Kuroda M, López-Mascaraque L, Price J L
Department of Anatomy and Neurobiology, Washington University, School of Medicine, St. Louis, Missouri 63110.
J Comp Neurol. 1992 Dec 1;326(1):61-81. doi: 10.1002/cne.903260106.
The distribution and dendritic domain of neurons in each segment of the mediodorsal thalamic nucleus (MD) have been studied in the rat with the Golgi technique. In addition, a combined Golgi method-electron microscopic (Golgi-EM) study was undertaken to determine the distribution of morphologically distinct synapse types along the dendrites of individual identified neurons in MD. All the subdivisions or "segments" of MD (medial, central, lateral) contained both stellate and fusiform cells. The dendritic domain of both types of cells was predominantly restricted to the same segment of MD that contained the cell body of the neuron. Typical stellate neurons were found near the center of each segment, with radiating dendrites that extended to but not across the boundaries of the segment. Fusiform cells were usually located close to the segmental or nuclear boundaries and tended to have dendrites oriented parallel to those borders; again, the dendrites tended not to extend across borders between segments or at the outer edge of MD. In the medial segment of MD many fusiform cells had especially bipolar dendritic configurations, generally with a dorsoventral orientation. Because no small neurons were identified that might correspond to thalamic interneurons, all the impregnated cells in MD are presumed to be thalamocortical projection neurons. These results indicate that cells and their major dendrites are confined to a single segment of MD, with little dendritic overlap across segmental or nuclear borders. The segments of MD may therefore be considered to be relatively independent subnuclei. The distribution of the four types of synapses previously identified in MD (Kuroda and Price, J. Comp. Neurol., 303:513-533, 1991) was determined along several identified dendrites studied with the Golgi-EM method. Primary dendrites were contacted mostly by large axon terminals, including both large, round vesicle (LR) terminals and large, pleomorphic vesicle (LP) terminals, as well as a few small to medium sized terminals with pleomorphic vesicles (SMP). No small terminals with round vesicles (SR terminals) were observed to make synapses with primary dendrites. Secondary and tertiary dendrites received synapses from all types of axon terminals. Higher order dendrites were contracted predominantly by SR boutons, but they also carried some LR and SMP terminals. In addition, SMP boutons were often found to form symmetric contacts with cell somata.
运用高尔基染色技术，对大鼠丘脑背内侧核（MD）各节段神经元的分布及树突域进行了研究。此外，还采用高尔基染色法与电子显微镜相结合的方法（高尔基-电子显微镜法），以确定MD中单个已识别神经元树突上形态各异的突触类型的分布情况。MD的所有亚区或“节段”（内侧、中央、外侧）均含有星形细胞和梭形细胞。这两种类型细胞的树突域主要局限于包含神经元胞体的MD同一节段内。典型的星形神经元位于每个节段的中心附近，其放射状树突延伸至节段边界但不越过边界。梭形细胞通常位于节段或核边界附近，其树突往往与这些边界平行；同样，树突往往不延伸至节段之间的边界或MD的外缘。在MD的内侧节段，许多梭形细胞具有特殊的双极树突形态，通常呈背腹方向。由于未识别出可能对应于丘脑中间神经元的小神经元，因此推测MD中所有被浸染的细胞均为丘脑皮质投射神经元。这些结果表明，细胞及其主要树突局限于MD的单个节段内，在节段或核边界处树突很少重叠。因此，MD的节段可被视为相对独立的亚核。采用高尔基-电子显微镜法，沿着几条已识别的树突，确定了先前在MD中识别出的四种突触类型（黑田和普赖斯，《比较神经学杂志》，303:513 - 533, 1991）的分布情况。初级树突主要与大型轴突终末接触，包括大型圆形囊泡（LR）终末和大型多形性囊泡（LP）终末，以及一些带有多形性囊泡的中小型终末（SMP）。未观察到带有圆形囊泡的小型终末（SR终末）与初级树突形成突触。二级和三级树突接受来自所有类型轴突终末的突触。高阶树突主要与SR终扣接触，但它们也带有一些LR和SMP终末。此外，经常发现SMP终扣与细胞体形成对称接触。
