Time allocation in a concurrent schedule of social interaction and monetary reinforcement: effects of d-amphetamine

Effects of amphetamine on pro-social ultrasonic communication in juvenile rats: Implications for mania models

Communication is the act of information transfer between sender and receiver. In rats, vocal communication can be studied through ultrasonic vocalizations (USV). 50-kHz USV occur in appetitive situations, most notably juvenile play, likely expressing the sender׳s positive affective state. Such appetitive 50-kHz USV serve important pro-social communicative functions and elicit social exploratory and approach behavior in the receiver. Emission of 50-kHz USV can be induced pharmacologically by the administration of psychostimulant drugs, such as amphetamine. However, it is unknown whether amphetamine affects the pro-social communicative function of 50-kHz USV in the receiver. We therefore assessed dose-response effects of amphetamine (0.0mg/kg, 0.5mg/kg, 1.0mg/kg, 2.5mg/kg, 5.0mg/kg) on pro-social ultrasonic communication on both, sender and receiver, in juvenile rats. We found an inverted U-shaped effect of amphetamine on 50-kHz USV emission, with 50-kHz USV levels being strongly enhanced by moderate doses, yet less prominent effects were seen following the highest dose. Likewise, amphetamine exerted inverted U-shaped effects on social exploratory and approach behavior induced by playback of appetitive 50-kHz USV. Social approach was enhanced by moderate amphetamine doses, but completely abolished following the highest dose. Amphetamine further dose-dependently promoted the emission of 50-kHz USV following playback of appetitive 50-kHz USV, indicating more vigorous attempts to establish social proximity. Our results support an important role of dopamine in closing a perception-and-action-loop through linking mechanisms relevant for detection and production of social vocalizations. Moreover, our approach possibly provides a new means to study mania-like aberrant social interaction and communication in animal models for bipolar disorder.

Naltrexone alters the processing of social and emotional stimuli in healthy adults

Endogenous opioids have complex social effects that may depend on specific receptor actions and vary depending on the "stage" of social behavior (e.g., seeking vs. responding to social stimuli). We tested the effects of a nonspecific opioid antagonist, naltrexone (NTX), on social processing in humans. NTX is used to treat alcohol and opiate dependence, and may affect both mu and kappa-opioid systems. We assessed attention ("seeking"), and subjective and psychophysiological responses ("responding") to positive and negative social stimuli. Based on literature suggesting mu-opioid blockade impairs positive social responses, we hypothesized that NTX would decrease responses to positive social stimuli. We also tested responses to negative stimuli, which might be either increased by NTX's mu-opioid effects or decreased by its kappa-opioid effects. Thirty-four healthy volunteers received placebo, 25 mg, or 50 mg NTX across three sessions under double-blind conditions. At each session, participants completed measures of attention, identification, and emotional responses for emotional faces and scenes. NTX increased attention to emotional expressions, slowed identification of sadness and fear, and decreased ratings of arousal for social and nonsocial emotional scenes. These findings are more consistent with anxiolytic kappa-antagonist than mu-blocking effects, suggesting effects on kappa receptors may contribute to the clinical effects of NTX.

Effects of MDMA and Intranasal oxytocin on social and emotional processing

MDMA (± 3,4-methylenedioxymethamphetamine, 'ecstasy') is used recreationally, reportedly because it increases feelings of empathy, sociability, and interpersonal closeness. One line of evidence suggests that MDMA produces these effects by releasing oxytocin, a peptide involved in social bonding. In the current study, we investigated the acute effects of MDMA and oxytocin on social and emotional processing in healthy human volunteers. MDMA users (N = 65) participated in a 4-session, within-between-subjects study in which they received oral MDMA (0.75, 1.5 mg/kg), intranasal oxytocin (20 or 40 IU), or placebo under double-blind conditions. The primary outcomes included measures of emotion recognition and sociability (desire to be with others). Cardiovascular and subjective effects were also assessed. As expected, MDMA dose-dependently increased heart rate and blood pressure and feelings of euphoria (eg, 'High' and 'Like Drug'). On measures of social function, MDMA impaired recognition of angry and fearful facial expressions, and the larger dose (1.5 mg/kg) increased desire to be with others, compared with placebo. Oxytocin produced small but significant increases in feelings of sociability and enhanced recognition of sad facial expressions. Additionally, responses to oxytocin were related to responses to MDMA with subjects on two subjective measures of sociability. Thus, MDMA increased euphoria and feelings of sociability, perhaps by reducing sensitivity to subtle signs of negative emotions in others. The present findings provide only limited support for the idea that oxytocin produces the prosocial effects of MDMA.

