The neuropsychological basis of addictive behaviour

Assessment of reduction in stimulus generalization of ethanol-seeking during recovery: A rapid procedure

Previously, we developed a procedure which showed that longer histories of reinforced alternative behavior decrease the risk of relapse caused by a range of stimuli which had previously occasioned drinking. The decrease in relapse risk was likely due to a decrease in attention to the stimuli over the course of repeated engagement in the alternative behavior. However, this previous procedure was time consuming and did not mirror the procedure we used to observe changes in relapse risk. This study aimed at replicating the previous relationship between the duration of engaging in an alternative behavior and shift in stimulus generalization for drinking using a procedure that allows longitudinal analysis over time and is consistent with other procedures we have developed. Rats were trained to respond for ethanol in the presence of one stimulus (16 kHz tone; food Fixed Ratio (FR)150 and ethanol FR5), and for food in the under another stimulus (8 kHz tone; food and ethanol FR5). Then, recovery-like sessions with food predominant responding occurred in the presence of only the low-cost food stimulus. During these sessions, rats were exposed to non-reinforced graded stimuli alternation from 8 to 16 kHz alternating with the reinforced low-cost food stimulus. The number of responses on each (food and ethanol) lever before completing 5 responses on either lever was the main measure. Consistent with the earlier procedure, the current procedure showed that graded variation of tone from 8 to 16 kHz produced a graded increase in responding for ethanol compared to responding for food. In addition, longer periods of engaging in recovery-like responding shift the generalization function downwards. This procedure confirms the earlier pattern of stimulus generalization over longer periods of behavior consistent with recovery. This strengthens our hypothesis that shifts in attention to alcohol-related stimuli are important to the development of relapse resistance during recovery.

Unraveling the influence of Pavlovian cues on decision-making: A pre-registered meta-analysis on Pavlovian-to-instrumental transfer

Amidst the replicability crisis, promoting transparency and rigor in research becomes imperative. The Pavlovian-to-Instrumental Transfer (PIT) paradigm is increasingly used in human studies to offer insights into how Pavlovian cues, by anticipating rewards or punishments, influence decision-making and potentially contribute to the development of clinical conditions. However, research on this topic faces challenges, including methodological variability and the need for standardized approaches, which can undermine the quality and robustness of experimental findings. Hence, we conducted a meta-analysis to unravel the methodological, task-related, individual, training, and learning factors that can modulate PIT. By scrutinizing these factors, the present meta-analysis reviews the current literature on human PIT, provides practical guidelines for future research to enhance study outcomes and refine methodologies, and identifies knowledge gaps that can serve as a direction for future studies aiming to advance the comprehension of how Pavlovian cues shape decision-making.

Learning and memory processes in behavioural addiction: A systematic review

Similar to addictive substances, addictive behaviours such as gambling and gaming are associated with maladaptive modulation of key brain areas and functional networks implicated in learning and memory. Therefore, this review sought to understand how different learning and memory processes relate to behavioural addictions and to unravel their underlying neural mechanisms. Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we systematically searched four databases - PsycINFO, PubMed, Scopus, and Web of Science using the agreed-upon search string. Findings suggest altered executive function-dependent learning processes and enhanced habit learning in behavioural addiction. Whereas the relationship between working memory and behavioural addiction is influenced by addiction type, working memory aspect, and task nature. Additionally, long-term memory is incoherent in individuals with addictive behaviours. Consistently, neurophysiological evidence indicates alterations in brain areas and networks implicated in learning and memory processes in behavioural addictions. Overall, the present review argues that, like substance use disorders, alteration in learning and memory processes may underlie the development and maintenance of behavioural addictions.

A Cocaine-Activated Ensemble Exerts Increased Control Over Behavior While Decreasing in Size

BACKGROUND

Substance use disorder is characterized by long-lasting changes in reward-related brain regions, such as the nucleus accumbens. Previous work has shown that cocaine exposure induces plasticity in broad, genetically defined cell types in the nucleus accumbens; however, in response to a stimulus, only a small percentage of neurons are transcriptionally active-termed an ensemble. Here, we identify an Arc-expressing neuronal ensemble that has a unique trajectory of recruitment and causally controls drug self-administration after repeated, but not acute, cocaine exposure.

METHODS

Using Arc-CreERT2 transgenic mice, we expressed transgenes in Arc+ ensembles activated by cocaine exposure (either acute [1 × 10 mg/kg intraperitoneally] or repeated [10 × 10 mg/kg intraperitoneally]). Using genetic, optical, and physiological recording and manipulation strategies, we assessed the contribution of these ensembles to behaviors associated with substance use disorder.

RESULTS

Repeated cocaine exposure reduced the size of the ensemble while simultaneously increasing its control over behavior. Neurons within the repeated cocaine ensemble were hyperexcitable, and their optogenetic excitation was sufficient for reinforcement. Finally, lesioning the repeated cocaine, but not the acute cocaine, ensemble blunted cocaine self-administration. Thus, repeated cocaine exposure reduced the size of the ensemble while simultaneously increasing its contributions to drug reinforcement.

CONCLUSIONS

We showed that repeated, but not acute, cocaine exposure induced a physiologically distinct ensemble characterized by the expression of the immediate early gene Arc, which was uniquely capable of modulating reinforcement behavior.

Inhibition of ERK1/2 or CRMP2 Disrupts Alcohol Memory Reconsolidation and Prevents Relapse in Rats

Relapse to alcohol abuse, often caused by cue-induced alcohol craving, is a major challenge in alcohol addiction treatment. Therefore, disrupting the cue-alcohol memories can suppress relapse. Upon retrieval, memories transiently destabilize before they reconsolidate in a process that requires protein synthesis. Evidence suggests that the mammalian target of rapamycin complex 1 (mTORC1), governing the translation of a subset of dendritic proteins, is crucial for memory reconsolidation. Here, we explored the involvement of two regulatory pathways of mTORC1, phosphoinositide 3-kinase (PI3K)-AKT and extracellular regulated kinase 1/2 (ERK1/2), in the reconsolidation process in a rat (Wistar) model of alcohol self-administration. We found that retrieval of alcohol memories using an odor-taste cue increased ERK1/2 activation in the amygdala, while the PI3K-AKT pathway remained unaffected. Importantly, ERK1/2 inhibition after alcohol memory retrieval impaired alcohol-memory reconsolidation and led to long-lasting relapse suppression. Attenuation of relapse was also induced by post-retrieval administration of lacosamide, an inhibitor of collapsin response mediator protein-2 (CRMP2)-a translational product of mTORC1. Together, our findings indicate the crucial role of ERK1/2 and CRMP2 in the reconsolidation of alcohol memories, with their inhibition as potential treatment targets for relapse prevention.

Targeting the cytoskeleton as a therapeutic approach to substance use disorders

Substance use disorders (SUD) are chronic relapsing disorders governed by continually shifting cycles of positive drug reward experiences and drug withdrawal-induced negative experiences. A large body of research points to plasticity within systems regulating emotional, motivational, and cognitive processes as drivers of continued compulsive pursuit and consumption of substances despite negative consequences. This plasticity is observed at all levels of analysis from molecules to networks, providing multiple avenues for intervention in SUD. The cytoskeleton and its regulatory proteins within neurons and glia are fundamental to the structural and functional integrity of brain processes and are potentially the major drivers of the morphological and behavioral plasticity associated with substance use. In this review, we discuss preclinical studies that provide support for targeting the brain cytoskeleton as a therapeutic approach to SUD. We focus on the interplay between actin cytoskeleton dynamics and exposure to cocaine, methamphetamine, alcohol, opioids, and nicotine and highlight preclinical studies pointing to a wide range of potential therapeutic targets, such as nonmuscle myosin II, Rac1, cofilin, prosapip 1, and drebrin. These studies broaden our understanding of substance-induced plasticity driving behaviors associated with SUD and provide new research directions for the development of SUD therapeutics.

