bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensory Feedback During Active Movements of Stick Insects
Authors: Weiland G. , Koch U. T.
Published: April 2021

In the stick insect Carausius morosus, the role of the chordotonal organ was investigated using a new experimental arrangement which artificially closes the femur-tibia control system. The chordotonal organ was stimulated during voluntary movements by applying trapezoidal ramp stimuli in the closed-loop configuration.

The results demonstrate that the feedback loop is used to control the end points of joint movement. In addition, it was found that the control system counteracts experimentally applied velocity changes imposed during the middle part of the movements. Acceleration-sensitive units are shown to contribute to the reaction.

The results show that during active voluntary movements reflexes measured in the inactive animal are neither simply incorporated in a servo-system nor suppressed. Instead their characteristics are altered so that the voluntary movements are executed as intended by the animal. Thus reflexes cannot be considered as a fixed behavioural unit; rather their changing role must be analysed in the context of the behaviour studied.
EXCITATORY ACTIONS OF Antho-RFamide, AN ANTHOZOAN NEUROPEPTIDE, ON MUSCLES AND CONDUCTING SYSTEMS IN THE SEA ANEMONE CALLIACTIS PARASITICA
Authors: McFARLANE I. D. , Graff D. , Grimmelikhuijzen C. J. P.
Published: April 2021

In the sea anemone Calliactis parasitica endodermal application of the anthozoan neuropeptide Antho-RFamide (<Glu-Gly-Arg-Phe-amide), at a concentration of 10−6 or 10−7moll−1, caused a long-lasting increase in tone, contraction frequency and contraction amplitude in several slow muscle groups but had no effect on contractions in fast muscles. The effects were investigated further in isolated muscle preparations. Ectodermal application to whole animals had no effect on muscle contractions. Both ectodermal and endodermal application, at 10−7moll−1, raised electrical activity in an ectodermal conduction system, the SSI, but had no effect on an endodermal conduction system, the SS2. Electrical activity in the SS2 was increased by application at 10−6moll−1 to the endoderm but not to the ectoderm. The peptide had no effect on the through-conducting nerve net. It is concluded that contractions evoked by Antho-RFamide may be partly due to neuronal activity, but probably also involve direct excitation of the muscles. The diverse excitatory actions of Antho-RFamide suggest that it may be a neurotransmitter or neuromodulator in sea anemones.
Thermal Dependence of Passive Electrical Properties of Lizard Muscle Fibres
Authors: Adams Brett A.
Published: April 2021

The thermal dependence of passive electrical properties was determined for twitch fibres from the white region of the iliofibularis (IF) muscle of Anolis cristatellus (15–35°C) and Sceloporus accidentalis (15–40°C), and for twitch fibres from the white (15–45°C) and red (15–40°C) regions of the IF of Dipsosaurus dorsalis. These species differ in thermal ecology, with Anolis being the least thermophilic and Dipsosaurus the most thermophilic. Iliofibularis fibres from the three species reacted similarly to changing temperature. As temperature was increased, input resistance (Rm) decreased (average R10 = 0·7), length constant (L) decreased (average R10 = 0·9), time constant (τ) decreased (average R10 = 0·8), sarcoplasmic resistivity (Rs) decreased (average R10 = 0·8) and apparent membrane resistance (Rm) decreased (average R10 = 0·7). In contrast, apparent membrane capacitance (Cm) increased with increasing temperature (average R10= 1·3). Rin, L, τand apparent Rm were lowest in fibres from Anolis (the least thermophilic species) and highest in fibres from Dipsosaurus (the most thermophilic species). Anolis had the largest and Dipsosaurus the smallest diameter fibres (126 and 57 μm, respectively). Apparent Cm was highest in fibres from Sceloporus, which had fibres of intermediate diameter (101μm). Rs did not differ significantly among species. The effect of temperature on the passive electrical properties of these lizard fibres was similar to that reported for muscle fibres from other ectothermic animals (crustaceans, insects, fish and amphibians) but qualitatively different from that reported for some mammalian (cat tenuissimus, goat intercostal) fibres. The changes that occur in the passive electrical properties render the fibres less excitable as temperature increases.
Kinetics of Extracellular Solute Movement in the Isolated Midgut of Tobacco Hornworm (Manduca Sexta)
Authors: Koch Alan , Moffett David F.
Published: April 2021

