M.I. Colado

In vivo evidence for free radical involvement in the degeneration of rat brain 5‐HT following administration of MDMA (‘ecstasy’) and p‐chloroamphetamine but not the degeneration following fenfluramine

Administration of 3,4‐methylenedioxymethamphetamine (MDMA or ‘ecstasy’) to several species results in a long lasting neurotoxic degeneration of 5‐hydroxytryptaminergic neurones in several regions of the brain. We have now investigated whether this degeneration is likely to be the result of free radical‐induced damage. Free radical formation can be assessed by measuring the formation of 2,3‐ and 2,5‐dihydroxybenzoic acid (2,3‐DHBA and 2,5‐DHBA) from salicylic acid. An existing method involving implantation of a probe into the hippocampus and in vivo microdialysis was modified and validated. Administration of MDMA (15 mg kg−1, i.p.) to Dark Agouti (DA) rats increased the formation of 2,3‐DHBA (but not 2,5‐DHBA) for at least 6 h. Seven days after this dose of MDMA, the concentration of 5‐hydroxytryptamine (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) was reduced by over 50% in hippocampus, cortex and striatum, reflecting neurotoxic damage. There was no change in the concentration of dopamine or 3,4‐dihydroxyphenylacetic acid (DOPAC) in the striatum. p‐Chloroamphetamine (PCA), another compound which produces a neurotoxic loss of cerebral 5‐HT content, when given at a dose of 5 mg kg−1 also significantly increased the formation of 2,3‐DHBA (but not 2,5‐DHBA) in the dialysate for over 4.5 h. post‐injection starting 2 h after treatment. In contrast, fenfluramine administration (15 mg kg−1, i.p.) failed to increase the 2,3‐DHBA or 2,5‐DHBA concentration in the dialysate. A single fenfluramine injection nevertheless also markedly decreased the concentration of 5‐HT and 5‐HIAA in the hippocampus, cortex and striatum seven days later. When rats pretreated with fenfluramine (15 mg kg−1, i.p.) seven days earlier were given MDMA (15 mg kg−1, i.p.) no increase in 2,3‐DHBA was seen in the dialysate from the hippocampal probe. This indicates that the increase in free radical formation following MDMA is occurring in 5‐HT neurones which have been damaged by the prior fenfluramine injection. Administration of the free radical scavenging agent α‐phenyl‐N‐tert‐butyl nitrone (PBN; 120 mg kg−1, i.p.) 10 min before and 120 min after an MDMA (15 mg kg−1, i.p.) injection prevented the acute rise in the 2,3‐DHBA concentration in the dialysate and attenuated by 30% the long term damage to hippocampal 5‐HT neurones (as indicated by a smaller MDMA‐induced decrease in both the concentration of 5‐HT and 5‐HIAA and also the binding of [3H]‐paroxetine). These data indicate that a major mechanism by which MDMA and PCA induce damage to 5‐hydroxytryptaminergic neurones in rat brain is by increasing the formation of free radicals. These probably result from the degradation of catechol and quinone metabolites of these substituted amphetamines. In contrast, fenfluramine induces damage by another mechanism not involving free radicals; a proposal supported by some of our earlier indirect studies. We suggest that these different modes of action render untenable the recent suggestion that MDMA will not be neurotoxic in humans because fenfluramine appears safe at clinical doses.

A study of the neurotoxic effect of MDMA ('ecstasy') on 5-HT neurones in the brains of mothers and neonates following administration of the drug during pregnancy

