Factors involved in the development of ipsilateral retinothalamic projections in Xenopus laevis

Development ◽  
1981 ◽  
Vol 65 (1) ◽  
pp. 199-217
Author(s):  
C. Kennard
Keyword(s):  
Visual Field ◽  
Xenopus Laevis ◽  
Visual Information ◽  
Experimental Manipulation ◽  
Larval Life ◽  
Optic Chiasma ◽  
Larval Stages ◽  
Ipsilateral Projection ◽  
Terminal Degeneration ◽  
Selective Pattern

The extent, and the development, of the ipsilateral retinothalamic projection in the frog Xenopus laevis have been studied using terminal degeneration and autoradiographic techniques. This ipsilateral projection derives only from those retinal areas receiving visual information from the binocular portion of the visual field. In Xenopus, the ipsilateral retinothalamic projection arises from a larger area of the retina than was found to be the case in earlier studies on Rana. This correlates with the fact that Xenopus has a larger binocular visual field than does Rana. The ipsilateral retinothalamic projection is just detectable at about stage 56 of larval life, considerably later than its contralateral counterpart. Experimental manipulation of the developing eye vesicle at early larval stages followed by histological studies of the ipsilateral retinothalamic projections showed, however, that the retinal areas which give rise to this projection are determined by stage 32 of larval life. Further studies, in which monocular enucleation was performed at different larval stages with subsequent examination of the retinothalamic projections from the remaining eye, indicated that the selective pattern of decussation and non-decussation of retinothalamic fibres at the optic chiasma does not require interactions, at the chiasma, between optic fibres from the two eyes.

Ocular migration and the metamorphic and postmetamorphic maturation of the retinotectal system in Xenopus laevis: an autoradiographic and morphometric study

Development ◽  
1986 ◽  
Vol 92 (1) ◽  
pp. 43-69
Author(s):  
S. Grant ◽  
M. J. Keating
Keyword(s):  
Visual Field ◽  
The Body ◽  
Eye Position ◽  
Larval Life ◽  
Larval Stages ◽  
Cell Counts ◽  
Metamorphic Climax ◽  
Retinal Growth ◽  
The Asymmetry ◽  
Thymidine Autoradiography

The growth of the retina and tectum during larval life in Xenopus has previously been studied extensively. These two structures continue to grow in metamorphosing and postmetamorphic animals. During these later stages there are marked changes in eye position. We have used histogenetic and morphometric techniques to monitor retinal and tectal growth in Xenopus aged from stage 58 of larval life to ten years postmetamorphosis. The relative eye migration was quantified with optical techniques. An attempt has been made to relate modes of retinal growth to problems associated with changing interocular geometry. The predominant mode of growth during this period is hypertrophic, that is, it is due largely to an increase in size and complexity of existing elements, rather than the histogenetic creation of new elements. In the retina, however, tritiated thymidine autoradiography reveals that histogenesis does persist until at least six months after metamorphosis. The rate of histogenesis is much decreased compared with that of larval stages but, like that of larval stages, it takes place at the ciliary margin. It is asymmetrically distributed in the retina, most histogenesis occurring at the ventral retinal pole and very little at the dorsal retinal pole. Some histogenesis occurs at the nasal and temporal retinal poles. Thymidine autoradiography and cell counts indicated that little significant histogenesis occurs in the tectum after metamorphic climax. Two possible biological reasons for the asymmetry of retinal histogenesis have been examined. The first was the suggestion that the asymmetry was related to the emergence, during this period, of a binocular visual field secondary to the relative migration of the two eyes. It is shown that the asymmetric pattern of histogenesis is not closely related to those retinal areas that come to view binocular visual space. It was found, however, that the asymmetry of retinal growth from metamorphic climax was that required to stabilize retinal visual field positions with respect to body position. It is suggested that this minimizes the requirements for visuomotor readjustments that would otherwise be necessary to compensate for a situation in which eye position, relative to the body, is changing.

