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Amplatz K, Zieger E, Abed-Navandi D, Weissenbacher A, Wanninger A. Neuromuscular development in the emerging scyphozoan model system, Cassiopea xamachana: implications for the evolution of cnidarian nervous systems. Front Neurosci 2024; 17:1324980. [PMID: 38274504 PMCID: PMC10808518 DOI: 10.3389/fnins.2023.1324980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 12/18/2023] [Indexed: 01/27/2024] Open
Abstract
The scyphozoan Cassiopea xamachana is an emerging cnidarian model system for studying regeneration, animal-algae symbiotic relationships, and various aspects of evolutionary biology including the early emergence of animal nervous systems. Cassiopea has a life cycle similar to other scyphozoans, which includes the alternation between a sessile, asexual form (polyp) and a sexually reproducing stage, the medusa. The transition between the two forms is called strobilation, where the polyp releases a miniature medusa, the iconic ephyra, that subsequently develops into the adult medusa. In addition, Cassiopea polyps may reproduce asexually by budding off free-swimming so-called planuloid buds. While the development of planuloid buds and polyps has been studied in some detail, little is known about the ontogeny of the sexually produced planula larva. Using immunofluorescence labeling and confocal microscopy, we examined neuromuscular development during metamorphosis of the planula larva into the juvenile polyp in C. xamachana. For this purpose, we used tyrosinated α-tubulin-, FMRFamide- and serotonin-like immunoreactivity together with phalloidin labeling. Our results show a planula nervous system that consists of a basiectodermal neural plexus with mostly longitudinally oriented neurites. This neural meshwork is connected to sensory neurons in the superficial stratum of the ectoderm, which are exclusively localized in the aboral half of the larva. During settlement, this aborally concentrated nervous system of the planula is replaced completely by the orally concentrated nervous system of the polyp. Adult polyps show an extensive nerve net with a loose concentration around the oral disc. These findings are consistent with data from other scyphozoans and most likely constitute a conserved feature of scyphozoan discomedusae. Taken together, the data currently available suggest an aborally concentrated nervous system including sensory cells as part of the neural ground pattern of cnidarian planula larvae. The reorganization of the nervous system from anterior to posterior in planula-to-polyp metamorphosis most likely also constitutes an ancestral trait in cnidarian evolution.
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Affiliation(s)
- Klara Amplatz
- Department of Evolutionary Biology, University of Vienna, Vienna, Austria
| | - Elisabeth Zieger
- Department of Evolutionary Biology, University of Vienna, Vienna, Austria
| | - Daniel Abed-Navandi
- Department of Evolutionary Biology, University of Vienna, Vienna, Austria
- Haus des Meeres, Vienna, Austria
| | | | - Andreas Wanninger
- Department of Evolutionary Biology, University of Vienna, Vienna, Austria
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2
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Segev A, Jung S. Common knowledge processing patterns in networks of different systems. PLoS One 2023; 18:e0290326. [PMID: 37796927 PMCID: PMC10553345 DOI: 10.1371/journal.pone.0290326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 08/01/2023] [Indexed: 10/07/2023] Open
Abstract
Knowledge processing has patterns which can be found in biological neuron activity and artificial neural networks. The work explores whether an underlying structure exists for knowledge which crosses domains. The results show common data processing patterns in biological systems and human-made knowledge-based systems, present examples of human-generated knowledge processing systems, such as artificial neural networks and research topic knowledge networks, and explore change of system patterns over time. The work analyzes nature-based systems, which are animal connectomes, and observes neuron circuitry of knowledge processing based on complexity of the knowledge processing system. The variety of domains and similarity in processing mechanisms raise the question: if it is common in natural and artificial systems to see this pattern-based knowledge processing, how unique is knowledge processing in humans.
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Affiliation(s)
- Aviv Segev
- Department of Computer Science, University of South Alabama, Mobile, AL, United States of America
| | - Sukhwan Jung
- Department of Computer Science, University of South Alabama, Mobile, AL, United States of America
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3
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Napoli FR, Daly CM, Neal S, McCulloch KJ, Zaloga AR, Liu A, Koenig KM. Cephalopod retinal development shows vertebrate-like mechanisms of neurogenesis. Curr Biol 2022; 32:5045-5056.e3. [PMID: 36356573 PMCID: PMC9729453 DOI: 10.1016/j.cub.2022.10.027] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 09/30/2022] [Accepted: 10/14/2022] [Indexed: 11/10/2022]
Abstract
Coleoid cephalopods, including squid, cuttlefish, and octopus, have large and complex nervous systems and high-acuity, camera-type eyes. These traits are comparable only to features that are independently evolved in the vertebrate lineage. The size of animal nervous systems and the diversity of their constituent cell types is a result of the tight regulation of cellular proliferation and differentiation in development. Changes in the process of development during evolution that result in a diversity of neural cell types and variable nervous system size are not well understood. Here, we have pioneered live-imaging techniques and performed functional interrogation to show that the squid Doryteuthis pealeii utilizes mechanisms during retinal neurogenesis that are hallmarks of vertebrate processes. We find that retinal progenitor cells in the squid undergo nuclear migration until they exit the cell cycle. We identify retinal organization corresponding to progenitor, post-mitotic, and differentiated cells. Finally, we find that Notch signaling may regulate both retinal cell cycle and cell fate. Given the convergent evolution of elaborate visual systems in cephalopods and vertebrates, these results reveal common mechanisms that underlie the growth of highly proliferative neurogenic primordia. This work highlights mechanisms that may alter ontogenetic allometry and contribute to the evolution of complexity and growth in animal nervous systems.
