bluuebunny/crossref_metadata_2025 huggingface dataset:
Intratesticular Distribution Of Cyritestin, A Protein Involved In Gamete Interaction
Authors: Forsbach Alexandra , Heinlein Uwe A. O.
Published: April 2021

Cyritestin, a member of the ADAM family of proteins, has been shown to be involved in the interaction between sperm and egg during fertilization. The protein is a transmembrane protein associated with the sperm acrosome. In the present study, electron microscopy was used to trace the distribution of the cyritestin molecule in intratesticular germ cells, particularly in haploid round spermatids where the acrosomal structure is differentiating. Our results indicate that cyritestin is transported to the forming acrosomal vesicle through the Golgi apparatus to become part of the acrosomal membrane. Differential staining with antibodies recognizing either the metalloprotease-like domain or the cytoplasmic domain of cyritestin indicates that processing of the molecule leading to the loss of the pro- and metalloproteinase-like domains begins during germ cell stage 6 and is completed before stage 15.
Predicting Force Generation by Lamprey Muscle During Applied Sinusoidal Movement Using A Simple Dynamic Model
Authors: Williams Thelma L. , Bowtell Graham , Curtin N. A.
Published: April 2021

Experiments were performed on single-myotome preparations of lamprey muscle, to discover whether force developed by intermittent tetanic stimulation during imposed sinusoidal movement could be predicted by data collected from isometric and constant-velocity experiments. We developed a simple dynamic model consisting of a set of simultaneous ordinary differential equations with unknown parameters. Appropriate values of the parameters were found by fitting numerical solutions of the differential equations to data from the isometric and constant-velocity experiments. Predictions were made of the time course of force developed during imposed sinusoidal movement in which the phase between muscle shortening and tetanic stimulation was varied to cover the whole phase spectrum. The match between the predicted and recorded time courses was very good for all phases, and particularly for those phases that are seen during swimming in the intact animal.
Salt and Water Relations, and Nitrogen Excretion, in the Amphibious African Freshwater Crab Potamonautes Warreni in Water and in Air
Authors: Morris S. , Aardt W. J. Van
Published: April 2021

Mechanisms of salt and water conservation, and nitrogen excretion, were investigated in the freshwater amphibious crab Potamonautes warreni from the High Veld of South Africa. Adaptations to fresh water were assessed as pre-adaptations to air-breathing, and nitrogen excretion was examined as a potential constraint to terrestrial excursions. P. warreni was able to regulate water and salt loss in water up to 40 % sea water, but not in 80 % sea water. The water permeability of P. warreni was low and, since 97 % of the haemolymph filtrate was reabsorbed in the antennal organ, urinary water loss was minimal (0.7 μl g−1 h−1). The minimum equilibrium [Na] of P. warreni was low (0.116 mmol l−1), as were the rates of both Na loss (0.22 μmol g−1 h−1) and Ca loss (0.29 μmol g−1 h−1). The low loss rates were due to urinary salt conservation of approximately 90 % or better and to low permeability , and were compensated for by a high-affinity uptake mechanism (Jmax=0.76 μmol g−1 h−1 and Km=0.18 mmol l−1). Acclimating P. warreni to low Na concentrations increased maximum net Na uptake rate to 1.77 μmol g−1 h−1.

Nitrogen excretion in P. warreni was almost 100 % ammoniotelic, and there was no accumulation of haemolymph or urinary ammonia or urea when in air. P. warreni was unable to excrete ammonia to air, but in water the rate of excretion was nearly 70 μmol kg−1 h−1. Crabs in amphibious conditions showed pulses of elevated NH3 excretion (350 μmol kg−1 h−1) when subsequently submerged, while for crabs breathing air for 3 days this pulse reached 4.9 mmol kg−1 h−1. Air-breathing P. warreni with artificially irrigated branchial chambers excreted double the amount of NH3via the gills compared with crabs from amphibious conditions.

