Effects of d-amphetamine in grouped versus isolated humans

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.

Methamphetamine, amphetamine, and aggression in humans: A systematic review of drug administration studies

The relationship between amphetamine use and aggressive or violent behaviour is unclear. This review examined laboratory data collected in humans, who were administered an acute dose of amphetamine or methamphetamine, in order to investigate the link between amphetamines and aggression. It is registered with PROSPERO (CRD42019127711). Included in the analysis are data from twenty-eight studies. Behavioural and/or subjective measures of aggression were assessed in one thousand and sixty-nine research participants, with limited amphetamine-use histories, following a single amphetamine dose (0-35mg). The available published evidence indicates that neither amphetamine nor methamphetamine acutely increased aggression as assessed by traditional laboratory measures. Future research should assess supratherapeutic amphetamine doses as well as include a broader range of multiple aggression measures, facilitating simultaneous assessment of the various components that comprise this complex, multifaceted construct.

Sympathomimetic amine compounds and hepatotoxicity: Not all are alike-Key distinctions noted in a short review

Sympathomimetic amine compounds are often pooled together and incorrectly assumed to be interchangeable with respect to potential adverse effects. A brief and specific review of sympathomimetic compounds and one instance (i.e., hepatotoxicity) where these compounds have been improperly grouped together is covered. A review of the proposed mechanisms through which known hepatotoxic sympathomimetic agents (e.g., 3,4-methylenedioxymethamphetamine or MDMA, methamphetamine and amphetamine) cause liver injury, along with a corresponding review of in vitro data, interventional data, animal model studies and observational data allow for a comparison/contrast of different agents and reveals a lack of potential toxicity for some agents (e.g., pseudoephedrine, phenylephrine, ephedrine, 1,3-dimethylamylamine, phentermine) in this broad category. Data show that compounds within the broad group of sympathomimetics display divergent pharmacological and toxicological profiles and can be clearly distinguished with respect to liver injury. These data serve as a reminder to clinicians and others, that even small structural differences between molecules can lead to drastically different pharmacological/toxicological profiles and that one should not assume that all sympathomimetic agents are hepatotoxic. Such assumptions could lead to diagnostic errors and incorrect or insufficient treatment.

Considering the context: social factors in responses to drugs in humans

BACKGROUND

Drugs are typically used in social settings. Here, we consider two factors that may contribute to this observation: (i) the presence of other people may enhance the positive mood effects of a drug, and conversely, (ii) drugs may enhance the value of social stimuli.

METHODS

We review evidence from controlled laboratory studies with human volunteers, which investigated either of these interactions between social factors and responses to drugs. We examine the bidirectional effects of social stimuli and single doses of alcohol, stimulants, opioids, and cannabis.

RESULTS

All four classes of drugs interact with social contexts, but the nature of these interactions varies across drugs, and depends on whether the context is positive or negative.

CONCLUSIONS

Alcohol and stimulant drugs enhance the attractiveness of social stimuli and the desire to socialize, and social contexts, in turn, enhance these drugs' effects. In contrast, opioids and cannabis have subtler effects on social interactions and their effects are less influenced by the presence of others. Overall, there is stronger evidence that drugs enhance positive social contexts than that they dampen the negativity of unpleasant social settings. Controlled research is needed to understand the interactions between drugs of abuse and social contexts, to model and understand the determinants of drug use outside the laboratory.

The Forensic Implications of Amphetamine Intoxication in Cases of Inflicted Blunt Craniocerebral Trauma

The effects of D-amphetamine on outcome after blunt craniocerebral trauma are characterized and the potential legal implications discussed. Traumatic brain injury (TBI) was induced under general anesthesia in adult, male Sprague Dawley rats using the impact acceleration model. At 10 min prior to injury, D-amphetamine (5 mg/kg) or saline vehicle was administered subcutaneously; animals were subsequently assessed over a 7-day period post-trauma for motor outcome using a rotarod device. D-amphetamine treated animals performed significantly better (p < 0.001; ANOVA) than vehicle treated controls on their motor assessment, suggesting that D-amphetamine exposure prior to injury either is neuroprotective or enhances motor performance. It is possible, therefore, that an individual who has taken amphetamines may function at a better motor level after head trauma than one who has not been exposed to the drug. Future interpretations of the potential effects of amphetamines on TBI should include this possibility.