Examination of reward processing dysfunctions in the left dorsal striatum and other brain regions among psychiatric inpatients with substance use

BACKGROUND

Substance misuse is a major public health issue and research has established attenuated reward responses to drug cues in those who misuse substances. Yet, little is known about whether the expectation of natural reinforcers engages distinct brain regions in substance misuse.

METHODS

Using functional magnetic resonance imaging (fMRI), we delivered juice at expected and unexpected times to examine reward processing dysfunctions. We focused on the responses within the left dorsal striatum (DS) in individuals with high-risk substance use (HRU, n = 65), low-risk substance use (psychiatric controls, PC, n = 65), and healthy controls (HC, n = 65). Additionally, we investigated whether the dysfunction in reward processing within the left DS is correlated with other common psychiatric symptoms. Finally, we conducted a comprehensive analysis of the whole brain to investigate other non-hypothesized brain regions.

RESULTS

Compared to HC, HRU displayed lower responses to juice delivery (i.e., reward) in the left DS (p <.05). The whole-brain analysis demonstrated that compared to HC, HRU displayed significantly lower responses to reward stimuli in various brain regions, including the bilateral caudate, temporal gyrus, left frontal gyrus, middle frontal gyrus, and right thalamus.

LIMITATIONS

Participants were individuals with polysubstance use; therefore, we were not able to examine the effects of individual substances.

CONCLUSIONS

Our findings suggest that HRU displays lower responses to reward stimuli within the left DS and other non-hypothesized brain regions. Our findings may help further elucidate reward processing dysfunctions related to substance misuse.

Positive correlation between measures of habitual responding and motivated responding in mice

Habit and motivation are thought to be separate processes, with motivated behavior often considered to be goal directed, whereas habits are defined by the absence of goal-directed control over behavior. However, there has been increasing interrogation of the binary nature of habitual versus goal-directed behavior. Furthermore, although drug and alcohol exposure can promote the formation of habits, drug seeking itself can also be highly flexible, pointing toward the need for complex consideration of the parallel processes that drive behavior. The goal of the current study was to determine whether there was a relation between motivation-as measured by progressive ratio-and habit-as measured by contingency degradation-and whether this relation was affected by ethanol exposure history and sex. The results showed that these measures were positively correlated such that greater contingency insensitivity was associated with achieving higher break points on the progressive-ratio task. However, this relation depended on reinforcement schedule history, ethanol exposure history, and sex. These point to potential relations between measures of habit and motivation and stress the importance of carefully parsing behavioral findings and assays. These findings are also expected to inform future substance use research, as drug history may affect these relations.

Drug memory reconsolidation: from molecular mechanisms to the clinical context

Since its rediscovery at the beginning of the 21st Century, memory reconsolidation has been proposed to be a therapeutic target for reducing the impact of emotional memories that can go awry in mental health disorders such as drug addiction (substance use disorder, SUD). Addiction can be conceptualised as a disorder of learning and memory, in which both pavlovian and instrumental learning systems become hijacked into supporting drug-seeking and drug-taking behaviours. The past two decades of research have characterised the details of the molecular pathways supporting the reconsolidation of pavlovian cue-drug memories, with more recent work indicating that the reconsolidation of instrumental drug-seeking memories also relies upon similar mechanisms. This narrative review considers what is known about the mechanisms underlying the reconsolidation of pavlovian and instrumental memories associated with drug use, how these approaches have translated to experimental medicine studies, and the challenges and opportunities for the clinical use of reconsolidation-based therapies.

Sex-biased effects of outcome devaluation by sensory-specific satiety on Pavlovian-conditioned behavior

Goal-directed behavior relies on accurate mental representations of the value of expected outcomes. Disruptions to this process are a central feature of several neuropsychiatric disorders, including addiction. Goal-directed behavior is most frequently studied using instrumental paradigms paired with outcome devaluation, but cue-evoked behaviors in Pavlovian settings can also be goal-directed and therefore sensitive to changes in outcome value. Emerging literature suggests that male and female rats may differ in the degree to which their Pavlovian-conditioned responses are goal-directed, but interpretation of these findings is complicated by the tendency of female and male rats to engage in distinct types of Pavlovian responses when trained with localizable cues. Here, we used outcome devaluation via sensory-specific satiety to assess the behavioral responses in male and female Long Evans rats trained to respond to an auditory CS (conditioned stimulus) in a Pavlovian-conditioning paradigm. We found that satiety-induced devaluation led to a decrease in behavioral responding to the reward-predictive CS, with males showing an effect on both port entry latency and probability and females showing an effect only on port entry probability. Overall, our results suggest that outcome devaluation affects Pavlovian-conditioned responses in both male and female rats, but that females may be less sensitive to outcome devaluation.

α4-Containing GABAA Receptors on DRD2 Neurons of the Nucleus Accumbens Mediate Instrumental Responding for Conditioned Reinforcers and Its Potentiation by Cocaine

Extrasynaptic GABAA receptors (GABAARs) composed of α4, β, and δ subunits mediate GABAergic tonic inhibition and are potential molecular targets in the modulation of behavioral responses to natural and drug rewards. These GABAARs are highly expressed within the nucleus accumbens (NAc), where they influence the excitability of the medium spiny neurons. Here, we explore their role in modulating behavioral responses to food-conditioned cues and the behavior-potentiating effects of cocaine. α4-Subunit constitutive knock-out mice (α4-/-) showed higher rates of instrumental responding for reward-paired stimuli in a test of conditioned reinforcement (CRf). A similar effect was seen following viral knockdown of GABAAR α4 subunits within the NAc. Local infusion of the α4βδ-GABAAR-preferring agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol; Gaboxadol) into the NAc had no effect on responding when given alone but reduced cocaine potentiation of responding for conditioned reinforcers in wild-type, but not α4-/- mice. Finally, specific deletion of α4-subunits from dopamine D2, but not D1, receptor-expressing neurons (DRD2 and DRD1 neurons), mimicked the phenotype of the constitutive knockout, potentiating CRf responding, and blocking intra-accumbal THIP attenuation of cocaine-potentiated CRf responding. These data demonstrate that α4-GABAAR-mediated inhibition of DRD2 neurons reduces instrumental responding for a conditioned reinforcer and its potentiation by cocaine and emphasize the importance of GABAergic signaling within the NAc in mediating the effects of cocaine.

Outcome devaluation by sensory-specific satiety alters Pavlovian-conditioned behavior in male and female rats

Goal-directed behavior relies on accurate mental representations of the value of expected outcomes. Disruptions to this process are a central feature of several neuropsychiatric disorders, including addiction. Goal-directed behavior is most frequently studied using instrumental paradigms paired with outcome devaluation, but cue-evoked behaviors in Pavlovian settings can also be goal-directed and therefore sensitive to changes in outcome value. Emerging literature suggests that male and female rats may differ in the degree to which their Pavlovian-conditioned responses are goal-directed, but interpretation of these findings is complicated by the tendency of female and male rats to engage in distinct types of Pavlovian responses when trained with localizable cues. Here, we used outcome devaluation via sensory-specific satiety to assess the behavioral responses in male and female Long Evans rats trained to respond to an auditory CS (conditioned stimulus) in a Pavlovian-conditioning paradigm. We found that satiety-induced devaluation led to a decrease in behavioral responding to the reward-predictive CS, with males showing an effect on both port entry latency and probability and females showing an effect only on port entry probability. Overall, our results suggest that outcome devaluation affects Pavlovian-conditioned responses in both male and female rats, but that females may be less sensitive to outcome devaluation.

