bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cardiovascular Effects of Hypercarbia in Rainbow Trout (Oncorhynchus Mykiss): A Role for Externally Oriented Chemoreceptors
Authors: Mckendry J. E. , Perry S. F. 
Published: April 2021

ABSTRACT
In situ and in vivo experiments were performed on rainbow trout (Oncorhynchus mykiss) to examine (i) the direct effect of CO2 on the systemic vasculature and (ii) the influence of internal versus external hypercapnic acidosis on cardiovascular variables including blood pressure, cardiac output and systemic vascular resistance. Results from in situ saline-perfused trunk preparations indicated that CO2 (0.6, 1.0 or 2.0 % CO2) elicited a significant vasodilation, but only in the presence of pre-existing humoral adrenergic tone. In the absence of pre-existing vascular tone, CO2 was without effect on systemic resistance. In contrast, hypercarbia in vivo triggered a statistically significant increase in systemic resistance (approximately 70 %) that was associated with elevated ventral aortic (approximately 42 %) and dorsal aortic (approximately 43 %) blood pressures and with a significant bradycardia (approximately 12 %); cardiac output was not significantly affected.
To determine the potential roles of internal versus external chemoreceptors in mediating the cardiovascular responses to hypercarbia, experiments were performed to elevate the endogenous arterial partial pressure of CO2 without an accompanying increase in external . In one series, trout were given a bolus injection of the carbonic anhydrase inhibitor acetazolamide (30 mg kg−1) to inhibit CO2 excretion, and thus raise , 5–7 h prior to being exposed to an acute increase in (maximum =6.3±0.4mmHg; 1mmHg=0.133 kPa). Despite a marked increase in (approximately 7 mmHg) after injection of acetazolamide, there was no increase in dorsal aortic blood pressure (PDA) or systemic resistance (RS). The ensuing exposure to hypercarbia, however, significantly increased PDA (by approximately 20 %) and RS (by approximately 35 %). A second series of experiments used a 5–7 h period of exposure to hyperoxia to establish a new, elevated baseline (7.8±1.1 mmHg) without any change in . Despite a steadily increasing during the 5–7 h of hyperoxia, there was no associated increase in PDA or RS. Ensuing exposure to hypercarbia, however, significantly increased PDA (by approximately 20 %) and RS (by approximately 150 %). Plasma adrenaline levels were increased significantly during exposure to hypercarbia and, therefore, probably contributed to the accompanying cardiovascular effects.
These findings demonstrate that the cardiovascular effects associated with hypercarbia in rainbow trout are unrelated to any direct constrictory effects of CO2 on the systemic vasculature and are unlikely to be triggered by activation of internally oriented receptors. Instead, the data suggest that the cardiovascular responses associated with hypercarbia are mediated exclusively by externally oriented chemoreceptors.
Intrinsic Noise at Synapses Between a Wing Hinge Stretch Receptor and Flight Motor Neurons in the Locust
Authors: Simmons Peter J. 
Published: April 2021

ABSTRACT
Variability in postsynaptic potential (PSP) amplitude due to intrinsic noise limits the reliability of communication between neurons. I measured PSP variability at synapses between a forewing stretch receptor and wing depressor motor neurons in locusts, a pathway that is important in the control of flying. The intrinsic noise in the stretch receptor output synapse was measured by subtracting the background noise, originating in other synaptic pathways onto the motor neuron, from the variability in the amplitudes of PSPs evoked by the stretch receptor. Intrinsic synaptic noise caused successive PSPs to vary by 4–10 % in basalar and subalar flight motor neurons. Recordings from pairs of these wing depressor motor neurons showed that the amount of transmitter released varied independently between different output sites from the stretch receptor. Histograms of excitatory postsynaptic potential amplitude were normal distributions that lacked separate peaks. I estimate that quantal amplitude is significantly less than 0.1 mV and that several hundred quanta are released for each presynaptic spike. This accords well with a previous estimate of the number of discrete anatomical synapses and would facilitate modulation of output from the stretch receptor.
Limits to human performance: elevated risks on high mountains
Authors: Huey Raymond B. , Eguskitza Xavier 
Published: April 2021

