Kuroda M, Price J L
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
J Comp Neurol. 1991 Jan 22;303(4):513-33. doi: 10.1002/cne.903030402.
The synaptic organization of the mediodorsal thalamic nucleus (MD) in the rat was studied with the electron microscope, and correlated with the termination of afferent fibers labeled with wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Presynaptic axon terminals were classified into four categories in MD on the basis of the size, synaptic vesicle morphology, and synaptic membrane specializations: 1) small axon terminals with round synaptic vesicles (SR), which made asymmetrical synaptic contacts predominantly with small dendritic shafts; 2) large axon terminals with round vesicles (LR), which established asymmetrical synaptic junctions mainly with large dendritic shafts; 3) small to medium axon terminals with pleomorphic vesicles (SMP), which formed symmetrical synaptic contacts with somata and small-diameter dendrites; 4) large axon terminals with pleomorphic vesicles (LP), which made symmetrical synaptic contacts with large dendritic shafts. Synaptic glomeruli were also identified in MD that contained either LR or LP terminals as the central presynaptic components. No presynaptic dendrites were identified. In order to identify terminals arising from different sources, injections of WGA-HRP were made into cortical and subcortical structures known to project to MD, including the prefrontal cortex, piriform cortex, amygdala, ventral pallidum and thalamic reticular nucleus. Axons from the amygdala formed LR terminals, while those from the prefrontal and insular cortex ended exclusively in SR terminals. Fibers labeled from the piriform cortex formed both LR and SR endings. Based on their morphology, all of these are presumed to be excitatory. In contrast, the axons from the ventral pallidum ended as LP terminals, and those from the thalamic reticular nucleus formed SMP terminals. Both are presumed to be inhibitory. At least some terminals from these sources have also been identified as GABAergic, based on double labeling with anterogradely transported WGA-HRP and glutamic acid decarboxylase (GAD) immunocytochemistry.
用电子显微镜研究了大鼠背内侧丘脑核（MD）的突触组织，并将其与用与辣根过氧化物酶（WGA-HRP）偶联的麦胚凝集素标记的传入纤维的终末进行了关联。根据大小、突触小泡形态和突触膜特化，MD中的突触前轴突终末分为四类：1）具有圆形突触小泡的小轴突终末（SR），主要与小的树突干形成不对称突触联系；2）具有圆形小泡的大轴突终末（LR），主要与大的树突干建立不对称突触连接；3）具有多形性小泡的中小轴突终末（SMP），与胞体和小直径树突形成对称突触联系；4）具有多形性小泡的大轴突终末（LP），与大的树突干形成对称突触联系。在MD中还鉴定出了突触小球，其中包含LR或LP终末作为中央突触前成分。未鉴定出突触前树突。为了鉴定来自不同来源的终末，将WGA-HRP注射到已知投射到MD的皮质和皮质下结构中，包括前额叶皮质、梨状皮质、杏仁核、腹侧苍白球和丘脑网状核。来自杏仁核的轴突形成LR终末，而来自前额叶皮质和岛叶皮质的轴突仅终止于SR终末。来自梨状皮质的标记纤维形成LR和SR终末。根据它们的形态，所有这些都被认为是兴奋性的。相反，来自腹侧苍白球的轴突以LP终末结束，而来自丘脑网状核的轴突形成SMP终末。两者都被认为是抑制性的。基于顺行运输的WGA-HRP和谷氨酸脱羧酶（GAD）免疫细胞化学的双重标记，这些来源的至少一些终末也被鉴定为GABA能。
