TRIGEMINOTHALAMIC ORGANIZATION AND PLASTICITY

在这个应用程序中的实验将评估传入的作用， 腹侧触须相关神经元发育中的活性 后内侧核（VPM）的大鼠的丘脑。 指导性假设 所有的实验都表明， 活动子集、模式化活动（区分 不同的传入子集），可能有非常不同的 对靶神经元发育的影响。l我们认为， 传入活动可以促进轴突的存活和加工， 特定神经元群体的树突状乔木。 相反，模式化 可能需要传入活动的轴突之间的竞争， 神经元的问题，在他们的目标，它可能会促进细胞死亡和 轴突和可能还有树突乔木的收缩。 我们将测试这个 通过操纵VPM神经元的传入活动来验证这一假说。 我们将 通过应用河豚毒素减少这些细胞的所有传入活动 (TTX)至眶下神经（供应眶下神经的三叉神经分支）， 触须毛囊）的前3周的生活。 我们只会减少 通过简单地将迷走神经的轴粘在一起， 同一时期的鼻毛。 我们将评估 这些操作通过：1）计数VPM细胞，2）确定感受性细胞， VPM神经元的场特性和树突形态 细胞内记录和辣根过氧化物酶（HRP）注射，和3） 重建小分子标记的VPM细胞的皮质轴突主干， 菜豆白细胞凝集素的丘脑沉积。 如果模式化的传入活动对神经群体的影响 细胞是轴突之间竞争活动的一个功能 神经元在其目标上的位置， 通过阻断VPM细胞的传入纤维， 大脑皮层轴突的活动。 我们将通过应用TTX来实现这一点 在出生后的头三周， 评估上述因变量。 在最后一系列研究中，我们将使用简单的细胞计数， 顺行和逆行运输的Di-I，以确定这两个数量 的VPM细胞和这些神经元及其轴突的形态学特性 在新生大鼠中。 这将定义 在我们开始操作的时候，身体感觉系统。 的 建立这一“基线”将有助于解释 在前面的段落中概述的研究。

The experiments in this application will assess the role of afferent activity in the development of vibrissa-related neurons in the ventral posteromedial nucleus (VPM) of the rat's thalamus. The guiding hypothesis for all of the experiments is that afferent activity in general and a subset of that activity, patterned activity (activity that distinguishes distinct subsets of afferents from each other), may have very different effects upon the development of target neurons.l We suggest that all afferent activity may promote both survival and elaboration of axonal and dendritic arbors for a given population of neurons. Conversely, patterned afferent activity may be required for competition among the axons of the neurons in question at their target and it may promote cell death and the retraction of axonal and perhaps also dendritic arbors. We will test this hypothesis by manipulating the afferent activity to VPM neurons. We will reduce all afferent activity to these cells by application of tetrodotoxin (TTX) to the infraorbital nerve (the trigeminal branch that supplies the vibrissa follicles) for the first 3 weeks of life. We will reduce only patterned afferent activity by simply gluing the shafts of the mystacial vibrissae together for this same period. We will assess the effects of these manipulations by: 1) counting VPM cells, 2) determining the receptive field characteristics and dendritic morphology of VPM neurons via intracellular recording and horseradish peroxidase (HRP) injection, and 3) reconstructing the cortical axon arbors of VPM cells labeled by small thalamic deposits of Phaseolus vulgaris leucoagglutinin. If the effects of patterned afferent activity upon a population of nerve cells are a function of that activity's role in competition among the axons of the neurons in question at their target, it should be possible to mimic the effects of a loss patterned afferent input to VPM cells by blocking the activity of their axons in cortex. We will accomplish this by applying TTX to the somatosensory cortex for the first 3 weeks of life and then assessing the dependent variables listed above. In a final series of studies, we will use simple cell counting and anterograde and retrograde transport of Di-I to determine both the number of VPM cells and morphological properties of these neurons and their axons in newborn rats. This will define the status of this portion of the somatosensory system at the time when we initiate our manipulations. The establishment of this "baseline" will aid interpreting the results of the studies outlined in the preceding paragraphs.