Water and salt conservation form useful pre-adaptations to terrestrial forays. While the relatively low water loss extends the duration of emersion, P. warreni is required to return briefly to water to excrete stored nitrogenous waste. The nature of the store remains to be determined.
Environmental Effects on Undulatory Locomotion in the American Eel Anguilla Rostrata: Kinematics in Water and on Land
Authors: Gillis Gary B.
Published: April 2021

Historically, the study of swimming eels (genus Anguilla) has been integral to our understanding of the mechanics and muscle activity patterns used by fish to propel themselves in the aquatic environment. However, no quantitative kinematic analysis has been reported for these animals. Additionally, eels are known to make transient terrestrial excursions, and in the past it has been presumed (but never tested) that the patterns of undulatory movement used terrestrially are similar to those used during swimming. In this study, high-speed video was used to characterize the kinematic patterns of undulatory locomotion in water and on land in the American eel Anguilla rostrata. During swimming, eels show a nonlinear increase in the amplitude of lateral undulations along their bodies, reaching an average maximum of 0.08L, where L is total length, at the tip of the tail. However, in contrast to previous observations, the most anterior regions of their bodies do not undergo significant undulation. In addition, a temporal lag (typically 10–15% of an undulatory cycle) exists between maximal flexion and displacement at any given longitudinal position. Swimming speed does not have a consistent effect on this lag or on the stride length (distance moved per tailbeat) of the animal. Speed does have subtle (although statistically insignificant) effects on the patterns of undulatory amplitude and intervertebral flexion along the body. On land, eels also use lateral undulations to propel themselves; however, their entire bodies are typically bent into waves, and the undulatory amplitude at all body positions is significantly greater than during swimming at equivalent speeds. The temporal lag between flexion and displacement seen during swimming is not present during terrestrial locomotion. While eels cannot move forwards as quickly on land as they do in water, they do increase locomotor speed with increasing tailbeat frequency. The clear kinematic distinctions present between aquatic and terrestrial locomotor sequences suggest that eels might be using different axial muscle activity patterns to locomote in the different environments.
Flight Thermogenesis and Energy Conservation in Hovering Hummingbirds
Authors: Chai Peng , Chang Andrew C. , Dudley Robert
Published: April 2021

As the smallest homeotherms, hummingbirds suffer from low thermal inertia and high heat loss. Flapping flight is energetically expensive, and convective cooling due to wing and air movements could further exacerbate energy drain. Energy conservation during flight is thus profoundly important for hummingbirds. The present study demonstrates that heat produced by flight activity can contribute to thermoregulatory requirements in hovering hummingbirds. The rate of oxygen consumption, as an indicator of metabolic cost, was measured during hover-feeding and compared with that during perch-feeding. In hover-feeding, oxygen consumption increased only moderately between 35 and 5°C in contrast to the sharp increase during perch-feeding over the same temperature range. This result suggests that heat produced by contraction of the flight muscles substituted for regulatory thermogenesis to accommodate for heat loss during exposure to low temperature. With declining air temperatures, the mechanical power requirements of hovering decreased slightly, but metabolic costs increased moderately. As a result, the mechanical efficiency of the muscle in converting metabolic power to mechanical power was reduced. Changes in wingbeat kinematics also accompanied the reduction in muscle efficiency. Wingbeat frequency increased but stroke amplitude decreased when hovering in the cold, suggesting thermoregulatory roles for the flight muscles. Hovering hummingbirds modulated their wingbeat frequency within a narrow range, reflecting the physical constraints of tuning to a natural resonant frequency with an elastic restoring force. We hypothesize that, by forcing the resonant system of the wings and thorax to oscillate at different frequencies, muscle contraction in the cold generates more heat at the expense of mechanical efficiency. This mechanism of modulating the efficiency of muscle contraction and heat production allows flying hummingbirds to achieve energy conservation at low air temperatures.
Mitochondrial Oxygen Affinity, Respiratory Flux Control And Excess Capacity Of Cytochrome c Oxidase
Authors: Gnaiger Erich , Lassnig Barbara , Kuznetsov Andrey , Rieger Gunde , Margreiter Raimund
Published: April 2021

