Stochastic synaptic plasticity underlying compulsion in a model of addiction

Dual action of ketamine confines addiction liability

Ketamine is used clinically as an anaesthetic and a fast-acting antidepressant, and recreationally for its dissociative properties, raising concerns of addiction as a possible side effect. Addictive drugs such as cocaine increase the levels of dopamine in the nucleus accumbens. This facilitates synaptic plasticity in the mesolimbic system, which causes behavioural adaptations and eventually drives the transition to compulsion^1-4. The addiction liability of ketamine is a matter of much debate, in part because of its complex pharmacology that among several targets includes N-methyl-D-aspartic acid (NMDA) receptor (NMDAR) antagonism^5,6. Here we show that ketamine does not induce the synaptic plasticity that is typically observed with addictive drugs in mice, despite eliciting robust dopamine transients in the nucleus accumbens. Ketamine nevertheless supported reinforcement through the disinhibition of dopamine neurons in the ventral tegmental area (VTA). This effect was mediated by NMDAR antagonism in GABA (γ-aminobutyric acid) neurons of the VTA, but was quickly terminated by type-2 dopamine receptors on dopamine neurons. The rapid off-kinetics of the dopamine transients along with the NMDAR antagonism precluded the induction of synaptic plasticity in the VTA and the nucleus accumbens, and did not elicit locomotor sensitization or uncontrolled self-administration. In summary, the dual action of ketamine leads to a unique constellation of dopamine-driven positive reinforcement, but low addiction liability.

Inactivation of the Lateral Hypothalamus Attenuates Methamphetamine-Induced Conditioned Place Preference through Regulation of Kcnq3 Expression

Repeated administration of methylamphetamine (MA) induces MA addiction, which is featured by awfully unpleasant physical and emotional experiences after drug use is terminated. Neurophysiological studies show that the lateral hypothalamus (LH) is involved in reward development and addictive behaviors. Here, we show that repeated administration of MA activates the expression of c-Fos in LH neurons responding to conditioned place preference (CPP). Chemogenetic inhibition of the LH can disrupt the addiction behavior, demonstrating that the LH plays an important role in MA-induced reward processing. Critically, MA remodels the neurons of LH synaptic plasticity, increases intracellular calcium level, and enhances spontaneous current and evoked potentials of neurons compared to the saline group. Furthermore, overexpression of the potassium voltage-gated channel subfamily Q member 3 (Kcnq3) expression can reverse the CPP score and alleviate the occurrence of addictive behaviors. Together, these results unravel a new neurobiological mechanism underlying the MA-induced addiction in the lateral hypothalamus, which could pave the way toward new and effective interventions for this addiction disease.

Dopamine signaling in the dorsomedial striatum promotes compulsive behavior

Compulsive behavior is a defining feature of disorders such as substance use disorders. Current evidence suggests that corticostriatal circuits control the expression of established compulsions, but little is known about the mechanisms regulating the development of compulsions. We hypothesized that dopamine, a critical modulator of striatal synaptic plasticity, could control alterations in corticostriatal circuits leading to the development of compulsions (defined here as continued reward seeking in the face of punishment). We used dual-site fiber photometry to measure dopamine axon activity in the dorsomedial striatum (DMS) and the dorsolateral striatum (DLS) as compulsions emerged. Individual variability in the speed with which compulsions emerged was predicted by DMS dopamine axon activity. Amplifying this dopamine signal accelerated animals' transitions to compulsion, whereas inhibition delayed it. In contrast, amplifying DLS dopamine signaling had no effect on the emergence of compulsions. These results establish DMS dopamine signaling as a key controller of the development of compulsive reward seeking.

What Have We Learned (or Expect to) From Analysis of Murine Genetic Models Related to Substance Use Disorders?

The tremendous public health problem created by substance use disorders (SUDs) presents a major opportunity for mouse genetics. Inbred mouse strains exhibit substantial and heritable differences in their responses to drugs of abuse (DOA) and in many of the behaviors associated with susceptibility to SUD. Therefore, genetic discoveries emerging from analysis of murine genetic models can provide critically needed insight into the neurobiological effects of DOA, and they can reveal how genetic factors affect susceptibility drug addiction. There are already indications, emerging from our prior analyses of murine genetic models of responses related to SUDs that mouse genetic models of SUD can provide actionable information, which can lead to new approaches for alleviating SUDs. Lastly, we consider the features of murine genetic models that enable causative genetic factors to be successfully identified; and the methodologies that facilitate genetic discovery.

New directions in modelling dysregulated reward seeking for food and drugs

Behavioral models are central to behavioral neuroscience. To study the neural mechanisms of maladaptive behaviors (including binge eating and drug addiction), it is essential to develop and utilize appropriate animal models that specifically focus on dysregulated reward seeking. Both food and cocaine are typically consumed in a regulated manner by rodents, motivated by reward and homeostatic mechanisms. However, both food and cocaine seeking can become dysregulated, resulting in binge-like consumption and compulsive patterns of intake. The speakers in this symposium for the 2021 International Behavioral Neuroscience Meeting utilize behavioral models of dysregulated reward-seeking to investigate the neural mechanisms of binge-like consumption, enhanced cue-driven reward seeking, excessive motivation, and continued use despite negative consequences. In this review, we outline examples of maladaptive patterns of intake and explore recent animal models that drive behavior to become dysregulated, including stress exposure and intermittent access to rewards. Lastly, we explore select behavioral and neural mechanisms underlying dysregulated reward-seeking for both food and drugs.

Cell-Type-Specific Adaptions in Striatal Medium-Sized Spiny Neurons and Their Roles in Behavioral Responses to Drugs of Abuse

