bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Electrophysiology of Cnidocytes
Authors: Anderson Peter A. V. , Mckay M. Craig 
Published: April 2021

ABSTRACT
Electrical properties of cnidocytes isolated from the hydroid Cladonema and the scyphomedusa Chrysaora were examined using current- and voltage-clamp recording techniques. The stenoteles of Cladonema produced action potentials when depolarized above 0mV. The inward current that produced the action potential was a Na+ current. These cells also possessed an A-current and a K-current. Atrichous isorhizas from Chrysaora did not spike and did not have any inward currents. All cells examined had K-currents, some had A-currents also. Very few cnidocytes discharged during the course of the recordings, irrespective of the degree to which they were depolarized or hyperpolarized, or the presence or selective blockade of any ionic currents. When discharge did occur it could never be correlated with any obvious electrophysiological event. Recordings from cnidocytes in situ in tentacles of the siphonophore Physalia indicate that these cells do not spike. Their current/voltage relationships were linear. They too did not discharge in response to changes in membrane potential, suggesting that the failure of isolated cnidocytes to discharge cannot be attributed to the isolation procedure.
Properties and Pharmacology of a Ttx-Insensitive Na+ Current in Neurones of the Jellyfish Cyanea Capillata
Authors: Anderson Peter A. V. 
Published: April 2021

ABSTRACT
Neurones of the motor nerve net of the jellyfish Cyanea capillata were axotomized, and voltage-clamped using the whole-cell configuration of the patchclamp technique. Outward currents were blocked by a combination of extracellular 4-aminopyridine (4-AP) and intracellular Cs+, tetraethylammonium (TEA+) and 4-AP. Under normal conditions, the inward current consisted of a fast, transient current which could be abolished by removal of extracellular Na+ and whose reversal potential was dependent on the extracellular Na+ concentration. This current was completely insensitive to tetrodotoxin (TTX), saxitoxin (STX) and conotoxin GIIIA but could be blocked by extracellular Cd2+, lidocaine, W7 pV-(6aminohexyl)-5-chloro-l-napthalenesulphonamide] and verapamil. Inactivation was voltage-dependent with a Vh of – 15mV, and was unaffected by veratridme, batrachotoxin (BTX), sea anemone toxin and scorpion (Leiurus) venom. Reactivation required repolarization to a negative membrane potential for 12 ms for half-maximal reactivation. In the absence of extracellular Na+ no inward current was visible unless [Ca2+]o was elevated. In Na+-free, 95 mmol l−1 Ca2+ saline, a slightly slower, inward current was recorded. This current is believed to be the Ca2+ current that underlies synaptic transmission. These findings are discussed with reference to synaptic transmission in these cells and the evolution of ion channels.
The Physiology and Morphology of Visual Commissures in the Honeybee Brain
Authors: Hertel Horst , Schäfer Sabine , Maronde Ulrike 
Published: April 2021

ABSTRACT
Visual commissures of the honeybee brain were investigated by electrophysiological and histological methods.
A newly described serpentine optic commissure (SOC) consists of four neurones each of which has widely extending arborizations in both medullae and lobulae. The cells are monocularly sensitive, the best stimulus being a moving target. Neurones of the posterior optic commissure (POC) connect the two medullae and show spatial opponency; the sign of the tonic response depends on the position of the stimulus in the receptive field of the cell. The inferior optic commissure (IOC) assembles neurones that have ramifications in both lobulae. They show directional selectivity to a moving stimulus and this is often combined with an opponent tonic response. The anterior optic commissure (AOC) contains neurones which are similar to those of the IOC and which connect the two lobulae. These show a preferential sensitivity to one direction of movement. A single pair of cells close to the interoptic tubercle commissure is identified as being movement-sensitive without directional selectivity.
The Physiology and Morphology of Centrally Projecting Visual Interneurones in the Honeybee Brain
Authors: Hertel Horst , Maronde Ulrike 
Published: April 2021