Behavioral pharmacology and verbal behavior: Diazepam effects on verbal self-reports

Diazepam (10 mg) was administered to two men performing a delayed matching-to-sample task in which the number of elements in a compound sample stimulus (one of which appeared among 4 comparison stimuli) was manipulated from 1 to 3. After each trial, subjects pressed either a "Yes" or "No" button in response to a computer-presented query about whether the last choice met a point contingency requiring selection of the matching comparison stimulus within a time limit. Diazepam simultaneously produced marginal decreases in matching-to-sample performance and more pronounced decreases in the accuracy of self-reports about the same performance. Diazepam selectively increased false reports of success; false reports of failure were not systematically affected. A signal-detection analysis summarized these patterns as a decrease in self-report discriminability (A') with no systematic change in bias (B'(H)). These preliminary results converge with those of clinical lore and the results of studies with other benzodiazepine drugs in suggesting that diazepam can produce an "overconfidence" in performance self-evaluation, the mechanisms and parameters of which remain to be identified. The results were inconsistent with those of one previous study of diazepam's effects on performance self-evaluation, but given procedural differences between the two studies, the discrepancy may reflect the functional independence of verbal operant classes in Skinner's (1957) taxonomy.

Amphetamine analogs methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) differentially affect speech

RATIONALE

Most reports of the effects of methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) on speech have been anecdotal.

OBJECTIVES

The current study used a within-participant design to assess the effects of methamphetamine and MDMA on speech.

MATERIALS AND METHODS

Eleven recreational users of amphetamines completed this inpatient, within-participant, double-blind study, during which they received placebo, methamphetamine (20, 40 mg), and MDMA (100 mg) on separate days. Following drug administration, study participants described movies viewed the previous evening and completed mood scales.

RESULTS

Methamphetamine increased quantity of speech, fluency, and self-ratings of talkativeness and alertness, while it decreased the average duration of nonjuncture unfilled pauses. MDMA decreased fluency and increased self-ratings of inability to concentrate. To determine if methamphetamine- and MDMA-related effects were perceptible, undergraduates listened to the participants' movie descriptions and rated their coherence and the speaker's mood. Following methamphetamine, descriptions were judged to be more coherent and focused than they were following MDMA.

CONCLUSIONS

Methamphetamine improved verbal fluency and MDMA adversely affected fluency. This pattern of effects is consistent with the effects of these drugs on functioning in other cognitive domains. In general, methamphetamine effects on speech were inconsistent with effects popularly attributed to this drug, while MDMA-related effects were in agreement with some anecdotal reports and discordant with others.

Acute effects of D-amphetamine on progressive-ratio performance maintained by cigarette smoking and money

RATIONALE

Psychomotor stimulants often increase cigarette smoking, although the mechanisms responsible for that effect remain unclear.

OBJECTIVE

The present study was conducted to extend our investigation of the effects of psychomotor stimulant use on the reinforcing effects of cigarette smoking.

METHODS

A progressive-ratio (PR) schedule was used to examine the acute effects of orally administered D-amphetamine (placebo, 5, 10, 15 mg/70 kg) on the reinforcing effects of smoking (2 puffs/ratio) and money (1.00 US dollar/ratio) in 18 adult smokers.

RESULTS

Among the overall sample of 18 smokers, D-amphetamine produced only a modest, non-significant increase in the amount of responding maintained by smoking (PR break point), but effects varied systematically between subjects. D-Amphetamine increased the smoking break point among ten subjects (responders), while leaving unchanged or decreasing the break point in the remaining eight individuals (non-responders). Responders also were more sensitive than non-responders to d-amphetamine's effects on visual-analog ratings of "high", "good effects", "drowsy", and "slurred speech", but not on other subject ratings (i.e., "bad effects", "jittery", "confused") or on any physiological measures (i.e., heart rate, blood pressure, skin temperature). D-Amphetamine did not significantly alter PR break point maintained by money.

CONCLUSIONS

These results provide further evidence that D-amphetamine can increase the reinforcing effects of cigarette smoking, at least among a subset of smokers.

Effects of d-amphetamine in grouped versus isolated humans

This study was designed to determine whether the subjective, behavioral or physiological effects of a stimulant drug in humans depend on whether subjects are tested under isolated or social conditions. Forty-two subjects were randomly assigned to either the Social (SOC) or Isolated (ISO) condition. SOC subjects participated in 4 h laboratory sessions in groups of 3 or 4, whereas ISO subjects participated in the sessions alone. All subjects participated in three sessions, during which they received capsules containing d-amphetamine (10 or 20 mg) or placebo, in mixed order under double blind conditions. Subjective, physiological and behavioral measures were obtained at regular intervals, d-amphetamine produced dose-related, prototypic stimulant effects on many measures, including self-reported mood states, behavioral indices and physiological measures. Most of these effects were unaffected by the setting in which subjects were tested (SOC vs ISO). However, body temperature was overall higher in the SOC group, and there was a trend for d-amphetamine to produce greater hyperthermic effects in the SOC group. In addition, 10 mg d-amphetamine increased heart rate in the SOC group but not in the ISO group. The results suggest that, like in laboratory animals, some of the effects of stimulants in humans are greater under aggregated conditions. However, unlike in the animal studies, this observed enhancement of the drug's effects under aggregated conditions was limited to physiological measures and did not apply to other subjective or behavioral measures.

