bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological significance of behavioral hypothermia in hypoxic toads (Bufo marinus)
Authors: Wood S. C. , Malvin G. M.
Published: April 2021

We tested the hypotheses that hypoxic toads (Bufo marinus) in a thermal gradient would select a lower than normal temperature and that this behavioral response would be beneficial. Under normoxic conditions, selected body temperature was 24.2 +/− 3.6 degrees C. When inspired O2 was 10% or less, mean selected temperature decreased to 15.3 +/− 2.4 degrees C. The theoretical advantages of hypoxia-induced hypothermia we tested include (1) a reduction of oxygen uptake (VO2) by a Q10 effect; (2) increased arterial saturation (SaO2), (3) a decreased ventilatory response, and (4) a decreased stress response. Gas exchange, hematocrit, hemoglobin, SaO2, PaO2 and pH were measured at 25 degrees C (normal preferred temperature) and 15 degrees C (hypoxia preferred temperature) in toads breathing normoxic or hypoxic gas mixtures. During graded hypoxia at 15 degrees C, SaO2 was significantly increased and VO2 was significantly reduced compared with 25 degrees C. Graded hypoxia did not significantly affect VO2 at 25 degrees C, despite evidence for increased ventilation at that temperature (increased pH and respiratory exchange ratio, RE). At 15 degrees C, graded hypoxia had a significant effect on VO2 only at an inspired O2 of 4%. Increased RE with hypoxia was significant at 25 degrees C but not at 15 degrees C. Hematocrit and [hemoglobin] rose significantly during graded hypoxia at 25 degrees C but did not change at 15 degrees C. Toads exposed to 10% O2 (the value that elicits behavioral hypothermia) showed a significant respiratory alkalosis at 25 degrees C but not at 15 degrees C. Likewise, hypoxia caused a significant drop in SaO2 and PO2 at 25 degrees C. Cooling to 15 degrees C during hypoxia caused a significant rise in SaO2 but no change in PaO2. In conclusion, behavioral hypothermia is a beneficial response to hypoxia in Bufo marinus.
Effect of Load on Leg Movement and Step Coordination of the Stick Insect Carausius Morosus
Authors: DEAN JEFFREY
Published: April 2021

A treadwheel mounted on a torque motor was used to study changes in step coordination as a function of the magnitude and direction of external forces resisting and assisting leg retraction. The apparent contradiction in the literature concerning the shift in the posterior extreme point is shown to depend upon the magnitude of the load. External forces resisting leg retraction generally shift step end-points rostrally and those assisting leg retraction shift them caudally, shifting leg movement so that the active muscles can provide greater force. However, this primary trend reverses for external forces equivalent to or less than the weight of the body. Together, these results indicate that the decision to end stance does not simply depend upon the leg's loading but rather on its efficiency in contributing propulsion. As expected, loads resisting leg retraction decrease retraction speed and increase step period. They also decrease protraction speed, increase swing duration and shift phase relationships of adjacent ipsilateral legs away from alternation towards a metachronal pattern. Moderate to large assisting loads evoke similar changes: they increase swing duration less but shift the phase of middle and rear legs more than the corresponding resisting loads. Thus, by itself, a reduction in the force required during retraction does not transform the gait from metachronal to tripod. The mean phase of contralateral leg pairs is unaffected by load: these legs continue to alternate.
Identification of a Basolateral Membrane Potassium Channel from Teleost Intestinal Epithelial Cells
Authors: LORETZ CHRISTOPHER A. , FOURTNER CHARLES R.
Published: April 2021

Using patch-clamp techniques, a Ca2+-dependent, voltage-gated K+ channel [K(Ca) channel] was isolated from the basolateral membrane of NaCl-absorbing intestinal epithelial cells of the goby Gillichthys mirabilis. This K(Ca) channel had a high conductance (approximately 150 pS) in the physiological range of membrane potential. Conclusive identification as a K+ channel is supported by dependence of the reversal potential for single-channel current on the K+ concentration gradient and the ability of Ba2+, Cs+ and other pharmacological agents to block the channel. The channel was highly selective for K+ over Na+ (PNa/PK=0.04). Channel activity, expressed as open probability (Po), was dependent on membrane potential with depolarization increasing Po over the physiological range in the presence of Ca2+. Channel activity was also dependent on cytoplasmic-side Ca2+. Po was reduced to near-zero levels following EGTA chelation of Ca2+ in the solution bathing the cytoplasmic face of excised membrane patches; channel activity was most sensitive to changes in Ca2+ concentration between 10nmoll−1 and 10μmoll−1. This K(Ca) channel may be one of several avenues for K+ exit across the basolateral cell membrane and, as such, may play roles in both transepithelial salt transport and maintenance of intracellular ionic composition.
New Experiments on Colour Vision in Bees
Authors: Hertz Mathilde
Published: April 2021

Under the condition of full, normal daylight illumination a surface which reflects a fair proportion of ultra-violet, as well as the visible spectrum, is neutral or white in the vision of the bee. If the percentage of reflexion of 3600 A. is less than one-third, or about one-quarter, of the percentage of reflexion in the visible light, a degree of coloration is obtained which is sufficient to be noticed by the bees in training experiments.

