bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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<0.01). (3) The number of parallel-type preterminals increased from 13 % (control) to 27 % after grafting, which was also statistically significant (P<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

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

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

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 (<0.4 g) and one for the period following complete yolk absorption (>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

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

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

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.
Temperature Acclimation Effects on Carp Nerve: a Comparison of Nerve Conduction, Membrane Fluidity and Lipid Composition
Authors: Harper A. A. , Watt P. W. , Hancock N. A. , Macdonald A. G.
Published: April 2021

This paper describes the effects in vitro of temperature (5–35°C) on the conduction properties of vagus nerves from freshwater carp Cyprinus carpio L., either cold-(8°C) or warm-(28°C) acclimated. The results are related to changes in the physical state and lipid composition of brain membrane fractions. The temperature dependence of the conduction velocity of the C (unmyelinated) component of the compound action potential (AP) were determined using Arrhenius plots. The relationship between log time-to-peak AP and the reciprocal of absolute temperature (1/K) is best described by two linear components. The grouped data for the warm-acclimated group had a break point at 23.6°C. At temperatures above 24°C the activation energy Ea was 18.3±8.33kJmol−1 and below 24°C Ea was 49.7±3.78kJmol−1. The break-point for cold-acclimated nerves was 17.4°C with Ea values of 41.2±2.65 and 13.2±3.63 kJ mol−1 below and above this temperature, respectively. The Arrhenius plots of the fast-conducting A (myelinated) component of the AP for the warm-and for the cold-acclimated group were better fitted by two linear relationships with Ea values of 42.0±2.16 and 86.9±4.55 Kj mol−1 above and below the break at 13.1°C for the warm-and cold-activated nerves, respectively, and Ea values of 18.0±5.45 and 58.8±4.08 kJ mol−1 above and below the break point, 19.3°C, for warm-and cold-acclimated nerves, respectively. Steady-state fluorescent polarization of 1,6-diphenyl-1,3,5-hexatriene-(DPH) labelled synaptosomal and myelin fractions of carp brain indicated partial homeoviscous adaptation in the membranes. Since there were no appreciable differences in their fatty acids, changes in membrane composition other than in the phospholipid fatty acids presumably occurred.
Is ‘Reflectance’ Basking Real?
Authors: Heinrich Bernd
Published: April 2021

Various kinds of butterflies raise both (or sometimes one) of their pairs of wings while basking with their body at approximately right angles to the incident solar radiation and with their wings held at an acute angle to the incident sunlight. I here test the effects of wing posture on thoracic temperature in so-called ‘reflectance’ basking.

Butterflies with pale yellow or white dorsal wing surfaces held with their wings at 45, 90 or 180° with respect to each other (or 22–23, 45 and 90°with respect to the solar radiation) heated to mean thoracic temperatures (Tth) of 38.2, 39.5 and 39.9°C, respectively, in direct sunlight. These closely similar values of Tth are significantly different (P<0.02) from each other, but the difference is in the opposite direction to that predicted by the solar reflectance hypothesis. The Tth of butterflies tested under a sun lamp in the laboratory showed the same trend of Tth with wing angle. Reflectance from the wings thus makes little or no practical contribution to the animal’s heating response. Butterflies with wings at 45°that were heated from above with a sun lamp showed an immediate increase in Tth when turned at right angles to a gentle air stream. Thoracic temperature immediately declined when they were again turned to face the air stream. Those butterflies that were at right angles to the air stream showed an immediate increase in Tth when the wings were raised from 180 to 45°, and their Tth again declined to previous values when the wings were again lowered. However, little or no effect of wing angle on Tth was observed when the wing angle of butterflies parallel to the air stream was altered.

These results indicate that wing elevation in basking butterflies does not increase Tth by way of solar reflection from the wings. Instead, the raised wings increase Tth by reducing convective cooling. ‘Reflectance’ basking is a form of dorsal basking used by species of butterflies that perch above vegetation rather than above a heated substratum.
Pyruvate Kinase From the Land Snail Otala Lactea: Regulation by Reversible Phosphorylation During Estivation and Anoxia
Authors: Whitwam Ross E. , Storey Kenneth B.
Published: April 2021

