bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Efferent Stimulation on the Phase and Amplitude of Extracellular Receptor Potentials in the Lateral Line System of the Perch (Perca Fluviatius)
Authors: Russell I. J. , Lowe D. A.
Published: April 2021

Microphonic and summating potentials were recorded extracellularly from lateral line organs in the suborbital canal of the perch in response to sinusoidal movements of canal fluid. These potentials were changed in amplitude, shape and phase, relative to the mechanical stimulus, by electrical stimulation of efferent fibres in the lateral line nerve. The receptor potential amplitude/stimulus intensity relationships for the microphonic and summating potentials saturated at high levels of stimulation, and at progressively lower amplitudes with increasing frequencies of mechanical stimulation. Efferent stimulation tended to reduce this rate of saturation. Amplitude versus frequency relationships plotted at different stimulus intensities for the microphonic potential showed that the lateral line organs were most sensitive to frequencies between 35–65 Hz (centre frequency), and at these frequencies efferent stimulation caused the greatest increase in amplitude. Analysis of the second order and third order harmonic components of the microphonic showed that these were reduced by efferent stimulation and that the strongest reduction occurred at the centre frequency. The phase of the receptor potential led that of the mechanical stimulus at very low frequencies by nearly 90 °. This changed to zero phase at the centre frequency and to a phase lag at higher frequencies. Efferent stimulation caused no change in phase of the microphonic relative to the control state at the centre frequency, but caused a progressive phase lead and lag as the frequency was decreased and increased respectively about the centre frequency. In the linear response range, the lateral line organs responded as critically damped low frequency resonators to the velocity of the stimulus. Efferent stimulation appeared to alter the damping of this resonance. The possibility is discussed that efferent stimulation can alter the mechanical properties of the lateral line hair cells.
A Directionally Sensitive Motion Detecting Neurone in the Brain of A Moth
Authors: Rind F. Claire
Published: April 2021

In the moth, Manduca sexta, a pair of neurones, one on each side of the brain, were characterized morphologically and physiologically as descending interneurones, selective for horizontal motion over a large area of the moth’s visual field. Their cell bodies and dendritic processes are located in the protocerebrum of the brain. Their axons, 12–15μm in diameter, project down the ipsilateral connective, branching profusely on the ipsilateral side of the suboesophageal, prothoracic and pterothoracic ganglia. Each neurone responds to movement over either retina. Their preferred directions are from front to back across the ipsilateral eye and back to front over the contralateral one. Movement in the opposite direction supresses their usual ‘resting’ discharge. The neurones are particularly sensitive to movements within the frontal, ventral visual field. Each neurone responds repeatedly, for up to 5 h, to a stimulus oscillating back and forth across the retinae. The response is not diminished during concurrent wing flapping. An increase in the velocity of stimulus movement produces a proportional increase in firing frequency. For stripes of 2·5 cm wavelength and subtending 32° at the eye, the maximum response occurs at a velocity of 3cm/s which gives a contrast frequency of 1-2 Hz. The latency of the neurone’s response, measured from its axon as it enters the pterothoracic ganglion, depends on at least two factors: light intensity and the speed of stimulus movement. The neurone gives a directional response to stripes of period 6·4° in bright light. The response falls to 16· in dim light. At night, in dim light, the latency of response is much reduced and the threshold light intensity, necessary for a directional response, decreases by two orders of magnitude.
Hormonal Influence on Diurnal Glycogen Rhythms in Rat Skeletal Muscles
Authors: IV C. W. Saubert , Armstrong R. B.
Published: April 2021

Normal, diabetic, and sympathectomized rats were killed at intervals during a 12h light (6a.m. to 6p.m.)/12h dark cycle to determine (1) the patterns of diurnal glycogen rhythms in skeletal muscle fibre types, and (2) if the absence of insulin or the catecholamines epinephrine and norepinephrine abolished these rhythms. Normal rat muscles lost and restored 40–60 % of their glycogen stores during one 24-h cycle. Glycogen losses were linear between 6.30 a.m. (acrophase time for all muscles) and 8.30a.m. and between 8.30a.m. and nadir points (4.30 p.m. to 8.30 p.m.), but the rates of loss were non-uniform between these time frames and among fibre types. All muscles had similar linear restoration rates. Glycogen stores in most muscles from diabetic and sympathectomized rats exhibited changes similar to those seen in normal animals. Skeletal muscle fibre types have notable and non-uniform diurnal glycogen rhythms that should be considered in the design of metabolic and exercise experiments. These rhythms do not appear to be regulated, either differentially or in toto, either by insulin or by the catecholamines epinephrine and norepinephrine.
An Analysis of Waving Behaviour: an Alternative Motor Programme for the Thoracic Appendages of Decapod Crustacea
Authors: Pasztor V. M. , Clarac F.
Published: April 2021

