Liu Y S, Schweitzer L, Renehan W E
Division of Gastroenterology, Henry Ford Health System, Detroit, Michigan 48202, USA.
J Comp Neurol. 2000 Sep 18;425(2):219-32. doi: 10.1002/1096-9861(20000918)425:2<219::aid-cne5>3.0.co;2-4.
The rodent gustatory system has become a popular and useful model for the study of brain development because of this system's protracted period of postnatal maturation and its sensitivity to subtle changes in the animal's sensory environment. The goal of this investigation was to improve our understanding of dendritic remodeling exhibited by second-order gustatory neurons by presenting a comprehensive and definitive description of the development of the dendritic architecture of taste-sensitive neurons in the rostral nucleus of the solitary tract. Extracellular and intracellular recording and intracellular labeling techniques were used to examine the structure and function of individual gustatory neurons in three groups of rats: (1) Postnatal day 13-21 (PND13-21), (2) Postnatal day 22-28 (PND22-28), and (3) Adult (postnatal day 60-90). We found that neurons that responded to all three of the salts in our taste array ("Salt Sensitive") exhibited a striking increase in the number of dendritic branch points, maximum branch order, swelling density, and spine density between the PND13-21 and PND22-28 periods. These increases were followed by a period of dendritic remodeling during which the values for all measures except spine density decreased significantly. The neurons that did not respond to all three salts exhibited no change in the number of dendritic branches, branch order, or spine density during development, but they did undergo a decrease in swelling density. We also found that there was a significant decrease in the total dendritic length and cell volume of Salt Sensitive neurons between the PND22-28 and Adult periods, whereas the cells that did not respond to all three salts exhibited an increase in dendritic length and cell volume between postnatal day 28 and adulthood. Finally, we found that the dendrites of the Adult Salt Sensitive neurons were more restricted in the rostrocaudal axis than either the PND13-21 or PND22-28 Salt Sensitive cells. In contrast, there were no significant changes in the rostrocaudal extent of the dendritic arbors of cells that did not respond to all three salts. When viewed in the context of the extant literature and our own preliminary studies that used modified salt diets, we propose that these results provide strong support for the hypothesis that there is a relationship between postnatal dendritic development (particularly remodeling) and the animal's sensitivity to salts.
由于啮齿动物味觉系统在出生后有较长的成熟时期，且对动物感觉环境的细微变化敏感，它已成为研究大脑发育的一个流行且有用的模型。本研究的目的是通过对孤束吻侧核中味觉敏感神经元树突结构发育进行全面而确切的描述，增进我们对二级味觉神经元所表现出的树突重塑的理解。采用细胞外和细胞内记录以及细胞内标记技术，对三组大鼠的单个味觉神经元的结构和功能进行了研究：(1)出生后第13 - 21天（PND13 - 21），(2)出生后第22 - 28天（PND22 - 28），以及(3)成年大鼠（出生后第60 - 90天）。我们发现，对我们味觉阵列中的所有三种盐都有反应的神经元（“盐敏感”神经元）在PND13 - 21期和PND22 - 28期之间，树突分支点数量、最大分支阶数、肿胀密度和棘密度显著增加。这些增加之后是一个树突重塑期，在此期间，除棘密度外，所有测量值均显著下降。对所有三种盐都无反应的神经元在发育过程中，树突分支数量、分支阶数或棘密度没有变化，但它们的肿胀密度确实有所下降。我们还发现，在PND22 - 28期和成年期之间，盐敏感神经元的总树突长度和细胞体积显著减小，而对所有三种盐都无反应的细胞在出生后第28天到成年期之间，树突长度和细胞体积增加。最后，我们发现成年盐敏感神经元的树突在前后轴上比PND13 - 21期或PND22 - 28期的盐敏感细胞受到的限制更大。相比之下，对所有三种盐都无反应的细胞的树突分支在前后范围上没有显著变化。结合现有文献以及我们自己使用改良盐饮食的初步研究来看，我们认为这些结果为出生后树突发育（特别是重塑）与动物对盐的敏感性之间存在关联这一假说提供了有力支持。
