bluuebunny/crossref_metadata_2025 huggingface dataset:
Biophysical Aspects of Directional Hearing in the Tammar Wallaby, Macropus Eugenii
Authors: Coles Roger B. , Guppy Anna
Published: April 2021

The biophysical properties of the external ear of the Tammar wallaby, Macropus eugenii (Desmarest), have been investigated using probe microphones implanted in the ear canal. An acoustic axis of the pinna exists above 2kHz which is located close to the horizonal plane for natural ear positions, whereas azimuthal location of the acoustic axis is determined by pinna orientation on the head. The maximum on-axis acoustic pressure gain of the external ear reaches 25–30 dB for frequencies near 5 kHz. This results from pressure transformation by the horn-like pinna combined with resonance of the auditory meatus. The directionality of the pinna is similar to the sound diffraction properties of a circular aperture with an average radius based on the circumference of the pinna face. These properties determine the acceptance angle of the main lobe containing the acoustic axis and the spatial location of nulls. Large binaural intensity differences, exceeding 30dB, can be produced by the interaction of peaks and nulls between monaural directivity patterns, depending on the relative position of each pinna.
Octopaminergic Modulation of the Membrane Potential of the Schwann Cell of the Squid Giant Nerve Fibre
Authors: Reale Vincenzina , Evans Peter D. , Villegas Jorge
Published: April 2021

The actions of octopamine on the Schwann cells of the giant nerve fibre of the tropical squid are described. The pharmacology of the receptors mediating the actions of octopamine has been investigated in terms of stereospecificity, amine specificity and interactions with a range of agonists and antagonists. The receptors are maximally activated by D(−)-octopamine and share many of the characteristics of OCTOPAMINE2 class receptors in other preparations. The octopamine receptors appear to mediate their actions by increasing the intracellular levels of cyclic AMP in the Schwann cells. Low concentrations of octopamine potentiate the actions of the nicotinic cholinergic activation system of the Schwann cells. The results are discussed in terms of the possible physiological role of octopamine in the modulation of Schwann cell activity during stressful conditions when the giant axon system is likely to be used at a high frequency to facilitate the escape response of the squid.
Responses Of a Stenohaline Freshwater Teleost (Catostomus Commersoni) To Hypersaline Exposure II. Transepithelial Flux of Sodium, Chloride and ‘Acidic Equivalents’
Authors: Wilkes P. R. H. , McMahon B. R.
Published: April 2021

The effects of exposure to 300mosmoll−1 sodium chloride on the transepithelial movement of sodium, chloride and ‘acidic equivalents’ was examined in the stenohaline freshwater teleost Catostomus commersoni (Lacépéde), the white sucker. The transepithelial potential (TEP) was negative in control fish acclimated to soft freshwater ([Ca2+] <0– 1 mmol I−1) but positive in control fish acclimated to hard-water ([Ca2+] > 1–0mmoll−1). Using permeability coefficients calculated from measured unidirectional effluxes of sodium and chloride for both groups above, the Goldman equation predicts the observed change in polarity of the TEP. During saline exposure the ability of external calcium to influence the TEP was greatly attenuated, and the TEP remained positive throughout 96 h exposure to either hard or soft saline water. As a consequence of the reduced (and reversed) chemical potential and of the prevailing TEP, the electrochemical difference for sodium was directed out from the fish while that for chloride was directed inwards. Thus, the passive movement of sodium and chloride in opposite directions could potentially account for the previously reported decrease in plasma strong ion difference (SID), and therefore the prevailing acid-base status. Unfortunately, the existence of possible exchange diffusion processes for sodium and chloride observed in saline-exposed fish prevented a more detailed examination of this hypothesis. Since the change in plasma SID occurred gradually over a 96-h period, there was no measurable change in the net flux of ‘acidic equivalents’ which could have been associated with the active and passive transbranchial movement of sodium and chloride. The significance (or lack of it) of the Na+/H+-NH4+ and C1−/HCO3−-OH− exchange pumps to systemic acid-base balance is discussed.
A New Technique for Measuring Water Transport Across the Seawater Eel Intestine
Authors: Ando Masaaki , Sasaki Hiroshi , Huang Kee C.
Published: April 2021

A new technique was developed for measuring net water flux across the eel intestine in vitro. The new perfusion method was suitable for long duration experiments because of continuous oxygen supply to both the external and the perfusion medium. Net water flux was calculated directly from the difference between the rates of effluent and perfusate flow without measuring the concentration of marker substances. The calculated value of net flux appears to be reliable because: its direction is always from mucosa to serosa in both everted and non-everted intestine; ouabain diminishes it to zero; it is identical with the standard water flux obtained under zero perfusion ; and it is identical with the value obtained by means of [14C]PEG following the previous perfusion method. The net water fluxes obtained by the new method were steadier than those obtained with the previous complicated perfusion method. In this new experimental system, the net water flux and the transepithelial potential difference (PD) decreased gradually with time, and were not restored by application of adrenergic agonists or cortisol. These parameters were stimulated by 5 mmol l−1 L-alanine, but not by D-glucose, L-valine or L-glycine, indicating a specific action of L-alanine.
Peptidergic and Aminergic Modulation of Insect Skeletal Muscle
Authors: Evans Peter D. , Myers Camilla M.
Published: April 2021

Insect skeletal muscles are frequently innervated by small numbers of motor neurones, all of which can be uniquely identified physiologically. They therefore present excellent model systems in which to study the basic principles of neuromuscular transmission and the modulation of these effects by biogenic amines and peptides. The extensor-tibiae muscle of the hind leg of the locust is a much studied, large muscle that is innervated by three identified motor neurones and one identified modulatory neurone. Much attention has recently been focused on the modulation of neuromuscular transmission and muscular contraction in this muscle by biogenic amines and peptides.