Decapod Crustacea display a slow metachronal rhythm of the third maxillipeds and pereiopod pairs one to four when undisturbed in the natural habitat. The dactyl tips are lifted off the substrate, and the unweighted limbs promote and remote at a slow frequency (range for all species 9–30min− 1). Movement is limited to the T-C joint. This behaviour, called waving, has been observed in many macrurans and an analogous activity, limited to the third maxillipeds, has been seen in several brachyurans. Analysis of EMGs shows: (a) the promotor activity increases in strength during a burst due to facilitation and motoneurone recruitment; (b) the rhythm period is stable throughout long waving sessions; (c) the promotor and remotor strokes are of equal duration and co-vary with period. Ipsilateral coupling is strong, with equal phases between adjacent limbs of 0· 05. The metachronal wave can pass anteriorly or posteriorly along an ipsilateral row. Bilateral coupling is weak. The two sides maintain equal frequency, and antiphasic coordination between the two ipsilateral sets of limbs is favoured. Possible functions for waving include gill grooming and supplementary gill ventilation. Comparisons between waving and other rhythmical motor programmes are discussed. Waving is an alternative programme for the walking legs, and is expressed when proprioceptive feedback is reduced.
Coupled Neuronal Oscillators in the Snail Lymnaea Stagnalis: Endogenous Cellular Properties and Network Interactions
Authors: Egelhaaf M. , Benjamin P. R.
Published: April 2021

The role of endogenous cellular properties and network interactions due to electrotonic coupling were investigated in two bilateral populations of 2–7 peripheral neurones (‘Peripheral Bursters’) in the snail Lymnaea stagnalis.

These cells are endogenously capable of bursting. Their burst frequency does not depend on the level of steady membrane polarization. Short hyperpolarizing current pulses injected during the bursting cycle induce phase advance and no phase delay in subsequent cycles, the phase advance being a function of the phase of stimulus application. Phase response and inter-burst interval curves have been constructed for short hyperpolarizing current pulses. Their shape depends on the intensity and sign of tonically injected current. This property of Peripheral Bursters is one reason for the independence of period duration from membrane polarization. Coordination of burst activity of Peripheral Bursters has been studied as a function of coupling strength : whereas homolateral cells are relatively strongly electrotonically coupled and always burst synchronously, thus forming a single oscillatory unit, heterolateral cells are only weakly electrotonically coupled. Accordingly, they show more variable, though coordinated, patterns of activity. Most commonly, periods with 1:1 entrainment alternate with periods with 1:2 entrainment. The duration and frequency of occurrence of either mode of entrainment are highly variable in different preparations.
Fine Structure and Mechanical Properties of the Catch Apparatus of the Sea-Urchin Spine, A Collagenous Connective Tissue with Muscle-Like Holding Capacity
Authors: Hidaka Michio , Takahashi Keiichi
Published: April 2021

The catch apparatus (CA) of the sea-urchin spine has been known to have a muscle-like holding property, though it is composed mainly of extracellular collagen fibres. An electron microscopic study has been made on the CA of the sea urchin, Anthocidaris crassispina, with special reference to its content of muscle cells and to structural changes of the collagen components on elongation of the CA. The stretch resistance of the CA in a highly extensible state and in a very inextensible state was also measured. Although very thin smooth muscle cells were found scattered among the collagen fibres in the CA, the difference in the passive tension was greater than the estimated stress which could be generated by the muscle cells in the CA by three orders of magnitude. The collagen fibrils remained undeformed but slid along one another during the length change of the CA. The present results suggest that the cohesive force between the collagen fibrils rather than the contractile activity of the muscle cells plays a significant role in determining the mechanical properties of the CA.
Locomotory Stresses in the Limb Bones of Two Small Mammals: The Ground Squirrel and Chipmunk
Authors: Biewener Andrew A.
Published: April 2021

Peak stresses acting in limb bones should increase with increasing size if the forces acting on the bones increase in direct proportion to the animal’s body weight. This is a direct consequence of the scaling of limb bone geometry over a wide range in size in mammals. In addition, recent work has shown that the material strength of bone is similar in large and small animals. If the assumptions in this analysis are correct, large animals would have a lower safety factor to failure than small animals. The purpose of this study was to measure peak stresses acting in the limb bones of small animals during locomotion and compare the results with similar measurements available for larger animals. Locomotory stresses acting in the fore and hindlimb bones of two rodents, the ground squirrel (Spermophilus tridecem-lineatus) and chipmunk (Tamais striatus), were calculated using ground force recordings and measurements of limb position taken from high speed x-ray cine films. Peak (compressive) stresses calculated to act in the bones of these animals (—31 to —86MN/m2) are similar in magnitude to those determined for much larger mammals. The more proximal bones of the fore and hindlimb, the humerus and femur, were found to develop stresses ( — 31 to —42MN/m2) significantly lower than those acting in the more distal bones of each limb: the radius, ulna and tibia (—58 to —86MN/m2). All of the long bones from both species, except their femora, were found to be loaded principally in bending. The caudal cortices of each bone developed a peak compressive stress, whereas the cranial cortices were loaded in tension. Various features of the musculo-skeletal organization and manner of locomotion in these rodents are considered to explain how animals of different size maintain a uniform safety factor to failure.
Effects of Certain Physico-Chemical Agents On the Mechanical Properties of the Catch Apparatus of the Sea-Urchin Spine
Authors: Hidaka M.
Published: April 2021

