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  • 1
    Electronic Resource
    Electronic Resource
    Modulation of swimming speed in the pteropod mollusc,Clione limacina: Role of a compartmental serotonergic system (1996)
    Springer
    Invertebrate neuroscience 2 (1996), S. 157-165 
    Details
    ISSN: 1439-1104
    Keywords: locomotion ; serotonin ; central pattern generator ; motoneuron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In locomotory systems, the central pattern generator and motoneuron output must be modulated in order to achieve variability in locomotory speed, particularly when speed changes are important components of different behavior acts. The swimming system of the pteropod molluscClione limacina is an excellent model system for investigating such modulation. In particular, a system of central serotonergic neurons has been shown to be intimately involved in regulating output of the locomotory pattern generator and motor system ofClione. There are approximately 27 pairs of serotonin-immunoreactive neurons in the central nervous system ofClione, with about 75% of these identified. The majority of these identified immunoreactive neurons are involved in various aspects of locomotory speed modulation. A symmetrical cluster of pedal serotonergic neurons serves to increase wing contractility without affecting wing-beat frequency or motoneuron activity. Two clusters of cerebral cells produce widespread responses that lead to an increase in pattern generator cycle frequency, recruitment of swim motoneurons, activation of the pedal serotonergic neurons and excitation of the heart excitor neuron. A pair of ventral cerebral neurons provides weak excitatory inputs to the swimming system, and strongly inhibits neurons of the competing whole-body withdrawal network. Overall, the serotonergic system inClione is compartmentalized so that each subsystem (usually neuron cluster) can act independently or in concert to produce variability in locomotory speed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02214171
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  • 2
    Electronic Resource
    Electronic Resource
    Neuronal mechanisms underlying behavioral switching in a pteropod mollusc (1990)
    Springer
    Journal of comparative physiology 166 (1990), S. 875-887 
    Details
    ISSN: 1432-1351
    Keywords: Behavioral switching ; Reflex ; Mollusc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the pteropod mollusc Clione limacina, wing retraction takes precedence over spontaneous and continuous swimming, a phenomenon here defined as behavioral switching. The wing retraction system is organized as a simple reflex in which wing mechanoreceptors activate a pair of retraction interneurons which in turn excite at least two pairs of retraction motoneurons. Activation of individual mechanoreceptors does not inhibit swimming or trigger wing retraction. A pair of retraction interneurons can fully suppress swimming when induced to fire at physiological frequencies, and may be both sufficient and necessary for swim inhibition. Retraction interneurons monosynaptically inhibit both swim interneurons and swim motoneurons. Retraction motoneurons inhibit swim motoneurons through a polysynaptic pathway. A model summarizing the neural circuitry underlying behavioral switching in Clione is presented. A comparison of this model with the behavioral choice model in Pleurobranchaea reveals that the overall neural mechanisms for behavioral choice and behavioral switching are similar as both involve dual function interneurons that not only activate their own motor pathway, but also inhibit the competing motor system. While inhibition is biased toward the afferent side of the competing circuit in behavioral choice, it is biased to the efferent side in behavioral switching.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00187335
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  • 3
    Electronic Resource
    Electronic Resource
    Neuronal control of locomotion in hydrozoan medusae (1983)
    Springer
    Journal of comparative physiology 150 (1983), S. 195-206 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The swimming control systems of 13 hydromedusan species were examined electrophysiologically and morphologically. Despite obvious differences in the structure, behavior and life style of these medusae, the basic organization of swimming system components is similar. 2. Motor neurons that activate swimming muscles are located in the inner nerve-ring comprising electrically-coupled condensed networks (Figs. 2, 3). Individual neurons of these networks are of far larger diameter than other neurons of the nerve-rings (Figs. 4–6). 3. Spontaneous activity persists in the swim motor neuron networks in seawater containing excess Mg++ suggesting that the network may perform a pacemaker function. 