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Affiliation(s)
- Francesca R Napoli
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA; Department of Organismic and Evolutionary Biology, Harvard University, Harvard University, Cambridge, MA 02138, USA
| | - Christina M Daly
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA; Department of Organismic and Evolutionary Biology, Harvard University, Harvard University, Cambridge, MA 02138, USA
| | - Stephanie Neal
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA; Department of Organismic and Evolutionary Biology, Harvard University, Harvard University, Cambridge, MA 02138, USA
| | - Kyle J McCulloch
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA; Department of Organismic and Evolutionary Biology, Harvard University, Harvard University, Cambridge, MA 02138, USA
| | - Alexandra R Zaloga
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA; Department of Organismic and Evolutionary Biology, Harvard University, Harvard University, Cambridge, MA 02138, USA
| | - Alicia Liu
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA; Department of Organismic and Evolutionary Biology, Harvard University, Harvard University, Cambridge, MA 02138, USA
| | - Kristen M Koenig
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA; Department of Organismic and Evolutionary Biology, Harvard University, Harvard University, Cambridge, MA 02138, USA.
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4
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Nielsen SKD, Koch TL, Wiisbye SH, Grimmelikhuijzen CJP, Garm A. Neuropeptide expression in the box jellyfish Tripedalia cystophora-New insights into the complexity of a "simple" nervous system. J Comp Neurol 2021; 529:2865-2882. [PMID: 33660861 DOI: 10.1002/cne.25133] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 02/11/2021] [Accepted: 02/23/2021] [Indexed: 01/09/2023]
Abstract
Box jellyfish have an elaborate visual system and perform advanced visually guided behaviors. However, the rhopalial nervous system (RNS), believed to be the main visual processing center, only has 1000 neurons in each of the four eye carrying rhopalia. We have examined the detailed structure of the RNS of the box jellyfish Tripedalia cystophora, using immunolabeling with antibodies raised against four putative neuropeptides (T. cystophora RFamide, VWamide, RAamide, and FRamide). In the RNS, T. cystophora RF-, VW-, and RAamide antibodies stain sensory neurons, the pit eyes, the neuropil, and peptide-specific subpopulations of stalk-associated neurons and giant neurons. Furthermore, RFamide ir+ neurites are seen in the epidermal stalk nerve, whereas VWamide antibodies stain the gastrodermal stalk nerve. RFamide has the most widespread expression including in the ring and radial nerves, the pedalium nerve plexus, and the tentacular nerve net. RAamide is the putative neurotransmitter in the motor neurons of the subumbrellar nerve net, and VWamide is a potential marker for neuronal differentiation as it is found in subpopulations of undifferentiated cells both in the rhopalia and in the bell. The results from the FRamide antibodies were not included as only few cells were stained, and in an unreproducible way. Our studies show hitherto-unseen details of the nervous system of T. cystophora and allowed us to identify specific functional groups of neurons. This identification is important for understanding visual processing in the RNS and enables experimental work, directly addressing the role of the different neuropeptides in vision.
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Affiliation(s)
- Sofie K D Nielsen
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Thomas L Koch
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Sofus H Wiisbye
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | | | - Anders Garm
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
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5
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Arnellos A, Moreno A. Visual Perception and the Emergence of Minimal Representation. Front Psychol 2021; 12:660807. [PMID: 34079497 PMCID: PMC8166269 DOI: 10.3389/fpsyg.2021.660807] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 04/26/2021] [Indexed: 11/29/2022] Open
Abstract
There is a long-lasting quest of demarcating a minimally representational behavior. Based on neurophysiologically-informed behavioral studies, we argue in detail that one of the simplest cases of organismic behavior based on low-resolution spatial vision–the visually-guided obstacle avoidance in the cubozoan medusa Tripedalia cystophora–implies already a minimal form of representation. We further argue that the characteristics and properties of this form of constancy-employing structural representation distinguish it substantially from putative representational states associated with mere sensory indicators, and we reply to some possible objections from the liberal representationalists camp by defending and qualitatively demarcating the minimal nature of our case. Finally, we briefly discuss the implications of our thesis within a naturalistic framework.
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Affiliation(s)
- Argyris Arnellos
- Complex Systems and Service Design Lab, Department of Product and Systems Design Engineering, University of the Aegean, Syros, Greece.,Department of Logic and Philosophy of Science, IAS-Research Center for Life, Mind and Society, University of the Basque Country, San Sebastián, Spain
| | - Alvaro Moreno
- Department of Logic and Philosophy of Science, IAS-Research Center for Life, Mind and Society, University of the Basque Country, San Sebastián, Spain
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6
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Rey S, Zalc B, Klämbt C. Evolution of glial wrapping: A new hypothesis. Dev Neurobiol 2020; 81:453-463. [PMID: 32133794 DOI: 10.1002/dneu.22739] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 01/16/2020] [Accepted: 02/27/2020] [Indexed: 12/12/2022]
Abstract
Animals are able to move and react in numerous ways to external stimuli. Thus, environmental stimuli need to be detected, information must be processed and finally an output decision must be transmitted to the musculature to get the animal moving. All these processes depend on the nervous system which comprises an intricate neuronal network and many glial cells. In the last decades, a neurono-centric view on nervous system function channeled most of the scientific interest toward the analysis of neurons and neuronal functions. Neurons appeared early in animal evolution and the main principles of neuronal function from synaptic transmission to propagation of action potentials are conserved during evolution. In contrast, not much is known on the evolution of glial cells that were initially considered merely as static support cells. Although it is now accepted that glial cells have an equally important contribution as their neuronal counterpart to nervous system function, their evolutionary origin is unknown. Did glial cells appear several times during evolution? What were the first roles glial cells had to fulfil in the nervous system? What triggered the formation of the amazing diversity of glial morphologies and functions? Is there a possible mechanism that might explain the appearance of complex structures such as myelin in vertebrates? Here, we postulate a common evolutionary origin of glia and depict a number of selective forces that might have paved the way from a simple supporting cell to a wrapping and myelin forming glial cell.
