What is MDMA Neurotoxicity?

In laboratory animals, large or frequent doses of MDMA can destroy serotonin axons. Serotonin neurons (brain cells) form a sort of control system in your brain, regulating emotions, appetite, sleep and other functions. The serotonin axons are 'communication cables' that the serotonin system uses to send its signals to the rest of the brain. (MDMA works primarily by causing these serotonin axons to release a lot of serotonin at once, causing euphoria.)

These two pictures show slices of a monkey's brain. The serotonin axons have been stained to make them appear as bright lines. The picture on the left (A) is from a normal monkey. The picture on the right (B) is from a monkey that was injected with a very large dose of MDMA. As you can see, many of its serotonin axons have been lost. (Animal research suggests that when a neurotoxic dosage of MDMA is given, damage to the axons starts to occur in as little as an hour or two.) Animal experiments suggest that if neurotoxicity occurs, some new serotonin axons can grow to replace them...but they grow in different places than where the original ones were.The long-term effects of this 'rewiring' are not known.