Ostapoff E M, Morest D K
Department of Anatomy, University of Connecticut Health Center, Farmington 06030.
J Comp Neurol. 1991 Dec 15;314(3):598-613. doi: 10.1002/cne.903140314.
The synaptic organization of globular bushy cells of the anteroventral cochlear nucleus was quantitatively analyzed in order to understand better their functional attributes. A method was devised to estimate the concentrations and relative proportions of synapses on the entire postsynaptic surface of Golgi-impregnated neurons, by sampling with limited series of sections for electron microscopy. This provided a characteristic synaptic profile which was homogeneous for the population measured. The total concentration of synaptic endings decreases with distance from the soma. The cochlear, presumably glutamatergic and excitatory, endings with large spherical vesicles (LS) account for most of this decrease. Of the noncochlear inputs, the putative glycinergic endings with flattened vesicles (FL) decrease slightly, and the presumed GABAergic terminals with pleomorphic vesicles (PL) maintain a relatively constant concentration, while endings with small spherical vesicles (SS) increase on the distal dendrites. LS endings have the largest proportion of synapses near the soma, while FL synapses maintain a constant proportion in all cell regions, and PL and SS proportions increase on higher-order dendrites. Excitatory and inhibitory synapses have significant inputs to the axon hillock and initial segment, as well as to the distal dendrites, where dual synapses may provide a way to sample the activity of surrounding neurons. These features must be considered in explanations of physiological properties, such as the synaptic security, level of spontaneous activity, and well-timed, rapid onset responses, as well as their potential for normalizing and synchronizing an important inhibitory pathway involved in binaural signal processing. Synaptic profile analysis should be useful for experimental studies and for developing realistic computational models.
为了更好地理解前腹侧蜗神经核球状浓密细胞的功能特性，对其突触组织进行了定量分析。设计了一种方法，通过对有限系列的电子显微镜切片进行采样，来估计高尔基染色神经元整个突触后表面上突触的浓度和相对比例。这提供了一个特征性的突触图谱，在所测量的群体中是均匀的。突触终末的总浓度随着与胞体距离的增加而降低。耳蜗的终末，可能是谷氨酸能且兴奋性的，带有大球形囊泡（LS），这种降低主要是由它们造成的。在非耳蜗输入中，带有扁平囊泡的假定甘氨酸能终末（FL）略有减少，带有多形囊泡的假定GABA能终末（PL）保持相对恒定的浓度，而带有小球形囊泡的终末（SS）在远端树突上增加。LS终末在胞体附近的突触比例最大，而FL突触在所有细胞区域保持恒定比例，PL和SS比例在高阶树突上增加。兴奋性和抑制性突触对轴丘和起始段以及远端树突都有显著输入，在远端树突上双突触可能提供了一种对周围神经元活动进行采样的方式。在解释生理特性时，如突触安全性、自发活动水平、及时且快速起始的反应，以及它们在使参与双耳信号处理重要抑制通路正常化和同步化方面的潜力时，必须考虑这些特征。突触图谱分析对于实验研究和开发逼真的计算模型应该是有用的。