SUMMARY
In 1950, Maurice Herzog and Louis Lachenal became the first climbers to reach the summit of an 8000m peak (Annapurna, 8091m). In the half century since that pioneering climb, mountaineers have increasingly sought to climb the fourteen ‘8K peaks’ of the Himalayas and Karakoram, with remarkable success; they have made 5085 ascents of those peaks up to the year 2000. While seeking adventure on those great peaks, mountaineers are inevitably exposed to hypoxia, cold and dehydration as well as to the physical hazards of climbing. Those few mountaineers who successfully summit an 8K peak are likely to be at or near their physiological limits and probably confront an elevated probability of dying during their descent. We will briefly review some of the physiological challenges climbers face at extreme elevation and then compare success rates and death rates on mountains of different heights (Rainer, Foraker, Denali, K2, Everest). Success rates decline with summit height, but overall death rates and death rates during descent from the summit increase with summit height. Although these patterns are based on non-experimental and uncontrolled data, our findings are consistent with the hypothesis that increasing altitude is associated with decreased success and with increased risk of death.
The high-altitude brain
Authors: Hornbein Thomas F. 
Published: April 2021

SUMMARY
The highest place on our planet, Mount Everest (8850m), appears to be close to the limit of how high an acclimatized human can go, albeit slowly. In this paper, I will explore the possibility that what limits human performance at such extreme degrees of hypoxia is the availability of oxygen to the brain. Also, one of the known costs of such extreme exposure is residual mild impairment of performance on neuropsychometric tests after return to sea level, implying injury to brain cells. That such injury could occur in the absence of any overt impairment of function, much less without loss of consciousness, is unexpected. I will speculate about physiological mechanisms that might cause or contribute to both decrements in real-time performance while at altitude and residual deficits for a time after return to low elevations; the effects of hypoxia on brain cells are an even greater puzzle at the present time.
Frontiers of hypoxia research: acute mountain sickness
Authors: Roach Robert C. , Hackett Peter H. 
Published: April 2021

SUMMARYTraditionally, scientists and clinicians have explored peripheral physiological responses to acute hypoxia to explain the pathophysiological processes that lead to acute mountain sickness (AMS) and high-altitude cerebral edema (HACE). After more than 100 years of investigation, little is yet known about the fundamental causes of the headache and nausea that are the main symptoms of AMS. Thus, we review the evidence supporting a change in focus to the role of the central nervous system in AMS. Our justification is (i) that the symptoms of AMS and HACE are largely neurological, (ii) that HACE is considered to be the end-stage of severe AMS and was recently identified as a vasogenic edema, opening the door for a role for blood–brain barrier permeability in AMS, (iii) that new, non-invasive techniques make measurement of brain water levels and cerebral blood volume possible and (iv) that the available experimental evidence and theoretical arguments support a significant role for brain swelling in the pathophysiology of AMS. We believe that an examination of the responses of the central nervous system to acute hypoxia will reveal important new pathophysiological processes that may help explain AMS and HACE.
Limits to sustainable muscle performance: interaction between glycolysis and oxidative phosphorylation
Authors: Conley Kevin E. , Kemper William F. , Crowther Gregory J. 
Published: April 2021

SUMMARYThis paper proposes a mechanism responsible for setting the sustainable level of muscle performance. Our contentions are that the sustainable work rate is determined (i) at the muscle level, (ii) by the ability to maintain ATP supply and (iii) by the products of glycolysis that may inhibit the signal for oxidative phosphorylation. We argue below that no single factor ‘limits’ sustainable performance, but rather that the flux through and the interaction between glycolysis and oxidative phosphorylation set the level of sustainable ATP supply. This argument is based on magnetic resonance spectroscopy measurements of the sources and sinks for energy in vivo in human muscle and rattlesnake tailshaker muscle during sustained contractions. These measurements show that glycolysis provides between 20% (human muscle) and 40% (tailshaker muscle) of the ATP supply during sustained contractions in these muscles. We cite evidence showing that this high glycolytic flux does not reflect an O2 limitation or mitochondria operating at their capacity. Instead, this flux reflects a pathway independent of oxidative phosphorylation for ATP supply during aerobic exercise. The consequence of this high glycolytic flux is accumulation of H+, which we argue inhibits the rise in the signal activating oxidative phosphorylation, thereby restricting oxidative ATP supply to below the oxidative capacity. Thus, both glycolysis and oxidative phosphorylation play important roles in setting the highest steady-state ATP synthesis flux and thereby determine the sustainable level of work by exercising muscle.
Fluid volume control during short-term space flight and implications for human performance
Authors: Watenpaugh Donald E. 
Published: April 2021

