LEPTIN & NEUROPEPTIDE-Y ALTERS FETAL SWALLOWING ACTIVITY

胎儿吞咽在胎儿胃肠道发育中起着重要的作用，也可能影响胎儿的躯体生长和成熟。摄食行为反应必须在子宫内形成，以便在新生儿时期获得水和食物。在出生时，大鼠、羊和人类胎儿已经发展出通过哺乳和吞咽获得食物的机制，味觉机制也在发挥作用。因此，在绵羊和可能的人类胎儿中，在妊娠的最后三分之一出现了双原介导的吞咽和抗利尿反应。我们假设食欲和饱腹机制也在子宫内发育，参与这一过程的相关神经递质是功能性的，可能影响胎儿的生长发育。两种潜在的摄取行为调节候选者是瘦素和神经肽- y （NPY）。在成人中，瘦素是一种由脂肪细胞产生的蛋白质，在下丘脑中起减少食物摄入的作用。NPY主要在下丘脑产生，增加食物摄入。我们假设：(1)中央NPY会刺激大量营养物质特异性溶液的吞咽，而瘦素刺激的反应将独立于溶液的含量（即，dipsogen介导）；(2)侧室瘦素和NPY会刺激早产儿吞咽活动；(3)心室内给药瘦素和NPY会不同程度地刺激胎儿大脑的离散区域。拟开展的研究将利用生理实验和免疫组织化学的综合方法，探讨瘦素和NPY在调节胎儿吞咽中的个体发生和机制。我们将扩展我们的初步研究，专门解决食欲介导的摄食行为，通过为胎儿提供口服（舌下）美味的营养液。我们的目的是确定胎儿吞咽活动是否被中枢瘦素和NPY改变。此外，我们将检查的个体活性，并确定中枢瘦素和NPY管理激活的中枢神经元位点。长期制备的近期羊胎儿将在人工脑脊液（aCSF）中注射中央（侧脑室）重组人瘦素或羊NPY，并监测胎儿的吞咽活动。在牺牲时，胎儿大脑将被移除，灌注固定，切片和免疫染色神经元活动。神经活动，在食欲和肥胖中心，将检查激活的即时早期基因产物Fos。Fos的激活与胎儿吞咽反应相关。虽然神经发育已经在胚胎学时期进行了研究，但对摄食行为的近期成熟的研究有限。这些研究将提供有关子宫内进食行为成熟的重要新信息。此外，这些研究为研究调节胎儿生理的神经通路和机制的发育和功能提供了一个模型。

Fetal swallowing has important roles in fetal gastrointestinal development, and perhaps fetal somatic growth and maturation. Ingestive behavior responses must develop in utero to provide for acquisition of water and food intake during the neonatal period. At birth, the rat, ovine and human fetus have developed mechanisms to acquire food via suckling and swallowing and taste mechanisms are functional. Thus, in sheep and likely human fetuses, dipsogen-mediated swallowing and antidiuretic responses are present during the last third of gestation. We hypothesize that appetite and satiety mechanisms also develop in utero and the related neurotransmitters involved in this process are functional and may influence fetal growth and development. Two potential candidates for ingestive behavior regulation are leptin and neuropeptide-Y (NPY). In adults, leptin is a protein produced in adipocytes with actions in the hypothalamus to decrease food intake. NPY, produced primarily in the hypothalamus, increases food intake. We hypothesize: (1) Central NPY will stimulate swallowing of a macronutrient specific solution while leptin stimulated responses will be independent of solution content (i.e., dipsogen mediated), (2) Lateral ventricular leptin and NPY will stimulate preterm swallowing activity, and (3) Intra-ventricular administration of leptin and NPY will differentially stimulate discrete areas of the fetal brain. The proposed studies will explore the ontogeny and mechanisms of leptin and NPY in the modulation of fetal swallowing, utilizing an integrative approach of physiologic experiments and immunohistochemistry. We will expand upon our preliminary studies to specifically address appetite-mediated ingestive behavior, by providing the fetus the oral-availability (sublingual) of a palatable nutrient solution. Our objective is to determine whether fetal swallowing activity is altered by central leptin and NPY. Moreover, we will examine the ontogenic activity of, and identify central neuronal sites activated upon by central leptin and NPY administration. Chronically prepared, near term ovine fetuses will be administered central (lateral ventricle) recombinant human leptin or ovine NPY in artificial cerebral spinal fluid (aCSF) and fetuses monitored for swallowing activity. At time of sacrifice, fetal brains will be removed, perfusion fixed, sectioned and immunostained for neuronal activity. Neuronal activity, in both appetite and dipsogenic centers, will be examined for activation of the immediate-early gene product Fos. Fos activation and fetal swallowing responses will be correlated. Although neurodevelopment has been investigated during embryologic periods, there has been limited investigation of the near term maturation of ingestive behavior. These studies will provide important new information concerning the in utero maturation of ingestive behavior. In addition, these studies represent a model to examine the development and function of neuronal pathways and mechanisms which regulate fetal physiology.