The lateral line system at metamorphosis in Xenopus laevis (Daudin).
TL;DR: Marked changes in the anatomy of the lateral line system occur during the metamorphosis of Xenopus, which takes place at a time when the adult method of locomotion is developed.
Abstract: Marked changes in the anatomy of the lateral line system occur during the metamorphosis of Xenopus. The distribution of rows differs in larva and adult and the orientation and number of organs are modified at metamorphosis. Larval plaques are functional, as shown by recording from their nerves. Two classes of cells with polarized cilia are present in the tadpole well before the orientation of individual organ plaques is rearranged at metamorphosis. The topography of the skin surface around individual plaques changes at metamorphosis. This change may reduce the directional sensitivity of organs. Myelinated inhibitory axons in the lateralis nerve are found only when the tadpole matures. This change takes place at a time when the adult method of locomotion is developed.
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TL;DR: Anurans show a distinct dichotomy among the sources of energy used during larval growth and development, endotrophy and exotrophy, which allows more exact definitions of direct development, ovoviviparity, vivip parity, and related terms.
Abstract: Anurans show a distinct dichotomy among the sources of energy used during larval growth and development, endotrophy and exotrophy. This distinction allows more exact definitions of direct development, ovoviviparity, viviparity, and related terms. Endotrophic larvae, whether as a non-hatched embryo or a free-swimming, non-feeding tadpole, gain immediate developmental nutrition solely from parental sources, most frequently from the yolk allotted to each egg during vitellogenesis. Exotrophic larvae are always free-swimming, feeding tadpoles and orally consume numerous sources of energy not derived from a parent. The morphology of exotrophic tadpoles is surveyed with an emphasis on oral structures. Speculative scenarios and hypotheses concerning the functions of the various morphologies and the relationship of trophic structures to the ecology of the tadpoles are offered. Larval morphology and behavior permit the recognition of six developmental guilds of endotrophic larvae and 18 ecomorphological guilds of exotrophic larvae; these guilds are fully characterized.
397 citations
TL;DR: The development of neurogenic placodes in Xenopus laevis from the time of neural fold closure to larval stages is described and suggests that Delta‐Notch‐mediated lateral inhibition may be involved not only in placodal neurogenesis, but also in the patterning of lateral line neuromasts.
Abstract: The development of neurogenic placodes in Xenopus laevis from the time of neural fold closure to larval stages is described. Placodes were reconstructed from camera lucida drawings of serial sections, and the spatiotemporal pattern of placodal neurogenesis was analyzed using in situ hybridization for the genes X-NGNR-1, XNeuroD, X-MyT1, and X-Delta-1, all of which have been implicated in the regulation of neurogenesis. Olfactory, profundal, and trigeminal placodes, a series of dorsolateral placodes (otic placode and five lateral line placodes), a series of epibranchial placodes, and two hypobranchial placodes were identified. Earlier claims that all placodes in anurans develop from a common primordium could not be confirmed. Profundal and trigeminal placodes, however, are partially fused, and all lateral line placodes arise from a common precursor. Epibranchial and hypobranchial placodes develop ventral to other placodes and dorsal and ventral to the pharyngeal pouches, respectively. Hypobranchial placodes give rise to neurons that become intimately associated with the developing heart. All neurogenic placodes strongly express the neuronal differentiation gene XNeuroD. The neuronal determination gene X-NGNR-1, however, is expressed strongly in only some placodes and not in dorsolateral placodes, indicating that neurogenesis in the latter relies on other determination genes. X-Delta-1 is expressed not only in the neurogenic parts of the placodes but also in the primordia of the lateral lines. This suggests that Delta-Notch-mediated lateral inhibition may be involved not only in placodal neurogenesis, but also in the patterning of lateral line neuromasts. J. Comp. Neurol. 418:121–146, 2000. © 2000 Wiley-Liss, Inc.
177 citations
01 Jan 1999
TL;DR: One of the interesting stories of hearing in general, and in aquatic vertebrates in particular, is how the structures associated with hair cell organs play a major role in modifying or channeling the environmental stimulus onto the hair cell receptors.
Abstract: Hearing in its broadest sense is the detection, by specialized mechanoreceptors, of mechanical energy propagated through the environment. In terrestrial vertebrates, this typically means inner ear transduction of air pressure waves radiating out from a sound source, though the detection of substrate vibrations can also be considered as a form of hearing. In aquatic environments, the extended contribution of incompressible flow in the near field of the source adds additional complexities, and both incompressible flow and propagated pressure waves are detected by a range of specialized hair cell mechanosensory systems. Hair cells are generalized mechanical transducers that respond to mechanical deformation of the receptor hairs at their apical surface. One of the interesting stories of hearing in general, and in aquatic vertebrates in particular, is how the structures associated with hair cell organs play a major role in modifying or channeling the environmental stimulus onto the hair cell receptors. Hence the peripheral anatomy determines to a large degree what particular stimulus feature is being encoded at the level of the hair cell.
175 citations
TL;DR: The structuredre and ultrastructure of the neuromast is described, as well as the growth of cupulae and other structures, are described.
Abstract: (A) Teleosts . . . . . . . . (B) Elasmobranchs . . . . . . (C) Cyclostomes . . . . . . . (D) Other fish groups . . . . . . (E) Ampullary and tuberous organs . . . (F) Amphibians . . . . . . . (G) Growth of cupulae . . . . . . (H) Other structures . . . . . . V. Development . . . . . . . . (A) Teleosts . . . . . . . . (B) Elasmobranchs . . . . . . (C) Amphibians . . . . . . . IV. Structdre and ultrastructure of the neuromast. .
125 citations
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TL;DR: Fixation experiments with buffered OsO4 solutions have shown that the appearance of the fixed cells is conditioned by the pH of the fixative, and the quality of fixation can be materially improved by buffering the OsO 4 solutions at pH 7.3-7.5 with acetate-veronal buffer.
Abstract: Osmium tetroxide fixation of tissue blocks, as usually effected, is preceded by an acidification of the tissue. This acidification is probably responsible for morphological alterations which are notably disturbing in electron microscopy. The acidification and the resulting morphological alterations cannot be prevented by homogenizing the tissue directly in OsO4 solutions or by adding enzyme inhibitors (fluoride, iodoscetamide) to the fixative. Fixation experiments with buffered OsO4 solutions have shown that the appearance of the fixed cells is conditioned by the pH of the fixative. The quality of fixation can be materially improved by buffering the OsO4 solutions at pH 7.3-7.5, The acetate-veronal buffer appeared to be the most favorable of the buffers tested, Because of these findings, 1 per cent OsO4 buffered at pH 7.3-7.5 with acetate-veronal buffer is recommended as an appropriate fixative for electron microscopy.
2,815 citations
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773 citations
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250 citations
TL;DR: Two types of nerve fibres terminate close to the hair cells of lateral line organs, and have been reported as afferent arid efferent and lateralis nerves, and recent work suggests that sensory activity is not influenced by efferent impulses.
Abstract: Two types of nerve fibres terminate close to the hair cells of lateral line organs, and have been reported as afferent arid efferent. Evidence for this view has been largely derived from electron microscopy1,2, and by analogy with labyrinthine hair cells3 it has been assumed that efferent fibres may exert an inhibitory influence on the sensory system. Even though afferent and efferent impulse traffic has been recorded from lateralis nerves in the South African clawed toad4, recent work suggests that sensory activity is not influenced by efferent impulses5.
65 citations