bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Low Extracellular Calcium Concentration on Photosensitivity of Isolated Rods From Frog Retina
Authors: Azuma Katsu
Published: April 2021

The effects of extracellular calcium concentration ([Ca2+]o) on the light sensitivity of isolated single rods from the retina of the frog (Rana catesbeiana) were investigated by sucking the rod inner segments into tightly fitting pipettes.

Light flashes (500nm, 1 s duration) evoked transient outward changes of membrane current (photoresponses). The peak amplitude of maximal photoresponses in normal physiological solution varied between 6 and 12 pA. Reducing [Ca2+]o from 0·9 mmol l−1 (normal Ca2+) to 90 μmol l−1 (low Ca2+) increased the peak amplitude of photoresponses and shortened the recovery phase of the responses.

The effects of larger changes in light intensity were also investigated. After light-on there was a steady outward change of membrane current, and after light-off the current recovered to the initial dark level. With a low external Ca2+ concentration, light-off induced a large inward change of membrane current which transiently overshot the initial dark level. During the overshoot stage, light flashes evoked photoresponses which were larger than those in the initial dark period.
In Situ Dye-Visualization and Photoinactivation Using an Epifluorescent Compound Microscope
Authors: Heitler W. J. , Fraser K.
Published: April 2021

A very useful technique to emerge in recent years in the field of neural circuit analysis is in situ dye-visualization and photoinactivation using Lucifer Yellow (Stewart, 1978). This allows direct anatomical identification of neurones during an experiment, and greatly facilitates placing several microelectrodes within a single neurone (Reichert & Krenz, 1986). If the visualization is kept brief, the neurone is not damaged, but with continued exposure the neurone is specifically killed (Miller & Selverston, 1979). This enables neurones to be selectively deleted from a circuit.
“Tho’ she kneel’d in that place where they grew…” The uses and origins of primate colour vision
Authors: Mollon J. D.
Published: April 2021

The disabilities experienced by colour-blind people show us the biological advantages of colour vision in detecting targets, in segregating the visual field and in identifying particular objects or states. Human dichromats have especial difficulty in detecting coloured fruit against dappled foliage that varies randomly in luminosity; it is suggested that yellow and orange tropical fruits have co-evolved with the trichromatic colour vision of Old World monkeys. It is argued that the colour vision of man and of the Old World monkeys depends on two subsystems that remain parallel and independent at early stages of the visual pathway. The primordial subsystem, which is shared with most mammals, depends on a comparison of the rates of quantum catch in the short-and middle-wave cones; this system exists almost exclusively for colour vision, although the chromatic signals carry with them a local sign that allows them to sustain several of the functions of spatiochromatic vision. The second subsystem arose from the phylogenetically recent duplication of a gene on the X-chromosome, and depends on a comparison of the rates of quantum catch in the long-and middle-wave receptors. At the early stages of the visual pathway, this chromatic information is carried by a channel that is also sensitive to spatial contrast. The New World monkeys have taken a different route to trichromacy: in species that are basically dichromatic, heterozygous females gain trichromacy as a result of X-chromosome inactivation, which ensures that different photopigments are expressed in two subsets of retinal photoreceptor.
Sensory coding and corollary discharge effects in mormyrid electric fish
Authors: Bell C. C.
Published: April 2021

Weakly electric fish use their electrosensory systems for electrocommunication, active electrolocation and low-frequency passive electrolocation. In electric fish of the family Mormyridae, these three purposes are mediated by separate classes of electro receptors: electrocommunication by Knollenorgan electroreceptors, active electrolocation by Mormyromast electroreceptors and low-frequency passive electrolocation by ampullary electroreceptors. The primary afferent fibres from each class of electroreceptors terminate in a separate central region. Thus, the mormyrid electrosensory system has three anatomically and functionally distinct subsystems.

This review describes the sensory coding and initial processing in each of the three subsystems, with an emphasis on the Knollenorgan and Mormyromast subsystems. The Knollenorgan subsystem is specialized for the measurement of temporal information but appears to ignore both intensity and spatial information. In contrast, the Mormyromast subsystem is specialized for the measurement of both intensity and spatial information. The morphological and physiological characteristics of the primary afferents and their central projection regions are quite different for the two subsystems and reflect the type of information which the subsystems preserve.

This review also describes the electric organ corollary discharge (EOCD) effects which are present in the central projection regions of each of the three electrosensory subsystems. These EOCD effects are driven by the motor command that drives the electric organ to discharge. The EOCD effects are different in each of the three subsystems and these differences reflect differences in both the pattern and significance of the sensory information that is evoked by the fish’s own electric organ discharge. Some of the EOCD effects are invariant, whereas others are plastic and depend on previous afferent input.

