bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of contact-rehydration in terrestrial gastropods: absorption of 14C-inulin through the epithelium of the foot
Authors: Prior D. J. , Uglem G. L. 
Published: April 2021

ABSTRACT
Contact-rehydration in terrestrial slugs involves a specific drinking behaviour during which water is rapidly absorbed through the integument of the foot. When dehydrated slugs were placed on wet filter paper containing 14C-inulin, they displayed the characteristic drinking posture and absorbed both water and 14C-inulin. Samples of haemolymph from dehydrated slugs after 12 min of contact-rehydration contained about 6µg of 14C-inulin 100 mg−1 of haemolymph (0·24 mmol l−14C-inulin in the substrate). The haemolymph of hydrated slugs however contained no detectable radioactivity after 12 min on the filter paper. Electron microscopy revealed that the intercellular spaces between the epithelial cells of the foot were reduced in dehydrated slugs, but were rapidly enlarged during contact-rehydration. It is concluded that contact-rehydration in terrestrial slugs is mediated by bulk flow of water through an epithelial paracellular pathway in the integument of the foot.
Momentum and Energy in the Wake of a Pigeon (Columba Livia) in Slow Flight
Authors: Spedding G. R. , Rayner J. M. V. , Pennycuick C. J. 
Published: April 2021

ABSTRACT
A technique is described whereby the vortex wake of birds in slow forward flight may be investigated with a view towards testing some of the assumptions and predictions of existing theoretical models of bird flight. Multiflash stereophotogrammetry was used to analyse the wake as a pigeon passed through a cloud of neutrally-buoyant helium bubbles.
All photographs obtained support the hypothesis that the wake is composed of a chain of discrete, small-cored vortex rings. This being the case, velocity profiles taken from sections through the wake allow us to estimate the momentum in the wake as represented by vortex rings.
The momentum in the wake appears to be approximately half that required for weight support in unaccelerated, level flight. The possible causes and consequences of this paradoxical result are discussed.
The Search for Principles of Neuronal Organization
Authors: Burrows M. 
Published: April 2021

ABSTRACT
To say that the brain is complex is to state the obvious, and yet from that statement inevitably comes the realization that there will be no single explanation of how it works. Our understanding is likely to accumulate by the identification of general principles of organization at many levels. Recognizing the necessity for an interdisciplinary approach, this conference dealt with developmental, anatomical, physiological and biochemical levels of explanation. The deliberately intimate size of the conference prevented the inclusion of many exciting molecular neurobiological studies.
Relationships Between Neuronal Structure and Function
Authors: Miller John P. , Jacobs Gwen A. 
Published: April 2021

ABSTRACT
The geometry and electrical properties of a neurone determine how synaptic inputs and endogenously generated currents are integrated and transformed into the signals it transmits to other cells. The dependence of neuronal integration upon dendritic geometry has been studied extensively over the last three decades, both by experimentalists and by theoreticians. We review some of the general principles that have emerged from this work, and summarize recent studies that serve to illustrate these principles. The discussion is organized around the analysis of neuronal structure at three different levels. At the ‘macroscopic’ level, we show how the dendritic branching structure of an identified interneurone in the cricket cereal afferent system determines the directional sensitivity within its receptive field. At the ‘microscopic’ level, we illustrate the dependence of synaptic efficacy upon dendritic length, and demonstrate a very surprising result: that the extension (or ‘growth’) of a dendrite out beyond the point of a synaptic contact can increase the efficacy of that synapse. At the ‘ultrastructural’ level, we show how the structural and electrical properties of dendritic spines might have profound effects upon synaptic integration.
Roles for Electrical Coupling in Neural Circuits as Revealed by Selective Neuronal Deletions
Authors: Marder Eve 
Published: April 2021

