LEPTIN & NEUROPEPTIDE-Y ALTERS FETAL SWALLOWING ACTIVITY

胎儿吞咽对胎儿胃肠道发育，甚至胎儿躯体的生长和成熟都有重要作用。摄食行为反应必须在子宫内发展，以提供新生儿期的水和食物摄入。在出生时，大鼠、绵羊和人类胎儿已经形成了通过吮吸和吞咽获得食物的机制，并且味觉机制是功能性的。因此，在绵羊和可能的人类胎儿中，在妊娠的最后三分之一期间存在dipsogen介导的吞咽和抗利尿反应。我们假设食欲和饱腹感机制也在子宫内发展，参与这一过程的相关神经递质是功能性的，可能会影响胎儿的生长和发育。两个潜在的候选人的摄食行为调节是瘦素和神经肽Y（NPY）。在成年人中，瘦素是脂肪细胞中产生的蛋白质，在下丘脑中起作用以减少食物摄入。NPY主要在下丘脑中产生，增加食物摄入。我们假设：（1）中枢NPY将刺激大量营养素特异性溶液的吞咽，而瘦素刺激的反应将不依赖于溶液含量（即，（2）侧脑室瘦素和NPY将刺激早产儿吞咽活动，和（3）脑室内施用瘦素和NPY将差异性地刺激胎儿脑的离散区域。本研究拟采用生理学实验和免疫组织化学相结合的方法，探讨瘦素和神经肽Y在胎儿吞咽调控中的个体发生和机制。我们将扩大我们的初步研究，特别是解决食欲介导的摄食行为，通过提供胎儿的口腔可用性（舌下）可口的营养液。我们的目的是确定胎儿吞咽活动是否被中枢瘦素和神经肽Y改变。此外，我们将研究个体发育的活动，并确定中央神经元网站激活后，中央瘦素和神经肽Y管理。长期制备的近足月绵羊胎仔将在人工脑脊液（aCSF）中给予中央（侧脑室）重组人瘦素或绵羊NPY，并监测胎仔的吞咽活动。处死时，将取出胎仔脑，灌注固定，切片并免疫染色以检测神经元活性。神经元活动，在食欲和dissogenic中心，将检查即时早期基因产物Fos的激活。Fos激活和胎儿吞咽反应将是相关的。虽然在胚胎时期已经研究了神经发育，但对摄食行为的近期成熟的研究有限。这些研究将提供重要的新信息，子宫内成熟的摄食行为。此外，这些研究代表了一个模型，以检查发育和功能的神经元通路和机制，调节胎儿生理。

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.