bluuebunny/crossref_metadata_2025 huggingface dataset:
The Water Relations of Snails and Slugs
Authors: Wells G. P.
Published: April 2021

If H. pomatia are kept under conditions of constant temperature, humidity, illumination, food supply and water supply, their daily weight curves show great spontaneous fluctuations of an irregularly cyclical character, with a period of several days. Snails kept without food, but under otherwise identical conditions, show similar fluctuations of smaller amplitude (Fig. 1). A number of measurements of the oxygen consumption of H. pomatia were made at different points on the weight cycle. In fed animals, oxygen consumption tends to rise with weight. In fasting animals, the relationship between the two variables is less marked, and the oxygen consumption is always low (Figs. 2, 3). Aestivation tends to occur, even if environmental conditions are favourable, whenever the weight is low (Fig. 4). Feeding and digestion are apparently confined to the weight peaks, and incompatible with aestivation. The interrelations of internal and external factors in determining the activity level of H. pomatia are discussed. In drought, the activity outbursts are inhibited and the snail remains withdrawn, with low weight and oxygen consumption. Rain, after drought, releases the cycles again; the immediate mechanism of activation is not hydration of the tissues, but a stimulation effect.
Quantitative Analysis of Jaw and Hyolingual Muscle Activity During Feeding in the Lizard Agama Stellio
Authors: Herrel Anthony , Cleuren Johan , Vree Frits De
Published: April 2021

The activity of jaw and hyolingual muscles during the entire feeding sequence is examined in the lizard Agama stellio, with special focus on the intraoral transport and swallowing stages. Correlation of electromyography (EMG) data with kinematics shows that the kinematic phases (slow opening, SO; fast opening, FO; fast closing, FC; slow closing/power stroke, SC/PS) are characterised by distinct activities in the jaw and hyolingual muscles. The SO phase is clearly the result of tongue protraction (upon protraction, the tongue is pulled against the prey and consequently the lower jaw is pushed down), whereas the FO phase is caused by activity in the jaw opener and dorsal cervical muscles. Both the FC and SC/PS phases are characterised by pronounced activity in the jaw adductor muscles. Tongue retraction is produced by activity in the hyoid and tongue retractor muscles. A quantitative analysis of time-related EMG data shows that, in accordance with the kinematic analyses, three different stages can be recognised as components of the feeding cycle: prey capture, intraoral transport and swallowing. However, analysis of intensity-related data allowed a fourth stage, crushing, to be detected. Whereas there are indications that prey capture, intraoral transport and swallowing are controlled by different motor patterns, the differences between crushing and transport are likely to be caused by feedback mechanisms. Our results show the importance of including intensity-related data in quantitative analyses of EMG recordings in order to discriminate between feeding stages. Additionally, it is shown that both the jaw and the hyolingual muscles play crucial roles during feeding. During all stages, movements of the hyolingual apparatus are an essential part of the feeding cycle. Thus, when examining lizard feeding mechanisms, the activity patterns of the hyolingual muscles should not be neglected.
Correlation Between Changes in Host Behaviour and Octopamine Levels in the Tobacco Hornworm Manduca Sexta Parasitized by the Gregarious Braconid Parasitoid Wasp Cotesia Congregata
Authors: Adamo Shelley A. , Linn Charles E. , Beckage Nancy E.
Published: April 2021

The parasitoid wasp Cotesia congregata lays its eggs within the body of its host, the larval form of the tobacco hornworm Manduca sexta. Host behaviour appeared normal until approximately 8 h prior to the emergence of the parasitoids from their host at which time M. sexta feeding and locomotion declined irreversibly. This change in host behaviour may be to the advantage of the wasp since unparasitized M. sexta presented with wasp pupae ate them. Despite the decline in feeding and locomotion, hosts with emerged parasitoids had normal reflexes and showed no other signs of debilitation. Concomitant with the change in host behaviour, octopamine concentration measured using high-performance liquid chromatography with electrochemical detection (HPLC-ED) increased from 22.2±2.1 pg μl−1 to 143.7±7.8 pg μl−1 in the haemolymph of the host. In unparasitized M. sexta, however, increased octopamine levels were correlated with increased activity. We discuss possible explanations for the co-occurrence of high haemolymph octopamine levels and low behavioural arousal in parasitized M. sexta.
K+ REABSORPTION BY THE LOWER MALPIGHIAN TUBULE OF RHODNIUS PROLIXUS: INHIBITION BY Ba2+ AND BLOCKERS OF H+/K+-ATPases
Authors: Haley Charlene A. , O’Donnell Michael J.
Published: April 2021

Active K+ reabsorption by the lower Malpighian tubule of the blood-feeding hemipteran Rhodnius prolixus does not involve the amiloride-sensitive K+/H+ exchangers or V-type H+-ATPases implicated in secretion of ions from haemolymph to lumen in the upper tubule. Amiloride, N-ethylmaleimide, 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol and bafilomycin A1 inhibit haemolymph-to-lumen secretion of Na+ and K+ by the upper Malpighian tubule, but have little or no effect on lumen-to-haemolymph reabsorption of K+ by the lower tubule. The effects of inhibitors of H+/K+-ATPases, including omeprazole and SCH 28080, suggest that a pump similar to the H+/K+-ATPase of the gastric mucosa is involved in KCl reabsorption. The presence of K+ channels in the basolateral membrane in the lower Malpighian tubule is suggested by inhibition of KCl reabsorption by basolateral but not apical application of the K+ channel blocker Ba2+, and by blockade of K+-dependent changes in membrane potential by Ba2+. It is proposed, therefore, that K+ is pumped from lumen to cell by an ATP-dependent pump resembling the H+/K+-ATPase of the gastric mucosa, and that K+ leaks from cell to bathing saline (haemolymph) via an electrodiffusive pathway (i.e. K+ channels).
Prey Ingestion Revealed By Oesophagus And Stomach Temperature Recordings In Cormorants
Authors: Ancel A. , Horning M. , Kooyman G. L.
Published: April 2021