The oxygen affinity of the enzyme system involved in mitochondrial respiration indicates, in relation to intracellular oxygen levels and interpreted with the aid of flux control analysis, a significant role of oxygen supply in limiting maximum exercise. This implies that the flux control coefficient of mitochondria is not excessively high, based on a capacity of mitochondrial oxygen consumption that is slightly higher than the capacity for oxygen supply through the respiratory cascade. Close matching of the capacities and distribution of flux control is consistent with the concept of symmorphosis. Within the respiratory chain, however, the large excess capacity of cytochrome c oxidase, COX, appears to be inconsistent with the economic design of the respiratory cascade. To address this apparent discrepancy, we used three model systems: cultured endothelial cells and mitochondria isolated from heart and liver. Intracellular oxygen gradients increase with oxygen flux, explaining part of the observed decrease in oxygen affinity with increasing metabolic rate in cells. In addition, mitochondrial oxygen affinities decrease from the resting to the active state. The oxygen affinity in the active ADP-stimulated state is higher in mitochondria from heart than in those from liver, in direct relationship to the higher excess capacity of COX in heart. This yields, in turn, a lower turnover rate of COX even at maximum flux through the respiratory chain, which is necessary to prevent a large decrease in oxygen affinity in the active state. Up-regulation of oxygen affinity provides a functional explanation of the excess capacity of COX. The concept of symmorphosis, a matching of capacities in the respiratory cascade, is therefore complemented by ‘synkinetic’ considerations on optimum enzyme ratios in the respiratory chain. Accordingly, enzymatic capacities are matched in terms of optimum ratios, rather than equal levels, to meet the specific kinetic and thermodynamic demands set by the low-oxygen environment in the cell.
Structure/Function Of Oxygen-Regulated Isoforms In Cytochrome c Oxidase
Authors: Burke Patricia V. , Poyton Robert O.
Published: April 2021

Eukaryotic cytochrome c oxidases are complex oligomeric membrane proteins composed of subunit polypeptides encoded by both nuclear and mitochondrial genomes. While the mitochondrially encoded subunits are encoded by unique genes, some of the nuclear-encoded subunits are encoded by multigene families. The isoforms produced by these multigene families are tissue-specific and/or developmentally regulated in mammals and environmentally regulated in lower eukaryotes. Isoforms for one of the subunits, V, in the yeast Saccharomyces cerevisiae and one of the subunits, VII, in the slime mold Dictyostelium discoideum are regulated differentially by oxygen concentration. Extensive studies with the yeast subunit V isoforms have revealed that the genes for these proteins are switched on or off at very low oxygen concentrations (0.5–1 μmol l−1 O2) and that they affect the catalytic properties of holocytochrome c oxidase differentially. By altering an internal step in electron transfer between heme a and the binuclear reaction center (composed of heme a3 and CuB), the ‘hypoxic’ isoform, Vb, enhances the catalytic constant three-to fourfold relative to the ‘aerobic’ isoform, Va. Modeling studies suggest that this occurs by an interaction between transmembrane helix VII of subunit I and the transmembrane helix in subunit V. The inverse regulation of these two isoforms allows cells to assemble different types of holoenzyme isoenzymes in response to oxygen concentration. Oxygen also regulates the level of transcription of the genes for the other nuclear-coded subunits of yeast cytochrome c oxidase and affects the level of two of the mitochondrially encoded subunits (I and II) post-transcriptionally. Thus, the level of cytochrome c oxidase activity that is produced at different oxygen tensions in yeast is determined in part by the number of holoenzyme molecules that are assembled and in part by the oxygen-regulated isoforms of subunit V. The possibility that this type of control exists in other organisms is considered.
Oxygen Sensing and the Transcriptional Regulation of Oxygen-Responsive Genes in Yeast
Authors: Kwast Kurt E. , Burke Patricia V. , Poyton Robert O.
Published: April 2021

The budding yeast Saccharomyces cerevisiae is a facultative aerobe that responds to changes in oxygen availability (and carbon source) by initiating a biochemically complex program that ensures that energy demands are met under two different physiological states: aerobic growth, supported by oxidative and fermentative pathways, and anaerobic growth, supported solely by fermentative processes. This program includes the differential expression of a large number of genes, many of which are involved in the direct utilization of oxygen. Research over the past decade has defined many of the cis-sites and trans-acting factors that control the transcription of these oxygen-responsive genes. However, the manner in which oxygen is sensed and the subsequent steps involved in the transduction of this signal have not been precisely determined. Heme is known to play a pivotal role in the expression of these genes, acting as a positive modulator for the transcription of the aerobic genes and as a negative modulator for the transcription of the hypoxic genes. Consequently, cellular concentrations of heme, whose biosynthesis is oxygen-dependent, are thought to provide a gauge of oxygen availability and dictate which set of genes will be transcribed. But the precise role of heme in oxygen sensing and the transcriptional regulation of oxygen-responsive genes is presently unclear. Here, we provide an overview of the transcriptional regulation of oxygen-responsive genes, address the functional roles that heme and hemoproteins may play in this regulation, and discuss possible mechanisms of oxygen sensing in this simple eukaryotic organism.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
The role of orientation flights on homing performance in honeybees
Authors: Capaldi Elizabeth A. , Dyer Fred C.
Published: April 2021

