M. Isabel Colado

The Pharmacology and Clinical Pharmacology of 3,4-Methylenedioxymethamphetamine (MDMA, “Ecstasy”)

The amphetamine derivative (±)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a popular recreational drug among young people, particularly those involved in the dance culture. MDMA produces an acute, rapid enhancement in the release of both serotonin (5-HT) and dopamine from nerve endings in the brains of experimental animals. It produces increased locomotor activity and the serotonin behavioral syndrome in rats. Crucially, it produces dose-dependent hyperthermia that is potentially fatal in rodents, primates, and humans. Some recovery of 5-HT stores can be seen within 24 h of MDMA administration. However, cerebral 5-HT concentrations then decline due to specific neurotoxic damage to 5-HT nerve endings in the forebrain. This neurodegeneration, which has been demonstrated both biochemically and histologically, lasts for months in rats and years in primates. In general, other neurotransmitters appear unaffected. In contrast, MDMA produces a selective long-term loss of dopamine nerve endings in mice. Studies on the mechanisms involved in the neurotoxicity in both rats and mice implicate the formation of tissue-damaging free radicals. Increased free radical formation may result from the further breakdown of MDMA metabolic products. Evidence for the occurrence of MDMA-induced neurotoxic damage in human users remains equivocal, although some biochemical and functional data suggest that damage may occur in the brains of heavy users. There is also some evidence for long-term physiological and psychological changes occurring in human recreational users. However, such evidence is complicated by the lack of knowledge of doses ingested and the fact that many subjects studied are or have been poly-drug users.

The pharmacology of the acute hyperthermic response that follows administration of 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') to rats

The pharmacology of the acute hyperthermia that follows 3,4‐methylenedioxymethamphetamine (MDMA, ‘ecstasy’) administration to rats has been investigated. MDMA (12.5 mg kg−1 i.p.) produced acute hyperthermia (measured rectally). The tail skin temperature did not increase, suggesting that MDMA may impair heat dissipation. Pretreatment with the 5‐HT1/2 antagonist methysergide (10 mg kg−1), the 5‐HT2A antagonist MDL 100,907 (0.1 mg kg−1) or the 5‐HT2C antagonist SB 242084 (3 mg kg−1) failed to alter the hyperthermia. The 5‐HT2 antagonist ritanserin (1 mg kg−1) was without effect, but MDL 11,939 (5 mg kg−1) blocked the hyperthermia, possibly because of activity at non‐serotonergic receptors. The 5‐HT uptake inhibitor zimeldine (10 mg kg−1) had no effect on MDMA‐induced hyperthermia. The uptake inhibitor fluoxetine (10 mg kg−1) markedly attenuated the MDMA‐induced increase in hippocampal extracellular 5‐HT, also without altering hyperthermia. The dopamine D2 antagonist remoxipride (10 mg kg−1) did not alter MDMA‐induced hyperthermia, but the D1 antagonist SCH 23390 (0.3 – 2.0 mg kg−1) dose‐dependently antagonized it. The dopamine uptake inhibitor GBR 12909 (10 mg kg−1) did not alter the hyperthermic response and microdialysis demonstrated that it did not inhibit MDMA‐induced striatal dopamine release. These results demonstrate that in vivo MDMA‐induced 5‐HT release is inhibited by 5‐HT uptake inhibitors, but MDMA‐induced dopamine release may not be altered by a dopamine uptake inhibitor. It is suggested that MDMA‐induced hyperthermia results not from MDMA‐induced 5‐HT release, but rather from the increased release of dopamine that acts at D1 receptors. This has implications for the clinical treatment of MDMA‐induced hyperthermia.