SUMMARYSpace flight exerts substantial effects on fluid volume control in humans. Cardiac distension occurs during the first 1–2 days of space flight relative to supine and especially upright 1g conditions. Plasma volume contraction occurs quickly in microgravity, probably as a result of transcapillary fluid filtration into upper-body interstitial spaces. No natriuresis or diuresis has been observed in microgravity, such that diuresis cannot explain microgravity-induced hypovolemia. Reduction of fluid intake occurs irrespective of space motion sickness and leads to hypovolemia. The fourfold elevation of urinary antidiuretic hormone (ADH) levels on flight day 1 probably results from acceleration exposures and other stresses of launch. Nevertheless, it is fascinating that elevated ADH levels and reduced fluid intake occur simultaneously early in flight. Extracellular fluid volume decreases by 10–15% in microgravity, and intracellular fluid volume appears to increase. Total red blood cell mass decreases by approximately 10% within 1 week in space. Inflight Na+ and volume excretory responses to saline infusion are approximately half those seen in pre-flight supine conditions. Fluid volume acclimation to microgravity sets the central circulation to homeostatic conditions similar to those found in an upright sitting posture on Earth. Fluid loss in space contributes to reduced exercise performance upon return to 1g, although not necessarily in flight. In-flight exercise training may help prevent microgravity-induced losses of fluid and, therefore, preserve the capacity for upright exercise post-flight. Protection of orthostatic tolerance during space flight probably requires stimulation of orthostatic blood pressure control systems in addition to fluid maintenance or replacement.
Limits to human locomotor performance: phylogenetic origins and comparative perspectives
Authors: Dudley Robert 
Published: April 2021

SUMMARYStudies of human exercise physiology have been conducted from a largely ahistorical perspective. This approach usefully elucidates proximate limits to locomotor performance, but ignores potential sources of biomechanical and physiological variation that derive from adaptation to ancestral environments. Phylogenetic reconstruction suggests that multiple hominoid lineages, including that leading to Homo sapiens, evolved in African highlands at altitudes of 1000–2000m. The evolution of human locomotor physiology therefore occurred under conditions of hypobaric hypoxia. In contrast to present-day humans running on treadmills or exercising in otherwise rectilinear trajectories, ancestral patterns of hominid locomotion probably involved intermittent knuckle-walking over variable terrain, occasional bouts of arboreality and an evolving capacity for bipedalism. All such factors represent potential axes of locomotor variation at present unstudied in extant hominoid taxa. As with humans, hummingbirds evolved in mid-montane contexts but pose an extreme contrast with respect to body size, locomotor mode and metabolic capacity. Substantial biomechanical and physiological challenges are associated with flight in hypobaria. Nonetheless, hummingbird lineages demonstrate a progressive invasion of higher elevations and a remarkable tolerance to hypoxia during hovering. Upregulation of aerobic capacity and parallel resistance to hypoxia may represent coupled evolutionary adaptations to flight under high-altitude conditions.
Behavioural, Physiological and Metabolic Responses to Long-Term Starvation and Refeeding in a Blind Cave-Dwelling (Proteus Anguinus) and a Surface-Dwelling (Euproctus Asper) Salamander
Authors: Hervant Frédéric , Mathieu Jacques , Durand Jacques 
Published: April 2021

ABSTRACT
The effects of long-term starvation and subsequent refeeding on haematological variables, behaviour, rates of oxygen consumption and intermediary and energy metabolism were studied in morphologically similar surface-and cave-dwelling salamanders. To provide a hypothetical general model representing the responses of amphibians to food stress, a sequential energy strategy has been proposed, suggesting that four successive phases (termed stress, transition, adaptation and recovery) can be distinguished. The metabolic response to prolonged food deprivation was monophasic in the epigean Euproctus asper (Salamandridae), showing an immediate, linear and large decrease in all the energy reserves. In contrast, the hypogean Proteus anguinus (Proteidae) displayed successive periods of glucidic, lipidic and finally lipido-proteic-dominant catabolism during the course of food deprivation. The remarkable resistance to long-term fasting and the very quick recovery from nutritional stress of this cave organism may be explained partly by its ability to remain in an extremely prolonged state of protein sparing and temporary torpor. Proteus anguinus had reduced metabolic and activity rates (considerably lower than those of most surface-dwelling amphibians). These results are interpreted as adaptations to a subterranean existence in which poor and discontinuous food supplies and/or intermittent hypoxia may occur for long periods. Therefore, P. anguinus appears to be a good example of a low-energy-system vertebrate.
How External Osmolarity affects the Activity of the Contractile Vacuole Complex, the Cytosolic Osmolarity and the Water Permeability of the Plasma Membrane in Paramecium Multimicronucleatum
Authors: Stock Christian , Allen Richard D. , Naitoh Yutaka 
Published: April 2021

