Rohon-Beard cells are detected in the larval spinal cord of a viviparous Amphibian (Salamandra salamandra salamandra L.). These elements rarefy in the larvae near the metamorphosis and are lacking in metamorphosed animals. The disagreement with the findings on viviparous Teleosts may be due to different developmental patters.
Rohon-Beard cells in Coregonus (forma hybrida) spinal cord early differentiate during embryonal life and gradually degenerate after hatching. Some dorso-medial large neuroblasts are observed in the spinal cord of the oldest embryos; these elements are about 30 in number after hatching and differentiate as supramedullary neurons in the adults. The homology between the Rohon-Beard cells and supramedullary neurons may be excluded.
Large dorso-medial neuroblasts are observed in the embryo spinal cord of Hippocampus guttulatus Cuv.; these elements differentiate as supramedullary neurons in the adult. Cytomorphosis is described. Rohon-Beard cells are not detected in the developing spinal cord of this oviparous Teleost. The lack of this embryonal sensitive system is related to the peculiar conditions of embryo development which is isolated from the external environment. It is confirmed that Rohon-Beard cells and supramedullary...
In an oviparous teleost, Brachydanio rerio, the Rohon-Beard cells begin to differentiate early in the dorso-lateral region of the spinal cord (st. 19), then they reach the dorso-medial position (st. 20-23). The Rohon-Beard cells are completely differentiated at the hatching time (st. 25) when they attain the highest number. Six days later the Rohon-Beard cells begin to rarefy and then disappear. The involutive features of these neurons are described.
The Rohon-Beard cells were investigated during the development of Jordanella floridae, an oviparous Teleost. These neurons begin to differentiate when the embryo is 1,5 mm long, are completely differentiated in the embryo 2,5 mm long and are lacking at the 3rd day after the matching. As in previous works no Rohon-Beard cells were found in Gambusia and Poecilia, viviparous fishes belonging to the same order of Teleosts, the presence of Rohon-Beard cells in Jordanella must be related to the conditions...
In the spinal cord of Perca fluviatilis the Rohon-Beard cells differentiate early during the embryonal life but after the hatching gradually degenerate, therefore they are transient neurons. In new-born fishes 25 large neuroblasts are present in dorso-medial position and differentiate as supramedullary neurons in the adult Perea. These data indicate that the supramedullary neurons are not persistent Rohon-Beard cells.
The Rohon-Beard cells are not detected in the developing spinal cord of an ovoviviparous fish, Gambusia affinis. The lack of this embryonal sensitive system is supposed to be due to the development within the maternal body, the embryo being isolated from the external environnement. In the cervical spinal cord of adult fishes some large dorsal neurons are found, similar to the "supramedullary neurons" already described in other species of adult Teolosts.
In the viviparous Teleost Poecilia reticulata the Rohon-Beard cells are not detected in the developing spinal cord. This agrees with observations made on another Teleost (Gambusia affinis) belonging to the same family and correlates the viviparous condition with the absence of the Rohon-Beard cells. The "supramedullary neurons" detected in adult Gambusia are not observed in Poecilia. This indicates a different pattern of these neurons also in species belonging to the same family.
The number, distribution and morphology of the supramedullary neurons are investigated in two genera of Teleosts belonging to the same family (Labridae). The supramedullary neurons of the two genera (Crenilabrus and Coris) differ in number, size and cytological aspect; these morphological disagreements may be due to a different functional activity.
The Rohon-Beard cells of an urodelan Amphibian (Triturus cristatus) show their typical aspect and their highest number in the first larval stage. In the trunk region these neurons begin to degenerate at early larval stages and disappear a month before the metamorphosis. In the tail region, on the contrary, these neurons maintain the same number and morphological aspects till the oldest larval stages. Most of them degenerate in the last larval month. The Rohon-Beard cells of urodelan Amphibians progressively...
In the oviparous Teleost, Jordanella floridae, the Reissner fibre is early formed by the generalized secretory activity of the cells lining the ventricles. Subsequently the secretory activity becomes restricted to the subcommissural organ and the Reissner fibre is connected only with this structure. In Jordanella there is no secretory activity of the flexural organ. This finding differs from the data found in Gambusia (viviparous fish of the same suborder of Teleosts) and may be due to a different...
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