Measurements were made of the uptake of 14C-labelled sucrose in the short-circuited isolated midgut of fifth instar larvae of the tobacco hornworm. The longterm volume of distribution after bilateral exposure indicates that the extracellular space is about 0 ·26 ml g−1 wet tissue, much less than has been previously suggested. The results of unilateral exposure yield a value of about 0 04 ml g−1 for luminal goblet cell cavities and 0·22 ml g−1 for interstitial space. The kinetics of uptake suggest that the interstitial space is best modelled as a distributed volume rather than as a single compartment. This mathematical result fits the physical picture of an interstitial fluid in long, narrow channels which communicate freely with the haemolymph but are nearly impermeable to sucrose at the luminal end; that is, they are sealed by septate junctions. The electrical conductance of the epithelium is high, but the transepithelial permeability to sucrose is very much lower than to K+. Thus, the tissue is a physically tight epithelium.
The Electrophysiology of Cnidocytes
Authors: Anderson Peter A. V. , Mckay M. Craig
Published: April 2021

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

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

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

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

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

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

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

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

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

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

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

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

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

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 (>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.
Specificity of Connections Formed by Nociceptive Cells of the Leech in Tissue Culture
Authors: Vyklicky L. , Nicholls J.
Published: April 2021

Individual medial and lateral nociceptive (N) cells of the leech have been paired with a variety of different target cells to determine the patterns and the properties of the connections made in culture.

Lateral nociceptive N cells did not make electrical or chemical connections with other N cells or with P sensory cells. N cells made electrical connections with Retzius cells, anterior pagoda cells (AP) and annulus erector (AE) and L motor neurones in culture. Lateral and medial N cells, which differ in the animal, exhibited consistent differences in culture. Well-established electrical junctions made by lateral N cells showed clear rectification. In contrast, medial N cells could make either non-rectifying or rectifying connections with target cells. In spite of the presence of strong electrical coupling, evidence for chemically mediated synaptic interactions between N cells and other neurones was obtained on occasion. These findings emphasize the specific nature of connections formed in culture. Unlike P sensory cells, N cells in culture did become electrically connected to Retzius cells and could make both rectifying and non-rectifying electrical junctions with appropriate targets.
Indoor Flight Experiments with Trained Kestrels:II. The Effect of Added Weight on Flapping Flight Kinematics
Authors: Videler J. J. , Groenewegen A. , Gnodde M. , Vossebelt G.
Published: April 2021

A male and a female kestrel were trained to fly over a mirror in a corridor, with lead weights attached to the feet to increase weight in the range 0–0·6 N (0–61 g). Films taken at 200 frames s−1 allowed three-dimensional analysis of the displacements of the head, tail and wingtips. A kinematic analysis, based on Fourier series, was made of the displacements in three perpendicular directions and of periodic changes of wing areas and tail areas.

With increased mass, there was a decrease in flight speed, increase in wing beat frequency, increase in vertical wing beat amplitude, and an increase in the inclination of the tail. The shorter wing beat cycle under load was mainly due to a decreased upstroke duration, implying that the relative importance of the down-stroke was increased. The tail area and to a lesser extent the wing areas were enlarged during flights with the largest added weight.
Functional Design of the Feeding Mechanism in Salamanders: Causal Bases of Ontogenetic Changes in Function
Authors: Lauder George V. , Reilly Stephen M.
Published: April 2021

Many correlated changes in the structure and function of the skull occur during metamorphosis in salamanders. To separate correlated from causal changes in form and function, we experimentally converted the unidirectional flow feeding system in axolotls (Ambystoma mexicanum) to a bidirectional system by suturing closed the gill slits. This mimics one of the major structural changes in the feeding mechanism that occur at metamorphosis. Eleven variables were measured from the intra-oral pressure traces recorded during feeding. The major changes in buccal pressure produced by suturing the gill slits were in the duration and area of the negative pressure traces. In addition, the ratio of positive to negative pressure areas increased by four times following closure of the gill slits. In contrast to pressure changes during metamorphosis in tiger salamanders, increases in the positive portion of the pressure traces occur in axolotls. These data corroborate the hypothesis that the decreased feeding performance after metamorphosis is a direct consequence of the change from a unidirectional to a bidirectional feeding mechanism, and demonstrate the causes of ontogenetic changes in function.
Potency of Adrenaline and Noradrenaline for β-Adrenergic Proton Extrusion From Red Cells of Rainbow Trout, Salmo Gairdneri
Authors: Tetens Vilhelm , Lykkeboe Gunnar , Christensen Niels Juel
Published: April 2021

