Discriminative profile of MDMA

2-Aminoindan and its ring-substituted derivatives interact with plasma membrane monoamine transporters and α2-adrenergic receptors

RATIONALE

Over the last decade, many new psychostimulant analogues have appeared on the recreational drug market and most are derivatives of amphetamine or cathinone. Another class of designer drugs is derived from the 2-aminoindan structural template. Several members of this class, including the parent compound 2-aminoindan (2-AI), have been sold as designer drugs. Another aminoindan derivative, 5-methoxy-2-aminoindan (5-MeO-AI or MEAI), is the active ingredient in a product marketed online as an alcohol substitute.

METHODS

Here, we tested 2-AI and its ring-substituted derivatives 5-MeO-AI, 5-methoxy-6-methyl-2-aminoindan (MMAI), and 5,6-methylenedioxy-2-aminoindan (MDAI) for their abilities to interact with plasma membrane monoamine transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT). We also compared the binding affinities of the aminoindans at 29 receptor and transporter binding sites.

RESULTS

2-AI was a selective substrate for NET and DAT. Ring substitution increased potency at SERT while reducing potency at DAT and NET. MDAI was moderately selective for SERT and NET, with tenfold weaker effects on DAT. 5-MeO-AI exhibited some selectivity for SERT, having sixfold lower potency at NET and 20-fold lower potency at DAT. MMAI was highly selective for SERT, with 100-fold lower potency at NET and DAT. The aminoindans had relatively high affinity for α₂-adrenoceptor subtypes. 2-AI had particularly high affinity for α_2C receptors (K_i = 41 nM) and slightly lower affinity for the α_2A (K_i = 134 nM) and α_2B (K_i = 211 nM) subtypes. 5-MeO-AI and MMAI also had moderate affinity for the 5-HT_2B receptor.

CONCLUSIONS

2-AI is predicted to have (+)-amphetamine-like effects and abuse potential whereas the ring-substituted derivatives may produce 3,4-methylenedioxymethamphetamine (MDMA)-like effects but with less abuse liability.

Generalization of serotonin and dopamine ligands to the discriminative stimulus effects of different doses of ±3,4-methylenedioxymethamphetamine

Studies that have attributed the discriminative stimulus effects of ±3,4-methylenedioxymethamphetamine (MDMA) to serotonergic mechanisms typically use a relatively low training dose of 1.5 mg/kg. The role of serotonin in the discriminative stimulus effects of higher doses of MDMA is, however, unknown. Separate groups of rats were trained to discriminate MDMA (1.5 or 3.0 mg/kg) from saline using a two-lever, food-reinforced drug-discrimination procedure. Generalization tests were carried out with a range of serotonin and dopamine ligands. Fluoxetine (0.3-3 mg/kg), clomipramine (1-10 mg/kg) and meta-chlorophenylpiperazine (0.3-2 mg/kg) dose-dependently substituted for the 1.5 mg/kg MDMA stimulus, but not the 3.0 mg/kg MDMA stimulus. 8-OH-DPAT (0.03-0.3 mg/kg) and RU-24969 (0.3-3 mg/kg) substituted for both the low-dose and the high-dose MDMA stimulus. The generalization dose-effect curve produced by 2,5-dimethoxy-4-iodoamphetamine (0.3-3 mg/kg) was shifted to the right for the 3.0 mg/kg MDMA-trained group. Amphetamine (0.25 and 0.5 mg/kg) and apomorphine (0.125 and 0.25 mg/kg) substituted for the 3.0 mg/kg, but not the 1.5 mg/kg MDMA stimulus. The results suggest some differences in the role of serotonin and dopamine in the discriminative stimulus effects of a low versus a higher dose of MDMA.

Evaluating the abuse potential of psychedelic drugs as part of the safety pharmacology assessment for medical use in humans

Psychedelics comprise drugs come from various pharmacological classes including 5-HT_2A agonists, indirect 5-HT agonists, e.g., MDMA, NMDA antagonists and κ-opioid receptor agonists. There is resurgence in developing psychedelics to treat psychiatric disorders with high unmet clinical need. Many, but not all, psychedelics are schedule 1 controlled drugs (CDs), i.e., no approved medical use. For existing psychedelics in development, regulatory approval will require a move from schedule 1 to a CD schedule for drugs with medical use, i.e., schedules 2-5. Although abuse of the psychedelics is well documented, a systematic preclinical and clinical evaluation of the risks they pose in a medical-use setting does not exist. We describe the non-clinical tests required for a regulatory evaluation of abuse/dependence risks, i.e., drug-discrimination, intravenous self-administration and physical dependence liability. A synopsis of the existing data for the various types of psychedelics is provided and we describe our findings with psychedelic drugs in these models. FDA recently issued its guidance on abuse/dependence evaluation of drug-candidates (CDER/FDA, 2017). We critically review the guidance, discuss the impact this document will have on non-clinical abuse/dependence testing, and offer advice on how non-clinical abuse/dependence experiments can be designed to meet not only the expectations of FDA, but also other regulatory agencies. Finally, we offer views on how these non-clinical tests can be refined to provide more meaningful information to aid the assessment of the risks posed by CNS drug-candidates for abuse and physical dependence. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.

"Ecstasy" to addiction: Mechanisms and reinforcing effects of three synthetic cathinone analogs of MDMA

This study aimed to address the mechanisms and reinforcing effects of three synthetic cathinone analogs of MDMA commonly reported in "Ecstasy" formulations: methylone, butylone, and pentylone. Whole-cell patch clamp techniques were used to assess the mechanism of each compound at the dopamine and serotonin transporters. Separate groups of rats were trained to discriminate methamphetamine, DOM, or MDMA from vehicle. Substitution studies were performed in each group and antagonism studies with SCH23390 were performed against each compound that produced substitution. Self-administration of each compound was evaluated under a progressive ratio schedule of reinforcement. Each compound produced an inward current at the serotonin transporter, but little or no current at the dopamine transporter. Each of the test compounds substituted fully for the discriminative stimulus effects of methamphetamine, methylone and butylone substituted partially for DOM and fully for MDMA, whereas pentylone failed to substitute for DOM and substituted only partially for MDMA. SCH23390 fully and dose-dependently attenuated methamphetamine-appropriate responding produced by each test compound, but was least potent against pentylone. MDMA-appropriate responding was minimally affected by SCH23390. Each test compound was robustly self-administered with pentylone producing the greatest self-administration at the doses tested. Given the prevalence of synthetic cathinones in "Ecstasy" formulations, these data indicate that adulterated "Ecstasy" formulations may drive more compulsive drug use than those containing only MDMA.

MDMA-assisted therapy: A new treatment model for social anxiety in autistic adults

The first study of 3,4-methylenedioxymethamphetamine (MDMA)-assisted therapy for the treatment of social anxiety in autistic adults commenced in the spring of 2014. The search for psychotherapeutic options for autistic individuals is imperative considering the lack of effective conventional treatments for mental health diagnoses that are common in this population. Serious Adverse Events (SAEs) involving the administration of MDMA in clinical trials have been rare and non-life threatening. To date, MDMA has been administered to over 1133 individuals for research purposes without the occurrence of unexpected drug-related SAEs that require expedited reporting per FDA regulations. Now that safety parameters for limited use of MDMA in clinical settings have been established, a case can be made to further develop MDMA-assisted therapeutic interventions that could support autistic adults in increasing social adaptability among the typically developing population. As in the case with classic hallucinogens and other psychedelic drugs, MDMA catalyzes shifts toward openness and introspection that do not require ongoing administration to achieve lasting benefits. This infrequent dosing mitigates adverse event frequency and improves the risk/benefit ratio of MDMA, which may provide a significant advantage over medications that require daily dosing. Consequently, clinicians could employ new treatment models for social anxiety or similar types of distress administering MDMA on one to several occasions within the context of a supportive and integrative psychotherapy protocol.