Transdiagnostic Approach and Obsessive Compulsive Disorder

The categorical approach of traditional psychiatric nosology has been a forceful approach for a very long time for explaining psychological disorders which are defined by symptom based diagnostic categories. However, in recent years, the importance of the "transdiagnostic" approach which is a new classification system is increasing. The transdiagnostic approach aims to examine dimensionally the common cognitive, behavioral, interpersonal and biological processes underlying many psychopathologies away from the categorical approach that classifies psychopathologies according to observable symptoms. This approach intends to treat the disorders through the common underlying processes and risk factors, thus heterogeneous and comorbid symptoms are better addressed and diagnostic categories that may change during treatment are avoided. In this review study, the current problems in diagnosing based on classification and gaps in the field were examined, and the approach itself was proposed as a solution. RDoC (Research Domain Criteria) which is a new classification system for psychiatric disorders within the scope of the approach, has created a new structure using modern research approaches in genetics, neuroscience and behavioral sciences. In the present study, the definition and emergence of the transdiagnostic approach, obsessive compulsive disorder and RDoC in the context of transdiagnostic approach and transdiagnostic treatment are explained. This review is intended to be a resource for both basic psychopathology research and the development of treatment methods within the framework of a transdiagnostic approach.

DARPP-32 cells and neuropil define striosomal system and isolated matrix cells in human striatum

The dorsal striatum forms a central node of the basal ganglia interconnecting the neocortex and thalamus with circuits modulating mood and movement. Striatal projection neurons (SPNs) include relatively intermixed populations expressing D1-type or D2-type dopamine receptors (dSPNs and iSPNs) that give rise to the direct (D1) and indirect (D2) output systems of the basal ganglia. Overlaid on this organization is a compartmental organization, in which a labyrinthine system of striosomes made up of sequestered SPNs is embedded within the larger striatal matrix. Striosomal SPNs also include D1-SPNs and D2-SPNs, but they can be distinguished from matrix SPNs by many neurochemical markers. In the rodent striatum the key signaling molecule, DARPP-32, is a exception to these compartmental expression patterns, thought to befit its functions through opposite actions in both D1- and D2-expressing SPNs. We demonstrate here, however, that in the dorsal human striatum, DARPP-32 is concentrated in the neuropil and SPNs of striosomes, especially in the caudate nucleus and dorsomedial putamen, relative to the matrix neuropil in these regions. The generally DARPP-32-poor matrix contains scattered DARPP-32-positive cells. DARPP-32 cell bodies in both compartments proved negative for conventional intraneuronal markers. These findings raise the potential for specialized DARPP-32 expression in the human striosomal system and in a set of DARPP-32-positive neurons in the matrix. If DARPP-32 immunohistochemical positivity predicts differential functional DARPP-32 activity, then the distributions demonstrated here could render striosomes and dispersed matrix cells susceptible to differential signaling through cAMP and other signaling systems in health and disease. DARPP-32 is highly concentrated in cells and neuropil of striosomes in post-mortem human brain tissue, particularly in the dorsal caudate nucleus. Scattered DARPP-32-positive cells are found in the human striatal matrix. Calbindin and DARPP-32 do not colocalize within every spiny projection neuron in the dorsal human caudate nucleus.

A neuromarker for drug and food craving distinguishes drug users from non-users

Craving is a core feature of substance use disorders. It is a strong predictor of substance use and relapse and is linked to overeating, gambling, and other maladaptive behaviors. Craving is measured via self-report, which is limited by introspective access and sociocultural contexts. Neurobiological markers of craving are both needed and lacking, and it remains unclear whether craving for drugs and food involve similar mechanisms. Across three functional magnetic resonance imaging studies (n = 99), we used machine learning to identify a cross-validated neuromarker that predicts self-reported intensity of cue-induced drug and food craving (P < 0.0002). This pattern, which we term the Neurobiological Craving Signature (NCS), includes ventromedial prefrontal and cingulate cortices, ventral striatum, temporal/parietal association areas, mediodorsal thalamus and cerebellum. Importantly, NCS responses to drug versus food cues discriminate drug users versus non-users with 82% accuracy. The NCS is also modulated by a self-regulation strategy. Transfer between separate neuromarkers for drug and food craving suggests shared neurobiological mechanisms. Future studies can assess the discriminant and convergent validity of the NCS and test whether it responds to clinical interventions and predicts long-term clinical outcomes.

The relationship between sleep and appetitive conditioning: A systematic review and meta-analysis

This systematic review and meta-analysis (PROSPERO registration animal/human studies: CRD42021234793/CRD42021234790) examined the relationship between sleep and appetitive conditioning. Inclusion criteria included: a) appetitive conditioning paradigm; b) measure of conditioning; c) sleep measurement and/or sleep loss; d) human and/etor non-human animal samples; and e) written in English. Searches of seven databases returned 3777 publications. The final sample consisted of 42 studies using primarily animal samples and involving food- and drug-related conditioning tasks. We found sleep loss disrupted appetitive conditioning of food rewards (p < 0.001) but potentiated appetitive conditioning of drug rewards (p < 0.001). Furthermore, sleep loss negatively impacted extinction learning irrespective of the reward type. Post-learning sleep was associated with increases in REM sleep (p = 0.02). Findings suggest sleep loss potentiates the impact of psychoactive substances in a manner likely to produce an increased risk of problematic substance use. In obese/overweight populations, sleep loss may be associated with deficits in the conditioning and extinction of reward-related behaviours. Further research should assess the relationship between sleep and appetitive conditioning in humans.

No significant effect of frequent online sexual behaviour on Pavlovian-to-instrumental transfer (PIT): Implications for compulsive sexual behaviour disorder

Reward based learning is broadly acknowledged to underpin the development and maintenance of addictive behaviour although the mechanism in sexual compulsivity is less understood. Using a Pavlovian-to-Instrumental Transfer (PIT) task we tested whether the motivational aspect of conditioned Pavlovian conditioned stimulus invigorated instrumental responding in relation to specific compatible monetary rewards. Performance on the task was analysed between two groups of males based on Low (N = 38) and High (N = 41) self-report online sexual behaviour (OSB). Psychometric tests including sexual compulsivity scale and behavioural activation/behavioural inhibition (BIS/BAS) were also administered to determine the relationship between OSB and general reward sensitivity. We show clear evidence of acquisition in the Pavlovian and instrumental conditioning phases. Specific transfer effect was greater in the High-OSB group although the difference compared to the Low-OSB group was non-significant. OSB negatively correlated with both BIS and BAS indicative of introversion and low reward sensitivity. OSB positively correlated with sexual compulsivity although it is unclear whether individuals in the High-OSB group considered their behaviour either excessive or problematic. These findings contribute to the ongoing debate regarding the nature of problematic OSB. Fundamental differences in motivational characteristics and mechanism contributing to compulsive behaviour in relation to high-OSB might indicate incompatibility with behavioural addiction models. PIT was not enhanced in high-OSB by appetitive conditioning, although problematic OSB could stem from failure to inhibit actions. Further research should investigate whether aversive conditioning differentially affects responding in high-OSB individuals, potentially explaining perseverant behaviour despite negative consequences.

