bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Tracer Coupling Between Pairs of Identified Neurones of the Mollusc Lymnaea Stagnalis
Authors: Ewadinger N. M. , Syed N. I. , Lukowiak K. , Bulloch A. G. M.
Published: April 2021

Electrical coupling is a common means of cell-to-cell communication in both neuronal and non-neuronal tissues (Lowenstein, 1985). Within the nervous system, many electrically coupled neurones exhibit dye coupling (Bennett, 1973; Stewart, 1978; Glantz and Kirk, 1980; Spencer and Satterlie, 1980; Fraser and Heitler, 1993); however, some electrically coupled cells do not dye-couple (Audesirk et al. 1982; Murphy et al. 1983; Berdan, 1987; Robinson et al. 1993; Veenstra et al. 1993). Electrical coupling and dye coupling, often considered in parallel, are in fact two different parameters that can vary independently (e.g. Audesirk et al. 1982; Perez-Armendariz et al. 1991). The giant identified neurones of pulmonate and opisthobranch molluscs have frequently been used for studies of neuronal communication and its plasticity (Winlow and McCrohan, 1987; Bulloch, 1989). In the present study, we explored the relationship between electrical and tracer coupling in both strongly and weakly coupled pairs of molluscan neurones. Specifically, we examined electrically coupled, identified neurones in a freshwater pond snail, Lymnaea stagnalis L., and tested for tracer coupling with Lucifer Yellow CH and biocytin. The cells examined were the strongly electrically coupled neurones, visceral dorsal 1 (VD1) and right parietal dorsal 2 (RPD2) (Boer et al. 1979; Benjamin and Pilkington, 1986), and the weakly coupled neurones, left buccal 1 (LB1) and right buccal 1 (RB1) (Benjamin and Rose, 1979). The use of these particular neurones made it possible to compare electrical coupling with tracer coupling in the molluscan central nervous system (CNS).
Studies of Tropical Tuna Swimming Performance in a Large Water Tunnel: II. Thermoregulation
Authors: Dewar Heidi , Graham Jeffrey B. , Brill Richard W.
Published: April 2021

The body temperatures (Tb) of nine yellowfin tuna (Thunnus albacares) were monitored while fish swam in a large water tunnel at controlled velocities (U) and ambient temperatures (Ta). Monitoring Tb during step changes in Ta at constant U permitted estimation of the thermal rate coefficient (k), an index of heat transfer. In the yellowfin, k is dependent on both Ta and the direction of the thermal gradient (i.e. whether Ta is greater or less than Tb). Modulation of k in response to Ta was further demonstrated during tests in which U was varied; the elevation of Tb in response to equal increases in U was 3–4 times less at 30°C than at 25 and 20°C. These experiments demonstrate that the yellowfin tuna can modulate heat transfer. This ability could prevent overheating during intense activity, retard heat loss during a descent into cool water and permit increased heat gain upon returning to warm surface waters (i.e. when Tb<Ta).
Studies of Tropical Tuna Swimming Performance in a Large Water Tunnel: III. Kinematics
Authors: Dewar Heidi , Graham Jeffrey B.
Published: April 2021

Yellowfin tuna (Thunnus albacares) swimming kinematics was studied in a large water tunnel at controlled swimming velocities (U). Quantified kinematic variables included the tail-beat frequency, stride length (l), caudal amplitude, yaw, the propulsive wavelength, the speed of the propulsive wave (C) and the sweepback angle of the pectoral fins. In general, all variables, except the propulsive wavelength and consequently C, are comparable to values determined for other teleosts. The propulsive wavelength for the tunas (1.23–1.29 L, where L is fork length) is 30–60% longer than in other cruise-adapted teleosts such as salmonids. The resulting thunniform swimming mode and the morphological and anatomical adaptations associated with the long propulsive wavelength (e.g. fusiform body shape, rigid vertebral column) act to minimize anterior resistance and maximize caudal thrust. The long propulsive wavelength also increases the maximum l which, in concert with the elevated muscle temperatures of tunas, increases their maximum swimming velocity.
Reconstitution of Metachronal Waves in Ciliated Cortical Sheets of Paramecium: I. Wave Stabilities
Authors: Okamoto Ken-Ichi , Nakaoka Yasuo
Published: April 2021

We reconstituted metachronal waves on ciliated cortical sheets prepared from detergent-extracted Paramecium multimicronucleatum cells. Ciliary movements of the cortical sheet, whose intracellular side adhered to a glass coverslip, were reactivated by perfusion of a basic reactivation medium containing ATP. In this condition, the ciliary field showed only unstable localised ripples. Addition of either cyclic AMP or cyclic GMP to the basic reactivation medium generated propagating metachronal waves characteristic of each nucleotide. In order to estimate the stability of the metachronal waves, autocorrelation coefficients were calculated from images of an 8 μm diameter region within the reactivated ciliary field. The decay time for the correlation coefficient to decrease to 0.5 was only 0.04 s in the basic reactivation medium, but was increased to 0.4 or 0.9 s by the addition of cyclic AMP or cyclic GMP, respectively. The decay time was dependent not only on the concentration of cyclic nucleotide but also on the wave frequency. In order to test whether cyclic-nucleotide-dependent phosphorylation affected the generation of waves, the ciliated cortical sheets were thiophosphorylated by incubation in ATP-γ-S (adenosine-5′-o-3-thiotriphosphate) medium containing either cyclic AMP or cyclic GMP. Following this, perfusion with the basic reactivation medium generated metachronal waves only after cyclic GMP treatment. The effect of cyclic GMP is probably related to phosphorylation of ciliary proteins.
Stepping Patterns in Ants: I. Influence of Speed and Curvature
Authors: Zollikofer Christoph P. E.
Published: April 2021

