bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Quantitative Description of Nodal Membrane Currents in Myelinated Nerve Fibres of theLizard Anous Carolinensis
Authors: Benoit Evelyne 
Published: April 2021

ABSTRACTExperiments were performed on individual nodes of Ranvier from a lizard at 15–16°C, using the method of Nonner (1969). In addition to a leakage current (mean conductance of 19·7 nS), the membrane ionic currents consisted of a Na+ current, completely inhibited by lμmol l−1 external tetrodotoxin, and a K+ current, sensitive to external tetraethylammonium ions and to internal caesium ions. The inactivation time course of the Na+ current at 0 mV was well fitted by the sum of two exponential phases, one fast and one slow, with mean time constants of 0·68 and 2·92 ms, respectively. In contrast to observations on amphibian and mammalian preparations, the peak Na+ current showed an almost linear potential dependence at large positive membrane potentials. A mean maximum Na+ conductance of 146·8 nS was calculated. Both the time and potential dependence of the K+ current indicated that it was similar to that found in amphibian nodes of Ranvier. The mean maximum K+ conductance was 51·9 nS. Furthermore, as described in amphibians, three different components of the K+ current (s, ft and f2) could be separated. We conclude that, under similar experimental conditions, nodal ionic currents are qualitatively and quantitatively similar in lizard and amphibian myelinated nerve fibres, suggesting that the nodal membrane of these two preparations contains similar types of ionic channels. These results strengthen the view that the near absence of nodal K+ channels is a peculiarity of mammalian nerves.
Dynamic Mechanical Properties of Extensor Muscle Cells of the ShrimpPandalus Danae:Cell Design for Escape Locomotion
Authors: Meyhöfer Edgar , Daniel Thomas 
Published: April 2021

ABSTRACTWe measured the dynamic stiffness of passive single extensor cells from the abdomen of the shrimp Pandalus danae. These stiffness measurements, consisting of both elastic and viscous moduli, were carried out by imposing sinusoidal length changes on single cells and recording, simultaneously, the resultant force. Our measurements were made over a broad range of loading frequencies (1–120 Hz) and sarcomere lengths (1·9–3·2μm), encompassing the physiological range of these parameters.We found that: (1) there is an exponential increase in both elastic and viscous moduli with increases in sarcomere length; (2) there is a weak increase in these moduli with increasing frequency; (3) the relative energy dissipated by the viscous behavior of cells is largest in the relevant physiological range of loading frequencies and sarcomere lengths, with the magnitude of the viscous modulus nearly equal to the elastic modulus; and (4) the energy dissipated by the viscous behavior of these cells alone constitutes about 10 % of the total energy required to accelerate the animal in its aquatic environment. We propose that such large values for viscous energy dissipation in passive cells may be necessary to prevent unstable responses of muscle to the rapid dynamic loads imposed by the escape event.
The Neuromuscular Junction Revisited: Ca2+ Channels and Transmitter Release in Cholinergic Neurones in Xenopus Nerve and Muscle Cell Culture
Authors: Feng T. P. , Dai Zheng-Shan 
Published: April 2021

ABSTRACT
Although the entry of calcium ions into the presynaptic nerve terminals through voltage-gated Ca2+ channels is now universally recognized as playing an essential role in evoked transmitter release at the neuromuscular junction (NMJ), and indeed in chemical synapses generally, we have as yet very little direct knowledge of the Ca2+ channels of the presynaptic terminals. In this work, making use of cocultured nerve and muscle cells from Xenopus embryos, we studied the NMJ formed between the soma of identified cholinergic neurones and myoball, which allowed the use of patch-clamps on both the pre- and postsynaptic components. Both whole-cell and single-channel recordings of Ca2+ channels in the presynaptic cell were made. We found only one type of voltage-gated Ca2+ channel with high-voltage activation and slow inactivation characteristics, allowing its classification either as the L or the N type. The channels were susceptible to block by met-enkephalin but not to block by nifedipine or to enhancement by Bay K 8644. This combination of pharmacological properties favours their classification as the N type. Preliminary observations on the correlation between calcium currents and transmitter release disclosed a strikingly rapid run-down of the evoked release with unchanged calcium currents and spontaneous release during whole-cell recording, indicating a specific wash-out effect on some link between calcium entry and evoked transmitter release.
The Specificity of Synapse Formation by identified Leech Neurones in culture
Authors: Nicholls J. G. , Liu Y. , Payton B. W. , Kuffler D. P. 
Published: April 2021