The red cell adrenoceptor affinity for the unspecific agonists adrenaline and noradrenaline and the specific β-agonist isoprenaline was studied in vitro on whole blood of rainbow trout, Salmo gairdneri at 15°C. The erythrocytic adrenoceptors could be pharmacologically characterized as β-receptors of the ‘noradrenaline’-type (β1-type), with an order of potency of isoprénaline > noradrenaline ⪢ adrenaline. The adrenoceptor affinities, expressed as agonist concentrations for 50% response (ECSo), were 1·3×10−8 and 7·6× 10−7 mol I−1 for noradrenaline and adrenaline, respectively. Winter fish showed a red cell adrenergic response identical to that of summer-acclimated fish. It is concluded that most red cell β-adrenergic responses in vivo are exclusively elicited by noradrenaline.
Chromatophore Motor Fields in the Squid, Lolliguncula Brevis
Authors: Ferguson Graham P. , Martini Frank M. , Pinsker Harold M.
Published: April 2021

Chromatophore motoneurones in Lolliguncula brevis are known to originate in the suboesophageal lobes of the brain and to project directly to the mantle and fin through bilateral stellate ganglia and fin nerves. The chromatophore motor fields of stellar and fin nerves were investigated by stimulation of the cut end of individual nerves in a semi-intact preparation. This elicited expansion of yellow and brown chromatophores in distinct motor fields. Brown chromatophores extended over the entire mantle, whereas yellow chromatophores were limited to the dorsal and lateral mantle areas. Combined nerve stimulation and lesions demonstrated substantial overlap between adjacent chromatophore motor fields and innervation of individual chromatophores by different stellar nerves.
Mechanics of Jet Propulsion in the Hydromedusan Jellyfish, Polyorchis Penicillatus: I. Mechanical Properties of the Locomotor Structure
Authors: Demont M. Edwin , Gosline John M.
Published: April 2021

A non-destructive test was developed to measure the static mechanical properties of the locomotor structure (bell) in the hydromedusan jellyfish, Polyorchis penicillatus (Eschscholtz, 1829). A nonlinear stress-strain relationship was found, and the mean static structural stiffness of the bell was 150 N m−2. Visualization procedures that showed the natural changes in the geometry of the deformation of the bell were used to calculate the static modulus of elasticity of the mesoglea, and gave a modulus of 400 N m−2. Dynamic measurements on isolated samples of mesoglea gave a mean storage modulus of 1000 Nm−2. The resilience of the material was about 58%. These data were integrated to imply that the dynamic structural stiffness of the bell is at least 400 N m−2. Attempts to measure the dynamic structural stiffness directly indicate that the dynamic stiffness of the intact bell lies between 400 and 1000 N m−2. All, or most, of the potential energy stored in the mesoglea during contractions of the bell is stored as strain energy in the radial mesogleal fibres.
Cardiovascular and Respiratory Responses in Thoroughbred Horses During Treadmill Exercise
Authors: Evans D. L. , Rose R. J.
Published: April 2021

Six detrained Thoroughbred horses performed incremental treadmill tests. Maximal oxygen uptake was measured during exercise by analysis of expired gas. The relationships between oxygen consumption and work rate, heart rate (HR), cardiac output (Q̇), stroke volume (SV) and arteriovenous oxygen content difference were examined during submaximal and maximal exercise. The relative contributions of blood flow and extraction of oxygen from muscle capillaries were assessed during exercise at . Mean was 129·7 ± 2·9 (mean ± S.E.M.) ml kg−1 min−1, which occurred at a mean speed of 8·0ms−1, with the treadmill set at a slope of 10%. At the mean HR was 222± 7 beats min−1. Maximal Q̇ was 534 ± 22 ml kg−1 min−1 and mean SV was 2·4 ± 0·1 ml kg−1. Mean was 24·5 ± 1·2 ml 100 ml−1 blood. Linear relationships were found between and work rate, HR, Q̇ and . Stroke volume did not increase significantly during exercise. Increasing metabolic rate during exercise was associated with linear increases in arterial haemoglobin concentration and oxygen content, and decreases in arterial oxygen partial pressures and haemoglobin saturation. We conclude that the relatively high in the detrained Thoroughbred racehorse is dependent on the generation of a large , despite development of hypoxaemia and haemoglobin desaturation, during strenuous exercise.
An in vitro and in vivo Study of the Distribution of Ammonia Between Plasma and Red Cells of Rainbow Trout (Salmo Gairdneri)
Authors: Wright P. A. , Wood C. M. , Randall D. J.
Published: April 2021