Honeybees have long served as a model organism for investigating insect navigation. Bees, like many other nesting animals, primarily use learned visual features of the environment to guide their movement between the nest and foraging sites. Although much is known about the spatial information encoded in memory by experienced bees, the development of large-scale spatial memory in naive bees is not clearly understood. Past studies suggest that learning occurs during orientation flights taken before the start of foraging. We investigated what honeybees learn during their initial experience in a new landscape by examining the homing of bees displaced after a single orientation flight lasting only 5 — 10 min. Homing ability was assessed using vanishing bearings and homing speed. At release sites with a view of the landmarks immediately surrounding the hive, ‘first-flight’ bees, tested after their very first orientation flight, had faster homing rates than ‘reorienting foragers’, which had previous experience in a different site prior to their orientation flight in the test landscape. First-flight bees also had faster homing rates from these sites than did ‘resident’ bees with full experience of the terrain. At distant sites, resident bees returned to the hive more rapidly than reorienting or first-flight bees; however, in some cases, the reorienting bees were as successful as the resident bees. Vanishing bearings indicated that all three types of bees were oriented homewards when in the vicinity of landmarks near the hive. When bees were released out of sight of these landmarks, hence forcing them to rely on a route memory, the ‘first-flight’ bees were confused, the ‘reorienting’ bees chose the homeward direction except at the most distant site and the ‘resident’ bees were consistently oriented homewards.
Blood pressure regulation during hypotension in two teleost species: differential involvement of the renin–angiotensin and adrenergic systems
Authors: Bernier Nicholas J. , McKendry John E. , Perry Steve F.
Published: April 2021

The stimulatory effects of angiotensin II (Ang II) on catecholamine release and the contributions of the renin–angiotensin system, humoral catecholamines and adrenergic nerves to blood pressure regulation were investigated in rainbow trout (Oncorhynchus mykiss) and American eel (Anguilla rostrata). In trout, bolus injections of homologous [Asn1,Val5]-Ang II (100 or 500 pmol kg−1) increased catecholamine secretion rates and plasma catecholamine concentrations from in situ posterior cardinal vein preparations and chronically cannulated fish, respectively. In contrast, in situ or in vivo injections of similar doses of Ang II in eel did not affect catecholamine release. α-Adrenoceptor blockade (prazosin; 1 mgkg−1) reduced the pressor effect of exogenous Ang II (500 pmol kg−1) in both species. In eel, intravenous injection of the smooth muscle relaxant papaverine (10 mg kg−1) elicited a rapid decrease in dorsal aortic pressure (PDA; 58 %) followed by a gradual recovery back to the baseline value 85 min after the treatment. In trout, papaverine elicited a similar decrease in blood pressure (62 %); however, PDA recovered fully 20 min after treatment. Blockade of either α-adrenoceptors with prazosin or adrenergic nerves with bretylium (10 mg kg−1) prior to papaverine treatment did not alter PDA recovery in eel. In trout, α-adrenoceptor and adrenergic nerve blockade prior to the papaverine treatment prevented and attenuated PDA recovery, respectively. In both species, papaverine treatment elicited significant increases in plasma catecholamine and Ang II concentrations. However, the increases in plasma catecholamine concentrations were markedly greater in trout than in eel. Similarly, the papaverine-elicited increase in plasma Ang II levels occurred earlier and was greater in trout than in eel. Thus, while Ang II stimulates humoral catecholamine release in trout, there is no evidence for a similar interaction in eel. Moreover, during hypotensive stress, although the renin–angiotensin system is recruited in both species, an essential involvement of adrenergic nerves and humoral catecholamines in the restoration of blood pressure is only apparent in trout.
Hiding responses of locusts to approaching objects
Authors: Hassenstein Bernhard , Hustert Reinhold
Published: April 2021

