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A common antipsychotic chemical used in emergency rooms against methamphetamine overdose has been found to damage neurons in those brain zones involved in regulating movement. The new findings were noticed in experiments on rats and point that only mixing the drug, haloperidol and methamphetamine causes the destructive effects, not each chemical by itself.
The research team at Boston University School of Medicine believes that the neuronal damage is due to an overstimulation by the amino acid glutamate, which poisons the cells through oversynthesis of the neurotransmitter gamma-aminobutyric acid (GABA).
"This work in laboratory animals raises immediate concerns that a standard treatment for methamphetamine overdose in humans might worsen drug abuse-related brain injuries," said Dr. William Carlezon, at Harvard's McLean Hospital, not involved in this research.
"A crucial next step is to determine how atypical antipsychotic medications would affect methamphetamine toxicity in the same model."
The lab rats were injected with either methamphetamine or a control saline solution over an interval of eight hours. When the rodents received haloperidol before and nearly halfway through the eight-hour period, the team counted an over 5 times rise in base levels of glutamate in the substantia nigra, the brain area linked to movement disorders, Huntington's disease being an example.
Two days after the injections, glutamate levels in the substantia nigra were double in methamphetamine-treated rats as in saline-treated ones.
The high glutamate levels were connected to the death of GABA-containing cells in parts of the substantia nigra. This can render patients treated for a methamphetamine overdose vulnerable to seizures and movement disorders, even if this research did not investigate movement specifically.
"In addition to future studies of other antipsychotic medications, we hope to examine if the loss of cells results in abnormal involuntary movements resembling Tourette's syndrome and Huntington's disease." said senior author Dr. Bryan Yamamoto.