bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reflexes, fictive respiration and cell division in the brain and spinal cord of the newborn opossum, Monodelphis domestica, isolated and maintained in vitro
Authors: Nicholls J. G. , Stewart R. R. , Erulkar S. D. , Saunders N. R. 
Published: April 2021

ABSTRACT
The entire central nervous system (CNS) was isolated from 1-to 4-day-old newborn South American opossums (Monodelphis domestica). At this stage the CNS has only an embryonic forebrain (two-layered) and no cerebellum and corresponds to a 14-day rat embryo. Its eyes, ears and hind-limbs are only at an early stage of formation. The isolated CNS preparations continue to develop and to produce electrical signals for up to 4 days in oxygenated Krebs’ fluid at 23 °C. The longitudinal axis of the CNS showed markedly different stages of development. More neuroblast cells were present in the proliferative zone in lumbosacral than in cervical or thoracic regions of the cord. The progeny of dividing cells were labelled in isolated preparations by applying bromodeoxyuridine (BrdU) to the bathing solution for 2h. Stained precursor cells were observed in CNS that had been left in Krebs’ fluid for 4 days before applying BrdU and also in CNS that had been exposed to BrdU shortly after dissection and then left for 4 days. Compound action potentials were evoked from the isolated CNS by stimulation with extracellular electrodes. Compound action potentials increased in amplitude with stronger stimulation and showed discrete peaks of conduction velocity. All electrical activity was eliminated reversibly by 0.1μmol l−1 tetrodo-toxin applied to the bathing solution. Block and recovery occurred with a halftime of approximately 5 min. High concentrations of magnesium (20 mmol l−1) reversibly blocked slower components of the volley. Reflexes in cervical and thoracic segments of the spinal cord continued to function in isolated preparations. Stimulation of a dorsal root evoked bursts of impulses in the appropriate ventral root. Spontaneous and evoked activity in ventral roots was eliminated reversibly by 20 mmol l−1 magnesium. In thoracic segments, spontaneous rhythmical bursts of action potentials were recorded. Burst activity was correlated with respiratory movements of the ribs in semi-intact preparations in which a few ribs and muscles were left attached to the isolated CNS. At raised temperatures of 28°C compared to 23°C both spontaneous and evoked electrical activity were reversibly reduced. Together these results show that the isolated CNS of the newborn opossum survives well in culture. The preparation offers advantages for pharmacological and physiological studies of spinal reflexes, for analysis of the mechanisms underlying rhythmical respiratory activity and for following the time course of CNS development in vitro.
Developmental Changes in Cardiac and Metabolic Physiology of the Direct-Developing Tropical FrogEleutherodactylus Coqui
Authors: Burggren Warren W. , Infantino Robert L. , Townsend Daniel S. 
Published: April 2021

ABSTRACTThe neotropical frog Eleutherodactylus coqui (Thomas) undergoes direct development within the egg, emerging at hatching as a juvenile frog. The aim of this study was to investigate cardiorespiratory changes that accompany development, as well as to determine how the developmental physiology of direct-developing anurans differs from anurans with free-living larval stages. Heart rate (fH), oxygen uptake , vitelline fluid pH, and the protein and lactate concentrations of vitelline fluid were measured as a function of development. At 24–25 °C, fH doubled from 50 to 100 beats min−1 during the early stages of heart development, then increased more slowly with later embryonic development to 120 beats min−1 at hatching. The act of hatching itself was accompanied by a transient increase in fH to 155 beats min−1, this mild tachycardia lasting for at least 2 h. In juveniles and adults, heart rate decreased with increasing body mass, falling to about 80beats min−1 in 6 g frogs at 24–25°C. at 24–25 °C increased from about 2μmol g egg−1h−1 for the earliest embryos examined to about 12μmolg egg−1h−1 at hatching. in adults decreased with increasing body size, ranging from 4 to 5μmolg−1h−1 in the largest adults examined (6g). Both fH and were also measured at 18°C. The Q10 for/it was between 1.5 and 2 throughout development. The Q10 for in embryos ranged between 3.5 and 6.5 until hatching, falling to 1.6–2.0 in juveniles and small adults. Vitelline fluid pH (24–25°C) decreased from 5.2’ in early embryonic stages to 4.7 at the time of hatching. Egg dehydration caused a significant decrease in the pH of vitelline fluid and was associated with a significant rise in fH. Vitelline fluid protein concentration was about 5–6mgdl−1, and showed no consistent change with development. Whole-egg lactate concentration ranged from 4 to 11 μ g g egg−1, and also showed no consistent change during development. These findings indicate considerable changes in cardiac and metabolic physiology associated with opment in Eleutherodactylus coqui. These changes appear to be associated with both organogenesis (primary influence before hatching) and body mass changes (primary influence after hatching).
Effects of taurine on Ca2+-dependent force development of skinned muscle fibre preparations
Authors: Galler S. , Hutzler C. , Haller T. 
Published: April 2021

