Tolerance to 3,4-methylenedioxymethamphetamine in rats exposed to single high-dose binges

Behavioral metabolomics: how behavioral data can guide metabolomics research on neuropsychiatric disorders

INTRODUCTION

Metabolomics produces vast quantities of data but determining which metabolites are the most relevant to the disease or disorder of interest can be challenging.

OBJECTIVES

This study sought to demonstrate how behavioral models of psychiatric disorders can be combined with metabolomics research to overcome this limitation.

METHODS

We designed a preclinical, untargeted metabolomics procedure, that focuses on the determination of central metabolites relevant to substance use disorders that are (a) associated with changes in behavior produced by acute drug exposure and (b) impacted by repeated drug exposure. Untargeted metabolomics analysis was carried out on liquid chromatography-mass spectrometry data obtained from 336 microdialysis samples. Samples were collected from the medial striatum of male Sprague-Dawley (N = 21) rats whilst behavioral data were simultaneously collected as part of a (±)-3,4-methylenedioxymethamphetamine (MDMA)-induced behavioral sensitization experiment. Analysis was conducted by orthogonal partial least squares, where the Y variable was the behavioral data, and the X variables were the relative concentrations of the 737 detected features.

RESULTS

MDMA and its derivatives, serotonin, and several dopamine/norepinephrine metabolites were the greatest predictors of acute MDMA-produced behavior. Subsequent univariate analyses showed that repeated MDMA exposure produced significant changes in MDMA metabolism, which may contribute to the increased abuse liability of the drug as a function of repeated exposure.

CONCLUSION

These findings highlight how the inclusion of behavioral data can guide metabolomics data analysis and increase the relevance of the results to the phenotype of interest.

Sensitization to the prosocial effects of 3,4-methylenedioxymethamphetamine (MDMA)

The recreational drug 3,4-methylenedioxymethamphetamine (MDMA) has well documented prosocial effects and is currently under clinical investigation as a treatment for patients with PTSD, autism, and other conditions. Early clinical trials have found that MDMA-assisted therapy may have robust long-lasting therapeutic effects, yet the mechanism by which acute treatments produce these long-term effects is unclear. Sensitization to certain behavioral drug effects is a common rodent model used to assess long-lasting neurobiological adaptations induced by acute drug treatments. Nine independent experiments were undertaken to investigate if and how mice sensitize to the prosocial effects of MDMA. When treated with 7.8 mg/kg MDMA and paired every other day for a week, MDMA-induced social interaction increased precipitously across treatment sessions. This previously unreported phenomenon was investigated and found to be heavily influenced by a social context and 5-HT_2AR activation. Social sensitization did not appear to develop if mice were administered MDMA in isolation, and pretreatment with MDL100907, a selective 5-HT_2AR antagonist, inhibited the development of social sensitization. However, when MDL100907 was administered to mice that had already been sensitized, it did not attenuate social interaction, suggesting that 5-HT_2AR activity may be necessary for the development of social sensitization but not the expression of MDMA-induced social behavior. Additional investigation is warranted to further explore the phenomenon of social sensitization and to determine the underlying neurobiological mechanisms.

Individuals with Hyperthyroidism are More Susceptible to having a Serious Serotonin Syndrome Following MDMA (Ecstasy) Administration in Rats

In a recreational use of 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy"), some but not all users are stricken with a serious serotonin (5-hydroxytryptamine; 5-HT) syndrome. This raises a question as to whether there exist subpopulations that are more susceptible to MDMA intoxication. The hypothesis was tested with hyperthyroid versus euthyroid rats by measuring changes in body-core temperature (T _cor) and 5-HT in the hypothalamus. In the euthyroid rats, injection of MDMA at a recreationally relevant dose had no serious effect on T _cor. In contrast, the same dose was sufficient to evoke life-threatening hyperthermia in hyperthyroid rats. Neurochemical studies revealed that there was greater 5-HT efflux in the hyperthyroid than the euthyroid rats. These effects were blocked by pretreatment with M100907, a 5-HT_2A receptor antagonist. In summary, our data support the hypothesis that individuals with hyperthyroidism are more susceptible to having a serious serotonin syndrome following MDMA administration.

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.

Environment Influencing Serotonin Syndrome Induced by Ecstasy Abuse

Ecstasy is a recreational drug containing 3,4-methylenedioxymethamphetamine (MDMA). In the U.S., there are several millions of lifetime users, and millions each year added to the list as new users. Only several thousand every year show signs of severe toxicity and require emergency intervention. The illness is known as serotonin (5-HT) syndrome, which can be mild, moderate or severe. The relationship between mild, moderate and severe syndromes appears to be interchangeable, but the severe syndrome is life-threatening. The serotonergic mechanisms of how the mild or moderate syndrome becomes severe and life-threatening have attracted considerable attention in the last few years as an effort to explore new treatments potentially to manage illness and prevent death of patients. High levels of extracellular 5-HT in the brain produced by large doses of MDMA are not always necessary to cause a severe serotonin syndrome. Additional mechanisms may be more important. Recent research has demonstrated that environmental conditions (i.e., non-drug factors) are more critical in determining the severity of MDMA-induced serotonin syndrome than the drug dose. The purpose of the current article was to review available evidence regarding the effect of non-drug factors on serotonergic extrasynaptic receptor responsivity and the severity of MDMA-induced serotonin syndrome.

Contribution of Impulsivity and Serotonin Receptor Neuroadaptations to the Development of an MDMA ('Ecstasy') Substance Use Disorder

As is the case with other drugs of abuse, a proportion of ecstasy users develop symptoms consistent with a substance use disorder (SUD). In this paper, we propose that the pharmacology of MDMA, the primary psychoactive component of ecstasy tablets, changes markedly with repeated exposure and that neuroadaptations in dopamine and serotonin brain systems underlie the shift from MDMA use to MDMA misuse in susceptible subjects. Data from both the human and laboratory animal literature are synthesized to support the idea that (1) MDMA becomes a less efficacious serotonin releaser and a more efficacious dopamine releaser with the development of behaviour consistent with an SUD and (2) that upregulated serotonin receptor mechanisms contribute to the development of the MDMA SUD via dysregulated inhibitory control associated with the trait of impulsivity.

Neuropharmacology of 3,4-Methylenedioxypyrovalerone (MDPV), Its Metabolites, and Related Analogs

3,4-Methylenedioxypyrovalerone (MDPV) is a psychoactive component of so-called bath salts products that has caused serious medical consequences in humans. In this chapter, we review the neuropharmacology of MDPV and related analogs, and supplement the discussion with new results from our preclinical experiments. MDPV acts as a potent uptake inhibitor at plasma membrane transporters for dopamine (DAT) and norepinephrine (NET) in nervous tissue. The MDPV formulation in bath salts is a racemic mixture, and the S isomer is much more potent than the R isomer at blocking DAT and producing abuse-related effects. Elevations in brain extracellular dopamine produced by MDPV are likely to underlie its locomotor stimulant and addictive properties. MDPV displays rapid pharmacokinetics when injected into rats (0.5-2.0 mg/kg), with peak plasma concentrations achieved by 10-20 min and declining quickly thereafter. MDPV is metabolized to 3,4-dihydroxypyrovalerone (3,4-catechol-PV) and 4-hydroxy-3-methoxypyrovalerone (4-OH-3-MeO-PV) in vivo, but motor activation produced by the drug is positively correlated with plasma concentrations of parent drug and not its metabolites. 3,4-Catechol-PV is a potent uptake blocker at DAT in vitro but has little activity after administration in vivo. 4-OH-3-MeO-PV is the main MDPV metabolite but is weak at DAT and NET. MDPV analogs, such as α-pyrrolidinovalerophenone (α-PVP), display similar ability to inhibit DAT and increase extracellular dopamine concentrations. Taken together, these findings demonstrate that MDPV and its analogs represent a unique class of transporter inhibitors with a high propensity for abuse and addiction.