ABSTRACT
Understanding fully the operation of a neural circuit requires both a description of the individual neurones within the circuit as well as the characterization of their synaptic interactions. These aims are often particularly difficult to achieve in neural circuits containing electrically-coupled neurones. In recent years two new methods (photoinactivation after Lucifer Yellow injection and intracellular injection of pronase) have been employed to delete selectively single neurones or small groups of neurones from neural circuits. These techniques have been successfully used in the analysis of circuits containing electrically-coupled neurones. In several systems new roles for electrical synapses in the integrative function of neural circuits have been proposed.
In the nervous systems of both the leech and lobster it is now thought that synaptic interactions previously thought to be direct are mediated through an interposed, electrically-coupled neurone. In the pyloric system of the stomatogastric ganglion of the lobster, Panulirus interruptus, the Lucifer Yellow photoinactivation technique has permitted a separate analysis of the properties of several electrically-coupled neurones previously thought quite similar. We now know that the Anterior Burster (AB) interneurone and the Pyloric Dilator (PD) motor neurones, which together act as the pacemaker ensemble for the pyloric network, differ in many regards including (a) their intrinsic ability to generate bursting pacemaker potentials, (b) their neurotransmitters, (c) their sensitivity to some neurotransmitters and hormones, (d) the neural inputs they receive and (e) their pattern of synaptic connectivity.
These results will be discussed in the context of the role of electrical coupling in neuronal integration.
Local Interneurones and Local Interactions in Arthropods
Authors: Siegler M. V. S. 
Published: April 2021

ABSTRACT
As their name implies, local interneurones arborize within anatomically restricted regions of a nervous system, and the connections that they make establish local circuits. In arthropods, they may arborize wholly within a segmental ganglion, or within a specialized region of the brain. Local interneurones can be divided into two physiological types: spiking and nonspiking. In segmental ganglia, spiking local interneurones are largely responsible for the local processing of primary sensory inputs, whereas non-spiking ones play a major role in the control and coordination of motor neurone activity at the segmental level. By contrast, in the brain, primary visual inputs are processed mainly by non-spiking interneurones.
Local interactions between neurones may occur in three ways: by the graded release of transmitter, by the presynaptic modulation of spike-evoked PSPs and by the ‘conventional’ mechanism where spike frequency is translated across a synapse as the summed amplitude of discrete spikeevoked PSPs. Although graded synaptic transmission is the only mechanism so far described for the local interactions of non-spiking interneurones, it is not limited to them. It may occur also in non-spiking neurones specialized to transmit graded signals over long distances, or in local, intraganglionic regions of motor neurones or long interneurones. The ability of spiking neurones to exert graded effects may depend upon input and output synapses being intermingled on their fine branches, at sites relatively distant from the region of spike initiation. Since these synapses are widely distributed over the neurones, local intraganglionic interactions can be seen as the summed effect of many, yet more restricted local interactions. Restricted local interactions also may occur within parts of non-spiking interneurones, but this is a conjecture, based on modelling studies, and upon considerable EM evidence for serial and reciprocal synapses in most other types of arthropod neurones.
Sustained Responses to Brief Stimuli: Swimming in Xenopus Embryos
Authors: Roberts Alan , Dale N. , Soffe S. R. 
Published: April 2021

ABSTRACT
Prolonged responses to brief triggering or releasing stimuli are commonplace in animal behaviour. The initiation of locomotion is an example but hypotheses for the central nervous origin of locomotory rhythms generally do not explain how activity is sustained. After a brief review, which suggests that positive feedback excitation could be involved, evidence fromXenopus embryos is considered. Here a brief skin stimulus can evoke long episodes of swimming even in curarized embryos. Feedback excitation provides a possible explanation for sustaining fictive swimming. This hypothesis is evaluated by simulation of simple neuronal networks using a physiologically realistic digital computer modelling programme. The results from simulations suggest that: (1) positive feedback excitation could sustain activity either in central pattern generators for locomotion or in postural motor systems and (2) that the model networks tested here are not appropriate to produce the pattern of motor output from the Xenopus embryo spinal cord.
How Does The Lamprey Central Nervous System Make The Lamprey Swim?
Authors: Grillner Sten , Wallén Peter 
Published: April 2021

