bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of Ionic Currents by Synaptic Action and 5-Ht Application in the Identified Heart Excitatory Neurone of the African Giant Snail, Achatina Fulica Férussac
Authors: Furukawa Yasuo , Kobayashi Makoto 
Published: April 2021

ABSTRACT
In the African giant snail, Achatina fulica Férussac, the ionic mechanisms underlying slow depolarization of a heart excitatory neurone, PON, induced by the activity of two cerebral ganglionic neurones, d-RCDN and d-LCDN, were investigated under voltage-clamp.
The slow depolarization of PON that was induced by the activity of the cerebral neurones was blocked by the serotonin (5-HT) antagonist, methysergide. Bath application of 5-HT to the axotomized PON produced a similar slow depolarization, which was also blocked by methysergide. These results suggest that the neurotransmitter of d-RCDN and d-LCDN is 5-HT.
Under voltage-clamp, activity of the cerebral neurones usually produced an inward shift in the holding current of PON with a decrease of conductance. Ionic substitution experiments and injection of Cs+ into PON showed that the response was mainly due to a decrease in K+ conductance. In some cases, this inward shift showed two components: an early component with increased conductance and a late one with decreased conductance. The early component was not decreased by Cs+ injection but was augmented by EGTA injection into PON, which may suggest the involvement of a Ca2+ conductance in this synaptic response.
Application of 5-HT produced a similar inward shift in holding current which was also mainly the result of a decrease in the background K+ current. 5-HT was also found to increase the voltage-dependent Ca2+ current and the inward rectifying K+ current.
The significance of these results is discussed in relation to the heart regulation of this snail.
Visually Guided Chases in Polyphemus Pediculus
Authors: Young Stephen , Taylor Victoria A. 
Published: April 2021

ABSTRACT
Polyphemus chases were video-recorded in a laboratory tank, and the positions and orientations of the chaser and target were digitized at 100-ms intervals. Analysis of the resulting track reveals three main phases: chaser pauses, shadowing prey at a constant distance, and rapid leaps onto prey. Chases do not all end in contact – they are sometimes terminated by the chaser peeling off. Pauses are triggered by rapid image expansions, and persist for as long as the image continues to expand. The shadowing phase includes intermittent sudden forward movements, which could provide visual information about the absolute size of the prey, using a triangulation method. Chasers are successful in avoiding contact with very large and very small prey.
Chasing with a Model Eye
Authors: Young Stephen 
Published: April 2021

ABSTRACT
A simulation model for Polyphemus eye movements was based on an openloop saccadic control system, derived from previous observations of eye movements in response to sinusoidally oscillating targets. The model was checked against new observations of Polyphemus eye movements in response to erratically moving targets. It was used to predict eye movements in response to stimulus patterns deduced from an analysis of video-recordings of Polyphemus chases. The results show that the system is limited to tracking slow target movements, but that this is consistent with observed chasing behaviour.
Switch From Metabolic to Ventilatory Compensation of Extracellular pH in Crayfish
Authors: Burtin B. , Massabuau J.-C. 
Published: April 2021

ABSTRACT
The mechanisms of extracellular pH regulation were studied in crayfish Astacus leptodactylus under conditions that were either favourable or unfavourable for ionoregulation. Animals in intermoult or premoult stages were kept in normoxic artificial waters at 13°C. In intermoult, acid–base balance (ABB) and ionoregulatory disturbances were induced by increasing the ambient partial pressure of CO2, by decreasing the concentration of NaCl in the water ([NaCl]w) or by associating both changes. In premoult we took advantage of the spontaneously occurring endogenous problems of ionoregulation which are linked to shell shedding.
In intermoult, an increase of , alone induced a hypercapnic acidosis compensated by metabolic means, whereas in association with a decrease of [NaCl]w (which induced a decrease of [NaCl] in the haemolymph) it led to a ventilatory compensation. In intermoult a decrease of [NaCl]w alone induced a metabolic acidosis that was compensated by metabolic means, whereas in premoult it was compensated by ventilatory adjustments.
It is concluded that when water breathers are facing experimentally induced or spontaneous ionoregulatory problems, compensation for superimposed ABB disturbances can be made by ventilatory adjustments instead of by metabolic means.
Time Course of the Establishment of Uterine Seawater Conditions in Late-Term Pregnant Spiny Dogfish (Squalus Acanthias)
Authors: Kormanik Gregg A. 
Published: April 2021

