The special cutaneous receptor organs of the fresh water weakly electric fish have previously been proposed to be electroreceptors. In the gymnotid, E. virescens, two types of special cutaneous receptor organs, ampullary and tuberous, are distinguished from each other, as well as from the ordinary lateral line receptor organs, by their characteristic distribution and size. The tuberous organs usually contain 25 to 35 elongate nonciliated receptor cells within a cellular capsule. A single layer of supporting cells is present between the base of the receptor cells and the base of the capsule. A single thin myelinated nerve fiber innervates each group of organs and branches so that the base of each receptor cell is supplied with a single nerve ending. Synaptic contact is made at many points on each nerve ending. The synapses are characterized by k g e r s of receptor cell cytoplasm which contain dense presynaptic rods. The organ capsule is open toward the surface of the fish. A cellular plug partly obscures the opening, but continuity is maintained between the intracapsular fluid and the external water. Microvilli, projecting from the surfaces of the receptor cells, maintain an open gap between adjacent receptor cells. About 95% of the surface area of these cells is therefore in contact with the fluid. The functional implications of some of the ultrastructural observations are discussed.It has been known for many years that a number of different kinds of fish respond to small electric potential fields. More recently it has been recognized that fresh water weakly electric fish have the greatest electric sensitivity, and are able to detect currents which are at least several orders of magnitude smaller than those to which most other fish will respond (Lissmann and Machin, '58). Lissmann and Machin ( ' 5 8 ) , and Machin and Lissman ('60) have demonstrated that in these fish the electric sense can serve as the receptor component of a sensitive object locating system. Some other kinds of fish have sensitivities to electric fields which approach those of the fresh water weakly electric fish. Murray ('62a), by electrophysiological studies of the ampullae of Lorenzini of rajids, and Lissmann and Machin ('63), by behavioral studies of the nonelectric catfish Clarias, have shown that these fish can detect electric potential fields about one order of magnitude greater than those to which the fresh water weakly electric fish will respond. Among the catfish, only Mnlapterzirus is electric; among the elasmobranchs the Torpedinidae and the Rajidae are electric.The weakly electric fish, the elasmobranchs, and the siluroids have several kinds of special cutaneous receptor organs associated with the lateral line system (Dijkgraaf, '63) in addition to the lateral line canal receptor organs and free neuromasts common to most fish. On the basis of physiological data, and because of their distribution in fish which have a highly developed electric sense, the special cutaneous receptor organs have come to be regarded as special...
Abstract. Electron microscopic study of the canine transmissible venereal sarcoma (N = 26) at different stages of growth showed that tumors in a progressive phase of growth (N = 12) were comprised mostly of large, round cells with prominent nuclei and nucleoli, a few spindle-shaped cells and collagen fibers, focal areas of necrosis, and lymphocyte infiltrates. Regressing tumors (N = 9) had the fewest viable round cells, greater numbers of infiltrating leukocytes, and were comprised almost entirely of connective tissue (collagen bundles) in the latest stages of regression. The infiltrating leukocytes consisted primarily of lymphocytes, some eosinophils, and neutrophils, but very few macrophages.Round-cell nuclei contained numerous perichromatin and interchromatin granules. Their cytoplasm often had annulate lamellae complexes and large deposits of glycogen. Loosely packed tumor cells had extensive proliferation and elongation of cytoplasmic extensions (filopodia). Evidence for cell-mediated tumor cell lysis was demonstrated by degenerative changes in tumor cells which were closely apposed to lymphocytes. Spindle-shaped cells in regressing tumors had intravacuolar collagen fragments, suggesting a possible degradative capacity by these cells.
Ampullary organs of the transparent catfish, Kryptopterus bicirrhus, are present in large numbers on the head and in a regular pattern of lines on the body and fins. The organs lie in the epidermis, and have a pore that opens t o the surface. Flattened cells form a roof and walls. On the floor of the organ there are a "seiisory hillock," coniposed o€ spherical receptor cells and columnar supporting cells, and a "secretory hillock" composed of columnar secretory cells. The receptor cells are nonciliated and have only afferent innervation. The organ cavity is filled with jelly. The organs are coinpared with ampullary organs of the weakly electric fish Eigenmannia, ampullae of Lorenzini of Raja, and small pit organs of Amiurus. Structural characteristics of the ampullary organs of Kryptopterus make them especially suitable for electrophysiological studies.
Ampullary receptor organs of the South American weakly electric gymnotid fish Eigenmannia virescens consist of a pore at the surface of the skin, a canal through the epidermis, and the expanded basal end of the canal in the corium. The cavity of the organ contains a jelly that is filled with fine fibers. The canal wall consists of three to six layers of flattened cells that appear to be derived from the adjacent skin. Along the lumen of the organ the cells are joined by tight junctions. Usually there are four spherical receptor cells in the base of the organ. They are innervated by single neural terminals. These organs are compared to tuberous receptor organs found in the same species, and the functional significance of the fine structure observed in these cells is discussed.
The torpedine electric fish Narcine brasiliensis has two morphologically distinct electric organs (main and accessory) which alsodiffer with respect to anumberofelectrophysiological properties. The fine structure of the electroplaques of these organs has been examined by electron microscopy and by a histochemical method for localizing esterase activity with a high degree of resolution. In both kinds of electroplaques the innervated surface (ventral in those of the main organ, dorsal in those of the accessory) is the only site of esterase activity. The latter is further confined to the regions of synaptic contact between vesicle-con taining axon terminals and the electroplaque membrane. The synaptic apparatus is similar to, but less elaborate than, that of neuromuscular junctions. The axon terminals and electroplaque membranes are free of connective tissue envelopments. The membrane of the uninnervated surfaces forms a continuum with a dense canalicular network which penetrates deeply into the 7 # thick electroplaques of the main organ. The canalicular network has about the same thickness in the 20 # electroplaques of the accessory organ. Except for this difference, the two kinds of cells appear to have the same fine structure. This finding is discussed in relation to the electrophysiological data on functional differences.
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