Sham feeding corn oil increases accumbens dopamine in the rat

Both real and sham feeding of sucrose increase dopamine (DA) overflow in the nucleus accumbens (NAc). Fat is another constituent of foods that is inherently preferred by humans and rodents. We examined the affect of sham feeding corn oil in rats that were food and water deprived overnight. Rats were implanted with guide cannulas aimed at the NAc, as well as gastric fistulas. On alternate days, they were trained to sham lick 100% corn oil or distilled water (dH₂O) for 20 min in the morning. Twenty-minute microdialysis samples were taken before, during, and after sham licking. DA and monoamines were analyzed by reverse-phase HPLC with coulometric detection. The results show that DA release in the NAc was significantly increased during sham licking of corn oil compared with the prior baseline (157.5 ± 18.8%, n = 12). During sham licking of dH₂O, DA release in the NAc was not changed (93.0 ± 4.0%, n = 15). This experiment demonstrates that sham feeding of corn oil releases accumbens DA in a manner similar to ingestion of sucrose. Although both stimuli may have an olfactory component, sucrose is a gustatory, and 100% corn oil appears to be a trigeminal stimulus. Thus these data support the hypothesis that different sensory modalities produce reward using the same or closely related substrates in the forebrain.