When both are placed under ultra-violet absorbing filters, white paper in the vision of the bee most closely resembles a blue-green paper that possesses the highest amount of reflexion at 4900 A. Bees which have been trained to visit a blue-green surface covered by a filter glass do not do so any longer, if, by removing the filter, ultra-violet fight is added to the reflexion. The paper that possesses now two peaks of maximum reflexion, one at 4900 and the other at 3600 A., appears a light grey to the bee. On the other hand, when bees have been trained to visit an ultra-violet surface—white paper under a filter that absorbs the visible light completely—do not do so any longer if by lifting the filter the whole range of visible light is added to the reflexion of ultra-violet. The white paper at once becomes unattractive to the bee.

There remains no doubt, that among the four qualities of colour discriminated by the bee (see Fig. 1) the first and the third on one side and the second and fourth on the other are complementary colours for this insect and presumably for many others.

In the European flowers visited by bees three principal colours are now finally known: (1) that colour which is perceived if the main bulk of light reflected by the petals lies between 6500 and 4900 A. (orange-yellow for bee and man), (2) that which is perceived if the reflexion’extends from 4900 to 4000 or 3500 A. (blueviolet for bee and man), and (3) that which is perceived if the reflexion extends from 6500 A., or nearer to the red end of the visible spectrum, to 4000 A. (blue-green for the bee, but white, pink, light purple, bluish or yellowish for man).

Ultra-violet seems never to occur in European flowers in such a way as to make petals which are brilliantly white for man to appear equally white for the bee.
The Physiology of Contractile Vacuoles
Authors: Kitching J. A.
Published: April 2021

In peritrich ciliates many food vacuoles without visible solid contents may be formed. The water in these vacuoles passes into the general cytoplasm. In fresh-water Peritricha the rate of uptake of fluid in food vacuoles generally amounts to between 8 and 20% of the rate of output of fluid by the contractile vacuole. The greater part of the water evacuated is presumed to enter the animal by osmosis through the general body surface. In marine Peritricha the rate of uptake of fluid by food vacuoles approximately balances the rate of output by the contractile vacuole. The elimination of the water taken in by food vacuoles is believed to be the main function of the contractile vacuole in marine ciliates.
Chemical Mediation in Crustaceans
Authors: Welsh John H.
Published: April 2021

A heart-accelerating principle for crustaceans which had been found in extracts of their eye-stalks is shown not to be identical with the chromatophorotropic hormone, and is present in nerve tissues other than those of the eye. Extracts of muscle have an inhibitory action on the various hearts. Excess potassium stimulates the action of nerve extracts but it is not present in them in sufficient amounts to be responsible for their effects. Adrenalin excites the crustacean heart but it is probably not the nerve substance in question. Acetylcholine excites this heart and in various concentrations produces a series of effects very similar to those produced by nerve extracts. By appropriate extraction methods and methods of bioassay relatively large amounts of acetylcholine were found in crustacean nerve tissues ; more being present in ganglia than in nerve fibres. Hence the active principle in question is, with little doubt, acetylcholine.
Studies on the Growth of Tissues in Vitro
Authors: Pomerat C. M. , Willmer E. N.
Published: April 2021

In a previous paper of this series (Trowell & Willmer, 1939) an account was given of the effects on the growth of chick periosteal fibroblasts of the addition of saline extracts of various organs from the growing and fully grown bird. Attention was called to the fact that those organs and tissues which yielded growth-promoting extracts were just those which have been shown by Warburg and his school (Warburg, 1930) to possess considerable powers of glycolysis. The parallelism is illustrated in Fig. 1. In the upper series are plotted the mean mitotic indices for the fibroblast cultures during the period from the tenth to the twentieth hour after the addition of the tissue extracts, at which time the effects produced by such extracts have been shown to be most comparable. In the lower series, the anaerobic glycolytic activities, as measured by lactic acid production, of the corresponding tissues are plotted. Comparison of these two sets of figures at once suggests that the organ extracts may exert their effects by influencing the carbohydrate metabolism of the tissues to which they are applied. The only apparent exception is the thyroid, and the effects of extracts of that organ on the growth of cultures were very variable and probably other factors were involved.
The Function of the Gills of Mayfly Nymphs from Different Habitats
Authors: Wingfield C. A.
Published: April 2021

The oxygen consumption of normal and gill-less nymphs of the mayflies Baetis sp., Cloeon dipterum and Ephemera vulgata has been measured at various oxygen concentrations. It has been found that over the complete range of oxygen concentrations studied, the tracheal gills do not aid oxygen consumption in Baetis sp. In Cloeon dipterum, at all oxygen concentrations tested, no gaseous exchange takes place through the gills ; at low oxygen concentrations, however, the gills function as an accessory respiratory mechanism in ventilating the respiratory surface of the body and so aid oxygen consumption. In Ephemera vulgata the gills aid oxygen consumption even at high oxygen concentrations. In this species the gills may function both as true respiratory organs and as a ventilating mechanism. It is shown that the differences in gill function can be related to the oxygen content of the habitat of each species.
The Thermal Resistance of Mayfly Nymphs from Ponds and Streams
Authors: Whitney R. J.
Published: April 2021

