The role played by dopamine in the induction of MDMA neurotoxicity was investigated by suppressing the dopamine transporter (DAT) via infusion of antisense oligonucleotide into substantia nigra in rats, with infusion performed via osmotic minipump in one hemisphere only. Seven days after receiving continuous infusion of DAT antisense, rats were given two doses of 20 mg/kg MDMA 12 hours apart, and rats were killed and their brains examined 7 days after the last dose of MDMA. A microdialysis study was also performed to directly measure amount of DA released by MDMA, with microdialysate sampled from caudate putamen. Serotonin (5-HT), its metabolite 5-HIAA and dopamine (DA) were measured in striatum via high performance liquid chromatography (HPLC), and 5-HT transporter (SERT) density was measured via measuring radioactive paroxetine binding. Infusion of DAT antisense did not reduce MDMA-induced hyperthermia, yet it significantly attenuated reductions in striatal 5-HT and 5-HIAA without affecting MDMA-associated reductions in 5-HT and 5-HIAA in hippocampus. Reductions in SERT density were also attenuated with DAT antisense treatment. (A preliminary study with one version of antisense failed to find significant attenuation of reduced 5-HT, but this antisense was found to be only 86% of a match for DAT, so a better antisense nucleotide was used in the second study). DAT antisense also reduced the increase in DA release seen after MDMA administration, as measured via microdialysis. These findings suggest that DA release plays a role in MDMA neurotoxicity in the striatum, though not necessarily in other brain areas, such as the hippocampus. Failing to find attenuation of hyperthermia in rats given DAT antisense, and reliance on a "knockdown" strategy rather than on pharmacological treatments strengthens the case for neuroprotection arising directly from reduced DA release rather than through attenuation of hyperthermia or through direct antioxidant effects of treatment. However, the authors failed to measure oxidizing reactions in brain or in vitro, leaving open to question whether DAT antisense reduced oxidative stress directly or indirectly. If DA plays a role in MDMA neurotoxicity, then it may be important for ecstasy users to avoid other DA releasers, such as methamphetamine, when taking ecstasy. In their discussion, the authors propose that multiple processes may be involved in MDMA neurotoxicity, and some processes may be region-specific.