5,7-Dihydroxytryptamine

5,7-Dihydroxytryptamine (5,7-DHT) is a purported neurotoxin used in scientific research to decrease concentrations of serotonin in the brain. The mechanism behind this effect isn't well understood, but many believe (without clear substantiation) that it selectively kills serotonergic neurons, in a similar way that 6-hydroxydopamine (6-OHDA) is used to kill dopaminergic cells. What is known is that this compound is in fact not selective in depleting serotonin content, but also depletes norepinephrine. To selectively deplete serotonin stores, it is commonly administered in conjunction with desmethylimipramine (desipramine)[3], which inhibits the norepinephrine transporter.
References.
3. Martin-Iverson, M.T., Leclere, J.F. and Fibiger, H.C., Cholinergic-dopaminergic interactions and the mechanisms of action of antidepressants, "European Journal of Pharmacology", 94 (1983) 193–201.