Synergistic interaction between nicotine and social rewards in adolescent male rats

Varenicline but not cotinine increased the value of a visual stimulus reinforcer in rats: No evidence for synergy of the two compounds

Smoking is the leading cause of preventable death worldwide, with <7 % of smoking cessation attempts being met with success. Nicotine, the main addictive agent in cigarettes, enhances the reinforcing value of other environmental rewards. Under some circumstances, this reward enhancement maintains nicotine consumption. Varenicline (i.e., cessation aid Chantix™) also has reward-enhancement effects via nicotinic acetylcholine receptor agonism (nAChRs) - albeit less robust than nicotine. Cotinine is the major metabolite of nicotine. Recent studies suggest that cotinine is a positive allosteric modulator (PAM) and/or a weak agonist at nAChRs. Thus, cotinine may enhance the behavioral effects of nAChR compounds such as varenicline and/or exert some behavioral effects alone. We used 20 (10M, 10F) Sprague-Dawley rats to assess reward-enhancement within-subjects by examining responding maintained by a reinforcing visual stimulus on a Variable Ratio 2 schedule of reinforcement. To assess the reward-enhancing effects of cotinine, rats received one injection of cotinine (saline, 0.1, 0.3, 1.0, 3.0, 6.0 mg/kg) before each 1 h session. To assess cotinine and varenicline interactions, rats received an injection of cotinine (saline, 0.1, 1.0, or 6.0 mg/kg) and of varenicline (saline, 0.1, 0.3, 1.0, or 3.0 mg/kg) before the session. While we replicated prior work identifying reward-enhancement by 0.1, 0.3, and 1.0 mg/kg varenicline, cotinine alone did not produce reward-enhancement nor augment the reward-enhancing effects of varenicline. Future studies may consider examining the reward-enhancing effects of cotinine with other reinforcers or co-administered with other smoking cessation aids such as bupropion.

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.

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.

Elucidating the reinforcing effects of nicotine: a tribute to Nadia Chaudhri

Nadia Chaudhri worked with us as a graduate student in the Center for Neuroscience at the University of Pittsburgh from 1999 until she earned her PhD in 2005, a time that coincided with the discovery in our lab of the dual reinforcing actions of nicotine, a concept that she played an important role in shaping. The research that was described in her doctoral thesis is among the foundational pillars of the now well-accepted notion that nicotine acts as both a primary reinforcer and an amplifier of other reinforcer stimuli. This reinforcement-enhancing action of nicotine is robust and likely to be a powerful driver of nicotine use. Below, we discuss the evidence that these two actions of nicotine - primary reinforcement and reinforcement enhancement - are distinct and dissociable, a finding that Nadia was closely associated with. We go on to address two other topics that greatly interested Nadia during that time, the generalizability of the reinforcement-enhancing action of nicotine to multiple classes of reinforcing stimuli and potential sex differences in the dual reinforcing actions of nicotine. The research has greatly expanded since Nadia's involvement, but the core ideas that she helped to develop remain central to the concept of the dual reinforcing actions of nicotine and its importance for understanding the drivers of nicotine use.

The effect of intraperitoneal and intra-RMTg infusions of CTAP on rats' social interaction

Social interaction is necessary for the development of individuals and society. Social interaction behaviors are rewarding. Similar to exogenous opioids, social interaction behaviors are able to induce rewarding effects that are regulated by the endogenous opioid system as well. As one type of opioid receptor, μ-opioid receptors (MORs), are densely expressed in the rostromedial tegmental nucleus (RMTg), which results in the RMTg being extremely sensitive to rewarding effects induced by exogenous and endogenous opioids. Here, we investigated how RMTg MORs played a role in rewarding effects induced by social interaction behaviors of male Wistar rats, using a conditioned place preference (CPP) model. Results showed that the CPP induced by social interaction behaviors was inhibited when the function of MORs was blocked via injecting CTAP (a selective MOR antagonist) intraperitoneally, and intra-RMTg injections of lower doses of CTAP affected the CPP in the same way. In addition, injecting CTAP intraperitoneally significantly inhibited the expression of pouncing behavior, while intra-RMTg injections of CTAP significantly inhibited the expression of all three types of social behaviors. These results suggest that RMTg MORs may be a crucial target and remain to be further explored in order to better understand the mechanism of the rewarding effects of social interaction behaviors.

Post-weaning social isolation increases the incentive value of nicotine-related contexts and decreases the accumulation of ΔFosB in nucleus accumbens in adolescent rats

Adolescent social conditions profoundly affect vulnerability to drug abuse. Preclinical studies have shown that preventing social interactions during adolescence increases the rewarding effects of drugs like alcohol, cocaine, or amphetamines, however, little data exist regarding the impact of social isolation on nicotine effects. The current study evaluated the effects of differential rearing conditions during adolescence (isolation or group rearing) on (1) conditioned place preference induced by low nicotine doses (0.1 or 0.3 mg/kg) and (2) sensitization to the locomotor effects of nicotine after sub-chronic administration (3) and accumulation of ΔFosB in nucleus accumbens (NAc). Results showed that nicotine induced place preference in isolated and grouped rats, but the effect was more persistent for the rats reared in isolation. Isolated reared rats also exhibited lower levels of ΔFosB accumulation in NAc. No differences were found in the behavioral sensitization to nicotine effects between rearing conditions. The results suggest that isolation engenders a more robust incentive value of nicotine-related contexts. This effect could be related to the basal expression of ΔFosB: lower levels of this transcription factor seem to impair the motivation of isolated reared rats and increase their vulnerability to the effects of drugs like nicotine.

The Protective Effect of Social Reward on Opioid and Psychostimulant Reward and Relapse: Behavior, Pharmacology, and Brain Regions

Until recently, most modern neuroscience research on addiction using animal models did not incorporate manipulations of social factors. Social factors play a critical role in human addiction: social isolation and exclusion can promote drug use and relapse, while social connections and inclusion tend to be protective. Here, we discuss the state of the literature on social factors in animal models of opioid and psychostimulant preference, self-administration, and relapse. We first summarize results from rodent studies on behavioral, pharmacological, and circuit mechanisms of the protective effect of traditional experimenter-controlled social interaction procedures on opioid and psychostimulant conditioned place preference, self-administration, and relapse. Next, we summarize behavioral and brain-mechanism results from studies using newer operant social-interaction procedures that inhibit opioid and psychostimulant self-administration and relapse. We conclude by discussing how the reviewed studies point to future directions for the addiction field and other neuroscience and psychiatric fields, and their implications for mechanistic understanding of addiction and development of new treatments.SIGNIFICANCE STATEMENT In this review, we propose that incorporating social factors into modern neuroscience research on addiction could improve mechanistic accounts of addiction and help close gaps in translating discovery to treatment. We first summarize rodent studies on behavioral, pharmacological, and circuit mechanisms of the protective effect of both traditional experimenter-controlled and newer operant social-interaction procedures. We then discuss potential future directions and clinical implications.

