bluuebunny/crossref_metadata_2025 huggingface dataset:
The myth of scorpion suicide: are scorpions insensitive to their own venom?
Authors: Legros Christian , Martin-Eauclaire Marie-France , Cattaert Daniel
Published: April 2021

The resistance of the scorpion Androctonus australis to its own venom, as well as to the venom of other species, was investigated. A comparison of the electrical and pharmacological properties of muscle and nerve fibres from Androctonus australis with those from the crayfish Procambarus clarkii enabled us to understand the lack of effect of scorpion venom (110–180 μg ml−1) and purified toxins, which are active on voltage-gated Na+ and K+ channels, Ca2+-activated K+ channels, on scorpion tissues. Voltage-clamp experiments showed that peptide K+ channel blockers from scorpion and snake have no effect on currents in muscle and nerve fibres from either scorpions or crayfish. The scorpion toxin kaliotoxin (KTX), a specific blocker of Kv1.1 and Kv1.3 K+ channels, had no effect on muscle fibres of A. australis (2 μmol l−1) or P. clarkii (400 nmol l−1). Similarly, charybdotoxin (ChTX) had no effect on the muscle fibres of A. australis (10 μmol l−1) or P. clarkii (200 nmol l−1) and neither did the snake toxin dendrotoxin (DTX) at concentrations of 100 nmol l−1 in A. australis and 200 nmol l−1 in P. clarkii. These three toxins (KTX, ChTX and DTX) did not block K+ currents recorded from nerve fibres in P. clarkii. The pharmacology of the K+ channels in these two arthropods did not conform to that previously described for K+ channels in other species. Current-clamp experiments clearly indicated that the venom of A. australis (50 μg ml−1) had no effect on the shape of the action potential recorded from nerve cord axons from A. australis. At a concentration of 50 μg ml−1, A. australis venom greatly prolonged the action potential in the crayfish giant axon. The absence of any effect of the anti-mammal α-toxin AaH II (100 nmol l−1) and the anti-insect toxin AaH IT1 (100 nmol l−1) on scorpion nerve fibres revealed strong pharmacological differences between the voltage-gated Na+ channels of scorpion and crayfish. We conclude that the venom from A. australis is pharmacologically inactive on K+ channels and on voltage-sensitive Na+ channels from this scorpion.
Cyclic changes in the tension of the contractile vacuole complex membrane control its exocytotic cycle
Authors: Tominaga Takashi , Allen Richard D. , Naitoh Yutaka
Published: April 2021

The freshwater protozoan Paramecium multimicronucleatum maintains a constant cytosolic osmolarity through the exocytotic activity of its contractile vacuole complex. The contractile vacuole (CV) expels the excess cytosolic water, acquired osmotically, to the exterior of the cell at fairly regular intervals. In a single exocytotic cycle, the CV swells as the cytosolic water enters the vacuole, rounds up, and then rapidly shrinks as the fluid is expelled through the pore of the CV. The exocytotic activity of the CV complex can sometimes be slowed and distorted by microelectrode impalement. Using a CV with exocytotic activity slowed in this way makes it possible to determine more precisely the time course of changes in the exocytotic-activity-related membrane capacitance and membrane potential of the organelle. We have clearly demonstrated that the radial arms of the CV were always severed after the CV had exhibited rounding. Microelectrode impalement sometimes caused a failure of the CV pore to open after rounding up, so that the CV entered the next fluid-filling phase without expelling its fluid. The radial arms remained severed from the CV during such prolonged rounding phases and then rejoined the CV at the start of the next fluid-filling phase. The rounding of the CV corresponds to an increase in the tension of the CV membrane. This suggested that the periodic development of increased tension in the CV membrane might be the primary event leading to periodic severing of the radial arms and the opening of the pore. We then observed that the CV and its radial arms sometimes became fragmented into vesicles when the cell had been mechanically ruptured in a salt solution. Many of the resulting in vitro vesicles showed periodic rounding and slackening which occurred at different times so that they were out of phase one with the other. This indicates that the membranes of the CV and the radial arms maintain their ability to develop a periodic increase in tension even after the cell has been ruptured. We propose the hypothesis that the CV membrane (together with its associated cytoskeletal structures) possesses a mechanism by which its tension is periodically increased. Such a periodic change in membrane tension may govern the exocytotic cycle of the contractile vacuole complex by increasing the tension to a point that the radial arms sever from the CV and the pore opens. Conversely, a decrease in the tension causes closure of the pore and rejoining of the radial arms to the CV. Transformation of the CV membrane into 40 nm tubules is assumed to be responsible for the development of tension in the planar CV membrane. The causes of this periodic tubulation must now be sought.
Differential air sac pressures in diving tufted ducks Aythya fuligula
Authors: Boggs Dona F. , Butler Patrick J. , Wallace Stacy E.
Published: April 2021

The air in the respiratory system of diving birds contains a large proportion of the body oxygen stores, but it must be in the lungs for gas exchange with blood to occur. To test the hypothesis that locomotion induces mixing of air sac air with lung air during dives, we measured differential pressures between the interclavicular and posterior thoracic air sacs in five diving tufted ducks Aythya fuligula. The peak differential pressure between posterior thoracic and interclavicular air sacs, 0.49±0.13 kPa (mean ± S.D.), varied substantially during underwater paddling as indicated by gastrocnemius muscle activity. These data support the hypothesis that locomotion, perhaps through associated abdominal muscle activity, intermittently compresses the posterior air sacs more than the anterior ones. The result is differential pressure fluctuations that might induce the movement of air between air sacs and through the lungs during dives.
Initial Recruitment of Anaerobic Metabolism During Sub-Maximal Swimming in Rainbow Trout (Oncorhynchus Mykiss)
Authors: Burgetz Ingrid J. , Rojas-Vargas Anibal , Hinch Scott G. , Randall David J.
Published: April 2021

