Reinforcing effects of MDMA ("ecstasy") in drug-naive and cocaine-trained rats

Effects of “Legal X” Piperazine Analogs on Dopamine and Serotonin Release in Rat Brain

3,4-Methylenedioxymethamphetamine (MDMA) is a popular illicit drug that evokes transporter-mediated release of serotonin (5-HT) and dopamine (DA) from nerve cells. Recently, drug users have ingested combinations of the piperazine analogs, 1-benzylpiperazine (BZP) and 1-(m-trifluoromethylphenyl)piperazine (TFMPP), in an attempt to mimic the subjective effects of MDMA. In the present study, we compared neurochemical effects of MDMA, BZP, and TFMPP in rat brain. The ability of MDMA, BZP, and TFMPP to stimulate efflux of [3H]5-HT and [3H]MPP+ (a DA transporter substrate) was determined in vitro using release assays in synaptosomes. The ability of these drugs to increase extracellular 5-HT and DA in vivo was assessed using intracranial microdialysis in nucleus accumbens. MDMA stimulated transporter-mediated release of 5-HT (EC50 = 58 nM) and MPP+ (EC50 = 119 nM). BZP was a selective releaser of MPP+ (EC50 = 175 nM), whereas TFMPP was a selective releaser of 5-HT (EC50 = 121 nM). MDMA injections (1 and 3 mg/kg, i.v.) increased dialysate 5-HT and DA in a dose-related manner, but actions on 5-HT were predominant. BZP (3 and 10 mg/kg, i.v.) elevated dialysate DA and 5-HT, while TFMPP (3 and 10 mg/kg, i.v.) elevated only 5-HT. The coadministration of BZP plus TFMPP (BZP/TFMPP) produced marked elevations in extracellular 5-HT and DA that mirrored the effects of MDMA. At the high dose of BZP/TFMPP (10 mg/kg, i.v.), the rise in dialysate DA exceeded the summed effects of the drugs alone. Our results support the hypothesis that the BZP/TFMPP combination mimics the neurochemical mechanism of MDMA, providing a basis for recreational use of these agents. Additionally, the findings suggest possible drug-drug synergism when piperazine drugs are coadministered at high doses.

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 rewarding properties of MDMA are preserved in mice lacking mu-opioid receptors

The involvement of mu-opioid receptors in the rewarding properties of MDMA was explored in mu-opioid receptor knockout mice using the conditioning place preference paradigm. The associated release of dopamine in the nucleus accumbens was investigated by in vivo microdialysis. A significant rewarding effect of MDMA (10 mg/kg, i.p.) was observed in both wild-type and mu-opioid receptor knockout mice. MDMA (10 mg/kg, i.p.) also induced similar increases in dopamine and decreases in 3,4-dihydroxyphenylacetic acid and homovanillic acid in the nucleus accumbens dialysates of both wild-type and mu-opioid receptor knockout mice. No significant differences in basal levels of dopamine, 3,4-dihydroxyphenylacetic or homovanillic acids between wild-type and mu-opioid receptor knockout mice were observed. In summary, the present results suggest that, in contrast to what has been reported for other drugs of abuse such as opioids, ethanol, nicotine and Delta(9)-tetrahydrocannabinol, mu-opioid receptors do not play a major role in the rewarding properties of MDMA. These differences could be due to distinct mechanisms controlling dopamine release in the nucleus accumbens and suggest that the effects of MDMA on dopaminergic neurons are independent of micro -opioid receptors.

Methylenedioxymethamphetamine (MDMA, 'ecstasy') serves as a robust positive reinforcer in a rat runway procedure

Although 'ecstasy' (3,4-methylenedioxymethamphetamine, MDMA) is, after marijuana, the second most prevalent illegal drug of abuse in European adolescents, animal experimental evidence of MDMA's reinforcing effect has remained scarce, particularly in the rodent model, raising questions about the robustness of MDMA's reinforcing effect under controlled laboratory conditions. In the present rat runway study, Sprague-Dawley and Long-Evans rats were given the opportunity to run for intravenous injections of saline or MDMA (1 mg/kg). MDMA significantly decreased runtimes in both rat strains. Thus, MDMA's positive reinforcing effect can be demonstrated not only across rat strains but also across operant conditioning paradigms. These findings should reassure the drug abuse research community that the investigation of MDMA's reinforcing effect in the inexpensive and widely used rodent model is indeed feasible.

Effect of SCH 23390 on (±)-3,4-methylenedioxymethamphetamine hyperactivity and self-administration in rats

Recently, we demonstrated that (+/-)-3,4-methylenedioxymethamphetamine (MDMA; ecstasy) was reliably and dose-dependently self-administered by previously drug-naïve laboratory rats. The neurochemical basis of MDMA self-administration has not, however, been extensively studied. The present study investigated the role of dopamine in MDMA self-administration and hyperactivity. Pretreatment with the D1-like antagonist, SCH 23390 (0.01-0.08 mg/kg) produced a dose-dependent attenuation of MDMA (20.0 mg/kg)-produced hyperactivity. In self-administration tests, the baseline rate of responding maintained by intravenous infusions varied inversely with MDMA dose; as the dose available was changed, responding also changed so that about 10.0 mg/kg MDMA was self-administered during each daily 2-h session. Pretreatment with SCH 23390 (0.02 mg/kg) produced a rightward shift in the MDMA dose-response curve. These findings suggest that MDMA self-administration, like self-administration of other drugs of abuse, is dependent on the activation of dopaminergic substrates.

