The effects of social contact on drug use: behavioral mechanisms controlling drug intake

Treatment with dextroamphetamine decreases the reacquisition of cocaine self-administration: Consistency across social contexts

RATIONALE

A return to cocaine use following abstinence frequently occurs in a social context, and the presence of other individuals using cocaine may contribute to the likelihood of use. Previous studies have reported that chronic d-amphetamine treatment decreases cocaine self-administration in laboratory animals and reduces a return to cocaine use following abstinence in humans.

OBJECTIVE

The purpose of this study was to examine the effects of chronic d-amphetamine treatment on the reacquisition of cocaine use in rats self-administering cocaine in different social contexts.

METHODS

Male and female rats were implanted with intravenous catheters and trained to self-administer cocaine during daily 6-hr sessions. After 14 days, cocaine self-administration was extinguished by substituting saline for the cocaine stimulus. At this time, rats were randomized to receive chronic treatment with either d-amphetamine or saline. After 9 days of extinction, cocaine was again made available during daily 6-hr sessions. At this time, rats were further randomized into three social conditions: (1) rats continued self-administering cocaine in isolation, (2) rats self-administered cocaine in the presence of a same-sex partner that also self-administered cocaine, or (3) rats self-administered cocaine in the presence of a same-sex partner that did not have access to cocaine. Daily treatment with d-amphetamine or saline continued for the duration of reacquisition testing.

RESULTS

Chronic treatment with d-amphetamine decreased cocaine intake during reacquisition, but these effects were not influenced by the social context. No sex differences were observed.

CONCLUSION

These data support previous studies reporting that d-amphetamine decreases cocaine intake and demonstrate its efficacy across social contexts.

No change in substance use disorders or overdose after implementation of state Earned Income Tax Credit (EITC)

BACKGROUND

Inadequate income is associated with higher likelihood of experiencing a substance use disorder (SUD). This study tests whether the earned income tax credit (EITC), which issues supplemental income for workers with children in the U.S., is associated with lower rates of SUD and fatal overdose.

METHODS

We examined the effects of state-level refundable EITC presence and generosity (i.e., state EITC rate as a % of federal rate) on SUD-related outcomes (SUD prevalence and intentional and unintentional fatal overdose) using a difference-in-difference methodology, with both two-way fixed-effects models and event study plots. Several sensitivity analyses were conducted to assess the robustness of findings. Five data sources were used to create a combined state-level longitudinal dataset.

RESULTS

We did not find significant effects of refundable EITC presence or generosity on unintentional or intentional fatal overdose or SUD prevalence in two-way models. Event study models detected a very slight upward shift in SUD prevalence following refundable EITC implementation (not seen in sensitivity analyses) and no significant effects of EITC implementation on any of the fatal overdose outcomes.

CONCLUSIONS

Evidence regarding income support programs is being highly sought by policy makers as income support programs have become increasingly popular policy levers since the start of the COVID-19 pandemic. Our study indicates EITC policies likely have no impact on SUD or overdose, however, other income support programs without family restrictions are important to investigate further.

Predictors of drug and substance abuse among school-going adolescents living in drug hotspot in Malaysia

This study explored the pressing issue of drug and substance abuse (DSA) among adolescents in drug hotspots in Malaysia. The Malaysian Anti-drug Agency (AADK) has identified 155 hotspot areas across Malaysia, of which 78 were randomly selected as the study sites. These areas were identified as having extreme drug-related activities such as drug trafficking and drug-related crimes. According to the literature, several factors influence adolescents to be involved in DSA. Therefore, understanding the risk factors in the context of Malaysian school-going adolescents is of utmost importance. The study examined, in particular, a wide range of potential predictors, including socioeconomic factors, peer influence, family dynamics, educational experiences, drug access, and community characteristics. Adolescents in the hotspot areas were selected by means of a cross-sectional survey design with a cluster sampling method. The sample comprised 3382 school-going adolescents, and the data were collected through face-to-face interviews. The logit model method with STATA software was used to analyse the data. The findings of the study revealed that school-going adolescents with disciplinary issues face a two-fold increase in the risk of becoming current drug users compared to their peers. Further, those exhibiting externalising behaviours, such as aggression and rule-breaking, also face greater odds of becoming involved in DSA. Drug pushers were identified as the most significant risk factor, with adolescents exposed to them being 46 times more likely to become current drug users. The factors of friends and family also contribute significantly to adolescent drug involvement. However, adolescents with academic-related issues may be less involved if they have the protective factor of better coping skills. These findings will contribute to efforts to mitigate drug addiction and drug-related activities, particularly in high-risk communities, as well as help policymakers and healthcare professionals develop targeted interventions and generally promote the well-being of adolescents.

Contextual and psychosocial factors influencing drug reward in humans: The importance of non-drug reinforcement

The reinforcing efficacy, or behavior-strengthening effect, of a substance is a critical determinant of substance use typically quantified by measuring behavioral allocation to the substance under schedules of reinforcement with escalating response requirements. Although responses on these tasks are often used to indicate stable reinforcing effects or trait-level abuse potential for an individual, task designs often demonstrate within-person variability across varying degrees of a constraint within experimental procedures. As a result, quantifying behavioral allocation is an effective approach for measuring the impact of contextual and psychosocial factors on substance reward. We review studies using laboratory self-administration, behavioral economic purchase tasks, and ambulatory assessments to quantify the impact of various contextual and psychosocial factors on behavioral allocation toward consumption of a substance. We selected these assessment approaches because they cover the translational spectrum from experimental control to ecological relevance, with consistent support across these approaches representing greater confidence in the effect. Conceptually, we organized factors that influence substance value into two broad categories: factors that influence the cost/benefit ratio of the substance (social context, stress and affect, cue exposure), and factors that influence the cost/benefit ratio of an alternative (alternative non-drug reinforcers, alternative drug reinforcers, and opportunity costs). We conclude with an overview of future research directions and considerations for clinical application.

Human laboratory models of reward in substance use disorder

Human laboratory models in substance use disorder provide a key intermediary step between highly controlled and mechanistically informative non-human preclinical methods and clinical trials conducted in human populations. Much like preclinical models, the variety of human laboratory methods provide insights into specific features of substance use disorder rather than modelling the diverse causes and consequences simultaneously in a single model. This narrative review provides a discussion of popular models of reward used in human laboratory research on substance use disorder with a focus on the specific contributions that each model has towards informing clinical outcomes (forward translation) and analogs within preclinical models (backward translation). Four core areas of human laboratory research are discussed: drug self-administration, subjective effects, behavioral economics, and cognitive and executive function. Discussion of common measures and models used, the features of substance use disorder that these methods are purported to evaluate, unique issues for measure validity and application, and translational links to preclinical models and special considerations for studies wishing to evaluate homology across species is provided.

Response-contingent cocaine increases the reinforcing effectiveness of social contact

Epidemiological studies report a high concordance rate of drug use within groups, suggesting an interplay between drug reinforcement and social cohesion. Preclinical studies reveal that (a) contingent access to a social partner increases cocaine intake and (b) experimenter-delivered cocaine increases the reinforcing effects of social contact. The purpose of this study was to determine if response-contingent cocaine increases the reinforcing effectiveness of social contact. Male rats were implanted with intravenous catheters and trained on a fixed ratio (FR1) schedule for 30-s access to a social partner. The reinforcing effectiveness of social contact was then determined using a progressive ratio (PR) schedule. After the PR test, rats were divided into two groups in which each response on an FR1 schedule produced social access and either response-contingent cocaine (0.5 mg/kg/infusion) or saline. After 9 days, the reinforcing effectiveness of social contact in the absence of infusions was determined again on the PR schedule. The cocaine and saline reinforcers were then switched between groups and the latter procedures were repeated. Recent exposure to response-contingent cocaine increased the reinforcing effectiveness of social contact on the PR schedule. This effect was transient, and the reinforcing effectiveness of social contact returned to baseline levels once response-contingent cocaine was replaced with saline. These data indicate that recent exposure to response-contingent cocaine transiently increases the reinforcing effectiveness of social contact and suggest that cocaine use may strengthen social cohesion by increasing the reinforcing effects of social contact with other individuals. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

An ecological study of the correlation between COVID-19 support payments and overdose events in British Columbia, Canada

BACKGROUND

Pandemic income support payments have been speculatively linked to an increased incidence of illicit drug poisoning (overdose). However, existing research is limited.