Cortical dopamine reduces the impact of motivational biases governing automated behaviour

Motivations shape our behaviour: the promise of reward invigorates, while in the face of punishment, we hold back. Abnormalities of motivational processing are implicated in clinical disorders characterised by excessive habits and loss of top-down control, notably substance and behavioural addictions. Striatal and frontal dopamine have been hypothesised to play complementary roles in the respective generation and control of these motivational biases. However, while dopaminergic interventions have indeed been found to modulate motivational biases, these previous pharmacological studies used regionally non-selective pharmacological agents. Here, we tested the hypothesis that frontal dopamine controls the balance between Pavlovian, bias-driven automated responding and instrumentally learned action values. Specifically, we examined whether selective enhancement of cortical dopamine either (i) enables adaptive suppression of Pavlovian control when biases are maladaptive; or (ii) non-specifically modulates the degree of bias-driven automated responding. Healthy individuals (n = 35) received the catechol-o-methyltransferase (COMT) inhibitor tolcapone in a randomised, double-blind, placebo-controlled cross-over design, and completed a motivational Go NoGo task known to elicit motivational biases. In support of hypothesis (ii), tolcapone globally decreased motivational bias. Specifically, tolcapone improved performance on trials where the bias was unhelpful, but impaired performance in bias-congruent conditions. These results indicate a non-selective role for cortical dopamine in the regulation of motivational processes underpinning top-down control over automated behaviour. The findings have direct relevance to understanding neurobiological mechanisms underpinning addiction and obsessive-compulsive disorders, as well as highlighting a potential trans-diagnostic novel mechanism to address such symptoms.

Involvement of the ghrelin system in the maintenance and reinstatement of cocaine-motivated behaviors: a role of adrenergic action at peripheral β1 receptors

Cocaine addiction is a significant medical and public concern. Despite decades of research effort, development of pharmacotherapy for cocaine use disorder remains largely unsuccessful. This may be partially due to insufficient understanding of the complex biological mechanisms involved in the pathophysiology of this disorder. In the present study, we show that: (1) elevation of ghrelin by cocaine plays a critical role in maintenance of cocaine self-administration and cocaine-seeking motivated by cocaine-conditioned stimuli; (2) acquisition of cocaine-taking behavior is associated with the acquisition of stimulatory effects of cocaine by cocaine-conditioned stimuli on ghrelin secretion, and with an upregulation of ghrelin receptor mRNA levels in the ventral tegmental area (VTA); (3) blockade of ghrelin signaling by pretreatment with JMV2959, a selective ghrelin receptor antagonist, dose-dependently inhibits reinstatement of cocaine-seeking triggered by either cocaine or yohimbine in behaviorally extinguished animals with a history of cocaine self-administration; (4) JMV2959 pretreatment also inhibits brain stimulation reward (BSR) and cocaine-potentiated BSR maintained by optogenetic stimulation of VTA dopamine neurons in DAT-Cre mice; (5) blockade of peripheral adrenergic β1 receptors by atenolol potently attenuates the elevation in circulating ghrelin induced by cocaine and inhibits cocaine self-administration and cocaine reinstatement triggered by cocaine. These findings demonstrate that the endogenous ghrelin system plays an important role in cocaine-related addictive behaviors and suggest that manipulating and targeting this system may be viable for mitigating cocaine use disorder.

Brain tract structure predicts relapse to stimulant drug use

Diffusion tractography allows identification and measurement of structural tracts in the human brain previously associated with motivated behavior in animal models. Recent findings indicate that the structural properties of a tract connecting the midbrain to nucleus accumbens (NAcc) are associated with a diagnosis of stimulant use disorder (SUD), but not relapse. In this preregistered study, we used diffusion tractography in a sample of patients treated for SUD (n = 60) to determine whether qualities of tracts projecting from medial prefrontal, anterior insular, and amygdalar cortices to NAcc might instead foreshadow relapse. As predicted, reduced diffusion metrics of a tract projecting from the right anterior insula to the NAcc were associated with subsequent relapse to stimulant use, but not with previous diagnosis. These findings highlight a structural target for predicting relapse to stimulant use and further suggest that distinct connections to the NAcc may confer risk for relapse versus diagnosis.

Placenta-Derived Mesenchymal-like Adherent Stromal Cells as an Effective Cell Therapy for Cocaine Addiction in a Rat Model

Recent research points to mesenchymal stem cells’ potential for treating neurological disorders, especially drug addiction. We examined the longitudinal effect of placenta-derived mesenchymal stromal-like cells (PLX-PAD) in a rat model for cocaine addiction. Sprague–Dawley male rats were trained to self-administer cocaine or saline daily until stable maintenance. Before the extinction phase, PLX-PAD cells were administered by intracerebroventricular or intranasal routes. Neurogenesis was evaluated, as was behavioral monitoring for craving. We labeled the PLX-PAD cells with gold nanoparticles and followed their longitudinal migration in the brain parallel to their infiltration of essential peripheral organs both by micro-CT and by inductively coupled plasma-optical emission spectrometry. Cell locations in the brain were confirmed by immunohistochemistry. We found that PLX-PAD cells attenuated cocaine-seeking behavior through their capacity to migrate to specific mesolimbic regions, homed on the parenchyma in the dentate gyrus of the hippocampus, and restored neurogenesis. We believe that intranasal cell therapy is a safe and effective approach to treating addiction and may offer a novel and efficient approach to rehabilitation.

Cyclic estrogen and progesterone during instrumental acquisition contributes to habit formation in female rats

Habit formation is thought to involve two parallel processes that are mediated by distinct neural substates: one that suppresses goal-directed behavior, and one that facilitates stimulus-response (S-R) learning, which underscores habitual behavior. In previous studies we showed that habitual responding emerges early during instrumental training in gonadally-intact female, compared to male, rats. The present study aimed to determine the role of ovarian hormones during instrumental acquisition in the transition from goal-directed to habitual behavior in female rats. Ovariectomized (OVX) female rats were given subcutaneous silastic capsules that released low levels of 17-β estradiol (E2) to maintain estrogen receptor availability. Rats were assigned to one of three hormone treatment conditions: no additional hormone replacement (Control group), replacement with high E2 (High E2 group), or replacement with high E2 followed by progesterone (High E2 + P4 group). Hormone replacement occurred twice during acquisition to mimic natural hormone fluctuations. At test, the Control and High E2 groups demonstrated responding that was sensitive to devaluation by lithium chloride-induced illness, indicating goal-directed behavior. In contrast, the High E2 + P4 group exhibited a pattern of devaluation-insensitive, habitual responding, that suggested the suppression of goal-directed processes. In a follow-up experiment, similar procedures were conducted, however during acquisition, OVX rats were given cyclic high E2 plus medroxy-progesterone (MPA), a form of progesterone that does not metabolize to neuroactive metabolites. In this group, goal-directed behavior was observed. These data indicate that habit formation is not facilitated in low estrogen states, nor in the presence of cyclic high E2. However, cyclic high E2, together with progesterone during acquisition, appears to facilitate the early emergence of habitual responding. Furthermore, these data suggest that a neuroactive progesterone metabolite, like allopregnanolone, in combination with high cyclic E2, supports this phenomenon.

Chronic ∆-9-tetrahydrocannabinol administration delays acquisition of schedule-induced drinking in rats and retains long-lasting effects

RATIONALE

Schedule-induced drinking (SID) is a behavioural phenomenon characterized by an excessive and repetitive drinking pattern with a distinctive temporal distribution that has been proposed as a robust and replicable animal model of compulsivity. Despite cannabis currently being the most widely consumed illicit drug, with growing interest in its clinical applications, little is known about the effects of ∆-9-tetrahydrocannabinol (THC) on SID.

