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  • 1
    Electronic Resource
    Electronic Resource
    Neural control of circadian rhythmicity in the crayfish (1975)
    Springer
    Journal of comparative physiology 97 (1975), S. 59-80 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Gross locomotor activity, as well as the movements of single walking legs, were monitored in intact and surgically altered crayfish (Procambarus clarkii). Section of the circumesophageal connectives (CEC) abolished the circadian activity rhythm in both the first and fourth pair of walking legs (Figs. 1–3), while section of the nerve cord between the third and fourth thoracic ganglia abolished rhythmicity in only the fourth pair (Fig. 4). Bilateral ablation of the eyestalks led to a several fold increase in total daily activity and caused the animal to be continually active; however, quantitative measurements of the locomotor activity revealed that a circadian rhythm in the level of activity persists for 6–12 days following eyestalk removal (Figs. 7, 8, 13, 14). These results suggest that the circadian oscillation for the locomotor rhythm originates in the supraesophageal ganglion and is coupled to thoracic locomotor centers via axons in the CEC. The activity rhythm of eyestalkless animals could also be entrained to a light cycle even after ablation of the caudal photoreceptor; however, certain features of entrainment were altered (Figs. 9–12). Thus, although the eyestalks are not required for rhythmicity, eyestalk structures apparently do participate in entrainment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00635649
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  • 2
    Electronic Resource
    Electronic Resource
    Neural control of circadian rhythmicity in the crayfish (1975)
    Springer
    Journal of comparative physiology 97 (1975), S. 81-96 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The circadian rhythm of the ERG response to a standard light pulse presented once per hour was monitored in both intact and surgically altered crayfish (Procambarus clarkii). Section of the circumesophageal connectives did not interfere with the ERG amplitude rhythm, or its entrainment (Fig. 2); however, rhythmicity was abolished if the optic tract was severed (Figs. 3, 4). These results suggest that the circadian oscillation originates in the supraesophageal ganglion, and is coupled to the eyevia axons in the optic tract. These conclusions were supported by the results of experiments in which the brain was surgically manipulated. Bisection of the brain at the midline eliminated the ERG amplitude rhythm in both eyes, while splitting the brain slightly off-center left the rhythm in the eye associated with the larger half of the brain unaffected (Figs. 8, 9). Histological examination of the operated brains suggested that the olfactory-globular tract may be the pathway by which the circadian oscillation reaches the eyestalk. Finally, the results of bilateral recordings of the ERG amplitude from both intact and operated animals suggested that the rhythms in the two eyes are coupled by a central neural mechanism (Figs. 1, 7, 8).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00635650
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  • 3
    Electronic Resource
    Electronic Resource
    Interactions between the tonic and cyclic postural motor programs in the crayfish abdomen (1988)
    Springer
    Journal of comparative physiology 163 (1988), S. 187-199 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. In the crayfish (Procambarus clarkii) abdomen, the superficial flexor and extensor muscles and the motoneurons that innervate them are employed during two completely different modes of behavior: (1) tonic postural adjustments and (2) cyclic movements associated with backwards terrestrial walking. We have tested the possibility that these two behavioral subsystems share at least some of the same tonic premotor interneurons. 2. Of the 108 tonic flexion- and extension-producing interneurons monitored during cyclic pattern generation, only 25 were recruited while 36 were inhibited. None of the recruited interneurons made a measurable contribution to the cyclic motor output. Similarly, none of the 20 inhibitory interneurons of the tonic subsystem recorded in this study was found to play a role in shaping the cyclic motor pattern. 3. Simultaneous activation of single tonic postural interneurons with the cyclic motor pattern revealed that the two behavioral subsystems interact in complex ways. Some tonic interneurons produced motor outputs that overrode the cyclic motor outputs while the motor outputs of other tonic interneurons were completely overwhelmed by the cyclic motor program. Still other tonic interneurons generated motor outputs that predominated over cyclic patterned outputs in some ganglia but were masked by the cyclic motor pattern in other ganglia. 4. Although weak interactions between the two subsystems occur at the premotor level, they have little effect on the normal generation of the cyclic pattern. Stronger interactions apparently occur at the level of the motoneurons and these interactions presumably may form the basis of switching from one behavior to the other. We conclude, therefore, that each behavioral subsystem relies upon its own unique set of premotor interneurons. Finally, those interneurons contributing to the cyclic motor pattern have not yet been identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00612428
