behaviors needing further study. This article is part of the Special Issue entitled "Alcoholism".