Paired Housing or a Socially-Paired Context Decreases Ethanol Conditioned Place Preference in Male Rats

Alcohol abuse dramatically affects individuals’ lives nationwide. The 2020 National Survey on Drug Use and Health (NSDUH) estimated that 10.2% of Americans suffer from alcohol use disorder. Although social support has been shown to aid in general addiction prevention and rehabilitation, the benefits of social support are not entirely understood. The present study sought to compare the benefits of social interaction on the conditioned ethanol approach behavior in rats through a conditioned place preference (CPP) paradigm in which a drug is paired with one of two distinct contexts. In experiment 1A, rats were single-housed and received conditioning trials in which ethanol was paired with the less preferred context. In experiment 1B, rats underwent procedures identical to experiment 1A, but were pair-housed throughout the paradigm. In experiment 1C, rats were single-housed, but concurrently conditioned to a socially-paired context and an ethanol-paired context. By comparing the time spent between the ethanol-paired environment and the saline-paired or socially-paired environment, we extrapolated the extent of ethanol approach behavior in the pair-housed, single-housed, and concurrently conditioned rats. Our results revealed that social interaction, both in pair-housed animals or concurrently socially-conditioned animals, diminished the ethanol approach behavior, which highlights the importance of social support in addiction prevention, treatment, and recovery programs.

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.

Is It Possible to Shift from Down to Top Rank? A Focus on the Mesolimbic Dopaminergic System and Cocaine Abuse

Impaired social behavior is a common feature of many psychiatric disorders, in particular with substance abuse disorders. Switching the preference of the substance-dependent individual toward social interaction activities remains one of the major challenges in drug dependence therapy. However, social interactions yield to the emergence of social ranking. In this review, we provide an overview of the studies that examined how social status can influence the dopaminergic mesolimbic system and how drug-seeking behavior is affected. Generally, social dominance is associated with an increase in dopamine D_2/3 receptor binding in the striatum and a reduced behavioral response to drugs of abuse. However, it is not clear whether higher D₂ receptor availability is a result of increased D₂ receptor density and/or reduced dopamine release in the striatum. Here, we discuss the possibility of a potential shift from down to top rank via manipulation of the mesolimbic system. Identifying the neurobiology underlying a potential rank switch to a resilient phenotype is of particular interest in order to promote a positive coping behavior toward long-term abstinence from drugs of abuse and a protection against relapse to drugs. Such a shift may contribute to a more successful therapeutic approach to cocaine addiction.

Time-dependent regulation of perineuronal nets in the cerebellar cortex during abstinence of cocaine-self administration

RATIONALE

The probability of structural remodeling in brain circuits may be modulated by molecules of perineuronal nets (PNNs) that restrict neuronal plasticity to stabilize circuits. Animal research demonstrates that addictive drugs can remodel PNNs in different brain regions, including the cerebellum.

OBJECTIVE

This study aimed to investigate the effects of short versus extended access to cocaine self-administration on PNN expression around Golgi interneurons in the cerebellar cortex after different periods of abstinence.

METHODS

After 1 week of training (2 h/day), Sprague-Dawley rats self-administered cocaine daily for 20 days under short (ShA) or extended (LgA) access. PNN expression in the cerebellum was assessed after 1 day, 7 days, and 28 days of forced abstinence. PNNs were immunolabeled using Wisteria floribunda agglutinin (WFA) and captured by confocal microscopy.

RESULTS

WFA intensity increased in PNN-bearing Golgi neurons over the abstinence period and a higher proportion of more intense PNNs were formed throughout the first month of abstinence. After the first 24 h of cocaine abstinence, however, we found a reduction in WFA intensity in the cerebellar cortex of rats with ShA to cocaine as compared to naïve animals. When comparing with naïve rats, LgA rats showed consistent PNN upregulation at 28 days of cocaine abstinence.

CONCLUSIONS

Our results suggest that cocaine self-administration produces modifications in PNN that enhance conditions for synaptic plasticity in the cerebellar cortex. These modifications are revealed shortly after the cessation of drug intake but PNNs become more intense during protracted abstinence in the LgA group, pointing to the stabilization of drug-induced synaptic changes. These findings indicate that extended access to cocaine self-administration dynamically regulates conditions for plasticity in the cerebellum during abstinence.

The neurochemistry of social reward during development: What have we learned from rodent models?

Social rewards are fundamental to survival and overall health. Several studies suggest that adequate social stimuli during early life are critical for developing appropriate socioemotional and cognitive skills, whereas adverse social experiences negatively affect the proper development of brain and behavior, by increasing the susceptibility to develop neuropsychiatric conditions. Therefore, a better understanding of the neural mechanisms underlying social interactions, and their rewarding components in particular, is an important challenge of current neuroscience research. In this context, preclinical research has a crucial role: Animal models allow to investigate the neurobiological aspects of social reward in order to shed light on possible neurochemical alterations causing aberrant social reward processing in neuropsychiatric diseases, and they allow to test the validity and safety of innovative therapeutic strategies. Here, we discuss preclinical research that has investigated the rewarding properties of two forms of social interaction that occur in different phases of the lifespan of mammals, that is, mother-infant interaction and social interactions with peers, by focusing on the main neurotransmitter systems mediating their rewarding components. Together, the research performed so far helped to elucidate the mechanisms of social reward and its psychobiological components throughout development, thus increasing our understanding of the neurobiological substrates sustaining social functioning in health conditions and social dysfunction in major psychiatric disorders.

Western Diet Consumption During Development: Setting the Stage for Neurocognitive Dysfunction

The dietary pattern in industrialized countries has changed substantially over the past century due to technological advances in agriculture, food processing, storage, marketing, and distribution practices. The availability of highly palatable, calorically dense foods that are shelf-stable has facilitated a food environment where overconsumption of foods that have a high percentage of calories derived from fat (particularly saturated fat) and sugar is extremely common in modern Westernized societies. In addition to being a predictor of obesity and metabolic dysfunction, consumption of a Western diet (WD) is related to poorer cognitive performance across the lifespan. In particular, WD consumption during critical early life stages of development has negative consequences on various cognitive abilities later in adulthood. This review highlights rodent model research identifying dietary, metabolic, and neurobiological mechanisms linking consumption of a WD during early life periods of development (gestation, lactation, juvenile and adolescence) with behavioral impairments in multiple cognitive domains, including anxiety-like behavior, learning and memory function, reward-motivated behavior, and social behavior. The literature supports a model in which early life WD consumption leads to long-lasting neurocognitive impairments that are largely dissociable from WD effects on obesity and metabolic dysfunction.

