Blanca Esteban

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.

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.

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.

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.

Studies on the neuroprotective effect of pentobarbitone on MDMA-induced neurodegeneration.

Abstract Administration of a dose of 15 mg/kg of the recreationally used drug 3,4-methylenedioxymethamphetamine (MDMA or “ecstasy”) to Dark Agouti rats resulted in an acute hyperthermic response which was followed 7 days later by a marked (≈45%) loss of 5-HT and its metabolite 5-HIAA in cortex, hippocampus and striatum and a similar loss of [3H]-paroxetine binding in cortex. These losses reflect the MDMA-induced neurotoxic degeneration of 5-HT nerve endings. Administration of pentobarbitone (40 mg/kg) concurrently with MDMA produced a significant attenuation of the neurotoxic damage, but also acute hypothermia. When the temperature of the MDMA plus pentobarbitone-treated group was kept elevated to that of the MDMA-treated group by the use of a homeothermic blanket, the neuroprotective effect of pentobarbitone was lost. These data demonstrate that pentobarbitone appears to possess no intrinsic neuroprotective activity and the previously reported activity is due to a hypothermic action of the drug.