Acute and long-term effects of MDMA on cerebral dopamine biochemistry and function

Rationale and objectivesThe majority of experimental and clinical studies on the pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) tend to focus on its action on 5-HT biochemistry and function. However, there is considerable evidence for MDMA having marked acute effects on dopamine release. Furthermore, while MDMA produces long-term effects on 5-HT neurones in most species examined, in mice its long-term effects appear to be restricted to the dopamine system. The objective of this review is to examine the actions of MDMA on dopamine biochemistry and function in mice, rats, guinea pigs, monkeys and humans.Results and discussionMDMA appears to produce a major release of dopamine from its nerve endings in all species investigated. This release plays a significant role in the expression of many of the behaviours that occur, including behavioural changes, alterations of the mental state in humans and the potentially life-threatening hyperthermia that can occur. While MDMA appears to be a selective 5-HT neurotoxin in most species examined (rats, guinea pigs and primates), it is a selective dopamine neurotoxin in mice. Selectivity may be a consequence of what neurotoxic metabolites are produced (which may depend on dosing schedules), their selectivity for monoamine nerve endings, or the endogenous free radical trapping ability of specific nerve endings, or both. We suggest more focus be made on the actions of MDMA on dopamine neurochemistry and function to provide a better understanding of the acute and long-term consequences of using this popular recreational drug.

A study of the mechanisms involved in the neurotoxic action of 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') on dopamine neurones in mouse brain

Administration of 3,4‐methylenedioxymethamphetamine (MDMA, ‘ecstasy’) to mice produces acute hyperthermia and long‐term degeneration of striatal dopamine nerve terminals. Attenuation of the hyperthermia decreases the neurodegeneration. We have investigated the mechanisms involved in producing the neurotoxic loss of striatal dopamine. MDMA produced a dose‐dependent loss in striatal dopamine concentration 7 days later with 3 doses of 25 mg kg−1 (3 h apart) producing a 70% loss. Pretreatment 30 min before each MDMA dose with either of the N‐methyl‐D‐aspartate antagonists AR‐R15896AR (20, 5, 5 mg kg−1) or MK‐801 (0.5 mg kg−1×3) failed to provide neuroprotection. Pretreatment with clomethiazole (50 mg kg−1×3) was similarly ineffective in protecting against MDMA‐induced dopamine loss. The free radical trapping compound PBN (150 mg kg−1×3) was neuroprotective, but it proved impossible to separate neuroprotection from a hypothermic effect on body temperature. Pretreatment with the nitric oxide synthase (NOS) inhibitor 7‐NI (50 mg kg−1×3) produced neuroprotection, but also significant hypothermia. Two other NOS inhibitors, S‐methyl‐L‐thiocitrulline (10 mg kg−1×3) and AR‐R17477AR (5 mg kg−1×3), provided significant neuroprotection and had little effect on MDMA‐induced hyperthermia. MDMA (20 mg kg−1) increased 2,3‐dihydroxybenzoic acid formation from salicylic acid perfused through a microdialysis tube implanted in the striatum, indicating increased free radical formation. This increase was prevented by AR‐R17477AR administration. Since AR‐R17477AR was also found to have no radical trapping activity this result suggests that MDMA‐induced neurotoxicity results from MDMA or dopamine metabolites producing radicals that combine with NO to form tissue‐damaging peroxynitrites.

Neuroprotective effect of aspirin by inhibition of glutamate release after permanent focal cerebral ischaemia in rats.

Aspirin reduces the size of infarcts after ischaemic stroke. Although this fact has been attributed to its anti‐platelet actions, direct neuroprotective effects have also been reported. We have recently demonstrated that aspirin is neuroprotective by inhibiting glutamate release in ‘in vitro’ models of brain ischaemia, via an increase in ATP production. The present study was designed to determine whether the inhibition of glutamate release induced by aspirin might be protective in a whole‐animal model of permanent focal brain ischaemia. Focal brain ischaemia was produced in male adult Fischer rats by occluding both the common carotid and middle cerebral arteries. Central and serum glutamate levels were determined at fixed intervals after occlusion. The animals were then killed and infarct volume was measured. Aspirin (30 mg/kg i.p. administered 2 h before the occlusion) produced a significant reduction in infarct volume, an effect that correlated with the inhibition caused by aspirin on ischaemia‐induced increase in brain and serum glutamate concentrations after the onset of the ischaemia. Aspirin also inhibited ischaemia‐induced decrease in brain ATP levels. Our present findings show a novel mechanism for the neuroprotective effects of aspirin, which takes place at concentrations in the anti‐aggregant–analgesic range, useful in the management of patients with risk of ischaemic events.

