bluuebunny/crossref_metadata_2025 huggingface dataset:
Flight Energetics of Euglossine Bees in Relation to Morphology and Wing Stroke Frequency
Authors: Casey Timothy M. , May Michael L. , Morgan Kenneth R.
Published: April 2021

Mass-specific oxygen consumption of euglossine bees during free hovering flight is inversely related to body mass, varying from 66mlO2g−1h−1 in a 1−0·10 bee to 154mlO2g−1h−1 in a 0·10-g bee. Individuals of Eulaema and Eufreisea spp. have smaller wings and higher wing stroke frequency and energy metabolism at any given mass than bees of Euglossa spp. or Exaerete frontalis. Calculated aerodynamic power requirements represent only a small fraction of the energy metabolism, and apparent flight efficiency [aerodynamic power (= induced + profile power)/power input] decreases as size declines. If efficiency of flight muscle = 0·2, the mechanical power output of hovering bees varies inversely with body mass from about 480 to 1130 W kg−1 of muscle. These values are 1·9 to 4·5 times greater than previous predictions of maximum mechanical power output (Weis-Fogh & Alexander, 1977; see also Ellington, 1984c). Mass-specific energy expenditure per wing stroke is independent of body mass and essentially the same for all euglossines. Differences in energy metabolism among bees having similar body mass is primarily related to differences in wing stroke frequency. Scaling of energy metabolism in relation to mass is generally similar to the relationship for sphingid moths despite the fact that bees have asynchronous flight muscle whereas moths have synchronous muscle.
Which Parameters Control the Leg Movement of A Walking Insect?: I. Velocity Control During the Stance Phase
Authors: Cruse H.
Published: April 2021

In treadwheel walking, the front and middle legs of the stick insect (Carausius morosus) propel the wheel, while the hind legs exert very little force and can even decelerate the wheel. This result is compared with observations on the function of the legs in different walking situations.

Several hypotheses assuming different types of position servo-mechanisms have been proposed in the literature on the control of leg movement during walking in insects. The experimental results support none of these hypotheses. Instead, they indicate that velocity rather than position is the variable controlled during the stance phase.
Plasticity And Proprioception In Insects I. Responses and Cellular Properties of Individual Receptors of the Locust Metathoracic Femoral Chordotonal Organ
Authors: Zill Sasha N.
Published: April 2021

The metathoracic femoral chordotonal organ is a joint angle receptor of the locust hindleg. It consists of 45–55 bipolar sensory neurones located distally in the femur and mechanically coupled to the tibia. Responses of receptors of the organ were examined by extracellular and intracellular recording. The organ as a whole encodes the angle of the femoro-tibial joint but shows substantial hysteresis. Tonic activity is greatest at the extremes of joint position. The organ possesses no direct linkage to tibial muscle fibres and shows no response to resisted muscle contractions in most ranges of joint angle. However, responses to extensor muscle contractions are obtained when the tibia is held in full flexion due to specializations of the femoro-tibial joint. These responses could be of importance in signalling preparedness for a jump. Intracellular soma recordings of activity in individual receptors indicate that the organ contains two types of receptors: phasic units that respond to joint movement and tonic units that encode joint position and also show some response to movement. All units are directionally sensitive and respond only in limited ranges of joint angle. Some phasic units increase firing frequency with increasing rate of movement and thus encode joint velocity. Other phasic units fire only single action potentials and can encode only the occurrence and direction of joint movement. All tonic units increase activity in the extremes of joint position and show substantial hysteresis upon return to more median positions. Direct soma depolarization produces different responses in different types of units: phasic receptors show only transient discharges to current injection; tonic receptors exhibit sustained increases in activity that are followed by periods of inhibition of background firing upon cessation of current injection. Receptors of the chordotonal organ are separable into two major groups, based upon their response characteristics, soma location and dendritic orientation: a dorsal group of receptors contains tonic units that respond in ranges of joint flexion (joint angle 0–80°) and phasic units that respond to flexion movements; a ventral group of sensilla contains tonic units active in ranges of joint extension (joint angle 80–170°) and phasic receptors that respond to extension movements. The response properties of these receptors are discussed with reference to the potential functions of the chordotonal organ in the locust’s behavioural repertoire.
Energetic Efficiency of Vocalization by the Frog Physalaemus Pustulosus
Authors: Ryan Michael J.
Published: April 2021

Male Physalaemus pustulosas consume, on average, 1.2µl of oxygen in the production of a single call, which is equivalent to an energy input per call of 0.024 J. The total power of complex calls, which can have a varying number of components, ranged from 0.36 to 0.46mW. The total acoustic energy contained in these complex calls ranged from 0.12 to 0.30mJ. The energetic efficiency of the vocalizations ranged from 0.5 to 1.2%, which is similar to the range estimated for some other animals. The low energetic efficiency of vocalization by these frogs is due, in part, to the fact that the wavelengths of the call are too long, relative to the size of the frog, to be radiated efficiently. Although shorter wavelengths (higher frequencies) are radiated by the frog at relatively greater intensities, longer wavelengths (lower frequencies) attenuate less rapidly in the environment. It is suggested that selection generated by the acoustics of the environment favours calls with lower frequencies, but the morphology of the animal sets a lower limit to which frequencies can evolve.
Analysis Of Respiratory Pattern During Panting In Fowl, Gallus Domesticus
Authors: Gleeson M.
Published: April 2021

