bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intersegmental Coordination of Central Neural Oscillators for Rhythmic Movements of the Walking Legs in Crayfish, Pacifastacus Leniusculus
Authors: Sillar Keith T. , Clarac François , Bush Brian M. H. 
Published: April 2021

ABSTRACT
The neuronal circuits underlying rhythmical movements of the walking legs in crayfish Pacifastacus leniusculus are organized into central oscillators within each thoracic hemiganglion. These segmental networks are coupled in different modes of coordination during activities such as walking and limb waving. This paper examines the nature of the coupling between hemisegmental oscillators in the absence of sensory feedback, and the effect of phasic input from a major limb proprioceptor.
In isolated preparations of the thoracic nerve cord, adjacent ipsilateral hemiganglia can generate a rhythmic motor output pattern in which homologous motor roots discharge approximately synchronously (the ‘in-phase’ rhythm). In contrast, contralateral hemiganglia show no evidence of any such phase-locking in their activity. A single proprioceptor at the base of each limb, the thoracic-coxal muscle receptor organ (TCMRO), can influence the timing and intensity of the rhythmic output of two or more ipsilateral thoracic ganglia. Rhythmical stretch-release of the TCMRO of the fourth ganglion on one side can entrain the motor rhythms of both the third and fourth ipsilateral hemiganglia, in the in-phase pattern of coordination. The TCMRO also elicits intra- and intersegmental reflexes during expression of the in-phase motor rhythm. These reflexes are centrally modulated in a phasedependent manner. Thus mechanical stimulation of the TCMRO co-activates homologous sets of motoneurones in adjacent ipsilateral hemiganglia only during their active (spiking) phase in the motor rhythm.
We discuss the implications of these results for the generation and coordination of walking and other rhythmic behaviour of the thoracic limbs in decapod Crustacea. Our data shed further light on the properties of the motor rhythm generator for walking in crayfish, and suggest that the concept of a central pattern generator cannot be rigorously applied in this system.
Spontaneous and Evoked Eye Movements in Polyphemus Pediculus (Cladocera: Crustacea): A Case of Open-Loop Tracking?
Authors: Young Stephen , Taylor Victoria A. 
Published: April 2021

ABSTRACT
Polyphemus eye movements were recorded in both pitching and yawing planes, both in a static visual environment and with a sinusoidally moving stimulus. Spontaneous eye movements (average amplitude 1·7°) had different properties in the two planes, with trembling movements predominating in the pitching plane. A contour-sharpening function is proposed for these movements. An attempt to analyse the eye movement response system using a Bode diagram shows a very poor fit to the data, leading to the conclusion that a closed-loop control system is an inappropriate model in this case. The evoked eye movements are most convincingly represented by a model in which the time the stimulus takes to traverse a restricted sensitive zone in the central region of the eye controls the duration of a subsequent constant angular velocity saccade. The direction of the response movement follows the direction of the stimulus. A small-object tracking function is proposed for these movements.
Energy-Dependent Facilitation of Transcuticular Water Flux Contributes to Evaporative Cooling in the Sonoran Desert Cicada, Diceroprocta Apache (Homoptera: Cicadidae)
Authors: Toolson Eric C. , Hadley Neil F. 
Published: April 2021

ABSTRACT
Terrestrial arthropods exhibit an array of impressive adaptations for conserving water, including highly waterproof cuticles, the ability to reduce excretory losses by resorption of water from the faeces and, in some species, the ability to absorb water vapour from subsaturated atmospheres (Edney, 1977). The possibility of an additional adaptation has been inferred from the observation that gravimetric water loss rates of many terrestrial arthropods increase significantly following death, even when body openings, e.g. spiracles, are sealed. This increase, which may be as large as five-fold (Toolson & Hadley, 1979), has been interpreted as evidence for an energy-dependent process that actively retards loss of water through the cuticle (Winston & Beament, 1969). The mechanistic basis for the phenomenon, however, is controversial (Berridge, 1970; Riddle, 1981; Machin, Lampert & O’Donnell, 1985).
Contributions of anaerobic metabolism to pH regulation in animal tissues: theory
Authors: Pörtner Hans-Otto 
Published: April 2021