We examined the accuracy of both stomach and oesophagus temperature sensors – deployed on captive Brandt’s cormorants – for determination of the mass of food ingested and the number of prey items swallowed. The oesophageal temperature sensor was a better detector of all feeding events, including that of small prey which were missed by the stomach sensor. Adapted to free-ranging animals (and coupled to data loggers for recording seawater temperature), oesophagus temperature recorders, in conjunction with both recordings of energy expenditure (e.g. doubly labelled water, heart rate) and determination of position (e.g. Argos transmitter, time/depth recorder), should provide further important insights into the foraging success of marine endotherms.
Extracellular Carbonic Anhydrase and an Acid–Base Disequilibrium in the Blood of the Dogfish Squalus Acanthias
Authors: Gilmour K. M. , Henry R. P. , Wood C. M. , Perry S. F.
Published: April 2021

The electrometric ΔpH method and an in vitro radioisotopic HCO3− dehydration assay were used to demonstrate the presence of true extracellular carbonic anhydrase (CA) activity in the blood of the Pacific spiny dogfish Squalus acanthias.

An extracorporeal circulation and stopflow technique were then used to characterise the acid–base disequilibrium in the arterial (postbranchial) blood. During the stopflow period, arterial pH (pHa) decreased by 0.028±0.003 units (mean ± S.E.M., N=27), in contrast to the increase in pHa of 0.029±0.006 units (mean ± S.E.M., N=6) observed in seawater-acclimated rainbow trout Oncorhynchus mykiss under similar conditions. The negative disequilibrium in dogfish blood was abolished by the addition of bovine CA to the circulation, while inhibition by benzolamide of extracellular and gill membrane-bound CA activities reversed the direction of the acid–base disequilibrium such that pHa increased by 0.059±0.016 units (mean ± S.E.M., N=6) during the stopflow period. When the CA activity of red blood cells (rbcs) was additionally inhibited using acetazolamide, the magnitude of the negative disequilibrium was increased significantly to −0.045±0.007 units (mean ± S.E.M., N=6). Blockage of the rbc Cl−/HCO3− exchanger using 4,4′-diisothiocyanostilbene-2,2′-disulphonic acid (DIDS) also increased the magnitude of the negative disequilibrium, in this case to −0.089±0.008 units (mean ± S.E.M., N=6). Exposure of dogfish to hypercapnia had no effect on the disequilibrium, whereas the disequilibrium was significantly larger under hypoxic conditions, at −0.049±0.008 units (mean ± S.E.M., N=6).

The results are interpreted within a framework in which the absence of a positive CO2 excretion disequilibrium in the arterial blood of the spiny dogfish is attributed to the membrane-bound and extracellular CA activities. The negative disequilibrium may arise from the continuation of Cl−/HCO3− exchange in the postbranchial blood and/or the hydration of CO2 added to the plasma postbranchially. Two possible sources of this CO2 are discussed; rbc CO2 production or the admixture of blood having ‘low’ and ‘high’ CO2 tensions, i.e. the mixing of postbranchial blood with blood which has bypassed the respiratory exchange surface.
cDNA Cloning of Myosin Heavy Chain Isoforms From Carp Fast Skeletal Muscle and Their Gene Expression Associated With Temperature Acclimation
Authors: Imai Jun-Ichi , Hirayama Yasushi , Kikuchi Kiyoshi , Kakinuma Makoto , Watabe Shugo
Published: April 2021

We have isolated cDNA clones encoding fast skeletal muscle myosin heavy chains of carp acclimated to 10, 20 and 30 °C for over 5 weeks. All clones covered at least the full length of L-meromyosin, the C-terminal part of the myosin molecule. Nucleotide sequence analysis on cDNA clones showed three types of 3′ untranslated sequences, demonstrating that carp expresses at least three myosin heavy chain isoforms in fast skeletal muscle in an acclimation-temperature-dependent manner. cDNAs were identified which were the predominant types expressed in 10 °C-and 30 °C-acclimated fish, as well as an intermediate type present at all acclimation temperatures. Northern blot analysis using probes of three kinds of DNA fragments from the 3′ untranslated region of carp acclimated to 10, 20 and 30 °C further confirmed the presence of acclimation-temperature-specific isoforms. In addition, it was found that mRNA levels of three isoforms were altered in an acclimation-temperature-dependent manner. When the deduced amino acid sequences of three types of carp L-meromyosin were compared with those of homoiotherms, the 30 °C-acclimated type was more similar to those of homoiotherms than was the 10 °C-acclimated type.
A Kinematic Analysis of Tentacle Extension in the Squid Loligo Pealei
Authors: Kier William M. , Leeuwen Johan L. Van
Published: April 2021