OBJECTIVES

The effects of chronic and acute THC administration on SID acquisition, maintenance and extinction were studied, as were the effects of such administrations on the distinctive temporal distribution pattern of SID.

METHODS

THC (5 mg/kg i.p.), or the corresponding vehicle, was administered to adult Wistar rats for 14 days in a row. Subsequently, THC effects on SID acquisition were tested during 21 sessions using a 1-h fixed-time 60-s food delivery schedule. Acute effects of THC were also evaluated after SID development. Finally, two extinction sessions were conducted to assess behavioural persistence.

RESULTS

The results showed that previous chronic THC treatment delayed SID acquisition and altered the distinctive behavioural temporal distribution pattern during sessions. Moreover, acute THC administration after SID development decreased SID performance in animals chronically pre-treated with the drug. No great persistence effects were observed during extinction in animals pre-treated with THC.

CONCLUSIONS

These results suggest that chronic THC affects SID development, confirming that it can disrupt learning, possibly causing alterations in time estimation, and also leads to animals being sensitized when they are re-exposed to the drug after long periods without drug exposure.

Tracing 20 years of research on problematic use of the internet and social media: Theoretical models, assessment tools, and an agenda for future work

Over the past two decades, there has been increasing interest in the impact of internet use and growing concern about whether problematic use of the internet (PUI) constitutes an addiction. Despite the growing number of studies investigating PUI and PUI subtypes, its conceptualization and inclusion in a classification system have not been possible yet. Several models aimed at inspiring clinical research and practice have proposed possible mechanisms involved in PUI and problematic use of social media, and multiple self-report instruments have been consequentially developed. The diversity of theoretical models and instruments currently hinders standardized assessment procedures across studies and, in turn, their comparability. The purpose of the present overview is to highlight the current conceptualization and assessment of both PUI and problematic use of social media, in order to critically discuss the existing fragmentation in the field and the need to achieve conceptual convergence. Two suggestions for future directions are also provided, i.e., define diagnostic criteria by bottom-up and top-down processes and develop a psychobiological hypothesis including the description of higher-order mechanisms involved in PUI and not other psychopathological conditions (e.g., the multiple available internet-related cues and outcomes that may lead to parallel forms of associative learning; probabilities of obtaining internet-related reinforcements; and intrinsic motivation processes).

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.

Diminished cognitive control in Internet gaming disorder: A multimodal approach with magnetic resonance imaging and real-time heart rate variability

OBJECTIVE

Recently, the addiction to online games, classified as Internet gaming disorder (IGD) on DSM-V, has emerged as an important mental health problem. The loss of control over gaming in IGD is associated with diminished cognitive control. This study aimed to link the neurobiological mechanism reflected by brain imaging and the diminished cognitive control reflected by heart rate variability (HRV) measurements during real-time gameplay.

METHODS

HRV was assessed in 33 young males with IGD and 29 controls while playing their favorite games. Seed-based functional connectivity (FC) was evaluated in the dorsolateral prefrontal cortex, anterior cingulate cortex, and dorsal striatum. Associations between HRV and alterations in FC were tested.

RESULTS

Individuals with IGD showed a reduction of high-frequency HRV during real-time gaming, which is correlated with self-reported severity of IGD. Subjects with IGD showed decreased FC between the right dorsolateral prefrontal cortex and the right inferior frontal gyrus, corresponding to the cognitive control network. They showed decreased FC between the right anterior cingulate cortex and the superior parietal lobule. They also showed increased FC between the left dorsal putamen and the postcentral gyrus, corresponding to the sensorimotor network. Game-related high-frequency HRV was correlated with dorsolateral prefrontal cortex-inferior frontal gyrus connectivity.

CONCLUSION

The diminished cognitive control reflected by HRV measurements during real-time gameplay was associated with FC alterations, involving a weak FC in the cognitive control network. Individuals with IGD may have less cognitive control, particularly when playing games, and consequently end up playing games in a habitual manner rather than in a goal-oriented manner.

The Effect of Dehydroepiandrosterone Treatment on Neurogenesis, Astrogliosis and Long-Term Cocaine-Seeking Behavior in a Cocaine Self-Administration Model in Rats

Cocaine addiction is an acquired behavioral state developed in vulnerable individuals after cocaine exposure. It is characterized by compulsive drug-seeking and high vulnerability to relapse even after prolonged abstinence, associated with decreased neurogenesis in the hippocampus. This addictive state is hypothesized to be a form of “memory disease” in which the drug exploits the physiological neuroplasticity mechanisms that mediate regular learning and memory processes. Therefore, a major focus of the field has been to identify the cocaine-induced neuroadaptations occurring in the usurped brain’s reward circuit. The neurosteroid dehydroepiandrosterone (DHEA) affects brain cell morphology, differentiation, neurotransmission, and memory. It also reduces drug-seeking behavior in an animal model of cocaine self-administration. Here, we examined the long-lasting effects of DHEA treatment on the attenuation of cocaine-seeking behavior. We also examined its short- and long-term influence on hippocampal cells architecture (neurons and astrocytes). Using a behavioral examination, immunohistochemical staining, and diffusion tensor imaging, we found an immediate effect on tissue density and activation of astrocytes, which has a continuous beneficial effect on neurogenesis and tissue organization. This research emphasizes the requites concert between astrocytes and neurons in the rehabilitation from addiction behavior. Thus, DHEA may serve as a treatment that corrects brain damage following exposure to and abstinence from cocaine.

Infralimbic cortex functioning across motivated behaviors: Can the differences be reconciled?

The rodent infralimbic cortex (IL) is implicated in higher order executive functions such as reward seeking and flexible decision making. However, the precise nature of its role in these processes is unclear. Early evidence indicated that the IL promotes the extinction and ongoing inhibition of fear conditioning and cocaine seeking. However, evidence spanning other behavioral domains, such as natural reward seeking and habit-based learning, suggests a more nuanced understanding of IL function. As techniques have advanced and more studies have examined IL function, identifying a unifying explanation for its behavioral function has become increasingly difficult. Here, we discuss evidence of IL function across motivated behaviors, including associative learning, drug seeking, natural reward seeking, and goal-directed versus habit-based behaviors, and emphasize how context-specific encoding and heterogeneous IL neuronal populations may underlie seemingly conflicting findings in the literature. Together, the evidence suggests that a major IL function is to facilitate the encoding and updating of contingencies between cues and behaviors to guide subsequent behaviors.

Metabotropic group II glutamate receptors in the basolateral amygdala mediate cue-triggered increases in incentive motivation

RATIONALE

Reward-associated cues can trigger incentive motivation for reward and invigorate reward-seeking behaviour via Pavlovian-to-instrumental transfer (PIT). Glutamate signaling within the basolateral amygdala (BLA) modulates cue-triggered increases in incentive motivation. However, the role of BLA metabotropic group II glutamate (mGlu_2/3) receptors is largely unknown.

OBJECTIVES

In Experiment 1, we characterized cue-triggered increases in incentive motivation for water reward using the PIT paradigm. In Experiment 2, we assessed the influence of intra-BLA microinjections of the mGlu_2/3 receptor agonist LY379268 on this effect.

METHODS

Water-restricted male Sprague-Dawley rats learned to press a lever for water. Separately, they learned to associate one of two auditory cues with free water. On test days, rats could lever press under extinction conditions (no water), with intermittent, non-contingent CS+ and CS- presentations. In Experiment 1, rats were tested under baseline conditions. In Experiment 2, rats received intra-BLA microinjections of LY379268 (0, 3 and 6 [Formula: see text]g/hemisphere) before testing.

