bluuebunny/crossref_metadata_2025_split huggingface dataset:
Erythropoietin: a Model System for Studying Oxygen-Dependent Gene Regulation
Authors: Bunn H. Franklin , Gu Jie , Huang L. Eric , Park Jong-Wan , Zhu Hao 
Published: April 2021

ABSTRACT
The physiological regulation of the red cell mass depends upon enhanced transcription of the erythropoietin (Epo) gene in response to hypoxia. Studies of Epo gene expression have been useful in investigating the mechanism by which cells and tissues sense hypoxia and respond with biologically appropriate alterations in gene expression. It is likely that oxygen sensing involves a heme protein in which cobalt and nickel can substitute for iron in the porphyrin ring. Indirect evidence suggests that the sensor is present in all cells and is a multi-subunit assembly containing an NAD(P)H oxidase capable of generating peroxide and reactive oxygen intermediates, which serve as signaling molecules. The up-regulation of Epo gene transcription by hypoxia is mediated by at least two known DNA-binding transcription factors, hypoxia-inducible factor 1 (HIF-1) and hepatic nuclear factor 4 (HNF-4), which bind to cognate response elements in a critical 3´ enhancer approximately 50 bp in length. HIF-1 binding is induced by hypoxia as well as by cobalt. The activation of HIF-1 by hypoxia depends upon the selective protection of its α subunit from ubiquitin-dependent proteolysis by means of a mechanism that involves redox chemistry and perhaps phosphorylation. HNF-4 is an orphan nuclear receptor that is constitutively expressed in kidney and liver and which cooperates with HIF-1 to give maximal hypoxic induction. In hypoxic cells, p300 or a related family member forms a macromolecular assembly with HIF-1 and HNF-4, enabling transduction from the Epo 3´ enhancer to the apparatus on the promoter responsible for the initiation of transcription.
Oxygen Toxicity: A Radical Explanation
Authors: Fridovich Irwin 
Published: April 2021

ABSTRACT
During its reduction to water, O2 readily gives rise to dangerously reactive intermediates. This threat is diminished by families of defensive enzymes which include the superoxide dismutases, catalases and peroxidases. Free radical chain reactions are controlled by antioxidants, such as ascorbate and the tocopherols, and oxidative damage, which occurs in spite of these defenses, is largely repaired or is nullified by de novo biosynthesis. Yet some damage is sustained and it contributes to mutagenesis, to senescence and to numerous pathological processes.
Intracellular Electrolyte Levels And Transport Of Secretory Granules In Exocrine Gland Cells
Authors: Sasaki Sadao , Nakagaki Ikuko , Hori Seiki , Kondo Hisao , Sakaguchi Bungo 
Published: April 2021

ABSTRACT
We demonstrate the intracellular transport of secretory granules of a silk protein, fibroin, from the Golgi region to the apical cytoplasm with special reference to microtubule organization, electrolyte concentrations and the acidic intragranular pH of normal and mutant posterior silk gland cells, using the techniques of electrophysiological microelectrode and microprobe analysis and of light and electron microscopic autoradiography. The silk gland cells of a recessive mutant making only flimsy cocoons were defective in the microtubule systems, did not stain with an anti-tubulin antibody in immunofluorescent microscopy, and accumulated intracellular granules in the apical and basal cytoplasm. The increase in intracellular calcium concentration and levels of chloride secretion were also reduced in the mutant cells. A carboxylic ionophore, monensin, which collapsed the granular H+ gradient, induced the transport of chloride and an increase in the intracellular calcium concentration, while it blocked the intracellular transport of granules from the Golgi region to the apical cytoplasm in normal cells. Thus, we conclude that the H+ gradient across the membrane of secretory granules is responsible for the intracellular transport of the secretory granules along the microtubule systems in silk gland cells, while Ca2+ is thought to be required for the exocytosis of the granules.
Neuronal Mechanisms Underlying the Facilitatory Control of Uropod Steering Behaviour During Treadmill Walking in Crayfish:II. Modulation of Uropod Motoneurone Excitation by Leg Proprioception
Authors: Murayama Maki , Takahata Masakazu 
Published: April 2021