High-speed ciné recordings of prey capture by the squid Loligo pealei were used to analyze the kinematics of the rapid tentacular strike. The proximal portion of the tentacle, the stalk, elongates during the strike. The non-extensible distal portion of the tentacle, the club, contacts the prey and attaches using suckers. Seven sequences of prey capture filmed at 750 frames s−1 were analyzed frame by frame. The positions of the head, the tentacles and the prey were digitized, and the data were smoothed using quintic natural B-splines and the generalized cross-validation (GCV) criterion. During the strike, the animal swims forward at velocities ranging from 0.7–1.2 m s−1, and as the eight arms are flared, the tentacular stalks elongate. Tentacular extension occurred in approximately 20–40 ms with peak strains in the tentacular stalk ranging from 0.43–0.8. Peak longitudinal strain rates varied from 23–45 s−1. Maximum extension velocities of the stalk were calculated to be over 2 m s−1 with peak accelerations of approximately 250 m s−2. Once the tentacular clubs have contacted the prey, the tentacular stalks are frequently observed to buckle.
D-Glucose-Sensitive Neurosecretory Cells of the Crab Cancer Borealis and Negative Feedback Regulation of Blood Glucose Level
Authors: Glowik Regina M. , Golowasch Jorge , Keller Rainer , Marder Eve
Published: April 2021

We studied the effects of glucose on cultured X-organ neurons of the crab Cancer borealis using single-electrode current- and voltage-clamp techniques. A subpopulation of the cells responded to D-glucose with a hyperpolarization. These cells, but not glucose-insensitive cells, showed immunoreactivity to crustacean hyperglycemic hormone (CHH), the hormone responsible for the elevation of blood glucose levels in crustaceans. Glucose-sensitive cells were also inhibited by serotonin and γ-aminobutyric acid but were not affected by dopamine and Leu-enkephalin. The response was specific for D-glucose, with an EC50 of 0.25 mmol l−1. No response was seen to L-glucose, sucrose, galactose, mannose or fructose. The glucose response persisted in the absence of extracellular Na+ and in low-Ca2+/Mn2+ saline. In voltage-clamp experiments, D-glucose evoked a small current with a reversal potential close to that of voltage-dependent K+ currents. We conclude that D-glucose activates a K+ current in CHH-immunoreactive cells that, in normal saline, induces a hyperpolarization. We propose that this enables glucose to regulate directly the release of CHH into the hemolymph, thus constituting a negative feedback mechanism regulating hemolymph glucose concentration.
Vestibular Compensation in Lampreys: Impairment and Recovery of Equilibrium Control During Locomotion
Authors: Deliagina T. G.
Published: April 2021

Removal of a vestibular organ (unilateral labyrinthectomy, UL) in the lamprey (Lampetra fluviatilis) results in a loss of equilibrium, so that the animal rolls (rotates around its longitudinal axis) almost continuously when swimming. This paper describes (i) UL-evoked disturbances of the pattern of locomotory movements responsible for rolling, (ii) recovery of equilibrium control after UL (vestibular compensation), and (iii) the role of vision in the recovery of equilibrium control.

It was found that rolling is caused by an asymmetry in the undulatory locomotory movements, with larger deviations of the head towards the side with an intact labyrinth. The rolling appeared to be synchronized with the undulatory locomotory rhythm: during one complete roll turn (360 °), two cycles of locomotion were performed. A characteristic feature of the UL-induced motor deficit in the lamprey is the alternation of episodes of impaired swimming (with a distortion of the body shape and of the locomotor pattern and with a loss of equilibrium) with episodes of normal swimming (without any marked distortion of the locomotor pattern or loss of equilibrium). In the course of recovery after UL, the duration and frequency of the appearance of episodes of normal swimming increased, whereas episodes of impaired swimming became less frequent and shorter.

The recovery of equilibrium control and the role of vision in recovery were investigated in lampreys with different combinations of lesions to the vestibular and visual sensory organs. In group 1 (UL only) animals, the time required for 80 % recovery was, on average, 33 days. In group 2 (UL and removal of both eyes) and in group 3 (UL and removal of the contralateral eye) animals, vestibular compensation was considerably retarded, and normal functioning of the roll control system was not regained even 3 months after UL. In contrast, in group 4 (UL and removal of the ipsilateral eye) animals, no impairment of the equilibrium control was observed, and the animals swam without rolling immediately after surgery. These findings indicate (i) that the visual system is important for the process of vestibular compensation, and (ii) that the deficiency in equilibrium control caused by UL can be abolished by means of unilateral (contralateral to UL) visual input.

