bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature Effects on Membrane Chloride Conductance and Electrical Excitability of Lizard Skeletal Muscle Fibres
Authors: Adams Brett A. 
Published: April 2021

ABSTRACTIntracellular recording techniques were used to study the effects of temperature on resting membrane conductances, electrical excitability and synaptic efficacy in fast-glycolytic (FG) skeletal muscle fibres from the lizard Dipsosaurus dorsalis. The conductance of the resting muscle membrane to chloride ions (gci) increased from 488 μS cm−2 at 15°C (pH7-8) to 730 μS cm−2 at 45°C (pH7·4), yielding a temperature coefficient (thermal ratio, Rio) of 1·14. Resting potassium conductance (gK) increased from 84μS cm−2 at 15 °C to 236 μS cm−2 at 45 °C (R10=1·41). Fibres bathed in Cl−-free Ringer’s solution were hyperexcitable, and produced repetitive action potentials both during and following intracellular current injection. At the preferred body temperature of Dipsosaurus (near 40°C) the fibres also fired repetitively in response to single nerve shock. The electrical excitability of Dipsosaurus fibres decreased with increasing temperature. Threshold current, measured at endplate regions of fibres bathed in normal Ringer’s solution, was 146 nA at 15°C and 353 nA at 45°C (R10= 1·34). Despite the temperature-dependent change in threshold current, at both 15 and 45 °C all fibres examined had suprathreshold neuromuscular transmission in response to single nerve shock. The relative thermal independence of gCl in Dipsosaurus fibres may be an adaptation that contributes to a large safety factor for neuromuscular transmission at the high body temperatures preferred by this lizard species.
High Concentrations of Zinc in the Fangs and Manganese in the Teeth of Spiders
Authors: Schofield Robert , Lefevre Harlan 
Published: April 2021

ABSTRACT
Various organisms have recently been shown to contain significant amounts of zinc and manganese in mechanical structures such as mandibular teeth. These accumulations are different from those in the bones and teeth of vertebrates and the shells and teeth of some mollusks in that the elements are both less common and are not obviously incorporated in biominerals. High concentrations of zinc (about 1 % of dry mass) were reported in the jaws of polychaete worms by Bryan & Gibbs (1979), using wet-ash analysis. These authors suggested that the zinc influences the mechanical properties of the jaw in a fashion analogous to the role of biominerals in the teeth of many organisms. Hillerton & Vincent (1982) detected zinc and manganese in the cutting edge of the mandibles of herbivorous insects from several orders using an electron microprobe. They determined the zinc concentration, averaged over the whole mandible, with wet chemical analysis, finding about 0·5% in a locust species. Hillerton et al. (1984) found either manganese or zinc in large quantities in the mandibles of separate species of beetles. Hillerton & Vincent (1982) went on to suggest that zinc may increase the density and fracture toughness of the mandibular teeth by increasing the number of secondary bonds in the cuticle. The hardening hypothesis has been accepted by Bone et al. (1983), who studied zinc in chaetognath teeth and spines, and by Perry et al. (1988), who studied zinc in copepod mandibles.
Nitrogen Budget in Developing Embryos of the Spiny Dogfish Squalus Acanthias
Authors: Kormanik Gregg A. 
Published: April 2021

ABSTRACT
Embryos of the dogfish Squalus acanthias (L.) complete their development in a uterine environment that is quite unusual. During the latter portion of a gestation period which lasts nearly 2 years (Hisaw & Albert, 1947), the embryos are bathed by a uterine solution that resembles sea water with respect to the major ions, but the ammonia concentration may approach 22 mmol l−1 and the pH is about 6 (Kormanik & Evans, 1986).
The Effects of Morphology and Perch Diameter on Sprint Performance of Anolis Lizards
Authors: Losos Jonathan B. , Sinervo Barry 
Published: April 2021

