Individual differences in drug abuse vulnerability: d-amphetamine and sensation-seeking status

Incubation of methamphetamine craving in punishment-resistant individuals is associated with activation of specific gene networks in the rat dorsal striatum

Methamphetamine use disorder (MUD) is characterized by loss of control over compulsive drug use. Here, we used a self-administration (SA) model to investigate transcriptional changes associated with the development of early and late compulsivity during contingent footshocks. Punishment initially separated methamphetamine taking rats into always shock-resistant (ASR) rats that continued active lever pressing and shock-sensitive (SS) rats that reduced their lever pressing. At the end of the punishment phase, rats underwent 15 days of forced abstinence at the end of which they were re-introduced to the SA paradigm followed by SA plus contingent shocks. Interestingly, 36 percent of the initial SS rats developed delayed shock-resistance (DSR). Of translational relevance, ASR rats showed more incubation of methamphetamine craving than DSR and always sensitive (AS) rats. RNA sequencing revealed increased striatal Rab37 and Dipk2b mRNA levels that correlated with incubation of methamphetamine craving. Interestingly, Bdnf mRNA levels showed HDAC2-dependent decreased expression in the AS rats. The present SA paradigm should help to elucidate the molecular substrates of early and late addiction-like behaviors.

Electrocortical correlates of hypersensitivity to large immediate rewards in sensation seeking

Sensation seeking and delay discounting are strong predictors of various risk-taking behaviors. However, the relationship between sensation seeking and delay discounting remains elusive. Here, we addressed this issue by examining how high sensation seekers (HSS; N = 40) and low sensation seekers (LSS; N = 40) evaluated immediate and delayed rewards with low and high amounts during a behavioral task and an EEG task of delay discounting. Although HSS and LSS exhibited comparable discounting preference at the behavioral level, HSS relative to LSS was associated with a greater delay discounting effect at the neural level when earned rewards were large. This abnormality of reward magnitude was further corroborated by an electrocortical hypersensitivity to large immediate rewards and a stronger neural coding of reward magnitude for HSS as compared to LSS. Our findings support both the hyperactive approach theory and the optimal arousal theory in sensation seeking and have implications for the prevention and intervention targeting sensation seeking to reduce maladaptive risk-taking behaviors.

Operant novelty seeking predicts cue-induced reinstatement following cocaine but not water reinforcement in male rats

RATIONALE

An important facet of cocaine addiction is a high propensity to relapse, with increasing research investigating factors that predispose individuals toward uncontrolled drug use and relapse. A personality trait linked to drug addiction is high sensation seeking, i.e., a preference for novel sensations/experiences. In an animal model of sensation seeking, operant novelty seeking predicts the acquisition of drug self-administration.

OBJECTIVE

The primary goal of this research was to evaluate the hypothesis that sensitivity to the reinforcing effects of novel sensory stimuli predicts more intensive aspects of drug-taking behaviors, such as relapse.

METHODS

Rats were first tested for Operant Novelty Seeking, during which responses resulted in complex visual/auditory stimuli. Next, rats were trained to respond to water/cocaine reinforcers signaled by a cue light. Finally, rats were exposed to extinction in the absence of discrete cues and subsequently tested in a single session of cue-induced reinstatement, during which active responses resulted in cues previously paired with water/cocaine delivery.

RESULTS

The present study showed operant responses to produce novel sensory stimuli positively correlate with responding for cocaine during self-administration and during discrete cue-induced reinstatement, but no association with performance during extinction. A different pattern of associations was observed for a natural reward, in this case, water reinforcement. Here, the degree of novelty seeking also correlated with responding to water reinforcement and extinction responding; however, operant novelty seeking did not correlate with responding to water cues during testing of cue-induced reinstatement. Taken together, the incongruence of relationships indicates an underlying difference between natural and drug reinforcers.

CONCLUSION

In summary, we found a reinforcer-dependent relationship between operant novelty seeking (i.e., sensation seeking) and responsivity to extinction and discrete cues signaling availability for cocaine (i.e., craving), demonstrating the validity of the operant novelty seeking model to investigate drug seeking and relapse.

Association between vmPFC gray matter volume and smoking initiation in adolescents

Smoking of cigarettes among young adolescents is a pressing public health issue. However, the neural mechanisms underlying smoking initiation and sustenance during adolescence, especially the potential causal interactions between altered brain development and smoking behaviour, remain elusive. Here, using large longitudinal adolescence imaging genetic cohorts, we identify associations between left ventromedial prefrontal cortex (vmPFC) gray matter volume (GMV) and subsequent self-reported smoking initiation, and between right vmPFC GMV and the maintenance of smoking behaviour. Rule-breaking behaviour mediates the association between smaller left vmPFC GMV and smoking behaviour based on longitudinal cross-lagged analysis and Mendelian randomisation. In contrast, smoking behaviour associated longitudinal covariation of right vmPFC GMV and sensation seeking (especially hedonic experience) highlights a potential reward-based mechanism for sustaining addictive behaviour. Taken together, our findings reveal vmPFC GMV as a possible biomarker for the early stages of nicotine addiction, with implications for its prevention and treatment.

Subtypes in addiction and their neurobehavioral profiles across three functional domains

Rates of return to use in addiction treatment remain high. We argue that the development of improved treatment options will require advanced understanding of individual heterogeneity in Substance Use Disorders (SUDs). We hypothesized that considerable individual differences exist in the three functional domains underlying addiction-approach-related behavior, executive function, and negative emotionality. We included N = 593 participants from the enhanced Nathan Kline Institute-Rockland Sample community sample (ages 18-59, 67% female) that included N = 420 Controls and N = 173 with past SUDs [54% female; N = 75 Alcohol Use Disorder (AUD) only, N = 30 Cannabis Use Disorder (CUD) only, and N = 68 Multiple SUDs]. To test our a priori hypothesis that distinct neuro-behavioral subtypes exist within individuals with past SUDs, we conducted a latent profile analysis with all available phenotypic data as input (74 subscales from 18 measures), and then characterized resting-state brain function for each discovered subtype. Three subtypes with distinct neurobehavioral profiles were recovered (p < 0.05, Cohen's D: 0.4-2.8): a "Reward type" with higher approach-related behavior (N = 69); a "Cognitive type" with lower executive function (N = 70); and a "Relief type" with high negative emotionality (N = 34). For those in the Reward type, substance use mapped onto resting-state connectivity in the Value/Reward, Ventral-Frontoparietal and Salience networks; for the Cognitive type in the Auditory, Parietal Association, Frontoparietal and Salience networks; and for the Relief type in the Parietal Association, Higher Visual and Salience networks (pFDR < 0.05). Subtypes were equally distributed amongst individuals with different primary SUDs (χ2 = 4.71, p = 0.32) and gender (χ2 = 3.44, p = 0.18). Results support functionally derived subtypes, demonstrating considerable individual heterogeneity in the multi-dimensional impairments in addiction. This confirms the need for mechanism-based subtyping to inform the development of personalized addiction medicine approaches.

Are problem buying and problem gambling addictive, impulsive, or compulsive in nature? A network analysis and latent dimension analysis study in Italian community-dwelling adults

Prominent scholars suggested that the impulsive-obsessive compulsive continuum may represent a framework to understand both substance and behavioral addictions. However, the characterization of pathological buying (PB) and problem gambling (PG) within the compulsive-impulsive spectrum has not been extensively investigated. To explore the relationships among PB, PG, alcohol and substance abuse, DSM-5 obsessive-compulsive and related disorders, and impulsive dimensions, a sample of 1,005 Italian community-dwelling adult participants (55.5% female), was administered self-reported measures of PB, PG, and other theoretically-relevant constructs. We expected to observe a multidimensional structure in our data; moreover, DSM-5 obsessive compulsive and related disorders were hypothesized to be accounted for by a common dimension. Three dimensions were identified and replicated across two different, non-redundant methods (i.e., exploratory graph analysis and exploratory factor analysis), namely, substance use and gambling, obsessive and compulsive phenomena, and impulsivity dimensions. Specifically, PG seemed to represent a behavioral variant of addiction vulnerability, PB seemed more akin to obsessive-compulsive spectrum disorders, and disinhibition dimension represented the common core of negative urgency, lack of premeditation, lack of perseverance, sensation seeking (SS), and positive urgency. Our findings may be helpful in improving our knowledge on the similarities and differences between PB and PG.