The mormyrid work is placed within two general contexts: (a) the measurement of time and intensity in sensory systems, and (b) the various roles of motor command (efferent) signals and self-induced sensory (reafferent) signals in sensorimotor systems.
On the So-called Constant-lift Reaction of Migratory Locusts
Authors: Zarnack Wolfram , Wortmann Michael
Published: April 2021

Locusts were fastened to a force transducer in front of a wind tunnel to measure their lift and thrust during tethered flight heading into the wind. The thrust measurement was used to adapt the wind speed to the flight speed of the animals. Thus, the locusts could choose their flight speed freely in the range 0.5– 7ms− 1. At light intensities of about 0.02 lx (twilight), the locusts generally produced a maximum lift greater than 100% of their body weight. A miniature motor mounted on the force transducer could alter the body angle of the locusts without further interference. Lift was found to be influenced by body angle. No ‘constant-lift reaction’ evoked by exteroceptive information of the aerodynamic flow was found. Flight speed was almost independent of the imposed body angle. Generally, a flight speed of about 3 m s− 1 was necessary for level flight. There was no further correlation between lift and flight speed.
Modulation of Haemocyanin Oxygen-Affinity by L-Lactate and Urate in the PrawnPenaeus Japonicus
Authors: Lallier F. , Truchot J. P.
Published: April 2021

The addition of either L-lactate or urate to dialysed haemolymph from the prawn Penaeus japonicus (Bate) increased the in vitro haemocyanin oxygen affinity. The quantitative values of these two effects, expressed as ΔlogP50/ Δlog[effector], were found to be −0·077 for L-lactate and −0. ·032 for urate, at pH7·6 and 25°C. The normal, significant Bohr effect (ΔlogP50/ΔpH approx. −1·5 at pH 7·.6, 25°C) was not modified by the two effectors tested, nor was the cooperativity of haemocyanin oxygen-binding (n50 approx. 4).

Hypoxic exposure of the prawns to or 4·4 kPa(1 kPa=7·5 mmHg) for up to 48 h at 25°C induced only a small, less than 2·5-fold, elevation of L-lactate concentration in the haemolymph, all values remaining below 0·5 mmol 1−1, but urate concentration increased to a greater extent (12-fold maximum increase from 0·01 to 0·12 mmol 1−1). Haemocyanin oxygen-affinity, measured in vitro on haemolymph samples drawn from hypoxic prawns, increased slightly during the first 3h of hypoxia acclimation (ΔP50=0·8–0·9kPa at pH7·6), returning to near normoxic control values after a 48 h hypoxic exposure.

The respective roles of L-lactate and urate in enhancing oxygen transport during hypoxia are discussed on the basis of their in vitro effects on haemocyanin oxygen affinity and their in vivo concentration variations in haemolymph.
Regulation of Hepatic Gluconeogenesis and Glycogenolysis By Catecholamines in Rainbow Trout During Environmental Hypoxia
Authors: Wright Patricia A. , Perry Steve F. , Moon Thomas W.
Published: April 2021

This study tests the hypothesis that catecholamines regulate glucose availability during hypoxia in the rainbow trout by activating glycogen phosphorylase (GPase) while inhibiting pyruvate kinase (PK) in the liver. The net result would be an increase in liver glycogenolysis and a reduction of glycolysis and/or enhancement of gluconeogenesis. We used the criteria of Stalmans & Hers (1975) and report much lower resting percent GPase a (active) values (20–30%) than those previously published. Dorsal aortic injections of epinephrine or norepinephrine increased plasma glucose (16–46%), had no effect on liver or muscle glycogen levels, decreased the activity of PK, and increased total and percent GPase a activities. Pre-treatment with the β-adrenoreceptor antagonist propranolol eliminated these effects. During moderate hypoxia, plasma glucose remained unchanged, while lactate levels increased fourfold. When fish were pre-treated with propranolol, hypoxia depressed plasma glucose levels (−26%), total and percent GPase a, and increased PK activity, suggesting that hypoxia mediated the dephosphorylation of these enzymes. We conclude that catecholamines stimulate hepatic β-adrenoreceptors during hypoxia and sustain plasma glucose levels by nullifying the deleterious effects of hypoxia on metabolic function. The specific metabolic consequences of these catecholamine-mediated effects are an increase in the activity of the active form of GPase and a reduction in PK activity, which suggests an activation of glycogenolysis and an inhibition of glycolysis and/or activation of gluconeogenesis, respectively.
Control of metabolism and growth in embryonic turtles: a test of the urea hypothesis
Authors: Packard G. C. , Packard M. J.
Published: April 2021

We performed two experiments to determine (1) whether the metabolism and growth of embryonic snapping turtles (Chelydra serpentina) incubating in wet and dry environments are correlated inversely with the concentration of urea inside their eggs, and (2) whether urea accumulating inside eggs might be the cause of reductions in metabolism and growth by embryos. Eggs in the first experiment were incubated in different hydric environments to induce different patterns of net water exchange between the eggs and their surroundings. Turtles hatching from eggs that were in positive water balance had larger carcasses, smaller residual yolks and lower concentrations of urea in their blood than animals emerging from eggs that were in negative water balance. Thus, we confirmed the existence of correlations among water exchange by eggs, concentrations of urea in fluid compartments inside eggs, and metabolism and growth of embryos. In the second experiment, eggs were injected with solutions of urea at the mid-point of incubation to induce different levels of uremia in developing embryos. The injection protocol induced variation in the concentration of urea in blood of hatchlings similar to that observed in the first experiment for turtles hatching in wet and dry environments. However, the injection protocol did not induce variation in size of hatchlings or in mass of their residual yolk. Thus, the reduction in metabolism and growth of chelonian embryos developing in dry environments does not result from an inhibition of intermediary metabolism caused by urea, and the ‘urea hypothesis’ for control of metabolism cannot be accepted in its present form.
Tracheal Hypertrophy in Mealworms: Design and Plasticity in Oxygen Supply Systems
Authors: Loudon Catherine
Published: April 2021

Larval Tenebrio molitor L. (Insecta) were reared in three different levels of oxygen: 21 % (normal), 15 % and 10.5 %, all at 101.3kPa (=1atm) total pressure (remainder nitrogen). Some larvae were transferred from one oxygen level to another during development.