ABSTRACT
The physiological and fine structural events accompanying synapse formation have been followed while identified neurones of known function make contact in tissue culture. Particular pairs of identified neurones isolated from the central nervous system (CNS) of the leech form chemical synapses; other pairs of cells form nonrectifying electrical junctions, rectifying electrical junctions, mixed chemical and electrical synapses or no synapses at all, depending upon the partners that have been paired. Moreover, certain specific regions on the cell surface (such as the soma, initial cell segment or axon tips) preferentially develop chemical or electrical synapses. Of particular interest are the large, serotonergic Retzius cells that form mixed chemical and electrical synapses in culture, as in the animal. When these cells are juxtaposed at their initial segments, it has been shown that chemical synapses can develop reliably within 6 h of contact in culture. Shortly after transmission can be detected physiologically, the principal features of synaptic structure are evident. The physiological and morphological characteristics resemble those of mature synapses studied within the central nervous system. Only at later times, after the chemical synapses have been formed, do electrical connections appear. By contrast, when other specialized regions of the Retzius cells are apposed (the tips of their axons), electrical synapses appear earlier. By comparing the connections that different types of serotonergic neurones make in culture we have been able to assess the role played by the transmitter in determining specificity: the results show that the transmitter does not determine what type of synapse is made on a particular partner. For example, Retzius cells make purely chemical synapses upon the sensory P neurone in culture; other serotonergic neurones (known as DL and VL) make purely electrical connections on this same pressure sensory neurone. Together, these results demonstrate that highly specific cell-cell recognition is a necessary feature of synapse formation after neurones have grown to their appropriate destinations.
Cerebellar synaptogenesis: what we can learn from mutant mice
Authors: Sotelo C. 
Published: April 2021

ABSTRACT
Examination of perturbations in the adult cerebellar connectivity, that follow well-defined lesions produced by gene mutations in the mouse, reveals a few of the numerous and intricate cellular interactions taking place during synaptogenesis. In weaver and in the central ectopia of reeler, Purkinje cells form innumerable dendritic spines, despite the absence of parallel fibers. Only a small proportion of these spines are innervated, and their presynaptic partners are mossy fibers (heterologous synapses) originating from spinal cord, but not from pontine nuclei. Hence, the early phase of membrane recognition is based more on a hierarchical choice between a wide range of graded preferences, than on the complementarity of a narrow range of synaptic affinities. The comparative analysis of weaver, reeler, staggerer and hyperspiny Purkinje cell has allowed us to establish that the late phase of synapse stabilization or elimination, leading to the numerical matching of one climbing fiber per Purkinje cell, is not based on climbing fiber translocation. Conversely, this regression appears to be the result of a process of competition between climbing fibers and parallel fibers. Whatever the mechanisms of the competition are, the results obtained with the mutants suggest that activity of the forming cerebellar circuitry is involved in their regulation. Finally, a new mutation is reported, the nodding mouse, to illustrate the fact that the ultimate morphology of presynaptic boutons results from an interplay between intrinsically regulated factors (features of presynaptic organelles) and the morphogenetic influence of postsynaptic partners. This accounts for the size and shape of the boutons as well as for the class of synaptic junction. Furthermore, this morphogenetic influence is not restricted to early life but occurs whenever the originally established balance between pre-and postsynaptic elements is upset.
Synapse formation in the adult brain after lesions and after transplantation of embryonic tissue
Authors: Raisman G. , Field P. M. 
Published: April 2021