When exposed to hot environments, birds depend mostly on respiratory evaporative cooling in order to maintain body temperature since cutaneous evaporation is limited for most species because they lack sweat glands. As well as serving this thermoregulatory function the respiratory system must also accommodate the obligatory requirement of adequate gaseous exchange. The hyperthermic bird must increase ventilation rates over evaporative surfaces in the respiratory system and buccopharynx for cooling purposes and yet avoid a severe blood hypocapnia and alkalosis (Calder & Schmidt-Nielsen, 1968). Recently Bech, Johansen & Maloiy (1979) showed that flamingoes, Phoenicopterus ruber, avoid hypocapnia during panting by restricting hyperventilation to the respiratory dead-space. This is achieved by increasing respiratory frequency, f, but reducing tidal volume, VT, to a value which closely matches the tracheal dead-space volume, VD. AS a result of the diminished VT, carbon dioxide accumulated within the respiratory system and rapid, shallow panting was periodically interrupted by bursts of 1–3 deeper breaths which served to flush out the excess carbon dioxide. A similar pattern of breathing has been observed in domestic fowl by Gleeson & Brackenbury (1983). These authors showed that the carbon dioxide accumulated during rapid shallow breathing in the posterior (abdominal) air sacs as a result of the increase in the VD/VT ratio. Other authors have reported an increased f and reduced VT in the panting fowl (Kassim & Sykes, 1982; Arad & Marder, 1983) but the diphasic pattern of breathing during panting has not been adequately described or quantified although its presence is apparent from earlier records of breathing movements in the panting fowl (Romijn & Lokhorst, 1961). Some forms of diphasic panting also occur in other species of bird, although there is considerable variation in the frequency and regularity of the alternating patterns of breathing between species (for a review see Bech et al. 1979).
The Role of the Tympanal Membranes in the Tuning of Auditory Receptors in Tettigoniidae (Orthoptera: Ensifera)
Authors: Oldfield Brian Phillip
Published: April 2021

One of the fundamental problems in auditory research is the origin of the frequency selectivity of auditory receptors. Horridge (1960) demonstrated that the auditory interneurones in locusts were tuned to different sound frequencies, thus suggesting that the auditory receptors were frequency selective. Michelsen (1968, 1971) established that the auditory organ of locusts contained four groups of receptors with different characteristic sound frequencies and proposed that the frequency selectivity of the individual groups was dependent on the resonant properties of the tympanum. Investigation using the more sensitive of the two auditory receptors in the moth Prodenia eridania extended this proposal by suggesting that the tuning of this receptor depended on both resonant properties of the auditory organ (scoloparium) and filtering properties of the acoustic system (Adams, 1972), the most important factor in the latter being the tympanal membranes. In crickets and bushcrickets, however, the tympanal membranes vibrate in a simple mode for a wide band of sound frequencies (Paton, Capranica, Dragsten & Webb, 1977; Michelsen & Larsen, 1978), thus making it unlikely that the motion of the tympanum is responsible for the frequency selectivity (Zhantiev & Korsunovskaya, 1978; Esch, Huber & Wohlers, 1980) of the individual auditory receptors. Similarly, Ball & Hill (1978) demonstrated that auditory intemeurones of larval instar crickets are tuned even though they have no tympanal membranes. A recent study of the tonotopic organization of the auditory organ in bushcrickets (Oldfield, 1982) revealed that the auditory receptors remained tuned after the removal of one tympanum. This result, like those obtained from crickets, suggests that the resonant properties of the tympanal membranes are not responsible for the tuning of the individual auditory receptors. Conclusive evidence on this proposal, however, requires the removal of both tympanal membranes, thus eliminating the possibility that the remaining tympanum in the study by Oldfield (1982) determined the tuning of the auditory receptors.
A Protective Effect of Adrenalin on the Acidotic Teleost Heart
Authors: Farrell A. P.
Published: April 2021

In the teleost heart, catecholamines improve the tension development in isolated muscle strips and increase stroke volume (SVH) in perfused hearts working at sub-physiological levels (see Laurent, Holmgren & Nilsson, 1983 and Farrell, 1984 for recent reviews). Adrenalin (AD) can also restore or improve tension development during acidosis and anoxia (Gesser, Andresen, Brams & Sund-Laursen, 1982). However, physiological concentrations of AD do not increase SVH in any marked or consistent fashion in either intact fish or perfused hearts working at physiological levels (see Farrell, 1984), and only restore control levels of cardiac output in perfused hearts exposed to pH 7·4 at constant preload (Farrell, MacLeod, Driedzic & Wood, 1983). These observations pose the question: what is the role of catecholamine-mediated inotropic stimulation in fish?
Calcium Action Potentials in the Developing Oocytes of an Insect, Rhodnius Prolixus
Authors: O’Donnell M. J.
Published: April 2021

