Twenty-four hour rhythms of the hypothalamic CRF production and release, and the afferent pathways from the light- and food-entrainable circadian oscillations.

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The purpose of the present study is to clarify the afferent pathways from the lightand food-entrainable circadian oscillations to the hypothalamic CRF neurons which play a key role in the regulation of the hypothalamus-pitultary-adrenocortical axis. The light-entrainable circadian rhythm is expressed in rats under ad libitum feeding, while the food-entrainable circadian rhythm become apparent under restricted feeding.The CRF concentrations in the paraventricular nucleus(PVN)where CRF is produced, and in the median eminence(ME)where CRF is released varied around the clock under both feeding conditions. The CRF concentration is high in the early light period and low in the early dark period under ad libitum feeding. On the other hand, the CRF concentration is low prior to the time of daily meal and increases after meal supply. The findings indicate that the food-entrainable circadian oscillation manifests itself on the functions of the CRF neurons In the PVN as well as in the ME.To clari … More fy the afferent pathway from the food-entrainable oscillation, various neurotoxic agents were microinjected into several areas In the brain. Among them, 6hydroxydopamine(6-OHDA)into the PVN or into the ascending bundle of catecholaminergic neurons in the midbrain abolished the food-entrainable circadian corticosterone rhythm.To have better understanding of the role of catecholaminergic neurons in the food-entrainable CRF rhythm, noradrenaline in the PVN was continuously monitored by means of in vivo microdialysis. As a result, noradrenaline In the PVN Increased prior to the daily meal and decreased after meal supply. The finding suggests, together with the 6-OHDA effect, that noradrenaline accelerates the pre-feeding CRF release.Neuropeptide Y(NPY)coexists with noradrenaline in the ascending catecholaminergic neurons which innervate the PVN. NPY in the PVN increased after the daily meal, which suggests the termination of NPY release. The synergistic action of NPY with noradrenaline on CRF release is most plausible. Less