One proximal bundle of muscle fibres in the extensor-tibiae muscle exhibits a myogenic rhythm of contraction and relaxation. The rhythm is stimulated by a variety of peptides including proctolin, the AKH-related peptides M1 and M2, and by small cardioactive peptide (SCPB). In addition, it is activated by 5-hydroxy-tryptamine and by one class of adenosine analogues. The rhythm is inhibited by octopamine and by a second class of adenosine analogues. The actions of these various modulatory compounds will be discussed in terms of the likely numbers of pharmacologically distinct receptors in this preparation and their modes of action.

Neuromuscular transmission and muscular contraction in the extensor-tibiae muscle is modulated by the biogenic amine octopamine and by the peptides, proctolin and FMRFamide. The actions of these modulators are discussed in relation to differences in the responsiveness of various regions of the muscle, to the frequency dependence of their effects on motor neurone activity and to their modes of action.

The cellular locations and mode of transmission to the muscle of some of these modulators will be considered. Octopamine and proctolin are contained within neurones which innervate the muscle, whilst FMRFamide-and SCPB-like peptides appear to be released into the locust haemolymph as neurohormones.
Different Types of Calcium Channels
Authors: Mccleskey E. W. , Fox A. P. , Feldman D. , Tsien R. W.
Published: April 2021

Ca2+ channels allow passage of Ca2+ ions into the cytoplasm through a selective pore which is opened in response to depolarization of the cell membrane (for reviews see Hagiwara & Byerly, 1981, 1983; Tsien, 1983; Reuter, 1983). The Ca2+ flux creates a net inward, depolarizing current and the resulting accumulation of Ca2+ in the cytoplasm can act as a chemical trigger for secretion of hormones and neurotransmitters, contraction of muscle and a-variety of other Ca2+-sensitive events. Thus, upon sensing membrane potential changes, Ca2+ channels simultaneously generate an electrical signal while directly creating an intracellular chemical messenger. This dual ability is unique among the family of ion channels and allows the Ca2+ channel to play a variety of roles in excitation-secretion and excitation-contraction coupling.

It has now become clear that versatility of function is reflected by diversity of the types of Ca2+ channels on the membrane of individual cells. This article describes the nature of data which have demonstrated multiple channel types, reviews the literature suggesting that many cells have several kinds of Ca2+ channels, and discusses newer data regarding a neurotoxin that distinguishes among different Ca2+ channels.
Slow Synaptic Transmission in Frog Sympathetic Ganglia
Authors: Adams P. R. , Jones S. W. , Pennefather P. , Brown D. A. , Koch C. , Lancaster B.
Published: April 2021

Bullfrog ganglia contain two classes of neurone, B and C cells, which receive different inputs and exhibit different slow synaptic potentials. B cells, to which most effort has been directed, possess slow and late slow EPSPs. The sEPSP reflects a muscarinic action of acetylcholine released from boutons on B cells, whereas the late sEPSP is caused by a peptide (similar to teleost LHRH) released from boutons on C cells. During either sEPSP there is a selective reduction in two slow potassium conductances, designated ‘M’ and ‘AHP’. The M conductance is voltage dependent and the AHP conductance is calcium dependent. Normally they act synergistically to prevent repetitive firing of action potentials during maintained stimuli. Computer simulation of the interactions of these conductances with the other five voltagedependent conductances present in the membrane allows a complete reconstruction of the effects of slow synaptic transmission on electrical behaviour.
The Size Factor in the Action of Arsenic Upon Silkworm Larvae
Authors: Bliss C. I.
Published: April 2021

The customary method of adjusting dosages of drugs and poisons as simple ratios of the body weight of the individual is questioned. Data recorded by F. L. Campbell on the survival time of silkworm larvae following the ingestion of sodium arsenate were used for analysis. By the method of covariance it is shown that there is a significant residual effect of individual body weight upon the rate of toxic action when the dosage is made proportional to the body weight. By graphic test the rate of toxic action seemed to be a linear function of the log of the dose per larva and the log of the body weight. Accordingly partial regression equations were computed separately for the 2nd to the 5th instars expressing the rate of toxic action in terms of these two dosage characteristics. The adjustment in dosage that was necessary to eliminate the effect upon the rate of toxic action of body size could be expressed as a size factor, where w is the body weight of the individual and h is determined from the partial regression coefficients of each equation. When based upon the reciprocal of the survival time, h increased from 1· 67 to 1· 96 from the 2nd to the 5th instars, but when similar values were computed for the logarithm of the rate, h was the same in all instars and averaged 1· 511 ± 0· 089. Also supporting the theoretical superiority of the log rate as a measure of toxic action was the fact that the data for the separate instars formed parts of a single straight line when log rate was plotted against the log of dose adjusted by the size factor w1’6 and the statistical demonstration that the distribution of rates was significantly skewed and that of log rates symmetrical. If the adjusted dose is considered as a type of con-centration, the final equation for all four instars could be written as C0.49t = 309, a type of formula having wide toxicological applicability. A method is proposed for computing the mean lethal dose from the rate of toxic action.
Metabolic Rates of Trout Fry from Swift and Slow-Running Waters
Authors: Washbourn R.
Published: April 2021

