Presence of the ruffed cell in the olfactory bulb of the catfish,Parasilurus asotus, and the sea eel,Conger myriaster

Abstract

The ruffed cell is present in the olfactory bulb of the catfish, Parasilurus asotus, and of the sea eel, Conger myriaster. Its morphological features have been studied by light microscopy, high‐voltage electron microscopy, and conventional electron microscopy. The ruffed cell of the catfish is very similar to that of the goldfish in its location and in its structural features. It has a spheroidal or ovoid cell body about 15 to 30 μm in diameter. Several dendrites arise from the cell body to form a rounded dendritic field about 100 μm in diameter near the cell body. The initial unmyelinated portion of its axon (IP) consists of a shaft and many protrusions arising from it. The shaft, about 1 μm in diameter, extends for about 100 to 200 μm, where it acquires a myelin sheath. The protrusions intermingle with one another in a complex manner to form a rather discrete spheroidal field about 20 to 50 μm in diameter, located in the vicinity of the cell body. In contrast, the ruffed cell of the sea eel differs rather significantly from that of the goldfish in its morphological features. The ruffed cell of the sea eel is of a bipolar type. One thick dendrite arises from the cell body and extends for about 50 to 100 μm, where it gives rise to many thread‐like dendritic branches. The IP arises from the cell body as a smooth thin process. However, about 30 to 70 μm distant from its origin, many elaborate protrusions arise from the axonal shaft. These intermingle with one another to form a spheroidal or ovoid field about 20 to 40 μm in diameter. Distal to this protrusion‐bearing part, the axon continues as a smooth, thin process. In spite of these differences in structural features, the ruffed cell of the catfish and that of the sea eel are very similar in their synaptic features in the nest (the special synaptic field around the ruffed cell IP, composed of its protrusions, of granule cell dendrites, and of other neuronal processes); that is, synapses between the ruffed cell IP (its shaft and protrusions) and granule cell dendrites and serial synapses made by the ruffed cell IP, granule cell dendrites, and perinest cell dendrites. These results suggest that the ruffed cell is generally present in the teleostean olfactory bulb, although its detailed structural features may vary from species to species. Moreover, the neuronal organization of the olfactory bulb seems to be fundamentally similar in various species of teleosts.