METHODS

Collating Canadian Emergency Response Benefit (CERB) payment data with data on paramedic attended overdose and illicit drug toxicity deaths for the province of British Columbia at the Local Health Area (LHA) level, we conducted a correlation analysis to compare overdose rates before, during and after active CERB disbursement.

RESULTS

There were 20,014,270 CERB-entitled weeks identified among residents of British Columbia for the duration of the pandemic response program. Approximately 52 % of all CERB entitled weeks in the study were among females and approximately 48 % were among males. Paramedic-attended overdoses increased uniformly across the pre-CERB, CERB and post-CERB periods, while illicit drug toxicity deaths sharply increased and then remained high over the period of the study. Correlation analyses between overdose and CERB-entitled weeks approached zero for both paramedic-attended overdoses and illicit drug toxicity deaths.

CONCLUSIONS

These findings suggest that attributing the pandemic increase in overdose to income support payments is unfounded. Sustained levels of unacceptably high non-fatal and fatal drug poisonings that further increased at the start of the pandemic are reflective of complex pre-existing and pandemic-driven changes to overdose risk.

Subthalamic high-frequency deep brain stimulation reduces addiction-like alcohol use and the possible negative influence of a peer presence

RATIONALE

The immediate social context significantly influences alcohol consumption in humans. Recent studies have revealed that peer presence could modulate drugs use in rats. The most efficient condition to reduce cocaine intake is the presence of a stranger peer, naive to drugs. Deep brain stimulation (DBS) of the Subthalamic Nucleus (STN), which was shown to have beneficial effects on addiction to cocaine or alcohol, also modulates the protective influence of peer's presence on cocaine use.

OBJECTIVES

This study aimed to: 1) explore how the presence of an alcohol-naive stranger peer affects recreational and escalated alcohol intake, and 2) assess the involvement of STN on alcohol use and in the modulation induced by the presence of an alcohol-naïve stranger peer.

METHODS

Rats with STN DBS and control animals self-administered 10% (v/v) ethanol in presence, or absence, of an alcohol-naive stranger peer, before and after escalation of ethanol intake (observed after intermittent alcohol (20% (v/v) ethanol) access).

RESULTS

Neither STN DBS nor the presence of an alcohol-naive stranger peer modulated significantly recreational alcohol intake. After the escalation procedure, STN DBS reduced ethanol consumption. The presence of an alcohol-naive stranger peer increased consumption only in low drinkers, which effect was suppressed by STN DBS.

CONCLUSIONS

These results highlight the influence of a peer's presence on escalated alcohol intake, and confirm the role of STN in addiction-like alcohol intake and in the social influence on drug consumption.

Social Context and Reward Sensitivity Enhance Corticostriatal Function during Experiences of Shared Rewards

Although prior research has demonstrated enhanced striatal response when sharing rewards with close social connections, less is known about how individual differences affect ventral striatal (VS) activation and connectivity when experiencing rewards within social contexts. Given that self-reported reward sensitivity and level of substance use have been associated with differences in VS activation, we set out to investigate whether these factors would be independently associated with enhancements to neural reward responses within social contexts. In this pre-registered study, participants (N=45) underwent fMRI while playing a card guessing game in which correct or incorrect guesses resulted in monetary gains and losses that were shared evenly with either a close friend, stranger (confederate), or non-human partner. Consistent with our prior work, we found increased VS activation when sharing rewards with a socially close peer as opposed to an out-of-network stranger. As self-reported reward sensitivity increased, the difference in VS response to rewards shared with friends and strangers decreased. We also found enhanced connectivity between the VS and temporoparietal junction when sharing rewards with close friends as opposed to strangers. Finally, exploratory analyses revealed that as reward sensitivity and sub-clinical substance use increase, the difference in VS connectivity with the right fusiform face area increases as a function of social context. These findings demonstrate that responsivity to the context of close friends may be tied to individual reward sensitivity or sub-clinical substance use habits; together these factors may inform predictions of risk for future mental health disorders.

Social influence and the likelihood of using cannabis: Role of source physical attractiveness

The presence of another individual may increase or decrease the likelihood a person will use drugs, depending on factors such as whether the source (i.e., the other individual) is also using drugs. The purpose of this study was to determine whether the physical attractiveness of the source influences the likelihood a person will use cannabis. Heterosexual men and women were recruited via a crowdsourcing platform and asked to rank order the physical attractiveness of 13 opposite-gender people. Participants were then presented with hypothetical scenarios in which they reported the likelihood of engaging in drug use (i.e., "use marijuana") and a nondrug control activity ("enjoy the view" from a private balcony) when they were alone versus in the presence of an opposite-gender person they rated low, moderate, or high in relative physical attractiveness. The likelihood of participating in both drug and nondrug activities increased as a function of the relative physical attractiveness of the other individual (i.e., the source); however, notable gender differences were observed in the likelihood of using cannabis. Women were less likely to use cannabis in the presence of less attractive men relative to using cannabis alone, whereas men were more likely to use cannabis in the presence of more attractive women than using cannabis alone. These data suggest the presence of an opposite-gender person can either inhibit or facilitate drug use depending on the physical attractiveness of the source and gender of the subject. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Role of social context in addiction etiology and recovery

While social context has long been considered central to substance use disorder prevention and treatment and many drug-taking events occur in social settings, experimental research on social context has historically been limited. Recent years have seen an emergence of concerted preclinical and human laboratory research documenting the direct impact of social context on substance use, delineating behavioral and neurobiological mechanisms underlying social influence's role. We review this emerging preclinical and human laboratory literature from a theoretical lens that considers distinct stages of the addiction process including drug initiation/acquisition, escalation, and recovery. A key conclusion of existing research is that the impact of the social environment is critically moderated by the drug-taking behavior and drug use history of a social peer. Specifically, while drug-free social contexts can reduce the likelihood of drug use initiation and act as a competitive non-drug alternative preventing escalation, drug-using peers can equally facilitate initiation and escalation through peer modeling as a contingent reward of use. Likewise, social context may facilitate recovery or serve as a barrier that increases the chances of a return to regular use. We conclude by discussing evidence-based treatments and recovery support services that explicitly target social mechanisms or that have identified social context as a mechanism of change within treatment. Ultimately, new areas for research including the expansion of drug classes studied and novel human laboratory designs are needed to further translate emerging findings into clinical practice.

Association between Depressive Symptoms and Adherence to the Mediterranean Diet in Nursing Students

With university admission, there are major changes in students' daily habits that can lead to mental health problems. In this respect, adherence to a healthy diet, such as the Mediterranean diet (MD), can be very beneficial. The present study examines the associations between adherence to the MD and mental health among Spanish nursing students (n = 289). Sociodemographic data and life habits were collected electronically using a self-administered questionnaire. The participants also completed the Mediterranean Diet Adherence Screener (MEDAS-14) and the Goldberg Anxiety and Depression Scale (GADS). The percentage of anxiety and depression symptoms was high: 45.3% (n = 131) and 46.4% (n = 134), respectively. Only 35.6% reported good adherence to the MD (score ≥ 9). The statistical analysis showed poor adherence to the MD to be significantly and positively associated with depressive symptoms (p = 0.013) and the total score on the GADS (p = 0.039). A multivariable regression model analysis identified the depression subscale score as a predictor variable, with a mean risk of low adherence to the MD being 0.803 times (95%CI: 0.666-0.968, p = 0.021) among participants with greater depressive symptoms. These results support the implementation of prevention programs in universities focused on health and mental health issues.

Renewal of cocaine seeking using social and nonsocial contextual stimuli

RATIONALE

Various nonsocial cues have been used as stimuli to examine the contextual control of drug seeking behavior, but little is known about the role of social stimuli.

OBJECTIVES

This study determined if renewal of cocaine seeking is differentially controlled using a context consisting of either a social peer and/or house light illumination.

