Physological and anatomical study of the developmental process of rat trigeminal sensory branch.

连接外周神经系统和中枢神经系统的初级感觉传入神经在与靶细胞接触之前要经过各种底物和相当长的距离，然而这些纤维成功地将感觉外周神经的空间组织以惊人的精度传递给中枢中继核。多年来，了解这种机制是如何在发育过程中被编程的一直是神经生物学的一个主要问题。在本研究中，我们发现一种具有9- o乙酰化gd3样结构的碳水化合物抗原可能参与支配胡须的神经纤维的束控。当感觉神经和运动神经在外围同时运动时，上述分子可能作为感觉神经的识别分子来区分自己与运动神经。在胫束初级传入神经终止的胫束核，出生后形成桶状结构。在大鼠围生期（E19-PO），胫神经不同分支（上颌和下颌）的纤维末端树突占据重叠区域。然而，这两个神经末梢之间的重叠比例在围产期前后减少，表明精细修剪在出生前就开始了。出生后，随着桶状结构的形成，三叉神经的两个分支所占据的区域更加清晰地分开。体外共培养系统的研究表明，一定有特定于胫神经突伸长的粘附分子。我们还没有鉴定出这样的分子，然而，胚胎皮肤组织中的细胞表达的分子比在视网膜细胞中表达的分子对胫神经突更有亲和力。

Primary sensory afferents that connect the peripheral to the central nervous system navigate through a variety of substrates and across considerable distances before making contact with target cells, yet these fibers succeed in conveying the spatial organization of the sensory periphery to central relay nuclei with remarkable precision. Understanding how this mechanism is programd in development has been a major issue in neurobiology for many years.In this study, we showed that one of carbohydrate antigens which has 9-O-acetylated GD3-like structure might be involved in the fasciculation of nerve fibers which innervate whiskers in the same portion. The above molecule might be working as a recognition molecule for sensory nerves to distinguish itself from motor nerves when sensory and moter nerves travell together in the periphery.In the tigeminal nuclei where tigeminal primary afferents terminate, the barrel structure is formed after birth. In this perinatal period (E19-PO) of rat, the terminal arborization of fibers from different branches of the tigeminal nerve (maxillary vs.mandibular) occupy areas with overlap. The proportion of overlap between these two nerve terminals, however, decreases around perinatal period, suggesting fine pruning begin to take place before birth. After birth, as barrel structure is formed, the territories occupied by two branches of the trigeminal nerve are more clearly separated.In vitro study using co-culture system showed that there must be adhesion molecules which are specific to the tigeminal neurite elongation. We have not identified such molecules yet, however, cells in the embryonic skin tissue express molecules with more affinity for tigeminal neurites than that are expressed in retinal cells.