Temperature is a factor of great importance in determining the distribution of animals. There are many references in ecological literature to a correlation between distribution of animals and the temperature conditions prevailing in the habitats occupied by the animals. Particular instances of this correlation are the distribution of stream turbellarians (Steinmann, 1906; Thienemann, 1913) and the effects of abnormal temperature conditions on local faunas (Allee, 1923; Stephens, 1938). The great significance of temperature to the animals themselves is shown by the many physiological studies of its action on living matter (Bélehrádek, 1935), and is also evident in the ecologists’ use of the terms stenotherm and eurytherm. This correlation between temperature and distribution has rarely, however, been investi-gated from the experimental standpoint. One line of approach has been the experimental investigation of the thermal resistances of animals from different habitats.
An Identifiable Molluscan Neuron Responds to Changes in Earth-Strength Magnetic Fields
Authors: Lohmann Kenneth J. , Willows A. O. Dennis , Pinter Robert B.
Published: April 2021

Diverse animals can orient using geomagnetic cues, but little is known about the neurophysiological mechanisms that underlie magnetic field detection. The marine mollusc Tritonia diomedea (Bergh) has a magnetic sense and its nervous system is amenable to cellular-level electrophysiological analysis. In a semi-intact whole-animal preparation, intracellular recordings from the large, visually identifiable neurons left pedal 5 (LPe5) and right pedal 5 (RPe5) in the brain of Tritonia revealed enhanced electrical activity in response to changes in ambient earth-strength magnetic fields. No such changes in activity were observed in approximately 50 other neurons subjected to identical magnetic stimuli. The responses of LPe5 were characterized by increases in spiking frequency occurring about 6–16 min after the ambient magnetic field had been rotated to a new position. The response was abolished when the brain had been isolated from the periphery of the animal by severing nerves, a procedure that also transected prominent neurites of LPe5. We hypothesize that LPe5 is one component of a neural circuit mediating detection of the earth’ s magnetic field or orientation to it.
Evidence for the Presence of an Electrogenic Proton Pump on the Trout Gill Epithelium
Authors: Lin Hong , Randall David
Published: April 2021

Ion transport inhibitors, amiloride, SITS, vanadate and acetazolamide, were added to the water to determine the effect of ion transfer mechanisms on the acidification of water passing over the gills. In neutral water, proton excretion causes a marked reduction in gill water pH. If water pH is 2.5 units lower than blood pH, however, then this proton excretion is inhibited and all water pH changes can be accounted for by CO2 hydration and ammonia protonation. Proton excretion across the gills is insensitive to 0.1 mmol l−1 amiloride and SITS but sensitive to vanadate, acetazolamide and water pH; thus, we conclude that proton excretion is mediated by an active proton pump on the apical membrane of the gill epithelium similar to that reported for the frog skin. Higher concentrations of amiloride (0.5 and 1 mmol l−1) reduced both ammonia and acid excretion, presumably because of inhibition of Na+/K+-ATPase on the basolateral border of the gill epithelium.
The Initial Orientation of Homing Pigeons at the Magnetic Equator: Compass Mechanisms and The Effect of Applied Magnets
Authors: Ranvaud Ronald , Schmidt-Koenig Klaus , Ganzhorn Jörg U. , Kiepenheuer Jakob , Gasparotto Odival C. , Britto Luiz R. G.
Published: April 2021

Homing pigeons are thought to use the earth’s magnetic field for direction finding. Though the sensory system and the characteristics of the magnetic field used are unknown, it can be hypothesized that pigeons have an inclination compass, as do some migratory birds. When released at the magnetic equator, this inclination compass ought to be suspended. In addition, releasing pigeons when the sun is at or very close to the zenith renders the sun compass inoperational. However, released under these conditions, homing pigeons are not disorientated. Though they vanish on average in a different direction from pigeons released when the sun compass is available, they still show a directional preference close to magnetic north. This directional preference could be disrupted in some years by the application of magnets to the pigeons’ back. In other years this treatment as well as another magnetic treatment did not produce any difference between experimental pigeons and controls. These results confirm once more that, if magnetic effects exist, they are of a rather discrete nature.
The Effects of Branchial Denervation and Pseudobranch Ablation on Cardioventilatory Control in an Air-Breathing Fish
Authors: McKenzie David J. , Burleson Mark L. , Randall David J.
Published: April 2021

The role of sensory afferent information from the gills of Amia calva in cardiovascular and ventilatory control was investigated by bilateral branchial denervation and pseudobranch ablation.

Aquatic hypoxia or 1 mg of sodium cyanide (NaCN) in the water flowing over the gills stimulated bradycardia, and gill and air ventilation in sham-operated fish. Sodium cyanide, noradrenaline (NA) and adrenaline (A) infusion into the dorsal aorta increased gill ventilation, and NA and A infusion also stimulated tachycardia and an increase in blood pressure.

Following denervation and pseudobranch ablation, O2 consumption (V˙O2) air-breathing frequency (fAB) and arterial O2 tension (PaO2) declined, and circulating NA levels increased, as compared with sham-operated fish. Cardiovascular and air-breathing responses to hypoxia were abolished and gill ventilatory responses attenuated. All ventilatory and cardiovascular responses to NaCN were abolished and gill ventilatory responses to NA and A were attenuated in animals following denervation and pseudobranch ablation.