Pyruvate kinase (PK) from tissues of the desert snail Otala lactea (Müller) undergoes a stable modification of its kinetic properties during estivation or in response to anoxia stress. In foot muscle and mantle, the kinetic changes induced by either state were virtually identical and were consistent with a less active enzyme form in estivation or anoxia: S0.5 PEP increased, and I50 values for Mg-ATP and L-alanine decreased, compared to the enzyme in control (aroused) snails. Estivation and anoxia also changed the properties of PK from hepatopancreas; some changes were consistent with a more active enzyme form (S0.5 PEP decreased, I50 values for Mg-ATP and L-alanine increased) but the enzyme lost all sensitivity to the potent activator fructose-l,6-bisphosphate. A time course of changes in I50 Mg-ATP for foot PK and S0.5 PEP for hepatopancreas PK revealed that estivation-induced changes in enzyme properties occurred between 12 and 48 h after snails were deprived of access to food and water, whereas the reversal of these changes occurred within as little as 10 min in foot muscle after arousal was initiated. The molecular basis of the stable modification of PK kinetics appears to be reversible protein phoshorylation. The action of added cyclic-AMP-dependent protein kinase on foot or hepatopancreas PK from control (aroused) snails changed PK kinetic parameters to those characteristic of the enzyme form in estivating animals; the addition of stimulators of endogenous cyclic-GMP-dependent protein kinase or protein kinase C had the same effect. Conversely, treatment with added phosphatases reconverted the properties of foot muscle PK from estivating snails to those characteristic of the control enzyme. The data suggest that reversible phosphorylation control over the activity state of regulatory enzymes of glycolysis is one mechanism contributing to the overall metabolic rate depression of the estivating state.
Regional Variation in the Current Flow Across an Insect Blood–Brain Barrier
Authors: Smith P. J. S. , Shipley A.
Published: April 2021

One notable characteristic of the insect and vertebrate central nervous system is the presence of a clearly defined blood-brain barrier. In the insect this barrier is made up of the perineurial glial cells, and shows a heterogeneity in structure and possibly function between the connectives and ganglia. In this paper we have used a two-dimensional vibrating probe to investigate the net flow of electrical current across the barrier at various locations in the abdominal nervous system. The results show clear differences between different areas. There is a strong and consistent outward current flow (3.16 μAcm−2) perpendicular to the ganglion surface over the equatorial plane. Current returns through the peripheral nerves and the connectives. A detailed study of the latter shows that the net inward flow is principally over the initial section, immediately adjacent to the ganglia (2.1μAcm−2). The different current polarities can be correlated with structural differences in the underlying glial cells.
Characteristics of Five Types of K+ Channel in Cultured Locust Muscle
Authors: Miller B. A. , Usherwood P. N. R.
Published: April 2021

K+ channel activity in cultured locust myofibres was investigated using gigaohm patch-clamp techniques. After 2 months in vitro the myofibres had a mean resting potential of -39±7mV (±S.D., N=42). Five types of K+ channel were identified at this time. The majority of single-channel events recorded from cell-attached patches were due to a small-conductance (type 1) and a large-conductance (type 2), inward rectifier, K+ channel. In cell-attached patches, with 180 mmol 1−1 KC1 in the patch pipette, the type 1 channel had a chord conductance of 43 pS for inward currents and 8pS for outward currents; the type 2 channel had a chord conductance of 115 pS for inward currents and 29 pS for outward currents. The type 2 channel exhibited bursting kinetics, was ATP-sensitive and could be blocked by Ba2+. Two other channels (types 3 and 4) had linear conductances of 130pS and 207pS, respectively. The type 3 channel was Ca2+-sensitive. A further channel (type 5) appeared to be an inward rectifier with a conductance of 5pS. Openings of types 3, 4 and 5 channels occurred less frequently than openings of the other two channels. Types 1, 2, 3 and 4 channels possessed multiple closed and open states with non-linear gating mechanisms.
A Temperature-Induced Switch From Diffusive to Convective Ventilation in the Honeybee
Authors: Lighton John R. B. , Lovegrove Barry G.
Published: April 2021