The catch apparatus (CA), a collagenous connective tissue which connects the sea-urchin spine to the test, is known to undergo a remarkable change in its mechanical properties. Effects of various physico-chemical factors on the mechanical properties of the CA have been investigated in order to characterize the linkages which are responsible for determining the mechanical properties of the CA. The stress-strain relations obtained by stretching the specimen at a slow constant speed, 7 μm s−1, were taken as a measure of the viscous resistance of the CA. The viscous resistance of the CA depended largely on the pH and the ionic strength of the medium. It increased with increasing pH and with decreasing ionic strength. The viscous resistance was markedly reduced in a Ca-free medium containing 5mm-EGTA. It is suggested that linkages sensitive to low pH and those mediated by Ca2+ play a significant role in determining the mechanical properties of the CA.
Stick Insect Locomotion On A Walking Wheel: Interleg Coordination of Leg Position
Authors: Dean Jeffrey , Wendler Gernot
Published: April 2021

Continuous measurements of anterior-posterior leg position recorded from stick insects walking on a wheel were tested for relationships among spatial and temporal parameters of leg coordination. This analysis revealed that the protraction of middle and rear legs is guided by the ipsilateral front and middle legs respectively. Protraction endpoint for each rear leg shows a significant positive correlation with the simultaneous position of the ipsilateral middle leg (Figs 1, 2; Table 1). An analogous, but somewhat weaker, correlation exists between the protraction endpoint of each middle leg and the position of the ipsilateral front leg.

This coordination of spatial parameters was tested experimentally by manipulating the position of the forward leg. When a middle leg is restrained in various positions, the ipsilateral rear leg adjusts its protraction endpoint accordingly (Fig. 3). However, its retraction endpoint does not undergo parallel shifts; consequently, step amplitude, protraction duration, and step frequency all change as a function of middle leg position. When a sinusoidal movement is imposed on either a middle or front leg, the adjacent, caudal leg continuously adjusts its protraction endpoint according to the momentary position of the forward leg (Fig. 4). This adjustment is again accompanied by changes in step amplitude and step period, changes which may affect all five unrestrained legs.

The anterior-posterior leg position measured in our experiments primarily reflects the angle of the coxo-thoracic joint; this angle is monitored by hair rows and hairplates located on the coxa (Wendler, 1964; Baessler, 1965). Modifying these external proprioceptive inputs revealed both inter-and intrasegmental control functions. The caudally situated hair rows are important for measuring the small variations in the position of the target leg which occur during normal walking. Immobilization of these hairs on a middle leg causes the mean protraction endpoint of the ipsilateral rear leg to shift forward (Fig. 5: 01 versus C) and reduces or eliminates the step by step correlation of this protraction endpoint with middle leg position (Table 1). The additional immobilization of the cranially situated hairplates usually leads to a caudal shift in the protraction endpoint of the ipsilateral rear leg (Fig. 5: 02 versus 01) and reduces any residual correlation (Table 1). The actual position of the protraction endpoint reflects an integration of intersegmental signals representing the position of the target leg and intrasegmental signals from the sensory hairs on the protracting leg. Both operations may affect the duration of protraction in both the operated target leg and the adjacent, caudal leg.
Potassium Metabolism in Seawater Teleosts : I. The Use of 86Rb as a Tracer for Potassium
Authors: Sanders Martin J. , Kirschner Leonard B.
Published: April 2021

Comparison of the movements of rubidium and potassium between blood and tissues, and between blood and external medium, was undertaken in seawater adapted rainbow trout (Salmo gairdneri) and sculpin (Leptocottus armatus). Qualitative observations suggested that the two ions behaved similarly in exchanges within both fish. More than 90 % of an injected dose of both ions disappeared from the blood within 1 h. Complete equilibration of both required about 5 h, and the decrease in blood concentration during the last 4h followed similar kinetics. After injection and equilibration of 86Rb into trout the specific activity of most tissue pools (c.p.m. 86Rb /μeq tissue K) was close to that of blood (c.p.m. Rb/µeq plasma K). Skeletal muscle was the sole exception; its specific activity was less than 15 % that of plasma even 4–5 h after injection. Injection of ouabain into trout caused cells to lose both 86Rb and K at similar rates. The same thing occurred when [K] in the external medium was raised abruptly.

Exchanges of the two ions between blood and the external medium were also similar. Both ions were extruded and taken up rapidly across the gills. Double-labelling (86Rb and 42K fluxes measured simultaneously) showed that JK/JRb = l·27 for both influx and efflux in trout. The same value was obtained for effluxes in sculpin. Exposing sculpin to seawater lacking Na and K caused both 42K and 86Rb efflux to fall by 75–80%; 86Rb efflux decreased similarly in trout. Alkali metal-free sea water also caused the voltage across the trout gill to change from +10 mV to −20 mV, and in the sculpin from +25 mV to −25 mV. Addition of either Rb or K to the ion-deficient medium partially repolarized the gill in both fish. Repolarization was slightly greater after K repletion than after Rb repletion.