Lactate and phosphocreatine concentrations were monitored in the white muscle of rainbow trout Oncorhynchus mykiss following swimming at 70, 80 and 100 % of critical swimming speed (Ucrit) using 31P-nuclear magnetic resonance (NMR) spectroscopy. Lactate was detected following swimming at all speeds, but its concentration was greatest following swimming at 80 and 100 %Ucrit. Phosphocreatine stores were reduced following swimming at 70 and 80 %Ucrit, but were further depleted following swimming at 100 %Ucrit. Following swimming at 70 and 80 %Ucrit, lactate concentrations were higher in the rostral, relative to the caudal, musculature, whereas phosphocreatine stores were least depleted in the mid, relative to the rostral and caudal, musculature. There were no differences among muscle locations in concentrations of lactate and phosphocreatine following swimming to 100 %Ucrit. Our results indicate that anaerobic metabolism is required to support swimming at speeds equal to and greater than 70 %Ucrit. Estimates of the relative cost of anaerobic metabolism during sub-maximal swimming are presented for swimming at 70 %, 80 % and 100 %Ucrit, and the implications of these results to energy budgets are discussed.
Influence of Cycle Frequency, Muscle Strain and Muscle Length on work and Power Production of Rainbow Trout (Oncorhynchus Mykiss) Ventricular Muscle
Authors: Harwood Claire L. , Young Iain S. , Altringham John D.
Published: April 2021

This study investigates the effects of cycle frequency, strain and length on work and power output of isolated rainbow trout (Oncorhynchus mykiss) ventricular preparations using the work loop technique. These effects are discussed in the context of the whole heart using analogies with heart rate, stroke volume and end-diastolic volume.

Power output was dependent on cycle frequency, increasing threefold beween 0.3 and 1.1 Hz. The frequency for maximum power output was approximately 1.1 Hz, corresponding to the frequency for maximum power in perfused heart experiments.

The length for maximum work production (Lopt) was found to be the same as the length for maximum isometric force production (Lmax). The decline in net work at lengths greater than Lopt/Lmax was attributed to an increase in passive work (the work done on an unstimulated muscle) or to hysteresis and to a large increase in lengthening work.

The strain yielding maximum work decreased with increasing frequency. This is discussed in the context of the decline in stroke volume observed at increased heart rates in vivo.

Muscle strain in intact hearts paced at 0.3 Hz was ±11.9 % (23.8 % peak to peak), a value similar to the optimum strain at 0.3 Hz in vitro (±12 %).
Cardiac Output as a Predictor of Metabolic Rate in Cod Gadus Morhua
Authors: Webber D. M. , Boutilier R. G. , Kerr S. R.
Published: April 2021

Adult Atlantic cod (2 kg Gadus morhua) were fitted with Doppler ultrasonic flow-probes to measure ventral aortic outflow (i.e. cardiac output). The probes remained patent for upwards of 3 months, during which time detailed relationships between cardiac output (Q̇), heart rate (fH) and rate of oxygen consumption were determined as a function of swimming speed and temperature (5 °C and 10 °C).The rate of oxygen consumption increased linearly with Q̇ and exponentially with swimming speed. A verygood correlation was observed between and Q̇ (r2=0.86) compared with the correlation between and fH (r2=0.50 for all 10 °C data and r2=0.86 for all 5 °C data). However, the versus fH correlation gradually improved over approximately 1 week after surgery (r2=0.86). The relationship between and Q̇ was independent of temperature, while the relationship between and fH changed with temperature. Hence, calculating from Q̇ is simpler and does not require that temperature be recorded simultaneously. Variations in cardiac output were determined more by changes in stroke volume (Vs) than by fH; therefore, fH was a less reliable predictor of metabolic rate than was Q̇. Given that Q̇ can be used to estimate so faithfully, the advent of a cardiac output telemeter would enable robust estimates to be made of the activity metabolism of free-ranging fish in nature, thereby strengthening one of the weakest links in the bioenergetic models of fisheries biology.
Effects Of Nonylphenol And 17β-Oestradiol On Vitellogenin Synthesis, Testicular Structure And Cytology In Male Eelpout Zoarces Viviparus
Authors: Christiansen T. , Korsgaard B. , Jespersen Å.
Published: April 2021