Electrophysiological Evidence of Enhanced Processing of Novel Pornographic Images in Individuals With Tendencies Toward Problematic Internet Pornography Use

Novelty seeking is regarded as a core feature in substance use disorders. However, few studies thus far have investigated this feature in problematic Internet pornography use (PIPU). The main aim of the present study was to examine group differences in electrophysiological activity associated with novelty processing in participants with high tendencies toward PIPU vs. low tendencies using event-related potentials (ERPs). Twenty-seven participants with high tendencies toward PIPU and 25 with low tendencies toward PIPU completed a modified three-stimulus oddball task while electroencephalogram (EEG) was recorded. Participants were instructed to detect neutral target stimuli from distracting stimuli. The distracting stimuli contained a familiar sexual stimulus and a set of novel sexual stimuli. The novel-familiar difference waves were calculated to identify specific group difference in novelty effect. While both groups demonstrated a sustained novelty effect in the late positive potential (LPP) within the 500–800 ms time windows, the novelty effect was greater in the high tendencies toward PIPU group than in the low tendencies toward PIPU group. This result suggests that individuals with high tendencies toward PIPU allocate more attentional resources for novelty processing. Enhanced brain responding to novel sexual stimuli may facilitate pornographic consumption and play an essential role in the development and maintenance of PIPU.

Exploratory examination of the effects of d-amphetamine on active-state functional connectivity: Influence of impulsivity and sensation-seeking status

Recent advances in diagnostic research identified that individuals with higher impulsivity and sensation-seeking scores tend to report more positive subjective responses to stimulant drugs such as amphetamine. The current exploratory study hypothesized that differences in underlying mesocorticolimbic circuitry may mediate the relationship between personality and responses to stimulants due to its previously established implication in reward processes as well as the overlap between its dopaminergic projections and the pharmacodynamics of many stimulants. Forty participants (20 female) were recruited with relatively high- and low-impulsivity and sensation-seeking scores as defined by the Zuckerman-Kuhlman Personality Questionnaire (Form IIIR; Zuckerman, Kuhlman, Joireman, Teta, & Kraft, 1993) for a double-blind, placebo-controlled, intranasal amphetamine administration study conducted within an MRI scanner. Active state seed-to-voxel connectivity analyses assessed the effects of amphetamine, personality, subjective responses to amphetamine, and their interactions with mesocorticolimbic seeds on data collected during monetary incentive delay and go/no-go task performance. Results indicated that amphetamine administration largely disrupted brain activity as evidenced by connectivity values shifting toward no correlation among brain stem, striatal, and frontal cortex regions. Additionally, associations of impulsivity and connectivity between ventral tegmental and medial orbitofrontal as well as lateral orbitofrontal and putamen regions were inverted from negative to positive during the placebo and amphetamine conditions, respectively. Personality was unrelated to subjective responses to amphetamine. Results are interpreted as providing evidence of underlying differences in mesocorticolimbic circuitry being a potential target for requisite diagnostic and treatment strategies implicated with stimulant use disorders, but further research is needed. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Acute effects of amphetamine and related psychostimulants on impulsivity: a systematic review of clinical trials

Evidence for acute amphetamine effects on behavioural impulsivity in healthy populations remains elusive and, at times, mixed. This review collates and reviews the clinical literature on the acute effects of amphetamines on measures of behavioural impulsivity in healthy adults. Randomised and placebo-controlled clinical trials that assessed behavioural impulsivity following the administration of an acute dose of amphetamine or a related psychostimulant (including amphetamine analogues and methylphenidate) were eligible for inclusion. The EBSCOHost, SCOPUS, PsychNet, Web of Science and ProQuest databases were searched from inception to 26 April 2021. Study selection, data extraction and the Cochrane risk of bias assessments were conducted by two independent reviewers. Reporting follows PRISMA guidelines, and the review was registered a priori on the PROSPERO database (Registration No: CRD42021249861). A total of 20 studies were included, comprising a total of 737 participants. Overall, results indicate that low-moderate doses of amphetamine and related psychostimulants may improve (i.e., reduce) impulsive responding without compromising performance, reflecting enhanced inhibitory control of behaviour. These effects are mild and appear most pronounced in individuals with high baseline impulsivity. This review highlights the need for greater consistency in behavioural task selection and future high-quality and well-designed studies to address current concerns around growing prescription psychostimulant use and misuse.

On the learning of addictive behavior: Sensation-seeking propensity predicts dopamine turnover in dorsal striatum

We asked if sensation-seeking is linked to premorbid personality characteristics in patients with addictive disorders, or the characteristics follow the sensation-seeking activity. We interpreted the former as a state associated with normal rates of dopamine synthesis, and the latter as a trait of individuals with abnormally high rates of synthesis. We previously determined dopaminergic receptor density in striatum, and we now tested the hypothesis that an elevated dopaminergic condition with increased extracellular dopamine and receptor density follows increased dopamine synthesis capacity in highly sensation-seeking individuals, as measured by positron emission tomography of 18 men with tracer fluorodopa (FDOPA). We detected a site in left caudate nucleus where the volume of distribution of FDOPA-derived metabolites correlated negatively with FDOPA metabolite turnover, consistent with decreased metabolite breakdown in highly sensation-seeking subjects. High rates of sensation-seeking attenuated the dopamine turnover in association with a low rate of dopamine recycling, low dopamine oxidation, and elevated extracellular dopamine and receptors in caudate nucleus. In contrast, low rates of sensation-seeking were associated with rapid dopamine recycling, rapid dopamine oxidation, low extracellular dopamine, and low receptor density. We conclude that the modulation of dopaminergic neurotransmission associated with sensation-seeking is a state of sensation-seeking, rather than a trait of personality following abnormal regulation of dopaminergic neurotransmission.

Potential Role of Serum S-100β Protein as a Predictor of Cardiotoxicity and Clinical Poor Outcome in Acute Amphetamine Intoxication

Cardio- and neurotoxicity of amphetamines play an important role in worsening morbidity, making the initial evaluation of the patient's status a potentially lifesaving action. The current study hypothesized that the S-100β serum level could predict the severity of acute amphetamine toxicity and the in-hospital outcome. The current study is a prospective cohort study conducted on 77 patients diagnosed with acute amphetamine exposure and referred to Aseer Poison Control Center, Saudi Arabia. The patients admitted to ICU showed significantly higher serum levels of S-100β in comparison to those not admitted (p < 0.05). Moreover, the S-100β level was significantly elevated among patients with prolonged QTc intervals. Receiver-operating characteristic curve of S-100β serum level as an in-hospital outcome predictor showed that at a cutoff value > 0.430 ug/L, the sensitivity of S-100β serum level as severity predictor was 100%, and the specificity was 74.1%. In conclusion, the current study revealed that the S-100β serum level could be used as an outcome predictor in hospital admission cases due to toxic amphetamine exposure and offers an idea about the cardiac and neuronal involvement. This can help select patients who will benefit most from ICU admission and early management and assess the severity of cases in settings where GC-MS is not available.