Development of Testis Cords and the Formation of Efferent Ducts in Xenopus laevis: Differences and Similarities with Other Vertebrates

2021 ◽  
pp. 1-14
Author(s):  
Yuanyuan Li ◽  
Jinbo Li ◽  
Man Cai ◽  
Zhanfen Qin
Keyword(s):  
Cell Proliferation ◽  
Xenopus Laevis ◽  
Germ Cells ◽  
Sertoli Cells ◽  
Testis Development ◽  
Larval Stages ◽  
Efferent Ducts ◽  
Steroidogenic Cells ◽  
Testis Cord ◽  
Anterior Posterior

The knowledge of testis development in amphibians relative to amniotes remains limited. Here, we used Xenopus laevis to investigate the process of testis cord development. Morphological observations revealed the presence of segmental gonomeres consisting of medullary knots in male gonads at stages 52–53, with no distinct gonomeres in female gonads. Further observations showed that cell proliferation occurs at specific sites along the anterior-posterior axis of the future testis at stage 50, which contributes to the formation of medullary knots. At stage 53, adjacent gonomeres become close to each other, resulting in fusion; then (pre-)Sertoli cells aggregate and form primitive testis cords, which ultimately become testis cords when germ cells are present inside. The process of testis cord formation in X. laevis appears to be more complex than in amniotes. Strikingly, steroidogenic cells appear earlier than (pre-)Sertoli cells in differentiating testes of X. laevis, which differs from earlier differentiation of (pre-)Sertoli cells in amniotes. Importantly, we found that the mesonephros is connected to the testis gonomere at a specific site at early larval stages and that these connections become efferent ducts after metamorphosis, which challenges the previous concept that the mesonephric side and the gonadal side initially develop in isolation and then connect to each other in amphibians and amniotes.

Neurogenesis in the thoracic neuromeres of two crustaceans with different types of metamorphic development

1998 ◽  
Vol 201 (17) ◽  
pp. 2465-2479 ◽  
Author(s):  
S Harzsch ◽  
J Miller ◽  
J Benton ◽  
RR Dawirs ◽  
B Beltz
Keyword(s):  
Embryonic Development ◽  
Larval Development ◽  
Neuronal Development ◽  
Temporal Patterns ◽  
Homarus Americanus ◽  
Spider Crab ◽  
Larval Life ◽  
Larval Stages ◽  
Metamorphic Development ◽  
Embryonic And Larval Development

The mode of embryonic and larval development and the ethology of metamorphosis in the spider crab and the American lobster are very different, and we took advantage of this to compare neuronal development in the two species. The goals of this study were to discover whether the differences in the maturation of the neuromuscular system in the pereopods and the metamorphic changes of motor behavior between the two species are reflected at the level of the developing nervous system ('neurometamorphosis'). Furthermore, we wanted to broaden our understanding of the mechanisms that govern neuronal development in arthropods. Proliferation of neuronal stem cells in thoracic neuromeres 4-8 of the lobster Homarus americanus and the crab Hyas araneus was monitored over the course of embryonic and larval development using the in vivo incorporation of bromodeoxyuridine (BrdU). Neuropil structure was visualized using an antibody against Drosophila synapsin. While proliferation of neuronal precursors has ceased when embryogenesis is 80 % complete (E80%) in the lobster thoracic neuromeres, proliferation of neuroblasts in the crab persists throughout embryonic development and into larval life. The divergent temporal patterns of neurogenesis in the two crustacean species can be correlated with differences in larval life style and in the degree of maturation of the thoracic legs during metamorphic development. Several unusual aspects of neurogenesis reported here distinguish these crustaceans from other arthropods. Lobsters apparently lack a postembryonic period of proliferation in the thoracic neuromeres despite the metamorphic remodeling that takes place in the larval stages. In contrast, an increase in mitotic activity towards the end of embryonic development is found in crabs, and neuroblast proliferation persists throughout the process of hatching into the larval stages. In both E20% lobster embryos and mid-embryonic crabs, expression of engrailed was found in a corresponding set of neurons and putative glial cells at the posterior neuromere border, suggesting that these cells have acquired similar specific identities and might, therefore, be homologous. None of the BrdU-labeled neuroblasts (typically 6-8 per hemineuromere over a long period of embryogenesis) was positive for engrailed at this and subsequent stages. Our findings are discussed in relation to the spatial and temporal patterns of neurogenesis in insects.

