George Ricaurte is the man from John Hopkins University who supposedly proved MDMA's potential for neurotoxicity with an article he and other researchers published in Science magazine. First of all, the research was based on experiments funded by the government. Primates were injected with what they considered to be recreational doses of MDMA and the result was an article about severe dopaminergic neurotoxicity.
Ricaurte retracted this article a year later because his team fucked up and used methamphetamine instead of MDMA. Above all, that recreational dosage of MDMA they thought they administered was in reality a 50-fold overdose of meth.
http://www.laweekly.com/ink/03/43/news-lewis.php

After this the subject of MDMA neurotoxicity remains very controversal. Maybe frequent, heavy doses will start to cause damage to serotonin axons but serotonin itself will replenish itself. Maybe the only real risk of MDMA neurotoxicity comes with complications such as overheating. Perhaps antioxidants can be taken to lessen the severity of any such toxicity exhibited by MDMA.
Right now we don't really know, and we wont so long as there are jackasses like George Ricaurte and the government encouraging research that only shows the negative consequences of drug use.
This hasn't stoped me from doing ecstasy in the past and it wont prevent me from doing it again. I believe if MDMA did cause any significant or even moderate damage to the brain, considering all the people who have used it, we should be in some MPTP-type scenerio.

Over time, these receptors get more and more burnt out and your seretonin levels get mroe and more fucked up. This is why it doesnt work after a certain amount of times, cuz you dont have any more seretonin to waste.
The secret is to not do ecstasy often. Even at a rate of every other week a user will notice diminished effects. I've rolled more times than I can count, always taking breaks in between. I still feel the effects, never have very bad come downs nor any after-roll depression. Am I some sort of anomaly or just someone who understands the concept of mind over matter?
If you come down and think "Ohh life sucks so much now that I am not on ecstasy, I need to kill myself" that means you're a bitch.

http://thedea.org/neurotoxicity.html - Best MDMA resource on the internet.