Synaptic plasticity involving rearrangments of synaptic connections in the sympathetic ganglion

交感神经节被认为是主要神经元与来源于胸脊髓的神经节前轴突之间突触传递的中继站。使用生物细胞素对上颈神经节（SCG）神经元进行细胞内标记，然后对相关突触进行电镜观察，我发现一些SCG神经元的树突不仅是神经节前轴突的受体，也是其他SCG神经元的突触前元件。这些树突突触应被认为是作为交感神经节中继站的传统方案的重要补充。由于主神经元使用去甲肾上腺素作为递质，这些树突突触在形态学上被解释为肾上腺素能。我已经发现，在一些SCG神经元中，在神经节前刺激后观察到超极化，这种突触引起的超极化被育亨宾（一种α 2-肾上腺素受体拮抗剂）阻断。这一结果表明，在交感神经节中也存在肾上腺素能传递。此外，这些神经元已被澄清接受肾上腺素能型树突突触。这些树突突触被观察到与特化的树突形态，肾小球树突有关。我有一些证据表明这些结构可能表现出非常敏锐的可塑性。这个问题应该在不久的将来进一步的实验中加以解决。

It has been considered that the sympathetic ganglion is relay station in which synaptic transmission occurs between the principal neurons and the preganglionic axons derived from the thoracic spinal cord. Using an intracellular labeling of the superior cervical ganglion (SCG) neurons with biocytin followed by electron microscopic observation of the synapses involved, I have revealed that dendrites of some SCG neurons serve as not only recipients to the preganglionic axons but also presynaptic elements to other SCG neurons. These dendrodendritic synapses should be considered as an important addition to the conventional scheme as a relay station of the sympathetic ganglion. Since the principal neurons use noradrenaline as a transmitter, these dendrodendritic synapses were interpreted as adrenergic in terms of morphology. I have revealed that in some SCG neurons hyperpolarizations are observed after the preganglionic stimulation and that this synaptically evoked hyperpolarizations are blocked by yohimbine, an alpha2-adrenoceptor antagonist. This result shows that there are adrenergic transmission in the sympathetic ganglion also in terms of pharmacology. Furthermore, these neurons have been clarified to receive dendrodendritic synapses of adrenergic type.These dendrodendritic synapses were observed associated with specialized dendritic morphology, glomerular dendrites. I have got some evidence that these structures may show very acute plasticity. This problem should be addressed in further experiments in the near future.