The locomotory behaviour of workers of 12 ant species belonging to four different genera (Formicinae: Cataglyphis, Formica, Lasius; Myrmicinae: Myrmica) was studied by filming individuals walking on smoked-glass plates. Subsequent multivariate analyses of footfall positions and walking kinematics revealed a set of constant features characterizing ant locomotion. The alternating tripod gait prevails over a wide range of speeds. The temporal rigidity of tripod coordination is paralleled by spatially rigid footfall patterns. Tripod geometry is preserved irrespective of speed and curvature. When walking around curves, tripods are rotated relative to the walking trajectory. Whereas stride length on the inner side of the curve is shortened, that on the outer side is independent of curvature.
Detection of Magnetic Inclination Angle by Sea Turtles: A Possible Mechanism for Determining Latitude
Authors: Lohmann Kenneth J. , Lohmann Catherine M. F.
Published: April 2021

For animals that migrate long distances, the magnetic field of the earth provides not only a possible cue for compass orientation, but a potential source of world-wide positional information. At each location on the globe, the geomagnetic field lines intersect the earth’s surface at a specific angle of inclination. Because inclination angles vary with latitude, an animal able to distinguish between different field inclinations might, in principle, determine its approximate latitude. Such an ability, however, has never been demonstrated in any animal.

We studied the magnetic orientation behavior of hatchling loggerhead sea turtles (Caretta caretta L.) exposed to earth-strength magnetic fields of different inclinations. Hatchlings exposed to the natural field of their natal beach swam eastward, as they normally do during their offshore migration. In contrast, those subjected to an inclination angle found on the northern boundary of the North Atlantic gyre (their presumed migratory path) swam south-southwest. Hatchlings exposed to an inclination angle found near the southern boundary of the gyre swam in a northeasterly direction, and those exposed to inclination angles they do not normally encounter, or to a field inclination found well within the northern and southern extremes of the gyre, were not significantly oriented.

These results demonstrate that sea turtles can distinguish between different magnetic inclination angles and perhaps derive from them an approximation of latitude. Most sea turtles nest on coastlines that are aligned approximately north–south, so that each region of nesting beach has a unique inclination angle associated with it. We therefore hypothesize that the ability to recognize specific inclination angles may largely explain how adult sea turtles can identify their natal beaches after years at sea.
Hydrodynamic Aspects of Design and Attachment of A Back-Mounted Device in Penguins
Authors: Bannasch Rudolf , Wilson Rory P. , Culik Boris
Published: April 2021

Wind tunnel and water tank experiments were carried out on a penguin model in order to optimise the shape and attachment of a back-mounted datalogger. Device-induced turbulence was minimised when the unit was placed in the most caudal position. Drag was further reduced by shaping the device to match the body contour. The hydrodynamic resistance of the package could be reduced by 65% compared with an earlier unit. These results are discussed together with results from new studies on kinematics and energetics of underwater swimming of live instrumented penguins.
The Flexible Fly: Experience-Dependent Development of Complex Behaviors in Drosophila Melanogaster
Authors: Hirsch Helmut V. B. , Tompkins Laurie
Published: April 2021

We demonstrate that Drosophila melanogaster provides a rich model system for studying behavioral development. Two additions to the many well-known advantages of this species are exploited here. First, as in mammals and higher vertebrates, early experience affects behavioral development of Drosophila. Second, the affected behaviors are complex and yet readily studied in the laboratory. Thus, Drosophila can be used to study the developmental mechanisms by which organisms can optimize their behavioral repertoires to enhance their chances for survival. Evidence that early experience affects development of preferences for specific visual patterns, male courtship and female responsiveness to courting males is reviewed; in each case, experience modifies responses to behavioral targets. Our results demonstrate that developmental plasticity allows adjustment of intrinsically determined responses to visual targets so that they can take into account the actual characteristics of the developing animal’s environment. Furthermore, plasticity makes it possible to introduce ‘cultural’ and ‘social’ elements into courtship and mate choice in insects. This previously unrecognized role for developmental plasticity in insects has broad theoretical and practical implications.
Calcium transport in gill plasma membranes of the crab Carcinus Maenas: Evidence for carriers driven by ATP and A Na+ Gradient
Authors: Flik Gert , Verbost Pieter M. , Atsma Wim , Lucu Cedomil
Published: April 2021