RESULTS

Across experiments, CS+, but not CS-, presentations increased water-associated lever pressing during testing, even though responding was reinforced neither by water nor the CS+. Intra-BLA LY379268 abolished both CS+ potentiated pressing on the water-associated lever and CS+ evoked conditioned approach to the site of water delivery. LY379268 did not influence locomotion or instrumental and Pavlovian response rates during intervals between CS presentations or during the CS-, indicating no motor effects.

CONCLUSIONS

mGlu_2/3 receptor activity in the BLA mediates cue-triggered potentiation of incentive motivation for reward, suppressing both cue-induced increases in instrumental pursuit of the reward and anticipatory approach behaviour.

Molecular Mechanism of Neuroprotective Effect of Melatonin on Morphine Addiction and Analgesic Tolerance: an Update

Drug addiction is a global health problem and continues to place an enormous financial burden on society. This addiction is characterized by drug dependence sensitization and craving. Morphine has been widely used for pain relief, but chronic administration of morphine causes analgesic tolerance, hyperalgesia, and addiction, all of which limit its clinical usage. Alterations of multiple molecular pathways have been reported to be involved in the development of drug addiction, including mitochondrial dysfunction, excessive oxidative stress and nitric oxide stress, and increased levels of apoptosis, autophagy, and neuroinflammation. Preclinical and clinical studies have shown that the co-administration of melatonin with morphine leads to a reversal of these affected pathways. In addition, murine models have shown that melatonin improves morphine-induced analgesic tolerance and addictive behaviors, such as behavioral sensitization, reward effect, and physical dependence. In this review, we attempt to summarize the recent findings about the beneficial effect and molecular mechanism of melatonin on mitochondrial dysfunction, uncontrolled autophagy, and neuroinflammation in morphine addiction and morphine analgesic tolerance. We propose that melatonin might be a useful supplement in the treatment opiate abuse.

Altered functional connectivity of the dorsal attention network among problematic social network users

Many smartphone users spend excessive amounts of time online and cannot control their behavior, and the addictive overuse of social-networking services has been shown to be associated with diminished executive control. Attentional control is a cognitive process crucial to exerting executive functions. The purpose of this study was to investigate functional connectivity (FC) characteristics of attention networks in problematic social-network users. We performed seed-based resting-state FC analyses for 29 males and 10 females with excessive social network use and 32 healthy males and 17 healthy females. The right intraparietal sulcus and frontal eye fields were considered seeds of the dorsal attention network (DAN), and the right temporoparietal junction and ventral frontal cortex were considered seeds of the ventral attention network (VAN). Clinical characteristics predictive of FC findings in problematic social network users were identified through hierarchical multiple regression analysis. In FC analysis with DAN seeds, FC between the right intraparietal sulcus and the right middle occipital gyrus was stronger in problematic social network users than in controls, and FC between the right frontal eye field and the right dorsolateral prefrontal cortex was weaker than that in controls. There was no significant difference between the groups in FC analysis with VAN seeds. Hierarchical regression analyses showed that usage times on social networking platforms significantly predicted the negative effects on the strength of FC between the intraparietal sulcus and the dorsolateral prefrontal cortex. These findings indicated that problematic social network use reflects changes in the neural circuits underlying attentional control. Weaking of prefrontal control for attention networks would have a significant impact on failure to control one's time spent on social networks.

Rapamycin Improves Spatial Learning Deficits, Vulnerability to Alcohol Addiction and Altered Expression of the GluN2B Subunit of the NMDA Receptor in Adult Rats Exposed to Ethanol during the Neonatal Period

Ethanol exposure during pregnancy alters the mammalian target of rapamycin (mTOR) signaling pathway in the fetal brain. Hence, in adult rats exposed to ethanol during the neonatal period, we investigated the influence of rapamycin, an mTOR Complex 1 (mTORC1) inhibitor, on deficits in spatial memory and reversal learning in the Barnes maze task, as well as the ethanol-induced rewarding effects (1.0 or 1.5 g/kg) using the conditioning place preference (CPP) paradigm. Rapamycin (3 and 10 mg/kg) was given before intragastric ethanol (5 g/kg/day) administration at postnatal day (PND)4–9 (an equivalent to the third trimester of human pregnancy). Spatial memory/reversal learning and rewarding ethanol effect were evaluated in adult (PND60–70) rats. Additionally, the impact of rapamycin pre-treatment on the expression of the GluN2B subunit of NMDA receptor in the brain was assessed in adult rats. Our results show that neonatal ethanol exposure induced deficits in spatial memory and reversal learning in adulthood, but the reversal learning outcome may have been due to spatial learning impairments rather than cognitive flexibility impairments. Furthermore, in adulthood the ethanol treated rats were also more sensitive to the rewarding effect of ethanol than the control group. Rapamycin prevented the neonatal effect of ethanol and normalized the GluN2B down-regulation in the hippocampus and the prefrontal cortex, as well as normalized this subunit’s up-regulation in the striatum of adult rats. Our results suggest that rapamycin and related drugs may hold promise as a preventive therapy for fetal alcohol spectrum disorders.

Neural Substrates and Circuits of Drug Addiction

Drug addiction is a chronic relapsing disorder, and a significant amount of research has been devoted to understand the factors that contribute to the development, loss of control, and persistence of compulsive addictive behaviors. In this review, we provide an overview of various theories of addiction to drugs of abuse and the neurobiology involved in elements of the addiction cycle. Specific focus is devoted to the role of the mesolimbic pathway in acute drug reinforcement and occasional drug use, the role of the mesocortical pathway and associated areas (e.g., the dorsal striatum) in escalation/dependence, and the contribution of these pathways and associated circuits to conditioned responses, drug craving, and loss of behavioral control that may underlie drug relapse. By enhancing the understanding of the neurobiological factors that mediate drug addiction, continued preclinical and clinical research will aid in the development of novel therapeutic interventions that can serve as effective long-term treatment strategies for drug-dependent individuals.

Addiction history moderates the effect of prefrontal 10-Hz transcranial alternating current stimulation on habitual action selection

Individuals with substance use disorders (SUDs) transition more quickly from goal-directed to habitual action-selection, but the neural mechanisms underlying this phenomenon remain unclear. Data from animal models suggest that drugs of abuse can modify the neurocircuits that regulate action-selection, enhancing circuits that drive inflexible, habit-based stimulus-response (S-R) action-selection and weakening circuits that drive flexible, goal-directed actions. Here, we tested the effect of bilateral 10-Hz transcranial alternating current stimulation (10Ηz-tACs) of the dorsolateral prefrontal cortex on action-selection in men and women with a SUD history and an age- and sex-matched control group. We tested the hypothesis that true 10Ηz-tACS versus active sham stimulation would reduce perseverative errors after changed response contingencies for well-learned S-R associations, reflecting reduced habit-based action-selection, specifically in the SUD group. We found that 10 Hz-tACS increased perseverative errors in the control group, but in the SUD group, 10 Hz-tACS effects on perseverative errors depended on substance abuse duration: a longer addiction history was associated with a greater reduction of perseverative errors. These results suggest that 10Ηz-tACs altered circuit level dynamics regulating behavioral flexibility, and provide a foundation for future studies to test stimulation site, frequency, and timing specificity. Moreover, these data suggest that chronic substance abuse is associated with altered circuit dynamics that are ameliorated by 10Ηz-tACs. Determining the generalizability of these effects and their duration merits investigation as a direction for novel therapeutic interventions. These findings are timely based on growing interest in transcranial stimulation methods for treating SUDs.NEW & NOTEWORTHY Treating the executive dysfunction associated with addiction is hampered by redundancies in pharmacological regulation of different behavioral control circuits. Thus, nonpharmacological interventions hold promise for addiction treatment. Here, we show that, among people with an addiction history, 10-Hz transcranial alternating current stimulation (10Hz-tACS) of the dorsolateral prefrontal cortex can reduce habitual actions. The fact that 10Hz-tACS can regulate behavioral flexibility suggests its possible utility in reducing harmful habitual actions.