Contribution of serotonin and dopamine to changes in core body temperature and locomotor activity in rats following repeated administration of mephedrone

The psychoactive effects of mephedrone are commonly compared with those of 3,4-methylenedioxymethamphetamine, but because of a shorter duration of action, users often employ repeated administration to maintain its psychoactive effects. This study examined the effects of repeated mephedrone administration on locomotor activity, body temperature and striatal dopamine and 5-hydroxytryptamine (5-HT) levels and the role of dopaminergic and serotonergic neurons in these responses. Adult male Lister hooded rats received three injections of vehicle (1 ml/kg, i.p.) or mephedrone HCl (10 mg/kg) at 2 h intervals for radiotelemetry (temperature and activity) or microdialysis (dopamine and 5-HT) measurements. Intracerebroventricular pre-treatment (21 to 28 days earlier) with 5,7-dihydroxytryptamine (150 µg) or 6-hydroxydopamine (300 µg) was used to examine the impact of 5-HT or dopamine depletion on mephedrone-induced changes in temperature and activity. A final study examined the influence of i.p. pre-treatment (-30 min) with the 5-HT_1A receptor antagonist WAY-100635 (0.5 mg/kg), 5-HT_1B receptor antagonist GR 127935 (3 mg/kg) or the 5-HT₇ receptor antagonist SB-258719 (10 mg/kg) on mephedrone-induced changes in locomotor activity and rectal temperature. Mephedrone caused rapid-onset hyperactivity, hypothermia (attenuated on repeat dosing) and increased striatal dopamine and 5-HT release following each injection. Mephedrone-induced hyperactivity was attenuated by 5-HT depletion and 5-HT_1B receptor antagonism, whereas the hypothermia was completely abolished by 5-HT depletion and lessened by 5-HT_1A receptor antagonism. These findings suggest that stimulation of central 5-HT release and/or inhibition of 5-HT reuptake play a pivotal role in both the hyperlocomotor and hypothermic effects of mephedrone, which are mediated in part via 5-HT_1B and 5-HT_1A receptors.

New Insights on Different Response of MDMA-Elicited Serotonin Syndrome to Systemic and Intracranial Administrations in the Rat Brain

In spite of the fact that systemic administration of MDMA elicits serotonin syndrome, direct intracranial administration fails to reproduce the effect. To reconcile these findings, it has been suggested that the cause of serotonin syndrome is attributed mainly to MDMA hepatic metabolites, and less likely to MDMA itself. Recently, however, this explanation has been challenged, and alternative hypotheses need to be explored. Here, we tested the hypothesis that serotonin syndrome is the result of excessive 5HT simultaneously in many brain areas, while MDMA administered intracranially fails to cause serotonin syndrome because it produces only a localized effect at the delivery site and not to other parts of the brain. This hypothesis was examined using adult male Sprague Dawley rats by comparing 5HT responses in the right and left hemispheric frontal cortices, right and left hemispheric diencephalons, and medullar raphe nucleus. Occurrence of serotonin syndrome was confirmed by measuring change in body temperature. Administration routes included intraperitoneal (IP), intracerebroventricular (ICV) and reverse microdialysis. First, we found that IP administration caused excessive 5HT in all five sites investigated and induced hypothermia, suggesting the development of the serotonin syndrome. In contrast, ICV and reverse microdialysis caused excessive 5HT only in regions of delivery sites without changes in body-core temperature, suggesting the absence of the syndrome. Next, chemical dyes were used to trace differences in distribution and diffusion patterns between administration routes. After systemic administration, the dyes were found to be evenly distributed in the brain. However, the dyes administered through ICV or reverse microdialysis injection still remained in the delivery sites, poorly diffusing to the brain. In conclusion, intracranial MDMA administration in one area has no or little effect on other areas, which must be considered a plausible reason for the difference in MDMA-elicited serotonin syndrome between systemic and intracranial administrations.

Repeated administration of the 5-HT₁B/₁A agonist, RU 24969, facilitates the acquisition of MDMA self-administration: role of 5-HT₁A and 5-HT₁B receptor mechanisms

RATIONALE

3,4 Methylenedioxymethamphetamine (MDMA) preferentially stimulates the release of serotonin (5-HT) that subsequently produces behavioral responses by activation of post-synaptic receptor mechanisms. The 5-HT1A and 5-HT1B receptors are both well localized to regulate dopamine (DA) release, and have been implicated in modulating the reinforcing effects of many drugs of abuse, but a role in acquisition of self-administration has not been determined.

OBJECTIVES

This study was designed to determine the effect of pharmacological manipulation of 5-HT1A and 5-HT1B receptor mechanisms on the acquisition of MDMA self-administration.

METHODS

The 5-HT1B/1A receptor agonist, RU 24969 (0.0 or 3.0 mg/kg, bid), was administered for 3 days in order to down-regulate both 5-HT1A and 5-HT1B receptors. Following the pretreatment phase, latency to acquisition of MDMA self-administration was measured.

RESULTS

Repeated administration of RU 24969 significantly decreased the latency to acquisition and increased the proportion of animals that acquired MDMA self-administration. Dose-effect curves for the 5-HT1A-mediated hyperactivity produced by the 5-HT1A agonist, 8-OH-DPAT, and the 5-HT1B-mediated adipsic response produced by RU 24969 were shifted rightward, suggesting a desensitization of 5-HT1A and 5-HT1B receptor mechanisms.

CONCLUSIONS

These data suggest that the initial reinforcing effects of MDMA are modulated by 5-HT1A and/or 5-HT1B receptor mechanisms. The potential impact of these changes on the DAergic response relevant to self-administration and a possible role in conditioned reinforcement pertaining to acquisition of self-administration are discussed.

Linear pharmacokinetics of 3,4-methylenedioxypyrovalerone (MDPV) and its metabolites in the rat: relationship to pharmacodynamic effects

3,4-Methylenedioxypyrovalerone (MDPV) is a commonly abused synthetic cathinone in the United States and is associated with dangerous side effects. MDPV is a dopamine transporter blocker that is 10-fold more potent than cocaine as a locomotor stimulant in rats. Previous in vitro and in vivo metabolism studies identified 3,4-dihydroxypyrovalerone (3,4-catechol-PV) and 4-hydroxy-3-methoxypyrovalerone (4-OH-3-MeO-PV) as the two primary MDPV metabolites. This study examined MDPV pharmacokinetics and metabolism, along with associated pharmacodynamic effects in rats receiving 0.5, 1.0 and 2.0 mg/kg subcutaneous (s.c.) MDPV. Blood was collected by an indwelling jugular catheter before dosing and at 10, 20, 30, 60, 120, 240 and 480 minutes thereafter. Plasma specimens were analyzed by liquid chromatography coupled to high-resolution tandem mass spectrometry. Maximum concentrations (Cmax ) and area-under-the-curve (AUC) for MDPV and two metabolites increased proportionally with administered dose, showing linear pharmacokinetics. MDPV exhibited the highest Cmax at all doses (74.2-271.3 μg/l) and 4-OH-3-MeOH-PV the highest AUC (11 366-47 724 minutes per μg/l), being the predominant metabolite. MDPV time to Cmax (Tmax ) was 12.9-18.6 minutes, while 3,4-catechol-PV and 4-OH-3-MeO-PV peaked later with Tmax 188.6-240 minutes after s.c. dosing. Horizontal locomotor activity (HLA) and stereotypy correlated positively with plasma MDPV concentrations, while HLA correlated negatively with MDPV metabolites. These results suggest that the parent compound mediates motor stimulation after systemic MDPV administration, but additionally, metabolites may be inhibitory, may not be active or may not pass the blood brain barrier.

Methylone-induced hyperthermia and lethal toxicity: role of the dopamine and serotonin transporters

Methylone (2-methylamino-1-[3,4-methylenedioxy-phenyl]propan-1-one), an amphetamine analog, has emerged as a popular drug of abuse worldwide. Methylone induces hyperthermia, which is thought to contribute toward the lethal consequences of methylone overdose. Methylone has been assumed to induce hyperthermic effects through inhibition of serotonin and/or dopamine transporters (SERT and DAT, respectively). To examine the roles of each of these proteins in methylone-induced toxic effects, we used SERT and DAT knockout (KO) mice and assessed the hyperthermic and lethal effects caused by a single administration of methylone. Methylone produced higher rates of lethal toxicity compared with other amphetamine analogs in wild-type mice. Compared with wild-type mice, lethality was significantly lower in DAT KO mice, but not in SERT KO mice. By contrast, only a slight diminution in the hyperthermic effects of methylone was observed in DAT KO mice, whereas a slight enhancement of these effects was observed in SERT KO mice. Administration of the selective D1 receptor antagonist SCH 23390 and the D2 receptor antagonist raclopride reduced methylone-induced hyperthermia, but these drugs also had hypothermic effects in saline-treated mice, albeit to a smaller extent than the effects observed in methylone-treated mice. In contradistinction to 3,4-methylenedioxymethamphetamine, which induces its toxicity through SERT and DAT, these data indicate that DAT, but not SERT, is strongly associated with the lethal toxicity produced by methylone, which did not seem to be dependent on the hyperthermic effects of methylone. DAT is therefore a strong candidate molecule for interventions aimed at preventing acute neurotoxic and lethal effects of methylone.