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Affiliation(s)
- Simone Rey
- Institut für Neuro- und Verhaltensbiologie, Universität Münster, Münster, Germany
| | - Bernard Zalc
- Institut du Cerveau et de la Moelle Épinière, GH Pitié-Salpêtrière, Sorbonne Université, Inserm, CNRS, Paris, France
| | - Christian Klämbt
- Institut für Neuro- und Verhaltensbiologie, Universität Münster, Münster, Germany
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7
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Pallasdies F, Goedeke S, Braun W, Memmesheimer RM. From single neurons to behavior in the jellyfish Aurelia aurita. eLife 2019; 8:e50084. [PMID: 31868586 PMCID: PMC6999044 DOI: 10.7554/elife.50084] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 12/22/2019] [Indexed: 01/13/2023] Open
Abstract
Jellyfish nerve nets provide insight into the origins of nervous systems, as both their taxonomic position and their evolutionary age imply that jellyfish resemble some of the earliest neuron-bearing, actively-swimming animals. Here, we develop the first neuronal network model for the nerve nets of jellyfish. Specifically, we focus on the moon jelly Aurelia aurita and the control of its energy-efficient swimming motion. The proposed single neuron model disentangles the contributions of different currents to a spike. The network model identifies factors ensuring non-pathological activity and suggests an optimization for the transmission of signals. After modeling the jellyfish's muscle system and its bell in a hydrodynamic environment, we explore the swimming elicited by neural activity. We find that different delays between nerve net activations lead to well-controlled, differently directed movements. Our model bridges the scales from single neurons to behavior, allowing for a comprehensive understanding of jellyfish neural control of locomotion.
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Affiliation(s)
- Fabian Pallasdies
- Neural Network Dynamics and Computation, Institute of GeneticsUniversity of BonnBonnGermany
| | - Sven Goedeke
- Neural Network Dynamics and Computation, Institute of GeneticsUniversity of BonnBonnGermany
| | - Wilhelm Braun
- Neural Network Dynamics and Computation, Institute of GeneticsUniversity of BonnBonnGermany
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8
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Attenborough RM, Hayward DC, Wiedemann U, Forêt S, Miller DJ, Ball EE. Expression of the neuropeptides RFamide and LWamide during development of the coral Acropora millepora in relation to settlement and metamorphosis. Dev Biol 2019; 446:56-67. [DOI: 10.1016/j.ydbio.2018.11.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Revised: 11/22/2018] [Accepted: 11/30/2018] [Indexed: 10/27/2022]
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9
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Bielecki J, Garm A. Vision Made Easy: Cubozoans Can Advance Our Understanding of Systems-Level Visual Information Processing. Results Probl Cell Differ 2018; 65:599-624. [PMID: 30083938 DOI: 10.1007/978-3-319-92486-1_27] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Animals relying on vision as their main sensory modality reserve a large part of their central nervous system to appropriately navigate their environment. In general, neural involvement correlates to the complexity of the visual system and behavioural repertoire. In humans, one third of the available neural capacity supports our single-chambered general-purpose eyes, whereas animals with less elaborate visual systems need less computational power, and generally have smaller brains, and thereby lack in visual behaviour. As a consequence, both traditional model animals (mice, zebrafish, and flies) and more experimentally tractable animals (Hydra, Planaria, and C. elegans) cannot contribute to our understanding of systems-level visual information processing-a Goldilocks case of too big and too small.However, one animal, the box jellyfish Tripedalia cystophora, possesses a rather complex visual system, displays multiple visual behaviours, yet processes visual information by means of a relatively simple central nervous system. This-just right-model system could not only provide information on how visual stimuli are processed through distinct combinations of neural circuitry but also provide a processing algorithm for extracting specific information from a complex visual scene.
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Affiliation(s)
- Jan Bielecki
- GEOMAR - Helmholtz Centre for Ocean Research, Kiel, Germany.
- Institute of Physiology, Christian Albrechts University, Kiel, Germany.
| | - Anders Garm
- Marine Biological Section, University of Copenhagen, Copenhagen, Denmark
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10
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Zhang H, Yu P, Zhong S, Ge T, Peng S, Zhou Z, Guo X. Gliocyte and synapse analyses in cerebral ganglia of the Chinese mitten crab, Eriocheir sinensis: ultrastructural study. Eur J Histochem 2016; 60:2655. [PMID: 27734995 PMCID: PMC5062632 DOI: 10.4081/ejh.2016.2655] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Revised: 06/16/2016] [Accepted: 07/01/2016] [Indexed: 01/13/2023] Open
Abstract
The Chinese mitten crab Eriocheir sinensis is an economically important aquatic species in China. Many studies on gene structure, breeding, and diseases of the crab have been reported. However, knowledge about the organization of the nerve system of the crab remains largely unknown. To study the ultrastructure of the cerebral ganglia of E. sinensis and to compare the histological findings regarding the nerve systems of crustaceans, the cerebral ganglia were observed by transmission electron microscopy. The results showed that four types of gliocytes, including type I, II, III, and IV gliocytes were located in the cerebral ganglia. In addition, three types of synapses were present in the cerebral ganglia, including unidirectional synapses, bidirectional synapses, and combined type synapses.