Amphetamine-like Neurochemical and Cardiovascular Effects of α-Ethylphenethylamine Analogs Found in Dietary Supplements

Dietary supplements often contain additives not listed on the label, including α-ethyl homologs of amphetamine such as N,α-diethylphenethylamine (DEPEA). Here, we examined the neurochemical and cardiovascular effects of α-ethylphenethylamine (AEPEA), N-methyl-α-ethylphenethylamine (MEPEA), and DEPEA as compared with the effects of amphetamine. All drugs were tested in vitro using uptake inhibition and release assays for monoamine transporters. As expected, amphetamine acted as a potent and efficacious releasing agent at dopamine transporters (DAT) and norepinephrine transporters (NET) in vitro. AEPEA and MEPEA were also releasers at catecholamine transporters, with greater potency at NET than DAT. DEPEA displayed fully efficacious release at NET but weak partial release at DAT (i.e., 40% of maximal effect). In freely moving, conscious male rats fitted with biotelemetry transmitters for physiologic monitoring, amphetamine (0.1–3.0 mg/kg, s.c.) produced robust dose-related increases in blood pressure (BP), heart rate (HR), and motor activity. AEPEA (1–10 mg/kg, s.c.) produced significant increases in BP but not HR or activity, whereas DEPEA and MEPEA (1–10 mg/kg, s.c.) increased BP, HR, and activity. In general, the phenethylamine analogs were approximately 10-fold less potent than amphetamine. Our results show that α-ethylphenethylamine analogs are biologically active. Although less potent than amphetamine, they produce cardiovascular effects that could pose risks to humans. Given that MEPEA and DEPEA increased locomotor activity, these substances may also have significant abuse potential.

Enrichment-induced differences in methamphetamine drug discrimination in male rats

Rats raised in an enriched environment show a decrease in sensitivity to the subjective effects of the psychostimulant d-amphetamine. The purpose of the present study was to determine if environmental enrichment during development alters the subjective effects of the more commonly abused drug methamphetamine. Male Sprague-Dawley rats were raised in either an enriched (EC) or an isolated condition (IC). EC and IC rats were trained on a two-lever operant procedure to discriminate 1.0 mg/kg (i.p.) methamphetamine from saline. Following acquisition of the discrimination a methamphetamine generalization curve (0.1-1.0 mg/kg) was determined. The antagonistic effects of dopamine D₁ receptor antagonist SCH23390 (0.0075-0.06 mg/kg) and the dopamine D₂ receptor antagonist eticlopride (0.01-0.3 mg/kg) were also tested. Finally, the ability of nicotine (0.05-0.5 mg/kg) to generalize and the ability of the nicotinic receptor antagonist mecamylamine (0.125-0.5 mg/kg) to antagonize the discriminative stimulus effects of methamphetamine were determined. EC rats were less sensitive to discriminative stimulus effects of methamphetamine compared to IC rats at a low 0.3 mg/kg dose and showed full antagonism of methamphetamine discrimination following SCH23390 compared to IC rats. There were no environmentally-induced differences in the effects of eticlopride. Nicotine only partially generalized to the effects of methamphetamine in both EC and IC rats. While mecamylamine failed to antagonize the effects of methamphetamine in either EC or IC rats. These results suggest that environmental enrichment decreases sensitivity to the discriminative effects of methamphetamine and the differences may be mediated through changes in the D₁ dopamine receptor.

Greater tolerance to losses in sensation seeking: Evidence from probability and delay discounting

BACKGROUND

Sensation seeking is a behavioral endophenotype of substance use and is associated with abnormalities in financial reward processing. Previous research suggests that high sensation seekers (HSS) relative to low sensation seekers (LSS) show either an enhanced sensitivity to financial rewards or a reduced sensitivity to financial punishments. However, there are few studies investigating the valuation of financial rewards and punishments as a function of delivery probability and delay, two important aspects of reward processing that influence the valuation.

METHODS

We administrated a probability discounting task and a delay discounting task to 56 HSS and 57 LSS selected from a large sample. Each task was crossed with two factors: valence (gain vs. loss) and amount (Ұ1000 vs. Ұ50000).

RESULTS

For the probability discounting task, HSS discounted probabilistic losses but not gains more steeply than LSS, irrespective of the amount of outcome. For the delay discounting task, HSS discounted delayed losses more steeply than LSS, for the large but not small amount condition. In contrast, both groups exhibited comparable discounting rates for gains across the two amount conditions. These results remained significant when impulsivity levels were controlled for.

CONCLUSIONS

Together, our data strengthen the argument that the dysfunctional valuation in sensation seeking is valence specific, which may be driven by a weaker avoidance system, rather than by a stronger approach system.

Animal Models of the Impact of Social Stress on Cocaine Use Disorders

Cocaine use disorders are strongly influenced by the social conditions prior, during, and after exposure to cocaine. In this chapter, we discuss how social factors such as early life stress, social rank stress, and environmental stress impact vulnerability and resilience to cocaine. The discussion of each animal model begins with a brief review of examples from the human literature, which provide the psychosocial background these models attempt to capture. We then discuss preclinical findings from use of each model, with emphasis on how social factors influence cocaine-related behaviors and how sex and age influence the behaviors and neurobiology. Models discussed include (1) early life social stress, such as maternal separation and neonatal isolation, (2) social defeat stress, (3) social hierarchies, and (4) social isolation and environmental enrichment. The cocaine-related behaviors reviewed for each of these animal models include cocaine-induced conditioned place preference, behavioral sensitization, and self-administration. Together, our review suggests that the degree of psychosocial stress experienced yields robust effects on cocaine-related behaviors and neurobiology, and these preclinical findings have translational impact for the future of cocaine use disorder treatment.

Communicating with Sensation Seekers: An fMRI Study of Neural Responses to Antidrug Public Service Announcements

This study examined the neural basis of processing high- and low-message sensation value (MSV) antidrug public service announcements (PSAs) in high (HSS) and low sensation seekers (LSS) using fMRI. HSS more strongly engaged the salience network when processing PSAs (versus LSS), suggesting that high-MSV PSAs attracted their attention. HSS and LSS participants who engaged higher level cognitive processing regions reported that the PSAs were more convincing and believable and recalled the PSAs better immediately after testing. In contrast, HSS and LSS participants who strongly engaged visual attention regions for viewing PSAs reported lower personal relevance. These findings provide neurobiological evidence that high-MSV content is salient to HSS, a primary target group for antidrug messages, and additional cognitive processing is associated with higher perceived message effectiveness.

Cortisol and behavioral reaction of low and high sensation seekers differ in responding to a sport-specific stressor

BACKGROUND/OBJECTIVES

Sensation seeking is closely related to practicing high-risk sports. This domain offers individuals an opportunity to achieve an increased level of arousal. Moreover, stress reactivity implies interindividual differences in the capacity to respond to a stressor. The purpose of this study was to examine whether high sensation seekers (HSS) compared to low sensation seekers (LSS) experience lower levels of stress on a physiological and psychological basis. Stress was induced in a sport-specific experimental paradigm with a climbing task through a jump into the rope.

METHODS

Two extreme groups (n = 28 male athletes) were examined in a mixed-factorial design (between: HSS vs. LSS; within: repeated measurements of several variables related to stress reactivity - cortisol, heart rate, anxiety).

RESULTS

In response to the stressor HSS compared to LSS released a significantly lower amount of cortisol and needed less time for the climbing task. Heart rate and anxiety were not significant.

CONCLUSIONS

Individuals seem to react physiologically differently to a sport-specific stressor, depending on their level of sensation seeking. HSS seem to be less strained, and seem to perform better. These findings might be relevant not only for the evaluation of (sport-) psychological interventions but also for other contexts (e.g., special forces).

Rewarding effects of physical activity predict sensitivity to the acute subjective effects of d-amphetamine in healthy volunteers

While individual differences in reward sensitivity are believed to generalize across drugs and alternative rewards, this notion has received little empirical attention in human research. Here, we tested whether individual differences in the subjective rewarding effects of physical activity were associated with the subjective response to d-amphetamine administration. Healthy volunteers ( n=95; age 18-35 years) completed questionnaires measuring the self-reported pleasurable effects of physical activity and other covariates, and this was followed by two double-blind counterbalanced sessions during which they received either 20 mg oral d-amphetamine or placebo. Subjective drug effects measures were collected before and repeatedly after drug administration. Subjective d-amphetamine-related effects were then reduced via principal components analysis into latent factors of "positive mood," "arousal," and "drug high." Multiple regression models controlling for placebo-related scores, session order, demographics, body mass index, level of physical activity, and use of other drugs showed that degree of self-reported physical activity reward was positively associated with d-amphetamine-induced positive mood and arousal ( βs≥0.25, ps≤0.04), but was not associated with d-amphetamine-induced changes in drug high ( β=0.13, p=0.24). These results provide novel evidence suggesting that individual differences in reward sensitivity cross over between d-amphetamine reward and physical activity reward in humans.