The effects of MDMA on socio-emotional processing: Does MDMA differ from other stimulants?

±3,4-Methylenedioxymethamphetamine (MDMA) is a popular recreational drug that enhances sociability and feelings of closeness with others. These "prosocial" effects appear to motivate the recreational use of MDMA and may also form the basis of its potential as an adjunct to psychotherapy. However, the extent to which MDMA differs from prototypic stimulant drugs, such as dextroamphetamine, methamphetamine, and methylphenidate, in either its behavioral effects or mechanisms of action, is not fully known. The purpose of this review is to evaluate human laboratory findings of the social effects of MDMA compared to other stimulants, ranging from simple subjective ratings of sociability to more complex elements of social processing and behavior. We also review the neurochemical mechanisms by which these drugs may impact sociability. Together, the findings reviewed here lay the groundwork for better understanding the socially enhancing effects of MDMA that distinguish it from other stimulant drugs, especially as these effects relate to the reinforcing and potentially therapeutic effects of the drug.

MDMA: a social drug in a social context

RATIONALE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

MDMA effects consistent across laboratories

RATIONALE

Several laboratories have conducted placebo-controlled drug challenge studies with 3,4-methylenedioxymethamphetamine (MDMA), providing a unique source of data to examine the reliability of the acute effects of the drug across subject samples and settings. We examined the subjective and physiological responses to the drug across three different laboratories and investigated the influence of prior MDMA use.

METHODS

Overall, 220 healthy volunteers with varying levels of previous MDMA experience participated in laboratory-based studies in which they received placebo or MDMA orally (1.5 mg/kg or 125-mg fixed dose) under double-blind conditions. Cardiovascular and subjective effects were assessed before and repeatedly after drug administration. The studies were conducted independently by investigators in Basel, San Francisco, and Chicago.

RESULTS

Despite methodological differences between the studies and differences in the subjects' drug use histories, MDMA produced very similar cardiovascular and subjective effects across the sites. The participants' prior use of MDMA was inversely related to feeling "Any Drug Effect" only at sites testing more experienced users.

CONCLUSIONS

These data indicate that the pharmacological effects of MDMA are robust and highly reproducible across settings. There was also modest evidence for tolerance to the effects of MDMA in regular users.

In the company of others: social factors alter acute alcohol effects

RATIONALE

Alcohol is usually consumed in social contexts. However, the drug has been studied mainly under socially isolated conditions, and our understanding of how social setting affects response to alcohol is limited.

OBJECTIVES

The current study compared the subjective, physiological, and behavioral effects of a moderate dose of alcohol in moderate social drinkers who were tested in either a social or an isolated context and in the presence of others who had or had not consumed alcohol.

METHODS

Healthy men and women were randomly assigned to either a social group tested in pairs (SOC; N = 24), or an isolated group tested individually (ISO; N = 20). They participated in four sessions, in which they received oral alcohol (0.8 g/kg) or placebo on two sessions each, in quasi-randomized order under double-blind conditions. In the SOC condition, the drug conditions of the co-participants were varied systematically: on two sessions, both participants received the same substance (placebo or alcohol) and on the other two sessions one received alcohol while the other received placebo. Cardiovascular measures, breath alcohol levels, and mood were assessed at regular intervals, and measures of social interaction were obtained in the SOC group.

RESULTS

Alcohol produced greater effects on certain subjective measures in the SOC condition compared with the ISO condition, including feelings of intoxication and stimulation, but not on other measures such as feeling sedated or high, or on cardiovascular measures. Within the SOC condition, participants rated themselves as more intoxicated when their partner received alcohol, and paired subjects interacted more when at least one participant received alcohol.

CONCLUSIONS

The presence of others enhances some of the subjective and behavioral effects of alcohol, especially the presence of another intoxicated individual. This enhancement of alcohol effects may explain, in part, why it is used in a social context.

