Almeida A, Tavares I, Lima D
Institute of Histology and Embryology of the Faculty of Medicine and IBMC, University of Oporto, Porto, 4200, Portugal.
Eur J Pain. 2000;4(4):373-87. doi: 10.1053/eujp.2000.0193.
The synaptic architecture of spinal afferents of the dorsal portion (DRtd) of the medullary dorsal reticular nucleus (DRt) is studied. After iontophoretic injections of cholera toxin subunit B (CTb) into the superficial (laminae I-II), deep (laminae IV-V) or entire (laminae I-V) dorso-ventral extent of the spinal dorsal horn at the cervico-thoracic or lumbo-sacral levels, axonal boutons of two distinct types were labelled in the DRtd. Type A boutons (82% after cervico-thoracic injections and 92% after lumbo-sacral injections) were roundish, small and presented few mitochondria and small, round synaptic vesicles. Type B boutons (18% after cervico-thoracic injections and 8% after lumbo-sacral injections) were elongated, two to three times larger, and exhibited numerous mitochondria and larger round vesicles. Both types of bouton established asymmetrical synaptic contacts with small dendritic profiles and, less frequently, with dendritic trunks and perikarya. Retrograde labelling occurred in the postsynaptic profile of 15-18% type A boutons labelled from any injection site. Taken together with previous data on DRt-spinal synaptic contacts at the superficial dorsal horn, the present results point to the occurrence of a reciprocal excitatory loop connecting the dorsal DRt and lamina I, which may be at the basis of the DRt-mediated pain-facilitating effects described recently.
对延髓背侧网状核（DRt）背侧部分（DRtd）的脊髓传入神经的突触结构进行了研究。在颈胸段或腰骶段脊髓背角的腹背范围的浅层（I-II层）、深层（IV-V层）或整个（I-V层）进行霍乱毒素B亚基（CTb）的离子电渗注入后，在DRtd中标记出了两种不同类型的轴突终扣。A型终扣（颈胸段注射后占82%，腰骶段注射后占92%）呈圆形，较小，线粒体较少，有小的圆形突触小泡。B型终扣（颈胸段注射后占18%，腰骶段注射后占8%）呈细长形，大小为A型的两到三倍，有大量线粒体和较大的圆形小泡。两种类型的终扣都与小的树突轮廓建立不对称突触联系，与树突干和胞体建立联系的频率较低。在从任何注射部位标记的A型终扣的突触后轮廓中出现逆行标记。结合先前关于DRt与脊髓背角浅层突触联系的数据，目前的结果表明存在一个连接背侧DRt和I层的相互兴奋性环路，这可能是最近描述的DRt介导的疼痛促进作用的基础。