The main tracheae (branching off from the spiracular tracheae) were of greater cross-sectional area in lower ambient oxygen. Compared to larvae of the same body mass reared in 21 % oxygen, larvae reared in 15 % oxygen had main tracheae 40% larger in cross-sectional area on average, and larvae in 10.5% oxygen had main tracheae 120% larger. This hypertrophy is not consistent with the widely accepted hypothesis that tracheae contribute an insignificant resistance to the net movement of oxygen in insect tracheal systems.

The magnitude of the hypertrophy is consistent with predictions from Fick’s law of diffusion and with the hypothesis that diffusion is the primary mechanism for oxygen movement in the larval tracheal system of holometabolous insects.
A rapid cold-hardening response protecting against cold shock injury in Drosophila melanogaster
Authors: Czajka Maureen C. , Lee Richard E.
Published: April 2021

In studies of insect cold-hardiness, the supercooling point (SCP) is defined as the temperature at which spontaneous nucleation of body fluids occurs. Despite having an SCP of − 20°C, adults of Drosophila melanogaster did not survive exposure to −5°C, which suggests that cold shock causes lethal injury that is not associated with freezing. If, however, flies were chilled at 5 °C, for as little as 30min, approximately 50% of the flies survived exposure to −5°C for 2h. This capacity to cold-harden rapidly was greatest in 3-and 5-day-old adults. The rapid cold-hardening response was also observed in larvae and pupae: no larvae survived 2 h of exposure to − 5 °C, whereas 63 % pupariated if chilled at 5 °C before subzero exposure. Similarly, although exposure of pupae to −8°C was lethal, if pre-chilled at 5°C 22% eclosed. This extremely rapid cold-hardening response may function to allow insects to enhance cold-tolerance in response to diurnal or unexpected seasonal decreases in environmental temperature.
Compensation of progressive hypercapnia in the toad (Bufo marinus) and the bullfrog (Rana catesbeiana)
Authors: Toews D. P. , Stiffler D. F.
Published: April 2021

Toads (Bufo marinus L.) and bullfrogs (Rana catesbeiana Shaw) were subjected to a series of 24 h step increases in aerial CO2 (2, 4, 6 and 8%) to assess the degree of extracellular pH compensation at each CO2 level and to ascertain the importance of cutaneous ion transport in this process. Elevation of plasma [HCO3−] occurs during the 24 h period, with the bullfrogs showing a greater ability to compensate at each step. There was no indication that a [HCO3−] threshold of 30 mmol l−1 existed in either species, although bullfrogs appeared to have a greater compensatory potential when exposed to the higher levels of CO2. The results of the ion flux experiments suggest that neither the terrestrial Bufo nor the semi-aquatic Rana use their skin to any great extent for acid-base balance during hypercapnia.
Interactions of light and gravity reception with magnetic fields in Xenopus laevis
Authors: Leucht T.
Published: April 2021

Tadpoles of Xenopus laevis are shown to respond to magnetic fields using a gravity-related test paradigm. They exhibit a directional selectivity with respect to angular variations of the inclination of low-intensity magnetic fields. This response is abolished when the optic nerves of the tadpole are transected, indicating that the peripheral optical system is involved in the detection of magnetic fields.
Oscillations of Glial Membrane Potential in a Localized Region of the Blood-Brain Barrier of an Insect
Authors: Schofield P. K.
Published: April 2021

In an abdominal ganglion of the American cockroach, Periplaneta americana, electrophysiological characteristics of the perineurium, the glial layer that forms the insect blood-brain barrier, were investigated by microelectrode recording. The potential across the barrier was positive relative to the bathing medium. Its value increased when the external K concentration was raised, as to be expected from a depolarization of the perineurial cell membrane facing the saline, the basolateral membrane. A negative ‘all-or-nothing’ transient, having an amplitude of some 30mV and a half-amplitude duration of about 1·5 min, was also induced, either during the K elevation or after. Given sufficient K exposure, a series of these transients occurred, with a periodicity of 3–15 min, indicating that a cellular oscillator had been activated. The delay between application of high K and the appearance of the first transient was variable, and could be as long as 60 min for a threefold increase in K level. The transients could persist upon return of normal saline, for at least 85min, with little change in amplitude. By recording transperineurial potential simultaneously with recording from superficial cells, one of which was identified as a perineurial cell by peroxidase injection, the transients were found to be generated by a depolarization of the membrane adjacent to the underlying nerve cells, the adglial membrane. Analysis using a simple electrical model yielded values for the resting electromotive force (e.m.f.) generated by the membranes, – 50mV for the basolateral, –71 mV for the adglial, and indicated that the paracellular pathway had a resistance 4·3 times larger than the transcellular resistance. These results reveal a cellular oscillator, apparently of cytosolic type, in the perineurial glia of an insect ganglion, and demonstrate physiological differences between the perineurium of the ganglion and that of other regions of the insect nervous system.
Luminescent Flash Avoidance in the Nocturnal Crab Portunus Xantusii : I. The Effects of Luminescence and Mechanical Stimulation on Heart Rate
Authors: Grober Matthew S.
Published: April 2021