The hypothesis is advanced that the main UL-evoked motor deficit in the lamprey (loss of equilibrium) is primarily caused not by a persistent static distortion of the body shape, but by a loss of function of the roll control system responsible for stabilization of the dorsal-side-up orientation during swimming. A conceptual model of the roll control system of the lamprey, formulated in our previous studies, is used here to present arguments in favour of this hypothesis.
Molecular analysis of FMRFamide- and FMRFamide-related peptides (FaRPS) in the cuttlefish Sepia officinalis
Authors: Loi Poh Kheng , Tublitz Nathan
Published: April 2021

The display of complex color patterns of the cuttlefish Sepia officinalis is under the regulation of the FMRFamide-related peptide (FaRP) family, but their exact identities are unknown. We report the isolation and characterization of a full-length FaRP cDNA from the brain of S. officinalis. This cDNA is 1850 base pairs long, including an open reading frame of 996 base pairs. The cDNA encodes a precursor protein containing four FaRPs: ALSGDAFLRF, FIRF, FLRF and FMRF. Each propeptide has a C-terminal glycine residue that is presumably converted post-translationally to an amide. Every FaRP propeptide is also flanked by basic amino acid residues at the amino and carboxy termini, indicative of putative cleavage sites during post-translational processing. Each of the four FaRPs encoded by this cDNA causes chromatophore expansion when assayed in an in vitro chromatophore bioassay. Thus, it is likely that one or more of the FaRPs identified in this study are involved in controlling chromatophore activity in cuttlefish.
Reporter Gene Constructs Suggest That the Caenorhabditis Elegans Avermectin Receptor β-Subunit is Expressed Solely in the Pharynx
Authors: Laughton David L. , Lunt George G. , Wolstenholme Adrian J.
Published: April 2021

Gene promoter/LacZ reporter constructs were made in order to analyse the expression of the β-subunit of the Caenorhabditis elegans glutamate-gated Cl− channel (Glu-Cl) receptor. Southern blot analysis of the C. elegans cosmid C35E8 identified a 4 kbp EcoRI fragment which contained the 5′ portion of the Glu-Cl β coding sequence together with 5′ flanking sequences. This was subcloned and used as the template for polymerase chain reaction (PCR) amplification of a DNA fragment encoding the first 24 amino acid residues of Glu-Cl β together with 1.4 kbp of 5′ genomic sequence. The fragment was subcloned into the LacZ expression vector pPD22.11 to form a translational reporter fusion. After injection of the construct into worms, six stably transformed lines were established and assayed for β-galactosidase activity. Stained nuclei were observed in the pharyngeal metacorpus in adults and in all larval stages, and stained nuclei were seen in many embryos undergoing morphogenesis. Additional stained nuclei towards the terminal bulb of the pharynx were observed in larval stages. These results provide further evidence that the Glu-Cl receptor mediates the glutamatergic inhibition of pharyngeal muscle via the M3 motor neurone and point to inhibition of pharyngeal pumping as a major mode of action for avermectins.
Wavelengths of Bioconvection Patterns
Authors: Bees M. A. , Hill N. A.
Published: April 2021

Bioconvection occurs as the result of the collective behaviour of many micro-organisms swimming in a fluid and is realised as patterns similar to those of thermal convection which occur when a layer of water is heated from below. A methodology is developed to record the bioconvection patterns that are formed by aqueous cultures of the single-celled alga Chlamydomonas nivalis. The analysis that is used to quantify the patterns as a function of cell concentration, suspension depth and time is described and experimental results are presented.
Hummingbird Hovering Energetics During Moult of Primary Flight Feathers
Authors: Chai Peng
Published: April 2021

How does a hovering hummingbird compensate for the loss of flight feathers during moult when the mechanism of lift force generation by flapping wings is impaired? The flight performance of five individual ruby-throated hummingbirds with moulting primary flight feathers and reduced wing area was compared with that before their moult. Hummingbirds were flown in reduced air densities using normoxic heliox so that a range of flight energetics was displayed. The rate of moulting and the extent of wing area loss varied among individuals. One female could tolerate a 30 % loss of wing area in moulting and flew with only three outer primaries per wing. Further exploratory study using the artificial reduction of wing area, either by cutting the tips of the outer primaries of a male or by plucking the secondaries of two females, suggested that secondaries play a minor role in lift force generation during hovering whereas the tip area of primaries is crucial. For the five birds, ranges of whole-bird oxygen consumption rates, wingbeat kinematics (stroke amplitude) and lift coefficients did not vary during the moult. This constancy was mainly achieved through weight loss that alleviated aerodynamic force requirements for weight support during hovering. Since the metabolic power expenditure during moult was similar to that of normal birds but the mechanical power requirement was reduced, the flight efficiency also showed a sharp reduction during moult. This increased cost of flight may result from disruption of the integrity of the flight machinery. Overall, the control of body mass in hummingbirds can provide similar aerodynamic, muscle mechanical and physiological capacities under conditions of variable flight demand.
Serotonin-Induced Modulation of Excitability in an Identified Helisoma Trivolvis Neuron
Authors: Achee Nicole L. , Zoran Mark J.
Published: April 2021