Prefrontal cortex nicotinic receptor inhibition by methyllycaconitine impaired cocaine-associated memory acquisition and retrieval

Cocaine administration has been shown to induce plastic changes in the medial prefrontal cortex (mPFC), which could represent a mechanism by which cocaine facilitates the association between cocaine rewarding effects with contextual cues. Nicotinic acetylcholine receptors (nAChRs) in the mPFC have critical roles in cognitive function including attention and memory and are key players in plasticity processes. However, whether nAChRs in the mPFC are required for the acquisition and maintenance of cocaine-associated memories is still unknown. To assess this question, we used the conditioning place preference (CPP) model to study the effect of intra-mPFC infusion of methyllycaconitine, a selective antagonist of α7 nAChRs, on the acquisition, consolidation and expression of cocaine-associated memory in adult rats. Our findings reveal that mPFC α7 nAChRs activation is necessary for the acquisition and retrieval, but not consolidation, of cocaine induced CPP. Moreover, cocaine-induced sensitization during CPP conditioning sessions was abolished by methyllycaconitine infusion in the mPFC. Together, these results identify mPFC α7 nAChRs as critical players involved in both acquiring and retrieving cocaine-associated memories. Considering that drug seeking often depends on the association between drug-paired cues and the rewarding effects of the drug, α7 nAChRs in the mPFC could be considered as potential targets for the prevention or treatment of cocaine use disorder.

Cocaine-Seeking Behavior Induced by Orexin A Administration in the Posterior Paraventricular Nucleus of the Thalamus Is Not Long-Lasting: Neuroadaptation of the Orexin System During Cocaine Abstinence

Hypothalamic orexin (Orx) projections to the paraventricular nucleus of the thalamus (PVT) have received growing interest because of their role in drug-seeking behavior. Using an established model of cocaine dependence (i.e., long access [LgA] to cocaine), we previously showed that OrxA injections in the posterior PVT (pPVT) reinstated extinguished cocaine-seeking behavior in rats after an intermediate period of abstinence (2-3 weeks). Considering the long-lasting nature of drug-seeking behavior, the present study examined whether the priming effect of intra-pPVT OrxA administration was preserved after a period of protracted abstinence (4-5 weeks) in rats that self-administered cocaine under LgA conditions. Furthermore, to better understand whether a history of cocaine dependence affects the Orx system-particularly the hypothalamic Orx↔pPVT connection-the number of Orx-expressing cells in the lateral hypothalamus (LH), dorsomedial hypothalamus (DMH), and perifornical area (PFA) and number of orexin receptor 1 (OrxR1)- and OrxR2-expressing cells in the pPVT were quantified. Orexin A administration in the pPVT induced cocaine-seeking behavior after intermediate abstinence, as reported previously. At protracted abstinence, however, the priming effect of OrxA was absent. A higher number of cells that expressed Orx was observed in the LH/DMH/PFA at both intermediate and protracted abstinence. In the pPVT, the number of OrxR2-expressing cells was significantly higher only at intermediate abstinence, with no changes in the number of OrxR1-expressing cells. These data build on our previous findings that the hypothalamic Orx↔pPVT connection is strongly recruited shortly after cocaine abstinence and demonstrate that the priming effect of OrxA is not long lasting. Furthermore, these findings suggest that throughout abstinence, the Orx↔pPVT connection undergoes neuroadaptive changes, reflected by alterations of the number of OrxR2-expressing cells in the pPVT.

Early-life adversity selectively interrupts the dendritic differentiation of dorsolateral striatal neurons in male mice

The effects of early-life adversity (ELA) on dendritic differentiation of striatal neurons were investigated in the dorsal striatum including the dorsomedial striatum and dorsolateral striatum (DMS and DLS, respectively). An animal model of ELA was created by changing the growth environment of newborn mouse pups by giving limited bedding and nesting materials from postnatal day 2 to day 9 (P2-P9). One week after the stress paradigm (P16), the dendritic branches and spines of striatal spiny neurons as well as the synapses represented by postsynaptic density protein-95 (PSD-95) in DMS and DLS were stereologically analyzed. Adverse experience in early life selectively affected the spiny neurons in DLS, leading to abundant proximal dendritic branches and an increased number of filopodia-like protrusions, but a reduced number of dendritic spines. The selective effects of stress on neurons in DLS were further identified by reduced expression of PSD-95, including a reduced optical density of PSD-95 immunoreactivity and fewer individual PSD-95 immunoreactive synapses in this region. Notably, stress in early life affected either D1 or D2 dopamine receptor-expressing DLS neurons. These findings suggest that adverse early-life experience delayed the maturation of dendritic spines on neurons in the dorsolateral striatum. Altered dendritic differentiation provoked by stress in early life may contribute critically to the formation of proper neuronal circuits in the dorsal striatum and, therefore, affect striatum-dependent habitual behavior and emotional function later in life.

Decision Models and Technology Can Help Psychiatry Develop Biomarkers

Why is psychiatry unable to define clinically useful biomarkers? We explore this question from the vantage of data and decision science and consider biomarkers as a form of phenotypic data that resolves a well-defined clinical decision. We introduce a framework that systematizes different forms of phenotypic data and further introduce the concept of decision model to describe the strategies a clinician uses to seek out, combine, and act on clinical data. Though many medical specialties rely on quantitative clinical data and operationalized decision models, we observe that, in psychiatry, clinical data are gathered and used in idiosyncratic decision models that exist solely in the clinician's mind and therefore are outside empirical evaluation. This, we argue, is a fundamental reason why psychiatry is unable to define clinically useful biomarkers: because psychiatry does not currently quantify clinical data, decision models cannot be operationalized and, in the absence of an operationalized decision model, it is impossible to define how a biomarker might be of use. Here, psychiatry might benefit from digital technologies that have recently emerged specifically to quantify clinically relevant facets of human behavior. We propose that digital tools might help psychiatry in two ways: first, by quantifying data already present in the standard clinical interaction and by allowing decision models to be operationalized and evaluated; second, by testing whether new forms of data might have value within an operationalized decision model. We reference successes from other medical specialties to illustrate how quantitative data and operationalized decision models improve patient care.

Double dissociation of inhibitory effects between the hippocampal TET1 and TET3 in the acquisition of morphine self-administration in rats

The development of opioid addiction involves DNA methylation. Accordingly, the DNA demethylation, induced by ten-eleven translocation (Tet) enzymes, may represent a novel approach to prevent opioid addiction. The present study examined the role of TET1 and TET3 in the development of morphine-seeking behavior in rats. We showed that 1 day of morphine self-administration (SA) training upregulated TET3 but not TET1 expression in the hippocampal CA1. With 7 days of morphine SA training, the expression of TET3 in the CA1 returned to the baseline level, while the TET1 expression was downregulated. No change of TET1 and TET3 in the nucleus accumbens shell was observed in morphine SA trained rats, or in the yoked morphine rats, or in rats trained for saccharin SA. Furthermore, we found that knocking down TET3 expression in the CA1 accelerated the acquisition of morphine SA, while overexpression of the catalytic domain of TET1 in the CA1 attenuated the acquisition. Together, these findings suggest that TET1 and TET3 in the CA1 are important epigenetic modulators involved in the morphine-seeking behavior and provide a new strategy in the treatment of opioid addiction.