ABSTRACT
We investigated the mechanistic basis for the observed correlation between leg length and perch size among West Indian Anolis lizards by testing the hypothesis that species use those perches upon which they can move most effectively. We used four Anolis species which differed in leg length and perch use in nature. We measured maximum sprint speed on rods of several sizes. Longer-legged species ran faster on thick rods. The speed of all species declined on thinner rods, but long-legged species were affected to a greater extent in that all species ran at approximately the same speed on the smallest rod. The short-legged A. valen-cienni experienced much less difficulty moving on thin rods than did the other species. Variation in leg length among Anolis might thus represent an evolutionary trade-off between maximizing sprint speed and maximizing stability on thin perches.
Metabolic Heat Dissipation and Internal Solute Levels of Artemia Embryos During Changes in Cell-Associated Water
Authors: Glasheen J. S. , Hand Steven C. 
Published: April 2021

ABSTRACT
Embryos (cysts) of the brine shrimp Artemia enter a profound, yet reversible, state of metabolic arrest in response to cellular dehydration. We have monitored metabolic activity during this transition in embryos from the Great Salt Lake population by using microcalorimetric measurements of heat dissipation. Embryo hydration states can be precisely controlled by immersing cysts in solutions of varying ionic strength. When developing embryos were incubated in a 2·0 mol 1−2 NaCl solution, heat dissipation fell after 20 h to 1·13 mW g−2 dry mass, or 21 % of the value obtained when embryos were in control solutions of 0·25 mol 1−2. At higher ionic concentrations, heat dissipation declined to as low as 3 % of control values. Recovery from dehydration was rapid. Energy flow increased to 135 % of control values within 2h after returning cysts to the control medium.
These metabolic transitions were correlated with embryo hydration levels measured across the same dehydration series. Total cyst water ranged from 112 ± 2·6 g H2O 100 g−2 dry mass in 0·25 mol 1−2 NaCl to 46 ± 0·6gH2O 100 g−2 dry mass in 5·0 mol 1−2 NaCl. At the first point where heat dissipation was markedly suppressed (the 2·0 mol 1−2 incubation), cyst water content was 72·8±0·9gH2O 100g−2drymass. This water content is similar to the ‘critical’ hydration level required to suppress carbohydrate catabolism and respiration in San Francisco Bay Artemia embryos (Clegg, 1976a,b). However, hydration characteristics of the two populations differed in solutions of lower ionic concentration.
Total osmotic pressure in fully hydrated cysts was 1300 mosmolkg−2H2O. A comprehensive inventory of the internal osmolytes indicated that inorganic ions (Na+, K+, Cl-, Mg2−2-, Ca2+, Pi) accounted for 21 % of the osmotic activity and 1·48% of embryo dry mass. Organic solutes (trehalose, glycerol, ninhydrinpositive substances, and trimethylamine-N-oxide+betaine) contributed 60% of the osmotic pressure and 22% of the dry mass. Macromolecular components (protein, lipids, glycogen and DNA) were also quantified and formed the bulk of embryo mass. Taken together, 97·4% of the cyst dry mass was identified. At the cellular dehydration state promoting metabolic arrest, the concentrations of inorganic and organic osmolytes were 480–590 mmol kg−2H2O and 1200–1480 mmol kg−2 H2O, respectively. The influence of these osmolyte concentrations is considered in the context of macromolecular assembly and metabolic control.
Basic functional properties of the cardiac muscle of the common shrew (Sorex araneus) and some other small mammals
Authors: Vornanen M. 
Published: April 2021

ABSTRACT
The resting heartbeat frequency of all the studied wild small mammals (body mass 3–20 g) was lower than that predicted by the allometric equation for a typical mammal. The heart rate of the laboratory mouse was a little higher than the expected value.
The ventricular mass of the small wild mammals was higher than predicted for their size, but that of the laboratory mouse was below the expected value. Thus, adequate cardiac output in the wild small mammals is achieved by compensating the low heartbeat frequency with greater stroke volume. The shrew species are notable exceptions, which, despite having a metabolic rate 2–3 times higher than the mammalian average, neither have exceptionally high heart rates nor larger hearts than other wild small mammals.
The adaptation of the shrew heart to high metabolic rate may reside in the shape of heart. The ventricular myocardium of shrews is characteristically long and narrow with a tapered apex, whereas other small mammals have rounder hearts.
The duration of the ventricular action potential was short and inversely proportional to the resting heart rate of the mammalian species. Caffeine (5 mmol l−1) strongly decreased the isometric contractile force of right ventricular strips in all the studied mammals. These findings suggest that in the small mammals intracellular stores are the main source of activating Ca2+, whereas transsarcolemmal Ca2+ movement may only serve the triggering function.
Cold tolerance mechanisms of the free-living stages of Trichostrongylus colubriformis (Nematoda)
Authors: Wharton D. A. , Allan G. S. 
Published: April 2021