ABSTRACT
Visual interneurones with projections into the median protocerebrum of the honeybee brain were characterized by electrophysiological and neuroanatomical methods. Extrinsic medulla neurones with wide ramifications in the medulla and terminations in the median posterior protocerebrum show spatial opponency in their tonic responses to stationary light.
Wide-field lobula neurones projecting into the dorsal lobe code the direction of movement of visual stimuli by changing the sign of their tonic response. Lobula neurones, with two branches ipsi- and contralateral to the oesophagus, are binocularly sensitive. A moving stimulus in either direction causes excitation or inhibition of these neurones, the sign of the response being dependent on the side of stimulation.
The presumed dendrites of an extrinsic lobula neurone, showing combined spectral and spatial opponcncy, differ markedly in shape from those of lobula movement-detecting neurones.
Neurones that connect the optic tubercle with the contralateral dorsal lobe are characterized. They show a non-directionally selective movement sensitivity within a binocular receptive field.
Gliding Birds: The Effect of Variable Wing Span
Authors: Tucker Vance A. 
Published: April 2021

ABSTRACT
The equilibrium gliding performance of a bird is described by the relationship between sinking speed (V8) and air speed (V). When V3 is plotted against V, the points fall in a ‘performance area’ because the wing span is changed during gliding. The lowest Vs for each V in the performance area defines a ‘maximum performance curve’. This curve can be predicted by a mathematical model that changes the wing span, area and profile drag coefficient (CD pr) of a hypothetical bird to minimize drag. The model can be evaluated for a particular species given (a) a linear function relating wing area to wing span, and (b) a ‘polar curve’ that relates Cp.pr and the lift coefficient (CL) of the wings. For rigid wings, a single polar curve relates CD,pr to CL values at a given Reynolds number. The position and shape of the polar curve depend on the aerofoil section of the wing and the Reynolds number. In contrast, the adjustable wings of a laggar falcon (Falco jugger) and a black vulture (Coragyps atratus) gliding in a wind tunnel have CL, and CD,pr values that fall in a ‘polar area’ rather than on a curve. The minimum values of CD,pr at each CL bound the polar area and define a polar curve that is suitable for evaluating the model. Although the falcon and the vulture have wings that are markedly different in appearance, the data for either bird are enclosed by the same polar area, and fitted by the same polar curve for minimum CD,pr at each CL value. This curve is a composite of the polar curves for rigid wings with aerofoils similar to those found in avian wings. These observations suggest that the polar curves of other gliding birds may be similar to that of the falcon and the vulture. Other polar curves are defined by CL and CD,pr values for the falcon and the vulture gliding at a constant speed but at different glide angles. Each speed has a different polar curve; but for a given speed, the same polar curve fits the data for either bird. The falcon and the vulture gliding in the wind tunnel at a given speed were found to increase their drag by decreasing their wing span. This change increases induced drag and probably increases CD,pr for the inner parts of the wing because of an unusual property of bird-like aerofoil sections: wings with such sections have minimum values of CD,pr at CL values near 1, while conventional wings have minimum values of CD,pr at CL values near 0.
The Regulation of Haemocyanin Oxygen Affinity During Emersion of the Crayfish Austropotamobius Pallipes : III. The Dependence of Ca2+-Haemocyanin Binding on the Concentration of L-Lactate
Authors: Morris S. , Bridges C. R. , Grieshaber M. K. 
Published: April 2021

ABSTRACT
The binding of Ca2+ to the haemocyanin of the crayfish Austropotamobius pallipes was investigated. The amount of bound Ca2+ was determined using an ultrafiltration technique to produce haemocyanin-free solutions, the Ca2+ concentration of which could then be compared with that of the original, unfiltered solution. Any difference between the two values would indicate the amount of calcium bound by haemocyanin.
The effect of L-lactate on Ca2+ binding was investigated by determining the amount of bound ion at different concentrations of L-lactate. In addition, oxygen equilibrium curves were constructed for some of the solutions to verify that the haemocyanin oxygen affinity remained sensitive to L-lactate and to determine whether the haemocyanin was functionally similar to that used in previous investigations.
With 17 mmol 1−1 total Ca2+ and approximately 1 mmol 1−1 L-lactate the number of Ca2+ binding sites was estimated to be between eight and nine per haemocyanin molecule. Without taking into account the formation of calcium lactate, the observed dependency of Ca2+-haemocyanm binding on L-lactate concentration could best be described by the equation: Ca2+/Hc = 8·64– 0·32[lactate−].
A ‘worst case’ estimate for maximum calcium lactate formation, assuming Ca2+ to be the only counterion available to lactate, altered the relationship slightly to: Ca2+/Hc = 8 ·65– 0·35[lactate-]
Interactions of the Giant Fibres and Motor Giant Neurones of the Hermit Crab
Authors: Heitler W. J. , Fraser K. 
Published: April 2021