ABSTRACT
The effects of the naturally occurring amino acid taurine (2-aminoethanesul-phonic acid) on isometric force development were investigated using skinned muscle fibre preparations. In atrial and ventricular pig heart muscles, as well as in fibres of slow abdominal extensor muscle of crayfish, an increase of submaximal isometric force was observed in Ca2+-activated skinned fibre preparations at physiological concentrations of taurine. The maximal isometric force remained unaffected in all preparations. It is assumed that taurine increases the Ca2+ sensitivity of the force-generating myofilaments in mammalian hearts and tacean slow skeletal muscle fibres.
Control of Locomotion in the Freshwater SnailPlanorbis CorneusI. Locomotory Repertoire of the Snail
Authors: Deliagina T. G. , Orlovsky G. N. 
Published: April 2021

ABSTRACTThe freshwater snail Planorbis corneus moves as a result of the beating of cilia covering the sole of the foot. The tracks of snails crawling on the walls and on the bottom of an aquarium were recorded visually under various conditions of snail feeding. The following results were obtained.In the absence of food, the snails exhibited diurnal changes in locomotor activity, with a maximum during the day. Horizontal tracks on the aquarium walls were commonest during the day and vertical ones at night. When crawling on the aquarium wall, the snail actively stabilized its horizontal or vertical orientation: when encountering an obstacle or after a forced turn, the snail re-established the initial direction of locomotion. When fed on the water surface, the snail decreased its locomotor speed if food particles entered its mouth. The decrease in speed resulted from the slowing down of ciliary beating in the anterior part of the sole of the foot. This finding demonstrates that motor activity in different parts of the ciliated epithelium can be controlled independently by the nervous system. When searching for food particles, the snail exhibited very sinuous tracks, the turns occurring spontaneously at irregular intervals. This finding shows that there is a programme of ‘looping’ in the nervous system. When the snail was fed on the bottom near a vertical wall, it used the wall to climb to the water surface for lung ventilation. After ventilation, the snail performed a standard 180° turn and then returned to the food along the original outward track. Motion along a track was performed with high accuracy. The locomotor apparatus of a snail allowed it to crawl not only on a flat surface but also along the very thin mucus thread that it makes.
Adaptations to a Terrestrial Existence by the Robber CrabBirgus Latro: VI. The Role of the Excretory System in Fluid Balance
Authors: Greenaway Peter , Taylor H. H. , Morris S. 
Published: April 2021

ABSTRACTPrimary urine is formed by filtration in the antennal organ of Birgus latro L. Urine isosmotic with the haemolymph is released into the anterior branchial chambers where substantial reabsorption of water and ions may occur. Some of the branchial fluid is ingested and the remainder (final excretory fluid, P) is released.Crabs supplied with fresh water have a low drinking rate (1.82ml 100g−1 day−1). Primary urine is partially reabsorbed (27%) in the antennal organ and urine flow (4.48 ml 100 g−1 day−1) is significantly lower than filtration rate (5.77ml 100g−1 day−1). The volume of P released is small in crabs drinking fresh water (0.45 ml 100 g−1 day−1) and the fluid is dilute (≈25mmoll−1 NaCl). The difference between P flow and drinking rate (1.37ml 100 g−1 day−1) represents evaporative and faecal water losses.Provision of saline drinking water (300, 600 or 1000mosmolkg−1 sea water) doubles rates of drinking, filtration and urine flow and increases P flow fourfold. Evaporative/faecal water loss remains constant. Reabsorption of salts from the P rapidly decreases when saline media are provided for drinking.
The Cooling Power of Pigeon Wings
Authors: Craig Albert , Larochelle Jacques 
Published: April 2021