Action potentials (APs) have been recorded for the first time from the oocytes of an arthropod, the haematophagous insect Rhodnius prolixus. In saline containing 2 mmol 1−1 calcium, APs could be evoked by depolarizing the oocyte membrane from its resting potential of –50 mV to a threshold between –35 and –40 mV. The mean duration and overshoot of the APs were 2·6 s and +16 mV, respectively. APs could not be evoked by depolarization of follicular epithelia that had been separated from the oocyte. It is concluded that the APs are generated at the oocyte cell membrane.. The overshoot of the APs was unaffected by the addition of tetrodotoxin (3 μmol 1−1) or the removal of Na+ (choline replacement) from the bathing saline. APs could be reversibly blocked by 1 mmol l− La or 10 mmol 1−1 Co2+. Verapamil at 50μmoll−1 and 100μmoll−1 reduced AP duration by 30% and 50%, respectively. The overshoot increased by 30 mV when bathing saline Ca2+ concentration was increased from 2 to 20 mmol 1−1. These results suggested the occurrence of a Ca2+ influx during the rising phase of the AP. Addition of Ba2+ increased the overshoot and duration of APs. In Ca2+-free saline, addition of 2 mmol 1−1 Ba2+ resulted in the spontaneous production of a series of action potentials. The duration of APs was as long as 120 s in 20 mmol 1−1 Ba2+ saline. It is suggested that Ba2+ may block a voltage-sensitive potassium conductance. Possible functions of action potentials during fertilization and early development are discussed.
The Maximum Shortening Velocity of Holothurian Muscle and Effects of Tonicity Change on It
Authors: Tsuchiya T.
Published: April 2021

The maximum shortening velocity of the longitudinal retractor muscle of the holothurian, Isostichopus badionotus, was measured using a ‘slack test’ in solutions of normal, increased and reduced osmotic strength. At normal osmotic strength, the average maximum shortening velocity was 0·44 ± 0·04L0s−1(N = 14) which is fast compared to other smooth muscles. This is unexpected considering the slow locomotion of these animals. Raising the osmotic strength by 55% by addition of sucrose reduced the shortening velocity by more than 50%. Raising the osmotic strength by 52% with NaCl caused a 35% reduction in shortening velocity. Lowering the osmotic strength by 19% or 39%, by reducing NaCl concentration, did not significantly affect shortening velocity. The shortening velocity was found to be proportional to the volume of the muscle preparation.
Visual Position Information Controlling Smooth-Tracking in the Praying Mantis
Authors: Kirmse Wolfgang
Published: April 2021

Smooth-tracking in the praying mantis was regarded by Rossel (1980, p. 325) as being driven by a velocity input signal in the same way that the optokinetic reaction is governed by the retinal image velocity of the surroundings. However, the following results indicate that the angular error between target position and midline of sight is also important in the control of smooth-tracking since there were increases in both saccadic and smooth torsion responses towards a stationary eccentric target in the open loop arrangement.
Mechanical Properties of the Myotomal Musculo-Skeletal System of Rainbow Trout, Salmo Gairdneri
Authors: Johnsrude C. L. , Webb P. W.
Published: April 2021

Net forces and velocities resulting from in situ contractions of the myotomal musculature on one side of the body were measured at the hypural bones. Forces, velocities and power were determined with the body bent into a range of postures typical of those observed during fast-start swimming. For trout averaging 0·178 m in length and 0·0605 kg in body mass, the muscle system exerts a maximum normal force of 2·2 N at the base of the caudal fin. This force is equivalent to 11·8 kN m−2 based on the mean crosssectional area of the myotomal muscle. The maximum velocity was 1·11 ms−1, and the maximum mechanical power output, 0·64W, or 42·4 W kg−1 muscle.

Based on estimates of swimming resistance, these results would suggest acceleration rates of 7·5 to 16·5 ms−2, similar to averages observed during fast-starts. Maximum sprint speeds would range from 6·5 to 17·8 body lengths s−1, spanning the range of maximum speeds reported in the literature. It is suggested that maximum speed is limited by interactions between muscle contraction frequency and endurance.

Losses in the mechanical linkages between muscle fibres and propulsive surfaces were estimated at about 50% for power with possibly greater losses in force transmission.

Maximum force and power did not vary over the range of postures tested, supporting Alexander’s (1969) suggestions that white muscle should contract over a small portion of the resting length of the fibres.
Accessory Lymph Sacs and Body Fluid Partitioning in the Lizard, Sauromalus Hispidus
Authors: Smits Allan W.
Published: April 2021

Chuckwalla lizards (genus Sauromalus) may accumulate substantial quantities of body fluid in extracoelomic, lateral abdominal spaces called accessory lymph sacs. The lymph sac fluid (LSF) of S. hispidus is similar to that of serum in Na+, K+ and Cl− concentrations, but the total protein content (3·58 ± 0·20 g dl−1) is only half that measured in serum (7·05 ± 0·26gdl−1). These analyses confirm that LSF is an extravascular form of extracellular fluid, similar in composition to true lymph. Measurements of body fluid partitioning by dilution analysis indicate that Sauromalus hispidus Stejnejer possesses a comparatively large (38·9% body mass) and labile extracellular fluid volume (ECFV), and that the volume of LSF is dependent on the ECFV. Expansion of the ECFV (and subsequent accumulation of LSF) is observed following large, intercompartmental fluid shifts from intracellular to extra cellular locations when lizards (1) are kept inactive in simulated hibernation, (2) are injected with KC1 in amounts similar to those found in their field diet, and (3) are hydrated with NaCl that is isotonic to their body fluids. These data collectively suggest that the lymph sacs of chuckwallas facilitate expansion of the ECFV, and may be adaptive not only as a means to store body water, but to accommodate transient shifts in body fluid from intracellular to extracellular locations.
Effect of Thermal Acclimation on Locomotor Energetics and Locomotor Performance in A Lungless Salamander, Desmognathus Ochrophaeus
Authors: Feder Martin E.
Published: April 2021