ABSTRACT
The rate of fluid expulsion, RCVC, from the contractile vacuole complex (CVC) of Paramecium multimicronucleatum was estimated from the volume of the contractile vacuoles (CVs) immediately before the start of fluid discharge and from the time elapsing between discharges. The RCVC increased when the cell was exposed to a strongly hypotonic solution and decreased in a weakly hypotonic solution. When the cell was exposed to an isotonic or a hypertonic solution, RCVC fell to zero. The time constant, τ, used to describe the change in RCVC in response to a change in external osmolarity shortened after a short-term exposure to a strongly hypotonic solution and lengthened after a short-term exposure to a less hypotonic solution. A remarkable lengthening of τ occurred after a short-term exposure to isotonic or hypertonic solution. Under natural conditions, mechanisms for controlling RCVC are effective in maintaining the cytosolic osmolarity hypertonic within a narrow concentration range despite changes in the external osmolarity, which is normally hypotonic to the cytosol. Cells exposed to an isotonic or hypertonic solution resumed CV activity when left in the solution for 12 h. The cytosolic osmolarity was found to increase and to remain hypertonic to the external solution. This will permit cells to continue to acquire water. The increase in the cytosolic osmolarity occurred in a stepwise fashion, rather than linearly, as the external osmolarity increased. That is, the cytosolic osmolarity first remained more-or-less constant at an increased level until the external osmolarity exceeded this level. Thereupon, the cytosolic osmolarity increased to a new higher level in 12 h, so that the cytosol again became hypertonic to the external solution and the cells resumed CV activity. These results imply that the cell needs to maintain water segregation activity even after it has been exposed to an isotonic or hypertonic environment. This supports the idea that the CVC might be involved not only in the elimination of excess cytosolic water but also in the excretion of some metabolic waste substances.
The Novel Guanylyl Cyclase Msgc-I is Strongly Expressed in Higher-Order Neuropils in the Brain of Manduca Sexta
Authors: Nighorn A. , Simpson P. J. , Morton D. B. 
Published: April 2021

ABSTRACT
Guanylyl cyclases are usually characterized as being either soluble (sGCs) or receptor (rGCs). We have recently cloned a novel guanylyl cyclase, MsGC-I, from the developing nervous system of the hawkmoth Manduca sexta that cannot be classified as either an sGC or an rGC. MsGC-I shows highest sequence identity with receptor guanylyl cyclases throughout its catalytic and dimerization domains, but does not contain the ligand-binding, transmembrane or kinase-like domains characteristic of receptor guanylyl cyclases. In addition, MsGC-I contains a C-terminal extension of 149 amino acid residues. In this paper, we report the expression of MsGC-I in the adult. Northern blots show that it is expressed preferentially in the nervous system, with high levels in the pharate adult brain and antennae. In the antennae, immunohistochemical analyses show that it is expressed in the cell bodies and dendrites, but not axons, of olfactory receptor neurons. In the brain, it is expressed in a variety of sensory neuropils including the antennal and optic lobes. It is also expressed in structures involved in higher-order processing including the mushroom bodies and central complex. This complicated expression pattern suggests that this novel guanylyl cyclase plays an important role in mediating cyclic GMP levels in the nervous system of Manduca sexta.
Laboratory Selection at Different Temperatures Modifies Heat-Shock Transcription Factor (HSF) Activation in Drosophila Melanogaster
Authors: Lerman Daniel N. , Feder Martin E. 
Published: April 2021