ABSTRACT
The rate of heat loss through the stretched wings (Ḣwings) was studied in resting pigeons preheated to a body temperature (43.7°C) within the range of those recorded during flight. The experimental system was designed to allow the calculation of Ḣwings from the increase in whole-body cooling rates resulting from exposure of the wings to various wind speeds (0–50 km h−1) at 23°C. The maximum value of Ḣwings was 3.8 W, less than twice the heat production of a resting pigeon. This indicates that the contribution of the wings to heat dissipation during flight may not be nearly as important as has been supposed. At low windspeeds (0–12.5 km h−1), Ḣwings corresponded to about 40% of the resting rate of heat production, and this value is discussed in connection with the various wing postures observed in hyperthermic birds.
Mechanics of Breathing in Horses at Rest and During Exercise
Authors: Lafortuna Claudio L. , Saibene Franco 
Published: April 2021

ABSTRACT
The respiratory mechanics together with the rate of work of breathing were studied in five healthy adult Standardbred horses at rest and during different levels of exercise on a treadmill (0.8–2.3 ms−1, 7% slope). In three of the horses the stride frequency was also determined.
The ventilatory response to exercise increased linearly with treadmill speed up to 9.6 times the resting values and was sustained more by an increase in respiratory frequency than by an increase in tidal volume. At the most elevated work load, respiratory frequency and tidal volume averaged 5.2 and 1.4 times the resting values, respectively. Lung resistance decreased during the most intense level of exercise to about 30% of the average value observed at rest, while lung dynamic compliance remained unchanged. The rate of work of breathing (Ẇresp, in W) increased exponentially with ventilation (, in 1min−1) according to the equation: . In the three animals investigated a definite locomotor-respiratory coupling was observed at a trot and in two animals also during walking. This observation, together with other considerations based on available data on the energetics of respiration, suggests that the efficiency of the equine respiratory system is relatively high. In addition, when compared with other smaller mammals (man and dog), horses are, in mechanical terms, more economical breathers.
Temperature Acclimation in the Common Carp: Force-Velocity Characteristics and Myosin Subunit Composition of Slow Muscle Fibres
Authors: Langfeld Karen S. , Crockford Tony , Johnston Ian A. 
Published: April 2021

ABSTRACT
Live slow fibre bundles were isolated from the superficial region of the pectoral fin abductor superficialis muscle of common carp (Cyprinus carpio L.) acclimated to either 8 or 20°C.
The maximum tetanic tension (P0) of fibre bundles was similar when measured at the acclimation temperature of each group. However, at 8°C, P0 was significantly higher in 8 °C-than in 20°C-acclimated fish (202 ±8 versus 153±4kNm−2, respectively). For isometric tetani at 8°C, the times to 50% peak force and from peak force to 50 % relaxation were 15–20 % faster in preparations from cold-than from warm-acclimated carp. Force-velocity (P–V) curves were fitted using a hyperbolic-linear equation. The curvature of the P–V relationship was found to be independent of acclimation temperature. Unloaded contraction velocity (Vmax) was 17 % higher at 8°C in fibres from fish acclimated to 8°C than in fish acclimated to 20°C (1.18±0.04 and 0.98±0.04 muscle lengths s−1, respectively). Calculated values for maximum power output at 8°C were 26.5 W kg−1 for cold-acclimated and 18.0 W kg−1 for warm-acclimated fish.
Native myosin was purified from isolated fibre bundles using sodium pyrophosphate gel electrophoresis. The mobility of myosin heavy chains on 8% SDS– PAGE gels was similar for both acclimation groups. Myosin light chain subunits were separated on 15% SDS–PAGE gels. Fibre bundles from warm-acclimated fish contained almost exclusively slow myosin light chains (LC1S and LC2S). Preparations from cold-acclimated fish contained a significant proportion of fast myosin light chains (LClf and LC2f) in addition to LC1S and LC2S. Histochemical studies revealed no differences in the fibre composition of preparations from warm- and cold-acclimated fish: both contained an average of 3% fast oxidative fibres in addition to slow fibres.
It is concluded that cold-acclimation results in modest improvements in the contractile performance of slow muscle fibres at low temperatures. The mechanism may involve the expression of myosin light chain isoforms normally associated with faster-contracting fibre types.
Cytoplasmic pH and Goblet Cavity pH in the Posterior Midgut of the Tobacco Hornworm Manduca Sexta
Authors: Chao Anthony C. , Moffett David F. , Koch Alan 
Published: April 2021