ABSTRACT
The synaptic activities underlying the uropod steering behaviour of crayfish evoked by tilting the substratum beneath the legs have been studied intracellularly in unanaesthetized animals standing or walking on a treadmill. The uropod motoneurones showed little or no synaptic response when the treadmill was tilted while the animal was in a quiescent state and the membrane potential was at its resting value. When the same stimulus was given while the animal was walking or in an active stance on the treadmill, the motoneurones showed transient much-enhanced excitatory or inhibitory responses to tilt, depending on the tilt direction. These responses were superimposed on a sustained level of background excitation so that the spike activity of the motoneurones either increased or decreased. Premotor nonspiking interneurones also showed little or no synaptic response to the tilt stimulus while the animal was resting, but greatly enhanced responses, in either a depolarizing or a hyperpolarizing direction, while the animal was walking or in the active-standing state. The results indicate that the proprioceptor inputs converging onto the uropod motoneurones, either directly or through premotor nonspiking interneurones, are gated not only in the uropod motor system in the terminal abdominal ganglion but also at as yet unidentified sites upstream in anterior ganglia, thus suggesting multiple gate control of the descending proprioceptor pathway.
Ventilation And Acid–Base Recovery Following Exhausting Activity In An Air-Breathing Fish
Authors: Burleson Mark L. , Shipman Bradley N. , Smatresk Neal J. 
Published: April 2021

ABSTRACT
The effects of exhausting activity in normoxic and hypoxic water on ventilatory, metabolic and acid–base variables were examined in spotted gar (Lepisosteus oculatus) to determine the role of the air-breathing organ in supporting active metabolism and recovery. The level of aquatic hypoxia used effectively eliminated the gills as a site of O2 uptake, forcing the fish to respire as a unimodal air-breather. Swimming duration (until exhaustion) was not significantly different in normoxic and hypoxic water. Blood gas, acid–base, cardiovascular and ventilatory variables were monitored at intervals from 15 min to 24 h post-exercise. Fish survived exhaustive exercise using a combination of anaerobic metabolism and increased ventilation (aerial and aquatic), despite respiratory and metabolic acidoses. The cardiovascular effects of exercise (heart rate and dorsal aortic blood pressure) were minor. The metabolic effects of exercise were similar to those in unimodal water-breathing fish; however, even hypoxic animals recovered from exhaustive exercise by 24 h. Thus, the results of this study show that air breathing in L. oculatus allows gar to exercise to the same extent in normoxic and hypoxic water and enables them to re-establish blood gas and acid–base balance after exhaustive activity even in hypoxic water.
Effect of Cyclical Salinity Changes on Cell Volume and Function in Geukensia Demissa Gills
Authors: Neufeld Douglas S. , Wright Stephen H. 
Published: April 2021

