University of Virginia, Charlottesville, Virginia 22904, USA.
J Comp Neurol. 2012 Oct 1;520(14):3217-35. doi: 10.1002/cne.23093.
The chorda tympani nerve (CT), one of three nerves that convey gustatory information to the nucleus of the solitary tract (NTS), displays terminal field reorganization after postnatal day 15 in the rat. Aiming to gain insight into mechanisms of this phenomenon, CT axon projection field and terminal morphology in NTS subdivisions were examined using tract tracing, light microscopy, and immunoelectron microscopy at four postnatal ages: P15, P25, P35, and adult. The CT axons that innervated NTS rostrolateral subdivision both in the adult and in P15 rats were morphologically distinct from those that innervated the rostrocentral, gustatory subdivision. In both subdivisions, CT terminals reached morphological maturity before P15. Rostrolateral, but not rostrocentral axons, went through substantial axonal branch elimination after P15. Rostrocentral CT synapses, however, redistribute onto postsynaptic targets in the following weeks. CT terminal preference for GABAergic postsynaptic targets was drastically reduced after P15. Furthermore, CT synapses became a smaller component of the total synaptic input to the rostrocentral NTS after P35. The results underlined that CT axons in rostrocentral and rostrolateral subdivisions represent two distinct populations of CT input, displaying different morphological properties and structural reorganization mechanisms during postnatal development.
鼓索神经（CT）是将味觉信息传递到孤束核（NTS）的 3 条神经之一，在大鼠出生后第 15 天显示出终末场重组。为了深入了解这一现象的机制，我们在四个出生后年龄（P15、P25、P35 和成年）使用轨迹追踪、光镜和免疫电镜检查了 CT 轴突投射场和 NTS 亚区的终末形态。在成年和 P15 大鼠中支配 NTS 前外侧亚区的 CT 轴突在形态上与支配前中央、味觉亚区的 CT 轴突明显不同。在前外侧和前中央亚区，CT 终末在 P15 之前达到形态成熟。在 P15 之后，前外侧轴突经历了大量的轴突分支消除，但前中央轴突没有。然而，在前中央 CT 突触在接下来的几周内重新分配到突触后靶标上。P15 后，CT 终末对 GABA 能突触后靶标的偏好急剧降低。此外，在 P35 之后，CT 突触成为 NTS 前中央区总突触输入的较小组成部分。研究结果强调了前中央和前外侧亚区的 CT 轴突代表了两种不同的 CT 输入群体，它们在出生后发育过程中表现出不同的形态特性和结构重组机制。
