bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature-Dependence of L-Type Ca2+ Channel Current in Atrial Myocytes From Rainbow Trout
Authors: Shiels H. A. , Vornanen M. , Farrell A. P. 
Published: April 2021

ABSTRACT
Rainbow trout, Oncorhynchus mykiss, inhabit eurythermal environments and must therefore be able to cope with changes in environmental temperature. As ectotherms, their heart is required to maintain cardiac function over a range of ambient water temperatures. This raises important questions concerning the temperature-dependence of cardiac ion channel function in fish hearts, in particular, the channels involved in Ca2+ transport. Thus, we studied the effects of acute, physiologically relevant temperature changes on the density and kinetics of the L-type Ca2+ channel current (ICa) in rainbow trout atrial myocytes using the whole-cell patch-clamp technique. Myocytes from fish acclimated to 14 °C were first tested at 14 °C, then at 21 °C and finally at 7 °C. Using a square-pulse voltage-clamp in the first series of experiments, the peak density of ICa increased (Q10=1.9) as temperature was increased from 14 to 21 °C and decreased (Q10=2.1) as temperature was decreased from 14 to 7 °C. In contrast to current density, the charge carried by ICa was inversely related to temperature as a result of changes in the kinetic properties of the channel; both the fast (τf) and slow (τs) components of inactivation were slower at 7 °C than at 14 and 21 °C. Action potentials were recorded at the three test temperatures and then used as voltage-clamp stimulus waveforms to reassess ICa in a second series of experiments. While the temperature-dependency of ICa was similar to that found with the square-pulse voltage-clamp, the charge carried by ICa was temperature-independent. These results show that the temperature-dependency of ICa in rainbow trout is in the lower range of that reported in mammals and, although this could have profound effects on Ca2+ delivery to the myofilaments, the temperature-induced modifications in the action potential may help to maintain a fairly constant Ca2+ delivery during an acute temperature change in rainbow trout.
Ultraviolet and Violet Receptors Express Identical mRNA Encoding an Ultraviolet-Absorbing Opsin: Identification and Histological Localization of two Mrnas Encoding Short-Wavelength-Absorbing Opsins in the Retina of the Butterfly Papilio Xuthus
Authors: Kitamoto Junko , Ozaki Koichi , Arikawa Kentaro 
Published: April 2021

ABSTRACT
This paper describes the primary structures of two opsins of short-wavelength-absorbing visual pigments deduced from the mRNA sequences in the retina of the Japanese yellow swallowtail butterfly Papilio xuthus. A phylogenetic analysis of the amino acid sequences indicates that one of these visual pigments is of the ultraviolet-absorbing type and that the other is of the blue-absorbing type. We identified the photoreceptor cells that express these mRNAs by histological in situ hybridization. The mRNA of the ultraviolet type is expressed in two distinct photoreceptor types previously identified as ultraviolet and violet receptors, providing the first molecular biological evidence that different types of spectral receptor probably express a visual pigment with an identical amino acid sequence. The mRNA of the blue type is expressed exclusively in cells classified as blue receptors.
The Adrenergic Volume Changes of Immature and Mature Rainbow Trout (Oncorhynchus Mykiss) Erythrocytes
Authors: Lecklin Tiina , Tuominen Antti , Nikinmaa Mikko 
Published: April 2021

ABSTRACT
In this study, we examined whether the adrenergic volume response of teleost erythrocytes is related to cell maturity. Rainbow trout (Oncorhynchus mykiss) were made anaemic by reducing their haematocrit to approximately 50 % of the original value. After 3–4 weeks, small, young erythrocytes were seen in the circulation. By measuring the volume distribution of blood samples from anaemic fish before and after noradrenaline stimulation (10 min, 10−5 mol l−1 final concentration), we were able to show that the volume response of young, immature erythrocytes to catecholamine stimulation was greater than that of mature erythrocytes. In addition, the membrane fluidity, measured using the steady-state fluorescence polarisation method, was greater in anaemic fish after 24 days of recovery from bleeding than in control fish. Since blood from anaemic fish contained a large fraction of immature erythrocytes, this result indicates that the fluidity of the membrane of immature erythrocytes is greater than that of mature erythrocytes.
Ventilatory Mechanics and the Effects of Water Depth on Breathing Pattern in the Aquatic Caecilian Typhlonectes Natans
Authors: Prabha KC , Bernard David G. , Gardner Manuela , Smatresk Neal J. 
Published: April 2021

