Morphine-stimulated metabolism of striatal and limbic dopamine is dissimilarly sensitized in rats upon withdrawal from chronic morphine treatment.

The effects of acute morphine on the release of dopamine (DA) in the striatum and limbic forebrain of rats upon 48 h withdrawal from 20-day morphine treatment were studied using 3-methoxytyramine (3-MT) in tissue as an index of DA release. Homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were also measured. The chronic morphine treatment did not alter the concentrations of DA metabolites. Acute morphine (10 mg/kg) elevated all three DA metabolites in both brain areas. Morphine withdrawal potentiated the elevation of striatal and limbic 3-MT as well as that of striatal but not limbic HVA. These findings show that both striatal and limbic DA mechanisms are sensitized to morphine upon withdrawal but that sensitization of DA metabolism in these two brain areas occurs differently.