bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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 /&gt;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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.
Suprarenal “Virilism” in A Domestic Hen, Its Possible Significance
Authors: Mcgowan J. P. 
Published: April 2021

ABSTRACT
The great majority of hermaphrodites or sex reversals, hitherto described in domestic fowls, have been in old hens and have usually been associated with disease of the ovary and neoformation of testicular tissue. The present case differs essentially in several respects.