ABSTRACT
The breathing pattern in the aquatic caecilian Typhlonectes natans was investigated by recording airflow via a pneumotachograph under unrestrained normal physiological conditions. Ventilatory mechanics were assessed using airflow and pressure measurements from the buccal cavity and trachea. The breathing pattern consisted of an expiratory phase followed by a series of 10–15 small buccal pumps to inflate the lung, succeeded by a long non-ventilatory period. T. natans separate the expiratory and inspiratory gases in the buccal cavity and take several inspiratory pumps, distinguishing their breathing pattern from that of sarcopterygians. Hydrostatic pressure assisted exhalation. The tracheal pressure was greater than the water pressure at that depth, suggesting that pleuroperitoneal pressure as well as axial or pulmonary smooth muscles may have contributed to the process of exhalation. The frequency of lung ventilation was 6.33±0.84 breaths h−1, and ventilation occurred via the nares. Compared with other amphibians, this low ventilatory frequency suggests that T. natans may have acquired very efficient pulmonary respiration as an adaptation for survival in their seasonally fluctuating natural habitat. Their respiratory pathway is quite unique, with the trachea separated into anterior, central and posterior regions. The anterior region serves as an air channel, the central region is attached to the tracheal lung, and the posterior region consists of a bifurcated air channel leading to the left and right posterior lungs. The lungs are narrow, elongated, profusely vascularized and compartmentalized. The posterior lungs extend to approximately two-thirds of the body length. On the basis of their breathing pattern, it appears that caecilians are phylogenetically derived from two-stroke breathers.
The Influence of Temperature on Power Production During Swimming: II. Mechanics of Red Muscle Fibres In Vivo
Authors: Rome Lawrence C. , Swank Douglas M. , Coughlin David J. 
Published: April 2021

ABSTRACT
We found previously that scup (Stenotomus chrysops) reduce neither their stimulation duration nor their tail-beat frequency to compensate for the slow relaxation rates of their muscles at low swimming temperatures. To assess the impact of this ‘lack of compensation’ on power generation during swimming, we drove red muscle bundles under their in vivo conditions and measured the resulting power output. Although these in vivo conditions were near the optimal conditions for much of the muscle at 20 °C, they were far from optimal at 10 °C. Accordingly, in vivo power output was extremely low at 10 °C. Although at 30 cm s−1, muscles from all regions of the fish generated positive work, at 40 and 50 cm s−1, only the POST region (70 % total length) generated positive work, and that level was low. This led to a Q10 of 4–14 in the POST region (depending on swimming speed), and extremely high or indeterminate Q10 values (if power at 10 °C is zero or negative, Q10 is indeterminate) for the other regions while swimming at 40 or 50 cm s−1.
To assess whether errors in measurement of the in vivo conditions could cause artificially reduced power measurements at 10 °C, we drove muscle bundles through a series of conditions in which the stimulation duration was shortened and other parameters were made closer to optimal. This sensitivity analysis revealed that the low power output could not be explained by realistic levels of systematic or random error. By integrating the muscle power output over the fish’s mass and comparing it with power requirements for swimming, we conclude that, although the fish could swim at 30 cm s−1 with the red muscle alone, it is very unlikely that it could do so at 40 and 50 cm s−1, thus raising the question of how the fish powers swimming at these speeds. By integrating in vivo pink muscle power output along the length of the fish, we obtained the surprising finding that, at 50 cm s−1, the pink muscle (despite having one-third the mass) contributes six times more power to swimming than does the red muscle. Thus, in scup, pink muscle is crucial for powering swimming at low temperatures.
This overall analysis shows that Q10 values determined in experiments on isolated tissue under arbitrarily selected conditions can be very different from Q10 values in vivo, and therefore that predicting whole-animal performance from these isolated tissue experiments may lead to qualitatively incorrect conclusions. To make a meaningful assessment of the effects of temperature on muscle and locomotory performance, muscle performance must be studied under the conditions at which the muscle operates in vivo.
Discontinuous Gas Exchange Cycles in Aphodius Fossor (Scarabaeidae): A Test of Hypotheses Concerning Origins and Mechanisms
Authors: Chown Steven L. , Holter Peter 
Published: April 2021