METHODS

In Experiment 1, male and female rats trained to self-administer cocaine in the presence of a same-sex social peer and house light illumination (context A). Following self-administration, rats were randomly assigned to either an AAA (control) or ABA (renewal) group for extinction. For AAA rats, extinction consisted of the same context A as self-administration; for ABA rats, extinction occurred without the peer or house light (context B). Following extinction, renewal of cocaine seeking occurred by testing the peer alone, house light alone, and the peer + house light combination. Experiment 2 was conducted to ensure that the house light alone was sufficiently salient to produce renewal.

RESULTS

Both experiments showed that rats acquired cocaine self-administration and extinguished lever pressing. In Experiment 1, the ABA group renewed cocaine seeking to the peer and peer + house light, but not to the house light alone. In Experiment 2, ABA rats renewed cocaine seeking to the house light alone, indicating it was sufficiently salient to produce renewal. The AAA group did not show renewal in either experiment.

CONCLUSION

Social peers serve as powerful stimuli that can overshadow nonsocial visual stimuli in the renewal of cocaine seeking.

Sensitivity and specificity in affective and social learning in adolescence

Adolescence is a period of heightened affective and social sensitivity. In this review we address how this increased sensitivity influences associative learning. Based on recent evidence from human and rodent studies, as well as advances in computational biology, we suggest that, compared to other age groups, adolescents show features of heightened Pavlovian learning but tend to perform worse than adults at instrumental learning. Because Pavlovian learning does not involve decision-making, whereas instrumental learning does, we propose that these developmental differences might be due to heightened sensitivity to rewards and threats in adolescence, coupled with a lower specificity of responding. We discuss the implications of these findings for adolescent mental health and education.

Morphine exposure during adolescence induces enduring social changes dependent on adolescent stage of exposure, sex, and social test

Drug exposure during adolescence, when the 'reward' circuitry of the brain is developing, can permanently impact reward-related behavior. Epidemiological studies show that opioid treatment during adolescence, such as pain management for a dental procedure or surgery, increases the incidence of psychiatric illness including substance use disorders. Moreover, the opioid epidemic currently in the United States is affecting younger individuals raising the impetus to understand the pathogenesis of the negative effects of opioids. One reward-related behavior that develops during adolescence is social behavior. We previously demonstrated that social development occurs in rats during sex-specific adolescent periods: early to mid-adolescence in males (postnatal day (P)30-40) and pre-early adolescence in females (P20-30). We thus hypothesized that morphine exposure during the female critical period would result in adult sociability deficits in females, but not males, and morphine administered during the male critical period would result in adult sociability deficits in males, but not females. We found that morphine exposure during the female critical period primarily resulted in deficits in sociability in females, while morphine exposure during the male critical period primarily resulted in deficits in sociability primarily in males. However, depending on the test performed and the social parameter measured, social alterations could be found in both sexes that received morphine exposure at either adolescent stage. These data indicate that when drug exposure occurs during adolescence, and how the endpoint data are measured, will play a large role in determining the effects of drug exposures on social development.

Interaction of Nicotine and Social reward in group-reared male adolescent rats

Adolescents exhibit great sensitivity to nicotine and social interaction; accordingly, when both stimuli are presented together, they interact to enhance the incentive value of the context in which they occur. Noteworthy, most studies assessing the interaction between nicotine and social reward have used isolated-reared rats. Adolescent isolation is an adverse condition that impacts brain development and behavior, so it is not known if the interaction also occurs in rats without social deprivation. The present study used a conditioned place preference model (CPP) to examine the interaction between nicotine and social reward in group-reared male adolescent rats. At weaning, Wistar rats were randomly assigned to four groups: vehicle, vehicle and a social partner, nicotine (0.1mg/Kg s.c.), and nicotine and a social partner. Conditioning trials occurred on eight consecutive days followed by a test session in which the preference change was assessed. Besides the establishment of CPP, we examined the effects of nicotine on (1) social behaviors during CPP trials and (2) tyrosine hydroxylase (TH) and oxytocin (OT) as markers of changes in the neuronal mechanisms for reward and social affiliation. Similar to previous results, the joint presentation of nicotine and social reward induced CPP, whereas either nicotine or social interaction presented alone did not. This finding coincided with an increase in TH levels observed after nicotine administration only in socially conditioned rats. The interaction between nicotine and social reward is not related to the effects of nicotine on social investigation or social play.

The intersection of empathy and addiction

Empathy, the ability to perceive the affective state of another, is a complex process that is integral to many of the prosocial behaviors expressed in humans and across the animal kingdom. Research into the behavioral and neurobiological underpinnings of empathic behaviors has increased in recent years. Growing evidence suggests changes in empathy may contribute to a myriad of psychiatric illnesses, including substance use disorder (SUD). Indeed, both clinical and preclinical research in SUD demonstrates a strong relationship between drug taking or relapse events and changes to empathic behavior. Further, there is significant overlap in the underlying neural substrates of these complex behaviors, including the insula, paraventricular nucleus of thalamus (PVT), and the paraventricular nucleus of the hypothalamus (PVN). In this review, we will discuss our current understanding of the interplay between empathic behaviors and SUD. We will also examine the underlying neurobiology that may regulate this interaction, focusing specifically on the insula, PVT, and PVN. Finally, we discuss the biologic and therapeutic importance of taking empathic processes into consideration when discussing SUD.

Demand and cross-price elasticity of cocaine and social contact in a free-operant procedure of nonexclusive choice

Research examining the social determinants of addiction has advanced significantly with the recent development of preclinical models of drug use and the social environment. These models reveal that drug use and social contact compete with one another for behavioral expression in discrete-trial choice procedures using concurrent schedules of reinforcement. The purpose of this study was to determine how concurrent access to cocaine and a social partner influences the demand for each alternative under free-operant conditions in which responding maintained by each reinforcer is independent and nonexclusive of the other. To this end, male rats were trained under a free-operant, concurrent schedule of reinforcement in which responding maintained by cocaine and access to a social partner operated independently of one another. Measures of economic demand (e.g., intensity, Omax, cross-price elasticity) were determined by manipulating the response requirement (i.e., fixed ratio value) across sessions. Tests were conducted in which the social partner was either treated or not treated with cocaine to determine whether the intoxication state of the partner influenced demand. The principal findings of this study are (1) demand for a cocaine-treated partner is greater than demand for a cocaine-free partner, (2) demand for cocaine is greater in the presence of a cocaine-treated partner than a cocaine-free partner, and (3) concurrent access to cocaine decreases demand for social contact. Notably, measures of cross-price elasticity indicated that social contact is a robust economic substitute for cocaine.

Wistar rats choose alcohol over social interaction in a discrete-choice model

Animal models of substance use disorders have been criticized for their limited translation. One important factor behind seeking and taking that has so far been largely overlooked is the availability of alternative non-drug rewards. We recently reported that only about 15% of outbred Wistar rats will choose alcohol over a sweet solution of saccharin. It was also shown using a novel operant model of choice of drugs over social rewards that social interaction consistently attenuates self-administration and incubation of craving for stimulants and opioids. Whether this is also true for alcohol and choice of alcohol over a sweet reward translates to social rewards is currently unknown. We therefore evaluated choice between alcohol and a social reward in different experimental settings in both male and female Wistar rats. We found, in contrast to prior work that employed discrete choice of drugs vs. social reward, that rats almost exclusively prefer alcohol over social interaction, irrespective of the nature of the social partner (cagemate vs. novel rat), the length of interaction, housing conditions and sex. Alcohol choice was reduced when the response requirement for alcohol was increased. However, rats persisted in choosing alcohol, even when the effort required to obtain it was 10-16 times higher (for females and males respectively) than the one for the social reward. Altogether, these results indicate that the social choice model may not generalize to alcohol, pointing to the possibility that specific interactions between alcohol and social reward, not seen when a sweet solution is used as an alternative to the drug, may play a crucial role in alcohol vs. social choice experiments.

Can we enhance the clinical efficacy of cognitive and psychological approaches to treat substance use disorders through understanding their neurobiological mechanisms?