MDMA ("ecstasy") abuse as an example of dopamine neuroplasticity

A number of reviews have focused on the short- and long-term effects of MDMA and, in particular, on the persistent deficits in serotonin neurotransmission that accompany some exposure regimens. The mechanisms underlying the serotonin deficits and their relevance to various behavioral and cognitive consequences of MDMA use are still being debated. It has become clear, however, that some individuals develop compulsive and uncontrolled drug-taking that is consistent with abuse. For other drugs of abuse, this transition has been attributed to neuroadaptations in central dopamine mechanisms that occur as a function of repeated drug exposure. A question remains as to whether similar neuroadaptations occur as a function of exposure to MDMA and the impact of serotonin neurotoxicity in the transition from use to abuse. This review focuses specifically on this issue by first providing an overview of human studies and then reviewing the animal literature with specific emphasis on paradigms that measure subjective effects of drugs and self-administration as indices of abuse liability. It is suggested that serotonin deficits resulting from repeated exposure to MDMA self-administration lead to a sensitized dopaminergic response to the drug and that this sensitized response renders MDMA comparable to other drugs of abuse.

Reinstatement of extinguished amphetamine self-administration by 3,4-methylenedioxymethamphetamine (MDMA) and its enantiomers in rhesus monkeys

RATIONALE

The effectiveness of MDMA and its enantiomers to reinstate responding previously maintained by drug self-administration has not been thoroughly investigated.

OBJECTIVES

The present study was designed to compare the reinstatement effects of amphetamine, the piperazine-analog BZP, SR(+/-)-MDMA, S(+)-MDMA, R(-)-MDMA, and fenfluramine on behavior maintained under a second-order schedule of intravenous amphetamine self-administration in rhesus monkeys (n=4).

METHODS

Following saline substitution and extinction, a range of doses of amphetamine, BZP, SR(+/-)-MDMA, S(+)-MDMA, R(-)-MDMA, and fenfluramine were administered i.v. as non-contingent priming injections in order to characterize their effectiveness to reinstate responding previously maintained by amphetamine self-administration.

RESULTS

Priming injections of amphetamine, BZP, SR(+/-)-MDMA, and S(+)-MDMA induced significant reinstatement effects. In contrast, neither R(-)-MDMA nor fenfluramine effectively reinstated behavior. Pretreatment with the selective serotonin transporter inhibitor, fluoxetine, attenuated the reinstatement effects of SR(+/-)-MDMA, S(+)-MDMA, and BZP but had no significant effect on amphetamine-primed reinstatement.

CONCLUSIONS

Given the profile of neurochemical effects published previously, these findings suggest that the reinstatement effects of MDMA are mediated primarily by dopamine release; however, the attenuation of MDMA-induced reinstatement by fluoxetine supports previous research demonstrating the complex behavioral pharmacology of MDMA-like drugs and that the reinstatement effects of MDMA are at least partially mediated by serotonergic mechanisms.

The effects of fluoxetine on the subjective and physiological effects of 3,4-methylenedioxymethamphetamine (MDMA) in humans

OBJECTIVE

The purpose of this study was to investigate the role of serotonin (5-HT) in the effects of oral 3,4-methylenedioxymethamphetamine (MDMA) in humans.

MATERIALS AND METHODS

The subjective and physiological effects of 1.5 mg/kg MDMA were evaluated after 20 mg fluoxetine in eight recreational MDMA users in a double-blind, placebo-controlled study. During phase 1, participants were maintained on placebo for at least 5 days and tested with MDMA and placebo on separate sessions. In phase 2, the procedure was the same except fluoxetine was administered daily for at least 5 days. During sessions, placebo or fluoxetine was given 1 h before the session drug and effects were measured over the next 7 h.

RESULTS

MDMA increased positive-like subjective effects on all the Addiction Research Center Inventory scales; Arousal, Elation, Positive Mood, and Vigor on the Profile of Mood States; Drug Liking, Friendly, Good Drug Effect, High, Stimulated, and Talkative on the Visual Analog Scale; and End-of-Session Liking and Crossover Point on the Multiple Choice Procedure. MDMA also increased measures of anxiety. On the Hallucinogenic Rating Scale, all scales except Volition were increased. MDMA also increased blood pressure and heart rate. Fluoxetine treatment attenuated most of the positive-like subjective effects including the Affect and Soma scales of the Hallucinogen Rating Scale. In addition, heart rate but not blood pressure increases were reduced.

CONCLUSIONS

These results suggest that blockade of 5-HT reuptake by fluoxetine can dampen the effects of MDMA and further supports the role of 5-HT in its behavioral effects in humans.

Discriminative stimulus effects of 3,4-methylenedioxymethamphetamine (MDMA) in humans trained to discriminate among d-amphetamine, meta-chlorophenylpiperazine and placebo

In animals, two-choice drug discrimination studies have demonstrated that the behavioral effects of 3,4-methylenedioxymethamphetamine (MDMA) are mediated by dopaminergic and serotonergic systems. In order to delineate the relative role of these systems, three-choice paradigms have been used in animals, with findings indicating a more prominent role for serotonin. Human studies assessing the subjective and physiological effects of MDMA have also indicated a mixed action. To parallel animal studies, the participants in the present study were trained to discriminate among a prototypic dopaminergic agonist, d-amphetamine, a prototypic serotonergic agonist, meta-chlorophenylpiperazine (mCPP) and placebo and then were tested with two doses of MDMA. In addition, subjective and physiological effects were measured. The results demonstrated that humans could be trained to discriminate among 20 mg d-amphetamine, 0.75 mg/kg mCPP and placebo. When tested with 1.0 and 1.5 mg/kg, half the participants reported MDMA to be like amphetamine and half like mCPP. There were no clear differences between these two groups in other dimensions, although there was an indication that the individuals who discriminated MDMA as d-amphetamine were more sensitive to the effects of all the drugs. The subjective effects of all three drugs overlapped, although the effects of MDMA appeared more amphetamine-like.

Preexposure to MDMA (“Ecstasy”) delays acquisition but facilitates MDMA-induced reinstatement of amphetamine self-administration behavior in rats

The current experiment investigated the effect of 3,4-methylenedioxymethamphetamine (MDMA; 'Ecstasy') preexposure on the acquisition of intravenous amphetamine self-administration and the reinstatement of amphetamine-seeking behavior by either MDMA or amphetamine. Rats were preexposed to a 5-HT depleting regime of MDMA (5 mg/kg every hour for 4 h on two consecutive days) or equivalent vehicle injections. Intravenous self-administration of low dose d-amphetamine (0.03 mg/kg/infusion) on a FR1 schedule was subsequently assessed. The rats were then given 2 weeks of extinction and tested for drug-seeking behavior with priming doses of amphetamine or MDMA. Brains were analysed for monoamine content using high-performance liquid chromatography (HPLC). MDMA-preexposed rats were initially slower to acquire amphetamine self-administration. However, by day 6 of acquisition, there was no difference from controls. Following extinction, amphetamine (1 mg/kg, i.p.) reinstated drug seeking and produced locomotor hyperactivity in both MDMA- and vehicle-pretreated animals. However, MDMA (5 mg/kg, i.p.) was only effective in producing amphetamine seeking and hyperactivity in MDMA-pretreated rats. MDMA pretreatment caused significant decreases in 5-hydroxy-indolacetic acid (5-HIAA) and 5-HT in several brain regions. These results suggest that 5-HT depletion induced by MDMA may initially slow the acquisition of amphetamine self-administration but that MDMA preexposure may also sensitize animals to the locomotor stimulating and priming effects of MDMA on drug-seeking behavior.

