Dopamine antagonist binding: A significant decrease with morphine dependence in the rat striatum

Abstract ( 3 H)-Spiroperidol specific binding was determined in striatal tissue of rats which received a single dose of, or made dependent on morphine. Acute morphine (30 mg/kg i.p.) did not alter ( 3 H)-spiroperidol specific binding. However, morphine-dependent rats with two 50 mg pellets when withdrawn for 24 or 48 hours, significantly decreased the binding and increased K d . Binding sites were reduced with a decrease in K d in rats implanted with four-50 mg pellets or receiving high doses of morphine. These results indicate that binding characteristics of ( 3 H)-spiroperidol depend on the relative dose of morphine used to induce dependence. Low dose dependence (2 pellets) results in a decrease in binding affinity while high dose dependence (4 pellets or chronic injection) results in an increase of ( 3 H)-spiroperidol affinity in the presence of fewer binding sites.