ABSTRACT
All free-living stages of the nematode parasite of sheep, Trichostrongylus colubriformis Giles, survived exposure to freezing temperatures in contact with water, with the exception of the first-stage juvenile (JI). The third-stage juvenile (J3) was the most resistant stage. The order of relative survival of the different stages was different from that of the lowest Fx (the temperature at which 50 % froze), suggesting that an ability to supercool was not the only determinant of survival. The F50 was shown to be a good measure of the degree of supercooling and to extend greatly the lower size limit of organisms that could be measured. The J3 uses a freeze-avoiding strategy by supercooling when in air or covered by liquid paraffin. In water it uses a mixture of freeze-avoiding and freeze-tolerant strategies, with a proportion of the population surviving freezing caused by exogenous ice nucleation. Removal of the J3 sheath results in a shift from freeze avoidance to freeze tolerance, with an overall reduction in survival. A major function of the sheath may be to reduce the probability of exogenous ice nucleation.
Serotonin differentially modulates two K+ currents in the Retzius cell of the leech
Authors: Acosta-Urquidi Juan , Sahley Christie L. , Kleinhaus Anna L. 
Published: April 2021

ABSTRACTThe effects of 100 μmol I−1 serotonin (5-HT) were investigated on the Na+- and Ca2+-dependent action potential and distinct K+ currents in the Retzius (R) cells of the hirudinid leeches Macrobdella decora and Hirudo medicinalis by conventional current-clamp and two-microelectrode voltage-clamp techniques.In normal Na+-containing Ringer, 5-HT decreased the duration of the action potential prolonged by 5 mmol I−1 tetraethylammonium (TEA+) chloride. In Na+-free saline containing 25μmol I−1 TEA+ to block IK, 5-HT reduced the amplitude and duration of Ca2+ spikes evoked by intracellular current injection. Under voltage-clamp, 5-HT enhanced the peak amplitude of an early transient 4-aminopyridine (4-AP)-sensitive, voltage-dependent outward current, termed IA-A small but significant increase in the time constant of inactivation (τoff) of IA was also measured after exposure to 5-HT. 5-HT suppressed the peak and steady-state amplitudes of a delayed TEA+-sensitive, voltage-dependent outward current, termed IK.These results demonstrate differential simultaneous modulation of distinct K+ currents in the Retzius cell of the leech by the endogenous transmitter serotonin. These cells contain and release 5-HT, and are believed to be multifunction neurons implicated in feeding and swimming. This modulation may change the excitable properties of the cell, leading to a negative feedback autoregulation of its transmitter output.
Separation of Hydrogen Ion Currents in Intact Molluscan Neurones
Authors: Mahaut-Smith M. P. 
Published: April 2021

ABSTRACT
The amplitude and rate of activation of the voltage-dependent H+ pathway in intact Helix neurones were investigated using standard two-electrode voltage clamp techniques. Na+ and K+ currents were inhibited by a Na+-free, tetraethylammonium (TEA+) (low-Cl−) saline and by use of Cs+-filled electrodes. Ca2+ currents were abolished by holding the membrane at –15 to –10 mV. Depolarizing voltage pulses from these low potentials activated outward currents whose tail current reversal potential shifted with changes in intracellular and extracellular pH, but not with changes in external KC1; thus these remaining currents are carried by hydrogen ions. Furthermore, the amplitude of the voltage-dependent outward current increased as the outward gradient for H+ was increased and a rise in pHi shifted the activation towards negative potentials. At physiological pH levels, H+ currents were typically 60 nA at 30 mV (cell diameter 200–250 μm). H+ currents were rapidly activated; the time to half maximal current at 30 mV was less than 5 ms in the pHi range tested (7·4–0·9) (pHe 7·4). The H+ pathway will therefore be activated by individual action potentials and may play an important role in pH homeostasis during intense neural activity.
Strain, Muscle Length and Work Output in a Crab Muscle
Authors: Josephson Robert K. , Stokes Darrell R. 
Published: April 2021