To determine the effects of thermal acclimation upon locomotor performance and the rate of oxygen consumption during activity, small (<3g), lungless salamanders, Desmognathus ochrophaeus Cope, were acclimated to three temperatures (5,13 and 21 °C) and exercised at various controlled speeds within an exercise wheel while their was measured. increased with speed at low speeds (< 14 cm min−1). Although animals could sustain greater speeds, did not increase further. These small, exclusively skin-breathing salamanders could increase their 9–11 times during exercise and could sustain nearly half of the oxygen flux expected across a similar surface area of the mammalian lung. However, their maximum aerobic speed was remarkably slow (14cmmin−1) and their net cost of transport remarkably large (15–17 ml O2g−1km−1). Thermal acclimation affected during activity, the maximum sustainable speed and locomotor stamina in different ways. During exercise at 13°C, cold-acclimated animals had a significantly greater than warm-acclimated animals, but did not differ in stamina or the maximum sustainable speed. During exercise at 21 °C, cold acclimation did not affect the , significantly, but it decreased the stamina and increased the rate of lactate accumulation. Thus, these results suggest that thermal acclimation of the is not tightly coupled to thermal acclimation of locomotor performance in salamanders.
Respiratory Properties of Blood From Voluntarily and Forcibly Submerged Xenopus Laevis
Authors: Boutilier R. G. , Shelton G.
Published: April 2021

The respiratory properties of blood from voluntarily diving Xenopus seem well matched to the animal’s habit of ventilating its lungs in an intermittent fashion. Compared with more terrestrial anurans, the high oxyhaemoglobin affinity (P50 = 29·6 Torr, pH 7·73, 25°C), Bohr effect (ΔlogP50/ΔpH = −0·37) and Haldane effect (0·37 mol CO2mol−1 O2) can be viewed collectively as adaptations towards effective blood gas storage during periods of apnoea and blood gas exchange during episodes of air breathing. It appears, therefore, that these biochemical adaptations are linked to the changes in respiratory blood flow that are made possible by the partially divided double circulation of Xenopus.

In comparison with blood from voluntarily diving Xenopus, that taken from animals at the end of a 30-min enforced dive was haemoconcentrated and contained 4 and 8 mmol l−1 higher concentrations of true plasma lactate and metabolic acid equivalents respectively. The pH-induced effects of the latter led to reductions in oxyhaemoglobin affinity and blood CO2 carriage, both of which persisted for up to 4h following emergence from an enforced dive. The associated haemoconcentration led to a secondary series of effects of which the most obvious were an elevated blood oxygen-carrying capacity and an increased non-bicarbonate buffer slope for true plasma. Marked changes, such as these, were never observed in blood samples taken at various stages of voluntary dives lasting upwards of 30 min.
The Regulation of Haemocyanin Oxygen Affinity During Emersion Of the Crayfish Austropotamobius Pallipes: II. An Investigation of In Vivo Changes in Oxygen Affinity
Authors: Morris S. , Tyler-Jones R. , Bridges C. R. , Taylor E. W.
Published: April 2021

The oxygen-transporting properties of the haemolymph from the crayfish Austropotamobius pallipes were investigated. The haemolymph concentrations of K+, Mg2+ and Ca2+ ions, together with the concentration of L-lactate were measured in crayfish before, during and after 24 h emersion.

The concentrations of K+ and Mg2+ increased during aerial exposure and returned to pre-emersion levels during immersed recovery. Large increases in the level of circulating L-lactate and Ca2+ were correlated with short- and long-term aerial exposure respectively. Changes in the concentrations of these ions could also be correlated with changes in haemocyanin oxygen affinity. Reimmersion and recovery returned all parameters to near control values.

The effect, on haemocyanin oxygen affinity, of the Bohr shift alone was calculated and compared with the change in oxygen affinity (ΔP50) actually determined during aerial exposure. These data were also compared with predictions, calculated from in vitro data, for the potentiation of haemocyanin oxygen affinity by Ca2+ and L-lactate ions in aerially exposed crayfish. The physiological significance of the regulation of haemocyanin oxygen affinity by these ions is discussed.
Intercellular Communication in An Insect Endocrine Gland
Authors: Lococo D. J. , Thompson C. S. , Tobe S. S.
Published: April 2021

The parenchymal cells of the corpora allata (CA) of the cockroach Diploptera punctata are coupled through low-resistance intercellular pathways. Extensive dye coupling of cells of CA from fourth instar and adult female cockroaches was revealed following iontophoretic injection of Lucifer Yellow. Freeze-etch electron microscopy revealed numerous gap-junction-like particles in CA cell plasma membranes. The spread of ionic current from cell to cell was demonstrated by injecting current pulses into one cell and recording electrotonic potentials from other cells. The amplitude of electrotonic potentials elicited by negative current injection varied inversely with the rate of juvenile hormone biosynthesis by the CA. The ‘length constant’ (distance at which an electrotonic potential in CA cells decays to 37% of its magnitude at the site of current injection) could not be measured accurately, but was found to be much greater than the length of the CA. Forskolin- and IBMX-induced elevation of intracellular cAMP increased the electrotonic potential but reduced juvenile hormone release of day 8 CA.
The Segmental Giant Neurone of the Signal Crayfish, Pacifastacus Leniusculus, and its Interactions With Abdominal Fast Flexor and Swimmeret Motor Neurones
Authors: Heitler W. J. , Darrig S.
Published: April 2021