These results demonstrate that O2-sensitive chemoreceptors in the gills and pseudobranch control reflex bradycardia and air-breathing responses in Amia, but that gill ventilatory responses to hypoxia, NA and A are partially mediated by extrabranchial mechanisms. Plasma NA levels increased during hypoxia in sham-operated and denervated animals, indicating that circulating NA may have mediated gill ventilatory responses in denervated animals.
Activities of Key Metabolic Enzymes in the Heater Organs of Scombroid Fishes
Authors: Tullis Alexa , Block Barbara A. , Sidell Bruce D.
Published: April 2021

Maximal in vitro activities of key metabolic enzymes were measured in brain and eye heaters of five species of scombroid fishes. Istiophorid billfishes (blue marlin, striped marlin and Mediterranean spearfish), xiphiid billfishes (Pacific and Mediterranean stocks) and a scombrid fish (butterfly mackerel) were included in the analysis. Our main objectives were (1) to assess the maximum possible substrate flux in heater tissue, and (2) to determine what metabolic substrates could fuel heat production. Heater tissue of all scombroids examined showed extremely high oxidative capacity. Activities of citrate synthase, a commonly measured index of oxidative metabolism, included the highest value ever reported for vertebrate tissue. In most billfishes, citrate synthase activities were similar to or higher than those found for mammalian cardiac and avian flight muscle. Marker enzymes for aerobic carbohydrate metabolism (hexokinase) and fatty acid metabolism (carnitine palmitoyltransferase and 3-hydroxyacyl-CoA dehydrogenase) also displayed extraordinarily high activities. Activities of carnitine palmitoyl-transferase measured in heater organs were among the highest reported for vertebrates. These results indicate that heat production could be fueled aerobically by either lipid or carbohydrate metabolism. Inter- and intraspecifically, heater organs of fishes from the colder Mediterranean waters had a higher aerobic capacity and, hence, a greater heat-generating potential, than fishes from the warmer waters of the Pacific. This difference may be attributed to different thermal environments or it may result from allometry, since fishes caught in the Mediterranean were considerably smaller than those caught in the Pacific.
Hydroid Stolonal Contractions Mediated by Contractile Vacuoles
Authors: Schierwater B. , Piekos B. , Buss L. W.
Published: April 2021

The growth and development of colonial hydroids is dependent upon a flow of gastrovascular fluid through a common vasculature. Gastrovascular flow is believed to be driven by polyp contractions, stolonal contractions and endodermal ciliation. In the athecate hydroid Hydractinia symbiolongicarpus we found that polyp contractions, stolonal contractions and gastrovascular flow were only weakly correlated on a local scale. Stolons isolated from vascular continuity to polyps were found to display contraction frequencies indistinguishable from those observed in intact colonies. Transmission electron micrographs reveal a unique organelle, with characteristics of a contractile vacuole, in the apical stolonal endoderm. The activity of this organelle, inferred from static observations, correlates with the observed pattern of stolonal contractions. This is the first record of a contractile vacuole in an eumetazoan animal. Its description calls for a revision of existing interpretations of the mechanism of stolonal contractions in hydroids.
Stiffness and Damping Forces in the Intervertebral Joints of Blue Marlin (Makaira Nigricans)
Authors: Long John H.
Published: April 2021

The stiffness and damping moments that are transmitted by intervertebral joints during sinusoidal bending were determined in the blue marlin, Makaira nigricans Lacépède. Using a dynamic bending machine, the angular stiffness (N m rad−1) and damping coefficient (kgm2 rad−2 s−1) of the intervertebral joints were measured over a range of bending frequencies, amplitudes and positions along the backbone. Angular stiffness increases with increasing bending amplitude, but, for some joints, the rate at which it changes with increasing bending frequency is negative. The precaudal intervertebral joints are less stiff than the caudal joints. The damping coefficient, which also shows regional variation, does not change with amplitude but does decrease with increasing bending frequency in joint positions three and five. Stiffness moments along the vertebral column, given the same amount of bending at each joint, are always greater than the damping moments. However, damping moments increase by an order of magnitude with an increase in bending frequency from 0.5 to 5.0Hz. The stiffness and damping moments determine the work that an external moment, such as muscle, must do over a complete cycle of bending. The external moments and work needed to bend an intervertebral joint are determined largely by the stiffness moments of the intervertebral joints.
Is the High Cost of Body/Caudal Fin Undulatory Swimming Due to Increased Friction Drag or Inertial Recoil?
Authors: Webb Paul W.
Published: April 2021

Deep-bodied fish, such as the bluegill sunfish (Lepomis macrochirus), are considered to have relatively larger wetted surface areas for their size than fusiform fish. On the basis of the boundary layer thinning hypothesis attributing high power requirements of undulatory swimming to enhanced friction drag, power (=drag) coefficients should be higher for such fish. Areas are typically normalized with total length, L, as L2 for comparison among species. Bluegill had a wetted surface area of 0.65 L2, compared with areas of about 0.41 L2 for trout of similar mass. However, absolute areas and volume2/3 of bluegill and trout were similar. Power requirements and power coefficients calculated from kinematics during steady swimming were lower for bluegill sunfish than for cruisers, such as trout, and power coefficients were also lower than those of accelerators, such as tiger musky. Large body depth also damps inertial recoil arising from the side force generated largely by the tail. Inertial energy losses appear to be more important contributors than friction to mechanical power requirements.
A Time-Dependent Excitability Change in the Soma of an Identified Insect Motoneurone
Authors: Hancox Jules C. , Pitman Robert M.
Published: April 2021