Nonylphenol has been found to be oestrogenic in fish and may influence the reproductive system of male fish. In the present study, the effects of low (10 µg g−1 week−1 ) and high (100 µg g−1 week−1 ) doses of nonylphenol and of 17β-oestradiol on the synthesis of vitellogenin and on testicular structure and cytology were investigated in male eelpout Zoarces viviparus during active spermatogenesis (May) and late spermatogenesis (June). Twenty-five days after injection, a significant dose-dependent increase in the plasma vitellogenin concentration, measured by enzyme-linked immunosorbent assay, was observed in the treated groups. A highly significant reduction in the gonadosomatic index was observed concomitant with the increase in the plasma vitellogenin concentration. Macroscopically, milt was observed to be present in the control fish, but was sparse or absent in the treated fish. Histological examination using light microscopy revealed severe effects of nonylphenol as well as of oestradiol treatment on testicular structure. Control fish had seminiferous lobules containing spermatogenic cysts and only a few spermatozoa (May) or had the walls of their seminiferous lobules lined with cuboidal Sertoli cells (June). In the treated fish, the seminiferous lobules were degenerated (May) or were filled with numerous spermatozoa and the Sertoli cells appeared very squamous (June). Electron microscopy revealed greater numbers of phagocytozed spermatozoa in these Sertoli cells. In rats, γ-glutamyl transpeptidase (γ-GTP) has been used as a specific marker of Sertoli cell function. In the present study, both nonylphenol and 17β-oestradiol treatment resulted in a reduction in the activity of this enzyme. The study provides evidence that nonylphenol is oestrogenic, as indicated by the large increase in vitellogenin synthesis, and that both nonylphenol and oestradiol have marked effects on the testicular structure and cytology of germ cells and Sertoli cells of male Z. viviparus.
Two Types of mRNA Encoding Myosin Regulatory Light Chain in Carp Fast Skeletal Muscle Differ in Their 3′ Non-Coding Regions and Expression Patterns Following Temperature Acclimation
Authors: Hirayama Yasushi , Kobiyama Atsushi , Ochiai Yoshihiro , Watabe Shugo
Published: April 2021

cDNA clones encoding the myosin regulatory light chain (RLC) were isolated from a cDNA library prepared from fast skeletal muscle of the carp Cyprinus carpio L. Two types of cDNA clone encoding carp RLC were found with identical deduced amino acid sequences. The two mRNAs differed in the number of polyadenylation signals prior to the poly(A) tail in the 3′ non-coding region. The two mRNA species, with approximate sizes of 1.4 and 0.8 kilobases, were also observed in northern blot analysis. Carp were acclimated for a minimum of 5 weeks to either 10 °C or 30 °C (14 h:10 h light:dark photoperiod). The total levels of mRNA transcripts coding for the RLC and myosin heavy chain were, respectively, 3.3 and 3.9 times higher in cold-than in warm-acclimated fish. Differences in the levels of RLC in mRNA transcripts were largely due to the concentration of the 1.4 kilobase mRNA species.
Receptor Cell Habituation in the a1 Auditory Receptor of Four Noctuoid Moths
Authors: Coro Frank , Pérez Martha , Mora Emanuel , Boada Danilo , Conner William E. , Sanderford Mark V. , Avila Héctor
Published: April 2021

Moths of both sexes of Empyreuma affinis (=pugione) and Syntomeida epilais (Arctiidae, Ctenuchinae), Maenas jussiae (Arctiidae, Arctiinae) and Spodoptera frugiperda (Noctuidae, Amphipyrinae) were studied. Spike activity in the A1 cell was recorded using a stainless-steel hook electrode from the tympanic nerve in the mesothorax. Acoustic stimuli consisting of 25 and 100 ms pulses at the best frequency for the species and at intensities that evoke A1 cell saturation response were used at repetition rates of 0.5 and 5 Hz for 100 ms stimuli, and between 2 and 20 Hz for 25 ms stimuli. Stimuli at a repetition rate corresponding to a duty cycle of 5 % (25 ms at 2 Hz and 100 ms at 0.5 Hz) did not evoke monotonic changes in the responses of the A1 cell. With 25 ms pulses, rates above 5 Hz evoked an exponential decrease in the number of spikes and an increase in the latency of the responses of all the 37 specimens tested. The response duration showed no apparent change with stimulus repetition rates even at the highest duty cycle used (50 %), i.e. 25 ms at 20 Hz and 100 ms at 5 Hz. The higher the rate of stimulus repetition, the more marked were the changes in the A1 cell responses. In 16 of 17 preparations from two species, habituation had no effect on the adaptation rate in each response, while in seven of eight specimens of another species, the adaptation rate decreased with stimulus repetition. These results, and those from another mechanoreceptor cell, indicate that receptor cell adaptation (changes evoked in the response by a stimulus of constant intensity) and habituation (changes in the responses due to stimulus repetition rate) are two distinctive phenomena. The A1 cell in its habituated state showed an increase in its response to incremental increases in stimulus intensity of 10 dB. This result supports the idea that receptor cell habituation does not seem to be due to fatigue, i.e. to a temporary loss of the ability to respond to stimulation induced in a sensory receptor by continued stimulation.
Structure and function of the vomeronasal organ
Authors: Døving Kjell B. , Trotier Didier
Published: April 2021

Many animals use their vomeronasal organs to gain direct and specific contact with chemical cues released by congeners and in biological fluids. These cues provide information about the physiological status of the emitter and facilitate or regulate social interactions such as sexual relationships. The present review gives a short description of the discovery of the vomeronasal organ and the pivotal findings of Jacobson. The distribution of the organ and its anatomy in some vertebrates are described. The mechanisms for stimulus entry and egress are discussed, and the findings that led to the appreciation of the vomeronasal organ in mammals as a main chemosensory organ for pheromones mediating reproductive status and inducing sexual behaviour are reported. The anatomical, biochemical and functional properties of the receptor neurones are described.
The effect of respiratory pattern on water loss in desiccation-resistant Drosophila melanogaster
Authors: Williams Adrienne E. , Bradley Timothy J.
Published: April 2021