A procedure was developed for the preparation of inside-out vesicles from plasma membranes isolated from the branchial epithelium of the green shore crab Carcinus maenas (L.). Procedures normally applied to fish branchial epithelium required the introduction of an additional hypotonic shock to obtain a preparation containing 22% inside-out vesicles, 33% right-side-out vesicles and 45% leaky membrane fragments. In such membrane preparations, the first direct evidence for uphill (against a [Ca2+] gradient) ATP-dependent and Na+-gradient-dependent Ca2+ transport in crustacean gills was found. The affinity for Ca2+ of the ATP-driven Ca2+ transporter was 149 nmol l−1 and that of the Na+/Ca2+ exchanger was 1.78 μmol l−1; the Vmax values were 1.73 and 9.88 nmol min−1 mg−1 protein respectively. The relative importance of these carriers for Ca2+ transport in the branchial epithelium of the crab is evaluated on the basis of their calcium kinetics.
The Functional Morphology of Singing in the Cricket
Authors: Pfau H. K. , Koch U. T.
Published: April 2021

We describe the functional morphology of the singing apparatus of the cricket. There are three main functional sections of song mechanics, which partly overlap: (1) preparation for singing (lifting of the wings) and the reverse process (lowering of the wings at the end of the song); (2) singing movements (closing and opening of the wings); and (3) movements that adjust the pressure of the plectrum on the file (engagement force).

In the case of song preparation, the mesotergum + first axillaries + second axillaries + wings form a functional unit. This unit is moved around a transverse hinge axis, which runs through both fulcrum joints. The muscles suitable for wing lifting are the prothoracic furca muscle and the mesothoracic tegula muscle. Those suitable for wing lowering are the prothoracic dorsolongitudinal muscles and the mesothoracic axillary 4, subalar and furca muscles. Lifting and lowering of the wings are superimposed by bistable mechanisms, which are adjustable (mesothoracic medial dorsolongitudinal muscles).

In the case of closing movements (dorsoventral muscles) and opening movements (basalar and subalar muscles), the mesotergum and the wings are moved relative to each other, as for flight movements, but with the wings remaining folded back. The mesotergum is rotated down (closing) and up (opening) around a transverse hinge axis that runs through the caudal joints between the mesotergum and postnota. The path of movement of the wing and its sound-generating structure (i.e. plectrum or file respectively) is determined by an obliquely oriented hinge axis between the mesotergum and first axillary. During opening and closing, the lifted singing position of the wings is stabilized by the medial dorsolongitudinal muscles. We also discuss the role of other muscles that affect singing movements.

The third axillary (and its muscle) and the postnotum [and its muscles, the furca muscle and the lateral (short) dorsolongitudinal muscle] are the main elements in the system that adjusts the engagement force of the wings. When left axillary 3 muscle contracts, the medial part of the left third axillary is rotated caudally (in its vertical hinge joint with the first median plate) against the anal part of the wing. The anal part is bent and rotated upwards, increasing the pressure of the left plectrum against the right file. Conversely, the right axillary 3 muscle, which moves the file away from the plectrum, is able to reduce the pressure. The left furca muscle (the antagonist of left axillary 3 muscle) and the left lateral (short) dorsolongitudinal muscle (the ‘synergist’ of left axillary 3 muscle), and the corresponding muscles on the right side (which have opposite functions), allow a large range of different engagement forces. The results are compared with the work of other authors on the functional morphology of this system and with the results of electrophysiological investigations. New aspects of the evolution of the singing mechanisms are discussed.
Integrated Responses to Exhaustive Exercise and Recovery in Rainbow Trout White Muscle: Acid–Base, Phosphogen, Carbohydrate, Lipid, Ammonia, Fluid Volume and Electrolyte Metabolism
Authors: Wang Yuxiang , Heigenhauser George J. F. , Wood Chris M.
Published: April 2021

White muscle and arterial blood plasma were sampled at rest and during 4 h of recovery from exhaustive exercise in rainbow trout. A compound respiratory and metabolic acidosis in the blood was accompanied by increases in plasma lactate (in excess of the metabolic acid load), pyruvate, glucose, ammonia and inorganic phosphate levels, large elevations in haemoglobin concentration and haematocrit, red cell swelling, increases in the levels of most plasma electrolytes, but no shift of fluid out of the extracellular fluid (ECF) into the intracellular fluid (ICF) of white muscle. The decrease in white muscle pHi was comparable to that in pHe; both recovered by 4 h. Creatine phosphate and ATP levels were both reduced by 40% after exercise, the former recovering within 0.25 h, whereas the latter remained depressed until 4 h. Changes in creatine concentration mirrored those in creatine phosphate, whereas changes in IMP and ammonia concentration mirrored those in ATP. White muscle glycogen concentration was reduced 90% primarily by conversion to lactate; recovery was slow, to only 40% of resting glycogen levels by 4 h. During this period, most of the lactate and metabolic acid were retained in white muscle and there was excellent conservation of carbohydrate, suggesting that in situ glycogenesis rather than oxidation was the major fate of lactate. The redox state ([NAD+]/[NADH]) of the muscle cytoplasm, estimated from ICF lactate and pyruvate levels and pHi, remained unchanged from resting levels, challenging the traditional view of the ‘anaerobic’ production of lactate. Furthermore, the membrane potential, estimated from levels of ICF and ECF electrolytes using the Goldman equation, remained unchanged throughout, challenging the view that white muscle becomes depolarized after exhaustive exercise. Indeed, ICF K+ concentration was elevated. Lactate was distributed well out of electrochemical equilibrium with either the membrane potential (Em) or the pHe–pHi difference, supporting the view that lactate is actively retained in white muscle. In contrast, H+ was actively extruded. Ammonia was distributed passively according to Em rather than pHe–pHi throughout recovery, providing a mechanism for retaining high ICF ammonia levels for adenylate resynthesis in situ. Although lipid is not traditionally considered to be a fuel for burst exercise, substantial decreases in free carnitine and elevations in acyl-carnitines and acetyl-CoA concentrations indicated an important contribution of fatty acid oxidation by white muscle during both exercise and recovery.
The Acquisition of Forward Motility in the Spermatozoa of the PolychaeteArenicola Marina
Authors: Pacey A. A. , Cosson J. C. , Bentley M. G.
Published: April 2021

