[A neuroendocrinological study on the mechanism of feeding-associated circadian rhythm of plasma corticosterone and feeding behaviour in rats: a role of neuropeptide Y in the paraventricular nucleus].

Plasma corticosterone (CORT) level in rats increases before meal (pre-feeding peak), when rats are subjected to restricted daily feeding (RF), in which food is supplied only at a fixed time of day. Corticotropin-releasing hormones (CRH) release is also suggested to increase prior to meal. Cell bodies of CRH neurons exist in the paraventricular nucleus (PVN) which receives neuropeptide Y (NPY) containing neurons of two different origins: one from the brainstem, in which catecholamine (CA) coexists, and the other from the arcuate nucleus (ARC). The aim of the present study is to examine the role of NPY neurons from the brainstem in feeding and CRH secretion. To accomplish this aim, NPY in the discrete areas of brain and in the extracellular space of the PVN were measured under ad-lib feeding, food deprivation, and RF, together with plasma CORT level. Under ad-lib feeding, NPY in the PVN didn't variate throughout the day. The extracellular NPY in the PVN, however, increased under food deprivation, which decreased rapidly after refeeding, and increased just before the daily meal under RF. And this preprandial increase reappeared by 3 day food deprivation even after RF was terminated and replaced by ad-lib feeding for 7 days. The preprandial increase was suppressed by 6-hydroxy-dopamine (6-OHDA), a CA deprivator, injected into the PVN or the ascending bundle of noradrenaline fibers. It is concluded that, (1) the NPY neurons in the PVN aren't involved in the regulation of plasma CORT level and feeding behavior under ad-lib feeding, but involved under food deprivation, (2) the prefeeding increase of the extracellular NPY in the PVN is an expression of a feeding-associated circadian oscillation under RF. By contrast, the prandial decrease in the extracellular NPY is a result of food intake, (3) the noradrenergic neurons innervating the PVN are important for the expression of the prefeeding NPY peak under RF.