Rainey W T, Ulinski P S
J Comp Neurol. 1982 Aug 1;209(2):187-207. doi: 10.1002/cne.902090206.
Nucleus rotundus in a large, tectorecipient nucleus in the dorsal thalamus of the pond turtles Pseudemys scripta and Chrysemys picta. Rotundal neurons form a single, morphologically homogeneous population (Rainey, '79) that projects to the dorsal ventricular ridge in the telencephalon. The present paper examines the morphology of and the distribution of synapses upon rotundal neurons. Astrocytes, oligodendrocytes, and neurons can be identified in both 1-micrometer sections stained with toluidine blue and electron micrographs of nucleus rotundus. Rotundal neurons contain euchromatic nuclei and the usual complement of mitochondria, rough endoplasmic reticulum, and free ribosomes in their cytoplasm. They are morphologically homogeneous. Two types of terminal boutons can be defined in rotundus. RA boutons contain round synaptic vesicles and form asymmetric synaptic junctions with rotundal dendrites. FS boutons contain small, flattened or pleomorphic vesicles and form nearly symmetric synaptic junctions with rotundal dendrites and somata. RA boutons occasionally form clusters of contiguous boutons that are presynaptic to one or more thin, central profiles. These profiles are probably the dendritic appendages observed on peripheral dendrites in Golgi material. The distribution of RA and FS boutons along dendrites was investigated by a two-step procedure. First, rotundal neurons were retrogradely solid-filled with horseradish peroxidase reaction product. Dendritic diameters were measured at 20 micrometer intervals along dendritic shafts to produce a plot of dendritic diameter as a function of distance from the soma. Second, the percentage of membrane on dendritic profiles of different diameters that was contacted by RA and FS terminals was determined from electron micrographs. Comparison of the two plots indicates that both bouton types are distributed along the full extent of the dendritic tree, but RA boutons are much more common on the distal two-thirds of rotundal dendrites. This analysis suggests that rotundal neurons form a single population of cells that are morphologically homogeneous and project to the forebrain. There is no indication of interaction between neurons in nucleus rotundus, either via axonal collaterals or presynaptic dendrites. Boutons are distributed on rotundal neurons such that FS boutons are prevalent on the somata and most proximal segments of the dendritic shafts, while RA boutons are most common on the more distal dendritic shafts. RA boutons also contribute to synaptic clusters that may center around complex dendritic appendages.
在锦龟（滑龟）和彩龟的背侧丘脑中有一个大的顶盖接受核——圆核。圆核神经元形成一个单一的、形态学上均一的群体（雷尼，1979年），投射到端脑的背侧室嵴。本文研究了圆核神经元的形态以及其突触的分布。在经甲苯胺蓝染色的1微米切片和圆核的电子显微照片中均可识别出星形胶质细胞、少突胶质细胞和神经元。圆核神经元含有常染色质核，其细胞质中含有线粒体、粗面内质网和游离核糖体的正常成分。它们在形态上是均一的。在圆核中可定义两种类型的终末小体。RA小体含有圆形突触小泡，与圆核树突形成不对称突触连接。FS小体含有小的、扁平或多形性小泡，与圆核树突和胞体形成近乎对称的突触连接。RA小体偶尔会形成相邻小体的簇，这些小体是一个或多个细的中央轮廓的突触前成分。这些轮廓可能是在高尔基材料中在外周树突上观察到的树突附属物。通过两步程序研究了RA和FS小体沿树突的分布。首先，用辣根过氧化物酶反应产物对圆核神经元进行逆行实心填充。沿树突干每隔20微米测量树突直径，以绘制树突直径与距胞体距离的函数图。其次，从电子显微照片中确定不同直径的树突轮廓上被RA和FS终末接触的膜的百分比。对这两个图的比较表明，两种小体类型都分布在整个树突树的范围内，但RA小体在圆核树突的远端三分之二处更为常见。该分析表明，圆核神经元形成一个形态学上均一且投射到前脑的单一细胞群体。没有迹象表明圆核中的神经元之间通过轴突侧支或突触前树突发生相互作用。小体分布在圆核神经元上，使得FS小体在胞体和树突干的最近端节段中普遍存在，而RA小体在更远端的树突干中最常见。RA小体还参与可能围绕复杂树突附属物的突触簇的形成。