It is known that many insects emit CO2 in widely spaced ‘bursts’ or discontinuous ventilation events, usually characterized by active abdominal ventilation. We describe the discontinuous CO2 emission characteristics of the honeybee (Apis mellifera ligustica Spinola), and utilize its ‘chill coma’ temperature threshold (12°C) to effect transitions from continuous, diffusive to discontinuous, convective ventilation regimes. Increasing temperature abruptly switched the dynamics of ventilation from diffusive and continuous (⩽11 °C) to convective and discontinuous (>12°C). The ventilation cycle frequency was 7.84 mHz and CO2 output per ventilation event (burst phase) was 1.56μl neither variable was temperaturedependent in the range 12–15 °C. The rate of CO2 emission did not change significantly in the range 7–15 °C, possibly owing to increased membrane leakiness at lower temperatures. At 15°C, honeybee metabolic rate (2.69 W kg−1, mean mass 0.094 g) is similar to that of other similarly sized insects capable of significant endothermy.
An Interneurone Mediating Motor Programme Switching In The Ventilatory System of the Crab
Authors: Dicaprio Ralph A.
Published: April 2021

The central pattern generator controlling ventilation in the crab can generate two distinct motor programmes, which determine the direction of water flow during irrigation of the gills. An interneurone has been identified that depolarizes when the ventilatory motor output switches from forward to reverse ventilation and remains depolarized for the duration of the reverse motor progamme. Depolarization of this neurone by intracellular current injection causes a switch in the motor programme from forward to reverse ventilation, which persists for the duration of the current step. Hyperpolarization of this cell during reverse ventilation terminates the reverse motor programme. The possible role of this reversal switch interneurone is considered in the context of the observed changes in the activity of other ventilatory interneurones and motor neurones during reverse ventilation.
Haemolymph Buffering in the Locust Schistocerca Gregaria
Authors: Harrison Jon F. , Wong Calvin J. H. , Phillips John E.
Published: April 2021

The biochemical basis of buffering in the haemolymph of insects has received little attention, and the chemical complexity of insect haemolymph (reviewed by Mullins, 1985) suggests that the relative importance of various compounds to buffering may be quite different from that in other arthropods or vertebrates. Moreover, the role of bicarbonate as a buffer in insect haemolymph is difficult to evaluate because precautions to prevent carbon dioxide loss during sampling from insect haemolymph have generally been ignored, and titration techniques previously used to measure haemolymph buffer value allowed inadequate time for equilibration of the bicarbonate buffer system. In this study, we describe the biochemical basis of haemolymph buffering in the migratory locust Schistocerca gregaria.
Effect Of Boundary Layers On Cutaneous Gas Exchange
Authors: Pinder Alan W. , Feder Martin E.
Published: April 2021

Boundary layers may offer significant resistance to cutaneous oxygen uptake by amphibians in water. This hypothesis was tested by measuring resistance to oxygen uptake as a function of water velocity in bullfrogs submerged at 5 °C and by direct measurements of the boundary layer with oxygen microelectrodes.

The oxygen diffusion boundary layer was easily measurable with oxygen microelectrodes. The proportion of the total resistance to oxygen uptake represented by the boundary layer increased from 35 % at a water velocity of 5cms−1 to over 90% at 0.1 cm s−1. At water velocities below 1cms−1 oxygen uptake was limited by the resistance of the boundary layer. At 0.1 cm s−1, the partial pressure of oxygen immediately adjacent to the skin was only 2 kPa (15 mmHg); placing an immobilized frog ln still water was tantamount to placing lt in anoxic water. Body movements disrupted boundary layers efficiently; even occasional small movements by the animal (1min−1) were sufficient to maintain oxygen uptake in still water.
GTP-γ-S Increases the Duration of Backward Swimming Behavior and the Calcium Action Potential in Marine Paramecium
Authors: Bernal Juan , Kelsey Anita Mcilveen , Ehrlich Barbara E.
Published: April 2021

Behavioral and electrophysiological experiments were made to examine the hypothesis that G-proteins modulate the voltage-dependent calcium channel in the marine ciliate Paramecium calkinsi. It was found that guanosine-5’-O-(3-thiotriphosphate) (GTP-γ-S), an analogue of GTP that binds to and activates G-proteins, increased the duration of backward swimming behavior in reversibly permeabilized Paramecium in an irreversible and concentration-dependent manner. At 1 μmol 1−1 GTP-γ-S, the duration of backward swimming behavior was increased fivefold. Other nucleotides and related compounds did not have a significant effect on the backward swimming behavior. To evaluate whether the behavioral effects were due to ion channel modulation, the calcium action potential in intact Paramecium was monitored before and after guanine nucleotide injection. Within 5 min after the injection of GTP-γ-S or GTP into the cell, the duration of the calcium action potential was prolonged at least threefold. Like the behavioral response, the GTP-y-S effect on the calcium action potential duration was irreversible, whereas the effect of GTP began to decay after 6 min. GDP-β-S, which binds to and inactivates G-proteins, markedly reduced the calcium action potential within 5 min after injection. These results support the hypothesis that the voltage-dependent calcium channels present in Paramecium are modulated by GTP-binding proteins.
Cold-Tolerance Mechanisms of the Antarctic NematodePanagrolaimus Davidi
Authors: Wharton D. A. , Brown I. M.
Published: April 2021

