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 s triatum and limbic forebrain of rats upon 48 h withdrawal from 20-day morphine treatment were studied using 3-methoxytyramine (3-MT) in tiss ue as an index of DA release. Homovanillic acid (HVA) and 3,4-dihydrox yphenylacetic acid (DOPAC) were also measured. The chronic morphine tr eatment did not alter the concentrations of DA metabolites. Acute morp hine (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 sh ow that both striatal and limbic DA mechanisms are sensitized to morph ine upon withdrawal but that sensitization of DA metabolism in these t wo brain areas occurs differently.