In crabs, the ratio of the heart rate before to that after sensory stimulation (the response ratio) provides a reliable indicator of the effects of sensory stimulation on cardiac activity. The nocturnally active crab Portunus xantusii (Stimpson) exhibits rapid decreases in heart rate in response to the luminescent flashes produced by the sea pansy Renilla kollikeri (Pfeffer) and to mechanical stimulation. Crabs move away from luminescent and mechanical stimuli and this behavior is well correlated with the cardiac responses. Therefore, cardiac response ratios can be used as a reliable bioassay to determine the components of sensory stimuli that are important in eliciting behavioral responses. The similar cardiac responses to both luminescent and mechanical stimuli suggest that a single command pathway may be responsible for triggering startle behavior in response to a wide variety of rapid, brief and intense sensory stimuli. Heart rate also varied depending on the body size of the crab and the ambient temperature. Small crabs had faster heart rates than larger crabs, and the relationship between heart rate and body size is described by the equation: f H=794 · 3X-− 0· 59222, where/H is heart rate in beats per minute and x is carapace length in millimeters. Heart rate increased with increasing temperature over a range of 10 – 22 ° C, but no further increases occurred at higher temperatures. TheQ10for the range 10 – 20 ° C was 1 · 8.
Luminescent Flash Avoidance in the Nocturnal Crab Portunus Xantusii:: II. Cardiac and Visual Responses to Variations in Simulated Luminescent Flashes
Authors: Grober Matthew S.
Published: April 2021

Cardiac responses of Portunus xantusii (Stimpson) (Crustacea: Decapoda) to simulated luminescent flashes were similar to responses to real flashes produced by the sea pansy Renilla kollikeri (Pfeffer). Tethering the crabs did not significantly affect cardiac responses to light flashes and allowed for more control over stimulus presentation. Crabs were maximally responsive to wavelengths from 500 to 510 nm (175 nm width at half-maximum response). The wavelength of maximal sensitivity based on the electroretinogram was 510nm. The critical fusion frequency for P. xantusii was 25·6 Hz. Pulse rate and train duration of light flashes were the most important features of the stimulus for eliciting maximal cardiac responses, with pulse duration and inter-pulse interval having minor effects on flash effectiveness. Pulse rates of 4–5 Hz within a train elicited the largest cardiac responses. Increases in train duration from 1 to 5 s resulted in a linear increase in heart response, but stimuli with train durations longer than 5 s did not elicit concomitant increases in heart response. Habituation to pairs of stimulus trains occurred if inter-train intervals were less than 8–10 min. The characteristics of the luminescent signals produced by benthic invertebrates are well matched to the characteristics of light stimuli that are most effective at eliciting physiological and behavioral responses from Portunus xantusii.
Mechanics of Forward Flight in Bumblebees: II. QUASI-STEADY LIFT AND POWER REQUIREMENTS
Authors: Dudley R. , Ellington C. P.
Published: April 2021

This paper examines the aerodynamics and power requirements of forward flight in bumblebees. Measurements were made of the steady-state lift and drag forces acting on bumblebee wings and bodies. The aerodynamic force and pitching moment balances for bumblebees previously filmed in free flight were calculated. A detailed aerodynamic analysis was used to show that quasi-steady aerodynamic mechanisms are inadequate to explain even fast forward flight. Calculations of the mechanical power requirements of forward flight show that the power required to fly is independent of airspeed over a range from hovering flight to an airspeed of 4·5ms−1.
Influence of organic phosphates on the root effect of multiple fish haemoglobins
Authors: Pelster Bernd , Weber Roy E.
Published: April 2021

The influence of organic phosphates on the reduction in oxygen-carrying capacity at low pH (Root effect) in multiple fish haemoglobins has been analysed spectrophotometrically. In stripped haemolysates of carp, trout and eel, the Root effect in the presence of ATP was manifested below pH 7.0. In the absence of phosphates, it was only found in trout haemolysate.

In the pH range between 8.5 and 6.1 no Root effect could be induced in the cathodic component (Hbl) of either trout or eel haemoglobin, even in the presence of very high concentrations of ATP or GTP. This was also true for component II (Hbll) of trout. The anodic component (HblV) of both species, however, exhibited a strong Root effect potentiated by NTP. At the same NTP/Hb4 concentration ratio, GTP was much more effective than ATP in both species.