ABSTRACT
In the larval lepidopteran midgut, the major energy-requiring step of transepi-thelial K+ secretion occurs across the goblet cell apical membrane. Studies of vesicles of goblet cell apical membrane suggest that K+ secretion across this membrane is a secondary active process in which electroneutral K+/H+ antiport is driven by primary electrogenic H+ secretion. Transbasal K+ movement is thermodynamically passive under standard conditions, but the presence of an active process is revealed in hypoxic solutions or at low extracellular K+ concentration.
We measured the pH of cytoplasm and goblet cell cavities, together with the corresponding transmembrane voltages, using double-barreled pH and voltage-sensing microelectrodes. For short-circuited midguts in standard bathing solution (pH 8.0) the weighted mean of cytoplasmic pH was 7.14±0.06 (mean±s.E.M.), an average of 0.34 units more acid than expected for electrochemical equilibrium with the hemolymphal solution. The mean pH of goblet cavities was 7.23±0.11, 1.62 units more acid than expected for equilibrium with the luminal solution. The pH gradient across the goblet cell apical membrane is thus of the wrong polarity to drive K+ secretion by electroneutral K+/H+ antiport; however, if the exchange ratio were two or more H+ per K+, the cavity-positive electrical potential could drive H+ back to the goblet cell cytoplasm coupled to K+ secretion from cytoplasm to the goblet cavity.
Insensitivity of the goblet cavity pH to the change in the transvalve voltage caused by open-circuiting suggests either that the goblet cavity pH is well regulated or that the valve connecting the cavity to the gut lumen poses a significant barrier to protons. Transbasal potential and cytoplasmic pH were insensitive to a decrease of hemolymphal pH to 6.8, suggesting that the basal membrane is relatively nonconductive to H+. Intracellular pH was unaffected by a decrease of hemolymphal K+ to 5 mmol 1-1 suggesting that K+/H+ exchange is not important for transbasal K+ uptake.
Changes at the Surface of Nereis Limbata Eggs After Insemination
Authors: Novikoff Alex B. 
Published: April 2021

ABSTRACT
One of the classic descriptions of the insemination process is that of F. R. Lillie (1911) in the egg of the annelid, Nereis. According to Lillie, there exists beneath the vitelline membrane of the unfertilized Nereis egg a wide cortical layer. He describes it as “a coarsely alveolar layer with homogeneous alveolar contents. The walls of the alveoli are continuous internally with the protoplasm of egg, and unite externally to form a protoplasmic layer applied to the vitelline membrane.” Within 2 or 3 min. after the attachment of the spermatozoon to the egg, an outpouring of jelly from the cortical alveoli occurs, so that in about 15 min. this layer is represented only by the perivitelline space and the delicate walls of the original alveoli crossing this space to the vitelline membrane. A fertilization cone rises from the egg surface, moves gradually across the perivitelline space, and comes in contact with the membrane beneath the sperm. After the retraction of the cone, the sperm head passes through the membrane into the egg. There is no discussion of the nature of the alveolar walls, nor is there any account of how these walls disappear even though they are not visible in many of the figures.
The Relation Between the Electrolytic Solution Pressures of the Metals and Their Toxicity to the Stickleback (Gasterosteus Aculeatus L.)
Authors: Jones J. R. Erichsen 
Published: April 2021