We measured CO2 and H2O release from individual fruit flies from five populations of Drosophila melanogaster selected for resistance to desiccation (D flies). Our previous work found that these flies survive for an extended period in dry air, have an increase in the peak height and frequency of CO2 release, as measured by the standard error of a linear regression (SER) of CO2 release for the en. tire survival period, and have reduced water loss rates compared with their control or ancestor populations. In the present study, we examined the following respiratory characteristics: , the SER of CO2 release and the ratio of to in the D flies. Correlations between these characters were calculated in order to determine the effect of respiratory pattern on water loss. We found that, within the D flies, neither periodic release of CO2 nor an increased SER for CO2 release was associated with reduced water loss. In addition, an increased SER was positively correlated with both an increased water loss rate and a decreased survival time. Therefore, although selection for desiccation resistance leads to both an increased SER and a decreased rate of water loss in the D flies, the increased SER does not significantly reduce respiratory water loss.
Effects of food nutrient content, insect age and stage in the feeding cycle on the fmrfamide immunoreactivity of diffuse endocrine cells in the locust gut
Authors: Zudaire Enrique , Simpson Steve J. , Montuenga Luis M.
Published: April 2021

We have studied the influence of variations in dietary protein and digestible carbohydrate content, of insect age and of time during the feeding cycle on the endocrine cells of the ampullar region of the midgut in the African migratory locust Locusta migratoria L. Morphometric analysis of FMRFamide-like immunoreactivity was used as an indirect measure of the amount of FMRFamide-related peptides (FaRPs) stored in the gut endocrine cells. There was a highly significant correlation between FaRP content and the nutritional quality of the food, measured relative to the concentrations and ratio of protein to digestible carbohydrate in a nutritionally optimal diet. The direction of the relationship between FaRP content and diet quality varied with age during the fifth stadium. On day 1, FaRP levels increased with the nutritional quality of the food, while on day 4 the opposite relationship was observed. Release of peptide was triggered by the onset of a meal during ad libitum feeding, with cell FaRP levels returning to premeal values within 15 min of the meal ending. The results also suggested that cell contents were released during food deprivation beyond the normal intermeal interval. Locusts switched for a single meal during ad libitum feeding on day 4 from a low-to a high-carbohydrate food did not respond by reducing endocrine cell FaRP content. Our results show a relationship between the diffuse gut endocrine system and feeding and nutrition in locusts. The ampullar endocrine cells are in three-way contact with the midgut luminal contents, with the primary urine from the Malpighian tubules and with the haemolymph. They are thus ideally positioned to play an integrative receptor-secretory function in the regulation of a variety of post-ingestive processes, such as enzyme secretion, absorption, gut motility or nutrient metabolism.
Steroid-regulated morphological plasticity in a set of identified peptidergic neurons in the moth Manduca sexta
Authors: McGraw Hillary F. , Prier Kevin R. S. , Wiley Jesse C. , Tublitz Nathan J.
Published: April 2021

The lateral neurosecretory cells (LNCs) in the tobacco hornworm Manduca sexta undergo a switch in neurotransmitter phenotype during pupation. Concurrent with this change in function, the LNCs undergo a major morphological reorganization. This study characterizes the morphological change and its underlying cause. In the larva, the LNC has a very compact dendritic arborization in a small volume of neuropil ipsilateral to the cell soma. In the adult moth, the LNC arborization extends through a much larger volume of neuropil, including the contralateral side of the ganglion. Using both in vivo manipulations and a single-cell culture system, we show that this change in morphology is probably triggered by two pulses of the steroid hormone 20-hydroxyecdysone (20-HE): a small commitment peak and a larger prepupal pulse. These are the same two pulses of 20-HE as those previously shown jointly to cause the change in transmitter phenotype. This work, in conjunction with a previous study on the transmitter switch, documents the orchestration of major morphological and biochemical changes in a set of identified neurons by a single hormone.
Rostral–caudal variation in troponin T and parvalbumin correlates with differences in relaxation rates of cod axial muscle
Authors: Thys Tierney M. , Blank Jason M. , Schachat Fred H.
Published: April 2021

Relaxation rate is an important determinant of axial muscle power production during the oscillatory contractions of undulatory locomotion. Recently, significant differences have been reported in the relaxation rates of rostral versus caudal white muscle fibers of the Atlantic cod Gadus morhua L. The present study investigates the biochemical correlates of this rostral–caudal physiological variation. Using denaturing gel electrophoresis, a series of fresh muscle samples from the dorsal epaxial muscle region was analyzed and several differences were detected. First, a gradual shift occurs in the expression of two troponin T isoforms along the length of the body. Second, rostral muscles were found to contain significantly greater amounts of parvalbumin than caudal muscles. Third, two soluble Ca2+-binding proteins, in addition to parvalbumin, were also detected in the rostral muscle samples yet were absent from the caudal samples. This suite of rostral–caudal variations provides a strong biochemical basis for regional differences in the relaxation rates of cod white muscle.
Immunolocalization of Na+/K+-ATPase in Branchial Epithelium of Chum Salmon Fry During Seawater and Freshwater Acclimation
Authors: Shikano Takahito , Fujio Yoshihisa
Published: April 2021