The pre-clinical behavioural pharmacology of 3,4-methylenedioxymethamphetamine (MDMA)

3,4-Methylenedioxymethamphetamine (MDMA) is a relatively novel drug of abuse and as such little is currently known of its behavioural pharmacology. This review aims to examine whether MDMA represents a novel class of abused drug. MDMA is known as a selective serotonergic neurotoxin in a variety of animal species but acutely it is a potent releaser and/or reuptake inhibitor of presynaptic serotonin, dopamine, noradrenaline, and acetylcholine. Interaction of these effects contributes to its behavioural pharmacology, in particular its effects on body temperature. Drug discrimination studies indicate that MDMA and related drugs produce unique interoceptive effects which have led to their classification as entactogens. This is supported by results from other behavioural paradigms although there is evidence for dose dependency of MDMA-specific effects. MDMA also produces conditioned place preference but is not a potent reinforcer in self-administration studies. These unique behavioural effects probably underlie its current popularity. MDMA is found in the street drug ecstasy but it may not be appropriate to equate the two as other drugs are routinely found in ecstasy tablets

Serotonergic-dopaminergic mediation of MDMA's discriminative stimulus effects in a three-choice discrimination

(+/-)3,4-Methylenedioxymethamphetamine (MDMA; "Ecstasy") is a common drug of abuse that is often described as both a psychostimulant and a hallucinogen. Two-choice drug discriminations (i.e. drug vs. nondrug) in nonhumans comparing the discriminative stimulus properties of MDMA to psychostimulants or hallucinogens have produced somewhat inconsistent findings. The relative contribution of serotonergic versus dopaminergic actions to MDMA's discriminative stimulus effects may depend on the training stimulus conditions employed. We have previously demonstrated that rats can learn to discriminate the effects of MDMA and D-amphetamine in a three-choice drug discrimination procedure, and that LSD produced nearly complete substitution for MDMA under these conditions, and fenfluramine fully substituted for MDMA. In the present study, 12 rats were trained to discriminate LSD (0.08 mg/kg) and MDMA (1.5 mg/kg) from saline in a three-choice drug discrimination procedure under a fixed-ratio (FR) 10 schedule of food reinforcement. D-Amphetamine produced only partial substitution for MDMA while fenfluramine produced complete stimulus generalization. Low doses of D-amphetamine and fenfluramine produced greater stimulus generalization when administered in combination than when given alone. The serontonin(2) antagonist MDL-100,907 only partially blocked the MDMA cue, but completely antagonized LSD discrimination. The dopamine antagonist haloperidol also failed to block MDMA discrimination. These results indicate that 5-HT release is a salient feature to MDMA's discriminative stimulus effects but that MDMA produces a compound discriminative stimulus.

Further characterization of the stimulus properties of 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline

This investigation is based on the premise that conformational restriction of abused phenylalkylamines in a tetrahydroisoquinoline conformation alters their pharmacology in such a manner that their original action is lost and that a new action emerges. TDIQ or 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline, is a conformationally constrained phenylalkylamine that serves as a discriminative stimulus in animals. Although TDIQ bears structural resemblance to phenylalkylamine stimulants (e.g., amphetamine), hallucinogens (e.g., 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane [DOM]), and designer drugs (e.g., N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane [MDMA], N-methyl-1-(4-methoxyphenyl)-2-aminopropane [PMMA]), the TDIQ stimulus failed to generalize to (+)amphetamine or MDMA. In the present investigation, further evaluations were made of the stimulus nature of TDIQ. Specifically, the stimulus similarities of TDIQ, PMMA, and DOM were examined. In no case was stimulus generalization (substitution) observed. The results confirm that TDIQ produces stimulus effects distinct from those of the abovementioned phenylalkylamines. We also examined the structure-activity relationships of a series of TDIQ analogs, including several that might be viewed as conformationally restricted (CR) analogs of phenylalkylamine hallucinogens, stimulants, and designer drugs. These agents were examined in rats trained to discriminate either DOM (1.0 mg/kg), (+)amphetamine (1.0 mg/kg), MDMA (1.5 mg/kg), or TDIQ (5.0 mg/kg) from saline vehicle. Whereas we have demonstrated that none of these agents retains their respective phenylalkylamine stimulus actions, several of these agents were found to substitute for TDIQ. N-Methylation abolished TDIQ-stimulus action. These results, coupled with previous findings, imply that TDIQ derivatives represent a novel class of phenylalkylamines analogs with unique stimulus properties. Preliminary radioligand binding studies suggest that an alpha2-adrenergic mechanism might underlie the stimulus effects produced by TDIQ.

Time course analysis of the discriminative stimulus effects of the optical isomers of 3,4-methylenedioxymethamphetamine (MDMA)

The present study examined the discriminative stimulus effects of the MDMA optical isomers administered at different presession injection intervals. In the first experiment, male Sprague-Dawley rats were trained in a two-lever, food-reinforced operant procedure to discriminate either (+)-MDMA (1.25 mg/kg) or (-)-MDMA (3.50 mg kg) at either 20 or 90 min following injection. Animals administered (+)-MDMA or saline 90 min before training sessions failed to attain the discrimination criteria after 73 training sessions, whereas (-)-MDMA successfully established discriminative stimulus control at both the 20 min and the 90 min postinjection intervals. (+)-Amphetamine did not substitute for either isomer, although a significant amount of drug-appropriate responding occurred in animals trained to discriminate (+)-MDMA at 20 min and (-)-MDMA at 90 min. Sch 39166 partially reduced the discrimination of (+)-MDMA at 20 min and (-)-MDMA at 90 min, although this effect was not dose dependent. Sch 39166 had no effect on animals trained to discriminate (-)-MDMA at 20 min. Haloperidol did not alter the discrimination of (+)-MDMA at 20 min but partially reduced the discriminative stimulus control of (-)-MDMA at 20 min and (-)-MDMA at 90 min. Fenfluramine substituted for both isomers of MDMA. Pirenpirone completely blocked the discriminative stimulus effects of (-)-MDMA at 20 min, although (+)-MDMA at 20 min and (-)-MDMA at 90 min were only partly blocked. WAY 100,135 had little effect on drug-appropriate responding; however, the discrimination of (+)-MDMA at 20 min was partly reduced by this 5-HT1A antagonist. In a second experiment, rats trained to discriminate (+)-MDMA (1.5 mg/kg) or (-)-MDMA (3.0 mg/kg) from saline were administered substitution tests with both isomers 20, 60, 90 and 120 min after injection. Results confirmed those of the first experiment that (+)-MDMA appears to have a shorter duration of action than (-)-MDMA. These results are discussed in light of the training doses employed.