ABSTRACT
The lamprey spinal cord, in isolation or with the brainstem, can be used in vitro. The motor patterns underlying the swimming movements can be elicited by: (1) a pharmacological activation of a specific type of neuronal receptor (NMDA-receptor), that may in other systems give rise to an unstable membrane potential, (2) by stimulation of the brainstem or (3) by tactile activation of skin regions left innervated. In the latter case the initiation of ‘fictive’ swimming is partially caused by a release of a transmitter activating NMDA-receptors, as judged by the effect of NMDA-receptor blockers. The central pattern generator (CPG) is strongly influenced by feedback from mechanosensitive elements, which at least partially reside within the spinal cord. The edge cell in the lamprey spinal cord serves as an intraspinal mechanoreceptor.
The ability to generate a coordinated motor output is distributed, since spinal cord sections down to 1-5-2 segments can be made to generate alternating activity. Motor neurones receive an approximately synchronous alternating excitatory and inhibitory drive in each swim cycle and do not appear to be part of the CPG. Motor neurones supplying different parts of the body wall on the same side of a body segment have different morphology with ramifications around different descending axons. The input drive signal during fictive locomotion to motor neurones located close to each other but with different morphological characteristics may differ substantially with regard to the y-relationship (±25 %) and the shape of the oscillation. This implies that even at a segmental level motor neurones may be further subdivided, and furthermore that the ipsilateral network generating the drive signal to ipsilateral motor neurones generates a more complex and individualized output than previously assumed. Motor neurones are not part of the rhythm-generating circuit. The large identifiable interneurones are not required for rhythmic activity to occur although they may be phasically active in the swim cycle. The small segmental interneurones have not yet been completely characterized. Many are phasically active during ‘fictive locomotion’ and lack an apparent axon. Their phase relationships in relation to the burst patterns vary over the entire swim cycle.
Changes of Membrane Currents During Learning
Authors: Alkon Daniel L. 
Published: April 2021

ABSTRACT
In searching for cellular mechanisms by which nervous systems store learned information, it is helpful to differentiate properties which are genetically programmed from those which are conferred by the interaction of an organism with its environment. With mechanisms of learning, as with those underlying developmental transformations, a chronology must be reconstructed - a sequence of processes which arise as a consequence of preceding conditions. To construct such a chronology, the cellular site at which learned information is stored must be accessible to analysis so that we may watch it during sequential transformations, and so that we can measure with appropriate morphological, biophysical and biochemical techniques the nature and magnitude of the critical changes.
Ligand Activity in the Clearance of Metals from the Blood of the Crayfish (Austropotamobius Pallipes)
Authors: Lyon R. , Taylor Marina , Simkiss K. 
Published: April 2021

ABSTRACT
The rate at which metal ions are cleared from the blood of the crayfish Austropotamobius pallipes can be described as the sum of fast and slow exponential processes. The rate constants of these processes were determined and discussed in terms of ligand chemistry. The half life (t1/2) of the fast component shows a typical Irving-Williams series for the various metals. This is interpreted as showing that the retention of metals in the blood is due to binding to protein ligands. The concentrations of metals in the various tissues also reflect their binding characteristics. Class (a) metals (Ca and Sr) become associated with oxygen donors in the exoskeleton and stomach. Class (b) and borderline metals become bound to nitrogen and sulphur donor ligands in the hepatopancreas. The rapid disappearance of Cd2+ and Zn2+ from the blood can be attributed to specific ligands in the hepatopancreas.
On the Nervous Regulation of Gill Blood Flow in the Dogfish (Scyliorhinus Canicula)
Authors: Metcalfe J. D. , Butler P. J. 
Published: April 2021

ABSTRACT
The motor innervation of the gill blood vessels of the dogfish Scyliorhinus canicula L. has been investigated by electrical stimulation of (1) the branchial branches of the IXth and Xth cranial nerves in isolated perfused 1st holobranch preparations and (2) both Xth cranial nerves in whole anaesthetized fish. The observed vascular responses to nerve stimulation appear to be entirely due to contraction of the striated muscles of the gill arch and not to any direct motor innervation of the major gill blood vessels since the responses were blocked only by the drug pancuronium, which blocks striated muscle motor end-plates. The specificity of pancuronium for the motor end-plate of striated muscle in the dogfish was established by showing that it did not block nervous transmission across the cardiac ganglia.
The results from the nerve stimulation studies have been investigated further by pharmacological studies on isolated perfused gill preparations. Acetylcholine produces an atropine-sensitive increase in resistance to perfusion, while both adrenalin and noradrenalin decrease the resistance to perfusion.
Ionic Basis of Action Potential Propagation Along two Classes of ‘Giant’ Axons In the Ophiuroid, Ophiopteris Papillosa
Authors: Tuft Pamela J. , Gilly WM. F. 
Published: April 2021