It is well established that 3,4‐methylenedioxymethamphetamine (MDMA or ‘ecstasy’) is neurotoxic and produces long term degeneration of cerebral 5‐hydroxytryptamine (5‐HT) nerve terminals in many species. Since MDMA is used extensively as a recreational drug by young people, it is being ingested by many women of child bearing age. We have therefore examined the effect of administering high doses of MDMA to rats during pregnancy on the cerebral content of both the dams and the neonates. MDMA (20 mg kg−1, s.c.) was injected twice daily on days 14–17 of the gestation period. The initial dose produced a marked hyperthermic response in the dam which was progressively attenuated in both peak height and area under the curve following further doses of the drug. The body weight of the dams decreased during the period of treatment. There was a modest decrease in litter size (−20%) of the MDMA‐treated dams. The concentration of 5‐HT and its metabolite 5‐HIAA was decreased by over 65% in the hippocampus and striatum and 40% in the cortex of the dams 1 week after parturition. In contrast, the content of 5‐HT and 5‐HIAA in the dorsal telencephalon of the pups of the MDMA‐treated dams was the same as that seen in tissue from pups born to control animals. Administration of MDMA (40 mg kg−1, s.c.) to adult rats increased thiobarbituric acid reacting substances (TBARS) in cortical tissue 3 h and 6 h later, indicating increased lipid peroxidation. No increase in TBARS was seen in the cortical tissue of 7–10 day neonates injected with this dose of MDMA 3 h or 6 h earlier. The data suggest that exposure to MDMA in utero during the maturation phase does not produce damage to 5‐HT nerve terminals in the foetal rat brain, in contrast to the damage seen in the brains of the mothers. This may be due to MDMA being metabolized to free radical producing entities in the adult brain but not in the immature brain or, alternatively, to more effective or more active free radical scavenging mechanisms being present in the immature brain.

The mechanisms involved in the long-lasting neuroprotective effect of fluoxetine against MDMA (‘ecstasy')-induced degeneration of 5-HT nerve endings in rat brain

It has been reported that co‐administration of fluoxetine with 3,4‐methylenedioxymethamphetamine (MDMA, ‘ecstasy’) prevents MDMA‐induced degeneration of 5‐HT nerve endings in rat brain. The mechanisms involved have now been investigated. MDMA (15 mg kg−1, i.p.) administration produced a neurotoxic loss of 5‐HT and 5‐hydroxyindoleacetic acid (5‐HIAA) in cortex, hippocampus and striatum and a reduction in cortical [3H]‐paroxetine binding 7 days later. Fluoxetine (10 mg kg−1, i.p., ×2, 60 min apart) administered concurrently with MDMA or given 2 and 4 days earlier provided complete protection, and significant protection when given 7 days earlier. Fluvoxamine (15 mg kg−1, i.p., ×2, 60 min apart) only produced neuroprotection when administered concurrently. Fluoxetine (10 mg kg−1, ×2) markedly increased the KD and reduced the Bmax of cortical [3H]‐paroxetine binding 2 and 4 days later. The Bmax was still decreased 7 days later, but the KD was unchanged. [3H]‐Paroxetine binding characteristics were unchanged 24 h after fluvoxamine (15 mg kg−1, ×2). A significant cerebral concentration of fluoxetine plus norfluoxetine was detected over the 7 days following fluoxetine administration. The fluvoxamine concentration had decreased markedly by 24 h. Pretreatment with fluoxetine (10 mg kg−1, ×2) failed to alter cerebral MDMA accumulation compared to saline pretreated controls. Neither fluoxetine or fluvoxamine altered MDMA‐induced acute hyperthermia. These data demonstrate that fluoxetine produces long‐lasting protection against MDMA‐induced neurodegeneration, an effect apparently related to the presence of the drug and its active metabolite inhibiting the 5‐HT transporter. Fluoxetine does not alter the metabolism of MDMA or its rate of cerebral accumulation.