Recent studies on the respiration of fresh-water animals have shown that certain species of ephemerid nymphs and trichopterid larvae inhabiting swift streams have a higher oxygen consumption than other species, comparable in size, which live in still waters, the measurements being made under identical conditions (Fox, Simmonds and Washbourn, 1935). Moreover, within one species of crustacean, Asellus aquaticus, individuals from rapid water have a higher metabolic rate than those from slow water (Fox and Simmonds, 1933). The investigation reported below was undertaken to find out whether trout would show a similar phenomenon.
Studies in Animal Locomotion
Authors: Gray J.
Published: April 2021

In a previous paper (Gray, 1936) it has been shown that the rhythmical movements, characteristic of an eel swimming freely in water, are determined by the spinal cord and not upon impulses reaching the cord from receptors in the skin or muscles. It was also shown that a locomotory rhythm can be elicited from a spinal or decapitate preparation as a response to stimuli applied either to the spinal cord or to exteroceptive sense organs. In all these cases the experimental conditions were such that the muscles of the body were free to contract against the comparatively low resistance of the surrounding water. The present paper deals with the behaviour of the fish when the movements of the muscles are opposed by relatively strong external resistances.
Respiratory Cost of Swimming in Larval and Juvenile Cyprinids
Authors: Kaufmann Ruediger
Published: April 2021

The relationship between swimming speed and respiration rate for larvae and juveniles (1.5–600 mg fresh mass) of two cyprinid species, Chalcalburnus chalcoides and Rutilus rutilus, was measured in a flow-tunnel at 20°C.

A special tunnel respirometer with small volume and fast response had to be constructed to cope with the methodological difficulties encountered with the larvae. The oxygen uptake increased quadratically with swimming speed if the oxygen debt incurred at the highest speeds was included in the calculations. The maximum speeds sustainable over 2 min were 6–8 lengths s−1; the critical speed marking the onset of anaerobic processes was only 10–15 % lower. Energetics and performance were similar for both species. The cost of transport was much higher for larvae and juveniles than for adult fish and decreased rapidly during growth. Standard and routine metabolic rates scaled with an allometry of M−0.23, active rates with M−015, where M is body mass in grams. In the smallest larvae, however, the standard rates were nearly independent of body mass. Their active rates of 80μmol O2h−1g−1 fresh mass were twice as high as those of adults. The scope for activity was high on an absolute scale, but not when expressed as factorial scope, since the standard rate was also high. For the same reason, routine activity accounted for less than 25 % of the energy budget, despite the high cost of transport. The data are discussed with respect to the changing swimming pattern during ontogeny, the shift from cutaneous to branchial respiration and the metabolic processes involved.
Ion Transport Across the Midgut of the Tobacco Hornworm (Manduca Sexta)
Authors: Chamberlin M. E.
Published: April 2021

The transport of K+, Na+ and Cl− across the three morphologically distinct regions of the tobacco hornworm midgut was measured under open-circuit and short-circuit conditions. Using a saline which contained physiological levels of haemolymph ions, amino acids and sugars, it was shown that all three sections actively secrete K+ and Cl− and absorb Na+. The anterior section maintained the highest short-circuit current (Isc), transepithelial potential difference (PD) and net K+ secretion. The middle section had the lowest Isc, PD and K+ secretion, but absorbed Na+ at the greatest rate. The posterior section had the greatest rate of Cl− secretion. Omission of K+ depressed the Isc, Subsequent addition of K+ stimulated the Isc to control levels in the middle and posterior sections, but not in the anterior section. Omission of Cl− or Na+ also inhibited the Isc. Reintroduction of Cl− had no stimulatory effect and, although reintroduction of Na+ stimulated the Isc, control levels were not attained. Unlike the results reported in previous studies, the net K+ transport exceeded the Ix in all three midgut sections. The deficit in was not made up by the transport of Na+ and Cl−. The results are discussed with respect to proposed models of ion transport across this epithelium.
Short Communication: Luminal Alkalinization by the Isolated Midgut of the Tobacco Hornworm (Manduca Sexta)
Authors: Chamberlin M. E.
Published: April 2021

The midgut contents of lepidopteran larvae are often several pH units more basic than the haemolymph (Berenbaum, 1980). One species, Manduca sexta, maintains a luminal pH of 11.3 (Dow, 1984) while the haemolymph has a pH of 6.7-6.8 (Dow, 1984; Dow et al. 1984). The midgut of M. sexta is divided into three morphologically distinct regions (Cioffi, 1979), and Dow (1984) has shown that the luminal pH is greatest in the anterior and middle sections of the midgut. The posterior midgut lumen, while still more basic than the haemolymph, has a pH lower than the middle and anterior sections. Whereas these results suggest that alkaline secretion may differ along the length of the midgut, no direct measurements of alkaline secretion have been made. In this study the rate of luminal alkalinization in the three midgut sections was measured in vitro.
Activity Patterns of Inhibitory Motoneurones and their Impact on Leg Movement in Tethered Walking Locusts
Authors: Wolf Harald
Published: April 2021

A preparation is described which permits intracellular recording of neural activity in tethered walking locusts. Minimal dissection is required, leaving the animal nearly intact.

