Ultrastructural study on the granule-containing cells in the rat autonomic ganglia.

In the rat superior cervical ganglion, small granules, 100-150 nm in diameter, and large granules, 80-280 nm in diameter, were seen in the granule-containing (GC) cells. Most GC cells contained almost exclusively the small granules (SG type cell), while a few cells almost exclusively the large granules (LG type cell). The GC cells formed both efferent and cholinergic afferent synapses. The efferent synapses were about four times as many as the afferent ones. In the major pelvic ganglion of rats, SG type and LG type cells were present in comparable numbers. Cells with both types of granules were also noticed. Ovoid-shaped granules, 60 X 140 nm with a core of moderate electron density, were observed in some SG type cells. Both afferent and efferent synapses were noted on GC cells in this ganglion. The latter were more numerous than the former. SG type cells formed more synapses than LG type cells. Based on these observations, the physiological significance of GC cells was discussed.