The anatomy and physiology of the segmental giant (SG) of the crayfish Pacifastacus leniusculus is described. The peripheral axon of the SG terminates in the 1st root near the base of the swimmeret, and has no direct target organ. There is a tuft of fine dendritic branches in the lateral neuropile where the SG axon has its smallest diameter. The central region of the SG has a conduction velocity of 1·3 ms−1, a length constant of 0·4–0·7 mm and an input resistance greater than 1·8MΩ. Dual microelectrode penetrations of pre- and postsynaptic neurones confirm that the SG receives input from the giant fibres through rectifying electrical synapses, and excites the fast flexor motor neurones of the abdomen, also through electrical synapses. The SG also excites a variety of swimmeret motor neurones, including power-and return-stroke classes. Attention is drawn to the similarity in anatomy between the SG and return-stroke swimmeret motor neurones, and a possible evolutionary explanation for the existence of the SG is proposed.
Responses of A Stenohaline Freshwater Teleost (Catostomus Commersoni) to Hypersaline Exposure: I. The Dependence of Plasma Ph and Bicarbonate Concentration on Electrolyte Regulation
Authors: Wilkes P. R. H. , Mcmahon B. R.
Published: April 2021

The effects of exposure to 0·94% (300mosmoll−1) sodium chloride on plasma electrolyte and acid-base status were examined in the freshwater stenohaline teleost Catostomus commersoni (Lacépède), the white sucker. Four days’ exposure to this maximum sublethal salinity resulted in an increase in plasma concentrations of both sodium and chloride but a decrease in the Na+/Cl− ratio. Since the plasma concentrations of free amino acids and other strong ions - Ca2+, Mg2+ and K+ - remained unchanged, plasma strong ion difference (SID) decreased. Additionally, plasma pH and bicarbonate concentration decreased at constant. The changes in electrolyte and acid-base status that occurred after the 96 h were not appreciably altered after a further 2–3 weeks of saline exposure. The ambient calcium concentration had no influence on these results.

Haemolymph non-bicarbonate buffer capacity (β) calculated as Δ[HCO3−]/ ΔpH, increased in saline-exposed fish. Consequently ΔH+, the apparent proton load, was zero despite the apparent change in acid-base status. Although β was directly proportional to the haemoglobin concentration in both control and experimental fish, this could not account for the increase in β since haemoglobin remained at control values. These results can be explained solely by the change in plasma SID and serve to illustrate the dependence of plasma acid-base status on the prevailing electrolyte characteristics, weak acid concentration and .
The Kinematics of Swimming in Larvae of the Clawed Frog, Xenopus Laevis
Authors: Seckendorff Hoff Karin Von , Wassersug Richard Joel
Published: April 2021

The kinematics of swimming in larval Xenopus laevis has been studied using computer-assisted analysis of high-speed (200 frames s−1) ciné records. The major findings are as follows.

At speeds below 6 body lengths (L) per second, tail beat frequency is approximately 10 Hz and, unlike for most aquatic vertebrates, is not correlated with specific swimming speed. At higher speeds, tail beat frequency and speed are positively correlated. Xenopus tadpoles show an increase in the maximum amplitude of the tail beat with increasing velocity up to approximately 6Ls−1. Above that speed amplitude approaches an asymptote at 20 % of body length. Anterior yaw is absent at velocities below 6Ls−1, unlike for other anuran larvae, but is present at higher speeds. At speeds below 6 L s−1 there is a positive linear relationship between length of the propulsive wave (λ) and specific swimming speed. At higher speeds wavelength is constant at approximately 0·8 L. There is a shift in the modulation of wavelength and tail beat frequency with swimming speed around 5–6 L s−1, suggesting two different swimming modes. The slower mode is used during open water cruising and suspension feeding. The faster, sprinting mode may be used to avoid predators. Froude efficiencies are similar to those reported for fishes and other anuran larvae. Unlike Rana and Bufo larvae, the axial muscle mass of Xenopus increases dramatically with size from less than 10% of total mass for the smallest animals to more than 45 % of total mass for the largest animals. This increase is consistent with maintaining high locomotor performance throughout development.
Receptors and Ion Channels
Authors: Evans Peter D. , Levitan Irwin B.
Published: April 2021

Receptors and ion channels are membrane-bound proteins involved in fundamental regulatory mechanisms in cells. They govern both a cell’s homeostatic activity and its programmed responses to intra- and extracellular stimuli. Specific receptor molecules in a cell’s plasma membrane can be activated by signal molecules present either in the medium surrounding the cell or even generated within the cell itself. The activated receptors sometimes directly bring about changes in the conductances of ion channels. On other occasions the receptors generate changes in a cascade of intracellular second messengers that subsequently activate the ion channels or effect appropriate biochemical changes. In many cases the receptors themselves are actually part of the ion channel complex and in other cases the receptor properties reside in distinct molecular entities. Ion channels may also be regulated by changes in the potential across the membrane in which they are found and also by changes in the concentrations of specific ionic modulators within the cell. Thus the actions of receptors and ion channels in the regulation of cellular function are inextricably intertwined.
Properties And Modulation of Cardiac Calcium Channels
Authors: Reuter H. , Kokubun S. , Prod’hom B.
Published: April 2021