Sperm activation in the polychaete annelid Arenicola marina was investigated using video microscopy following the in vitro and in vivo manipulation of gametes. Careful observation of spermatozoa obtained from spawning animals indicated that they were immotile immediately after their release from the gonopores, but that they subsequently became motile following dilution in sea water. It was determined that under the pH conditions of the coelomic cavity (pH 7.3) sperm motility was suppressed, whereas upon dilution in sea water buffered at pH 8.2, motility was triggered. It is hypothesised that sperm activation, under normal conditions, occurs in two stages. The first results in the liberation of free spermatozoa from sperm morulae, allowing them to be spawned; this process is stimulated by an endocrine factor and occurs in vivo during normal spawning. The second involves the switching on of the sperm flagellar apparatus, which occurs when spermatozoa are subjected to change in extracellular pH associated with their dilution in sea water. Pharmacological agents such as ammonium chloride and quinacrine are shown to stimulate the breakdown of sperm morulae and the acquisition of sperm motility. Motile spermatozoa of A. marina, in artificial sea water buffered at pH 8.2, can remain motile for over 5 h, have a beat frequency of approximately 50 Hz and have average path velocities of between 100 and 120 μm s−1. Motile spermatozoa under these conditions can also display the phenomenon of intermittent swimming.
Sodium-Coupled Neurotransmitter Transport: Structure, Function And Regulation
Authors: Kanner Baruch I.
Published: April 2021

The removal of neurotransmitters by their transporters – located in the plasma membranes of nerve terminals and glial cells – plays an important role in the termination of synaptic transmission. In the last 3 years, many neurotransmitter transporters have been cloned. Structurally and functionally they can be divided into two groups: glutamate transporters, of which to date three have been cloned, couple the flow of glutamate to that of sodium and potassium. The second group of transporters includes those for GABA, glycine, taurine, norepinephrine, dopamine and serotonin. They are sodium-and chloride-dependent, but do not require potassium for function. One of these, the GABAA transporter, encoded by GAT-1, is perhaps the best characterized. It has been purified and reconstituted and has a molecular mass of around 80 kDa, of which 10–15 kDa is sugar. Amino and carboxyl termini (around 50 amino acids each) are not required for function. The transporter is protected against proteolysis at multiple sites by GABA, provided that the two cosubstrates – sodium and chloride – are present. Several amino acid residues that are critical for function have been identified in the GABA transporter. These include arginine-69 and tryptophan-222 located in the first and fourth putative transmembrane helices, respectively. The first is possibly involved in the binding of chloride. The tryptophan appears to serve as a binding site for the amino group of GABA.
Structure, Function and Brain Localization of Neurotransmitter Transporters
Authors: Jursky Frantisek , Tamura Shigehiko , Tamura Akiko , Mandiyan Sreekala , Nelson Hannah , Nelson Nathan
Published: April 2021

We studied four different cDNAs encoding GABA transporters and three different cDNAs encoding glycine transporters in mouse and rat brains. A genomic clone of two of the glycine transporters (GLYT1a and GLYT1b) revealed that they derive from differential splicing of a single gene. The third glycine transporter (GLYT2) is encoded by a separate gene. Antibodies were raised against seven of these neurotransmitter transporters and their cytochemical localization in the mouse brain was studied. In general, we observed a deviation from the classical separation of neuronal and glial transporters. It seems that each of the neurotransmitter transporters is present in specific places in the brain and is expressed in a different way in very specific areas. For example, the GABA transporter GAT4, which also transports β-alanine, was localized to neurons. However, GAT1, which is specific for GABA, was localized not only to neurons but also to glial cells. The recently discovered glycine transporter GLYT2 was of particular interest because of its deviation from the general structure by a very extended N terminus containing multiple potential phosphorylation sites. Western analysis and immunocytochemistry in frozen sections of mouse brain demonstrated a clear caudal–rostral gradient of GLYT2 distribution, with massive accumulation in the spinal cord and brainstem and less in the cerebellum. Its distribution is typically neuronal and it is present in processes with varicosities. A correlation was observed between the pattern we obtained and that observed previously from strychnine binding studies. The results indicate that GLYT2 is involved in the termination of glycine neurotransmission at the classical inhibitory system in the hindbrain. The availability of four different GABA transporters made it possible to look for specific binding sites upon the neurotransmitter transporters. An extensive program of site-directed mutagenesis led us to identify a potential neurotransmitter binding site on the GABA transporters.
Role of the Invertebrate Electrogenic 2Na+/1H+ Antiporter in Monovalent and Divalent Cation Transport
Authors: Ahearn G. A. , Zhuang Z. , Duerr J. , Pennington V.
Published: April 2021