The involvement of different haemoglobin components in the generation of high oxygen tensions in the fish swimbladder is discussed by comparing in vivo Root effect data obtained with an eel swimbladder preparation with in vitro data measured in eel blood and haemoglobin.
Effect of temperature on cardiac vagal action in the toad Bufo marinus
Authors: Courtice G. P.
Published: April 2021

The effect of temperature on the action of the vagus nerve on the heart was studied in the toad Bufo marinus. Experiments were performed on two groups of toads, in one the heart was perfused at a constant rate with oxygenated Ringer’s solution and in the other the circulation was left intact. In all toads there was a linear relationship between pulse interval (PI) and the frequency of vagal stimulation (fv) at any one temperature. The slope of this relationship changed with temperature, the effectiveness of the vagus (ΔPI/Δfv) increasing with decreasing temperature. At low temperatures the vagus nerves of intact toads were more effective than in those with perfused hearts. It is suggested that, in intact toads at low temperatures, cardiac output decreases and the consequent accumulation of acetylcholine leads to increased vagal effectiveness.
Effect of sprint training on swim performance and white muscle metabolism during exercise and recovery in rainbow trout (Salmo Gairdneri)
Authors: Pearson M. P. , Spriet L. L. , Stevens E. D.
Published: April 2021

Experimental fish were sprint trained by individual chasing for 30 s on alternate days for 9 weeks. Ten trained and 10 untrained animals were rapidly freezeclamped at rest and 0,1, 3 and 6h after a 5-min chase. Swimming speed of 10 fish in each group was measured in a 2-min chase. Phosphocreatine (PCr), creatine, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), glycogen, glucose-l-phosphate (G-l-P), glucose-6-phosphate (G-6-P), fructose-6-phosphate (Fru-6-P), glucose, glycerol-3-phosphate (Glyc-3-P), pyruvate and lactate were measured on extracts from freeze-dried white muscle. Trained fish swam 14% further in 2 min, with 90% of this difference occurring between 20 and 50 s. Trained fish accumulated 32% more lactate, but showed no differences in glycogen or PCr depletion, and 22 % less ATP depletion, suggesting increased use of exogenous glucose. Glycogen repletion in early recovery, and lactate clearance between 1 and 3h after exercise, were also enhanced in trained fish. Energy stores (ATP equivalents) were higher after exercise and especially during recovery in trained fish. Overall, sprint training minimizes endogenous fuel depletion during exhaustive swimming, even though swim speed (and distance) increases, and enhances the rate of metabolic recovery following the swim.
The Absorption Of Chloride Ions By The Anal Papillae Of Diptera Larvae
Authors: Koch H. J.
Published: April 2021

Until recently the respiratory function of the anal papillae of Diptera larvae was unquestioned; they were generally called “anal gills”. There has been, however, much discussion concerning the part played by these organs in the uptake of oxygen. Using Protozoa as indicators of oxygen tension, Fox (1920) proved that the uptake of oxygen was only slightly, if at all, higher in these organs than in the other parts of the skin. Wigglesworth (1933a) investigated, by the same method, the respiratory uptake in Aedes and obtained similar results.
Experimental Studies On The Sexual Cycle Of The South African Clawed Toad (Xenopus Laevis). I
Authors: Alexander S. S. , Bellerby C. W.
Published: April 2021

Retrogression of the ovaries of Xenopus laevis occurs if toads are kept for long periods in an insufficient volume of water. Atrophy takes place in spite of regular feeding and change of water and occurs more frequently and to a greater extent than in toads which are underfed. Overcrowding is followed by a diminution in food intake; the weekly consumption of food being halved in the case of females subjected to the maximum population density. Under natural conditions the seasonal decrease in water volume of the ponds in which Xenopus lives may induce or at least contribute to the maintenance of the retrogressive phase of ovarian activity which normally occurs.
The Respiration of Insects Through the Skin
Authors: Fraenkel Gottfried , Herford G. V. B.
Published: April 2021

When blowfly larvae are paralysed by ligaturing behind the ganglion the resultant respiration of the hind parts represents the basal metabolism of the animal. When the hind spiracles are also ligatured off, all respiration takes place by diffusion through the skin and is about one-quarter of the basal value. The R.Q. of the twice-ligatured larvae is 1 · 34. This indicates that part of the metabolic processes are maintained by anaerobic respiration. The O2 tension inside the larvae has been measured and is about 15% inside the normal larvae and 2 · 4% inside the double-ligatured larvae. Therefore a much larger amount of oxygen diffuses through the skin in the double-ligatured than in the normal larvae, and it has been found by calculation for the normal larva to be one-tenth of the basal value. When insects are submerged in water their spiracles are not able to function and all respiration takes place by diffusion through the skin. In the normal blowfly respiration is independent of the O2 tension from 100 % O2 down to about 7 · 5 %, whereas in the double-ligatured larvae it is entirely dependent on the oxygen tension. Experiments with other insects, Chaerocampa elpenor larvae (spiracles blocked with grease), Tenebrio molitor larvae and Culex sp. larvae (submerged in water), gave results similar to those obtained with the blowfly larvae.
The Reorganization of Tissue Masses ofCordylophora Lacustrisand the Effect of Oral Cone Grafts, with Supplementary Observations onObelia Gelatinosa
Authors: Beadle L. C. , Booth F. A.
Published: April 2021