ABSTRACT
It has been suggested that discontinuous gas exchange cycles (DGCs) in insects evolved in response to hypoxic and/or hypercapnic environments, and that the flutter phase of the DGC is predominantly diffusive. We tested these hypotheses by examining the rate of CO2 release at a declining series of oxygen partial pressures in adults of Aphodius fossor, an inhabitant of moist to wet dung pats that can have low oxygen and high carbon dioxide concentrations. This mesic species showed a pronounced DGC, but progressively abandoned it when exposed to declining oxygen concentrations. That is, in response to a reduction in oxygen concentration, the closed phase declined in length and eventually disappeared, the flutter phase declined in length, while the flutter phase rate of CO2 release increased, the open phase peak rate of CO2 release declined and DGC frequency increased. Nonetheless, overall CO2 release rate remained virtually unchanged. Thus, it appears that the flutter phase in A. fossor has a significant convective component. In addition, in response to declining oxygen concentrations, the spiracles are opened for prolonged periods to increase gas exchange. This behaviour is unlikely to incur a significant water loss penalty in the moist habitats in which A. fossor lives. Given the switch to continuous ventilation by A. fossor under hypoxic conditions, we conclude that current adaptive explanations for the DGC are inadequate. Rather, the DGC may be the default state of a system regulated by two interacting feedback loops when demands are absent.
Crushing Motor Patterns in Drum (Teleostei: Sciaenidae): Functional Novelties Associated with Molluscivory
Authors: Grubich Justin R. 
Published: April 2021

ABSTRACT
This study explores the evolution of molluscivory in the marine teleost family Sciaenidae by comparing the motor activity patterns of the pharyngeal muscles of two closely related taxa, the molluscivorous black drum (Pogonias cromis) and the generalist red drum (Sciaenops ocellatus). Muscle activity patterns were recorded simultaneously from eight pharyngeal muscles. Electromyographic (EMG) activity was recorded during feeding on three prey types that varied in shell hardness. Canonical variate and discriminant function analyses were used to describe the distinctness of drum pharyngeal processing behaviors. Discriminant functions built of EMG timing variables were more accurate than muscle activity intensity at identifying cycles by prey type and species. Both drum species demonstrated the ability to modulate pharyngeal motor patterns in response to prey hardness. The mean motor patterns and the canonical variate space of crushing behavior indicated that black drum employed a novel motor pattern during molluscivory. The mollusc-crushing motor pattern of black drum is different from other neoteleost pharyngeal behaviors in lacking upper jaw retraction by the retractor dorsalis muscle. This functional modification suggests that crushing hard-shelled marine bivalves requires a ‘vice-like’ compression bite in contrast to the shearing forces that are applied to weaker-shelled fiddler crabs by red drum and to freshwater snails by redear sunfish.
K + Currents in Cultured Neurones From a Polyclad Flatworm
Authors: Buckingham Steven D. , Spencer Andrew N. 
Published: April 2021