Long-term, current-clamp recordings were made from the cell body of the fast coxal depressor motoneurone (Df) of the third thoracic ganglion of the cockroach Periplaneta americana. In freshly dissected preparations the response to short-duration, suprathreshold, depolarising current pulses was a graded series of damped membrane oscillations similar to those reported previously in this neurone. The response to current injection changed, however, with increasing time after setting up the preparation: cells developed the ability to exhibit all-or-none action potentials. Their amplitude, however, was usually insufficient to overshoot 0mV. Our observations suggest that the enhancement in excitability is dependent on time following dissection rather than on time following impalement.

Recordings taken from neurone somata mechanically divided from their processes indicated that the time-dependent changes in excitability were not attributable to changes in synaptic input to the neurone and, moreover, that the cell body was involved in action potential genesis. The action potentials were resistant to treatment with the sodium channel blocker tetrodotoxin (up to 10−5moll-1), but were reversibly abolished when preparations were bathed in saline containing cadmium ions (1 mmol l-1) or manganese ions (20 or 40mmoll-1) and, therefore, the inward current underlying these events was largely, if not entirely, carried by calcium ions.

These time-dependent action potentials can co-exist with plateau potentials. In neurones giving both plateau potentials and time-dependent action potentials, plateau potentials can drive action potentials in bursts.
Temperature Dependency of Wing-Beat Frequency in Intact and Deafferented Locusts
Authors: Foster Jane A. , Robertson R. Meldrum
Published: April 2021

Locusts do not regulate thoracic temperature during flight and as a result the thoracic temperature of a flying locust generally exceeds ambient temperature by 5-8 °C. Elevated thoracic temperatures were shown to affect wing-beat frequency in intact and deafferented Locusta migratoria. Tethered locusts were flown in a wind tunnel. Temperature was elevated by increasing the ambient temperature of the apparatus and by exposing flying animals to heat pulses. Electromyographic (EMG) recordings were made in deafferented locusts perfused with salines at different temperatures. Wing-beat frequency was shown to vary with thoracic temperature in both the intact and the deafferented situation. The slope of the rise in wing-beat frequency with experimental increases in thoracic temperature was similar in intact and deafferented animals. These experiments demonstrate an effect of temperature on the central flight circuitry. Further intracellular investigations are needed to determine the neural basis of these effects.
Muscle Firing Patterns in two Arachnids Using Different Methods of Propulsive Leg Extension
Authors: Shultz Jeffrey W.
Published: April 2021

Activity patterns of six morphologically similar, homologous muscles were recorded from the fourth leg pair in two species of arachnids that use different mechanisms to extend the femur-patella (knee) joint during locomotion. The giant whipscorpion Mastigoproctus giganteus (Uropygi) lacks femur-patella extensor muscles but extends this joint with hydraulic pressure, a mechanism that appears to be phylogenetically primitive in arachnids. The black emperor scorpion Pandinus imperator (Scorpiones) has an unusual muscle that promotes simultaneous extension at the femur-patella joint and distally adjacent patella-tibia joint. Comparison of electromyograms from freely walking animals revealed similarities in muscle firing patterns of the two species, including asymmetrical alternation of trochanter-femur levator and depressor muscles, transfemoral muscle activation during protraction and abrupt termination just prior to levator activation, and persistence of flexor activity during retraction (extension). These results indicate that the apparent evolutionary transition from hydraulic to muscular extension occurred without substantial alteration of several components of the primitive motor programme. It is suggested that the patterns of extension force generated by hydraulic pressure and by bifunctional extensors are similar and that this similarity is associated with conservation of the motor programme.
A Simple Method for Construction of Flexible, Subminiature Ion-Selective Electrodes
Authors: O’donnell M. J.
Published: April 2021

Liquid membrane electrodes have greatly facilitated the measurement of pH and ion activities in intra- and extracellular fluids. Ion-selective microelectrodes (ISMEs) can be constructed by introducing a short column of a neutral carrier or ion-exchanger cocktail into the tip of a glass micropipette. The inner surface of the glass is first made hydrophobic by exposure to compounds containing silane (Thomas, 1978; Amman, 1986). This process, termed silanization, prevents subsequent displacement of the hydrophobic cocktail, either by entry of aqueous biological fluids through the tip of the micropipette or by migration of the backfilling solution. Macroscopic electrodes (5–10 mm diameter) can be produced by first incorporating appropriate neutral carriers into solvent polymeric membranes of polyvinyl chloride (PVC) or silicone rubber. Membranes can then be stamped out with a cork borer and glued or fused onto PVC tubing or commercially available electrode bodies (Meier et al. 1980). Electrodes with outer diameters of 1.5–1.7 mm have been formed by dipping tubing into a cocktail containing the ionophore, PVC and solvents. Solvent evaporation forms a membrane about 25 μm thick on the tip of the tubing (Oesch et al. 1987). A technique for the construction of miniature double-barrelled K+ electrodes with a total o.d. of 600 μm and a shank 1.3 cm long has been described by Hill et al. (1978).
Maternal and Paternal Nitrogen Investment in Blattella Germanica (L.) (Dictyoptera; Blattellidae)
Authors: Mullins Donald E. , Keil Clifford B. , White Robert H.
Published: April 2021