Voltage-dependent calcium channels are widely distributed in excitable membranes and are involved in the regulation of many cellular functions. These channels can be modulated by neurotransmitters and drugs. There is one particular type of calcium channel in cardiac cells (L-type) whose gating is affected in different ways by β-adrenoceptor and 1,4-dihydropyridine agonists. We have analysed single calcium channel currents (i) in myocytes from rat hearts in the absence and presence of isoproterenol or 8-bromo-cAMP. We have found that both compounds have similar effects on calcium channel properties. They increase the overall open state probability (po) of individual calcium channels while i remains unaffected. Analysis of the gating kinetics of calcium channels showed: (a) a slight increase in the mean open times of calcium channels, (b) a reduction in time intervals between bursts of channel openings, (c) an increase in burst length and (d) a prominent reduction in failures of calcium channels to open upon depolarization. These kinetic changes caused by isoproterenol and 8-bromo-cAMP can account for the increase in po. Since the macroscopic calcium current, ICa, can be described by Ica = N×po×i, the increase in po accounts for the well-known increase in Ica, by β-adrenergic catecholamines. Cyclic AMP-dependent phosphorylation of calcium channels is a likely metabolic step involved in this modulation. Another class of drug that modulates calcium channel gating is the 1,4-dihydropyridines which can either enhance or reduce Ic,, either by prolonging the open state of the channels or by facilitating the inactivated state. Both effects depend strongly on membrane potential and are independent of cyclic AMP-dependent phosphorylation reactions.
Cell Surface Glycoconjugates and Carbohydrate-Binding Proteins: Possible Recognition Signals in Sensory Neurone Development
Authors: Dodd Jane , Jessell Thomas M.
Published: April 2021

Dorsal root ganglion (DRG) neurones transmit cutaneous sensory information from the periphery to the dorsal horn of the spinal cord. Subpopulations of DRG neurones that subserve distinct sensory modalities project to discrete regions in the dorsal horn. The formation of specific sensory connections during development may involve cell-surface interactions with spinal cord cells. Molecules that are expressed on the surface of functional subpopulations of DRG and dorsal horn neurones have therefore been identified.

Distinct subsets of DRG neurones express globo-or lactoseries carbohydrate differentiation antigens. The expression of defined carbohydrate structures correlates with the embryonic lineage, peptide phenotype and the central termination site of DRG neurones. Similar or identical glycoconjugates have been implicated in cellular interactions that contribute to preimplantation embryonic development.

Small-diameter DRG neurones that project to the superficial dorsal horn express N-acetyllactosamine backbone structures that are potential ligands for β-galactosidespecific binding proteins (lectins). Two lectins have been identified that are expressed early in development in the superficial dorsal horn. These complementary molecules may contribute to the development of sensory afferent projections in the spinal cord.
Modulation of the Serotonin-Sensitive Potassium Channel in Aplysia Sensory Neurone Cell Body and Growth Cone
Authors: Siegelbaum S. A. , Belardetti F. , Camardo J. S. , Shuster M. J.
Published: April 2021

Using single-channel recording, we have been able to obtain some insight into the molecular mechanism of a modulatory transmitter action in Aplysia sensory neurones. Our results show that serotonin produces a slow EPSP and increases action potential duration in the sensory neurones by producing prolonged closures of the S potassium channel. Such closures appear to be mediated by cyclic AMPdependent phosphorylation of a membrane protein which may be the channel. Modulation of S channels by serotonin also occurs in sensory neurone growth cones. This provides the first direct evidence that channel modulation occurs in nerve processes and increases the likelihood of channel modulation at the nerve terminal.
Fine Tuning of Neuronal Electrical Activity: Modulation of Several Ion Channels by Intracellular Messengers in a Single Identified Nerve Cell
Authors: Lotshaw David P. , Levitan Edwin S. , Levitan Irwin B.
Published: April 2021

The identified neurone R15 in the abdominal ganglion of the marine mollusc, Aplysia californica, exhibits a rhythmic bursting pattern of electrical activity. This pattern, which is generated endogenously by the interaction of several voltage-and time-dependent ion currents in R15’s membrane, is subject to long-term modulation by synaptic stimulation and application of several neurotransmitters. At micromolar concentrations the transmitter serotonin causes neurone R15 to hyperpolarize, as a result of the activation of an anomalously rectifying potassium conductance. Furthermore under some conditions serotonin can excite R15, as a result of the activation of a voltage-dependent calcium current. Both of these effects of serotonin are mediated by the intracellular second messenger cyclic AMP. In addition, serotonin can modulate a chloride current by a cyclic-AMP-dependent mechanism. In contrast to the activation of the voltage-dependent calcium current by serotonin/ cyclic AMP, a cyclic GMP analogue alters the bursting pattern by inhibiting this current. The results indicate that a single neurotransmitter, acting via a single intracellular messenger, can modulate several classes of ion channels in a single nerve cell. Furthermore a single class of ion channel, that is responsible for a voltage dependent calcium current, may be the target for modulation by at least two different intracellular messengers. These findings emphasize the intricacy of the regulatory pathways which contribute to fine tuning of neuronal electrical activity.
Modulation of the Calcium Current of Molluscan Neurones By Neurotransmitters
Authors: Gerschenfeld H. M. , Hammond Constance , Paupardin-Tritsch Danièle
Published: April 2021

In identified neurones of the snail Helix aspersa, the Ca2+ current can be modulated by biogenic amines and peptides in different ways.