When free of surface water in air or liquid paraffin, the antarctic nematode Panagrolaimus davidi is freezing intolerant but avoids freezing by supercooling. Survival of long-term exposure is enhanced by sub-zero temperatures compared with controls maintained at 99% relative humidity and 15 °C. In water the nematodes are seeded by exogenous ice nucleation and a proportion are freezing tolerant. Ice formation appears to be restricted to the pseudocoel. The degree of freezing tolerance is dependent upon the age of the culture and its thermal history. P. davidi is freezing tolerant when exposed to sub-zero temperatures in water and freezing intolerant when free of surface water and able to supercool. These two strategies are not mutually exclusive as they are often thought to be in arthropods.
Five Different States of Ciliary Activity in the Epaulette of Echinoplutei
Authors: Mogami Yoshihiro , Fujima Kikuyo , Baba Shoji A.
Published: April 2021

Movement and spontaneous responses of the epaulette cilia of free-swimming eight-armed echinoplutei were analyzed by means of high-speed video microscopy. In addition to the two cyclic activities, normal beating for forward swimming and reversed beating for backward swimming, we identified another cyclic and two noncyclic states of ciliary activity. Intermediate beating was found during the transition from reversed beating to normal beating. One of the noncyclic states, the upright-inactive state, was found only after reversed beating and then changed to another noncyclic state, the inclined-inactive state, prior to a return to normal beating. Transitions within the cyclic and noncyclic states occurred in both directions, while transitions between the cyclic and the noncyclic states were in one direction.
Three Anthozoan Neuropeptides, Antho-RFamide and Antho-RWamides I and II, Modulate Spontaneous Tentacle Contractions in Sea Anemones
Authors: McFarlane Ian D. , Grimmelikhuijzen Cornelis J. P.
Published: April 2021

Behavioural coordination in sea anemones involves both excitation and inhibition. Examples include reciprocal inhibition between longitudinal and circular muscles (Batham and Pantin, 1954), inhibitory actions during peristalsis (Ewer, 1960; McFarlane, 1974a), joint excitatory and inhibitory innervation of sphincter muscle (Lawn, 1976) and inhibition of neural pacemakers (McFarlane, 1974b).
Different Hemocyanin Oxygen-Affinities in Carcinus Maenas from Maine and Arcachon
Authors: Burnett Louis E. , Mangum Charlotte P.
Published: April 2021

The green or shore crab Carcinus maenas (Linnaeus) is believed to have emigrated by ship from its native Europe to the Atlantic coast of North America. The chronological sequence of new records suggests the arrival in New York of pioneer individuals in the early 19th century, followed by gradual northward extension of the species range (Almaca, 1963; J. T. Carlton, personal communication). The number of immigrations and the present genetic relationships of various populations are unknown.
Patterns of Synaptic Drive to Ventrally Located Spinal Neurones inRana TemporariaEmbryos During Rhythmic And Non-Rhythmic Motor Responses
Authors: Soffe S. R. , Sillar K. T.
Published: April 2021

Intracellular recordings have been made from ventrally located neurones in the spinal cord of Rana temporaria embryos at around the time of hatching. Both short-latency ‘reflex’ and more prolonged rhythmic motor responses can be elicited by stimulation of the skin in immobilized embryos. Initial responses to single-sided skin stimuli usually involve excitation of neurones on the opposite side and strychnine-sensitive inhibition of neurones on the same side. Less reliable responses to dimming the lights also involve initial excitation on one side associated with inhibition on the opposite side. Intracellular recordings from single neurones during rhythmic activity show that on each cycle the same neurone can fire one or many spikes during the course of a single evoked or spontaneous episode. Bursts occur at longer cycle periods, generally at the start of episodes; single spikes occur at shorter cycle periods, generally later in episodes. During sustained rhythmic responses, neuronal membrane potential is generally depolarised and returns gradually to its resting level at the end of the episode. During the episode, relatively depolarising phases of synaptic excitation alternate with relatively hyperpolarising phases of chloride-dependent synaptic inhibition. Cell input resistance is reduced by around 50% throughout each episode. Within each cycle, input resistance is reduced further during the hyperpolarising phase than during the depolarising phase. Rhythmic excitation and inhibition of ventrally located neurones appears to be similar throughout the whole range of cycle periods, supporting the suggestion that a single rhythm-generating system with a wide ‘permissive’ range drives rhythmic movements in R. temporaria embryos.
Gigaohm Single-Channel Recording From Isolated Hermissenda Crassicornis Type B Photoreceptors
Authors: Etcheberrigaray R. , Huddie P. L. , Alkon D. L.
Published: April 2021