Immunolocalization of the α-subunit of Na+/K+-ATPase was examined in the gill epithelium of chum salmon (Oncorhynchus keta) fry during acclimation to brackish water (25 ‰ salinity) and reintroduction to fresh water. In freshwater fish, strong immunoreactivity was associated with the large spherical cells located on the free surface of the primary lamellae, especially in those found at the base of the secondary lamellae, and with the large spherical cells located on the secondary lamellae.The large spherical cells located near the central venous sinus at the base of the secondary lamellae and in the interlamellar regions, however, showed little or no immunoreactivity. When freshwater fish were acclimated to brackish water, immunoreactivity developed in the large spherical cells near the central venous sinus concomitant with an increase in the hypo-osmoregulatory ability of the fish. In contrast, reintroduction from brackish water to fresh water caused the disappearance of the immunoreactivity in the large spherical cells near the central venous sinus and a reduction in hypo-osmoregulatory ability. During acclimation to brackish water and reintroduction to fresh water, the hypo-osmoregulatory ability of the fish did not correlate with the total number of large spherical cells located on the primary lamellae but was closely correlated with the number of large spherical cells showing strong immunoreactivity for Na+/K+-ATPase. We conjecture that these immunopositive large spherical cells are mature differentiated chloride cells, whereas the immunonegative large spherical cells are young developing chloride cells. The development of immunoreactivity for Na+/K+-ATPase in young chloride cells may be one of the most important factors in the development of hypo-osmoregulatory ability by chum salmon fry.
Na+ -dependent phosphate cotransporters: the NaPi protein families
Authors: Werner Andreas , Dehmelt Leif , Nalbant Perihan
Published: April 2021

In vertebrates, the level of inorganic phosphate (Pi) is tightly balanced both inside the cell and in the whole organism. A number of different Na+ -dependent Pi cotransport systems involved in Pi homeostasis have been identified and characterized at the molecular level in the past 7 years. The transporters constitute three different protein families denoted NaPi-I, NaPi-II and NaPi-III. NaPi-I from the rabbit was the first member of this family to be cloned. However, it still resists efforts to unravel its physiological role and a clear-cut functional identity: is it a Cl− channel, a Na+ /Pi cotransporter, a regulator, or does it perform a combination of these functions? These questions provide a slight taste of the problems associated with orphan genes derived from sequencing projects. The members of the NaPi-II protein family are crucially involved in tightly controlled renal Pi excretion and, as recently discovered, intestinal Pi absorption. The expression and the cellular distribution of NaPi-II in the proximal tubular epithelium are affected by hormonal and metabolic factors known to influence extracellular fluid Pi homeostasis. Recently, the expression of NaPi-II has been demonstrated in osteoclasts and brain; however, the physiological roles of NaPi-II in these tissues remain to be established. The members of the third protein family, NaPi-III, have been identified on the basis of their function as viral receptors. The widespread expression of this family suggests that NaPi-III is involved in supplying the basic cellular metabolic needs for Pi.
Strategies for migration in the terrestrial christmas island red crab gecarcoidea natalis: intermittent versus continuous locomotion
Authors: Adamczewska Agnieszka M. , Morris Stephen
Published: April 2021

The terrestrial red crab Gecarcoidea natalis undertakes an annual breeding migration and must sustain locomotion for prolonged periods. The migrating crabs must travel a specific distance in a fixed time and can either walk at a constant speed or walk faster for short periods and then pause to feed or rest. To simulate the potential differences between continuous and intermittent locomotion during the migration, red crabs were sampled after walking at a voluntary speed for 5 or 20 min without pausing or after 20 min of enforced walking intermittently at approximately twice that speed. The respiratory and metabolic status of the crabs was investigated during the different exercise regimes to assess which strategy might be more advantageous during the migration.

The gills and lungs appeared to function similarly in gas exchange, and the in the haemolymph was 8.2 kPa which fully saturated the haemocyanin with O2. The uptake of O2 by red crabs was diffusion-limited and the diffusion coefficient (Ldiff) varied from 0.53 in resting crabs to 0.8 post-exercise. Post-exercise, red crabs experienced a mixed respiratory/metabolic acidosis which was greatest (0.2 pH units) in crabs walking intermittently, i.e. at a higher speed. Haemolymph L- lactate concentrations peaked at 5 mmol l−1 immediately post-exercise in the intermittent exercise group, whereas after 20 min of continuous exercise haemolymph L-lactate continued to increase, reaching a maximum of 2.5 mmol l−1 at 1 h post-exercise. L-Lactate recovered slowly to basal levels within 5 h. The maximum rate of L- lactate clearance from the haemolymph was only 1.75 mmol l−1 h−1, and short pauses in exercise were insufficient for substantial L-lactate reoxidation. Exercise regimes in the laboratory were within the locomotor speeds determined for migrating red crabs, which overall have a mean walking speed close to their aerobic limit but periodically pause and also exceed this limit by three- to fourfold.
Are Integrins Involved in the Aggregatory and Phagocytic Behaviour of Fish Haemostatic Cells?
Authors: Hill Darryl J. , Rowley Andrew F.
Published: April 2021

The involvement of a putative integrin-like fibrinogen receptor in the aggregatory and phagocytic behaviour of thrombocytes (platelet equivalents of fish) from the rainbow trout Oncorhynchus mykiss was studied. Aggregation of trout thrombocytes was induced by the thromboxane mimetic U-46619 in the presence of trout fibrinogen. Thrombocyte aggregation was inhibited by the tetrapeptide RGDS, but not by RGES or fibrinogen binding inhibitor peptide (HHLGGAKQAGDV). A range of monoclonal antibodies against the human platelet integrin α IIbα 3 (anti-CD41a, anti-α 3 and LK7r) showed no reactivity with trout thrombocytes. Subsequently, a panel of monoclonal antibodies was raised against thrombocyte membrane preparations in an attempt to obtain an antibody against the putative integrin fibrinogen receptor. Of these monoclonal antibodies, four were found to inhibit thrombocyte aggregation, namely 12G2, 30D8, 32F8 and 32H10. The antibody 32H10 was shown significantly to inhibit the attachment of thrombocytes to immobilised trout fibrinogen, suggesting that it and the other antibodies recognise the putative fibrinogen receptor on trout thrombocytes. FITC-labelled Bacillus cereus were employed as test particles to prove that thrombocytes internalise bacteria via an active process and not simply by passive sequestration into the open canalicular system. Preincubation of bacteria with trout fibrinogen resulted in a significant increase in the number of thrombocytes exhibiting phagocytosis. This enhancement of phagocytosis by preincubation of B. cereus with trout fibrinogen could be inhibited by the tetrapeptide RGDS, but not by RGES, hence implicating the putative fibrinogen receptor in the internalisation of microorganisms. The relevance of these findings to the possible existence of an integrin-like receptor on trout thrombocytes is discussed.
Sound Radiation by the Bladder Cicada Cystosoma Saundersii
Authors: Bennet-Clark H. C. , Young D.
Published: April 2021

