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  • 1
    Electronic Resource
    Electronic Resource
    Quantitative evidence concerning the stabilization of sediments by marine benthic diatoms (1974)
    Springer
    Marine biology 27 (1974), S. 191-196 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Six species of benthic diatoms and a natural benthic diatom community were cultured in flasks on a variety of sediments. Diatom species which secreted large quantities of mucilage were effective sediment stabilizers. These mucilage-secreting species significantly reduced resuspension and retarded laminar flow of the sediments when the culture flasks were agitated. Diatom species which secreted little or no mucilage were not effective sediment stabilizers. These non-mucilage-secreting species did not significantly effect resuspension or laminar flow of the sediments when the culture flasks were agitated. A sediment stabilizing mechanism based on the secretion of mucilage by pennate benthic diatoms is proposed. The effect such a process may have on distributional patterns of benthic invertebrates in areas where extensive diatom or other microalgal films occur is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391943
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of thermal stress and total residual chlorination on early life stages of the mummichog Fundulus heteroclitus (1978)
    Springer
    Marine biology 46 (1978), S. 1-8 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Effects of simultaneous short-term (7.5 to 60 min) thermal stress (24° to 34°C) and total residual chlorination (0.05 to 1.0 mg l-1) on specific development stages of the mummichog Fundulus heteroclitus (Pisces: Cyprinodontidae), were investigated. For the embryonic stages, the total number of successfully hatched larvae was used as the criterion to measure effect. For the larval stages, survival 24 h after exposure was used. In the embryonic stages, temperature was the most important main variable. Only one embryonic stage (gastrula) was confounded by second-order interactions (temperature x duration of exposure x total residual chlorination). Both 0-day and 7-day-old larval stages showed significant higher-order interactions for all combinations of test parameters, suggesting the presence of synergistic effects of the three main experimental variables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393813
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  • 3
    Electronic Resource
    Electronic Resource
    PACAP-38 is a chemorepellent and an agonist for the lysozyme receptor in Tetrahymena thermophila (2000)
    Springer
    Journal of comparative physiology 186 (2000), S. 39-43 
    Details
    ISSN: 1432-1351
    Keywords: Key words Chemorepellent ; PACAP-38 ; Tetrahymena ; Chemosensory transduction ; Behavioral adaptation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Pituitary adenylate cyclase activating peptide (PACAP-38) is a peptide hormone which functions in many mammalian systems, including the nervous and digestive systems. Using in vivo behavioral studies, we have found that this hormone functions as a chemorepellent in Tetrahymena thermophila with an EC50 of 10 nM. Cells previously adapted to PACAP-38 were found to be adapted to lysozyme, and vice versa. Furthermore, the in vivo behavioral activity of PACAP-38 was blocked by addition of the anti-lysozyme receptor antibody, 5545. Chemorepellent activity of PACAP-38 was also inhibited by the addition of neomycin sulfate (inhibition constant K i=0.080 μmol · l−1), a competitive inhibitor of lysozyme binding to its receptor. PACAP-38 is a more potent and specific agonist for the lysozyme receptor than either intact lysozyme or CB2, a 24-amino acid fragment of lysozyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003590050005
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  • 4
    Electronic Resource
    Electronic Resource
    Incorporation of mouse zona pellucida proteins into the envelope of Xenopus laevis oocytes (1999)
    Springer
    Development genes and evolution 209 (1999), S. 330-339 
    Details
    ISSN: 1432-041X
    Keywords: Key words Zona pellucida ; Vitelline envelope ; Egg coat ; Mouse ; Xenopus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  All vertebrate eggs have extracellular matrices, referred to as the zona pellucida in Mus musculus and the vitelline envelope in Xenopus laevis. The mouse zona, composed of three sulfated glycoproteins (ZP1, ZP2, ZP3), is critical for fertilization and early development, and mice lacking a zona pellucida produce no live offspring. The primary structures of mouse ZP1 (623 amino acids), ZP2 (713 amino acids) and ZP3 (424 amino acids) have been deduced from full-length cDNAs, but posttranslational modifications result in mature zona proteins with molecular masses of 200–180 kDa, 140–120 kDa, and 83 kDa, respectively. The vitelline envelope forms a similar structure around Xenopus eggs and contains three glycoproteins that are structurally related (39–48% amino acid similarity) to the three mouse zona proteins. To investigate whether the structural semblances are sufficient to allow incorporation of the mouse zona proteins into the Xenopus vitelline envelope, capped synthetic mRNAs encoding ZP1, ZP2, and ZP3 proteins were injected into the cytoplasm of stage VI Xenopus oocytes. After 20 h of incubation the oocytes were harvested, and posttranslationally modified zona proteins were detected with monoclonal antibodies specific to mouse ZP1, ZP2, and ZP3. The oocytes were imaged with confocal microscopy to detect individual zona proteins in the extracellular matrix of the oocytes, and this localization was confirmed biochemically. Thus the mouse zona proteins appear to have been sufficiently conserved through 350 million years of evolution to be incorporated into the extracellular envelope surrounding Xenopus eggs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050261