Assessment of the MDA and MDMA optical isomers in a stimulant-hallucinogen discrimination

The phenylisopropylamine derivatives 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA) have been compared to both psychostimulants and hallucinogens in drug discrimination investigations. The stereoisomers of these compounds, in particular those of MDA, appear to produce differential effects. Previous studies have demonstrated that animals trained to discriminate amphetamine from vehicle generalize to the S(+)-isomers but not the R(-)-isomers of MDA and MDMA while animals trained to discriminate LSD from saline generalize to R(-)-MDA and neither isomer of MDMA. However, animals trained to discriminate mescaline from vehicle generalize to both stereoisomers of these phenylisopropylamine derivatives. The present study consisted of two experiments in which a three-choice drug discrimination procedure was employed to compare the stereoisomers of MDA and MDMA to both amphetamine and either mescaline (experiment one) or LSD (experiment two). Sixteen male Sprague-Dawley rats were trained to discriminate S(+)-amphetamine (1.0 mg/kg) and mescaline (12.5 mg/kg) and eight rats were trained to discriminate S(+)-amphetamine (1.0 mg/kg) and LSD (0.08 mg/kg) from saline in three-choice, food reinforced drug discrimination procedures. Substitution tests were administered with the isomers of MDA and MDMA. In the second experiment, substitution tests were also administered with lower doses of each training compound and with the stimulant cocaine and the hallucinogen 2,5-dimethoxy-4-methylphenylisopropylamine (DOM). In both experiments, all of the isomers produced very few responses on the S(+)-amphetamine lever. In the first experiment, R(-)-MDA and R(-)-MDMA produced nearly complete substitution for mescaline. The results of the second experiment revealed partial substitution for LSD with both isomers of MDMA and S(+)-MDA, and nearly complete substitution with R(-)MDA for LSD. The present findings do not support previous reports that S(+)-MDMA and S(+)-MDMA substitute for S(+)-amphetamine. The three-lever drug discrimination procedure may provide a more sensitive behavioral assay in which to examine the discriminative stimulus effects of drugs with compound stimulus properties.

MDMA and d-amphetamine produce comparable effects in pigeons performing under a multiple fixed-ratio interresponse-time-greater-than-t schedule of food delivery

The purpose of this study was to gain further information about the behavioral effects of (+/-) 3.4-methylenedioxymethamphetamine (MDMA) on schedule-controlled responding. MDMA (0.32, 0.56, 1.0, 3.2, 5.6, and 10 mg/kg) and d-amphetamine (0.32, 0.56, 1.0, 3.2, 5.6, and 10 mg/kg) were administered to pigeons performing under a multiple fixed-ratio 30 (FR 30) interresponse-time-greater-than-15-s (IRT > 15-s) schedule of food delivery. In general, both drugs had no significant effect on response rates under the IRT > 15-s component at doses that decreased rates under the FR component. Results of the present experiment indicate that under some conditions MDMA and d-amphetamine produce similar, and rate-dependent, effects.

Serotonergic modulation of 3,4-methylenedioxymethamphetamine (MDMA)-elicited reduction of response rate but not rewarding threshold in accumbal self-stimulation

In a fixed interval 5-s rate-frequency function paradigm with rats, 3,4-methylenedioxymethamphetamine (MDMA; 0.5, 2 and 4 mg/kg) dose-dependently decreased response rate for nucleus accumbens self-stimulation while both D-amphetamine (0.3 and 1 mg/kg) and cocaine (5 and 15 mg /kg) increased response rates. The highest doses of MDMA caused a cessation of responding in many of the rats tested, but in those rats that continued to respond a significant reduction in frequency threshold for self-stimulation was seen. Cocaine and amphetamine dose-dependently reduced frequency threshold in all rats tested. The non-specific serotonin antagonist, methysergide (5 mg/kg), reversed the inhibitory effects of MDMA on response rates and caused all rats to respond following MDMA (4 mg/kg). Methysergide did not affect MDMA's threshold-lowering properties and when administered alone methysergide had not effect on self-stimulation. These results suggest serotonergic involvement in the performance but not reinforcement-modulating effect of MDMA in the self-stimulation paradigm.

Effects of MDMA on complex brain function in laboratory animals

This review surveys experiments that have examined the effects of acute and chronic MDMA exposure on schedule-controlled operant behaviors thought to engender responses that reflect the expression of complex brain functions. Such functions include time estimation, short-term memory, learning, motivation, and color and position discrimination. Recent experiments conducted in the Behavioral Toxicology Laboratory at the National Center for Toxicological Research concerning MDMA's acute and long-term effects on rhesus monkey performance in an operant test battery are compared to previous studies involving the effects of MDMA on operant behaviors. Results of these experiments suggest that when given acutely, MDMA disrupts complex brain functions associated with learning and time estimation more than those associated with short-term memory and visual discrimination, and that behavioral tasks requiring relatively high rates of responding are particularly sensitive to the disruptive effects of MDMA. Repeated exposure to doses of MDMA sufficient to produce long-lasting changes in brain neurotransmitter systems results in residual effects (e.g. tolerance, sensitivity) on behavioral task performance when subjects are subsequently challenged with acute MDMA, whereas baseline (non-challenged) performance of these tasks after such exposure generally remains unchanged. Although the experiments described herein were conducted on a relatively small number of non-human subjects, they raise the possibility that long-term effects on cognitive processes may also occur in humans exposed to repeated or acute high doses of MDMA.

Dexfenfluramine lacks amphetamine-like abuse potential

1. The amphetamine-like abuse potential of dexfenfluramine (dFEN) was evaluated using drug discrimination and self-administration procedures. 2. Male Fischer rats were trained to discriminate either dFEN (1.0 mg/kg) or d-amphetamine (dAMP; 1.0 mg/kg) from saline in a two-choice discrete-trial avoidance paradigm. 3. In dAMP-trained rats, dFEN (0.5-4.0 mg/kg) engendered almost exclusively saline-appropriate responding. In dFEN-trained rats, dAMP (1.0-4.0 mg/kg) engendered entirely saline-appropriate responding in 3 of 6 rats and intermediate levels of dFEN-appropriate responding in the remaining animals. 4. Potential reinforcing effects of dFEN were also evaluated in 3 male rhesus monkeys trained to self-administer cocaine (i.v.) during daily 60 min sessions under a fixed-ratio (FR)-10 schedule. 5. Various doses of dFEN (30-1000 micrograms/kg/infusion) and dAMP (10 micrograms/kg/infusion) were substituted for cocaine in 4 consecutive daily sessions. In all subjects, dFEN maintained rates of self-administration within the range of rates maintained by saline and considerably below those maintained by cocaine and dAMP. Furthermore, the within-session distribution of responding with dFEN resembled that produced by saline. 6. Taken together, these results strongly suggest that dFEN will not have amphetamine-like abuse potential in humans.

