Neurotrophin regulation of taste system development

描述（由申请人提供）：在发育过程中，味觉神经支配是一个严格调控的过程，在这个过程中，特定数量的初级味觉传入投射到口腔的离散区域。本研究旨在研究味觉神经支配，以支持两个长期目标：1)确定允许味觉神经元以特定的神经支配量支配正确的目标（味蕾）的细胞和分子机制；2)确定这些连接是否和/或如何对中枢味觉发育或味觉功能重要。该项目主要关注神经营养因子在胚胎发育过程中调节味觉神经元数量和外周和中枢靶向中的作用。众所周知，出生时存在的用于支配舌头和上颚味蕾的味觉神经节神经元的数量在某种程度上是由脑源性神经营养因子（BDNI0）和神经营养因子-4 （NT4）决定的。然而，BDNF和NT4调节神经支配的机制尚不清楚，可能涉及许多不同胚胎阶段的许多不同发育过程。拟议的研究结合了基因敲除小鼠的原位杂交，细胞计数，道示踪，免疫组织化学和扫描电镜：1)确定胚胎味觉系统何时何地暴露于BDNF和NT4, 2)确定BDNF和NT4何时调节味觉神经元数量，以及这种调节是通过减少增殖还是增加细胞死亡来完成的，3)确定BDNF和/或NT4是否需要初始目标入侵，4)确定BDNF和/或NT4是否调节舌和腭感觉传入的中心分布。综上所述，这些研究验证了以下假设：1)NT4沿味觉纤维投射通路表达，在外周和中枢靶点神经初始支配前调节味觉神经元存活；2)BDNF在味觉上皮中表达，在外周和中枢靶点神经初始支配后调节神经元存活。由于这些实验研究了神经营养因子如何调节感觉神经支配的数量和位置，因此该项目对这些强大的信号分子在控制损伤后神经再生方面的潜在治疗用途具有重要意义。

DESCRIPTION (provided by applicant): During development, gustatory innervation is a tightly regulated process in which specific numbers of primary taste afferents project to discrete regions of the oral cavity. The present research is designed to investigate gustatory innervation in support of two long terms goals: 1) to determine the cellular and molecular mechanisms that allow gustatory neurons to innervate the correct target (taste buds) with a specific mount of innervation, and 2) to determine if and/or how these connections are important for central gustatory development or taste function. The proposed project focuses on the role of neurotrophins in regulating gustatory neuron number and peripheral and central targeting during embryonic development. It is known that the number of gustatory ganglion neurons that will exist at birth to innervate taste buds on the tongue and palate is somehow determined by brain-derived neurotrophic factor (BDNI0 and neurotrophin-4 (NT4). However, the mechanism(s) by which BDNF and NT4 regulate innervation are unknown, and could involve any number of different developmental processes during numerous different embryonic stages. The proposed studies combine in situ hybridization, cell counting, tract tracing, immunohistochemistry, and SEM in gene knockout mice to: 1) determine when and where the embryonic taste system is exposed to BDNF and NT4, 2) determine when BDNF and NT4 regulate gustatory neuron number and whether this regulation is accomplished by reducing proliferation or by increasing cell death, 3) determine whether BDNF and/or NT4 is required for initial target invasion, and 4) determine if BDNF and/or NT4 regulate the central distribution of tongue and palatal sensory afferents. Together, these studies test the hypotheses that: 1) NT4 is expressed along gustatory fiber projection pathways and regulates gustatory neuron survival before initial innervation of peripheral and central targets, and 2) BDNF is expressed in gustatory epithelia and regulates neuron survival after initial peripheral and central target innervation. Because these experiments examine how neurotrophins regulate the amount and location of sensory innervation, this project has important implications for the potential therapeutic use of these powerful signaling molecules in controlling neural regeneration following injury.