ABSTRACT
Lethal concentration limits have been determined for the hydrogen ion and the ions of eighteen metals. The three-spined stickleback (Gasterosteus aculeatus L.) has been employed as test animal. According to their lethal concentration limits on a mg./l. basis their order of increasing toxicity is : Sr Ca Na Ba Mg K Mn″ Co″ Cr″ Ni″ Au″ Zn Cd″ Pb″ Al Cu″ H Hg″ Ag. On a molar concentration basis the order is as follows: Na Ca Sr Mg Ba K Mn″ Co″ Cr″′ Ni″ H Zn Al Au″′ Cd″ Pb″ Cu″ Hg″ Ag. All these ions, with the exception of the first six (the metals of the alkalis and alkaline earths), bring about the death of fish by precipitating the gill secretions, thus causing asphyxiation. The alkali and alkaline earth metals appear to enter the body and act as true internal poisons. The position of iron is uncertain. The toxicity of solutions of iron salts appears to be due, mainly if not entirely, to their acidity. On a mg./l. or molar concentration basis there is a marked relationship between the toxicity of the metals and their solution pressures. The metals of very low solution pressure (Ag, Cu, etc.), i.e. those whose ions are most ready to part with their charges and enter into combination with other ions or compounds, are the most toxic as they precipitate the gill secretions and bring about asphyxiation with extreme rapidity. Metals of somewhat higher solution pressure (Zn, Pb, Cd) act in the same way but more slowly. Manganese, which of all the heavy metals has the highest solution pressure, takes effect very slowly and the ions of the alkali and alkaline earth metals, which have a high affinity for their charges, do not precipitate the gill secretions at all. In the case of all the ions other than those of the alkali and alkaline earth metals the reactions responsible for the death of the fish take place outside the body. Thus their speed of action does not depend on their penetrating power and the permeability factor does not enter. This is probably responsible in great measure for the good agreement observed between their toxicity and their affinity for their electrical charges.
The Micro-Estimation of Sulphates in Sea Water and The Body Fluids of Marine Animals
Authors: Webb D. A. 
Published: April 2021

ABSTRACT
In a series of methods recently proposed (Robertson & Webb, 1939) for the micro-estimation of the principal constituents of sea water and of the body fluids of marine animals, that for sulphate was on the whole the least satisfactory. As there described it consists of precipitation by means of barium chloride and direct titration of the excess barium with sodium sulphate, using rhodizonic acid as indicator. The simplicity of the method is to some extent outweighed by the capricious behaviour of the indicator, which renders the judging of the end-point an operation which, even after considerable practice, it is difficult to perform with great confidence. Although the error may usually be kept without difficulty below 2 %, duplicate titrations are necessary if an occasional error somewhat larger than this is to be avoided. In cases where speed is of greater importance than the highest accuracy the method is probably the best that is available, but it was thought that an alternative method, based on that of Van Slyke et al. (1927) for total base in blood, might be made to yield more accurate results and require less practice.
Photomechanical Changes in the Pineal of Lampreys
Authors: Knowles F. G. W. 
Published: April 2021

ABSTRACT
The pigment present in the pineals of ammocoete larvae is a reflecting pigment. There are indications from its solubilities that this pigment is guanin. No differences in the distribution of this pineal pigment can be seen in animals kept under various conditions of illumination, or when examined soon after transference from light to darkness. The position of the nuclei in the pineal retinal cells changes under different conditions of illumination. They are diffusely scattered in the retinal region of the pineals of animals kept in the dark for seven days, but in animals kept in moderate illumination, the nuclei take up the same position in each retinal cell, thus presenting the appearance of a line of nuclei when viewed laterally. Strong illumination further accentuates this linear distribution of the nuclei. These changes further substantiate the view that the pineals of ammocoete larvae are sensitive to changes of illumination.