Influence of the amount of food ingested on mesolimbic dopaminergic system activity: a microdialysis study

The mesolimbic dopaminergic system (MDS) has been shown to be activated by ingestive behaviors, and it has been suggested that this activation may be related to the rewarding properties of foods. Because rats eat more when given a more palatable diet, this study was undertaken to determine-the relationship between the amount of food ingested and DA release in the nucleus accumbens of freely moving rats. The extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured by high-performance liquid chromatography with electrochemical detection on microdialysis samples from the nucleus accumbens. Each rat underwent three microdialysis sessions that differed in feeding conditions: on the first day they had access to a highly palatable diet (short cakes) ad lib; on the second day they were given half the amount consumed on the previous day of the same food; and on the third day they were deprived of food. In the absence of food, there were no significant alterations in extracellular levels of DA, DOPAC, and HVA. During feeding, levels of DA and its two metabolites rose. DA release in the nucleus accumbens was related to the amount of food ingested. As the amount ingested is a component of the reinforcement associated with food intake, this result is consistent with a direct relationship between MDS activity and food reward.