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Affiliation(s)
- H Zhang
- Jiangxi Agricultural University.
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11
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Hufnagel LA, Kass-Simon G. The two nerve rings of the hypostomal nervous system of Hydra vulgaris-an immunohistochemical analysis. Cell Tissue Res 2016; 366:255-269. [PMID: 27344671 DOI: 10.1007/s00441-016-2447-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 06/02/2016] [Indexed: 01/08/2023]
Abstract
In Hydra vulgaris, physiological and pharmacological evidence exists for a hypostomal circumferential neuro-effector pathway that initiates ectodermal pacemaker activity at tentacular-hypostomal loci coordinating body and tentacle contractions. Here, we describe an ectodermal nerve ring that runs below and between the tentacles, and an anti-GABAB receptor antibody-labeled ring coincident with it. The location of this ring is consistent with the physiology of the hypostomal pacemaker systems of hydra. We also describe a distally located, ectodermal ring of nerve fibers that is not associated with anti-GABAB receptor antibody labeling. The neurites and cell bodies of sensory cells contribute to both rings. The location of the distal ring and its sensory cell neurites suggests an involvement in the behavior of the mouth. Between the two rings is a network of anastomosing sensory and ganglion cell bodies and their neurites. Phase contrast, darkfield, and antibody-labeled images reveal that the mouth of hydra comprises five or six epithelial folds whose endoderm extensively labels with anti-GABAB receptor antibody, suggesting that endodermal metabotrobic GABA receptors are also involved in regulating mouth behavior.
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Affiliation(s)
- L A Hufnagel
- Department of Cell and Molecular Biology, University of Rhode Island, Kingston, RI 02881, USA.,Interdisciplinary Neurosciences Program, University of Rhode Island, Kingston, RI 02881, USA
| | - G Kass-Simon
- Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA. .,Interdisciplinary Neurosciences Program, University of Rhode Island, Kingston, RI 02881, USA.
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12
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Garm A, Bielecki J, Petie R, Nilsson DE. Hunting in Bioluminescent Light: Vision in the Nocturnal Box Jellyfish Copula sivickisi. Front Physiol 2016; 7:99. [PMID: 27065877 PMCID: PMC4812875 DOI: 10.3389/fphys.2016.00099] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2015] [Accepted: 03/01/2016] [Indexed: 11/13/2022] Open
Abstract
Cubomedusae all have a similar set of six eyes on each of their four rhopalia. Still, there is a great variation in activity patterns with some species being strictly day active while others are strictly night active. Here we have examined the visual ecology of the medusa of the night active Copula sivickisi from Okinawa using optics, morphology, electrophysiology, and behavioral experiments. We found the lenses of both the upper and the lower lens eyes to be image forming but under-focused, resulting in low spatial resolution in the order of 10-15°. The photoreceptor physiology is similar in the two lens eyes and they have a single opsin peaking around 460 nm and low temporal resolution with a flicker fusion frequency (fff) of 2.5 Hz indicating adaptions to vision in low light intensities. Further, the outer segments have fluid filled swellings, which may concentrate the light in the photoreceptor membrane by total internal reflections, and thus enhance the signal to noise ratio in the eyes. Finally our behavioral experiments confirmed that the animals use vision when hunting. When they are active at night they seek out high prey-concentration by visual attraction to areas with abundant bioluminescent flashes triggered by their prey.
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Affiliation(s)
- Anders Garm
- Marine Biological Section, Department of Biology, University of Copenhagen Copenhagen, Denmark
| | - Jan Bielecki
- Department of Ecology evolution and Marin Biology, University of California, Santa Barbara Santa Barbara, CA, USA
| | - Ronald Petie
- Marine Biological Section, Department of Biology, University of Copenhagen Copenhagen, Denmark
| | - Dan-Eric Nilsson
- Vision Group, Department of Biology, Lund University Lund, Sweden
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13
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Comparative Connectomics. Trends Cogn Sci 2016; 20:345-361. [PMID: 27026480 DOI: 10.1016/j.tics.2016.03.001] [Citation(s) in RCA: 196] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Revised: 02/23/2016] [Accepted: 03/01/2016] [Indexed: 12/30/2022]
Abstract
We introduce comparative connectomics, the quantitative study of cross-species commonalities and variations in brain network topology that aims to discover general principles of network architecture of nervous systems and the identification of species-specific features of brain connectivity. By comparing connectomes derived from simple to more advanced species, we identify two conserved themes of wiring: the tendency to organize network topology into communities that serve specialized functionality and the general drive to enable high topological integration by means of investment of neural resources in short communication paths, hubs, and rich clubs. Within the space of wiring possibilities that conform to these common principles, we argue that differences in connectome organization between closely related species support adaptations in cognition and behavior.