ABSTRACT
Proton balance is analysed in relation to the anaerobic and aerobic metabolism of carbohydrates, carbonic acids, amino acids and fat by considering oxidation, carboxylation, decarboxylation and phosphorylation reactions, as well as the influence of ammonium, on the acid—base status of animal tissues. The functional role of the adenylates, phosphagens and inorganic phosphate in acid-base balance is investigated with respect to differences in the physicochemical properties of organic and inorganic phosphates.
General principles are established for different anaerobic metabolic pathways in species from several phyla. It is concluded that proton release from the substrate, which is always involved in substrate-level phosphorylations, is essential for the mechanism of ATP formation. Anaerobic metabolism, which is characterized by incomplete oxidation of carbon chains and an accumulation of acidic groups, supports pH regulation in facultative anaerobes by minimizing the amount of accumulated protons. High levels of phosphagens mean high proton absorption during hydrolysis and an increase in the intracellular buffer value. Decarboxylation reactions in catabolic pathways are equivalent to proton consumption. The degradation of carbonic acids during anaerobiosis, therefore, contributes to pH regulation. Release of ammonia or ammonium ions in catabolism is also linked to the buffering of protons originating from the formation of carboxyl groups and net cleavage of ATP. Net disposal of amino groups or ammonium ions by transamination, reductive amination or ion exchange does not change this general picture. The proton, bicarbonate and CO2 turnover in metabolic pathways is discussed with respect to the interrelationships between pH and metabolic regulation.
Substrate Interactions Affecting Motor Growth Cone Guidance During Development and Regeneration
Authors: Westerfield Monte 
Published: April 2021

ABSTRACT
Most serious injuries of spinal nerves or roots in man and other higher vertebrates lead to permanent loss of control of skeletal muscles. In some cases this may be due to a failure of motor axons to regenerate, although even when functional neuromuscular connections are re-established, coordinated use of body and limb muscles may be absent. In both mammals and lower vertebrates, damaged motor axons usually regrow and reform functional connections with muscles, although these connections are often inappropriate. The selectivity of reinnervation is improved by maintaining alignment of the severed ends of the nerve. Thus, factors operating near the lesion site may direct regenerating motor axons into fascicles in the distal nerve stump that lead to inappropriate muscles. The identity of some of these factors is suggested by recent studies of developing systems which have shown that motor axons are directed in their growth, (a) The filopodia of their growth cones sample a limited region of the periphery. If motor growth cones extend too far from their normal pathways they establish connections with inappropriate muscles, (b) Motor growth cones normally extend into regions of embryos rich in the extracellular matrix molecule laminin, and avoid regions containing fibronectin. Moreover, motor growth cones extend on laminin but not on fibronectin substrates in vitro. In peripheral nerves, these two molecules are differentially distributed; laminin is expressed by Schwann cells in the endoneurium whereas fibronectin is expressed by fibroblasts primarily in the perineurium. These studies suggest that regenerating motor growth cones may be directed to appropriate muscles if their original fascicles within the distal nerve stump are within filopodial reach but may not be able to escape the fibronectin-rich perineurial sheath once directed into an inappropriate fascicle.
Nerve Growth Factor in Neuronal Development and Maintenance
Authors: Misko Thomas P. , Radeke Monte J. , Shooter Eric M. 
Published: April 2021