Developmental differences in reward sensitivity and sensation seeking in adolescence: Testing sex-specific associations with gonadal hormones and pubertal development

Sensation seeking has been found to increase, on average, from childhood to adolescence. Developmental scientists have hypothesized that this change could be driven by the rise of gonadal hormones at puberty, which affect reward-related processing in the brain. In a large, age-heterogeneous, population-based sample of adolescents and young adults (N = 810; ages 13-20 years), we tested for sex-specific associations between age, self-reported pubertal development, gonadal hormones (estradiol and testosterone) as measured in saliva, reward sensitivity as measured by a multivariate battery of in-laboratory tasks (including the Iowa gambling task, balloon analogue risk task, and stoplight task), and self-reported sensation seeking. Reward sensitivity was more strongly associated with sensation seeking in males than females. For both males and females, reward sensitivity was unrelated to age but was higher among those who reported more advanced pubertal development. There were significant sex differences in the effects of self-reported pubertal development on sensation seeking, with a positive association evident in males but a negative association in females. Moreover, gonadal hormones also showed diverging associations with sensation seeking-positive with testosterone but negative with estradiol. Overall, the results indicate that sensation seeking among adolescents and young adults depends on a complex constellation of developmental influences that operate via sex-specific mechanisms. (PsycINFO Database Record

Impulsive personality dimensions are associated with altered behavioral performance and neural responses in the monetary incentive delay task

Individual differences in dimensions of impulsivity personality including disinhibition and sensation seeking modulate approach responses to reinforcing stimuli, such as drugs and money. The current study examined the effects of monetary incentive on both behavioral performance and electrophysiological activity among individuals varying in disinhibition and sensation seeking. The monetary incentive delay (MID) task was completed under electroencephalogram (EEG) recording. Behavioral data showed that higher disinhibition and sensation-seeking were associated with lower performance accuracy. Event-related potential (ERP) data showed that high reinforcement cues elicited a larger late positive component (LPC) than other conditions among high disinhibition participants, indicating its strong emotional influence. Additionally, in the neutral incentive condition, the feedback-related negativity (FRN) elicited by correct outcomes was larger than that elicited by incorrect outcomes in the high disinhibition group only. This novel finding indicates that high disinhibition participants were less likely to expect correct outcomes compared to incorrect outcomes in the neutral incentive condition. Finally, the P3 component elicited by outcome presentation showed an interaction between two impulsivity dimensions; when disinhibition level was low, the P3 was larger among high than low sensation seeking participants.

Differential housing and novelty response: Protection and risk from locomotor sensitization

High novelty seeking increases the risk for drug experimentation and locomotor sensitization. Locomotor sensitization to psychostimulants is thought to reflect neurological adaptations that promote the transition to compulsive drug taking. Rats reared in enrichment (EC) show less locomotor sensitization when compared to rats reared in isolation (IC) or standard conditions (SC). The current research study was designed to test if novelty response contributed locomotor sensitization and more importantly, if the different housing environments could change the novelty response to protect against the development of locomotor sensitization in both adolescence and adulthood. Experiment 1: rats were tested for their response to novelty using the inescapable novelty test (IEN) and pseudorandomly assigned to enriched (EC), isolated (IC), or standard (SC) housing conditions for 30days. After housing, they were tested with IEN. Rats were then administered amphetamine (0.5mg/kg) or saline and locomotor activity was measured followed by a sensitization test 14days later. Experiment 2: rats were tested in the IEN test early adulthood and given five administrations of amphetamine (0.3mg/kg) or saline and then either stayed in or switched housing environments for 30days. Rats were then re-tested in the IEN test in late adulthood and administered five more injections of their respective treatments and tested for locomotor sensitization. Results indicate that IC and SC increased the response to novelty. EC housing decreased locomotor response to amphetamine and saline, and SC housing increased the locomotor response to amphetamine. Mediation results indicated that the late adult novelty response fully mediates the locomotor response to amphetamine and saline, while the early adulthood novelty response did not.

CONCLUSIONS

Differential housing changes novelty and amphetamine locomotor response. Novelty response is altered into adulthood and provides evidence that enrichment can be used to reduce drug vulnerability.

Beyond Sensation Seeking: A Conceptual Framework for Individual Differences in Psychostimulant Drug Effects in Healthy Humans

Psychostimulant addiction is an important, relapsing condition for which there is no effective pharmacological treatment. Countering this problem requires an understanding of the specific risk factors that predispose individuals to initial misuse of these drugs. Healthy individuals display marked individual differences in emotional, behavioral and brain responses to low and moderate doses of stimulant drugs. These between-person differences have been most often studied using personality measures of sensation seeking. However, a growing body of work in healthy adults indicates potentially unique sources of variance in these responses that are related to four dissociable personality domains: extraversion, fearlessness, impulsivity and absorption. These four domains are empirically dissociable and can serve as endophenotypic markers of dopamine, norepinephrine and serotonin function in healthy individuals. The relationship between normal variation in these traits and the pharmacological effects of these drugs is here proposed as a framework for better understanding the specific sources of between-person variation in stimulant drug effects on mood, behavior and brain responses in healthy humans.

Individual differences in the reinforcing and subjective effects of d-amphetamine: Dimensions of impulsivity

Previous research has shown a relationship between impulsive personality and the subjective and reinforcing effects of d-amphetamine. Impulsive personality, however, is comprised of multiple dimensions. The association between different dimensions of impulsive personality and the subjective and reinforcing effects of d-amphetamine is unknown. The objective of this study was to assess the independent contributions of the "sensation-seeking" and "impulsivity" dimensions of the impulsive sensation-seeking subscale of the Zuckerman-Kuhlman Personality Questionnaire (ZKPQ) to the subjective and reinforcing effects of d-amphetamine. Forty healthy emerging adults varying in scores on the sensation-seeking and impulsivity dimensions of the ZKPQ participated in a double-blind, placebo-controlled, randomized study comprised of 4 2-day blocks. Each 2-day block consisted of a sample day and self-administration day. Subjective effects and physiological measurements were taken prior to, and hourly for 3 hr following, dose administration. On sample days participants were given 8 capsules containing 0, 1, or 2 mg d-amphetamine. On self-administration days participants were able to earn capsules containing the same dose of d-amphetamine that was administered on the previous sample day by responding on a Modified Progressive Ratio Task. The "sensation-seeking" dimension was positively associated with drug taking on the Modified Progressive Ratio Task, subjective effects (e.g., "good effect"), and heart rate. However, no clear relationship between the "impulsivity" dimension and outcome measures was observed. In conclusion, these data suggest that the narrow sensation-seeking dimension of impulsive sensation-seeking is associated with initial drug liking and drug taking behavior and may be a key predictor of drug use initiation. (PsycINFO Database Record

Influence of the Novelty-Seeking Endophenotype on the Rewarding Effects of Psychostimulant Drugs in Animal Models

Novelty seeking (NS), defined as a tendency to pursue novel and intense emotional sensations and experiences, is one of the most relevant individual factors predicting drug use among humans. High novelty seeking (HNS) individuals present an increased risk of drug use compared to low novelty seekers. The NS endophenotype may explain some of the differences observed among individuals exposed to drugs of abuse in adolescence. However, there is little research about the particular response of adolescents to drugs of abuse in function of this endophenotype, and the data that do exist are inconclusive. The present work reviews the literature regarding the influence of NS on psychostimulant reward, with particular focus on adolescent subjects. First, the different animal models of NS and the importance of this endophenotype in adolescence are discussed. Later, studies that have used the most common animal models of reward (self-administration, conditioned place preference paradigms) to evaluate how the NS trait influences the rewarding effects of psychostimulants are reviewed. Finally, possible explanations for the enhanced risk of developing substance dependence among HNS individuals are discussed. In conclusion, the studies referred to in this review show that the HNS trait is associated with: (1) increased initial sensitivity to the rewarding effects of psychostimulants, (2) a higher level of drug craving when the subject is exposed to the environmental cues associated with the drug, and (3) enhanced long-term vulnerability to relapse to drug consumption after prolonged abstinence.