Vulnerability factors for mephedrone-induced conditioned place preference in rats-the impact of sex differences, social-conditioning and stress

RATIONALE

Mephedrone is a frequently overused drug of abuse that belongs to the group of novel psychoactive substances. Although its mechanism of action, as well as toxic and psychoactive effects, has been widely studied, the role of different factors that could contribute to the increased vulnerability to mephedrone abuse is still poorly understood.

OBJECTIVES

The aim of the presented study was to assess the impact of several factors (sex differences, social-conditioning, and chronic mild unpredictable stress - CMUS) on the liability to mephedrone-induced reward in Wistar rats.

METHODS

The rewarding effects of mephedrone in male and female rats were assessed using the conditioned place preference (CPP) procedure. Furthermore, the impact of social factor and stress was evaluated in male rats using social-CPP and CMUS-dependent CPP, respectively.

RESULTS

Mephedrone induced classic-CPP in female (10 mg/kg), as well as in male (10 and 20 mg/kg) rats. However, the impact of mephedrone treatment during social-CPP was highly dose-dependent as the rewarding effects of low dose of mephedrone (5 mg/kg; non-active in classic-CPP) were potentiated when administered during social-conditioning. Interestingly, social-conditioning with a higher dose of 20 mg/kg (that induced classic-CPP) was able to reverse these effects. Finally, CMUS potentiated rewarding effects of a low dose of mephedrone (5 mg/kg) and increased the level of corticosterone in rats' prefrontal cortex and hippocampus.

CONCLUSIONS

Altogether, the presented results give new insight into possible factors underlying the vulnerability to mephedrone abuse and can serve as a basis for further studies assessing mechanisms underlying observed effects.

Methamphetamine and social rewards interact to produce enhanced conditioned place preference in male adolescent rats

Elucidating the influence of social context on drug reward is critical for understanding substance use disorders. Adolescents demonstrate enhanced sensitivity to drug and social rewards. However, the extent to which methamphetamine interacts with social reward in adolescents has not been thoroughly examined. Therefore, the present study used the conditioned place preference (CPP) model to examine the relationship between methamphetamine and social rewards in adolescent male rats. Sprague-Dawley rats (PND 30) were randomly assigned to one of the following four conditioning groups: saline alone (SA), methamphetamine alone (MA), saline with a social partner (SS) or methamphetamine with a social partner (MS). Testing occurred in a two-chamber biased apparatus across seven consecutive days using parameters presumed to be sub-threshold for establishing social- and methamphetamine-induced CPP. Similar to previous reports for nicotine and cocaine, the present results indicate that rats receiving methamphetamine with a social partner (i.e., MS) during conditioning demonstrated a significantly greater preference shift compared to all other groups. These findings further highlight the importance of social context in influencing the magnitude of drug reward during adolescence.

A review of psychosocial factors linked to adolescent substance use

PURPOSE

Informed by ecological theories and models of influence, this review discusses various psychosocial risk and protective factors that contribute to adolescent substance use behavior. Given typical patterns of substance use initiation during this developmental period, an emphasis is placed on alcohol, cigarette, and marijuana use.

FINDINGS

Consistent with bioecological theories, peers and parents tend to have the strongest effect on adolescent substance use behavior. Influences can be both direct, such as offers and availability to use substances, as well as indirect influences, such as the perception of substance use approval. Schools and neighborhoods also contribute to adolescent substance use behavior, but this effect is often less direct. Moreover, the effect of neighborhoods on adolescent behavior reflects both structural components (e.g., neighborhood racial composition, teacher-student ratios) in addition to social process (e.g., neighborhood social cohesion, school connectedness). A review of parallel studies conducted with animals is also provided.

SUMMARY

Adolescent substance use behavior does not occur in a vacuum. Investigations must encompass the relevant social ecologies that affect adolescent behavior, including family, peer, school, and neighborhood contexts to provide a more complete understanding of substance use etiology.

Social interaction reward: A resilience approach to overcome vulnerability to drugs of abuse

Drug addiction is a multifactorial disorder resulting from the complex interaction between biological, environmental and drug-induced effects. Generally, stress is a well-known risk factor for the development of drug addiction and relapse. While most of the research focuses on risk factors that increase the vulnerability to drugs of abuse, recent studies are focusing on the areas of strength/positive coping approaches that can increase resistance to drugs of abuse. In this review, we concentrate on resilience, seen as a dynamic process, which can allow individuals to positively adapt within the context of a specific risk for psychiatric illness. Here, we discuss the effects of social stress in animal models on drug use, particularly cocaine. In contrast, we suggest social interaction reward when available as an alternative to drug use as an approach contracting negative stress effects and increasing resistance to drug use. Indeed, interventions, which aim at enhancing resilience to stress through the facilitation of social interaction and the enhancement of social support, could be particularly effective in helping people cope with stress and preventing drug use problems or relapse. Finally, understanding the neurobiological mechanisms underlying protective factors such as social interaction reward should provide the basis for future evidence-based interventions targeting substance abuse and stress-related pathologies.

Relevance of number and physiological status of conspecifics in preventing stress-induced decreases in newly proliferated cells and neuroblasts

RATIONALE AND OBJECTIVE

The presence of three conspecifics prevents stress-induced decreases in newly proliferated cells and neuroblasts in mouse dentate gyrus (DG). In this study, we sought to determine how many conspecifics are required to exert these protective effects against stress. In addition, we manipulated the physiological status of those conspecifics in the context of their stress-buffering effects and used airborne oxytocin exposure as a substitute for the presence of conspecifics.

MATERIALS AND METHODS

Bromodeoxyuridine staining was used to indicate the newly proliferated cells and co-staining with doublecortin to reveal the proliferative neuroblasts.

RESULTS

Presentation of three intact and lipopolysaccharide-treated conspecifics prevented the stress-induced decreases in the number of newly proliferated cells and neuroblasts in DG. Presentation of one saline- or oxytocin (OT)-treated conspecific did not exert observable stress-buffering effects. In contrast, airborne oxytocin prevented the stress-induced decreases in DG cell proliferation and early neurogenesis, while pretreatment with L-371,257, a selective OT receptor antagonist, abolished the buffering effects of OT.