ABSTRACT
The gestation period for embryos of the spiny dogfish, Squalus acanthias (L.) lasts for nearly 2 years. During the latter part of this period the pups remain in the uterus and the fluid surrounding the embryos resembles sea water with respect to the major ions, but is low in pH (approx. 6), high in partial pressure of carbon dioxide (approx. 3 mmHg; 1 mmHg = 133·3 Pa), low in total carbon dioxide content (approx. 0·2 mmol 1−1), and may have a total ammonia concentration of up to 22 mmol l−1. Thus the conditions under which the pups complete their development in utero is quite remarkable.
The derivation of these conditions was examined in late-term pregnant females, from whose uterine horns the pups had been removed, by monitoring changes that occurred in instilled uterine sea water. The mother is responsible for reducing the pH, reducing the total carbon dioxide content and elevating the partial pressure of carbon dioxide to the levels observed in fresh-caught females, in less than 24h. The ammonia concentration is also elevated, but this takes rather longer. The decreased pH is responsible for the accumulation of ammonia in the uterine sea water, and it also serves to protect the pups from the toxic effects of NH3, by converting it to the relatively non-toxic ionic form, NH4+. The reasons for the establishment of these uterine seawater conditions are still not evident.
Effect of Adrenaline and Blood Gas Conditions on Red Cell Volume and Intra-Erythrocytic Electrolytes in the Carp, Cyprinus Carpio
Authors: Fuchs D. A. , Albers C. 
Published: April 2021

ABSTRACT
Carp, when subjected to air stress in vivo, developed a hypoxaemia associated with an acidosis due to elevation of and arterial lactate content. Adrenaline and noradrenaline levels rose markedly, and the mean corpuscular haemoglobin concentration (MCHC in mmol Hb l−1 red blood cells) decreased, indicating swelling of the erythrocytes. No effect of adrenaline could be observed in vitro after equilibration at normal pH and oxygenation level. Simulation of air stress in vitro, by using hypercapnic hypoxia together with adrenaline, caused appreciable swelling of the red cells. The effect of adrenaline could be blocked by propranolol and was reversible when the blood gases were readjusted to normal values. Swelling due to hypercapnic hypoxia was not affected by propranolol. At normal , lowering pH by increasing or adding HC1 to the blood at (l mmHg = 133·3 Pa) both led to swelling of red cells; further swelling occurred when adrenaline was added. At normal or even elevated intracellular pH, hypoxia led to red cell swelling; further swelling occurred when adrenaline was added. The swelling of red cells under hypoxic and/or acidotic conditions (induced by either added HC1 or increased ) was associated with an increase in the intracellular K+, Na+ and Cl− levels, together with an increase in the Donnan distribution ratio of Cl−, rCl. ΔK+: ΔNa+ was 4:1. The swelling associated with the addition of adrenaline was also accompanied by an increase in K+, Na+, Cl− aud rCl. In this case the ratio ΔK+: ΔNa+ was 1:2.4. There was a correlation between the Donnan ratio, rCl, and the change in MCHC, even in those cases where extracellular and intracellular pH were above normal. In addition to pH and oxygen saturation, rCl should therefore be considered as a possible triggering factor for the action of adrenaline. In addition to the increased catecholamine levels, stress during sampling may be inferred if low values of MCHC and high values of intraerythrocytic chloride and a high chloride distribution ratio, rCl, are found in whole blood.
The Rapid Tail Withdrawal Reflex of the Tubificid Worm, Branchiura Sowerbyi
Authors: Zoran Mark J. , Drewes Charles D. 
Published: April 2021