In recent years, an electrogenic 2Na+/1H+ antiporter has been identified in a variety of invertebrate epithelial brush-border membranes of gut, kidney and gill tissues. The antiporter differs significantly in its physiological properties from the electroneutral 1Na+/1H+ antiporter proposed for vertebrate cells. In all invertebrate cells examined, the antiporter displayed a 2:1 transport stoichiometry, responded to an induced transmembrane potential and exhibited a high binding affinity for the divalent cation Ca2+, which acted as a competitive inhibitor of Na+ transport. A monoclonal antibody specific for the crustacean electrogenic antiporter inhibited 2Na+/1H+ exchange, but was without effect on Na+-dependent D-glucose transport. Immunoreactivity was localized at hepatopancreatic brush-border and vacuolar membranes, antennal gland coelomosac podocytes and posterior gill epithelial cells – all locations where published reports described unique cation exchange kinetics. Significant fractions of Ca2+ transport into invertebrate cells across brush-border membranes occurred by an electrogenic, amiloride-sensitive exchange process, probably by the 2Na+/1H+ antiporter, and this transport was markedly inhibited by exogenous zinc and cadmium. A recently identified electroneutral, amiloride-sensitive, hepatopancreatic epithelial basolateral Na+/H+ antiporter was uninfluenced by the brush-border monoclonal antibody, exhibited an apparent 1:1 transport stoichiometry and possessed a minimal divalent cation specificity. Calcium transport at this epithelial pole occurred by the combination of a Ca2+/Na+ antiporter, an ATP-dependent Ca2+-ATPase and a verapamil-sensitive calcium channel. These crustacean brush-border and basolateral transporters may play significant roles in calcification and heavy metal detoxification.
The Molecular Basis of Chloride Transport in Shark Rectal Gland
Authors: Riordan John R. , Forbush Bliss , Hanrahan John W.
Published: April 2021

Transepithelial Cl− secretion in vertebrates is accomplished by a secondary active transport process brought about by the coordinated activity of apical and basolateral transport proteins. The principal basolateral components are the Na+/K+-ATPase pump, the Na+/K+/2Cl− cotransporter (symporter) and a K+ channel. The rate-limiting apical component is a cyclic-AMP-stimulated Cl− channel. As postulated nearly two decades ago, the net Cl− movement from the blood to the lumen involves entry into the epithelial cells with Na+ and K+, followed by active Na+ extrusion via the pump and passive K+ exit via a channel. Intracellular [Cl−] is raised above electrochemical equilibrium and exits into the lumen when the apical Cl− channel opens. Cl− secretion is accompanied by a passive paracellular flow of Na+. The tubules of the rectal glands of elasmobranchs are highly specialized for secreting concentrated NaCl by this mechanism and hence have served as an excellent experimental model in which to characterize the individual steps by electrophysiological and ion flux measurements. The recent molecular cloning and heterologous expression of the apical Cl− channel and basolateral cotransporter have enabled more detailed analyses of the mechanisms and their regulation. Not surprisingly, since hormones acting through kinases control secretion, both the Cl− channel, which is the shark counterpart of the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator), and the cotransporter are regulated by phosphorylation and dephosphorylation. The primary stimulation of secretion by hormones employing cyclic AMP as second messenger activates CFTR via the direct action of protein kinase A (PKA), which phosphorylates multiple sites on the R domain. In contrast, phosphorylation of the cotransporter by as yet unidentified kinases is apparently secondary to the decrease in intracellular chloride concentration caused by anion exit through CFTR.
Physiological Effects of two Fmrfamide-Related Peptides from the Crayfish Procambarus Clarkii
Authors: Skerrett Martha , Peaire Amy , Quigley Patricia , Mercierf A. Joffre
Published: April 2021

The present study examined the effects of two recently identified neuropeptides on crayfish hearts and on neuromuscular junctions of the crayfish deep abdominal extensor muscles. The two peptides, referred to as NF1 (Asn-Arg-Asn-Phe-Leu-Arg-Phe-NH2) and DF2 (Asp-Arg-Asn-Phe-Leu-Arg-Phe-NH2), increased the rate and amplitude of spontaneous cardiac contractions and increased the amplitude of excitatory junctional potentials (EJPs) in the deep extensors. Both effects were dose-dependent, but threshold and EC50 values for the cardiac effects were at least 10 times lower than for the deep extensor effects. The heart responded equally well to three sequential applications of peptide in any given preparation, but the responses of the deep extensors appeared to decline with successive peptide applications. The results support the hypothesis that these two neuropeptides act as neurohormones to modulate the cardiac and neuromuscular systems in crayfish.