Shared Neural Mechanisms for the Evaluation of Intense Sensory Stimulation and Economic Reward, Dependent on Stimulation-Seeking Behavior

Why are some people strongly motivated by intense sensory experiences? Here we investigated how people encode the value of an intense sensory experience compared with economic reward, and how this varies according to stimulation-seeking preference. Specifically, we used a novel behavioral task in combination with computational modeling to derive the value individuals assigned to the opportunity to experience an intense tactile stimulus (mild electric shock). We then examined functional imaging data recorded during task performance to see how the opportunity to experience the sensory stimulus was encoded in stimulation-seekers versus stimulation-avoiders. We found that for individuals who positively sought out this kind of sensory stimulation, there was common encoding of anticipated economic and sensory rewards in the ventromedial prefrontal cortex. Conversely, there was robust encoding of the modeled probability of receiving such stimulation in the insula only in stimulation-avoidant individuals. Finally, we found preliminary evidence that sensory prediction error signals may be positively signed for stimulation-seekers, but negatively signed for stimulation-avoiders, in the posterior cingulate cortex. These findings may help explain why high intensity sensory experiences are appetitive for some individuals, but not for others, and may have relevance for the increased vulnerability for some psychopathologies, but perhaps increased resilience for others, in high sensation-seeking individuals.

SIGNIFICANCE STATEMENT

People vary in their preference for intense sensory experiences. Here, we investigated how different individuals evaluate the prospect of an unusual sensory experience (electric shock), compared with the opportunity to gain a more traditional reward (money). We found that in a subset of individuals who sought out such unusual sensory stimulation, anticipation of the sensory outcome was encoded in the same way as that of monetary gain, in the ventromedial prefrontal cortex. Further understanding of stimulation-seeking behavior may shed light on the etiology of psychopathologies such as addiction, for which high or low sensation-seeking personality has been identified as a risk factor.

Novelty Seeking and Drug Addiction in Humans and Animals: From Behavior to Molecules

Global treatment of drug addiction costs society billions of dollars annually, but current psychopharmacological therapies have not been successful at desired rates. The increasing number of individuals suffering from substance abuse has turned attention to what makes some people more vulnerable to drug addiction than others. One personality trait that stands out as a contributing factor is novelty seeking. Novelty seeking, affected by both genetic and environmental factors, is defined as the tendency to desire novel stimuli and environments. It can be measured in humans through questionnaires and in rodents using behavioral tasks. On the behavioral level, both human and rodent studies demonstrate that high novelty seeking can predict the initiation of drug use and a transition to compulsive drug use and create a propensity to relapse. These predictions are valid for several drugs of abuse, such as alcohol, nicotine, cocaine, amphetamine, and opiates. On the molecular level, both novelty seeking and addiction are modulated by the central reward system in the brain. Dopamine is the primary neurotransmitter involved in the overlapping neural substrates of both parameters. In sum, the novelty-seeking trait can be valuable for predicting individual vulnerability to drug addiction and for generating successful treatment for patients with substance abuse disorders.

The effects of oral d-amphetamine on impulsivity in smoked and intranasal cocaine users

BACKGROUND

Effective treatments for cocaine use disorders remain elusive. Two factors that may be related to treatment failures are route of cocaine used and impulsivity. Smoked cocaine users are more likely to have poorer treatment outcomes compared to intranasal cocaine users. Further, cocaine users are impulsive and impulsivity is associated with poor treatment outcomes. While stimulants are used to treat Attention Deficit Hyperactivity Disorder (ADHD) and attenuate certain cocaine-related behaviors, few studies have comprehensively examined whether stimulants can reduce behavioral impulsivity in cocaine users, and none examined route of cocaine use as a factor.

METHODS

The effects of immediate release oral d-amphetamine (AMPH) were examined in 34 cocaine users (13 intranasal, 21 smoked). Participants had three separate sessions where they were administered AMPH (0, 10, or 20mg) and completed behavioral measures of impulsivity and risk-taking and subjective measures of abuse liability.

RESULTS

Smoked cocaine users were more impulsive on the Delayed Memory Task, the GoStop task and the Delay Discounting Task than intranasal cocaine users. Smoked cocaine users also reported more cocaine craving and negative mood than intranasal cocaine users. AMPH produced minimal increases on measures of abuse liability (e.g., Drug Liking).

CONCLUSIONS

Smoked cocaine users were more impulsive than intranasal cocaine users on measures of impulsivity that had a delay component. Additionally, although AMPH failed to attenuate impulsive responding, there was minimal evidence of abuse liability in cocaine users. These preliminary findings need to be confirmed in larger samples that control for route and duration of cocaine use.

Individual differences in timing of peak positive subjective responses to d-amphetamine: Relationship to pharmacokinetics and physiology

Rate of delivery of psychostimulants has been associated with their positive euphoric effects and potential addiction liability. However, information on individual differences in onset of d-amphetamine's effects remains scarce. We examined individual differences in the time to peak subjective and physiological effects and the pharmacokinetics/pharmacodynamics of oral d-amphetamine. We considered two independent studies that used different dosing regimens where subjects completed the drug effects questionnaire at multiple time points post d-amphetamine. Based on the observation of distinct individual differences in time course of drug effects questionnaire "feel", "high", and "like" ratings (DEQH+L+F) in Study 1, subjects in both studies were categorized as early peak responders (peak within 60 minutes), late peak responders (peak > 60 minutes) or nonresponders; 20-25% of participants were categorized as early peak responders, 50-55% as late peak responders and 20-30% as nonresponders. Physiological (both studies) and plasma d-amphetamine (Study 1) were compared among these groups. Early peak responders exhibited an earlier rise in plasma d-amphetamine levels and more sustained elevation in heart rate compared to late peak responders. The present data illustrate the presence of significant individual differences in the temporal pattern of responses to oral d-amphetamine, which may contribute to heightened abuse potential.

Sensation seeking as a potential screening tool for suicidality in adolescence

Background

Although suicide could be an adverse health problem related to sensation seeking, this relationship has not been rigorously evaluated. The purpose of this study was to evaluate the relationship between sensation seeking and suicidality (suicidal ideation and plan) among adolescents and to test the influence of depressive symptom on this relationship.

Methods

We surveyed 2,017 adolescents in seven middle and high schools located in urban and rural areas in 2012. A self-report questionnaire included items about demographic characteristics, sensation seeking, depressive symptom, and suicide plans. We evaluated the influence of sensation seeking on suicide plan using multiple logistic regression and causal mediation analysis.

Results

Sensation seeking was related to suicide ideation and plan. Sensation seeking was associated with a 13 % greater likelihood of a suicide plan during the past 12 months as the score increased by 1. After controlling for depressive symptom, the effect of sensation seeking was reduced, but still significantly increased the risk (adjusted odds ratio: 1.10; 95 % CI: 1.04–1.16). When depressive symptom was included as a potential mediator, depressive symptom exerted an indirect effect on suicide planning that constituted 37 % of the total effect of sensation seeking. There was no significant interaction between sensation seeking and either demographic variables or depressive symptom.

Conclusions

Sensation seeking can contribute to developing a suicide plan directly and indirectly via depressive symptom. Sensation seeking could be used to identify high-risk adolescents and provide proper interventions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-016-2729-2) contains supplementary material, which is available to authorized users.