Male Cystosoma saundersii have a distended thin-walled abdomen which is driven by the paired tymbals during sound production. The insect extends the abdomen from a rest length of 32–34 mm to a length of 39–42 mm while singing. This is accomplished through specialised apodemes at the anterior ends of abdominal segments 4–7, which cause each of these intersegmental membranes to unfold by approximately 2 mm.

The calling song frequency is approximately 850 Hz. The song pulses have a bimodal envelope and a duration of approximately 25 ms; they are produced by the asynchronous but overlapping action of the paired tymbals. The quality factor Q of the decay of the song pulses is approximately 17.

The abdomen was driven experimentally by an internal sound source attached to a hole in the front of the abdomen. This allowed the sound-radiating regions to be mapped. The loudest sound-radiating areas are on both sides of tergites 3–5, approximately 10 mm from the ventral surface. A subsidiary sound-radiating region is found mid-ventrally on sternites 4–6. Sound is radiated in the same phase from all these regions. As the abdomen was extended experimentally from its resting length to its maximum length, the amplitude of the radiated sound doubled and the Q of the resonance increased from 4 to 9. This resonance and effect are similar at both tergite 4 and sternite 5.

Increasing the effective volume of the abdominal air sac reduced its resonant frequency. The resonant frequency was proportional to 1/√(total volume), suggesting that the air sac volume was the major compliant element in the resonant system. Increasing the mass of tergite 4 and sternites 4–6 also reduced the resonant frequency of the abdomen. By extrapolation, it was shown that the effective mass of tergites 3–5 was between 13 and 30 mg and that the resonant frequency was proportional to 1/√(total mass), suggesting that the masses of the tergal sound-radiating areas were major elements in the resonant system.

The tymbal ribs buckle in sequence from posterior (rib 1) to anterior, producing a series of sound pulses. The frequency of the pulse decreases with the buckling of successive ribs: rib 1 produces approximately 1050 Hz, rib 2 approximately 870 Hz and rib 3 approximately 830 Hz. The sound pulse produced as the tymbal buckles outwards is between 1.6 and 1.9 kHz. Simultaneous recordings from close to the tymbal and from tergite 4 suggest that the song pulse is initiated by the pulses produced by ribs 2 and 3 of the leading tymbal and sustained by the pulses from ribs 2 and 3 of the second tymbal.

An earlier model suggested that the reactive elements of the abdominal resonance were the compliance of the abdominal air sac volume and the mass of the abdomen undergoing lengthwise telescoping. The present work confirms these suggestions for the role of the air sac but ascribes the mass element to the in–out vibrations of the lateral regions of tergites 3–5 and the central part of sternites 4–6.
Responses of the Na+/H+ exchanger of european flounder red blood cells to hypertonic, β-adrenergic and acidotic stimuli
Authors: Weaver Y. R. , Kiessling K. , Cossins A. R.
Published: April 2021

The transport pathways mediating regulatory volume increase (RVI) and β-adrenergic responses in red cells of the European flounder Platichthys flesus have been investigated. Hypertonic treatment under a low-atmosphere led to a complete RVI and to a three-to fourfold increase in Na+ influx. The RVI and the activated Na+ influx were blocked by the transport inhibitors amiloride and 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS), both at a concentration of 10−4 mol l−1, and the RVI was abolished in a Na+-free saline, indicating the involvement of a hypertonically induced Na+/H+ exchanger and an accompanying Cl−/HCO3− exchanger. Both the hypertonically induced Na+ influx and the RVI were blocked by oxygenation of shrunk cells. The β-adrenergic agonist isoproterenol also strongly activated a Na+ influx and caused cell swelling. This response was also inhibited by amiloride and DIDS but was unaffected by oxygenation. Simultaneous application of isoproterenol and hypertonic shrinkage did not lead to additive Na+ influxes, suggesting that both responses were mediated by the same pool of exchangers. Mild cell acidification activated a Na+ influx under iso-osmotic conditions; amiloride caused partial inhibition of this influx, but oxygenation had no effect. Acid-induced and isoproterenol-induced Na+ fluxes were again non-additive. Thus, the Na+/H+ exchanger of flounder red cells is strongly activated by three physiological stimuli: hypertonic shrinkage, β-adrenergic hormones and cell acidification. Of these responses, only the first is affected by oxygenation, indicating some differentiation of their respective transduction mechanisms. These characteristics contrast with those of the corresponding exchangers from rainbow trout and eel red cells.
Control of gill ventilation and air-breathing in the bowfin Amia calva
Authors: Hedrick Michael S. , Jones David R.
Published: April 2021

