Failure to detect increases in brain dopamine metabolism in rats sham feeding sucrose and corn oil

In a recent study we found that when rats sham fed 6% sucrose, 10% sucrose, and 100% corn oil, the rank order of inhibitory potency for D-1 and D-2 receptor antagonists was 6% sucrose > 10% sucrose > 100% corn oil. In a complementary study, sham-feeding rats preferred 100% corn oil > 10% sucrose > 6% sucrose as measured by two-bottle preference tests. The preferences are evidence for the rank order of reward value of these solutions. In the present study we tested the hypothesis that the relative antagonist potencies were due to differential release of DA, dependent on the reward value of the sham-fed solution. Dopamine metabolism, estimated by the ratio of dihydroxphenylacetic acid (DOPAC) to DA, was measured in forebrain-DA terminal fields during sham feeding of 100% corn oil, 6% sucrose, and 10% sucrose. The results did not support our hypothesis: no increase in DA metabolism was observed after the sham feeding of any solution.