ABSTRACT
A recent claim that the giant fibre of the hermit crab excites its contralateral motor giant neurone through a chemical rather than an electrical synapse (Stephens, 1986) was re-examined. We found that the reported increased latency (relative to the electrical ipsilateral synapse) was postsynaptic in origin, as was the increased spike ‘jitter’. There was no difference in synaptic latency between the electrical synapse and the supposed chemical one. We did not find a consistent resistance to N-ethylmaleimide (an uncoupler of electrical synapses) by the supposed chemical synapse, but the synapse was resistant to 2 mmol l−1 cadmium, which blocks known chemical synapses in the system. Sub-threshold depolarizing current passed from the presynaptic giant fibre to the postsynaptic contralateral motor giant, and hyperpolarizing current passed antidromically. We conclude that the svnapse is electrical and not chemical in nature.
Respiratory Physiology of Intestinal Air Breathing in the Teleost Fish Misgurnus Anguillicaudatus
Authors: Mcmahon Brian R. , Burggren Warren W. 
Published: April 2021

ABSTRACT
The Japanese weatherloach (Misgurns anguillicaudatus Cantor) can exchange gases both with water, via gills and skin, and with air, via the posterior region of the alimentary canal (intestine). Air breathing occurs by unidirectional ventilation of the alimentary canal with air taken in at the mouth and simultaneous expulsion of intestinal gas from the vent. Although the weatherloach is not an obligate airbreather, aerial gas exchange normally occurs even at 10°C in air-saturated water.
The alimentary canal was examined histologically to assess differences in capillary density and distribution and the diffusion distance for gases across those regions modified for aerial respiration. A respirometer system specifically designed for 2-to 3-g fish allowed continuous measurement of O2 and CO2 exchange via both aquatic and aerial routes at rest and at various ambient temperatures, and respiratory gas partial pressures. Air ventilation volumes, O2 and CO2 partial pressures of exhaled gas, O2 extraction, and O2 and CO2 exchange via the intestine were also determined, allowing the role of the intestine in total gas exchange in the w’eatherloach to be determined and compared with aerial gas exchange organs in other fishes.
The alimentary canal is divided into three zones, an anterior glandular portion separated bv a spiral section from the posterior, respiratory zone which has the greatest capillary densities and shortest gas diffusion distances. At rest (20°C), the intestine takes up about 20% of total O2 but accounts for less than 3 % of total CO2 elimination (gas exchange ratio = 0·08 for intestine). O2 extraction averages 50%. Increasing temperature causes only slight increases in total metabolic rate (Q10 for = 1·5–1·8), but highly significant increases in intestinal gas exchange relative to total gas exchange develop as temperature rises. Intestinal gas exchange also rises with decreasing O2 availability. A strong hypoxic drive and weak hypercapnic drive exist for aerial ventilation of the intestine, but are reduced or absent for aquatic ventilation of the gills. In spite of having to function in respiration, absorption, secretion and buoyancy regulation, the potential effectiveness of intestinal gas exchange is shown to be similar to that of other structures used for aerial gas exchange in facultative air-breathing fish.
Motor Pattern Analysis in the Shore Crab (Carcinus Maenas) Walking Freely in Water and on Land *
Authors: Clarac F. , Libersat F. , Pflüger H. J. , Rathmayer W. 
Published: April 2021