A method is described for the preparation of reconstitution masses from the expressed coenosarc tissues of Cordylophora lacustris. This brackish water hydroid is more suitable for the purpose than others which have so far been used. Under normal conditions (50 % sea water at 16–17° C.) such masses produce one or more hydranths within about 2 days and often additional unorganized outgrowths. The main histological features of the reconstitution masses as seen in sections are described. From these observations and from experiments with masses made from isolated ectoderm and endoderm it is concluded that there is no reduction of the cells to a pleuripotent condition. The cells of each original layer can form only the layer from which they were derived. Masses made from endoderm cells only are incapable of holding together for long and soon disintegrate. Pure ectoderm masses, however, rapidly round up and form hollow vesicles but do not produce hydranths. No signs of cell division during reconstitution were detected. The “interstitial” cells observed in the coenosarc ectoderm are thus not able to differentiate into endoderm when this is absent and there is no indication that they perform any essential part in the process of reconstitution. An oral cone when grafted into a mass will determine the position of the regenerated Hydranth which develops in relation to the graft. Evidence is given to prove that the action of the cone is one of pure induction and that it does not supply cells to the induced hydranth. The action of the cone is independent of its orientation and it will produce its effect even after previous chopping up and reuniting. Attempts to graft killed oral cones have so far failed. Grafts of distal halves of young gonophores do not induce hydranths. Calcium or magnesium deficiency in the medium results in complete suppression of hydranth formation from masses but not always of unorganized outgrowths. Oral cone grafts, however, can overcome this inhibition and tentacles are formed. A similar inhibitory effect is produced by potassium deficiency, but is not overcome by an oral cone graft. The quantity of calcium required to permit tentacle formation in plain masses is very small (c. 0·00006 M). Sodium cyanide (c. M/30,000), phenyl urethane (c. M/3000) and low temperature (5·5–0·5° C.) can inhibit hydranth formation in plain masses, but oral cone grafts overcome this inhibition and induce the formation of tentacles. Reconstitution masses which produced hydranths were also made from the coenosarc of another brackish water hydroid Obelia gelatinosa. Isolated ectoderm and endoderm were incapable of reorganization. Mixed masses of Cordylophora and Obelia coenosarc separated into regions composed of tissue from one species only and each produced hydranths independently.
The Double Innervation of Muscles in the Clam (Mya Arenaria)
Authors: Pumphrey R. J.
Published: April 2021

It is a matter of common observation that lamellibranch molluscs may close the valves of their shell by a fairly rapid twitch-like contraction of the adductor muscles, and may thereafter in certain circumstances relax the adductors, immediately allowing the valves to gape, while in other circumstances these muscles may be maintained for a considerable time in the shortened state even when large tensions are applied to the valves.
An Apparatus for Measuring the Propulsive Forces of the Locomotory Muscles of the Earthworm and Other Animals
Authors: Gray J. , Lissmann H. W.
Published: April 2021

A complete picture of the locomotory mechanism of any animal involves a knowledge of the forces required to overcome the external resistance of the animal’s environment. In the case of certain terrestrial animals (the earthworm in particular) it is possible to measure these forces by means of a modified form of the apparatus originally designed by one of us (H. W. L.) for the study of locomotion of the snail.
A Syringe Pipette Method for the Determination of Oxygen in the Field
Authors: Whitney R. J.
Published: April 2021

The method usually employed for the determination of oxygen in natural waters is that described in Standard Methods of Water Analysis (1925). The basis of this method is the Winkler chemical method for the estimation of dissolved oxygen. A sample of the water to be examined is collected in a bottle of about 250 c.c. capacity. The usual Winkler reagents are added and the iodine liberated is titrated against a standard sodium thiosulphate solution. The amount of oxygen originally present in the sample can then be deduced.1
Aspects of Shark Swimming Performance Determined Using a Large Water Tunnel
Authors: Graham Jeffrey B. , Dewar Heidi , Lai N. C. , Lowell William R. , Arce Steve M.
Published: April 2021

A large, sea-going water tunnel was used in various studies of shark swimming performance. The critical swimming velocity (Ucrit, an index of aerobically sustainable swimming speed) of a 70 cm long lemon shark (Negaprion brevirostris Poey) was determined to be 1.1 Ls−1, where L is body length. The Ucrit of the leopard shark (Triakis semifasciata Girard) was found to vary inversely with body size; from about 1.6Ls−1 in 30–50cm sharks to 0.6Ls−1 in 120cm sharks. Large Triakis adopt ram gill ventilation at swimming speeds between 27 and 60cms−1, which is similar to the speed at which this transition occurs in teleosts. Analyses of tail-beat frequency (TBF) in relation to velocity and body size show that smaller Triakis have a higher TBF and can swim at higher relative speeds. TBF, however, approaches a maximal value at speeds approaching Ucrit, suggesting that red muscle contraction velocity may limit sustained swimming speed. The TBF of both Triakis and Negaprion rises at a faster rate with swimming velocity than does that of the more thunniform mako shark (Isurus oxyrinchus Rafinesque). This is consistent with the expectation that, at comparable relative speeds, sharks adapted for efficient swimming should have a lower TBF. The rates of O2 consumption of swimming lemon and mako sharks are among the highest yet measured for elasmobranchs and are comparable to those of cruise-adapted teleosts.
The Role of Magnetic Statoconia in Dogfish (Squalus Acanthias)
Authors: Hanson M. , Westerberg H. , Öblad M.
Published: April 2021

Mineralogical and magnetic properties of the otolithic mass in the sacculus of dogfish, Squalus acanthias, were investigated. The endogenous statoconia were found to be either rhombohedral crystals of calcite or spherical particles of other calcium carbonate polymorphs. From 20 to 60% of the total otolithic mass consisted of exogenous material, sea sand, which had a high content of heavy mineral particles, some of which were magnetic. The concentration of the heavy particles was greater than that typically found in marine sand, and it is proposed that this could result from a separation process in the endolymphatic duct.