Drug addiction is defined as a compulsive pattern of drug-seeking- and taking- behavior, with recurrent episodes of abstinence and relapse, and a loss of control despite negative consequences. Addictive drugs promote reinforcement by increasing dopamine in the mesocorticolimbic system, which alters excitatory glutamate transmission within the reward circuitry, thereby hijacking reward processing. Within the reward circuitry, the striatum is a key target structure of drugs of abuse since it is at the crossroad of converging glutamate inputs from limbic, thalamic and cortical regions, encoding components of drug-associated stimuli and environment, and dopamine that mediates reward prediction error and incentive values. These signals are integrated by medium-sized spiny neurons (MSN), which receive glutamate and dopamine axons converging onto their dendritic spines. MSN primarily form two mostly distinct populations based on the expression of either DA-D1 (D1R) or DA-D2 (D2R) receptors. While a classical view is that the two MSN populations act in parallel, playing antagonistic functional roles, the picture seems much more complex. Herein, we review recent studies, based on the use of cell-type-specific manipulations, demonstrating that dopamine differentially modulates dendritic spine density and synapse formation, as well as glutamate transmission, at specific inputs projecting onto D1R-MSN and D2R-MSN to shape persistent pathological behavioral in response to drugs of abuse. We also discuss the identification of distinct molecular events underlying the detrimental interplay between dopamine and glutamate signaling in D1R-MSN and D2R-MSN and highlight the relevance of such cell-type-specific molecular studies for the development of innovative strategies with potential therapeutic value for addiction. Because drug addiction is highly prevalent in patients with other psychiatric disorders when compared to the general population, we last discuss the hypothesis that shared cellular and molecular adaptations within common circuits could explain the co-occurrence of addiction and depression. We will therefore conclude this review by examining how the nucleus accumbens (NAc) could constitute a key interface between addiction and depression.

Application of optogenetics and in vivo imaging approaches for elucidating the neurobiology of addiction

The neurobiology of addiction has been an intense topic of investigation for more than 50 years. Over this time, technological innovation in methods for studying brain function rapidly progressed, leading to increasingly sophisticated experimental approaches. To understand how specific brain regions, cell types, and circuits are affected by drugs of abuse and drive behaviors characteristic of addiction, it is necessary both to observe and manipulate neural activity in addiction-related behavioral paradigms. In pursuit of this goal, there have been several key technological advancements in in vivo imaging and neural circuit modulation in recent years, which have shed light on the cellular and circuit mechanisms of addiction. Here we discuss some of these key technologies, including circuit modulation with optogenetics, in vivo imaging with miniaturized single-photon microscopy (miniscope) and fiber photometry, and how the application of these technologies has garnered novel insights into the neurobiology of addiction.

Deconstructing and reconstructing behaviour relevant to mental health disorders: The benefits of a psychological approach, with a focus on addiction

RUTHERFORD, L.G. and Milton, A.L. Deconstructing and reconstructing behaviour relevant to mental health disorders: what can psychology offer? NEUROSCI BIOBEHAV REV XX(X)XXX-XXX, 2021. - Current treatments for mental health disorders are successful only for some patients, and there is an unmet clinical need for new treatment development. One challenge for treatment development has been how best to model complex human conditions in animals, where mechanism can be more readily studied with a range of neuroscientific techniques. We suggest that an approach to modelling based on associative animal learning theory provides a good framework for deconstructing complex mental health disorders such that they can be studied in animals. These individual simple models can subsequently be used in combination to 'reconstruct' a more complex model of the mental health disorder of interest. Using examples primarily from the field of drug addiction, we explore the 'psychological approach' and suggest that in addition to facilitating translation and backtranslation of tasks between animal models and patients, it is also highly concordant with the concept of triangulation.

Corticostriatal Activity Driving Compulsive Reward Seeking

BACKGROUND

Activation of the mesolimbic dopamine system is positively reinforcing. After repeated activation, some individuals develop compulsive reward-seeking behavior, which is a core symptom of addiction. However, the underlying neural mechanism remains elusive.

METHODS

We trained mice in a seek-take chain, rewarded by optogenetic dopamine neuron self-stimulation. After compulsivity was evaluated, AMPA/NMDA ratio was measured at three distinct corticostriatal pathways confirmed by retrograde labeling and anterograde synaptic connectivity. Fiber photometry method and chemogenetics were used to parse the contribution of orbitofrontal cortex afferents onto the dorsal striatum (DS) during the behavioral task. We established a causal link between DS activity and compulsivity using optogenetic inhibition.

RESULTS

Mice that persevered when seeking was punished exhibited an increased AMPA/NMDA ratio selectively at orbitofrontal cortex to DS synapses. In addition, an activity peak of spiny projection neurons in the DS at the moment of signaled reward availability was detected. Chemogenetic inhibition of orbitofrontal cortex neurons curbed the activity peak and reduced punished reward seeking, as did optogenetic hyperpolarization of spiny projection neurons time-locked to the cue predicting reward availability.

CONCLUSIONS

Our results suggest that compulsive individuals display stronger neuronal activity in the DS during the cue predicting reward availability even when at the risk of punishment, nurturing further compulsive reward seeking.

Relative salience signaling within a thalamo-orbitofrontal circuit governs learning rate

Learning to predict rewards is essential for the sustained fitness of animals. Contemporary views suggest that such learning is driven by a reward prediction error (RPE)-the difference between received and predicted rewards. The magnitude of learning induced by an RPE is proportional to the product of the RPE and a learning rate. Here we demonstrate using two-photon calcium imaging and optogenetics in mice that certain functionally distinct subpopulations of ventral/medial orbitofrontal cortex (vmOFC) neurons signal learning rate control. Consistent with learning rate control, trial-by-trial fluctuations in vmOFC activity positively correlate with behavioral updating when the RPE is positive, and negatively correlates with behavioral updating when the RPE is negative. Learning rate is affected by many variables including the salience of a reward. We found that the average reward response of these neurons signals the relative salience of a reward, because it decreases after reward prediction learning or the introduction of another highly salient aversive stimulus. The relative salience signaling in vmOFC is sculpted by medial thalamic inputs. These results support emerging theoretical views that prefrontal cortex encodes and controls learning parameters.

Disrupting D1-NMDA or D2-NMDA receptor heteromerization prevents cocaine's rewarding effects but preserves natural reward processing

Addictive drugs increase dopamine in the nucleus accumbens (NAc), where it persistently shapes excitatory glutamate transmission and hijacks natural reward processing. Here, we provide evidence, from mice to humans, that an underlying mechanism relies on drug-evoked heteromerization of glutamate N-methyl-d-aspartate receptors (NMDAR) with dopamine receptor 1 (D1R) or 2 (D2R). Using temporally controlled inhibition of D1R-NMDAR heteromerization, we unraveled their selective implication in early phases of cocaine-mediated synaptic, morphological, and behavioral responses. In contrast, preventing D2R-NMDAR heteromerization blocked the persistence of these adaptations. Interfering with these heteromers spared natural reward processing. Notably, we established that D2R-NMDAR complexes exist in human samples and showed that, despite a decreased D2R protein expression in the NAc, individuals with psychostimulant use disorder display a higher proportion of D2R forming heteromers with NMDAR. These findings contribute to a better understanding of molecular mechanisms underlying addiction and uncover D2R-NMDAR heteromers as targets with potential therapeutic value.