Invertebrate photoreceptor electrophysiology has mainly been studied with intracellular microelectrodes. Single-channel recording has proved to be difficult, possibly because of unusual plasma membrane configurations; in Limulus polyphemus successful gigaohm seals were obtained only after pronase treatment and brief sonication (Bacigalupo and Lisman, 1983). Here we describe an isolated Hermissenda eye preparation that permits single-channel recording (Hamill et al. 1981) from identified type B photoreceptors; this photoreceptor sub-type has been assiduously studied with intracellular microelectrodes, under both current-clamp and voltage-clamp conditions. Associative conditioning of Hermissenda crassicornis (in the paired fight and rotation paradigm) is attributable in part to the reduction of potassium conductances in the type B photoreceptors (Alkon, 1984, 1987; Alkon et al. 1985). We have used the isolated eye preparation to characterize two types of potassium channels in photoreceptor plasma membranes.
The Role of the Pectoral Fins in Station-Holding of Atlantic Salmon Parr (Salmo Salar L.)
Authors: Arnold G. P. , Webb Paul W. , Holford B. H.
Published: April 2021

Benthic fish resist downstream displacement in a current by balancing drag, the force orientated downstream, with the friction force. The friction force is μ (Wo—L), where μ is the friction coefficient, Wo the weight force of the fish in water (N), and L the lift force (N) acting on the body and fins (Arnold and Weihs, 1978). Above a critical speed, friction is insufficient to counteract drag and the fish must either swim or seek shelter from the flow. This note reports tests of the commonly proposed hypothesis (e.g. Kalleberg, 1958; Keenleyside and Yamamoto, 1962; Jones, 1975; Wankowski, 1981) that the pectoral fins are important to station-holding in Atlantic salmon, acting as hydrofoils generating negative lift.
Calcium Uptake by Mitochondria Isolated from Muskrat and Guinea Pig Hearts
Authors: McKEAN Thomas A.
Published: April 2021

Subsarcolemmal and interfibrillar mitochondria were isolated from the hearts of the diving muskrat and non-diving guinea pig and direct and indirect measurements of calcium uptake were examined in vitro. The calcium-stimulated respiration rate and 45Ca uptake were measured and found to be greater in muskrat than in guinea pig mitochondria. Muskrat mitochondria were able to endure a greater external calcium concentration than guinea pig mitochondria before exhibiting indications of inner membrane damage. Calcium uptake by muskrat heart mitochondria was inhibited more by 1 mmol 1−1 MgCl2 than was uptake by guinea pig mitochondria. No differences were detected between the interfibrillar and subsarcolemmal populations of mitochondria within species. An increased ability to sequester calcium by mitochondria without causing them damage may aid an animal during recovery from hypoxia, ischemia or acidosis.
Intra- and Extracellular Use and Evaluation of Ammonium-Selective Microelectrodes
Authors: Fresser F. , Moser H. , Mair N.
Published: April 2021