CONCLUSIONS

Physical interaction with the conspecifics and conspecifics' sickness, at best, play a minor role in mediating the buffering effects against stress-induced decreases in DG cell proliferation or early neurogenesis. Moreover, stress-buffering effects are negligible with the presence of only one conspecific. Finally, airborne OT produced stress-buffering effects possibly via its stimulation of OT receptors. Oxytocin merits further study as a substitute for the stress-buffering effects of companions.

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'.

Social influence shifts valuation of appetitive cues in early adolescence and adulthood

Other people can profoundly affect one's opinions and decisions. In the current study, we compared the effects of peer influence on responses to a primary reward-food-in both young adolescents and adults. Food is critical for survival, and in addition to its rewarding properties, habits and practices surrounding eating are heavily influenced by social and cultural norms. To address the impact of peer influence on food valuations, young adolescents ages 10-14 and young adults ages 18-22 rated the desirability of foods before and after seeing peer opinions about those foods. We then compared the degree to which participants changed their ratings of food desirability as a function of the type of social information received (e.g., peers liking a food more or less than did the participant). We found that all participants' ratings conformed to the peer ratings and that adolescents had less stable valuations across all conditions over time. These results provide evidence for the effectiveness of peer influence in shifting valuations of appetitive stimuli and can inform interventions aimed at improving healthy eating choices. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

A review of the effects of nicotine on social functioning

Many smokers are aware that smoking is a dangerous health behavior and eventually try to quit smoking. Unfortunately, most quit attempts end in failure. Traditionally, the addictive nature of smoking has been attributed to the pharmacologic effects of nicotine. In an effort to offer a more comprehensive, biobehavioral analysis of smoking behavior and motivation, some researchers have begun to consider the role of social factors in smoking. In line with recent recommendations to integrate social and pharmacological analyses of smoking, we reviewed the experimental literature examining the effects of nicotine and nicotine withdrawal on social functioning. The review identified 13 studies that experimentally manipulated nicotine and assessed social functioning, 12 of which found support for nicotine's enhancement of social functioning. Although few experiments have investigated social functioning, they nevertheless offer compelling evidence that nicotine enhances social functioning in smokers and suggest that nicotine deprivation may hamper social functioning in those dependent on nicotine. Future directions for investigating social outcomes and context in those who use nicotine products are discussed with a focus on leveraging advances in social and developmental psychology, animal research, sociology, and neuroimaging to more comprehensively understand smoking behavior. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Opioid modulation of social play reward in juvenile rats

Social play behaviour is a vigorous form of social interaction abundant during the juvenile and adolescent phases of life in many mammalian species, including rats and humans. Social play is thought to be important for social, emotional and cognitive development. Being a rewarding activity, the expression of social play depends on its pleasurable and motivational properties. Since opioids have been widely implicated in reward processes, in the present study we investigated the role of opioids in the pleasurable and motivational properties of social play behaviour in rats. To assess social play motivation, an operant conditioning setup was used in which rats responded for social play under a progressive ratio schedule of reinforcement. Treatment with the opioid receptor agonist morphine reduced responding for social play at the highest dose tested, likely due to its rate-limiting effects. Morphine treatment increased the expression of social play behaviour during reinforced periods. The acquisition of social play-induced conditioned place preference (CPP) in a subeffective conditioning protocol was enhanced by treatment with morphine. Morphine treatment alone also induced CPP. In contrast, antagonizing opioid receptors with naloxone reduced responding for social play, the expression of social play and blocked the development of social play-induced CPP. These data implicate opioid neurotransmission in both the pleasurable and the motivational aspects of social play behaviour in rats. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

The effects of nicotine on conditioning, extinction, and reinstatement in humans

Nicotine has been shown to enhance the reinforcement and reward-responsiveness of non-nicotine stimuli. To determine whether nicotine enhances the strength of conditioning to context, undergraduate participants with varying levels of nicotine dependence were recruited for a two-day study and tested on a virtual reality (VR) conditioned place preference (CPP) paradigm. On day one, participants explored two virtual rooms where they received multiple pairings of M&M rewards in one room and no rewards in the other room, followed by a free-access test session with no rewards. On day two, participants received three test sessions to assess extinction. Subsequently, participants received M&Ms. in a novel context and were then tested for reinstatement. Prior to testing on each day, subjects were administered either nicotine (4mg) or placebo lozenges, in a between-subjects, four-group, 2×2 design (nicotine or placebo on days 1 and 2). After conditioning on day one, only participants who received placebo exhibited a CPP by spending significantly more time in the room previously-paired with M&Ms. Contrary to our hypothesis, nicotine-treated participants did not display a significant CPP, and there were no significant differences between treatment groups. However, post hoc analysis indicated that in a subset of participants with greater nicotine dependence, the nicotine group displayed a CPP by rating the M&M-paired room as significantly more enjoyable than those who received placebo. Additionally, while neither treatment group showed significant place preferences during the first two extinction sessions on Day 2, individuals who received nicotine on Day 1 or placebo on Day 2 spent significantly more time in the M&M-paired room during the final extinction session. Finally, those who received nicotine on Day 2 exhibited significantly greater reinstatement compared to placebo-treated participants. These results partially support preclinical evidence that nicotine can affect learning, extinction, and reinstatement.

Effects of the phencyclidine model of schizophrenia and nicotine on total and categorized ultrasonic vocalizations in rats

Patients with schizophrenia smoke cigarettes at a higher rate than the general population. We hypothesized that a factor in this comorbidity is sensitivity to the reinforcing and reinforcement-enhancement effects of nicotine. Phencyclidine (PCP) was used to model behavioral changes resembling negative symptoms of schizophrenia in rats. Ultrasonic vocalizations (USVs) in rats have been used to measure emotional states, with 50 kHz USVs indicating positive states and 22 kHz USVs indicating negative states. Total and categorized numbers of 22 and 50 kHz USVs and USVs during a visual stimulus (e.g. a potential measure of reinforcement-enhancement) were examined in rats following injection of PCP (2.0 mg/kg) and/or nicotine (0.2 or 0.4 mg/kg) daily for 7 days. PCP was then discontinued and all rats received nicotine (0.2 and 0.4 mg/kg) and PCP (2.0 mg/kg) on three challenge days. PCP acutely decreased 50 kHz vocalizations, whereas repeated nicotine potentiated rates of vocalizations, with similar patterns during light presentations. Rats in the PCP and nicotine combination groups made more 50 kHz vocalizations compared with rats in the control groups on challenge days. We conclude that PCP may produce a reward deficit, which is shown by decreased 50 kHz USVs, and behaviors post-PCP exposure may best model the comorbidity between schizophrenia and nicotine.