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.

Compulsive alcohol consumption is regulated by dorsal striatum fast-spiking interneurons

Compulsive alcohol consumption is a core, treatment-resistant feature of alcohol use disorder. The dorsomedial and dorsolateral striatum support goal-directed and habitual action strategies, respectively. How ethanol targets dorsolateral striatum to drive compulsive consumption is poorly understood. Parvalbumin-expressing striatal fast-spiking interneurons comprise ~1% of the total neuronal striatal population, are enriched dorsolaterally and are functionally modulated by ethanol. To test whether fast-spiking interneurons are necessary for the development of compulsive ethanol consumption, we selectively ablated these neurons in adult male and female C57BL/6 J mice undergoing a voluntary chronic intermittent ethanol consumption paradigm followed by a compulsive ethanol drinking assay. Fast-spiking interneuron ablation curtailed the development of organized ethanol lick sequence behavior, reduced ethanol consumption, and abrogated compulsive consumption of ethanol with the added bitterant quinine. In contrast, fast-spiking interneuron ablation did not affect any index of water or sucrose consumption. These data causally implicate the minority striatal fast-spiking interneuron population as a key component of compulsive ethanol consumption.

Reduction of contextual control of conditioned responses by extended Pavlovian training in an insect

The effect of repetitive training on learned behavior has been an important subject in neuroscience. In instrumental conditioning in mammals, learned action early in training is often goal-driven and controlled by outcome expectancy, but as training progresses, it becomes more habitual and insensitive to outcome devaluation. Similarly, we recently showed in Pavlovian conditioning in crickets (Gryllus bimaculatus) that a conditioned response (CR) is initially sensitive to devaluation of the unconditioned stimulus but becomes insensitive to it after extended training. It is known that habitual responses after extended instrumental training are characterized by a higher context specificity than are initial goal-directed actions in mammals. In this study, we investigated whether this is applicable to Pavlovian conditioning in crickets. In crickets that received a standard amount of training to associate an odor with water reward under illumination, CR under illumination was stronger than that in the dark. In crickets that received extended training under illumination, on the other hand, the level of CR did not differ in different light conditions. Further experiments confirmed that context specificity decreases with the development of behavioral automaticity by extended training, as opposed to findings in instrumental training in mammals. We conclude that the nature of habitual behaviors after extended training differs in different learning systems of animals.

Retrieval-Dependent Mechanisms Affecting Emotional Memory Persistence: Reconsolidation, Extinction, and the Space in Between

Maladaptive emotional memories contribute to the persistence of many mental health disorders, and therefore the prospect of disrupting these memories to produce long-term reductions in relapse is of great clinical appeal. Reducing the impact of maladaptive emotional memories on behaviour could be achieved by two retrieval-dependent manipulations that engage separate mnemonic processes: "reconsolidation disruption" and "extinction enhancement." Extinction occurs during a prolonged re-exposure session in the absence of the expected emotional outcome and is widely accepted as reflecting the formation of a new, inhibitory memory that prevents behavioural expression of the original trace. Reconsolidation, by contrast, involves the destabilisation of the original memory, allowing for subsequent updating and restabilisation in specific brain regions, unless the re-stabilization process is prevented through specific pharmacological or behavioural interventions. Both destabilisation of the original memory and memory extinction require that re-exposure induces prediction error-a mismatch between what is expected and what actually occurs-but the parameters that allow reconsolidation and extinction to occur, and control the transition between them, have not been well-characterised. Here, we review what is known about the induction of memory destabilisation and extinction, and the transition period that separates these mnemonic processes, drawing on preclinical and clinical examples. A deeper understanding of the processes that determine the alternative routes to memory persistence or inhibition is critical for designing new and more reliable clinical treatments targeting maladaptive emotional memories.

Adolescents exhibit reduced Pavlovian biases on instrumental learning

Multiple learning systems allow individuals to flexibly respond to opportunities and challenges present in the environment. An evolutionarily conserved "Pavlovian" learning mechanism couples valence and action, promoting a tendency to approach cues associated with reward and to inhibit action in the face of anticipated punishment. Although this default response system may be adaptive, these hard-wired reactions can hinder the ability to learn flexible "instrumental" actions in pursuit of a goal. Such constraints on behavioral flexibility have been studied extensively in adults. However, the extent to which these valence-specific response tendencies bias instrumental learning across development remains poorly characterized. Here, we show that while Pavlovian response biases constrain flexible action learning in children and adults, these biases are attenuated in adolescents. This adolescent-specific reduction in Pavlovian bias may promote unbiased exploration of approach and avoidance responses, facilitating the discovery of rewarding behavior in the many novel contexts that adolescents encounter.

Targeting drug memory reconsolidation: a neural analysis

Addiction can be conceptualised as a disorder of maladaptive learning and memory. Therefore, maladaptive drug memories supporting drug-seeking and relapse behaviours may present novel treatment targets for therapeutic approaches based upon reconsolidation-blockade. It is known that different structures within the limbic corticostriatal system contribute differentially to different types of maladaptive drug memories, including pavlovian associations between environmental cues and contexts with the drug high, and instrumental memories underlying drug-seeking. Here, we review the mechanisms underlying drug memory reconsolidation in the amygdala, striatum, and hippocampus, noting similarities and differences, and opportunities for future research.

Cocaine reward and memory after chemogenetic inhibition of distinct serotonin neuron subtypes in mice

RATIONALE

We probed serotonin neurons, those denoted by their developmental gene expression as r2Hoxa2-Pet1 (experiment 1) and Drd1a-Pet1 (experiment 2), for differential modulation of cocaine reward and memory as revealed by the expression and development of conditioned place preference (CPP) in transgenic mice.

OBJECTIVES

To query roles in CPP, we inhibited neurons cell autonomously in vivo by activating the transgenically expressed, synthetic DREADD receptor hM₄Di (Di) with the exogenous ligand clozapine-N-oxide (CNO).

METHODS

To examine CPP expression, mice were conditioned using behaviorally active doses of cocaine (10.0 or 17.8 mg/kg) vs. saline followed by CPP assessment, first without neuron inhibition (post-conditioning session 1), and then with CNO-mediated neuron inhibition (post-conditioning session 2), followed by 4 more post-conditioning sessions. To examine CPP development, we administered CNO during conditioning sessions and then assayed CPP across 6 post-conditioning sessions.

RESULTS

In r2Hoxa2-Pet1-Di mice, post-conditioning CNO administration did not impact cocaine CPP expression, but after CNO administration during conditioning, cocaine CPP (17.8 mg/kg) persisted across post-conditioning sessions compared with that in controls, suggesting a deficit in extinguishing cocaine memory. Drd1a-Pet1-Di mice, prior to CNO-Di-triggered neuronal inhibition, unexpectedly expressed heightened cocaine CPP (10.0 and 17.8 mg/kg) compared with controls, and this basal phenotype was transiently blocked by acute post-conditioning CNO administration and persistently blocked by repeated CNO administration during conditioning.

CONCLUSION

Cocaine reward and memory likely map to distinct serotonergic Pet1 neuron subtypes. r2Hoxa2-Pet1 neurons normally may limit the durability of cocaine memory, without impacting initial cocaine reward magnitude. Drd1a-Pet1 neurons normally may help to promote cocaine reward.