Dopamine D2-receptor knockout mice are protected against dopaminergic neurotoxicity induced by methamphetamine or MDMA

Methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA), amphetamine derivatives widely used as recreational drugs, induce similar neurotoxic effects in mice, including a marked loss of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum. Although the role of dopamine in these neurotoxic effects is well established and pharmacological studies suggest involvement of a dopamine D2-like receptor, the specific dopamine receptor subtype involved has not been determined. In this study, we used dopamine D2 receptor knock-out mice (D2R(-/-)) to determine whether D2R is involved in METH- and MDMA-induced hyperthermia and neurotoxicity. In wild type animals, both drugs induced marked hyperthermia, decreased striatal dopamine content and TH- and DAT-immunoreactivity and increased striatal GFAP and Mac-1 expression as well as iNOS and interleukin 15 at 1 and 7days after drug exposure. They also caused dopaminergic cell loss in the SNpc. Inactivation of D2R blocked all these effects. Remarkably, D2R inactivation prevented METH-induced loss of dopaminergic neurons in the SNpc. In addition, striatal dopamine overflow, measured by fast scan cyclic voltammetry in the presence of METH, was significantly reduced in D2R(-/-) mice. Pre-treatment with reserpine indicated that the neuroprotective effect of D2R inactivation cannot be explained solely by its ability to prevent METH-induced hyperthermia: reserpine lowered body temperature in both genotypes, and potentiated METH toxicity in WT, but not D2R(-/-) mice. Our results demonstrate that the D2R is necessary for METH and MDMA neurotoxicity and that the neuroprotective effect of D2R inactivation is independent of its effect on body temperature.

Studies, using in vivo microdialysis, on the effect of the dopamine uptake inhibitor GBR 12909 on 3,4-methylenedioxymethamphetamine ('ecstasy')-induced dopamine release and free radical formation in the mouse striatum

The present study examined the mechanisms by which 3,4‐methylenedioxymethamphetamine (MDMA) produces long‐term neurotoxicity of striatal dopamine neurones in mice and the protective action of the dopamine uptake inhibitor GBR 12909. MDMA (30 mg/kg, i.p.), given three times at 3‐h intervals, produced a rapid increase in striatal dopamine release measured by in vivo microdialysis (maximum increase to 380 ± 64% of baseline). This increase was enhanced to 576 ± 109% of baseline by GBR 12909 (10 mg/kg, i.p.) administered 30 min before each dose of MDMA, supporting the contention that MDMA enters the terminal by diffusion and not via the dopamine uptake site. This, in addition to the fact that perfusion of the probe with a low Ca2+ medium inhibited the MDMA‐induced increase in extracellular dopamine, indicates that the neurotransmitter may be released by a Ca2+‐dependent mechanism not related to the dopamine transporter. MDMA (30 mg/kg × 3) increased the formation of 2,3‐dihydroxybenzoic acid (2,3‐DHBA) from salicylic acid perfused through a probe implanted in the striatum, indicating that MDMA increased free radical formation. GBR 12909 pre‐treatment attenuated the MDMA‐induced increase in 2,3‐DHBA formation by approximately 50%, but had no significant intrinsic radical trapping activity. MDMA administration increased lipid peroxidation in striatal synaptosomes, an effect reduced by approximately 60% by GBR 12909 pre‐treatment. GBR 12909 did not modify the MDMA‐induced changes in body temperature. These data suggest that MDMA‐induced toxicity of dopamine neurones in mice results from free radical formation which in turn induces an oxidative stress process. The data also indicate that the free radical formation is probably not associated with the MDMA‐induced dopamine release and that MDMA does not induce dopamine release via an action at the dopamine transporter.

3,4‐Methylenedioxymethamphetamine increases interleukin‐1β levels and activates microglia in rat brain: studies on the relationship with acute hyperthermia and 5‐HT depletion