Despite decades of research in the field of addiction, relapse rates for substance use disorders remain high. Consequently, there has been growing focus on providing evidence-based treatments for substance use disorders, resulting in the increased development and use of cognitive and psychological interventions. Such treatment approaches, including contingency management, community-reinforcement approach, and cognitive bias modification, have shown promising clinical efficacy in reducing substance use and promoting abstinence during treatment. However, these interventions are still somewhat limited in achieving sustained periods of abstinence post-treatment. The neurobiological mechanisms underpinning these treatment approaches remain largely unknown and under-studied, in part, due to a lack of translational animal models. The adoption of a reverse translational approach may assist in development of more representative models that can facilitate elucidation of the mechanisms behind these clinically relevant interventions. This review examines our current understanding of addiction neurobiology from clinical, preclinical research and existing animal models, and considers how the efficacy of such behavioral-oriented interventions alone, or in combination with pharmacotherapy, may be enhanced to improve treatment outcomes.

Amphetamine exposure alters behaviors, and neuronal and neurochemical activation in the brain of female prairie voles

Previous studies have shown that 3-day d-amphetamine (AMPH) treatment effectively induced conditioned place preferences (CPP) and impaired pair bonding behaviors in prairie voles (Microtus ochrogaster). Using this established animal model and treatment regimen, we examined the effects of the demonstrated threshold rewarding dose of AMPH on various behaviors and their potential underlying neurochemical systems in the brain of female prairie voles. Our data show that 3-day AMPH injections (0.2 mg/kg/day) impaired social recognition and decreased depressive-like behavior in females without affecting their locomotion and anxiety-like behaviors. AMPH treatment also decreased neuronal activation indicated by the labeling of the early growth response protein 1 (Egr-1) as well as the number of neurons double-labeled for Egr-1 and corticotrophin-releasing hormone (CRH) in the dentate gyrus (DG) of the hippocampus and paraventricular nucleus of the hypothalamus (PVN) in the brain. Further, AMPH treatment decreased the number of neurons double-labeled for Egr-1 and tyrosine hydroxylase (TH) but did not affect oxytocinergic neurons in the PVN or cell proliferation and neurogenesis markers in the DG. These data not only demonstrate potential roles of the brain CRH and dopamine systems in mediating disrupted social recognition and depressive-like behaviors by AMPH in female prairie voles, but also further confirm the utility of the prairie vole model for studying interactions between psychostimulants and social behaviors.

Peer presence and familiarity as key factors to reduce cocaine intake in both rats and humans: an effect mediated by the subthalamic nucleus

RATIONALE

Stimulant use, including cocaine, often occurs in a social context whose influence is important to understand to decrease intake and reduce associated harms. Although the importance of social influence in the context of drug addiction is known, there is a need for studies assessing its neurobiological substrate and for translational research.

OBJECTIVES

Here, we explored the influence of peer presence and familiarity on cocaine intake and its neurobiological basis. Given the regulatory role of the subthalamic nucleus (STN) on cocaine intake and emotions, we investigated its role on such influence of social context on cocaine intake.

METHODS

We first compared cocaine consumption in various conditions (with no peer present or with peers with different characteristics: abstinent peer or drug-taking peer, familiar or not, cocaine-naive or not, dominant or subordinate) in rats (n = 90). Then, with a translational approach, we assessed the influence of the social context (alone, in the group, in a dyad with familiar or non-familiar peers) on drug intake in human drug users (n = 77).

RESULTS

The drug consumption was reduced when a peer was present, abstinent, or drug-taking as well, and further diminished when the peer was non-familiar. The presence of a non-familiar and drug-naive peer represents key conditions to diminish cocaine intake. The STN lesion by itself reduced cocaine intake to the level reached in presence of a non-familiar naive peer and affected social cognition, positioning the STN as one neurobiological substrate of social influence on drug intake. Then, the human study confirmed the beneficial effect of social presence, especially of non-familiar peers.

CONCLUSION

Our results indirectly support the use of social interventions and harm reduction strategies and position the STN as a key cerebral structure to mediate these effects.

Social Contact Reinforces Cocaine Self-Administration in Young Adult Male Rats: The Role of Social Reinforcement in Vulnerability to Drug Use

Drug-using peers are recognized as a leading factor influencing drug use among adolescents and young adults. One mechanism by which peers influence drug use is by providing social reinforcement for using drugs. Social reinforcement may be provided in multiple ways, including by making social contact contingent on drug use (i.e., an individual must use drugs to gain/maintain access to a peer). The purpose of this study was to develop a preclinical model in which intravenous cocaine self-administration was positively reinforced by access to a social partner. Young adult male rats were trained to self-administer cocaine in operant conditioning chambers with a guillotine door that could be opened to an adjacent compartment housing either a social partner or a non-social stimulus. Once cocaine self-administration was established, the guillotine door was activated, and cocaine intake was reinforced by brief access to either a social (age- and sex-matched peer) or non-social (black-and-white athletic sock) stimulus. Contingent access to a social partner rapidly increased cocaine self-administration. Total cocaine intake was 2- to 3-fold greater in rats assigned to the social versus non-social condition across a 100-fold dose range. Cocaine intake rapidly increased when rats in the original non-social group were later provided with social partners, whereas cocaine intake resisted change and remained elevated when rats in the original social group had their partners removed. These data indicate that contingent access to a social partner increases drug intake and suggest that social reinforcement may represent a vulnerability factor that is particularly resistant to psychosocial interventions.

The impact of social variables in preclinical models of cocaine abuse

At present, there are no US Food and Drug Administration–approved treatments for cocaine use disorders. One consideration for this lack of treatment efficacy stems from the appropriate use of animal models. The premise of this commentary is that social behavior needs to be incorporated in animal models of cocaine use disorder. The goal of this commentary is to describe some of the strengths and limitations of recent preclinical animal models of cocaine abuse which have incorporated social behavior. There are many ways to include social variables into preclinical research, and the study design will depend on the questions asked. Four general types of studies incorporating social factors are described: those involving aggression (that is, maternal neglect and social defeat), modeling, social reward, and social housing, including social isolation. The inclusion of social variables into preclinical research will help identify biobehavioral markers that may lead to an individualized treatment approach that more effectively decreases cocaine use. These studies will aid in the development of novel pharmacotherapies as well as non-pharmacological interventions (for example, punishment, alternative reinforcers, and environmental enrichment) that would be critical for informing policy decisions.

Opposite Roles for Cannabidiol and δ-9-Tetrahydrocannabinol in Psychotomimetic Effects of Cannabis Extracts: A Naturalistic Controlled Study

BACKGROUND

Although δ-9-tetrahydrocannabinol (THC), the main cannabinoid from the cannabis plant, is responsible for the psychotomimetic effects of cannabis, cannabidiol (CBD), the second most abundant cannabinoid in the cannabis plant, does not show any psychotomimetic effect. Cannabidiol has even been proposed to be antipsychotic and to counteract some of the psychotomimetic effects of THC. The aim of this study was to test the potential antipsychotomimetic effects of CBD.

METHOD

Eighteen members from a cannabis social club were tested for subjective and psychotomimetic effects under the effects of different full-spectrum cannabis extracts containing either THC, CBD, THC + CBD, or placebo in a naturalistic, randomized, double-blind, crossover, placebo-controlled study.

RESULTS

Results showed that participants under the effects of THC + CBD showed lower psychotomimetic scores in subjective scales when compared with THC alone. Subjective scores were lower under the effects of CBD and placebo when compared with THC + CBD. Cannabidiol and placebo did not show any psychotomimetic effect.

CONCLUSIONS

This study provides evidence for both the psychotomimetic effects of THC and the antipsychotomimetic effects of CBD when it is coadministered with THC in real-world situations, which can be very relevant for the clinical practice of medical cannabis. Ultimately, this study substantiates the link between the endocannabinoid system and psychotic-like symptoms and has important implications for the understanding of schizophrenia and the therapeutic potential of CBD as an antipsychotic. Lastly, we demonstrate how reliable methodologies can be implemented in real situations to collect valid ecological evidence outside classic laboratory settings.

Effect of alternative income assistance schedules on drug use and drug-related harm: a randomised controlled trial

Background

The synchronised monthly disbursement of income assistance, whereby all recipients are paid on the same day, has been associated with increases in illicit drug use and serious associated harms. This phenomenon is often referred to as the cheque effect. Because payment variability can affect consumption patterns, this study aimed to assess whether these harms could be mitigated through a structural intervention that varied income assistance payment timing and frequency.