ABSTRACT
Cells from the brain of the polyclad flatworm Notoplana atomata were dispersed and maintained in primary culture for up to 3 weeks. Whole-cell patch-clamp of presumed neurones revealed outwardly directed K+ currents that comprised, in varying proportions, a rapidly activating (time constant τ=0.94±0.79 ms; N=15) and inactivating (τ=26.1±1.9 ms; N=22) current and a second current that also activated rapidly (τ=1.1±0.2 ms; N=9) (means ± S.E.M.) but did not inactivate within 100 ms. Both current types activated over similar voltage ranges. Activation and steady-state inactivation overlap and are markedly rightward-shifted compared with most Shaker-like currents (half-activation of 16.9±1.9 mV, N=7, half-inactivation of −35.4±3.0 mV, N=5). Recovery from inactivation was rapid (50±2.5 ms at −90 mV). Both currents were unaffected by tetraethylammonium (25 mmol l−1), whereas 4-aminopyridine (10 mmol l−1) selectively blocked the inactivating current. The rapidly inactivating current, like cloned K+ channels from cnidarians and certain cloned K+ channels from molluscs and the Kv3 family of vertebrate channels, differed from most A-type K+ currents reported to date. These findings suggest that K+ currents in Notoplana atomata play novel roles in shaping excitability properties.
Auditory Symmetry Analysis
Authors: Faure Paul A. , Hoy Ronald R. 
Published: April 2021

ABSTRACT
The study of biological symmetry continues to be an important and active area of research, yet in the hearing sciences there are no established quantitative methods for measuring auditory asymmetries and dissimilarities in threshold tuning curves (i.e. audiograms). Using a paired design and adopting methods from the analysis of fluctuating asymmetry, we describe methods for auditory researchers interested in delineating auditory asymmetries and comparing tuning curves, behavioral or neural. We illustrate the methods using audiograms of the prothoracic T-cell interneuron in a nocturnal katydid (Neoconocephalus ensiger). The results show that 87–92 % of T-cells had right-minus-left threshold asymmetries no larger than expected from measurement error alone. Thus, apart from small random fluctuating asymmetries, T-cell pairs in N. ensiger showed no sensory bias and were bilaterally symmetrical from 5 to 100 kHz. The sensitivity of the methods for detecting tuning curve dissimilarities was confirmed in a sound lateralization paradigm by comparing the ‘symmetry’ (i.e. similarity) of T-cell tuning curves measured at 0 ° stimulation with tuning curves measured at 90 ° stimulation for the same T-cell. The results show that T-cell thresholds measured frontally (0 °) were significantly higher than those measured laterally (90 °), particularly for ultrasonic frequencies. Statistically, the directional shift (increase) in auditory thresholds was detected as a directional asymmetry in T-cell tuning, whose origin and functional significance to an insect behaving normally are discussed. The paper discusses practical considerations for detecting auditory asymmetries and tuning curve dissimilarities in general, and closes by questioning the relevance of auditory symmetry for sound localization in both vertebrates and insects.
Neuroethology of the Katydid T-Cell: II. Responses to Acoustic Playback of Conspecific and Predatory Signals
Authors: Faure Paul A. , Hoy Ronald R. 
Published: April 2021

ABSTRACT
Although early work on the tettigoniid T large fiber suggested that it might mediate early-warning and escape behavior in katydids, the majority of research thereafter has focused on the ability of the T-cell to detect, localize and/or discriminate mate-calling song. Interestingly, T-cell responses to conspecific song are rarely examined for more than a few seconds, despite the fact that many katydids sing for minutes or hours at a time. In this paper, the second of a pair examining the physiology of the T-cell in Neoconocephalus ensiger, we recorded T-cell responses using longer-duration playbacks (3 min) of conspecific song (Katydid signal 30 ms syllables, 9–25 kHz bandwidth, 12–15 kHz peak frequency) and two types of bat-like ultrasound, a 10 ms, 80→30 kHz frequency-modulated sweep (Bat 10 signal) and a 30 ms, 80→30 kHz frequency-modulated sweep (Bat 30 signal). Spiking responses were distinctly biased towards the short-duration ultrasonic signal, with more spikes per pulse, at a shorter spike latency and at a higher instantaneous firing frequency to the Bat 10 signal than to the Katydid signal or, surprisingly, to the Bat 30 signal. The ability of the T-cell to encode the temporal pattern of the stimulus was particularly striking. Only for the predatory bat signals did T-cell spiking faithfully copy the stimulus; playbacks of conspecific song resulted in significantly weaker spiking responses, particularly in male katydids. The results demonstrate that responses from the T-cell alone may be sufficient for katydids to discriminate biologically relevant signals pertinent to the phonotactic behavior patterns involved in mate attraction and predator avoidance.
ELectroreception In Gymnotus Carapo: Pre-Receptor Processing And The Distribution Of Electroreceptor Types
Authors: Castelló María E. , Aguilera Pedro A. , Trujillo-Cenóz Omar , Caputi Angel A. 
Published: April 2021