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  • 5
    Electronic Resource
    Electronic Resource
    A model of leg coordination in the stick insect, Carausius morosus (1991)
    Springer
    Biological cybernetics 64 (1991), S. 393-402 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Mechanisms dependent upon leg position coordinate the alternate stepping of adjacent ipsilateral and contralateral legs in the stick insect. In this insect, swing duration and step amplitude are independent of walking speed. A simple geometrical model of the leg controller is used here to test different mechanisms for compatibility with these two invariant features. Leg position is the state variable of a relaxation oscillator and position thresholds determine the transitions between swing and stance. The coordination mechanisms alter these thresholds. The position-dependent mechanisms considered differ either in the form or the speed-dependence of the function relating the shift in the posterior threshold of the receiving leg to the position of the sending leg. The results identify parameter combinations leading to alternate stepping with symmetric or asymmetric phase distributions, to shifts in the posterior extreme position as a function of speed, to double stepping or to in-phase stepping. An optimal position-dependent excitatory mechanism is described. Finally the consequences of adding either inhibitory influences or time-dependent excitatory influences are analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00224706
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  • 6
    Electronic Resource
    Electronic Resource
    A model of leg coordination in the stick insect, Carausius morosus (1991)
    Springer
    Biological cybernetics 64 (1991), S. 403-411 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract An information-processing model of leg control is presented. The model incorporates the four primary mechanisms of interleg coordination in the stick insect (Fig. 1). It is formulated in terms of kinematic parameters of leg movement. The step pattern generator for each leg is represented as a relaxation oscillator with two states — swing and stance. The variable of integration corresponds to leg position; the oscillation corresponds to protraction and retraction of the leg between the end-points of swing and stance. Coordination mechanisms from adjacent legs modulate the movement end-points of the controlled leg, the receiver; these coordinating influences depend upon the state, the position and the retraction velocity of the controlling leg, the sender (Fig. 2). The simulations demonstrate that the four mechanisms produce a stable metachronal coordination and rapidly correct perturbations. When all six legs retract at the same speed, the simulated leg movements show a stable coordination over a wide range of step periods (Fig. 3). However, both the shape of the simulated leg movements (Fig. 3) and the inability to quantitatively simulate ipsilateral lag intervals (Fig. 4) point out the limitations of a model restricted to kinematic parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00224707
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  • 7
    Electronic Resource
    Electronic Resource
    Coding proprioceptive information to control movement to a target: Simulation with a simple neural network (1990)
    Springer
    Biological cybernetics 63 (1990), S. 115-120 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract When the stick insect walks, the middle and rear legs step to positions immediately behind the tarsus of the adjacent rostral leg. Previous reports have described this movement to a target as a relationship between the tarsus positions of the two legs in a Cartesian coordinate system. However, leg proprioceptors measure the position of the target leg in terms of joint angles and leg muscles bring the tarsus of the moving leg to the proper end-point by establishing appropriate angles at the joints. Representation of this task in Cartesian coordinates requires non-linear coordinate transformations; realizing such a transformation in the nervous system appears to require many neurons. The present simulation using the back-propagation algorithm shows that a simple network of only nine units — 3 sensory input units, 3 motor output units, and 3 hidden units — suffices. The simulation also shows that an analytic coordinate transformation can be replaced by a direct association of joint configurations in the moving leg with those in the target leg.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203033
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  • 8
    Electronic Resource
    Electronic Resource
    A modular artificial neural net for controlling a six-legged walking system (1995)