ABSTRACT
The relationships between muscle length, fractional change in length (strain) and work output during cyclic contraction were examined in scaphognathite levator muscle L2B of the green crab Carcinus maenas (L.). The muscle was subjected to sinusoidal strain at 2 Hz and to phasic stimulation in the strain cycle.
At an average length and stimulus phase which are optimum for net work output, the work from muscle L2B during shortening rises to a peak or a plateau with increasing strain. The failure of shortening work to increase continuously with strain is due, in part, to the greater shortening velocity associated with greater strain, and to the consequent reduction in muscle force during shortening at higher velocity. The work required to re-lengthen a muscle following contraction is a complex function of strain, with an initial peak followed by a work minimum and then a monotonic rise in work with further increase in strain. The early work minimum is a result of shortening inactivation which reduces muscle force and thus the work which must be done to re-lengthen the muscle. Because shortening work rises to a peak or plateau with increasing strain while lengthening work, for the most part, increases with strain, there is a sharp optimum strain (about 8 %) for net work output.
Muscle relaxation becomes slower with increasing muscle length. As muscle length is increased, fusion of tension from cycle to cycle becomes more pronounced and shortening inactivation becomes a more important determinant of optimum strain.
The Effect of Zinc on Calcium and Hydrogen Ion Currents in Intact Snail Neurones
Authors: Mahaut-Smith M. P. 
Published: April 2021

ABSTRACT
The effects of external Zn2+ on Ca2+ and H+ currents in the soma of intact Helix neurones were investigated using standard two-electrode voltage-clamp procedures. Cells were exposed to a 0Na+, tetraethylammonium (TEA+) saline and clamped with Cs+-filled electrodes, which allows separation of voltagedependent H+ and Ca2+ currents using different holding potentials. Outward H+ currents, activated by depolarizations from holding potentials in the range −15 to −10 mV, were rapidly blocked by low concentrations of external Zn2+ with a Kd of approximately 16/zmoll-1. H+ current activation was also markedly slowed and the block was slow to reverse. Ca2+ currents, largely free from contamination by outward current, were activated by small depolarizations from a holding potential of −55 mV. Ca2+ currents were reduced by Zn2+, but the Kd for block was more than 80 times greater than for block of H+ currents. Thus, low concentrations of Zn2+ provide a method of selectively inhibiting H+ current in studies of Ca2+ current. This was demonstrated in cells which slowly acidified following exposure to 0Na+, TEA+ saline, leading to an increased outward H+ current. Washing with low concentrations of Zn2+ blocked the H+ current and uncovered the underlying Ca2+ current. The results also suggest that Zn2+ will be a useful tool in studies of the physiological role of the H+ pathway.
Influence of Pregnancy on Behavioral Thermoregulation in the Northern Pacific Rattlesnake Crotalus Viridis Oreganus
Authors: Gier Paul J. , Wallace Richard L. , Ingermann Rolf L. 
Published: April 2021

ABSTRACT
Incubation within appropriate thermal limits is important for the normal development of the reptilian embryo (Maderson & Bellairs, 1962; Fox et al. 1966; Osgood, 1978; Burger et al. 1987). Among the viviparous reptiles in which the optimum temperature for embryonic development differs from the temperature of optimum activity in the adult, one would predict a shift in thermoregulatory behavior of the pregnant female. We have examined the influence of pregnancy on the thermoregulatory behavior of the northern Pacific rattlesnake (Crotalus viridis oreganus) to test this prediction.
Mechanical Properties and Morphological Correlates of Fragile Skin in Gekkonid Lizards
Authors: Bauer Aaron M. , Russell Anthony P. , Shadwick Robert E. 
Published: April 2021