Effects of (+)-fenfluramine on 3,4-methylenedioxymethamphetamine (MDMA) discrimination in rats

This study examined the effects of a presumed neurotoxic dose regimen of (+)-fenfluramine on the discrimination of MDMA and (+)-amphetamine in male Sprague-Dawley rats trained to discriminate 1.5 mg/kg MDMA from saline in a two-choice operant task. Substitution tests were conducted with saline, several doses of MDMA (0.19-1.5 mg/kg), and (+)-amphetamine (0.125-1.0 mg/kg) prior to and again following the administration of (+)-fenfluramine (4.0 mg/kg twice a day for 4 days; n = 11) or a similar pattern of saline injections (n = 10). During pretreatment substitution tests, lower doses of MDMA elicited drug-appropriate responding in a dose-dependent manner, although none of these doses substituted for the training dose. Likewise, no dose of (+)-amphetamine substituted for the training drug during pretreatment substitution tests. The discrimination of MDMA was disrupted in some animals following (+)-fenfluramine treatment, but with subsequent training, discrimination criteria were met. In posttreatment substitution tests, the lowest dose of MDMA produced significantly higher drug-appropriate responding in (+)-fenfluramine treated animals but not in saline-treated animals. The amount of drug-appropriate responding during posttreatment substitution tests with (+)-amphetamine varied little from pretreatment substitution tests in saline-treated animals, but was greater at all doses in (+)-fenfluramine-treated animals; the highest dose of (+)-amphetamine substituted for MDMA subsequent to (+)-fenfluramine treatment. These results support previous findings that the long-lasting serotonergic effects of fenfluramine may have functional consequences that can be detected using a drug discrimination procedure. Specifically, serotonin depletion may unmask or strengthen the stimulant-like effects of MDMA.

Behavioral and neurochemical effects of chronic methylenedioxymethamphetamine (MDMA) treatment in rhesus monkeys

Effects of chronic treatment with the putative serotonergic neurotoxicant MDMA were assessed in rhesus macaques using behavior in an operant test battery (OTB) designed to model aspects of time estimation, short-term memory, motivation, learning, and color and position discrimination. After an initial acute dose-response assessment, escalating doses of MDMA (0.10-20.0 mg/kg, im, twice daily, for 14 consecutive days at each dose) were administered, followed by three additional acute dose-response assessments. In general, tolerance to MDMA's acute effects was evident in all OTB tasks by the second week of repeated exposure to each individual MDMA dose and as doses escalated. Baseline OTB performance after chronic treatment was not significantly altered. Residual behavioral tolerance to MDMA's acute effects, however, was evident in all OTB tasks but was least pronounced in the motivation task. Monkeys were sacrificed (21 months after chronic treatment) and brains were dissected into several regions for neurochemical analyses. Serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were analyzed via HPLC. Although MDMA-treated monkeys tended to have lower 5-HT concentrations in the frontal cortex, chronic MDMA treatment had no significant effects on 5-HT concentrations in any brain area sampled. Hippocampal 5-HIAA concentration, 5-HT uptake sites, and turnover of 5-HT of MDMA-treated monkeys were significantly lower than control values. DA concentrations in the CN of MDMA-treated monkeys were significantly greater than control values. No significant effects on DA concentrations were noted in any other brain area sampled. The absence of significant decreases in 5-HT and the general increase in DA concentrations are dissimilar to neurochemical effects reported after a short course of MDMA treatment at relatively high doses. These data suggest that chronic administration of gradually increasing doses of MDMA results in long-lasting tolerance to the drugs acute effects on the complex brain functions modeled in the OTB. It is uncertain, however, if such tolerance is related to the observed decreases in uptake sites and turnover of 5-HT in the hippocampus of these monkeys.

Behavioral effects of the highly selective serotonin releasing agent 5-methoxy-6-methyl-2-aminoindan

The behavioral effects of 5-methoxy-6-methyl-2-aminoindan (MMAI) were examined using the drug discrimination procedure and direct observation for classification of the characteristic syndrome induced by MMAI. The stimulus effects of MMAI were studied in 5 different groups of rats trained to discriminate MMAI (1.71 mg/kg; 8 microM/kg), MDMA (3,4-methylenedioxymethamphetamine; 1.75 mg/kg; 7.6 microM/kg), (+)-MBDB ((+)-N-methylamino-(1,3-benzodioxo-5-yl)-2-butanamine; 1.75 mg/kg; 7.18 microM/kg), (+)-amphetamine (1 mg/kg; 5.4 microM/kg), or LSD ((+)-lysergic acid diethylamide tartrate; 0.08 mg/kg; 186 nM/kg) from saline. In substitution tests in rats trained to discriminate MMAI from saline, all the compounds which fully mimicked MMAI were serotonin (5-hydroxytryptamine, 5-HT) releasing agents. This substitution is symmetrical for MDMA and (+)-MBDB. Nevertheless, the dose-response curve of MMAI is parallel to those of (+)-fenfluramine (m-trifluoromethyl-N-ethylamphetamine) and p-chloroamphetamine. The results also show that MMAI lacks amphetamine-like and LSD-like discriminative stimulus effects, suggesting that MMAI is neither a psychostimulant nor a hallucinogen. Tests of the discriminability of MMAI after 5-HT depletion with the selective serotonin synthesis inhibitor, p-chlorophenylalanine (2 x 200 mg/kg i.p., pretreatment 72 h before test), showed only saline appropriate responding. Prolonged block (ca. 1 week) of the MMAI cue by p-chlorophenylalanine further supports the conclusion that endogenous 5-HT is essential for MMAI discrimination. Fluoxetine (10 mg/kg) or paroxetine (2.5 mg/kg), both selective 5-HT uptake inhibitors, reduced the discriminability of MMAI to 40% and 50%, respectively. None of the antagonists (ketanserin, methiothepin, pindolol, yohimbine, haloperidol) used in antagonism tests inhibited the stimulus properties of MMAI. These results and data from radioligand binding studies support the conclusion that direct activation or inhibition of known neurotransmitter receptors did not play a significant role in the discriminative cue of MMAI. The administration of 5, 10, or 20 mg/kg of MMAI to rats induced a behavioral syndrome consisting of hypolocomotion with accompanying catalepsy-like posture, turning, Straub tail, flat body posture, and suppressed sleeping time. In general, this is qualitatively similar to what is seen after administration of 5-HT precursors or 5-HT receptor agonists. In conclusion, the data from the drug discrimination study and the behavioral syndrome induced by MMAI suggest that MMAI is a potential selective releaser of serotonin.

3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy"): pharmacology and toxicology in animals and humans

(+/-)3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy"), a ring-substituted amphetamine derivative first synthesized in 1914, has emerged as a popular recreational drug of abuse over the last decade. Pharmacological studies indicate that MDMA produces a mixture of central stimulant and psychedelic effects, many of which appear to be mediated by brain monoamines, particularly serotonin and dopamine. In addition to its pharmacologic actions, MDMA has been found to possess toxic activity toward brain serotonin neurones. Serotonergic neurotoxicity after MDMA has been demonstrated in a variety of experimental animals (including non-human primates). In monkeys, the neurotoxic dose of MDMA closely approaches that used by humans. While the possibility that MDMA is also neurotoxic in humans is under investigation, other adverse effects of MDMA in humans have been documented, including various systemic complications and a number of untoward neuropsychiatric sequelae. Notably, many of the adverse neuropsychiatric consequences noted after MDMA involve behavioral domains putatively influenced by brain serotonin (e.g., mood, cognition and anxiety). Given the restricted status of MDMA use, retrospective clinical observations from suspecting clinicians will probably continue to be a primary source of information regarding MDMA's effects in humans. As such, this article is intended to familiarize the reader with the behavioral pharmacology and toxicology of MDMA, with the hope that improved recognition of MDMA-related syndromes will provide insight into the function of serotonin in the human brain, in health as well as disease.