Exogenous serotonin (5-hydroxytryptamine; 5-HT) induced inhibitory effects in Helisoma trivolvis buccal neuron 5 (B5), which included a hyperpolarization of the membrane potential, a reduction in input resistance and a decrease in the stimulus-evoked spiking rate. The reversal potential for the 5-HT-induced hyperpolarization was −88.7 mV, suggesting the involvement of an enhanced K+ conductance. Input/output curves measuring the number of action potentials evoked by current injection demonstrated a 5-HT-induced reduction in B5 neuronal excitability that was dose-dependent with a 50 % inhibitory concentration (IC50) of 1.1 μmol l−1. These inhibitory effects on neuron B5 were in striking contrast to the excitatory effects of this neurotransmitter on the buccal radular tensor motoneuron B19. In this neuron, 5-HT elicited a sustained depolarization and enhanced spiking activity. Previous cell culture studies have demonstrated that 5-HT also inhibits B19 growth cone motility and neurite outgrowth, but has no effect on the extension of neuritic processes from neuron B5. These effects, and the divergent effects of 5-HT on the outgrowth of neurons B5 and B19, probably result from differential effects of 5-HT on neuronal membrane potential and excitability. Modulation of the levels of spiking activity, translated into changes in neuronal Ca2+ levels, would cause alterations in growth cone motility. Previous studies have shown that the effects of 5-HT on B19 membrane potential and neurite extension are cyclic-AMP-dependent. We have used specific activators and inhibitors of signal transduction mechanisms to demonstrate that the 5-HT-induced reductions in B5 neuronal excitability are cyclic-AMP-independent and may involve the lipoxygenase pathway of arachidonic acid metabolism. Our results support the hypothesis that modulatory signals and signal transduction pathways regulating the plasticity of mature neural circuits may also modulate the differentiation of the neurons comprising those networks during development.
Characterization of Voltage- and Ca2+-Activated K+ Channels in Squid Olfactory Receptor Neurons
Authors: Lucero Mary T. , Chen Nansheng
Published: April 2021

We performed whole-cell voltage-clamp experiments on isolated olfactory receptor neurons from the squid Lolliguncula brevis. Total outward currents were composed of three identifiable K+ currents: a delayed rectifier K+ current that showed slow inactivation and was sensitive to 5 mmol l−1 tetraethylammonium; a rapidly inactivating, 4-aminopyridine (4-AP)-sensitive, A-type K+ current and a Ca2+-sensitive K+ current that was blocked by 200 nmol l−1 charybdotoxin and 10 mmol l−1 Cd2+ but was insensitive to apamin. The proportion of each current type varied from cell to cell, suggesting that responses to a given odorant would depend on the complement of channels present. The kinetics of the K+ currents were affected by temperature, with Q10 values ranging from 2 to 6. The identification and characterization of these K+ currents will greatly aid our understanding of action potential generation in these cells and will facilitate modelling of how odor responses are transduced and coded in squid olfactory receptor neurons.
The Role of Ca2+ in Deflection-Induced Excitation of Motile, Mechanoresponsive Balancer Cilia in the Ctenophore Statocyst
Authors: Lowe Brian
Published: April 2021

Motile, mechanoresponsive cilia (balancers) in ctenophore statocysts, like vertebrate hair cells, are excited or inhibited depending upon the direction in which they are deflected. Balancers, however, may become either excited (beat rapidly) or inhibited (beat slowly) by deflection in the same direction, depending on the sign of ctenophore geotaxis (positive or negative). The beat frequency of many cilia is controlled by concentrations of Ca2+, membrane potential and neural input. How these factors affect deflection-induced ciliary beating in balancers was investigated. Deflection-induced excitation of balancers in whole Mnemiopsis leidyi larvae and dissected adult (Mnemiopsis leidyi, Pleurobrachia pileus) statocysts was reversibly inhibited by the Ca2+ channel inhibitors Co2+, Mg2+, Ni2+ and Mn2+. Deflection-induced excitation in balancers of isolated adult M. leidyi balancer groups was also inhibited by Co2+ or by Ca2+-free medium. Isolated balancer group cilia, like balancer cilia of intact ctenophores, exhibited responses to either sign of geotaxis and graded responses to deflection. Isolated balancers that were chemically depolarized in high-[K+], Ca2+-free medium were excited by local application of Ca2+ onto the ciliary bases, but not onto the cell bases or the ciliary tips. It is proposed that deflection-induced excitation of balancers is due to influx of Ca2+ through stretch- and voltage-activated channel activity. The sign of geotaxis of whole larvae and dissected adult statocysts was switched by electrical stimulation. Thus, neural input may participate in reversing the directional sensitivity of balancer cells.
Analysis of Epithelial Transport by Measurement of K+, Cl− and pH Gradients in Extracellular Unstirred Layers: Ion Secretion and Reabsorption by Malpighian Tubules of Rhodnius Prolixus
Authors: Collier K. A. , O’donnell M. J.
Published: April 2021

The pH and concentrations of K+ and Cl− in the unstirred layer (USL) associated with the basolateral surfaces of the upper and lower Malpighian tubules of Rhodnius prolixus were measured using extracellular ion-selective microelectrodes. When stimulated with 5-hydroxytryptamine (5-HT) in vitro, the upper Malpighian tubule secretes Na+, K+, Cl− and water at high rates; the lower Malpighian tubule reabsorbs K+ and Cl− but not water. Concentrations of K+ and Cl− in the unstirred layer of the lower Malpighian tubule ([K+]USL, [Cl−]USL) were greater than those in the bathing saline, consistent with the accumulation of K+ and Cl− in the USL during 5-HT-stimulated KCl reabsorption. [K+]USL exceeded [K+]Bath by as much as 5.3-fold. Calculations of K+ flux based on measurements of [K+]USL at various distances from the tubule surface agreed well with flux calculated from the rate of fluid secretion and the change in K+ concentration of the secreted fluid during passage through the lower tubule. Concentrations of K+ in the unstirred layer of the upper Malpighian tubule were reduced relative to those in the bathing saline, consistent with depletion of K+ from the USL during 5-HT-stimulated secretion of K+ from bath to lumen. Changes in [K+]USL during 5-HT-stimulated K+ secretion from single upper Malpighian tubule cells could be resolved. Although differences between [K+]USL and [K+]Bath were apparent for upper and lower tubules in an in situ preparation, they were reduced relative to the differences measured using isolated tubules. We suggest that convective mixing of the fluids around the tubules by contractions of the midgut and hindgut reduces, but does not eliminate, differences between [K+]USL and [K+]Bathin situ. The USL was slightly acidic relative to the bath in 5-HT-stimulated upper and lower tubules; contributions to USL acidification are discussed. The results also show that the techniques described in this paper can resolve rapid and localized changes in ion transport across different regions of Malpighian tubules in response to stimulants or inhibitors of specific membrane transporters.
Kinematic and Electromyographic Analysis of Steady Pectoral Fin Swimming in the Surfperches
Authors: Drucker Eliot G. , Jensen Jeffrey S.
Published: April 2021

