Effects of restricted daily feeding on neuropeptide Y release in the rat paraventricular nucleus

Extracellular neuropeptide Y (NPY) in the vicinity of the paraventricular nucleus (PVN) and the NPY concentrations in the PVN, arcuate nucleus of the hypothalamus (ARC), and the nucleus tractus solitarius (NTS) were measured in rats under ad libitum and restricted daily feeding (RF) where meal was supplied at a fixed time of day. The extracellular NPY levels did not vary significantly between 0600 and 2200 in rats under ad libitum feeding but were increased before meal and decreased immediately after meal supply under the RF regimen. Similarly, the NPY concentrations in the PVN, ARC, and NTS were increased immediately before meal. When meal was omitted at the regular mealtime, the extracellular NPY levels were not decreased rapidly, and the NPY concentration in the PVN remained at a low level. Rats were subjected to the feeding-fasting paradigm after the termination of RF. The extracellular NPY levels were returned to basal levels during the feeding period but were elevated during the fasting period at almost the same time as that for meal supply under the RF regimen. It is concluded that the prefeeding enhancement of the NPY release in the PVN under the RF regimen is regulated by the feeding-associated circadian rhythm.