Kinnamon J C, Westfall J A
J Morphol. 1982 Jul;173(1):119-28. doi: 10.1002/jmor.1051730110.
Using transmission electron microscopy of thin sections we have examined neuronal concentrations at hypostome-tentacle junctions in Hydra littoralis. A total of 194 ganglion cells were counted in 587 serial thin sections of a single hypostome-tentacle junction. We found two distinct types of ganglion cells: those with and those lacking stereocilia. The majority of the neurons observed lacked stereocilia; in a single hypostome-tentacle junction only 37% of the ganglion cells possessed a kinocilium surrounded by rodlike stereocilia. Most of the ganglion cells (55%) were clustered together in the oral or upper epidermis of the hypostome-tentacle junction: Nineteen percent were in the lateral and 26% in the aboral or lower epidermis. The two types of ganglion cells did not differ significantly in their distribution. Both types of ganglion cell had synaptic contacts with other neurons and with epitheliomuscular cells. More than 85% of the neuroneuronal and 61% of the neuroepitheliomuscular cell synapses were located in the oral epidermis of a hypostome-tentacle junction. In addition, two-way chemical synapses and a gap junction between neurons were observed at hypostome-tentacle junctions. Our morphological evidence of synaptic connectivity in neuronal clusters at hypostome-tentacle junctions suggests that primitive ganglia are present in Hydra.
我们使用薄切片透射电子显微镜检查了海滨水螅口柄-触手连接处的神经元聚集情况。在单个口柄-触手连接处的587个连续薄切片中，共计数了194个神经节细胞。我们发现了两种不同类型的神经节细胞：有静纤毛的和没有静纤毛的。观察到的大多数神经元没有静纤毛；在单个口柄-触手连接处，只有37%的神经节细胞具有被棒状静纤毛包围的动纤毛。大多数神经节细胞（55%）聚集在口柄-触手连接处的口侧或上表皮：19%在侧面，26%在反口侧或下表皮。这两种类型的神经节细胞在分布上没有显著差异。两种类型的神经节细胞都与其他神经元以及上皮肌细胞有突触联系。超过85%的神经元-神经元突触和61%的神经-上皮肌细胞突触位于口柄-触手连接处的口侧表皮。此外，在口柄-触手连接处观察到了双向化学突触和神经元之间的缝隙连接。我们对口柄-触手连接处神经元簇中突触连接性的形态学证据表明，水螅中存在原始神经节。