These observations suggest that 86Rb is an adequate tracer for potassium movement in seawater-adapted fish. The gills of trout and sculpin are a little more permeable to K than to Rb, and Rb fluxes must be multiplied by 1·3 to provide accurate estimates of transbranchial K movement. The quantitative relationship between JK and JRb within the animal was not established, but some data suggest that cell membranes in fish, like the gills, are somewhat more permeable to K than to Rb.
3H-Ouabain Binding Autoradiography in the Abdominal Nerve Cord of the Hawk Moth, Manduca Sexta
Authors: Rubin Andrew L. , Stirling Charles E. , Stahl William L.
Published: April 2021

Ouabain, a specific inhibitor of the Na+,K+-ATPase, was used to study localization of this enzyme in the abdominal nerve cord of the hawk moth, Manduca sexta. Treatment of nerve cords with urea was necessary to permit access of ouabain to binding sites within the nerve cord, probably due to opening of the perineurial barrier. Specific, saturable 3H-ouabain binding below 10 μM was observed in the urea-treated nerve cord, and the total number of specific binding sites was 17·8 pmol/mg protein and those sites were half-occupied (KD) at 1·8 μM-ouabain. The urea treatment did not alter the total number of 3H-ouabain binding sites in this tissue. Localization of the 3H-ouabain binding sites was studied by light microscopic autoradiography. Potassium, an established inhibitor of ouabain binding, at 50 mm blocked 3H-ouabain binding in abdominal ganglia by 59%. The majority of ouabain binding sites in the ganglion are in the neuropil, consistent with the high transport requirement in active nerve processes of small diameter. Significant, but lower binding than found in the neuropil was present in the ganglionic perineurium and this structure may be involved in the transport of sodium from the haemolymph into the neural extracellular space.
Physiological Consequences of Severe Exercise in the Inactive Benthic Flathead Sole (Hippoglossoides Elassodon): a Comparison With the Active Pelagic Rainbow Trout (Salmo Gairdneri)
Authors: Turner Jeffrey D. , Wood Chris M. , Hōbe Helve
Published: April 2021

Chronically cannulated flathead sole were subjected to 10 min of either moderate or exhausting burst exercise and monitored over a 12 h recovery period. Acid-base disturbances were more severe after exhausting exercise, but ionic and haematological changes were the same in the two treatments. Most effects were qualitatively similar to those previously described in severely exercised rainbow trout (Turner, Wood & Clark, 1983). Specific differences are discussed and related to the different external environments (sea water vs fresh water), exercise capabilities and ecologies of the two species. The most striking divergence occurred in lactate (La−) and metabolic proton dynamics. Post-exercise La− levels in white muscle in sole were less than half those in trout but declined much more slowly. In contrast to the situation in trout, muscle [La−] remained significantly elevated and a large muscle to blood La− gradient persisted even after 12 h recovery. Blood [La−] underwent only minimal elevation (< 2 mequiv l−1), and blood metabolic proton load greatly exceeded ΔLa− throughout the recovery period, effects directly opposite those in trout. This observed excess of over ΔLa− in the blood of exercised sole is probably not due to a preferential removal mechanism, because and ΔLa− disappeared from the blood at similar rates after an intra-arterial infusion of lactic acid in resting animals. It is therefore argued that the phenomenon reflects a differential release of the two metabolites from the white muscle of the sole, La− being strictly retained in the muscle for gluconeogenesis in situ.
The Circulatory Response to Acute Hypoxia in Octopus
Authors: wells M. J. , wells J.
Published: April 2021

Octopus vulgaris can regulate its oxygen uptake in a closed respirometer down to a of less than 70 mmHg. As the tankwater falls the hearts slow down. Pulse amplitudes and mean pressures fall in the afferent branchial vessels and in the dorsal aorta. Despite behavioural changes – expansion of the interbrachial web and extension of the arms -that might imply this, the proportion of the total oxygen uptake attributable to cutaneous respiration (less than 13%) does not alter as the external falls. The response of the hearts to a low is not affected by severing the nerve supply from the central nervous system, or by removal of the heart ganglia. It is evidently determined by oxygen lack and not by the accumulation of CO2 or other metabolites, since the same effects are achieved by placing the animals in water where the has been reduced by boiling. The conclusion that regulation does not depend upon circulatory responses to hypoxia is considered in the light of recent work on the changes in blood oxygen affinity associated with acute hypoxia in cephalopods.
Studies of Ammonia in the Rainbow Trout Physico-Chemical Parameters, Acid-Base Behaviour and Respiratory Clearance
Authors: Cameron James N. , Heisler Norbert
Published: April 2021

Ammonia (NH3) is only slightly more soluble (+3·4%) in the plasma of rainbow trout than in water, and its pK′ is only 0·14 units higher than in fresh water at 15 °C. Determination of these physico-chemical parameters together with measurements of blood and water pH and total ammonia concentrations allowed calculation of the mean resting partial pressure gradient across the gills (54 × 10−s6Torr) and estimation of the gill permeability coefficient (D = 1·3 × 10−5cm−1).

Under normal resting conditions of low external NH3 and pH, diffusive movement of NH3 appears to account adequately for ammonia excretion in the rainbow trout; 90 ± 10% of the excreted ammonia appears to originate from the blood, rather than from de novo synthesis of ammonia in the gills.