Comparison of the behavioral effects of ibogaine from three sources: mediation of discriminative activity

Ibogaine is an alkaloid employed for its hallucinatory properties in West Central Africa which has been the subject of alleged efficacy as an aid in the interruption and treatment of chemical dependency. The major sources of the Schedule I agent are: Sigma Chemical Co., the National Institute on Drug Abuse and as NDA International Inc.'s Endabuse. The intent of the present study was to, for the first time, train rats to discriminate the interoceptive stimuli produced by (10 mg/kg, intraperitoneally administered) ibogaine. Once trained, these rats were used to investigate the dose-response effects to ibogaine from each of the three suppliers. In addition, stimulus generalization to the dopamine antagonist CGS 10476B, as well as to the serotonergically active compounds fenfluramine, TFMPP (1-(m-trifluoromethylphenyl)piperazine, DOI (1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane), MDMA (3,4-methylenedioxymethamphetamine), quipazine and LSD, was tested. The results indicate that ibogaine is readily discriminable from its vehicle and that ibogaine from each of the three supplies produced statistically similar discrimination with ED50 values ranging from 2.5 to 3.4 mg/kg. In addition, various doses of the novel drugs tested produced, at best, intermediate ibogaine-appropriate responding and, thus, no drug tested can be considered to generalize to ibogaine-like stimuli. Discussion concerns the multiple actions of ibogaine that have been cited in the scientific literature. The similarity in potency of ibogaine from three potential suppliers should allow for pre-clinical work using any of these research samples to be comparable.

Comparison of conditioned taste aversions produced by MDMA and d-amphetamine

Many drugs of abuse such as d-amphetamine support the development of taste aversion in a conditioned taste aversion paradigm. However, it has yet to be established whether methylenedioxymethamphetamine (MDMA), an amphetamine-like stimulant, has this property. A direct comparison was made between MDMA and d-amphetamine over a dose range of 0.125-2.0 mg/kg (SC). Two pairings of either drug with saccharin produced dose-related taste aversions to saccharin that were retained for at least three successive testing trials. The minimally effective dose was 1 mg/kg for MDMA and 0.5 mg/kg for d-amphetamine. The relative potency of MDMA to amphetamine was 4.5, similar to that previously reported for drug discrimination and self-stimulation.

MDMA and memory: the acute and chronic effects of MDMA in pigeons performing under a delayed-matching-to-sample procedure

The purpose of the present study was to examine the acute and chronic effects of (+/-)3,4-methylenedioxy-methamphetamine (MDMA) in pigeons responding under a delayed-matching-to-sample procedure with 0-, 3-, and 6-s delays. In the absence of drug, accuracy (percent correct responses) was inversely related to delay length. When administered pre-chronically, MDMA (0.32-5.6 mg/kg) generally decreased accuracy and response rates at doses of 3.2 mg/kg and above. Although humans report a distinct "hangover" when exposure to MDMA ends, performance of pigeons in the present study did not deteriorate when the chronic regimen ended, indicating an absence of behavioral dependence on the drug. Tolerance developed following chronic exposure to 3.2 mg/kg. In general, greater tolerance occurred at the 0-s delay than at longer delays. Although MDMA is reported to have neurotoxic effects, it does not inevitably produce long-lasting or cumulative behavioral impairment.

MDMA (Ecstasy) precipitation of panic disorder

The authors describe three patients whose panic disorder began during recreational use of MDMA (Ecstasy) and was subsequently complicated by agoraphobic avoidance that continued autonomously after cessation of the drug. Their panic disorder responded well to serotoninergic antidepressant drugs. Theoretical and practical implications are discussed.

Possible serotonergic and dopaminergic mediation of the N-ethyl-3,4-methylenedioxyamphetamine discriminative stimulus

Eight male rats previously trained to discriminate 2.0 mg/kg N-ethyl-3,4-methylenedioxyamphetamine (MDE) from its vehicle in a two-lever, food motivated task were utilized to characterize the stimulus properties of MDE. The 5-HT receptor agonists 1-(m-trifluoromethylphenyl)piperazine (TFMPP), quipazine and 6-methoxy-1,2,3,4 tetrahydro-beta-carboline were able to generalize to the stimulus produced by MDE. However, the 5-HT receptor agonists m-chlorophenylpiperazine (mCPP), buspirone and norfenfluramine, the dopamine receptor agonist amphetamine, as well as the acetylcholine receptor agonist arecoline did not completely generalize. In addition, the simultaneous administration of norfenfluramine and amphetamine generalized to MDE. Pretreatment with the serotonin receptor antagonists cinanserin and metergoline or the dopamine receptor antagonist haloperidol failed to completely inhibit the discriminative stimulus produced by MDE. Multiple p-chlorophenylalanine (PCPA) pretreatments significantly reduced MDE discrimination, whereas vehicle discrimination was unaffected. Five days following cessation of PCPA pretreatment, MDE discrimination returned to criterion levels and remained at that level. These results suggest that the stimulus produced by MDE involve a complex interaction of various neurotransmitters, with both serotonergic and dopaminergic components.

Behavioral and neurochemical effects of prenatal methylenedioxymethamphetamine (MDMA) exposure in rats

MDMA is a hallucinogenic drug that is used by the general public as a recreational drug of abuse. The neurobehavioral consequences of prenatal MDMA exposure are unknown. Groups of pregnant rats were gavaged with 0, 2.5, or 10 mg/kg MDMA during gestation on alternate gestational days 6-18. Gestational duration, litter size, neonatal birth weights and physical appearance at birth were unaffected by MDMA treatments. Pregnancy weight gain was significantly reduced by MDMA treatment. Progeny growth, maturational parameters (eye opening and incisor eruption times), surface righting reflex, swimming performance, forelimb grip strength, milk-induced behaviors, passive avoidance behavior, figure-8 maze activity over 48 hours, the density of brain serotonin (5-HT) uptake sites, and brain 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels were unaffected by MDMA treatments. Olfactory discrimination on postnatal days (PND) 9-11 was enhanced in both male and female MDMA-treated progeny, while negative geotaxis (PND 7-10) was delayed in female pups. In contrast to progeny, MDMA caused dose-dependent decreases in 5-HT and 5-HIAA levels in discrete brain areas of the dam. It is concluded that prenatal exposure to MDMA at the levels used here produces only subtle behavioral alterations in developing rats. The dam is more at risk for MDMA-induced 5-HT depletion than is the conceptus.

Antagonism of the neurotoxicity due to a single administration of methylenedioxymethamphetamine

The role of transmitter release in the serotonergic neurotoxicity of methylenedioxymethamphetamine (MDMA) was examined using treatments altering MDMA-induced release or its consequences. The long-term decrease in 5-HT concentrations and tryptophan hydroxylase activity produced by MDMA was antagonized by depletion of vesicular monoamines with reserpine or interruption of monoamine synthesis with the decarboxylase inhibitor, monofluoromethyl DOPA (dihydroxyphenylalanine). Similar results were achieved by selectively inhibiting dopamine synthesis with alpha-methyl-p-tyrosine or through bilateral lesions of the substantia nigra with 6-hydroxydopamine. The dopamine receptor antagonist haloperidol was also effective in this regard. Although these results strongly implicate dopamine release in the long-term neurochemical effects of MDMA, protection was also provided by selective 5-HT2 antagonists indicating that the neurotoxicity is dependent upon the release of both dopamine and 5-HT.

