NERVE-TARGET CELL INTERACTION IN TASTE BUD MAINTENANCE

描述(申请人提供)：味觉的一个关键问题是，当感受器细胞翻转时，系统如何维持关于味觉质量的稳定信息，不断改变味蕾及其神经纤维之间的连接。要做到这一点，味觉外周必须利用高度的感觉神经可塑性。我们开始了解感觉神经可塑性与神经节细胞与味蕾连接的精确度有关的神经化学基础。可塑性在味蕾失去神经时的退化和重新神经支配时的快速再生中最为显著。越来越多的证据表明，这种神经元-靶细胞的可塑性与神经营养因子及其酪氨酸激酶受体有关。在金黄地鼠的菌状芽中，我们发现在不抵抗去神经支配的瓣状或叶状芽中没有BDNF、TrkB和TrkC的丰富，例如，神经营养素阳性的真菌状芽细胞唯一地不受去神经支配的影响。可以想象，表达这些生长因子的细胞参与味蕾的维持和促进神经纤维的生长。这种维持包括增加生殖细胞发生以抵消因失神经造成的细胞损失或对细胞寿命的影响的可能性，将通过BrdU标记进行评估。神经营养因子在靶向神经纤维中的作用将通过多种颜色的亲脂染料来探索，以准确地展示小群体神经节细胞和单个芽之间的连接。味蕾神经营养因子的表达与去神经、神经再支配、生殖细胞发生和神经支配模式的关系的研究将侧重于对小鼠的分析。小鼠菌芽具有独特的离散神经支配模式，其神经营养因子的表达与仓鼠芽不同(例如，BDNF较少)。通过物种比较，可以提出关于神经营养因子和受体在味蕾维持和神经支配中的作用的假设。一种现有的BDNF上皮细胞过度表达的小鼠品系将被用来检验这样一种假设，即增加芽周神经营养因子会导致更密集、更少离散的神经支配，并增加芽细胞的发生或寿命。为了进行比较，将产生芽特异性BDNF基因敲除小鼠，以专门测试芽神经营养因子缺失对神经支配、再神经支配和生殖细胞分化的影响。此外，还将产生一只可诱导的BDNF基因敲除小鼠，以测试BDNF缺失的效果。

DESCRIPTION (provided by applicant): A key question in taste is how the system maintains a stable message about taste quality while receptor cells are turning over, constantly changing connections between the taste bud and its nerve fibers. To accomplish this the taste periphery must employ a high degree of receptoneural plasticity. We are beginning to understand the neurochemical basis of receptoneural plasticity in relation to the precision with which ganglion cells are connected to taste buds. Plasticity is most dramatic in the degeneration of taste buds when denervated, and their rapid regeneration when reinnervated. Evidence is growing that such neuron-target cell plasticity involves neurotrophins and their tyrosine kinase receptors. In hamster, the fungiform buds of which uniquely resist degeneration after denervation, we identified enrichments in BDNF, TrkB and TrkC not seen in vallate or foliate buds that do not resist denervation, e.g., neurotrophin-positive fungiform bud cells are uniquely unaffected by denervation. Conceivably, cells expressing these growth factors are involved in taste bud maintenance and in promoting nerve fiber in-growth. The possibilities that such maintenance involves increases in gemmal cell genesis to offset cell losses due to denervation, or influences on cell lifespan, will be evaluated by BrdU labeling. A role for neurotrophins in the targeting of nerve fibers will be explored with multicolored lipophilic dyes to demonstrate precisely the connectivity between small populations of ganglion cells and a single buds. Studies of taste bud neurotrophin expression in relation to denervation, reinnervation, gemmal cell genesis, and innervation patterns will emphasize analysis of the mouse. Mouse fungiform buds have uniquely discrete innervation patterns and express neurotrophins differently (e.g., less BDNF) than hamster buds. Species comparison allows formulation of hypotheses about the role of neurotrophins and receptors in taste bud maintenance and innervation. An existing BDNF epithelial overexpressing mouse line will be used to test the hypothesis that increased peri-bud neurotrophin results in denser, less discrete innervation and heightened bud cell genesis or lifespan. For comparison, bud-specific BDNF knockout mice will be generated to specifically test the effect of bud neurotrophin absence on innervation, reinnervation and gemmal cell differentiation. Additionally, an inducible BDNF bud knockout mouse will be generated to test the effect of BDNF loss.