During the high external ammonia treatments, the fish reached a steady state with a net inward ammonia gradient, which could be accounted for by a counter-balancing Na+/NH4+ exchange. Ammonium salt infusions or injections which stimulate Na+ influx are not sufficient demonstrations of Na+/NH4+ exchange, since acidosis is produced, and alternate interpretations of the Na+ flux stimulation are possible, such as enhanced Na+/H+ exchange.
Allometry of Quadrupedal Locomotion: the Scaling of Duty Factor, Bonecurvature and Limb Orientation to Body Size
Authors: Biewener Andrew A.
Published: April 2021

Measurements of the chord length (∝ M0·31) and diameter (∝ M0·35) of the femora, tibiae, humeri and radii from 32 species of mammals, ranging in approximate body mass from 0·020– 3500 kg, support previous data which show that mammalian long bones scale close to geometric similarity. Scaling of peak stresses based on these measurements of limb bone geometry predicts that peak stress increases ∝ M0·28, assuming that the forces acting on a bone are directly proportional to an animal’s weight. Peak locomotory stresses measured in small and large quadrupeds contradict this scaling prediction, however, showing that the magnitude of peak bone stress is similar over a range of size. Consequently, a uniform safety factor is maintained. Bone curvature (∝ M−0·09) and limb bone angle relative to the direc tion of ground force (∝ M−0·07) exhibit a slight, but significant, decrease with increasing body mass. Duty factor measured at the animal’s trot-gallop transition speed does not change significantly with body size. The moment arm ratio of ground force to muscular force exerted about a joint was found to decrease dramatically for horses as compared to ground squirrels and chipmunks. This six-fold decrease (∝ M−0·23) provides preliminary data which appear to explain, along with the decrease in bone curvature and angle, the similar magnitudes of peak bone stress developed during locomotion in different sized animals. The crouched posture adopted by small quadrupeds while running may allow greater changes in momentum (when accelerating or decelerating) or a decrease in the forces exerted on their limbs.
Behaviour and Motor Output of Stick Insects Walking on a Slippery Surface: I. Forward Walking
Authors: Epstein S. , Graham D.
Published: April 2021

The walking coordination and motor output of intact adult stick insects was examined when they were supported above an oiled glass surface. The viscosity of the silicone oil was adjusted so that the animal walked with either tripod or slow-walk coordination. In the absence of mechanical coupling through the substrate, the legs typically moved at different speeds in retraction. If these differences were not too large the walks were well-coordinated in the transitions from stance to swing phase. Motor output was variable and sometimes showed periods of very weak activity in depressors and retractors. Under these conditions an individual leg moved much more slowly than its neighbours, producing 2:1 coordination patterns.
Bony Nares Air Pressure And Nasal Plug Muscle Activity During Click Production in the Harbour Porpoise, Phocoena Phocoena, and the Bottlenosed Dolphin, Tursiops Truncatus
Authors: Amundin M. , Andersen S. H.
Published: April 2021

Sound production mechanisms have been studied in two delphinid species - the harbour porpoise, Phocoena phocoena (L.), and the bottlenosed dolphin, Tursiops truncatus (Montagu). It was found that, in both species, the click sound production was coupled to a considerable pressure increase in the bony nares. The maximum pressure recorded in Phocoena was approximately 54kPa and in Tursiops close to 81 kPa; it was equal in time and amplitude in both nares. The nasal plug muscle was found to be active up to 450 ms prior to and during sound production. Sound production without such activity was not seen. The results suggest that an identical mechanism underlies click production in both species, with, pressurized air being the driving force and the nasal plug muscle having some active regulating function.

Probes were inserted into the bony nares of three harbour porpoises, Phocoena phocoena, and one bottlenosed dolphin, Tursiops truncatus, in order to record air pressure variations together with sound production. Sounds were picked up by a hydrophone manually held to the forehead of the animals. In several of the Phocoena recordings, electromyographic activity in the nasal plug muscle was also recorded.
Aquatic and Aerial Respiration Rates,Muscle Capillary Supply and Mitochondrial Volume Density in the Air-Breathing Catfish (Clarias Mossambicus)Acclimated to Either Aerated or Hypoxic Water
Authors: Johnston Ian A. , Bernard Lynne M. , Maloiy Geoffrey M.
Published: April 2021

Specimens of the African air-breathing catfish Clarias mossambicus were acclimated to either aerated (15·3KPa) or hypoxic ( 2·4KPa) water for up to 27 days at 20 °C. Routine respiration rate for fish acclimated to aerated water was 85·7 mlO2 (kg bodyweight) −1 h−1. Gas exchange across the suprabranchial chambers accounted for 25% of the total. In aerated water the interval between air-breaths varied from 1·4 to 30·6 min. On acute exposure to hypoxia air-breathing frequency was unaltered (6·3 h−1) although aerial respiration rate increased by 70%. This suggests that ventilation of the suprabranchial chambers is variable and that air-breathing frequency is a poor measure of air-breathing effort. Total respiration decreased by 46% on acute exposure to hypoxia ( 2·4 KPa), reflecting a reduction in routine activity. Following acclimation to hypoxia, airbreathing frequency (84 h−1) was higher and total routine respiration rate increased from 46·3 to 67·8 mlO2kg−1 h−1. The increased oxygen consumption with hypoxia acclimation was largely the result of an increase in aquatic respiration from 10·4 to 27·5 mlO2kg−1 h−1

Measurements were made of mitochondrial volume densities [Vv(mt,f)] and capillary supply to fast and slow myotomal muscles. The fraction of fibre volume occupied by mitochondria was 15% for slow and 2·5% for fast muscles. Values for [Vv(mt,f)] obtained for fish slow fibres are much higher than for homologous muscles in birds and mammals and show a good correlation with capillary density [NA(c,f)].