Relationship between drug discrimination and ratings of subjective effects: implications for assessing and understanding the abuse potential of D-amphetamine in humans

The discriminative and subjective effects of drugs in humans are related, but the full extent of this relationship remains to be determined. To further explore this relationship, a retrospective analysis was conducted on data from six studies completed in our laboratory that used identical procedures. The relationship between the discriminative and subjective effects of a range of doses of D-amphetamine (i.e. 2.5-15 mg) was examined using correlational analyses. Significant correlations with discrimination performance were observed on 15 of 20 items from the Drug-Effect Questionnaire across a range of qualities [e.g. Pay For (a positive effect indicative of abuse potential) and Active (a stimulant-like effect)], but the magnitude of these relationships was modest (r<0.52). The current findings demonstrate that diverse subjective effects contribute to the discriminative effects of D-amphetamine and indicate that the former are a more practical means to assess the abuse potential of drugs. Although these procedures are fundamentally related in that they rely on the presence of an interoceptive drug state, they differ in the dimension(s) of the interoceptive effects that participants must quantify. The simultaneous use of drug discrimination and subjective effects may, therefore, reveal complimentary aspects of drug effects that underlie their potential for abuse.

Methamphetamine and core temperature in the rat: ambient temperature, dose, and the effect of a D2 receptor blocker

RATIONALE

Methamphetamine (METH) induces hyperthermia in warm and hypothermia in cool environments. Our first goal was to further study the role of ambient temperature in METH's effect on core temperature in rats. Previously, these effects were primarily demonstrated in high doses; we extended this investigation to the low-dose range (1 mg/kg METH). Our second goal was to identify the role of the D2 receptor in METH's effects in cool ambient temperatures.

METHOD

Rats received METH (saline, 1, 5, and 10 mg/kg), raclopride (saline, 0.3, 0.6, and 1.2 mg/kg), or a combination (all doses of raclopride combined with 10 mg/kg METH). Treatments occurred in ambient temperatures of 18, 24, or 30 °C.

RESULTS AND CONCLUSIONS

Consistent with prior research, 5 and 10 mg/kg METH caused hyperthermia or hypothermia in a dose- and ambient temperature-dependent manner (60 min after METH). In contrast, 1 mg/kg produced similar levels of hyperthermia at all ambient temperatures. These findings suggest that a threshold METH dose exists; below this dose, METH still changes core temperature, but CNS control over temperature regulation is left intact. In our experiments regarding D2 blockade, raclopride decreased METH-induced core temperature at 30 and 24 °C (60 min after METH), consistent with previous findings. We extended these findings by demonstrating that in a cool ambient temperature (18 °C), raclopride pretreatment also lowered the core temperature response to METH. Although the D2 receptor is known to mediate hypothermia, the combination of METH and D2 blockade suggests a complex mediation of the core temperature response, perhaps involving neurotransmitter interactions.

Amphetamine as a social drug: effects of d-amphetamine on social processing and behavior

RATIONALE

Drug users often report using drugs to enhance social situations, and empirical studies support the idea that drugs increase both social behavior and the value of social interactions. One way that drugs may affect social behavior is by altering social processing, for example by decreasing perceptions of negative emotion in others.

OBJECTIVES

We examined effects of d-amphetamine on processing of emotional facial expressions and on the social behavior of talking. We predicted amphetamine would enhance attention, identification, and responsivity to positive expressions, and that this in turn would predict increased talkativeness.

METHODS

Over three sessions, 36 healthy normal adults received placebo, 10, and 20 mg d-amphetamine under counterbalanced double-blind conditions. At each session, we measured processing of happy, fearful, sad, and angry expressions using an attentional visual probe task, a dynamic emotion identification task, and measures of facial muscle activity. We also measured talking.

RESULTS

Amphetamine decreased the threshold for identifying all emotions, increased negative facial responses to sad expressions, and increased talkativeness. Contrary to our hypotheses, amphetamine did not alter attention to, identification of, or facial responses to positive emotions specifically. Interestingly, the drug decreased the threshold to identify all emotions, and this effect was uniquely related to increased talkativeness, even after controlling for overall sensitivity to amphetamine.

CONCLUSIONS

The results suggest that amphetamine may encourage sociability by increasing sensitivity to subtle emotional expressions. These findings suggest novel social mechanisms that may contribute to the rewarding effects of amphetamine.

Norepinephrine transporter gene variation modulates acute response to D-amphetamine

BACKGROUND

Individual differences in subjective responses to stimulant drugs such as amphetamine may influence risk of abuse as well as clinical-treatment response to these drugs. Because the effects of amphetamine are mediated in part by the norepinephrine transporter (SLC6A2), we examined interindividual differences in mood response to amphetamine in relation to SLC6A2 gene polymorphisms.