scholarly journals Evaluation of Effective and Practical Euthanasia Methods for Larval African Clawed Frogs (Xenopus laevis)

2020 ◽  
Vol 59 (3) ◽  
pp. 269-274
Author(s):  
Ilana A Galex ◽  
Cameron M Gallant ◽  
Nicole D'Avignon ◽  
Lauren M Kuchenbrod ◽  
Craig A Fletcher ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Developmental Stages ◽  
Age Group ◽  
Research Model ◽  
Larval Stages ◽  
Large Numbers ◽  
Guidance Documents ◽  
Stock Solutions ◽  
Tricaine Methanesulfonate ◽  
Tank Water

Larval, or tadpole-stage Xenopus laevis frogs are a popular research model for developmental biology and disease studies. Existing euthanasia guidance documents offer recommendations for both eggs and adult stages, yet do not specifically address the larval stage. Data evaluating effective euthanasia methods for groups of X. laevis tadpoles would therefore be useful. The goal of the current study was to evaluate the efficacy of various immersion euthanasia procedures on tadpoles: tricaine methanesulfonate (MS222) at 6 g/L, eugenol at 800 μL/L and rapid chilling (2 to 4 °C). We also evaluated tadpoles at various developmental stages (NF stages 46, 47 and 49). Tadpoles (n = 70) were exposed to euthanasia solution for 15 min, and controls (n = 40) were placed in housing tank water for 15 min. All animals were then placed in recovery tanks containing housing tank water for 4 h to confirm irreversibility of each agent. Cessation of the heartbeat was assessed at the end of euthanasia solution exposure and at each hour thereafter. We found that immersion in a 6 g/L solution of MS222 resulted in 100% euthanasia of all larval stages tested. Conversely, eugenol produced variable euthanasia rates that were affected by both age group and batches of stock solutions. Rapid chilling was completely ineffective as a euthanasia method in our study. Based on our findings, we recommend MS222 as an effective and practical means of euthanizing large numbers of X. laevis tadpoles.

Split brains

2018 ◽  
Author(s):  
Elizabeth Schechter
Keyword(s):  
Visual Field ◽  
Information Exchange ◽  
Visual Information ◽  
Right Hemisphere ◽  
The Other ◽  
Brain Surgery ◽  
Interhemispheric Interaction ◽  
Split Brain ◽  
The One ◽  
The Right

The largest fibre tract in the human brain connects the two cerebral hemispheres. A ‘split-brain’ surgery severs this structure, sometimes together with other white matter tracts connecting the right hemisphere and the left. Split-brain surgeries have long been performed on non-human animals for experimental purposes, but a number of these surgeries were also performed on adult human beings in the second half of the twentieth century, as a medical treatment for severe cases of epilepsy. A number of these people afterwards agreed to participate in ongoing research into the psychobehavioural consequences of the procedure. These experiments have helped to show that the corpus callosum is a significant source of interhemispheric interaction and information exchange in the ‘neurotypical’ brain. After split-brain surgery, the two hemispheres operate unusually independently of each other in the realm of perception, cognition, and the control of action. For instance, each hemisphere receives visual information directly from the opposite (‘contralateral’) side of space, the right hemisphere from the left visual field and the left hemisphere from the right visual field. This is true of the normal (‘neurotypical’) brain too, but in the neurotypical case interhemispheric tracts allow either hemisphere to gain access to the information that the other has received. In a split-brain subject however the information more or less stays put in whatever hemisphere initially received it. And it isn’t just visual information that is confined to one hemisphere or the other after the surgery. Rather, after split-brain surgery, each hemisphere is the source of proprietary perceptual information of various kinds, and is also the source of proprietary memories, intentions, and aptitudes. Various notions of psychological unity or integration have always been central to notions of mind, personhood, and the self. Although split-brain surgery does not prevent interhemispheric interaction or exchange, it naturally alters and impedes it. So does the split-brain subject as a whole nonetheless remain a unitary psychological being? Or could there now be two such psychological beings within one human animal – sharing one body, one face, one voice? Prominent neuropsychologists working with the subjects have often appeared to argue or assume that a split-brain subject has a divided or disunified consciousness and even two minds. Although a number of philosophers agree, the majority seem to have resisted these conscious and mental ‘duality claims’, defending alternative interpretations of the split-brain experimental results. The sources of resistance are diverse, including everything from a commitment to the necessary unity of consciousness, to recognition of those psychological processes that remain interhemispherically integrated, to concerns about what the moral and legal consequences would be of recognizing multiple psychological beings in one body. On the other hand underlying most of these arguments against the various ‘duality’ claims is the simple fact that the split-brain subject does not appear to be two persons, but one – and there are powerful conceptual, social, and moral connections between being a unitary person on the one hand and having a unified consciousness and mind on the other.