Human pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) after repeated doses taken 4 h apart Human pharmacology of MDMA after repeated doses taken 4 h apart

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is a popular psychostimulant, frequently associated with multiple administrations over a short period of time. Repeated administration of MDMA in experimental settings induces tolerance and metabolic inhibition. The aim is to determine the acute pharmacological effects and pharmacokinetics resulting from two consecutive 100mg doses of MDMA separated by 4h. Ten male volunteers participated in a randomized, double-blind, crossover, placebo-controlled trial. The four conditions were placebo plus placebo, placebo plus MDMA, MDMA plus placebo, and MDMA plus MDMA. Outcome variables included pharmacological effects and pharmacokinetic parameters. After a second dose of MDMA, most effects were similar to those after a single dose, despite a doubling of MDMA concentrations (except for systolic blood pressure and reaction time). After repeated MDMA administration, a 2-fold increase was observed in MDMA plasma concentrations. For a simple dose accumulation MDMA and MDA concentrations were higher (+23.1% Cmax and +17.1% AUC for MDMA and +14.2% Cmax and +10.3% AUC for MDA) and HMMA and HMA concentrations lower (-43.3% Cmax and -39.9% AUC for HMMA and -33.2% Cmax and -35.1% AUC for HMA) than expected, probably related to MDMA metabolic autoinhibition. Although MDMA concentrations doubled after the second dose, most pharmacological effects were similar or slightly higher in comparison to the single administration, except for systolic blood pressure and reaction time which were greater than predicted. The pharmacokinetic-effects relationship suggests that when MDMA is administered at a 4h interval there exists a phenomenon of acute tolerance to its effects.

Mechanisms and environmental factors that underlying the intensification of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy)-induced serotonin syndrome in rats

RATIONALE

Illicit use of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) may cause a mild or severe form of the serotonin syndrome. The syndrome intensity is not just influenced by drug doses but also by environmental factors.

OBJECTIVES

Warm environmental temperatures and physical activity are features of raves. The purpose of this study was to assess how these two factors can potentially intensify the syndrome.

METHODS

Rats were administered MDMA at doses of 0.3, 1, or 3 mg/kg and examined in the absence or presence of warm temperature and physical activity. The syndrome intensity was estimated by visual scoring for behavioral syndrome and also instrumentally measuring changes in symptoms of the syndrome.

RESULTS

Our results showed that MDMA at 3 mg/kg, but not 0.3 or 1 mg/kg, caused a mild serotonin syndrome in rats. Each environmental factor alone moderately intensified the syndrome. When the two factors were combined, the intensification became more severe than each factor alone highlighting a synergistic effect. This intensification was blocked by the 5-HT2A receptor antagonist M100907, competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist CGS19755, autonomic ganglionic blocker hexamethonium, and the benzodiazepine-GABAA receptor agonist midazolam but not by the 5-HT1A receptor antagonist WAY100635 or nicotinic receptor antagonist methyllycaconitine.

CONCLUSIONS

Our data suggest that, in the absence of environmental factors, the MDMA-induced syndrome is mainly mediated through the serotonergic transmission (5-hydroxytryptamine (5HT)-dependent mechanism) and therefore is relatively mild. Warm temperature and physical activity facilitate serotonergic and other neural systems such as glutamatergic and autonomic transmissions, resulting in intensification of the syndrome (non-5HT mechanisms).

Acquisition of MDMA self-administration: pharmacokinetic factors and MDMA-induced serotonin release

The current study aimed to elucidate the role of pharmacokinetic (PK) parameters and neurotransmitter efflux in explaining variability in (±) 3, 4-methylenedioxymethamphetamine (MDMA) self-administration in rats. PK profiles of MDMA and its major metabolites were determined after the administration of 1.0 mg/kg MDMA (iv) prior to, and following, the acquisition of MDMA self-administration. Synaptic levels of 5-hydroxytryptamine (5HT) and dopamine (DA) in the nucleus accumbens were measured following administration of MDMA (1.0 and 3.0 mg/kg, iv) using in vivo microdialysis and compared for rats that acquired or failed to acquire MDMA self-administration. Effects of the 5HT neurotoxin, 5,7 dihydroxytryptamine (5, 7-DHT), on the acquisition of MDMA and cocaine self-administration were also determined. In keeping with previous findings, approximately 50% of rats failed to meet a criterion for acquisition of MDMA self-administration. The PK profiles of MDMA and its metabolites did not differ between rats that acquired or failed to acquire MDMA self-administration. MDMA produced more overflow of 5HT than DA. The MDMA-induced 5HT overflow was lower in rats that acquired MDMA self-administration compared with those that did not acquire self-administration. In contrast, MDMA-induced DA overflow was comparable for the two groups. Prior 5,7-DHT lesions reduced tissue levels of 5HT and markedly increased the percentage of rats that acquired MDMA self-administration and also decreased the latency to acquisition of cocaine self-administration. These data suggest that 5HT limits the initial sensitivity to the positively reinforcing effects of MDMA and delays the acquisition of reliable self-administration.

Nonlinear pharmacokinetics of (+/-)3,4-methylenedioxymethamphetamine (MDMA) and its pharmacodynamic consequences in the rat

3,4-Methylenedioxymethamphetamine (MDMA) is a widely abused illicit drug that can cause severe and even fatal adverse effects. However, interest remains for its possible clinical applications in posttraumatic stress disorder and anxiety treatment. Preclinical studies to determine MDMA's safety are needed. We evaluated MDMA's pharmacokinetics and metabolism in male rats receiving 2.5, 5, and 10 mg/kg s.c. MDMA, and the associated pharmacodynamic consequences. Blood was collected via jugular catheter at 0, 0.5, 1, 2, 4, 6, 8, 16, and 24 hours, with simultaneous serotonin (5-HT) behavioral syndrome and core temperature monitoring. Plasma specimens were analyzed for MDMA and the metabolites (±)-3,4-dihydroxymethamphetamine (HHMA), (±)-4-hydroxy-3-methoxymethamphetamine (HMMA), and (±)-3,4-methylenedioxyamphetamine (MDA) by liquid chromatography-tandem mass spectrometry. After 2.5 mg/kg MDMA, mean MDMA Cmax was 164 ± 47.1 ng/ml, HHMA and HMMA were major metabolites, and <20% of MDMA was metabolized to MDA. After 5- and 10-mg/kg doses, MDMA areas under the curve (AUCs) were 3- and 10-fold greater than those after 2.5 mg/kg; HHMA and HMMA AUC values were relatively constant across doses; and MDA AUC values were greater than dose-proportional. Our data provide decisive in vivo evidence that MDMA and MDA display nonlinear accumulation via metabolic autoinhibition in the rat. Importantly, 5-HT syndrome severity correlated with MDMA concentrations (r = 0.8083; P < 0.0001) and core temperature correlated with MDA concentrations (r = 0.7595; P < 0.0001), suggesting that MDMA's behavioral and hyperthermic effects may involve distinct mechanisms. Given key similarities between MDMA pharmacokinetics in rats and humans, data from rats can be useful when provided at clinically relevant doses.

Age differences in (±) 3,4-methylenedioxymethamphetamine (MDMA)-induced conditioned taste aversions and monoaminergic levels

Preclinical work indicates that adolescent rats appear more sensitive to the rewarding effects and less sensitive to the aversive effects of abused drugs. The present investigation utilized the conditioned taste aversion (CTA) design to measure the relative aversive effects of (±)3,4-methylenedioxymethamphetamine (MDMA; 0, 1.0, 1.8, or 3.2 mg/kg) in adolescent and adult Sprague-Dawley rats. After behavioral testing was complete, monoamine and associated metabolite levels in discrete brain regions were quantified using high-performance liquid chromatography coupled to electrochemical detection (HPLC-ECD) to determine if adolescent animals displayed a different neurochemical profile than did adult animals after being exposed to subcutaneous low doses of MDMA. Adolescent rats displayed less robust MDMA-induced taste aversions than adults during acquisition and on a final two-bottle aversion test. MDMA at these doses had no consistent effect on monoamine levels in either age group, although levels did vary with age. The relative insensitivity of adolescents to MDMA's aversive effects may engender an increased vulnerability to MDMA abuse in this specific population.