ABSTRACT
This paper describes the peripheral mechanisms involved in signal processing of self- and conspecific-generated electric fields by the electric fish Gymnotus carapo. The distribution of the different types of tuberous electroreceptor and the occurrence of particular electric field patterns close to the body of the fish were studied. The density of tuberous electroreceptors was found to be maximal on the jaw (foveal region) and very high on the dorsal region of the snout (parafoveal region), decaying caudally. Tuberous type II electroreceptors were much more abundant than type I electroreceptors. Type I electroreceptors occurred exclusively on the head and rostral trunk regions, while type II electroreceptors were found along as much as 90 % of the fish. Electrophysiological data indicated that conspecific- and self-generated electric currents are ‘funnelled’ by the high conductivity and geometry of the body of the fish. These currents are concentrated at the peri-oral zone, where most electroreceptors are located. Moreover, within this region, field vector directions were collimated, constituting the most efficient stimulus for electroreceptors. It can be concluded that the passive properties of the fish tissue represent a pre-receptor device that enhances exafferent and reafferent electrical signals at the fovea–parafoveal region.
The Behavioral Detection Of Binary Mixtures Of Amino Acids And Their Individual Components By Catfish
Authors: Valentinčič T. , Kralj J. , Stenovec M. , Koce A. , Caprio J. 
Published: April 2021

ABSTRACT
The question of whether a binary mixture of amino acids is detected by fish as a unique odor or whether the qualities of the individual components are retained within the mixture was investigated in channel (Ictalurus punctatus) and brown bullhead (Ameiurus nebulosus) catfish, species that are highly similar in their olfactory receptor and behavioral responses to amino acid odorants. Catfish respond with greater appetitive food-searching (swimming) behavior to amino-acid-conditioned olfactory stimuli than to non-conditioned amino acids. In the present study, appetitive food-searching behavior was measured by counting the number of turns of the fish greater than 90 ° within 90 s of stimulus onset and, in some tests, by video tracking. The two methods yielded highly correlated results. Channel catfish conditioned to a binary mixture composed of equimolar amino acids responded with searching behavior to the amino acid that produced the larger-amplitude electro-olfactogram (EOG) response as they did to the conditioned stimulus. In further studies, bullhead catfish were conditioned either to a binary mixture or to a single amino acid and tested to determine whether a binary mixture was detected as the component evoking the larger EOG response. In all initial tests (trials 1–3), the more stimulatory component of a binary mixture was not discriminated from the binary mixture; however, the less stimulatory component and all other amino acids tested were discriminated from the mixture. By increasing the concentration of the originally less potent component in a binary mixture, making it the more stimulatory compound, it was now detected as not significantly different from the binary mixture; however, the original more potent component (i.e. now the less potent stimulus) was detected as significantly different from the mixture. However, with 5–10 additional discrimination training trials, the less stimulatory component in a binary mixture influenced the perception of the binary mixture because the binary mixture was no longer detected only as its more stimulatory component. The data suggest that a two-step learning process occurs within the olfactory bulb and possibly higher-order telencephalic nuclei.