METHODS

Ninety-nine healthy volunteers participated in three sessions in which they randomly received either placebo or D-amphetamine (10 mg or 20 mg) under double-blind conditions. Every subject completed self-report measures on subjective effects (Profile of Mood States). Afterward, all individuals were genotyped for eight SLC6A2 gene polymorphisms. Individual genotypes and haplotypes were investigated.

RESULTS

The intronic 36001C/C (rs47958) genotype was associated with increases in positive mood and elation after 20 mg of D-amphetamine. Positive mood and elation levels were also found to be associated with the haplotype GCC formed from 28257G/C (rs36017), 28323C/T (rs2270935), and 36001A/C (rs47958). These findings remained significant after adjustment for multiple testing.

CONCLUSIONS

Polymorphisms in the SLC6A2 gene were associated with mood responses to D-amphetamine. If confirmed, this observation may contribute to a better understanding of interindividual variations in the clinical response to amphetamine and in the risk of becoming addicted to amphetamine.

Family history of alcoholism and response to amphetamine: sex differences in the effect of risk

BACKGROUND

Individuals at risk for alcoholism exhibit an enhanced stimulant response to alcohol. It is not known whether individuals at risk also exhibit a heightened sensitivity to other drugs with stimulant properties.

METHODS

Healthy young men and women each received, in separate sessions, placebo and 10 mg of d-amphetamine in counterbalanced order. Stimulant and sedative subjective effects were recorded before and three times after capsule administration using the Biphasic Alcohol Effects Scale. The sample comprised 19 family-history-positive (FHP; 58% women) and 53 family-history-negative (FHN; 51% women) participants.

RESULTS

As compared with placebo, amphetamine increased ratings of stimulation in the sample as a whole. In addition, the ratings revealed an enhanced, as well as a protracted, stimulant response to amphetamine among FHP men, as compared with FHN men: for FHP men, ratings of stimulation made 3 and 6 hr after amphetamine administration were greater than baseline ratings. Moreover, in FHP men, the effect of amphetamine, as compared with placebo, was most evident 6 hr after capsule administration. In contrast, despite a dose x hour interaction in FHN men, post hoc comparisons revealed no differences between the baseline and any of the postamphetamine measurements or between amphetamine and placebo ratings at any of the time points. Among women, the drug effect did not differentiate the family-history groups.

CONCLUSIONS

Consistent with previous research on alcohol, high-risk men exhibited a heightened stimulant response to amphetamine. Thus, for men, sensitivity to the stimulant properties of drugs may be an endophenotype for alcoholism. Whereas the present results suggest that women at risk do not exhibit an enhanced stimulant response to amphetamine, further study is needed, including evaluation at various points in the menstrual cycle.

Relationship of plasma amphetamine levels to physiological, subjective, cognitive and biochemical measures in healthy volunteers

Acute administration of the stimulant dextro-amphetamine produces multiple physiological, subjective cognitive and biochemical changes. These effects are similar to those seen in mania, and may be a useful model for mania. The aim of the present study was more fully to determine the multiple effects of dextro-amphetamine and to relate these to changes in plasma levels of the drug. In a double-blind, placebo-controlled crossover study in 25 healthy volunteers (ages 18-45), the effects of 25 mg of oral dextro-amphetamine were examined. Physiological, subjective, cognitive changes, concentrations of amino acids and metabolites of biogenic amines period were related to changes in plasma amphetamine concentrations over 500 min. Peak concentrations of dextro-amphetamine occurred at 2.5-3.5 h post-administration and levels decreased to 75% of peak value after 500 min. The results from the present study indicate that the subjective psychological, cognitive and blood pressure changes frequently did not mirror the time course of plasma levels of the drug. Thus, there was no clear-cut relationship between plasma levels and effects. In addition, dextro-amphetamine caused no significant changes in amino acids or amino metabolite concentrations. In conclusion, while dextro-amphetamine administration definitely causes several changes which are seen in mania, there remain some physiological and metabolic differences between these two conditions.

