An electron microscopic study of autonomic nerve cells in the cloacal region of the lamprey,Lampetra japonica

Summary Two types of autonomic nerve cell in the cloacal region of lamprey,Lampetra japonica have been studied by electron microscopy. Large ganglion cells (LGC) were unipolar and individually invested with a satellite cell sheath. The LGC-satellite cell complex measured 24 m × 38 m on average. Granular endoplasmic reticulum and cored vesicles (80–140 nm in diameter) were scattered in the perikaryon. Two kinds of peculiar cytoplasmic filament were seen in LGC: one type was about 20 nm in diameter with periodic dense material on the surface and the other had a diameter of about 8 nm and showed an undulating profile. Nerve endings containing abundant small clear vesicles (30–50 nm in diameter) and a few larger cored vesicles (50–100 nm in diameter) were found in synaptic contact with LGC. Small ganglion cells (SGC) were also unipolar and covered incompletely by a satellite cell sheath. The SGC-satellite cell complex measured 6 and 12 m on average. The SGC was packed with organelles and the perikaryon appeared more electron dense than that of LGC. SGC perikaryonal cytoplasm contained dispersed granular endoplasmic reticulum and numerous large cored vesicles (55–220 nm in diameter). Nerve endings containing numerous large cored vesicles (70–170 nm in diameter) and variable numbers of small clear vesicles (30–50 nm in diameter) were seen on the surface of SGC.