Intraparaventricular neuropeptide Y and ghrelin induce learned behaviors that report food deprivation in rats.

Rats were trained to discriminate between 2 and 22-h food deprivation in a choice paradigm. During tests, 20 min of food consumption eliminated internal stimuli associated with 22-h food deprivation. In other tests, rats food-restricted for 2 h were given neuropeptide Y or ghrelin by administration into the paraventricular nucleus of the hypothalamus. Both neurochemicals induced effects similar to those following 22-h food restriction (increased behavior appropriate for 22-h deprivation). These findings suggest that internal stimuli produced by 22-h food deprivation are altered by food consumption and mimicked by feeding-inducing neurochemicals administered into a brain area associated with feeding regulation. Thus, hunger discrimination is a useful model to examine neurochemical and dietary factors that alter internal states associated with eating.