Zhang Jingdong, Luo Pifu
Department of Pathology, University of Vermont College of Medicine, 111 Colchester Avenue, Burlington VT 05401, USA.
Brain Res. 2003 Feb 14;963(1-2):262-73. doi: 10.1016/s0006-8993(02)04046-5.
The dorsal parvocellular reticular formation (PCRt) receives projection of the trigeminal mesencephalic nucleus neurons. It contains the dorsal group of interneurons that integrate and coordinate activity of the oral motor nuclei. Ultrastructural features of synaptic connection from the dorsal PCRt neurons to the motoneurons of the hypoglossal nucleus (XII) were examined at both the light and electron microscopic levels in rats. Biotinylated dextran amine (BDA) was initially iontophoresed into the dorsal part of PCRt unilaterally. Seven days later horseradish peroxidase (HRP) was injected into the body of the tongue. After histochemical reaction for visualization of HRP and BDA, the BDA-labeled fibers and terminals were seen distributing bilaterally in XII with ipsilateral predominance. BDA-labeled terminals were closely apposed upon HRP retrogradely labeled somata and dendrites of the XII motoneurons. A total of 1408 BDA-labeled boutons were examined ultrastructurally, which had mean size of 1.22+/-0.37 microm in diameter. Five hundred-ninety three of these boutons in both the ipsilateral (n=401) and contralateral (n=192) XII were seen to synapse on both the dendrites and somata of HRP-labeled motoneurons. The vast majorities of synapses were axodendritic (98%, 580/593), while 2% of them were axosomatic. Of the 1408 BDA-labeled boutons, 69.6% of them were S-type boutons containing small clear and spherical synaptic vesicles and 30.4% of them were PF-type boutons containing pleomorphic and flattened synaptic vesicles. Approximately 64% of synapses between BDA-labeled boutons and HRP-labeled motoneurons were asymmetric, and 33% of synapses were symmetric. No axoaxodendritic or axoaxosomatic synaptic triad was observed. The present study illustrated the anatomical pathway and synaptological characteristics of neuronal connection between the dorsal PCRt premotor neurons and the XII motoneurons. Its functional significance in coordinating activity of XII motoneurons during oral motor behaviors has been discussed.
背侧小细胞网状结构（PCRt）接受三叉神经中脑核神经元的投射。它包含中间神经元的背侧群，这些中间神经元整合并协调口面部运动核的活动。在大鼠中，从光镜和电镜水平检查了背侧PCRt神经元与舌下神经核（XII）运动神经元之间突触连接的超微结构特征。首先将生物素化葡聚糖胺（BDA）单侧离子导入PCRt的背侧部分。七天后，将辣根过氧化物酶（HRP）注入舌体。在进行用于可视化HRP和BDA的组织化学反应后，可见BDA标记的纤维和终末双侧分布于XII，同侧占优势。BDA标记的终末紧密贴附于HRP逆行标记的XII运动神经元的胞体和树突上。共对1408个BDA标记的终扣进行了超微结构检查，其平均直径为1.22±0.37微米。在同侧（n = 401）和对侧（n = 192）XII中的593个这样的终扣被观察到与HRP标记的运动神经元的树突和胞体都形成突触。绝大多数突触是轴-树突触（98%，580/593），而其中2%是轴-体突触。在1408个BDA标记的终扣中，69.6%是含有小而清亮球形突触小泡的S型终扣，30.4%是含有多形性扁平突触小泡的PF型终扣。BDA标记的终扣与HRP标记的运动神经元之间约64%的突触是不对称的，33%的突触是对称的。未观察到轴-轴-树或轴-轴-体突触三联体。本研究阐明了背侧PCRt运动前神经元与XII运动神经元之间神经元连接的解剖通路和突触学特征。并讨论了其在口面部运动行为中协调XII运动神经元活动的功能意义。
