Fernández A, Radmilovich M, Russo R E, Hounsgaard J, Trujillo-Cenóz O
Division of Comparative Neuroanatomy, Instituto de Investigaciones Biológicas Clemente Estable, Uruguay.
Exp Brain Res. 1996 Mar;108(3):347-56. doi: 10.1007/BF00227258.
This paper reports the occurrence of monosynaptic connections between dorsal root afferents and a distinct cell type-the giant neuron-deep in the dorsal horn of the turtle spinal cord. Light microscope studies combining Nissl stain and transganglionic HRP-labeling of the primary afferents have revealed the occurrence of axosomatic and axodendritic contacts between labeled boutons and giant neurons. The synaptic nature of these contacts has been confirmed by use of electron microscope procedures involving the partial three-dimensional reconstruction of identified giant neurons. Intracellular recording in spinal cord slices provided functional evidence indicating the monosynaptic connections between dorsal root afferents and giant neurons. The recorded neurons were morphologically identified by means of biocytin injection and with avidin conjugates. Electrical stimulation of the ipsilateral dorsal roots evoked synaptic responses with short, fixed latencies (1.6-5.6 ms), which remained unchanged at high frequencies (10 Hz). Excitatory polysynaptic potentials were also observed. By means of pharmacological procedures the short-latency response was dissected in two components: one insensitive to tetrodotoxin, the other abolished by the drug. The toxin-resistant component was presumed to be sustained by small-diameter C fibers. The synaptic response was mainly mediated by the glutamate-AMPA receptor subtype; however, a small component mediated by NMDA receptor was also present.
本文报道了在龟脊髓背角深处，背根传入神经与一种独特的细胞类型——巨神经元之间存在单突触连接。结合尼氏染色和初级传入神经的跨神经节辣根过氧化物酶标记的光学显微镜研究显示，标记的终扣与巨神经元之间存在轴-体和轴-树突接触。通过涉及对已识别的巨神经元进行部分三维重建的电子显微镜程序，证实了这些接触的突触性质。脊髓切片中的细胞内记录提供了功能证据，表明背根传入神经与巨神经元之间存在单突触连接。通过生物素注射和抗生物素蛋白缀合物对记录的神经元进行形态学鉴定。同侧背根的电刺激诱发了具有短而固定潜伏期（1.6 - 5.6毫秒）的突触反应，在高频（10赫兹）时保持不变。还观察到兴奋性多突触电位。通过药理学方法，将短潜伏期反应分为两个成分：一个对河豚毒素不敏感，另一个被该药物消除。抗毒素成分被认为由小直径C纤维维持。突触反应主要由谷氨酸 - AMPA受体亚型介导；然而，也存在由NMDA受体介导的一小部分成分。