ABSTRACT
The rapid tail withdrawal of the tubificid worm, Branchiura sowerbyi, was studied using correlated electrophysiological and behavioural analyses. The minimal response latency (i.e. time from onset of mechanical stimulus to onset of withdrawal) was approximately 7 ms, faster than the escape responses of any previously studied invertebrate. Factors contributing to the speed and efficacy of this response include: (1) a sensitive mechanosensory system for detecting potential prey, (2) a short latency for excitation along afferent and efferent pathways, (3) a rapid intersegmental conduction of lateral giant fibre spikes, (4) a short coupling time from muscle excitation to the onset of shortening, and (5) the requirement of only a single lateral giant fibre spike for a complete (all-or-none) response. Videotaped sequences of predator-prey interactions showed that such reflex speed permits effective escape from the strike of the bluegill (Lepomis macrochirus)
Protein Synthesis in a Fish Heart: Responses to Increased Power Output
Authors: Houlihan D. F. , Agnisola C. , Lyndon A. R. , Gray C. , Hamilton N. M. 
Published: April 2021

ABSTRACT
The effects of exercise on the rates of protein synthesis in the chambers of the trout heart were investigated in vitro and in vivo. An in vitro rainbow trout heart preparation was developed which permitted perfusion of the coronary supply to the compact region of the ventricular muscle. This preparation was used to examine the mechanical responses to preload pressures, the oxygen consumption at different power outputs and the rates of protein synthesis in the various heart components. By increasing preload pressure it was possible to double cardiac output, oxygen consumption and power output without changing heart rate. Mechanical efficiency of the hearts was approximately 20%. Perfusion of the coronary vessels improved cardiac output. Protein synthesis was measured in isolated hearts by the incorporation of [3H]phenylalanine added at high concentration (1·35 mmol l−1) to the perfusion medium. The various chambers of the heart showed marked differences in their rates of protein synthesis. Increasing cardiac output and power output in vitro by twofold over 20 min increased the fractional rate of protein synthesis by approximately 2·5-fold in the atrium and ventricle but did not affect the rates in the bulbus arteriosus. Perfusion of the coronary vessels significantly increased the rates of protein synthesis of the compact layer of the ventricle. In vivo there were no significant differences in the fractional protein synthesis rates between the atrium and ventricle; slow-speed continuous swimming over 40 min (1·5 body lengths s−1) caused an increase in the rates of protein synthesis in all the chambers except the bulbus arteriosus. The stimulation in the fractional rates of protein synthesis by approximately 32% was not as great as in vitro. Both in vivo and in vitro the increased rates of protein synthesis occurred without any change in RNA to protein ratios, indicating an improved activity of protein synthesis per unit of RNA. It is concluded that shortterm increases in cardiac contractility, possibly acting through the mechanical stretch on the cardiac muscle, stimulated protein synthesis, particularly in the ventricle, through increased ribosomal activity.
Water Depth Alters Respiratory Behaviour of Xenopus Laevis
Authors: Shannon Patrick , Kramer Donald L. 
Published: April 2021

ABSTRACT
Most studies of the control of air breathing in bimodally respiring aquatic animals neglect the influence of depth of dive. However, changes in respiratory patterns with depth may be expected on a number of grounds. Increased hydrostatic pressure will alter gas tensions in the lungs or accessory respiratory organs and may therefore increase the rate and degree of oxygen uptake (Butler & Jones, 1982). Changes in buoyancy may affect swimming energetics (Wassersug & Feder, 1983) or induce a compensatory rise in the amount of gas held during the dive (Graham, Gee, Motta & Rubinoff, 1987). The increased energetic cost of surfacing associated with greater distance may increase oxygen demand (Pandian & Vivekanandan, 1976). Finally, theories of optimal foraging applied to breathing suggest that animals diving to greater depths should load more oxygen at each trip to the surface, stay submerged longer, and increase reliance on dissolved oxygen (Kramer, 1988). Empirical evidence for effects of water depth on air breathing in fish and tadpoles is briefly reviewed by Bevan & Kramer (1987).
Lophotoxin Blocks Synaptic Acetylcholine Receptors in the Cockroach Periplaneta Americana
Authors: Blagburn Jonathan M. , Sattelle David B 
Published: April 2021