Hypoxia acclimation did not result in changes in either muscle Vv(mt,f) or NA(c,f). It is suggested that increased ventilation of the suprabranchial chambers and greater oxygen extraction across the gills obviates the need for modifications in these parameters.
Fluid Transport by Gallbladder Epithelium
Authors: Spring Kenneth R.
Published: April 2021

The absorption of fluid by epithelial tissues is thought to be due to the existence of hypertonic regions within the epithelium. The magnitude of the required hypertonicity as well as its localization have been the subject of considerable experimental and theoretical effort. Model calculations demonstrated the need for knowledge of the water permeability of the membranes of epithelial cells for the purpose of estimation of the osmotic gradients required for fluid absorption. We measured the hydraulic water permeability of the individual cell membranes of Necturus gallbladder by quantitative light microscopy. The water permeabilities were sufficiently high so that small osmotic gradients were required to achieve normal rates of fluid transport. The cell osmolality was calculated to exceed that of the mucosal bathing solution by about 2 mosmol kg−1, and the basolateral interstitial osmolality was calculated to be about 1 mosmol kg−1 greater than that of the cell. The fluid absorbed by the epithelium must be slightly hypertonic to the bathing solutions. Knowledge of the apical cell membrane water permeability and the relative area of the cell and tight junction allow a calculation of the relative flow of fluid across both pathways. It can be readily shown that osmotically induced flow across the epithelium occurs predominantly transcellularly because of the small area of the junctional pathway and the high water permeability of the cell membranes.
Syncytial Epithelia: Transport in the Absence of Paracellular Pathways
Authors: Podesta Ron B.
Published: April 2021

The syncytial epithelium of parasitic flatworms offers the opportunity to examine epithelial transport physiology in the absence of paracellular pathways. The asymmetric enzymatic and permeability properties of the apical and basal membranes confirm the transepithelial transport function of the syncytial epithelium. Although the absence of a paracellular pathway has led to the suggestion that the syncytium is a ‘tight’ epithelium, which would be consistent with its low osmotic and diffusive water permeability, the ion transport mechanisms in the apical membrane are more consistent with those predominating in ‘leaky’ epithelia. Contrary to that expected of an animal covered with a ‘tight’ epithelium, the parasitic flatworms are not good ion regulators. The apical membrane contains a Cl−: Na+ co-transport system characteristic of ‘leaky’ epithelia. Although external acidification occurs by an active H+ extrusion mechanism, a large part of H+ secretion is coupled to Na+ influx as in ‘leaky’ epithelia. Categorization of the syncytial epithelium as ‘tight’ or ‘leaky’ will have to await electrical potential profile determinations which are made difficult by the electrical coupling of the syncytium to the underlying nerve-muscle syncytium.
Occluding Junctions and Paracellular Pathways Studied in Monolayers of Mdck Cells
Authors: Cereijido M. , González-Mariscal L. , Borboa L.
Published: April 2021

MDCK cells (epithelioid, derived from the kidney of a normal dog) cultured in monolayers on a permeable support, exhibit properties of natural transporting epithelia. Comparisons of the electrical resistance across the plasma membrane of MDCK cells (as studied with microelectrodes) and the resistance across the whole monolayer, (mounted as a flat sheet between two chambers) indicate that most of the current flows through an extracellular pathway. Scanning of the electrical field over the apical surface shows that this pathway is located at the intercellular space. Yet conductance is not evenly distributed along the intercellular space as in leaky epithelia, but is restricted to sites scattered irregularly along the intercellular space. Studies of freeze fracture electron microscopy indicate that the number of strands of the junctions is also distributed irregularly, varying from 1 to 10 in a few nanometers. This suggests that regions with few strands would correspond to spots with high conductance and vice versa. However, in this preparation the sealing property of the junction bears little relationship to its structure. Thus by changing the temperature from 37 to 3 °C and back, the electrical resistance increases reversibly by 306%, while the number and arrangement of the strands show no significant modification. The resistance of the monolayer varies also with the age of the cells, suggesting that sealing and ion-permeating components of the junction may be dynamic entities that are not permanently installed, but can be accommodated to the requirements of the tissue.
Functional Properties of the Paracellular Pathway in Some Leaky Epithelia
Authors: Kottra Gabor , Frömter Eberhard
Published: April 2021

We here review the functional properties of the paracellular pathway of leaky epithelia such as gallbladder and renal proximal tubule. These epithelia are characterized by leaky terminal bars between adjacent cells which allow small ions, non-electrolytes and water to leak from lumen to interstitial fluid or back. In the past 10 years a great deal of information has been obtained about the properties of the misnamed ‘tight’ junctions in the terminal bars, by assuming that the overall permeation pattern reflected predominantly the junctional permeation properties. Although recent trans- and intraepithelial impedance analyses indicate that this assumption is not always justified (the contribution of the lateral intercellular space to the paracellular shunt resistance is not negligible, when the spaces are collapsed) it seems that the major conclusions are correct. The properties of the terminal junctions may thus be summarized as follows. (1) Large molecules such as horseradish peroxidase are not able to pass. (2) Passage of lipophilic substances is insignificant, as these substances permeate by the cellular route. (3) Depending on the tissue, ion permeation is either governed by channels with negative fixed charges, or positive fixed charges, or both. As inferred from ion selectivity patterns the channels of different epithelia are either wide and highly hydrated or narrow and poorly hydrated, thus allowing more or less water molecules to pass besides the ions. In narrow channels singlefile diffusion may occur. (4) Besides the selective channels a free solution shunt seems to be present in some epithelia. (5) When applied in millimolar concentrations 2,4,6-triaminopyrimidinium and amiloride block negatively charged junctional channels. However these substances do not simply turn leaky epithelia into tight epithelia, because they have additional effects on the cell membranes. (6) As observed in cell cultures, formation of tight junctions requires connecting particles to be present on the cell surface – which seems to be controlled by the cytoskeleton – and requires the presence of calcium ions as ligands. (7) Cellular control over paracellular permeability may be exerted through changes of intracellular calcium concentration.
Use of Cultured Epithelia to Study Transport and its Regulation
Authors: Handler Joseph S.
Published: April 2021