Corticostriatal Circuit Models of Cognitive Impairments Induced by Fetal Exposure to Alcohol

The term fetal alcohol spectrum disorder includes a group of diseases caused by fetal alcohol exposure (FAE). Patients with fetal alcohol spectrum disorder display heterogeneous socioemotional and cognitive deficits, particularly in the domain of executive function, that share symptoms with other neuropsychiatric disorders. Despite the availability of several preclinical models, the developmental brain defects causally linked to behavioral deficits induced by FAE remain poorly understood. Here, we first review the effects of FAE on corticostriatal development and its impact on both corticostriatal pathway function and cognitive abilities. We propose three non-mutually exclusive circuit models of corticostriatal dysfunctions to account for some of the FAE-induced cognitive deficits. One model posits that associative-sensorimotor imbalance causes hyper goal-directed behavior, and a second model implies that alteration of prefrontal-striatal behavioral suppression circuits results in loss of behavioral inhibition. A third model suggests that local striatal circuit deficits affect striatal neuronal ensemble function to impair action selection and performance. Finally, we discuss how preclinical approaches applied to these circuit models could offer potential rescue strategies for executive function deficits in patients with fetal alcohol spectrum disorder.

Synaptic mechanism underlying serotonin modulation of transition to cocaine addiction

Compulsive drug use despite adverse consequences defines addiction. While mesolimbic dopamine signaling is sufficient to drive compulsion, psychostimulants such as cocaine also boost extracellular serotonin (5-HT) by inhibiting reuptake. We used SERT Met172 knockin (SertKI) mice carrying a transporter that no longer binds cocaine to abolish 5-HT transients during drug self-administration. SertKI mice showed an enhanced transition to compulsion. Conversely, pharmacologically elevating 5-HT reversed the inherently high rate of compulsion transition with optogenetic dopamine self-stimulation. The bidirectional effect on behavior is explained by presynaptic depression of orbitofrontal cortex–to–dorsal striatum synapses induced by 5-HT via 5-HT1B receptors. Consequently, in projection-specific 5-HT1B receptor knockout mice, the fraction of individuals compulsively self-administering cocaine was elevated.

Increased serotonin prevents compulsion in addiction

[Figure: see text].

Addiction as a brain disease revised: why it still matters, and the need for consilience

The view that substance addiction is a brain disease, although widely accepted in the neuroscience community, has become subject to acerbic criticism in recent years. These criticisms state that the brain disease view is deterministic, fails to account for heterogeneity in remission and recovery, places too much emphasis on a compulsive dimension of addiction, and that a specific neural signature of addiction has not been identified. We acknowledge that some of these criticisms have merit, but assert that the foundational premise that addiction has a neurobiological basis is fundamentally sound. We also emphasize that denying that addiction is a brain disease is a harmful standpoint since it contributes to reducing access to healthcare and treatment, the consequences of which are catastrophic. Here, we therefore address these criticisms, and in doing so provide a contemporary update of the brain disease view of addiction. We provide arguments to support this view, discuss why apparently spontaneous remission does not negate it, and how seemingly compulsive behaviors can co-exist with the sensitivity to alternative reinforcement in addiction. Most importantly, we argue that the brain is the biological substrate from which both addiction and the capacity for behavior change arise, arguing for an intensified neuroscientific study of recovery. More broadly, we propose that these disagreements reveal the need for multidisciplinary research that integrates neuroscientific, behavioral, clinical, and sociocultural perspectives.

Wireless, battery-free, and fully implantable electrical neurostimulation in freely moving rodents

Implantable deep brain stimulation (DBS) systems are utilized for clinical treatment of diseases such as Parkinson's disease and chronic pain. However, long-term efficacy of DBS is limited, and chronic neuroplastic changes and associated therapeutic mechanisms are not well understood. Fundamental and mechanistic investigation, typically accomplished in small animal models, is difficult because of the need for chronic stimulators that currently require either frequent handling of test subjects to charge battery-powered systems or specialized setups to manage tethers that restrict experimental paradigms and compromise insight. To overcome these challenges, we demonstrate a fully implantable, wireless, battery-free platform that allows for chronic DBS in rodents with the capability to control stimulation parameters digitally in real time. The devices are able to provide stimulation over a wide range of frequencies with biphasic pulses and constant voltage control via low-impedance, surface-engineered platinum electrodes. The devices utilize off-the-shelf components and feature the ability to customize electrodes to enable broad utility and rapid dissemination. Efficacy of the system is demonstrated with a readout of stimulation-evoked neural activity in vivo and chronic stimulation of the medial forebrain bundle in freely moving rats to evoke characteristic head motion for over 36 days.

Drug addiction: from bench to bedside

Drug addiction is responsible for millions of deaths per year around the world. Still, its management as a chronic disease is shadowed by misconceptions from the general public. Indeed, drug consumers are often labelled as "weak", "immoral" or "depraved". Consequently, drug addiction is often perceived as an individual problem and not societal. In technical terms, drug addiction is defined as a chronic, relapsing disease resulting from sustained effects of drugs on the brain. Through a better characterisation of the cerebral circuits involved, and the long-term modifications of the brain induced by addictive drugs administrations, first, we might be able to change the way the general public see the patient who is suffering from drug addiction, and second, we might be able to find new treatments to normalise the altered brain homeostasis. In this review, we synthetise the contribution of fundamental research to the understanding drug addiction and its contribution to potential novel therapeutics. Mostly based on drug-induced modifications of synaptic plasticity and epigenetic mechanisms (and their behavioural correlates) and after demonstration of their reversibility, we tried to highlight promising therapeutics. We also underline the specific temporal dynamics and psychosocial aspects of this complex psychiatric disease adding parameters to be considered in clinical trials and paving the way to test new therapeutic venues.

A neural substrate of compulsive alcohol use

Alcohol intake remains controlled in a majority of users but becomes "compulsive," i.e., continues despite adverse consequences, in a minority who develop alcohol addiction. Here, using a footshock-punished alcohol self-administration procedure, we screened a large population of outbred rats to identify those showing compulsivity operationalized as punishment-resistant self-administration. Using unsupervised clustering, we found that this behavior emerged as a stable trait in a subpopulation of rats and was associated with activity of a brain network that included central nucleus of the amygdala (CeA). Activity of PKCδ+ inhibitory neurons in the lateral subdivision of CeA (CeL) accounted for ~75% of variance in punishment-resistant alcohol taking. Activity-dependent tagging, followed by chemogenetic inhibition of neurons activated during punishment-resistant self-administration, suppressed alcohol taking, as did a virally mediated shRNA knockdown of PKCδ in CeA. These findings identify a previously unknown mechanism for a core element of alcohol addiction and point to a novel candidate therapeutic target.

