Isomura G, Hámori J
J Hirnforsch. 1980;21(6):577-86.
An electronmicroscopical study using an analysis of thin sections and experimental degeneration of the medial cuneate nucleus of the cat has revealed five types of axon terminals: (1) Relatively large axon terminals characterized by a population of large (45-60 nm) spheroid vesicles which are the terminals of the spinal afferents: (2) Small axon terminals - probably of local interneuronal source - containing characteristic flattened vesicles: (3) Small axon terminals, mostly of local source (probably relay cell axon collaterals or possibly interneurons) containing small spheroid vesicles. A few axon terminals with similar small spheroid vesicles are of (contralateral) cortical origin from the somatosensory area; (4) Medium size axon terminals containing pleomorphic (ovoid to round) vesicles and being of local source (probably from local or neighbouring interneurons); (5) Occasionally axon terminals containing large dense-core vesicles (100-120 nm) were also observed. While types (1), (2), (3) and (4) are presynaptic to dendrites and (less frequently) to cell bodies, type (2), (3) and (4) were observed to be presynaptic also (axo-axonally) to type (1). Section series revealed that such axo-axonal synapses are in fact always arranged in "triadic combination" having the general formula of: 1 leads to dendrite (or soma), 2 (or 3, or 4) leads to 1, and 2 (or 3 or 4) leads to dendrite (or soma); the arrow indicating the morphological polarity of the synapse. -Presynaptic dendrites forming dendritic synapses and occasionally engaged in reciprocal synapses were also found, but in view of their rarity are probably only of secondary significance.
(1) 相对较大的轴突终末，其特征是有一群大的（45 - 60纳米）球形囊泡，它们是脊髓传入纤维的终末；(2) 小轴突终末——可能来自局部中间神经元——含有特征性扁平囊泡；(3) 小轴突终末，大多来自局部（可能是中继细胞轴突侧支或可能是中间神经元），含有小的球形囊泡。少数具有类似小球形囊泡的轴突终末来自体感区的（对侧）皮质；(4) 中等大小的轴突终末，含有多形性（卵形至圆形）囊泡，来自局部（可能来自局部或邻近的中间神经元）；(5) 偶尔也观察到含有大的致密核心囊泡（100 - 120纳米）的轴突终末。虽然类型(1)、(2)、(3)和(4)对树突是突触前的，对细胞体是突触前的情况较少见，但观察到类型(2)、(3)和(4)对类型(1)也是突触前的（轴 - 轴突触）。切片系列显示，这种轴 - 轴突触实际上总是以“三联组合”形式排列，其一般形式为：1通向树突（或胞体），2（或3或4）通向1，2（或3或4）通向树突（或胞体）；箭头表示突触的形态极性。还发现了形成树突突触并偶尔参与交互突触的突触前树突，但鉴于其罕见性，可能仅具有次要意义。