Social learning promotes nicotine self-administration by facilitating the extinction of conditioned aversion in isogenic strains of rats

Both social environment and genetic factors are critical for smoking initiation and nicotine addiction. We reported that rats developed conditioned flavor (i.e., taste and odor) aversion to intravenously self-administered (IVSA) nicotine, and that social learning promoted nicotine IVSA with flavor cues. We thus tested the hypothesis that socially acquired nicotine IVSA is a heritable trait by using female rats of six inbred strains and six F1 hybrids. Each strain was tested for 10 daily IVSA sessions. We found that the intake of nicotine (15 and 30 μg/kg/inf) varied among these strains by 33.7–56.6-fold. The heritability of nicotine intake was estimated to be 0.54–0.65. Further, there was a strong correlation in nicotine intake (R² = 0.85, p < 0.0001) between the two nicotine doses. Another cohort of rats was given three daily IVSA sessions followed by five sessions that tested conditioned flavor aversion. Nicotine intake was highly correlated with the extinction of the conditioned aversion (R² = 0.58, p < 0.005). These data showed that nicotine intake in the socially acquired nicotine self-administration model is controlled by genetic factors and that the role of social learning is likely in facilitating the extinction of conditioned aversive response to nicotine.

Differential effects of pair housing on voluntary nicotine consumption: a comparison between male and female adolescent rats

RATIONALE

Tobacco smoking occurs in a wide array of social circumstances. Social support for quitting is generally used to stop smoking, while peer interactions may be a crucial factor in triggering tobacco use among adolescents.

OBJECTIVES

To determine the role of social factors on nicotine dependence, we compared single- and pair-housed rats subjected to voluntary oral nicotine consumption tests.

METHODS

Six-week-old adolescent rats were subjected to experimental procedures and assigned to one of the following groups: a male single group, a male pair group with a sibling, a female single group, and a female pair group with a sibling. To measure voluntary nicotine intake, we adopted a two-bottle free-choice paradigm for each two days using 25 μg/ml and 100 μg/ml nicotine solution.

RESULTS

There were no differences in change in body weight or food intake between the two groups of either sex. Pair-housed female rats showed a reduction in nicotine consumption and preference for both low- and high-dose nicotine solution, while pair-housed male rats showed only reduced consumption and preference for high-dose nicotine solution, but not low-dose solution, as compared to single-housed male rats.

CONCLUSIONS

Nicotine consumption is sex-dependently controlled by the social circumstances of rats. This study broadens our perspectives on the role of social interactions as a therapeutic strategy to treat nicotine addiction-related behaviors depending on sex.

Social context has differential effects on acquisition of nicotine self-administration in male and female rats

RATIONAL

Smoking typically begins during adolescence or early adulthood in a social context, yet the role of social context in animal models is poorly understood.

OBJECTIVES

The present study examined the effect of social context on acquisition of nicotine self-administration.

METHODS

Sixty-day-old male and female Sprague-Dawley rats were trained to press a lever for nicotine (0.015 mg/kg, IV) or saline infusions (males only) on a fixed ratio (FR1) schedule of reinforcement across nine sessions in duplex chambers that were conjoined with either a solid wall or a wall containing wire mesh creating a social context between rat dyads (social visual, auditory, and olfactory cues). In a subsequent experiment, sex differences and dose-dependent effects of nicotine [0 (saline), 0.015 or 0.03 mg/kg, IV] were directly compared in rats trained in the isolated or social context on a schedule progressing from FR1 to FR3. These rats were given 20 sessions followed by 3 extinction sessions.

RESULTS

We consistently found transient social facilitation of low-dose nicotine self-administration in males during the first session. However, across training overall, we found social suppression of nicotine intake that was most prominent in females during later sessions.

CONCLUSIONS

Collectively, these findings suggest that at the age of transition from adolescence to adulthood, a social context enhances the initial reinforcing effects of nicotine in males, but protects against nicotine intake during later sessions especially in females. These findings highlight the importance of sex and social context in studying neural mechanisms involved in initiation of nicotine use.

Nicotine Acutely Enhances Reinforcement from Non-Drug Rewards in Humans

Preclinical research documents that, aside from the primary and secondary reinforcing effects of nicotine intake itself, nicotine also acutely enhances the reinforcing efficacy of non-drug reinforcers ("rewards"). Study of these effects in humans has largely been overlooked, but very recent findings suggest they may have clinical implications for more fully understanding the persistence of tobacco dependence. This overview first outlines the topic and notes some recent human studies indirectly addressing nicotine effects on related responses (e.g., subjective ratings), explaining why those findings do not directly confirm enhancement of behavioral reinforcement per se due to nicotine. Then, the methodology used in the subsequently presented studies is described, demonstrating how those studies specifically did demonstrate enhancement of reinforced responding for non-drug rewards. The main section focuses on the limited controlled research to date directly assessing nicotine's acute reinforcement-enhancing effects in humans, particularly as it relates to reinforced behavioral responding for non-drug rewards in non-human animal models. After detailing those few existing human studies, we address potential consequences of these effects for dependence and tobacco cessation efforts and then suggest directions for future research. This research indicates that nicotine per se increases responding in humans that is reinforced by some rewards (auditory stimuli via music, visual stimuli via video), but perhaps not by others (e.g., money). These reinforcement-enhancing effects in smokers are not due to dependence or withdrawal relief and can be restored by a small amount of nicotine (similar to a smoking lapse), including from e-cigarettes, a non-tobacco nicotine product. Future clinical research should examine factors determining which types of rewards are (or are not) enhanced by nicotine, consequences of the loss of these nicotine effects after quitting smoking, potential individual differences in these effects, and the possibility that nicotine via nicotine replacement therapy and non-nicotine quit medications may attenuate loss of these effects upon quitting. Further study with humans of nicotine's reinforcement-enhancing effects may provide a more complete understanding of smoking persistence and added mechanisms of cessation medication efficacy.

The case for investigating social context in laboratory studies of smoking

BACKGROUND

With increasing frequency, addiction is conceived of as a brain disease, and such accounts seem especially pertinent with regard to the rapid delivery of nicotine to the brain via cigarette smoke. Moreover, drug administration trials (cigarette puffs) suggest that the behavior of smoking becomes automatized, with individuals developing prototypical approaches to smoking a cigarette. Compared with presumably more social activities, such as drinking alcohol, there may be little opportunity for social processes to influence smoking behavior. However, survey research examining smoking motivation often reveals a broadly defined 'social' factor and field research suggests that social context does influence smoking.