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  • 4
    Electronic Resource
    Electronic Resource
    Synaptic interactions between neurons involved in the production of abdominal posture in crayfish (1985)
    Springer
    Journal of comparative physiology 156 (1985), S. 861-873 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Pairs of neurons that produce or influence motor outputs in the abdominal positioning system of the crayfish (Procambarus clarkii) were impaled in isolated nerve cords with Lucifer Yellow-filled microelectrodes to determine their morphologies and the nature and extent of the synaptic interactions between them. Although the motor programs for positional adjustments can be produced by directly stimulating single interneurons, we found extensive interactions between these neurons, often involving the recruitment of one interneuron by another. The data indicate that the positioning interneurons do not operate as labelled lines, each independently producing a discrete position. Pairs of interneurons, each producing similar motor outputs when activated, were often found to be connected by unidirectional excitatory synapses. In contrast, central inhibition was commonly found between pairs of interneurons that produced antagonistic motor effects. Finally, the unidirectional interactions between positioning interneurons revealed a hierarchy of at least two tiers in this system. Based on these observations, we suggest that abdominal positioning in crustaceans is produced by constellations of interacting interneurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00610837
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  • 5
    Electronic Resource
    Electronic Resource
    Neural control of a cyclic postural behavior in the crayfish,Procambarus clarkii: the pattern-initiating interneurons (1987)
    Springer
    Journal of comparative physiology 160 (1987), S. 169-179 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. As part of its repertoire of defensive behaviors, the crayfish,Procambarus clarkii, may respond to mildly threatening tactile or visual stimuli from the front of its body by walking backwards. During this behavior, the abdomen undergoes complex cyclical movements involving flexion and extension of the postural musculature which cause the tail to alternately contact and withdraw from the substrate. Intracellular neuropil recordings and dye injections were used to search for the interneurons responsible for initiating this postural motor pattern in the crayfish abdomen. Several diverse morphological types of interganglionic pattern-initiating (PI) interneurons were found. Each interneuron, when driven intracellularly, was capable of eliciting the same motor program, in its entirety, throughout the abdominal nerve cord. 2. During pattern generation, PI interneurons exhibited a burst of spikes preceding the motor output. Silencing single PI interneurons with hyperpolarizing current during pattern generation failed to affect the motor program, indicating a redundancy of pattern-initiating function. The observations of extensive dye-coupling with other parallel axons, consistent dye-coupling with other identified cells in the pattern-initiating system, and the presence of multiple spike amplitudes in the bursts suggested electrotonic coupling among the PI interneurons. 3. An additional group of interganglionic interneurons, the partial pattern-initiating (PPI) interneurons, were found to comprise a significant subset of the pattern-initiating system. As with the PI cells, the PPI interneurons exhibited a complex burst of spikes just preceding the patterned motor program. However, the PPI interneurons were only capable of eliciting an incomplete, though recognizable, postural motor pattern. Silencing any PPI interneuron during pattern generation caused a deficit in the motor pattern, indicating either an absence or lesser degree of functional redundancy within the PPI interneuron population compared to that occurring within the PI interneuron group. 4. We conclude that a large number of PI interneurons are presynaptic to a relatively small group of PPI interneurons which, in turn, conduct pattern-initiating signals to the ganglionic oscillators. Our results indicate that pattern-initiation is accomplished through a command system involving multiple command elements organized in a coordinated interganglionic network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00609724
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  • 6
    Electronic Resource
    Electronic Resource
    Abdominal positioning interneurons in crayfish: participation in behavioral acts (1989)
    Springer