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14
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15
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Koizumi O, Hamada S, Minobe S, Hamaguchi-Hamada K, Kurumata-Shigeto M, Nakamura M, Namikawa H. The nerve ring in cnidarians: its presence and structure in hydrozoan medusae. ZOOLOGY 2015; 118:79-88. [DOI: 10.1016/j.zool.2014.10.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 07/23/2014] [Accepted: 10/04/2014] [Indexed: 11/29/2022]
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16
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Satterlie RA. Multiple conducting systems in the cubomedusa Carybdea marsupialis. THE BIOLOGICAL BULLETIN 2014; 227:274-284. [PMID: 25572215 DOI: 10.1086/bblv227n3p274] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Acute responses to mechanical, electrical, and photic stimuli were used to describe neural conducting systems in the cubomedusan jellyfish Carybdea marsupialis underlying three behaviors: contractile responses of single tentacles, protective crumple responses, and alterations of swimming activity by the visual system. Responses of single tentacles consisted of tentacular shortening and inward pedalial bending, and were accompanied by bursts of extracellularly recorded spike activity that were restricted to the stimulated tentacle. With nociceptive stimuli delivered to the subumbrella or margin, all four tentacles produced similar responses in a crumple response. The spike bursts in all four tentacles showed coordinated firing as long as the nerve ring was intact. Crumples were still produced following cuts through the nerve ring, but the activity in individual tentacles was no longer coordinated. Responses to light-on stimulation of a rhopalium, as recorded from the pacemaker region, were weak and inconsistent, but when present, resulted in a stimulation of swimming activity. In comparison, light-off responses were robust and resulted in temporary inhibition of swimming activity. Light-off responses were conducted in the nerve ring to unstimulated rhopalia. In conclusion, three conducting systems have been described as components of the rhopalia-nerve ring centralized system in Carybdea: the swim motor system, the crumple coordination system, and the light-off response system.
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Affiliation(s)
- Richard A Satterlie
- Department of Biology and Marine Biology and Center for Marine Science, University of North Carolina Wilmington, Wilmington, North Carolina 28403
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17
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Eichinger JM, Satterlie RA. Organization of the ectodermal nervous structures in medusae: cubomedusae. THE BIOLOGICAL BULLETIN 2014; 226:41-55. [PMID: 24648206 DOI: 10.1086/bblv226n1p41] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
At least two conducting systems are well documented in cubomedusae. A variably diffuse network of large neurons innervates the swim musculature and can be visualized immunohistochemically using antibodies against α- or β-tubulin. Despite the non-specificity of these antibodies, multiple lines of evidence suggest that staining highlights the primary motor networks. These networks exhibit unique neurite distributions among the muscle sheets in that network density is greatest in the perradial frenula, where neurites are oriented in parallel with radial muscle fibers. This highly innervated, buttress-like muscle sheet may serve a critical role in the cubomedusan mechanism of turning. In scyphomedusae, a second subumbrellar network immunoreactive to antibodies against the neuropeptide FMRFamide innervates the swim musculature, but it is absent in cubomedusae. Immunoreactivity to FMRFamide in cubomedusae is mostly limited to a small network of neurons in the pacemaker region of the rhopalia, the pedalial apex at the nerve ring junction, and a few neuron tracts in the nerve ring. However, FMRFamide-immunoreactive networks, as well as tubulin-immunoreactive networks, are nearly ubiquitous outside of the swim muscle sheets in the perradial smooth muscle bands, manubrium, pedalia, and tentacles. Here we describe in detail the peripheral nerve nets of box jellyfish on the basis of immunoreactivity to the antibodies above. Our results offer insight into how the peripheral nerve nets are organized to produce the complex swimming, feeding, and defensive behaviors observed in cubomedusae.
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Affiliation(s)
- Justin M Eichinger
- Department of Biology and Marine Biology and Center for Marine Science, University of North Carolina Wilmington, Wilmington, North Carolina 28409
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18
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Garm A, Hedal I, Islin M, Gurska D. Pattern- and contrast-dependent visual response in the box jellyfish Tripedalia cystophora. ACTA ACUST UNITED AC 2013; 216:4520-9. [PMID: 24031055 DOI: 10.1242/jeb.091934] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cubomedusae possess a total of 24 eyes, some of which are structurally similar to vertebrate eyes. Accordingly, the medusae also display a range of light-guided behaviours including obstacle avoidance, diurnal activity patterns and navigation. Navigation is supported by spatial resolution and image formation in the so-called upper lens eye. Further, there are indications that obstacle avoidance requires image information from the lower lens eye. Here we use a behavioural assay to examine the obstacle avoidance behaviour of the Caribbean cubomedusa Tripedalia cystophora and test whether it requires spatial resolution. The possible influence of the contrast and orientation of the obstacles is also examined. We show that the medusae can only perform the behaviour when spatial information is present, and fail to avoid a uniformly dark wall, directly proving the use of spatial vision. We also show that the medusae respond stronger to high contrast lines than to low contrast lines in a graded fashion, and propose that the medusae use contrast as a semi-reliable measure of distance to the obstacle.