Fish are ammoniotelic animals and therefore produce ammonia as the end-product of protein metabolism. (The term ammonia or Tamm will be used to indicate the total ammonia concentration, while NH4+ and NH3 will refer to ammonium ion and ammonia, respectively.) Ammonia is a weak base that is produced as NH3 or NH4+ depending on the biochemical reaction and exists in solution as NH3 and NH4+. Owing to the relatively high pK of ammonia (pK = 9-7 at 10°C) and the physiological pH of body fluids, the predominant form of ammonia in tissue compartments is the ionic form, NH4+. Biological membranes are highly permeable to NH3 and much less permeable to NH4+ (Klocke, Andersson, Rotman & Forster, 1972; Castell & Moore, 1971; Bown et al. 1975; Boron, 1980; Lockwood, Finn, Campbell & Richman, 1980), which requires ion carriers for transport. Thus, the extent of movement of NH4+ between tissue compartments depends on the availability of these carriers and their affinity for NH4+. Transfer of ammonia between tissue compartments is largely determined by NH3 gradients (see Randall & Wright, 1987), but NH4+ electrochemical gradients may also be important (Thomas, 1974; Boron & DeWeer, 1976). The purpose of this study was to determine whether ammonia was passively distributed between red cells and plasma at rest and during an extracellular acidosis. Protons are passively distributed across red cell membranes over a range of pH values in trout (Heming et al. 1986). Thus, if ammonia is passively distributed, the distribution will be determined by red cell-to-plasma pH gradients.
A Simple, Sensitive and Versatile Solid-State Pressure Transducer
Authors: Lighton John R. B.
Published: April 2021

Sensitive and accurate pressure transducers are useful in many areas of biology. Two common applications are the measurement of pressure changes within the respiratory system of an animal, and quantification of the small pressure fluctuations that accompany the humidification and warming of inspired air in whole-body closed-system or open-system flow-through plethysmography (see Malan, 1973; Bucher, 1981). The design of such transducers is often complicated by the requirement to measure very small pressure fluctuations in the presence of a substantial pressure offset. Moreover, such pressure offsets often vary slowly with time. Frequent adjustments are then required to keep the output of the pressure transducer from saturating in either direction.
Behavioural Responses to Light in Paramecium Bursaria in Relation to its Symbiotic Green Alga Chlorella
Authors: Iwatsuki Kenji , Naitoh Yutaka
Published: April 2021

The behavioural responses to light in the ciliate Paramecium bursaria Focke, which normally contains hundreds of the symbiotic green alga Chlorella in its cytoplasm, were analysed quantitatively to clarify the mechanisms governing photoreception in the cell. P. bursana was found to possess three kinds of photoreceptor systems for (1) the step-up photophobic response (system I), (2) the step-down photophobic response (system II), and (3) the photokinetic response (system III). Under the influence of light, the symbiotic algae inhibited systems I and HI, but activated system II. Thus the cells showed the avoiding reaction when they encountered shade (the step-down photophobic response), and consequently gathered in the light region (photoaccumulation). Inhibition of system I and activation of system II were assumed to be mediated by products of the blue-light effect of the algae, while inhibition of system III was due to photosynthetic products of the algae. The cells whose algae were experimentally removed gathered in the shade (photodispersal) due to the avoiding reaction exhibited by them when they encountered a lighted region (the step-up photophobic response mediated by system I). Lowered swimming velocity and increased frequency of spontaneous changes in the swimming direction in the shade (photokinetic responses mediated by system III) also caused photodispersal.
Heart Rate and Gas Exchange in Freely Diving American Mink (Mustela Vison)
Authors: Stephenson R. , Butler P. J. , Dunstone N. , Woakes A. J.
Published: April 2021

Several studies have shown that the diet of the North American mink can vary according to habitat, season and sex (Gerell, 1967;Akande, 1972; Day & Linn, 1972; Birks & Dunstone, 1985; Dunstone & Birks, 1987). It is clear that at times, particularly in autumn and winter, both male and female mink may obtain over 50 % of their food (as fish and crustaceans) from an aquatic environment. Thus, mink will readily take to water and dive to capture prey despite the fact that they possess very few anatomical adaptations which enhance their ability to hunt underwater. Indeed, the unusually high resting metabolic rate of mustelids (Iversen, 1972) and the high energetic cost of transport during surface swimming (Williams, 1983) argue against the successful use of a diving foraging strategy. Brown & Lasiewski (1972) proposed that the adaptive advantage of the elongated body shape of mink (which is energetically expensive because of high rates of heat loss as a result of the high surface area to body volume ratio) lies in the increased ability to capture prey in confined spaces (e.g. lagomorphs in their burrows; Dunstone & Birks, 1987). Perhaps an enhanced ability to capture fish and crustaceans in underwater hides (e.g. Dunstone, 1978) compensates for their presumed locomotory inefficiency underwater.
Non-Spiking Interneurones in the Pedal Ganglia of a Swimming Mollusc
Authors: Spencer Andrew N.
Published: April 2021