In this preparation, the activities of the three common inhibitory motoneurones (CIs) supplying the muscles of the middle leg were recorded. CIs were completely or almost completely silent in quiescent locusts but often produced a tonic spike discharge during walking activity. This tonic discharge was modulated in the step cycle, bursts of action potentials being generated in conjunction with the swing phase of the leg movement. The bursts peaked at around the start of leg protraction. They were remarkably similar in all three CIs and in a variety of different walking situations (forward and backward walking, searching, etc.). The only notable difference was that bursts of CI1 normally peaked some 40 ms before those of CI2. These results indicate that CI activity is timed according to the muscle group innervated but that no further functional specializations exist.

Activity of CI1 was manipulated by current injection. For example, decreasing CI spike discharge by the application of hyperpolarizing current reduced the velocity of leg protraction in the walking animal. This demonstrates that CI1 plays an important role in determining the speed of the swing movement.
Control of Locomotion in the Freshwater SnailPlanorbis Corneus: II. Differential Control of Various Zones of the Ciliated Epithelium
Authors: Deliagina T. G. , Orlovsky G. N.
Published: April 2021

In the freshwater snail Planorbis corneus, the neuronal mechanisms of the pedal ganglia that control ciliary locomotion were studied. The foot was attached to the bottom of a recording chamber with the ciliated epithelium facing upwards. To record the total motor effect produced by ciliary beating, a small disk with its edge lying on the sole of the foot was used. The ciliary beating forced the disk to rotate.

In the pedal ganglia, efferent locomotor neurones (ELNs) were found, which control the locomotor activity of the ciliated epithelium. This locomotor activity increased with excitation of an ELN, and decreased with its inhibition. Axons of the ELNs, controlling the anterior, middle and posterior zones, traverse the corresponding pedal nerves. For the anterior zone, two ELNs were found. For the middle and posterior zones, only one ELN per zone was found. The activity of ELNs correlated with the intensity of ciliary beating during the following central and reflex influences upon the locomotor mechanisms: (1) spontaneous fluctuations of the locomotor activity, (2) changes of temperature, (3) transections of central connections (interganglionic connectives), (4) defensive reactions evoked by tactile stimuli or switching off the light, and (5) activation of feeding behaviour by natural stimuli. The data strongly suggest that ELNs are responsible for the differential control of locomotor activity in various zones of the ciliated epithelium during different behavioural acts.
Ultrasound-Triggered, Flight-Gated Evasive Maneuvers in the Praying MantisParasphendale Agrionina: II. Tethered Flight
Authors: Yager David D. , May Michael L.
Published: April 2021

In tethered flight, Parasphendale agrionina (Gerst.) males respond to ultrasonic stimuli with a unique suite of behaviors that includes full extension of the forelegs, strong dorsiflexion of the abdomen, a head roll, a 5% decrease in wingbeat frequency and a 33% increase in forewing excursion. Latency for the foreleg extension averages 66 ms while the latency to onset of yaw is 174 ms. The direction of the turn is unrelated to the location of the speaker. Yaw magnitude and latency are only weakly related to sound pressure level, and variability in these and other parameters is high. The behavior shows moderately sharp tuning to 40–60 kHz with a lowest mean threshold of 60 dB SPL. A male will not respond to ultrasound unless in flight, and the context-gating is independent of sensory input from the tarsi. Several components of the in-flight evasive behavior resemble defensive displays on the ground, and we suggest that this mantis has responded to predation pressure from bats with both flight-derived maneuvers and an aerial deimatic display.
Magnesium Transport in Fish Intestine
Authors: Van Der Velden J. A. , Groot J. A. , Flik G. , Polak P. , Kolar Z. I.
Published: April 2021

Literature on the mechanisms of magnesium transport through fish intestine is scarce. Indirect evidence for a net magnesium transport via the intestinal tract of fish has been established by dietary experiments (e.g. with carp Cyprinus carpio L. and nile perch Oreochromis niloticus Peters), showing that dietary magnesium is essential for the growth of these fish (Ogino and Chiou, 1976; Dabrowska et al. 1989). Nakamura and Hirano (1986) suggested ‘solvent drag’ as a mechanism for net magnesium transport in eel Anguilla japonica intestine. For mammals, the reports on this topic are equivocal. In the small intestine of the rat, diffusion (Ross, 1962; Aldor and Moore, 1970; O’Donnell and Smith, 1973) as well as solvent drag (Behar, 1974) were reported to underlie magnesium absorption, although the possibility of an active transport component was kept open by these authors. For the intestine of guinea pig, active transport of magnesium was demonstrated (Ross and Care, 1962; Partridge et al. 1987). This communication deals with magnesium transport across stripped intestinal epithelium of freshwater tilapia and its possible mechanisms.
Adhesion and Detachment of the Toe Pads of Tree Frogs
Authors: Hanna Gavin , Barnes W. Jon P.
Published: April 2021

The mechanisms by which the toe pads of tree frogs adhere to and detach from surfaces during climbing have been studied in Osteopilus septentrionalis and other tree frogs using a variety of techniques.