A calculation of the acceleration of the otolithic mass in the sacculus caused by the geomagnetic field showed that the maximum linear acceleration due to magnetic forces would be one or two orders of magnitude smaller than the minimum sensitivity to acceleration in the auditory frequency range. This makes it unlikely that the magnetic particles are involved in detection of the geomagnetic field.

The exogenous material raises the mass and density of the otolithic mass in the sacculus, thus increasing the sensitivity of this otolith organ.
Influence of input from the Forewing Stretch Receptors on Motoneurones in Flying Locusts
Authors: Pearson K. G. , Ramirez J. M.
Published: April 2021

Previous studies on the forewing stretch receptors (FSRs) of locusts have suggested that feedback from these receptors during flight contributes to the excitation of depressor motoneurones and reduces the duration of depolarizations in elevator motoneurones. We have investigated these proposals by measuring the timing of FSR activity relative to depressor activity and by examining the effects of stimulating the FSRs on the membrane potential oscillations in flight motoneurones. Activity in the FSRs was recorded in tethered intact animals flying in a windstream and in preparations that allowed intracellular recordings from motoneurones during flight activity. The timing of FSR activity was similar in both preparations. In most animals we observed that at normal wingbeat frequencies (about 20 Hz) the activity in the FSRs commenced after the onset of activity in the wing depressor muscles. As wingbeat frequency declined there was a progressive advance of FSR activity relative to depressor activity. Most of the spikes in each burst of FSR activity occurred during the time that the membrane potential in depressor motoneurones was repolarizing. Electrical stimulation of the FSRs timed to follow the onset of depressor activity slowed the rate of repolarization, decreased the peak hyperpolarization and increased the rate of the following depolarization in depressor motoneurones. In elevator motoneurones, the same pattern of FSR stimulation produced an additional excitatory input during the depolarization phase and, at low wingbeat frequencies, reduced the duration of the peak depolarizations. The reduction in the duration of the peak depolarization in elevator motoneurones was not strongly correlated to the reduction in cycle period. We propose that the primary reason why input from the FSRs increases wingbeat frequency is because this input reduces the degree of hyperpolarization in depressor neurones and thus promotes an earlier onset of the next depolarization in these neurones.
The Effects of Reducing Water pH and Total CO2 on a Teleost Fish Adapted to an Extremely Alkaline Environment
Authors: Wright P. A. , Perry S. F. , Randall D. J. , Wood C. M. , Bergman H.
Published: April 2021

The teleost fish Oreochromis alcalicus grahami is well adapted to an extremely alkaline environment (pH 10, total CO2 184 mmol I−1) in Lake Magadi, Kenya. O. a. grahami excretes all nitrogenous wastes as urea, and exposure to neutral water (pH7, total CO2<1mmol l−1) results in a complete inhibition of urea excretion. In the present study, we further characterized the physiological effects of transferring O. a. grahami from alkaline to neutral water. Exposure to neutral water resulted in a significant decrease in blood pH, a large reduction in plasma HCO3− levels, a severe impairment of swimming ability, an increase in Na+ influx, but no change in O2 consumption. A closely related species of tilapia, O. nilotica, living in neutral waters of the Sagana River, was relatively unaffected by acute exposure to tapwater at pH 10, but showed a marked alkalosis in Lake Magadi water prior to death. These results demonstrate that O. a. grahami thrive in an environment of high pH and bicarbonate/carbonate concentration, conditions that are fatal to other species adapted to neutrality. O. a. grahami, however, is extremely unusual amongst aquatic animals in its adverse response to neutral water.
Reduction in extrasynaptic acetylcholine sensitivity of axotomized anterior pagoda neurones in the leech
Authors: Bigiani A. , Pellegrino M.
Published: April 2021

The effects of axotomy on the sensitivity of the leech anterior pagoda (AP) neurone to acetylcholine (ACh) and carbamylcholine (CCh) have been studied 1–5 days after axon interruption. Hyperpolarizing responses to ionophoretically applied ACh and CCh have been recorded intracellularly from desheathed cell bodies of normal and axotom-ized neurones. The electrical properties of the membrane have also been measured in the same neurones. Axotomy produced a progressive loss of sensitivity to both ACh and CCh with a similar percentage reduction. No significant changes have been found in the time to peak and in the reversal potential of the responses to agonists, or in the number of drug molecules needed to combine with a single receptor to produce a response. Interruption of nerve roots and connectives which do not contain the AP axon did not induce the alterations of ACh sensitivity observed after axotomy. It is concluded that the loss of ACh sensitivity following axotomy is due to a reduction in density of functional ACh receptors (AChRs).
A Possible Role for Catecholamines in the Ventilatory Responses Associated with Internal Aciosis or External Hypoxia in Rainbow TroutOncorhynchus Mykiss
Authors: Aota S. , Holmgren K. D. , Gallaugher P. , Randall D. J.
Published: April 2021

