Influence of dynorphin on estradiol- and cervical stimulation-induced prolactin surges in ovariectomized rats
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ORIGINAL ARTICLE
Influence of dynorphin on estradiol- and cervical stimulationinduced prolactin surges in ovariectomized rats Andrea M. Stathopoulos1 • Cleyde V. Helena1 • Ruth Cristancho-Gordo1 Arturo E. Gonzalez-Iglesias1 • Richard Bertram2
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Received: 7 December 2015 / Accepted: 21 March 2016 Ó Springer Science+Business Media New York 2016
Abstract Prolactin is an anterior pituitary hormone necessary for fertility, pregnancy maintenance, lactation, and aspects of maternal behavior. In rodents, there is a surge of prolactin on the afternoon of proestrus, and a semi-circadian pattern of prolactin surges during early pregnancy, with a diurnal and nocturnal surge every day. Both of these patterns can be replicated in ovariectomized rats. A prior study demonstrated that central antagonism of j-opioid receptors, the target of dynorphin, largely abolished the nocturnal prolactin surge in pregnant rats. We build on this to determine whether dynorphin, perhaps from the arcuate population that co-express kisspeptin, neurokinin B, and dynorphin (KNDy neurons), also contributes to the estradiol- or cervical stimulation-induced surges in ovariectomized rats. Ovariectomized rats were treated with either estradiol or cervical stimulation to induce prolactin surge(s). Blood samples were taken around the expected surge time to determine the effect of either acute j-opioid receptor antagonism or previous chemical ablation of the KNDy population on prolactin levels. Dynorphin antagonism does significantly disrupt the nocturnal prolactin surge, but it does not contribute to the estradiol-induced surge. Chemical ablation of KNDy neurons had opposite effects; ablation of 40 % of the KNDy neurons had no impact on the nocturnal prolactin surge, while a somewhat larger ablation significantly reduced the size of the
estradiol-induced surge. We conclude that dynorphin is likely a controlling factor for the nocturnal surge induced by cervical stimulation, and that other KNDy neuron products must play a role in the estradiol-induced surge.
& Richard Bertram [email protected]
Introduction
1
Program in Neuroscience and Departments of Biological Sciences, Florida State University, Tallahassee, FL 32306, USA
2
Program in Neuroscience and Departments of Mathematics, Florida State University, Tallahassee, FL 32306, USA
Keywords KNDy
Prolactin Dopamine TIDA Nor-BNI
Abbreviations CS Cervical stimulation DA Dopamine DOPAC 3,4-Dihydroxyphenylacetic acid E2 Estradiol EDTA Ethylenediaminetetraacetic acid HPLC High performance liquid chromatography KNDy Kisspeptin, neurokinin B, & dynorphin KOR j opioid receptor LH Luteinizing hormone nor-BNI Norbinaltorphimine OVE Ovariectomized with estrogen replacement OVX Ovariectomized PBS Phospho-buffered saline RIA Radioimmunoassay TH Tyrosine hydroxylase
The anterior pituitary hormone prolactin is necessary for fertility, reproduction, and aspects of maternal behavior [1]. Besides its role in lactation, prolactin is also elevated on the afternoon of proestrus during the rodent estrous
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