The experiments on attachment lend general support to the theory that toe pads stick by wet adhesion. First, the presence of a meniscus surrounding the area of contact shows that pad and surface are connected by a fluid-filled joint. Second, experiments on single toe pads of anaesthetised frogs demonstrate that the pads exhibit the velocity-dependent resistance to shear forces expected of any system employing a fluid as an adhesive mechanism. Third, the largest adhesive forces that toe pads can generate (approx. 1.2mNmm−2, calculated from data on sticking ability) are within the range that can be produced by wet adhesion. Simple measurements of the forces needed to separate a pair of metal discs joined by mucus demonstrate that both viscous forces (Stefan adhesion) and surface tension (the two components of wet adhesion) are likely to play significant roles in the tree frog’s adhesive mechanism.

The experiments on detachment demonstrate that toe pads are detached from surfaces by peeling, the pads being removed from the rear forwards during forward locomotion up a vertical surface. When the frogs were induced to walk backwards down this vertical slope, peeling occurred from the front of the pad rearwards. Use of a force platform to measure directly the forces exerted by the feet during climbing shows that, during forward locomotion up a vertical slope, this peeling is not accompanied by any detectable detachment forces. Such forces of detachment are seen, however, during backward walking down the slope and when belly skin comes into contact with the platform. That peeling occurs automatically during forward locomotion is supported both by observations of peeling in single toe pads of anaesthetised frogs and by the inability of frogs to adhere to vertical surfaces in a head-down orientation. Indeed, frogs on a rotating vertical surface were observed to adjust their orientations back towards the vertical whenever their deviation from the vertical reached 85.1 ±21.5°. During forward locomotion peeling seems to occur as a natural consequence of the way in which the toes are lifted off surfaces from the rear forwards, while during backward locomotion it is an active process involving the distal tendons of the toes.
Serotonin Depresses the After-Hyperpolarization Through the Inhibition of the Na+/K+ Electrogenic Pump in T Sensory Neurones of the Leech
Authors: Catarsi Stefano , Brunelli Marcello
Published: April 2021

In T sensory neurones of the leech, a train of impulses elicited by intracellular electrical stimulation leads to an after-hyperpolarization of up to 30 mV, mainly due to the activation of the electrogenic Na+/K+-ATPase but partly to a Ca2+-activated K+ conductance. It was found that serotonin reversibly reduced the amplitude of this after-hyperpolarization. We investigated the mechanism of action of serotonin and found: (1) after inhibition of the Ca2+-activated K+ conductance with BaCl2 or CdCl2, serotonin was still able to reduce the afterhyperpolarization; (2) when penetration of T cells with microelectrodes leaking sodium was preceded by serotonin perfusion of the ganglia, the normal hyperpolarization due to the activation of the electrogenic pump was converted to a depolarization; (3) after long-lasting perfusion with K+-free saline solution (which inhibits the Na+/K+ pump), the application of CsCl caused repolarization by reactivating the electrogenic ATPase; serotonin slowed and reduced this repolarization; (4) serotonin potentiated the depolarization of T neurones caused by the inhibition of the Na+/K+ pump following cooling of ganglia and depressed the hyperpolarization after rewarming to room temperature. These data taken together suggest that serotonin directly inhibits the Na+/K+ electrogenic pump.
Ion Activities and Electrochemical Gradients in the Mealworm Rectal Complex
Authors: O’donnell M. J. , Machin J.
Published: April 2021

Ion activities and potential differences in cellular and extracellular compartments of the rectal complex of Tenebrio molitor L. larvae have been recorded simultaneously using double-barrelled ion-sensitive microelectrodes. On average, the tubule lumen (TL) was 44mV positive to the haemolymph. Values of aK in the posterior rectal complex exceeding 2700 mmol I-1 were measured, sufficient to account for much of the osmolality of 6.8osmolkg-1 driving uptake of water from the rectal lumen. The mean value of 797 mmol l-1 exceeded the Nernst equilibrium activity more than 75-fold, indicating active transport of K+. Intracellular potassium activities in the tubules (153 mmol l-1) were high relative to the values in other insect cells, but moderate relative to TL values. Tubule lumen Na+ activities as high as 400 mmol l-1 and pH values of 6.8 were well above the equilibrium values of 11 mmol I-1 and 7.9, respectively, indicating active transport of these cations as well. The ease and frequency of impaling a perinephric space (PNS) surrounding the tubules established it as a functional compartment. On average, the PNS was 22 mV negative to the haemolymph. Potassium activities in the PNS were close to electrochemical equilibrium with the haemolymph, whereas mean aNa and pH were reduced fivefold and 0.5 units, respectively, below the corresponding Nernst equilibrium values. The results suggest that cations move from haemolymph to PNS, and that the PNS is the immediate source for cation transport into the tubule lumen. Cl- was close to electrochemical equilibrium with the haemolymph in both compartments, and presumably enters the tubule lumen as a passive consequence of positive potential differences (PDs) in the tubule lumen.
Neural Control of the Buccal Muscle Movement in the African Giant Snail Achatina Fulica
Authors: Yoshida Masayuki , Kobayashi Makoto
Published: April 2021

