Synapses from labeled type II axons in the mouse cochlear nucleus
Synapses from labeled type II axons in the mouse cochlear nucleus
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DOI：
10.1016/0378-5955(95)00231-6
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发表时间：
1996-05-01
期刊：
影响因子：
2.8
通讯作者：
Brown, MC
中科院分区：
文献类型：
--
作者：
Berglund, AM;Benson, TE;Brown, MC
本研究探讨了II型初级传入神经元轴突肿胀时耳蜗核的超微结构和中枢靶点。II型轴突仅占总轴突的5-10%；哺乳动物的听觉神经的一部分，但它们单独提供外部冰雹细胞的传入神经支配。本研究用辣根过氧化物酶标记II型轴突，用连续切片电镜观察其在(1)与耳蜗后腹侧核交界的颗粒细胞层、(2)耳蜗前腹侧核吻侧和(3)听神经根的肿胀。只有一些（18%）II型终末和行进中的肿胀形成突触。突触不对称，含有清晰的圆形突触囊泡，表明它们是兴奋性的。II型突触与I型纤维的突触进行了比较，I型纤维为内毛细胞提供传入神经支配。II型突触的突触囊泡略小，突触囊泡较少，膜贴壁比例较大，伴突触后密度，且密度不连续或“穿孔”。在所有耳蜗核区，II型突触的突触后靶点具有树突特征；在大多数情况下，这些树突不能追溯到它们的细胞体起源。然而，一些证据表明，目标可能包括颗粒细胞、球形细胞和神经根中的其他细胞。这些结果表明，来自外毛细胞的传入信息可到达耳蜗核内的不同区域和目标。
This study investigates the ultrastructure and central targets in the cochlear nucleus of axonal swellings of type II primary afferent neurons. Type II axons comprise only 5-10% of the ar;uns of the auditory nerve of mammals, but they alone provide the afferent innervation of the outer hail cells. In this study, type II axons were labeled with horseradish peroxidase, and serial-section electron microscopy was used to examine their swellings in: (1) the granule-cell lamina at its boundary with posteroventral cochlear nucleus, (2) the rostral anteroventral cochlear nucleus, and (3) the auditory nerve root. Only some (18%) of the type II terminal and en-passant swellings formed synapses. The synapses were asymmetric and contained clear round synaptic vesicles, suggesting that they are excitatory. Type II synapses were compared to those from type I fibers, the fibers providing the afferent innervation of the inner hair cells. Type II synapses tended to have slightly smaller and fewer synaptic vesicles had a greater proportion of the membrane apposition accompanied by a postsynaptic density, and often had densities that were discontinuous or 'perforated'. In all cochlear nucleus regions examined, the postsynaptic targets of type II synapses had characteristics of dendrites; in most cases these dendrites could not be traced to their cell bodies of origin. Some evidence suggests, however, that targets may include granule cells, spherical cells, and other cells in the nerve root. These results suggest afferent information from outer hair cells reaches diverse regions and targets within the cochlear nucleus.