Quantal synaptic current recordings from the deep extensor muscles indicate that both peptides increase the number of quanta of transmitter released from synaptic terminals. Neither peptide elicited a measurable change in the size of quantal synaptic currents. NF1 caused a small increase in muscle cell input resistance, while DF2 did not alter input resistance. These data suggest that DF2 increases EJP amplitudes primarily by increasing transmitter release, while the increase elicited by NF1 appears to involve presynaptic and postsynaptic mechanisms.
Localisation And Characteristics of Natriuretic Peptide Receptors in the Gills of the Atlantic Hagfish Myxine Glutinosa (Agnatha)
Authors: Toop Tes , Donald John A. , Evans David H.
Published: April 2021

Specific binding of iodinated natriuretic peptides 125I-ANP and 125I-CNP was examined in the gill of the Atlantic hagfish Myxine glutinosa by tissue section autoradiography, saturation and competition analysis of binding to membrane preparations, affinity cross-linking, followed by SDS-PAGE and guanylate cyclase assays. Autoradiographs showed specific, saturable binding on the respiratory lamellar epithelium. In vitro analysis of the binding sites demonstrated that 125I-ANP bound to two receptor sites with the same affinity (Kd=15.4±1.6 pmoll−1; Bmax=45.9±3.0fmol mg−1 protein). 125I-CNP bound to high- and low-affinity receptor sites; variables for the high-affinity site (Kd=12.9±4.7pmoll’; Bmax=23.4±6.5fmol mg−1 protein) did not differ from those for the 125I-ANP sites. The low-affinity site had an apparent Kd and Bmax of 380±80 pmoll−1 and 120±21fmol mg−1 protein, respectively. All receptors had an apparent molecular mass of approximately 150 kDa, with no indication of a mammalian type NPR-C at a lower apparent molecular mass. 1 nmol l−1 unlabelled rANP and 20 and 30 nmol l−1 unlabelled pCNP and C-ANF, respectively, competed for 50% of 125I-ANP sites. 0.1nmoll−1 rANP and pCNP and 8 nmol l−1 C-ANF competitively inhibited 50 % of 125I-CNP binding. Both rANP and pCNP stimulated cyclic GMP production, although rANP was a more potent stimulator than was pCNP. C-ANF did not stimulate cyclic GMP production. These data suggest the existence of an ANP guanylate-cyclase-linked receptor similar to the mammalian NPR-A and an ANP/CNP receptor that may be similar to, although not structurally homologous with, the mammalian NPR-C clearance receptor.
Behavioural Evidence for the Use of Magnetic Material in Magnetoreception by a Migratory Bird
Authors: Beason Robert C. , Dussourd Natalie , Deutschlander Mark E.
Published: April 2021

The biophysical mechanism of vertebrate magnetic sensory perception has not been completely resolved. We here provide evidence for the use of a magnetic material (probably magnetite) by a vertebrate to detect the earth’s magnetic field. The role of magnetite in bobolink (Dolichonyx oryzivorus) orientation was assessed by magnetizing the birds with a magnetic pulse in one of three orientations. Bobolinks magnetized with different polarities were significantly oriented in directions different from one another and from their controls. Treatment with a second pulse having the opposite polarity to the first resulted in random orientation for each group. These results indicate an effect specific to a particle-based magnetoreceptor. The use of magnetite particles for magnetoreception is not in conflict with other reports on the use of photopigments for this purpose. The two mechanisms could be used in a complementary manner for detecting the same or different aspects of the magnetic field.
Variation in the Respiratory Quotient of Birds and Implications for Indirect Calorimetry Using Measurements of Carbon Dioxide Production
Authors: Walsberg Glenn E. , Wolf Blair O.
Published: April 2021

Determination of animal power consumption by indirect calorimetry relies upon accurate estimation of the thermal equivalent of oxygen consumed or carbon dioxide produced. This estimate is typically based upon measurement or assumption of the respiratory quotient (RQ), the ratio of CO2 produced to O2 consumed. This ratio is used to indicate the mixture of lipids, carbohydrates and proteins in the metabolic substrate. In this analysis, we report the RQ for two bird species, Passer domesticus and Auriparus flaviceps, under several dietary and fasting regimes. RQ commonly differed substantially from those typically assumed in studies of energy metabolism and often included values below those explainable by current knowledge. Errors that could result from these unexpected RQ values can be large and could present the primary limit to the accuracy of power consumption estimates based upon measurement of carbon dioxide production.
Physiology and Behaviour of Free-Swimming Atlantic COD (Gadus Morhua) Facing Fluctuating Temperature Conditions
Authors: Claireaux G. , Webber D. M. , Kerr S. R. , Boutilier R. G.
Published: April 2021

Atlantic cod (Gadus morhua L.), acclimated to 5 °C, were equipped with ultrasonic transmitters which allowed the continuous monitoring of their vertical movements and heart rate. Fish were then placed in a 125 m3 tower tank in which the various thermal conditions they encounter in their natural environment were reproduced. Physiological and behavioural responses of cod were followed in parallel to the induced environmental changes. The experimental conditions studied in the tower tank were also reproduced in a swimming respirometer, where oxygen consumption and heart rate could be monitored within the activity range of a free-swimming animal.