The musculoskeletal mechanism of pectoral fin propulsion was investigated in representatives of the two subfamilies of the Embiotocidae (surfperches). Kinematic and electromyographic records of steady swimming by the open-water cruiser Amphistichus rhodoterus and the benthic maneuverer Embiotoca lateralis were compared at 80 % of the species’ respective pectoral–caudal gait transition speeds. Synchronized records of fin movement and the intensity of pectoral muscle activity allowed previous hypotheses of muscle function, based on anatomical lines of action, to be tested. Divisions of the pectoral musculature inserting on the central and trailing-edge fin rays serve simple functions of abduction and adduction. Muscles controlling the fin’s leading edge, by contrast, play more complex roles during the fin stroke, including deceleration of the fin at the downstroke–upstroke transition and rotation of the adducted fin during the non-propulsive period between fin beats.

In spite of their phylogenetic and ecological divergence, the surfperches exhibit a number of mechanistic similarities which probably characterize the family. The timings of kinematic events and the maximal excursions of the fin tip, as well as the temporal order of muscle activation and the time to peak activity, are largely conserved. The predominant dorsoventral component of fin movement during the stride is consistent with a lift-based mechanism of propulsion. E. lateralis exhibits a greater anteroposterior range of motion and a more continuous period of fine motor control of the fin than A. rhodoterus, differences which may correspond to the species’ respective capacities for maneuvering. Mechanistic variation in the family is associated with rather minor structural differences (in fin shape and fin base orientation). Owing to the similar functional demands placed on the pectoral fins of many fishes, it is probable that the mechanistic details of embiotociform swimming are widely distributed within the Perciformes.
Plateau Potentials in Motor Neurons in the Ventilatory System of the Crab
Authors: Dicaprio Ralph A.
Published: April 2021

The motor neurons in the crab ventilatory system have previously been considered to be passive output elements in that the generation of bursts of action potentials in these neurons during ventilation was thought to be due to cyclic inhibition and excitation from the interneurons in the ventilatory central pattern generator. This study demonstrates that the large-amplitude depolarization that underlies bursts of action potentials in ventilatory motor neurons is produced by a plateau potential. These motor neurons satisfy a number of the experimental tests that have been proposed for plateau potentials, such as triggering of the burst by a brief depolarization, termination of the burst by a hyperpolarizing input, and an all-or-none suppression of the depolarizing potential by the injection of hyperpolarizing current.
Heat Increment of Feeding in Brünnich’s Guillemot Uria Lomvia
Authors: Hawkins P. A. J. , Butler P. J. , Woakes A. J. , Gabrielsen G. W.
Published: April 2021

The rate of oxygen consumption , respiratory quotient (RQ) and deep body temperature (TB) were recorded during a single, voluntary ingestion of Arctic cod Boreogadus saida (mean mass 18.9±1.1 g, S.E.M., N=13) by five postabsorptive Brünnich’s guillemots (thick-billed murre, Uria lomvia). The birds were resting in air within their thermoneutral zone, and the fish were refrigerated to 0–2 °C. The rate of oxygen consumption increased by a factor of 1.4 during the first few minutes after ingestion, but there was no significant change in TB. Mean rate of oxygen consumption returned to preingestive levels 85 min after the birds ate the fish. The telemetered temperature of one fish reached TB within 20 min. This suggests that the persistent elevation in over the next hour corresponded to the obligatory component of the heat increment of feeding (HIF) and was not related to heating the fish. Abdominal temperature increases after diving bouts in free-ranging common guillemots (common murre, Uria aalge) are possibly achieved through the HIF, since meals are processed at sea. Of the increase in measured in the laboratory, it is calculated that 30 % is required to heat the fish, while 70 % is due to the HIF. In free-ranging birds, the excess heat provided by the HIF could contribute 6 % of the daily energy expenditure. This suggests that the HIF augments heat production in Uria spp. and thus reduces the energetic cost of thermoregulation.
The Role of the Nucleus Isthmi in Respiratory Pattern Formation in Bullfrogs
Authors: Kinkead Richard , Harris Michael B. , Milsom William K.
Published: April 2021