All-optical approaches to studying psychiatric disease

Improvements in all-optical means of monitoring and manipulating neural activity have generated new ways of studying psychiatric disease. The combination of calcium imaging techniques with optogenetics to concurrently record and manipulate neural activity has been used to create new disease models that link distinct circuit abnormalities to specific disease dimensions. These approaches represent a new path towards the development of more effective treatments, as they allow researchers to identify circuit manipulations that normalize pathological network activity. In this review we highlight the utility of all-optical approaches to generate new psychiatric disease models where the specific circuit abnormalities associated with disease symptomology can be assessed in vivo and in response to manipulations designed to normalize disease states. We then outline the principles underlying all-optical interrogations of neural circuits and discuss practical considerations for experimental design.

Over-representation of fundamental decision variables in the prefrontal cortex underlies decision bias

The brain is organized into anatomically distinct structures consisting of a variety of projection neurons. While such evolutionarily conserved neural circuit organization underlies the innate ability of animals to swiftly adapt to environments, they can cause biased cognition and behavior. Although recent studies have begun to address the causal importance of projection-neuron types as distinct computational units, it remains unclear how projection types are functionally organized in encoding variables during cognitive tasks. This review focuses on the neural computation of decision making in the prefrontal cortex and discusses what decision variables are encoded by single neurons, neuronal populations, and projection type, alongside how specific projection types constrain decision making. We focus particularly on "over-representations" of distinct decision variables in the prefrontal cortex that reflect the biological and subjective significance of the variables for the decision makers. We suggest that task-specific over-representation in the prefrontal cortex involves the refinement of the given decision making, while generalized over-representation of fundamental decision variables is associated with suboptimal decision biases, including pathological ones such as those in patients with psychiatric disorders. Such over-representation of the fundamental decision variables in the prefrontal cortex appear to be tightly constrained by afferent and efferent connections that can be optogenetically intervened on. These ideas may provide critical insights into potential therapeutic targets for psychiatric disorders, including addiction and depression.

Advances in understanding meso-cortico-limbic-striatal systems mediating risky reward seeking

The risk of an aversive consequence occurring as the result of a reward-seeking action can have a profound effect on subsequent behavior. Such aversive events can be described as punishers, as they decrease the probability that the same action will be produced again in the future and increase the exploration of less risky alternatives. Punishment can involve the omission of an expected rewarding event ("negative" punishment) or the addition of an unpleasant event ("positive" punishment). Although many individuals adaptively navigate situations associated with the risk of negative or positive punishment, those suffering from substance use disorders or behavioral addictions tend to be less able to curtail addictive behaviors despite the aversive consequences associated with them. Here, we discuss the psychological processes underpinning reward seeking despite the risk of negative and positive punishment and consider how behavioral assays in animals have been employed to provide insights into the neural mechanisms underlying addictive disorders. We then review the critical contributions of dopamine signaling to punishment learning and risky reward seeking, and address the roles of interconnected ventral striatal, cortical, and amygdala regions to these processes. We conclude by discussing the ample opportunities for future study to clarify critical gaps in the literature, particularly as related to delineating neural contributions to distinct phases of the risky decision-making process.

The mouse prefrontal cortex: Unity in diversity

The prefrontal cortex (PFC) is considered to constitute the highest stage of neural integration and to be devoted to representation and production of actions. Studies in primates have laid the foundation for theories regarding the principles of prefrontal function and provided mechanistic insights. The recent surge of studies of the PFC in mice holds promise for evolvement of present theories and development of novel concepts, particularly regarding principles shared across mammals. Here we review recent empirical work on the mouse PFC capitalizing on the experimental toolbox currently privileged to studies in this species. We conclude that this line of research has revealed cellular and structural distinctions of the PFC and neuronal activity with direct relevance to theories regarding the functions of the PFC. We foresee that data-rich mouse studies will be key to shed light on the general prefrontal architecture and mechanisms underlying cognitive aspects of organized actions.

Different Effects of Alcohol Exposure on Action and Outcome-Related Orbitofrontal Cortex Activity

Alcohol dependence can result in long-lasting deficits to decision-making and action control. Neurobiological investigations have identified orbitofrontal cortex (OFC) as important for outcome-related contributions to goal-directed actions during decision-making. Prior work has shown that alcohol dependence induces long-lasting changes to OFC function that persist into protracted withdrawal and disrupts goal-directed control over actions. However, it is unclear whether these changes in function alter representation of action and outcome-related neural activity in OFC. Here, we used the well-validated chronic intermittent ethanol (CIE) exposure and withdrawal procedure to model alcohol dependence in mice and performed in vivo extracellular recordings during an instrumental task in which lever-press actions made for a food outcome. We found alcohol dependence disrupted goal-directed action control and increased OFC activity associated with lever-pressing but decreased OFC activity during outcome-related epochs. The ability to decode outcome-related information, but not action information, from OFC activity following CIE exposure was reduced. Hence, chronic alcohol exposure induced a long-lasting disruption to OFC function such that activity associated with actions was enhanced, but OFC activity contributions to outcome-related information was diminished. This has important implications for hypotheses regarding compulsive and habitual phenotypes observed in addiction.

Subthalamic low-frequency oscillations predict vulnerability to cocaine addiction

Identifying vulnerable individuals before they transition to a compulsive pattern of drug seeking and taking is a key challenge in addiction to develop efficient prevention strategies. Oscillatory activity within the subthalamic nucleus (STN) has been associated with compulsive-related disorders. To study compulsive cocaine-seeking behavior, a core component of drug addiction, we have used a rat model in which cocaine seeking despite a foot-shock contingency only emerges in some vulnerable individuals having escalated their cocaine intake. We show that abnormal oscillatory activity within the alpha/theta and low-beta bands during the escalation of cocaine intake phase predicts the subsequent emergence of compulsive-like seeking behavior. In fact, mimicking STN pathological activity in noncompulsive rats during cocaine escalation turns them into compulsive ones. We also find that 30 Hz, but not 130 Hz, STN deep brain stimulation (DBS) reduces pathological cocaine seeking in compulsive individuals. Our results identify an early electrical signature of future compulsive-like cocaine-seeking behavior and further advocates the use of frequency-dependent STN DBS for the treatment of addiction.