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Affiliation(s)
- Anders Garm
- Section of Marine Biology, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
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Swim pacemaker response to bath applied neurotransmitters in the cubozoan Tripedalia cystophora. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2013; 199:785-97. [PMID: 23893247 DOI: 10.1007/s00359-013-0839-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 07/05/2013] [Accepted: 07/11/2013] [Indexed: 10/26/2022]
Abstract
The four rhopalia of cubomedusae are integrated parts of the central nervous system carrying their many eyes and thought to be the centres of visual information processing. Rhopalial pacemakers control locomotion through a complex neural signal transmitted to the ring nerve and the signal frequency is modulated by the visual input. Since electrical synapses have never been found in the cubozoan nervous system all signals are thought to be transmitted across chemical synapses, and so far information about the neurotransmitters involved are based on immunocytochemical or behavioural data. Here we present the first direct physiological evidence for the types of neurotransmitters involved in sensory information processing in the rhopalial nervous system. FMRFamide, serotonin and dopamine are shown to have inhibitory effect on the pacemaker frequency. There are some indications that the fast acting acetylcholine and glycine have an initial effect and then rapidly desensitise. Other tested neuroactive compounds (GABA, glutamate, and taurine) could not be shown to have a significant effect.
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Velarium control and visual steering in box jellyfish. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2013; 199:315-24. [PMID: 23417442 PMCID: PMC3604586 DOI: 10.1007/s00359-013-0795-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 01/08/2013] [Accepted: 01/12/2013] [Indexed: 10/28/2022]
Abstract
Directional swimming in the box jellyfish Tripedalia cystophora (cubozoa, cnidaria) is controlled by the shape of the velarium, which is a thin muscular sheet that forms the opening of the bell. It was unclear how different patterns of visual stimulation control directional swimming and that is the focus of this study. Jellyfish were tethered inside a small experimental tank, where the four vertical walls formed light panels. All four panels were lit at the start of an experiment. The shape of the opening in the velarium was recorded in response to switching off different combinations of panels. We found that under the experimental conditions the opening in the velarium assumed three distinct shapes during a swim contraction. The opening was (1) centred or it was off-centred and pocketed out either towards (2) a rhopalium or (3) a pedalium. The shape of the opening in the velarium followed the direction of the stimulus as long as the stimulus contained directional information. When the stimulus contained no directional information, the percentage of centred pulses increased and the shape of the off-centred pulses had a random orientation. Removing one rhopalium did not change the directional response of the animals, however, the number of centred pulses increased. When three rhopalia were removed, the percentage of centred pulses increased even further and the animals lost their ability to respond to directional information.
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Roopin M, Levy O. Melatonin distribution reveals clues to its biological significance in basal metazoans. PLoS One 2012; 7:e52266. [PMID: 23300630 PMCID: PMC3530593 DOI: 10.1371/journal.pone.0052266] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Accepted: 11/12/2012] [Indexed: 12/25/2022] Open
Abstract
Although nearly ubiquitous in nature, the precise biological significance of endogenous melatonin is poorly understood in phylogenetically basal taxa. In the present work, we describe insights into the functional role of melatonin at the most “basal” level of metazoan evolution. Hitherto unknown morphological determinants of melatonin distribution were evaluated in Nematostella vectensis by detecting melatonin immunoreactivity and examining the spatial gene expression patterns of putative melatonin biosynthetic and receptor elements that are located at opposing ends of the melatonin signaling pathway. Immuno-melatonin profiling indicated an elaborate interaction with reproductive tissues, reinforcing previous conjectures of a melatonin-responsive component in anthozoan reproduction. In situ hybridization (ISH) to putative melatonin receptor elements highlighted the possibility that the bioregulatory effects of melatonin in anthozoan reproduction may be mediated by interactions with membrane receptors, as in higher vertebrates. Another intriguing finding of the present study pertains to the prevalence of melatonin in centralized nervous structures. This pattern may be of great significance given that it 1) identifies an ancestral association between melatonin and key neuronal components and 2) potentially implies that certain effects of melatonin in basal species may be spread widely by regionalized nerve centers.
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Affiliation(s)
- Modi Roopin
- The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
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Abstract
Cnidarians belong to the first phylum differentiating a nervous system, thus providing suitable model systems to trace the origins of neurogenesis. Indeed corals, sea anemones, jellyfish and hydra contract, swim and catch their food thanks to sophisticated nervous systems that share with bilaterians common neurophysiological mechanisms. However, cnidarian neuroanatomies are quite diverse, and reconstructing the urcnidarian nervous system is ambiguous. At least a series of characters recognized in all classes appear plesiomorphic: (1) the three cell types that build cnidarian nervous systems (sensory-motor cells, ganglionic neurons and mechanosensory cells called nematocytes or cnidocytes); (2) an organization of nerve nets and nerve rings [those working as annular central nervous system (CNS)]; (3) a neuronal conduction via neurotransmitters; (4) a larval anterior sensory organ required for metamorphosis; (5) a persisting neurogenesis in adulthood. By contrast, the origin of the larval and adult neural stem cells differs between hydrozoans and other cnidarians; the sensory organs (ocelli, lens-eyes, statocysts) are present in medusae but absent in anthozoans; the electrical neuroid conduction is restricted to hydrozoans. Evo-devo approaches might help reconstruct the neurogenic status of the last common cnidarian ancestor. In fact, recent genomic analyses show that if most components of the postsynaptic density predate metazoan origin, the bilaterian neurogenic gene families originated later, in basal metazoans or as eumetazoan novelties. Striking examples are the ParaHox Gsx, Pax, Six, COUP-TF and Twist-type regulators, which seemingly exert neurogenic functions in cnidarians, including eye differentiation, and support the view of a two-step process in the emergence of neurogenesis.
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Affiliation(s)
- Brigitte Galliot
- Department of Genetics and Evolution, Faculty of Science, University of Geneva, Sciences III, 30 quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland.
