Falls W M
J Comp Neurol. 1986 Feb 1;244(1):96-110. doi: 10.1002/cne.902440108.
Neurons in the ventrolateral (VL) subdivision of rat trigeminal nucleus oralis (Vo) have most of their dendritic arbors confined within this region. This study examines the morphology and synaptic connections of a population of myelinated primary trigeminal axons that arborize within VL and are in a position to provide input directly to VL neurons. Primary axons were visualized for light and electron microscopic analysis by injecting 30% horseradish peroxidase (HRP) in 2% dimethylsulfoxide (DMSO) into the sensory root of the trigeminal nerve and allowing 24-36 hours for the anterograde transport of HRP into the terminal axonal arbors. This population is characterized by its cone-shaped terminal arbors, which generate many axonal endings (2-8 micron in diameter) along unmyelinated terminal strands. These arbors arise from collaterals emanating from thinly myelinated (2-5 micron in diameter) parent branches descending in the spinal V tract, which, on the basis of their size, are considered to be small myelinated (A sigma) primary trigeminal axons. HRP-labeled P endings belonging to this population of primary axons are scalloped, filled with spherical to ovoid (40-70 nm in diameter) synaptic vesicles, and lie centrally in glomeruli where they make asymmetrical axodendritic synapses on dendritic shafts and spine heads. It is at these synapses that this population of primary trigeminal axons is probably transferring its input directly to the dendritic arbors of VL neurons. The dendritic shafts and spine heads also receive symmetrical to intermediate axodendritic synapses from endings containing flattened (70 X 29 nm) synaptic vesicles. These terminals also establish axo-axonic synapses on the P ending. Other synaptic components found less often in the glomeruli include small terminals containing oval (14-23 nm) synaptic vesicles that establish symmetrical to intermediate synapses on the P ending, boutons containing pleomorphic (35-80 nm) synaptic vesicles that form symmetrical to intermediate synapses on the P ending as well as on dendritic shafts, and small peripheral endings containing round (20-40 nm) synaptic vesicles that establish asymmetrical synapses on dendritic shafts.
大鼠三叉神经中脑核（Vo）腹外侧（VL）亚区的神经元，其树突分支大多局限于该区域。本研究考察了一群有髓鞘的三叉神经初级轴突的形态和突触连接，这些轴突在VL内形成分支，能够直接向VL神经元提供输入。通过将30%辣根过氧化物酶（HRP）溶于2%二甲基亚砜（DMSO）中注入三叉神经感觉根，并让HRP顺行运输24 - 36小时至轴突终末分支，从而使初级轴突在光镜和电镜下可视化。这群轴突的特征是其锥形终末分支，在无髓鞘的终末丝上产生许多轴突终末（直径2 - 8微米）。这些分支源自脊髓V束中下行的细有髓鞘（直径2 - 5微米）母支发出的侧支，根据其大小，这些母支被认为是小的有髓鞘（A sigma）三叉神经初级轴突。属于这群初级轴突的HRP标记的P终末呈扇形，充满球形至椭圆形（直径40 - 70纳米）的突触小泡，位于小球体中央，在那里它们在树突干和棘突头部形成不对称的轴 - 树突触。正是在这些突触处，这群三叉神经初级轴突可能将其输入直接传递给VL神经元的树突分支。树突干和棘突头部还从含有扁平（70×29纳米）突触小泡的终末接受对称至中等类型的轴 - 树突触。这些终末也在P终末上建立轴 - 轴突触。在小球体中较少见的其他突触成分包括含有椭圆形（14 - 23纳米）突触小泡的小终末，它们在P终末上建立对称至中等类型的突触；含有多形性（35 - 80纳米）突触小泡的终扣，它们在P终末以及树突干上形成对称至中等类型的突触；以及含有圆形（20 - 40纳米）突触小泡的小外周终末，它们在树突干上建立不对称突触。