4. The swimming muscle sheet includes circular, striated epitheliomuscular cells of the subumbrella and velum, and an interposed non-muscular epithelial region which overlies the inner nerve-ring (Fig. 1). Gap junctions are common throughout this tissue sheet (Figs. 13, 14, 18). Electrical(Fig. 10) and dye-coupling (Fig. 3) of cells in this sheet suggests that direct current spread between myocytes is important in transmission of excitation throughout the subumbrella. 5. Recordings from epithelial cells immediately adjacent to swim motor neurons reveal graded potentials presumably of synaptic origin (Figs. 2, 10). The synaptic potentials, and muscle action potentials, are blocked in seawater containing excess Mg++. Synaptic contacts were observed between swim motor neurons and overlying epithelial cells throughout the inner nerve-rings of all medusae examined (Figs. 19–21).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00606369
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  • 4
    Electronic Resource
    Electronic Resource
    Central control of swimming in the cubomedusan jellyfishCarybdea rastonii (1979)
    Springer
    Journal of comparative physiology 133 (1979), S. 357-367 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Swimming in the cubomedusaCarybdea rastonii is controlled by a subumbrellar nerve net. Neurons that make up this net, including “giant” neurons, make random synaptic contacts with each other and with the circular subumbrellar swimming muscles (Figs. 1–3). 2. Extracellularly recorded swimming impulses originate in the rhopalia and spread throughout the subumbrellar nerve net, initiating contractions of the subumbrellar musculature (Fig. 4). 3. Intracellular recordings from the subumbrellar giant neurons indicate that all-or-none overshooting action potentials precede each swimming contraction (Fig. 6). Synaptic depolarizations were occasionally recorded alone, and triggering an action potential (Fig. 6C, E). 4. Extracellularly recorded muscle potentials exhibit frequency-dependent facilitation, with normal swimming at about 80% of the maximal contraction of the muscle sheet (Figs. 4 and 5). 5. Intracellular recordings from subumbrellar muscle cells reveal graded depolarizations with each contraction of the muscle sheet. The jagged potentials are initially small and increase in amplitude with the first few contractions in a series (Fig. 7). The increases in muscle cell depolarizations may be related to the facilitation in the size of extracellularly recorded muscle potentials. 6. Pacemakers of the four rhopalia interact by a dominance hierarchy; the rhopalium with the highest firing frequency controls swimming. Dominance shifts have been observed in two-rhopalia preparations (Fig. 8 A), and facilitation of the musculature often occurs independently of rhopalial sequence (Fig. 8B). 7. The swimming system ofCarybdea is comparable to the “giant fiber nerve net (GFNN)” of other scyphomedusae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00661138
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  • 5
    Electronic Resource
    Electronic Resource
    An identified cerebral interneuron initiates different elements of prey capture behavior in the pteropod mollusc,Clione limacina (1995)
    Springer
    Invertebrate neuroscience 1 (1995), S. 235-248 
    Details
    ISSN: 1439-1104
    Keywords: mollusc ; feeding ; swimming ; cerebral interneuron ; command neuron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The prey capture phase of feeding behavior in the pteropod molluscClione limacina consists of an explosive extrusion of buccal cones, specialized oral appendages which are used to catch the prey, and significant acceleration of swimming. Several groups of neurons which control different components of prey capture behavior inClione have been previously identified in the CNS. However, the question of their coordination in order to develop a normal behavioral reaction still remains open. We describe here a cerebral interneuron which has wide-spread excitatory and inhibitory effects on a number of neurons in the cerebral and pedal ganglia, directed toward the initiation of prey capture behavior inClione. This bilaterally symmetrical neuron, designated Cr-PC (Cerebral interneuron initiating Prey Capture), produced monosynaptic activation of Cr-A motoneurons, which control buccal cone extrusion, and inhibition of Cr-B and Cr-L motoneurons, whose spike activities maintain buccal cones in a withdrawn position inside the head in non-feeding animals. In addition, Cr-PC produced monosynaptic activation of a number of swim motoneurons and interneurons of the swim central pattern generator (CPG) in the pedal ganglia, pedal serotonergic Pd-SW neurons involved in a peripheral modulation of swimming and the serotonergic Heart Excitor neuron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02211025