ABSTRACT
Some years ago it was demonstrated that when the adult rat septal nuclei are partially deafferented the remaining afferent fibres form new connections. The conclusion that new synaptic connections form in the adult central nervous system (CNS) was greeted initially with much scepticism, later with over-enthusiasm and unwarranted generalisation to all lesion situations, together with even less warranted attribution of various beneficial functional properties.
Today, as the pendulum swings into a more reasonable position, some of the original observations, which at the time attracted little attention, have become more interesting.
The observation that in the normal septal nuclei the ratio of spine to shaft synapses is extraordinarily constant (to an accuracy better than 1 % ) from one animal to another. How could such almost crystalline rigidity of structure be produced in normal development and maintained in the face of major lesion-induced changes in connectivity? The observation that synaptic re-occupation by sprouting axons restores exactly the normal number of synapses, presumably indicating that the neurones have a fixed number (as well as spine/shaft distribution) of postsynaptic sites. Thus, the septal lesion paradigm is as strong a method for investigating synaptic rigidity as for investigating plasticity.
In the intervening years, the use of embryo to adult transplantation has made it obvious that considerable reconstruction of adult brain synaptology is possible, and that many of the normal rules of connectivity are maintained (most prominently for the ‘point-to-point’ axonal systems). What could lead to further fruitful investigation is the extent to which the observations (e.g. relating to hierarchies of axonal preference, the need for denervation, and the involvement of glial cells) in partially deafferented adult systems, such as the septal nuclei, are retained, or modified, in face of the ingrowing fibres from embryonic transplants.
Development of the rodent cerebellum and synaptic re-formation of donor climbing terminals on spines of the host purkinje dendrites after chemical deafferentation
Authors: Kawamura K. , Murase S. , Yuasa S. 
Published: April 2021

ABSTRACT
Reinnervation of host Purkinje cells by donor climbing fibers was observed in the following experiments. Medullary primordial tissue (from E14-E16) containing the inferior olive was grafted into a host rat cerebellum, in which the inferior olivary complex and climbing fibers had been destroyed by intraperitoneal injection of 3-acetylpyridine (3-AP). After 3 weeks, immature as well as mature types of climbing fiber terminals bearing packed round vesicles were found that had established synaptic contacts on dendritic spines of the host Purkinje cells. Quantitative analysis at the ultrastructural level has been carried out. The main results are as follows. (1) The number of preterminals that formed synaptic contacts with spines of the host Purkinje dendrites in the transplanted material increased by 3.4-fold compared to the control (3-AP-treated non-grafted material). (2) The number of mature climbing-type preterminals increased from 0.3–0.9 % to 5 % after grafting (cf. 22 % in normal brain tissue), and the number of immature climbing-type preterminals also increased from 2–10 % (control) to 20% after grafting. These changes were statistically significant (P&lt;0.01). (3) The number of parallel-type preterminals increased from 13 % (control) to 27 % after grafting, which was also statistically significant (P&lt;0.01). Thus, it appears that the donor climbing fibers grow and develop to find unoccupied spines on the host Purkinje dendrites and establish synaptic contacts, and also that the host parallel fibers may generate axonal sprouts to search their new targets and ultimately to form synaptic contacts with unoccupied spines. In the process of re-modeling the brain, competition for targets is likely to occur between the two kinds of axonal processes, i.e. the donor climbing fibers and the host parallel fibers.
In situ analysis of neuronal dynamics and positional cues in the patterning of nerve connections
Authors: Fraser S. E. , O’Rourke N. A. 
Published: April 2021

ABSTRACT
Recently developed imaging techniques permit individual cells to be uniquely labeled and followed over time as development proceeds in intact vertebrate embryos. Small groups of cells in the developing eye rudiment of the frog Xenopus have been labeled with the vital dyes Dil, lysinated fluorescein dextran (LFD) or lysinated rhodamine dextran (LRD). Individual optic axons and their growth cones were clearly visible in the intact living animal using confocal microscopy or epifluorescence microscopy with a low light level video camera and computer-based video image enhancement. To follow the dynamics of single optic nerve fiber terminal arborizations, small groups of cells, or even single retinal ganglion cells, were labeled with Dil, and the resulting labeled optic nerve fibers were imaged using a confocal microscope. The images show a profound alteration in morphology from day to day, demonstrating that optic nerve terminal arborizations are dynamic structures constantly extending and retracting branches.
To follow the topography of the developing projection and analyze the cues that guide its formation, small groups of eyebud cells from LFD-and LRD-labeled donor embryos were grafted to an unlabeled host in either a location equivalent to that from which they had been removed (homotopic grafts) or a non-equivalent location (heterotopic grafts). Axons from homotopic grafts projected to the tectum as expected from the adult topography of the retinotectal projection. Dorsoventral topography was present from the time that the optic nerve fibers were observable in the tectum, in agreement with previous work. Nasotemporal topography was subtle or absent for the first few days, and then slowly refined. The importance of positional cues was tested by performing heterotopic eyebud grafts, in which the labeled eyebud cells are grafted to inappropriate places in the host eyebud. The heterotopic grafts appeared to integrate with the ectopic site in the eyebud in a functional manner. They should, therefore, project to the tectum together with their new neighbors if neighbor interactions or activity-based cues were of primary importance in the initial patterning of the map. However, the experiments showed that the axons from heterotopic grafts always behaved in a fashion appropriate to their position of origin in the donor, regardless of their final position in the host. These observations indicate that small groups of eyebud cells (as small as a single cell) possess positional information that plays a dominant role in guiding the optic nerve fibers to their target sites in the tectum.
Specification of synaptic connections mediating the simple stretch reflex
Authors: Frank E. , Mendelson B. 
Published: April 2021