Five pairs of neurones, R(L)-B1, R(L)-B2, R(L)-B3, R(L)-B4 and R(L)-B5, controlling buccal muscle movement, were identified in the buccal ganglia of the African giant snail Achatina fulica Férussac. All these neurones fired during the radula retraction phase of rhythmic buccal activity. Neurones Bl, B2, B4 and B5 made direct excitatory connections to the radula retractor, and Bl, B2, B3 and B5 also made direct excitatory connections with the outer muscle of the buccal mass. Of these neurones, B4 had the most potent effect on contraction of the ipsilateral radula retractor. Physiological and pharmacological analyses suggested that the principal excitatory transmitter of B4 at the neuromuscular junctions was acetylcholine (ACh), although glutamate and aspartate also elicited the contraction. A pair of cerebral ganglion cells, v-RCDN and v-LCDN, was found to have modulatory effects on the muscle contraction evoked by B4 firing and ACh application. Morphological, physiological and immunohistochemical analyses suggested that the modulatory actions of v-CDN on muscle contraction are mediated by serotonin, which may be released from nerve terminals of v-CDN and act directly on the muscle. v-CDN also increased the activity of motoneurone B4. v-CDN shared several common features with serotonergic cerebral cells in other gastropod molluscs.
Magnetic Orientation Of Migratory Wheatears (Oenanthe Oenanthe) In Sweden And Greenland
Authors: Sandberg Roland , Ottosson Ulf , Pettersson Jan
Published: April 2021

Orientation experiments were performed with wheatears (Oenanthe oenanthe) subjected to artificially manipulated magnetic fields, in Sweden and Western Greenland, during the autumn migration period. The objective was to compare responses by birds exposed to widely different geomagnetic conditions and, specifically, to clarify if birds are able to use magnetic cues for orientation at high geomagnetic latitudes, as in Western Greenland. Orientation experiments were run under clear sunset skies and under simulated total overcast. Clear-sky tests did not reveal any clearcut orientation responses by wheatears in deflected and vertical magnetic fields. There was a tendency, however, for previous experience of the relationship between geomagnetic cues and visual information to affect the birds’ orientation in a vertical magnetic field. Under simulated overcast, the birds closely followed a 90° shift in magnetic direction in both study areas, and both samples failed to exhibit statistically significant mean directions when tested in vertical magnetic fields. The results clearly demonstrate that wheatears possess a magnetic compass. Furthermore, the birds are able to detect and use local geomagnetic information even at high magnetic latitudes in Western Greenland, notwithstanding the steep inclination (+81°) and large declination (—46°). A persistent attraction towards magnetic northwesterly headings, under both clear and overcast skies, is not consistent with migratory directions according to ringing recoveries and warrants further investigation.
The Relationship Between Oxygen Consumption and Ion Loss in A Freshwater Fish
Authors: Gonzalez Richard J. , Mcdonald D. G.
Published: April 2021

An increase in the functional surface area (FSA) of the gills of freshwater fish facilitates increased oxygen consumption but also increases ion loss across the gills - a phenomenon that has been termed the osmorespiratory compromise. This study on the rainbow trout confirms that Na+ loss accelerates with increasing but also shows that the former always exceeds the latter, i.e. the ion/gas ratio (IGR, ) increases. Since an increase in FSA should affect and equally, the increase in the IGR is attributed to an increase in ion permeability and is thought to arise through opening of paracellular diffusion channels via disruption of tight junctions - a conclusion supported by the effects of brief osmotic shock, low external Ca2+ concentration and catecholamine infusion on ion losses across the gills. By analogy with extensive studies on ‘leaky’ epithelia, these treatments disrupt tight junctions by cell shrinkage, by displacement of Ca2+ from tight junction surfaces or by increasing intralamellar pressure, respectively. While enforced exercise or handling stress substantially increased the IGR of the trout above routine levels, animals were also capable of reducing IGR to about one-tenth of routine levels. This regulation may, in part, be due to decreasing intralamellar pressure, achieved in part by down-regulation of adrenergic receptors, but there appears to be a significant additional level of control that is probably exerted directly at the tight junctions. Such a degree of control is only possible, however, if animals do not continue to exercise and if Ca2+ levels in the water are not reduced. With continued exercise, the IGR returns to routine levels. Consequently, ion losses remain substantially elevated, suggesting that they may ultimately limit maximum sustainable activity. Measurement of the IGR under routine conditions is proposed as a simple means of predicting ion losses during activity and of analyzing the nature of the osmorespiratory compromise.
Mechanisms Controlling Stomach Volume of the Atlantic Cod (Gadus Morhua) Following Gastric Distension
Authors: Grove David J. , Holmgren Susanne
Published: April 2021