The investment of nitrogenous materials by female and male German cockroaches Blattella germanica (L.) into their progeny was examined. Adult females maintained on dog food invested 34 % of their dry mass and 26 % of their nitrogen into an ootheca during their first gonadotrophic cycle. Females maintained on a low-(5%) protein diet and injected simultaneously with [3H]leucine and [14C]hypoxanthine incorporated less [3H]leucine-derived radiolabel in their oothecae than those on a dog food diet (25% crude protein). Females on the lowprotein diet incorporated more [14C]hypoxanthine-derived material (primarily as [14C]urates) into their oothecae than they retained in their bodies. Stored [L4C]urates were metabolized more readily by females on the low-protein diet. Oothecae obtained from females provided with an [15N]urate-amended diet contained at least four 15N-enriched amino acids, which supports the hypothesis that urates are utilized as a nitrogen resource in these insects.

Dietary effects on paternal investment were also found to be significant. Females fed a low-protein diet and their oothecae contained 63 % of the radiolabel made available to them at mating when paired with males injected simultaneously with [3H]leucine and [14C]hypoxanthine, whereas dog-food-fed females and their oothecae contained only 17 % of the total radiolabel made available to them at mating.
Degenerative Changes in the Structure of Neuromuscular Junctions of Manduca Sexta During Metamorphosis
Authors: Rheuben Mary B.
Published: April 2021

During the degenerative processes that precede and accompany metamorphosis of the larval mesothoracic dorsal longitudinal muscles of Manduca sexta, the motor nerves and neuromuscular junctions undergo a variety of structural changes that are largely secondary to the changing morphologies of their respective glia. In the central region of the main motor nerve, the multiple layers of glial processes surrounding each of the large axons withdraw, leaving them apposed. In the peripheral region of the main motor nerve and in the secondary and tertiary nerve branches supplying the muscle, the outer glial processes of the nerve sheath and those that loosely wrap accompanying small neurosecretory axons all swell. Phagocytic cells and cells of unknown function invade the outer region of the nerve. In the neuromuscular junctions, the glial cells withdraw their processes from a complicated interdigitation with processes from the muscle fiber and from their relationship with the nerve terminal. As degeneration proceeds, this allows a greater area of contact between each nerve terminal and the muscle fiber. Within each junction there is a mixture of both functional and non-functional regions and active zones, as determined by both thin-section and freeze-fracture observations. No correlation was found between the degree of degeneration of a neuromuscular junction and its association with a particular muscle fiber or its position on the fiber relative to the origin or insertion.
Degenerative Changes in the Muscle Fibers of Manduca Sexta During Metamorphosis
Authors: Rheuben Mary B.
Published: April 2021

The ultrastructural changes associated with the early stages of degeneration of the larval mesothoracic muscle fibers of Manduca sexta were examined during the prepupal period and on the first day after ecdysis. Over this 5 day period, the muscle fibers decrease in cross-sectional area but increase in apparent surface area compared to the dimensions of early fifth-instar fibers. Large numbers of electrondense granules or droplets are formed and extruded from the muscle cytoplasm into the hemolymph; this process may account for some of the decrease in muscle fiber mass and may represent a developmental mechanism for recycling nutrients. As the fibers shrink, the thick basal lamina is thrown into folds. Phagocytic hemocytes (granulocytes) congregate in clusters over the surface of the degenerating fibers and appear to remove specifically the basal lamina. The timely removal of the thick larval basal lamina may be essential for subsequent fusion of myoblasts to the residual larval myofibers. The contractile elements within the degenerating muscle fibers become disorganized but are not dysfunctional at the end of the first 12 h after the pupal ecdysis. Tracheoles withdraw from intimate contact with each muscle fiber in its clefts and T-tubules and associate in groups adjacent to it. Mitochondria appear to be degenerating. These structural changes are concurrent with a previously observed decline in resting potential and suggest that a significant change in the electrical properties of the muscle fibers should be expected as well.
Sodium-Extruding and Calcium-Extruding Sodium/Calcium Exchangers Display Similar Calcium Affinities
Authors: Schoenmakers TH. J. M. , Flik G.
Published: April 2021

Na+/Ca2+ exchange activities in purely inside-out and mixed inside-out and right-side-out fish enterocyte basolateral plasma membrane vesicle preparations display equal affinities for Ca2+, showing that only the intracellular Ca2+ transport site of the Na+/Ca2+ exchanger is detected in experiments on vesicle preparations with mixed orientation. Therefore, Ca2+ pump and Na+/Ca2+ exchange activity may be compared directly without correction for vesicle orientation. The Na+/Ca2+ exchange activity in fish enterocyte vesicles is compared to the activity found in dog erythrocyte vesicles. The calcium-extruding exchanger in fish basolateral plasma membranes shows values of Km and Vmax for calcium similar to those found for the sodium-extruding exchanger in dog erythrocyte membranes, indicating that differences in electrochemical gradients underlie the difference in cellular function of the two exchangers.
The Effect of Catecholamines, Substance P and Vasoactive Intestinal Polypeptide on Blood Flow to the Gut In the Dogfish Squalus Acanthias
Authors: Holmgren Susanne , Axelsson Michael , Farrell Anthony P.
Published: April 2021