An NH4+-selective membrane for microelectrodes (NH4ISMs) was tested under ‘biological conditions’ in normal Astacus saline (NAS), two simulated intracellular salines (SIS) and the sensory neurone of the crayfish stretch receptor. The effects of several physiological variables on intracellular NH4+ measurements were tested in vitro. Changes in the background K+ and Na+ concentrations, the ratio K+/Na+, pH, ionic strength, osmotic pressure and volume were examined. Phenomena specific for NH4ISMs, such as a positive potential shift, an undershoot and a difference between pre-and postcalibration curves are described and discussed. We propose to consider the values of intracellular NH4+ concentration as apparent. The detection limit of the NH4ISM is closely related to background K+ concentration. It is in the region of 0.1mmoll-1 NH4+ in NAS (at 5.4mmoll-1 K+) and about 5 mmol l-1 in SIS (at 194 mmol l-1 K+). When comparing levels of intracellular NH4+, either measured directly by NH4ISM or calculated, according to Boron and de Weer (J. gen. Physiol. 67, 91–112), from simultaneously recorded pHi, we found that [NH4+] i obtained by direct measurement differed quantitatively from that of the Boron and de Weer model, but that some of the qualitative and temporal aspects of the model agreed with our results. The quantitative difference in [NH4+]i determined by the two methods cannot be attributed to temporal and/or quantitative limitations of the NH4ISM.
An X-Ray Study of the Influence of Vasoactive Intestinal Polypeptide and Substance p on the Secretion of gas Into the Swimbladder of a Teleost Gadus Morhua
Authors: Lundin Kersti , Holmgren Susanne
Published: April 2021

The rate of gas secretion into the swimbladder of the Atlantic cod Gadus tnorhua was studied with X-ray measurements of swimbladder size. A direct correlation was found between the area of the swimbladder in the X-ray photographs and the volume of the swimbladder. Removal of the swimbladder gas stimulates the fish to produce new gas, and the mean rate of refilling of the swimbladder in the cod was found to be 1.5 ml kg-1 h-1 during the first 24 h. The influence of drugs and of vagotomy on the rate of filling was measured. Gas secretion was completely inhibited by vagotomy and partly inhibited by injections of atropine or porcine vasoactive intestinal polypeptide (VIP). Substance P and VIP both increased the rate of secretion in atropinized fish, while 5-hydroxytryptamine (5-HT) and noradrenaline did not affect the rate of filling in either control or atropinized fish. Carbachol, VIP and substance P did not induce secretion in vagotomized fish, indicating that certain other fibres in the vagus might be necessary for gas secretion. It is concluded that a VIP-like and a substance-P-like peptide might be involved in the control of the secretion of gas in the cod swimbladder, VIP by a neuronal mechanism and substance P by a neuronal and/or humoral mechanism.
Adrenergic Inhibition of Carbon Dioxide Excretion by Trout Red Blood Cells In Vitro is Mediated by Activation of Na+/H+ Exchange
Authors: Perry S. F. , Wood C. M. , Thomas S. , Walsh P. J.
Published: April 2021

We have used a sensitive new technique to assess the mechanism(s) of adrenergic inhibition of rainbow trout (Oncorhynchus mykiss) red blood cell (RBC) carbon dioxide excretion in vitro. The effect was only apparent using blood acidified to simulate metabolic acidosis. Red blood cell CO2 excretion was inhibited in a dose-dependent manner by physiologically relevant concentrations of noradrenaline (10– 1000 nmol l−1) or adrenaline (100– 1000 nmol l−1). The β -adrenoceptor antagonist propranolol abolished the inhibitory effect of noradrenaline, whereas the ir-adrenoceptor antagonist phentolamine was without effect. The action of noradrenaline on RBC CO2 excretion was mimicked by the β-adrenoceptor agonist isoproterenol, but not by the α-adrenoceptor agonist phenylephrine. Therefore, adrenergic inhibition of CO2 excretion is mediated by RBC β -adrenoceptors, presumably of the β1 subtype. The Na+/H+ exchange inhibitor amiloride effectively blocked adrenergic stimulation of Na+/H+ exchange (as indicated from measurements of pHe and RBC pHi) and entirely prevented the inhibition of CO2 excretion. Noradrenaline significantly reduced the rate of CO2 excretion even in the presence of the C1−/HCO3− exchange inhibitor SITS. Therefore, adrenergic inhibition of CO2 excretion is accomplished via activation of RBC Na+/H+ exchange rather than by a direct inhibition of CC/ HCO3− exchange. The observed relationship between CO2 excretion rates and the RBC transmembrane pH difference (pHe —pHi) and the occurrence of the inhibition only at low pHe provide further evidence of the linkage with RBC Na+/H+ exchange. We suggest that adrenergic activation of RBC Na+/H+ exchange impedes CO2 excretion by causing a rise in intracellular HCO3−levels concurrent with a reduction of intracellular . The net result is a reduced gradient for HCO3− entry into the RBC in conjunction with a diminution of the outwardly directed gradient. Thus, the rate of formation of CO2 from the dehydration of plasma HCO3− is reduced and, in turn, a portion of this CO2 is not excreted but recycled through the red blood cell.