Three-choice discrimination among (+)-amphetamine, fenfluramine and saline in pigeons

Five pigeons were trained to discriminate among (+)-amphetamine (AMPH; 1.7 or 3.0 mg/kg), fenfluramine (FEN; 5.6 or 10 mg/kg), and saline using a three-choice drug discrimination procedure. The results of the study demonstrated that a reliable discrimination between AMPH and FEN could be obtained and the discriminative stimulus (DS) effects of these two drugs did not overlap, i.e., were mutually exclusive. Phenmetrazine produced a dose-related increase in AMPH-appropriate responding with no responding occurring on the FEN-appropriate key. Two serotonin agonists, quipazine (5-HT2) and MK 212 (5-HT1), produced FEN-appropriate responding in two of three pigeons, while a third pigeon responded predominantly on the AMPH-appropriate key following their administration. In contrast, phencyclidine produced predominantly (greater than 50%) saline-appropriate responding, indicating that the DS effect of phencyclidine was unlike either AMPH or FEN. Finally, compounds known to have multiple DS properties such as MDA and MDMA were tested. The results with these compounds confirmed that these drugs have complex DS effects both within and across individual pigeons.

Tolerance and cross-tolerance to 3,4-methylenedioxymethamphetamine (MDMA), methamphetamine and methylenedioxyamphetamine

The effects of (+-)-3,4-methylenedioxymethamphetamine (MDMA) (0.62-20.0 mg/kg), (+)-methamphetamine (MA) (0.62-5.0 mg/kg) and (+/-)-3,4-methylenedioxyamphetamine (MDA) (0.62-5.0 mg/kg) on milk intake in rats were determined before and during a period of repeated daily administration of MDMA. Experimental sessions consisted of 15-min access to a sweetened milk solution each day, 5 days a week. After initial determination of the effects of MDMA, MA and MDA on milk intake, rats were injected daily with either MDMA (2.5-5.0 mg/kg) or saline. Two groups of rats were injected with MDMA, one group 15 min before, and the other group 15 min after the milk-drinking sessions. Two more groups of rats were injected with saline, one group 15 min before, and the other group 15 min after the sessions. During this repeated administration period the effects of MDMA, MA and MDA (injected 15 min prior to the session) were redetermined. In rats that had been injected with MDMA on a daily basis either before or after the milk-drinking sessions, the dose-response function of MDMA was shifted to the right, indicating that tolerance had developed. Cross-tolerance to MA appeared to develop only in the group of rats that had been injected with MDMA on a daily basis before the milk-drinking sessions. Cross-tolerance to MDA did not develop in any of the 4 groups of rats.

Enantiomeric differences in the effects of 3,4-methylenedioxymethamphetamine on extracellular monoamines and metabolites in the striatum of freely-moving rats: an in vivo microdialysis study

The effects of (+) and (-) 3,4-methylenedioxymethamphetamine (MDMA) and racemic p-chloroamphetamine (PCA) on extracellular dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), as well as the metabolite of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), were determined in dialysates of the striatum conscious rats by using intracerebral dialysis and high performance liquid chromatography with electrochemical detection (HPLC-EC). The (+) and (-)MDMA isomers (5, 10 mg/kg, s.c.) and PCA (2.5, 5 mg/kg, s.c.) caused a rapid increase of extracellular levels of dopamine and decreased extracellular levels of DOPAC and HVA immediately after administration in dialysates of striatum. The order of potency for this effect was PCA greater than (+)MDMA greater than (-)MDMA. The levels of 5-HIAA also decreased after the administration of drugs, but the effect had a slower time course than DOPAC and HVA and did not exhibit an enantiomeric difference. The data indicate that, although these drugs are thought to affect the 5-HT neuronal system preferentially, they also affect dopamine systems and by a mechanism in which the (+) isomer was more potent than the (-).

Effects of methylenedioxymethamphetamine on local cerebral glucose utilization in the rat

The effects of (+-)3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") (5, 10, 15 or 30 mg/kg, i.p.) on local cerebral utilization of glucose were studied by the quantitative autoradiographic 2-deoxy-D-[1-14C]glucose method in awake adult male Fischer-344 rats. Statistically significant effects on local utilization of glucose, 5 min after the administration of MDMA were observed in 20 of 60 areas of brain sampled. Marked stimulation was seen in components of the extrapyramidal motor system (substantia nigra, globus pallidus, entopenduncular nucleus, subthalamic nucleus, cerebellar vermis). The limbic system showed decrements in the medial cortex and hippocampal dentate gyrus (outer blade) and the lateral habenula, while there was stimulation in the mammillary body and the basolateral amygdaloid nucleus. Glucose utilization in MDMA-treated rats was reduced in the superior colliculus and medial terminal nucleus of the accessory optic system, but was unchanged in the visual cortex and components of the auditory system. Some of the effects of MDMA on cerebral utilization of glucose resembled those previously reported with l-cocaine, d-amphetamine, and phencyclidine, implicating some common mechanisms in the actions of these drugs.

Stimulus effects of N-monoethyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDE) and N-hydroxy-1-(3,4-methylenedioxyphenyl)-2-aminopropane (N-OH MDA) in rats trained to discriminate MDMA from saline

Tests of stimulus generalization were conducted using rats trained to discriminate 1.5 mg/kg of N-monomethyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane HCl (MDMA) from saline in order to determine if two structurally related analogs (MDE and N-OH MDA) would produce similar stimulus effects. The MDMA-stimulus (MDMA, ED50 value = 0.76 mg/kg) generalized both to MDE (ED50 value = 0.73 mg/kg) and N-OH MDA (ED50 value = 0.47 mg/kg). Administration of (+)amphetamine resulted in partial generalization (maximum of 49% MDMA-appropriate responding) in the MDMA-trained animals. Taken together with our previous studies showing that MDMA substitutes for the phenylisopropylamine stimulant (+)amphetamine, but that neither MDE nor N-OH MDA substitute for (+)amphetamine or for the phenylisopropylamine hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), the present results [i.e., MDMA-stimulus generalization to MDE, N-OH MDA, but not to (+)amphetamine] suggest that 1) MDMA produces effects other than those that may be considered amphetamine-like, and 2) MDE and N-OH MDA are MDMA-like agents with even less of an amphetamine-like component of action than MDMA itself.

MDMA produces stimulant-like conditioned locomotor activity

Daily administration of a drug in a distinctive environment establishes contingencies that support Pavlovian conditioning. Environmental cues that are paired with the drug injection and that predict the onset of drug action can become conditioned stimuli. Ultimately, the conditioned stimuli come to predict the availability of drug and develop the potential to engender conditioned drug responses. Various psychostimulant drugs can produce conditioned locomotion when tested in the presence of environmental cues that were repeatedly associated with the drug experience. The ability of amphetamine and cocaine to produce conditioned locomotion was demonstrated in the present study. Stimulant-like properties of methylenedioxy-methamphetamine (MDMA) have been reported in locomotor paradigms, drug discrimination procedures, and human subjective questionnaires. MDMA (5 mg/kg), paired for 5 days to a distinct environment signalled by the presence of a distinct odor, produced enhanced locomotion during a test probe with the odor alone indicating that MDMA can also produce conditioned locomotion. The observation that the stimulus properties of MDMA can also become associated with environmental cues supports the hypothesis that some of the behavioral effects of MDMA resemble those of other classical psychostimulants such as amphetamine and cocaine.

