Dopamine and preparatory behavior: II. A neurochemical analysis.

Changes in the activity of dopamine-containing systems in relation to preparatory and consummatory feeding responses were investigated. In Experiment 1 rats were conditioned to associate food delivery with the presentation of a conditional stimulus (CS+). When sacrificed after exposure to the CS+ alone on a test trial, the ratio of the dopamine metabolite 3,4-dihydroxyphenylacetic acid to dopamine (DOPAC/DA ratio) was increased significantly in the nucleus accumbens. A similar trend in the ratio of homovanillic acid to dopamine (HVA/DA ratio) was also observed. Similar increases were observed in the striatum, but these were not statistically significant. In contrast, no increases were observed in the DOPAC/DA ratio or the HVA/DA ratio in either brain region when rats were permitted to consume an unsignaled meal for 7 min. These findings suggest that activation of dopamine terminals in the nucleus accumbens occurs during the anticipation of a meal, at which times the rat is engaged in preparatory feeding behaviors, but does not accompany the performance of short bouts of consummatory feeding behavior.