Food-related stimuli increase the ratio of 3,4-dihydroxyphenylacetic acid to dopamine in the hypothalamus.

Rats were restricted for three weeks to a schedule of 4-hr daily access to food. The regional concentrations of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the forebrain were then determined after the rats: (1) were food-deprived overnight; (2) ate for the first hour of the scheduled feeding period; or (3) remained in their cages without receiving food but while other rats fed. A group of controls had food available continuously. The DOPAC/DA ratio, a metabolic index of DA activity, increased in the hypothalamus of rats that fed and in the rats exposed to food-related stimuli without eating. This ratio did not change in the striatum, olfactory tubercle, amygdala-pyriform lobe or nucleus accumbens. Furthermore, this index did not differ from controls in any region of the forebrain in deprived rats that were not exposed to stimuli signalling the availability of food. Together, these data suggest that environmental stimuli associated with feeding after deprivation, and not the act of feeding, increased dopaminergic activity in the hypothalamus.