In a homogeneous water column, a rise in temperature induced marked increases in fish swimming activity, heart rate and heart beat-to-beat variability. In a thermally stratified environment, voluntary activity also increased when the thermal structure of the water column was altered, though no temperature-dependent changes in heart rate were observed. In this case, fish avoided the new temperature conditions, exhibiting distinct thermoregulatory behaviour. Stratification of the water column also prompted daily cyclic changes in fish distribution, animals tending to be in deeper and colder water layers during the day and in shallower and warmer layers at night.

Respirometry experiments revealed that the thermoregulatory behaviour observed in free-ranging fish was probably driven by the energetic expedient of maintaining the physiological status quo – i.e. avoiding bioenergically costly reacclimation processes. Indeed, acute temperature increases or decreases of 2.5 °C led to marked differences in oxygen consumption, with metabolic rate changes of 15 and 30 %, respectively. The persistent linear relationship between heart rate and oxygen consumption allowed us to estimate, from the heart rate recorded in free-swimming fish, the entire range of metabolic responses that cod underwent voluntarily while experiencing a thermally stratified water column. The most profound metabolic effect, however, was observed with feeding, when oxygen consumption increased by as much as 80 %, resulting in an estimated 90 % reduction in their subsequent scope for activity.
Physiology and Behaviour of Free-Swimming Atlantic COD (Gadus Morhua) Facing Fluctuating Salinity and Oxygenation Conditions
Authors: Claireaux G. , Webber D. M. , Kerr S. R. , Boutilier R. G.
Published: April 2021

Atlantic cod (Gadus morhua L.) acclimated to a temperature of 5 °C and 30 ‰ salinity were equipped with ultrasonic transmitters which allowed continuous monitoring of their heart rate and their position in the water column. Fish were placed in a 125 m3 tower tank which permitted various environmentally relevant modifications of the salinity and oxygenation conditions. Cod physiological and behavioural responses were followed in parallel to the environmental manipulations. Some of the experimental conditions studied in the tower tank were also reproduced in a swimming respirometer where fish oxygen consumption and heart rate were monitored at various levels of activity. Lowering salinity from 30 to 26 ‰ did not change resting oxygen consumption, but increased active oxygen consumption. Lowering salinity from 30 to 26 ‰ increased heart rate over the whole range of swimming speeds except at maximum speed. Lowering oxygen tension to 9 kPa decreased oxygen consumption over the whole range of swimming speeds and decreased resting heart rate. Low salinity did not significantly affect the relationship between heart rate and oxygen consumption. Low oxygen levels decreased the oxygen transported per heart beat. In the tower tank, bursts of activity were associated with tachycardias. In uniform conditions, fish swam more deeply during the day than at night. After an exploratory period of approximately 6 h, fish chose to remain in a low-salinity upper layer of the tank. Thereafter, high salinities were avoided. Fish tended to select low salinities if a choice was provided. Fish generally avoided zones of low oxygen (<9 kPa) but continued voluntarily to enter regions with values as low as 3.0 kPa for short excursions or if food was offered.
Peptide F1, an N-Terminally Extended Analog of Fmrfamide, Enhances Contractile Activity in Multiple Target Tissues in Lobster
Authors: Worden Mary Kate , Kravitz Edward A. , Goy Michael F.
Published: April 2021

The physiological actions of lobster peptide F1 (TNRNFLRFamide) have been examined on three different lobster nerve-muscle preparations (exoskeletal, cardiac and visceral). The peptide, which is found at high concentrations in a lobster neurosecretory gland, causes a long-lasting enhancement of contractility in each target tissue. On exoskeletal nerve-muscle preparations, peptide F1 has the following actions: (1) it potentiates transmitter release from nerve terminals innervating exoskeletal muscle, leading to an increase in both spontaneous and nerve-evoked release of transmitter; (2) it acts directly on the muscle, in the absence of nerve activity, to induce tonic contractions; and (3) it shows a potent desensitization that does not reverse with prolonged washing of the tissue. On each of the types of muscle examined, peptide F1 is active at nanomolar concentrations and is 3–4 orders of magnitude more potent than FMRFamide. These findings suggest that peptide F1 is a neurohormone with widespread myogenic actions throughout lobster peripheral tissues. The molecular mechanism(s) by which the peptide acts are not yet known, but do not appear to involve cyclic AMP or cyclic GMP.
Visual Distance Discrimination Between Stationary Targets in Praying Mantis: an Index of the Use of Motion Parallax
Authors: Poteser Michael , Kral Karl
Published: April 2021