Call for a more balanced approach to understanding orbital frontal cortex function

Orbital frontal cortex (OFC) research has historically emphasized the function of this associative cortical area within top-down theoretical frameworks. This approach has largely focused on mapping OFC activity onto human-defined psychological or cognitive constructs and has often led to OFC circuitry bearing the weight of entire theoretical frameworks. New techniques and tools developed in the last decade have made it possible to revisit long-standing basic science questions in neuroscience and answer them with increasing sophistication. We can now study and specify the genetic, molecular, cellular, and circuit architecture of a brain region in much greater detail, which allows us to piece together how they contribute to emergent circuit functions. For instance, adopting such systematic and unbiased bottom-up approaches to elucidating the function of the visual system has paved the way to building a greater understanding of the spectrum of its computational capabilities. In the same vein, we argue that OFC research would benefit from a more balanced approach that also places focus on novel bottom-up investigations into OFC's computational capabilities. Furthermore, we believe that the knowledge gained by employing a more bottom-up approach to investigating OFC function will ultimately allow us to look at OFC's dysfunction in disease through a more nuanced biological lens. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Drug-Evoked Synaptic Plasticity of Excitatory Transmission in the Ventral Tegmental Area

Cocaine leads to a strong euphoria, which is at the origin of its recreational use. Past the acute effects, the drug leaves traces in the brain that persist long after it has been cleared from the body. These traces eventually shape behavior such that drug use may become compulsive, and addiction develops. Here, we discuss cocaine-evoked synaptic plasticity of glutamatergic transmission onto dopamine (DA) neurons of the ventral tegmental area (VTA) as one of the earliest traces after a first injection of cocaine. We review the literature that has examined the induction requirements, as well as the expression mechanism of this form of plasticity, and ask the question about its functional significance.

Mechanism for differential recruitment of orbitostriatal transmission during actions and outcomes following chronic alcohol exposure

Psychiatric disease often produces symptoms that have divergent effects on neural activity. For example, in drug dependence, dysfunctional value-based decision-making and compulsive-like actions have been linked to hypo- and hyperactivity of orbital frontal cortex (OFC)-basal ganglia circuits, respectively; however, the underlying mechanisms are unknown. Here we show that alcohol-exposed mice have enhanced activity in OFC terminals in dorsal striatum (OFC-DS) associated with actions, but reduced activity of the same terminals during periods of outcome retrieval, corresponding with a loss of outcome control over decision-making. Disrupted OFC-DS terminal activity was due to a dysfunction of dopamine-type 1 receptors on spiny projection neurons (D1R SPNs) that resulted in increased retrograde endocannabinoid signaling at OFC-D1R SPN synapses reducing OFC-DS transmission. Blocking CB1 receptors restored OFC-DS activity in vivo and rescued outcome-based control over decision-making. These findings demonstrate a circuit-, synapse-, and computation-specific mechanism gating OFC activity in alcohol-exposed mice.

Consolidating the Circuit Model for Addiction

Addiction is a disease characterized by compulsive drug seeking and consumption observed in 20-30% of users. An addicted individual will favor drug reward over natural rewards, despite major negative consequences. Mechanistic research on rodents modeling core components of the disease has identified altered synaptic transmission as the functional substrate of pathological behavior. While the initial version of a circuit model for addiction focused on early drug adaptive behaviors observed in all individuals, it fell short of accounting for the stochastic nature of the transition to compulsion. The model builds on the initial pharmacological effect common to all addictive drugs-an increase in dopamine levels in the mesolimbic system. Here, we consolidate this early model by integrating circuits underlying compulsion and negative reinforcement. We discuss the genetic and epigenetic correlates of individual vulnerability. Many recent data converge on a gain-of-function explanation for circuit remodeling, revealing blueprints for novel addiction therapies.

Habit, choice, and addiction

Addiction was suggested to emerge from the progressive dominance of habits over goal-directed behaviors. However, it is generally assumed that habits do not persist in choice settings. Therefore, it is unclear how drug habits may persist in real-world scenarios where this factor predominates. Here, we discuss the poor translational validity of the habit construct, which impedes our ability to determine its role in addiction. New evidence of habitual behavior in a drug choice setting are then described and discussed. Interestingly, habitual preference did not promote drug choice but instead favored abstinence. Here, we propose several clues to reconcile these unexpected results with the habit theory of addiction, and we highlight the need in experimental research to face the complexity of drug addicts' decision-making environments by investigating drug habits in the context of choice and in the presence of cues. On a theoretical level, we need to consider more complex frameworks, taking into account continuous interactions between goal-directed and habitual systems, and alternative decision-making models more representative of real-world conditions.

Stress undermines reward-guided cognitive performance through synaptic depression in the lateral habenula

Weighing alternatives during reward pursuit is a vital cognitive computation that, when disrupted by stress, yields aspects of neuropsychiatric disorders. To examine the neural mechanisms underlying these phenomena, we employed a behavioral task in which mice were confronted by a reward and its omission (i.e., error). The experience of error outcomes engaged neuronal dynamics within the lateral habenula (LHb), a subcortical structure that supports appetitive behaviors and is susceptible to stress. A high incidence of errors predicted low strength of habenular excitatory synapses. Accordingly, stressful experiences increased error choices while decreasing glutamatergic neurotransmission onto LHb neurons. This synaptic adaptation required a reduction in postsynaptic AMPA receptors (AMPARs), irrespective of the anatomical source of glutamate. Bidirectional control of habenular AMPAR transmission recapitulated and averted stress-driven cognitive deficits. Thus, a subcortical synaptic mechanism vulnerable to stress underlies behavioral efficiency during cognitive performance.

Vulnerability to addiction

Addiction is a chronic brain disease that has dramatic health and socioeconomic consequences worldwide. Multiple approaches have been used for decades to clarify the neurobiological basis of this disease and to identify novel potential treatments. This review summarizes the main brain networks involved in the vulnerability to addiction and specific innovative technological approaches to investigate these neural circuits. First, the evolution of the definition of addiction across the Diagnostic and Statistical Manual of Mental Disorders (DSM) is revised. We next discuss several innovative experimental techniques that, combined with behavioral approaches, have allowed recent critical advances in understanding the neural circuits involved in addiction, including DREADDs, calcium imaging, and electrophysiology. All these techniques have been used to investigate specific neural circuits involved in vulnerability to addiction and have been extremely useful to clarify the neurobiological basis of each specific component of the addictive process. These novel tools targeting specific brain regions are of great interest to further understand the different aspects of this complex disease. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'.