Locusts, Locusta migratoria, sitting on a plant stem hide from dark moving or expanding shapes in their environment. The fore- and middle legs perform this avoidance response by making lateral tilting movements, while the hindlegs slide laterally and guide rotation of the posterior body over the stem. During larger turns, the legs take lateral steps when lateral tilting is limited by the joints. Slow hiding movements of less than 300 ° s−1 of angular velocity are induced by slowly changing (looming) shapes, and interposed stops or slowing of the movement can delay the progress of this hiding manoeuvre. Fast hiding movements with angular velocities between 120 ° s−1 and 860° s−1 proceed continuously and rapidly in response to rapidly expanding stimuli. Hiding responses to expanding shapes occur only after the expanding image has exceeded a threshold visual angle of 8–9.5 °. Hiding response latencies range between 220 ms and 1.2 s for fast hiding and are approximately 1.2 s for most slow hiding responses. Predator-avoidance responses such as freezing, jerking, crouching, walking backwards, dropping or jumping can be used instead of or in conjunction with hiding behaviour. We conclude that the fast hiding behaviour of locusts is a specific goal-directed type of optomotor behaviour requiring positional information from small-field detectors of shape expansion in the interneurone layers of the locust eye.
Fenestration nodes and the wide submyelinic space form the basis for the unusually fast impulse conduction of shrimp myelinated axons
Authors: Xu (Ke Hsu) Ke , Terakawa Susumu
Published: April 2021

Saltatory impulse conduction in invertebrates is rare and has only been found in a few giant nerve fibres, such as the pairs of medial giant fibres with a compact multilayered myelin sheath found in shrimps (Penaeus chinensis and Penaeus japonicus) and the median giant fibre with a loose multilayered myelin sheath found in the earthworm Lumbricus terrestris. Small regions of these nerve fibres are not covered by a myelin sheath and serve as functional nodes for saltatory conduction. Remarkably, shrimp giant nerve fibres have conduction speeds of more than 200 m s−1, making them among the fastest-conducting fibres recorded, even when compared with vertebrate myelinated fibres. A common nodal structure for saltatory conduction has recently been found in the myelinated nerve fibres of the nervous systems of at least six species of Penaeus shrimp, including P. chinensis and P. japonicus. This novel node consists of fenestrated openings that are regularly spaced in the myelin sheath and are designated as fenestration nodes. The myelinated nerve fibres of the Penaeus shrimp also speed impulse conduction by broadening the gap between the axon and the myelin sheath rather than by enlarging the axon diameter as in other invertebrates. In this review, we document and discuss some of the structural and functional characteristics of the myelinated nerve fibres of Penaeus shrimp: (1) the fenestration node, which enables saltatory conduction, (2) a new type of compact multilayered myelin sheath, (3) the unique microtubular sheath that tightly surrounds the axon, (4) the extraordinarily wide space present between the microtubular sheath and the myelin sheath and (5) the main factors contributing to the fastest impulse conduction velocity so far recorded in the Animal Kingdom.
The distribution of a crf-like diuretic peptide in the blood-feeding bug Rhodnius prolixus
Authors: Brugge V. A. Te , Miksys S. M. , Coast G. M. , Schooley D. A. , Orchard I.
Published: April 2021

The blood-feeding bug Rhodnius prolixus ingests a large blood meal, and this is followed by a rapid diuresis to eliminate excess water and salt. Previous studies have demonstrated that serotonin and an unidentified peptide act as diuretic factors. In other insects, members of the corticotropin-releasing factor (CRF)-related peptide family have been shown to play a role in post-feeding diuresis. Using fluorescence immunohistochemistry and immunogold labelling with antibodies to the Locusta CRF-like diuretic hormone (Locusta-DH) and serotonin, we have mapped the distribution of neurones displaying these phenotypes in R. prolixus. Strong Locusta-DH-like immunoreactivity was found in numerous neurones of the central nervous system (CNS) and, in particular, in medial neurosecretory cells of the brain and in posterior lateral neurosecretory cells of the mesothoracic ganglionic mass (MTGM). Positively stained neurohaemal areas were found associated with the corpus cardiacum (CC) and on abdominal nerves 1 and 2. In addition, Locusta-DH-like immunoreactive nerve processes were found over the posterior midgut and hindgut. Double-labelling studies for Locusta-DH-like and serotonin-like immunoreactivity demonstrated some co-localisation in the CNS; however, no co-localisation was found in the medial neurosecretory cells of the brain, the posterior lateral neurosecretory cells of the MTGM or neurohaemal areas. To confirm the presence of a diuretic factor in the CC and abdominal nerves, extracts were tested in Malpighian tubule secretion assays and cyclic AMP assays. Extracts of the CC and abdominal nerves caused an increase in the rate of secretion and an increase in the level of cyclic AMP in the Malpighian tubules of fifth-instar R. prolixus. The presence of the peptide in neurohaemal terminals of the CC and abdominal nerves that are distinct from serotonin-containing terminals indicates that the peptide is capable of being released into the haemolymph and that this release can be independent of the release of serotonin.