Effect of GBR 12909 and fluoxetine on the acute and long term changes induced by MDMA ('ecstasy') on the 5-HT and dopamine concentrations in mouse brain

We examined the long term effect of 3,4 methylenedioxymethamphetamine (MDMA, 10, 20 and 30 mg/kg, i.p.) on the cerebral 5-hydroxytryptamine (5-HT) and dopamine content in Swiss Webster mice. Three injections of MDMA (20 or 30 mg/kg, i.p.) given 3 h apart produced a marked depletion in the striatal content of dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) 7 days later. None of the doses administered altered the concentration of 5-HT or its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in several brain areas. Pre-treatment with the dopamine uptake inhibitor GBR 12909 (10 mg/kg, i.p.), 30 min before each of the three MDMA (30 mg/kg, i.p.) injections, completely prevented the long term loss in the striatal catechol concentrations. However, GBR 12909 (10 mg/kg, i.p.) not only failed to prevent the acute effects induced by MDMA (30 mg/kg x 3, i.p.) on dopamine metabolism 30 min later, but in fact potentiated them. The 5-HT uptake inhibitor, fluoxetine (10 mg/kg, i. p.) failed to prevent both the acute and long term dopaminergic deficits. MDMA (30 mg/kg x 3) altered the body temperature of the mice biphasically, producing a rapid hyperthermia followed by prolonged hypothermia. In contrast, MDMA (20 mg/kg x 3) produced an initial hypothermia followed by hyperthermia. The present experiments therefore appear to rule out any direct relationship between the neurotoxic effects of MDMA and its acute effects on body temperature in mice. Fluoxetine administered 30 min before each MDMA (30 mg/kg) injection prevented these temperature changes, while GBR 12909 was without effect. This suggests that the neuroprotective effect of GBR 12909 against MDMA-induced neurotoxicity is not directly related to its ability to inhibit the MDMA-induced acute effects on dopamine metabolism or alter the MDMA-induced temperature change. The data illustrate major differences in the neurotoxic profile of MDMA in mice and rats.

Studies on the role of dopamine in the degeneration of 5‐HT nerve endings in the brain of Dark Agouti rats following 3,4‐methylenedioxymethamphetamine (MDMA or ‘ecstasy’) administration

We investigated whether dopamine plays a role in the neurodegeneration of 5‐hydroxytryptamine (5‐HT) nerve endings occurring in Dark Agouti rat brain after 3,4‐methylenedioxymethamphetamine (MDMA or ‘ecstasy’) administration. Haloperidol (2 mg kg−1 i.p.) injected 5 min prior and 55 min post MDMA (15 mg kg−1 i.p.) abolished the acute MDMA‐induced hyperthermia and attenuated the neurotoxic loss of 5‐HT 7 days later. When the rectal temperature of MDMA+haloperidol treated rats was kept elevated, this protective effect was marginal. MDMA (15 mg kg−1) increased the dopamine concentration in the dialysate from a striatal microdialysis probe by 800%. L‐DOPA (25 mg kg−1 i.p., plus benserazide, 6.25 mg kg−1 i.p.) injected 2 h after MDMA (15 mg kg−1) enhanced the increase in dopamine in the dialysate, but subsequent neurodegeneration was unaltered. L‐DOPA (25 mg kg−1) injected before a sub‐toxic dose of MDMA (5 mg kg−1) failed to induce neurodegeneration. The MDMA‐induced increase in free radical formation in the hippocampus (indicated by increased 2,3‐ and 2,5‐dihydroxybenzoic acid in a microdialysis probe perfused with salicylic acid) was unaltered by L‐DOPA. The neuroprotective drug clomethiazole (50 mg kg−1 i.p.) did not influence the MDMA‐induced increase in extracellular dopamine. These data suggest that previous observations on the protective effect of haloperidol and potentiating effect of L‐DOPA on MDMA‐induced neurodegeneration may have resulted from effects on MDMA‐induced hyperthermia. The increased extracellular dopamine concentration following MDMA may result from effects of MDMA on dopamine re‐uptake, monoamine oxidase and 5‐HT release rather than an ‘amphetamine‐like’ action on dopamine release, thus explaining why the drug does not induce degeneration of dopamine nerve endings.

