The sympathetic ganglion of the toad was studied with the electron microscope.
The ganglion cells can be divided electronmicroscopically into the clear and dark cells because of their different concentration and shape of the Nissl substance in the cytoplasm.
Electron dense granules of 80 to 150mμ in diameter are occassionally observed in the Golgi regions of the ganglion cells. They are very similar in fine structure to the so-called granular vesicles in the presynaptic terminals of the sympathetic axons.
The granular cells in the ganglion have, in many respects, the morphological analogy to chromaffine cells in higher vertebrates. They are occassionally located adjacent to larger blood vessels in the ganglion.
Furthermore, the endothelial cytoplasm of the blood vessels sometimes contain specific granules similar in size and structure to those found in the granular cells.
These last two results suggest that the granules in the endothelial cells may be originated from the granular cells and that the granular cells may have a glandular character like adrenomedullary cells.
Morphological changes in synapses after intense presynaptic volleys are observed. In the stimulated ganglia, synaptic vesicles are often arranged in a regular array being clustered like a crystalloid at a short distance away from the synaptic membrane. This characteristic distribution of the synaptic vesicles after the electrical stimulation may be related to the synaptic blockage which may occur in the neurons during the prolonged stimulation.