Inflation of the cardiac stomach of the cod induced rhythmic contractions of the muscles and a slow increase in stomach volume towards a maximum. After deflation, the stomach remained relaxed and easily distensible for one or more hours. Section of the vagal tracts to the stomach did not change the response. Inflation in vitro produced a somewhat faster relaxation and a much faster recovery to the pre-distended state than occurred in vivo. Stimulation of the cut ends of the vagus raised gastric tone and increased resistance to distension, an effect mediated by cholinergic nerves. Tetrodotoxin and atropine relaxed the stomach so that distension was rapid and the maximal volume increased, revealing slower, possibly myogenic, contractions. The 5-hydroxytryptamine (5-HT) antagonist methysergide, vasoactive intestinal polypeptide (VIP), met-enkephalin and neurotensin did not affect the responses to distension. Somatostatin abolished spontaneous contractions in the resting stomach and lowered gastric tone, but did not further affect the responses to distension. In conclusion, cholinergic nerves maintain gastric tone in the cod. 5-HT neurones are absent in the cod stomach, and there are no indications of a 5-HT/VIP-controlled mechanism operating during distension. The effect of somatostatin differs from that in rainbow trout. For comparison with trout and cod, responses to in vivo gastric distension are also described for the flatfish Scophthalmus maximus, Scophthalmus rhombus, Limanda limanda and Pleuronectes platessa.
Interneurones Mediating the Escape Reaction of the marine Mollusc Clione Limacina
Authors: Arshavsky Yu. I. , Deliagina T. G. , Orlovsky G. N. , Panchin YU. V. , Popova L. B.
Published: April 2021

Neural mechanisms underlying the escape reaction have been extensively studied for over 20 years in many species of animals belonging to several different phyla (for a review, see Eaton, 1984). Among molluscs, the escape reaction has been most thoroughly studied in Tritonia. In this animal a strong mechanical or chemical stimulus applied to the posterior part of the body evokes swimming (for a review, see Getting, 1983; Getting and Dekin, 1985). Electrophysiological experiments on the isolated nervous system revealed that neurones constituting the central pattern generator (CPG) for swimming were strongly depolarized in response to sensory stimulation and that this depolarization caused rhythmic activity in the CPG. However, attempts to identify command neurones mediating the escape reaction in Tritonia have failed (Getting, 1983).
Metabolic Rates of Freely Diving Weddell Seals: Correlations With Oxygen Stores, Swim Velocity and Diving Duration
Authors: Castellini Michael A. , Kooyman Gerald L. , Ponganis Paul J.
Published: April 2021

The metabolic rates of freely diving Weddell seals were measured using modern methods of on-line computer analysis coupled to oxygen consumption instrumentation. Oxygen consumption values were collected during sleep, resting periods while awake and during diving periods with the seals breathing at the surface of the water in an experimental sea-ice hole in Antarctica. Oxygen consumption during diving was not elevated over resting values but was statistically about 1.5 times greater than sleeping values. The metabolic rate of diving declined with increasing dive duration, but there was no significant difference between resting rates and rates in dives lasting up to 82 min. Swimming speed, measured with a microprocessor velocity recorder, was constant in each animal. Calculations of the aerobic dive limit of these seals were made from the oxygen consumption values and demonstrated that most dives were within this theoretical limit. The results indicate that the cost of diving is remarkably low in Weddell seals relative to other diving mammals and birds.
Multiple Serotonin-Activated Currents in Isolated, Neuronal Somata from Locust Thoracic Ganglia
Authors: Bermudez Isabel , Beadle David J. , Benson Jack A.
Published: April 2021

Three different responses were evoked by pressure micro-application of serotonin onto freshly dissociated, current- and voltage-clamped neuronal somata from the thoracic ganglia of the locust Locusta migratoria. In some neurones, an inward current, I(5HT)K, resulting from a decrease in potassium conductance, with slow kinetics and maximum activation at membrane potentials of –60 to –70 mV, was evoked by serotonin and by the 5-HT3 agonist 2-methyl serotonin. This current was completely abolished by either 10 mmol l-1 caesium or 5 mmol I-1 rubidium and partially blocked by 50mmoll-1 tetraethylammonium or 5 mmol l-1 4-aminopyridine. The response was antagonised by the 5-HT2-specific compounds, ketanserin and ritanserin. In other somata, serotonin, 2-methyl serotonin and the 5-HT3 antagonist ICS 205 930 evoked a second current, I(5HT)Na, which was due to an increase in sodium permeability and had slow kinetics similar to that of I(5HT)K. This current was inward over the membrane potential range –30 to –80 mV and increased with hyperpolarisation. The response was blocked by sodium-free saline and the 5-HT3 receptor antagonist MDL 72222. In other neurones, at membrane potentials more positive than –50 mV, serotonin pulses could activate a third current, I(5HT)X, which increased with depolarisation of the membrane potential and had comparatively fast kinetics. Activation of the current was accompanied by a decrease in membrane conductance. This response was completely blocked by 4-aminopyridine and weakly inhibited by both caesium and tetraethylammonium and is, therefore, probably a potassium current. The three currents described here differ in their pharmacology, their ionic mechanisms and their dependence on membrane potential from the serotonin-activated currents reported for vertebrates and they provide evidence for the mechanism of action of serotonin as a neurotransmitter in insects.
Recovery From Acute Haemolymph Acidosis in Unfed Locusts: I. Acid Transfer to the Alimentary Lumen is the Dominant Mechanism
Authors: Harrison Jon F. , Wong Calvin J. H. , Phillips John E.
Published: April 2021