ABSTRACT
A variety of mechanisms underlie the specification of synaptic connections during development. In the monosynaptic stretch reflex in vertebrates, sensory neurones innervating muscle spindles are not determined until they make contact with a particular muscle. Instead, the muscle they supply appears to specify the pattern of central connections they establish with motoneurones. Developing thoracic sensory neurones made to project to novel peripheral targets in the forelimb of tadpoles project into the brachial spinal cord, something they never do in normal frogs. Moreover, these foreign sensory neurones make monosynaptic connections with the now functionally appropriate brachial motoneurones. Normal patterns of neuronal activity are not necessary for the formation of specific central connections. Neuromuscular blockade of developing chick embryos with curare during the period of synaptogenesis does not prevent the formation of correct sensory-motor connections. Competitive interactions among the afferent fibres also do not appear to be important in this process. When the number of sensory neurones projecting to the forelimb is drastically reduced during development, each afferent fibre still makes central connections of the same strength and specificity as normal. Together, these results suggest that peripheral targets induce some molecular change in developing sensory neurones such that they can recognize their appropriate synaptic partners in the spinal cord.
The Scaling and Potential Importance of Cutaneous and Branchial Surfaces in Respiratory Gas Exchange in Young Chinook Salmon (Oncorhynchus Tshawytscha)
Authors: Rombough Peter J. , Moroz Brenda M. 
Published: April 2021

ABSTRACT
Measurements were made of the surface areas of the yolk sac, the fins, the head and trunk, the gill filaments and the gill lamellae of chinook salmon (Oncorhyn-chus tshawytscha Walbaum) weighing between 0.045 g (3.7 days posthatch) and 13.4g (180 days posthatch). Cutaneous surfaces initially accounted for the vast majority (approx. 96%) of the total area available for respiratory gas exchange. As fish grew, total branchial surface area expanded at a more rapid rate than cutaneous surface area and, thus, came to represent a progressively larger fraction of total surface area. The transition was relatively slow, however, and it was not until fish reached 2.5–4.0g that branchial area exceeded cutaneous area.
Although some individual surfaces (e.g. the gill lamellae) followed rather complex patterns of expansion, the overall increase in respiratory surface area with tissue mass could be described reasonably well using only two equations; one for the period prior to complete yolk absorption (&lt;0.4 g) and one for the period following complete yolk absorption (&gt;0.4 g). Mass exponents for total surface area (6=0.85) and metabolic rate (b≈=0.8–0.9) were not significantly different for the larger fish. In contrast, the mass exponent for total surface area (6=0.39) was significantly less than that for metabolic rate (b≈=0.9–1.0) for fish weighing less than 0.4 g. Changes in the relative efficiencies of the various exchange surfaces during the course of larval development probably account for this discrepancy.
Physiology and Structure of Three New Uropod Proprioceptors in the Crayfish Procambarus Clarkii
Authors: Field Laurence H. , Newland Philip L. , Hisada Mituhiko 
Published: April 2021