Neurones that produce graded potentials and not action potentials are found in a diverse range of species (Roberts & Bush, 1981), and are usually associated with situations where sensory information is being integrated, for example in the vertebrate retina. Nevertheless, in several arthropod species, non-spiking interneurones can participate in the production of a centrally generated motor pattern (Mendelson, 1971; Pearson & Fourtner, 1975; Heitler & Pearson, 1980; Simmers & Bush, 1980; Takahata, Nagayama & Hisada, 1981; Paul & Mulloney, 1985). Surprisingly, such interneurones with similar functions have not been reported for other phyla. In this study, non-spiking interneurones are described in the pedal ganglia of a mollusc that are probably the source of the motor pattern controlling swimming.
Some Motor Neurones of the Abdominal Longitudinal Muscles of Grasshoppers and Their Role in Steering Behaviour
Authors: Baader A.
Published: April 2021

The abdomen is used by acridid grasshoppers for steering during flight (Camhi, 1970a ; Gewecke & Philippen, 1978; Taylor, 1981 ; Altman, 1982; Arbas, 1986; for a review see Rowell, Reichert & Bacon, 1985). The aim of the present study is to characterize some of the various motor neurones innervating the dorsal and ventral longitudinal muscles of the previously undescribed second abdominal segment (ASG2) of Locusta and to describe their activity during steering.
High Blood CO2 Levels in Rainbow Trout Exposed to Hypercapnia In Bicarbonate-Rich Hard Fresh Water - A Methodological Verification
Authors: Dimberg Kenth
Published: April 2021

Heisler (1984, 1986) suggested that fish have a maximum extracellular bicarbonate concentration of about 30 mmol l−1, which can be attained and used for the compensation of blood acidosis induced during environmental hypercapnia. In contrast, Börjeson (1977) and Dimberg & Höglund (1987) reported HCO3−concentrations, analysed using Astrup’s tonometric method (Astrup, 1956), of 40–50 mmol l−1 in venous blood drawn by a syringe from captured fish. However, blood pH in rainbow trout is greatly affected by sampling stress induced by venous puncture (Railo, Nikinmaa & Soivio, 1985). This may introduce error into the determination of blood [HCO3−] when using a tonometric technique based on pH measurements. Consequently, the present study was performed to determine whether the maximal blood HCO3− level in hypercapnic fish is limited to 30 mmol l−1, and if the higher reported blood bicarbonate values could be the result of sampling and/or analytical errors. Rainbow trout (Salmo gairdneri) were exposed to different levels of hypercapnia and acid-base variables were analysed either in venous blood taken with a syringe in the ductus Cuvieri from captured fish or in blood sampled via a dorsal aortic catheter from undisturbed fish. In addition, tonometry and gasometry were carried out separately to determine total blood CO2 concentration.
Acid–Base Regulation and Blood Gases in the Anuran Amphibian, Bufo Marinus, During Environmental Hypercapnia
Authors: Boutilier R. G. , Heisler N.
Published: April 2021

Specimens of Bufo marinus were exposed to aerial and aquatic hypercapnia (5 % CO2) in a closed, water recirculation system to evaluate mechanisms involved in the compensation of a respiratory acidosis in these animals. Arterial was elevated from about 9 mmHg (1 mmHg = 133·3 Pa) to 35 (1h) and 37 mmHg (2h), and gradually approached about 40mmHg (24h of hypercapnia). The typical hypercapnia-induced reduction in plasma pH from about 7·9 to below 7·4 was partially offset, at least during the first hours of hypercapnia, by a reduction in the inspired/arterial difference, presumably brought about by pulmonary hyperventilation. The predominant contributor to extracellular pH compensation, however, was a net gain of bicarbonate from the environment, mainly facilitated by ammonia excretion. Bicarbonate originating from the environment was accumulated in the body fluids, increasing the plasma concentration from the control of about 9 to 36 mmol 1-1 after 24 h. Extracellular pH was compensated to only about 30% of the shift expected at constant bicarbonate level and, according to the steady reduction of pH, non-bicarbonate buffering of CO2 also contributed significantly to the elevation of bicarbonate. This relatively poor pH compensation (compared with fishes) could not be improved either by direct administration of bicarbonate into the bloodstream or by increased environmental ion concentrations. It is concluded that the availability of bicarbonate is not a limiting factor for pH compensation during hypercapnia, and that the inability of Bufo to accumulate bicarbonate to concentrations sufficient for better hypercapnia compensation is based on a constitutional ‘bicarbonate threshold’ of the resorbing and retaining structures for acid-base-relevant ions.