Organismal homeostasis requires regulation of extracellular acid-base status; however, the mechanisms by which insects regulate haemolymph pH are poorly known. We evaluated the recovery of desert locusts Schistocerca gregaria Forskål from acute acid loads, initiated by HCl injections into the haemolymph (0.5 pH unit decrease). Haemolymph pH, and [HCO3−] recovered in 8–24h, providing the first unequivocal evidence that insects regulate extracellular pH. There were no changes in the concentrations of the primary haemolymph buffer compounds (protein, inorganic phosphate) during recovery. Within 1 h, the tracheal system effectively eliminated the carbon dioxide derived from bicarbonate buffering. During the remainder of the recovery, haemolymph was similar to control values; there was no respiratory compensation for decreased haemolymph pH. Approximately 75 % of the acid equivalents removed from the haemolymph during the recovery process were transferred to the lumens of the crop and midgut. Transfer of acid equivalents to the alimentary lumen provides unfed locusts with a mechanism of haemolymph pH regulation that does not compromise intracellular acid-base status or increase ventilatory water loss.
Power Output of Two Sizes of Atlantic Salmon (Salmo Salar) at Their Maximum Sustained Swimming Speeds
Authors: Tang J. , Wardle C. S.
Published: April 2021

The maximum sustained swimming speeds (Ums) for large (0.45 m long) and small (0.15m) Atlantic salmon were respectively 0.91 ms−1 and 0.54ms−1. Video and ciné films of fish swimming close to Ums were analysed to obtain variables required for the application of two hydrodynamic models, those of Lighthill and Yates, to determine the mean thrust and mean power output at these swimming speeds (U) close to Ums. A large fish (‘Salmon’) and a small fish (‘Smolt’) were selected for analysis. For salmon using Lighthill’s model, and , and using Yates’ model, and (U=0.87ms−1=0.96Ums). For smolt using Lighthill’s model, and , and using Yates’ model, and (U=0.37ms−1=0.69Ums). The power output for smolt swimming at 0.69Ums was corrected to that required to swim at Ums, giving (Lighthill’s model) and (Yates’ model).

At Ums it was assumed that all the red muscle was used. Two fish were selected from each size group and cross-sectioned to estimate their red muscle masses. Using a maximum mass-specific power output of 5–8 W kg−1 for slow red muscle fibres allowed us to calculate that the large and small fish have a power output capacity of 0.125–0.3 W and 0.007–0.019 W, respectively.

The power output values at Ums derived from the different approaches for the large (0.25–0.26 W) and small (0.0059–0.0074 W) salmon agree closely. Effects of scaling are discussed.
Dimensional Analysis of The Ventricle of an in Situ Perfused Trout Heart Using Echocardiography
Authors: Franklin Craig E. , Davie Peter S.
Published: April 2021

The linear dimensions of the ventricle of an in situ perfused trout heart were measured with an ultrasound scanner. Using a pyramidal model, linear dimensions taken from real-time, two-dimensional, echotomographic images of the ventricle were used to calculate ventricular end-diastolic and end-systolic volumes and, by the difference between them, stroke volumes for various filling and output pressures. Stroke volumes calculated from the ultrasound measurements were significantly correlated with actual stroke volumes determined from cardiac output and heart rate and had a regression line slope close to one. Increases in stroke volume with greater filling pressures resulted from increased ventricular end-diastolic volume with constant end-systolic volume; end-systolic volumes were negligible. Maintenance of stroke volume with increasing output pressure was by increases in both end-diastolic and end-systolic volumes. Decreases in stroke volume with very high output pressures may result from convergence of end-systolic and end-diastolic volumes.
On the Mechanism of Ventilation inAphrodite Aculeata
Authors: van Dam L.
Published: April 2021

Aphrodite aculeata L., the sea mouse, is generally dredged from muddy bottoms, where it burrows head-first into the mud. Usually only the anal extremity, which is very mobile and often held in an upturned position, remains uncovered.
The Reflex Mechanism of the Insect Leg
Authors: Pringle J. W. S.
Published: April 2021

Variations in the frequency of the motor discharges to the leg muscles of Periplaneta americana are followed in the intact animal under different types of sensory stimulation by electrical recording from the muscles. Two main reflexes are described: the depressor reflex, evoked by stimulation of the campaniform sensilla on the legs, and a levator response to touch on the upper side of the leg. There is a direct antagonism in the excitation of the depressor and levator sets of muscles: also between similar muscles in the two legs of a segment. Reflex effects are not transmitted up or down the animal to other segments. The conditions for the reflex excitation of the two types of motor fibre are discussed. A suggestion is put forward for the explanation of rhythmic movements.
Studies of Tropical Tuna Swimming Performance in a Large Water Tunnel:I. Energetics
Authors: Dewar Heidi , Graham Jeffrey B.
Published: April 2021

The metabolic rates of three tropical tunas [yellowfin tuna (Thunnus albacares), kawakawa (Euthynnus affinis) and skipjack (Katsuwonus pelamis)] were estimated using a large water-tunnel respirometer. Experiments lasting up to 31 h were used to determine the effects of velocity (U) on tuna over a range of U (17–150 cm s−1) and temperatures (18–30°C). Replicate tests were carried out on several fish. The swimming of yellowfin is temperature-dependent (Q10=1.67, determined over intervals of 3–5°C). For yellowfin and skipjack, it was also possible to partition metabolic costs between maintenance and locomotion. The standard metabolic rate was estimated by extrapolation of the function to U=0. Comparisons of for different size groups of yellowfin show that the mass-specific scaling exponent for is −0.40. The of tuna is comparable to values determined previously by stasis respirometry and is approximately three times higher than that of salmonids. Further comparisons with salmonids show that the slope of the function is less for tunas, which demonstrate a greater swimming efficiency.