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Stöckl AL, Petie R, Nilsson DE. Setting the pace: new insights into central pattern generator interactions in box jellyfish swimming. PLoS One 2011; 6:e27201. [PMID: 22073288 PMCID: PMC3206948 DOI: 10.1371/journal.pone.0027201] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Accepted: 10/11/2011] [Indexed: 11/18/2022] Open
Abstract
Central Pattern Generators (CPGs) produce rhythmic behaviour across all animal phyla. Cnidarians, which have a radially symmetric nervous system and pacemaker centres in multiples of four, provide an interesting comparison to bilaterian animals for studying the coordination between CPGs. The box jellyfish Tripedalia cystophora is remarkable among cnidarians due to its most elaborate visual system. Together with their ability to actively swim and steer, they use their visual system for multiple types of behaviour. The four swim CPGs are directly regulated by visual input. In this study, we addressed the question of how the four pacemaker centres of this radial symmetric cnidarian interact. We based our investigation on high speed camera observations of the timing of swim pulses of tethered animals (Tripedalia cystophora) with one or four rhopalia, under different simple light regimes. Additionally, we developed a numerical model of pacemaker interactions based on the inter pulse interval distribution of animals with one rhopalium. We showed that the model with fully resetting coupling and hyperpolarization of the pacemaker potential below baseline fitted the experimental data best. Moreover, the model of four swim pacemakers alone underscored the proportion of long inter pulse intervals (IPIs) considerably. Both in terms of the long IPIs as well as the overall swim pulse distribution, the simulation of two CPGs provided a better fit than that of four. We therefore suggest additional sources of pacemaker control than just visual input. We provide guidelines for future research on the physiological linkage of the cubozoan CPGs and show the insight from bilaterian CPG research, which show that pacemakers have to be studied in their bodily and nervous environment to capture all their functional features, are also manifest in cnidarians.
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Affiliation(s)
- Anna Lisa Stöckl
- Vision Group, Department of Biology, Lund University, Lund, Sweden.
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Abstract
The traditional view of the cnidarian nervous system is of a diffuse nerve net that functions as both a conducting and an integrating system; this is considered an indicator of a primitive condition. Yet, in medusoid members, varying degrees of nerve net compression and neuronal condensation into ganglion-like structures represent more centralized integrating centers. In some jellyfish, this relegates nerve nets to motor distribution systems. The neuronal condensation follows a precept of neuronal organization of higher animals with a relatively close association with the development and elaboration of sensory structures. Nerve nets still represent an efficient system for diffuse, non-directional activation of broad, two-dimensional effector sheets, as required by the radial, non-cephalized body construction. However, in most jellyfish, an argument can be made for the presence of centralized nervous systems that interact with the more diffuse nerve nets.
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Affiliation(s)
- Richard A Satterlie
- Department of Biology and Marine Biology, University of North Carolina Wilmington and Center for Marine Science, 5600 Marvin K. Moss Lane, Wilmington, NC 28409, USA
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Piraino S, Zega G, Di Benedetto C, Leone A, Dell'Anna A, Pennati R, Candia Carnevali D, Schmid V, Reichert H. Complex neural architecture in the diploblastic larva of Clava multicornis (Hydrozoa, Cnidaria). J Comp Neurol 2011; 519:1931-51. [DOI: 10.1002/cne.22614] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Garm A, Ekström P. Evidence for multiple photosystems in jellyfish. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2010; 280:41-78. [PMID: 20797681 DOI: 10.1016/s1937-6448(10)80002-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Cnidarians are often used as model animals in studies of eye and photopigment evolution. Most cnidarians display photosensitivity at some point in their lifecycle ranging from extraocular photoreception to image formation in camera-type eyes. The available information strongly suggests that some cnidarians even possess multiple photosystems. The evidence is strongest within Cubomedusae where all known species posses 24 eyes of four morphological types. Physiological experiments show that each cubomedusan eye type likely constitutes a separate photosystem controlling separate visually guided behaviors. Further, the visual system of cubomedusae also includes extraocular photoreception. The evidence is supported by immunocytochemical and molecular data indicating multiple photopigments in cubomedusae as well as in other cnidarians. Taken together, available data suggest that multiple photosystems had evolved already in early eumetazoans and that their original level of organization was discrete sets of special-purpose eyes and/or photosensory cells.
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Affiliation(s)
- Anders Garm
- Department of Comparative Zoology, University of Copenhagen, Copenhagen, Denmark
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Garm A, Mori S. Multiple photoreceptor systems control the swim pacemaker activity in box jellyfish. ACTA ACUST UNITED AC 2010; 212:3951-60. [PMID: 19946073 DOI: 10.1242/jeb.031559] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Like all other cnidarian medusae, box jellyfish propel themselves through the water by contracting their bell-shaped body in discrete swim pulses. These pulses are controlled by a swim pacemaker system situated in their sensory structures, the rhopalia. Each medusa has four rhopalia each with a similar set of six eyes of four morphologically different types. We have examined how each of the four eye types influences the swim pacemaker. Multiple photoreceptor systems, three of the four eye types, plus the rhopalial neuropil, affect the swim pacemaker. The lower lens eye inhibits the pacemaker when stimulated and provokes a strong increase in the pacemaker frequency upon light-off. The upper lens eye, the pit eyes and the rhopalial neuropil all have close to the opposite effect. When these responses are compared with all-eye stimulations it is seen that some advanced integration must take place.
