Neuroendocrine regulation and transduction mechanisms in pituitary hormone release in fish

垂体黄体生成素（LH）和生长激素（GH）是脊椎动物生殖和生长的重要调节因子。多种刺激和抑制性脑下丘脑神经激素反过来控制LH和GH的分泌和产生。因此，研究这些神经激素在垂体细胞水平上的作用机制对于理解生长和繁殖的生理控制具有重要意义。在金鱼体内，LH和gh细胞既有共同的调节因子，也有不同的调节因子。例如，两种促性腺激素释放激素（GnRH2和GnRH3），垂体腺苷酸环化酶激活多肽（PACAP）和生长素（gGRLN）同时刺激LH和GH的分泌，而多巴胺（DA）抑制LH，但刺激GH的释放。相反，GH释放激素（gGHRH）刺激GH，但减弱LH的分泌。了解这些神经激素影响的细胞内细胞变化（信号转导事件）如何相互作用，介导它们对LH和GH释放和合成的影响，对于研究生殖和生长的生理控制是不可或缺的。我们之前关注的是细胞外和细胞内Ca2+、蛋白激酶A （PKA）、PKC、一氧化氮、细胞外调节激酶（ERK）、磷酸肌肽3激酶（PI3K）如何介导金鱼垂体细胞中LH和GH分泌和合成的神经内分泌控制。

Pituitary luteinizing hormone (LH) and growth hormone (GH) are important regulators of reproduction and growth in vertebrates. Multiple stimulatory and inhibitory brain hypothalamic neurohormones in turn control LH and GH secretion and production. Thus, studying the mechanisms by which the effects of these neurohormones are manifested at the level of the pituitary cells is important for understanding the physiological control of growth and reproduction. In goldfish, LH- and GH-cells share common, as well as distinct, regulators. For example, two gonadotropin-releasing hormones (GnRH2 and GnRH3), pituitary adenylate cyclase-activating polypeptide (PACAP) and ghrelin (gGRLN) stimulate both LH and GH secretion while dopamine (DA) inhibits LH, but stimulates GH, release. In contrast, GH-releasing hormone (gGHRH) stimulates GH, but attenuates LH, secretion. Understanding how the intracellular cellular changes (signal tranduction events) effected by these neurohormones interact to mediate their influences on LH and GH release and synthesis is integral to studying the physiological control of reproduction and growth. We have previously focused on how extracellular and intracellular Ca2+, protein kinase A (PKA), PKC, nitric oxide, extracellular-regulated kinase (ERK), phosphoinositide 3-kinase (PI3K) mediate the neuroendocrine control of LH and GH secretion and synthesis in goldfish pituitary cells. Using dispersed goldfish pituitary cells in primary culture, this grant proposal focuses on: 1) whether intracellular Ca2+ stores, PI3K and ERK mediate gGRLN actions on LH- and GH-cells, and how gGRLN receptor expression is affected by GnRH, DA, PACAP and gGHRH treatments; 2) the mechanisms mediating gGHRH stimulation of GH secretion and its novel inhibitory influence on LH release; 3) the transduction pathways mediating the LH and GH release responses to two goldfish kisspeptins, peptides that are thought to be involved in the regulation of puberty in vertebrates; 4) the mechanisms by which goldfish gonadotropin-inhibitory hormone exerts its seasonal-dependent inhibitory and stimulatory effects on hormone release and synthesis in LH- and GH-cells; 5) how PI3K interacts with other signal transduction components in mediating LH and GH release and synthesis, and in particular the differential actions of GnRH2 and GnRH3 on these processes; and 6) the differential expression and role of two known goldfish GnRH receptor isoforms on LH- and GH-cells. Results will contribute to our understanding of how neuroendocrine control of goldfish LH- and GH-cell functions are mediated and integrated, as well as the regulation control of growth and reproduction in goldfish and other teleosts, including important aquaculture species (such as cyprinids). Results will also be important for the basic understanding of ligand- and function-specific intracellular signaling in general.