Pharmacokinetics trumps pharmacodynamics during cocaine choice: a reconciliation with the dopamine hypothesis of addiction

Cocaine is known to increase brain dopamine at supranormal levels in comparison to alternative nondrug rewards. According to the dopamine hypothesis of addiction, this abnormally large dopamine response would explain why cocaine use is initially highly rewarding and addictive. Though resting on solid neuroscientific foundations, this hypothesis has nevertheless proven difficult to reconcile with research on cocaine choice in experimental animals. When facing a choice between an intravenous bolus of cocaine and a nondrug alternative (e.g., sweet water), both delivered immediately after choice, rats do not choose the drug, as would be predicted, but instead develop a strong preference for the nondrug alternative. Here we report evidence that reconciles this finding with the dopamine hypothesis of addiction. First, a systematic literature analysis revealed that the delays of effects of intravenous cocaine on nucleus accumbens dopamine are of the order of tens of seconds and are considerably longer than those of nondrug reward. Second, this was confirmed by measuring response times to cocaine omission during self-administration as a behavioral proxy of these delays. Finally, when the influence of the drug delays was reduced during choice by adding an increasing delay to both the drug and nondrug rewards, rats shifted their choice to cocaine. Overall, this study suggests that cocaine is indeed supranormal in reward magnitude, as postulated by the dopamine hypothesis of addiction, but is less preferred during choice because its pharmacokinetics makes it an inherently more delayed reward than the alternative. Reframing previous drug choice studies in rats as intertemporal choice studies reveals that the discounting effects of delays spare no rewards, including supranormal ones, and that during choice, pharmacokinetics trumps pharmacodynamics.

CRHCeA→VTA inputs inhibit the positive ensembles to induce negative effect of opiate withdrawal

Plasticity of neurons in the ventral tegmental area (VTA) is critical for establishment of drug dependence. However, the remodeling of the circuits mediating the transition between positive and negative effect remains unclear. Here, we used neuronal activity-dependent labeling technique to characterize and temporarily control the VTA neuronal ensembles recruited by the initial morphine exposure (morphine-positive ensembles, Mor-Ens). Mor-Ens preferentially projected to NAc, and induced dopamine-dependent positive reinforcement. Electrophysiology and rabies viral tracing revealed the preferential connections between the VTA-projective corticotrophin-releasing hormone (CRH) neurons of central amygdala (CRH^CeA→VTA) and Mor-Ens, which was enhanced after escalating morphine exposure and mediated the negative effect during opiate withdrawal. Pharmacologic intervention or CRISPR-mediated repression of CRHR1 in Mor-Ens weakened the inhibitory CRH^CeA→VTA inputs, and alleviated the negative effect during opiate withdrawal. These data suggest that neurons encoding opioid reward experience are inhibited by enhanced CRH^CeA→VTA inputs induced by chronic morphine exposure, leading to negative effect during opiate withdrawal, and provide new insight into the pathological changes in VTA plasticity after drug abuse and mechanism of opiate dependence.

Projection-specific deficits in synaptic transmission in adult Sapap3-knockout mice

Obsessive-compulsive disorder (OCD) is a circuit disorder involving corticostriatal projections, which play a role in motor control. The Sapap3-knockout (KO) mouse is a mouse model to study OCD and recapitulates OCD-like compulsion through excessive grooming behavior, with skin lesions appearing at advanced age. Deficits in corticostriatal control provide a link to the pathophysiology of OCD. However, there remain significant gaps in the characterization of the Sapap3-KO mouse, with respect to age, specificity of synaptic dysfunction, and locomotor phenotype. We therefore investigated the corticostriatal synaptic phenotype of Sapap3-KO mice using patch-clamp slice electrophysiology, in adult mice and with projection specificity. We also analyzed grooming across age and locomotor phenotype with a novel, unsupervised machine learning technique (MoSeq). Increased grooming in Sapap3-KO mice without skin lesions was age independent. Synaptic deficits persisted in adulthood and involved the projections from the motor cortices and cingulate cortex to the dorsolateral and dorsomedial striatum. Decreased synaptic strength was evident at the input from the primary motor cortex by reduction in AMPA receptor function. Hypolocomotion, i.e., slowness of movement, was consistently observed in Sapap3-KO mice. Our findings emphasize the utility of young adult Sapap3-KO mice to investigate corticostriatal synaptic dysfunction in motor control.

Improving translation of animal models of addiction and relapse by reverse translation

Critical features of human addiction are increasingly being incorporated into complementary animal models, including escalation of drug intake, punished drug seeking and taking, intermittent drug access, choice between drug and non-drug rewards, and assessment of individual differences based on criteria in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Combined with new technologies, these models advanced our understanding of brain mechanisms of drug self-administration and relapse, but these mechanistic gains have not led to improvements in addiction treatment. This problem is not unique to addiction neuroscience, but it is an increasing source of disappointment and calls to regroup. Here we first summarize behavioural and neurobiological results from the animal models mentioned above. We then propose a reverse translational approach, whose goal is to develop models that mimic successful treatments: opioid agonist maintenance, contingency management and the community-reinforcement approach. These reverse-translated 'treatments' may provide an ecologically relevant platform from which to discover new circuits, test new medications and improve translation.

A Genetically Defined Compartmentalized Striatal Direct Pathway for Negative Reinforcement

The striosome compartment within the dorsal striatum has been implicated in reinforcement learning and regulation of motivation, but how striosomal neurons contribute to these functions remains elusive. Here, we show that a genetically identified striosomal population, which expresses the Teashirt family zinc finger 1 (Tshz1) and belongs to the direct pathway, drives negative reinforcement and is essential for aversive learning in mice. Contrasting a "conventional" striosomal direct pathway, the Tshz1 neurons cause aversion, movement suppression, and negative reinforcement once activated, and they receive a distinct set of synaptic inputs. These neurons are predominantly excited by punishment rather than reward and represent the anticipation of punishment or the motivation for avoidance. Furthermore, inhibiting these neurons impairs punishment-based learning without affecting reward learning or movement. These results establish a major role of striosomal neurons in behaviors reinforced by punishment and moreover uncover functions of the direct pathway unaccounted for in classic models.