ARGUMENT

We posit that laboratory smoking research has largely ignored social contextual factors that may help to understand better the precise mechanisms underlying smoking behavior and smoking motivation.

METHOD

We reviewed laboratory studies examining the effect of social context (operationalized as modeling) on smoking behavior. Studies were identified by searching PsychInfo and Medline using the following keywords: smoking, nicotine, tobacco, cigarette, consumption, topography, puff, smoking behavior, cigarettes smoked, modeling, imitation, social context, social influence and peer pressure. The reference and citation lists of these studies were then searched to identify additional studies.

CONCLUSIONS

Few laboratory smoking studies target social context. Those few studies indicate that smoking behavior can be influenced by the presence of others. There is also some evidence that social context influences the effects of smoking as well as processes related to self-perception and self-regulation that reinforce smoking and hamper smoking cessation efforts.

Reward-centricity and attenuated aversions: An adolescent phenotype emerging from studies in laboratory animals

Adolescence is an evolutionarily conserved developmental period, with neural circuits and behaviors contributing to the detection, procurement, and receipt of rewards bearing similarity across species. Studies with laboratory animals suggest that adolescence is typified by a "reward-centric" phenotype-an increased sensitivity to rewards relative to adults. In contrast, adolescent rodents are reportedly less sensitive to the aversive properties of many drugs and naturally aversive stimuli. Alterations within the mesocorticolimbic dopamine and endocannabinoid systems likely contribute to an adolescent reward-sensitive, yet aversion-resistant, phenotype. Although early hypotheses postulated that developmental changes in dopaminergic circuitry would result in a "reward deficiency" syndrome, evidence now suggests the opposite: that adolescents are uniquely poised to seek out hedonic stimuli, experience greater "pleasure" from rewards, and consume rewarding stimuli in excess. Future studies that more clearly define the role of specific brain regions and neurotransmitter systems in the expression of behaviors toward reward- and aversive-related cues and stimuli are necessary to more fully understand an adolescent-proclivity for and vulnerability to rewards and drugs of potential abuse.

The neurobiology of social play and its rewarding value in rats

In the young of many mammalian species, including humans, a vigorous and highly rewarding social activity is abundantly expressed, known as social play behaviour. Social play is thought to be important for the development of social, cognitive and emotional processes and their neural underpinnings, and it is disrupted in pediatric psychiatric disorders. Here, we summarize recent progress in our understanding of the brain mechanisms of social play behaviour, with a focus on its rewarding properties. Opioid, endocannabinoid, dopamine and noradrenaline systems play a prominent role in the modulation of social play. Of these, dopamine is particularly important for the motivational properties of social play. The nucleus accumbens has been identified as a key site for opioid and dopamine modulation of social play. Endocannabinoid influences on social play rely on the basolateral amygdala, whereas noradrenaline modulates social play through the basolateral amygdala, habenula and prefrontal cortex. In sum, social play behaviour is the result of coordinated activity in a network of corticolimbic structures, and its monoamine, opioid and endocannabinoid innervation.

Immediate early gene expression reveals interactions between social and nicotine rewards on brain activity in adolescent male rats

Smoking initiation predominantly occurs during adolescence, often in the presence of peers. Therefore, understanding the neural mechanisms underlying the rewarding effects of nicotine and social stimuli is vital. Using the conditioned place preference (CPP) procedure, we measured immediate early gene (IEG) expression in animals following exposure either to a reward-conditioned environment or to the unconditioned stimuli (US). Adolescent, male rats were assigned to the following CPP US conditions: (1) Saline+Isolated, (2) Nicotine+Isolated, (3) Saline+Social, or (4) Nicotine+Social. For Experiment 1, brain tissue was collected 90min following the CPP expression test and processed for Fos immunohistochemistry. We found that rats conditioned with nicotine with or without a social partner exhibited CPP; however, we found no group differences in Fos expression in any brain region analyzed, with the exception of the nucleus accumbens core that exhibited a social-induced attenuation in Fos expression. For Experiment 2, brain tissue was collected 90min following US exposure during the last conditioning session. We found social reward-induced increases in IEG expression in striatal and amydalar subregions. In contrast, nicotine reduced IEG expression in prefrontal and striatal subregions. Reward interactions were also found in the dorsolateral striatum, basolateral amygdala, and ventral tegmental area where nicotine alone attenuated IEG expression and social reward reversed this effect. These results suggest that in general social rewards enhance, whereas nicotine attenuates, activation of mesocorticolimbic regions; however, the rewards given together interact to enhance activation in some regions. The findings contribute to knowledge of how a social environment influences nicotine effects.

Common experience modifies the reinforcing properties of methamphetamine-injected cage mates but not morphine-injected cage mates in C57 mice

The aim of this study was to determine whether previous exposure to a drug affects the social facilitation of conditioned place preference (CPP) for a drug-injected cage mate. Twenty-two male C57/BL6J mice received drug injections (methamphetamine or morphine) and 22 male C57/BL6J mice received saline injections. All 44 mice then received CPP training, during which one compartment of a conventional CPP apparatus was associated with a drug-injected cage mate (stimulus mouse) and the other compartment was associated with a saline-injected cage mate (stimulus mouse). The subject mice did not receive any drug injection during this CPP training. Time spent in the compartment associated with the drug-injected cage mate was measured before and after training. Subject mice that had previously received methamphetamine injections showed an increase in the time spent in the compartment associated with the methamphetamine-injected cage mate after CPP training. This effect was not observed in subject mice that had previously received saline injections. Subject mice did not show an increase in the time spent in the compartment associated with the morphine-injected cage mate irrespective of whether they had previously received morphine or saline injections. Therefore, in agreement with previous reports, common experience with methamphetamine induced reinforcing properties, but that with morphine did not.

The effects of a shared history of drug exposure on social choice

Selection theories of drug use propose that individuals choose or self-select into peer groups on the basis of perceived similarities with other group members with regard to their beliefs, attitudes, and histories of drug use. The purpose of the present study was to determine whether a shared history of drug exposure would influence choice of a social partner. Adolescent male rats were treated with either cocaine (3.0 mg/kg, intraperitoneally) or saline and their preference for a cocaine-treated rat or a saline-treated rat was measured in a partner preference test. Next, a series of conditioning trials were conducted in which rats were paired with a cocaine-treated and a saline-treated partner on alternating days for 10 days. Finally, a second partner preference test was conducted, in which preference for cocaine-treated and saline-treated partners was reassessed. Relative to baseline, rats showed an increase in the amount of time they spent with their similarly treated partner, and this effect was driven by cocaine-treated rats increasing the amount of time spent in proximity to their cocaine-treated partner after conditioning. These findings support a selection model of drug use by showing that a shared history of drug exposure is sufficient to establish a social preference for one individual over another.