ABSTRACT
Neuromuscular activity underlying lateral walking was studied in the shore crab Carcinus maenas. Electromyograms (EMGs) were recorded from legs on both the trailing and leading sides during free walking on land and under water in a pool (Figs 1, 2, 6, 7). In a trailing leg, the levator, flexor and closer muscles were active during the return stroke (RS) in alternation with the depressor, extensor and opener muscles which were responsible for the power stroke (PS). In a leading leg a different pattern of activity was observed. The flexor and closer muscles were active during the PS, and the extensor and opener muscles during the RS. Trailing steps were shorter and less variable in duration than leading steps (Figs 2, 3 for walking under water, Fig. 6 for walking on land, see also Fig. 7). A comparison of the activity patterns of the single common motor neurone innervating the opener and the stretcher muscle during trailing and leading showed a difference in burst length and instantaneous frequency (Fig. 2C,D). The discharge of this motor neurone usually lasted longer in leading steps. The discharge frequency started at a high level and then decreased during a trailing step, whereas in a leading step it was irregular (Fig. 8). In all walking situations the stretcher and opener muscles, which share a common excitatory motor neurone, received identical excitatory input (Fig. 4). The discharge frequencies of motor neurones innervating the extensor, the stretcher/opener and the closer muscles were investigated (Fig. 5). For motor neurones active during the PS, the frequency was high at the onset of the burst and then declined gradually. With the exception of the closer muscle, the discharge of motor neurones during the RS was more or less constant during the burst. A comparison between walking under water and on land showed that the overall EMG patterns were essentially similar (Fig. 7). However, on land the PS lasted longer and involved the activation of additional motor neurones in muscles which are innervated by several motor neurones, e.g. the extensor (Fig. 6). During walking on land maximal discharge frequencies up to 350 Hz were recorded. Homologous muscles in the three different walking legs operated similarly during trailing or leading movements without major differences in their EMG patterns. This indicates a similar load distribution on the different legs (Fig. 9).
Respiratory Characteristics of Muscle Fibres in A Fish (Chaenocephalus Aceratus) that Lacks Haem Pigments
Authors: Johnston Ian A. 
Published: April 2021

ABSTRACT
Oxygen consumption, mitochondrial content and enzyme activities were determined in identified muscle fibre types of the ‘haemoglobin-less’ icefish Chaenocephalus aceratus Lonnberg. Small bundles (2–12) of fast and slow fibres were isolated from the myotomal and superficial pectoral fin abductor muscles, respectively. At 0°C the time to 50% peak force and the half-relaxation time of isometric twitches were, respectively, 18 ± 1 and 38 ±4 ms for fast and 43 ± 3 and 119 ±21 ms for slow muscle fibres (mean ± S.E.). Measurements of enzyme activities in homogenates suggest that phosphocreatine hydrolysis and oxidative phosphorylation are the main energy-supplying pathways in fast and slow muscles, respectively. Activities of glycolytic enzymes were relatively modest and showed no consistent differences between fibre types. The relationship between oxygen consumption and mitochondria in slow muscle was also determined for a ‘red-blooded’ antarctic (Xotothenia gibberifmns), a cold-temperate (Myoxocephalus scorpius) and a warm-temperate (Oreochromis niloticus) fish. Volume densities of mitochondria were as follows (mean±s.D.): C. aceratus, 0 ·50 ±0·08; N. gibberifrons, 0·30 ±0·10; M. scorpius, 0·23 ±0·05; and O. niloticus, 0·20 ±0 ‘05. ADP-stimulated respiration rates were measured in isolated fibre segments. In spite of their different mitochondrial contents, slow fibres from the two antarctic fish utilized pyruvate and palmitoyl-l-carnitine at similar rates (l·0–l·2;μmol O2g−1 wetmassmin−1 at 0°C). This suggests that the high density of mitochondria in icefish muscle is related, in part, to diffusion limitations.
Branchial and Antennal Gland Na+/K+-Dependent ATPase and Carbonic Anhydrase Activity During Salinity Acclimation of the Euryhaline Crayfish Pacifastacus Leniusculus
Authors: Wheatly Michèle G. , Henry Raymond P. 
Published: April 2021

