Fine Structure of the Eighth Nerve Ganglion in the Toad

Abstract

In the eighth nerve ganglion of the toad, the nerve cells could be divided microscopically into small dark cells and large light cells. About 20% of the nerve cells in the ganglion were myelinated with compact myeline and were recognized as corresponding to the large light cells. In the cytoplasm of the dark cells, there was an abundance of Nissl substance and mitochondria, while in the perikaryon of the light cells, the granular aggregates and mitochondrial profiles were widely dispersed, but neurofilaments were obviously scattered. Electron-microscopically, the small dark cells could be divided further into the unmyelinated neuron ensheathed with a single layer of the satellite cell cytoplasm and the neuron encapsulated by a sheath consisting of loose myelin. The large light neurons have the compact myelin looked like the myelinated nerve fibers because their figures resembled elongated spindles which were connected with heavy axons leaving their opposite poles and their perikaryal peculiarity was provided with abundant neurofilaments in their perikarya. The fine structures of both the above-mentioned neurons were compared with those of the various neurons in the acoustic ganglia of the rat, goldfish, guinea pig and cat. Finally, it was concluded that no significant relationship could be recognized between the structural features of perikarya of those neurons and the types of myelin sheath surrounding their perikarya.