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Presynaptic and Postsynaptic Effects of Neuropeptide Y in the Rat Pineal Gland
Authors:Valérie Simonneaux  AH Ouichou  Cheryl Craft  Paul Pévet
Institution:Neurobiologie des Fonctions Rythmiques et Saisonnières, URA-CNRS1332, UniversitéLouis Pasteur, Strasbourg, France;Laboratory of Molecular Neuroendocrinology, Department of Psychiatry, University of Texas Southwestern Medical School, Dallas, Texas, U.S.A.
Abstract:Abstract: Neuropeptide Y is colocalized with noradrena-line in sympathetic fibers innervating the rat pineal gland. In this article we present a study of the effects and mechanisms of action of neuropeptide Y on the pineal noradrenergic transmission, the main input leading to the rhythmic secretion of melatonin. At the presynaptic level, neuropeptide Y inhibits by 45%, with an EC50 of 50 n M , the potassium-evoked noradrenaline release from pineal nerve endings. This neuropeptide Y inhibition occurs via the activation of pertussis toxin-sensitive G protein-coupled neuropeptide Y-Y2 receptors and is independent from, but additive to, the α2-adrenergic inhibition of noradrenaline release. At the postsynaptic level, neuropeptide Y decreases by a maximum of 35%, with an EC50 of 5 n M , the β-adrenergic induction of cyclic AMP elevation via the activation of neuropeptide Y-Y1 receptors. This moderate neuropeptide Y-induced inhibition of cyclic AMP accumulation, however, has no effect on the melatonin secretion induced by a β-adrenergic stimulation. On the contrary, in the presence of 1 m M ascorbic acid, neuropeptide Y potentiates (up to threefold) the melatonin secretion. In conclusion, this study has demonstrated that neuropeptide Y modulates the noradrenergic transmission in the rat pineal gland at both presynaptic and postsynaptic levels, using different receptor subtypes and transduction pathways.
Keywords:Pineal  Melatonin  Cyclic AMP  Neuropeptide Y
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