Plasma catecholamine levels and gill ventilation were measured in rainbow trout (Oncorhynchus mykiss) during acidosis and hypoxia. There was an increase in both plasma catecholamines and ventilation correlated with the acidosis. Fish exposed to hyperoxia prior to acid infusion did not show significant changes in catecholamines or ventilation. Those treated with the β-adrenergic antagonist propranolol before acidosis showed increases in catecholamines but not ventilation. Hypoxia was also associated with increases in endogenous catecholamines and ventilation, and the increase in ventilation could be partially blocked with propranolol. This increase in ventilation during hypoxia was not inhibited by a saline injection alone. It is proposed that catecholamines act to modulate ventilatory responses in fish under both acidotic and hypoxic conditions. If a central H+ chemoreceptor exists in fish to control breathing, it can be inhibited by hyperoxia or by β-receptor blockade.
Characteristics of neurones projecting from the supraoesophageal ganglion in the shadow reflex pathway of the barnacle
Authors: Gwilliam G. F. , Stuart A. E.
Published: April 2021

Barnacles respond to decreases in light intensity (shadows). Previous evidence indicates that the first stages of the visual pathway within the supraoesophageal ganglion comprise a limited number of neurones: a single pair of second-order neurones (I-cells), a pair of third-order projection neurones (A-cells), and at least five other projection neurones (four A-like shadow-excited cells and one shadow-inhibited cell) whose spikes may be recorded extracellularly from the circumoesophageal connective nerve. Here we present evidence that information in this pathway diverges at the A-cell stage. Destruction of both A-cells by intense illumination of cells injected with carboxyfluorescein abolishes all shadow-evoked activity in the connectives and also the ability of shadows to influence motor neurones in the ventral ganglion.

In addition, we have located the somata of these previously unidentified projection neurones, injected them with carboxyfluorescein, and observed that they have distinct branching patterns different from that of the A-cell. We name these cells ‘alpha’ (α), ‘beta’ (β) and ‘gamma’ (γ) cells. Simultaneous impalements show that A-cells drive at least one of the β-cells but not vice versa. The same observation has not yet been made with regard to α- or γ-cells. Depolarizing an I-cell does not readily drive a β-cell impaled simultaneously. These observations support our conclusion that information diverges from the A-cells and not from the second-order I-cells to the other projection neurones in this ganglion.
Activity-dependent and age-dependent recruitment and regulation of synapses in identified Crustacean Neurones1
Authors: Atwood H. L. , Govind C. K.
Published: April 2021

Adaptation of neural systems to altered activity and age often involves recruitment, inactivation or modification of synapses. Crustacean motor systems are amenable to experimental investigation of these processes. They possess large identifiable neurones that can be observed over long periods during development, adulthood, regeneration and degeneration. Numerous small individual synapses are present on the transmitting terminals of the motor neurones; their ultrastructural features are non-uniform, indicating different degrees of functional potency. Ultrastructural studies show many more individual synapses than required for maximal quantal output; probably some are ineffective, but can be brought into a transmitting state in a short time by neural activity. During development, progressive reorganization and relocation of synapses take place. As the size of a postsynaptic target changes, synapses are added, and functionally adaptive alterations in quantal content and quantal effectiveness occur. Sectioning an axon results in slow degeneration of distal processes, but transmission is sustained for months. Short-term adjustments in number of effective synapses occur in response to altered activity. If activity of a neurone is chronically increased or decreased, characteristic semi-permanent adaptations in physiology and ultrastructure are seen. Synaptic transmission at low frequencies is down-regulated, while resistance to synaptic depression increases. These effects require protein synthesis, and at least two different changes - one related to down-regulation of synapses, the other related to fatigue resistance - can be selectively demonstrated through critically timed interruption of axoplasmic transport or imposition of different patterns of neural activity. In older animals, the ability to adapt to activity is reduced in some neurones, but may be restored during regeneration of neural processes. Selective changes in activity in one of several neurones innervating a common postsynaptic target lead to adaptive changes in synaptic transmission of non-active neurones, indicating activity-mediated interaction and adjustment. Mechanisms of adaptation similar to those outlined here probably occur in nervous systems of other species.
Cell recognition and pattern formation in the developing nervous system
Authors: Trisler David
Published: April 2021

Laboratory of Biochemical Genetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.

The topographic map of cell position in the avian retina is conserved and inverted when retinal ganglion neurons synapse with neurons in the optic tectum. Developmental mechanisms based on molecular gradients that specify positional information and pattern formation have been postulated in the establishment of these topographic maps of cells in retina and optic tectum. Two cell surface proteins in retina, TOPDV and TOPAP, are distributed in dorsoventral and anteroposterior topographic gradients, respectively. Corresponding gradients of TOP molecules present in the tectum are inverted with respect to the retinal gradients. These orthogonal gradients of TOPDV and TOPAP molecules provide a possible Cartesian coordinate system for designation of cell position at all points in the retinotectal map.