Synaptic structures of the nociceptive primary afferent central terminals in the substantia gelatinosa of spinal trigeminal nucleus candalis

本研究旨在阐明小鼠背角CGRP-、sp -免疫反应性（CGRP-、SP-IR）初级传入中枢末梢与gaba -免疫反应性（GABA-IR）中间神经元的关系。用ABC法对自由漂浮切片进行GABA预包埋免疫染色。超薄切片收集在formvar涂层镍网格上。用包埋后免疫金技术对网格进行CGRP或SP免疫染色。GABA-IR细胞体分布于浅表背角。CGRP-或SP-IR末端与明胶质中间神经元的CABA-IR树突突触前连接。这些发现表明，初级传入纤维传递的信息可以直接传递到gaba能神经元，并且抑制回路被伤害性信息激活。为了直接展示ci -末端与GABA-和met -脑啡肽能中间神经元之间的突触，我们采用了辣椒素处理和免疫标记方法。免疫金标后电镜观察小鼠腰椎背角浅层和脊髓三叉神经candalis核。GABA （15nm）和Met-Enk （5nm）采用不同大小的IgG金双标记。肾小球ci末端与周围树突发生突触前接触，表现出GABA和Met-Enk免疫反应性（IR）。非球粒ci末端也与GABA-和Met-Enk-IR体发生突触前接触。单个树突和体细胞经常出现双重标记，即gaba和Met-Enk可能在某些中间神经元中共存。研究结果表明，痛觉性初级传入神经元通过位于背角浅层和脊髓三叉神经尾核的抑制性gaba能和氨基脑啡肽能中间神经元自行调节疼痛传递。

The present study was designed to elucidate the relationship of CGRP-, SP-immunoreactive (CGRP-, SP-IR) primary afferent central terminals with GABA-immunoreactive (GABA-IR) interneurons in the mouse dorsal horn. Pre-embedding immunostaining for GABA was done on free-floating sections with ABC method. Ultrathin sections were collected on Formvar-coated nickel grids. The grids were immunostained for CGRP or SP with postembedding immunogold technique. The GABA-IR cell bodies were distributed throughout the superficial dorsal horn. The CGRP- or SP-IR terminals were presynaptic to the CABA-IR dendrite of interneurons in the substantia gelatinosa. These findings suggest that the information transmitted by primary afferent fibers can be relayd directly to GABAergic neurons, and inhibitory circuits are activated by nociceptive information.In order to directly demonstrate the synapses between CI-terminals and GABA- and Met-Enkephalinergic interneurons, capsaicin treatment and immunolabeling methods were utilized. Superficial layr of the lumbar spinal cord dorsal horn and spinal trigeminal nucleus candalis of the mouse were examined by electron microscopy after post-embedding immunogold labeling procedures. Double-labeling with different size of IgG gold was used for GABA (15nm) and Met-Enk (5nm). Glomerular CI-terminals made presynaptic contacts with surrounding dendrites exhibiting GABA and Met-Enk immunoreactivities (IR). Nonglomerular CI-terminals also made presynaptic contacts with GABA- and Met-Enk-IR soma. Frequently a single dendrite and somata showed double labeling, i.e.GABA and Met-Enk might coexist in some of the interneurons. The present findings strongly suggest that nociceptive primary afferent neurons modulate the pain transmission by themselves via inhibitory GABAergic and Met-Enkephalinergic interneurons in the superficial layr of dorsal horn and spinal trigeminal nucleus caudalis.