Ethanol intake under social circumstances or alone in sprague-dawley rats: impact of age, sex, social activity, and social anxiety-like behavior

BACKGROUND

In human adolescents, heavy drinking is often predicted by high sociability in males and high social anxiety in females. This study assessed the impact of baseline levels of social activity and social anxiety-like behavior in group-housed adolescent and adult male and female Sprague-Dawley rats on ethanol (EtOH) intake when drinking alone or in a social group.

METHODS

Social activity and anxiety-like behavior initially were assessed in a modified social interaction test, followed by 6 drinking sessions that occurred every other day in animals given ad libitum food and water. Sessions consisted of 30-minute access to 10% EtOH in a "supersac" (3% sucrose + 0.1% saccharin) solution given alone as well as in groups of 5 same-sex littermates, with order of the alternating session types counterbalanced across animals.

RESULTS

Adolescent males and adults of both sexes overall consumed more EtOH under social than alone circumstances, whereas adolescent females ingested more EtOH when alone. Highly socially active adolescent males demonstrated elevated levels of EtOH intake relative to their low and medium socially active counterparts when drinking in groups, but not when tested alone. Adolescent females with high levels of social anxiety-like behavior demonstrated the highest EtOH intake under social, but not alone circumstances. Among adults, baseline levels of social anxiety-like behavior did not contribute to individual differences in EtOH intake in either sex.

CONCLUSIONS

The results clearly demonstrate that in adolescent rats, but not their adult counterparts, responsiveness to a social peer predicts EtOH intake in a social setting-circumstances under which drinking typically occurs in human adolescents. High levels of social activity in males and high levels of social anxiety-like behavior in females were associated with elevated social drinking, suggesting that males ingest EtOH for its socially enhancing properties, whereas females ingest EtOH for its socially anxiolytic effects.

Nicotine Enhances Footshock- and Lithium Chloride-Conditioned Place Avoidance in Male Rats

INTRODUCTION

Numerous studies have shown that nicotine (NIC) can enhance the reinforcing effects of non-NIC stimuli through a nonassociative mechanism. To date, it is unclear whether NIC reinforcement enhancement serves to increase behaviors motivated by rewarding stimuli only, or whether NIC potentiates behavior motivated by all stimuli, regardless of valence.

METHODS

The current study used a place conditioning procedure to examine whether acute NIC injection modulates avoidance of an environment previously associated with an aversive stimulus. Separate groups of rats underwent place conditioning using either lithium chloride (125mg/kg/ml, i.p.) or footshock (0.75 mA) as the aversive stimulus. Other rats served as nonconditioned controls. The magnitude of place avoidance was assessed after acute NIC (0.1 or 0.4mg/kg/ml, s.c.) or saline.

RESULTS

Rats avoided chambers previously paired with either lithium chloride or footshock, and conditioned place avoidance was significantly enhanced by NIC pre-treatment.

CONCLUSIONS

These results demonstrate that the ability of NIC to enhance motivated behavior extends to behaviors elicited by aversive stimuli, evidence that NIC affects behavior motivated by a broader range of stimuli than previously appreciated.

IMPLICATIONS

The current study examined whether the reinforcement enhancement properties of NIC apply to aversive stimuli by testing NIC enhancement of conditioned place avoidance in rats. The results demonstrate that NIC enhances the motivational impact of these distinct aversive stimuli, providing novel evidence that NIC affects behavior motivated by a broader range of stimuli than has previously been demonstrated.

Socially acquired nicotine self-administration with an aversive flavor cue in adolescent female rats

RATIONALE

Establishing a behavioral model for the effect of social environment on nicotine intake in rodents facilitates the investigation of molecular mechanisms critical for the interaction between social environment and cigarette smoking.

OBJECTIVES

Our main objective was to test the hypothesis that nicotine is the primary reinforcer in the socially acquired nicotine intravenous self-administration (IVSA) model by using an aversive flavor cue.

METHODS

Adolescent female rats were placed in operant conditioning chambers equipped with two lickometers. Operant licking triggered concurrent deliveries of a flavor (i.e., taste and odor) cue containing either quinine or saccharin and an i.v. infusion (30 μg/kg nicotine or saline). An audiovisual cue was provided for some groups of rats. A second rat that did not receive nicotine was placed in the operant conditioning chambers to provide either a neutral or an inducing (i.e., by consuming the flavored solution) social environment. These two rats were separated by a divider that allowed orofacial interactions.

RESULTS

Rats acquired stable nicotine IVSA with either the aversive or the appetitive flavor cue in the inducing social environment, and obtained similar amounts of infusions. The neutral social environment did not support nicotine IVSA with either cue. The audiovisual cue per se did not support nicotine IVSA but enhanced nicotine intake. Nicotine increased the number of concurrent nose pokes by the two rats into the center divider, a measure of social interaction.

CONCLUSIONS

Despite its aversive effects, nicotine is the primary reinforcer for the operant responses in the socially acquired nicotine IVSA model.

Familiar companions diminish cocaine conditioning and attenuate cocaine-stimulated dopamine release in the nucleus accumbens

This study aimed to assess the impact of companions on the rewarding effects of cocaine. Three cage mates, serving as companions, were housed with each experimental mouse throughout cocaine-place conditioning in a cocaine-induced conditioned place preference (CPP) paradigm using conditioning doses of 10 and 20mg/kg. The presence of companions decreased the magnitude of the CPP. At 20mg/kg, cocaine stimulated dopamine (DA) release in the nucleus accumbens as evidenced by a significant decrease in total (spontaneous and electrical stimulation-provoked) DA release in accumbal superfusate samples. The presence of companions prevented this cocaine-stimulated DA release; such a reduction in cocaine-induced DA release may account for the reduction in the magnitude of the CPP in the presence of the companions. Furthermore, cocaine pretreatment (2.5mg/kg) was found to prevent the companion-produced decreases in cocaine (10mg/kg/conditioning)-induced CPP as well as the cocaine (10mg/kg)-stimulated DA release. Moreover, the presence of methamphetamine (MA) (1mg/kg)-treated companions decreased cocaine (20mg/kg/conditioning)-induced CPP and prevented the cocaine (20mg/kg)-stimulated DA release. Finally, the presence of companions decreased the magnitude of the CPP could not seem to be accounted for by cocaine-stimulated corticosterone (CORT) release. Taken together, these results indicate that familiar companions, regardless of their pharmacological status, may exert dampening effects on CPP induced by moderate to high conditioning doses of cocaine, at least in part, by preventing cocaine-stimulated DA release in the nucleus accumbens.