The nucleus isthmi (NI) is a mesencephalic structure of the amphibian brain located between the roof of the midbrain and the cerebellum. From a neuroanatomical perspective, the NI can be compared with the pons which, in mammals, contributes to the control of breathing pattern. This study tested the hypothesis that the NI plays a critical role in breathing pattern formation in the bullfrog. More specifically, we postulated that this nucleus was the site responsible for clustering breaths into distinct episodes of breathing. This hypothesis was tested by comparing the respiratory motor output of decerebrate, paralyzed and artificially ventilated bullfrogs before and after bilateral lesions of the NI by pressure microinjections of lidocaine or kainic acid (KA) into this area. Bilateral microinjections of lidocaine or KA into the NI transformed the breathing pattern from episodic (many breaths per episode) to one of evenly spaced single breaths, without affecting the amplitude of the fictive breaths. These changes in breathing pattern were associated with an overall decrease in breathing frequency and a reduction in CO2-chemosensitivity. Breathing episodes of more than one breath reappeared during hypercarbia (3.5 % CO2 in air) after KA lesioning. Bilateral lesions to the NI did not affect the changes in the timing or the amplitude of the respiratory-related bursts elicited by pulmonary stretch receptor feedback, indicating that mechanoreflexes do not require NI input. We conclude that the NI is not responsible for the genesis of breathing episodes, but provides a tonic excitatory input to respiratory centers in the lower brainstem. The NI also plays an important role in either CO2 chemodetection or, more probably, integration of CO2 chemoreceptor information. This, in turn, contributes to the production of episodes of more than one breath.
Central Projections of the Maxillary and Antennal Nerves in the Mosquito Aedes Aegypti
Authors: Distler Paul G. , Boeckh Jürgen
Published: April 2021

In the mosquito Aedes aegypti, CO2-sensitive receptor neurones are located together with two other types of chemoreceptor neurones in club-shaped sensilla basiconica on the most distal segment of the maxillary palps. In order to identify the central target neuropiles of these neurones and to determine whether antennal receptor neurones project into the same area, the palpal and antennal nerves were labelled by anterograde staining with horseradish peroxidase and by experimentally induced degeneration. The different methods revealed a consistent projection pattern. (1) Maxillary afferents project into the suboesophageal ganglion and ascend further into the ipsilateral antennal lobe. There, they terminate within an identified glomerulus of the ventroposterior lobe. (2) Afferents of the antennal flagellum project into all glomeruli of the ipsilateral antennal lobe, with the exception of the glomerulus innervated by the maxillary nerve. The present anatomical findings suggest that primary processing of information about CO2 levels takes place in a defined glomerulus which also receives input from other palpal chemoreceptor neurones.
Motor Patterns of Labriform Locomotion: Kinematic and Electromyographic Analysis of Pectoral Fin Swimming in The Labrid Fish Gomphosus Varius
Authors: Westneat Mark W. , Walker Jeffrey A.
Published: April 2021

Labriform locomotion is a widespread swimming mechanism in fishes during which propulsive forces are generated by oscillating the pectoral fins. We examined the activity of the six major muscles that power the pectoral fin of the bird wrasse Gomphosus varius (Labridae: Perciformes). The muscles studied included the fin abductors (arrector ventralis, abductor superficialis and abductor profundus) and the fin adductors (arrector dorsalis, adductor superficialis and adductor profundus). Our goals were to determine the pattern of muscle activity that drives the fins in abduction and adduction cycles during pectoral fin locomotion, to examine changes in the timing and amplitude of electromyographic (EMG) patterns with increases in swimming speed and to correlate EMG patterns with the kinematics of pectoral fin propulsion. EMG data were recorded from three individuals over a range of swimming speeds from 15 to 70 cm s−1 (1–4.8 TL s−1, where TL is total body length). The basic motor pattern of pectoral propulsion is alternating activity of the antagonist abductor and adductor groups. The downstroke is characterized by activity of the arrector ventralis muscle before the other abductors, whereas the upstroke involves nearly synchronous activity of the three adductors. Most EMG variables (duration, onset time, amplitude and integrated area) showed significant correlations with swimming speeds. However, the timing and duration of muscle activity are relatively constant across speeds when expressed as a fraction of the stride period, which decreases with increased velocity. Synchronous recordings of kinematic data (maximal abduction and adduction) with EMG data revealed that activity in the abductors began after maximal adduction and that activity in the adductors began nearly synchronously with maximal abduction. Thus, the pectoral fin mechanism of G. varius is activated by positive work from both abductor and adductor muscle groups over most of the range of swimming speeds. The adductors produce some negative work only at the highest swimming velocities. We combine information from pectoral fin morphology, swimming kinematics and motor patterns to interpret the musculoskeletal mechanism of pectoral propulsion in labrid fishes.
The Aminergic and Peptidergic Innervation of Insect Salivary Glands
Authors: Ali Declan W.
Published: April 2021

Insect salivary glands are glands associated with nutrient intake whose secretions are generally involved in the digestion and lubrication of food. They are under the control of neuroactive substances and may be innervated from several sources including the suboesophageal ganglion, the stomatogastric nervous system and the unpaired median nerves. Both amines and peptides have been suggested to play roles in the control of insect salivation, as indicated by their association with terminals on salivary glands, their effects in salivary gland bioassays and their ability to alter second messenger levels and ion channel conformations. Serotonin and dopamine appear to be the most prominent amines associated with insect salivary glands. Either one or both of these amines are found associated with the salivary glands of the locust, stick insect, cockroach, cricket, dragonfly, mosquito, adult moth and kissing bug. Their roles, although not fully elucidated, appear to be in the control of salivary secretion. Several peptides, including members of the FMRFamide-related family of peptides, are also found associated with insect salivary glands. Sources of peptidergic innervation are as varied as those for aminergic innervation, but information regarding the physiological role of these peptides is lacking. The relevance of the different levels of complexity of salivary gland innervation, which range from the absence of innervation in some species (blowfly) to the presence of several distinct sources in others (locust, cockroach), is not well understood. This review serves to consolidate what is known of the phenotype of salivary neurones in relation to the control of salivation.
Modulation of Prey-Capture Behavior in the Plethodontid Salamander Ensatina Eschscholtzii
Authors: Deban Stephen M.
Published: April 2021