Effect of setting on the reinforcing and subjective effects of ethanol in social drinkers

The reinforcing and subjective effects of two doses of ethanol [0.5 g/kg (LOW) and 0.8 g/kg (HIGH)] were evaluated under two conditions, a social condition (SOC), in which subjects were tested with two or three other subjects, and a socially isolated condition (ISO), in which subjects were tested alone. Forty-one social drinkers participated in a double-blind, seven-session choice procedure. Subjects were randomly assigned to one of four experimental groups: SOC-LOW, SOC-HIGH, ISO-LOW, or ISO-HIGH. On the first four sessions, subjects sampled ethanol (0.5 or 0.8 g/kg) on two occasions and placebo on the other two occasions. On the three remaining sessions, subjects selected and consumed whichever of the two previously sampled substances they preferred. The number of sessions on which they chose ethanol was the primary measure of the reinforcing effects of ethanol. Standardized self-report questionnaires and a psychomotor test were used to measure subjective and objective drug effects. Subjects in the SOC condition chose ethanol over placebo on significantly more sessions than subjects in the ISO condition. Ethanol produced positive subjective effects (e.g., increased ratings of drug liking and euphoria) for subjects in the SOC condition, but for subjects in the ISO condition, it produced apparently negative effects (e.g., increased ratings of dysphoria). These results extend previous reports that the behavioral effects of ethanol depend upon the social condition in which it is consumed.

Effects of methylphenidate on response rate and measures of motor performance and reinforcement efficacy

This experiment evaluated the effects of methylphenidate on reinforced responding in rats. In each session the subjects (rats) earned reinforcement on seven different variable-interval reinforcement schedules. The average intervals varied from 108 to 3 s and provided reinforcement rates ranging from about 30 to 1100/h. Response rate was a negatively accelerated function of reinforcement rate. Low doses of methylphenidate (1.0 and 2.0 mg/kg) increased responding maintained by the four leanest schedules, but had little effect on responding maintained by the three densest schedules. In contrast, an 8.0 mg/kg dose increased responding maintained by the three densest schedules and slightly decreased responding maintained by leaner schedules. A quantitative model of reinforced responding, referred to as the matching law or response strength equation, was fitted to the data. This equation has two parameters. On the basis of previous experiments, one was used to measure changes in reinforcement efficacy and the other was used to measure changes in motor performance. The 1.0 and 2.0 mg/kg doses changed the reinforcement parameter in the same way as did increases in deprivation and reward magnitude. The 8.0 mg/kg dose changed the motor parameter in the same was as did decreases in lever weight. It was concluded that methylphenidate increases reinforcement efficacy, and that the highest dose changed the topography of responding. The results are discussed in terms of the response strength equation, the rate dependency principle, and the question of how to interpret changes in reinforcement efficacy and motor performance.

The effects of repeated amphetamine exposure on multiple measures of human behavior

Two groups of three healthy adult male volunteers (n = 6) participated in 15-day residential studies. Each study day was divided into a private work period (1000 to 1630), during which subjects had access to four work tasks, and a social period (1700 to 2330), during which subjects had access to a number of recreational activities available under social or private conditions. Occasionally during the study, access to high-probability activities was made contingent upon participating in low-probability activities. Tobacco cigarettes and food were available throughout each day (0900 to 2330). Each subject received active and placebo d-amphetamine doses (0 or 10 mg/70 kg) twice daily during two, three-consecutive-day intervals. Active and placebo dose intervals were presented in an alternating fashion, with order of exposure counterbalanced between groups. Amphetamine consistently decreased food intake, improved accuracy of performance on some work tasks, and increased verbal interaction and cigarette smoking. No tolerance to these effects was observed. Increases in VAS ratings of dose "potency" and "liking," as well as "stimulated" and "anxious," and decreases in "sedated" were observed during initial amphetamine exposure, but tolerance to these effects developed rapidly. The simultaneous measurement of multiple dimensions of human behavior establishes a profile of amphetamine's effects which is useful for comparison with the behavioral profiles of other drugs, such as marijuana.