The effects of adrenaline, noradrenaline, substance P and vasoactive intestinal polypeptide (VIP) on dorsal aortic blood pressure, coeliac artery blood flow and heart rate were studied in unrestrained dogfish, Squalus acanthias. Changes in the coeliac vascular bed were calculated from these variables. Perfused tail preparations were used to study the effects of the various drugs on the somatic vascular bed. Corrosion casts were made to study the gross architecture of the coeliac vascular bed.

Adrenaline and noradrenaline increased dorsal aortic pressure and reduced the coeliac artery blood flow. Adrenaline caused a small increase in heart rate while noradrenaline caused a small decrease. Both drugs increased the resistance in the coeliac vascular bed. VIP increased dorsal aortic pressure, heart rate and resistance in the coeliac vascular bed. Substance P caused an increase in heart rate, cardiac output and, in particular, in coeliac artery blood flow; dorsal aortic pressure was simultaneously reduced. Voluntary swimming or fright immediately caused a pronounced reduction in blood flow in the coeliac artery, even though cardiac output and dorsal aortic pressure increased.

It is concluded that adrenergic mechanisms and possibly VIP are involved in reducing the blood flow to the gut, while substance P increases the flow to the gut.
A Mechanosensory Mechanism for Evoking Cellular Contraction in Vorticella
Authors: Katoh Kaoru , Naitoh Yutaka
Published: April 2021

Vorticella contracted (i.e. shrinkage of the cell body and coiling of the stalk) in response to being touched with a microneedle. The threshold excursion of the microneedle required to evoke a contraction was smallest on the cell body. On the stalk, it was larger in regions farther from the cell body. Hitting the stalk did not evoke a contraction if the stalk was mechanically clamped in a region between the site of the hit and the cell body. Rapidly drawing a small portion of the cell body into a micropipette by suction evoked a contraction, whereas a similar stimulus applied to the stalk did not. The threshold depression of the surface membrane of the cell body required to evoke a contraction was inversely proportional to the rate of depression. Tilting the stalk of a specimen detached from its substratum evoked a contraction. The threshold degree of tilting was inversely proportional to the angular velocity of tilting. Tilting the stalk is assumed to cause a localized depression of the surface membrane of the cell body around the stalk. We concluded (1) that the cell body is mechanosensitive and is the site where contractions are initiated; (2) that hitting the stalk evokes a contraction because the hit exerts a mechanical effect on the cell body; and (3) that the rate of expansion of the membrane of the cell body is responsible for activation of a hypothetical mechanoreceptor mechanism which initiates a contraction.
‘Facilitation’ of Melanophore Responses in Winter Flounder Pseudopleuronectes Americanus
Authors: Burton D. , O’driscoll M. P.
Published: April 2021

Melanophores of winter flounder (Pseudopleuronectes americanus) subjected to repeated transfers between black and white backgrounds display pronounced enhancement of the rates of melanosome aggregation and dispersion. Melano-some aggregation in response to repeated injection of noradrenaline displays a similar enhancement. In vitro preparations of microscopic skin samples on scales removed during successive cycles of background changes also display increasing melanophore response rates to K+ stimulation. It is concluded that a physiological ‘priming’ mechanism is involved peripherally at the melanophore level and it is proposed that this represents a form of facilitation. Also, it is deduced from these experiments that a modulation of the microtubular channels associated with melanosome translocation is probably the basis of the facilitation process.
The Photic Environment of a Salmonid Nursery Lake
Authors: Novales-Flamarique Iñigo , Hendry Andrew , Hawryshyn Craig W.
Published: April 2021

The spectral characteristics of Lake Cowichan (Vancouver Island) were examined using a LiCor underwater spectroradiometer. The results were analyzed in terms of salmonid vision with special emphasis placed on the ultraviolet part of the spectrum. Irradiance measurements were taken by SCUBA divers every 3 m from 18m to the surface at each of seven locations. The measurements at each depth consisted of four scans from 300 to 850 nm of downwelling, upwelling and horizontal light in the sun and antisun directions. The study covered different times of day and variable atmospheric conditions. According to predictions from the absorptive properties of water molecules and scattering by these and suspended particulates, it was found that the ultraviolet part of the spectrum was the least transmitted. The light field varied in intensity and dominant wavelengths depending on direction and time of day. The relative proportion of ultraviolet, short and middle wavelengths with respect to the entire spectrum peaked during crepuscular periods; the opposite was true for long wavelengths. An analysis of the irradiance values with respect to salmonid vision showed that there was enough light to stimulate all the photoreceptor mechanisms found in juvenile salmonid retinae (sensitive to ultraviolet, short, middle and long wavelengths) at all depths studied. Nevertheless, 18 m was found to be the limiting depth for stimulation of the ultraviolet cone mechanism, which is required for perception of ultraviolet polarized fight. This depth restriction may be linked to the observed salmonid movements close to the surface during crepuscular periods.
Compartmental Distributions of Carbon Dioxide and Ammonia in Rainbow Trout at Rest and Following Exercise, and the Effect of Bicarbonate Infusion
Authors: Tang Y. , Lin H. , Randall D. J.
Published: April 2021