    Springer
    Biological cybernetics 72 (1995), S. 421-430 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A system that controls the leg movement of an animal or a robot walking over irregular ground has to ensure stable support for the body and at the same time propel it forward. To do so, it has to react adaptively to unpredictable features of the environment. As part of our study of the underlying mechanisms, we present here a model for the control of the leg movement of a 6-legged walking system. The model is based on biological data obtained from the stick insect. It represents a combined treatment of realistic kinematics and biologically motivated, adaptive gait generation. The model extends a previous algorithmic model by substituting simple networks of artificial neurons for the algorithms previously used to control leg state and interleg coordination. Each system controlling an individual leg consists of three subnets. A hierarchically superior net contains two sensory and two ‘premotor’ units; it rhythmically suppresses the out-put of one or the other of the two subordinate nets. These are continuously active. They might be called the ‘swing module’ and the ‘stance module’ because they are responsible for controlling the swing (return stroke) and the stance (power stroke) movements, respectively. The swing module consists of three motor units and seven sensory units. It can produce appropriate return stroke movements for a broad range of initial and final positions, can cope with mechanical disturbances of the leg movement, and is able to react to an obstacle which hinders the normal performance of the swing movement. The complete model is able to walk at different speeds over irregular surfaces. The control system rapidly reestablishes a stable gait when the movement of the legs is disturbed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201417
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  • 9
    Electronic Resource
    Electronic Resource
    A modular artificial neural net for controlling a six-legged walking system (1995)
    Springer
    Biological cybernetics 72 (1995), S. 421-430 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract.  A system that controls the leg movement of an animal or a robot walking over irregular ground has to ensure stable support for the body and at the same time propel it forward. To do so, it has to react adaptively to unpredictable features of the environment. As part of our study of the underlying mechanisms, we present here a model for the control of the leg movement of a 6-legged walking system. The model is based on biological data obtained from the stick insect. It represents a combined treatment of realistic kinematics and biologically motivated, adaptive gait generation. The model extends a previous algorithmic model by substituting simple networks of artificial neurons for the algorithms previously used to control leg state and interleg coordination. Each system controlling an individual leg consists of three subnets. A hierarchically superior net contains two sensory and two ‘premotor’ units; it rhythmically suppresses the output of one or the other of the two subordinate nets. These are continuously active. They might be called the ‘swing module’ and the ‘stance module’ because they are responsible for controlling the swing (return stroke) and the stance (power stroke) movements, respectively. The swing module consists of three motor units and seven sensory units. It can produce appropriate return stroke movements for a broad range of initial and final positions, can cope with mechanical disturbances of the leg movement, and is able to react to an obstacle which hinders the normal performance of the swing movement. The complete model is able to walk at different speeds over irregular surfaces. The control system rapidly reestablishes a stable gait when the movement of the legs is disturbed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004220050144
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  • 10
    Electronic Resource
    Electronic Resource
    The contributions of diverse sense organs to the control of leg movement by a walking insect (1984)
    Springer
    Journal of comparative physiology 154 (1984), S. 695-705 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary During locomotion, stick insectsCarausius morosus, place the tarsus of the rear leg near the tarsus of the ipsilateral middle leg, whatever the position of the latter. This adjustment by the hind leg requires that it receive information on the actual position of the middle leg tarsus. It is shown by ablation experiments that such information is contributed by the following proprioceptors of the middle leg: the ventral and dorsal coxal hairplates, the coxal hair rows, the trochanteral hairplate and the femoral chordotonal organ. Additional information comes from other, as yet unidentified, sense organs. Several alternatives are considered to explain how the signals from the diverse sense organs of the subcoxal joint might be combined in computing the target position for the protracting hind leg. The experimental results support the hypothesis that the signals are added nonlinearly and that a signal deviating from the majority pattern is weighted less.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01350223
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