Prolactin Feedback to Hypothalamic Dopaminergic Neurons

描述(申请人提供)：催乳素对正常哺乳是绝对必要的，母乳被认为是新生儿的最佳营养。作为维持母体过程的一部分，催乳素在中枢神经系统中有多种重要的作用。虽然催乳素对生殖成功的某些方面是至关重要的，但过多的催乳素对生育是有害的。催乳素分泌肿瘤是最常见的垂体缺陷，由此导致的高催乳素血症导致男性和女性不育。下丘脑中的漏斗状多巴胺能神经元提供主要的神经内分泌控制，以维持血液中低水平的催乳素水平，但足以维持正常的生殖功能。多巴胺是主要的催乳素抑制因子，催乳素反过来反馈增加多巴胺能神经元的活性，酪氨酸羟基酶是多巴胺生物合成的限速酶，其活性在酪氨酸羟基酶基因转录水平上受到高度调控，并受到翻译后控制机制的高度调控，如现有酶的磷酸化/去磷酸化。然而，我们对下丘脑多巴胺能神经元如何整合催乳素诱导的信号以增强神经元活性知之甚少。这项拟议的研究将利用几个模型来阐明催乳素控制下丘脑多巴胺能神经元中酪氨酸羟化酶的机制。当所有下丘脑和下丘脑外的输入都完好无损时，完整的动物将被用来确定催乳素的综合效应。原代下丘脑细胞培养将用于从下丘脑外输入分离多巴胺能神经元。神经细胞系将被用来全面探索细胞和分子机制。实验将检验基因表达和翻译后修饰对提高多巴胺能神经元功能的贡献。将分析急性和长时间催乳素诱导的信号在下丘脑中的表达和磷酸化/激活，特别是在多巴胺能神经元中。这些催乳素激活的信号通路启动或维持酪氨酸羟基酶活性增加的作用将被检验。最后一组实验将评估催乳素促进酪氨酸羟基酶基因表达的分子机制。关于催乳素在中枢神经系统内的作用的关键新信息应该会从拟议的实验中产生。

DESCRIPTION (provided by applicant): Prolactin is absolutely essential for normal lactation and breast milk is considered the optimal nourishment for newborn infants. As part of its role in maintaining the maternal process, prolactin has multiple and important effects within the central nervous system. Although prolactin is critical for some aspects of reproductive success, too much prolactin is detrimental for fertility. Prolactin-secreting tumors are the most prevalent pituitary defect and the resulting hyperprolactinemia causes infertility in men and women. The tuberoinfundibular dopaminergic neurons in the hypothalamus provide the major neuroendocrine control to maintain circulating prolactin levels low, but sufficient, for normal reproductive function. Dopamine acts as the major prolactin-inhibiting factor and prolactin, in turn, feeds back to increase dopaminergic neuronal activity, Tyrosine hydroxylase is the rate-limiting enzyme in dopamine biosynthesis and its activity is highly regulated at the level of transcription of the tyrosine hydroxylase gene and by post-translational control mechanisms such as phosphorylation/dephosphorylation of the existing enzyme. Yet, we know very little about how hypothalamic dopaminergic neurons integrate the prolactin-induced signals to enhance neuronal activity. The proposed studies will utilize several models to elucidate mechanisms involved in prolactin control of tyrosine hydroxylase in hypothalamic dopaminergic neurons. Intact animals will be used to determine the integrative effects of prolactin when all hypothalamic and extrahypothalamic inputs are intact. Primary hypothalamic cell cultures will be used to isolate dopaminergic neurons from extrahypothalamic inputs. Neuronal cell lines will be used to fully explore cellular and molecular mechanisms. Experiments will examine contributions of gene expression and post-translational modifications to increase dopaminergic neuronal function. The expression and phosphorylation/ activation of acute and prolonged prolactin-induced signals within the hypothalamus and specifically within dopaminergic neurons will be analyzed. The roles of these prolactin activated signaling pathways to initiate or sustain the increase in tyrosine hydroxylase activity will be examined. The last set of experiments will evaluate molecular mechanisms that contribute to prolactin enhancement of tyrosine hydroxylase gene expression. Critical new information on prolactin's actions within the central nervous system should result from the proposed experiments.