ABSTRACT
The actions of lophotoxin on synaptic acetylcholine receptors were investigated, using the cholinergic synapse between the lateral filiform hair sensory neurone and giant interneurone 3 in the first-instar cockroach Periplaneta americana. Lophotoxin (1·0×10−6mol l−1) blocked transmission without affecting the passive or active membrane properties of the pre- and postsynaptic neurones, and without affecting non-cholinergic synaptic inputs. Micromolar concentrations of lophotoxin also blocked the depolarizing response of giant interneurone 3 to carbamylcholine, when applied ionophoretically to its dendritic branches. The toxin shifted the dose-response curve to the right by two orders of magnitude, suggesting that it was acting as a competitive antagonist.
In vivo Analysis of Partitioning of Cardiac Output Between Systemic and Central Venous Sinus Circuits In Rainbow Trout: A New Approach Using Chronic Cannulation of the Branchial Vein
Authors: Ishimatsu Atsushi , Iwama George K. , Heisler Norbert 
Published: April 2021

ABSTRACT
Freshwater-acclimated rainbow trout were chronically and non-occlusively cannulated in the dorsal aorta (DA), sinus venosus (SV) and branchial vein (BV), the latter returning the blood perfusing the central venous sinus (CVS) of the gill after being shunted away from the systemic circuit. After recovery, blood samples from these three sites were analysed for haematocrit (Het) and [Hb]. Branchial venous blood was found to have considerably lower Hct and [Hb] (Het = 3·5 ± 3·1%; [Hb] = 1·04 ± 0·75g 100 ml−1) than systemic blood (DA: Hct = 24·3 ± 8·9%, [Hb] = 6·54 ± 2·90 g 100 ml−1; SV: Hct = 23·1 ± 8·8%, [Hb] = 6·15 ±2·55 g 100 ml−1; means ±S.D. N = 8), which strongly suggests that plasma skimming occurred at arteriovenous anastomoses and arterioles draining into the CVS. The partitioning of cardiac output, calculated on the basis of the [Hb] data, showed that the systemic flow accounted for 93 ± 4·6% (N = 7) of the total cardiac output with only 7 ± 4·7% of cardiac output being diverted into the CVS, thus bypassing the systemic vasculature. Previous results using in vitro experiments are compared with the present data in an evaluation of the usefulness of the isolated perfused gill and head preparations in the experimental analysis of circulatory physiology in fish gills.
Intracellular Calcium Translocation: Mechanism of Activation by Guanine Nucleotides and Inositol Phosphates
Authors: Gill Donald L. , Mullaney Julienne M. , Ghosh Tarun K. 
Published: April 2021

ABSTRACT
The movements of Ca2+ within cells in response to external stimuli are complex. Internal Ca2+ release activated by inositol 1,4,5-trisphosphate (InsP3) is now widely established. However, the mechanism of InsP3-induced Ca2+ release, the identity and control of the InsP3-sensitive Ca2+ pool and its relationship to other internal and external Ca2+ pools all remain uncertain. We have characterized a highly sensitive and specific guanine nucleotide-regulatory mechanism that induces rapid and profound movements of intracellular Ca2+via a mechanism distinct from that activated by InsP3. Using permeabilized neural or smooth muscle cells, application of submicromolar concentrations of GTP induces rapid release of Ca2+ from a compartment that contains within it the InsP3-releasable Ca2+ pool. Although of similar GTP-sensitivity as G-protein-activated events, the apparent dependence on GTP hydrolysis and blockade by GTPγS suggest a mechanism distinct from those mediated by known G-proteins. Recent experiments in the presence of oxalate reveal rapid and profound GTP-activated uptake of Ca2+via a mechanism with identical nucleotide sensitivity and specificity to GTP-induced Ca2+ release. These results were interpreted to suggest that GTP induces a transmembrane conveyance of Ca2+ between different compartments distinguished by oxalate permeability; GTP-induced release probably occurs via a similar mechanism except involving transfer between closed compartments and nonclosed membranes (perhaps the plasma membrane). Recently, it has been revealed that GTP activates a translocation of Ca2+ into the Ca2+ pool from which InsP3 induces release. This is an important observation suggesting that the GTP-activated Ca2+ translocation process may control entry into and hence the size of the InsP3-releasable Ca2+ pool. Indeed, it is possible that GTP-induced Ca2+ release observed in permeabilized cells reflects a reversal of the pathway that functions in intact cells to permit external Ca2+ entry into the InsP3-releasable pool. This type of process could mediate the longer-term secretory or excitatory responses to external receptors which are known to be dependent on external Ca2+.
The Somatotrope: an Endocrine Cell With Functional Calcium Transients
Authors: Thorner Michael O. , Holl Reinhard W. , Leong Denis A. 
Published: April 2021