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  • 6
    Electronic Resource
    Electronic Resource
    Neurobiology of the gorgonian coelenterates, Murcea californca and Lophogorgia chilensis (1978)
    Springer
    Cell & tissue research 187 (1978), S. 379-396 
    Details
    ISSN: 1432-0878
    Keywords: Anthozoa ; Nerve net ; Sensory cells ; Nematocysts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Diffuse and synaptic nerve nets are present in the coenenchymal mesoglea and ectoderm of Muricea and Lophogorgia colonies. The nerve nets extend into the polyp column and tentacles maintaining a subectodermalmesogleal position. The density of nerve elements is low in comparison with similar nerve nets found in pennatulids. In the column of the polyp anthocodium, and throughout the oral disk region, neurons cross the mesoglea and enter the polyp endoderm. These neurons presumably connect with the endodermal nerve net which innervates the septal musculature. The trans-mesogleal neurons probably represent the connection between colonial and polyp nervous systems. In the tentacles, longitudinal ectodermal musculature is present with an overlying nerve plexus. These muscles and nerves, as well as tentacular sensory cells, are well represented in the oral side of the tentacles only. Presumed sensory cells form ciliary cone complexes in which one cell possesses an apical cilium. The other cells as well as the centrally located nematocyte contribute microvilli to the cone. The basal portion of the sensory cells is drawn into one or more neurite-like processes which enter the ectodermal nerve plexus. Similar processes form synapses with longitudinal muscle cells and nematocytes. The sensory cells of the ciliary cones presumably include chemoreceptors which can activate or modify nematocyst discharge, local muscle twitches, and tentacle bending.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229604
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  • 7
    Electronic Resource
    Electronic Resource
    Smooth muscle fiber types and a novel pattern of thick filaments in the wing of the pteropod mollusc Clione limacina (1989)
    Springer
    Cell & tissue research 257 (1989), S. 405-414 
    Details
    ISSN: 1432-0878
    Keywords: Mollusc ; Ultrastructure ; Musculature ; Hydroskeleton ; Retraction reflex ; Clione limacina (Mollusca)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Wing (parapodial) retraction in the pteropod mollusc Clione limacina is a reflex triggered by tactile stimulation. Light and transmission electron microscopy revealed three groups of smooth muscles in the wing hemocoel that participate in retraction movements: transverse, longitudinal, and dorsoventral. Among these, two subtypes of muscle cells were identified. The first (type A) appears in all three groups and forms a well-organized lattice-like structure. The second (type B) is the major component of transverse muscles and runs in one direction only. Quantitative ultrastructural comparisons of dimensions, abundance, and organization of dense bodies, thick and thin filaments, membrane invaginations, sarcoplasmic reticulum, and mitochondria suggest that type A cells are able to contract and relax more quickly with less endurance whereas type B cells are capable of generating stronger contractions with more endurance and slower relaxation speed. Furthermore, type A cells have a unique pattern of thick filament organization, here referred to as pseudosarcomeres. The roles played by the different cell types in wing retraction are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00261843
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  • 8
    Electronic Resource
    Electronic Resource
    Gap junctions suggest epithelial conduction within the comb plates of the ctenophore Pleurobrachia bachei (1978)
    Springer
    Cell & tissue research 193 (1978), S. 87-91 
    Details
    ISSN: 1432-0878
    Keywords: Gap junction ; Epithelial conduction ; Ctenophora ; Cilia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Intercellular gap junctions occur between the ciliated cells that make up the comb plates of the ctenophore Pleurobrachia. Similar junctions are found within the ciliated grooves which run from the apical organ to the first plate of each comb row, as well as throughout the endoderm of the meridional canals. Gap junctions were not found in the ectodermal tissue between the comb rows. The distribution of junctions suggests that excitation conduction within the ciliated grooves, comb plates and meridional canal endoderm may be epithelial.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00221603
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