The effects of MDMA pretreatment on the behavioural effects of other drugs of abuse in the rat elevated plus-maze test

Few preclinical studies have found long-term behavioural consequences of the serotonergic neurotoxicity produced by 3,4-methylenedioxymethamphetamine (MDMA). This study investigated whether pretreatment with MDMA altered the behavioural effects of other drugs of abuse. Adult male Lister hooded rats (n=10/group) were pretreated with 10 mg/kg MDMA or 1 ml/kg saline vehicle intraperitoneally every 2 h for 6 h. Fourteen days later, the behavioural effects of d-amphetamine (2 mg/kg), cocaine (10 mg/kg), ethanol (2.0 g/kg), heroin (0.5 mg/kg), or MDMA (10 mg/kg) were assessed in the elevated plus-maze test. MDMA pretreatment produced approximately 20-25% decrease in hippocampal 5-HT and 5-HIAA concentrations, and [(3)H]paroxetine binding when analysed 2 weeks later. Despite inducing neurotoxicity, this regimen had no effect upon the plus-maze behaviour induced by ethanol, heroin, and MDMA. Acutely, and independent of neurotoxic pretreatment, MDMA produced a clear anxiogenic-like behavioural profile with a reduction of open arm entries and suppression of explorative behaviours. Despite being acutely anxiogenic, pretreatment with a neurotoxic regimen of MDMA has little effect on the anxiety-related effects of other drugs of abuse. It is possible that extended time points would produce significant changes, although the available evidence suggests that the plus-maze may not be a suitable model for detection of behavioural dysfunction after neurotoxic MDMA.

Heat increases 3,4-methylenedioxymethamphetamine self-administration and social effects in rats

3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") is a drug frequently used under hot conditions in nightclubs. In rats tested in the social interaction paradigm, greater prosocial effects of MDMA (5.0 mg/kg) were seen at a hot temperature (30 degrees C) relative to normal laboratory temperature (21 degrees C). In the intravenous drug self-administration paradigm, hot temperature (30 degrees C) increased the number of MDMA infusions (0.1, 0.3 or 1.0 mg/kg/infusion) self-administered by rats. Hot temperatures thus appear to affect both the social and reinforcing effects of MDMA.

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

Reinforcing effect of subcutaneous morphine in a modified Ettenberg runway

Alley running has been successfully used as an operant to demonstrate both the positive and negative reinforcing effect of intravenously administered drugs of abuse in a bona fide operant conditioning paradigm, the Ettenberg runway, in which confounding drug effects on motor performance and drug accumulation are avoided. While Ettenberg and colleagues focus on the intravenous route of drug administration, we tested the practicability of the subcutaneous route of administration in this runway paradigm in Sprague Dawley rats, using morphine as the investigated drug of abuse. We also modified the Ettenberg runway, most notably in that either food (sweetened condensed milk), no food, morphine, or saline was presented outside the runway in a separate cage. This made shaping, i.e., the initial presentation of a food reinforcer within the runway, necessary to establish responding. The manipulations necessary to administer subcutaneous (sc) injections were well tolerated by over 90% of the tested rats (n = 93). However, sc injections increased runtimes to the experimenter cutoff of 60 s within 20 once-daily sessions. Because of strong experimenter effects, all morphine doses or saline had to be adminstered blind. Under these experimenter-blind conditions, 0.1 and 1 mg/kg subcutaneous morphine proved to be reinforcing in that these doses significantly slowed down the gradual increase in runtimes imposed upon by the sc injection procedure. Thus, morphine can be demonstrated to be a positive reinforcer in a modified Ettenberg runway even when given subcutaneously. This effect, however, is eventually overcome by the negative reinforcing effect of subjecting the animals to sc injection procedure.

Intravenous administration of ecstasy (3,4-methylendioxymethamphetamine) enhances cortical and striatal acetylcholine release in vivo

The effect of intravenous administration of 3,4-methylendioxymethamphetamine (MDMA), in a range of doses (0.32-3.2 mg/kg) that have been shown to maintain self-administration behaviour in rats, on in vivo acetylcholine release from rat prefrontal cortex and dorsal striatum was studied by means of microdialysis with vertical concentric probes. Intravenous administration of MDMA dose-dependently increased basal acetylcholine release from the prefrontal cortex to 57+/-21%, 98+/-20%, 102+/-7% and 141+/-14% above baseline, at doses of 0.32, 0.64, 1.0 and 3.2 mg/kg, respectively. MDMA also stimulated striatal acetylcholine release at the dose of 3.2 mg/kg i.v. (the maximal increase being 32+/-3% above baseline) while at the dose of 1 mg/kg i.v., MDMA failed to affect basal acetylcholine output. Administration of MDMA also dose-dependently stimulated behaviour. The results of the present study show that MDMA affects measures of central cholinergic neurotransmission in vivo and suggest that at least some of the psychomotor stimulant actions of MDMA might be positively coupled with an increase in prefrontal cortical and striatal acetylcholine release.