A reversible increase of Ca2+ current is evoked by 1 μmol l−1 serotonin (5-HT) in a group of identified snail ventral neurones (D6, D7, El). This 5-HT-induced enhancement of Ca2+ current is probably mediated by cyclic GMP. Neither cyclic AMP nor forskolin mimic the effect of 5-HT, but both the intracellular injection of cyclic GMP and the application of zaprinast (an inhibitor of a cyclic-GMP-dependent phosphodiesterase) induce a Ca2+ current increase. Moreover, when a maximal Ca2+ current increase is induced by cyclic GMP, 5-HT becomes ineffective and vice versa. Decreases in the Ca2+ current can be generated by two mechanisms, (a) A reversible decrease of the Ca2+ current is evoked by both dopamine (1 μmol l−1) and the neuropeptide FMRFamide (1 μmol l−1) on different identified neurones. Intracellular injections of either cyclic AMP or cyclic GMP do not mimic the effect of dopamine or FMRFamide. Moreover, the intracellular injection of EGTA does not affect the Ca2+ current decrease induced by these transmitters, (b) An ‘irreversible’ decrease of the Ca2+ current of the D2 neurone is elicited by 5–20μmol l−1 cholecystokinin octapeptide (CCK 8). Intracellular Ca2+ plays a key role in the intracellular mediation of this effect since the intracellular injection of EGTA prevents the CCK 8-induced decrease of the Ca2+ current.
The Physiology of Contractile Vacuoles
Authors: Kitching J. A.
Published: April 2021

There was no change in the body volume of marine Peritricha subjected to reductions in the salt concentration of the medium, so long as the osmotic pressure of the medium was kept constant by the addition of urea, glycerol, or cane-sugar. In mixtures of isotonic non-electrolytes with sea water the rate of vacuolar output was decreased—more so in the case of urea than of glycerol. It is concluded that the cell membrane is relatively impermeable to urea, glycerol, and cane-sugar, and also to neutral salts. Excretory substances could not be produced in sufficient quantity to attract water into the contractile vacuole by osmosis at the rate observed. The process of diastole therefore involves “secretion” of water by the vacuolar walls. Cyanide and sulphide in very low concentrations rapidly caused a great reduction in the rate of output of the contractile vacuole of marine Peritricha. In the case of cyanide this effect was rapidly reversible. Alcohols and urethane only decreased the rate of vacuolar output when present in much higher concentrations. It is suggested that possibly vacuolar activity depends directly on an oxidative process. When marine Peritricha were transferred from dilute sea water to dilute sea water of the same concentration + cyanide M/200 or M//500 (the />H being carefully controlled), the contractile vacuole was completely or almost completely stopped, and the body increased in volume. When the organism was transferred back to dilute sea water of the same concentration without cyanide, the contractile vacuole became active again and the body decreased in volume until a new steady value was attained which was rather below the value in dilute sea water before cyanide treatment. The increase in body volume consequent on treatment with cyanide was greater the more dilute was the sea water. For sea water of concentrations of 100-75 Per cent, no swelling was detectable when the organism was treated with cyanide. The rate of output of the contractile vacuole is sufficiently great to account for the decrease in body volume during recovery from cyanide. The permeability of the body surface to water is estimated as o-o5-O’io cubic miera per square micron per atmosphere per minute.
The Origin of Competence for Lens Formation in the Amphibia
Authors: Waddington C. H.
Published: April 2021

Presumptive ectoderm of Triton alpestris was removed from the young gastrula and cultivated in Holtfreter solution at 25° C. until control embryos had developed open neural plates. Presumptive eye material from neural plate embryos, with some attached archenteron roof, was then implanted into the isolated fragments of ectoderm. The grafted tissue formed single complete eyes, and bilaterally symmetrical portions of the brain, although the implant contained asymmetrical portions of the neural plate. In some of the expiants the competence for neural differentiation was retained even to this late stage, and neural tubes were induced. In other specimens the inner layer of ectoderm consists of long, cylindrical, regularly arranged cells, like those of the sensory inner layer of ectoderm in the mouth region of a normal larva. Still other specimens formed thin-walled vesicles with no sensorisation, and others again differentiated into the compact masses of tissue normally formed by isolated gastrula ectoderm. Lenses were induced in all types of explant mentioned above except the last. It is concluded that the formation of lens competence is not dependent on the presence of non-axial mesoderm or on the previous occurrence of a process of neural induction, but is dependent on the differentiation of the ectoderm into a thin layer, which differentiation may be brought about in various ways, and perhaps purely mechanically. The formation of a thin layer of ectoderm is probably a sufficient as well as a necessary condition for the origin of lens competence.
The Occurrence of the Evocator in Organisms Which Possess no Nerve Cord
Authors: Waddington C. H. , Wolsky A.
Published: April 2021