ABSTRACT
Electrical activity was recorded from the radial nerve cord with extracellular suction electrodes. Spontaneous unitary spikes are 20–50 μV in amplitude with a duration of about 10 ms. Compound action potentials evoked by brief electrical shocks consist of two distinct fast spikes followed by a much slower wave of activity. Fast spikes are graded in amplitude to a maximal level, with little change in time course, over a considerable range of stimulus intensities. The larger of the two fast spikes (spike 1) has a lower threshold and higher conduction velocity: 139 ± 14·3 cms−1 (mean±s.D., N=6) vs 55 ± 7·4cms−1 for spike 2. Spike 1 is reversibly eliminated by replacement of Na with choline in the bathing medium; spike 2 is unaffected. Spike 2 is reduced in amplitude by removal of Ca from the bathing medium; spike 1 is unaffected. Cadmium (2–10 mmol l−1) reversibly blocks spikes 1 and 2. Tetrodotoxin (TTX, l–2 μmol l−1) does not affect either spike. These results support the existence of at least two classes of relatively large axons. Type 1 axons, generating spike 1, rely on a TTX-insensitive Na action potential, whereas type 2 axons may utilize a Ca action potential. Each spike represents summed activity of a relatively small number of axons probably arranged in bundles. The nature of morphological pathways involved in ophiuroid neural conduction is discussed.
Initiation of Feeding Motor Output By an Identified Interneurone in the Snail Lymnaea Stagnalis
Authors: Mccrohan C. R. 
Published: April 2021

ABSTRACT
The cerebral ventral 1 (CV1) cells of Lymnaea are located in the cerebral ganglia, and have axonal projections to the buccal ganglia. Maintained depolarization of a CV1 neurone leads to initiation, maintenance and modulation of rhythmic feeding motor output from buccal and cerebral ganglia. The CV1 cells receive rhythmic synaptic inputs, in phase with feeding cycles, which probably originate from buccal rhythm-generating interneurones. CV1 cells initiate feeding cycles independently of the buccal slow oscillator (SO) neurone, previously described. The possible roles of CV1 and SO are discussed.
Venous Return and Cardiac Filling in Varanid Lizards
Authors: Johansen Kjell , Burggren Warren W. 
Published: April 2021

ABSTRACT
The duration of ventricular diastole relative to the cardiac cycle length is much shorter (46%) in varanids than in mammals (&gt;70%). Atrial systolic pressures were high (15–20 cmH2O), and atrial contraction was apparent in pressure waveforms from the ventricular cavum arteriosum and cavum pulmonale. Atrial contraction coincides with the short period of ventricular diastole and represents the filling agent for the ventricular cava. Increased central venous flow coincides with ventricular contraction, which by reducing the intrapericardial pressure will promote the expansion and filling of the atria and central veins, implying a suctional element of cardiac filling. Inspiration during spontaneous breathing will reduce central venous pressure, steepen the pressure gradient towards the heart and aid flow towards central veins. There is a positive correlation between the systolic level of central venous pressure and cardiac cycle duration.
The Contribution of Nasal Countercurrent Heat Exchange to Water Balance in the Northern Elephant Seal, Mirounga Angustirostris
Authors: Huntley Anthony C. , Costa Daniel P. , Rubin Robert D. 
Published: April 2021

ABSTRACT
Elephant seals fast completely from food and water for 1-3 months during terrestrial breeding. Temporal countercurrent heat exchange in the nasal passage reduces expired air temperature (Te) below body temperature (Tb) Ata mean ambient temperature of 13·7 °C, Te is 20·9 °C. This results in the recovery of 71·5 % of the water added to inspired air. The amount of cooling of the expired air (Tb–Te) and the percentage of water recovery varies inversely with ambient temperature. Total nasal surface area available for heat and water exchange, located in the highly convoluted nasal turbinates, is estimated to be 720 cm2 in weaned pups and 3140 cm2 in an adult male. Nasal temporal countercurrent heat exchange reduces total water loss sufficiently to allow maintenance of water balance using metabolic water production alone.
Circulation Time, Blood Reserves and Extracellular Space in a Cephalopod
Authors: O’Dor R. K. , Wells M. J. 
Published: April 2021