The purpose of this study was to investigate the roles of branchial and gas bladder reflex pathways in the control of gill ventilation and air-breathing in the bowfin Amia calva. We have previously determined that bowfin use two distinct air-breathing mechanisms to ventilate the gas bladder: type I air breaths are characterized by exhalation followed by inhalation, are stimulated by aquatic or aerial hypoxia and appear to regulate O2 gas exchange; type II air breaths are characterized by inhalation alone and possibly regulate gas bladder volume and buoyancy. In the present study, we test the hypotheses (1) that gill ventilation and type I air breaths are controlled by O2-sensitive chemoreceptors located in the branchial region, and (2) that type II air breaths are controlled by gas bladder mechanosensitive stretch receptors. Hypothesis 1 was tested by examining the effects of partial or complete branchial denervation of cranial nerves IX and X to the gill arches on gill ventilation frequency (fG) and the proportion of type I air breaths during normoxia and hypoxia; hypothesis II was tested by gas bladder inflation and deflation. Following complete bilateral branchial denervation, fG did not differ from that of sham-operated control fish; in addition, fG was not significantly affected by aquatic hypoxia in sham-operated or denervated fish. In sham-operated fish, aquatic hypoxia significantly increased overall air-breathing frequency (fAB) and the percentage of type I breaths. In fish with complete IX–X branchial denervation, fAB was also significantly increased during aquatic hypoxia, but there were equal percentages of type I and type II air breaths. Branchial denervation did not affect the frequency of type I air breaths during aquatic hypoxia. Gas bladder deflation via an indwelling catheter resulted in type II breaths almost exclusively; furthermore, fAB was significantly correlated with the volume removed from the gas bladder, suggesting a volume-regulating function for type II air breaths. These results indicate that chronic (3–4 weeks) branchial denervation does not significantly affect fG or type I air-breathing responses to aquatic hypoxia. Because type I air-breathing responses to aquatic hypoxia persist after IX–X cranial nerve denervation, O2-sensitive chemoreceptors that regulate air-breathing may be carried in other afferent pathways, such as the pseudobranch. Gas bladder deflation reflexly stimulates type II breaths, suggesting that gas bladder volume-sensitive stretch receptors control this particular air-breathing mechanism. It is likely that type II air breaths function to regulate buoyancy when gas bladder volume declines during the inter-breath interval.
Does Membrane Fluidity Contribute to Thermal Compensation of β-Adrenergic Signal Transduction in Isolated Trout Hepatocytes?
Authors: Mckinley Susan J. , Hazel Jeffrey R.
Published: April 2021

The potential role of compensatory adjustments to membrane components in determining the function of the β-adrenergic receptor/adenylyl cyclase (β-AR/AC) signal-transduction system was studied in isolated hepatocytes of 5 °C- and 20 °C-acclimated rainbow trout Oncorhynchus mykiss. Rates of epinephrine-stimulated cyclic AMP (cAMP) production, although slowed (by a factor of 1.6-to 2.4-fold) by an acute drop in assay temperature from 20 to 5 °C, were significantly temperature-compensated, being approximately twofold higher in hepatocytes of 5 °C-than of 20 °C-acclimated trout. Membrane order in the bilayer interior of hepatocyte plasma membranes (as assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene) was consistently lower in cold-than in warm-acclimated trout, reflecting an efficacy of homeoviscous adaptation of approximately 50 %. Temperature-induced changes in plasma membrane fatty acid composition (i.e. an increase in the proportions of polyunsaturated fatty acids with acclimation to 5 °C) were consistent with both the observed changes in the order of the bilayer interior and the extent of homeoviscous adaptation. However, isothermal fluidization of the bilayer interior by the addition of benzyl alcohol (30 mmol l−1) decreased rather than increased the rate of cAMP production. Significantly more (1.81-fold) β-adrenergic receptors were present in plasma membranes of hepatocytes from 5 °C-acclimated (6.23×104±4206 receptors per cell; mean ± S.E.M., N=3) than 20 °C-acclimated fish (3.44×104±4360 receptors per cell; N=3) when assayed at the acclimation temperature, whereas the equilibrium dissociation constants (Kd) (13.73±4.33 nmol l−1 at 5 °C; 9.75±3.29 nmol l−1 at 20 °C; N=3) were similar. On the basis of a strong correlation between β-adrenoceptor number and the rate of cAMP production (r2=0.956), regardless of assay or acclimation temperature, we conclude that modulation of receptor number is the primary acclimatory response of this signal-transduction pathway to temperature change in trout liver.
Thermal Thresholds of Lipid Restructuring and Δ9-Desaturase Expression in the Liver of Carp (Cyprinus Carpio L.)
Authors: Trueman R. J. , Tiku P. E. , Caddick M. X. , Cossins A. R.
Published: April 2021

Cold acclimation induces a transient enzymatic activation of the acyl CoA-Δ9-desaturase in carp liver. We have determined thresholds for two underlying mechanisms; namely, the activation of latent enzyme and the induced synthesis of new desaturase. Carp were progressively cooled from 30 °C to 23, 17 and 10 °C, where they were held for up to 5 days. Endoplasmic reticulum phospholipids showed substantial changes in fatty acid composition, with linear decreases in the proportion of saturates with temperature over the full range of cooling (11.3 % in phosphatidylcholine and 15.8 % in phosphatidylethanolamine). In the phosphatidyl-ethanolamine fraction, this was linked to increased proportions of monoenes, particularly 20:1(n-9).

