Maxwell D J, Kerr R, Jankowska E, Riddell J S
Institute of Biomedical and Life Sciences, University of Glasgow, United Kingdom.
J Comp Neurol. 1997 Mar 31;380(1):51-69.
Five dorsal horn interneurons with monosynaptic input from group II primary afferent fibres were physiologically characterized and intracellularly labelled with horseradish peroxidase. The cells were prepared for combined light and electron microscopy, and synaptic arrangements formed by axon collaterals of interneurons and synapses formed with their dendrites and somata were examined with the electron microscope. Immunogold reactions for gamma-aminobutyric acid, glycine and glutamate were performed to determine if these synapses were excitatory or inhibitory. Axon collaterals in lamina VI formed synapses with somata and dendrites of other neurons, and collaterals of one cell also formed axoaxonic synapses. It was concluded that one cell from the sample was inhibitory, whereas the remainder were probably excitatory. Dendrites and cell bodies of interneurons were contacted by several types of synaptic bouton. The first type of bouton displayed immunoreactivity for glutamate, the second type contained both gamma-aminobutyric acid and glycine, the third type contained glycine alone, and the fourth type contained gamma-aminobutyric acid alone. Some large glutamatergic boutons were postsynaptic to other boutons. Presynaptic boutons at these axoaxonic synapses always contained gamma-aminobutyric acid but a minority also contained glycine. The results of this study demonstrate the heterogeneity of dorsal horn group II interneurons and provide evidence that they include inhibitory and probably also excitatory neurons. Boutons originating from several chemically different classes of neuron are responsible for postsynaptic inhibition of these interneurons, and the presence of axoaxonic synapses indicates that their excitatory input is also controlled presynaptically.
对5个接受II类初级传入纤维单突触输入的背角中间神经元进行了生理学特征分析，并用辣根过氧化物酶进行了细胞内标记。将这些细胞制备用于光镜和电镜联合观察，并用电子显微镜检查中间神经元轴突侧支形成的突触结构以及与它们的树突和胞体形成的突触。进行了γ-氨基丁酸、甘氨酸和谷氨酸的免疫金反应，以确定这些突触是兴奋性还是抑制性的。VI层的轴突侧支与其他神经元的胞体和树突形成突触，一个细胞的侧支还形成了轴-轴突触。得出的结论是，样本中的一个细胞是抑制性的，而其余的可能是兴奋性的。中间神经元的树突和细胞体与几种类型的突触终扣接触。第一种突触终扣对谷氨酸呈免疫反应性，第二种同时含有γ-氨基丁酸和甘氨酸，第三种仅含有甘氨酸，第四种仅含有γ-氨基丁酸。一些大的谷氨酸能终扣是其他终扣的突触后成分。这些轴-轴突触处的突触前终扣总是含有γ-氨基丁酸，但少数也含有甘氨酸。本研究结果表明背角II类中间神经元具有异质性，并提供证据表明它们包括抑制性神经元，可能还包括兴奋性神经元。源自几种化学性质不同的神经元类别的终扣负责这些中间神经元的突触后抑制，轴-轴突触的存在表明它们的兴奋性输入也受到突触前控制。