Blunted striatal response to monetary reward anticipation during smoking abstinence predicts lapse during a contingency-managed quit attempt

RATIONALE

Tobacco smoking is associated with dysregulated reward processing within the striatum, characterized by hypersensitivity to smoking rewards and hyposensitivity to non-smoking rewards. This bias toward smoking reward at the expense of alternative rewards is further exacerbated by deprivation from smoking, which may contribute to difficulty maintaining abstinence during a quit attempt.

OBJECTIVE

We examined whether abstinence-induced changes in striatal processing of rewards predicted lapse likelihood during a quit attempt supported by contingency management (CM), in which abstinence from smoking was reinforced with money.

METHODS

Thirty-six non-treatment-seeking smokers participated in two functional MRI (fMRI) sessions, one following 24-h abstinence and one following smoking as usual. During each scan, participants completed a rewarded guessing task designed to elicit striatal activation in which they could earn smoking and monetary rewards delivered after the scan. Participants then engaged in a 3-week CM-supported quit attempt.

RESULTS

As previously reported, 24-h abstinence was associated with increased striatal activation in anticipation of smoking reward and decreased activation in anticipation of monetary reward. Individuals exhibiting greater decrements in right striatal activation to monetary reward during abstinence (controlling for activation during non-abstinence) were more likely to lapse during CM (p < 0.025), even when controlling for other predictors of lapse outcome (e.g., craving); no association was seen for smoking reward.

CONCLUSIONS

These results are consistent with a growing number of studies indicating the specific importance of disrupted striatal processing of non-drug reward in nicotine dependence and highlight the importance of individual differences in abstinence-induced deficits in striatal function for smoking cessation.

Stress is a principal factor that promotes tobacco use in females

Tobacco use is a major economic and health problem. It is particularly concerning that women consume more tobacco products, have a more difficult time quitting smoking, and are less likely to benefit from smoking cessation therapy than men. As a result, women are at higher risk of developing tobacco-related diseases. Clinical evidence suggests that women are more susceptible to anxiety disorders, and are more likely to smoke in order to cope with stress than men. During smoking abstinence, women experience more intense anxiety than men and report that the anxiety-reducing effects of smoking are the main reason for their continued tobacco use and relapse. Consistent with this, pre-clinical studies using rodent models suggest that females display more intense stress during nicotine withdrawal than males. This review posits that in women, stress is a principal factor that promotes the initiation of tobacco use and relapse behavior during abstinence. Studies are reviewed at both the clinical and pre-clinical levels to provide support for our hypothesis that stress plays a central role in promoting tobacco use vulnerability in females. The clinical implications of this work are also considered with regard to treatment approaches and the need for more research to help reduce health disparities produced by tobacco use in women.

Behavioral effects of phencyclidine on nicotine self-administration and reinstatement in the presence or absence of a visual stimulus in rats

RATIONALE

Tobacco use is a serious health problem in the USA, and this problem is potentiated in patients with schizophrenia. The reward system is implicated in schizophrenia and may contribute to the high comorbidity between nicotine use and schizophrenia, but very little research has been done on the topic. The reward-enhancement effect of nicotine has been shown to be important in nicotine use, but there have been no studies on this effect in animal models of schizophrenia.

OBJECTIVES

This study was designed to determine the effects of phencyclidine, used to model negative symptoms of schizophrenia, on self-administration of nicotine with or without a co-occurring sensory reinforcer [i.e., visual stimulus (VS)] in rats.

METHODS

Phencyclidine (2.0 mg/kg) was administered before each of seven nicotine self-administration sessions (0.01 mg/kg/inf) after which rats (n = 8-9 per group) were given 7 days of extinction without phencyclidine pretreatment. Reinstatement using phencyclidine (2.0 mg/kg), nicotine (0.2 mg/kg), and yohimbine (1.25 mg/kg, a pharmacological stressor) was tested after extinction to determine if previous exposure to phencyclidine would alter reinstatement of active lever pressing.

RESULTS

Phencyclidine initially decreased nicotine self-administration but only in the groups with a concurrent VS. This decrease in self-administration dissipated after 5 days. During reinstatement, rats that had previously received phencyclidine during self-administration with a VS were more sensitive to stress-induced reinstatement than any other group.

CONCLUSIONS

These results show a transitory effect of phencyclidine on nicotine self-administration. Phencyclidine may induce a potential sensitivity to pharmacological stressors contributing to reinstatement of nicotine.

Prenatal stress induces vulnerability to nicotine addiction and alters D2 receptors' expression in the nucleus accumbens in adult rats

Prenatal stress (PS) can induce several long-lasting behavioral and molecular abnormalities in rats. It can also be considered as a risk factor for many psychiatric diseases like schizophrenia, depression or PTSD and predispose to addiction. In this study, we investigated the effect of prenatal stress on the reinforcing properties of nicotine in the CPP paradigm. Then, we examined the mRNA expression of the D2 dopaminergic receptors using the quantitative real-time PCR technique in the nucleus accumbens (NAcc). We found that prenatally stressed rats exhibited a greater place preference for the nicotine-paired compartment than the control rats. Moreover, we observed an overexpression of the DRD2 gene in adult offspring stressed in utero and a downregulation in the PS NIC group (PS rats treated with nicotine) compared with their control counterparts (C NIC). These data suggest that maternal stress can permanently alter the offspring's addictive behavior and D2 receptors' expression.

The Two Faces of Social Interaction Reward in Animal Models of Drug Dependence

Drug dependence is a serious health and social problem. Social factors can modify vulnerability to developing drug dependence, acting as risk factors or protective factors. Whereas stress and peer environment that encourage substance use may increase drug taking, strong attachments between family members and peer environment that do not experience drug use may protect against drug taking and, ultimately, drug dependence. The rewarding effects of drug abuse and social interaction can be evaluated using animal models. In this review we focus on evaluating social interaction reward in the conditioned place preference paradigm. We give an overview of how social interaction, if made available within the drug context, may facilitate, promote and interact with the drug's effects. However, social interaction, if offered alternatively outside the drug context, may have pronounced protective effects against drug abuse and relapse. We also address the importance of the weight difference parameter between the social partners in determining the positive or "agonistic" versus the hostile or "antagonistic" social interaction. We conclude that understanding social interaction reward and its subsequent effects on drug reward is sorely needed for therapeutic interventions against drug dependence.