ABSTRACT
The mechanical properties of gekkonid lizard skin are investigated for the first time. Although the skin of certain geckos, such as Gekko gecko, behaves in ‘typical’ vertebrate fashion, that of others, such as Ailuronyx seychellensis, exhibits unusual properties associated with identifiable morphological specializations. Light and scanning electron microscopy reveal that Ailuronyx dermis is functionally bilayered; the stratum compactum is divided into inner and outer layers by intervening loose connective tissue. The inner layer is strong and tough and does not differ significantly in its properties from that of Gekko gecko whole skin. The much thicker outer layer, however, is only 1/20 as strong and 1/50 as tough as the inner layer, and exhibits preformed zones of weakness. In nature, Ailuronyx parts with considerable portions of the outer components of the skin as an antipredator escape mechanism. Skin samples from 17 additional gecko species varied considerably in their strength, stiffness and toughness. None of the forms with tough skin employs regional integumentary loss as a predator escape strategy. Weak skin alone is not sufficient to permit regional integumentary loss, as the capability to lose the skin involves not only inherent properties of the tissue, but also features of the mechanical interaction of skin layers with one another and with the underlying body wall.
Computing motion in the primate’s visual system
Authors: Koch C. , Wang H. T. , Mathur B. 
Published: April 2021

ABSTRACT
Computing motion on the basis of the time-varying image intensity is a difficult problem for both artificial and biological vision systems. We will show how one well-known gradient-based computer algorithm for estimating visual motion can be implemented within the primate’s visual system. This relaxation algorithm computes the optical flow field by minimizing a variational functional of a form commonly encountered in early vision, and is performed in two steps. In the first stage, local motion is computed, while in the second stage spatial integration occurs. Neurons in the second stage represent the optical flow field via a population-coding scheme, such that the vector sum of all neurons at each location codes for the direction and magnitude of the velocity at that location. The resulting network maps onto the magnocellular pathway of the primate visual system, in particular onto cells in the primary visual cortex (VI) as well as onto cells in the middle temporal area (MT). Our algorithm mimics a number of psychophysical phenomena and illusions (perception of coherent plaids, motion capture, motion coherence) as well as electrophysiological recordings. Thus, a single unifying principle ‘the final optical flow should be as smooth as possible’ (except at isolated motion discontinuities) explains a large number of phenomena and links single-cell behavior with perception and computational theory.
The evolution of complex sensory systems in mammals
Authors: Kaas J. H. 
Published: April 2021

ABSTRACT
Much of the forebrain of many extant species of mammals appears to be sensory-perceptual in nature. Thus, much of the forebrain, especially the dorsal thalamus and neocortex, consists of nuclei and areas that are parts of complex systems that analyze sensory information and allow behavior to be guided by accurate inferences about the external world. Since mammals vary tremendously in brain size, they vary in the amount of tissue devoted to sensory processing. In addition, mammals vary in the sizes and numbers of processing nuclei and areas, and in how neurons and neuron groups (modules) are differentiated within such structures. Sensory-perceptual systems with more, larger and more differentiated parts may allow more stimulus parameters to be considered, experience to play a greater role, and speed calculations through increased parallel processing.
The evolution of species differences in brain size, the sizes of individual parts, and internal structure of these parts are potentially understandable within a theoretical framework of gradual modifications of developmental processes. In addition to changes in the generation and specialization of neurons, alterations in the developmental timing that modify internal and external influences on neuron activity patterns seem to have a major role in the construction and maintenance of organization in the nervous system. Because similar selection pressures may arise over and over again and the mechanisms for producing changes may be few, similar changes in the nervous system are likely to occur in independent lines of evolution.
It is uncertain how new cortical areas and nuclei evolve. Comparative studies suggest that: (1) all mammals have a few basic sensory areas and nuclei in common, (2) the number of areas and nuclei has increased independently in several lines of mammalian evolution, and (3) new areas have been added to the middle levels of cortical processing sequences. New areas and nuclei may have evolved as a result of sudden duplications and/or by the process of single areas or nuclei gradually differentiating into two or more areas or nuclei. The process of gradual differentiation may have involved the initial step of differentiating functionally distinct classes of cells that are mixed in a representation, followed by the local groupings of such cells into functionally distinct sets, and finally the fusion of cell groups of the same types to form separate representations.