When larvae of the praying mantis Polyspilota sp. and Tenodera sinensis want to leave an exposed position and can choose to move between stationary objects at different distances, they usually choose the nearest. Their ability to select the nearest object is greatest when the background has horizontal stripes and is least when it has vertical stripes. Object preference is based on a successive distance comparison, which may involve content-related memory processes. Mantid larvae can determine the absolute distance to a stationary object. Vertical contrasting borders play an important role in this process. Side-to-side head movements (peering) are directly involved in the distance measurement, as shown (i) by the peering behaviour itself and (ii) by the fact that mantids can be deceived in distance measurement by arbitrary movements of target objects during the peering movement. It is supposed that the distance measurement involves the larger and faster retinal image shifts that near, as opposed to more distant, objects evoke. Mantid larvae can distinguish a black-and-white rectangle in the foreground from a black-and-white striped background, even when both are similar with respect to luminance, contrast and texture. The ability to distinguish between figures and background could be explained by motion parallaxes, i.e. by the fact that during peering movements the nearer object moves faster and by a larger angle than the background structure. From birth onwards, even when the eyes have yet to develop foveal specialization, mantids are capable of this visually controlled behaviour.
Dependence of Flight Behavior and Heat Production on air Temperature in the Green Darner Dragonfly Anax Junius (Odonata: Aeshnidae)
Authors: May Michael L.
Published: April 2021

The large, endothermic dragonfly Anax junius regulates the temperatures of its thorax (Tth ) and head (Th ) during flight. At high ambient temperature (Ta ) it is able to dispose of excess heat from the thorax by increasing hemolymph circulation to the abdomen, but recent evidence suggests that heat loss to the abdomen is largely passive at Ta <30 ˚C. Nevertheless, these insects continue to regulate Tth and Th at least down to 20 ˚C and probably at much lower values of Ta . As Ta declines, A. junius glide less, probably fly faster when feeding, and increase their wingbeat frequency when patrolling. Presumably as a result of these behavioral changes, heat production, and thus inferred flight metabolic rate, is inversely proportional to Ta . This is the first demonstration based on field data that an insect regulates body temperature while flying by altering heat production.
The Structure, Response Properties and Development of a Hair Plate on the Mesothoracic Leg of the Locust
Authors: Newland Philip L. , Watkins Branwen , Emptage Nigel J. , Nagayama Toshiki
Published: April 2021

A hair plate is present on the proximal anterior face of the pro-and mesothoracic tibiae of the legs of the locust Schistocerca gregaria, but not on the metathoracic legs. The hair plate is in a depression of the cuticle and contains about 11 hairs, which are all polarised with their tips pointing towards the dorsal surface of the tibia. The hairs are all of the same trichoid sensilla type and vary in length from 90 to 140 µm. Associated with the hair plate is a pronounced distal extension of the anterior femoral coverplate, the inner face of which is concave, that makes contact with the hairs during flexion and extension movements of the tibia. During postembryonic development, no tibial hair plate hairs are present in the first four larval stages. In fifth-instar larvae just three hairs are present, while the full complement is attained only after the final moult to adulthood. The distal extension of the posterior coverplate is present through all instar stages, becoming more pronounced after each moult.

Sensory neurones innervating the hairs of an adult may be divided into two classes on the basis of their responses. The first type responds phasically to imposed deflections and is velocity-sensitive. The second type responds phasotonically and is also sensitive to the velocity of the stimulus but has an additional tonic component sensitive to maintained angular deflections. Both types of afferents are directionally sensitive and respond best to deflections against the natural bend of the hair, equivalent to extension movements of the tibia. The hairs are deflected by the coverplate only at femoro-tibial angles of less than 90 ˚. During extension movements, they will be deflected in their most sensitive directions while during flexion movements they will be deflected in their least sensitive directions.
Maximum single leg force production: cockroaches righting on photoelastic gelatin
Authors: Full R. J. , Yamauchi A. , Jindrich D. L.
Published: April 2021

Integrating studies of mechanics, neural control and isolated muscle function are possible using arthropod legs. To evaluate leg performance, we measured the ground reaction forces generated by individual legs of the six-legged cockroach Blaberus discoidalis (3.1 g), during an emergency behavior, righting or over-turning. We used a photoelastic method to measure the forces generated by individual legs simultaneously. A gelatin track placed between crossed polarizing filters was illuminated from below, and a high-speed video camera recorded the stress-induced optical signals from above. The size and skew of the optical patterns were found to be related to the magnitude and direction of the force. We discovered that the ground reaction forces generated during the righting behavior of the death-head cockroach were eight times greater than those observed during high-speed running, supporting the possibility that relative leg forces (leg force per unit body weight) during running and maximal leg activity differ more in small arthropods than in larger vertebrates. Non-geometric scaling of relative leg force (i.e. scaling to less than body mass-0.33), along with the reduced force-generating ability of a single leg in animals with many legs, may help to explain why the maximum relative leg force production by six-legged cockroaches, as well as by some other small insects, can be similar to the relative single leg forces produced by two-and four-legged vertebrates that are almost 1000 times more massive. Leg number and body mass alone, however, appear to be insufficient to explain the variation observed in relative leg force production at a given body mass, because enormous diversity in musculo-skeletal parameters exists. The maximal relative leg force of the cockroach B. discoidalis during righting was at the low end of a 100-fold variation observed for smaller insects wedging (pushing through a small crevice) and pulling loads. Thus, this cockroach can be characterized as a moderately strong insect with the capacity for relatively high speed. Results from the present study question the predictive strength of the simple geometric scaling arguments involving a strength:weight ratio as they are applied to small arthropods and encourage further consideration of the importance of leg number, muscle force production and mechanical advantage in the derivation of general principles of leg performance.