scholarly journals The visual white matter connecting human area prostriata and the thalamus is retinotopically organized

2020 ◽  
Vol 225 (6) ◽  
pp. 1839-1853 ◽  
Author(s):  
Jan W. Kurzawski ◽  
Kyriaki Mikellidou ◽  
Maria Concetta Morrone ◽  
Franco Pestilli
Keyword(s):  
White Matter ◽  
Visual Field ◽  
Visual Information ◽  
Peripheral Visual Field ◽  
Wide Field ◽  
Central Visual Field ◽  
Field Representation ◽  
Computing Platform ◽  
Human Connectome Project ◽  
Plane Extraction

Abstract The human visual system is capable of processing visual information from fovea to the far peripheral visual field. Recent fMRI studies have shown a full and detailed retinotopic map in area prostriata, located ventro-dorsally and anterior to the calcarine sulcus along the parieto-occipital sulcus with strong preference for peripheral and wide-field stimulation. Here, we report the anatomical pattern of white matter connections between area prostriata and the thalamus encompassing the lateral geniculate nucleus (LGN). To this end, we developed and utilized an automated pipeline comprising a series of Apps that run openly on the cloud computing platform brainlife.io to analyse 139 subjects of the Human Connectome Project (HCP). We observe a continuous and extended bundle of white matter fibers from which two subcomponents can be extracted: one passing ventrally parallel to the optic radiations (OR) and another passing dorsally circumventing the lateral ventricle. Interestingly, the loop travelling dorsally connects the thalamus with the central visual field representation of prostriata located anteriorly, while the other loop travelling more ventrally connects the LGN with the more peripheral visual field representation located posteriorly. We then analyse an additional cohort of 10 HCP subjects using a manual plane extraction method outside brainlife.io to study the relationship between the two extracted white matter subcomponents and eccentricity, myelin and cortical thickness gradients within prostriata. Our results are consistent with a retinotopic segregation recently demonstrated in the OR, connecting the LGN and V1 in humans and reveal for the first time a retinotopic segregation regarding the trajectory of a fiber bundle between the thalamus and an associative visual area.

scholarly journals Changes in the Spatial Distribution of Visual Attention after Early Deafness

2002 ◽  
Vol 14 (5) ◽  
pp. 687-701 ◽  
Author(s):  
Jason Proksch ◽  
Daphne Bavelier
Keyword(s):  
Visual Field ◽  
Visual Attention ◽  
Visual Information ◽  
Search Task ◽  
Peripheral Visual Field ◽  
Auditory Deprivation ◽  
Attentional Processing ◽  
Attentional Resources ◽  
Visual Skills ◽  
Visual Tasks

There is much anecdotal suggestion of improved visual skills in congenitally deaf individuals. However, this claim has only been met by mixed results from careful investigations of visual skills in deaf individuals. Psychophysical assessments of visual functions have failed, for the most part, to validate the view of enhanced visual skills after deafness. Only a few studies have shown an advantage for deaf individuals in visual tasks. Interestingly, all of these studies share the requirement that participants process visual information in their peripheral visual field under demanding conditions of attention. This work has led us to propose that congenital auditory deprivation alters the gradient of visual attention from central to peripheral field by enhancing peripheral processing. This hypothesis was tested by adapting a search task from Lavie and colleagues in which the interference from distracting information on the search task provides a measure of attentional resources. These authors have established that during an easy central search for a target, any surplus attention remaining will involuntarily process a peripheral distractor that the subject has been instructed to ignore. Attentional resources can be measured by adjusting the difficulty of the search task to the point at which no surplus resources are available for the distractor. Through modification of this paradigm, central and peripheral attentional resources were compared in deaf and hearing individuals. Deaf individuals possessed greater attentional resources in the periphery but less in the center when compared to hearing individuals. Furthermore, based on results from native hearing signers, it was shown that sign language alone could not be responsible for these changes. We conclude that auditory deprivation from birth leads to compensatory changes within the visual system that enhance attentional processing of the peripheral visual field.

