Egli Marcel, Bertram Richard, Toporikova Natalia, Sellix Michael T, Blanco Wilfredo, Freeman Marc E
Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA.
Am J Physiol Endocrinol Metab. 2006 Mar;290(3):E566-72. doi: 10.1152/ajpendo.00427.2005.
Mating or vaginocervical stimulation [copulatory stimulus (CS)] induces two daily surges of the hormone prolactin (PRL) in rats. This unique secretory pattern of PRL surges is characteristic for the first half of pregnancy and is also present in ovariectomized (OVX) rats. Studies have shown that CS additionally provokes an acute release of the hormone oxytocin (OT). In this study, we tested whether a single injection of OT (iv) is sufficient to initiate the PRL secretion pattern of OVX/CS rats. Furthermore, we measured the 24-h profile of dopamine (DA) content in the anterior lobe of the pituitary gland, because DA is the major inhibitory factor of PRL secretion. The results indicated that a single injection of OT induces a PRL secretory rhythm and a DA release pattern similar to that initiated by CS. Immunocytochemical investigation showed that particular OTergic neurons in the hypothalamus express receptors for PRL, as well as for vasoactive intestinal polypeptide, which indicates an involvement in generating the PRL rhythm and entraining it to the ambient photoperiod. On the basis of this study, we suggest that the PRL-DA inhibitory feedback loop between lactotrophs and DAergic neurons plays a crucial role in generating the oscillatory PRL secretion pattern in CS rats. A timing signal, likely provided by the hypothalamic suprachiasmatic nucleus, entrains the autonomous PRL oscillation to a particular time of day. Mathematical modeling was used to illustrate the proposed network function. The experimental results further suggest an additional feedback mechanism in which certain hypothalamic OTergic neurons are influenced by PRL.
交配或阴道宫颈刺激（交配刺激）可诱导大鼠体内催乳素（PRL）每日出现两次分泌高峰。PRL分泌高峰这种独特的分泌模式是妊娠前半期的特征，在去卵巢（OVX）大鼠中也存在。研究表明，交配刺激还会额外引发激素催产素（OT）的急性释放。在本研究中，我们测试了单次静脉注射OT是否足以启动OVX/交配刺激大鼠的PRL分泌模式。此外，我们测量了垂体前叶中多巴胺（DA）含量的24小时变化情况，因为DA是PRL分泌的主要抑制因子。结果表明，单次注射OT可诱导出与交配刺激引发的PRL分泌节律和DA释放模式相似的情况。免疫细胞化学研究表明，下丘脑特定的OT能神经元表达PRL受体以及血管活性肠肽受体，这表明其参与了PRL节律的产生并使其与环境光周期同步。基于本研究，我们认为催乳细胞与DA能神经元之间的PRL-DA抑制性反馈回路在交配刺激大鼠产生振荡性PRL分泌模式中起关键作用。一个可能由下丘脑视交叉上核提供的定时信号将自主的PRL振荡与一天中的特定时间同步。数学建模被用于说明所提出的网络功能。实验结果进一步表明存在一种额外的反馈机制，即某些下丘脑OT能神经元受PRL影响。