Impulsivity in abstinent alcohol and polydrug dependence: a multidimensional approach

RATIONALE

Dependence on drugs and alcohol is associated with impaired impulse control, but deficits are rarely compared across individuals dependent on different substances using several measures within a single study.

OBJECTIVES

We investigated impulsivity in abstinent substance-dependent individuals (AbD) using three complementary techniques: self-report, neuropsychological and neuroimaging. We hypothesised that AbDs would show increased impulsivity across modalities, and that this would depend on length of abstinence.

METHODS

Data were collected from the ICCAM study: 57 control and 86 AbDs, comprising a group with a history of dependence on alcohol only (n = 27) and a group with history of dependence on multiple substances ("polydrug", n = 59). All participants completed self-report measures of impulsivity: Barratt Impulsiveness Scale, UPPS Impulsive Behaviour Scale, Behaviour Inhibition/Activation System and Obsessive-Compulsive Inventory. They also performed three behavioural tasks: Stop Signal, Intra-Extra Dimensional Set-Shift and Kirby Delay Discounting; and completed a Go/NoGo task during fMRI.

RESULTS

AbDs scored significantly higher than controls on self-report measures, but alcohol and polydrug dependent groups did not differ significantly from each other. Polydrug participants had significantly higher discounting scores than both controls and alcohol participants. There were no group differences on the other behavioural measures or on the fMRI measure.

CONCLUSIONS

The results suggest that the current set of self-report measures of impulsivity is more sensitive in abstinent individuals than the behavioural or fMRI measures of neuronal activity. This highlights the importance of developing behavioural measures to assess different, more relevant, aspects of impulsivity alongside corresponding cognitive challenges for fMRI.

Resting-state EEG, impulsiveness, and personality in daily and nondaily smokers

OBJECTIVES

Resting EEG is sensitive to transient, acute effects of nicotine administration and abstinence, but the chronic effects of smoking on EEG are poorly characterized. This study measures the resting EEG profile of chronic smokers in a non-deprived, non-peak state to test whether differences in smoking behavior and personality traits affect pharmaco-EEG response.

METHODS

Resting EEG, impulsiveness, and personality measures were collected from daily smokers (n=22), nondaily smokers (n=31), and non-smokers (n=30).

RESULTS

Daily smokers had reduced resting delta and alpha EEG power and higher impulsiveness (Barratt Impulsiveness Scale) compared to nondaily smokers and non-smokers. Both daily and nondaily smokers discounted delayed rewards more steeply, reported lower conscientiousness (NEO-FFI), and reported greater disinhibition and experience seeking (Sensation Seeking Scale) than non-smokers. Nondaily smokers reported greater sensory hedonia than nonsmokers.

CONCLUSIONS

Altered resting EEG power in daily smokers demonstrates differences in neural signaling that correlated with greater smoking behavior and dependence. Although nondaily smokers share some characteristics with daily smokers that may predict smoking initiation and maintenance, they differ on measures of impulsiveness and resting EEG power.

SIGNIFICANCE

Resting EEG in non-deprived chronic smokers provides a standard for comparison to peak and trough nicotine states and may serve as a biomarker for nicotine dependence, relapse risk, and recovery.

Social Novelty Investigation in the Juvenile Rat: Modulation by the μ-Opioid System

The drive to approach and explore novel conspecifics is inherent to social animals and may promote optimal social functioning. Juvenile animals seek out interactions with novel peers more frequently and find these interactions to be more rewarding than their adult counterparts. In the present study, we aimed to establish a behavioural paradigm to measure social novelty-seeking in juvenile rats and to determine the involvement of the opioid, dopamine, oxytocin and vasopressin systems in this behaviour. To this end, we developed the social novelty preference test to assess the preference of a juvenile rat to investigate a novel over a familiar (cage mate) conspecific. We show that across the juvenile period both male and female rats spend more time investigating a novel conspecific than a cage mate, independent of subject sex or repeated exposure to the test. We hypothesised that brain systems subserving social information processing and social motivation/reward (i.e. the opioid, dopamine, oxytocin, vasopressin systems) might support social novelty preference. To test this, receptor antagonists of each of these systems were administered i.c.v. prior to exposure to the social novelty preference test and, subsequently, to the social preference test, to examine the specificity of these effects. We find that μ-opioid receptor antagonism reduces novel social investigation in both the social novelty preference and social preference tests while leaving the investigation of a cage mate (social novelty preference test) or an object (social preference test) unaffected. In contrast, central blockade of dopamine D2 receptors (with eticlopride), oxytocin receptors (with des-Gly-NH2,d(CH2)5[Tyr(Me)2,Thr4]OVT) or vasopressin V1a receptors [with (CH2)5Tyr(Me2)AVP] failed to alter social novelty preference or social preference. Overall, we have established a new behavioural test to study social novelty-seeking behaviour in the juvenile rat and show that the μ-opioid system facilitates this behaviour, possibly by reducing risk avoidance and enhancing the hedonic and/or motivational value of social novelty.

Predicting Alcohol, Cigarette, and Marijuana Use From Preferential Music Consumption

This study investigated whether use of alcohol, cigarettes, and marijuana may be predicted from preferential consumption of particular music genres. Undergraduates (257 women and 78 men) completed a questionnaire assessing these variables. Partial correlation analyses, controlling for sensation-seeking tendencies and behaviors, revealed that listening to conventional music (pop, country, and religious genres) was negatively correlated with cigarette smoking (p=.001) and marijuana use (p<.001). Additionally, listening to energetic music (rap or hip-hop and soul or funk genres) was positively correlated with marijuana use (p=.004). The only significant predictor of alcohol use was country music, with which it was positively correlated (p=.04). This research suggests an especially harmful influence of energetic music on marijuana use.

Blunted neural responses to monetary risk in high sensation seekers

The sensation-seeking trait is a valid predictor of various risk-taking behaviors. However, the neural underpinnings of risk processing in sensation seeking are yet unclear. The present event-related potential (ERP) study examined electrophysiological correlates associated with different stages of risky reward processing in sensation seeking. Twenty-one high sensation seekers (HSS) and 22 low sensation seekers (LSS) performed a simple two-choice gambling task. Behaviorally, whereas LSS exhibited a risk-averse pattern, HSS showed a risk-neutral pattern. During the anticipation stage, an increased stimulus-preceding negativity was elicited by high-risk compared to low-risk choices in LSS but not in HSS. During the outcome-appraisal stage, the feedback-related negativity, when calculated as the difference between losses and gains, was enhanced in response to the high-risk versus low-risk outcomes, which appeared for LSS but not for HSS. Further, HSS as compared to LSS exhibited a diminished P300 to both gains and losses. These findings suggest that risk-taking behavior in sensation seeking is expressed as blunted neural responses to risk in the anticipation stage and in the outcome-appraisal stage, which represents a candidate target for drug prevention.

Development of a brief substance use sensation seeking scale: validation and prediction of injection-related behaviors

Sensation seeking, a personality trait, has been shown to predict engagement in high-risk behaviors. However, little is known regarding the impact of sensation seeking on substance use among street youth. We therefore sought to modify a sensation seeking scale (SSS) for use among this population. Street youth from the Vancouver-based At-Risk Youth Study (n = 226) completed the modified SSS. Exploratory and confirmatory factor analysis (EFA/CFA) were undertaken to establish the scale's dimensionality and internal validity. The association between SSS score and injection-related behaviors was tested using generalized estimating equation analysis. EFA results indicated scale unidimensionality. The comparative fit index (CFI) suggested acceptable fit (CFI = 0.914). In multivariate analysis, sensation seeking was independently associated with injection drug use, crystal methamphetamine use, polysubstance use, and binge drug use (all p < 0.05). Our findings provide preliminary support for the use of the modified SSS among street youth.

