A review by NIDA scientists explains that "neurotoxicity" arguments were based on overdosing animals, and that similar effects are seen with SSRI anti-depressants:
Psychopharmacology (Berl). 2007 Jan;189(4):407-24.
3,4-Methylenedioxymethamphetamine (MDMA) neurotoxicity in rats: a reappraisal of past and present findings.
Baumann MH, Wang X, Rothman RB.
Free full-text:
http://www.ncbi.nlm.nih.gov/pubmed/16541247
It has been previously claimed that overdoses of MDMA caused structural damage to serotonin axons ('axon pruning'), but there has never been any good evidence of this. Most evidence points to modulation of expression of serotonin transporters without damaging the axons themselves:
The Nature of 3, 4-Methylenedioxymethamphetamine (MDMA)-Induced Serotonergic Dysfunction: Evidence for and Against the Neurodegeneration Hypothesis.
Biezonski DK, Meyer JS.
Curr Neuropharmacol. 2011 Mar;9(1):84-90.
Free full-text:
http://www.ncbi.nlm.nih.gov/pubmed/21886568
Psychopharmacology (Berl). 2007 Jan;189(4):407-24. 3,4-Methylenedioxymethamphetamine (MDMA) neurotoxicity in rats: a reappraisal of past and present findings. Baumann MH, Wang X, Rothman RB. Free full-text: http://www.ncbi.nlm.nih.gov/pubmed/16541247
It has been previously claimed that overdoses of MDMA caused structural damage to serotonin axons ('axon pruning'), but there has never been any good evidence of this. Most evidence points to modulation of expression of serotonin transporters without damaging the axons themselves:
The Nature of 3, 4-Methylenedioxymethamphetamine (MDMA)-Induced Serotonergic Dysfunction: Evidence for and Against the Neurodegeneration Hypothesis. Biezonski DK, Meyer JS. Curr Neuropharmacol. 2011 Mar;9(1):84-90. Free full-text: http://www.ncbi.nlm.nih.gov/pubmed/21886568