ABSTRACT
The magnitude and time course of activation of the heat-shock transcription factor (HSF) differ among Drosophila melanogaster lines evolving at 18 °C, 25 °C or 28 °C for more than 20 years. At lower heat-shock temperatures (27–35 °C), flies from the 18 °C population had higher levels of activated HSF (as detected by an electrophoretic mobility shift assay) than those reared at 25 °C and 28 °C. At higher temperatures (36 and 37 °C), however, the 28 °C flies had the highest levels of HSF. These differences persisted after one generation of acclimation at 25 °C, suggesting that phenotypic plasticity was limited. In addition, larvae from the 28 °C lines activated HSF less rapidly after a 35 °C heat shock than those from the 18 °C and 25 °C populations. These results are similar but not identical to previously reported differences in expression of Hsp70 (the major heat-inducible stress protein in Drosophila melanogaster) among the experimental lines. We conclude that HSF activation evolves rapidly during laboratory culture at diverse temperatures and could play an important role in the evolution of the heat-shock response.
The Orienting Response of Lake Michigan Mottled Sculpin is Mediated by Canal Neuromasts
Authors: Coombs Sheryl , Braun Christopher B. , Donovan Brian 
Published: April 2021

ABSTRACT
Lake Michigan mottled sculpin, Cottus bairdi, exhibit a naturally occurring and unconditioned orienting response that can be triggered by both live prey and chemically inert vibrating spheres, even in blinded animals. CoCl2-induced reductions of the orienting response demonstrate that the lateral line is required for this behavior in the absence of non-mechanosensory cues (such as vision), but shed no light on the relative contributions of superficial and canal neuromasts to this behavior. To determine the relative roles of these two subsystems, we measured the frequency with which mottled sculpin oriented towards a small vibrating sphere before and after two treatments: (i) immersion of fish in a solution of gentamicin, an aminoglycoside antibiotic that damages hair cells in canal, but not superficial, neuromasts; and (ii) scraping the skin of the fish, which damages the superficial, but not the canal, neuromasts. To ensure that both superficial and canal neuromasts were adequately stimulated, we tested at different vibration frequencies (10 and 50 Hz) near or at the best frequency for each type of neuromast. At both test frequencies, response rates before treatment were greater than 70 % and were significantly greater than ‘spontaneous’ response frequencies measured in the absence of sphere vibration. Response rates fell to spontaneous levels after 1 day of gentamicin treatment and did not return to pre-treatment levels for 10–15 days. In contrast, response rates stayed approximately the same after superficial neuromasts had been damaged by skin abrasion. Scanning electron microscopy confirmed hair cell damage (loss of apical cilia) in canal, but not superficial, neuromasts of gentamicin-treated animals after as little as 24 h of treatment. The sensory epithelium of canal neuromasts gradually returned to normal, following a time course similar to behavioral loss and recovery of the orienting response, whereas that of superficial neuromasts appeared normal throughout the entire period. This study shows that the orienting response of the mottled sculpin is mediated by canal neuromasts.
Chloride Channels in Apical Membrane Patches of Stellate Cells of Malpighian Tubules of Aedes Aegypti
Authors: O’connor Kevin R. , Beyenbach Klaus W. 
Published: April 2021

ABSTRACT
Stellate cells of Aedes aegypti Malpighian tubules were investigated using patch-clamp methods to probe the route of transepithelial Cl− secretion. Two types of Cl− channel were identified in excised, inside-out apical membrane patches. The first Cl− channel, type I, had a conductance of 24 pS, an open probability of 0.816±0.067, an open time of 867±114 ms (mean ± S.E.M., four patches) and the selectivity sequence I−&gt;Cl−⪢isethionate&gt;gluconate. The I−/Cl− permeability ratio was 1.48, corresponding to Eisenman sequence I. The type I Cl− channel was blocked by 2,2′-iminodibenzoic acid (DPC) and niflumic acid {2-[3-(trifluoromethyl)anilo]nicotinic acid}. The removal of Ca2+ from the Ringer’s solution on the cytoplasmic side had no effect on channel activity. The second Cl− channel, type II, had a conductance of 8 pS, an open probability of 0.066±0.021 and an open time of 7.53±1.46 ms (mean ± S.E.M., four patches). The high density and halide selectivity sequence of the type I Cl− channel is consistent with a role in transepithelial Cl− secretion under control conditions, but it remains to be determined whether these Cl− channels also mediate transepithelial Cl− secretion under diuretic conditions in the presence of leucokinin.