ABSTRACT
One of the major roles of nerve growth factor (NGF) is to mediate the selective survival of a proportion of the developing sympathetic and sensory neurones as they innervate their particular target tissues. The underlying basis of this phenomenon is the synthesis of limited amounts of NGF in the target, its secretion around, and uptake by, the nerve terminal and its retrograde transport along axons to the neuronal cell bodies. The cascades of reactions which lead to neuronal survival and maintenance are initiated by signal transduction somewhere in this pathway. Retrograde transport and the initial signal transduction step begin when NGF binds to NGF receptors on the nerve terminal. Receptor-mediated internalization and the survival and maintenance function of NGF are mediated by the higher affinity receptors. These receptors have relative molecular masses of approx. 145 000 and are trypsin-resistant when occupied. In contrast, the larger population of lower affinity receptors have relative molecular masses of 85 000 and are rapidly degraded by trypsin. Clustering of the lower affinity receptors by a variety of agents gives them many of the characteristics of the higher affinity receptors, suggesting receptor interconversion may play a role in NGF actions. The structure of the lower affinity NGF receptor, determined by gene transfer and cloning, shows it to be a unique, heavily glycosylated protein. The extracellular domain is rich in cvsteine-containing repeat units while the intracellular domain lacks the consensus sequence for an endogenous kinase activity. It is likely that the higher affinity receptor contains this protein as the NGF binding subunit together with a second protein which determines both the nature of the signal transduction mechanism and the process of internalization.
Neurite Outgrowth and Synapse Formation by Identified Leech Neurones in Culture
Authors: Chiquet Matthias , Nicholls John G. 
Published: April 2021

ABSTRACT
After injury, neurones in the central nervous system (CNS) of the leech regenerate with a high degree of specificity. The aim of our experiments has been to study the sequential steps involved in neurite growth and synapse formation using isolated identified neurones in culture. An important requirement for sprouting of leech neurones is the substrate. Neurites grow only slowly and sparsely on polylysine or vertebrate laminin. The extracellular matrix of leech ganglion capsules contains a protease-sensitive factor which can be extracted with urea. With this material as substrate, growth proceeds rapidly in defined medium. Another neurite-promoting substrate is provided by the plant lectin concanavalin A (Con A). The activity of Con A, but not of the capsule matrix factor, is blocked by the Con A-specific hapten methyl cr-D-mannoside. The morphology and branching pattern of the neurites in culture depend on the specific substrate and on the type of neurone. During stimulation, less Ca2+ uptake occurs into growth cones than in cell bodies. The mechanism of neurite growth seems not to depend on activity-mediated Ca2+ influx or on interactions between neuronal cell surfaces. However, even without profuse outgrowth, electrical and chemical synapses develop between neighbouring neurones. The type of synapse depends predictably on the types of neurones within the cell pair. Since the development of a synapse can be followed with time in culture, the sequential events can each be studied separately for this multi-step process.
Tinkering With Successful Synapse Regeneration in the Leech: Adding Insult to Injury
Authors: Muller K. J. , McGLADE-McCULLOH E. , Mason A. 
Published: April 2021

ABSTRACT
In the leech, synapse regeneration in adults and synapse formation during embryonic development can be studied in single, identifiable cells that make precise connections with their targets. Certain cellular components, such as synaptic targets and glia, were selectively destroyed to study how the regenerating axons locate their targets, what triggers axons to start growing and what stops them. The results showed that glia and targets play only a limited role in synapse regeneration and in axon degeneration. For example, contact with the synaptic target may inhibit sprouting and availability of targets may promote it. Comparative studies on axon growth and synapse formation by interneurones in embryos showed that regeneration does not simply recapitulate embryonic development. There are clearly separate constraints on the two processes. Axon survival is a different problem. Although isolated axon segments can survive for up to a year in the leech, temperature is a major factor in survival. Axon segments in a tropical leech that regenerates synapses well at 31 °C degenerated within 2–3 weeks at this elevated temperature, even when regeneration was prevented. In similar leeches at room temperature (22°C), segments survived for months. Overall, results in the leech support the idea that degeneration as well as regeneration share fundamental mechanisms with other invertebrates and the vertebrates, including mammals. Perhaps long-lived axon segments and other features of the leech that speed or encourage functional regeneration can now be made to operate in repair of the mammalian nervous system.
Glial Cells in the Rat Optic Nerve and Some Thoughts on Remyelination in the Mammalian Cns
Authors: Raff Martin C. , Ffrench-Constant Charles , Miller Robert H. 
Published: April 2021