3,4‐Methylenedioxymethamphetamine (MDMA) administration to rats produces acute hyperthermia and 5‐HT release. Interleukin‐1β (IL‐1β) is a pro‐inflammatory pyrogen produced by activated microglia in the brain. We examined the effect of a neurotoxic dose of MDMA on IL‐1β concentration and glial activation and their relationship with acute hyperthermia and 5‐HT depletion. MDMA, given to rats housed at 22°C, increased IL‐1β levels in hypothalamus and cortex from 1 to 6 h and [3H]‐(1‐(2‐chlorophenyl)‐N‐methyl‐N‐(1‐methylpropyl)3‐isoquinolinecarboxamide) binding between 3 and 48 h. Increased immunoreactivity to OX‐42 was also detected. Rats became hyperthermic immediately after MDMA and up to at least 12 h later. The IL‐1 receptor antagonist did not modify MDMA‐induced hyperthermia indicating that IL‐1β release is a consequence, not the cause, of the rise in body temperature. When MDMA was given to rats housed at 4°C, hyperthermia was abolished and the IL‐1β increase significantly reduced. The MDMA‐induced acute 5‐HT depletion was prevented by fluoxetine coadministration but the IL‐1β increase and hyperthermia were unaffected. Therefore, the rise in IL‐1β is not related to the acute 5‐HT release but is linked to the hyperthermia. Contrary to IL‐1β levels, microglial activation is not significantly modified when hyperthermia is prevented, suggesting that it might be a process not dependent on the hyperthermic response induced by MDMA.

Elevation of Ambient Room Temperature has Differential Effects on MDMA-Induced 5-HT and Dopamine Release in Striatum and Nucleus Accumbens of Rats

3,4-Methylenedioxymethamphetamine (MDMA) produces acute dopamine and 5-HT release in rat brain and a hyperthermic response, which is dependent on the ambient room temperature in which the animal is housed. We examined the effect of ambient room temperature (20 and 30°C) on MDMA-induced dopamine and 5-HT efflux in the striatum and shell of nucleus accumbens (NAc) of freely moving rats by using microdialysis. Locomotor activity and rectal temperature were also evaluated. In the NAc, MDMA (2.5 or 5 mg/kg, i.p.) produced a substantial increase in extracellular dopamine, which was more marked at 30°C. 5-HT release was also increased by MDMA given at 30°C. In contrast, MDMA-induced extracellular dopamine and 5-HT increases in the striatum were unaffected by ambient temperature. At 20°C room temperature, MDMA did not modify the rectal temperature but at 30°C it produced a rapid and sustained hyperthermia. MDMA at 20°C room temperature produced a two-fold increase in activity compared with saline-treated controls. The MDMA-induced increase in locomotor activity was more marked at 30°C due to a decrease in the activity of the saline-treated controls at this high ambient temperature. These results show that high ambient temperature enhances MDMA-induced locomotor activity and monoamine release in the shell of NAc, a region involved in the incentive motivational properties of drugs of abuse, and suggest that the rewarding effects of MDMA may be more pronounced at high ambient temperature.

Studies on the effect of MDMA (‘ecstasy') on the body temperature of rats housed at different ambient room temperatures

3,4‐Methylenedioxymethamphetamine (MDMA, ‘ecstasy’) administration to rats produces hyperthermia if they are housed in normal or warm ambient room temperature (Ta) conditions (20°C), but hypothermia when in cool conditions (Ta17°C). We have now investigated some of the mechanisms involved. MDMA (5 mg kg−1 i.p.) produced a rapid decrease in rectal temperature in rats at Ta 15°C. This response was blocked by pretreatment with the dopamine D2 receptor antagonist remoxipride (10 mg kg−1 i.p.), but unaltered by pretreatment with the D1 antagonist SCH23390 (1.1 mg kg−1 i.p.). MDMA (5 mg kg−1) did not alter the tail temperature of rats at Ta 15°C, but decreased the tail temperature of rats at Ta 30°C. A neurotoxic dose of MDMA (three doses of 5 mg kg−1 given 3 h apart) decreased cortical and hippocampal 5‐HT content by approximately 30% 7 days later. This lesion did not influence the rise in tail temperature when rats were moved from Ta 20°C to 30°C compared to nonlesioned controls, but did result in a lower tail temperature than that of controls when they were returned to Ta 24°C. Acute administration of MDMA (5 mg kg−1) to MDMA‐lesioned rats produced a sustained decrease in tail temperature in rats housed at Ta 30°C compared to nonlesioned controls. These data suggest that the thermoregulatory problems previously observed in MDMA‐lesioned rats housed at Ta 30°C result, partially, from their inability to lose heat by vasodilation of the tail, a major heat‐loss organ in this species.