Simultaneous quantitation of norepinephrine, dopamine and serotonin in brain during and following chronic naltrexone...

The effects of chronic administration of the narcotic antagonist naltrexone on regional brain levels of norepinephrine, dopamine and serotonin were studied in order to determine whether central monoaminergic neurons are tonically modulated by central opioid systems. Chronic exposure to naltrexone (8 days) is associated with a significant increase in the content of norepinephrine in the mesolimbic forebrain and the content of dopamine in the frontal cortex and striatum. Ten days following naltrexone pellet removal the above levels returned to control values but thalamic dopamine content was reduced 10-fold. These data suggest that the affected brain regions receive an opioidergic input that is tonically active.