Epithelial cells from a variety of species and organs form polarized epithelia in culture. When epithelia are grown on a porous surface, such as a millipore filter, transport can be studied using adaptations of standard techniques. In the few years in which cultured epithelia have been studied by transport physiologists, most work has been focused on identification and description of the differentiated transport exhibited by cultured epithelia. Epithelia formed by a continuous line of cells derived from pig kidney (LLC-PK1) exhibit sodium-coupled glucose transport similar to that of the proximal tubule and have vasopressin-sensitive adenylate cyclase that has been studied in great detail. Also of interest are epithelia formed by con tinuous lines of cells derived from amphibian kidney (A6) and from am phibian urinary bladder (TBM). Each line forms epithelia that have high electrical resistance and amiloride-sensitive sodium transport. Transport is stimulated by aldosterone and by cAMP or hormones that raise cell cAMP levels. In LLC-PK1 and in A6 epithelia, transport and the response to hormones can be manipulated by manipulating the culture conditions. Cultured epithelia have also been used to explore the cell biology of epithelia. Most interesting in this regard are studies of the development and maintenance of epithelial cell polarity. This approach should be especially valuable.
Potassium Ion Transport Atpase in Insect Epithelia
Authors: Harvey William R. , Cioffi Moira , Dow Julian A. T. , Wolfersberger Michael G.
Published: April 2021

K+ transport by the epithelia of midgut, salivary glands, Malpighian tubules, sensory sensilla, possibly rectum, and other organs of certain insects appears to use a unique K+ ATPase. Ouabain inhibition of transport-related events has not been demonstrated in these epithelia. The K+ pump is unlike the Na+, K+ pump but resembles the H+ pump of phosphorylating membranes in its transport orientation, efficient thermodynamics, speculated two K+ per one MgATP2− stoichiometry, electrogenicity, and structure. Older electrochemical, tracer flux, and conductance evidence suggested that the K+ pump was on the apical plasma membrane of transporting cells in these epithelia. New X-ray microanalytical studies (XMA), reveal that the K+ concentration in all cells is more than 100 mm. Together with new microelectrode data these XMA results confirm the apical K+ pump location, resolve the K+ transport route, and suggest that the goblet cell cavity facilitates the generation of a large apical PD which may be used in nutrient absorption and pH regulation. K+ portasomes, which resemble F1-F0 ATPase particles, stud these K+ transporting apical membranes and are thought to be the unit of active K+ transport. We have suggested a K+ transport mechanism in which two cations (2K+) are abandoned in an isolated domain of the portasomes during ATP2− hydrolysis and are repelled to the opposite membrane side via a K+ channel. Small peptides hydrolysed from the δ-endotoxin ot Bacillus thuringiensis inhibit the K+ transport and may be useful as K+ pump inhibitors, apical membrane probes and insecticides. Goblet cell apical membrane fragments (GCAM) as well as fragments from columnar cell apical membrane (CCAM), lateral membrane (LM) and basal membranes (BM) were isolated as clean fractions using ultrasound, aspiration, and both differential and density gradient centrifugation; purification was monitored by electron microscopy. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE) reveals that GCAM, CCAM, LM and BM have very different protein compositions. Preliminary enzymology is consistent with the K+ ATPase being on the apical plasma membrane of the goblet cells of midgut and enveloping cells of sensilla.
Symmetrical Giant Neurones in Asymmetrical Ganglia: Implications for Evolution of the Nervous System in Pulmonate Molluscs
Authors: Munoz Douglas P. , Pawson Peter A. , Chase Ronald
Published: April 2021

Two of the largest neurones in the terrestrial snail Achatina fulica are RPrl, located in the right parietal ganglion, and VI, located in the visceral ganglion. Several characteristics of these cells were studied in detail, including morphology, passive and active electrical properties, synaptic inputs, sensory inputs, motor outputs and sensitivity to transmitter substances. The results suggest that RPrl and VI form a bilaterally homologous pair of cells, yet they reside in asymmetrically placed ganglia. An explanation of this paradox is offered in the proposal that RPrl and V1 were formerly located in the bilaterally symmetrical intestinal ganglia. Their contemporary asymmetrical locations are accounted for by the hypothesis that, during the evolution of the pulmonate nervous system, the supraintestinal ganglion fused with the right pallial ganglion and the subintestinal ganglion fused with the visceral ganglion.
CO2 and H+ Excretion By Swimming Coho Salmon, Oncorhynchus Kisutch
Authors: Thillart Guido Van Den , Randall David , Hoa-Ren Lin
Published: April 2021