ABSTRACT
Octopus vulgaris Cuvier has a fully enclosed blood system that includes large blood sinuses behind the eyes and around the gut. Experiments on the response of the hearts in exercise and hypoxic stress (Wells, 1979; Wells & Wells, 1983) and the response of the system to drugs or extracts from neurosecretory systems that discharge into the bloodstream (Wells & Mangold, 1980; Wells, 1983) have revealed a number of situations in which it would be useful to know the mean circulation time, the minimal number of heartbeats needed for blood to return to the hearts, and/or the extent to which the sinuses constitute a reserve of blood which can be mobilized in times of stress.
Gill Na+/H+ and Cl−/HCO3− Exchange Systems Evolved Before the Vertebrates Entered Fresh Water
Authors: Evans David H. 
Published: April 2021

ABSTRACT
Recent studies have demonstrated that the transport mechanisms for Na+ and Cl−uptake across freshwater fish gills (i.e. Na+/H+, Na+/NH4+ and C1−/HCO3− exchange systems) also occur in the branchial epithelium of marine teleosts and elasmobranchs, despite the presumed NaCl load in these hypo-regulating fishes (Evans, 1973, 1975a, 1977, 1982; Evans, Kormanik & Krasny, 1979). It was originally proposed (Evans, 1975b) that this occurrence was a remnant of the freshwater ancestry of the marine fishes. However, this proposition is based upon the assumption that the primary function of the system is NaCl regulation by freshwater organisms, and that the carrier which favoured the excretion of unwanted acid, nitrogen and base arose secondarily, as a means to maintain approximate electroneutrality across the epithelial membrane. The alternative proposition, viz, that acid/base regulation and nitrogen excretion by marine ancestors of the vertebrates were the driving forces for the origin of these ionic exchange systems, is an intriguing one, especially since a corollary is that the branchial transport systems necessary for NaCl regulation in fresh water actually arose before they were ‘needed’. One way to test this proposition is by examining the role that external Na+ and Cl− play in the excretion of H+, ammonia, and base by hagfishes, the only chordate group which has apparently never entered fresh water, and which represent the only modern relatives of the primitive chordates that predated the entry of the vertebrates into fresh water (Hardisty, 1979).
Calcium Enables Photoreceptor Pigment Migration in A Mutant Fly
Authors: Howard Jonathon 
Published: April 2021

ABSTRACT
Upon bright illumination, pigment granules in the photoreceptors of the fly compound eye migrate transversely toward the rhabdomeres (Kirschfeld & Franceschini, 1969). The granules absorb light passing down the rhabdomeric light guide, thereby reducing the light available to the visual pigment. This light-regulating mechanism is found in a number of invertebrate eyes (Stavenga, 1979) and has been termed the ‘longitudinal pupil’ (Franceschini, 1972).
pH Profile Along The Gut of the Silver Eel and its Modification During Seawater Acclimation
Authors: Gilles-Baillien M. , Meister M. F. , Kirsch R. , Gillard CH. 
Published: April 2021

ABSTRACT
It is generally accepted that the gut plays an essential role in the water economy of marine and seawater-acclimated teleosts, water losses being balanced by continuous ingestion of drinking water (e.g. Maetz, 1970). Desalting of the ingested sea water (SW) takes place in the oesophagus, which is very permeable to Na and Cl but relatively impermeable to water, and Na, Cl and water resorption continues in the intestine (Hirano, Morisawa, Ando & Utida, 1976; Kirsch & Meister, 1982). Since 1930, it has been believed that the intestinal fluids of marine teleosts are alkaline (Smith, 1930). This has since been confirmed by Hickman (1968) for the rectal fluid of SW-adapted southern flounders and by Oide (1973) for SW-adapted Japanese eels, whose intestinal fluid was shown to have an average pH of 8·7. Oide has also shown that an increase in the pH of the bathing medium results in greater water movement across everted eel intestine. Hence the alkalinity of intestinal fluid has been invoked as a possible factor involved in water and salt resorption in marine or in SW-adapted teleosts. However, the precise role, or the origin, of this alkalinity has not been elucidated. Moreover, pH measurements in samples collected from dead animals and exposed to the air should always be considered with extreme care, especially in this case, since alkaline pH values are somewhat uncommon in biological fluids.