Persistent MDMA-induced dopaminergic neurotoxicity in the striatum and substantia nigra of mice

Acute administration of repeated doses of 3,4‐methylenedioxymethamphetamine (MDMA, ecstasy) dramatically reduces striatal dopamine (DA) content, tyrosine hydroxylase (TH), and DA transporter‐immunoreactivity in mice. In this study, we show for the first time the spatiotemporal pattern of dopaminergic damage and related molecular events produced by MDMA administration in mice. Our results include the novel finding that MDMA produces a significant decrease in the number of TH‐immunoreactive neurons in the substantia nigra (SN). This decrease appears 1 day after injection, remains stable for at least 30 days, and is accompanied by a dose‐dependent long‐lasting decrease in TH‐ and DA transporter‐immunoreactivity in the striatum, which peaked 1 day after treatment and persisted for at least 30 days, however, some recovery was evident from day 3 onwards, evidencing sprouting of TH fibers. No change is observed in the NAc indicating that MDMA causes selective destruction of DA‐containing neurons in the nigrostriatal pathway, sparing the mesolimbic pathway. The expression of Mac‐1 increased 1 day after MDMA treatment and glial fibrillary acidic protein increased 3 days post‐treatment in the striatum and SN but not in the NAc, in strict anatomical correlation with dopaminergic damage. These data provide the first evidence that MDMA causes persistent loss of dopaminergic cell bodies in the SN.

Molecular mechanisms of pain: Serotonin1A receptor agonists trigger transactivation by c-fos of the prodynorphin gene in spinal cord neurons

By using spinal cord neurons cultured in chemically defined medium, a double labeling procedure, and blockage with antisense oligonucleotides, we show that induction of c-fos and the subsequent transactivation of the prodynorphin gene are coupled events, triggered by serotonin1A receptor agonists. Addition of the specific 1A agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) to the culture, at concentrations similar to that needed for transactivation of the prodynorphin gene, also significantly increases cAMP levels. Furthermore, in rats depleted of serotonin by intrathecal administration of 5,7-dihydroxytryptamine, the induction of prodynorphin after noxious stimulation is dramatically decreased compared with the induction in sham-operated rats. These results suggest that the expression of the prodynorphin gene in spinal cord is under the control of the raphe-spinal efferents containing serotonin.

Role of hyperthermia in the protective action of clomethiazole against MDMA ('ecstasy')-induced neurodegeneration, comparison with the novel NMDA channel blocker AR-R15896AR.

The immediate effect of administration of 3,4‐methylenedioxymethamphetamine (MDMA or ‘ecstasy’) on rectal temperature and the effect of putative neuroprotective agents on this change has been examined in rats. The influence of the temperature changes on the long term MDMA‐induced neurodegeneration of cerebral 5‐hydroxytryptamine (5‐HT) nerve terminals was also examined. The novel low affinity N‐methyl‐D‐aspartate (NMDA) receptor channel blocker AR‐R15896AR (20 mg kg−1, i.p.) given 5 min before and 55 min after MDMA (15 mg kg−1, i.p.) did not prevent the MDMA‐induced hyperthermia and did not alter either the MDMA‐induced neurodegenerative loss of 5‐HT and 5‐hydroxyindoleacetic acid (5‐HIAA) in cortex, striatum and hippocampus or loss of [3H]‐paroxetine binding in cortex 7 days later. The neuroprotective agent clomethiazole (50 mg kg−1, i.p.) given 5 min before and 55 min after MDMA (15 mg kg−1) abolished the MDMA‐induced hyperthermic response and markedly attenuated the loss of 5‐HT, 5‐HIAA and [3H]‐paroxetine binding in the brain regions examined 7 days later. When rats treated with MDMA plus clomethiazole were kept at high ambient temperature for 5 h post‐MDMA, thereby keeping their body temperature elevated to near that seen in rats given MDMA alone, the MDMA‐induced loss of 5‐HT, 5‐HIAA and [3H]‐paroxetine was still attenuated. However, the protection (39%) afforded by the clomethiazole administration was less than seen in rats kept at normal ambient temperature (75%). These data support the proposals of others that NMDA receptor antagonists are neuroprotective against MDMA‐induced degeneration only if they induce hypothermia and further suggest that increased glutamate activity may not be involved in the neurotoxic action of MDMA. These data further demonstrate that a proportion of the neuroprotective action of clomethiazole is due to an effect on body temperature but that, in addition, the compound protects against MDMA‐induced damage by an unrelated mechanism.

