Abstract：
Motilin (MLN) is a peptide hormone originally isolated from the mucosa of the porcine intestine. Its orthologs have been identified in various vertebrates. Although MLN regulates gastrointestinal motility in tetrapods from amphibians to mammals, recent studies indicate that MLN is not involved in the regulation of isolated intestinal motility in zebrafish, at least in vitro. To determine the unknown function of MLN in teleosts, we examined the expression of MLN and the MLN receptor (MLNR) at the cellular level in Japanese medaka (Oryzias latipes). Quantitative PCR revealed that mln mRNA was limitedly expressed in the gut, whereas mlnr mRNA was not detected in the gut but was expressed in the brain and kidney. By in situ hybridization and immunohistochemistry, mlnr mRNA was detected in the dopaminergic neurons of the area postrema in the brain and the noradrenaline-producing cells in the interrenal gland of the kidney. Furthermore, we observed efferent projections of mlnr-expressing dopaminergic neurons in the lobus vagi (XL) and nucleus motorius nervi vagi (NXm) of the medulla oblongata by establishing a transgenic medaka expressing the enhanced green fluorescence protein driven by the mlnr promoter. The expression of dopamine receptor mRNAs in the XL and cholinergic neurons in NXm was confirmed by in situ hybridization. These results indicate novel sites of MLN activity other than the gastrointestinal tract. MLN may exert central and peripheral actions through the regulation of catecholamine release in medaka.
摘要：
胃动素(MLN)是最初分离自猪肠粘膜的肽激素。已在各种脊椎动物中鉴定了其直系同源物。虽然MLN调节从两栖动物到哺乳动物的四足动物的胃肠运动,最近的研究表明，MLN不参与斑马鱼离体肠道运动的调节，至少在体外。为了确定硬骨鱼中MLN的未知函数，我们检测了MLN和MLN受体（MLNR）在日本medaka（Oryziaslatipes）细胞水平的表达。定量PCR显示，mlnmRNA在肠道中表达受限，而mlnrmRNA在肠道中未检测到，但在大脑和肾脏中表达。通过原位杂交和免疫组织化学，在脑后区域的多巴胺能神经元和肾脏肾中腺的去甲肾上腺素产生细胞中检测到mlnrmRNA。此外，我们通过建立表达由mlnr启动子驱动的增强绿色荧光蛋白的转基因medaka，观察了表达mlnr的多巴胺能神经元在延髓的小脑（XL）和神经迷走神经核（NXm）中的传出投射。原位杂交证实了XL中多巴胺受体mRNA和NXm中胆碱能神经元的表达。这些结果表明除了胃肠道之外的MLN活性的新位点。MLN可能通过调节中儿茶酚胺的释放而发挥中枢和外周作用。
