Shigenaga Y, Hirose Y, Yoshida A, Fukami H, Honma S, Bae Y C
Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, Suita, Osaka 565-0871, Japan.
J Comp Neurol. 2000 Oct 9;426(1):13-30.
Little is known about the ultrastructure of synaptic boutons contacting trigeminal motoneurons. To address this issue, physiologically identified premotor neurons (n = 5) in the rostrodorsomedial part of the oral nucleus (Vo.r) were labeled by intracellular injections of horseradish peroxidase (HRP) in cats. The ultrastructure of 182 serially sectioned axon terminals from the five neurons was both qualitatively and quantitatively analyzed. In addition, the effects of the glycine antagonist strychnine, GABA(A) antagonist bicuculline, NMDA antagonist 2-amino-5-phosphonovalerate (APV), and non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on Vo.r-induced postsynaptic potentials in trigeminal motoneurons (n = 11) were examined to evaluate potential signaling substances of the premotor neurons. Labeled boutons made synaptic contacts with either jaw-closing or -opening motoneurons. All the boutons contained pleomorphic vesicles, and most formed a single symmetric synapse either on the somata or on primary dendrites. Morphometric analyses indicated that bouton volume, bouton surface area, apposed surface area, total active zone area, and mitochondrial volume were not different between boutons on jaw-closing and -opening motoneurons. Vesicle number and density, however, were higher for boutons on jaw-closing motoneurons. The five morphological parameters were positively correlated with bouton volume. Vesicle density was the exception, which tending to be negatively correlated. Intravenous infusion of strychnine or bicuculline suppressed Vo.r-induced inhibitory postsynaptic potentials (IPSPs) in jaw-closing motoneurons. Abolition of Vo. r-induced excitatory postsynaptic potentials in jaw-opening motoneurons with APV and CNQX unmasked IPSPs. The present results suggest that premotor neurons in the Vo.r are inhibitory and that positive correlations between the ultrastructural parameters associated with synaptic release and bouton size are applicable to the interneurons, as they are in primary afferents.
关于与三叉神经运动神经元相接触的突触小体的超微结构，人们了解甚少。为了解决这个问题，在猫身上，通过细胞内注射辣根过氧化物酶（HRP）对位于口核（Vo.r） rostrodorsomedial 部分的生理上已确定的运动前神经元（n = 5）进行标记。对来自这五个神经元的182个连续切片的轴突终末的超微结构进行了定性和定量分析。此外，还研究了甘氨酸拮抗剂士的宁、GABA(A)拮抗剂荷包牡丹碱、NMDA拮抗剂2-氨基-5-磷酸戊酸（APV）和非NMDA拮抗剂6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）对三叉神经运动神经元（n = 11）中Vo.r诱导的突触后电位的影响，以评估运动前神经元的潜在信号物质。标记的小体与闭口或开口运动神经元形成突触联系。所有的小体都含有多形性囊泡，并且大多数在胞体或初级树突上形成单个对称突触。形态计量学分析表明，闭口和开口运动神经元上的小体在小体体积、小体表面积、并列表面积、总活性区面积和线粒体体积方面没有差异。然而，闭口运动神经元上的小体的囊泡数量和密度更高。这五个形态学参数与小体体积呈正相关。囊泡密度是个例外，它倾向于呈负相关。静脉注射士的宁或荷包牡丹碱可抑制闭口运动神经元中Vo.r诱导的抑制性突触后电位（IPSPs）。用APV和CNQX消除开口运动神经元中Vo.r诱导的兴奋性突触后电位可揭示IPSPs。目前的结果表明，Vo.r中的运动前神经元是抑制性的，并且与突触释放相关的超微结构参数和小体大小之间的正相关适用于中间神经元，就像它们在初级传入神经元中一样。
