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.

Delay discounting of potentially real and hypothetical rewards: II. Between- and within-subject comparisons.

Prior studies comparing discounting of delayed hypothetical or potentially real rewards have reported no differences, but they used within-subjects designs. This raises the possibility that participants remembered their choices in one condition and repeated them in the other. In Experiment 1, between-subjects comparisons were made with an adjusting-amount procedure. No significant effect of reward type on delay discounting was detected. Experiment 2 increased the proportion of real rewards and made between- and within-subject comparisons. These comparisons also failed to reveal a significant effect of reward type. Although these findings are consistent with prior findings, caution is urged because choices involving hypothetical rewards have yet to be compared with choices involving real rewards (i.e., the consequences of every choice are obtained) in an experiment using forced-choice trials and steady-state methodology.