Methods

This randomised, parallel group trial was done in Vancouver, Canada, and enrolled recipients of income assistance whose drug use increased around payment days. The recipients were randomly assigned 1:2:2 to a control group that received monthly synchronised income assistance payments on government payment days, a staggered group in which participants received single desynchronised monthly income assistance payments, or a split and staggered group in which participants received desynchronised income assistance payments split into two instalments per month, 2 weeks apart, for six monthly payment cycles. Desynchronised payments in the intervention groups were made on individual payment days outside the week of the standard government schedules. Randomisation was through a pre-established stratified block procedure. Investigators and statisticians were masked to group allocation, but participants and front-line staff were not. Complete final results are reported after scheduled interim analyses and the resulting early stoppage of recruitment. Under intention-to-treat specifications, generalised linear mixed models were used to analyse the primary outcome, which was escalations in drug use, predefined as a 40% increase in at least one of: use frequency; use quantity; or number of substances used during the 3 days after government payments. Secondary analyses examined analogous drug use outcomes coinciding with individual payments as well as exposure to violence. This trial is registered with ClinicalTrials.gov, NCT02457949.

Findings

Between Oct 27, 2015, and Jan 2, 2019, 45 participants were enrolled to the control group, 72 to the staggered group, and 77 to the split and staggered group. Intention-to-treat analyses showed a significantly reduced likelihood of increased drug use coinciding with government payment days, relative to the control group, in the staggered (adjusted odds ratio 0·38, 95% CI 0·20–0·74; p=0·0044) and split and staggered (0·44, 0·23–0·83; p=0·012) groups. Findings were consistent in the secondary analyses of drug use coinciding with individual payment days (staggered group 0·50, 0·27–0·96, p=0·036; split and staggered group 0·49, 0·26–0·94, p=0·030). However, secondary outcome analyses of exposure to violence showed increased harm in the staggered group compared with the control group (2·71, 1·06–6·91, p=0·037). Additionally, 51 individuals had a severe or life-threatening adverse event and there were six deaths, none of which was directly attributed to study participation.

Interpretation

Complex results indicate the potential for modified income assistance payment schedules to mitigate escalations in drug use, provided measures to address unintended harms are also undertaken. Additional research is needed to clarify whether desynchronised schedules produce other unanticipated consequences and if additional measures could mitigate these harms.

Funding

Canadian Institutes of Health Research, Providence Health Care Research Institute, Peter Wall Institute for Advanced Research, Michael Smith Foundation for Health Research.

Behavioral economics and the aggregate versus proximal impact of sociality on heavy drinking

BACKGROUND

Behavioral economic theory predicts decisions to drink are cost benefit analyses, and heavy episodic drinking occurs when benefits outweigh costs. Social interaction is a known benefit associated with alcohol use. Although heavy drinking is typically considered more likely during more social drinking events, people who drink heavily in isolation tend to report greater severity of use. This study explicitly disaggregates between-person and within-person effects of sociality on heavy episodic drinking and examines behavioral economic moderators.

METHODS

We used day-level survey data over an 18-week period in a community adult sample recruited through crowdsourcing (mTurk; N = 223). Behavioral economic indices were examined to determine if macro person-level variables (alcohol demand, delay discounting, proportionate alcohol-related reinforcement [R-ratio]) interact with event-level social context to predict heavy drinking episodes.

RESULTS

Mixed effect models indicated significant between-person and within-person social context associations. Specifically, people with a higher proportion of total drinking occasions in social contexts had decreased odds of heavy drinking, whereas being in a social context for a specific drinking occasion was associated with increased odds of heavy drinking. Person-level R-Ratio, demand elasticity, and breakpoint variables interacted with social context to predict heavy episodic drinking, such that the event-level social context association was stronger when R-Ratios, alcohol price insensitivity, and demand breakpoints were high.

CONCLUSIONS

These results demonstrate an ecological fallacy, in which the size and direction of effects were divergent at different levels of analysis, and highlight the potential for merging behavioral economic variables with proximal contextual effects to predict heavy drinking.

Drug-related harm coinciding with income assistance payments: results from a community-based cohort of people who use drugs

BACKGROUND AND AIMS

Income assistance is critical to the health and wellbeing of socio-economically marginalized people who use illicit drugs (PWUD). However, past literature paradoxically identifies unintended increases in drug-related harm coinciding with synchronized payments that may magnify signals for drug use. The scope of such harm has not been fully characterized among non-institutionalized populations. This study examined socio-demographic, health and drug use-related correlates of payment-coincident drug-related harm.

DESIGN

This observational study uses data from prospective community-based longitudinal cohorts of PWUD between December 2013 and May 2018.

SETTING

Vancouver, British Columbia, Canada.

PARTICIPANTS

A total of 1604 PWUD receiving monthly income assistance. Our sample included 586 (36.5%) women, 861 (53.7%) non-white participants and 685 (42.7%) people living with HIV.

MEASUREMENTS

The primary outcome was a self-reported composite measure of drug-related harm in the past 6 months coinciding with income assistance, including higher-frequency substance use, non-fatal overdose and service barriers or interruptions. Subanalyses disaggregated this outcome.

FINDINGS

Payment-coincident drug-related harm was reported among 77.7% of participants during the study period. In multivariable models, key correlates positively and significantly associated with payment-coincident harm included: street-based income generation [adjusted odds ratio (aOR) = 1.48, 95% confidence interval (CI) = 1.26-1.74, P < 0.001], sex work (aOR = 1.66, 95% CI = 1.35-2.04, P < 0.001), illegal income generation (aOR = 1.57, 95% CI = 1.35-1.83 P < 0.001), homelessness (aOR = 1.34, 95% CI = 1.13-1.58, P < 0.001), exposure to violence (aOR = 1.31, 95% CI = 1.03-1.66, P = 0.032), daily crack cocaine use (aOR = 1.99, 95% CI = 1.59-2.50, P <  0.001), heavy alcohol use (aOR = 1.64, 95% CI = 1.37-1.97, P < 0.001) and injection drug use (aOR = 2.55, 95% CI = 2.01-3.23, P < 0.001). In subanalyses, specific harms were more likely among individuals reporting social, structural and health vulnerabilities.

CONCLUSIONS

In Vancouver, Canada, people who use illicit drugs who receive income assistance report high prevalence of payment-coincident drug-related harm, particularly people experiencing socioeconomic and structural marginalization or engaging in high-intensity drug use.

Deconstructing the 'cheque effect': short-term changes in injection drug use after receiving income assistance and associated factors

BACKGROUND AND AIMS

Disbursement of income assistance has been temporally associated with intensified drug use and related harms (coined the 'cheque effect'). However, relationships to injection drug use (IDU) remain understudied. We examined short-term 'cheque effects' and associated factors among people who inject drugs (PWID).

DESIGN

Cross-sectional analysis nested within a cohort study.

SETTING

Montreal, Quebec, Canada.

PARTICIPANTS

PWID receiving income assistance, with no employment income. A total of 613 PWID (median age 41, 83% male) contributed 3269 observations from 2011 to 2017.

MEASUREMENTS AND METHODS

At each cohort visit, an interviewer-administered questionnaire captured retrospective reports of injection-related behaviour during the 2-day periods (i) before and (ii) including/after receiving last month's income assistance payment (number of injections; drugs injected; any receptive syringe-sharing). The relative likelihood (odds) and magnitude (rate) of an increase in injection frequency ('cheque effect') were estimated in relation to social and behavioural factors using logistic and negative binomial regression in a covariate-adjusted two-part model.

FINDINGS

Prevalence of IDU and syringe-sharing were, respectively, 1.80 and 2.50 times higher in the days following versus preceding cheque receipt (P < 0.001). Among people with past-month IDU, most observations showed increased injection frequency (52%) or no change in injection frequency (44%). The likelihood of a 'cheque effect' was positively associated with cocaine injection [versus injection of other substances, odds ratio (OR) = 2.639, 95% confidence interval (CI) = 2.04-3.41], unstable housing (OR = 1.272, 95% CI = 1.03-1.57) and receiving opioid agonist therapy (OR =1.597, 95% CI = 1.27-2.00) during the same month. Magnitude of the 'cheque effect' was positively associated with cocaine injection [rate ratio (RR) = 1.795, 95% CI = 1.43-2.16], unstable housing (RR = 1.198, 95% CI = 1.02-1.38) and frequent injection (RR = 2.938, 95% CI = 2.43-3.44), but inversely associated with opioid agonist therapy (RR = 0.817, 95% CI = 0.68-0.95) and prescription opioid injection (RR = 0.794, 95% CI = 0.66-0.93).