Modest cooling to 23 °C on day 1 induced a 2.5-fold transient increase in Δ9-desaturase activity without any change in the amount of desaturase protein or transcript. Further cooling to 17 °C induced a greater and more sustained increase in desaturase activity, reaching sevenfold on day 5, with a 10- to 20-fold increase in the amount of desaturase transcript. Extreme cooling to 10 °C led to a very large, but transient, 40- to 50-fold increase in desaturase transcript amounts, a modest 40–50 % increase in desaturase protein but no further increase in activity over that observed at 17 °C.

These results distinguish at least three mechanisms involved in cold-induced lipid restructuring; the activation of latent desaturase observed with gentle cooling, the induction of desaturase gene transcription and, finally, a third unidentified lipid compensatory mechanism that occurs with extreme cooling. The complex nature of cold-induced lipid restructuring also involves changes in the activity of other biosynthetic enzymes, including elongase and positional- and phospholipid-specific acyltransferases.
The Interplay Among Cardiac Ultrastructure, Metabolism and The Expression of Oxygen-Binding Proteins in Antarctic Fishes
Authors: O’Brien Kristin M. , Sidell Bruce D.
Published: April 2021

We examined heart ventricle from three species of Antarctic fishes that vary in their expression of oxygen-binding proteins to investigate how some of these fishes maintain cardiac function despite the loss of hemoglobin (Hb) and/or myoglobin (Mb). We quantified ultrastructural features and enzymatic indices of metabolic capacity in cardiac muscle from Gobionotothen gibberifrons, which expresses both Hb and Mb, Chionodraco rastrospinosus, which lacks Hb but expresses Mb, and Chaenocephalus aceratus, which lacks both Hb and Mb. The most striking difference in cellular architecture of the heart among these species is the percentage of cell volume occupied by mitochondria, Vv(mit,f), which is greatest in Chaenocephalus aceratus (36.53±2.07), intermediate in Chionodraco rastrospinosus (20.10±0.74) and lowest in G. gibberifrons (15.87±0.74). There are also differences in mitochondrial morphologies among the three species. The surface area of inner mitochondrial membrane per volume of mitochondria, Sv(imm,mit), varies inversely with mitochondrial volume density so that Sv(imm,mit) is greatest in G. gibberifrons (29.63±1.62 μm−1), lower in Chionodraco rastrospinosus (21.52±0.69 μm−1) and smallest in Chaenocephalus aceratus (20.04±0.79 μm−1). The surface area of mitochondrial cristae per gram of tissue, however, is greater in Chaenocephalus aceratus than in G. gibberifrons and Chionodraco rastrospinosus, whose surface areas are similar. Despite significant ultrastructural differences, oxidative capacities, estimated from measurements of maximal activities per gram of tissue of enzymes from aerobic metabolic pathways, are similar among the three species. The combination of ultrastructural and enzymatic data indicates that there are differences in the density of electron transport chain proteins within the inner mitochondrial membrane; proteins are less densely packed within the cristae of hearts from Chaenocephalus aceratus than in the other two species. High mitochondrial densities within hearts from species that lack oxygen-binding proteins may help maintain oxygen flux by decreasing the diffusion distance between the ventricular lumen and mitochondrial membrane. Also, high mitochondrial densities result in a high intracellular lipid content, which may enhance oxygen diffusion because of the higher solubility of oxygen in lipid compared with cytoplasm. These results indicate that features of cardiac myocyte architecture in species lacking oxygen-binding proteins may maintain oxygen flux, ensuring that aerobic metabolic capacity is not diminished and that cardiac function is maintained.
Sensory Preconditioning in Honeybees
Authors: Müller Dirk , Gerber Bertram , Hellstern Frank , Hammer Martin , Menzel Randolf
Published: April 2021

Sensory preconditioning means that reinforcement of stimulus A after unreinforced exposure to a compound AB also leads to responses to stimulus B. Here, we describe and analyze sensory preconditioning in an insect, the honeybee Apis mellifera. Using two-element odorant compounds in classical conditioning of the proboscis extension reflex, we found (i) that sensory preconditioning is not due to stimulus generalization, (ii) that paired, but not unpaired, presentation of elements supports sensory preconditioning, (iii) that simultaneous, but not sequential, exposure to the elements of the compound supports sensory preconditioning and (iv) that a single presentation of the compound yields maximal sensory preconditioning. The results are discussed with respect to configural and chain-like associative explanations for sensory preconditioning. We suggest an experience-dependent step of compound processing, establishing configural units, as an additional explanation for sensory preconditioning.
The Oxalate/Sulfate Antiporter in Lobster Hepatopancreas: Internal and External Binding Constants
Authors: A. Gerencser George , Burgin Charles , Robbins Frank , Ahearn Gregory A.
Published: April 2021

Utilizing a purified basolateral plasma membrane vesicle (BLMV) preparation containing a sulfate/oxalate antiporter, it was demonstrated that sulfate exhibited similar binding characteristics to the transporter whether bound internally or externally. It was also demonstrated that oxalate had similar binding characteristics to the antiporter whether it was bound internally or externally. Oxalate had a greater affinity to the transporter than did sulfate. Several organic anions affected binding and, therefore, overall transport by the antiporter. Most notably, sulfate was the only anion that stimulated oxalate uptake into BLMVs, which suggests a conservative binding specificity for the antiporter. 4-Acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid (SITS) and/or 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) inhibited the transport rate, confirming the existence of oxalate/sulfate exchange by the transporter. These results suggest that oxalate, not sulfate, regulates the transport rate because of its greater affinity to the transporter.