The carbon dioxide content of the intracellular compartment of fish muscle was determined by direct measurements of CO2 and pH in tissue homogenates of rainbow trout, Oncorhynchus mykiss. The results agree with the concept that compartmental distribution of CO2 is pH-dependent and that muscle membranes are not very permeable to bicarbonate. The interaction between CO2 and ammonia excreted from fish muscle was also investigated by altering plasma CO2 content using bicarbonate infusion following exhaustive exercise. Removal of the acid boundary layer in white muscle by bicarbonate infusion resulted in retention of ammonia in the muscle, indicating that ammonia excretion across the muscle membrane might be enhanced by the hydration of excreted CO2 in the extracellular fluid. Passive diffusion of NH3, rather than NH4+ transfer, is probably the dominant pathway of ammonia excretion through fish muscle membranes.
Uptake and Metabolism of L-Alanine by Freshly Isolated Trout (Salmo Trutta) Hepatocytes: The Effect of Fasting
Authors: Canals P. , Gallardo M. A. , Blasco J. , Sánchez J.
Published: April 2021

Uptake and metabolism of L-alanine by freshly isolated trout hepatocytes has been analyzed. This amino acid is incorporated ‘uphill’ by different carriers, either Na+-dependent or Na+-independent. Na+-dependent uptake shows the characteristics of an ASC system on the basis of cation dependence and substrate preferences. The Na+-independent uptake is split between an L-cysteine-sensitive system and a non-saturable component. No uptake through system A has been found, suggesting that this carrier is lacking in trout hepatocytes. On the basis of inhibition by several preferred amino acids, L-alanine is not taken up through either the L or N systems.

Fasting induced changes in both the uptake of L-alanine and its metabolism to CO2 and glucose. There was an increase in uptake that showed an inverse relationship with L-alanine plasma levels. Glucose production from L-alanine rose during food deprivation, while CO2 production showed an initial increase, similar to that of glucose. At the end of the fasting time considered, however, there was a drop in CO2 production, indicating a different kind of regulation for alanine oxidation and gluconeogenesis.
Activation by Membrane Stretch and Depolarization of an Epithelial Monovalent Cation Channel From Teleost Intestine
Authors: Chang Wenhan , Loretz Christopher A.
Published: April 2021

The intestine of euryhaline teleosts is an important osmoregulatory organ which actively absorbs Na+, Cl− and water from the lumen. This ion-transporting epithelium experiences a variety of physical stimuli resulting from variations in luminal osmolality and distension and from peristaltic contractions. Using patchclamp techniques in the inside-out configuration, single stretch-activated channels (SA channels) were identified and characterized. These SA channels had a conductance of about 67 pS in symmetrical solutions containing 140 mmol l−1 NaCl and were permeable to both Na+ and K+ (PNa/PK≈0.83) but not to anions. In excised, inside-out membrane patches, channel activity could be enhanced in the absence of membrane tension by strong depolarization of the membrane potential (Vm) to between 0 mV and +90 mV, with Vo [Vm at which the single-channel open probability (Po)=0.5] at +25.7mV. In the presence of membrane tension, the voltage-dependence of channel activity was shifted into the physiological range of Vm. Each kPa (10cmH2O) of applied pressure (ΔP) generated the same effect on Po as a membrane depolarization of 49 mV. Membrane tension also increased the single-channel current and single-channel conductance in a dose-dependent manner. The kinetic data suggest that this channel has two open states and three closed states. Both stretch- and depolarization-induced increases in Po were attributed to prolongation of the lifetime of the longer open state. Possible physiological roles for this channel include the cellular uptake of Na+ from the lumen as part of the salt and water absorptive process or a yet undefined involvement in cell volume regulation.
The Humidity Behaviour of the Mealworm Beetle, Tenebrio Molitor L
Authors: Pielou D. P.
Published: April 2021

The existence of sensillae sensitive to humidity has frequently been surmised, but there is no experimental evidence on their form or position in insects. Necheles (1925) suggested that the antennal hairs of the mosquito might be sensitive to humidity; Thomson (1938) made an attempt to locate the receptors in the mosquito, Culex fatigans, but found the experimental difficulties too great. Kennedy (1937) attempted unsuccessfully to locate the receptors in the locust, Locusta migratoria. Gunn & Cosway (1938) found that humidity behaviour in the cockroach, Blatta orientalis, became irregular when the antennae were infected with a fungus, and they suggested on these grounds that the receptors are located on the antennae. Thus there is no satisfactory evidence on the site of humidity receptors in insects. The problem has also been examined in other terrestrial arthropods. Blumenthal (1935), working on the olfactory sense of spiders, decided that certain organs on the tarsi of the legs are olfactory receptors. As he used water as one of his “odours” and found a reaction to it, he concluded that these organs were also humidity receptors. Gunn (1937) could not locate the humidity receptors in the wood-louse, Porcellio scaber.