Characterization of electroencephalographic and biochemical responses at 5-HT promoting drug-induced onset of serotonin syndrome in rats

Many psychotropic substances used either for medications or illicit recreational purposes are able to produce an increase in extracellular serotonin (5HT) in the CNS. 5HT is well known to improve mood; however, only when the levels of its release are in an appropriate range. Excessive 5HT is harmful, and will generally result in serotonin syndrome. To date, clinical diagnosis of serotonin syndrome relies exclusively on observation of symptoms because of a lack of available laboratory tests. The goal of this study was to characterize the onset of the syndrome using laboratory settings to determine excessive 5HT-evoked neurological abnormalities. Experiments were carried out in rats with the syndrome being elicited by three groups of 5HT-promoting drugs: (i) (±)-3,4-methylenedioxymethamphetamine (MDMA); (ii) a combination of the monoamine oxidase inhibitor clorgyline with the 5HT precursor 5-hydroxytryptophan; (iii) clorgyline combined with the serotonin-selective reuptake inhibitor paroxetine. The onset of the syndrome was characterized by electroencephalography (EEG), tremor, and brain/plasma 5HT tests. We found that a mild syndrome was associated with reduced EEG amplitudes while a severe syndrome strongly with seizure-like EEG activity and increased tremor activity. The occurrence of the syndrome was confirmed with microdialysis, showing excessive 5HT efflux in brain dialysate and the increased concentration of unbound 5HT in the plasma. Our findings suggest that the syndrome onset can be revealed with EEG recording, measurements of tremor activity and changes of unbound 5HT concentration in the plasma.

Contrasting effects of d-methamphetamine, 3,4-methylenedioxymethamphetamine, 3,4-methylenedioxypyrovalerone, and 4-methylmethcathinone on wheel activity in rats

BACKGROUND

Reports from U.S., U.K. and European drug policy entities, and ongoing media accounts, show increasing recreational use of 4-methylmethcathinone (4-MMC, mephedrone) and 3,4-methylenedioxypyrovalerone (MDPV). Severe sympathomimetic symptoms, hallucinations, psychoses, and even deaths have been reported, yet little scientific information is available on the effects of these compounds in laboratory models. Available studies on the neurochemistry of these drugs show that 4-MMC and MDPV enhance DA neurotransmission, while 4-MMC additionally enhances 5-HT neurotransmission--a pattern much like that reported for methamphetamine versus 3,4-methylenedioxymethamphetamine (MDMA). As is the case for designer amphetamines, these neurochemical distinctions may predict differential potential for repetitive versus episodic abuse and distinct lasting toxicities.

METHODS

This study determined relative locomotor stimulant effects of 4-MMC (1-10 mg/kg, s.c.) and MDPV (0.5-5.6 mg/kg, s.c.), in comparison with d-methamphetamine (MA; 0.5-5.6 mg/kg, s.c.) and MDMA (1-7.5 mg/kg, s.c.) on a measure of locomotor activity--voluntary wheel running--in male Wistar rats (N=8).

RESULTS

Compared to counts of wheel rotations after saline, a biphasic change in the pattern of counts was observed after injections of MA and MDPV, with relatively higher counts following lower doses and lower counts following the highest dose. However, monophasic, dose-dependent reductions in counts were observed in response to injections of MDMA and 4-MMC.

CONCLUSION

Thus, voluntary wheel running yielded the same categorical distinctions for these drugs as did prior experiments testing the effects of these drugs on monoaminergic neurotransmission. These data indicate that MDPV produces prototypical locomotor stimulant effects whereas 4-MMC is more similar to the entactogen MDMA.

(±)3,4-methylenedioxymethamphetamine ("ecstasy") treatment modulates expression of neurotrophins and their receptors in multiple regions of adult rat brain

(±)3,4-Methylenedioxymethamphetamine (MDMA), a widely used drug of abuse, rapidly reduces serotonin levels in the brain when ingested or administered in sufficient quantities, resulting in deficits in complex route-based learning, spatial learning, and reference memory. Neurotrophins are important for survival and preservation of neurons in the adult brain, including serotonergic neurons. In this study, we examined the effects of MDMA on the expression of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) and their respective high-affinity receptors, tropomyosin receptor kinase (trk)B and trkC, in multiple regions of the rat brain. A serotonergic-depleting dose of MDMA (10 mg/kg × 4 at 2-hour intervals on a single day) was administered to adult Sprague-Dawley rats, and brains were examined 1, 7, or 24 hours after the last dose. Messenger RNA levels of BDNF, NT-3, trkB, and trkC were analyzed by using in situ hybridization with cRNA probes. The prefrontal cortex was particularly vulnerable to MDMA-induced alterations in that BDNF, NT-3, trkB, and trkC mRNAs were all upregulated at multiple time points. MDMA-treated animals had increased BDNF expression in the frontal, parietal, piriform, and entorhinal cortices, increased NT-3 expression in the anterior cingulate cortex, and elevated trkC in the entorhinal cortex. In the nigrostriatal system, BDNF expression was upregulated in the substantia nigra pars compacta, and trkB was elevated in the striatum in MDMA-treated animals. Both neurotrophins and trkB were differentially regulated in several regions of the hippocampal formation. These findings suggest a possible role for neurotrophin signaling in the learning and memory deficits seen following MDMA treatment.

The designer methcathinone analogs, mephedrone and methylone, are substrates for monoamine transporters in brain tissue

The nonmedical use of 'designer' cathinone analogs, such as 4-methylmethcathinone (mephedrone) and 3,4-methylenedioxymethcathinone (methylone), is increasing worldwide, yet little information is available regarding the mechanism of action for these drugs. Here, we employed in vitro and in vivo methods to compare neurobiological effects of mephedrone and methylone with those produced by the structurally related compounds, 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine. In vitro release assays using rat brain synaptosomes revealed that mephedrone and methylone are nonselective substrates for plasma membrane monoamine transporters, similar to MDMA in potency and selectivity. In vivo microdialysis in rat nucleus accumbens showed that i.v. administration of 0.3 and 1.0 mg/kg of mephedrone or methylone produces dose-related increases in extracellular dopamine and serotonin (5-HT), with the magnitude of effect on 5-HT being greater. Both methcathinone analogs were weak motor stimulants when compared with methamphetamine. Repeated administrations of mephedrone or methylone (3.0 and 10.0 mg/kg, s.c., 3 doses) caused hyperthermia but no long-term change in cortical or striatal amines, whereas similar treatment with MDMA (2.5 and 7.5 mg/kg, s.c., 3 doses) evoked robust hyperthermia and persistent depletion of cortical and striatal 5-HT. Our data demonstrate that designer methcathinone analogs are substrates for monoamine transporters, with a profile of transmitter-releasing activity comparable to MDMA. Dopaminergic effects of mephedrone and methylone may contribute to their addictive potential, but this hypothesis awaits confirmation. Given the widespread use of mephedrone and methylone, determining the consequences of repeated drug exposure warrants further study.

The neuropharmacology of prolactin secretion elicited by 3,4-methylenedioxymethamphetamine ("ecstasy"): a concurrent microdialysis and plasma analysis study

3,4-methylenedioxymethamphetamine (MDMA) is a substituted phenethylamine that is widely abused as the street drug "ecstasy". Racemic MDMA (S,R(+/-)-MDMA) and its stereoisomers elicit complex spectrums of psychobiological, neurochemical, and hormonal effects. In this regard, recent findings demonstrated that S,R(+/-)-MDMA and its stereoisomer R(-)-MDMA elicit increases in striatal extracellular serotonin levels and plasma levels of the hormone prolactin in rhesus monkeys. In the present mechanistic study, we evaluated the role of the serotonin transporter and the 5-HT(2A) receptor in S,R(+/-)-MDMA- and R(-)-MDMA-elicited prolactin secretion in rhesus monkeys through concurrent microdialysis and plasma analysis determinations and drug interaction experiments. Concurrent neurochemical and hormone determinations showed a strong positive temporal correlation between serotonin release and prolactin secretion. Consistent with their distinct mechanisms of action and previous studies showing that the serotonin transporter inhibitor fluoxetine attenuates the behavioral and neurochemical effects of S,R(+/-)-MDMA, pretreatment with fluoxetine attenuated serotonin release elicited by either S,R(+/-)-MDMA or R(-)-MDMA. As hypothesized, at a dose that had no significant effects on circulating prolactin levels when administered alone, fluoxetine also attenuated prolactin secretion elicited by S,R(+/-)-MDMA. In contrast, combined pretreatment with both fluoxetine and the selective 5-HT(2A) receptor antagonist M100907 was required to attenuate prolactin secretion elicited by R(-)-MDMA, suggesting that this stereoisomer of S,R(+/-)-MDMA elicits prolactin secretion through both serotonin release and direct agonism of 5-HT(2A) receptors. Accordingly, these findings inform our understanding of the neuropharmacology of both S,R(+/-)-MDMA and R(-)-MDMA and the regulation of prolactin secretion.