The orbitofrontal cortex, food intake and obesity

Obesity is a major health challenge facing many people throughout the world. Increased consumption of palatable, high-caloric foods is one of the major drivers of obesity. Both orexigenic and anorexic states have been thoroughly reviewed elsewhere; here, we focus on the cognitive control of feeding in the context of obesity, and how the orbitofrontal cortex (OFC) is implicated, based on data from preclinical and clinical research. The OFC is important in decision-making and has been heavily researched in neuropsychiatric illnesses such as addiction and obsessive–compulsive disorder. However, activity in the OFC has only recently been described in research into food intake, obesity and eating disorders. The OFC integrates sensory modalities such as taste, smell and vision, and it has dense reciprocal projections into thalamic, midbrain and striatal regions to fine-tune decision-making. Thus, the OFC may be anatomically and functionally situated to play a critical role in the etiology and maintenance of excess feeding behaviour. We propose that the OFC serves as an integrative hub for orchestrating motivated feeding behaviour and suggest how its neurobiology and functional output might be altered in the obese state.

Orbitofrontal, dorsal striatum, and habenula functional connectivity in psychiatric patients with substance use problems

Substance abuse is commonly defined as the persistence of drug use despite negative consequences. Recent preclinical work has shown that higher input from the orbitofrontal cortex (OFC) to the dorsal striatum was associated with compulsive reward-seeking behavior despite negative effects. It remains unknown whether drug use is associated with the connectivity between the OFC and dorsal striatum in humans. We studied the resting state functional connectivity (RSFC) between the OFC, dorsal striatum, and habenula (and the whole brain in a separate analysis) in psychiatric inpatients with high (PU, problem users) and low (LU, low users) substance use. We matched PU and LU for psychiatric comorbidities. We found that PU showed higher RSFC between the left OFC and the left dorsal striatum than LU. RSFC between the habenula and both OFC and dorsal striatum was also higher in PU, which suggests the habenula may be a part of the same circuit. Finally, higher RSFC between the OFC and insula was also observed in PU. Our data shows that OFC, habenula, dorsal striatum, and insula may play an important role in PU. Furthermore, we postulate that the habenula may link the mesolimbic and cortico-striatal systems, which are altered in PU.

Orbitofrontal-striatal potentiation underlies cocaine-induced hyperactivity

Psychomotor stimulants increase dopamine levels in the striatum and promote locomotion; however, their effects on striatal pathway function in vivo remain unclear. One model that has been proposed to account for these motor effects suggests that stimulants drive hyperactivity via activation and inhibition of direct and indirect pathway striatal neurons, respectively. Although this hypothesis is consistent with the cellular actions of dopamine receptors and received support from optogenetic and chemogenetic studies, it has been rarely tested with in vivo recordings. Here, we test this model and observe that cocaine increases the activity of both pathways in the striatum of awake mice. These changes are linked to a dopamine-dependent cocaine-induced strengthening of upstream orbitofrontal cortex (OFC) inputs to the dorsomedial striatum (DMS) in vivo. Finally, depressing OFC-DMS pathway with a high frequency stimulation protocol in awake mice over-powers the cocaine-induced potentiation of OFC-DMS pathway and attenuates the expression of locomotor sensitization, directly linking OFC-DMS potentiation to cocaine-induced hyperactivity.

Behavior- and Modality-General Representation of Confidence in Orbitofrontal Cortex

Every decision we make is accompanied by a sense of confidence about its likely outcome. This sense informs subsequent behavior, such as investing more-whether time, effort, or money-when reward is more certain. A neural representation of confidence should originate from a statistical computation and predict confidence-guided behavior. An additional requirement for confidence representations to support metacognition is abstraction: they should emerge irrespective of the source of information and inform multiple confidence-guided behaviors. It is unknown whether neural confidence signals meet these criteria. Here, we show that single orbitofrontal cortex neurons in rats encode statistical decision confidence irrespective of the sensory modality, olfactory or auditory, used to make a choice. The activity of these neurons also predicts two confidence-guided behaviors: trial-by-trial time investment and cross-trial choice strategy updating. Orbitofrontal cortex thus represents decision confidence consistent with a metacognitive process that is useful for mediating confidence-guided economic decisions.

Orbitofrontal control of visual cortex gain promotes visual associative learning

The orbitofrontal cortex (OFC) encodes expected outcomes and plays a critical role in flexible, outcome-guided behavior. The OFC projects to primary visual cortex (V1), yet the function of this top-down projection is unclear. We find that optogenetic activation of OFC projection to V1 reduces the amplitude of V1 visual responses via the recruitment of local somatostatin-expressing (SST) interneurons. Using mice performing a Go/No-Go visual task, we show that the OFC projection to V1 mediates the outcome-expectancy modulation of V1 responses to the reward-irrelevant No-Go stimulus. Furthermore, V1-projecting OFC neurons reduce firing during expectation of reward. In addition, chronic optogenetic inactivation of OFC projection to V1 impairs, whereas chronic activation of SST interneurons in V1 improves the learning of Go/No-Go visual task, without affecting the immediate performance. Thus, OFC top-down projection to V1 is crucial to drive visual associative learning by modulating the response gain of V1 neurons to non-relevant stimulus.

The orbitofrontal cortex (OFC) encodes expected outcomes and plays a key role in outcome-guided behavior. The authors show here that the top-down projection from the OFC to the visual cortex drives visual associative learning by modulating the response gain of V1 neurons to non-relevant stimuli.

From Signaling Molecules to Circuits and Behaviors: Cell-Type-Specific Adaptations to Psychostimulant Exposure in the Striatum

Addiction is characterized by a compulsive pattern of drug seeking and consumption and a high risk of relapse after withdrawal that are thought to result from persistent adaptations within brain reward circuits. Drugs of abuse increase dopamine (DA) concentration in these brain areas, including the striatum, which shapes an abnormal memory trace of drug consumption that virtually highjacks reward processing. Long-term neuronal adaptations of gamma-aminobutyric acidergic striatal projection neurons (SPNs) evoked by drugs of abuse are critical for the development of addiction. These neurons form two mostly segregated populations, depending on the DA receptor they express and their output projections, constituting the so-called direct (D₁ receptor) and indirect (D₂ receptor) SPN pathways. Both SPN subtypes receive converging glutamate inputs from limbic and cortical regions, encoding contextual and emotional information, together with DA, which mediates reward prediction and incentive values. DA differentially modulates the efficacy of glutamate synapses onto direct and indirect SPN pathways by recruiting distinct striatal signaling pathways, epigenetic and genetic responses likely involved in the transition from casual drug use to addiction. Herein we focus on recent studies that have assessed psychostimulant-induced alterations in a cell-type-specific manner, from remodeling of input projections to the characterization of specific molecular events in each SPN subtype and their impact on long-lasting behavioral adaptations. We discuss recent evidence revealing the complex and concerted action of both SPN populations on drug-induced behavioral responses, as these studies can contribute to the design of future strategies to alleviate specific behavioral components of addiction.