ABSTRACT
We acclimated the estuarine mussel Geukensia demissa to a regime of sinusoidal salinity cycling (12 h cycle between 100 % and 60 % seawater) and correlated changes in the volume of gill cells with changes in several indicators of the functional status of gill cells (rate of O2 consumption, ATP content and amino acid transport). There was no indication of short-term volume regulation in the gill cells of mussels acclimated to salinity cycling. When exposed to cycling salinity, cell water space consistently increased to approximately 3 ml g−1 dry mass during the cycle troughs (60 % seawater) and returned to approximately 2 ml g−1 dry mass at the cycle peaks (100 % seawater). In mussels acclimated for 2 weeks to cycling salinity, the gill contents of betaine, taurine and K+ were unchanged (approximately 240, 230 and 160 µmol g−1 dry mass, respectively) between the 60 % and 100 % seawater portions of the salinity cycle. The changes in cell volume did not appear to be associated with large perturbations in the functional status of cells. The rate of O2 consumption was approximately 100 µl O2 g−1 dry mass min−1, and ATP content was approximately 30 µmol g−1 protein, in all salinities to which mussels were exposed. Rates of uptake of taurine, leucine and phenylalanine decreased by approximately 50 % during the first sinusoidal decrease to 60 % seawater, but recovered following re-exposure to 100 % seawater. Uptake rates of all three amino acids were unaffected by any subsequent salinity cycles. These results suggest (1) that the regulation of gill cell volume is normally absent from mussels exposed to repeated, gradual salinity changes, and (2) that any effects of changes in cell volume are not severe enough to justify the energetic expenditure that would be associated with repeated regulation of cell volume. Unlike the response of gill cells to cycling salinity, there was a decrease in the solute contents of ventricles during the salinity troughs compared with the salinity peaks, suggesting that the presence of short-term volume regulation may be more critical in the ventricle.
Electric organ discharges and electric images during electrolocation
Authors: Assad Christopher , Rasnow Brian , Stoddard Philip K. 
Published: April 2021

ABSTRACT
Weakly electric fish use active electrolocation – the generation and detection of electric currents – to explore their surroundings. Although electrosensory systems include some of the most extensively understood circuits in the vertebrate central nervous system, relatively little is known quantitatively about how fish electrolocate objects. We believe a prerequisite to understanding electrolocation and its underlying neural substrates is to quantify and visualize the peripheral electrosensory information measured by the electroreceptors. We have therefore focused on reconstructing both the electric organ discharges (EODs) and the electric images resulting from nearby objects and the fish’s exploratory behaviors. Here, we review results from a combination of techniques, including field measurements, numerical and semi-analytical simulations, and video imaging of behaviors. EOD maps are presented and interpreted for six gymnotiform species. They reveal diverse electric field patterns that have significant implications for both the electrosensory and electromotor systems. Our simulations generated predictions of the electric images from nearby objects as well as sequences of electric images during exploratory behaviors. These methods are leading to the identification of image features and computational algorithms that could reliably encode electrosensory information and may help guide electrophysiological experiments exploring the neural basis of electrolocation.
Active electrolocation of objects in weakly electric fish
Authors: von der Emde Gerhard 
Published: April 2021

ABSTRACT
Weakly electric fish produce electric signals (electric organ discharges, EODs) with a specialised electric organ creating an electric field around their body. Objects within this field alter the EOD-induced current at epidermal electroreceptor organs, which are distributed over almost the entire body surface. The detection, localisation and analysis of objects performed by monitoring self-produced electric signals is called active electrolocation.
Electric fish employ active electrolocation to detect objects that are less than 12 cm away and have electric properties that are different from those of the surrounding water. Within this range, the mormyrid Gnathonemus petersii can also perceive the distance of objects. Depth perception is independent of object parameters such as size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters of the electric image that the object projects onto the fish’s skin.
Electric fish can not only locate objects but can also analyse their electrical properties. Fish are informed about object impedance by measuring local amplitude changes at their receptor organs evoked by an object. In addition, all electric fish studied so far can independently determine the capacitative and resistive components of objects that possess complex impedances. This ability allows the fish to discriminate between living and non-living matter, because capacitance is a property of living organisms. African mormyrids and South American gymnotiforms use different mechanisms for capacitance detection. Mormyrids detect capacitance-evoked EOD waveform distortions, whereas gymnotiforms perform time measurements. Gymnotiforms measure the temporal phase shift of their EODs induced at body parts close to the object relative to unaffected body parts further away.
Mechanisms for generating temporal filters in the electrosensory system
Authors: Rose Gary J. , Fortune Eric S. 
Published: April 2021

