In 2mm long Gambusia embryos, glycogen is lacking in all the central nervous system (CNS). In 2,5 mm long embryos glycogen is present in some well definite areas of the brain and, during further development, it appears in other areas of the CNS. The glycogen content is always high in the nervous centers where the neuropil is well developed, for instance the axon-cup of the Mauthner cells and the nucleus rotundus. The Mauthner cells show a peculiar behaviour: their cytoplasm has an high glycogen...
In the romboencephalon of a developing viviparous Teleost (Gambusia affinis), the mitotic activity slowly decreases and falls at hatching, but rises in young fish; therefore mitoses are present till the end of somatic growth. The mitotic activity is higher in the alar plate than in the basal one: this is due to the late differentiation of the sensitive region. During the growth of the romboencephalon, mitoses rarefy rostrally and, in the oldest embryos they are present only near the calamus owing...
During the growth of the spinal cord in a viviparous Teleost (Gambusia affinis) the mitotic ratio slowly decreases and falls after birth, but it rises in young fishes. Therefore mitoses are present till the end of the somatic growth. The mitotic activity is higher in the sensitive than in the motor region of the spinal cord: this is due to the slow differentiation of the alar plate. Starting from 3,5 mm embryos most of the mitoses are extraventricular owing to quick reduction of the central canal....
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.
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