The active principle (the evocator) of the amphibian organisation centre is very widely distributed throughout the animal kingdom. We owe our knowledge of its occurrence mainly to the investigations of Holtfreter (1934), who systematically tested the inducing properties of tissues belonging to most of the main phyla, by the well-known technique of implanting them into the blastocoele of young newt gastrulae. Some of the tissues were poisonous to the gastrulae when they were implanted in the living state, but many of them could be rendered innocuous by a short immersion in boiling water. This treatment seemed in general to have little effect on the inducing properties of tissues which were non-poisonous in the living state, and it seems probable that the effect of the boiling on poisonous tissue has been to annul the deleterious effects of the implants rather than to alter their inducing properties. However, Holtfreter (1933) has also shown that in the ventral ectoderm and in the endoderm of the newt gastrula, the evocator exists in a masked form, so that these tissues have no inducing power until they have been killed ; and we cannot be certain that a similar state of affairs is not found in those tissues which are too poisonous to be tested while still alive.
Studies in Animal Locomotion
Authors: Gray J.
Published: April 2021

During the normal progression of a fish through water each segment of the body executes a series of transverse movements whose phase is slightly behind that of the segment lying anteriorly to itself, whilst the muscles on the two sides of each segment differ in phase from each other by one-half of a complete muscular cycle. So long as these conditions are fulfilled, regular waves of contraction pass alternately down each side of the body and tail of the fish. On the form, velocity and frequency of these waves depends the rate of progression of the animal through still water (Gray, 1933a). It is obvious that the form of the waves depends, in turn, on the degree of contraction taking place in each segment and on the phase difference which exists between successive segments. The present paper deals with the locomotory rhythm of the eel (Anguilla vulgaris), a form well suited to the purpose in view of its clearly defined muscular movements and of the remarkable viability of the fish. So far as is known, the mechanism controlling the co-ordination of fish movement has not been subjected to extensive experimental analysis, but, during the progress of the present work, important contributions have been made by von Holst (1934, 1935), to whose results reference is made in the text.
The Locomotory Rhythm of the Dogfish (Scyllium Canicula)
Authors: Gray J. , Sand A.
Published: April 2021

Recent experimental work ( v. Holst, 1935; Gray, 1936) has shown that the locomotory rhythms of certain teleostean fishes are determined by the intrinsic activity of the central nervous system, for they remain unaffected when the intervention of peripheral reflexes from the skin or muscles has been eliminated. This conclusion is at variance with that of ten Cate (1933) who removed all the muscles in the neighbourhood of the anterior dorsal fins of the dogfish (Scyllium canicula and A. catulus) and having transected the nerve cord, observed that a locomotory rhythm was propagated over the site of the operation thereby maintaining co-ordinated movement between the head and the posterior region of the body; the activity of the posterior region depends, according to ten Cate and ten Cate-Kazejewa (1933), on tensile stimuli applied to the posterior musculature whenever an active contraction occurs in the head region. If this conclusion be justified, the normal locomotory rhythm of the dogfish involves the activity of a chain of peripherally controlled reflexes whereas that of the eel is determined by a mechanism entirely independent of such reflexes. The situation appeared to be sufficiently anomalous to justify further investigation, and an attempt has been made to confirm ten Cate’s observations. The work was performed at Plymouth and Scyllium canícula was used as the most convenient material; a few observations made on 5. catulus indicated that there is no essential difference in the behaviour of the two species.
Experiments on the Development of the Head of the Chick Embryo
Authors: Waddington C. H. , Cohen A.
Published: April 2021

Experiments were made on the development of the head of chicken embryos cultivated in vitro. Defects in the presumptive head region of primitive streak embryos are regulated completely if the wound fills up before the histogenesis of neural tissue begins in the head-process stage. Different methods by which the hole is filled are described. No repair occurs in the head-process and head-fold stages, and in this period two masses of neural tissue cannot heal together. Median defects, even if repaired as regards neural tissue, cause a failure of the ventral closure of the foregut. The lateral evaginations of the gut develop typically in atypical situations. The headfold may break through and join up with the endoderm in such a way that the gut acquires an anterior opening. The paired heart rudiments may develop separately. The separate vesicles begin to contract at a time appropriate to the development of the embryo as a whole. The two hearts are mirror images, the left one having the normal curvature, but the embryos do not survive long enough for the hearts to acquire a very definite shape. The forebrain has a considerable capacity for repair in the early somite stages (five to twenty-five 80mites). One-half of the forebrain can remodel itself into a complete forebrain. In some cases the neural plate and epidermis grow together over the wound, in others the epidermis and mesenchyme make the first covering, leaving a space along the inside of which the neural tissue grows. The neural tissue may become a very thin sheet. The repaired forebrain may induce the formation of a nasal placode from the non-presumptive nasal epidermis which covers the wound. If the optic vesicle is entirely removed, a new one is not formed, but parts of the vesicle can regulate to complete eye-cups, either when still attached to the forebrain or after being isolated in the extra-embryonic regions of another embryo. Injured optic vesicles induce lenses from the non-presumptive epidermis which grows over the wound. Transplanted optic neural tissue from embryos of about five 80mites induces the formation-of lentoids from extra-embryonic ectoderm, but only in a small proportion of cases. The presumptive lens epidermis can produce a slight thickening even when contact with the optic cup is prevented. The significance of periods of minimum regulatory power for the concept of determination is discussed. The data concerning lens formation are discussed in terms of the field concept.