A comparative study on the acute and long‐term effects of MDMA and 3,4‐dihydroxymethamphetamine (HHMA) on brain monoamine levels after i.p. or striatal administration in mice

1 This study investigated whether the immediate and long‐term effects of 3,4‐methylenedioxymethamphetamine (MDMA) on monoamines in mouse brain are due to the parent compound and the possible contribution of a major reactive metabolite, 3,4‐dihydroxymethamphetamine (HHMA), to these changes. The acute effect of each compound on rectal temperature was also determined. 2 MDMA given i.p. (30 mg kg−1, three times at 3‐h intervals), but not into the striatum (1, 10 and 100 μg, three times at 3‐h intervals), produced a reduction in striatal dopamine content and modest 5‐HT reduction 1 h after the last dose. MDMA does not therefore appear to be responsible for the acute monoamine release that follows its peripheral injection. 3 HHMA does not contribute to the acute MDMA‐induced dopamine depletion as the acute central effects of MDMA and HHMA differed following i.p. injection. Both compounds induced hyperthermia, confirming that the acute dopamine depletion is not responsible for the temperature changes. 4 Peripheral administration of MDMA produced dopamine depletion 7 days later. Intrastriatal MDMA administration only produced a long‐term loss of dopamine at much higher concentrations than those reached after the i.p. dose and therefore bears little relevance to the neurotoxicity. This indicates that the long‐term effect is not attributable to the parent compound. HHMA also appeared not to be responsible as i.p. administration failed to alter the striatal dopamine concentration 7 days later. 5 HHMA was detected in plasma, but not in brain, following MDMA (i.p.), but it can cross the blood–brain barrier as it was detected in the brain following its peripheral injection. 6 The fact that the acute changes induced by i.p. or intrastriatal HHMA administration differed indicates that HHMA is metabolised to other compounds which are responsible for changes observed after i.p. administration.

MDMA-induced neurotoxicity: long-term effects on 5-HT biosynthesis and the influence of ambient temperature

1 3,4‐Methylenedioxymethamphetamine (MDMA or ‘ecstasy’) decreases the 5‐HT concentration, [3H]‐paroxetine binding and tryptophan hydroxylase activity in rat forebrain, which has been interpreted as indicating 5‐HT neurodegeneration. This has been questioned, particularly the 5‐HT loss, as MDMA can also inhibit tryptophan hydroxylase. We have now evaluated the validity of these parameters as a reflection of neurotoxicity. 2 Male DA rats were administered MDMA (12.5 mg kg−1, i.p.) and killed up to 32 weeks later. 5‐HT content and [3H]‐paroxetine binding were measured in the cortex, hippocampus and striatum. Parallel groups of treated animals were administered NSD‐1015 for determination of in vivo tryptophan hydroxylase activity and 5‐HT turnover rate constant. 3 Tissue 5‐HT content and [3H]‐paroxetine binding were reduced in the cortex (26–53%) and hippocampus (25–74%) at all time points (1, 2, 4, 8 and 32 weeks). Hydroxylase activity was similarly reduced up to 8 weeks, but had recovered at 32 weeks. The striatal 5‐HT concentration and [3H]‐paroxetine binding recovered by week 4 and hydroxylase activity after week 1. In all regions, the reduction in 5‐HT concentration did not result in an altered 5‐HT synthesis rate constant. 4 Administering MDMA to animals when housed at 4°C prevented the reduction in [3H]‐paroxetine binding and hydroxylase activity observed in rats housed at 22°C, but not the reduction in 5‐HT concentration. 5 These data indicate that MDMA produces long‐term damage to serotoninergic neurones, but this does not produce a compensatory increase in 5‐HT synthesis in remaining terminals. It also highlights the fact that measurement of tissue 5‐HT concentration may overestimate neurotoxic damage.