ABSTRACT
Studies on the rat optic nerve in the past 5 years have produced two surprises. First, they demonstrated that there are two biochemically, developmentally and functionally distinct types of astrocytes in the optic nerve, and probably in white matter tracts throughout the CNS: one seems to be responsible for inducing endothelial cells to form the blood–brain barrier while the other seems to service nodes of Ranvier. Second, they showed that oligodendrocytes and type-2 astrocytes develop from a common bipotential (O-2A) progenitor cell that seems to migrate into the developing optic nerve, and may well migrate all over the CNS to wherever myelination is required; this implies that the neuroepithelial cells of the optic stalk are restricted to forming type-1 astrocytes.
Some of the findings in the optic nerve may be relevant to the problem of CNS regeneration after injury. These include the following. (1) Reactive gliosis in white matter tracts seems to be mainly a function of type-1 astrocytes. (2) Proliferating O-2A progenitor cells are present in the adult CNS, raising the possibility that they may be able to produce new oligodendrocytes and type-2 astrocytes following injury and thereby aid regeneration. (3) Type-1 astrocytes seem to be able to respond to environmental signals and form localized barriers that block the migration of O-2A progenitor cells; it is conceivable that the same barriers block the migration of regenerating axonal growth cones.
Mechanisms of Glial Regeneration in an Insect Central Nervous System
Authors: Smith P. J. S. , Howes E. A. , Treherne J. E. 
Published: April 2021

ABSTRACT
As in other repairing systems, glial regeneration in insect central nervous connectives, following selective chemical lesioning, involves both exogenous and endogenous elements. Our current evidence, including that obtained with monoclonal antibodies, indicates that the reactive, granule-containing cells are derived from a sub-population of circulating haemocytes which, within 24 h, invade, and are restricted to, the lesion zone. The granule-containing cells are involved in the initial repair of the perineurial region. They also contribute to the first stage in the restoration of the blood-brain barrier and are responsible for recruiting reactive endogenous glia, apparently from the vicinity of the anterior abdominal ganglion. The granule-containing cells transform into or are replaced by functional glia between 3 and 5 days after selective glial disruption, coincident with the appearance in the lesion zone of dividing reactive cells.
Motor Activity During Searching and Walking Movements of Cockroach Legs
Authors: Delcomyn Fred 
Published: April 2021

ABSTRACT
Rhythmic motor activity may be recorded in the legs of cockroaches during the execution of several different types of behaviour that involve leg movements. It was examined in detail during searching and walking. During walking, motor activity always consisted of a series of bursts separated by silent periods. During searching, it was usually continual, but modulated in frequency. Sometimes, the motor pattern recorded from a searching leg was burst-like rather than modulated. In these cases, it could nevertheless be reliably distinguished from the motor pattern recorded during walking by a simple analysis of the burst pattern. An analysis of the motor pattern recorded during righting indicated that this pattern was more like that for walking than that for searching. Therefore, searching is not simply walking that lacks certain periodic sensory input due to leg contact with the ground. It is concluded that walking and searching can be reliably distinguished from one another on the basis of an analysis of a record of motor activity in a single leg muscle only. An ability to distinguish between similar types of behaviour on the basis of the motor pattern may prove useful in a variety of experiments.
Sensory Feedback During Active Movements of Stick Insects
Authors: Weiland G. , Koch U. T. 
Published: April 2021

ABSTRACT
In the stick insect Carausius morosus, the role of the chordotonal organ was investigated using a new experimental arrangement which artificially closes the femur-tibia control system. The chordotonal organ was stimulated during voluntary movements by applying trapezoidal ramp stimuli in the closed-loop configuration.
The results demonstrate that the feedback loop is used to control the end points of joint movement. In addition, it was found that the control system counteracts experimentally applied velocity changes imposed during the middle part of the movements. Acceleration-sensitive units are shown to contribute to the reaction.
The results show that during active voluntary movements reflexes measured in the inactive animal are neither simply incorporated in a servo-system nor suppressed. Instead their characteristics are altered so that the voluntary movements are executed as intended by the animal. Thus reflexes cannot be considered as a fixed behavioural unit; rather their changing role must be analysed in the context of the behaviour studied.
EXCITATORY ACTIONS OF Antho-RFamide, AN ANTHOZOAN NEUROPEPTIDE, ON MUSCLES AND CONDUCTING SYSTEMS IN THE SEA ANEMONE CALLIACTIS PARASITICA
Authors: McFARLANE I. D. , Graff D. , Grimmelikhuijzen C. J. P. 
Published: April 2021