CONCLUSION

Among people who inject drugs in Montreal, Canada, injection drug use and receptive syringe-sharing appear to be more prevalent in the 2 days after versus before receiving income assistance. The odds and rate of individual-level increases in injection frequency appear to be positively associated with cocaine injection (versus injection of other substances) and unstable housing.

The importance of psychology for shaping legal cannabis regulation

Different patterns of cannabis use can be traced directly back to different interactions between 2 types of variables: pharmacological and environmental. As legal cannabis expands in the U.S. and around the world, state and national regulatory agencies are gaining control over these variables. Specifically, regulatory agencies are increasingly capable of altering (a) the pharmacological properties of cannabis products and (b) the way these products are distributed to the population. Consequently, cannabis regulatory agencies are in a unique position to use evidence from psychological science to alter cannabis consumption patterns in ways that mitigate potential harm to public health. However, most state-level legal cannabis regulatory systems in the U.S. are not yet evidence-based or public health-oriented. This applied review and commentary draws on evidence from the psychological science literature to help regulators better understand the types of behaviors they must address and guide empirically supported regulation of THC-laden cannabis, whether used putatively for medical or recreational reasons. This review is organized into 3 parts that correspond to the 3 primary agents within the cannabis regulation ecosystem: (a) the cannabis consumer, (b) the cannabis industry, and (c) the cannabis regulatory agency. Within this structure, the review addresses critical psychological variables that drive cannabis consumer and industry behaviors and discusses how regulatory agencies can use this information to protect public health. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Alcohol substitution during one month of cannabis abstinence among non-treatment seeking youth

OBJECTIVE

Cannabis and alcohol use are correlated behaviors among youth. It is not known whether discontinuation of cannabis use is associated with changes in alcohol use. This study assessed alcohol use in youth before, during, and after 4 weeks of paid cannabis abstinence.

METHODS

Healthy, non-treatment seeking, cannabis users (n = 160), aged 14-25 years, 84% of whom used alcohol in the last month, were enrolled for a 4-week study with a 2-4 week follow-up. Participants were randomly assigned to 4 weeks of either biochemically-verified cannabis abstinence achieved through a contingency management framework (CB-Abst) or monitoring with no abstinence requirement (CB-Mon). Participants were assessed at baseline and approximately 4, 6, 10, 17, 24, and 31 days after enrollment. A follow-up visit with no cannabis abstinence requirement for CB-Abst was conducted after 2-4 weeks.

RESULTS

Sixty percent of individuals assigned to the CB-Abst condition increased in frequency and quantity of alcohol consumption during the 4-week period of incentivized cannabis abstinence. As a whole, CB-Abst increased by a mean of 0.6 drinking days and 0.2 drinks per day in the initial week of abstinence (p's < 0.006). There was no evidence for further increases in drinking frequency or quantity during the 30-day abstinence period (p's > 0.53). There was no change in drinking frequency or quantity during the 4-week monitoring or follow-up periods among CB-Mon.

CONCLUSIONS

On average, 4 weeks of incentivized (i.e., paid) cannabis abstinence among non-treatment seeking youth was associated with increased frequency and amount of alcohol use in week 1 that was sustained over 4 weeks and resolved with resumption of cannabis use. However, there was notable variability in individual-level response, with 60% increasing in alcohol use and 23% actually decreasing in alcohol use during cannabis abstinence. Findings suggest that increased alcohol use during cannabis abstinence among youth merits further study to determine whether this behavior occurs among treatment seeking youth and its clinical significance.

Social Learning and Addiction

Social learning theory, as originally proposed by Albert Bandura, followed 2000 years of intellectual inquiry into the determinants of human behavior. Reciprocal determinism is a central component of this theory and proposes that human behavior is determined by functional relationships between (1) personal factors, (2) the external environment, and (3) the behavior itself. Using this model, drug addiction can be viewed as resulting from the functional relationships between an individual's personal characteristics, social environment, and drug-centric behaviors. In other words, addiction can be viewed as a chronically evolving biopsychosocial disorder, encompassing dimensions that are both internal and external to the individual. Effective treatment interventions should thus target all nodes of the model and the functional relationships between them, and they must constantly evolve with the progression of the disorder. An argument is thus constructed that emphasizes the need for an organized structure of metacontingencies, operating within an individual's social environment, that targets the functional relationships between the factors that drive drug use. Optimally, these metacontingencies would operate within socially connected individuals who have the power to control the functional relationships that influence drug use, the vested interest to monitor individual and collective outcomes, the skills to determine what moment-to-moment decisions are needed to influence behavioral change, and the relative permanence necessary to carry through with the implementation of new strategies to produce outcomes that are cumulatively significant.

Behavioral economic demand as a unifying language for addiction science: Promoting collaboration and integration of animal and human models

The intersection of pharmacological, psychological, and economic theory within behavioral economics has helped advance an understanding of substance use disorder. A notable contribution of this approach is the conceptualization of reinforcement from a behavioral economic demand perspective. Demand analyses provide a multidimensional view of reinforcement in which distinct behavioral mechanisms are measured that impact decision making and drug consumption. This review describes the state of research on behavioral economic demand as a common language for addiction science researchers across varied model systems and stages of a translational continuum. We first provide an overview of the theoretical concepts and procedures used to evaluate demand in animal and human models. The potential for demand to serve as a common language for diverse research groups in psychopharmacology and addiction science (e.g., those evaluating neurobehavioral outcomes, medications development, clinical practice) is then described. An overview is also provided of existing empirical studies that, while small in number, suggest good linguistic and conceptual overlap between animal and human demand models when studying biological, environmental, and pharmacological individual difference vulnerabilities underlying drug-taking behavior. Refinement of methodological procedures and incorporation of more nuanced environmental features should help improve correspondence between animal and human demand studies as well as clinical translation of such findings. Our hope is that this review and commentary ultimately serves as inspiration for new collaborative efforts involving behavioral economic demand between animal and human researchers who share a common goal of improving substance use treatment outcomes and broader psychological wellbeing. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Contribution of alcohol- and cigarette-related cues to concurrent reinforcer choice in humans

Drug-related cues have been extensively studied for their contributions to decision-making processes involving drug consumption. Less studied is how drug-related stimuli may impact decisions involving outcomes not directly related to substance use. Studies using concurrent choice tasks have demonstrated that cocaine and cannabis cues result in robust and selective biases for monetary reinforcers contiguous with those cues. The purpose of this study was to provide a conceptual replication of these findings with alcohol and cigarettes. Participants recruited using crowdsourcing completed a cued concurrent choice task involving presentation of two cues (one drug and one neutral) followed by concurrent monetary offers below each image. Alcohol (Experiment 1; N = 103) and cigarette (Experiment 2; N = 256) visual cues were evaluated. Participants with hazardous alcohol use and current cigarette use showed greater-than-indifference selection for the alcohol- (p = .004) and cigarette-cued (p = .02) monetary choices, respectively. Qualitative responses indicated that the most popular rationale for responding was "image quality" despite images having no explicit impact on the reinforcer received. Low alcohol use (p = .03) and non-cigarette using controls (p < .001) showed an avoidance bias with lower-than-indifference selection for drug-cued choices. These findings replicate and extend observations that spatially contiguous drug-related cues can bias decisions involving concurrently presented non-drug reinforcers.

Opioid epidemics

In this paper, I propose an economic theory that addresses the epidemic character of opioid epidemics. I consider a community in which individuals are heterogenous with respect to the experience of chronic pain and susceptibility to addiction and live through two periods. In the first period they consider whether to treat pain with opioid pain relievers (OPRs). In the second period they consider whether to continue non-medical opioid use to mitigate cravings from addiction. Non-medical opioid use is subject to social disapproval, which depends negatively on the share of opioid addicts in the community. An opioid epidemic is conceptualized as the transition from an equilibrium at which opioid use is low and addiction is highly stigmatized to an equilibrium at which opioid use is prevalent and social disapproval is low. I show how such a transition is initiated by the wrong belief that OPRs are not very addictive. Under certain conditions there exists an opioid trap such that the community persists at the equilibrium of high opioid use after the wrong belief is corrected. Refinements of the basic model consider the recreational use of prescription OPRs and an interaction between income, pain, and addiction.