Effects of MDMA and related analogs on plasma 5-HT: relevance to 5-HT transporters in blood and brain

(±)-3,4-Methylenedioxymethamphetamine (MDMA) is an illicit drug that evokes transporter-mediated release of serotonin (5-HT) in the brain. 5-HT transporter (SERT) proteins are also expressed in non-neural tissues (e.g., blood), and evidence suggests that MDMA targets platelet SERT to increase plasma 5-HT. Here we tested two hypotheses related to the effects of MDMA on circulating 5-HT. First, to determine if MDMA metabolites might contribute to actions of the drug in vivo, we used in vitro microdialysis in rat blood specimens to examine the effects of MDMA and its metabolites on plasma 5-HT. Second, to determine whether effects of MDMA on plasma 5-HT might be used as an index of central SERT activity, we carried out in vivo microdialysis in blood and brain after intravenous MDMA administration. The in vitro results show that test drugs evoke dose-related increases in plasma 5-HT ranging from two- to sevenfold above baseline, with MDMA and its metabolite, (±)-3,4-methylenedioxyamphetamine (MDA), producing the largest effects. The ability of MDMA and related analogs to elevate plasma 5-HT is correlated with their potency as SERT substrates in rat brain synaptosomes. The in vivo results reveal that MDMA causes concurrent increases in extracellular 5-HT in blood and brain, but there are substantial individual differences in responsiveness to the drug. Collectively, our findings indicate that MDMA and its metabolites increase plasma 5-HT by a SERT-dependent mechanism, and suggest the possibility that measures of evoked 5-HT release in blood may reflect central SERT activity.

Effects of repeated 3,4-methylenedioxymethamphetamine administration on neurotransmitter efflux and sensory-evoked discharge in the ventral posterior medial thalamus

3,4-Methylenedioxymethamphetamine (MDMA) is known to enhance tactile sensory perception, an effect that contributes to its popularity as a recreational drug. The neurophysiological basis for the effects of MDMA on somatosensation are unknown. However, MDMA interactions with the serotonin transporter (SERT) and subsequent enhancement of serotonin neurotransmission are well known. The rat trigeminal somatosensory system receives serotonergic afferents from the dorsal raphe nucleus. Because these fibers express SERT, they should be vulnerable to MDMA-induced effects. We found that administration of a challenge injection of MDMA (3 mg/kg i.p.) after repeated MDMA treatment (3 mg/kg per day for 4 days) elicits both serotonin and norepinephrine efflux in the ventral posterior medial (VPM) thalamus of Long-Evans hooded rats, the main relay along the lemniscal portion of the rodent trigeminal somatosensory pathway. We evaluated the potential for repeated MDMA administration to modulate whisker-evoked discharge of individual neurons in this region. After surgically implanting stainless steel eight-wire multichannel electrode bundles, we recorded spike train activity of single cells while activating the whisker pathway using a piezoelectric mechanical stimulator. We found that repeated MDMA administration increased the spontaneous firing rate but reduced both the magnitude and duration of whisker-evoked discharge in individual VPM thalamic neurons. The time course of drug action on neuronal firing patterns was generally consistent with fluctuations in neurotransmitter efflux as shown from our microdialysis studies. On the basis of these results, we propose that single use and repeated administration of MDMA may "distort," rather than enhance, tactile experiences in humans, in part, by disrupting normal spike firing patterns through somatosensory thalamic relay circuits.

Dopaminergic mechanisms of reinstatement of MDMA-seeking behaviour in rats

BACKGROUND AND PURPOSE

Animal models of drug-seeking suggest that exposure to cues associated with self-administered drugs and drug primes might precipitate relapse via activation of central dopaminergic substrates.

EXPERIMENTAL APPROACH

The effects of priming injections of dopamine and 5-HT agonists on drug-seeking and effects of dopamine antagonists on methylenedioxymethamphetamine (MDMA)-produced potentiation of drug-seeking following extinguished MDMA self-administration were examined.

KEY RESULTS

Drug-seeking was produced by exposure to a light stimulus that had been paired with self-administered MDMA infusions and this effect was potentiated by experimenter-administered injections of the dopamine D(2) -like receptor agonist, quinpirole, the indirect agonist, amphetamine and the uptake inhibitor, GBR 12909. Drug-seeking was not elicited by the dopamine D(1) -like receptor agonist, SKF 81297 or the non-selective agonist, apomorphine. The 5-HT receptor agonists DOI or mCPP also failed to elicit drug-seeking. The 5-HT uptake inhibitor, clomipramine, attenuated drug-seeking produced by the MDMA-associated stimulus but failed to alter the potentiated response produced by GBR 12909. The D(1) receptor antagonist, SCH 23390 or the D(2) receptor antagonist, eticlopride attenuated the potentiation of drug-seeking produced by MDMA.

CONCLUSIONS AND IMPLICATIONS

These data provide evidence of dopaminergic mechanisms in drug-seeking following extinction of MDMA self-administration. Because tissue levels of 5-HT were significantly decreased following MDMA self-administration, we suggest that MDMA begins to preferentially activate dopaminergic substrates to potentiate the drug-seeking response.

Neuroimaging and drug taking in primates

RATIONALE

Neuroimaging techniques have led to significant advances in our understanding of the neurobiology of drug taking and the treatment of drug addiction in humans. Neuroimaging approaches provide a powerful translational approach that can link findings from humans and laboratory animals.

OBJECTIVE

This review describes the utility of neuroimaging toward understanding the neurobiological basis of drug taking and documents the close concordance that can be achieved among neuroimaging, neurochemical, and behavioral endpoints.

RESULTS

The study of drug interactions with dopamine and serotonin transporters in vivo has identified pharmacological mechanisms of action associated with the abuse liability of stimulants. Neuroimaging has identified the extended limbic system, including the prefrontal cortex and anterior cingulate, as important neuronal circuitry that underlies drug taking. The ability to conduct within-subject longitudinal assessments of brain chemistry and neuronal function has enhanced our efforts to document long-term changes in dopamine D2 receptors, monoamine transporters, and prefrontal metabolism due to chronic drug exposure. Dysregulation of dopamine function and brain metabolic changes in areas involved in reward circuitry have been linked to drug taking behavior, cognitive impairment, and treatment response.

CONCLUSIONS

Experimental designs employing neuroimaging should consider well-documented determinants of drug taking, including pharmacokinetic considerations, subject history, and environmental variables. Methodological issues to consider include limited molecular probes, lack of neurochemical specificity in brain activation studies, and the potential influence of anesthetics in animal studies. Nevertheless, these integrative approaches should have important implications for understanding drug taking behavior and the treatment of drug addiction.

The ugly side of amphetamines: short- and long-term toxicity of 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy'), methamphetamine and D-amphetamine

Amphetamine ('Speed'), methamphetamine ('Ice') and its congener 3,4-methylenedioxymethamphetamine (MDMA; 'Ecstasy') are illicit drugs abused worldwide for their euphoric and stimulant effects. Despite compelling evidence for chronic MDMA neurotoxicity in animal models, the physiological consequences of such toxicity in humans remain unclear. In addition, distinct differences in the metabolism and pharmacokinetics of MDMA between species and different strains of animals prevent the rationalisation of realistic human dose paradigms in animal studies. Here, we attempt to review amphetamine toxicity and in particular MDMA toxicity in the pathogenesis of exemplary human pathologies, independently of confounding environmental factors such as poly-drug use and drug purity.

Behavioral sensitization and cross-sensitization between methylphenidate amphetamine, and 3,4-methylenedioxymethamphetamine (MDMA) in female SD rats

The psychostimulants amphetamine and methylphenidate (MPD/Ritalin) are the drugs most often used to treat attention deficit hyperactivity disorder (ADHD). In addition, students of all ages take these drugs to improve academic performance but also abuse them for pleasurable enhancement. In addition, other psychostimulants such as 3,4-methylenedioxymethamphetamine (MDMA/ecstasy) are used/abused for similar objectives. One of the experimental markers for the potential of a drug to produce dependence is its ability to induce behavioral sensitization and cross sensitization with other drugs of abuse. The objective of this study is to use identical experimental protocols and behavioral assays to compare in female rats the effects of amphetamine, MPD and MDMA on locomotor activity and to determine if they induce behavioral sensitization and/or cross sensitization with each other. The main findings of this study are as follows: (1) acute amphetamine, MPD and MDMA all elicited increases in locomotor activity; (2) chronic administration of an intermediate dose of amphetamine or MPD elicited behavioral sensitization; (3) chronic administration of MDMA elicited behavioral sensitization in some animals and behavioral tolerance in others; (4) cross sensitization between MPD and amphetamine was observed; and (5) MDMA did not show either cross sensitization or cross tolerance with amphetamine. In conclusion, these results suggest that MDMA acts by different mechanisms compared to MPD and amphetamine.