ABSTRACT
Temporal patterns of sensory information are important cues in behaviors ranging from spatial analyses to communication. Neural representations of the temporal structure of sensory signals include fluctuations in the discharge rate of neurons over time (peripheral nervous system) and the differential level of activity in neurons tuned to particular temporal features (temporal filters in the central nervous system). This paper presents our current understanding of the mechanisms responsible for the transformations between these representations in electric fish of the genus Eigenmannia. The roles of passive and active membrane properties of neurons, and frequency-dependent gain-control mechanisms are discussed.
Structural organization of the mormyrid electrosensory lateral line lobe
Authors: Meek J. , Grant K. , Bell C. 
Published: April 2021

ABSTRACT
The electrosensory lateral line lobe (ELL) of mormyrid teleosts is the first central stage in electrosensory input processing. It is a well-developed structure with six main layers, located in the roof of the rhombencephalon. Its main layers are, from superficial to deep, the molecular, ganglionic, plexiform, granular, intermediate and deep fiber layers. An important input arises from electroreceptors, but corollary electromotor command signals and proprioceptive, mechanosensory lateral line and descending electrosensory feedback inputs reach the ELL as well. The ELL input is processed by at least 14 cell types, which frequently show plastic responses to different inputs. The large ganglionic and large fusiform cells are the ELL projection cells. They are glutamatergic and project to the isthmic preeminential nucleus and the midbrain lateral toral nucleus. Interneurons are located in all ELL layers and are mostly GABAergic. The most remarkable interneurons are large multipolar cells in the intermediate layer, which have myelinated dendrites making presynaptic terminals contacting granular cells. With respect to the synaptic organization and microcircuitry of the ELL, a number of qualitative and quantitative aspects have been elucidated using electron microscopical and intracellular labeling techniques. However, the pathways by which primary afferent input influences the ELL projection cells are still undetermined: primary afferents do not seem to contact large fusiform or large ganglionic cells directly, but seem to terminate exclusively on granular cells, the axonal properties of which are not known. Consequently, more information of the structural organization of the ELL is still necessary for a detailed understanding of the neural basis of the plastic electrosensory input processing in mormyrids.
Adaptive mechanisms in the elasmobranch hindbrain
Authors: Bodznick David , Montgomery John C. , Carey Megan 
Published: April 2021

ABSTRACT
The suppression of self-generated electrosensory noise (reafference) and other predictable signals in the elasmobranch medulla is accomplished in part by an adaptive filter mechanism, which now appears to represent a more universal form of the modifiable efference copy mechanism discovered by Bell. It also exists in the gymnotid electrosensory lateral lobe and mechanosensory lateral line nucleus in other teleosts. In the skate dorsal nucleus, motor corollary discharge, proprioceptive and descending electrosensory signals all contribute in an independent and additive fashion to a cancellation input to the projection neurons that suppresses their response to reafference. The form of the cancellation signal is quite stable and apparently well-preserved between bouts of a particular behavior, but it can also be modified within minutes to match changes in the form of the reafference associated with that behavior. Motor corollary discharge, proprioceptive and electrosensory inputs are each relayed to the dorsal nucleus from granule cells of the vestibulolateral cerebellum. Direct evidence from intracellular studies and direct electrical stimulation of the parallel fiber projection support an adaptive filter model that places a principal site of the filter’s plasticity at the synapses between parallel fibers and projection neurons.
Waveform discrimination, phase sensitivity and jamming avoidance in a wave-type electric fish
Authors: Kramer Bernd 
Published: April 2021

