Repeated injection of cocaine potentiates methamphetamine-induced toxicity to dopamine-containing neurons in rat striatum.

Rats were treated with daily injections of saline or cocaine (20 mg/kg i.p. x 15 days) and, beginning 24 h after the last injection, administered saline or methamphetamine (6.25-50 mg/kg s.c., BID x 4 days) and sacrificed two weeks later. Repeated daily administration of cocaine potentiated the long-lasting striatal dopamine depletions caused by methamphetamine. The results suggest that human use of cocaine may increase the likelihood of neurotoxicity resulting from ingestion of high doses of methamphetamine.