Contributions of serotonin in addiction vulnerability

The serotonin (5-hydroxytryptamine; 5-HT) system has long been associated with mood and its dysregulation implicated in the pathophysiology of mood and anxiety disorders. While modulation of 5-HT neurotransmission by drugs of abuse is also recognized, its role in drug addiction and vulnerability to drug relapse is a more recent focus of investigation. First, we review preclinical data supporting the serotonergic raphe nuclei and their forebrain projections as targets of drugs of abuse, with emphasis on the effects of psychostimulants, opioids and ethanol. Next, we examine the role of 5-HT receptors in impulsivity, a core behavior that contributes to the vulnerability to addiction and relapse. Finally, we discuss evidence for serotonergic dysregulation in comorbid mood and addictive disorders and suggest novel serotonergic targets for the treatment of addiction and the prevention of drug relapse.

Involvement of 5-HT2A receptors in the serotonin (5-HT) syndrome caused by excessive 5-HT efflux in rat brain

Previous studies have demonstrated that serotonin (5-HT) syndromes, particularly for the malignant cases, can be alleviated by ice water mists, cooling blankets and many other external cooling measures. In this study, we tested the hypothesis that external cooling measures reduce the responsivity of 5-HT(2A) receptors to excessive 5-HT efflux, which may be a possible mechanism underlying the treatment of serotonin syndrome. To test this, rat experiments were carried out in the standard and cool ambient temperature (T(amb) ) by administration of the 5-HT precursor 5-hydroxy-L-tryptophan combined with the monoamine oxidase inhibitor clorgyline. The first set of experiments was to assess severity of the syndromes by measuring body temperature responses. Consistent with the hypothesis, we found that the syndrome was malignant at the standard T(amb) of 22°C but alleviated at 12 or 6°C, these results being similar to those in rats pre-treated with the 5-HT(2A) receptor antagonist ketanserin. The second set of experiments was to utilize microdialysis to determine the relationship between the syndrome severity and 5-HT levels at the above-mentioned T(amb) . We found that excessive 5-HT efflux consisted of primary and secondary components through two distinct mechanisms. Furthermore, the secondary component efflux, which can be ascribed to 5-HT(2A) receptor activation, was proportionally reduced at the cool T(amb) of 12 and 6°C. In conclusion, results of this study support the hypothesis that cooling T(amb) reduces the functional activity of 5-HT(2A) receptors, thus alleviating the malignant syndrome.

Acute concomitant effects of MDMA binge dosing on extracellular 5-HT, locomotion and body temperature and the long-term effect on novel object discrimination in rats

RATIONALE

3,4-methylenedioxymethamphetamine (MDMA, ecstasy) produces an acute release of 5-HT in the brain, together with increased locomotion and hyperthermia.

OBJECTIVE

This study examined whether the acute functional changes of locomotor activity and body temperature are related to enhanced 5-HT release induced by MDMA.

METHODS

We concomitantly measured changes in extraneuronal 5-HT by in vivo brain microdialysis and used radiotelemetry to measure locomotion and body temperature to establish whether any positive correlations occur between these three parameters. 'Binge-type' repeated administration of low doses of MDMA (3 and 6 mg/kg given at 2-h intervals three times) were given to provide drug exposure similar to that experienced by recreational drug users.

RESULTS

MDMA induced acute hyperactivity, changes in core body temperature (both hypothermia and hyperthermia) and elevation of hippocampal 5-HT overflow, all of which were dependent on the dose of MDMA administered. The change in locomotor activity and the magnitude of the hyperthermia appeared to be unrelated both to each other and to the magnitude of MDMA-induced 5-HT release. The study also found evidence of long-term disruption of novel object discrimination 2 weeks following "binge-type" repeated MDMA administration.

CONCLUSIONS

MDMA-induced 5-HT release in the brain was not responsible for either the hyperthermia or increased locomotor activity that occurred. Since neither dose schedule of MDMA induced a neurotoxic loss of brain 5-HT 2 weeks after its administration, the impairment of recognition memory found in novel object discrimination probably results from other long-term changes yet to be established.

Methylenedioxymethamphetamine ('Ecstasy')-induced immunosuppression: a cause for concern?

Methylenedioxymethamphetamine (MDMA; 'Ecstasy') is a ring-substituted amphetamine and a popular drug of abuse. In addition to ability to induce euphoria, MDMA abuse is associated with a range of acute and long-term hazardous effects. This paper is focused on once such adverse effect: its ability to negatively impact on functioning of the immune system. Research demonstrates that MDMA has immunosuppressive properties, with both innate and adaptive arms of the immune system being affected. The ability of MDMA to suppress innate immunity is indicated by impaired neutrophil phagocytosis and reduced production of dendritic cell/macrophage-derived pro-inflammatory cytokines including tumour necrosis factor-alpha, interleukin (IL)-1beta, IL-12 and IL-15. MDMA also suppresses innate IFN-gamma production, and considering the role of IFN-gamma in priming antigen-presenting cells, it is not surprising that MDMA reduces MHC class II expression on dendritic cells and macrophages, and inhibits co-stimulatory molecule expression. Paradoxically, studies demonstrate that MDMA elicits pro-inflammatory actions in the CNS by activating microglia, the resident innate immune cells in the brain. In terms of adaptive immunity, MDMA reduces circulating lymphocyte numbers, particularly CD4(+) T-cells; suppresses T-cell proliferation; and skews cytokine production in a Th(2) direction. For the most part, the immunosuppressive effects of MDMA cannot be attributed to a direct action of the drug on immune cells, but rather due to the release of endogenous immunomodulatory substances. In this regard, peripheral beta-adrenoceptors and cholinergic receptors have been shown to mediate some immunosuppressive effects of MDMA. Finally, we discuss emerging evidence indicating that MDMA-induced immunosuppression can translate into significant health risks for abusers.

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.

Enhanced responsivity of 5-HT(2A) receptors at warm ambient temperatures is responsible for the augmentation of the 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced hyperthermia

Warm ambient temperature facilitates hyperthermia and other neurotoxic responses elicited by psychogenic drugs such as MDMA and methamphetamine. However, little is known about the neural mechanism underlying such effects. In the present study, we tested the hypothesis that a warm ambient temperature may enhance the responsivity of 5-HT(2A) receptors in the central nervous system and thereafter cause an augmented response to 5-HT(₂A) receptor agonists. This hypothesis was tested by measuring changes in body-core temperature in response to the 5-HT(2A) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) administered at four different ambient temperature levels: 12 °C (cold), 22 °C (standard), 27 °C (thermoneutral zone) and 32 °C (warm). It was found that DOI only evoked a small increase in body-core temperature at the standard (22 °C) or thermoneutral ambient temperature (27 °C). In contrast, there was a large increase in body-core temperature when the experiments were conducted at the warmer ambient temperature (32 °C). Interestingly, the effect of DOI at the cold ambient temperature of 12 °C was significantly reduced. Moreover, the ambient temperature-dependent response to DOI was completely blocked by pretreatment with the 5-HT(₂A) receptor antagonist ketanserin. Taken together, these findings support the hypothesis that 5-HT(₂A) receptors may be responsible for some neurotoxic effects of psychogenic drugs in the central nervous system, the activity of which is functionally inhibited at cold but enhanced at warm ambient temperature in contrast to that at standard experimental conditions.

Drug seeking in response to a priming injection of MDMA in rats: relationship to initial sensitivity to self-administered MDMA and dorsal striatal dopamine

In laboratory animals, exposure to priming injections of 3,4-methylenedioxymethamphetamine (MDMA) produced drug seeking following extinction of MDMA self-administration. This study aimed to evaluate whether the magnitude of drug seeking was related to latency to acquisition of MDMA self-administration and increases in striatal dopamine, as measured by in-vivo microdialysis. Rats were given daily access to MDMA self-administration until they earned a total of 240 infusions (total intake of 165 mg/kg MDMA). Twelve of the 20 rats acquired self-administration within the temporal limits of the study and the latency to meet the criterion ranged from 9 d to 37 d. An experimenter-administered injection of MDMA (10.0 mg/kg i.p.) produced drug seeking in these rats, and the number of responses was significantly higher than responses produced by rats that failed to meet the criterion or by yoked control rats that received the drug passively. For rats that met the criterion, drug seeking was negatively correlated with the number of days to self-administer the criterion number of MDMA infusions and positively correlated with MDMA-produced dopamine in the dorsal striatum. Importantly, MDMA-produced dopamine overflow was greater for the rats that met the criterion. These findings suggest that drug seeking is influenced by initial sensitivity to the reinforcing effects of MDMA and to drug-produced increases in striatal dopamine.