Context-dependent effects of steroid chemosignals on human physiology and mood

We examined the physiological and psychological effects of nanomolar amounts of steroids applied directly under the nose (Delta4,16-androstadien-3-one and 1,3,5,(10),16-estratetraen-3-ol). These potential human chemosignals were not consciously discernible in a strong-odor carrier (clove oil and propylene glycol). In a double-blind, within-subject, repeated-measures experiment with 65 subjects, we demonstrated that both steroids produced sustained changes in digit skin temperature and palmar skin conductance (an indicator of sympathetic nervous system tone) while the subjects were completing psychological questionnaires or reading. These effects, however, did not follow the sex-stereotyped pattern predicted by a sex attractant function. Both androstadienone and estratetraenol raised the skin temperature of men's hands and lowered it in women. Likewise, each steroid increased skin conductance, with a significantly greater effect on women than men. Women's responses were observed only in the sessions run by the male tester, an effect that may or may not be solely attributable to tester sex. Men's responses, in contrast, were not affected by this difference in socioexperimental condition. Similarly, women experienced an immediate increase in positive mood only in the presence of the male tester, while men's responses were unaffected by this socioexperimental context. One source of this sex difference may be the fact that the majority of women were in the late follicular phase of their menstrual cycle. Although it is premature to classify these steroids as pheromones, our data suggest that they function as chemosignals that modulate autonomic nervous system tone as well as psychological state.

A rapid method of determining amphetamine in plasma samples using pentafluorobenzenesulfonyl chloride and electron-capture gas chromatography

INTRODUCTION

Acute administration of (+)-amphetamine has been used as a model for mania in humans since it mimics the physiological, biochemical, and cognitive effects seen in mania. A rapid and sensitive method for the determination of amphetamine in human plasma samples using gas chromatography with electron-capture detection was developed in our laboratory to follow the time course of amphetamine levels in patients receiving this drug as part of a study using amphetamine as a model for mania.

METHODS

Blood samples were taken from healthy male volunteers at 30, 60, 90, 150, 210, 240, and 480 min after administration of 25 mg of (+)-amphetamine. Plasma was isolated by centrifugation and used for the analysis. This method is a modification of the procedure described by Paetsch et al. [J. Chromatogr. 573 (1992) 313] for the determination of amphetamine in rat brain tissue. Amphetamine was derivatized under basic conditions using pentafluorobenzenesulfonyl chloride (PFBSC) prior to analysis on a gas chromatograph equipped with a capillary column and an electron-capture detector. The internal standard used was benzylamine. The structure of the amphetamine derivative was confirmed using combined gas chromatography-mass spectrometry (GC-MS).

RESULTS

The limit of detection was <1 ng/ml, and the method was linear in the 1- to 100-ng range used. Mean amphetamine levels peaked at 3.5 h after drug administration, and were 40.8 +/- 1.5 ng/ml at that time.

DISCUSSION

This procedure produces a stable derivative with excellent chromatographic properties and is both simple and reproducible.

Psychological state and mood effects of steroidal chemosignals in women and men

We tested the hypothesis that isolated steroids, claimed to act like pheromones, affect human psychological state or mood. In the first experiment, we established that two steroids, Delta4, 16-androstadien-3-one and 1,3,5(10)16-estratetraen-3-ol, modulated emotional states within 6 min of exposure. In men and women, neither steroid had specific effects on states of alertness or negative-confused mood. However, both steroids increased positive stimulated mood state in women but decreased it in men. These psychological findings do not parallel the reported sexually specific effects of these two steroids on the surface potential activity of putative vomeronasal epithelium. In a second experiment on women, we replicated that Delta4,16-androstadien-3-one modulated their general mood state, even when women were not aware of its odor and gave identical olfactory descriptions for the steroid and the control carrier solutions. In this within-subjects, repeated-measures experiment, androstadienone prevented the deterioration in general mood which occurred during exposure to the clove oil carrier solution in the laboratory environment. Thus, androstadienone appears to modulate affect, rather than releasing stereotyped behaviors or emotions. It is premature to call these steroids human pheromones. They are nonetheless psychologically potent, mandating future work delineating their function-i.e., whether these steroids are communicative chemosignals, context specific, or related to unconscious associations. In light of these modulatory effects and the complexity of human behavior, the function of chemosignals and pheromonal systems in a variety of species may need to be expanded to include the concept of modulators, as well as the traditional releasers, primers, and signaling compounds.