ABSTRACT
Growth hormone (GH) secretion by the somatotrope is under dual regulation by the hypothalamic peptides, somatostatin (SS) and GH-releasing hormone (GHRH). Cytosolic free calcium concentration and cumulative GH release were measured simultaneously in anterior pituitary cells from adult male rats. This was made possible using a combination of digital imaging video microscopy with the fluorescent calcium indicator Fura-2 and the reverse haemolytic plaque assay (RHPA) to identify the cell type and measure hormone secretion from the cells under study. This technique allows calcium measurements to be made at very short time intervals (&lt;150 ms) in single cells. Spontaneous calcium transients were demonstrated in 85% of GH plaque-forming cells. These occurred at a frequency of 2–13 min−1 and had an amplitude of 50–500 nmol l−1. The somatotropes with the largest calcium fluctuations produced the largest plaques; thus, the calcium transients appeared to correlate with hormone release. Since the somatotrope alone shows these fluctuations, the mean intracellular calcium concentration is 238 ±18 nmol l−1 in somatotropes and 113±8nmoll−1 in non-somatotropes. Upon exposure to SS (1 nmol l−1) intracellular calcium fell from 200–250 nmol I−1 to 50–100 nmol l−1 with an apparent reduction in oscillations. Withdrawal of SS increased the intracellular calcium level. GHRH increased intracellular calcium but 10nmoll−1 GHRH given simultaneously with Inmoll−1 SS reduced intracellular calcium to that level observed during SS alone. Thus, the SS effect on intracellular calcium predominates. The effects of SS can be mimicked by removal of extracellular calcium, or by the addition of CoCl2 (2 nmol l−1) or by verapamil (lOOfzmol l−1), two agents which block calcium channels.
The hormone secretion index (indicated by the area of the plaque formed in RHPA) enables us to demonstrate that GHRH in this system increases GH secretion, and SS inhibits it. In combination, GHRH and SS oppose one another.
Spontaneous calcium oscillations are characteristic for normal somatotropes. These oscillations are related to spontaneous hormone secretion and due to influx of calcium through ion channels in the membrane. Intracellular signalling information may be encoded in both frequency and amplitude of calcium oscillations. The actions of GHRH and SS on regulation of GH secretion are proposed to be mediated, at least in part, by regulation of intracellular cytosolic free calcium. This modulation is dependent on extracellular calcium concentrations. We are now investigating the molecular mechanisms involved in this process.
Optical Studies of the Secretory Event at Vertebrate Nerve Terminals
Authors: Salzberg Brian M. , Obaid Ana Lia 
Published: April 2021

ABSTRACT
Potentiometric probes are small (300–500 Mr) amphipathic molecules that bind to, but do not cross, cell membranes and behave as fast linear transducers of membrane voltage. Their optical properties, particularly absorbance and fluorescence, respond to changes in potential in less than 2μs, and they may be used to follow electrical events in membranes which are inaccessible to microelectrodes. We have used these dyes to study the properties of the action potential in the neurosecretory terminals of vertebrate neurohypophyses and, in particular, to investigate the behaviour of the local population of calcium channels. These channels are sensitive to the peptide toxin ω-conotoxin GV1A, derived from the venom of the marine snail Conus geographicus, but insensitive to dihydropyridine channel modulators. In the neurohypophysis of the mouse, it is possible to demonstrate that the calcium channels that are blocked by ω-conotoxin are those that are required for secretion of peptide hormones.
In the terminals of the neurohypophysis, excitation is coupled to secretion, and the secretory event is accompanied by large and rapid changes in light scattering. These intrinsic optical signals provide a millisecond time-resolved monitor of events in the terminal that follow the entry of calcium, and may precede the release of hormones. We will consider how the changes in light scattering can be related to secretion, and how the extrinsic (absorption) and intrinsic optical signals may provide complementary information about excitation-secretion coupling.