A behavioral economics analysis of food choice in humans

Three studies on the behavioral economics of food choice were presented. In Experiment 1 subjects were provided a choice of working for food on concurrent VR4 VR20 schedules, and subjects allocated the majority of their responding to the VR4 schedule. Subjects in Experiment 2 were provided a choice between two foods differing in ratings of subjective liking. The lower rated food was available on an FR1 component of a concurrent schedule, while the higher rated food was available on the other component across six comparisons ranging from FR1 through VR32. Subjects initially chose to work for the higher rated food, but as the constraints for this food increased, subjects chose to work for the lower rated food. In Experiment 3, subjects were provided the choice of a breakfast they liked or the monetary equivalent during deprivation and non-deprivation conditions. The food and money were first compared on equal FR1 schedules. Schedule requirements for money were subsequently maintained on a VR2 schedule, while access to food was presented in four phases from VR4 through VR32. Under deprivation, subjects allocated their time to get the preferred food instead of money only at the FR1 FR1 comparison. Under non-deprivation subjects allocated almost all their responding to work for money. These results suggest that the laboratory choice task is sensitive to schedule differences when food is used as a reinforcer, that subjective liking and schedule constraints for food are both important in determining food choice, and that alternative reinforces can complete with food, but the effect is dependent on both the level of deprivation and constraints on access to food.

Monologue speech: effects of d-amphetamine, secobarbital and diazepam

Drugs of abuse from different pharmacological classes increase social conversation. Alcohol and d-amphetamine also increase rates of talking in subjects producing speech monologues in an isolated context. This latter finding suggests that the increases observed during dyadic social conversation may represent general increases in talking and not specific effects on social interaction. The present study was conducted to assess whether other abused drugs also increase monologue speaking. The acute effects of secobarbital (0, 50, 150, 250 mg), d-amphetamine (0, 25 mg) (Experiment 1), and diazepam (0, 10, 20, 40 mg) (Experiment 2) were investigated in healthy, adult volunteers. Secobarbital and d-amphetamine both increased the total amount of speech emitted, while diazepam generally had no effect or decreased talking. Experiment 3 was conducted to further compare the effects of secobarbital (0, 50, 150, 250 mg) and diazepam (0, 5, 15, 25 mg) using a within-subject, crossover design. Secobarbital increased talking in three of the four subjects studied, while diazepam, again, had no effect or decreased talking. In contrast to the differences noted with talking, secobarbital and diazepam both decreased response rates in a nonverbal performance task (i.e., circular-lights procedure); they also produced many similar effects on various subject-rated measures of drug effect. Thus, the differences in the effects of these two compounds on talking are not the result of a general difference in their overall profile of behavioral effects. In summary, the results obtained with secobarbital and d-amphetamine further demonstrate that an explicitly social context is not a necessary condition to observe drug-produced increases in speech quantity. The failure of diazepam to reliably increase talking in the present study illustrates the existence of some pharmacological specificity in the effect of drugs on human speech, and suggests another way in which the behavioral effects of the barbiturates and benzodiazepines may differ.

Effects of d-amphetamine on choice of social versus monetary reinforcement: a discrete-trial test

Two mutually exclusive options were concurrently available to eight volunteers during 60-min experimental sessions. Subjects chose every three minutes between conversing with another same-sex volunteer and providing speech monologues for monetary reinforcement. d-Amphetamine (12.5 and 25 mg/70 kg) significantly increased choice of social over monetary reinforcement. Drug-produced increases in choice of the social option were associated with increases in total seconds of speech and the rate of social conversation. d-Amphetamine also increased subject ratings of effects indicative of greater sociability such as friendliness, elation and energetic. These results suggest that d-amphetamine can increase the relative reinforcing effects of social interaction.

Effect of d-amphetamine, secobarbital, and marijuana on choice behavior: social versus nonsocial options

The effects of oral d-amphetamine and secobarbital and smoked marijuana on human social conversation and preference for socializing were studied in three separate experiments. During experimental sessions, active drug or placebo was administered using an acute or divided dosing procedure. Subjects who received drug then engaged in a discrete-trial choice procedure in which they made a series of mutually exclusive choices between a social (talking with their nondrugged partner) and nonsocial (sitting quietly alone) option. Lapel microphones and voice operated relays measured seconds of speech. Subjects engaged in greater amounts of conversation and chose the social option more frequently following acute dosing of d-amphetamine and secobarbital compared with placebo. Acute administration of marijuana did not significantly affect social speech or choice behavior, producing slight decreases in both measures. Acute dosing of all drugs significantly increased subjective drug effect or drug high; however, only secobarbital affected the circular lights task, producing significant performance decrements. The shifts in preference toward the social option observed with d-amphetamine and secobarbital suggest that these drugs increased the reinforcing effects of socializing relative to sitting alone. This may be one mechanism by which psychoactive drugs facilitate social conversation.