    Journal of comparative physiology 165 (1989), S. 461-470 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Premotor interneurons involved in the abdominal positioning behaviors of the crayfish,Procambarus clarkii, were studied intracellularly, along with motoneuron activity, in semi-intact preparations during episodes of fictive behavior. Each impaled cell was tested by injecting depolarizing current and examining the motor output. If a response was evoked then the cell was classified as a flexion-producing interneuron (FPI), extension-producing interneuron (EPI) or mixed output interneuron (MOI). A platform drop/rise procedure was then used to elicit abdominal extension-like and flexion-like responses. Interneurons that were active during positioning behavior were silenced by hyperpolarization to determine their contribution in generating the underlying motor program. The data were used to assess the degree of participation of these interneurons in abdominal positioning behavior. Fewer than half of the FPIs, EPIs and MOIs became active during the behavioral episodes. Strength of response to depolarizing current was not correlated with the probability that a cell would fire during behavior. Hyperpolarization tests showed that typical FPIs, EPIs and MOIs were only responsible for a small part of the overall motor output. Also, interneurons, regardless of their FPI or EPI classification, were often observed to fire during both flexion-like and extension-like behaviors. Responses of FPIs, EPIs and MOIs to repeated platform movements suggest that these cells may fire according to a probability distribution depending on: (1) strength of the stimulus; (2) location of the stimulus; (3) location of the interneuron. Most identified cells could not readily be assigned to a specific behavior except for the ‘T’ cell type, which seems intimately involved in most flexion behaviors. The results of this study support the hypothesis that there are few if any ‘command neurons’, as defined by Kupfermann and Weiss (1978), in the crayfish abdominal positioning system. Abdominal positioning behavior, therefore, is probably under the control of a large network of cells each contributing a small part to the overall motor output.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00611235
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  • 7
    Electronic Resource
    Electronic Resource
    Photosensitivity in the sixth abdominal ganglion of decapod crustaceans: A comparative study (1976)
    Springer
    Journal of comparative physiology 106 (1976), S. 69-75 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The existence of photosensitive neurons in the 6th abdominal ganglion of the crayfish has been known for over forty years. These structures have been considered unique to freshwater crayfish, largely due to their apparent absence in a closely related species, the lobsterHomarus. We have shown that abdominal photoreceptor neurons are widespread in occurrence among other marine decapod crustaceans. In addition to the electrical responses which result from illumination of the 6th ganglion, similarities in the distribution of afferent synaptic input and of the axon location in the nerve cord suggest that these cells are homologous central interneurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00606572
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  • 8
    Electronic Resource
    Electronic Resource
    Neural pathways of reflex-evoked behaviors and command systems in the abdomen of the crayfish (1981)
    Springer
    Journal of comparative physiology 143 (1981), S. 27-42 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The lifting of a crayfish (Procambarus)clarkii) from the substrate results in reflexive abdominal extension often accompanied by metachronous swimmeret beating. Cinematographic analyses show that the maintained, maximally extended abdominal position is stereotypic from trial to trial for each animal. 2. Complete transections at various levels of the abdominal nerve cord abolish the reflex-evoked extension and swimmeret behavior in all ganglia caudal to the lesion (Figs. 1, 2). Therefore, some essential portion of the pathways mediating these reflexive behaviors originates rostral to the abdomen and projects caudally. 3. Transection of any one of the paired abdominal connectives (i.e., hemiconnectives), or transection of up to 4 unilateral hemiconnectives has no effect on the reflex-evoked behaviors. 4. Transection of two hemiconnectives, done on opposite sides in adjacent abdominal segments, eliminates reflexive behavior in all ganglia caudal to the more posterior cut (Fig. 3). Hence, there is no evidence that the extension drive in one hemiconnective can cross within abdominal ganglia and travel in the opposite hemiconnective. 5. Similar transections of hemiconnectives in adjacent segments reveal that the swimmeret drive can cross ganglion 2 and course in the opposite hemiconnective (Fig. 3). No such ability was evident in ganglion 4 (Fig. 3). 6. Chronic recordings from postural motoneurons were also made during reflex-evoked behaviors (Figs. 4, 5). Compared to the intact animal, ligation of either hemiconnective in the segment anterior to the recorded ganglionic root reduces by approximately 50% the activity level of the extension motor program, even though the degree of movement remains the same (Figs. 4, 5). 