Stumbled upon an interesting article that talks about how self administered cocaine use increased SERT expression. They even speculate at one point how cocaine could possibly negate MDMA serotonin toxicity or at least the noticeable decrease in SERT availability when the two drugs are co-administered together. Makes me want some cocaine even more 
www.nature.com
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Effects of Cocaine and MDMA Self-Administration on Serotonin Transporter Availability in Monkeys - Neuropsychopharmacology
Although serotonin (5-HT) can interact with dopamine (DA) systems to modulate the subjective and reinforcing effects of psychostimulants such as cocaine and 3,4-methyldioxymethamphetamine (MDMA, ecstasy), the long-term effects of exposure to psychostimulants on brain 5-HT systems are not well...

-GC