The transition to compulsion in addiction

Compulsion is a cardinal symptom of drug addiction (severe substance use disorder). However, compulsion is observed in only a small proportion of individuals who repeatedly seek and use addictive substances. Here, we integrate accounts of the neuropharmacological mechanisms that underlie the transition to compulsion with overarching learning theories, to outline how compulsion develops in addiction. Importantly, we emphasize the conceptual distinctions between compulsive drug-seeking behaviour and compulsive drug-taking behaviour (that is, use). In the latter, an individual cannot stop using a drug despite major negative consequences, possibly reflecting an imbalance in frontostriatal circuits that encode reward and aversion. By contrast, an individual may compulsively seek drugs (that is, persist in seeking drugs despite the negative consequences of doing so) when the neural systems that underlie habitual behaviour dominate goal-directed behavioural systems, and when executive control over this maladaptive behaviour is diminished. This distinction between different aspects of addiction may help to identify its neural substrates and new treatment strategies.

Chronic calorie-dense diet drives differences in motivated food seeking between obesity-prone and resistant mice

Obesity results from overconsumption of energy, partly because of the inability to refrain from highly palatable rewarding foods. Even though palatable food is available to everyone, only a fraction of the population develops obesity. We previously showed that following chronic exposure to highly palatable food animals that gained the most weight also showed addictive-like motivation to seek for palatable food. An important question remains-is this extreme, addictive-like, motivation to consume palatable food the cause or the consequence of diet-induced obesity? Here, we show that obesity-prone (OP) mice exhibit higher motivation for palatable food consumption compared with obesity-resistant mice even before developing obesity, but that the full manifestation of this high motivation to eat is expressed only after chronic exposure to high-fat-high-sugar (HFHS) diet. HFHS diet also impairs performance in the operant food-seeking task selectively in OP mice, an impairment that persists even after 2 weeks of abstinence from HFHS food. Overall, our data suggest that while some aspects of food motivation are high in OP mice already before developing obesity, the chronic exposure to HFHS food accentuates it and drives the development of obesity.

Analyzing Event-Related Transients: Confidence Intervals, Permutation Tests, and Consecutive Thresholds

Fiber photometry has enabled neuroscientists to easily measure targeted brain activity patterns in awake, freely behaving animal. A focus of this technique is to identify functionally-relevant changes in activity around particular environmental and/or behavioral events, i.e., event-related activity transients (ERT). A simple and popular approach to identifying ERT is to summarize peri-event signal [e.g., area under the curve (AUC), peak activity, etc.,] and perform standard analyses on this summary statistic. We highlight the various issues with this approach and overview straightforward alternatives: waveform confidence intervals (CIs) and permutation tests. We introduce the rationale behind these approaches, describe the results of Monte Carlo simulations evaluating their effectiveness at controlling Type I and Type II error rates, and offer some recommendations for selecting appropriate analysis strategies for fiber photometry experiments.

Projection-Specific Potentiation of Ventral Pallidal Glutamatergic Outputs after Abstinence from Cocaine

The ventral pallidum (VP) is a central node in the reward system that is strongly implicated in reward and addiction. Although the majority of VP neurons are GABAergic and encode reward, recent studies revealed a novel glutamatergic neuronal population in the VP [VP neurons expressing the vesicular glutamate transporter 2 (VP_VGluT2)], whose activation generates aversion. Withdrawal from drugs has been shown to induce drastic synaptic changes in neuronal populations associated with reward, such as the ventral tegmental area (VTA) or nucleus accumbens neurons, but less is known about cocaine-induced synaptic changes in neurons classically linked with aversion. Here, we demonstrate that VP_VGluT2 neurons contact different targets with different intensities, and that cocaine conditioned place preference (CPP) training followed by abstinence selectively potentiates their synapses on targets that encode aversion. Using whole-cell patch-clamp recordings combined with optogenetics in male and female transgenic mice, we show that VP_VGluT2 neurons preferentially contact aversion-related neurons, such as lateral habenula neurons and VTA GABAergic neurons, with minor input to reward-related neurons, such as VTA dopamine and VP GABA neurons. Moreover, after cocaine CPP and abstinence, the VP_VGluT2 input to the aversion-related structures is potentiated, whereas the input to the reward-related structures is depressed. Thus, cocaine CPP followed by abstinence may allow VP_VGluT2 neurons to recruit aversion-related targets more readily and therefore be part of the mechanism underlying the aversive symptoms seen after withdrawal.SIGNIFICANCE STATEMENT The biggest problem in drug addiction is the high propensity to relapse. One central driver for relapse events is the negative aversive symptoms experienced by addicts during withdrawal. In this work, we propose a possible mechanism for the intensification of aversive feelings after withdrawal that involves the glutamatergic neurons of the ventral pallidum. We show not only that these neurons are most strongly connected to aversive targets, such as the lateral habenula, but also that, after abstinence, their synapses on aversive targets are strengthened, whereas the synapses on other rewarding targets are weakened. These data illustrate how after abstinence from cocaine, aversive pathways change in a manner that may contribute to relapse.

mTORC1 in the orbitofrontal cortex promotes habitual alcohol seeking

The mechanistic target of rapamycin complex 1 (mTORC1) plays an important role in dendritic translation and in learning and memory. We previously showed that heavy alcohol use activates mTORC1 in the orbitofrontal cortex (OFC) of rodents (Laguesse et al., 2017a). Here, we set out to determine the consequences of alcohol-dependent mTORC1 activation in the OFC. We found that inhibition of mTORC1 activity in the OFC attenuates alcohol seeking and restores sensitivity to outcome devaluation in rats that habitually seek alcohol. In contrast, habitual responding for sucrose was unaltered by mTORC1 inhibition, suggesting that mTORC1’s role in habitual behavior is specific to alcohol. We further show that inhibition of GluN2B in the OFC attenuates alcohol-dependent mTORC1 activation, alcohol seeking and habitual responding for alcohol. Together, these data suggest that the GluN2B/mTORC1 axis in the OFC drives alcohol seeking and habit.