The neurotoxicity of MPTP was first hinted at in 1976 after Barry Kidston, a 23-year-old graduate chemistry student in Maryland, synthesized MPPP (a synthetic opiate related to pethidine and the prodines) with MPTP as a major impurity, and self-injected the result. Within three days he began exhibiting symptoms of Parkinson's disease. The National Institute of Mental Health found traces of MPPP, MPTP, and other pethidine analogues in his lab. They tested the substances on rats, but due to rodents' tolerance for this type of neurotoxin nothing was observed. Kidston's parkinsonism was successfully treated with levodopa but he died 18 months later from a cocaine overdose. Upon autopsy, destruction of dopaminergic neurons in the substantia nigra was discovered.