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Affiliation(s)
- A Garm
- Section of Aquatic Biology, University of Copenhagen, Denmark.
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Parkefelt L, Ekström P. Prominent system of RFamide immunoreactive neurons in the rhopalia of box jellyfish (Cnidaria: Cubozoa). J Comp Neurol 2009; 516:157-65. [PMID: 19598151 DOI: 10.1002/cne.22072] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The four visual sensory structures of a cubomedusa, the rhopalia, display a surprisingly elaborate organization by containing two lens eyes and four bilaterally paired pigment cup eyes. Peptides containing the peptide sequence Arg-Phe-NH2 (RFamide) occur in close association with visual structures of cnidarians, including the rhopalia and rhopalial stalk of cubomedusae, suggesting that RFamide functions as a neuronal marker for certain parts of the visual system of medusae. Using immunofluorescence we give a detailed description of the organization of the RFamide-immunoreactive (ir) nervous system in the rhopalia and rhopalial stalk of the cubomedusae Tripedalia cystophora and Carybdea marsupialis. The bilaterally symmetric RFamide-ir nervous system contains four cell groups and three morphologically different cell types. Neurites spread throughout the rhopalia and occur in close vicinity of the pigment cup eyes and the lower lens eye. Two commissures connect the two sides of the system and neurites of one rhopalial cell group extend into the rhopalial stalk. The RFamide-ir nervous system in the rhopalia of cubomedusae is more widespread and comprises more cells than earlier discerned. We suggest that the system might not only integrate visual input but also signals from other senses. One of the RFamide-ir cell groups is favorably situated to represent pacemaker neurons that set the swimming rhythm of the medusa.
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Affiliation(s)
- Linda Parkefelt
- Department of Cell and Organism Biology, Lund University, S-22362 Lund, Sweden.
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Watanabe H, Fujisawa T, Holstein TW. Cnidarians and the evolutionary origin of the nervous system. Dev Growth Differ 2009; 51:167-83. [PMID: 19379274 DOI: 10.1111/j.1440-169x.2009.01103.x] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cnidarians are widely regarded as one of the first organisms in animal evolution possessing a nervous system. Conventional histological and electrophysiological studies have revealed a considerable degree of complexity of the cnidarian nervous system. Thanks to expressed sequence tags and genome projects and the availability of functional assay systems in cnidarians, this simple nervous system is now genetically accessible and becomes particularly valuable for understanding the origin and evolution of the genetic control mechanisms underlying its development. In the present review, the anatomical and physiological features of the cnidarian nervous system and the interesting parallels in neurodevelopmental mechanisms between Cnidaria and Bilateria are discussed.
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Affiliation(s)
- Hiroshi Watanabe
- University of Heidelberg, Department of Molecular Evolution and Genomics, Im Neuenheimer Feld 230, D-69120 Heidelberg, Germany.
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Origins of neurogenesis, a cnidarian view. Dev Biol 2009; 332:2-24. [PMID: 19465018 DOI: 10.1016/j.ydbio.2009.05.563] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 05/14/2009] [Accepted: 05/16/2009] [Indexed: 11/22/2022]
Abstract
New perspectives on the origin of neurogenesis emerged with the identification of genes encoding post-synaptic proteins as well as many "neurogenic" regulators as the NK, Six, Pax, bHLH proteins in the Demosponge genome, a species that might differentiate sensory cells but no neurons. However, poriferans seem to miss some key regulators of the neurogenic circuitry as the Hox/paraHox and Otx-like gene families. Moreover as a general feature, many gene families encoding evolutionarily-conserved signaling proteins and transcription factors were submitted to a wave of gene duplication in the last common eumetazoan ancestor, after Porifera divergence. In contrast gene duplications in the last common bilaterian ancestor, Urbilateria, are limited, except for the bHLH Atonal-class. Hence Cnidaria share with Bilateria a large number of genetic tools. The expression and functional analyses currently available suggest a neurogenic function for numerous orthologs in developing or adult cnidarians where neurogenesis takes place continuously. As an example, in the Hydra polyp, the Clytia medusa and the Acropora coral, the Gsx/cnox2/Anthox-2 ParaHox gene likely supports neurogenesis. Also neurons and nematocytes (mechanosensory cells) share in hydrozoans a common stem cell and several regulatory genes indicating that they can be considered as sister cells. Performed in anthozoan and medusozoan species, these studies should tell us more about the way(s) evolution hazards achieved the transition from epithelial to neuronal cell fate, and about the robustness of the genetic circuitry that allowed neuromuscular transmission to arise and be maintained across evolution.
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Unique structure and optics of the lesser eyes of the box jellyfish Tripedalia cystophora. Vision Res 2008; 48:1061-73. [PMID: 18308364 DOI: 10.1016/j.visres.2008.01.019] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2007] [Revised: 12/10/2007] [Accepted: 01/02/2008] [Indexed: 11/20/2022]
Abstract
The visual system of box jellyfish comprises a total of 24 eyes. These are of four types and each probably has a special function. To investigate this hypothesis the morphology and optics of the lesser eyes, the pit and slit eyes, were examined. The pit eyes hold one cell type only and are probably mere light meters. The slit eyes, comprising four cell types, are complex and highly asymmetric. They also hold a lens-like structure, but its optical power is minute. Optical modeling suggests spatial resolution, but only in one plane. These unique and intriguing traits support strong peripheral filtering.
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