A role for adenosine A(1) receptor blockade in the ability of caffeine to promote MDMA "Ecstasy"-induced striatal dopamine release

Co-administration of caffeine profoundly enhances the acute toxicity of 3,4 methylenedioxymethamphetamine (MDMA) in rats. The aim of this study was to determine the ability of caffeine to impact upon MDMA-induced dopamine release in superfused brain tissue slices as a contributing factor to this drug interaction. MDMA (100 and 300μM) induced a dose-dependent increase in dopamine release in striatal and hypothalamic tissue slices preloaded with [(3)H] dopamine (1μM). Caffeine (100μM) also induced dopamine release in the striatum and hypothalamus, albeit to a much lesser extent than MDMA. When striatal tissue slices were superfused with MDMA (30μM) in combination with caffeine (30μM), caffeine enhanced MDMA-induced dopamine release, provoking a greater response than that obtained following either caffeine or MDMA applications alone. The synergistic effects in the striatum were not observed in hypothalamic slices. As adenosine A(1) receptors are, one of the main pharmacological targets of caffeine, which are known to play an important role in the regulation of dopamine release, their role in the modulation of MDMA-induced dopamine release was investigated. 1μM 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a specific A(1) antagonist, like caffeine, enhanced MDMA-induced dopamine release from striatal slices while 1μM 2,chloro-N(6)-cyclopentyladenosine (CCPA), a selective adenosine A(1) receptor agonist, attenuated this. Treatment with either SCH 58261, a selective A(2A) receptor antagonist, or rolipram, a selective PDE-4 inhibitor, failed to reproduce a caffeine-like effect on MDMA-induced dopamine release. These results suggest that caffeine regulates MDMA-induced dopamine release in striatal tissue slices, via inhibition of adenosine A(1) receptors.

Effect of D1-like and D2-like receptor antagonists on methamphetamine and 3,4-methylenedioxymethamphetamine self-administration in rats

It has been suggested that activation of dopamine D1-like and D2-like receptors contribute equally to the maintenance of drug self-administration. This study compared the contribution of these receptor subtypes to 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (MA) self-administration. Effects of pretreatment with the D2-like receptor antagonist, eticlopride (0.0, 0.0125, 0.025 or 0.05 mg/kg, intraperitoneal), on responding maintained by several doses of MDMA (0.5, 1.0 and 2.0 mg/kg/infusion) and MA (0.05, 0.1 and 0.2 mg/kg/infusion) were determined. As we have published data showing the effects of the D1-like receptor antagonist, SCH23390 (0.0, 0.01 or 0.02 mg/kg, subcutaneous), on MDMA self-administration, effects of this dose range on the MA dose-response curve were determined. In our previous study, 0.02 mg/kg SCH23390 produced a rightward shift in the MDMA dose response curve, whereas in the present results, this dose decreased responding maintained by most doses of MA. Eticlopride increased the responding maintained by most doses of MDMA but failed to alter MA self-administration. The present results suggest that both D1-like and D2-like receptors contribute to the maintenance of MDMA self-administration, whereas MA self-administration was more sensitive to D1-like receptor blockade.

Tolerance to 3,4-methylenedioxymethamphetamine is associated with impaired serotonin release

Tolerance to the behavioural effects of 3,4-methylenedioxymethamphetamine (MDMA) following high dose exposure has been attributed to alterations in serotonergic systems. The present study aimed to determine whether decreased 5-HT release and/or 5-HT(2A/C) receptor desensitization might play a role in tolerance by measuring the response to selective ligands following MDMA exposure. To this end, the latency to nose poke and emerge from a hide box to an open field arena following administration of various ligands to MDMA pre-treated and control rats was measured. Acute exposure to MDMA (0.0-3.3 mg/kg), the 5-HT releasing stimulant fenfluramine (0.0-2.0 mg/kg) and the 5-HT(2) receptor agonist m-CPP (0.0-1.25 mg/kg) increased nose poke and emergence latency. Following administration of doses that produce 5-HT(2A) receptor-mediated behaviours, the 5-HT(2) receptor agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane failed to alter nose poke and emergence latency, suggesting a limited role of this receptor subtype in these behaviours. Activation of 5-HT(2C) receptors was implicated in the behavioural response to both MDMA and m-CPP since the increased emergence latency was dose-dependently attenuated by pre-treatment with the selective 5-HT(2C) receptor antagonist RS102221 (0.0-1.0 mg/kg). Tolerance to the behavioural effect of MDMA and fenfluramine but not m-CPP was produced by prior exposure to MDMA (10 mg/kg administered at two-hour intervals, total 40 mg/kg), and tissue levels of 5-HT and 5-HIAA were decreased. These findings suggest that tolerance to the increased nose poke and emergence latency produced by MDMA is due to impaired 5-HT release.

Endocrine and neurochemical effects of 3,4-methylenedioxymethamphetamine and its stereoisomers in rhesus monkeys

3,4-Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative that elicits complex biological effects in humans. One plausible mechanism for this phenomenon is that racemic MDMA is composed of two stereoisomers that exhibit qualitatively different pharmacological effects. In support of this, studies have shown that R(-)-MDMA tends to have hallucinogen-like effects, whereas S(+)-MDMA tends to have psychomotor stimulant-like effects. However, relatively little is known about whether these stereoisomers engender different endocrine and neurochemical effects. In the present study, the endocrine and neurochemical effects of each stereoisomer and the racemate were assessed in four rhesus monkeys after intravenous delivery at doses (1-3 mg/kg) that approximated voluntary self-administration by rhesus monkeys and human recreational users. Specifically, fluorescence-based enzyme-linked immunosorbent assay was used to assess plasma prolactin concentrations, and in vivo microdialysis was used to assess extracellular dopamine and serotonin concentrations in the dorsal striatum. R(-)-MDMA, but not S(+)-MDMA, significantly increased plasma prolactin levels and the effects of S,R(+/-)-MDMA were intermediate to each of its component stereoisomers. Although S(+)-MDMA did not alter prolactin levels, it did significantly increase extracellular serotonin concentrations. In addition, S(+)-MDMA, but not R(-)-MDMA, significantly increased dopamine concentrations. Furthermore, as in the prolactin experiment, the effects of the racemate were intermediate to each of the stereoisomers. These studies demonstrate the stereoisomers of MDMA engender qualitatively different endocrine and neurochemical effects, strengthening the inference that differences in these stereoisomers might be the mechanism producing the complex biological effects of the racemic mixture of MDMA in humans.

Behavioral, thermal and neurochemical effects of acute and chronic 3,4-methylenedioxymethamphetamine ("Ecstasy") self-administration

3,4-Methylenedioxymethamphetamine (MDMA) is a popular methamphetamine derivative associated with young adults and all-night dance parties. However, the enduring effects of MDMA at voluntary intake levels have not been extensively investigated. In this study, MDMA-influenced behaviors and core temperatures were assessed over the course of 20 daily MDMA self-administration sessions in rats. In vivo microdialysis techniques were used in a subsequent MDMA challenge test session to determine extracellular nucleus accumbens dopamine (NAcc DA) and serotonin (5-HT) levels in MDMA-experienced and naïve animals before and after a self-administered MDMA injection (3.0mg/kg, i.v.). During self-administration sessions, gradual and significant increases in MDMA intake and MDMA-stimulated locomotor activity were observed across sessions. Core temperature significantly decreased during initial MDMA sessions, but was unaltered by the last 10 sessions. In the MDMA challenge test, MDMA-naïve rats showed significantly higher NAcc 5-HT responses compared to MDMA-experienced rats, though MDMA experience did not affect the magnitude of NAcc DA response. The overall findings suggest that changes in MDMA-induced responses over the course of increasing levels of drug exposure may reflect the development of tolerance to a number of MDMA effects.

Glucose and corticosterone changes in developing and adult rats following exposure to (+/-)-3,4-methylendioxymethamphetamine or 5-methoxydiisopropyltryptamine

The use of the club drugs 3,4-methylenedioxymethamphetamine (MDMA) and 5-methoxy-n,n-diisopropyltryptamine (Foxy) is of growing concern, especially as many of the effects, particularly during development, are unknown. The effects of these drugs upon homeostasis may be important since both are known to stimulate the hypothalamic-pituitary-adrenal axis. The purpose of this experiment was to examine alterations in rats in corticosterone and glucose following an acute exposure to these drugs at different stages of development: preweaning, juvenile, and adulthood. Both MDMA and Foxy increased corticosterone levels significantly at all ages examined, while glucose was elevated at all stages except at the juvenile time point (postnatal day 28). For both measures, there were no differences between the sexes with either drug. The data indicate that an acute exposure to these drugs alters CORT and glucose levels, raising the possibility that these changes may have effects on behavioral and cognitive function, as we and others have previously demonstrated.