Subthalamic nucleus mediates the modulation on cocaine self-administration induced by ultrasonic vocalization playback in rats

Drug intake is known to be under the influence of social context. We have recently shown that presence of a peer influences drug intake in both rats and humans. Whether or not social acoustic communications between the peers play a role during cocaine or sucrose self-administration (SA) was investigated here using playback of ultrasonic vocalizations (USVs) at 50 and 22 kHz, conveying, respectively, positive and negative internal affective states in adult rats. To assess the neurobiological substrate of a potential USV influence on drug and food intake, we tested the effects of subthalamic nucleus (STN) lesions, given its role in emotional and motivational processes. In sham-control rats, playback of USV associated with positive affective states induced long-term decreased cocaine consumption, while USV associated with negative affective states induced short-term increase. Interestingly, no effect of USV playback was observed on sucrose intake, whatever the frequency. STN lesions abolished the influence of USV on cocaine intake, highlighting the influence of STN in emotional processes induced by USV emitted by a peer. These results show how acoustic social communication is important to regulate drug intake in rats and how STN modulation could interfere with addiction processes.

Alcohol Binge Drinking and Anxiety-Like Behavior in Socialized Versus Isolated C57BL/6J Mice

BACKGROUND

Binge alcohol drinking has been characterized as a key feature of alcoholism. The drinking-in-the-dark (DID) preclinical model, a procedure that promotes high levels of ethanol (EtOH) intake in short periods of time, has been extensively used to investigate neuropharmacological and genetic determinants of binge-like EtOH consumption. Using DID methodology, alcohol-preferring strains of mice such as C57BL/6J (B6) mice consume enough EtOH to achieve blood concentrations (≥1.0 mg/ml) associated with behavioral intoxication (i.e., motor incoordination). DID procedures typically involve the use of socially isolated animals (single-housed prior to and during the experiment). Previous research indicates that stress associated with social isolation can induce anxiety-like behavior and promote increases in EtOH intake. The present study investigates the role of housing conditions in anxiety-like behavior and binge-like EtOH intake using a DID procedure.

METHODS

Male and female B6 mice were isolated or pair-housed for a period of 6 weeks prior to evaluation of anxiety-like (elevated plus maze, light and dark box, open field) and drinking (water, 10% sucrose, 10 to 30% EtOH) behavior. In order to measure intake, a variation of the standard DID procedure using a removable, transparent, and perforated plastic barrier strip (designed to temporarily divide the cage in 2) was introduced. This allowed for individual intake records (2-hour test) of isolated and socially housed animals.

RESULTS

Increased anxiety-like behavior and reduced sucrose consumption were found in isolated mice. The effects of housing conditions on EtOH intake were sex- and concentration-dependent. In male mice, isolation increased 20 and 30% EtOH intake. In females, however, an increased intake of EtOH (30%) was found in socialized animals. No effects of housing or sex were found at EtOH 10%.

CONCLUSIONS

Together with previous literature, the present study suggests that social isolation can promote anxiety-associated behavior and produce sex-dependent changes in binge-like EtOH consumption.

Sleep quality and its association with substance abuse among university students

OBJECTIVE

Poor sleep is one of the greatest health problems with social significance whose prevalence started early in adolescence. The relationship between poor sleep quality and the use of alcohol and illicit substances among university students has not been studied. Our study aimed to determine these relationships and the factors influencing the risk of poor sleep in students from health sciences degrees which are the future healthcare providers.

PATIENTS AND METHODS

A cross-sectional study performed in European university students (n = 676). Sleep quality was assessed by measuring insomnia symptoms with the Athens insomnia scale (AIS). The CRAFFT screening test and AUDIT test were used to measure the use of substances of abuse.

RESULTS

Insomnia symptoms were highly prevalent (40.2%) and more common among the youngest students (p = 0.012), who had been studying at the university for less time (p = 0.018), and had high levels of illicit drug use (p = 0.037). Good sleep quality represented a significant protective factor for problematic drug use, with an OR of 0.8 (CI95%: 0.76-0.99). In contrast, the category "not having a job" represents risk 1.2 times higher (CI95%: 1.025-1.557) for problematic drug use. The CRAFFT score significantly predicted higher insomnia symptoms (AIS ≥ 6), yielding an OR of 1.2 (CI95%:1.10-1.32, p < 0.001).

CONCLUSIONS

Poor sleep quality is common in university students. There is an inverse association between higher insomnia symptoms and illicit drug abuse being a good sleep qualitya protective factor against problematic use of illicit drugs. Several personal and social consequences of illicit drug use are related to poor sleep in this population and it deserves future studies and interventions in order to improve both problems.

Social Housing Conditions Modulate the Long-Lasting Increase in Cocaine Reward Induced by Intermittent Social Defeat

Social defeat is considered the most representative animal model for studying the consequences of social stress. Intermittent social defeat (ISD) has proved to enhance the response to cocaine hedonic properties. In the present research, we evaluated if different social housing conditions, as housing with a familiar conspecific or with a female, exert a protective effect modulating the negative consequences of ISD as the increased sensitivity to cocaine and the induction of anxiety-like behavior. To achieve this objective, non-stressed or ISD OF1 male mice were divided into five different experimental groups according to their social environment: standard housing (four adult males per cage); male adolescent or adult in pairs (two males per cage); and adult males housed with a female for a short or long period (3 days vs. the whole duration of the study). Anxiety-like behavior was evaluated 19 days after the last episode of ISD using an elevated plus maze (EPM), and 24 h later the animals underwent a conditioned place preference paradigm (CPP) induced by a sub-threshold dose of cocaine (1 mg/kg). Following CPP, biological samples were taken to measure striatal levels of interleukin 6 (IL-6) and plasmatic levels of oxytocin (OT). Our results confirmed that ISD animals housed in standard condition displayed an anxious phenotype, developed CPP and had increased levels of IL-6 in the striatum. However, animals housed with a female or with a familiar male since adolescence did not develop CPP and were protected against the anxiogenic and neuroinflammatory potential of ISD stress. In the group of animals paired with a female throughout the experimental procedure, an increase in OT levels may have underlain this buffering effect, while the protective effect of being housed with a familiar male mouse seems to be related with a better resolution of the stress response. The present results expand our knowledge of the neurobiology of vulnerability to drug addiction and highlight the benefit of social support for recovery from the adverse effects of social stress.

Social modulation of drug use and drug addiction

This review aims to demonstrate how social science and behavioral neurosciences have highlighted the influence of social interactions on drug use in animal models. In neurosciences, the effect of global social context that are distal from drug use has been widely studied. For human and other social animals such as monkeys and rodents, positive social interactions are rewarding, can overcome drug reward and, in all, protect from drug use. In contrast, as other types of stress, negative social experiences facilitate the development and maintenance of drug abuse. However, interest recently emerged in the effect of so-called "proximal" social factors, that is, social interactions during drug-taking. These recent studies have characterized the role of the drug considered, the sharing of drug experience and the familiarity of the peer which interaction are made with. We also examine the few studies regarding the sensorial mediator of social behaviors and critically review the neural mediation of social factors on drug use. However, despite considerable characterization of the factors modulating distal influences, the mechanisms for proximal influences on drug use remain largely unknown. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Volitional social interaction prevents drug addiction in rat models

Addiction treatment has not been appreciably improved by neuroscientific research. One problem is that mechanistic studies using rodent models do not incorporate volitional social factors, which play a critical role in human addiction. Here, using rats, we introduce an operant model of choice between drugs and social interaction. Independent of sex, drug class, drug dose, training conditions, abstinence duration, social housing, or addiction score in Diagnostic & Statistical Manual IV-based and intermittent access models, operant social reward prevented drug self-administration. This protection was lessened by delay or punishment of the social reward but neither measure was correlated with the addiction score. Social-choice-induced abstinence also prevented incubation of methamphetamine craving. This protective effect was associated with activation of central amygdala PKCδ-expressing inhibitory neurons and inhibition of anterior insular cortex activity. These findings highlight the need for incorporating social factors into neuroscience-based addiction research and support the wider implantation of socially based addiction treatments.