Coho salmon, Oncorhynchus kisutch (Walbaum), were swum at constant speed in a ‘Brett-type’ tunnel respirometer. Blood , and pH as well as total CO2 content and red blood cell pH were unchanged during swim ming. The RE (respiratory exchange ratio) was slightly less than 0·7 when the fish was swimming in normal sea water, indicating that some CO2 is retained by the fish. Lowering seawater bicarbonate concentration increased HCO3− transfer, presumably because of passive bicarbonate loss. A reduc tion in seawater pH from 7 ·95 to 7 ·1 sharply reduced both CO2 and hydrogen ion transfer, resulting in very low RE values of about 0 ·2. Hydrogen ion excretion was elevated during prolonged swimming following high speed swimming activity. It would appear that CO2 and hydrogen ion transfer by fish need not be matched and changing internal and external conditions can have a marked and separate effect on hydrogen ion and CO2 excretion and therefore on the RE value.
Diffusion of Oxygen Through the Mesogloea of the Sea Anemone Calliactis Parasitica
Authors: Brafield A. E. , Chapman G.
Published: April 2021

The diffusion of oxygen through preparations of the mesogloea of Calliactis parasitica (Couch) has been measured with a custom-built diffusion cell and an oxygen microelectrode. The mean value for Fick’s diffusion coefficient was 7·29 × 10−6cm2s−1 and that for Krogh’s diffusion constant 10·00 × 10−6cm3 oxygen per min per cm2 area and cm thickness at a pressure difference of 1 atmosphere, at 25 °C. Comparison with the rather few values in the literature for oxygen diffusion through biological materials indicates that mesogloea is similar to connective tissue. The mesogloea of Calliactis seems to present a fairly significant barrier to the diffusion of oxygen between the two cell layers, and this is discussed in relation to the route whereby the endoderm obtains its oxygen.
Retinal Damage and Sensitivity Loss of A Light-Sensitive Crustacean Compound Eye (Cirolana Borealis): Electron Microscopy and Electrophysiology
Authors: Nilsson Heimo L. , Lindström Magnus
Published: April 2021

The compound eye of the deep-water-living crustacean Cirolana borealis has been exposed to measured amounts of white light, and the effects have been analysed by electron microscopy and electrophysiology (ERG). The threshold for damage of the retinula cells lies between 117 lx (0·47Wm−2) and 1250 lx (4·9 Wm−2). With daylight exposures of more than 70 W m−2, there is severe structural derangement and the amplitude of the electroretinogram (ERG) is abolished. No recovery of the retinula cell organization or of the ERG occurs after daylight exposure and a dark period of up to 5 days. A novel type of photoreceptor membrane shedding is described for both dark-adapted and light-exposed eyes. Hence, morphologically and functionally, the Cirolana eye is strictly adapted to a dim-light environment and is destroyed by too intense illumination.
The Elicitation of the Predatory Labial Strike of Dragonfly Larvae in Response to A Purely Mechanical Stimulus
Authors: Kanou Masamichi , Shimozawa Tateo
Published: April 2021

The predatory labial strike of dragonfly (Aeschna) larvae could be elicited by an artificial water jet stimulus.

The larvae showed fair prey-catching ability even when visually deprived, whereas when deprived of mechanosensory and visual information, the ability decreased sharply. Also, immobilized prey were unable to elicit a strike even from intact larvae.

The percentage of labial strike (PLS) increased in proportion to the logarithm of the water velocity at the body surface. Animals starved for 1 day or more showed higher PLS than satiated ones.

In addition to the water velocity, the movement of the jet nozzle (temporary change in the velocity) was also important in eliciting the labial strike. Although repetitive stimuli resulted in a rapid habituation of the labial strike, the second stimulus in a series was always the most effective: an arousal state to the newness was observed.

The anterior parts of the body surface (including the legs) showed higher sensitivity of PLS to the water jet stimulus, whereas the posterior parts elicited responses other than the labial strike: turning, head orientation and the setting of a posture.

These results explain nocturnal predation of larvae and predation in turbid pond beds where visual cues will be unavailable.
Effects of Osmolality and Potassium on Motility of Spermatozoa From Freshwater Cyprinid Fishes
Authors: Morisawa M. , Suzuki K. , Shimizu H. , Morisawa S. , Yasuda K.
Published: April 2021

Spermatozoa of freshwater Cyprinidae (goldfish, carp, crucian carp and dace) remained immotile when the semen was diluted in solutions of NaCl, KC1, mannitol or glucose iso-osmolar to the seminal plasma (300mosmol kg−1). The spermatozoa became motile in media containing these solutes if the osmolality was lower than that of the seminal plasma, suggesting that motility is suppressed by the osmolality of the seminal plasma in the sperm duct and initiated by a decrease of osmolality upon spawning into fresh water. Potassium was a major component of seminal plasma, having a concentration 20–30 times higher than that in the blood plasma in goldfish and carp. Sodium concentration in seminal plasma was lower than that in blood plasma. Potassium increased viability and speed of sperm movement at a concentration below that in the seminal plasma, whereas sodium and the nonelectrolytes were less effective. Potassium released with spermatozoa at spawning may therefore stimulate motility which has already been initiated by the decrease of osmolality.