Differential effects of neuropeptide Y and the μ-agonist DAMGO on 'palatability' vs. 'energy'

Differential effects of neuropeptide Y (NPY) and μ-opioid DAMGO on 'palatability' vs. 'energy'. A variety of studies suggest that NPY is an important manager of energy metabolism. In contrast, the opioid peptides appear to influence the 'rewarding' aspects of feeding. In the current study, we stimulated feeding by injecting NPY (110 pmol) or the μ-opioid agonist DAMGO (2 nmol) into the paraventricular nucleus of rats. Following injection, rats were given free access to laboratory chow and a 10% sucrose solution. Animals injected with saline derived 10% of their kilocalories from the chow and 90% from the sucrose solution (total kcal/4 h = 12.2±1.0). Those rats injected with NPY derived 48% of their energy from chow and 52% from the sucrose solution (total kcal/4 h = 24.8±1.7). The DAMGO-injected rats derived only 15% of their kilocalories from chow and the remainder from the sucrose solution (total kcal/4 h = 23.0±2.3). Thus, while NPY and DAMGO both stimulated energy intake compared to saline controls (P < 0.0001), the effect on intake of a palatable dilute energy solution (0.4 kcal/g) vs. a 'bland' laboratory chow (3.95 kcal/g) was different. The results of this study reinforce the notion that NPY has a major effect on energy needs, whereas opioids influence the 'rewarding' characteristics of foods.