Sex differences in nicotine preference

Smoking is the major cause of preventable deaths worldwide, and although there is a decline in overall smoking prevalence in developed countries, the decline in women is less pronounced than in men. Women become dependent faster and experience greater difficulties in quitting. Similar trends have been observed in animal models of nicotine/tobacco addiction. Individual differences in vulnerability to drug abuse are also observed in nicotine/tobacco addiction and point to the importance of sex differences. This Review, summarizes findings from three experimental approaches used to depict nicotine preference in animal models, intravenous and oral nicotine self-administration and nicotine-induced conditioned place preference. Nicotine preference is considered to be reflected in the animal's motivation to administer the drug (intravenously or orally) or to prefer an environment paired with the presence of the drug (conditioned place preference). These approaches all point to the importance of sex and age of the subjects; the preference of females and adolescents appear to be more pronounced than that of males and adults, respectively. A closer look at these factors will help us understand the mechanisms that underlie nicotine addiction and develop strategies to cope. Ignoring sex differences and reaching conclusions based only on studies using male subjects has resulted in erroneous generalizations in the past. Sex differences in nicotine preference have been clearly documented, and awareness on this aspect of nicotine dependence will significantly impact our success in translational research. © 2016 Wiley Periodicals, Inc.

The effects of social contact on cocaine intake in female rats

BACKGROUND

Studies conducted in male rats report that social contact can either facilitate or inhibit drug intake depending on the behavior of social partners. The purpose of the present study was to: (1) examine the effects of social contact on cocaine intake in female rats, (2) examine the behavioral mechanisms by which social contact influences cocaine intake, and (3) examine whether the estrous cycle moderates the effects of social contact on cocaine intake.

METHODS

Female rats were assigned to either isolated or pair-housed conditions in which a social partner either had access to cocaine (cocaine partner) or did not have access to cocaine (abstinent partner). Pair-housed rats were tested in custom-built operant conditioning chambers that allowed both rats to be tested simultaneously in the same chamber.

RESULTS

Rats housed with a cocaine partner self-administered more cocaine than isolated rats and rats housed with an abstinent partner. A behavioral economic analysis indicated that these differences were driven by a greater intensity of cocaine demand (i.e., greater intake at lower unit prices) in rats housed with a cocaine partner. Multivariate modeling revealed that the estrous cycle did not moderate the effects of social contact on cocaine intake.

CONCLUSIONS

These findings indicate that: (1) social contact influences cocaine self-administration in females in a manner similar to that reported in males, (2) these effects are due to differences in the effects of social contact on the intensity of cocaine demand, and (3) these effects are consistent across all phases of the estrous cycle.

The effects of sex, estrous cycle, and social contact on cocaine and heroin self-administration in rats

RATIONALE

Preclinical studies indicate that gonadal hormones are important determinants of drug self-administration. To date, little is known about the influence of sex and estrous cycle on drug self-administration in ecologically relevant social contexts.

OBJECTIVE

The objective of this study was to examine the role of sex and estrous cycle in a rat model during cocaine and heroin self-administration with male-female and female-female social dyads.

METHODS

Male and female virgin rats were trained to self-administer cocaine and heroin in operant conditioning chambers that permitted two rats to self-administer concurrently, but prevented physical contact. Experiment 1 examined cocaine self-administration on a progressive ratio schedule in male-female dyads. Experiments 2 and 3 examined heroin self-administration on a fixed ratio schedule in male-female dyads at constant and varying doses, respectively. Experiment 4 examined heroin self-administration in female-female dyads on a fixed ratio schedule.

RESULTS

Cocaine-maintained breakpoints increased by ∼17 % in females during estrus, but remained consistent in males. Heroin self-administration decreased by ∼70 % during proestrus in females whether they were isolated, housed with males, or housed with females. Heroin self-administration was lower in males than females under some conditions and was not consistently associated with the responding of females.

CONCLUSIONS

Cocaine and heroin self-administration is influenced by the estrous cycle in females when in the presence of a male partner. As a novel finding, these data illustrate that heroin self-administration is reduced in females during proestrus regardless of the social context tested. Finally, these data suggest that drug self-administration in males is only minimally influenced by the hormonal status of a female partner.

The effects of social contact on cocaine intake under extended-access conditions in male rats

Social learning theories of drug use propose that drug use is influenced by the behavior of peers. We previously reported that cocaine self-administration under limited-access conditions can be either facilitated or inhibited by social contact, depending on the behavior of a peer. The purpose of this study was to determine whether social contact influences cocaine self-administration under conditions that are more representative of problematic patterns of drug use. Male rats were assigned to either isolated or pair-housed conditions in which a social partner either had access to cocaine or did not have access to cocaine. Pair-housed rats were tested in custom-built operant conditioning chambers that allowed both rats to be tested simultaneously in the same chamber. In Experiment 1, rats were tested for 14 consecutive days during daily 6-hr test sessions. In Experiment 2, different doses of cocaine were tested in 23-hr test sessions conducted every 3 days. All groups of rats escalated their cocaine intake in Experiment 1; however, pair-housed rats with a partner without access to cocaine had lower levels of intake throughout the 14 days of testing. In Experiment 2, pair-housed rats with a partner without access to cocaine had lower levels of cocaine intake than did rats with a partner with access to cocaine, and this effect was observed at all doses of cocaine tested. These data indicate that the behavior of a social partner (i.e., whether or not that partner is also self-administering cocaine) influences cocaine self-administration under conditions that model problematic patterns of drug use. (PsycINFO Database Record

Animal models of social contact and drug self-administration

Social learning theories of drug abuse propose that individuals imitate drug use behaviors modeled by social peers, and that these behaviors are selectively reinforced and/or punished depending on group norms. Historically, animal models of social influence have focused on distal factors (i.e., those factors outside the drug-taking context) in drug self-administration studies. Recently, several investigators have developed novel models, or significantly modified existing models, to examine the role of proximal factors (i.e., those factors that are immediately present at the time of drug taking) on measures of drug self-administration. Studies using these newer models have revealed several important conclusions regarding the effects of social learning on drug abuse: 1) the presence of a social partner influences drug self-administration, 2) the behavior of a social partner determines whether social contact will increase or decrease drug intake, and 3) social partners can model and imitate specific patterns of drug self-administration. These findings are congruent with those obtained in the human laboratory, providing support for the cross-species generality and validity of these preclinical models. This mini-review describes in detail some of the preclinical animal models used to study social contact and drug self-administration to guide future research on social learning and drug abuse.

MDMA: a social drug in a social context

RATIONALE

The drug ±3,4-methylenedioxymethamphetamine (MDMA, "ecstasy," "molly") is thought to produce prosocial effects and enhance social interaction. However, in most laboratory studies to date, the participants have been tested under nonsocial conditions, which may not simulate the effects the drug produces in more naturalistic social settings.

METHODS

Healthy experienced MDMA users participated in three laboratory sessions in which they received MDMA (0.5 or 1.0 mg/kg or placebo, double blind). They were randomly assigned to one of three social conditions, in which they were tested alone (solitary (SOL); N = 10), in the presence of a research assistant (research assistant present (RAP); N = 11) or in the presence of another participant who also received the drug (other participant present (OPP); N = 11).

RESULTS

As expected, MDMA increased heart rate and blood pressure and produced positive subjective effects in all the three groups. It also increased ratings of attractiveness of another person and increased social interaction in RAP and OPP. The social context affected certain responses to the drug. The effects of MDMA were greater in the OPP condition, compared to the SOL or RAP conditions, on measures of "feel drug," "dizzy," and on cardiovascular. But responses to the drug on other measures, including social behavior, did not differ across the conditions.

CONCLUSIONS

These findings provide some support for the idea that drugs produce greater effects when they are used in the presence of other drug users. However, the influence of the social context was modest, and it remains to be determined whether other variables related to social context would substantially alter the effects of MDMA or other drugs.