"So when you refer to the serotonin neurotoxicity associated with MDMA…"

“…what in the heck are you talking about DM?”
Here’s the fantastic thing about being a lazy blogger. You wait long enough and someone will come along and write the post you really should have written ages ago. Not only that, but someone will write one that is about eleventy-million times better than what you would have done in your lassitude and preferred, um, bloggy style.
Well, as I’ve referred to now and again, one of the consequences of the drug 3,4-methylenedioxymethamphetamine (MDMA) which is the molecule people generally mean by “Ecstasy” is a lasting, possibly permanent, decrement in the function of neurons in the brain which use serotonin as a neurotransmitter. Well so what? Why should we care about serotonin function? What are those neurons up to, anyway?
Go read scicurious’ excellent overview of serotonin neuropharmacology.