scholarly journals Immune Response to “Self” Lens in Xenopus laevis Enucleated during Larval Life

1999 ◽  
Vol 7 (1) ◽  
pp. 23-32 ◽  
Author(s):  
Takeshi Enomoto ◽  
Shin Tochinai
Keyword(s):  
Immune Response ◽  
Xenopus Laevis ◽  
Larval Life

The Detection of Orientation of Small Objects

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 59-59
Author(s):  
J M Zanker ◽  
M P Davey
Keyword(s):  
Visual Field ◽  
Visual System ◽  
Computer Simulations ◽  
Visual Information ◽  
Human Performance ◽  
Receptive Fields ◽  
Experimental Result ◽  
Orientation Tuning ◽  
Basic Question ◽  
Visual Stream

Visual information processing in primate cortex is based on a highly ordered representation of the surrounding world. In addition to the retinotopic mapping of the visual field, systematic variations of the orientation tuning of neurons are described electrophysiologically for the first stages of the visual stream. On the way to understanding the relation of position and orientation representation, in order to give an adequate account of cortical architecture, it will be an essential step to define the minimum spatial requirements for detection of orientation. We addressed the basic question of spatial limits for detecting orientation by comparing computer simulations of simple orientation filters with psychophysical experiments in which the orientation of small lines had to be detected at various positions in the visual field. At sufficiently high contrast levels, the minimum physical length of a line whose orientation can just be resolved is not constant when presented at various eccentricities, but covaries inversely with the cortical magnification factor. A line needs to span less than 0.2 mm on the cortical surface in order to be recognised as oriented, independently of the actual eccentricity at which the stimulus is presented. This seems to indicate that human performance for this task approaches the physical limits, requiring hardly more than approximately three input elements to be activated, in order to detect the orientation of a highly visible line segment. Combined with the estimates for receptive field sizes of orientation-selective filters derived from computer simulations, this experimental result may nourish speculations of how the rather local elementary process underlying orientation detection in the human visual system can be assembled to form much larger receptive fields of the orientation-sensitive neurons known to exist in the primate visual system.

Crustacean Visual Circuits Underlying Behavior

2019 ◽  
Author(s):  
Daniel Tomsic ◽  
Julieta Sztarker
Keyword(s):  
Visual Processing ◽  
Visual Information ◽  
General Structure ◽  
Visual Space ◽  
Experimental Manipulation ◽  
Visually Guided ◽  
Decapod Crustaceans ◽  
Behavioral Experiments ◽  
Electrophysiological Recordings ◽  
Visual Behaviors

Decapod crustaceans, in particular semiterrestrial crabs, are highly visual animals that greatly rely on visual information. Their responsiveness to visual moving stimuli, with behavioral displays that can be easily and reliably elicited in the laboratory, together with their sturdiness for experimental manipulation and the accessibility of their nervous system for intracellular electrophysiological recordings in the intact animal, make decapod crustaceans excellent experimental subjects for investigating the neurobiology of visually guided behaviors. Investigations of crustaceans have elucidated the general structure of their eyes and some of their specializations, the anatomical organization of the main brain areas involved in visual processing and their retinotopic mapping of visual space, and the morphology, physiology, and stimulus feature preferences of a number of well-identified classes of neurons, with emphasis on motion-sensitive elements. This anatomical and physiological knowledge, in connection with results of behavioral experiments in the laboratory and the field, are revealing the neural circuits and computations involved in important visual behaviors, as well as the substrate and mechanisms underlying visual memories in decapod crustaceans.

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