The hypothesis that salamander prey-capture behavior is highly stereotyped was tested in the plethodontid salamander Ensatina eschscholtzii using high-speed videography and kinematic analysis of feedings on two types of prey (waxworms and termites). The results show that E. eschscholtzii is capable of modulating the timing and magnitude of tongue and jaw movements in response to prey type. Feedings on waxworms, the larger prey, were characterized by shorter durations and higher velocities of tongue and jaw movements compared with feedings on termites, particularly in the latter portion of the feeding sequence (i.e. after prey contact). To test the hypothesis that sensory feedback through the tongue pad plays a role in modulating feeding movements in response to prey type, the ramus lingualis of the glossopharyngeal nerve (cranial nerve IX), which is known to carry sensory information from the tongue pad in salamanders, was transected bilaterally. This experimental deafferentation of the tongue pad had no effect on the degree or direction of differences in feeding kinematics across prey type. These results refute the glossopharyngeal feedback hypothesis, but are consistent with the hypothesis that E. eschscholtzii responds more vigorously to larger prey by assessing prey size visually.
Heart Rate and Stroke Volume Contributions to Cardiac Output in Swimming Yellowfin Tuna: Response to Exercise and Temperature
Authors: Korsmeyer Keith E. , Lai N. Chin , Shadwick Robert E. , Graham Jeffrey B.
Published: April 2021

Cardiac performance in the yellowfin tuna (Thunnus albacares, 673–2470 g, 33–53 cm fork length, FL) was examined in unanesthetized fish swimming in a large water tunnel. Yellowfin tuna were fitted with either electrocardiogram electrodes or a transcutaneous Doppler blood-flow probe over the ventral aorta and exposed to changes in swimming velocity (range 0.8–2.9 FL s−1) or to an acute change in temperature (18–28 °C). Heart rates (fH) at 24±1 °C (30–130 beats min−1) were lower on average than previous measurements with non-swimming (restrained) tunas and comparable with those for other active teleosts at similar relative swimming velocities. Although highly variable among individuals, fH increased with velocity (U, in FL s−1) in all fish (fH=17.93U+49.93, r2=0.14, P<0.0001). Heart rate was rapidly and strongly affected by temperature (Q10=2.37).

Blood flow measurements revealed a mean increase in relative cardiac output of 13.6±3.0 % with exercise (mean velocities 1.23–2.10 FL s−1) caused by an 18.8±5.4 % increase in fH and a 3.9±2.3 % decrease in stroke volume. These results indicate that, unlike most other fishes, cardiac output in yellowfin tuna is regulated primarily through increases in fH. Acute reductions in ambient temperature at slow swimming velocities resulted in decreases in cardiac output (Q10=1.52) and fH (Q10=2.16), but increases in stroke volume (Q10=0.78). This observation suggests that the lack of an increase in stroke volume during exercise is not due to the tuna heart operating at maximal anatomical limits.
Oxygen Transport and Cardiovascular Responses to Exercise In The Yellowfin Tuna Thunnus Albacares
Authors: Korsmeyer Keith E. , Lai N. Chin , Shadwick Robert E. , Graham Jeffrey B.
Published: April 2021

Yellowfin tuna Thunnus albacares (1400–2175 g) instrumented with electrocardiogram electrodes and pre- and post-branchial catheters were subjected to incremental swimming velocity tests. Increasing velocity, from a minimal speed of 1.0 FL s−1, where FL is fork length, resulted in a 1.4-fold increase in heart rate (from 61.4 to 84.6 beats min−1), an elevated ventral-aortic blood pressure (from 10.8 to 12.2 kPa) and a decreased systemic vascular resistance. Relative branchial vascular resistance at minimal speed ranged from 24.4 to 40.0 % of total vascular resistance and tended to increase with velocity. Yellowfin blood has a high oxygen-carrying capacity (16–18 ml O2 dl−1), and a low in vivo oxygen affinity (P50=5.3 kPa). Exercise caused a rise in arterial saturation (from 74 to 88 %) and a decline in venous saturation (from 48 to 44 %), resulting in a 1.3-fold increase in tissue oxygen extraction from the blood (arterial–venous oxygen content difference). Whereas arterial oxygen partial pressure () tended to increase with exercise, venous remained unchanged (approximately 5.3 kPa). The observed decrease in venous oxygen content was brought about by a lowered blood pH (from 7.80 to 7.76) and a large Bohr shift. Cardiac output and the increased blood oxygen extraction are estimated to have contributed nearly equally to the increased oxygen consumption during exercise. The large venous oxygen reserve still available to yellowfin tuna at maximal prolonged velocities suggests that the maximal oxygen delivery potential of the cardiovascular system in this species is not fully utilized during aerobic swimming. This reserve may serve other aerobic metabolic processes in addition to continuous swimming.