SUMMARY
Haemolymph and urine electrolyte status and branchial and antennal gland activities of Na+/K+-ATPase and carbonic anhydrase (CA) were determined in the crayfish Pacifastacus leniusculus after 3 weeks acclimation in fresh water (FW) and 350 and 750 mosmol kg−1 sea water (SW). In FW the crayfish maintained haemolymph osmolality around 370 mosmol kg−1 due to hyperionic regulation of the major electrolytes. Involved in this are ion uptake mechanisms situated on the gills, and mechanisms of ion reabsorption from the primary urinary filtrate in the antennal gland (AG). Both of these processes are associated with high activities of Na+/K+-ATPase and CA. The two enzymes are uniformly distributed on gill sets 2– 7, unlike the situation in euryhaline marine species. Additionally, activity levels of both enzymes are extremely high in the AG and can be correlated with the ability to produce a hypo-osmotic urine. In comparison, enzyme activity is negligible in marine species which produce isosmotic urine.
Crayfish continued to hyperosmoregulate in 350 mosmol kg−1 SW. High levels of Na+/K+-ATPase confirmed the presence of a component active in the uptake of major electrolytes in the gills and also in the AG, where ion reabsorption persisted. In 750 mosmol kg−1 SW crayfish became isosmotic. Since ATPase is regulated chiefly by deactivation/activation of pre-existing enzyme, overall activity was mostly unchanged. CA activity was significantly reduced in both 350 and 750 mosmol kg−1 SW and correlated with the transition from osmoregulation to osmoconformity, suggesting that it is regulated primarily by deinduction/induction of new enzyme. The difference in the mechanism of regulation exhibited by these two enzymes is believed to relate to their subcellular distribution.
Sulphate Entry Into Soft-Water Fish (Salmo Gairdneri, Catostomus Commersoni) During Low Ambient pH Exposure
Authors: Hōbe Helve 
Published: April 2021

ABSTRACT
The physiological responses of white sucker (Catostomus commersoni Lacépède) and rainbow trout (Salmo gairdneri Richardson), both reared in natural soft water, to a reduction in ambient pH were compared by simultaneous analyses of ion levels in various body compartments (plasma, muscle, whole fish) and net ion transfer rates. Following 24 h of exposure to acidified (H2SO4) natural soft-water, both species displayed a net influx of protons (or loss of base) and net losses of body Na+, Cl−, Ca2+, Mg2+, K+ and phosphate. The magnitude of ion loss from plasma was twice as large in the trout as in the sucker. Shifts of fluid from the extracellular to the intracellular fluid occurred in both species. Losses of ions from epaxial white muscle were small relative to intracellular ion losses from the rest of the body in both species.
The most notable finding was the entry of sulphate into the body fluids of both species, accumulating primarily in plasma and in the intracellular compartment of sucker and trout, respectively. The possible mechanism(s) and implications of sulphate influx into fish are discussed.
Visual Acuity in Octopus Pallidus and Octopus Australis
Authors: Muntz W. R. A. , Gwyther J. 
Published: April 2021

ABSTRACT
Specimens of Octopus pallidus and 0. australis were trained to discriminate vertical from horizontal rectangles, vertical from horizontal gratings, and vertical and horizontal gratings from uniform grey. In the discriminations that involved gratings a conditional simultaneous discrimination procedure was used, in which the two stimuli to be discriminated were presented stationary at the two ends of the tank, and a moving white disc was shown in front of each of them. Attacks on a disc were then rewarded or punished depending on the background against which it was shown. Animals rapidly reached performance levels of better than 80% correct responses on all discriminations.
With one specimen of 0. pallidus and three of 0. australis when progressively finer gratings were used the discrimination broke down with stripe widths between 4·4′ and 9·7′, showing that for both species the minimum separable visual acuity is less than 9·7′.
The behaviour of the two species is very similar to that of 0. vulgaris, except that they accept less food per day, so fewer trials could be given.
Voltage-Dependent Block of Locust Muscle Glutamate Channels by Chlorisondamine
Authors: Ashford M. L. J. , Boden P. , Ramsey R. L. , Sansom M. S. P. , Shinozaki H. , Usherwood P. N. R. 
Published: April 2021

ABSTRACT
Chlorisondamine reversibly reduced the amplitude of the neurally evoked twitch of locust retractor unguis muscle in a dose-dependent manner and also blocked agonist-induced contractions. Depolarizations elicited by ionophoresis of L-glutamate were also reduced in amplitude by chlorisondamine, but there was no effect of this drug on desensitization. Neurally evoked synaptic currents were reduced in amplitude, their rise time was decreased and their decay phase made biphasic (or more complex) by chlorisondamine (&gt;10−5 mol l−1). These effects of chlorisondamine were voltage-dependent, such that at very hyperpolarized potentials (−120 mV and −140 mV) there was an apparent reduction in the degree of block. Singlechannel studies indicate that chlorisondamine acts to block the channel both in the open and the closed form and that these actions are dependent on concentration and voltage. The actions of chlorisondamine are discussed in relation to the basic kinetic models of channel block.