Sham feeding of sucrose increases the ratio of 3,4-dihydroxyphenylacetic acid to dopamine in the hypothalamus

Recent pharmacological experiments suggested that central dopaminergic (DA) mechanisms are necessary for the normal eating response to sweet stimuli. To test this hypothesis, we measured the ratio of dihydroxyphenylacetic acid (DOPAC) to dopamine (DA) in forebrain DA terminal fields during the sham feeding of sucrose (1-40%) by rats after 17 hr of food deprivation. After 9 min of sham feeding 10% or 40% sucrose, DOPAC/DA increased in the hypothalamus, but not in other forebrain regions including the n. accumbens, amygdala, and pyriform cortex. This increase in hypothalamic DOPAC/DA did not occur after 9 min of sham feeding 1%, 1.25%, or 2.5% sucros. The increased DA metabolism required that sham feeding of 10% or 40% sucrose be maintained for longer than 3 min, because no increase of DOPAC/DA was observed in any forebrain region after 3 min of sham feeding. These results are strong evidence that hypothalamic DA mechanisms are activated by the sham feeding of sucrose solutions and they support the hypothesis that central DA mechanisms are necessary for the normal eating response to sweet stimuli.