7. A map of abdominal extension-evoking interneurons was made in cross-section of a thoraco-abdominal hemiconnective. Over 83% of these interneurons were found to occupy six loci (Fig. 6). 8. At least three of the locus-specific units have uninterrupted axonal projections through the abdominal cord (Figs. 7, 8). 9. No excitatory interactions between nonhomologous interneurons on one side of the nervous system or between bilateral homologous units were evident (Figs. 8, 9). 10. These characteristics of extension-evoking interneurons correspond closely to those of reflex-evoked extension drives, suggesting that their activity underlies reflexive abdominal extension behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00606066
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  • 9
    Electronic Resource
    Electronic Resource
    Synaptic interactions among neurons that coordinate swimmeret and abdominal movements in the crayfish (1992)
    Springer
    Journal of comparative physiology 170 (1992), S. 739-747 
    Details
    ISSN: 1432-1351
    Keywords: Crayfish ; Abdomen ; Swimmerets ; Inter-neuron ; Coordination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. Many interneurons in the crayfish (Procambarus clarkii) abdominal nervous system influence two behaviors, abdominal positioning and swimmeret movements. Such neurons are referred to as dual output cells. Other neurons which influence either one behavior or the other are single output cells. 2. Extensive synaptic interactions were observed between both dual and single output neurons involved in the control of abdominal positioning and swimmeret movements. Over 60% of all neuron pairs examined displayed interactions. Pairs of agonist neurons displayed excitatory interactions, while pairs of antagonists had inhibitory interactions. This pattern of interaction was observed in about 75% of interactive neuron pairs whether abdominal positioning or swimmeret outputs were considered. 3. Evidence for both serial and parallel connectivity, as well as, reciprocal or looping connections was observed. Looping connections can be found both between the abdominal positioning and swimmeret systems and within each system. 4. Most (28/34) single output neurons were not presynaptic to dual output neurons. No single output neurons were found to excite dual output neurons to spiking, although inhibitory interactions and weak excitations were observed. 5. Abdominal positioning inhibitors displayed properties consistent with a role in mediating some of the coordination between the swimmeret and abdominal positioning systems. 6. None of the dual output neurons examined influenced the swimmeret motoneurons directly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198985
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  • 10
    Electronic Resource
    Electronic Resource
    Phase-sensitivity of Gymnotus carapo to low-amplitude electrical stimuli (1970)
    Springer
    Journal of comparative physiology 70 (1970), S. 322-334 
    Details
    ISSN: 1432-1351
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Undisturbed specimens of Gymnotus carapo discharge their electric organs at a rate of approximately 50 Hz, with a standard deviation of 3 Hz; stimuli of several sensory modalities (touch, vibration, light, electric fields) are capable of eliciting transient increases in discharge frequency rising to a maximum near 30 Hz above resting frequency and returning exponentially over several seconds. Such frequency transients may be evoked by sudden increases or decreases in the electrical resistance of the environment caused by shunting recording electrodes on either end of the fish. Threshold responses are seen to resistance changes of 10 to 20 ohms, which create changes of approximately 50 μV/cm in the amplitude of the electric discharge measured along the length of the fish. Gymnotus proves remarkably sensitive to electrical stimuli occuring in phase with the discharge train of its own electric organs, with a threshold near 50 μV/cm; out-of-phase stimuli ten times this amplitude fail to elicit frequency transients. Responses are also seen to small changes in latency between stimulus and discharge trains within the time span of an individual organ discharge. Phase-sensitivity is apparently a consequence of the sigmoid stimulus/response curve common to most receptors; a large “activating” pulse, normally generated by the electric organs, raises electroreceptor activity into the receptor's dynamic range, after which a relatively small stimulus is capable of causing a significant change in output. Such a mechanism probably serves as a peripheral filter, eliminating low-level interference from other electric fish. The frequency transients themselves are interpreted as arousal responses, momentarily increasing the fish's sensory resolution in the face of potential hazards or prey.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297752
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