Prescription Stimulants' Effects on Healthy Inhibitory Control, Working Memory, and Episodic Memory: A Meta-analysis

The use of prescription stimulants to enhance healthy cognition has significant social, ethical, and public health implications. The large number of enhancement users across various ages and occupations emphasizes the importance of examining these drugs' efficacy in a nonclinical sample. The present meta-analysis was conducted to estimate the magnitude of the effects of methylphenidate and amphetamine on cognitive functions central to academic and occupational functioning, including inhibitory control, working memory, short-term episodic memory, and delayed episodic memory. In addition, we examined the evidence for publication bias. Forty-eight studies (total of 1,409 participants) were included in the analyses. We found evidence for small but significant stimulant enhancement effects on inhibitory control and short-term episodic memory. Small effects on working memory reached significance, based on one of our two analytical approaches. Effects on delayed episodic memory were medium in size. However, because the effects on long-term and working memory were qualified by evidence for publication bias, we conclude that the effect of amphetamine and methylphenidate on the examined facets of healthy cognition is probably modest overall. In some situations, a small advantage may be valuable, although it is also possible that healthy users resort to stimulants to enhance their energy and motivation more than their cognition.

The novelty-seeking phenotype modulates the long-lasting effects of intermittent ethanol administration during adolescence

The aim of the present study was to investigate if a novelty-seeking phenotype mediates the long-lasting consequences of intermittent EtOH intoxication during adolescence. The hole board test was employed to classify adolescent mice as High- or Low-Novelty Seekers. Subsequently, animals were administered ethanol (1.25 or 2.5 g/kg) on two consecutive days at 48-h intervals over a 14-day period. Anxiety levels--measured using the elevated plus maze- spontaneous motor activity and social interaction test were studied 3 weeks later. A different set of mice underwent the same procedure, but received only the 2.5 g/kg dose of ethanol. Three weeks later, in order to induce CPP, the same animals were administered 1 or 6 mg/kg of cocaine or 1 or 2.5 mg/kg MDMA. The results revealed a decrease in aggressive behaviors and an anxiolytic profile in HNS mice and longer latency to explore the novel object by LNS mice. Ethanol exposure enhanced the reinforcing effects of cocaine and MDMA in both groups when CPP was induced with a sub-threshold dose of the drugs. The extinguished cocaine-induced CPP (1 and 6 mg/kg) was reinstated after a priming dose in HNS animals only. Our results confirm that intermittent EtOH administration during adolescence induces long-lasting effects that are manifested in adult life, and that there is an association between these effects and the novelty-seeking phenotype.

Comparison of Caffeine and d-amphetamine in Cocaine-Dependent Subjects: Differential Outcomes on Subjective and Cardiovascular Effects, Reward Learning, and Salivary Paraxanthine

Due to indirect modulation of dopamine transmission, adenosine receptor antagonists may be useful in either treating cocaine use or improving disrupted cognitive-behavioral functions associated with chronic cocaine use. To compare and contrast the stimulant effects of adenosine antagonism to direct dopamine stimulation, we administered 150 mg and 300 mg caffeine, 20 mg amphetamine, and placebo to cocaine-dependent vs. healthy control subjects, matched on moderate caffeine use. Data were obtained on measures of cardiovascular effects, subjective drug effects (ARCI, VAS, DEQ), and a probabilistic reward-learning task sensitive to dopamine modulation. Levels of salivary caffeine and the primary caffeine metabolite paraxanthine were obtained on placebo and caffeine dosing days. Cardiovascular results revealed main effects of dose for diastolic blood pressure and heart rate; follow up tests showed that controls were most sensitive to 300 mg caffeine and 20 mg amphetamine; cocaine-dependent subjects were sensitive only to 300 mg caffeine. Subjective effects results revealed dose × time and dose × group interactions on the ARCI A, ARCI LSD, and VAS 'elated' scales; follow up tests did not show systematic differences between groups with regard to caffeine or d-amphetamine. Large between-group differences in salivary paraxanthine (but not salivary caffeine) levels were obtained under both caffeine doses. The cocaine-dependent group expressed significantly higher paraxanthine levels than controls under 150 mg and 3-4 fold greater levels under 300 mg at 90 min and 150 min post caffeine dose. However, these differences also covaried with cigarette smoking status (not balanced between groups), and nicotine smoking is known to alter caffeine/paraxanthine metabolism via cytochrome P450 enzymes. These preliminary data raise the possibility that adenosine antagonists may affect cocaine-dependent and non-dependent subjects differently. In conjunction with previous preclinical and human studies, the data suggest that adenosine modulating drugs may have value in the treatment of stimulant use disorders.

Volunteerism and self-selection bias in human positron emission tomography neuroimaging research

Scientists have known for decades that persons who volunteer for behavioral research may be different from those who decline participation and that characteristics differentiating volunteers from non-volunteers may vary depending on the nature of the research. There is evidence that volunteer self-selection can impact representativeness of samples in studies involving physically or psychologically stressful procedures, such as electric shocks, sensory isolation, or drug effects. However, the degree to which self-selection influences sample characteristics in "stressful" studies involving positron emission tomography (PET) has not been evaluated. Since estimation of population parameters, robustness of findings, and validity of inferred relationships can all be impacted by volunteer bias, it is important to determine if self-selection may act as an unrecognized confound in such studies. In the present investigation, we obtained baseline data on 114 (56M, 58F) subjects who participated in a study involving completion of several self-report questionnaires and behavioral performance tasks. Participants were later given the opportunity to enroll in an [11C]raclopride PET study involving intravenous amphetamine (AMPH) administration. Demographic characteristics, personality traits, and task performance of subjects who consented to the latter study were compared with those who declined participation. Findings showed that the principal personality trait that distinguished the two groups was sensation-seeking; volunteers scored significantly higher on this dimension than non-volunteers. Males were more likely to volunteer than females. However, results of mediation analysis suggested that the relationship between gender and volunteer status was mediated by greater sensation-seeking traits in the males. Implications of these findings are discussed.

Dopamine modulates risk-taking as a function of baseline sensation-seeking trait

Trait sensation-seeking, defined as a need for varied, complex, and intense sensations, represents a relatively underexplored hedonic drive in human behavioral neuroscience research. It is related to increased risk for a range of behaviors including substance use, gambling, and risky sexual practice. Individual differences in self-reported sensation-seeking have been linked to brain dopamine function, particularly at D2-like receptors, but so far no causal evidence exists for a role of dopamine in sensation-seeking behavior in humans. Here, we investigated the effects of the selective D2/D3 agonist cabergoline on performance of a probabilistic risky choice task in healthy humans using a sensitive within-subject, placebo-controlled design. Cabergoline significantly influenced the way participants combined different explicit signals regarding probability and loss when choosing between response options associated with uncertain outcomes. Importantly, these effects were strongly dependent on baseline sensation-seeking score. Overall, cabergoline increased sensitivity of choice to information about probability of winning; while decreasing discrimination according to magnitude of potential losses associated with different options. The largest effects of the drug were observed in participants with lower sensation-seeking scores. These findings provide evidence that risk-taking behavior in humans can be directly manipulated by a dopaminergic drug, but that the effectiveness of such a manipulation depends on baseline differences in sensation-seeking trait. This emphasizes the importance of considering individual differences when investigating manipulation of risky decision-making, and may have relevance for the development of pharmacotherapies for disorders involving excessive risk-taking in humans, such as pathological gambling.

Inattention, impulsive action, and subjective response to D-amphetamine

BACKGROUND

Both impulsivity and sensitivity to the rewarding effects of drugs have long been considered risk factors for drug abuse. There is some preclinical evidence to suggest that the two are related; however, there is little information about how specific behavioral components of impulsivity are related to the acute euphorigenic effects of drugs in humans. The aim of the current study was to examine the degree to which both inattention and impulsive action predicted subjective response to amphetamine.

METHODS

Healthy adults (n=165) performed the behavioral tasks and rated their subjective response to amphetamine (0, 5, 10, and 20 mg). Inattention was assessed as attention lapses on a simple reaction time task, and impulsive action was measured by stop RT on the stop task. Subjective response to amphetamine was assessed with the Drug Effects Questionnaire (DEQ) and the Profile of Mood States (POMS).