Effects of dose and route of administration on pharmacokinetics of (+ or -)-3,4-methylenedioxymethamphetamine in the rat

Based on animal data, there is speculation that (+ or -)-3,4-methylenedioxymethamphetamine (MDMA) is neurotoxic to humans. Extrapolation of MDMA findings from animals to humans requires assessment of pharmacokinetics in various species, and low-dose administration data from rats are lacking. In this study, we examine MDMA pharmacokinetics in rats given low (2 mg/kg) and high (10 mg/kg) doses of racemic MDMA via intraperitoneal, subcutaneous, and oral routes. Repeated blood specimens were collected from venous catheters, and plasma was assayed for MDMA and its metabolites, 4-hydroxy-3-methoxymethamphetamine (HMMA) and 3,4-methylenedioxyamphetamine (MDA), by gas chromatography-mass spectrometry. After 2 mg/kg, maximum MDMA concentrations (C(max)) were approximately 200 ng/ml for intraperitoneal and subcutaneous routes, but less for the oral route. MDMA plasma half-lives were <1 h for low-dose groups, whereas HMMA and MDA half-lives were >2 h. After 10 mg/kg, MDMA areas under the curve (AUCs) were 21-fold (intraperitoneal), 10-fold (subcutaneous), and 36-fold (oral) greater than those at 2 mg/kg. In contrast, HMMA AUC values in high-dose groups were <3-fold above those at 2 mg/kg. Several new findings emerge from this report of low-dose MDMA pharmacokinetics in rats. First, 2 mg/kg MDMA in rats can produce MDMA C(max) values similar to those in humans, perhaps explaining why both species discriminate 1.5 mg/kg MDMA in laboratory paradigms. Second, our data provide additional support for nonlinear kinetics of MDMA in rats, and, analogous to humans, this phenomenon appears to involve impaired drug metabolism. Finally, given key similarities between MDMA pharmacokinetics in rats and humans, data from rats may be clinically relevant when appropriate dosing conditions are used.

Differential changes in mesolimbic dopamine following contingent and non-contingent MDMA self-administration in mice

RATIONALE

There is evidence demonstrating changes in dopamine (DA) transmission in the nucleus accumbens (NAc) related to contingent versus non-contingent drug administration.

OBJECTIVES

The aim of this study was to evaluate basal and 3,4-methylenedioxymethamphetamine (MDMA)-stimulated DA levels in the NAc of mice that had previously received contingent and non-contingent infusions of MDMA. Contingent mice were trained to self-administer MDMA (0.125 mg/kg/infusion) in 2-h sessions for 10 days. Yoked mice received either MDMA at the same dose or saline. Forty-eight hours after the last MDMA or saline administration, DA levels were measured by in vivo microdialysis before and after an MDMA (10 mg/kg, i.p.) challenge. Binding of [(3)H]-mazindol and [(3)H]-citalopram was evaluated by autoradiography.

RESULTS

Animals receiving MDMA infusions showed significantly lower basal DA levels than the yoked saline group. A reduced activation of DA was observed following MDMA in contingent mice with respect to both yoked MDMA and saline mice. No significant alterations in DA transporter or serotonin transporter were observed in the three groups of mice.

CONCLUSIONS

These results suggest that prolonged exposure to MDMA in mice produces changes in basal DA levels after drug withdrawal and a decreased neurochemical response at the level of the mesolimbic DA reward pathway that is, in part, related to instrumental learning during self-administration.

Repeated exposure to MDMA provides neuroprotection against subsequent MDMA-induced serotonin depletion in brain

Repeated exposure to sub-lethal insults has been reported to result in neuroprotection against a subsequent deleterious insult. The purpose of this study was to evaluate whether repeated exposure (preconditioning) to a non-5-HT depleting dose of MDMA in adult rats provides neuroprotection against subsequent MDMA-induced 5-HT depletion. Treatment of rats with MDMA (10 mg/kg, ip every 2 h for 4 injections) resulted in a 50-65% depletion of 5-HT in the striatum, hippocampus and cortex, and these depletions were significantly attenuated in rats that received a preconditioning regimen of MDMA (10 mg/kg, ip daily for 4 days). The 5-HT depleting regimen of MDMA also resulted in a 40-80% reduction in 5-HT transporter immunoreactivity (SERT(ir)), and the reduction in SERT(ir) also was completely attenuated in MDMA-preconditioned animals. Preconditioning with MDMA (10 mg/kg, ip) daily for 4 days provided neuroprotection against methamphetamine-induced 5-HT depletion, but not dopamine depletion, in the striatum. Additional studies were conducted to exclude the possibility that alterations in MDMA pharmacokinetics or MDMA-induced hyperthermia in rats previously exposed to MDMA contribute towards neuroprotection. During the administration of the 5-HT depleting regimen of MDMA, there was no difference in the extracellular concentration of the drug in the striatum of rats that had received 4 prior, daily injections of vehicle or MDMA. Moreover, there was no difference in the hyperthermic response to the 5-HT depleting regimen of MDMA in rats that had earlier received 4 daily injections of vehicle or MDMA. Furthermore, hyperthermia induced by MDMA during preconditioning appears not to contribute towards neuroprotection, inasmuch as preconditioning with MDMA at a low ambient temperature at which hyperthermia was absent did not alter the neuroprotection provided by the preconditioning regimen. Thus, prior exposure to MDMA affords protection against the long-term depletion of brain 5-HT produced by subsequent MDMA administration. The mechanisms underlying preconditioning-induced neuroprotection for MDMA remain to be determined.

Neural and cardiac toxicities associated with 3,4-methylenedioxymethamphetamine (MDMA)

(+/-)-3,4-Methylenedioxymethamphetamine (MDMA) is a commonly abused illicit drug which affects multiple organ systems. In animals, high-dose administration of MDMA produces deficits in serotonin (5-HT) neurons (e.g., depletion of forebrain 5-HT) that have been viewed as neurotoxicity. Recent data implicate MDMA in the development of valvular heart disease (VHD). The present paper reviews several issues related to MDMA-associated neural and cardiac toxicities. The hypothesis of MDMA neurotoxicity in rats is evaluated in terms of the effects of MDMA on monoamine neurons, the use of scaling methods to extrapolate MDMA doses across species, and functional consequences of MDMA exposure. A potential treatment regimen (l-5-hydroxytryptophan plus carbidopa) for MDMA-associated neural deficits is discussed. The pathogenesis of MDMA-associated VHD is reviewed with specific reference to the role of valvular 5-HT(2B) receptors. We conclude that pharmacological effects of MDMA occur at the same doses in rats and humans. High doses of MDMA that produce 5-HT depletions in rats are associated with tolerance and impaired 5-HT release. Doses of MDMA that fail to deplete 5-HT in rats can cause persistent behavioral dysfunction, suggesting even moderate doses may pose risks. Finally, the MDMA metabolite, 3,4-methylenedioxyamphetamine (MDA), is a potent 5-HT(2B) agonist which could contribute to the increased risk of VHD observed in heavy MDMA users.

(+/-)-3,4-Methylenedioxymethamphetamine treatment in adult rats impairs path integration learning: a comparison of single vs once per week treatment for 5 weeks

3,4-Methlylenedioxymethamphetamine (MDMA) administration (4 x 15 mg/kg) on a single day has been shown to cause path integration deficits in rats. While most animal experiments focus on single binge-type models of MDMA use, many MDMA users take the drug on a recurring basis. The purpose of this study was to compare the effects of repeated single-day treatments with MDMA (4 x 15 mg/kg) once weekly for 5 weeks to animals that only received MDMA on week 5 and saline on weeks 1-4. In animals treated with MDMA for 5 weeks, there was an increase in time spent in the open area of the elevated zero maze suggesting a decrease in anxiety or increase in impulsivity compared to the animals given MDMA for 1 week and saline treated controls. Regardless of dosing regimen, MDMA treatment produced path integration deficits as evidenced by an increase in latency to find the goal in the Cincinnati water maze. Animals treated with MDMA also showed a transient hypoactivity that was not present when the animals were re-tested at the end of cognitive testing. In addition, both MDMA-treated groups showed comparable hyperactive responses to a later methamphetamine challenge. No differences were observed in spatial learning in the Morris water maze during acquisition or reversal but MDMA-related deficits were seen on reduced platform-size trials. Taken together, the data show that a single-day regimen of MDMA induces deficits similar to that of multiple weekly treatments.