ABSTRACT
The electric organ discharge (EOD) of most species of the freshwater knifefishes (Gymnotiformes) of South America is of the wave, not the pulse, type. Wave EODs are usually of constant frequency and amplitude, and show a bewildering multitude of species-characteristic waveforms. The EOD of Eigenmannia is sexually dimorphic in waveform and in the intensity of its higher harmonics. In a go/no go paradigm, trained food-rewarded fish discriminated between these waveforms, and naive (untrained) fish showed a significant preference. To determine whether spectral or waveform (time) cues are used by the fish, artificial stimuli of identical amplitude spectrum were synthesized that differed only in phase relationship between their harmonics, i.e. waveform, and the fish discriminated even among these stimulus waveforms (i.e. spectral cues are not required). Our sensory model predicts that, for successful waveform detection, a minimum frequency difference is required between the stimulus and the EOD. As expected, trained fish confused test stimuli of different waveform that were frequency-clamped and phase-locked to the EOD (frequency difference 0 Hz). Opening the electronic feedback loop immediately restored discrimination performance on an on/off basis, and a strong jamming avoidance response (JAR; a frequency shift away from the stimulus) accompanied every behavioural decision (to go for a food reward). The strong habituation of the JAR that occurs in response to stimuli of no behavioural consequence (the usual test situation) was not seen in the present experiments. The proposed sensory model (which is based on time-marking T electroreceptors) is supported by these experiments, and a biological function for the JAR – subserving EOD waveform discrimination is shown to be useful in a social context.
The future of research on electroreception and electrocommunication
Authors: Bullock Theodore Holmes 
Published: April 2021

ABSTRACT
Beyond continuation of currently active areas, some less studied ones are selected for predictions of marked advance. (1) Most discoveries will be in cellular components and molecular mechanisms for different classes of receptor or central pathways. (2) More major taxa, possibly birds, reptiles or invertebrates, will be found to have electroreceptive species representing independent evolutionary ‘inventions’. (3) Electric organs with weak and episodic electric discharges will be found in new taxa; first, among siluriforms. (4) New examples are to be expected, such as lampreys, where synchronized muscle action potentials sum to voltages in the range of weakly electric fish. Some of these will look like intermediates in the evolution of electric organs. (5) Ethological significance will be found for a variety of known physiological features; e.g. uranoscopids, skates and weakly electric catfish with episodic electric discharges; electroreceptive ability of animals such as lampreys, chimaeras, lungfish, sturgeons, paddlefish and salamanders with Lorenzinian-type ampullae; gymnotiform and mormyrid detection of the capacitative component of impedance. (6) The organization of some higher functions in the cerebellum and forebrain will gradually come to light.
An olfactory-specific glutathione-S-transferase in the sphinx moth Manduca sexta
Authors: Rogers Matthew E. , Jani Mudra K. , Vogt Richard G. 
Published: April 2021

ABSTRACT
Insect antennae have a primary function of detecting odors including sex pheromones and plant volatiles. The assumption that genes uniquely expressed in these antennae have an olfactory role has led to the identification of several genes that are integral components of odorant transduction. In the present study, differential display polymerase chain reaction (ddPCR) was used to isolate 25 antennal-specific mRNAs from the male sphinx moth Manduca sexta. Northern blot analyses revealed that one clone, designated G7-9, was antennal-specific and was highly enriched in male antennae relative to female antennae. In situ hybridization indicated that G7-9 expression was restricted to a spatial domain of the olfactory epithelium occupied exclusively by sex-pheromone-sensitive olfactory sensilla. Amino acid homology and phylogenetic analyses identified G7-9 as a glutathione-S-transferase (GST); we have named the full-length clone GST-msolf1. GSTs are known to function primarily in the detoxification of noxious compounds. Spectrophotometric and chromatographic analyses of total GST activity indicate that the endogenous GSTs of male and female antennae can modify trans-2-hexenal, a plant-derived green leaf aldehyde known to stimulate the olfactory system of M. sexta. The restricted localization of GST-msolf1 to sex-pheromone-sensitive sensilla, the fact that the sex pheromone of M. sexta consists of a complex mixture of aldehyde components, and the observation that antennal GSTs can modify an aldehyde odorant suggest that GST-msolf1 may have a role in signal termination. In the light of the more commonly observed role of GSTs in xenobiotic metabolism, we propose that GST-msolf1 may play a dual role of protecting the olfactory system from harmful xenobiotics and inactivating aldehyde odorants, especially components of the M. sexta sex pheromone.