ABSTRACT
Three new chordotonal organs are described: APCO for the abdominal-proto-podite joint, PExCO for the protopodite-exopodite joint and PEnCO for the protopodite-endopodite joint of the crayfish uropod. The PEnCO is a distinct strand chordotonal organ, while the APCO and PExCO are webbed structures arising from peripheral nerve roots 2 and 3 of the terminal abdominal ganglion, in which some of their somata are located (‘root cells’).
Physiological experiments showed that the organs monitor position and movement at all three joints. Position monitoring is limited to open angles of the exopodite and extended angles of the protopodite (no limits on endopodite position sensitivity). Distinct hysteresis is shown by most position-sensitive units.
The abdomen-protopodite joint is monitored through four orders of velocity magnitude, while the exopodite and endopodite, which are involved in tailfan flare, are primarily monitored at high movement velocities. Large, phasic units in all three chordotonal organs (COs) can monitor continuous, high-velocity movement with little adaptation.
These results are discussed in relation to known motor control mechanisms for crayfish uropods during swimming, walking, escape and righting behaviours.
31P-NMR Studies on Acid-Base Balance and Energy Metabolism of Acid-Exposed Fish
Authors: Van Waarde Aren , Van Dijk Peter , Van Den Thillart Guido , Verhagen Maria , Erkelens Cees , Bonga Sjoerd Wendelaar , Addink Albert , Lugtenburg Johan 
Published: April 2021

ABSTRACT
Tilapias (Oreochromis mossambicus), acclimated to 25 °C and water with a Ca2+ content of 0.68 mmol I−1, were subjected to gradual water acidification (from pH 7.6 to 4.0 in 4h), followed by 10 h of exposure to low pH (pH4.0), gradual environmental alkalization (from pH 4.0 to 7.6 in 2 h) and 6h of recovery at normal pH (pH 7.6). Intermediates of energy metabolism were measured in perchloric acid extracts of gill, muscle and blood. In a separate series of experiments, the intracellular pH (pHi) and the levels of high-energy phosphate compounds were continuously monitored by in vivo31P-NMR spectroscopy. We used a 10mm surface coil, which was positioned above the gill arches or the epaxial white muscle. With the coil above the gill, splitting of the inorganic phosphate peak indicated that the signal was picked up from three different compartments. These were tentatively identified as plasma, muscle and gill epithelium. Water acidification induced a transient pH drop of the plasma (0.24 units) and the gill (0.19 units) but the pH of both compartments slowly recovered during the 10-h exposure to acid water. In contrast, the pHi of muscle tissue was only slightly affected. Alkalization of the environment caused a surprising transient decline of the plasma pH, which was not due to lactic acidosis, but may be related to the precipitation of a buffer compound like CaCO3 in scales and bone. The high-energy phosphate stores in the tissues were unchanged during the whole experimental protocol.
Adrenergic Control of Red Cell pH in Salmonid Fish: Roles of the Sodium/Proton Exchange, Jacobs-Stewart Cycle and Membrane Potential
Authors: Nikinmaa Mikko , Tiihonen Kirsti , Paajaste Marita 
Published: April 2021

ABSTRACT
We investigated the mechanisms by which adrenergic activation of sodium/proton exchange reduces the pH gradient across the membrane of rainbow trout red cells. In untreated cells, adrenergic stimulation caused a significant increase in the proton distribution ratio ([H+]e/[H+]i) across the red cell membrane. The increase in the proton distribution ratio caused by adrenergic stimulation was inhibited by the protonophore 2,4-dinitrophenol (2,4-DNP). Thus, sodium/proton exchange displaces protons from electrochemical equilibrium. Active regulation of intracellular pH by sodium/proton exchange is possible, because the extracellular dehydration of carbonic acid to carbon dioxide is uncatalyzed. The increase in proton distribution ratio caused by adrenergic stimulation was inhibited in red cell suspensions to which extracellular carbonic anhydrase had been added before stimulation. In contrast, inhibition of intracellular carbonic anhydrase markedly increased the pH changes induced by adrenergic stimulation, suggesting that the net direction of the intracellular hydration/dehydration reaction may markedly affect the intracellular pH changes. Membrane potential changes are not a necessary component of the adrenergic response. The increases in red cell volume and sodium and chloride concentrations induced by adrenergic stimulation were unaffected in cells ‘voltage-clamped’ by valinomycin.