RESULTS

Hierarchical linear regression analyses showed significant negative associations between attention lapses and subjective response to amphetamine on DEQ measures. By contrast, stop RT was positively associated with responses on both DEQ and POMS measures. Additionally, a dose-response relationship was observed, such that the strength of these associations increased with higher doses of amphetamine.

CONCLUSIONS

These findings suggest that inattention is associated with less subjective response to amphetamine. By contrast, the heightened sensitivity to stimulant drug reward observed in individuals high in impulsive action suggests that this might be one mechanism contributing to increased risk for stimulant drug abuse in these individuals.

Neonatal allopregnanolone levels alteration: effects on behavior and role of the hippocampus

Several works have pointed out the importance of the neurosteroid allopregnanolone for the maturation of the central nervous system and for adult behavior. The alteration of neonatal allopregnanolone levels in the first weeks of life alters emotional adult behavior and sensory gating processes. Without ruling out brain structures, some of these behavioral alterations seem to be related to a different functioning of the hippocampus in adult age. We focus here on the different behavioral studies that have revealed the importance of neonatal allopregnanolone levels for the adult response to novel environmental stimuli, anxiety-related behaviors and processing of sensory inputs (prepulse inhibition). An increase in neonatal physiological allopregnanolone levels decreases anxiety and increases novelty responses in adult age, thus affecting the individual response to environmental cues. These effects are also accompanied by a decrease in prepulse inhibition, indicating alterations in sensory gating that have been related to that present in disorders, such as schizophrenia. Moreover, behavioral studies have shown that some of these effects are related to a different functioning of the dorsal hippocampus, as the behavioral effects (decrease in anxiety and locomotion or increase in prepulse inhibition) of intrahippocampal allopregnanolone infusions in adult age are not present in those subjects in whom neonatal allopregnanolone levels were altered. Recent data indicated that this hippocampal involvement may be related to alterations in the expression of gamma-aminobutyric-acid receptors containing α4 and δ subunits, molecular alterations that can persist into adult age and that can, in part, explain the reported behavioral disturbances.

Contribution of impulsivity and novelty-seeking to the acquisition and maintenance of MDMA self-administration

It has been suggested that the response to novelty and impulsivity predict the latency to acquisition and maintenance of drug self-administration, respectively. The aim of this study was to examine the relationship between these two traits and (1) the latency to acquisition and (2) maintenance (drug-seeking) of 3,4-methylenedioxymethamphetamine (MDMA) self -administration. Impulsivity, measured as premature responding on the five-choice serial reaction time task (5-CSRTT), and novelty-seeking, measured as the locomotor response in a novel environment, were measured prior to self-administration. Latency to acquisition was determined as the number of test sessions required to self-administer an initial criterion of 90 infusions of 1.0 mg/kg/infusion, as well as an additional 150 infusions of 0.5 mg/kg/infusion MDMA. For some rats, the ability of MDMA [0, 5.0 or 10.0 mg/kg, intraperitoneal (IP)] to produce drug-seeking was subsequently measured, and for others, impulsivity was again measured following self-administration. Novelty-seeking was not significantly correlated with either the acquisition or drug-seeking measures of MDMA self-administration. Impulsivity was not significantly correlated with the latency to acquire self-administration of MDMA, but was significantly and positively correlated with the magnitude of MDMA-produced drug-seeking. Furthermore, MDMA self-administration produced a number of notable, but transient, deficits in the 5-CSRTT; there was an increase in omission rate and a delayed increase in premature responses in particular. These findings suggest that impulsivity, but not sensation seeking, might be a risk factor for the development of compulsive drug-seeking following withdrawal from MDMA self-administration.

Behavioural stimulation and sensation-seeking among prisoners: applications to substance dependency

BACKGROUND

Sensation-seeking among prisoners with substance dependence difficulties (drug and/or alcohol) was examined. This topic is under-researched in a prisoner sample.

AIMS

The aims are to examine the association between sensation-seeking, other personality variables, and substance dependency among prisoners, and to examine if sensation-seeking can be refined.

METHODS

Adult male prisoners (n=200) completed self-report measures examining the constructs of interest.

RESULTS

Sensation-seeking comprised extraversion and openness to experience. It was more appropriately described as Behavioural-Stimulation-and-Sensation-Seeking (BStim-SS). BStim-SS is related to drug and poly-substance dependency but not alcohol-only dependency. Increased impulsivity was related to all substance use dependencies.

CONCLUSIONS AND IMPLICATIONS FOR PRACTISE

BStim-SS presents as a valuable concept to apply to forensic populations. It captures the need for behavioural and emotional stimulation and lends support to Reward Discounting theory as valuable concept to apply across substance dependency. Implications for practise include: • A need to identify a broader concept of sensation-seeking for prisoner samples; • The recognition of differences within substance dependent samples, with impulsivity presenting differently across drug and/or alcohol dependent groups; • Recognition that concepts regularly applied to community samples need to be examined more specifically among forensic samples to ascertain validity.

Personality and the acute subjective effects of d-amphetamine in humans

There is evidence that subjective responses to psychoactive drugs are related to personality traits. Here, we extend previous findings by examining personality measures in relation to acute responses to d-amphetamine (AMPH) in a large sample of healthy volunteers. Healthy adults (n=286) completed the Multidimensional Personality Questionnaire Brief Form (MPQ-BF) and participated in four sessions during which they received oral AMPH (0, 5, 10, 20 mg), under double-blind conditions. Subjective responses to the drug were measured using the Profile of Mood States, Addiction Research Center Inventory, and Drug Effects Questionnaire. Drug responses were reduced via principal components analysis to three higher-order factors ('Euphoria', 'Arousal', 'Dysphoria'). Participants were rank ordered on selected MPQ-BF scales; the top and bottom third on each trait were compared on the drug response factors. High trait physical fearlessness was significantly associated with greater amphetamine-related Arousal, and high trait reward sensitivity was significantly associated with greater Euphoria. In addition, high trait impulsivity was significantly associated with greater Arousal and Euphoria. These results provide further evidence that individual differences in the subjective effects of AMPH are partially explained by differences in personality, and are consistent with the idea that both personality and responses to stimulants depend upon shared neurochemical systems.

The amphetamine response moderates the relationship between negative emotionality and alcohol use

BACKGROUND

Considerable evidence suggests that sensitivity to the stimulant effects of alcohol and other drugs is a risk marker for heavy or problematic use of those substances. A separate body of research implicates negative emotionality. The goal of the present study was to evaluate the independent and interactive effects of the stimulant response, assessed with an amphetamine challenge, and negative emotionality on alcohol and drug use.

METHODS

Healthy young women and men completed the Multidimensional Personality Questionnaire (MPQ) and an inventory assessing alcohol and other drug use. Subsequently, the effects of 10-mg d-amphetamine were determined in the laboratory using the Stimulant scale of the Biphasic Alcohol Effects Scale. Hierarchical regression analyses evaluated the effects of amphetamine response and the MPQ factor Negative Emotionality on measures of substance use.

RESULTS

The amphetamine response moderated relationships between negative emotionality and alcohol use: in combination with a robust amphetamine response (i.e., enhanced stimulant effects as compared with baseline), negative emotionality predicted greater alcohol consumption, more episodes of binge drinking, and more frequent intoxication in regression models. A strong stimulant response independently predicted having used an illicit drug, and there was a trend for it to predict having used alcohol. Negative emotionality alone was not associated with any measure of alcohol or drug use.

CONCLUSIONS

Consistent with the idea that emotion-based behavioral dysregulation promotes reward seeking, a high level of negative emotionality was associated with maladaptive alcohol use when it co-occurred with sensitivity to drug-based reward. The findings contribute to our understanding of how differences in personality may interact with those in drug response to affect alcohol use.