ABSTRACT
In the sea anemone Calliactis parasitica endodermal application of the anthozoan neuropeptide Antho-RFamide (&lt;Glu-Gly-Arg-Phe-amide), at a concentration of 10−6 or 10−7moll−1, caused a long-lasting increase in tone, contraction frequency and contraction amplitude in several slow muscle groups but had no effect on contractions in fast muscles. The effects were investigated further in isolated muscle preparations. Ectodermal application to whole animals had no effect on muscle contractions. Both ectodermal and endodermal application, at 10−7moll−1, raised electrical activity in an ectodermal conduction system, the SSI, but had no effect on an endodermal conduction system, the SS2. Electrical activity in the SS2 was increased by application at 10−6moll−1 to the endoderm but not to the ectoderm. The peptide had no effect on the through-conducting nerve net. It is concluded that contractions evoked by Antho-RFamide may be partly due to neuronal activity, but probably also involve direct excitation of the muscles. The diverse excitatory actions of Antho-RFamide suggest that it may be a neurotransmitter or neuromodulator in sea anemones.
Thermal Dependence of Passive Electrical Properties of Lizard Muscle Fibres
Authors: Adams Brett A. 
Published: April 2021

ABSTRACT
The thermal dependence of passive electrical properties was determined for twitch fibres from the white region of the iliofibularis (IF) muscle of Anolis cristatellus (15–35°C) and Sceloporus accidentalis (15–40°C), and for twitch fibres from the white (15–45°C) and red (15–40°C) regions of the IF of Dipsosaurus dorsalis. These species differ in thermal ecology, with Anolis being the least thermophilic and Dipsosaurus the most thermophilic. Iliofibularis fibres from the three species reacted similarly to changing temperature. As temperature was increased, input resistance (Rm) decreased (average R10 = 0·7), length constant (L) decreased (average R10 = 0·9), time constant (τ) decreased (average R10 = 0·8), sarcoplasmic resistivity (Rs) decreased (average R10 = 0·8) and apparent membrane resistance (Rm) decreased (average R10 = 0·7). In contrast, apparent membrane capacitance (Cm) increased with increasing temperature (average R10= 1·3). Rin, L, τand apparent Rm were lowest in fibres from Anolis (the least thermophilic species) and highest in fibres from Dipsosaurus (the most thermophilic species). Anolis had the largest and Dipsosaurus the smallest diameter fibres (126 and 57 μm, respectively). Apparent Cm was highest in fibres from Sceloporus, which had fibres of intermediate diameter (101μm). Rs did not differ significantly among species. The effect of temperature on the passive electrical properties of these lizard fibres was similar to that reported for muscle fibres from other ectothermic animals (crustaceans, insects, fish and amphibians) but qualitatively different from that reported for some mammalian (cat tenuissimus, goat intercostal) fibres. The changes that occur in the passive electrical properties render the fibres less excitable as temperature increases.
Kinetics of Extracellular Solute Movement in the Isolated Midgut of Tobacco Hornworm (Manduca Sexta)
Authors: Koch Alan , Moffett David F. 
Published: April 2021

ABSTRACT
Measurements were made of the uptake of 14C-labelled sucrose in the short-circuited isolated midgut of fifth instar larvae of the tobacco hornworm. The longterm volume of distribution after bilateral exposure indicates that the extracellular space is about 0 ·26 ml g−1 wet tissue, much less than has been previously suggested. The results of unilateral exposure yield a value of about 0 04 ml g−1 for luminal goblet cell cavities and 0·22 ml g−1 for interstitial space. The kinetics of uptake suggest that the interstitial space is best modelled as a distributed volume rather than as a single compartment. This mathematical result fits the physical picture of an interstitial fluid in long, narrow channels which communicate freely with the haemolymph but are nearly impermeable to sucrose at the luminal end; that is, they are sealed by septate junctions. The electrical conductance of the epithelium is high, but the transepithelial permeability to sucrose is very much lower than to K+. Thus, the tissue is a physically tight epithelium.