A role for the mesolimbic dopamine system in the psychostimulant actions of MDMA

Methylenedioxymethamphetamine (MDMA) is a phenylethylamine with a chemical structure that resembles both the amphetamines and mescaline and has both stimulant and perception altering properties. The stimulant properties of MDMA were assessed in photocell cages designed to measure locomotor activity in rats. MDMA, over a range of doses (2.5-10.0 mg/kg, SC) produced locomotor hyperactivity which lasted up to 4 h. Further studies examined the role of the mesolimbic dopamine system in the hyperactivity induced by MDMA. 6-Hydroxydopamine lesions of the Nucleus accumbens attenuated the locomotor response produced by MDMA. The well characterized attenuation of the locomotor response produced by amphetamine was also demonstrated in the same rats. The present study demonstrates similarities in the stimulant properties of MDMA and amphetamine, and also suggests that as with amphetamine, the locomotor activation associated with MDMA may involve the presynaptic release of dopamine in the region of the Nucleus accumbens. However, MDMA may have a more unusual pharmacological profile because of its longer duration of action, neurotoxic potential, and differences in the qualitative aspects of its psychoactive effects.

Serotonergic-dopaminergic mediation of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy")

A series of three experiments were conducted to investigate the possible serotonergic and dopaminergic mediation of the discriminative stimulus properties of the "designer" drug MDMA. In Experiment 1, rats trained to discriminate 1.5 mg/kg (+/-)-MDMA from its vehicle at 20 min postadministration were shown to generalize to another drug of abuse, N-ethyl-3,4-methylenedioxyamphetamine (MDE) and to the serotonergically-active agents norfenfluramine and TFMPP. In contrast, testing of various dopaminergically-active agonists did not result in MDMA-like responding. In Experiment 2, dopaminergic and serotonergic antagonist were employed to observe their effect upon MDMA discrimination at 20 min postinjection. The serotonin antagonist pirenperone significantly decreased MDMA discrimination, whereas the dopamine decreasing drugs CGS 10746B and haloperidol had no effect. In Experiment 3, another group of rats were trained to discriminate MDMA at 105 min postadministration to investigate if, at this (later) time, the dopaminergic properties of MDMA may be more salient. Indeed, the dopaminergically-active drugs had a heightened effect upon MDMA at this later time, although the serotonergic component of the MDMA discriminative stimulus was predominant. The results suggest that the effects of MDMA at 20 min postadministration are solely serotonergic in nature. At 105 min postinjection there appears to be the presence of a weak dopaminergic component. This biphasic serotonergic-then-dopaminergic action of MDMA may explain the reported human experience with the drug, as well as the often controversial results in the literature.

Direct central effects of acute methylenedioxymethamphetamine on serotonergic neurons

Acute peripheral administration of either the (+) or (-) stereoisomer of methylenedioxymethamphetamine (MDMA) to rats results in a rapid loss of tryptophan hydroxylase (TPH) activity in several brain regions. This decline in enzyme activity precedes a decrease in serotonin (5-HT) concentrations in the same areas. An initial rise in the concentration of 5-hydroxyindole acetic acid after drug administration suggests that an increase in the turnover of 5-HT is an early event in the development of these changes. Unsuccessful attempts to reproduce the in vivo effects of MDMA on TPH activity using in vitro preparations such as cortical slices or the mouse mastocytoma cell line, P-815, suggested a requirement for an intact neuronal system or metabolism of the drug. Injection of MDMA directly into several brain regions also had no effect on TPH activity or 5-HT concentrations. However, when brain concentrations of MDMA were maintained using a constant i.c.v. infusion, TPH activity declined as observed following peripheral administration. The results, therefore, indicate that the acute effect of MDMA on 5-HT synthesis is a direct central effect of the drug which may be triggered by a sustained increase in transmitter turnover.

Pharmacologic profile of MDMA (3,4-methylenedioxymethamphetamine) at various brain recognition sites

We report here an in vitro pharmacologic profile for MDMA (3,4-methylenedioxymethamphetamine) at various brain recognition sites. The rank order of affinities of MDMA at various brain receptors and uptake sites are as follows: 5-HT uptake greater than alpha 2-adrenoceptors = 5-HT2 serotonin = M-1 muscarinic = H-1 histamine greater than norepinephrine uptake = M-2 muscarinic = alpha 1-adrenoceptors = beta-adrenoceptors greater than or equal to dopamine uptake = 5-HT1 serotonin much greater than D-2 dopamine greater than D-1 dopamine. MDMA exhibited negligible affinities (greater than 500 microM) at opioid (mu, delta and kappa), central-type benzodiazepine, and corticotropin-releasing factor receptors, and at choline uptake sites and calcium channels.

Methysergide potentiates the hyperactivity produced by MDMA in rats

Although some substituted amphetamines, like MDA, produce a combination of sympathomimetic stimulation and perceptual alterations, the psychoactive qualities of MDMA are less distinctive. MDMA binds to serotonergic receptors and has been shown to potently deplete brain serotonin concentrations. Biochemical and behavioral evidence suggests that MDMA may also act on the dopamine system. The present study explored the effects of blocking serotonin receptors on MDMA and amphetamine induced locomotor hyperactivity in rats. Locomotor activity was measured in photocell cages for 120 minutes following injection of methysergide (0, 2.5, 5, 10 mg/kg) or methysergide in combination with amphetamine (0.5 mg/kg) or MDMA (10 mg/kg). Methysergide, which had no effect on its own, significantly potentiated the locomotor hyperactivity produced by MDMA but not amphetamine. Thus, the intrinsic serotonergic agonist properties of MDMA may actually counteract the indirect sympathomimetic effects thought to be responsible for the locomotor hyperactivity MDMA produces.

The threshold lowering effects of MDMA (ecstasy) on brain-stimulation reward

3,4-Methylenedioxymethamphetamine (MDMA) is a psychoactive phenylisopropylamine which is structurally similar to both amphetamine-related sympathomimetics and the hallucinogen, mescaline. MDMA produces pleasurable effects which include euphoria, and recent reports continue to demonstrate its widespread recreational use. The aim of the present study was to assess the effects of racemic MDMA on the threshold for rewarding intracranial self-stimulation, an animal model used to assess a drug's abuse liability in man. Rewarding electrical stimulation was delivered via electrodes stereotaxically implanted in the medial forebrain bundle-lateral hypothalamic area of the rat brain. Thresholds were determined by means of a rate-independent psychophysical method. MDMA produced a dose-related lowering of the reward threshold in all four animals tested. Given that increased sensitivity for rewarding brain stimulation, measured as a lowering of the reward threshold, is an animal model of drug-induced euphoria these results suggest a similar mode of action for its reinforcing effects as other abused substances.

Behavioral effects of N-ethyl-3,4-methylenedioxyamphetamine (MDE; "EVE")

Eight male rats were trained to discriminate 2.0 mg/kg N-ethyl-3,4-methylenedioxyamphetamine (MDE) from its vehicle using a two-lever, food-motivated operant discrimination task. Once trained, the rats showed a dose-dependent decrease in discriminative accuracy following administration of decreased doses of MDE (ED50 = 0.75 mg/kg). Administration of 1.5 mg/kg 3,4-methylenedioxymethamphetamine (MDMA), a recently restricted Schedule I drug, produced 100% MDE-appropriate responding in the MDE-trained rats and decreased discriminative performance was similarly observed following lower doses of MDMA (ED50 = 0.62 mg/kg). The difference in relative potencies of MDE and MDMA in rats is reminiscent of those seen in human abusers who report effective oral psychotomimetic doses. Time-course data indicated that MDE has a fast onset, 100% drug-correct responding 10 min post-injection, and a peak effect between 10-20 min with declining effect at 60-120 min post-administration. These findings along with those of others show a pharmacological similarity between MDE and MDMA. Implications as to the future scheduling of MDE are discussed.