Reduced feeding response to neuropeptide Y in senescent Fischer 344 rats

The anorexia of aging syndrome in humans is characterized by spontaneous bo dy weight loss reflecting diminished food intake. We reported previously th at old rats undergoing a similar phenomenon of progressive weight loss (i.e ., senescent rats) also display altered feeding behavior, including reduced meal size and duration. Here, we tested the hypothesis that blunted respon siveness to neuropeptide Y (NPY), a feeding stimulant, occurs concurrently with senescence-associated anorexia/hypophagia. Young (8 mo old, n = 9) and old (24-30 mo old, n = 11) male Fischer 344 rats received intracerebrovent ricular NPY or artificial cerbrospinal fluid injections. In response to a m aximum effective NPY dose (10 mug), the net increase in size of the first m eal after injection was similar in old weight-stable (presenescent) and you ng rats (10.85 +/- 1.73 and 12.63 +/- 2.52 g/kg body wt(0.67), respectively ). In contrast, senescent rats that had spontaneously lost similar to 10% o f body weight had significantly lower net increases at their first post-NPY meal (1.33 +/- 0.33 g/kg body wt 0.67) than before they began losing weigh t. Thus altered feeding responses to NPY occur in aging rats concomitantly with spontaneous decrements in food intake and body weight near the end of life.